unit7,硕士生英语综合教程2 课本原文 电子版
群众路线对照材料-在挫折中成长作文
Unit7
(Para. 1a) Exploration is an
important survival strategy in evolution. The
migration of
expansive species depends on
exploring their immediate or distant surroundings
for new food
sources or safe habitats; it can
also come as a result of population pressures or
environmental
changes. The human species has
added another reason for exploration, namely
curiosity. This
intellectual urge to explore
the unknown led the great European explorers to
the Americas,
Australia and Antarctica between
the fifteenth and seventeenth centuries.
(Para. 1b) Inquisitiveness about
nature is also
the driving force behind
humans exploring the polar caps, climbing mountain
peaks and
diving into the abysses of the
oceans. Now, the ultimate frontier to explore in
the
twenty-first century is space.
Astronomical observations and satellites have
already yielded
immense knowledge about our
solar system and the universe beyond. But these
technologies
can provide only a limited
picture of what is out there; eventually humans
themselves will have
to travel to other
planets to investigate them in more intimate
detail.
(Para. 1c) Tremendous
advances in rocket and spaceship technologies
during the
past 50 years, driven mainly by
national security considerations, the need for
better
communication or a desire to observe
environmental changes and human activity on the
ground, have made it possible to send humans
into near-Earth orbit and to the Moon.
Conceivably, these advances will eventually make
it possible to transport astronauts to
other
planets, and Mars in particular.
(Para. 2a)
But there are significant differences between
exploring Earth and exploring
space. First and
foremost, space is an unforgiving environment that
does not tolerate human
errors or technical
failure. For humans leaving Earth’s orbit for
extended periods, there are
even more dangers.
One is the near absence of gravity in space; the
presence of high-energy,
ionizing
cosmic ray (HZE) nuclei is another.
(Para.
2b) Because both zero gravity and cosmic
rays would have severe health
implications for
astronauts on a Mars-bound spaceship, we first
need to investigate their
effects on cells,
tissues and our hormonal and immune systems.
However, although we are
able to produce HZE
nuclei on Earth and study their effects on
biological material, we cannot
simulate
extended periods of low gravity and their additive
effects on cells and tissues. Thus,
the
International Space Station (ISS) will have an
enormously important role in assessing the
health dangers for humans in space and in the
development of potential countermeasures.
(Para. 3) There is much information on
the adaptation of astronauts to zero gravity
(0g) in space and on their return to 1g on
Earth. Nevertheless, our understanding of these
effects is not complete; nor have
countermeasures to
mitigate them
been identified.
(Para. 4a) Observations
of astronauts travelling on the Space Shuttle and
Russian
cosmonauts’ long-term visits to the
Mir space station indicate that time spent in 0g
has serious
effects on bone and muscle
physiology and the cardiovascular system. For
instance, the return
from 0g to 1g leads to an
inability to maintain an appropriate blood
pressure when in an
upright position —
orthostatic
intolerance—and
insufficient blood flow to the brain.
(Para.
4b) Astronauts returning from orbit therefore
have to rest for several minutes, and
the time
needed to normalize their blood pressure
increases with the time spent in 0g.
This could mean that astronauts
travelling to Mars—which would take at least one
year in
0g—would need considerable time to
readapt to gravity after landing there or after
their return
to Earth, unless we find a
technological solution to the creation of
artificial gravity on a
spaceship.
(Para.
4c) Moreover, there are other cardiovascular
effects, such as cardiac arrhythmia and
atrophy, which need to be studied in more
detail before we can ensure the safety of
astronauts
on a Mars mission. Other effects of
extended time in low gravity are loss of bone mass
and
muscle deterioration. Without adequate
countermeasures, these could impair the ability of
astronauts to perform necessary functions on a
spacecraft or on the surface of Mars.
(Para.
5a) The second main danger for human travelers
is the presence of the
aforementioned HZE
nuclei in cosmic rays, because of the ionizing
effect that they exert on
atoms or molecules.
(Para. 5b) Although they do not reach
the Earth’s surface because they are either
absorbed by the atmosphere or deflected by
Earth’s magnetic field,
there are
already some experimental data on the cancer-
inducing properties of
electrons, neutrons and
protons in cosmic rays and other potential
deleterious effects on
biological material
from numerous Earth-based experiments on
laboratory animals. In addition,
studies of
the effects of the atomic bombs dropped on Japan
in 1945 provided further data
about the health
dangers of radiation and high-energy nuclei.
