March 2nd, 2010
Human vision like that of other primates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well that to develop an acute sense of smell. In the course of evolution members of the primate line have acquired large eyes while the snout has shrunk to give the eye an unimpeded view. Of mammals only humans and some primates enjoy color vision. The red flag is black to the bull. Horses live in a monochrome world .light visible to human eyes however occupies only a very narrow band in the whole electromagnetic spectrum. Ultraviolet rays are invisible to humans though ants and honeybees are sensitive to them. Humans though ants and honeybees are sensitive to them. Humans have no direct perception of infrared rays unlike the rattlesnake which has receptors tuned into wavelengths longer than 0.7 micron. The world would look eerily different if human eyes were sensitive to infrared radiation. Then instead of the darkness of night, we would be able to move easily in a strange shadowless world where objects glowed with varying degrees of intensity. But human eyes excel in other ways. They are in fact remarkably discerning in color gradation. The color sensitivity of normal human vision is rarely surpassed even by sophisticated technical devices.
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March 1st, 2010
A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun’s very center. It is here that is to be found the source of the energy that the Sun constantly pours out into space as light and heat. This energy is librated at the center of the Sun as billions upon billions of nuclei of hydrogen atoms collide with each other and fuse together to form nuclei of helium, and in doing so, release some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun requires that some 600 million tons of hydrogen be converted into helium in the Sun every second. This the Sun has been doing for several thousands of millions of year.
The nuclear energy is released at the Sun’s center as high-energy gamma radiation, a form of electromagnetic radiation like light and radio waves, only of very much shorter wavelength. This gamma radiation is absorbed by atoms inside the Sun to be reemitted at slightly longer wavelengths. This radiation , in its turn is absorbed and reemitted. As the energy filters through the layers of the solar interior, it passes through the X-ray part of the spectrum eventually becoming light. At this stage, it has reached what we call the solar surface, and can escape into space without being absorbed further by solar atoms. A very small fraction of the Sun’s light and heat is emitted in such directions that after passing unhindered through interplanetary space, it hits the Earth.
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February 28th, 2010
Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher; the sequoia tree can pump water to its very top more than 100 meters above the ground. Until the end of the nineteenth century, the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps. But many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure, a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore, the conifers, which are among the tallest trees, have unusually low root pressures.
If water is not pumped to the top of a tall tree, and if it is not pushed to the top of a tall tree, then we may ask: how does it get there? According to the currently accepted cohesion-tension theory, water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves, a negative pressure, or tension, is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore, the forces of cohesion (the attraction between water molecules) are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to.
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February 24th, 2010
If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation— conversion of liquid water to water vapor. In this manner the salinity is increased, since the salts stay behind. If this is carried to the extreme, of course, white crystals of salt would be left behind.
The opposite of evaporation is precipitation, such as rain, by which water is added to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas of high rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by evaporation, or decreased by the addition of fresh water by precipitation or runoff.
Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea, salinity is somewhat lower than in other oceanic areas.
A third process by which salinity may be altered is associated with the formation and melting of sea ice. When sea water is frozen, the dissolved materials are left behind. In this manner, sea water directly materials are left behind. In this manner, sea water directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water.
In the Weddell Sea Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of the oceans of the world.
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February 23rd, 2010
The theory of plate tectonics describes the motions of the lithosphere, the comparatively rigid outer layer of the Earth that includes all the crust and part of the underlying mantle. The lithosphere(n.[地]岩石圈)is divided into a few dozen plates of various sizes and shapes, in general the plates are in motion with respect to one another. A mid-ocean ridge is a boundary between plates where new lithospheric material is injected from below. As the plates diverge from a mid-ocean ridge they slide on a more yielding layer at the base of the lithosphere.
Since the size of the Earth is essentially constant, new lithosphere can be created at the mid-ocean ridges only if an equal amount of lithospheric material is consumed elsewhere. The site of this destruction is another kind of plate boundary: a subduction zone. There one plate dives under the edge of another and is reincorporated into the mantle. Both kinds of plate boundary are associated with fault systems, earthquakes and volcanism, but the kinds of geologic activity observed at the two boundaries are quite different.
The idea of sea-floor spreading actually preceded the theory of plate tectonics. In its original version, in the early 1960’s, it described the creation and destruction of the ocean floor, but it did not specify rigid lithospheric plates. The hypothesis was substantiated soon afterward by the discovery that periodic reversals of the Earth’s magnetic field are recorded in the oceanic crust. As magma rises under the mid-ocean ridge, ferromagnetic minerals in the magma become magnetized in the direction of the magma become magnetized in the direction of the geomagnetic field. When the magma cools and solidifies, the direction and the polarity of the field are preserved in the magnetized volcanic rock. Reversals of the field give rise to a series of magnetic stripes running parallel to the axis of the rift. The oceanic crust thus serves as a magnetic tape recording of the history of the geomagnetic field that can be dated independently; the width of the stripes indicates the rate of the sea-floor spreading.
