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In the 1950s, the pioneers of artificial intelligence (AI) predicted that, by the end of this century, computers would be conversing with us at work and robots would be performing our housework. But powerful as computers are, they"re nowhere close to achieving anything remotely resembling these early aspirations for humanlike behavior. Never mind something as complex as conversation: the most powerful computers struggle to reliably recognize the shape of an object, the most elementary of tasks for a ten-month-old kid.A growing group of AI researchers think they know where the field went wrong. The problem, the scientists say, is that AI has been trying to separate the highest, most abstract levels of thought, like language and mathematics, and to duplicate them with logical, step-by- step programs. A new movement in AI, on the other hand, takes a closer look at the more roundabout way in which nature came up with intelligence. Many of these researchers study evolution and natural adaptation instead of formal logic and conventional computer programs. Rather than digital computers and transistors, some want to work with brain cells and proteins. The results of these early efforts are as promising as they are peculiar, and the new nature-based AI movement is slowly but surely moving to the forefront of the field.Imitating the brain"s neural (神经的) network is a huge step in the right direction, says computer scientist and biophysicist Michael Conrad, but it still misses an important aspect of natural intelligence. "People tend to treat the brain as if it were made up of color-coded transistors", he explains, "but it"s not simply a clever network of switches. There are lots of important things going on inside the brain cells themselves. " Specifically, Conrad believes that many of the brain"s capabilities stem from the pattern recognition proficiency of the individual molecules that make up each brain cell. The best way to build and artificially intelligent device, he claims, would be to build it around the same sort of molecular skills.Right now, the option that conventional computers and software are fundamentally incapable of matching the processes that take place in the brain remains controversial. But if it proves true, then the efforts of Conrad and his fellow AI rebels could turn out to be the only game in town. The author says that the powerful computers of today ______.
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Nuclear power"s danger to health, safety, and even life itself can be summed up in one word: radiation. Nuclear radiation has a certain mystery about it, partly because it cannot be detected by human senses. It can"t be seen or heard, or touched or tasted, even though it may be all around us. There are other things like that. For example, radio waves are all around us but we can"t sense radioactivity without a radiation detector. But unlike common radio waves, nuclear radiation is not harmless to human beings and other living things.At very high levels, radiation can kill an animal or human being outright by killing masses of cell in vital organs. But even the lowest levels can do serious damage. There is no level of radiation that is completely safe. If the radiation does not hit anything important, the damage may not besignificant.This is the case when only a few cells are hit, and if they are killed outright. Your body will replace the dead cells with healthy ones. But if the few cells arc only damaged, and if they reproduce themselves, you may be in trouble. They reproduce themselves in a deformed way. They can grow into cancer. Sometimes this does not show up for many years.This is another reason for some of the mystery about nuclear radiation. Serious damage can be done without the victim being aware at the time that damage has occurred. A person can be irradiated and feel fine, then die of cancer five, ten, or twenty years later as a result. Or a child can be born weak or liable to serious illness as a result of radiation absorbed by its grandparents. It is not too careful to prevent from the radiation. Radiation can hurt us. We must know the truth. According to the passage, the danger of nuclear power lies in ______.
In the United States, the first day nursery, was opened in 1854. Nurseries were established in various areas during the 1 half of the 19th century; most of 2 were charitable. Both in Europe and in the U.S., the day nursery movement received great 3 during the First World War, when 4 of manpower caused the industrial employment of unprecedented (前所未有) numbers of women. In some European countries nurseries were established 5 in munitions (军火) plants, under direct government sponsorship. 6 the number of nurseries in the U.S. also rose 7 , this rise was accomplished without government aid of any kind. During the years following the First World War, 8 , federal, State, and local governments gradually began to exercise a measure of control 9 the day nurseries, chiefly by 10 them.The 11 of the Second World War was quickly followed by an increase in the number of day nurseries in almost all countries, as women were 12 called up on to replace men in the factories. On this 13 the U.S. government immediately came to the support of the nursery schools, 14 $6,000,000 in July, 1942, for a nursery school program for the children of working mothers. Many States and local communities 15 this Federal aid. By the end of the war, in August, 1945, more than 100, 000 children were being cared 16 in daycare centers receiving Federal 17 . Soon afterward, the Federal government 18 cut down its expenditures for this purpose and later 19 them, causing a sharp drop in the number of nursery schools in operation. However, the expectation that most employed mothers would leave their 20 at the end of the war was only partly fulfilled.
设A是3阶实对称矩阵，特征值是0，1，2．如果λ=0与λ=1的特征向量分别是α1=(1，2，1)T与α2=(1，一1，1)T，则λ=2的特征向量是__________．
设α0是A属于特征值λ0的特征向量，则α0不一定是其特征向量的矩阵是
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