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虽然海洋环境中的各种因素比较稳定，但是某些鱼类也有周期性的变动。()
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Great Inventions
There are some things we use every day. Can you imagine a world without zippers(拉链) to fasten clothing？ Have you ever wondered about the layout of the keyboard of a typewriter, which we see every day on the computer？ These are just two of the many inventions which have made our lives easier. Maybe that's why we don't think about them very much!
The zipper
Whatever did we do before the invention of the zipper？
In 1893 the world's first zipper was produced in Chicago. Although the inventor claimed that it was a reliable fastening for clothing, this was not the case. The Chicago zipper sprang open without warning, or jammed shut, and it swiftly lost popularity. Twenty years later a Swedish-born engineer called Sundback solved the problem. He attached tiny cups to the backs of the interlocking teeth, and this meant that the teeth could be enmeshed (使陷入) more firmly and reliably.
At first zippers were made of metal. They were heavy, and if they got stuck it was difficult to free them. Then came nylon zippers which were lighter and easier to use, and had smaller teeth. The fashion industry liked the new zippers far better because they did not distort the line of the garment or weigh down light fabrics. They were also easier for the machinists to fit into the garment.
Meanwhile a new fastening agent made its appearance at the end of the twentieth century: Velcro (维可牢尼龙褡链扣). Velcro is another product made from nylon. Nylon is a very tough synthetic fiber first developed in the 1930s, and bearing a name to remind the hearer of the two places where it was developed: NY for New York and LON for London. It is strong and durable.
Velcro is used on clothing, luggage and footwear. It is quick and easy to fasten and unfasten, and has taken a large part of the zipper's share of the market. It is also used in ways a zipper cannot be used—for instance as an easily changed fastening on plaster casts, and to hold furnishing fabrics in position.
The typewriter and the keyboard
The keyboard of the modern typewriter is laid out in a most odd fashion. Why would anyone place the letters on the left side of the top row of the keyboard in the order Q W E R T Y？ The answer is simple: to slow the typist down. But first, let's consider the history of the typewriter itself.
In the 1860's a newspaper editor called Christopher Sholes lived in Milwaukee, USA. Sholes invented the first of the modern typewriters, although there had been patents for typewriter-like machines as early as 1714, when Queen Anne of England granted a patent to a man called Henry Mill for a machine which would make marks on paper "so neat and exact as not to be distinguished from print." In 1829, across the Atlantic in Detroit, USA, William Austin Burt took out a patent on a typewriter-like machine, four years before the French inventor Xavier Projean produced his machine designed to record words at a speed comparable to someone writing with a pen.
So the typewriter was not a new idea, although there had not been a successful realization of the idea before Christopher Sholes' machine. His typewriter became very popular, and soon people learned to type very quickly—so quickly, in fact, that the keys became tangled (纠缠在一起). On manual typewriters the characters were set on the end of bars which rose to strike the paper when the key was pressed. In the first models, the keys were set alphabetically. When a quick typist tapped out a word like federal, it was very likely that the adjacent e and d keys would become entangled (缠住).
Sholes therefore set about finding ways to slow the typist down. He looked for the letters which were most often used in English, and then placed them far away from each other. For instance, q and u, which are almost always used together in English, are separated by five intervening
【C4】
【C17】
New model police
William Bratton, the chief of the Los Angeles Police Department (LAPD), likes to say that "cops count". They certainly seem to count when Mr Bratton is in charge of them. New York': crime rate withered when he ran its police force in the mid-1990s, and Los Angeles has be. come more law-abiding ever since he arrived in 2002. Burglaries are down by a fifth, murders by a third and serious assaults by more than half. The setting for innumerable hard boiled detective novels and violent television dramas is now safer than Salt Lake City in Utah
Yet Los Angeles's good fortune is not replicated everywhere. Compared to ten years ago, when crime was in remission across America, the current diagnosis is complex and worrying. Figures released this week by the FBI show that, while property crimes continue to fall, the number of violent crimes has begun to drift upwards. In some places it has soared. Oakland, in northern California, had 145 murders last year—more than half again as many as in 2005. No fewer than 406 people died in Philadelphia, putting the murder rate back where it had been in the bad old days of the early 1990s.
The most consistent and striking trend of the past few years is a benign one. America's three biggest cities are becoming safer. Robberies in Chicago, Los Angeles and New York have tumbled in the past few years, defying the national trend. Indeed, the big cities are now holding down increases in overall crime rates. Between 2000 and 2006, for example, the number of murders in America went up by 7%. Were it not for Chicago, Los Angeles and New York, all of which notched many fewer, the increase would have been 11%.
This is especially surprising given the big cities' recent woes. Thanks to a cut in starting salaries and poaching by suburban forces, New York's police department has lost more than 4,000 officers since 2000. Chicago and Los Angeles also have fewer cops than they did in the late 1990s—and the latter has more people. The LAPD labours under a court decree, imposed in 2001 following revelations of corruption and brutality, which forces it to spend precious time and money scrutinising itself.
The three police forces, though, look increasingly alike when it comes to methods of tackling crime. The new model was pioneered in New York. In the mid-1990s it began to map crimes, allocate officers accordingly (a strategy known as "putting cops on the dots") and hold local commanders accountable for crime on their turf. Since 2002 it has flooded high-crime areas with newly qualified officers. The cops' methods are sometimes crude—police stops in New York have increased five-fold in the past five years—but highly effective. Crime tends to go down by about a third in the flooded areas, which has a disproportionate impact on the overall tally.
In the past few years Chicago and Los Angeles have adopted similar methods: although, having fewer officers, they are less extravagant with them. The Los Angeles police targered just five hot spots last year. Both cities have put local commanders in charge of curting crime on their patches and, like New York, they are moving beyond putting cops on the dots. They now try to anticipate where crimes will occur based on gang intelligence. Wesley Skogan, a criminologist at Northwestern University, reckons such methods are the most likely cause of the continued drop in big-city crime. He has diligently tested most of the explanations proffered for Chicago's falling crime rate and has been able to rubbish most of them. Locking lots of people up, for example, may well have helped cut crime a decade ago, but it can't account for the trend of the past few years: the number of Chicagoans behind bars has declined since 1999. The police simply seem to be doing a better job of deterring lawlessness.
The big cities' methods may sound obvious, yet they are surprisingly rare. Many police forces are not divided into neighbour
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