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Sparklers are similar to firecrackers.
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Section B
Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice.
Are you a team person？ Are you at your best as part of a small ,tightly united group of dedicated workers？ If so, the future may hold more for you than you think.
High technology, some predicted, would make team work a thing of the past. That's happening in those areas of business and data processing where one person and a computer can replace a team of workers.
But, elsewhere, teamwork is very much alive. High technology has led to a new type of teamwork in a number of fields, including advertising, scientific research, engineering design, architecture and ocean exploration.
Through computer networking, scientists, engineers, and technicians at different locations--often thousands of miles apart--can work on the same project at once. They can exchange ideas, try out different designs, and test their results.
Examples？ An engineering team can now design and try out a robot system--a new manufacturing process, or an entire factory--before it is built. An architectural team can do the same with a building or a bridge. A medical team can simulate a dangerous operation before performing it on a patient.
Of course, computer-assisted team effort doesn't end with investigation and simulation. It now usually continues into actual design, manufacturing, and testing. "CAD--CAM--computer-aided design and manufacture--is breaking down barriers between traditional design and manufacturing functions." explains Dr. Prakash Rao, an engineering manager at General Electric. "Interdisciplinary (跨学科的) teams and engineers follow a product from concept to production. Everything is interconnected like a network."
Sometimes, a computer-aided effort can extend beyond production. A team that produces robots may use them to explore space and ocean depths. For high-technology teamwork, the future seems limitless.
The words "hold more" (Line 2, Para. 1) most probably means ______.
Fireworks
If you have ever been to an aerial fireworks show at an amusement park, baseball game, Fourth of July celebration or on New Year's Eve, then you know that fireworks have a special and beautiful magic all their own--a good show is absolutely amazing!
Have you ever wondered how this magic works？ What is launched into the sky to make these beautiful displays？ In this article, you will learn all about aerial fireworks.
Basic Components
Just about everyone in the United States has some personal experience with fireworks, either from Fourth of July or New Year's Eve celebrations. For example, you have probably seen both sparklers and firecrackers. It turns out that if you understand these two pyrotechnic (有关烟火制造术的) devices, then you are well on your way to understanding aerial fireworks! The sparkler demonstrates how to get bright, sparkling light from a firework, and the firecracker shows how to create an explosion.
Firecrackers have been around for hundreds of years. They consist of either black powder (also known as gunpowder) or flash powder in a tight paper tube with a fuse to light the powder. Black powder, discussed briefly in How Rocket Engines Work, contains charcoal, sulfur and potassium nitrate. A composition used in a firecracker might have aluminum instead of or in addition to charcoal in order to brighten the explosion.
Sparklers are very different from firecrackers. A sparkler burns over a long period of time (up to a minute) and produces extremely bright and showery light. Sparklers are often referred to as "snowball sparklers" because of the ball of sparks that surrounds the burning portion of the sparkler. If you look at Patent #3,862,865: Sparkler composition, you can see that a sparkler consists of several different compounds:
A fuel
An oxidizer
Iron or steel powder
A binder
The fuel is charcoal and sulfur, as in black powder. The binder can be sugar or starch. Mixed with water, these chemicals form. a slurry that can be coated on a wire (by dipping) or poured into a tube. Once it dries, you have a sparkler. When you light it, the sparkler bums from one end to the other (like a cigarette). The fuel and oxidizer are proportioned, along with the other chemicals, so that the sparkler burns slowly rather than exploding like a firecracker.
It is very common for fireworks to contain aluminum, iron, steel, zinc or magnesium dust in order to create bright, shimmering sparks. The metal flakes heat up until they are incandescent and shine brightly or, at a high enough temperature, actually burn. A variety of chemicals can be added to create colors. See lights and colors for a good explanation of the chemistry and physics of color in fireworks.
Aerial Fireworks
An aerial firework is normally formed as a shell that consists of four parts:
Container----usually pasted paper and string formed into a cylinder
Stars--spheres, cubes or cylinders of a sparkler-like composition
Bursting charge--firecracker-like charge at the center of the shell
Fuse—provides a time delay so the shell explodes at the right altitude
The shell is launched from a mortar. The mortar might be a short, steel pipe with a lifting charge of black powder that explodes in the pipe to launch the shell. When the lifting charge fires to launch the shell, it lights the shell's fuse. The shell's fuse bums while the shell rises to its correct altitude, and then ignites the bursting charge so it explodes.
Simple shells consist of a paper tube filled with stars and black powder. Stars come in all shapes and sizes, but you can imagine a simple star as something like sparkler compound formed into a ball the size of a pea or a dime. The stars are poured into the tube and then surrounded by b
The host is not polite if he sits down at the table before the guests do so.
【B8】
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