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Virtually everything astronomers known about objects outside the solar system is based on the detection of photons-quanta of electromagnetic radiation. Yet there is another form of radiation that permeates the universe: neutrinos (中微子). With (as its name implies) no electric charge, and negligible mass, the neutrino interacts with other particles so rarely that a neutrino can cross the entire universe, even traversing substantial aggregations of matter, without being absorbed or even deflected. Neutrinos can thus escape from regions of space where light and other kinds of electromagnetic radiation are blocked by matter. Furthermore, neutrinos carry with them information about the site and circumstances of their production: therefore, the detection of cosmic neutrinos could provide new information about a wide variety of cosmic phenomena and about the history of the universe.But how can scientists detect a particle that interacts so infrequently with other matter Twenty-five years passed between Pauli’s hypothesis that the neutrino existed and its actual detection: since then virtually all research with neutrinos has been with neutrinos created artificially in large particle accelerators and studied under neutrino microscopes. But a neutrino telescope, capable of detecting cosmic neutrinos, is difficult to construct. No apparatus can detect neutrinos unless it is extremely massive, because great mass is synonymous with huge numbers of nucleons (neutrons and protons), and the more massive the detector, the greater the probability of one of its nucleon’s reacting with a neutrino. In addition, the apparatus must be sufficiently shielded from the interfering effects of other particles.Fortunately, a group of astrophysicists has proposed a means of detecting cosmic neutrinos by harnessing the mass of the ocean. Named DUMAND, for Deep Underwater Muon and Neutrino Detector, the project calls for placing an array of light, sensors at a depth of five kilometers under the ocean surface. The detecting medium is the seawater itself: when a neutrino interacts with a particle in an atom of seawater, the result is a cascade of electrically charged particles and a flash of light that can be detected by the sensors. The five kilometers of seawater above the sensors will shield them from the interfering effects of other high-energy particles raining down through the atmosphere.The strongest motivation for the DUMAND project is that it wilt exploit an important source of information about the universe. The extension of astronomy from visible light to radio waves to x-rays and gamma rays never failed to lead to the discovery of unusual objects such as radio galaxies, quasars (类星体), and pulsars (脉冲星). Each of these discoveries came as a surprise. Neutrino astronomy will doubtless bring its own share of surprises. In the last paragraph, the author describes the development of astronomy in order to().

A. suggest the potential discovery of celestial bodies by means of neutrino astronomy.
B. illustrate the importance of surprises in making astronomic discoveries.
C. demonstrate the effectiveness of the DUMAND apparatus in detecting neutrinos.
D. name some cosmic phenomena that neutrino astronomy will illuminate.

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已知A、B、C均为n阶矩阵,其中C可逆,若AXA-BXB=AXB-BXA+C,则X=()。

A. (A2-B2)C
B. (A+B)C(A-B)
C. (A-B)-1C(A+B)-1
D. (A+B)-1C(A-B)-1

设A,B均为n阶矩阵,则下列运算中, ①|A+B|=|A|+|B| ②|A-B|=-|B-A| ③|AB|=|BA| ④|ATB|=|BTA| ⑤||A|B|=||B|A| 恒正确的个数为()。

A. 1
B. 2
C. 3
D. 4

设A、B、C均为n阶矩阵。 ①若A≠B,则|A|≠|B| ②若AB=AC,且A≠0,则B=C ③若A2=E,且A≠E,则A=-E ④若A可逆,且A-1B=CA-1,则B=C 则上述命题中,正确的命题个数为()。

A. 0
B. 1
C. 2
D. 3

The History of Eldertree CosmeticsEarly days1. The company was established in ______ by Olivia Jenkins.2. Her products sold well because of the ______ of natural products.3. In order to satisfy demand, the owners had to find ______ in 1977. The 1980s4. The introduction of new products resulted in the ______ of the business.5. By recruiting professional expertise, the company managed to secure ______ with major UK retailers.6. To support further growth, Eldertree needed both of a bigger ______ company.7. In 1987 the company was acquired by Greenaway, the UK’s largest ______.8. To improve productivity, Greenaway decided to build a ______ in 1988.9. Greenaway also decided to keep Eldertree’s ______ for its products.EIdertree Cosmetics today10. Greenaway has centralised functions such as its ______.11. In spite of its increased size, the company has kept a ______.12. In the last decade Eldertree has become a ______ both at home and abroad. 10()

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