HOW DOES AN LED WORK?

LED stands for Light-emitting diode. It is a semiconductor device that emits light when an electric current flows through it. Unlike others lights, LEDS never dim with time and have an extended lifespan that can last a couple of years. They also do not contain poisonous gases like mercury that are commonly used to make the traditional lights. These energy-efficient bulbs are made up of glass and aluminum, which can be recovered by recycling and used to create other products.

The LED is a specialised form of PN junction that uses a compound junction. The semiconductor material used for the junction must be a compound semiconductor. The commonly used semiconductor materials including silicon and germanium are simple elements and junction made from these materials do not emit light. Instead compound semiconductors including gallium arsenide, gallium phosphide and indium phosphide are compound semiconductors and junctions made from these materials do emit light.

These compound semiconductors are classified by the valence bands their constituents occupy. For gallium arsenide, gallium has a valency of three and arsenic a valency of five and this is what is termed a group III-V semiconductor and there are a number of other semiconductors that fit this category. It is also possible to have semiconductors that are formed from group III-V materials.

The light emitting diode emits light when it is forward biased. When a voltage is applied across the junction to make it forward biased, current flows as in the case of any PN junction. Holes from the p-type region and electrons from the n-type region enter the junction and recombine like a normal diode to enable the current to flow. When this occurs energy is released, some of which is in the form of light photons.

It is found that the majority of the light is produced from the area of the junction nearer to the P-type region. As a result the design of the diodes is made such that this area is kept as close to the surface of the device as possible to ensure that the minimum amount of light is absorbed in the structure.

To produce light which can be seen the junction must be optimised and the correct materials must be chosen. Pure gallium arsenide releases energy in the infra read portion of the spectrum. To bring the light emission into the visible red end of the spectrum aluminium is added to the semiconductor to give aluminium gallium arsenide (AlGaAs). Phosphorus can also be added to give red light. For other colours other materials are used. For example gallium phoshide gives green light and aluminium indium gallium phosphide is used for yellow and orange light. Most LEDs are based on gallium semiconductors.

Credit : Electronics notes 

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IS 3D-PRINTED ROCKET READIES FOR LAUNCH?

A U.S. start up is behind Terran 1, and could be a pioneering effort in the still-nascent commercial space industry.

Relativity Space is a Los Angeles aerospace start-up that builds rockets using advanced 3D printing technology.

Its debut rocket, the Terran 1, has completed pre-launch testing, ahead of a planned launch window beginning June 30. Originally intended to be ready by 2020, the project is running about 18 months behind schedule. The first rocket launch will carry no cargo and is purely a test flight. If successful, a second flight will carry a NASA payload-it is capable of lifting up to one tonne into low Earth orbit.

The Terran 1 is an intended stepping stone on the way to realising the Terran R, a reusable rocket currently under development, capable of carrying 20 times the cargo of the Terran 1, when it launches in 2024. In order to 3D-print large components, Relativity Space has created "Stargate" a system that it claims is the world's largest 3D printer of metals. It uses existing welding technology to melt metal wire, layer by layer, into precise and complex structures that have minimal joints and parts. The company says it will eventually be able to build an entire rocket (95% of which is 3D-printed) in two months. Traditional methods of construction take 24 months and use 100 times as many parts.

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WHO WAS THE FIRST AMERICAN WOMAN TO WALK IN SPACE?

On June 18, 1983, Sally K. Ride was onboard the space shuttle Challenger for the STS-7 mission, thereby becoming the first American woman to go into space. Apart from making two space flights, Ride championed the cause of science education for children.

The first decades of space exploration was largely dominated by two countries the US and the Soviet Union This period is even referred to as the Space Race as the two Cold War adversaries pitted themselves: against each other to achieve superior spaceflight capabilities.

While the two countries were neck and neck in most aspects. the Soviets sent a woman to space much before the US. Even though Valentina Tereshkova became the first woman in space in June 1963, it was another 20 years before Sally Ride became the first American woman in space

Urged to explore

Ride was the older of two daughters born  to Carol Joyce Ride and Dale Ride. Even though her mother was a counsellor and her father a professor of political science. Ride credits them for fostering her interest in science by enabling her to explore from a very young age.

An athletic teenager, Ride loved sports such as tennis, running, volleyball, and softball. In fact, she attended Westlake School for Girls in Los Angeles on a partial tennis scholarship. She even tried her luck in professional tennis, before returning to California to attend Stanford University.

