Available Balance
National Center for Research on Earthquake Engineering
storm_Nationwide Earthquake Drillphoto is mine

International Institute of Earthquake Engineering and Seismology (IIEES), founded by Mohsen Ghafory-Ashtiany, is an international earthquake engineering and seismology institute based in Iran. It was established as a result of the 24th UNESCO General Conference Resolution DR/250 under Iranian government approval in 1989. It was founded as an independent institute within the Iran’s Ministry of Science, Research and Technology.[1]

Mohsen Ghafory-Ashtiany distinguished professor of earthquake engineering and risk management at International Institute of Earthquake Engineering and seismology (IIEES) which was founded by him in 1989, is Chief Editor of JSEE and IDRiM Journals; author of more than 140 papers and 3 books in the field of earthquake engineering, seismic hazard and risk analysis, risk management and planning. Ashtiany is the Director and member of the Executive committee of International Association of Earthquake engineering (IAEE), Chairman of Earthquake Hazard, Risk and Strong Ground Motion Commission of IASPEI, member of UN-ISDR Scientific and Technical commission, Director and member of board of World Seismic Safety Initiative, member of Global Earthquake Risk Model Project; Member of Geo-Hazard Initiative, Member of GSHAP, Member of Global Risk Forum-Davos, and many other scientific communities. Ashtiany was born in Tehran, Iran in 1957 and graduated from Va. Tech (USA) in 1983 with honor, and is resident of US.

On its establishment, the IIEES drew up a seismic code in an attempt to improve the infrastructural response to earthquakes and seismic activity in the country. Its primary objective is to reduce the risk of seismic activity on buildings and roads and provide mitigation measures both in Iran and the region.[1]

The institute is responsible for much of the research and education in this field by conducting research and providing education and knowledge in seismotectonic studies, seismology and earthquake engineering.[1] In addition conducts research and educates in risk management and generating possibilities for an effective earthquake response strategy.

The IIEES is composed of the following research Centers: Seismology, Geotechnical Earthquake Engineering, Structural Earthquake Engineering, Risk Management; National center for Earthquake Prediction, and Graduate School, Public Education and Information Division.
NCREE was established in 1980 by the National Science Council (NSC), and they are working together with the National Taiwan University (NTU), as well as being part of the National Applied Research Laboratories (NARL, a non-profit organisation established in June 2003), whose purpose to improve efficiency between research institutions, and they are trying to decrease the impact of earthquakes on various structures.

They have published books and printed reports with all their findings. This is to try raise public awareness. They also hold international seminars, make videos, and hold a design construction competition every year.
NCREE is aiming to improve seismic resistant designs for all constructions and to provide feedback to the engineering community through research and development. The Center was built for researchers to collaborate and check their theories by doing various experiments. Their goals are:

– Establish and provide research facilities.

– Develop and improve the seismic engineering database.

– Create and carry-out regulations relating to seismic design codes.

– Co-ordinate and Integrate academic institutes and related industries.

– Introduce, Develop and Educate on seismic-resisting technology.
NCREE’s seismic simulation laboratory has international standard facilities, such as eighteen sets of static hydraulic actuators and six sets of dynamic hydraulic actuators.
The Tri-Axial Seismic Simulator, or Shaking Table, can produce earthquake ground motions in six degrees of freedom, with motion in 3 axes.

The shaking table is 5m x 5m and has a mass of 27 tons. It can take models of large scale buildings weighing up to 50 tons, and the square shape of the table provides large bending and torsional stiffness.

Small-scale or full-scale models are placed on the shaking table. To prevent the instrument vibration on surrounding areas during experiments, the shaking table has a vibration isolation system, including 80 dampers, 96 airbags and air springs, and a reaction mass (16m x 16m x 7.6m, weighing about four thousand tons.)

Under the table are twelve actuators, which produce the shaking movement in six degrees of freedom. There are four actuators for each axis, and the hydraulic power is provided by two electrical pumps and three diesel pumps. The weight of the shaky table and the model is balanced by four static supports.

By doing these experiments, engineers can understand a structure’s response to an earthquake. The results will show how stable the building is during earthquakes, and it will also accelerate the development of seismic isolation and minimize the damage caused by an earthquake.

Reaction Wall and Strong Floor
The Reaction Wall and Strong floor make it possible to test multiple full-scale structural experiments. The wall can be used to perform seismic tests by using experimental methods, such as traditional quasi-static tests, cyclic loading tests and pseudo-dynamic tests.

The wall is L-shaped and has 4 sections: 15m x 15.5m, 12m x 15.5m, 9m x 12m and 6m x 12m. The strong floor is a reinforced block of concrete 60m x 29m x 1.2m. The compressive strength of the concrete for both the reaction wall and the strong floor is 350 kg/cm2

During experiments, full-scale and large-scale constructions are mounted onto the strong floor. Hydraulic actuators then exert forces on the test objects, making it possible to see the resistance of various structures and performances of seismic isolators and energy dissipaters. The experimental data has helped proved that seismic theories can be applied, and are a reference to earthquake resistant building designs.Building Engineering Studies

– Seismic evaluation and retrofit technologies of existing buildings.

– Development of advanced innovative construction.

– Revision of building seismic design codes.

Bridge Engineering Studies

– performance-based design of bearing systs in bridges.

– Seismic evaluation and retrofit technologies of existing bridges.

Structural Control and System Identification Studies

– Studies on structural health monitoring and structural control.

– Seismic evaluation and retrofit technologies for high-tech industrial structures.

Geotechnical and Strong Ground Motion Studies

– Studies on earthquake prediction models.

– Establishment of Engineering Geological Databases for TSMIP (EGDT). TSMIP stands for Taiwan Strong Motion Instrumentation Program.

– Seismic behaviour of the investigation of soils in the large bi-axial shaking table shear box.

Earthquake Scenario Studies

– Establishment and application of geotechnical earth science hazard database.

– Development of Taiwan seismic scenario database and its applications.

– Development of Taiwan Earthquake Loss Estimation System.

Experimental Technology Studies

– Collaborative experiment technology using the Internet.

– Application of optical fiber sensors in civil engineering structures.

Information Technology Studies

– Establishment of an earthquake engineering database.

– Integration of numerical and experimental stimulation.
To educate people about earthquakes, there are published books, printed reports, international seminars and videos. NCREE also holds IDEERS and ITP to raise public awareness.

IDEERS Edit
IDEERS stands for “Introducing and Demonstrating Earthquake Engineering Research in Schools” and is held every year by the British council in Taipei, NCREE and the Bristol University. It is a science-based project with a competition developed by the Earthquake Engineering Research Centre of the Bristol University. The students participating are undergraduate students majoring in civil engineering related subjects and high school students. Students entering the competition will make their models using cheap materials which then will be put on the tri-axial seismic simulator (shaking-table). Models will be shaken to destruction, and the best-designed models will win prizes.

ITP Edit
ITP stands for The International Training Program (for Seismic Design of Structures and Hazard Mitigation) and is held by The National Science Council (NSC) and the Democratic Pacific Union. It is a short-term workshop to train government officials and engineers from different countries (In 2006, thirty-three people attended from fourteen different countries). The Program will try to improve the disaster-preventing technology and the earthquake-resisting ability of those countries and try reduce the impacts and losses caused by major earthquakes.

National Center for Research on Earthquake Engineering
storm_Nationwide Earthquake Drillphoto is mine

International Institute of Earthquake Engineering and Seismology (IIEES), founded by Mohsen Ghafory-Ashtiany, is an international earthquake engineering and seismology institute based in Iran. It was established as a result of the 24th UNESCO General Conference Resolution DR/250 under Iranian government approval in 1989. It was founded as an independent institute within the Iran’s Ministry of Science, Research and Technology.[1]

Mohsen Ghafory-Ashtiany distinguished professor of earthquake engineering and risk management at International Institute of Earthquake Engineering and seismology (IIEES) which was founded by him in 1989, is Chief Editor of JSEE and IDRiM Journals; author of more than 140 papers and 3 books in the field of earthquake engineering, seismic hazard and risk analysis, risk management and planning. Ashtiany is the Director and member of the Executive committee of International Association of Earthquake engineering (IAEE), Chairman of Earthquake Hazard, Risk and Strong Ground Motion Commission of IASPEI, member of UN-ISDR Scientific and Technical commission, Director and member of board of World Seismic Safety Initiative, member of Global Earthquake Risk Model Project; Member of Geo-Hazard Initiative, Member of GSHAP, Member of Global Risk Forum-Davos, and many other scientific communities. Ashtiany was born in Tehran, Iran in 1957 and graduated from Va. Tech (USA) in 1983 with honor, and is resident of US.

On its establishment, the IIEES drew up a seismic code in an attempt to improve the infrastructural response to earthquakes and seismic activity in the country. Its primary objective is to reduce the risk of seismic activity on buildings and roads and provide mitigation measures both in Iran and the region.[1]

The institute is responsible for much of the research and education in this field by conducting research and providing education and knowledge in seismotectonic studies, seismology and earthquake engineering.[1] In addition conducts research and educates in risk management and generating possibilities for an effective earthquake response strategy.

The IIEES is composed of the following research Centers: Seismology, Geotechnical Earthquake Engineering, Structural Earthquake Engineering, Risk Management; National center for Earthquake Prediction, and Graduate School, Public Education and Information Division.
NCREE was established in 1980 by the National Science Council (NSC), and they are working together with the National Taiwan University (NTU), as well as being part of the National Applied Research Laboratories (NARL, a non-profit organisation established in June 2003), whose purpose to improve efficiency between research institutions, and they are trying to decrease the impact of earthquakes on various structures.

They have published books and printed reports with all their findings. This is to try raise public awareness. They also hold international seminars, make videos, and hold a design construction competition every year.
NCREE is aiming to improve seismic resistant designs for all constructions and to provide feedback to the engineering community through research and development. The Center was built for researchers to collaborate and check their theories by doing various experiments. Their goals are:

– Establish and provide research facilities.

– Develop and improve the seismic engineering database.

– Create and carry-out regulations relating to seismic design codes.

– Co-ordinate and Integrate academic institutes and related industries.

– Introduce, Develop and Educate on seismic-resisting technology.
NCREE’s seismic simulation laboratory has international standard facilities, such as eighteen sets of static hydraulic actuators and six sets of dynamic hydraulic actuators.
The Tri-Axial Seismic Simulator, or Shaking Table, can produce earthquake ground motions in six degrees of freedom, with motion in 3 axes.

The shaking table is 5m x 5m and has a mass of 27 tons. It can take models of large scale buildings weighing up to 50 tons, and the square shape of the table provides large bending and torsional stiffness.

Small-scale or full-scale models are placed on the shaking table. To prevent the instrument vibration on surrounding areas during experiments, the shaking table has a vibration isolation system, including 80 dampers, 96 airbags and air springs, and a reaction mass (16m x 16m x 7.6m, weighing about four thousand tons.)

