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【篇一】Statistics
There were two widely divergent influences on the early development of statistical methods. Statistics had a mother who was dedicated to keeping orderly records of governmental units (states and statistics come from the same Latin root status) and a gentlemanly gambling father who relied on mathematics to increase his skill at playing the odds in games of chance. The influence of the mother on the offspring, statistics, is represented by counting, measuring, describing, tabulating, ordering, and the taking of censuses-all of which led to modern descriptive statistics. From the influence of the father came modern inferential statistics, which is based squarely on theories of probability.
Descriptive statistics involves tabulating, depicting and describing collections of data. These data may be quantitative such as measures of height, intelligence or grade level -- variables that are characterized by an underlying continuum -- or the data may represent qualitative variables, such as sex, college major or personality type. Large masses of data must generally undergo a process of summarization or reduction before they are comprehensible. Descriptive statistics is a tool for describing or summarizing or reducing to comprehensible form the properties of an otherwise unwieldy mass of data.
Inferential statistics is a formalized body of methods for solving another class of problems that present great difficulties for the unaided human mind. This general class of problems characteristically involve attempts to make predictions using a sample of observations. For example, a school superintendent wishes to determine the proportion of children in a large school system who come to school without breakfast, have been vaccinated for flu, or whatever. Having a little knowledge of statistics, the superintendent would know that it is unnecessary and inefficient to question each child: the proportion for the entire district could be estimated fairly accurately from a sample of as few as 100 children. Thus, the purpose of inferential statistics is to predict or estimate characteristics of a population from a knowledge of the characteristics of only a sample of the population.
【篇二】譯文
統(tǒng)計(jì)學(xué)
統(tǒng)計(jì)方法的早期發(fā)展受到兩種截然不同的影響。統(tǒng)計(jì)學(xué)有一個(gè)“母親”，她致力于井井有條地記錄政府機(jī)構(gòu)的文件（國(guó)家和統(tǒng)計(jì)學(xué)這兩個(gè)詞源于同一個(gè)拉丁語(yǔ)詞根，status），還有一個(gè)有紳士般的賭博“父親”，他依靠數(shù)學(xué)來(lái)提高賭技，以便在幾率的游戲中取勝。“母親”對(duì)其子女統(tǒng)計(jì)學(xué)的影響表現(xiàn)在計(jì)數(shù)、測(cè)量、描述、制表、歸類和人口普查。所有這些導(dǎo)致了現(xiàn)代描述統(tǒng)計(jì)學(xué)的誕生。由于“父親”的影響則產(chǎn)生了完全基于概率論原理的現(xiàn)代推理統(tǒng)計(jì)學(xué)。
描述統(tǒng)計(jì)學(xué)涉及對(duì)所收集數(shù)據(jù)的制表、制圖和描述。這些數(shù)據(jù)可以是數(shù)量性的數(shù)據(jù)，如高度、智商、或者是層級(jí)性的數(shù)據(jù)——具有連續(xù)性的變量——或數(shù)據(jù)也可以代表性質(zhì)變量，如性別、大學(xué)專業(yè)或性格類型等等。數(shù)量龐大的數(shù)據(jù)通常必須經(jīng)過(guò)概括或刪減的程序才能為人所理解。描述統(tǒng)計(jì)學(xué)就是這樣一個(gè)工具，它對(duì)極其龐雜的數(shù)據(jù)進(jìn)行描述、概括或刪減，使其變成能為人理解的東西。
推理統(tǒng)計(jì)學(xué)是一套已定形了的方法體系，它解決的是光憑人腦極難解決的另一類問(wèn)題。這類問(wèn)題的顯著特點(diǎn)是試圖通過(guò)取樣調(diào)查來(lái)作出預(yù)測(cè)。例如，有一位教育督察想知道在一個(gè)龐大的學(xué)校系統(tǒng)中，不吃早飯就上學(xué)的學(xué)生、已經(jīng)做過(guò)防感冒免疫的學(xué)生，或其它任何類型的學(xué)生占多大比例。若具備一些統(tǒng)計(jì)學(xué)的知識(shí)，這位督察應(yīng)明白，詢問(wèn)每個(gè)孩子是沒(méi)有必要而且沒(méi)有效率的，只要用100個(gè)孩子為樣本，他就可以相當(dāng)精確地得出這些孩子占整個(gè)學(xué)區(qū)的比例了。因此，推理統(tǒng)計(jì)學(xué)的目的就是通過(guò)了解一個(gè)群體中一些樣本的特性，從而對(duì)整個(gè)群體的特性進(jìn)行推測(cè)和估算。
【篇三】Coal-fired power plants
The invention of the incandescent light bulb by Thomas A. Edison in 1879 created a demand for a cheap, readily available fuel with which to generate large amounts of electric power. Coal seemed to fit the bill, and it fueled the earliest power stations (which were set up at the end of the nineteenth century by Edison himself). As more power plants were constructed throughout the country, the reliance on coal increased. Since the First World War, coal-fired power plants have accounted for about half of the electricity produced in the United States each year.
