Scientists divide ultraviolet rays into three bands: wavelengths between 100 and 290 nanometers (UVC), wavelengths between 290 and 320 nanometers (UVB), and wavelengths between 320 and 400 nanometers (UVA). UVC has the shortest wavelength and the most harmful. It can be used as an ultraviolet germicidal lamp, but it will be completely absorbed by the ozone layer; excessive UVB light will tan, burn, and even cause cancer. 95% of the UVB will also be absorbed by the ozone layer; UVA It can reach the dermis of the skin and damage the supporting structure of cells, leading to premature aging, cataracts and sunburn.
Although filtering out all UV rays can eliminate skin cancer and premature aging, it also has some negative effects. Not only does our body use ultraviolet light to make vitamin D, many animals also rely on ultraviolet light to survive. Certain species of butterflies use ultraviolet light to attract mates, and sockeye salmon use ultraviolet light to find food. In the Arctic, ultraviolet light allows reindeer to spot wolves, and the fur and urine of wolves on snow will appear black under ultraviolet light. In addition to the above examples, many other species can see the ultraviolet spectrum. If there is no ultraviolet light, their world will lack many colors, and some will even live in darkness.
Although magma contains many minerals we want, such as silicon and iron, these minerals are dispersed in the magma and the concentration is very small, so we cannot directly mine the ores and metals in the magma.
Before we try to mine these minerals, it is best to let nature gather them. Two natural processes can concentrate the minerals in the magma. One is that the magma moves to the surface and cools down, and the temperature drop will cause some minerals to crystallize and form mineral particles. Due to different crystallization points, some substances tend to crystallize preferentially, and the preferentially crystallized minerals are purer; another way of concentration is that magma combines with water and migrates to a place that is more convenient for mining and re-precipitation. For example, the magma that can form granite contains water. When the granite cools, anhydrous minerals crystallize preferentially, and certain rare chemical elements, such as lithium, beryllium, and niobium, will be concentrated in the aqueous solution. The water-rich residual magma is easier to flow and migrate, and when it reaches the right place, it will settle down.
First of all, how fast and far we can run depends on some objective physiological factors, including maximum oxygen uptake and lactate threshold. Maximum oxygen uptake refers to the highest value of the volume of oxygen that tissue cells can use or consume when a person is doing intense exercise. In addition, with the increase in exercise intensity, the rate of lactic acid produced by the human body’s anaerobic metabolism gradually increases. To a certain critical point, the rate of lactic acid production exceeds the maximum rate of the human body to clear lactic acid. This critical point is called the lactic acid threshold. . The higher the lactate threshold and the greater the maximum oxygen uptake, the better the athlete’s endurance will be.
Secondly, mental state is also an important factor affecting endurance. For long-distance runners, it is also necessary to master some psychological skills in order to run for longer periods of time and even endure physical soreness. Common psychological techniques include self-motivating dialogue and attention shifting methods.
Under normal circumstances, human cells with specific functions cannot be reversed to an undifferentiated state or become other types of differentiated cells. What is even more sad is that certain cells such as heart cells cannot regenerate after severe trauma, which means that the patient’s cardiovascular health will always be threatened and unable to maintain or heal itself. However, a kind of marine animal without heart tissue-the sea anemone may provide the key to heart regeneration.
The sea anemone is native to the east coast of the United States. It is a simple, translucent creature. Its magic is that even if it is cut into multiple pieces, each piece can still develop into a new individual. In 2017, a research team from the University of Florida found that the intestinal cells of sea anemones and human and other animal heart cells contain some of the same genes, and intestinal cells containing “heart genes” can be transformed into other types of cells , These cells can be used to restore damaged body parts. At present, scientists are further studying the gene expression of sea anemone intestinal cells. In the future, scientists may be able to clarify the mechanism of cell transformation and induce muscle cells to regenerate heart cells.
Venus is the brightest star in the sky except for the sun and the moon. People often call it “Taibai Star” or “Taibai Venus”. Since Venus is a planet, not a star, its light does not come from the interior of the celestial body. Venus is so bright because the atmosphere surrounding Venus is extremely reflective. In billions of years, due to the phenomenon of “uncontrolled greenhouse effect”, the abnormal volcanic activity on the surface of Venus has caused a very dense atmosphere. At the same time, the clouds of Venus contain a large number of sulfuric acid and acid crystals, and light can easily get from these crystals. Reflected from the surface of the planet, Venus can reflect 70% of the sun’s rays hitting the planet’s surface. In contrast, the moon actually reflects only 10% of the sun’s light, but because it is close to the earth, it seems to us that the moon is brighter.