Under the table are twelve actuators, which produce the shaking movement in six degrees of freedom. There are four actuators for each axis, and the hydraulic power is provided by two electrical pumps and three diesel pumps. The weight of the shaky table and the model is balanced by four static supports.

By doing these experiments, engineers can understand a structure’s response to an earthquake. The results will show how stable the building is during earthquakes, and it will also accelerate the development of seismic isolation and minimize the damage caused by an earthquake.

Reaction Wall and Strong Floor
The Reaction Wall and Strong floor make it possible to test multiple full-scale structural experiments. The wall can be used to perform seismic tests by using experimental methods, such as traditional quasi-static tests, cyclic loading tests and pseudo-dynamic tests.

The wall is L-shaped and has 4 sections: 15m x 15.5m, 12m x 15.5m, 9m x 12m and 6m x 12m. The strong floor is a reinforced block of concrete 60m x 29m x 1.2m. The compressive strength of the concrete for both the reaction wall and the strong floor is 350 kg/cm2

During experiments, full-scale and large-scale constructions are mounted onto the strong floor. Hydraulic actuators then exert forces on the test objects, making it possible to see the resistance of various structures and performances of seismic isolators and energy dissipaters. The experimental data has helped proved that seismic theories can be applied, and are a reference to earthquake resistant building designs.Building Engineering Studies

– Seismic evaluation and retrofit technologies of existing buildings.

– Development of advanced innovative construction.

– Revision of building seismic design codes.

Bridge Engineering Studies

– performance-based design of bearing systs in bridges.

– Seismic evaluation and retrofit technologies of existing bridges.

Structural Control and System Identification Studies

– Studies on structural health monitoring and structural control.

– Seismic evaluation and retrofit technologies for high-tech industrial structures.

Geotechnical and Strong Ground Motion Studies

– Studies on earthquake prediction models.

– Establishment of Engineering Geological Databases for TSMIP (EGDT). TSMIP stands for Taiwan Strong Motion Instrumentation Program.

– Seismic behaviour of the investigation of soils in the large bi-axial shaking table shear box.

Earthquake Scenario Studies

– Establishment and application of geotechnical earth science hazard database.

– Development of Taiwan seismic scenario database and its applications.

– Development of Taiwan Earthquake Loss Estimation System.

Experimental Technology Studies

– Collaborative experiment technology using the Internet.

– Application of optical fiber sensors in civil engineering structures.

Information Technology Studies

– Establishment of an earthquake engineering database.

– Integration of numerical and experimental stimulation.
To educate people about earthquakes, there are published books, printed reports, international seminars and videos. NCREE also holds IDEERS and ITP to raise public awareness.

IDEERS Edit
IDEERS stands for “Introducing and Demonstrating Earthquake Engineering Research in Schools” and is held every year by the British council in Taipei, NCREE and the Bristol University. It is a science-based project with a competition developed by the Earthquake Engineering Research Centre of the Bristol University. The students participating are undergraduate students majoring in civil engineering related subjects and high school students. Students entering the competition will make their models using cheap materials which then will be put on the tri-axial seismic simulator (shaking-table). Models will be shaken to destruction, and the best-designed models will win prizes.

ITP Edit
ITP stands for The International Training Program (for Seismic Design of Structures and Hazard Mitigation) and is held by The National Science Council (NSC) and the Democratic Pacific Union. It is a short-term workshop to train government officials and engineers from different countries (In 2006, thirty-three people attended from fourteen different countries). The Program will try to improve the disaster-preventing technology and the earthquake-resisting ability of those countries and try reduce the impacts and losses caused by major earthquakes.

Have you heard about earthquake engineering
Science behind the happinessThe Science Of Happiness

Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earthquake (or seismic) engineer aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in a major earthquake. Earthquake engineering is the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels.[1] Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading; it is considered as a subset of structural engineering, geotechnical engineering, mechanical engineering, chemical engineering, applied physics, etc. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering and from the social sciences, especially sociology, political science, economics and finance.

The main objectives of earthquake engineering are:

Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure.
Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.[2]
A properly engineered structure does not necessarily have to be extremely strong or expensive. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.
Seismic loading means application of an earthquake-generated excitation on a structure (or geo-structure). It happens at contact surfaces of a structure either with the ground,[4] with adjacent structures,[5] or with gravity waves from tsunami. The loading that is expected at a given location on the Earth’s surface is estimated by engineering seismology. It is related to the seismic hazard of the location.
Earthquake or seismic performance defines a structure’s ability to sustain its main functions, such as its safety and serviceability, at and after a particular earthquake exposure. A structure is normally considered safe if it does not endanger the lives and well-being of those in or around it by partially or completely collapsing. A structure may be considered serviceable if it is able to fulfill its operational functions for which it was designed.

Basic concepts of the earthquake engineering, implemented in the major building codes, assume that a building should survive a rare, very severe earthquake by sustaining significant damage but without globally collapsing.[6] On the other hand, it should remain operational for more frequent, but less severe seismic events.

Seismic performance assessment Edit
Engineers need to know the quantified level of the actual or anticipated seismic performance associated with the direct damage to an individual building subject to a specified ground shaking. Such an assessment may be performed either experimentally or analytically.

Experimental assessment Edit
Experimental evaluations are expensive tests that are typically done by placing a (scaled) model of the structure on a shake-table that simulates the earth shaking and observing its behavior.[7] Such kinds of experiments were first performed more than a century ago.[8] Only recently has it become possible to perform 1:1 scale testing on full structures.

Due to the costly nature of such tests, they tend to be used mainly for understanding the seismic behavior of structures, validating models and verifying analysis methods. Thus, once properly validated, computational models and numerical procedures tend to carry the major burden for the seismic performance assessment of structures.
Seismic performance assessment or seismic structural analysis is a powerful tool of earthquake engineering which utilizes detailed modelling of the structure together with methods of structural analysis to gain a better understanding of seismic performance of building and non-building structures. The technique as a formal concept is a relatively recent development.

In general, seismic structural analysis is based on the methods of structural dynamics.[9] For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method which also contributed to the proposed building code’s concept of today.[10]

However, such methods are good only for linear elastic systems, being largely unable to model the structural behavior when damage (i.e., non-linearity) appears. Numerical step-by-step integration proved to be a more effective method of analysis for multi-degree-of-freedom structural systems with significant non-linearity under a transient process of ground motion excitation.[11]

Basically, numerical analysis is conducted in order to evaluate the seismic performance of buildings. Performance evaluations are generally carried out by using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate non-linear modeling of structural components such as beams, columns, beam-column joints, shear walls etc. Thus, experimental results play an important role in determining the modeling parameters of individual components, especially those that are subject to significant non-linear deformations. The individual components are then assembled to create a full non-linear model of the structure. Thus created models are analyzed to evaluate the performance of buildings.

The capabilities of the structural analysis software are a major consideration in the above process as they restrict the possible component models, the analysis methods available and, most importantly, the numerical robustness. The latter becomes a major consideration for structures that venture into the non-linear range and approach global or local collapse as the numerical solution becomes increasingly unstable and thus difficult to reach. There are several commercially available Finite Element Analysis software’s such as CSI-SAP2000 and CSI-PERFORM-3D and Scia Engineer-ECtools which can be used for the seismic performance evaluation of buildings. Moreover, there is research-based finite element analysis platforms such as OpenSees, RUAUMOKO and the older DRAIN-2D/3D, several of which are now open source.
Research for earthquake engineering means both field and analytical investigation or experimentation intended for discovery and scientific explanation of earthquake engineering related facts, revision of conventional concepts in the light of new findings, and practical application of the developed theories.

The National Science Foundation (NSF) is the main United States government agency that supports fundamental research and education in all fields of earthquake engineering. In particular, it focuses on experimental, analytical and computational research on design and performance enhancement of structural systems.
The Earthquake Engineering Research Institute (EERI) is a leader in dissemination of earthquake engineering research related information both in the U.S. and globally.

A definitive list of earthquake engineering research related shaking tables around the world may be found in Experimental Facilities for Earthquake Engineering Simulation Worldwide.[13] The most prominent of them is now E-Defense Shake Table[14] in Japan.
NSF also supports the George E. Brown, Jr. Network for Earthquake Engineering Simulation

The NSF Hazard Mitigation and Structural Engineering program (HMSE) supports research on new technologies for improving the behavior and response of structural systems subject to earthquake hazards; fundamental research on safety and reliability of constructed systems; innovative developments in analysis and model based simulation of structural behavior and response including soil-structure interaction; design concepts that improve structure performance and flexibility; and application of new control techniques for structural systems.[15]

(NEES) that advances knowledge discovery and innovation for earthquakes and tsunami loss reduction of the nation’s civil infrastructure and new experimental simulation techniques and instrumentation.[16]

The NEES network features 14 geographically-distributed, shared-use laboratories that support several types of experimental work:[16] geotechnical centrifuge research, shake-table tests, large-scale structural testing, tsunami wave basin experiments, and field site research.[17] Participating universities include: Cornell University; Lehigh University; Oregon State University; Rensselaer Polytechnic Institute; University at Buffalo, State University of New York; University of California, Berkeley; University of California, Davis; University of California, Los Angeles; University of California, San Diego; University of California, Santa Barbara; University of Illinois, Urbana-Champaign; University of Minnesota; University of Nevada, Reno; and the University of Texas, Austin.[16]
The equipment sites (labs) and a central data repository are connected to the global earthquake engineering community via the NEEShub website. The NEES website is powered by HUBzero software developed at Purdue University for nanoHUB specifically to help the scientific community share resources and collaborate. The cyberinfrastructure, connected via Internet2, provides interactive simulation tools, a simulation tool development area, a curated central data repository, animated presentations, user support, telepresence, mechanism for uploading and sharing resources, and statistics about users and usage patterns.

This cyberinfrastructure allows researchers to: securely store, organize and share data within a standardized framework in a central location; remotely observe and participate in experiments through the use of synchronized real-time data and video; collaborate with colleagues to facilitate the planning, performance, analysis, and publication of research experiments; and conduct computational and hybrid simulations that may combine the results of multiple distributed experiments and link physical experiments with computer simulations to enable the investigation of overall system performance.

These resources jointly provide the means for collaboration and discovery to improve the seismic design and performance of civil and mechanical infrastructure systems.

Earthquake simulation Edit
The very first earthquake simulations were performed by statically applying some horizontal inertia forces based on scaled peak ground accelerations to a mathematical model of a building.[18] With the further development of computational technologies, static approaches began to give way to dynamic ones.

Dynamic experiments on building and non-building structures may be physical, like shake-table testing, or virtual ones. In both cases, to verify a structure’s expected seismic performance, some researchers prefer to deal with so called “real time-histories” though the last cannot be “real” for a hypothetical earthquake specified by either a building code or by some particular research requirements. Therefore, there is a strong incentive to engage an earthquake simulation which is the seismic input that possesses only essential features of a real event.

