攀登英语网 http://www.5pds.com 提供 demands are met, the plane will be blown up and all the passengers will be killed. These hijackers are often members of international terrorist organisations. They may want to change the system of government in their own country by using violence, or they may have hijacked a plane in order to try and force a government to release members of their organisation from prison.
There is not very much anyone can do once a hijacker is on board an aeroplane. He may
be carrying a gun or hand grenades, which, if used, would cause a disaster. The only thing to do is try to ensure that these people never get on the plane in the first instance. So airlines all over the world have security procedures. Before any passenger can get on an airplane at the airport, he must go through a series of security checks to make sure he isn't carrying anything that is potentially dangerous or could be used as a weapon on board. The security measures vary from airport to airport. At some airports there is very little security. At other airports the security checks are very strict and it can take up to half-an-hour to get through them all.
Kai Tak Airport in Hong Kong, China, has a good security system. No aircraft starting
its journey from Hong Kong has ever been hijacked. At Kai Tak, when a passenger first checks in, his or her name is matched with the computer list of passengers booked on that particular flight. If the name is not recognised, the passenger will be taken aside and questioned by security guards and may not be allowed on the plane. Next, every suitcase is X-ray checked before it goes into the plane. Any suitcase that seems to have something dangerous in it is not put on the plane. Then the hand baggage which the passengers will carry on to the plane is checked. Each passenger has to open his or her bag and the security clerk examines the contents. Cameras may be opened, even babies taken out of their prams and carry-cots. If there is anything that could be used as a weapon, a penknife for example, the security staff take it away and keep it in a safe place on the plane until the flight is over. The passenger can then collect it.
Finally there is a body check of all passengers. They must pass through a door where
X-rays will show if they are carrying anything made of metal, like a gun. If anything suspicious is found, they will be asked to explain. (At some other airports a security guard will \passenger as well, by running his hands over the passenger 's body to feel for guns and other weapons.) It is only after all these checks that a passenger is allowed to board the plane.
Brave New World of Biometrics
There are always people who can find a reason to criticize strongly any new technology
as too personally invasive, but I 'm all for biometrics. Among the amazing things biometrics enables us to do is to scan a person 's iris—the colored part of the eye—which displays a natural pattern that is even more distinct than the fingerprint.
Imagine what that will do to cut down on credit card fraud if the pattern of a person 's
iris must be scanned before the credit card can be used. Imagine how foolproof it will make Internet purchases, which are now extremely vulnerable to fraudulent abuse.
Biometries' ability to prevent theft against the government also is endless. When the
state of Connecticut required people to be fingerprinted in order to receive welfare benefits, 25
攀登英语网 http://www.5pds.com 提供 percent of the recipients dropped off the rolls (many of whom, we have to assume, were receiving benefits improperly).
Biometrics also will give law-enforcement officers terrific new powers to track and
capture international terrorists. Imagine what miniature face scans embedded secretly in passports will do to passport fraud, and the ability of terrorists to flee from one country to the next.
Does this mean the government and corporations will have more \
information\personal \ Ever since the invention of telemarketing and the ceaseless parade of phone calls
bombarding my home day and night began, I 've considered my privacy to be a thing of the past. But in the scheme of things, it is a minor inconvenience, not a major assault.
Of course, if biometrics is too much for some people, they always can cut up their
credit cards, disconnect their phones and computers and move to the Rockies and live alone away from people and society. Meanwhile, I'll continue to enjoy all the benefits modern technology offers.
The Deli
My husband and I were married about a year, when we were made an offer we couldn't
refuse. There was a delicatessen whose owner was anxious to sell. He was moving to another state. We could have the store at payments we could afford. We accepted. There was an apartment behind and connected to it which was included in the deal. We had no idea what the neighborhood was like, but with youthful energy and optimism, we moved in.
New York is a great big city; most folks call it unfriendly, and yet, I never found it so.
