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Where's the phone's antenna?

2025-02-14 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > IT Information >

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Shulou(Shulou.com)11/24 Report--

Q1. Since there are already international units such as kilometers (kilometers), why define such units as miles and nautical miles? And the length is not the same? By Emperor

A:

Because miles, nautical miles and other units were defined and used before the international system of units, it is natural that they will continue to be used after so many years. Although the international system of units has been widely accepted now, it took shape at the end of the 18th century. Before the formation of international units, people also have the need for measurement, so different systems of units are defined in different fields.

Miles are from the Roman Empire 2000 years ago, it is said that the corresponding length of two thousand steps for people, one mile is equal to 1.609 kilometers. The sea, as its name implies, was invented for navigation. Nautical miles are defined as 1/60 of the corresponding length of the earth's meridian, which is 21, 600 times the length of the meridian, usually 1.852 kilometers. Due to the curvature of the earth, a straight line in the real world will be transformed into a curve when projected on a traditional map. Therefore, when a ship is sailing at sea, in order to ensure the correct course, it is necessary to use the longitude and latitude map of isometric projection and refer to the longitude and latitude coordinates to determine its own position. The sea is defined as the distance corresponding to one latitude of 1/60, which is convenient for people at sea to better calculate the position.

At present, Britain has completed the conversion from imperial units to metric units, and only the United States and a small number of former British colonies still use imperial units. Because of its unique convenience in navigation, surveying and mapping, the sea is still widely used in related industries. In fact, in our daily life, there will also be some conventional non-metric units used. For example, the mu (1 mu = 666.67 square meters) commonly used to measure the area of cultivated land is a unit that has gradually evolved since the Qin Dynasty unified weights and measures. Because some units have long been widely accepted within the group, they have been handed down and have been used all the time.

By single male youth

Q2. Why are the "dark circles" of giant pandas so heavy? By 12321

A:

When I saw this problem, Yaya was eating hard and waiting to return home.

So why is Yaya's eye black?

First of all, during the ice age, the forest was a black-and-white world, and the panda's dark circles could also be used to protect its eyes. Now, pandas live in weak light environments such as bamboo forests and hills for a long time. At the same time, pandas do not have white eyes, and the black hair next to their eyes can prevent strong light from harming their eyesight and help giant pandas find natural enemies or food.

Second, researchers have suggested the reasons for the appearance of dozens of animal spots, which may be warning, camouflage, communicating, or regulating body temperature. In a 2017 study on why giant pandas are black and white, researchers compared pandas with 195 other terrestrial predators and 39 bear subspecies and found a link between light color and snow cover. Researchers believe that giant pandas in black and white can hide them both in the forest and in the snow. Black spots around the eyes may be used for communication, and these patches can be recognized between giant pandas. Giant pandas can also act as a deterrent in the face of other threats, covering their eyes with their claws when they don't want to show a threat.

Isn't it cute?

References:

[1] How pandas got their patches | Science | AAAS

By Minke

Q3. People stand next to the train track, and when the train passes at a constant speed, the frequency of the siren does not change. Why is the tone getting sharper and sharper? Mr. by Luo

A:

The frequency of the whistle is the same, but the frequency heard by the human ear is indeed higher than the frequency of the whistle, which is Kepler, no, Planck, no, Trump, not right, Doppler effect.

No kidding, this is a typical example of the Doppler effect. Doppler effect (or Doppler shift) refers to the phenomenon that the frequency is different from that of the wave source when the observer moves relative to the wave source. When the wave source moves toward the observer, that is, as the distance gets closer and closer, the observed frequency becomes higher, on the contrary, when the distance is farther and farther away, the frequency becomes lower.

The observed frequency and wave source frequency satisfy the following formula:

Among them, the frequency observed by the observer is the actual frequency of the wave emitted by the wave source, the propagation speed of the wave in the medium, and the moving speed of the observer relative to the medium. The positive sign represents the moving speed close to the emission source, and the negative sign is vice versa; it represents the moving speed of the wave source relative to the medium, the positive sign represents the distance from the observer, and the negative sign vice versa.

In daily life, both sound waves and electromagnetic waves have Doppler effect, and the train whistle in the topic is the Doppler effect of sound waves. We can understand the Doppler effect qualitatively in this way. Waves have peaks and troughs, and the period per unit time, that is, the number of peaks or troughs is frequency. When the wave source approaches us, the conduction distance of the peaks we observe now will be greater than the peaks observed later. Therefore, the time for the latter peaks to reach us is always shorter than the previous peaks. That is to say, for the next time, the number of peaks observed per unit time is always more than that of the present time, so the observed frequency will be higher than that of the wave source.

