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The traditional paintings are exhibited on the second floor.
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All the pupils seem to be very cheerful.
Radiocarbon Dating Nowadays scientists can answer many questions about the past through a technique called radiocarbon (放射性碳), or carbon-14, dating. One key to understanding how and by something happened is to discover when it happened. Radiocarbon dating was developed in the late 1940s by physicist Willard F. Libby at he University of Chicago. An atom of ordinary carbon, called carbon-12, has six protons(质子) and six neutrons (中子) in its nucleus(原子核). Carbon-14, or C-14, is a radioactive, unstable form of carbon that has two extra neutrons. It returns to a more stable form of carbon through a process called decay (衰减). This process involves the loss of he extra neutrons and energy from the nucleus. In Libby’s radiocarbon dating technique, the weak radioactive emissions (放射) from this decay process are counted by instruments such as a radiation detector and counter. The decay rate is used to determine the proportion of C-14 atoms in the sample being dated. Carbon-14 is produced in the Earth’s atmosphere when nitrogen (氮)-14, or N-14,interacts with cosmic rays (宇宙射线). Scientists believe since the Earth was formed, the mount of nitrogen in the atmosphere has remained constant. Consequently, C-14 formation is thought to occur at a constant rate. Now the ratio of C-14 to other carbon toms in the atmosphere is known. Most scientists agree that this ratio is useful for dating items back to at least 50,000 years. All life on Earth is made of organic molecules (分子) that contain carbon atoms coming from the atmosphere. So all living things have about the same ratio of C-14 atoms to other carbon atoms in their tissues (组织). Once an organism (有机体) dies it stops taking in carbon in any form, and the C-14 already present begins to decay. Over time the amount of C-14 in the material decreases, and the ratio of C-14 to other carbon atoms goes down. In terms of radiocarbon dating, the fewer C-14 atoms in a sample, the older that sample is. An atom of ordinary carbon has six protons and eight neutrons
开-闭原则(Open-Closed Principle, OCP)是面向对象的可复用设计的基石。开-闭原则是指一个软件实体应当对 (53) 开放，对 (54) 关闭；里氏代换原则(Liskov Substitution Principle, LSP)是指任何 (55) 可以出现的地方， (56) 一定可以出现。依赖倒转原则(Dependence Inversion Principle, DIP)就是要依赖于 (57) ，而不依赖于 (58) ，或者说要针对接口编程，不要针对实现编程。 57（）
第二篇 Mind-reading Machine A team of researchers in California has developed a way to predict what kinds of objects people are looking at by scanning (扫描) what’s happening in their brains. When you look at something, your eyes send a signal about that object to your brain. Different regions of the brain process the information your eyes send. Cells in your brain called neurons (神经元) are responsible for this processing. The fMRI (functional Magnetic Resonance Imaging) (功能性磁振造影) brain scans could generally match electrical activity in the brain to the basic shape of a picture that someone was looking at. Like cells anywhere else in your body, active neurons use oxygen. Blood brings oxygen to the neurons, and the more active a neuron is, the more oxygen it will consume. The more active a region of the brain, the more active its neurons, and in turn, the more blood will travel to that region. And by using fMRI, scientists can visualize (使…显现) which parts of the brain receive more oxygen-rich blood - and therefore, which parts are working to process information. An fMRI machine is a device that scans the brain and measures changes in blood flow to the brain. The technology shows researchers how brain activity changes when a person thinks, looks at something, or carries out an activity like speaking or reading. By highlighting the areas of the brain at work when a person looks at different images, fMRI may help scientists determine specific patterns of brain activity associated with different kinds of images. The California researchers tested brain activity by having two volunteers view hundreds of pictures of everyday objects, like people, animals, and fruits. The scientists used an fMRI machine to record the volunteers’ brain activity with each photograph they looked at. Different objects caused different regions of the volunteers’ brains to light up on the scan, indicating activity. The scientists used this information to build a model to predict how the brain might respond to any image the eyes see. In a second test, the scientists asked the volunteers to look at 120 new pictures. Like before, their brains were scanned every time they looked at a new image. This time, the scientists used their model to match the fMRI scans to the image. For example, if a scan in the second test showed the same pattern of brain activity that was strongly related to pictures of apples in the first test, their model would have predicted the volunteers were looking at apples. The expression "highlighting the areas of the brain at work’ in paragraph 5 means
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