Why does a person yawn and is it true that yawning is contagious? Detailed answer

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Why does a person yawn and is it true that yawning is contagious? Detailed answer

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Why does a person yawn and is it true that yawning is contagious?

Scientists have not yet figured out what the physiological cause of the yawning process is. There are several theories: for example, that when a person yawns, a person receives a large portion of oxygen when it is lacking in the body, or that an overheated brain “resets” its temperature in this way, but not a single theory has yet been convincingly proven. However, yawning has been proven to be contagious. A person is more likely to yawn at the sight of another yawning, or when a person on the phone yawns. Contagious yawning has also been identified in chimpanzees.

Authors: Jimmy Wales, Larry Sanger

Random interesting fact from the Great Encyclopedia:

How does a bullfinch look in the lens of a night vision device in a cold winter?

If you point the lens of a night vision device at a bullfinch in cold winter (as well as any other bird that feels comfortable in winter cold), only a bird's eye will appear on the screen.

The fact is that the thermal conductivity of bird feathers and down is very low (1,5-2 times less than the thermal conductivity of dry air), and therefore the down and feathers of a bullfinch reliably protect it from heat loss even in the most severe frosts.

The wool and fur of many animals have the same property. It is said that at one time attempts to detect with the help of night vision devices the caravans of the Mujahideen in Afghanistan, smuggling weapons from Pakistan at night, ended in failure: they were protected by blankets made of camel hair.

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A metallic substance that does not conduct heat when an electric current is passed 29.12.2019

Researchers from the American National Laboratory at Berkeley have discovered a new substance that, being in a metallic state, conducts electricity well, being, at the same time, a thermal insulator. This feature of this material can be very useful in some areas, however, it fundamentally breaks all established principles and understanding of how electrical conductors work.

The properties of a substance discovered back in 2017 violate the Wiedemann-Franz law, according to which the thermal conductivity of a conductive material is proportional to its electrical conductivity. It is in accordance with this law that things such as electric heaters, electromagnets and electric motors become warm and even hot during their use.

The substance detected is vanadium dioxide (VO2), a material that under normal conditions is a transparent dielectric. But when the temperature rises above 67 degrees Celsius, this material passes into a metallic conductive phase. "The unusual properties of vanadium dioxide destroy all our understanding derived from physics textbooks," the researchers write. "This discovery is of great importance for understanding the behavior of electrons in some materials."

In order to understand where such bizarre properties come from in vanadium dioxide (thermal conductivity, which is 10 times less than the value determined by the Wiedemann-Franz law), scientists studied how electrons move in the crystal lattice of this material. And the reason for this was the unusual synchronization of the movement of all electrons. "Electrons inside this material move all together as a fluid flow, and not as separate particles, which is the case in other metallic substances," the researchers write. other materials."

In their research, scientists began to introduce various additives into vanadium dioxide and see how this would affect the properties of the material. The addition of tungsten made it possible to lower the transition temperature of the material to the metallic state and to increase its thermal conductivity. This will allow, for example, to create cooling elements that will start working only when the temperature of the cooled object exceeds a certain threshold.

The new material has another unique property - under normal conditions, this material is transparent in all light ranges, but at temperatures above 60 degrees Celsius, it begins to reflect infrared light, remaining transparent to visible light. Thanks to these properties, vanadium dioxide with some additives can be used as a coating for "smart" windows that can lower the temperature in a room without the need for air conditioning.

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