By 1973, Ride not only had a Bachelor of Science degree in Physics, but had also obtained a Bachelor of Arts degree in English. She got her Master of Science degree in 1975 and obtained her Ph.D. in Physics by 1978

Restriction removed

Having restricted astronaut qualification to men for decades,  NASA expanded astronaut selection with the advent of the space shuttle from only pilots to engineers and scientists, opening the doorway for women finally. Having seen an ad in a newspaper inviting women to apply for the astronaut programme Ride decided to give it a shot

Out of more than 8,000 applications, Ride became one of six women who were chosen as an astronaut candidate in January 1978. Spaceflight training began soon after and it included parachute jumping, water survival, weightlessness, radio communications, and navigation, among others. She was also involved in developing the robot arm used to deploy and retrieve satellites.

Ride served as part of the ground-support crew for STS-2 and STS-3 missions in November 1981 and March 1982. In April 1982, NASA announced that Ride would be part of the STS-7 crew, serving as a mission specialist in a five-member crew.

First American woman in space

On June 18, 1983, Ride became the first American woman in space. By the time the STS-7 mission was completed and the space shuttle Challenger returned to Earth on June 24, they had launched communications satellites for Canada and Indonesia. As an expert in the use of the shuttle's robotic arm, Ride also helped deploy and retrieve a satellite in space using the robot arm.

Ride created history once again when she became the first American woman to travel to space a second time as part of the STS-41G in October 1984. During this nine-day mission, Ride employed the shuttle's robotic arm to remove ice from the shuttle's exterior and to also readjust a radar antenna. There could have even been a third, as she was supposed to join STS-61M, but that mission was cancelled following the 1986 Challenger disaster.

Even after her days of space travel were over, Ride was actively involved in influencing the space programme. When accident investigation boards were set up in response to two shuttle tragedies - Challenger in 1986 and Columbia in 2003 Ride was a part of them both.

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HOW DOCTORS STARTED USING STETHOSCOPES TO DIAGNOSE PROBLEMS WITH THE CHEST?

The practice of using stethoscopes started in a hospital in Paris, in the early 19th Century.

The Necker-Enfants Malades Hospital in Paris provided specialised medical care. Rene Laennec, one of the doctors there, was trained to use sound to diagnose diseases of the chest.

One day in 1816, a young woman who had a heart problem came to consult Dr. Laennec. Ordinarily, the physician would have put his ear to the woman's chest and listened to her heartbeats to detect if there was any aberration. But the woman who came to see Dr. Laennec was rather plump. Uncomfortable with the idea of putting his ear to her chest, the doctor's eyes fell on a newspaper lying there...and he got a brainwave!

He rolled the newspaper into a cylinder and applied one end of it to the region of the woman's heart and the other to his ear. And then his own heart thumped in joy and excitement! He could hear her heartbeats more clearly than if he had put his ear directly to her chest. It was a landmark moment in medical science.

Laennec fashioned a hollow, wooden cylinder and catalogued the various sounds he could hear through it when applied to a patient's chest, and what the sounds indicated about the health of the patient. He sent his findings to the Academy of Science, in Paris.

It was not long before his invention began to be used by physicians all over Europe.

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WHAT IS RESEARCH OF MAKING CEMENT FROM FOOD WASTE BY JAPANEES?

Food waste is a huge problem worldwide. In Japan alone, the edible food waste produced in 2019 amounts to 5.7 million tons. While their government aims to reduce that to around 2.7 million tons by 2030, there are others who are working on the same problem differently. Researchers from Tokyo University, for instance, have found a new method to create cement from food waste.

In addition to addressing the issue of food waste, the researchers also hope to reduce global warming in this way. Apart from the estimate that cement production accounts for 8% of the world's carbon dioxide emissions, there is also the fact that wasted food materials rotting in landfills emit methane. By using these materials to make cement, scientists hope to reduce global warming.

The researchers borrowed a heat pressing concept that they had employed to pulverise wood particles to make concrete. By using simple mixers and compressors that they could buy online, the researchers used a three-step process of drying. pulverising, and compressing to turn wood particles into concrete.

Heat pressing concept

Following this success, they decided to do the same to food waste. Months of failures followed as they tried to get the cement to bind by tuning the temperature and pressure. The researchers say that this was the toughest part of the process as different food stuff requires different temperatures and pressure levels.

The researchers were able to make cement using tea leaves, coffee grounds, Chinese cabbage, orange and onion peels, and even lunch-box leftovers. To make this cement waterproof and protect it from being eaten by rodents and other pests, the scientists suggest coatings of lacquer.

Cement that can be eaten!

Additionally, the researchers tweaked flavours with different spices to arrive at different colours, scents, and taste of the cement. Yes, you read that right. This material can even be eaten by breaking it into pieces and then boiling it.

The scientists hope that their material can be used to make edible makeshift housing materials for starters, as they are bound to be useful in times of disasters. If food cannot be delivered to evacuees, for instance, then they could maybe eat makeshift beds prepared from food cement. The food cement that they have created is reusable e and biodegradable.

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