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当胶片尺寸大于暗盒尺寸，或增感屏粘贴不平造成屏-片局部接触不良，是造成影片中某一部分出现模糊的常见现象。检查床颤动、患者移动、摄影时间长会造成影像的整体模糊。暗盒漏光会使影像某一边缘部分过度感光。 照片影像仅在某一部分出现模糊，可能性最大的是
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由X线管焦点辐射出的X线穿过被检体时，受到被检体各组织的吸收和散射而衰减，使透过的X线强度的分布呈现差异，到达屏-片系统，转换成可见光强度的分布差异，并传递给胶片，形成银颗粒的空间分布，再经显影处理成为二维光学分布，形成X线照片影像。 被检体各组织对X线的吸收和散射不同是由于
X线胶片特性曲线是描绘曝光量与所产生的密度之间关系的一条曲线，由于这条曲线可以表示出感光材料的感光特性，所以称之为特性曲线。特性曲线的横坐标为曝光量，以对数值lgE表示；纵坐标为密度，以D表示。特性曲线由足部、直线部、肩部和反转部组成。足部密度的上升与曝光量不呈正比，曝光量增加很多，密度只有较小的增加。直线部密度与曝光量的增加呈正比，密度差保持一定，此时曲线沿一定的斜率直线上升。肩部密度随曝光量的增加而增加，但不呈正比。反转部随曝光量的增加密度反而下降，影像密度呈现逆转。特性曲线可提供感光材料的本底灰雾(Dmin)、感光度(S)、对比度(γ)、最大密度(Dmax)、宽容度(L)等参数，以表示感光材料的感光性能。 下列叙述，错误的是
元认知是1976年由______提出来的，它由三个成分组成，即______、元认知体验和______。
It is hard for modern people to imagine the life one hundred years ago. No television, no plastic, no ATMs, no DVDs. Illnesses like tuberculosis, diphtheria, pneumonia meant only death. Of course, cloning appeared only in science fiction. Not to mention, computer and Internet. Today, our workplace are equipped with assembly lines, fax machines, computers. Our daily life is cushioned by air conditioners, cell phones. Antibiotics helped created a long list of miracle drugs. The bypass operation saved millions. The discovery of DNA has revolutionized the way scientists think about new therapies. Man finally stepped on the magical and mysterious Moon. With the rapid changes we have been experiencing, the anticipation for the future is higher than ever. A revolutionary manufacturing process made it possible for anyone to own a car. Henry Ford is the man who put the world on wheels. When it comes to singling out those who have made a difference in all our lives, you cannot overlook Henry Ford. A historian a century from now might well conclude that it was Henry Ford who most influenced all manufacturing everywhere, even to this day, by introducing a new way to make cars—one, strange to say, that originated in slaughter houses. Back in the early 1900s, slaughter houses used what could have been called a "disassembly line." That is, the carcass of a slain steer or a pig was moved past various meat-cutters, each of whom cut off only a certain portion. Ford reversed this process to see if it would speed up production of a part of an automobile engine called a magneto. Rather than have each worker completely assemble a magneto, one of its elements was placed on a conveyer, and each worker, as it passed, added another component to it, the same one each time. Professor David Hounshell, of The University of Delaware, an expert on industrial development tells what happened: "The previous day, workers carrying out the entire process had averaged one magneto every 20 minutes. But on that day, on the line, the assembly team averaged one every 13 minutes and 10 seconds per person." Within a year, the time had been reduced to five minutes. In 1913, Ford went all the way. Hooked together by ropes, partially assembled vehicles were towed past workers who completed them one piece at a time. It wasn’t long before Ford was turning out several hundred thousand cars a year, a remarkable achievement then. And so efficient and economical was this new system that he cut the price of his cars in half, to $260, putting them within reach of all those who, up until that time, could not afford them. Soon, auto makers over the world copied him. In fact, he encouraged them to do so by writing a book about all of his innovations, entitled Today and Tomorrow. The Age of the Automobile had arrived. Today, aided by robots and other forms of automation, everything from toasters to perfumes is made on assembly lines. Edsel Ford, Henry’s great-grandson, and a Ford vice president: “I think that my great-grandfather would just be amazed at how far technology has come." Many of today’s innovations come from Japan. Norman Bodek, who publishes books about manufacturing processes, finds this ironic. On a recent trip to Japan he talked to two of the top officials of Toyota. "When I asked them where these secrets came from, where their ideas came from to manufacture in a totally different way, they laughed, and they said. ’Well. We just read it in Henry Ford’s book from 1926: Today and Tomorrow.’\ The assembly line reduced the time to make a magneto by ______ within a year.
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