Sometimes earthquake simulation is understood as a re-creation of local effects of a strong earth shaking.
Theoretical or experimental evaluation of anticipated seismic performance mostly requires a structure simulation which is based on the concept of structural likeness or similarity. Similarity is some degree of analogy or resemblance between two or more objects. The notion of similarity rests either on exact or approximate repetitions of patterns in the compared items.

In general, a building model is said to have similarity with the real object if the two share geometric similarity, kinematic similarity and dynamic similarity. The most vivid and effective type of similarity is the kinematic one. Kinematic similarity exists when the paths and velocities of moving particles of a model and its prototype are similar.

The ultimate level of kinematic similarity is kinematic equivalence when, in the case of earthquake engineering, time-histories of each story lateral displacements of the model and its prototype would be the same.
Seismic vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures. All seismic vibration control devices may be classified as passive, active or hybrid[20] where:

passive control devices have no feedback capability between them, structural elements and the ground;
active control devices incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuators within the structure;
hybrid control devices have combined features of active and passive control systems.[21]
When ground seismic waves reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90%. However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential.

After the seismic waves enter a superstructure, there are a number of ways to control them in order to soothe their damaging effect and improve the building’s seismic performance, for instance:

to dissipate the wave energy inside a superstructure with properly engineered dampers;
to disperse the wave energy between a wider range of frequencies;
to absorb the resonant portions of the whole wave frequencies band with the help of so-called mass dampers.[22]
Devices of the last kind, abbreviated correspondingly as TMD for the tuned (passive), as AMD for the active, and as HMD for the hybrid mass dampers, have been studied and installed in high-rise buildings, predominantly in Japan, for a quarter of a century.[23]

However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as seismic or base isolation.

For this, some pads are inserted into or under all major load-carrying elements in the base of the building which should substantially decouple a superstructure from its substructure resting on a shaking ground.

The first evidence of earthquake protection by using the principle of base isolation was discovered in Pasargadae, a city in ancient Persia, now Iran, and dates back to the 6th century BCE. Below, there are some samples of seismic vibration control technologies of today.
People of Inca civilization were masters of the polished ‘dry-stone walls’, called ashlar, where blocks of stone were cut to fit together tightly without any mortar. The Incas were among the best stonemasons the world has ever seen[24] and many junctions in their masonry were so perfect that even blades of grass could not fit between the stones.

Peru is a highly seismic land and for centuries the mortar-free construction proved to be apparently more earthquake-resistant than using mortar. The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing, a passive structural control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications.

Have you heard about earthquake engineering
Science behind the happinessThe Science Of Happiness

Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earthquake (or seismic) engineer aims to construct structures that will not be damaged in minor shaking and will avoid serious damage or collapse in a major earthquake. Earthquake engineering is the scientific field concerned with protecting society, the natural environment, and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels.[1] Traditionally, it has been narrowly defined as the study of the behavior of structures and geo-structures subject to seismic loading; it is considered as a subset of structural engineering, geotechnical engineering, mechanical engineering, chemical engineering, applied physics, etc. However, the tremendous costs experienced in recent earthquakes have led to an expansion of its scope to encompass disciplines from the wider field of civil engineering, mechanical engineering and from the social sciences, especially sociology, political science, economics and finance.

The main objectives of earthquake engineering are:

Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure.
Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.[2]
A properly engineered structure does not necessarily have to be extremely strong or expensive. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.
Seismic loading means application of an earthquake-generated excitation on a structure (or geo-structure). It happens at contact surfaces of a structure either with the ground,[4] with adjacent structures,[5] or with gravity waves from tsunami. The loading that is expected at a given location on the Earth’s surface is estimated by engineering seismology. It is related to the seismic hazard of the location.
Earthquake or seismic performance defines a structure’s ability to sustain its main functions, such as its safety and serviceability, at and after a particular earthquake exposure. A structure is normally considered safe if it does not endanger the lives and well-being of those in or around it by partially or completely collapsing. A structure may be considered serviceable if it is able to fulfill its operational functions for which it was designed.

Basic concepts of the earthquake engineering, implemented in the major building codes, assume that a building should survive a rare, very severe earthquake by sustaining significant damage but without globally collapsing.[6] On the other hand, it should remain operational for more frequent, but less severe seismic events.

Seismic performance assessment Edit
Engineers need to know the quantified level of the actual or anticipated seismic performance associated with the direct damage to an individual building subject to a specified ground shaking. Such an assessment may be performed either experimentally or analytically.

Experimental assessment Edit
Experimental evaluations are expensive tests that are typically done by placing a (scaled) model of the structure on a shake-table that simulates the earth shaking and observing its behavior.[7] Such kinds of experiments were first performed more than a century ago.[8] Only recently has it become possible to perform 1:1 scale testing on full structures.

Due to the costly nature of such tests, they tend to be used mainly for understanding the seismic behavior of structures, validating models and verifying analysis methods. Thus, once properly validated, computational models and numerical procedures tend to carry the major burden for the seismic performance assessment of structures.
Seismic performance assessment or seismic structural analysis is a powerful tool of earthquake engineering which utilizes detailed modelling of the structure together with methods of structural analysis to gain a better understanding of seismic performance of building and non-building structures. The technique as a formal concept is a relatively recent development.

In general, seismic structural analysis is based on the methods of structural dynamics.[9] For decades, the most prominent instrument of seismic analysis has been the earthquake response spectrum method which also contributed to the proposed building code’s concept of today.[10]

However, such methods are good only for linear elastic systems, being largely unable to model the structural behavior when damage (i.e., non-linearity) appears. Numerical step-by-step integration proved to be a more effective method of analysis for multi-degree-of-freedom structural systems with significant non-linearity under a transient process of ground motion excitation.[11]

Basically, numerical analysis is conducted in order to evaluate the seismic performance of buildings. Performance evaluations are generally carried out by using nonlinear static pushover analysis or nonlinear time-history analysis. In such analyses, it is essential to achieve accurate non-linear modeling of structural components such as beams, columns, beam-column joints, shear walls etc. Thus, experimental results play an important role in determining the modeling parameters of individual components, especially those that are subject to significant non-linear deformations. The individual components are then assembled to create a full non-linear model of the structure. Thus created models are analyzed to evaluate the performance of buildings.

The capabilities of the structural analysis software are a major consideration in the above process as they restrict the possible component models, the analysis methods available and, most importantly, the numerical robustness. The latter becomes a major consideration for structures that venture into the non-linear range and approach global or local collapse as the numerical solution becomes increasingly unstable and thus difficult to reach. There are several commercially available Finite Element Analysis software’s such as CSI-SAP2000 and CSI-PERFORM-3D and Scia Engineer-ECtools which can be used for the seismic performance evaluation of buildings. Moreover, there is research-based finite element analysis platforms such as OpenSees, RUAUMOKO and the older DRAIN-2D/3D, several of which are now open source.
Research for earthquake engineering means both field and analytical investigation or experimentation intended for discovery and scientific explanation of earthquake engineering related facts, revision of conventional concepts in the light of new findings, and practical application of the developed theories.

The National Science Foundation (NSF) is the main United States government agency that supports fundamental research and education in all fields of earthquake engineering. In particular, it focuses on experimental, analytical and computational research on design and performance enhancement of structural systems.
The Earthquake Engineering Research Institute (EERI) is a leader in dissemination of earthquake engineering research related information both in the U.S. and globally.

A definitive list of earthquake engineering research related shaking tables around the world may be found in Experimental Facilities for Earthquake Engineering Simulation Worldwide.[13] The most prominent of them is now E-Defense Shake Table[14] in Japan.
NSF also supports the George E. Brown, Jr. Network for Earthquake Engineering Simulation

The NSF Hazard Mitigation and Structural Engineering program (HMSE) supports research on new technologies for improving the behavior and response of structural systems subject to earthquake hazards; fundamental research on safety and reliability of constructed systems; innovative developments in analysis and model based simulation of structural behavior and response including soil-structure interaction; design concepts that improve structure performance and flexibility; and application of new control techniques for structural systems.[15]

(NEES) that advances knowledge discovery and innovation for earthquakes and tsunami loss reduction of the nation’s civil infrastructure and new experimental simulation techniques and instrumentation.[16]

The NEES network features 14 geographically-distributed, shared-use laboratories that support several types of experimental work:[16] geotechnical centrifuge research, shake-table tests, large-scale structural testing, tsunami wave basin experiments, and field site research.[17] Participating universities include: Cornell University; Lehigh University; Oregon State University; Rensselaer Polytechnic Institute; University at Buffalo, State University of New York; University of California, Berkeley; University of California, Davis; University of California, Los Angeles; University of California, San Diego; University of California, Santa Barbara; University of Illinois, Urbana-Champaign; University of Minnesota; University of Nevada, Reno; and the University of Texas, Austin.[16]
The equipment sites (labs) and a central data repository are connected to the global earthquake engineering community via the NEEShub website. The NEES website is powered by HUBzero software developed at Purdue University for nanoHUB specifically to help the scientific community share resources and collaborate. The cyberinfrastructure, connected via Internet2, provides interactive simulation tools, a simulation tool development area, a curated central data repository, animated presentations, user support, telepresence, mechanism for uploading and sharing resources, and statistics about users and usage patterns.

This cyberinfrastructure allows researchers to: securely store, organize and share data within a standardized framework in a central location; remotely observe and participate in experiments through the use of synchronized real-time data and video; collaborate with colleagues to facilitate the planning, performance, analysis, and publication of research experiments; and conduct computational and hybrid simulations that may combine the results of multiple distributed experiments and link physical experiments with computer simulations to enable the investigation of overall system performance.

These resources jointly provide the means for collaboration and discovery to improve the seismic design and performance of civil and mechanical infrastructure systems.

Earthquake simulation Edit
The very first earthquake simulations were performed by statically applying some horizontal inertia forces based on scaled peak ground accelerations to a mathematical model of a building.[18] With the further development of computational technologies, static approaches began to give way to dynamic ones.

Dynamic experiments on building and non-building structures may be physical, like shake-table testing, or virtual ones. In both cases, to verify a structure’s expected seismic performance, some researchers prefer to deal with so called “real time-histories” though the last cannot be “real” for a hypothetical earthquake specified by either a building code or by some particular research requirements. Therefore, there is a strong incentive to engage an earthquake simulation which is the seismic input that possesses only essential features of a real event.

Sometimes earthquake simulation is understood as a re-creation of local effects of a strong earth shaking.
Theoretical or experimental evaluation of anticipated seismic performance mostly requires a structure simulation which is based on the concept of structural likeness or similarity. Similarity is some degree of analogy or resemblance between two or more objects. The notion of similarity rests either on exact or approximate repetitions of patterns in the compared items.

In general, a building model is said to have similarity with the real object if the two share geometric similarity, kinematic similarity and dynamic similarity. The most vivid and effective type of similarity is the kinematic one. Kinematic similarity exists when the paths and velocities of moving particles of a model and its prototype are similar.