In fact, pay attention to observe that when the train leaves you, the sound of the whistle you hear will become low, that is, the frequency is lower than the frequency of the whistle, of course, the frequency of the whistle itself is the same from beginning to end.

By Frost White

Q4. How does the mobile phone emit electromagnetic waves? By Emperor

A:

Electromagnetic waves are emitted through the antenna, of course. Alternating current is applied to a metal antenna, and the electrons in the antenna oscillate back and forth at both ends. This is equivalent to forming an oscillating electric dipole with a negative charge.

The yellow-green line represents the electric field and the blue line represents the magnetic field | Source: the wavelength of the electromagnetic wave emitted by the electronic engineer Hua GE @ bilibili antenna is related to the size of the antenna. The wavelength emitted by this centrally fed linear dipole antenna is concentrated at twice the length of the antenna, so it is also called a half-wave antenna. The monopole antenna is widely used in engineering, and its size is only half of that of the dipole antenna, that is, 1/4 of the wavelength.

In the early 1G era, the communication band was 800MHz, the wavelength was 37.5cm, and the antenna length had to reach 9.375cm, which often caused the antenna to go beyond the fuselage and expose a part of the outside. In the 5G era, the communication channel is raised to 3GHz, the wavelength is 10cm, and the antenna can be shortened to 2.5cm, which can be easily hidden into the fuselage.

In addition to the progress brought about by the improvement of the communication frequency band, the manufacturing process of the antenna itself is also improving. The previous antenna was printed in the fuselage circuit, called the FPC antenna; later, to make room for the battery, the antenna was carved with a laser attached to the plastic rear shell of the mobile phone, called the LDS antenna.

There is a printed FPC antenna on the left, and a LDS antenna on the back cover on the right, which realizes NFC, wireless charging, WiFi, calling and other functions.

What's more, it can be fused directly into the metal shell. For example, the following image is designed to integrate the antenna into the phone's two metal frames, one for Bluetooth, WiFi and GPS, and the other for calls.

By sheep herding

Q5, acid and alkali correspond, but why is there only sour taste and no "alkaline taste" in our language? What does alkali taste like? By cesium atomic clock

A:

First of all, let's not taste the taste of chemical reagents.

The editor carefully recalled the description of the taste in life and found that it was actually "alkaline". The difference in people's perception of acid-base taste reflects, to a large extent, people's instinct for food nutrition choices. For example, many people's favorite fruits and yogurt contain a lot of organic acids that are beneficial to the body, such as vitamin C. as an essential vitamin, it is also a kind of organic acid. There is reason to think that people prefer acids because they can get nutrients, which is so important to the survival of our ancestors that we drool when we see or think of acid; on the other hand, alkali is rarely found in natural food. and more in metal salts, that is, clay ores. Organic bases are rare and rarely linked to nutrients, so acids are more familiar to us. But in fact, alkaline substances are also quite common in food. for example, baking soda, or sodium bicarbonate, has become a necessity for us to make all kinds of pasta, such as steamed bread, bread, noodles and soda cracker, which can be used to neutralize organic acids produced by fermentation. it can also make noodles more fluffy. Pine flower eggs need to be made with strong alkali. So what exactly does "alkaline taste" mean?

Sour plum (do you want to drool hhh when you see it)? take noodle steamed bread as an example, the editor still remembers that my mother made a mistake in making steamed bread. When eating more alkali, I got the golden steamed bread (over-alkaline steamed bread) in the picture below, which made me eat two big bowls of tears. At this time, the steamed bread shows a touch of pungent, astringent and bitter taste, which is called "excessive alkaline taste" in my hometown.

Excessive alkali steamed bread | Tuyuan network editor also accidentally ate undercooked pine flower eggs, which is even more bitter and difficult to swallow. Therefore, alkaline taste often refers to this astringent and bitter taste. The editor tried to find the literature support. I'm sorry I couldn't find it. I can only find some empirical remarks such as "natural soda (sodium carbonate) is bitter" in the search engine.

This problem is based on the natural idea of acid-base symmetry. However, it can be seen that the acid in chemistry is marked by hydrogen ion, which obviously corresponds to the sour taste in life, and it is hydrogen ion that usually causes the taste receptor to feel sour taste. But the correspondence of alkali or hydroxide in taste is really not as clear as acid, there are both biological and chemical factors, it can be generally considered that weak base has astringent taste, but it should be noted that it is far more than hydroxide that causes astringent taste. As for strong alkali, it can be speculated to be spicy because of its strong corrosiveness, because it can actually cause a sense of pain. Generally speaking, the intuitive "correspondence" of acids and bases cannot rise to the height of "symmetry" at least in terms of food.

