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American Black Bears
American black bears appear in a variety of colors despite their name. In the eastern part of their range, most of these bears have shiny black fur, but in the west they grow brown, red, or even yellow coats. To the north, the black bear is actually gray or white in color. Even in the same litter, both brown and black furred bears may be born.Black bears are the smallest of all American bears, ranging in length from five to six feet, weighing from three hundred to five hundred pounds. Their eyes and ears are small and their eyesight and hearing are not as good as their sense of smell.
Like all bears, the black bear is timid, clumsy, and rarely dangerous, but if attacked, most can climb trees and cover ground at great speeds. When angry or frightened, it is a formidable enemy.Black bears feed on leaves, herbs, roots, fruit, berries, insects, fish, and even larger animals. One of the most interesting characteristics of bears, including the black bear, is their winter sleep. Unlike squirrels, woodchucks, and many other woodland animals, bears do not actually hibernate. Although the bear does not eat during the winter months,sustaining itself from body fat, its temperature remains almost normal, and it breathes regularly four or five times per minute.
Most black bears live alone, except during mating season. They prefer to live in caves, hollow logs, or dense thickets. A litter of one to four cubs is born in January or February after a gestation period of six to nine months, and they remain with their mother until they are fully grown or about one and a half years old. Black bears can live as long as thirty years in the wild, and even longer in game preserves set aside for them.
美國黑熊
美國黑熊雖然被叫區(qū)域的東部，大部分黑 熊長有富有光澤的黑毛，但在西部，他們則長著棕色、紅色甚至是黃色的毛。
在北部，黑熊其實(shí)長著灰色或白色的毛。 就是在一胎所生的小熊中，都可能混雜棕毛和黑毛。 黑熊是 所有美洲熊中最小的，5～6 英尺長，300～500磅重。它們的眼睛和耳朵都很小，他們的視 力和聽覺不如嗅覺那樣好。 像所有的熊一樣，黑熊膽小，笨拙，很少具有危險(xiǎn)性。 但如果受到攻擊，大部分黑熊會(huì)以很快的速度爬上樹和奔跑。 當(dāng)發(fā)怒或受驚嚇時(shí)，黑熊會(huì)成為可 怕的對(duì)手。
黑熊以樹葉、草、樹根、水果、漿果、昆蟲、魚，甚至更大的動(dòng)物為食。 熊類， 包括黑熊的最有趣的一個(gè)特點(diǎn)是他們的冬眠。與松鼠、旱獺和其它別的林地動(dòng)物不同，熊 并不真正地冬眠。 雖然熊在冬天的幾個(gè)月中不吃東西，靠體內(nèi)脂肪維持生命，但它們的體溫保持正常，并有規(guī)律地一分鐘呼吸 4 或 5 次。除交配季節(jié)外，大多數(shù)黑熊獨(dú)自生活。 他 們喜歡住在洞里、空心的大木頭里或茂密的樹叢里。 經(jīng)過 6到 9 個(gè)月的懷孕期后一胎 1～4 個(gè)小熊在 1 月或 2 月出生。 它們同母熊住在一起，直到它們完全長大，即 1 歲半左右。黑熊在野外可以活到長達(dá) 30 年，在專門的保護(hù)區(qū)中甚至能活得更長。
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 83percent 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, coalfired 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.
火力發(fā)電廠托馬斯.愛迪生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(正是愛迪生本人在19世紀(jì)末建造了第一批電廠)。全國到處興建電廠時(shí)，對(duì)煤的依賴加深了。
自第一次世界大戰(zhàn)以來，美國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)年全國開采的九億噸煤的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)電廠仍可能為美國提供多達(dá)70%的電力。 然而，盡管煤長期以來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)境問題。 從1960 年以來，排放控制和垃圾處理的問題極大地削弱了燃煤電廠的魅力。由于減輕這些環(huán)境問題需要大量資金，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，但人們正在開發(fā)全新的清潔燃煤的技術(shù)。
American Black Bears
American black bears appear in a variety of colors despite their name. In the eastern part of their range, most of these bears have shiny black fur, but in the west they grow brown, red, or even yellow coats. To the north, the black bear is actually gray or white in color. Even in the same litter, both brown and black furred bears may be born.Black bears are the smallest of all American bears, ranging in length from five to six feet, weighing from three hundred to five hundred pounds. Their eyes and ears are small and their eyesight and hearing are not as good as their sense of smell.