This area, from 96th Street to 100th Street, between Amsterdam and Columbus avenues, was absolutely small-townish. Everyone knew everybody else and most were related in some way. Outsiders who moved in had to prove themselves worthy of acceptance or remain forever strangers. We were fortunate. Even the local gang, called \place was located, accepted us whole-heartedly.
The \
be able to stay in business without being troubled by broken windows, shoplifting, out and out robberies, and, in certain cases, beatings, the Dukes were paid whatever they felt the shopkeepers, could bear. In their opinion, we were no exception.
One day three of the young men walked into the store. At the time, my husband was
outside arranging a shipment of goods that had just arrived, and I was preparing a sandwich which was to be my lunch. As I glanced up, I saw one of them quickly grab some candy bars and put them in his pocket; another leaned against the fruit bin which was immediately minus an apple. I was simple enough to believe that the only reason anyone stole food was hunger. My
攀登英语网 http://www.5pds.com 提供 heart broke and I really felt sorry for them. They asked to speak to my husband. \the moment, but if you don't mind waiting, he should be back in soon.\
As they started to turn to walk around the customer area, I introduced myself and, at the
same time, commenced making three more sandwiches. While I made small talk, they stood silent, looking fiercely, although hungrily at the sandwiches I was making: Italian rolls, piled high with juicy roast pork and, on top, my husband 's wonderful homemade pickles. I placed them on paper plates along with plenty of potato chips, then I said, \in the kitchen, because we 're not licensed to serve in the store. Do you want milk or cola?\
\
\
disbelief, then shrugging their shoulders, marched as one into the kitchen which was behind the store. They ate to their hearts' content and, before they left, emptied their pockets, putting each stolen article in its appointed place. No apologies were given, none were expected. But from that day on, we were protected, and the only payment we ever made was that which we also received: friendship, trust, and acceptance.
Unit 4
First Planet from the Sun
Mercury, the planet nearest the sun, is difficult to observe from the Earth because it
rises and sets within two hours of the sun. Consequently, little was known about the planet until the Mariner 10 spacecraft made several flybys in 1974 and 1975.
Planetary scientists can estimate the age of a planet 's surface by the number of impact
craters on it. In general, the older the surface, the more craters it has. Some regions on Mercury are heavily cratered, suggesting that they are very old surfaces that were probably formed about 4 billion years ago. Between these regions are areas of gently rolling plains that may have been smoothed by volcanic lava flows or by accumulated deposits of fine material ejected during impacts. These plains are also old enough to have accumulated a large number of impact craters. Elsewhere on the planet are smooth, flat plains that are probably younger and volcanic in origin. These plains have relatively few impact craters. Sometime between the formation of the intercrater plains and the formation of the smooth plains, the whole planet may have shrunk as it cooled, causing the crust to buckle and form the long, steep cliffs called scarps.
The largest impact basin on Mercury has a diameter of about 800 miles (1,300
kilometers) and is surrounded by mountains that rise to heights of about 1.2 miles (2 kilometers). The crater was probably created by the impact of a large planetesimal when Mercury was forming. On the opposite side of the planet is an area of hilly, linear terrain that probably resulted from seismic waves caused by the same impact.
攀登英语网 http://www.5pds.com 提供 Like other airless, solid bodies in the solar system, the entire surface of Mercury is
covered with a layer of rubble called regolith, which is composed of material, ranging from dust to boulders, that was scattered when impact craters were formed. This debris was in turn broken up and redistributed by subsequent impacts.
Mercury is very dense and has a magnetic field that is about 1 percent as strong as
Earth 's. This suggests the existence of a planetary core composed of iron and nickel and constituting about 40 percent of the planet 's volume. The surface gravity is about one-third as strong as Earth 's, and a thin atmosphere surrounds the planet. Radar images taken of Mercury in 1991 show what are considered to be large ice patches at the planet 's north pole.
Black Holes
It was a star vastly larger than our own sun. For hundreds of years this giant star burned
brightly in its corner of the universe. Then, at the end of its life span, a strange thing happened. The dying star began to collapse in on itself. While the star was in its death throes, all the matter that made up the star was squeezed together into a smaller and smaller area. Soon the star measured no more than a mile across. Its matter was so tightly packed that a piece of it the size of a small stone weighed as much as a mountain.