(don't taste chemicals, even baking soda, which distinguish between industrial grade and food grade.)

By Xiao Fan

Q6. How is the mushroom cloud formed? By Anonymous

A:

Mushroom clouds are generally produced after a huge explosion near the ground, and the higher the equivalent of the explosion, the easier it is to produce mushroom clouds.

At the moment of the explosion, the initiation center immediately produces high temperature and high pressure, and the surrounding air is violently squeezed in a very short time, forming a spherical normal shock wave moving at a high speed from the explosion center around. The solid particles produced by explosion combustion spread rapidly in the space in the form of smoke along with the direction of shock wave propagation. This forms the part of the mushroom umbrella.

Image source: as the network spreads this high pressure around, the initiation center will form a low-pressure area, and the surrounding air will supplement the low-pressure area. Due to the high temperature caused by the explosion, the hot air in the low-pressure area will continue to rise. With this rising heat, the dust from the ground rises into the air, forming the part of the mushroom stem.

In the effect pictures of some mushroom clouds, we can see that the smoke in the mushroom umbrella part is constantly rolling, because the rising high temperature smoke and the surrounding cold air interact with each other to form a "vortex ring". So that the smoke has a tumbling effect.

Photo Source: although wikipedia mushroom cloud looks spectacular, we sincerely hope that we don't see mushroom cloud in real life.

By Eric

Q7. The arrangement of extranuclear electrons of copper atom is [Ar] 3d104s1. Why is bivalent copper more common? By Anonymous

A:

First of all, for isolated copper atoms, the full shell structure formed after losing an electron does make it more difficult to lose electrons again, which can be illustrated by comparing the ionization energies of the three adjacent elements in the fourth cycle: Ni,Cu,Zn:

Element first ionization energy (eV) second ionization energy (eV) Ni7.6418.18Cu7.7320.30Zn9.4017.97

It can be seen from the table that the second ionization energy of copper is obviously higher than that of adjacent nickel and zinc, which reflects the stability of 3D full shell.

However, in practice, Cu (I) seems to be unstable. Burning elemental copper in air may form part of cuprous oxide on the surface, but over time, cuprous oxide will be further oxidized to divalent copper, and eventually absorb carbon dioxide and water to become basic copper carbonate (turquoise). How to explain this?

In fact, the seemingly abnormal stability of Cu (II) relative to Cu (I) can be attributed to the ubiquitous water molecules. Naked charged ions are very unstable and combine with surrounding polar molecules, while in air or aqueous solution, the binding is usually water molecules, and the energy released by binding is called hydration energy. The hydration energy of metal ions is usually very large, which can be compared with the bond energy of ionic bonds. Moreover, because the hydration energy can be regarded as the Coulomb energy in which positive and negative charges attract each other, the higher the charge of metal ions is, the smaller the radius is, the greater the hydration energy is. Taking copper ion as an example, the hydration energy of Cu (I) is 6.16 eV, while that of Cu (II) is 21.8eV. The difference between them almost offsets the energy required for univalent copper ion to lose an electron (that is, the second ionization energy), which makes Cu (I) very easy to oxidize in humid environment.

In fact, the stability of hydration energy to high-valent metal ions is not limited to divalent copper ions. Metallic iron burns in air to form ferric oxide, while rust produces hydrated iron oxide (III), indicating that hydration also has a stabilizing effect on trivalent iron ions.

By is happy in his heart.

Q8. Scientists have expanded imaginary numbers from the "meaningless" negative root sign (and found its geometric meaning). Can the logarithms of negative and complex numbers be expanded accordingly? Does it have a geometric or physical meaning? By imaginary number

A:

For a real variable function, an exponential function makes sense. Let's extend this function to a complex variable function. For example, what does it mean?

First of all, how to define this kind of function, the easiest way is to use the boss Taylor's method, we know that Taylor's expansion formula is

Naturally, we can define the exponential function of a complex variable

If there is an exponent, there is also a logarithm. If the module length of z is r and the amplitude is r, then it will be extended to the logarithmic function.

Because the amplitude can be added to the integer multiple at will, the above expression is not a function in the ordinary sense, and such a mapping is called a multi-valued function in a complex function.

According to the above definition, we can get the famous Euler formula.

Having written so much, what is the specific application in mathematical physics?

The most direct thing is something called the residue theorem, which starts with a definition of the residue theorem:

Let f be analytic in the region T except for bounded isolated singularities and continuous on the boundary of T, then the integral of f along the boundary of T is equal to the sum of residues of f at all isolated singularities.

Although it looks a little complicated, in fact its meaning is that the original function has changed around it.

Miss pi of by Circle

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Frions

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