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    Một đề tài khá thú vị cho tương lai khoa học

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    Một đề tài khá thú vị cho tương lai khoa học

    Bài gửi  Teacher on Thu Nov 25, 2010 6:33 am

    Chỉ với 1 ít, đất hiếm đang và sẽ làm thay đổi họat động của con người. Hãy đọc và cảm nhận để có thể hiểu tầm quan trọng của nó, dù chỉ với 1 ít thông tin đã được khám phá và ứng dụng hiện nay.


    2) When evaluating whether there might be a connection between cancer and static electric or magnetic fields, can all electromagnetic fields be considered the same?

    No. The nature of the interaction of an electromagnetic source with biological material depends on the frequency of the source, so that different types of electromagnetic sources must be evaluated separately.

    X-rays, ultraviolet (UV) light, visible light, MW/RF, magnetic fields from electrical power systems (power-frequency fields), and static magnetic fields are all sources of electromagnetic energy. These different electromagnetic sources are characterized by their frequency or wavelength.

    The frequency of an electromagnetic source is the rate at which the electromagnetic field changes direction and/or amplitude and is usually given in Hertz (Hz) where 1 Hz is one change (cycle) per second. The frequency and wavelength are related, and as the frequency rises the wavelength gets shorter. Power-frequency fields are 50 or 60 Hz and have a wavelength of about 5000 km. By contrast, microwave ovens have a frequency of 2.54 billion Hz and a wavelength of about 10 cm, and X-rays have frequencies of 10^15 Hz and, and wavelengths of much less than 100 nm. Static fields, or direct current (DC) fields do not vary regularly with time, and can be said to have a frequency of 0 Hz and an infinitely long wavelength.

    The interaction of biological material with an electromagnetic source depends on the frequency of the source. We usually talk about the electromagnetic spectrum as though it produced waves of energy. This is not strictly correct, because sometimes electromagnetic energy acts like particles rather than waves; this is particularly true at high frequencies. The particle nature of electromagnetic energy is important because it is the energy per particle (or photons, as these particles are called) that determines what biological effects electromagnetic energy will have [62].

    At the very high frequencies characteristic of hard UV and X-rays, electromagnetic particles (photons) have sufficient energy to break chemical bonds. This breaking of bonds is termed ionization, and this part of the electromagnetic spectrum is termed ionizing. The well-known biological effects of X-rays are associated with the ionization of molecules. At lower frequencies, such as those characteristic of visible light, RF, and MW, the energy of a photon is very much below those needed to disrupt chemical bonds. This part of the electromagnetic spectrum is termed non-ionizing. Because non-ionizing electromagnetic energy cannot break chemical bonds there is no analogy between the biological effects of ionizing and nonionizing electromagnetic energy [62].

    Non-ionizing electromagnetic sources can still produce biological effects. Many of the biological effects of soft UV, visible, and IR frequencies also depend on the photon energy, but they involve electronic excitation rather than ionization, and do not occur at frequencies below that of IR (below 3 x 10^11 Hz). RF and MW sources can cause effects by inducing electric currents in tissues, which cause heating. The efficiency with which an electromagnetic source can induce electric currents, and thus produce heating, depends on the frequency of the source, and the size and orientation of the object being heated. At frequencies below that used for broadcast AM radio (about 10^6 Hz), electromagnetic sources couple poorly with the bodies of humans and animals, and thus are very inefficient at inducing electric currents and causing heating [62].

    Thus in terms of potential biological effects the electromagnetic spectrum can be divided into four portions:

    The ionizing radiation portion, where direct chemical damage can occur (X-rays).
    The non-ionizing portion of the spectrum, which can be subdivided into:
    The optical radiation portion, were electron excitation can occur (visible light, infrared light)
    The portion where the wavelength is smaller than the body, and heating via induced currents can occur (MW and higher-frequency RF).
    The portion where the wavelength is much larger than the body, and heating via induced currents seldom occurs (lower-frequency RF, power frequencies, static fields).

    http://www.rareearth.org/magnets_health.htm

    LINDSEY HILSUM: It doesn't look very green. Rare earth processing in China is a messy, dangerous, polluting business. It uses toxic chemicals, acids, sulfates, ammonia. The workers have little or no protection.