The ultimate level of kinematic similarity is kinematic equivalence when, in the case of earthquake engineering, time-histories of each story lateral displacements of the model and its prototype would be the same.
Seismic vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures. All seismic vibration control devices may be classified as passive, active or hybrid[20] where:

passive control devices have no feedback capability between them, structural elements and the ground;
active control devices incorporate real-time recording instrumentation on the ground integrated with earthquake input processing equipment and actuators within the structure;
hybrid control devices have combined features of active and passive control systems.[21]
When ground seismic waves reach up and start to penetrate a base of a building, their energy flow density, due to reflections, reduces dramatically: usually, up to 90%. However, the remaining portions of the incident waves during a major earthquake still bear a huge devastating potential.

After the seismic waves enter a superstructure, there are a number of ways to control them in order to soothe their damaging effect and improve the building’s seismic performance, for instance:

to dissipate the wave energy inside a superstructure with properly engineered dampers;
to disperse the wave energy between a wider range of frequencies;
to absorb the resonant portions of the whole wave frequencies band with the help of so-called mass dampers.[22]
Devices of the last kind, abbreviated correspondingly as TMD for the tuned (passive), as AMD for the active, and as HMD for the hybrid mass dampers, have been studied and installed in high-rise buildings, predominantly in Japan, for a quarter of a century.[23]

However, there is quite another approach: partial suppression of the seismic energy flow into the superstructure known as seismic or base isolation.

For this, some pads are inserted into or under all major load-carrying elements in the base of the building which should substantially decouple a superstructure from its substructure resting on a shaking ground.

The first evidence of earthquake protection by using the principle of base isolation was discovered in Pasargadae, a city in ancient Persia, now Iran, and dates back to the 6th century BCE. Below, there are some samples of seismic vibration control technologies of today.
People of Inca civilization were masters of the polished ‘dry-stone walls’, called ashlar, where blocks of stone were cut to fit together tightly without any mortar. The Incas were among the best stonemasons the world has ever seen[24] and many junctions in their masonry were so perfect that even blades of grass could not fit between the stones.

Peru is a highly seismic land and for centuries the mortar-free construction proved to be apparently more earthquake-resistant than using mortar. The stones of the dry-stone walls built by the Incas could move slightly and resettle without the walls collapsing, a passive structural control technique employing both the principle of energy dissipation and that of suppressing resonant amplifications.

Where does light come from?????????
200w

Were you ever scared of the dark? It’s not surprising if you were, or if you still are today, because humans are creatures of the light, deeply programmed through millions of years of history to avoid the dark dangers of the night. Light is vitally important to us, but we don’t always take the trouble to understand it. Why does it make some things appear to be different colors from others? Does it travel as particles or as waves? Why does it move so quickly? Let’s take a closer look at some of these questions—let’s shed some light on light!
When we’re very young, we have a very simple idea about light: the world is either light or dark and we can change from one to the other just by flicking a switch on the wall. But we soon learn that light is more complex than this.

Light arrives on our planet after a speedy trip from the Sun, 149 million km (93 million miles away). Light travels at 186,000 miles (300,000 km) per second, so the light you’re seeing now was still tucked away in the Sun about eight minutes ago. Put it another way, light takes roughly twice as long to get from the Sun to Earth as it does to make a cup of coffee!

Light is a kind of energy

But why does light make this journey at all? As you probably know, the Sun is a nuclear fireball spewing energy in all directions. The light that we see it simply the one part of the energy that the Sun makes that our eyes can detect. When light travels between two places (from the Sun to the Earth or from a flashlight to the sidewalk in front of you on a dark night), energy makes a journey between those two points. The energy travels in the form of waves (similar to the waves on the sea but about 100 million times smaller)—a vibrating pattern of electricity and magnetism that we call electromagnetic energy. If our eyes could see electricity and magnetism, we might see each ray of light as a wave of electricity vibrating in one direction and a wave of magnetism vibrating at right angles to it. These two waves would travel in step and at the speed of light.
Is light a particle or a wave?

For hundreds of years, scientists have argued over whether light is really a wave at all. Back in the 17th century, the brilliant English scientist Sir Isaac Newton (1642–1727)—one of the first people to study the matter in detail—thought light was a stream of “corpuscles” or particles. But his great rival, a no-less-brilliant Dutchman named Christiaan Huygens (1629–1695), was quite adamant that light was made up of waves.
Thus began a controversy that still rumbles on today—and it’s easy to see why. In some ways, light behaves just like a wave: light reflects off a mirror, for example, in exactly the same way that waves crashing in from the sea “reflect” off sea walls and go back out again. In other ways, light behaves much more like a stream of particles—like bullets firing in rapid succession from a gun. During the 20th century, physicists came to believe that light could be both a particle and a wave at the same time. (This idea sounds quite simple, but goes by the rather complex name of wave-particle duality.)

The real answer to this problem is more a matter of philosophy and psychology than physics. Our understanding of the world is based on the way our eyes and brains interpret it. Sometimes it seems to us that light is behaving like a wave; sometimes it seems like light is a stream of particles. We have two mental pigeonholes and light doesn’t quite fit into either of them. It’s like the glass slipper that doesn’t fit either of the ugly sisters (particle or wave). We can pretend it nearly fits both of them, some of the time. But in truth, light is simply what it is—a form of energy that doesn’t neatly match our mental scheme of how things should be. One day, someone will come up with a better way of describing and explaining it that makes perfect sense in all situations.

How light behaves

Light waves (let’s assume they are indeed waves for now) behave in four particularly interesting and useful ways that we describe as reflection, refraction, diffraction, and interference.

Reflection

The most obvious thing about light is that it will reflect off things. The only reason we can see the things around us is that light, either from the Sun or from something like an electric lamp here on Earth, reflects off them into our eyes. Cut off the source of the light or stop it from reaching your eyes and those objects disappear. They don’t cease to exist, but you can no longer see them.
Reflection can happen in two quite different ways. If you have a smooth, highly polished surface and you shine a narrow beam of light at it, you get a narrow beam of light reflected back off it. This is called specular reflection and it’s what happens if you shine a flashlight or laser into a mirror: you get a well-defined beam of light bouncing back towards you. Most objects aren’t smooth and highly polished: they’re quite rough. So, when you shine light onto them, it’s scattered all over the place. This is called diffuse reflection and it’s how we see most objects around us as they scatter the light falling on them.

If you can see your face in something, it’s specular reflection; if you can’t see your face, it’s diffuse reflection. Polish up a teaspoon and you can see your face quite clearly. But if the spoon is dirty, all the bits of dirt and dust are scattering light in all directions and your face disappears.
Refraction

Light waves travel in straight lines through empty space (a vacuum), but more interesting things happen to them when they travel through other materials—especially when they move from one material to another. That’s not unusual: we do the same thing ourselves.

Have you noticed how your body slows down when you try to walk through water? You go racing down the beach at top speed but, as soon as you hit the sea, you slow right down. No matter how hard you try, you cannot run as quickly through water as through air. The dense liquid is harder to push out of the way, so it slows you down. Exactly the same thing happens to light if you shine it into water, glass, plastic or another more dense material: it slows down quite dramatically. This tends to make light waves bend—something we usually call refraction.
You’ve probably noticed that water can bend light. You can see this for yourself by putting a straw in a glass of water. Notice how the straw appears to kink at the point where the water meets the air above it. The bending happens not in the water itself but at the junction of the air and the water. You can see the same thing happening in this photo of laser light beams shining between two crystals. As the beams cross the junction, they bend quite noticeably.

Why does this happen? You may have learned that the speed of light is always the same, but that’s only true when light travels in a vacuum. In fact, light travels more slowly in some materials than others. It goes more slowly in water than in air. Or, to put it another way, light slows down when it moves from air to water and it speeds up when it moves from water to air. This is what causes the straw to look bent. Let’s look into this a bit more closely.

Imagine a light ray zooming along through the air at an angle to some water. Now imagine that the light ray is actually a line of people swimming along in formation, side-by-side, through the air. The swimmers on one side are going to enter the water more quickly than the swimmers on the other side and, as they do so, they are going to slow down—because people move more slowly in water than in air. That means the whole line is going to start slowing down, beginning with the swimmers at one side and ending with the swimmers on the other side some time later. That’s going to cause the entire line to bend at an angle. This is exactly how light behaves when it enters water—and why water makes a straw look bent.

Refraction is amazingly useful. If you wear eyeglasses, you probably know that the lenses they contain are curved-shape pieces of glass or plastic that bend (refract) the light from the things you’re looking at. Bending the light makes it seem to come from nearer or further away (depending on the type of lenses you have), which corrects the problem with your sight. To put it another way, your eyeglasses fix your vision by slowing down incoming light so it shifts direction slightly. Binoculars, telescopes, cameras, camcorders, night vision goggles, and many other things with lenses work in exactly the same way (collectively we call these things optical equipment).

Although light normally travels in straight lines, you can make it bend round corners by shooting it down thin glass or plastic pipes called fiber-optic cables. Reflection and refraction are at work inside these “light pipes” to make rays of light follow an unusual path they wouldn’t normally take.
We can hear sounds bending round doorways, but we can’t see round corners—why is that? Like light, sound travels in the form of waves (they’re very different kinds of waves, but the idea of energy traveling in a wave pattern is broadly the same). Sound waves tend to range in size from a few centimeters to a few meters, and they will spread out when they come to an opening that is roughly the same size as they are—something like a doorway, for example. If sound is rushing down a corridor in your general direction and there’s a doorway opening onto the room where you’re sitting, the sound waves will spread in through the doorway and travel to your ears. The same thing does not happen with light. But light will spread out in an identical way if you shine it on a tiny opening that’s of roughly similar size to its wavelength. You may have noticed this effect, which is called diffraction, if you screw your eyes up and look at a streetlight in the dark. As your eyes close, the light seems to spread out in strange stripes as it squeezes through the narrow gaps between your eyelids and eyelashes. The tighter you close your eyes, the more the light spreads (until it disappears when you close your eyes completely).

Interference

If you stand above a calm pond (or a bath full of water) and dip your finger in (or allow a single drop to drip down to the water surface from a height), you’ll see ripples of energy spreading outwards from the point of the impact. If you do this in two different places, the two sets of ripples will move toward one another, crash together, and form a new pattern of ripples called an interference pattern. Light behaves in exactly the same way. If two light sources produce waves of light that travel together and meet up, the waves will interfere with one another where they cross. In some places the crests of waves will reinforce and get bigger, but in other places the crest of one wave will meet the trough of another wave and the two will cancel out.
Interference causes effects like the swirling, colored spectrum patterns on the surface of soap bubbles and the similar rainbow effect you can see if you hold a compact disc up to the light. What happens is that two reflected light waves interfere. One light wave reflects from the outer layer of the soap film that wraps around the air bubble, while a second light wave carries on through the soap, only to reflect off its inner layer. The two light waves travel slightly different distances so they get out of step. When they meet up again on the way back out of the bubble, they interfere. This makes the color of the light change in a way that depends on the thickness of the soap bubble. As the soap gradually thins out, the amount of interference changes and the color of the reflected light changes too. Read more about this in our article on thin-film interference.

