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请你论述一下，什么是知觉以及它具有哪些特性。
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Rubidium, potassium and carbon are three common elements used to date the history of Earth. The rates of radioactive decay of these elements are absolutely regular when averaged out over a period of time; nothing is known to change them. To be useful as clocks, the elements have to be fairly common in natural minerals, unstable but decay slowly over millions of years to form recognizable "daughter" products which are preserved minerals. For example, an atom of radioactive rubidium decays to form an atom of strontium (another element) by converting a neutron in its nucleus to a proton and releasing an electron, generating energy in the process. The radiogenic daughter products of the decay-in this case strontium atoms--diffuse away and are lost above a certain very high temperature. So by measuring the exact proportions of rubidium and strontium atoms that are present in a mineral, researchers can work out how long it has been since the mineral cooled below that critical "blocking" temperature. The main problems with this dating method are the difficulty in finding minerals containing rubidium, the accuracy with which the proportions of rubidium and strontium are measured, and the fact that the method gives only the date when the mineral last cooled below the blocking temperature. Because the blocking temperature is very high, the method is used, mainly for recrystallized (igneous or metamorphic) rocks, not for sediments--rubidium-bearing minerals in sediments simply record the age of cooling of the rocks which were eroded to form the sediments, not the age of deposition of the sediments themselves. Potassium decays to form (a gas) which is sometimes lost from its host mineral by escaping through pores. Although potassium-argon dating is therefore rather unreliable, it can sometimes be useful in dating sedimentary rocks because potassium is common in some minerals which form in sediments at low temperatures. Assuming no argon has escaped, the potassium-argon date records the age of the sediments themselves. Carbon dating is mainly used in archaeology. Most carbon atoms (carbon-12) are stable and do not change over time. However, cosmic radiation bombarding the upper atmospheres constantly interacting with nitrogen in the atmosphere to create an unstable form of carbon, carbon-14. What is the common feature of rubidium, potassium and carbon
Opinion polls are now beginning to show an unwilling general agreement that, whoever is to blame and whatever happens from now on, high unemployment is probably here to stay. This means we shall have to find ways of sharing the available employment widely. But we need to go further. We must ask some fundamental questions about the future work. Should we continue to treat employment as the norm Should we not rather encourage many other ways for self respecting Should we not create conditions in which many of us can work for ourselves, rather than for an employer Should we not aim to revive the household and the neighborhood, as well as the factory and the office as centers of production and work The industrial age has been the only period of human history in which most people’s work has taken the form of jobs. The industrial age may now be coming to an end, and some of the changes in work patterns which it brought may have to be reversed. This seems a discouraging thought. But, in fact, it could offer the prospect of a better future for work. Universal employment, as its history shows has not meant economic freedom. Employment became widespread when the 17th and 18th centuries made many people dependent on paid work by depriving them of the use of the land, and thus of the means to provide a living for themselves. Then the factory system destroyed the cottage industries and removed work from people’s homes. Later, as transport improved, first by rail and then by road, people traveled longer distances to their places of employment until, eventually, many people’s work lost all connection with their home lives and the places in which they lived. Meanwhile, employment put women at disadvantage. It became customary for the husband to go out to paid employment, leaving the unpaid work of the home and family to his wife. All this may now have to change. The time has certainly come to switch some effort and resources away from the impractical goal of creating jobs for all, to the urgent practical task of helping many people to manage without full-time jobs. What idea did the author derive from the recent opinion polls
Rubidium, potassium and carbon are three common elements used to date the history of Earth. The rates of radioactive decay of these elements are absolutely regular when averaged out over a period of time; nothing is known to change them. To be useful as clocks, the elements have to be fairly common in natural minerals, unstable but decay slowly over millions of years to form recognizable "daughter" products which are preserved minerals. For example, an atom of radioactive rubidium decays to form an atom of strontium (another element) by converting a neutron in its nucleus to a proton and releasing an electron, generating energy in the process. The radiogenic daughter products of the decay-in this case strontium atoms--diffuse away and are lost above a certain very high temperature. So by measuring the exact proportions of rubidium and strontium atoms that are present in a mineral, researchers can work out how long it has been since the mineral cooled below that critical "blocking" temperature. The main problems with this dating method are the difficulty in finding minerals containing rubidium, the accuracy with which the proportions of rubidium and strontium are measured, and the fact that the method gives only the date when the mineral last cooled below the blocking temperature. Because the blocking temperature is very high, the method is used, mainly for recrystallized (igneous or metamorphic) rocks, not for sediments--rubidium-bearing minerals in sediments simply record the age of cooling of the rocks which were eroded to form the sediments, not the age of deposition of the sediments themselves. Potassium decays to form (a gas) which is sometimes lost from its host mineral by escaping through pores. Although potassium-argon dating is therefore rather unreliable, it can sometimes be useful in dating sedimentary rocks because potassium is common in some minerals which form in sediments at low temperatures. Assuming no argon has escaped, the potassium-argon date records the age of the sediments themselves. Carbon dating is mainly used in archaeology. Most carbon atoms (carbon-12) are stable and do not change over time. However, cosmic radiation bombarding the upper atmospheres constantly interacting with nitrogen in the atmosphere to create an unstable form of carbon, carbon-14. Which of the following is the major factor that affects the accuracy of potassium dating
Consumers and producers obviously make decisions that mold the economy, but there is a third major (61) to consider the role of government. Government has a powerful (62) on the economy in at least four ways: Direct Services. The postal system, for example, is a federal system (63) the entire nation, as is the large and complex establishment. Conversely the construction and (64) of most highways, the (65) of the individual states, and the public educational systems, despite a large funding role by the federal government, are primarily (66) for by country or city governments. Police and fire protection and sanitation (67) are also the responsibilities of local government. Regulation and Control. The government regulates and controls private (68) in, many ways, for the (69) of assuring that business serves the best (70) of the people as a whole. Regulation is necessary in areas where private enterprise is granted a(n) (71) , such as in telephone or electric service. Public policy permits such companies to make a reasonable (72) , but limits their ability to raise prices (73) , since the public depends on their services. Often control is (74) to protect the public, as for example, when the Food and Drug Administration bans harmful drugs, or requires standards of (75) in food. In other industries, government sets guidelines to ensure fair competition without using direct control. Stabilization and Growth. Branches of government, including Congress and such entities as the Federal Reserve Board, attempt to control the extremes of boom and bust of inflation and depression, by (76) tax rates, the money supply, and the use of credit. They can also (77) the economy through changes in the amount of public spending by the government itself. Direct Assistance. The government provides many kinds of help to (78) and individuals. For example, tariffs (79) certain products to remain relatively free of foreign competition; imports are sometimes taxed so that American products are able to (80) better with certain foreign goods. In quite a different area, government supports individuals who cannot adequately care for themselves, by making grants to working parents with dependent children, by providing medical care for the aged and the indigent, and through social welfare system.
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