Like all bears, the black bear is timid, clumsy, and rarely dangerous, but if attacked, most can climb trees and cover ground at great speeds. When angry or frightened, it is a formidable enemy.Black bears feed on leaves, herbs, roots, fruit, berries, insects, fish, and even larger animals. One of the most interesting characteristics of bears, including the black bear, is their winter sleep. Unlike squirrels, woodchucks, and many other woodland animals, bears do not actually hibernate. Although the bear does not eat during the winter months,sustaining itself from body fat, its temperature remains almost normal, and it breathes regularly four or five times per minute.
Most black bears live alone, except during mating season. They prefer to live in caves, hollow logs, or dense thickets. A litter of one to four cubs is born in January or February after a gestation period of six to nine months, and they remain with their mother until they are fully grown or about one and a half years old. Black bears can live as long as thirty years in the wild, and even longer in game preserves set aside for them.
美國黑熊
美國黑熊雖然被叫區(qū)域的東部，大部分黑 熊長有富有光澤的黑毛，但在西部，他們則長著棕色、紅色甚至是黃色的毛。
在北部，黑熊其實(shí)長著灰色或白色的毛。 就是在一胎所生的小熊中，都可能混雜棕毛和黑毛。 黑熊是 所有美洲熊中最小的，5～6 英尺長，300～500磅重。它們的眼睛和耳朵都很小，他們的視 力和聽覺不如嗅覺那樣好。 像所有的熊一樣，黑熊膽小，笨拙，很少具有危險(xiǎn)性。 但如果受到攻擊，大部分黑熊會(huì)以很快的速度爬上樹和奔跑。 當(dāng)發(fā)怒或受驚嚇時(shí)，黑熊會(huì)成為可 怕的對(duì)手。
黑熊以樹葉、草、樹根、水果、漿果、昆蟲、魚，甚至更大的動(dòng)物為食。 熊類， 包括黑熊的最有趣的一個(gè)特點(diǎn)是他們的冬眠。與松鼠、旱獺和其它別的林地動(dòng)物不同，熊 并不真正地冬眠。 雖然熊在冬天的幾個(gè)月中不吃東西，靠體內(nèi)脂肪維持生命，但它們的體溫保持正常，并有規(guī)律地一分鐘呼吸 4 或 5 次。除交配季節(jié)外，大多數(shù)黑熊獨(dú)自生活。 他 們喜歡住在洞里、空心的大木頭里或茂密的樹叢里。 經(jīng)過 6到 9 個(gè)月的懷孕期后一胎 1～4 個(gè)小熊在 1 月或 2 月出生。 它們同母熊住在一起，直到它們完全長大，即 1 歲半左右。黑熊在野外可以活到長達(dá) 30 年，在專門的保護(hù)區(qū)中甚至能活得更長。
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 83percent 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, coalfired 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.
火力發(fā)電廠托馬斯.愛迪生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(正是愛迪生本人在19世紀(jì)末建造了第一批電廠)。全國到處興建電廠時(shí)，對(duì)煤的依賴加深了。
自第一次世界大戰(zhàn)以來，美國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)年全國開采的九億噸煤的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)電廠仍可能為美國提供多達(dá)70%的電力。 然而，盡管煤長期以來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)境問題。 從1960 年以來，排放控制和垃圾處理的問題極大地削弱了燃煤電廠的魅力。由于減輕這些環(huán)境問題需要大量資金，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，但人們正在開發(fā)全新的清潔燃煤的技術(shù)。