Interference is very colorful, but it has practical uses too. A technique called interferometry can use interfering laser beams to measure incredibly small distances.
If you’ve read our article on energy, you’ll know that energy is something that doesn’t just turn up out of the blue: it has to come from somewhere. There is a fixed amount of energy in the Universe and no process ever creates or destroys energy—it simply turns some of the existing energy into one or more other forms. This idea is a basic law of physics called the conservation of energy and it applies to light as much as anything else. So where then does light comes from? How exactly do you “make” light?

It turns out that light is made inside atoms when they get “excited”. That’s not excited in the silly, giggling sense of the word, but in a more specialized scientific sense. Think of the electrons inside atoms as a bit like fireflies sitting on a ladder. When an atom absorbs energy, for one reason or another, the electrons get promoted to higher energy levels. Visualize one of the fireflies moving up to a higher rung on the ladder. Unfortunately, the ladder isn’t quite so stable with the firefly wobbling about up there, so the fly takes very little persuading to leap back down to where it was before. In so doing, it has to give back the energy it absorbed—and it does that by flashing its tail.

That’s pretty much what happens when an atom absorbs energy. An electron inside it jumps to a higher energy level, but makes the atom unstable. As the electron returns to its original level, it gives back the energy as a flash of light called a photon.
Atoms are the tiny particles from which all things are made. Simplified greatly, an atom looks a bit like our solar system, which has the Sun at its center and planets orbiting around it.

Most of the atom’s mass is concentrated in the nucleus at the center (red), made from protons and neutrons packed together.

Electrons (blue) are arranged around the nucleus in shells (sometimes called orbitals, or energy levels). The more energy an electron has, the farther it is from the nucleus.

Atoms make light in a three-step process:

They start off in their stable “ground state” with electrons in their normal places.
When they absorb energy, one or more electrons are kicked out farther from the nucleus into higher energy levels. We say the atom is now “excited.”
However, an excited atom is unstable and quickly tries to get back to its stable, ground state. So it gives off the excess energy it originally gained as a photon of energy (wiggly line): a packet of light.
How light really works

Once you understand how atoms take in and give out energy, the science of light makes sense in a very interesting new way. Think about mirrors, for example. When you look at a mirror and see your face reflected, what’s actually going on? Light (maybe from a window) is hitting your face and bouncing into the mirror. Inside the mirror, atoms of silver (or another very reflective metal) are catching the incoming light energy and becoming excited. That makes them unstable, so they throw out new photons of light that travel back out of the mirror towards you. In effect, the mirror is playing throw and catch with you using photons of light as the balls!

The same idea can help us explain things like photocopiers and solar panels (flat sheets of the chemical element silicon that turn sunlight into electricity). Have you ever wondered why solar panels look black even when they’re in full sunlight? That’s because they’re reflecting back little or none of the light that falls on them and absorbing all the energy instead. (Things that are black absorb light, and reflect little or none, while things that are white reflect virtually all the light that falls on them, and absorb little or none. That’s why it’s best to wear white clothes on a scorching hot day.) Where does the energy go in a solar panel if it’s not reflected? If you shine sunlight onto the solar cells in a solar panel, the atoms of silicon in the cells catch the energy from the sunlight. Then, instead of producing new photons, they produce a flow of electricity instead through what’s known as the photoelectric (or photovoltaic) effect. In other words, the incoming solar energy (from the Sun) is converted to outgoing electricity.

Hot light and cold light

What would make an atom absorb energy in the first place? You might give it some energy by heating it up. If you put an iron bar in a blazing fire, the bar would eventually heat up so much that it glowed red hot. What’s happening is that you’re supplying energy to the iron atoms inside the bar and getting them excited. Their electrons are being promoted to higher energy levels and making the atoms unstable. As the electrons return to lower levels, they’re giving off their energy as photons of red light—and that’s why the bar seems to glow red. The fire gives off light for exactly the same reason.

Old-style electric lamps work this way too. They make light by passing electricity through a very thin wire filament so it gets incredibly hot. Excited atoms inside the hot filament turn the electrical energy passing through them into light you can see by constantly giving off photons. When we make light by heating things, that’s called incandescence. So old-style lamps are sometimes called incandescent lamps.

You can also get atoms excited in other ways. Energy-saving light bulbs that use fluorescence are more energy efficient because they make atoms crash about and collide, making lots of light without making heat. In effect, they make cold light rather than the hot light produced by older-style, energy-wasting bulbs. Creatures like fireflies make their light through a chemical process using a substance called luciferin. The broad name for the various different ways of making light by exciting the atoms inside things is luminescence.

(Let’s note in passing that light has some other interesting effects when it gets involved in chemistry. That’s how photochromic sunglass lenses work.)
Color (spelled “colour” in the UK) is one of the strangest things about light. Here’s one obvious riddle: if we see things because sunlight is reflected off them, how come everything isn’t the same color? Why isn’t everything the color of sunlight? You probably know the answer to this already. Sunlight isn’t light of just one color—it’s what we call white light, made up of all the different colors mixed together. We know this because we can see rainbows, those colorful curves that appear in the sky when droplets of water split sunlight into its component colors by refracting (bending) different colors of light by different amounts.

Why does a tomato look red? When sunlight shines on a tomato, the red part of the sunlight is reflected back again off the tomato’s skin, while all the other colors of lights are absorbed (soaked into) the tomato, so you don’t see them. That’s just as true of a blue book, which reflects only the blue part of sunlight but absorbs light of other colors.

Why does a tomato appear red and not blue or green? Think back to how atoms make light. When sunlight falls on a tomato, the incoming light energy excites atoms in the tomato’s skin. Electrons are promoted to higher energy levels to capture the energy, but soon fall back down again. As they do so, they give off photons of new light—and that just happens to correspond to the kind of light that our eyes see as red. Tomatoes, in other words, are like precise optical machines programmed to produce photons of red light when sunlight falls on them.

If you shone light of other colors on tomatoes, what would happen? Let’s suppose you made some green light by passing sunlight through a piece of green plastic (something we call a filter). If you shone this on a red tomato, the tomato would appear black. That’s because tomatoes absorb green light. There is simply no red light for them to reflect.
It’s not how it is—it’s how you see it

Many of the things we think are true of the world turn out to be true only of ourselves. We think tomatoes are red, but in fact we only see them that way. If our eyes were built differently, we might see the light photons that tomatoes produce as light of a totally different color. And there’s no real way any of us can be sure that what we see as “red” is the same as what anyone else sees as red: there’s no way to prove that my red is the same as yours. Some of the most interesting aspects of the things we see come down to the psychology of perception (how our eyes see the world and how our brains make sense of that), not the physics of light. Color blindness and optical illusions are two examples of this.

Understanding light is a brilliant example of what being a scientist is all about. Science isn’t like other subjects. It’s not like history (a collection of facts about past events) or law (the rights and wrongs of how people behave). It’s an entirely different way of thinking about the world and making sense of it. When you understand the science of light, you feel you’ve turned part of the world inside out—you’re looking from the inside, seeing everything in a totally new way, and understanding for the first time why it all makes sense. Science can throw a completely different light on the world—it can even throw light on light itself!

Where does light come from?????????
200w

Were you ever scared of the dark? It’s not surprising if you were, or if you still are today, because humans are creatures of the light, deeply programmed through millions of years of history to avoid the dark dangers of the night. Light is vitally important to us, but we don’t always take the trouble to understand it. Why does it make some things appear to be different colors from others? Does it travel as particles or as waves? Why does it move so quickly? Let’s take a closer look at some of these questions—let’s shed some light on light!
When we’re very young, we have a very simple idea about light: the world is either light or dark and we can change from one to the other just by flicking a switch on the wall. But we soon learn that light is more complex than this.

Light arrives on our planet after a speedy trip from the Sun, 149 million km (93 million miles away). Light travels at 186,000 miles (300,000 km) per second, so the light you’re seeing now was still tucked away in the Sun about eight minutes ago. Put it another way, light takes roughly twice as long to get from the Sun to Earth as it does to make a cup of coffee!

Light is a kind of energy

But why does light make this journey at all? As you probably know, the Sun is a nuclear fireball spewing energy in all directions. The light that we see it simply the one part of the energy that the Sun makes that our eyes can detect. When light travels between two places (from the Sun to the Earth or from a flashlight to the sidewalk in front of you on a dark night), energy makes a journey between those two points. The energy travels in the form of waves (similar to the waves on the sea but about 100 million times smaller)—a vibrating pattern of electricity and magnetism that we call electromagnetic energy. If our eyes could see electricity and magnetism, we might see each ray of light as a wave of electricity vibrating in one direction and a wave of magnetism vibrating at right angles to it. These two waves would travel in step and at the speed of light.
Is light a particle or a wave?

For hundreds of years, scientists have argued over whether light is really a wave at all. Back in the 17th century, the brilliant English scientist Sir Isaac Newton (1642–1727)—one of the first people to study the matter in detail—thought light was a stream of “corpuscles” or particles. But his great rival, a no-less-brilliant Dutchman named Christiaan Huygens (1629–1695), was quite adamant that light was made up of waves.
Thus began a controversy that still rumbles on today—and it’s easy to see why. In some ways, light behaves just like a wave: light reflects off a mirror, for example, in exactly the same way that waves crashing in from the sea “reflect” off sea walls and go back out again. In other ways, light behaves much more like a stream of particles—like bullets firing in rapid succession from a gun. During the 20th century, physicists came to believe that light could be both a particle and a wave at the same time. (This idea sounds quite simple, but goes by the rather complex name of wave-particle duality.)

The real answer to this problem is more a matter of philosophy and psychology than physics. Our understanding of the world is based on the way our eyes and brains interpret it. Sometimes it seems to us that light is behaving like a wave; sometimes it seems like light is a stream of particles. We have two mental pigeonholes and light doesn’t quite fit into either of them. It’s like the glass slipper that doesn’t fit either of the ugly sisters (particle or wave). We can pretend it nearly fits both of them, some of the time. But in truth, light is simply what it is—a form of energy that doesn’t neatly match our mental scheme of how things should be. One day, someone will come up with a better way of describing and explaining it that makes perfect sense in all situations.

How light behaves

Light waves (let’s assume they are indeed waves for now) behave in four particularly interesting and useful ways that we describe as reflection, refraction, diffraction, and interference.

Reflection

The most obvious thing about light is that it will reflect off things. The only reason we can see the things around us is that light, either from the Sun or from something like an electric lamp here on Earth, reflects off them into our eyes. Cut off the source of the light or stop it from reaching your eyes and those objects disappear. They don’t cease to exist, but you can no longer see them.
Reflection can happen in two quite different ways. If you have a smooth, highly polished surface and you shine a narrow beam of light at it, you get a narrow beam of light reflected back off it. This is called specular reflection and it’s what happens if you shine a flashlight or laser into a mirror: you get a well-defined beam of light bouncing back towards you. Most objects aren’t smooth and highly polished: they’re quite rough. So, when you shine light onto them, it’s scattered all over the place. This is called diffuse reflection and it’s how we see most objects around us as they scatter the light falling on them.