    But, without rare earth, Copenhagen means nothing. You buy a Prius hybrid car and think you're saving the planet. But each motor contains a kilo of neodymium and each battery more than 10 kilos of lanthanum, rare earth elements from China.

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    Green campaigners love wind turbines, but the permanent magnets used to manufacture a 3-megawatt turbine contain some two tons of rare earth. The head of China's Rare Earth Research Institute shows me one of those permanent magnets. He's well aware of the issues.

    ZHAO ZENGQI, Baotou Rare Earth Research Institute: The environmental problems include air emissions with harmful elements, such as fluorine and sulfur, wastewater that contains excessive acid, and radioactive materials, too. China meets 95 percent of the world's demand for rare earth, and most of the separation and extraction is done here. So, the pollution stays in China, too.

    LINDSEY HILSUM: The authorities gave us a DVD of Baiyunebo in Inner Mongolia, where most of the world's rare earth is mined, along with iron ore. They wouldn't let us film it ourselves.

    But at Baotou, 100 miles away, we found the frozen tailing lake where rare earth mixes with mud, waiting for processing at nearby factories. Technologies we all use, like computers, mobile phones and energy-saving light bulbs use rare earths processed here. And local villagers whose farmland has been ruined by seepage from the lake pay the price.

    WANG CUN GUANG, farmer: The Baotou Environmental Protection Bureau tested our water, and they concluded that it wasn't fit for people or animals to drink or for irrigation.

    LINDSEY HILSUM: For those who remember the old life, it's hard to understand. The authorities pay compensation, acknowledging that the land has been ruined, but they haven't yet relocated the villagers.

    JIA BAO CHENG, farmer: Rare earth is the country's resource, but small people like us need to eat, too. We live on farming, but the crops no longer grow, and we will go hungry.

    LINDSEY HILSUM: At a rare earth conference in Hong Kong, the talk is of how to reduce dependence on China, which achieved 95 percent dominance by undercutting other producers.

    MARK SMITH, CEO, Molycorp Minerals: If the purpose is to lower our dependence on foreign oil, and all We're doing is asking that we put hybrid cars on the road that need Chinese rare earth materials, aren't we changing, you know, inter-trading one dependence for another?

    LINDSEY HILSUM: High on the frozen steppe of Inner Mongolia, a huge wind farm. China is aiming to be the world leader in wind energy. Chinese negotiators at Copenhagen may resist political commitments, but the government is already subsidizing new technologies to boost the economy and be sustainable.

    Deal or no deal at Copenhagen, there's going to be an increased demand for wind turbines, both inside China and outside. But what the Chinese want to ensure is that they're not just providing the essential raw materials, the rare earths, and doing the manufacturing, but that they also have access to the most advanced low-carbon technologies.

    We were shown plans for what they're calling the Silicon Valley of rare earth, a high-tech industrial park in Baotou to attract international investors. This year, there was an outcry when the Chinese said they would restrict the export of rare earth to conserve their supply, and to make foreign companies produce their high-end technologies here in China.

    ZHAO ZENGQI: Although China has the largest reserves, we only have 50 percent of global deposits. We are supplying too much rare earth, and it's not sustainable, so we must restrict export.

    LINDSEY HILSUM: The writing on the wall says: Become the leader of the world in rare earth industry.

    But China can't produce enough for everyone anymore, and if governments are serious about low-carbon technologies, other countries will have to start producing.

    MARK SMITH: I think that, if we don't get a couple of projects up and running very, very quickly, there's going to be very severe shortage of rare earths in the world, and all of these clean-energy technologies that we're legislating and trying to implement through policy changes are not going to be possible.

    LINDSEY HILSUM: Champions of a low-carbon future have yet to wake up to the environmental price Chinese workers and villagers are paying. At Copenhagen, politicians talk of cutting carbon emissions, but they can't meet any targets without rare earth, and that means a sustainable supply, and not all from China.

    http://www.pbs.org/newshour/bb/asia/july-dec09/china_12-14.html

      Hôm nay: Sun Dec 04, 2016 1:15 am