In 1986 such plants had a combined generating capacity of 289, 000 megawatts and consumed 83 percent of the nearly 900 million tons of coal mined in the country that year. Given the uncertainty in the future growth of nuclear power and in the supply of oil and natural gas, coal-fired power plants could well provide up to 70 percent of the electric power in the United States by the end of the century.
Yet, in spite of the fact that coal has long been a source of electricity and may remain one for many years (coal represents about 80 percent of United States fossil-fuel reserves), it has actually never been the most desirable fossil fuel for power plants. Coal contains less energy per unit of weight than natural gas or oil; it is difficult to transport, and it is associated with a host of environmental issues, among them acid rain. Since the late 1960's problems of emission control and waste disposal have sharply reduced the appeal of coal-fired power plants. The cost of ameliorating these environmental problems along with the rising cost of building a facility as large and complex as a coal-fired power plant, have also made such plants less attractive from a purely economic perspective.
Changes in the technological base of coal-fired power plants could restore their attractiveness, however. Whereas some of these changes are evolutionary and are intended mainly to increase the productivity of existing plants, completely new technologies for burning coal cleanly are also being developed.
【篇四】譯文
火力發(fā)電廠
托馬斯·愛(ài)迪生1879年發(fā)明的白熾燈導(dǎo)致對(duì)便宜、易得、可生產(chǎn)大量電能的燃料的需求。煤似乎符合這個(gè)要求，并成為第一批電廠的燃料（正是愛(ài)迪生本人在19世紀(jì)末建造了第一批電廠）。 全國(guó)到處興建電廠時(shí)，對(duì)煤的依賴加深了。自第世界大戰(zhàn)以來(lái)，美國(guó)每年約有一半的電力是以煤為燃料的電廠提供的。
1986年這些電廠的總發(fā)電能力達(dá)到28,900千瓦并且消耗了當(dāng)年全國(guó)開(kāi)采的九億噸煤的83%。 考慮到核能發(fā)展以及石油、天然氣供應(yīng)中的不確定因素，到本世紀(jì)末，火力發(fā)電廠仍可能為美國(guó)提供多達(dá)70%的電力。
然而，盡管煤長(zhǎng)期以來(lái)一直是電力的原料之一并且可能會(huì)繼續(xù)如此（煤占美國(guó)化石燃料儲(chǔ)量的80%），它卻不是電廠的理想燃料。 煤的單位能量含量低于石油和天然氣，而且會(huì)導(dǎo)致包括酸雨在內(nèi)的一系列環(huán)境問(wèn)題。 從1960年以來(lái)，排放控制和垃圾處理的問(wèn)題極大地削弱了燃煤電廠的魅力。 由于減輕這些環(huán)境問(wèn)題需要大量資金，而且建造龐大復(fù)雜的燃煤電廠的費(fèi)用不斷上漲，也使得這些電廠從經(jīng)濟(jì)角度上不具備吸引力。
改變火力發(fā)電廠的基礎(chǔ)技術(shù)卻可能恢復(fù)它們的吸引力。 雖然某些技術(shù)改進(jìn)是漸進(jìn)的，其目的只是提高現(xiàn)有電廠的生產(chǎn)率，但人們正在開(kāi)發(fā)全新的清潔燃煤的技術(shù)。