If you can see your face in something, it’s specular reflection; if you can’t see your face, it’s diffuse reflection. Polish up a teaspoon and you can see your face quite clearly. But if the spoon is dirty, all the bits of dirt and dust are scattering light in all directions and your face disappears.
Refraction

Light waves travel in straight lines through empty space (a vacuum), but more interesting things happen to them when they travel through other materials—especially when they move from one material to another. That’s not unusual: we do the same thing ourselves.

Have you noticed how your body slows down when you try to walk through water? You go racing down the beach at top speed but, as soon as you hit the sea, you slow right down. No matter how hard you try, you cannot run as quickly through water as through air. The dense liquid is harder to push out of the way, so it slows you down. Exactly the same thing happens to light if you shine it into water, glass, plastic or another more dense material: it slows down quite dramatically. This tends to make light waves bend—something we usually call refraction.
You’ve probably noticed that water can bend light. You can see this for yourself by putting a straw in a glass of water. Notice how the straw appears to kink at the point where the water meets the air above it. The bending happens not in the water itself but at the junction of the air and the water. You can see the same thing happening in this photo of laser light beams shining between two crystals. As the beams cross the junction, they bend quite noticeably.

Why does this happen? You may have learned that the speed of light is always the same, but that’s only true when light travels in a vacuum. In fact, light travels more slowly in some materials than others. It goes more slowly in water than in air. Or, to put it another way, light slows down when it moves from air to water and it speeds up when it moves from water to air. This is what causes the straw to look bent. Let’s look into this a bit more closely.

Imagine a light ray zooming along through the air at an angle to some water. Now imagine that the light ray is actually a line of people swimming along in formation, side-by-side, through the air. The swimmers on one side are going to enter the water more quickly than the swimmers on the other side and, as they do so, they are going to slow down—because people move more slowly in water than in air. That means the whole line is going to start slowing down, beginning with the swimmers at one side and ending with the swimmers on the other side some time later. That’s going to cause the entire line to bend at an angle. This is exactly how light behaves when it enters water—and why water makes a straw look bent.

Refraction is amazingly useful. If you wear eyeglasses, you probably know that the lenses they contain are curved-shape pieces of glass or plastic that bend (refract) the light from the things you’re looking at. Bending the light makes it seem to come from nearer or further away (depending on the type of lenses you have), which corrects the problem with your sight. To put it another way, your eyeglasses fix your vision by slowing down incoming light so it shifts direction slightly. Binoculars, telescopes, cameras, camcorders, night vision goggles, and many other things with lenses work in exactly the same way (collectively we call these things optical equipment).

Although light normally travels in straight lines, you can make it bend round corners by shooting it down thin glass or plastic pipes called fiber-optic cables. Reflection and refraction are at work inside these “light pipes” to make rays of light follow an unusual path they wouldn’t normally take.
We can hear sounds bending round doorways, but we can’t see round corners—why is that? Like light, sound travels in the form of waves (they’re very different kinds of waves, but the idea of energy traveling in a wave pattern is broadly the same). Sound waves tend to range in size from a few centimeters to a few meters, and they will spread out when they come to an opening that is roughly the same size as they are—something like a doorway, for example. If sound is rushing down a corridor in your general direction and there’s a doorway opening onto the room where you’re sitting, the sound waves will spread in through the doorway and travel to your ears. The same thing does not happen with light. But light will spread out in an identical way if you shine it on a tiny opening that’s of roughly similar size to its wavelength. You may have noticed this effect, which is called diffraction, if you screw your eyes up and look at a streetlight in the dark. As your eyes close, the light seems to spread out in strange stripes as it squeezes through the narrow gaps between your eyelids and eyelashes. The tighter you close your eyes, the more the light spreads (until it disappears when you close your eyes completely).

Interference

If you stand above a calm pond (or a bath full of water) and dip your finger in (or allow a single drop to drip down to the water surface from a height), you’ll see ripples of energy spreading outwards from the point of the impact. If you do this in two different places, the two sets of ripples will move toward one another, crash together, and form a new pattern of ripples called an interference pattern. Light behaves in exactly the same way. If two light sources produce waves of light that travel together and meet up, the waves will interfere with one another where they cross. In some places the crests of waves will reinforce and get bigger, but in other places the crest of one wave will meet the trough of another wave and the two will cancel out.
Interference causes effects like the swirling, colored spectrum patterns on the surface of soap bubbles and the similar rainbow effect you can see if you hold a compact disc up to the light. What happens is that two reflected light waves interfere. One light wave reflects from the outer layer of the soap film that wraps around the air bubble, while a second light wave carries on through the soap, only to reflect off its inner layer. The two light waves travel slightly different distances so they get out of step. When they meet up again on the way back out of the bubble, they interfere. This makes the color of the light change in a way that depends on the thickness of the soap bubble. As the soap gradually thins out, the amount of interference changes and the color of the reflected light changes too. Read more about this in our article on thin-film interference.

Interference is very colorful, but it has practical uses too. A technique called interferometry can use interfering laser beams to measure incredibly small distances.
If you’ve read our article on energy, you’ll know that energy is something that doesn’t just turn up out of the blue: it has to come from somewhere. There is a fixed amount of energy in the Universe and no process ever creates or destroys energy—it simply turns some of the existing energy into one or more other forms. This idea is a basic law of physics called the conservation of energy and it applies to light as much as anything else. So where then does light comes from? How exactly do you “make” light?

It turns out that light is made inside atoms when they get “excited”. That’s not excited in the silly, giggling sense of the word, but in a more specialized scientific sense. Think of the electrons inside atoms as a bit like fireflies sitting on a ladder. When an atom absorbs energy, for one reason or another, the electrons get promoted to higher energy levels. Visualize one of the fireflies moving up to a higher rung on the ladder. Unfortunately, the ladder isn’t quite so stable with the firefly wobbling about up there, so the fly takes very little persuading to leap back down to where it was before. In so doing, it has to give back the energy it absorbed—and it does that by flashing its tail.

That’s pretty much what happens when an atom absorbs energy. An electron inside it jumps to a higher energy level, but makes the atom unstable. As the electron returns to its original level, it gives back the energy as a flash of light called a photon.
Atoms are the tiny particles from which all things are made. Simplified greatly, an atom looks a bit like our solar system, which has the Sun at its center and planets orbiting around it.

Most of the atom’s mass is concentrated in the nucleus at the center (red), made from protons and neutrons packed together.

Electrons (blue) are arranged around the nucleus in shells (sometimes called orbitals, or energy levels). The more energy an electron has, the farther it is from the nucleus.

Atoms make light in a three-step process:

They start off in their stable “ground state” with electrons in their normal places.
When they absorb energy, one or more electrons are kicked out farther from the nucleus into higher energy levels. We say the atom is now “excited.”
However, an excited atom is unstable and quickly tries to get back to its stable, ground state. So it gives off the excess energy it originally gained as a photon of energy (wiggly line): a packet of light.
How light really works

Once you understand how atoms take in and give out energy, the science of light makes sense in a very interesting new way. Think about mirrors, for example. When you look at a mirror and see your face reflected, what’s actually going on? Light (maybe from a window) is hitting your face and bouncing into the mirror. Inside the mirror, atoms of silver (or another very reflective metal) are catching the incoming light energy and becoming excited. That makes them unstable, so they throw out new photons of light that travel back out of the mirror towards you. In effect, the mirror is playing throw and catch with you using photons of light as the balls!

The same idea can help us explain things like photocopiers and solar panels (flat sheets of the chemical element silicon that turn sunlight into electricity). Have you ever wondered why solar panels look black even when they’re in full sunlight? That’s because they’re reflecting back little or none of the light that falls on them and absorbing all the energy instead. (Things that are black absorb light, and reflect little or none, while things that are white reflect virtually all the light that falls on them, and absorb little or none. That’s why it’s best to wear white clothes on a scorching hot day.) Where does the energy go in a solar panel if it’s not reflected? If you shine sunlight onto the solar cells in a solar panel, the atoms of silicon in the cells catch the energy from the sunlight. Then, instead of producing new photons, they produce a flow of electricity instead through what’s known as the photoelectric (or photovoltaic) effect. In other words, the incoming solar energy (from the Sun) is converted to outgoing electricity.

Hot light and cold light

What would make an atom absorb energy in the first place? You might give it some energy by heating it up. If you put an iron bar in a blazing fire, the bar would eventually heat up so much that it glowed red hot. What’s happening is that you’re supplying energy to the iron atoms inside the bar and getting them excited. Their electrons are being promoted to higher energy levels and making the atoms unstable. As the electrons return to lower levels, they’re giving off their energy as photons of red light—and that’s why the bar seems to glow red. The fire gives off light for exactly the same reason.

Old-style electric lamps work this way too. They make light by passing electricity through a very thin wire filament so it gets incredibly hot. Excited atoms inside the hot filament turn the electrical energy passing through them into light you can see by constantly giving off photons. When we make light by heating things, that’s called incandescence. So old-style lamps are sometimes called incandescent lamps.

You can also get atoms excited in other ways. Energy-saving light bulbs that use fluorescence are more energy efficient because they make atoms crash about and collide, making lots of light without making heat. In effect, they make cold light rather than the hot light produced by older-style, energy-wasting bulbs. Creatures like fireflies make their light through a chemical process using a substance called luciferin. The broad name for the various different ways of making light by exciting the atoms inside things is luminescence.

(Let’s note in passing that light has some other interesting effects when it gets involved in chemistry. That’s how photochromic sunglass lenses work.)
Color (spelled “colour” in the UK) is one of the strangest things about light. Here’s one obvious riddle: if we see things because sunlight is reflected off them, how come everything isn’t the same color? Why isn’t everything the color of sunlight? You probably know the answer to this already. Sunlight isn’t light of just one color—it’s what we call white light, made up of all the different colors mixed together. We know this because we can see rainbows, those colorful curves that appear in the sky when droplets of water split sunlight into its component colors by refracting (bending) different colors of light by different amounts.

Why does a tomato look red? When sunlight shines on a tomato, the red part of the sunlight is reflected back again off the tomato’s skin, while all the other colors of lights are absorbed (soaked into) the tomato, so you don’t see them. That’s just as true of a blue book, which reflects only the blue part of sunlight but absorbs light of other colors.

Why does a tomato appear red and not blue or green? Think back to how atoms make light. When sunlight falls on a tomato, the incoming light energy excites atoms in the tomato’s skin. Electrons are promoted to higher energy levels to capture the energy, but soon fall back down again. As they do so, they give off photons of new light—and that just happens to correspond to the kind of light that our eyes see as red. Tomatoes, in other words, are like precise optical machines programmed to produce photons of red light when sunlight falls on them.

