2015考研英语作文素材精选 (十三)
考研英语作文是一个考察综合运用语言的部分，需要同学们运用逻辑思维下笔成文，因此，考前看一些意义深远、质量好的文章很有必要。以下是2015考研英语作文备考素材精选，请作参考。2015考研英语作文素材精选 (十三)
45.The source of Energy
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.
46.Vision
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.
47 Folk Cultures
A folk culture is a small isolated, cohesive, conservative, nearly
self-sufficient group that is homogeneous in custom and race with a strong
family or clan structure and highly developed rituals. Order is maintained
through sanctions based in the religion or family and interpersonal.
Relationships are strong. Tradition is paramount, and change comes infrequently
and slowly. There is relatively little division of labor into specialized
duties. Rather, each person is expected to perform a great variety of tasks,
though duties may differ between the sexes. Most goods are handmade and
subsistence economy prevails. Individualism is weakly developed in folk cultures
as are social classes. Unaltered folk cultures no longer exist in industrialized
countries such as the United States and Canada. Perhaps the nearest modern
equivalent in Anglo America is the Amish, a German American farming sect that
largely renounces the products and labor saving devices of the industrial age.
In Amish areas, horse drawn buggies still serve as a local transportation device
and the faithful are not permitted to own automobiles. The Amish's central
religious concept of Demut "humility", clearly reflects the weakness of
individualism and social class so typical of folk cultures and there is a
corresponding strength of Amish group identity. Rarely do the Amish marry
outside their sect. The religion, a variety of the Mennonite faith, provides the
principal mechanism for maintaining order.
By contrast a popular culture is a large heterogeneous group often highly
individualistic and a pronounced many specialized professions. Secular
institutions of control such as the police and army take the place of religion
and family in maintaining order, and a money-based economy prevails. Because of
these contrasts, "popular" may be viewed as clearly different from "folk". The
popular is replacing the folk in industrialized countries and in many developing
nations. Folk-made objects give way to their popular equivalent, usually because
the popular item is more quickly or cheaply produced, is easier or time saving
to use or leads more prestige to the owner.
48 Bacteria
Bacteria are extremely small living things. While we measure our own sizes
in inches or centimeters, bacterial size is measured in microns. One micron is a
thousandth of a millimeter: a pinhead is about a millimeter across. Rod-shaped
bacteria are usually from two to four microns long, while rounded ones are
generally one micron in diameter. Thus if you enlarged a rounded bacterium a
thousand times, it would be just about the size of a pinhead. An adult human
magnified by the same amount would be over a mile(1.6 kilometer) tall.
Even with an ordinary microscope, you must look closely to see bacteria.
Using a magnification of 100 times, one finds that bacteria are barely visible
as tiny rods or dots. One cannot make out anything of their structure. Using
special stains, one can see that some bacteria have attached to them
wavy-looking "hairs" called flagella. Others have only one flagellum. The
flagella rotate, pushing the bacteria through the water. Many bacteria lack
flagella and cannot move about by their own power, while others can glide along
over surfaces by some little-understood mechanism.
From the bacteria point of view, the world is a very different place from
what it is to humans. To a bacterium water is as thick as molasses is to us.
Bacteria are so small that they are influenced by the movements of the chemical
molecules around them. Bacteria under the microscope, even those with no
flagella, often bounce about in the water. This is because they collide with the
watery molecules and are pushed this way and that. Molecules move so rapidly
that within a tenth of a second the molecules around a bacteria have all been
replaced by new ones; even bacteria without flagella are thus constantly exposed
to a changing environment.
页:
[1]