(Para. 6) However, cosmic rays are quite
different from nuclear explosions because they
include considerably higher numbers of HZE
nuclei—leftovers from collapsing stars and
supernova explosions that were thrown into
space. The biological effects of HZE nuclei on
cancer induction, the central nervous system,
the immune system and the eyes are not well
known, nor have the interaction of radiation
effects at 0g been studied. Consequently we need
to conduct many more experiments on Earth as
well as on the ISS before the health and safety
of astronauts travelling to Mars and beyond
can be assured.
(Para. 7)
Ironically, the health dangers of radiation in
space only became an issue
when the potential
dangers of material brought back from space were
discussed. In 1975 I
joined the Space Science
Board of the US National Research Council (NRC)
that considered,
among other issues, the
problem of whether objects returned from the Moon
or elsewhere
from space could harbor
deleterious organisms that would be
to life
on Earth. The
hazardous
appropriate solution at that time was to isolate
these objects and extensively sterilize
them
with X-rays or ultraviolet radiation, or high
temperatures.
(Para. 8a) Understanding and
evaluating the physiological effects of radiation
and gravity
require not only experiments on
Earth but also extensive research on the ISS with
an adequate
number of animals andor human
subjects. However, further expansion and work on
the ISS
has been stalled because of cuts
in funding by NASA and, more recently, by the loss
of
the Columbia space shuttle in
February 2003. In addition, the ISS faces
employment problems.
(Para. 8b)
Originally, a crew of six or seven astronauts was
planned for the ISS to maintain
and run the
station and to do scientific experiments.
However, the shortage of funds means
that there are not enough large space vehicles,
such as space shuttles, available to transport
crew, equipment and supplies and to serve as a
rescue vehicle in case of a serious accident
on the ISS.
(Para. 8c) Hence, for
safety reasons the crew size was reduced in 2002
to three, because
only the Russian spacecraft,
Soyuz, was available and that can carry only three
crew members
in an emergency. The loss of the
Columbia shuttle has exacerbated this problem. As
the crew
size has been decreased from six to
three, most of the astronauts’ time will be spent
on
operation and
maintenance of the
station, which leaves little time for conducting
scientific
experiments.
(Para. 9)
Without a significantly large infusion of funds to
supply the equipment
and to support a larger
crew, the collection of basic information about
the hazards of space
travel will not be
accomplished within the next 10–20 years. We
also need a continuing,
rotating crew of at
least six astronauts to obtain epidemiologically
significant data on the
physiological and
psychological effects of 0g on astronauts and the
efficacy of
countermeasures. Unless these
experiments can be done, it will not be possible
to guarantee
the safety and well-being of
astronauts on a three-year trip to Mars and back.
(Para. 10) So, how can we satisfy our
curiosity about the Solar System and beyond, and
continue to investigate the nearest planets in
more detail?
(Para. 11a) There are three
possible solutions. The first, and most obvious,
is to use
unmanned spacecraft to
investigate the planets’ surface and to land, for
example, on Mars or
Europa —one of Jupiter’s
moons — and return samples to Earth. This might
very well be done
within the next 10 years.
(Para. 11b) The second solution is to
provide massively increased funding for the ISS. I
cannot guess how much this would be, because,
judging from past experience, there are large
uncertainties in such estimates. And these
funds would even
eclipse the amount of
money needed for a spacecraft that could transport
a crew of six
or seven astronauts on a three-
year trip to Mars and back.
In the
present global economic circumstances, this is
certainly not feasible without
significant
physical and financial collaboration and
cooperation among many countries.
(Para. 11c)
The third possible solution is to construct new
lift-off capabilities
and a much faster
spacecraft to drastically reduce the time
being spent in space and thus
the radiation
exposure and other stresses on astronauts. Science
reported that Russia is
working on plans for a
nuclear-powered spacecraft to accomplish this
goal.
(Para. 11d) However, it is
hard to envisage take-off and landing
scenarios that
would satisfy environmental
concerns. Given the current situation, I therefore
think that we
will need to upgrade the ISS
further and will have to
stick with
robot probes for at least the next 15 years before
we can re-evaluate the
rationale for sending
humans to Mars.