If you shone light of other colors on tomatoes, what would happen? Let’s suppose you made some green light by passing sunlight through a piece of green plastic (something we call a filter). If you shone this on a red tomato, the tomato would appear black. That’s because tomatoes absorb green light. There is simply no red light for them to reflect.
It’s not how it is—it’s how you see it

Many of the things we think are true of the world turn out to be true only of ourselves. We think tomatoes are red, but in fact we only see them that way. If our eyes were built differently, we might see the light photons that tomatoes produce as light of a totally different color. And there’s no real way any of us can be sure that what we see as “red” is the same as what anyone else sees as red: there’s no way to prove that my red is the same as yours. Some of the most interesting aspects of the things we see come down to the psychology of perception (how our eyes see the world and how our brains make sense of that), not the physics of light. Color blindness and optical illusions are two examples of this.

Understanding light is a brilliant example of what being a scientist is all about. Science isn’t like other subjects. It’s not like history (a collection of facts about past events) or law (the rights and wrongs of how people behave). It’s an entirely different way of thinking about the world and making sense of it. When you understand the science of light, you feel you’ve turned part of the world inside out—you’re looking from the inside, seeing everything in a totally new way, and understanding for the first time why it all makes sense. Science can throw a completely different light on the world—it can even throw light on light itself!

An illustration on how light wor
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Once Maxwell introduced the concept of electromagnetic waves, everything clicked into place. Scientists now could develop a complete working model of light using terms and concepts, such as wavelength and frequency, based on the structure and function of waves. According to that model, light waves come in many sizes. The size of a wave is measured as its wavelength, which is the distance between any two corresponding points on successive waves, usually peak to peak or trough to trough. The wavelengths of the light we can see range from 400 to 700 nanometers (or billionths of a meter). But the full range of wavelengths included in the definition of electromagnetic radiation extends from 0.1 nanometers, as in gamma rays, to centimeters and meters, as in radio waves.

Light waves also come in many frequencies. The frequency is the number of waves that pass a point in space during any time interval, usually one second. We measure it in units of cycles (waves) per second, or hertz. The frequency of visible light is referred to as color, and ranges from 430 trillion hertz, seen as red, to 750 trillion hertz, seen as violet. Again, the full range of frequencies extends beyond the visible portion, from less than 3 billion hertz, as in radio waves, to greater than 3 billion billion hertz (3 x 1019), as in gamma rays.

The amount of energy in a light wave is proportionally related to its frequency: High frequency light has high energy; low frequency light has low energy. So, gamma rays have the most energy (part of what makes them so dangerous to humans), and radio waves have the least. Of visible light, violet has the most energy and red the least. The whole range of frequencies and energies, shown in the accompanying figure, is known as the electromagnetic spectrum. Note that the figure isn’t drawn to scale and that visible light occupies only one-thousandth of a percent of the spectrum.

This might be the end of the discussion, except that Albert Einstein couldn’t let speeding light waves lie. His work in the early 20th century resurrected the old idea that light, just maybe, was a particle after all.
Maxwell’s theoretical treatment of electromagnetic radiation, including its description of light waves, was so elegant and predictive that many physicists in the 1890s thought that there was nothing more to say about light and how it worked. Then, on Dec. 14, 1900, Max Planck came along and introduced a stunningly simple, yet strangely unsettling, concept: that light must carry energy in discrete quantities. Those quantities, he proposed, must be units of the basic energy increment, hf, where h is a universal constant now known as Planck’s constant and f is the frequency of the radiation.

Albert Einstein advanced Planck’s theory in 1905 when he studied the photoelectric effect. First, he began by shining ultraviolet light on the surface of a metal. When he did this, he was able to detect electrons being emitted from the surface. This was Einstein’s explanation: If the energy in light comes in bundles, then one can think of light as containing tiny lumps, or photons. When these photons strike a metal surface, they act like billiard balls, transferring their energy to electrons, which become dislodged from their “parent” atoms. Once freed, the electrons move along the metal or get ejected from the surface.

The particle theory of light had returned — with a vengeance. Next, Niels Bohr applied Planck’s ideas to refine the model of an atom. Earlier scientists had demonstrated that atoms consist of positively charged nuclei surrounded by electrons orbiting like planets, but they couldn’t explain why electrons didn’t simply spiral into the nucleus. In 1913, Bohr proposed that electrons exist in discrete orbits based on their energy. When an electron jumps from one orbit to a lower orbit, it gives off energy in the form of a photon.

The quantum theory of light — the idea that light exists as tiny packets, or particles, called photons — slowly began to emerge. Our understanding of the physical world would no longer be the same.
Wave-Particle Duality
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At first, physicists were reluctant to accept the dual nature of light. After all, many of us humans like to have one right answer. But Einstein paved the way in 1905 by embracing wave-particle duality. We’ve already discussed the photoelectric effect, which led Einstein to describe light as a photon. Later that year, however, he added a twist to the story in a paper introducing special relativity. In this paper, Einstein treated light as a continuous field of waves — an apparent contradiction to his description of light as a stream of particles. Yet that was part of his genius. He willingly accepted the strange nature of light and chose whichever attribute best addressed the problem he was trying to solve.

Today, physicists accept the dual nature of light. In this modern view, they define light as a collection of one or more photons propagating through space as electromagnetic waves. This definition, which combines light’s wave and particle nature, makes it possible to rethink Thomas Young’s double-slit experiment in this way: Light travels away from a source as an electromagnetic wave. When it encounters the slits, it passes through and divides into two wave fronts. These wave fronts overlap and approach the screen. At the moment of impact, however, the entire wave field disappears and a photon appears. Quantum physicists often describe this by saying the spread-out wave “collapses” into a small point.

Similarly, photons make it possible for us to see the world around us. In total darkness, our eyes are actually able to sense single photons, but generally what we see in our daily lives comes to us in the form of zillions of photons produced by light sources and reflected off objects. If you look around you right now, there is probably a light source in the room producing photons, and objects in the room that reflect those photons. Your eyes absorb some of the photons flowing through the room, and that’s how you see.

But wait. What makes a light source produce photons? We’ll get to that. Next.
There are many different ways to produce photons, but all of them use the same mechanism inside an atom to do it. This mechanism involves the energizing of electrons orbiting each atom’s nucleus. How Nuclear Radiation Works describes protons, neutrons and electrons in some detail. For example, hydrogen atoms have one electron orbiting the nucleus. Helium atoms have two electrons orbiting the nucleus. Aluminum atoms have 13 electrons circling the nucleus. Each atom has a preferred number of electrons zipping around its nucleus.

Electrons circle the nucleus in fixed orbits — a simplified way to think about it is to imagine how satellites orbit the Earth. There’s a huge amount of theory around electron orbitals, but to understand light there is just one key fact to understand: An electron has a natural orbit that it occupies, but if you energize an atom, you can move its electrons to higher orbitals. A photon is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit. During the fall from high energy to normal energy, the electron emits a photon — a packet of energy — with very specific characteristics. The photon has a frequency, or color, that exactly matches the distance the electron falls.

You can see this phenomenon quite clearly in gas-discharge lamps. Fluorescent lamps, neon signs and sodium-vapor lamps are common examples of this kind of electric lighting, which passes an electric current through a gas to make the gas emit light. The colors of gas-discharge lamps vary widely depending on the identity of the gas and the construction of the lamp.

For example, along highways and in parking lots, you often see sodium vapor lights. You can tell a sodium vapor light because it’s really yellow when you look at it. A sodium vapor light energizes sodium atoms to generate photons. A sodium atom has 11 electrons, and because of the way they’re stacked in orbitals one of those electrons is most likely to accept and emit energy. The energy packets that this electron is most likely to emit fall right around a wavelength of 590 nanometers. This wavelength corresponds to yellow light. If you run sodium light through a prism, you don’t see a rainbow — you see a pair of yellow lines.
Another way to make photons, known as chemiluminescence, involves chemical reactions. When these reactions occur in living organisms such as bacteria, fireflies, squid and deep-sea fishes, the process is known as bioluminescence. At least two chemicals are required to make light. Chemists use the generic term luciferin to describe the one producing the light. They use the term luciferase to describe the enzyme that drives, or catalyzes, the reaction.

The basic reaction follows a straightforward sequence. First, the luciferase catalyzes the oxidation of luciferin. In other words, luciferin combines chemically with oxygen to produce oxyluciferin. The reaction also produces light, usually in the blue or green region of the spectrum. Sometimes, the luciferin binds with a catalyzing protein and oxygen in a large structure known as a photoprotein. When an ion — typically calcium — is added to the photoprotein, it oxidizes the luciferin, resulting in light and inactive oxyluciferin.

In marine organisms, the blue light produced by bioluminescence is most helpful because the wavelength of the light, around 470 nanometers, transmits much farther in water. Also, most organisms don’t have pigments in their visual organs that enable them to see longer (yellow, red) or shorter (indigo, ultraviolet) wavelengths. One exception can be found in the Malacosteid family of fishes, also known as loosejaws. These animals can both produce red light and detect it when other organisms can’t.

Want to know more about how and why living things make light? Check out How Bioluminescence Works for a deep dive.

We’ll heat things up next with incandescence.
Probably the most common way to energize atoms is with heat, and this is the basis of incandescence. If you heat up a horseshoe with a blowtorch, it will eventually get red-hot, and if you indulge your inner pyromaniac and heat it even more, it gets white hot. Red is the lowest-energy visible light, so in a red-hot object the atoms are just getting enough energy to begin emitting light that we can see. Once you apply enough heat to cause white light, you are energizing so many different electrons in so many different ways that all of the colors are being generated — they all mix together to look white.

Heat is the most common way we see light being generated — a normal 75-watt incandescent bulb is generating light by using electricity to create heat. Electricity runs through a tungsten filament housed inside a glass sphere. Because the filament is so thin, it offers a good bit of resistance to the electricity, and this resistance turns electrical energy into heat. The heat is enough to make the filament glow white-hot. Unfortunately, this isn’t very efficient. Most of the energy that goes into an incandescent bulb is lost as heat. In fact, a typical light bulb produces perhaps 15 lumens per watt of input power compared to a fluorescent bulb, which produces between 50 and 100 lumens per watt.

Combustion offers another way to produce photons. Combustion occurs when a substance — the fuel — combines rapidly with oxygen, producing heat and light. If you study a campfire or even a candle flame carefully, you will notice a small colorless gap between the wood or the wick and the flames. In this gap, gases are rising and getting heated. When they finally get hot enough, the gases combine with oxygen and are able to emit light. The flame, then, is nothing more than a mixture of reacting gases emitting visible, infrared and some ultraviolet light.

Next up we’ll shine a light on lasers.

