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蛋白质-能量营养不良最常见的维生素缺乏是
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Text 4The recent, apparently successful prediction by mathematical models of an appearance of El Nifio—the warm ocean current that periodically develops along the Pacific coast of South America -- has excited researchers. Jacob Bjerkness pointed out over 20 years ago how winds might create either abnormally warm or abnormally cold water in the eastern equatorial Pacific. Nonetheless, until the development of the models no one could explain why conditions should regularly shift from one to the other, as happens in the periodic oscillations between appearance of the warm El Nifio and the cold so-called anti-El Nifio. The answer, al least if the current model that links the behavior of the ocean to that of the atmosphere is correct, is to be found in the ocean.It has long been known that during an El Niflo, two conditions exist: (1) unusually warm water extends along the eastern Pacific, principally along the coasts of Ecuador and Peru, and (2) winds blow from the west into the warmer air rising over the warm water in the east. These winds tend to create a feedback mechanism by driving the warmer surface water into a "pile" that blocks the normal upwelling of deeper, cold water in the east and further warms the eastern water, thus strengthening the wind still more. The contribution of the model is to show that the winds of an El Nifio, which raise sea level in the east, simultaneously send a signal to the west lowering sea level. According to the model, that signal is generated as a negative Rossby wave, a wave of depressed, or negative, sea level that moves westward parallel to the equator at 25 to 85 kilometers per day. Taking months to traverse the Pacific, Rossby waves march to the western boundary of the Pacific basin, which is modeled as a smooth wall but in reality consists of quite irregular island chains, such as the Philippines and Indonesia.When the waves meet the western boundary, they are reflected, and the model predicts that Rossby waves will be broken into numerous coastal Kelvin waves carrying the same negative sea-level signal. These eventually shoot toward the equator, and then head eastward along the equator propelled by the rotation of the Earth at a speed of about 250 kilometers per day. When enough Kelvin waves of sufficient amplitude arrive from the western Pacific, their negative sea-level signal overcomes the feedback mechanism tending to raise the sea level, and they begin to drive the system into the opposite cold mode. This produces a gradual shift in winds, one that will eventually send positive sea-level Rossby waves westward, waves that will eventually return as cold cycle-ending positive Kelvin waves beginning another warming cycle. One characteristic of the El Nifio is（）
SLE病人最典型的面部表现是
Text 3Of all the truths that this generation of Americans hold self-evident, few are more deeply embedded in the national psyche than the maxim "It pays to go to college." Since the GI Bill trans-formed higher education in the aftermath of WWII, a college diploma, once a birthright of the leisured few, has become an attraction for the upwardly mobile, as integral to the American dream as the pursuit of happiness itself. The numbers tell the story: in 1950s, 43% of high-school graduates went on to pursue some form of higher education; at tile same time, only 6% of Americans were college graduates. But by 1998, almost 2 to out of 3 secondary-school graduates were opting for higher education -- and 21% of a much larger U.S. population had college diplomas. As Prof. Herbert London of New York University told a commencement audience last June: "the college experience has gone from a rite passage to a right of passage."However, as the class of 2004 is so painfully discovering, while a college diploma remains a requisite credential for ascending the economic ladder, it no longer guarantees the good life. Rarely since the end of the Great Depression has the job outlook for college graduates appeared so bleak: of the 1.1 million students who received their bachelor degrees last spring, fewer than 20% had lined up full-time employment by commencement. Indeed, an uncertain job market has precipitated a wave of economic fear and trembling among the young. "Many of my classmates are absolutely terrified," says one of the fortunate few who did manage to land a permanent position. "They wonder if they’ll ever find a job."Some of this recession-induced anxiety will disappear if a recovery finally begins to generate jobs at what economists consider a normal rate. But the sad fact is that for the foreseeable future, college graduates will in considerable surplus, enabling employers to require a degree even for jobs for which a college education is really unnecessary. According to Kristina Shelley of the Bureau of Labor Statistics -- who bases her estimate on a "moderate projection" of current trends -- 30 per- cent of college graduates entering the labor t0rce between now and the year 2008 will be unemployed or will find employment in jobs for which they will be overqualified, joining what economists call the "educationally underutilized."Indeed, it may be quite a while-- if ever -- before those working temporarily as cocktail waitresses or taxi drivers will be able to pursue their primary, career paths. Of course waiting on tables and bustling cab fares are respectable ways to earn a living. But they are not quite what so many young Americans -- and their parents -- had in mind as the end product of four expensive years in college. The author tries to convince us that（）
小儿痰湿咳嗽的临床特点是
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