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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 vh-tually 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 .sefisors 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 will 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. The ocean may be used to detect neutrinos for the following reasons EXCEPT that
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World War II initiated the concept of "total war"--war that involved all, civilians and military alike, in the war effort. This was not really new. Lazare Camot had anticipated it during the French Revolution with his call for "a nation in arms". But never before World War II had nation been required to draw so heavily upon the total human resources available to them. In each country, there was a propaganda effort to portray every person in the state as personally involves in the struggle being waged. In the United States, "Rosie the Riveter" was as much a part of the picture as "G. I. Joe". The German "Rosies" were not as likely as their American counterparts to be working as riveters, but from 1942 on, they and their children were to face terrors of war as severe as those experienced by their front-line soldiers. Shivering from fear of being buried alive in the cellars that served as air-raid shelters, they had to emerge from those areas of modest security to extinguish the fire bombs that sizzled in the attics above before entire houses were incinerated. Each explosive bomb that fell could mean life or death for each person who heard it coming, depending on where it fell and how big it was. There is no rational way of rendering judgment on the moral aspects of the Allied bombing. It did, of course, kill Nazis and anti-Nazis alike; women and children as well as men; prisoners of war and foreign workers as well as Germans; professors, artists, musicians, and farmers, as well as workers in munitions factories. And the mode of death, as will be seen, was often shocking and gruesome. But it is faulty to assume that without the bombing all those who perished would have survived and would have met death more peacefully. Land invasion would have meant the ravaging of cities by heavy artillery, tanks, and flame throwers, the desperate flight of thousands of civilians (which indeed occurred on Germany’s eastern front), and the ultimate collapse of all forces of order, with internecine fighting, famine, and disease as likely accompaniments. Neither can one assume that more churches, famous monuments, paintings, library books, and so forth would have survived. That those who stopped the bombs had pangs of guilt in respect to the suffering they caused and the cultural wealth they destroyed is a credit to their humanitarian sensitivities. But sentiments of revulsion are more appropriately directed at war itself, which inevitably brutalizes those involved, destroys normal sensitivities, and opens the way to rape, pillage, and want of destruction. A "clean", "humane" war is an impossibility. According to the author, without the Allied bombing,
Teachers need to be aware of the emotional, intellectual, and physical changes that young adults experience. And they also need to give serious (31) to how they can best (32) such changes. Growing bodies need movement and (33) , but not just in ways that emphasize competition. (34) they are adjusting to their new bodies and a whole host of new intellectual and emotional challenges, teenagers are especially self-conscious and need the (35) that comes from achieving success and knowing that their accomplishments are (36) by others. However, the typical teenage lifestyle is already filled with so much competition that it would be (37) to plan activities in which there are more winners than losers, (38) publishing newsletters with many student-written book reviews, (39) student artwork, and sponsoring book discussion clubs. A variety of small clubs can provide (40) opportunities for leadership, as well as for practice in successful (41) dynamics. Making friends is extremely important to teenagers, and many shy students need the (42) of some kind of organization with a supportive adult (43) l visible in the background. In these activities, it is important to remember that young teens have (44) attention spans. A variety of activities should be organized (45) participants can remain active as long as they want and then go on to (46) else without feeling guilty and without letting the other participants (47) . This does not mean that adults must accept irresponsibility. (48) they can help students acquire a sense of commitment by (49) for roles that are within their (50) and their attention spans and by having clearly stated rules.
Write on ANSWER SHEET TWO a note of about 50-60 words based on the following situation: Because of your carelessness you lost your school bag in the library. Write a "LOST" note for it. You are supposed to be Wang Hal. Marks will be awarded for content, organization, grammar and appropriateness.
Suppose you are driving on a highway with three lanes going in your direction and you come upon a toll plaza with six toll booths. Three toll booths are straight ahead in the three lanes of traffic, and the three other booths are off to the right. Which lane should you choose There are usually enough people searching for the shortest line so as to make all the lines about the same length. The term profit in economics has a very precise meaning. Economists, however, often loosely refer to "good deals" or profitable ventures with no risk as profit opportunities. Using the term loosely, a profit opportunity exists at the toll booths if one line is shorter than the others. The general view of economics is that profit opportunities are rare. At any one time there are many people searching for such opportunities, and as a consequence few exist. At major banks in big cities, you can buy foreign currencies. The prices of these currencies are determined in world money markets. With dollars we can buy marks; with these marks we can buy francs; and with these francs we can buy back dollars. Can we make money on this transaction If this is possible, we say that there are profit opportunities in the market. There are in fact almost never any profit opportunities of this kind in foreign currency markets. There are always individuals looking for such opportunities, and if any opportunity does arise it is quickly eliminated. If, for example, the mark-franc price is too low with respect to the other prices, there is an immediate rash to buy marks and sell francs, not by ordinary citizens at bank windows, but by a few large currency traders in Tokyo, London, or Zurich who watch prices every minute. Such a rush drives up the mark-franc price to the no-profit-opportunity point. Markets like this, where any profit opportunities are eliminated almost instantaneously are said to be efficient markets. The common language way of expressing the efficient markets hypothesis is "there’s no such thing as a free lunch". How should one react when a stock broker calls up with a hot tip on the stock market With skepticism. There are thousands of individuals each day looking for hot tips in the market, and if a particular tip about a stock is valid there will be an immediate rush to buy the stock, which will quickly drive its price up. By the time the tip gets to your broker and then to you, the profit opportunity that arose from the tip (assuming that there was one) is likely to have been eliminated. Similar arguments can be made for bond markets and commodity markets. They are many "expert" in these markets, who take quick advantage of any news that affects prices. This economist’s view that there are very limited profit opportunities around can, of course, be carried too far. There are clearly times when profit opportunities exist. Someone has to be first to get the news, and some people have quicker insights than others. Nevertheless, news does get disseminated quickly, and there are thousands of people with quick insights. The general view that profit opportunities are rare is close to the mark. What is the author’s attitude towards the idea that "profit opportunities are rare"
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