Gruesome But True – A Male Snake Caught On Camera Lovingly Embracing Corpse Of A Female Snake
snakes-embrace

Gruesome But True – A Male Snake Caught On Camera Lovingly Embracing Corpse Of A Female Snake
By erlymags ( @cely / @lovern )

Look at the picture in this blog; this is the picture of the two snakes embracing. You may not believe this, but it happens this day. A male snake has shown a tender feeling towards a female snake. We thought that animals do not have affection towards their opposite sex. It is proven this day when a man from northern Australia came across a horrifying sight two snakes embracing lovingly, but that male snake had embraced the newly found dead body of a female snake thought to be its mate. What is bitter to think about is the female snake dead and pregnant. Australia is noted to having many snakes and different kinds of animals. Children there are taught at their young age about nature and characteristics of animals.

This man who has seen this scene is a science teacher who brought with him his students early morning to teach them about reptiles only to get shocked when saw these two snakes in dept feeling of something except the female dead. As they get closer to the scene they realized the female snake was pregnant with that male snake and all her eggs scattered on the road. It was told that the female snake was hit by a car. What a terrible moment seeing animals like this. These snakes are non-venomous and the driver should have not killed the pregnant snake, so pitiful view. We are also affected with this happening. Everyone should realize that animals should not just be killed brutally for they also have life. They are part of nature and they in return protect nature from danger.

It also important to science teachers to inculcate onto the minds of the children to give value to lives of animals so they could also develop appreciation to animals lives like snakes. The children will also have interest to share their role in their community and to the society as a whole develop a safe and protection behavior to animals especially in dealing with snakes and other reptiles. Their young minds need to equip with the right values about love to animals. Further, the children can have awareness of their role to share to their peer and group mates these animals need protection and they are also entitled to safety. The snakes are mainly feed on amphibians and small lizards. They do not eat humans just bite, LOL. They can also eat cane toads which are poisonous to other animals for they safe. The snakes are also important to other animals.

Look at the picture as photo image, these are the two snakes that lovingly embracing each other. What a pity to them. They also have their instinct of love. The male snake showed its feeling this way gruesome, but true as backed by science. You may see a YouTube on this just search about two snakes in embracing mood yet the female died. My heart goes to the feeling of these two snakes.

Image shown here, the two snakes showing their affection

Source: World News

The Incredible Healing Power Of A Horse
HORSE HEALING POWER

The Incredible Healing Power Of A Horse
By erlymags ( @cely / @lovern )

Many of you may not believe that a horse is very important to man not only to a sport he likes or to have horse to serve his family as carriage in the absence of wheel. It has been proven as best animal friendly despite alone in his house. Who could believe now that a horse could be a help to people that deal with physical, emotional, social, cognitive and behavioral problems? I think many of you would laugh at this, but this is backed by science. Almost all animals play great role to man not only providing him with its meat for is food, skin for clothing, carriage, fields plowing, but all of those mentioned above that related to man’s healing
need.

What do you notice to animals like horse? All animals know how to take care of themselves. They are all equipped with a ready-instinct to take care of them in nature. Even if they are exposed to sun they could still survive for many hours, though there are some animals that cannot survive under the extreme heat of the sun like a cow. What do you notice to a cow? To those farmers, they have a carabao with them as their partner in the field. A carabao has a strong endurance against the incredibly heat of the sun. It can also withstand under a circumstance in a pace exposed to sun. Carabao only requires daily dipping in mud, a cow not. It requires a daily bath in a river or plain water in spring, faucet or well.

Let us go back to horse and its healing power. At first I was amazed. I was not able to sleep right away at night thinking about how nice to own a horse. Yes, after knowing this, I have a great desire to own a horse. Scientists have made their research on different varieties of animals. Their purpose is to know how we humans can learn from their different health mechanisms. Other animals have been found to possess amazing healing powers that can treat human illness. Their healing powers could also help rehabilitate patients. This is so incredible especially on a horse. We thought a horse is nothing but an animal. I wonder why those horse owners and horse racers find life in calm and serene because the ability of the horse to have these have been acquired by the horse lovers.

A horse can stay calm despite alone in the lonely field. It can withstand abuses of man. A horse could also withstand against a ferocious storm and bad climate alone. Anyone who can inhibit these attitudes of a horse could have a strong will to willingly undergo any circumstances and outsmart life’s problems. A horse
Is important to people who have depressive attitude and killer minded – mind. The best is to always talk to a horse, touch its forehead many times to inhibit the inherent characteristics of a horse- the healing power of the mind to stop loneliness, worries and uncertainties of feeling and beliefs. If you want to be physically, emotionally and socially strong, see a horse or pet a horse. Life is indeed mysterious. All that we have on earth came from God for all His children on earth to inherit them, yet others never care and never understand. To have peace of mind is sometimes hard to do for those that lack power to survive and lack power to accept some realities, so you need a horse to pacify you and give you a serene life. Life chaotic and problematic gives anyone an unhappy life. You need a horse. Go find a horse to stabilize your entire needs: physical, social, emotional, spiritual and financial needs.

This time many of us are restless .There are so many reasons why feel this way. I believe the primary factor that drives many of us to feel this way is money. Despite of the fact that money cannot buy happiness, many also oppose for in the absence of money, one can be in a total loss of everything, A life can be extended because a patient could be treated well in a hospital; a debt can be paid already having surcharges accumulated ; foods could always be available on dining table; there is always money for children’s tuition; there is always money to pay many bills; there is always money to buy important materials needed at home and more only money can do. All these can make life miserable without money. That is why we cannot despise those who are always feeling down and out of control. They might have lost their control not to spend much to avoid extravagance for this can lead life to live on LOSS.

We have to be thankful to the scientists for everyday they study and research some possibilities that could help the human beings. There are many landed six feet below the ground through ending their lives shortly for they cannot anymore suffice to live in too many complications. There are also many life’s gone astray just to survive in a wrong way. From the standpoint of the researchers, it seems that animals are better than humans for animals have their own ways to heal themselves. They have their own healing power despite they have minds only they understand. Look at dogs despite others cruel to them , but look at the way they are treated well by their masters, they are superb pet that could convert the mind of man in peace.

From now on, let us think like a horse so we can always heal all our weak body and mind. From now on, let us love animals. Let us not be cruel to them. They are family member so love is all they need. From them, love and healing power can be inhibited so we all can live in peace and satisfaction of what we have. Life is beautiful worth to live. Don’t waste life, rather love it to the fullest for we only have one life to live and enjoy. To God Be The Glory.

Image credit to Pixabay

Do you know you can verify the science you read???
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Verifying the science you read can be tricky. After reading a scientific publication, check the underlying assumptions and look for internal consistencies. Look up references and studies the publication was based on. Talk to a scientist in a relevant field for more verification and clarification. Save yourself a lot of time and energy by choosing only high-quality sources published by peer-reviewed journals, governments, and trustworthy nonprofits.

Method One of Three:
Checking the Sources
Edit

1
Take note of verifiable facts as you read. Whether the science you read is an article, book, or web page, read the text in its entirety. As you read, pay attention to details. Write down or make a mental note of things that are confusing or unclear. Use a highlighter or pen to underline, circle, or highlight facts that can be verified.[1]
Verifiable facts are those which are based in objective reality rather than on opinion, conjecture, or unfounded belief.

2
Consult referenced data. All verifiable science relies on the work of other scientists to establish its credibility and inspire further studies. One way to verify the science you read is to follow up on the information provided in the study’s footnotes. Check referenced sources to ensure that their conclusions and statistics match those presented in the science literature you’re attempting to verify.[2]
If you’re reading science in a popular publication, sources will be cited in the text rather than in footnotes or endnotes.
Non-specialized sources should describe specific studies but might not refer to published peer-reviewed article by name. They might also refer to certain scientists or authors, or to the titles of scientific journals where relevant publications appeared. Use this information to track down more information whenever possible.

3
Talk to a scientist. If you’re confused about the science you read, contact a relevant scientist to help you verify it. For instance, if you wish to verify an astronomical report you read, you could contact an astronomer. If you wish to verify a physics issue, contact a physics professor.[3]
When you’ve discovered someone to help you verify the science you read, contact them and pose your question. Always be polite and professional when communicating with professional scientists.
Preferably, you will contact more than one expert in the field of the science you read. This will give you a range of opinions regarding whether the science you read is accurate.
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No
Was this method helpful?
Checking the Sources
Yes
Method Two of Three:
Taking a Second, Careful Look
Edit

1
Look at declarative statements. If you read science that has lots of declarative statements (for instance, “It is large”) and is low on quantifiable (numbers-based) data, steer clear. Verifiable science will utilize specific numbers, measurements, and sizes when reporting results.[4]
Check the terms used. Look out for vague or imprecise language. Likewise, avoid science that uses common scientific terms in a novel way. Verifiable science will use terms that other scientists in the field would readily understand.[5]
For instance, if the science you read says, “The heart-consciousness will heal you when you are ready,” you can safely discount it, since there is no “heart-consciousness” known to heal the human body.

3
Beware of facts that are stated absolutely. Many scientific questions are settled and have been for many years. For instance, the science you read might contain clear and categorical explanations regarding why the stars shine or why trees grow. However, some scientific questions are still open to exploration, and the answers are less clear. If the science you read contains facts stated absolutely with little or no corroborating research behind them, you should consider that a red flag.[6]
For instance, the scientific understanding of why we dream remains imperfect. So if the science you read states, “This is why we dream,” instead of a more cautious statement like, “This may be why we dream” or “This could be why we dream,” be wary.

4
Look for internal inconsistencies. If the science you read has charts and statistics that do not jive with the conclusions drawn by the author, you can discount the publication as flawed. Likewise, if the science you read has two conclusions which are at odds, or two data points that contradict each other, the science should be considered untrustworthy.[7]
Choose trusted publications. High-quality science might come from trusted governments, universities, individuals, peer-reviewed journals, and some nonprofit organizations. When checking a book or article for quality, it should be written by someone with significant experience in their scientific field. If you’re reading a scientific article or textbook, the scientist who authored it should have a PhD and long experience at a university or research institution.[8]
Lay publications will, of course, likely be written by someone without a PhD. The author might even be a student. If the lay publication is trusted, you may consider it a reliable source.
Choosing high-quality sources means someone has already verified the science for you before you read it.

2
Only use sources which are free of apparent bias. Poor quality sources are those which have a vested interest in the scientific results or data they are verifying or refuting. For instance, if you read science produced by a fossil fuel company regarding the polluting impact of their products, the company is producing scientific research which could directly impact its fortunes. In such a situation, you should be skeptical of the data.[9]
Good sources will provide a high degree of transparency, and include disclaimers regarding funding sources. They will also name all participants in the scientific research.

3
Compare the science you read to other publications on the subject. One way to verify the science you read is to check it against other sources on the topic. After reading a scientific article or publication, look the topic up in an encyclopedia or another trusted text. This way, you will learn what the consensus view on the subject is.[10]
Comparing the science you read against many other publications will help you determine whether the science you read is consistent with mainstream scientific thought.