As the dead star continued to fall into itself, it brought with it every bit of matter in the
area. Every speck of dust, every stray atom, was dragged into it. The star had become a black hole. A black hole is a small area of matter so dense that not even a light beam can escape the pull of its gravity.
Since no light can leave black holes, there is no way for us to see them. They are
invisible. We know of their existence because of the strange things that happen around them. Light that is traveling through space just vanishes.
Just how wild is a black hole? Let 's take a look at gravity. A common expression
related to gravity is, \it must return to Earth. This happens because Earth attracts the ball, or pulls it toward itself. A flowerpot that is knocked off a third-story window will always hit the sidewalk. It is only the great thrust of giant rockets that allows the space shuttle to escape the pull of Earth 's gravity. On a planet with double or triple Earth 's gravity, objects would act quite differently,
because the pull, or attraction, would be much stronger. A ball thrown into the air would not go very high, and it would plunge quickly back to the surface of the planet. A falling flowerpot would be a deadly weapon. It would kill any luckless pedestrian who might happen to get hit by it. Rockets far more powerful than those used on Earth would be needed to break away from the pull of the planet 's gravity.
Beams of light, however, would have no trouble at all escaping from this planet. Even
if the force of gravity were increased to a million times that of Earth, light beams would still not be affected. Humans on such a world, though, would be crushed flatter than their own shadows.
攀登英语网 http://www.5pds.com 提供 Only if the amount of gravity were many billions of times stronger than Earth 's would
light beams bend back to the surface. That is the case with a black hole. It is hard to imagine just how dense and heavy black hole matter is. A penny made from black hole matter would rip through your pocket and plunge through the earth with the greatest of ease. When it emerged on the other side, it would hover in the air for a moment and then plunge back through the earth. Black holes are the strangest objects in the universe. Nothing ever leaves a black hole.
No light leaves it. No physical objects leave it. Once something enters a black hole, it is there forever. Black holes are like permanent detention halls in the sky. If a travel agent were to arrange a flight to a black hole, it would have to be a one-way trip. As the scientist Robert Jastrow said, %universe.\
Suppose, just for the sake of amusement, that you happened to drop into a black hole.
What would happen to you? Think of going feet first. Your feet would be pulled down faster than your ears. As a result, you would be drawn into a very thin thread of matter. Then the individual atoms in your body would be pulled apart.
Were you to survive the trip, however, some scientists believe that you would emerge
in the fourth dimension. You would be in a totally different universe. The point where matter exits from this universe and goes into the next is referred to as a white hole. Many scientists believe that there are at least five black holes in our section of the universe. But, then, no one really knows for sure. Our knowledge of black holes is based only on informed guesswork.
The Cosmos
When I was little, I lived in a section of Brooklyn in the City of New York. I knew my
immediate neighborhood intimately, every apartment building, backyard, empty lot, and elm tree. I knew where my friends lived. But more than a few blocks away, north of the noisy automobile traffic on 86th Street, was a strange unknown territory, off-limits to my wanderings. It could have been Mars for all I knew.
Even with an early bedtime, in winter you could sometimes see the stars. I would look
at them, twinkling and remote, and wonder what they were. I would ask older children and adults, who would only reply, \sky. But what were they? Just small hovering lamps? Whatever for? There had to be some answer.
As soon as I was old enough, my parents gave me my first library card. Immediately, I
asked the librarian for something on stars. She returned with a picture book displaying pictures of men and women with names like Clark Gable and Jean Harlow. I complained, and for some reason then strange to me, she smiled and found another book—the right kind of book. I opened it in excitement and read until I found it. The book said something astonishing, a very big thought. It said that the stars were suns, only very far away. The Sun was a star, but close up. Imagine that you took the Sun and moved it so far away that it was just a tiny point of light. How far away would you have to move it? I did not have any idea of angular size. I was ignorant