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February 21st, 2010
British Columbia is the third largest Canadian provinces, both in area and population. It is nearly 1.5 times as large as Texas, and extends 800 miles(1,280km) north from the United States border. It includes Canada’s entire west coast and the islands just off the coast.
Most of British Columbia is mountainous, with long rugged ranges running north and south. Even the coastal islands are the remains of a mountain range that existed thousands of years ago. During the last Ice Age, this range was scoured by glaciers until most of it was beneath the sea. Its peaks now show as islands scattered along the coast.
The southwestern coastal region has a humid mild marine climate. Sea winds that blow inland from the west are warmed by a current of warm water that flows through the Pacific Ocean. As a result, winter temperatures average above freezing and summers are mild. These warm western winds also carry moisture from the ocean.
Inland from the coast, the winds from the Pacific meet the mountain barriers of the coastal ranges and the Rocky Mountains. As they rise to cross the mountains, the winds are cooled, and their moisture begins to fall as rain. On some of the western slopes almost 200 inches (500cm) of rain fall each year.
More than half of British Columbia is heavily forested. On mountain slopes that receive plentiful rainfall, huge Douglas firs rise in towering columns. These forest giants often grow to be as much as 300 feet(90m) tall, with diameters up to 10 feet(3m). More lumber is produced from these trees than from any other kind of tree in North America. Hemlock, red cedar, and balsam fir are among the other trees found in British Columbia.
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February 19th, 2010
Economics, as we know it, is the social science concerned with the production, distribution, exchange, and consumption of goods and services. Economists focus on the way in which individuals, groups, business enterprises, and governments seek to achieve efficiently any economic objective they select. Other fields of study also contribute to this knowledge: Psychology and ethics try to explain how objectives are formed, history records changes in human objectives, and sociology interprets human behavior in social contexts.
Standard economics can be divided into two major fields. The first, price theory or microeconomics, explains how the interplay of supply and demand in competitive markets creates a multitude of individual prices, wage rates, profit margins, and rental changes. Microeconomics assumes that people behave rationally. Consumers try to spend their income in ways that give them as much pleasure as possible. As economists say, they maximize utility. For their part, entrepreneurs seek as much profit as they can extract from their operations.
The second field, macroeconomics, deals with modern explanations of national income and employment. Macroeconomics dates from the book, The General Theory of Employment, Interest, and Money (1935), by the British economist John Maynard Keynes. His explanation of prosperity and depression centers on the total or aggregate demand for goods and services by consumers, business investors, and governments, Because, according to Keynes, inadequate total demand increases unemployment, the indicated cure is either more investment by businesses or more spending and consequently larger budget deficits by government.
Economic issues have occupied people’s minds throughout the ages. Aristotle and Plato in ancient Greece wrote about problems of wealth, property, and trade, both of whom were prejudiced against commerce, feeling that to live by trade was undesirable. The Romans borrowed their economic ideas from the Greeks and showed the same contempt for trade. During the Middle Ages the economic ideas of the Roman Catholic church were expressed in the law of the church, which condemned the taking of interest for money loaned and regarded commerce as inferior to agriculture.
Economics as a subject of modern study, distinguishable from moral philosophy and politics, dates from the work, Inquiry into the Nature and Causes of the Wealth of Nations (1776), by the Scottish philosopher and economist Adam Smith. Mercantilism and physiocracy were precursors of the classical economics of Smith and his 19th-century successors.
Tags: ancient, field, macroeconomics, microeconomics
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February 17th, 2010
Scholastic thinkers held a wide variety of doctrines in both philosophy and theology, the study of religion. What gives unity to the whole Scholastic movement, the academic practice in Europe from the 9th to the 17th centuries, are the common aims, attitudes, and methods generally accepted by all its members. The chief concern of the Scholastics was not to discover new facts but to integrate the knowledge already acquired separately by Greek reasoning and Christian revelation. This concern is one of the most characteristic differences between Scholasticism and modern thought since the Renaissance.
The basic aim of the Scholastics determined certain common attitudes, the most important of which was their conviction of the fundamental harmony between reason and revelation. The Scholastics maintained that because the same God was the source of both types of knowledge and truth was one of his chief attributes, he could not contradict himself in these two ways of speaking. Any apparent opposition between revelation and reason could be traced either to an incorrect use of reason or to an inaccurate interpretation of the words of revelation. Because the Scholastics believed that revelation was the direct teaching of God, it possessed for them a higher degree of truth and certainty than did natural reason. In apparent conflicts between religious faith and philosophic reasoning, faith was thus always the supreme arbiter; the theologians decision overruled that of the philosopher. After the early 13th century, Scholastic thought emphasized more the independence of philosophy within its own domain. Nonetheless, throughout the Scholastic period, philosophy was called the servant of theology, not only because the truth of philosophy was subordinated to that of theology, but also because the theologian used philosophy to understand and explain revelation.
This attitude of Scholasticism stands in sharp contrast to the so-called double-truth theory of the Spanish-Arab philosopher and physician Averroёs. His theory assumed that truth was accessible to both philosophy and Islamic theology but that only philosophy could attain it perfectly. The so-called truths of theology served, hence, as imperfect imaginative expressions for the common people of the authentic truth accessible only to philosophy. Averroёs maintained that philosophic truth could even contradict, at least verbally, the teachings of Islamic theology.
As a result of their belief in the harmony between faith and reason, the Scholastics attempted to determine the precise scope and competence of each of these faculties. Many early Scholastics, such as the Italian ecclesiastic and philosopher St. Anselm, did not clearly distinguish the two and were overconfident that reason could prove certain doctrines of revelation. Later, at the height of the mature period of Scholasticism, the Italian theologian and philosopher St. Thomas Aquinas worked out a balance between reason and revelation.
Tags: attitude, harmony, scholastic, theory
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January 29th, 2010
Advertisements come into our lives in a variety of forms. Newspapers carry advertisements. Billboards carry advertisements. More conspicuously, TV advertisements are incessantly influencing people’s life from various aspects.
Advertisements have many advantages. Firstly, advertising is informative, which provides us with a quick access to the product needed. Secondly, many advertisements, especially TV advertisemnts are so beautifully made that they themselves can bring us great enjoyment. Maybe that’s why the daughter in the picture is so attracted by them.
However, advertising involves some defects. Firstly, the cost of adverting will definitely be passed on to the customers, which makes the products be sold at much higher prices. Thirdly, Secondly, The advertisers often mispresent the truth by exaggerating the benefits of the merchandise they want to sell. Thirdly, advertisements often interrupt audiences’ appreciation of their favorite programs, which may lead to diasspointment and frustration, the expression written on the face of the father in the picuture,
As far as I am concerned, I tend to be in favor of the positive effects. Undoubtedly, nothing is more important than convenience for people living in a so quick-paced society. I believe that the negative effects can be minimized through sustainable economic growth and education.
Tags: advantage, advertisement, defect
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January 28th, 2010
Vinton Cerf, known as the father of the Internet, said on Wednesday that the Web was outgrowing the planet Earth and the time had come to take the information superhighway to outer space.
“The Internet is growing quickly, and we still have a lot of work to do to cover the planet.” Cerf told the first day of the annual conference of Internet Society in Geneva where more than 1500 cyberspace fans have gathered to seek answers to questions about the tangled web of the Internet.
Cerf believed that it would soon be possible to send real-time science data on the Internet from a space mission orbiting another planet such as Mars. “There is now an effort under way to design and build an interplanetary Internet. The space research community is coming closer and closer and merging. We think that we will see interplanetary Internet networks that look very much like the ones we use today. We will need interplanetary gateways and there will be protocols to transmit data between these gateways, ” Cerf said.
Francois Fluckiger, a scientist attending the conference from the European Particle Physics Laboratory near Geneva, was not entirely convinced, saying: “We need dreams like this. But I don’t know any Martian whom I’d like to communicate with through the Internet.”
Cerf has been working with NASA’s Pasadena Jet Propulsion Laboratory—the people behind the recent Mars expedition—to design what he calls an “interplanetary Internet protocol.” He believes that astronauts will want to use the Internet, although special problems remain with interference and delay.
“This is quite real. The effort is becoming extraordinarily concrete over the next few months because the next Mars mission is in planning stages now,” Cerf told the conference.
“If we use domain names like Earth or Mars…jet propulsion laboratory people would be coming together with people from the Internet community.” He added.
“The idea is to take the interplanetary Internet design and make it a part of the infrastructure of the Mars mission.”
He later told a news conference that designing this system now would prepare mankind for future technological advances.
“The whole idea is to create an architecture so the design works anywhere. I don’t know where we’re going to have to put it but my guess is that we’ll be going out there some time,” Cerf said.
“If you think 100 years from now, it is entirely possible that what will be purely research 50 years from now will become commercial 100 years from now. The Internet was the same—it started as pure research but now it is commercialized.”
Tags: architecture, cyberspace, interplanetary Internet
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