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更多“After the formation of the pn junction, there is a built-in voltage across the junction.”相关的问题
A．amount of time it took to form. the galaxy
B．size of the galaxy immediately after its formation
C．particular gas involved in the formation of the galaxy
D．importnce of the age of globular clusters in determining how the galaxy was formed
E．shape of the halo that formed around the galaxy
The theory that ocean basins were caused by meteoroid impact______.
A．has fallen into wide dispute ever since it was proposed
B．fails to explain how continents were originated and have changed
C．was discarded as unacceptable immediately after it was proposed
D．rightly explains the formation of most of the ocean basins
A、Failure of the buccopharyngeal membrane to rupture
B、Failure of the tracheoesophageal ridges to fuse
C、Incomplete formation of the septum secundum
D、Incomplete recanalization of the largnx
E、Patent thyroglossal duct
How the First Stars in the Universe Came into Existence
Researchers believe that our universe began with the Big Bang(宇宙大爆炸)about 13 billion years ago，and that soon after that event，matter began to form. as small dust grains and gases．How the first stars formed from this dust and gas has been a burning question for years，but a state of-the-art computer simulation now offers the most detailed picture yet of how these first stars in the universe came into existence．
The composition of the early universe was quite different from that of today，and the physics that governed the early universe were also somewhat simpler．Dr．Naoki Yoshida and colleagues in Japan and the U．S．incorporated these conditions of the early universe，sometimes referred to as the“cosmic dark ages，”to simulate the formation of an astronomical object that would eventually shine its light into this darkness．
The result is a detailed description of the formation of a protostar(原恒星)-the early stage of a massive primordial(原始的)star of our universe-and the researchers'computer simulation sets the bar for further investigation into the star formation process．The question of how the first stars evolved is so important because their formations and eventual explosions provided the seeds for subsequent stars to come into being．
According to their simulation，gravity acted on minute density variations in matter，gases，and the mysterious“dark matter”of the universe after the Big Bang in order to form. this early stage of a star-a protostar with a mass of just one percent of our sun．The simulation reveals how pre-stellar(前恒星的) gases would have actually evolved under the simpler physics of the early universe to form. this protostar． Dr．Yoshida's simulation also shows that the protostar would likely evolve into a massive star capable of synthesizing(合成)heavy elements，not just in later generations of stars，but soon after the Big Bang．
Their simulation of the birth of a protostar in the early universe signifies a key step toward the ambitious goal of piecing together the formation of an entire primordial star and of predicting the mass and properties of these first stars of the universe．More powerful computers，more physical data，and an even larger range will be needed for further calculations and simulations，but these researchers hope to eventually extend this simulation to the point of nuclear reaction initiation-when a stellar(星球的)object be comes a true star．
According to the first two paragraphs，the early universe
A．was governed by simpler physics．
B．got fewer stars shinning in it．
C．started over 13 billion years ago．
D．was composed in a way similar to that of today．
The function of a pinhole is to screen out all light rays except those coming in a perfectly straight line from the object, thus improving the sharpness of the image. After passing through a point the rays again spread out a little bit, and the size of the image formed will depend upon how far back the wall, screen, or film is from the pinhole.
The full exploitation of this phenomenon had to wait for the development of the lens, which gathered in a much larger number of light rays and still brought them to form. an image, just as the pinhole did, but with a difference: in a pinhole camera, the light rays form. an image that is equally sharp regardless of the distance to the film. When a lens is used, there may be a choice of planes of focus determined by adjusting the lens-to-film distance. Each plane is located some distance behind and relatively parallel to the lens.
Actual blown glass was developed early in Egyptian times, and the first lens may have been the bottom of a wine bottle. However, the first deliberate grinding of lenses did not take place until the thirteenth century, and the art did not become established until the sixteenth century. A book on the grinding and polishing of lenses was issued by B. Battista della Porta in 1589, but it was not until 1611 that Kepler compared a lens of glass to the lens in the eye and showed that rays from each point of an object were brought to a focus at each corresponding point of an image on the retina. Then, in 1619, Scheiner demonstrated the actual formation of an inverted image on the retina.
A good title for this selection would be ______ .
A．Modern Lenses
B．The Modern Camera
C．Lenses and Image Formation
D．Development in Photography
Directions: Put the following sentences in the proper order so that they make a complete paragraph. FOR EXAMPLE: 123456789 1. It was, in fact, the little known Cleisthenes. 2. Who is the father of democracy？ 3. Not Thomas Jefferson, as many people oddly seem to think. 4. From 508 to 502 BC, he began to develop a series of major reforms, leading to the formation of Athenian Democracy. 5. He first introduced democracy to the Greek city states in 508 BC, after he gained political power in Athens. 6. All citizens over the age of thirty were eligible to sit on the council, encouraging public involvement in the government. 7. He made all free men living in Athens and Attica citizens, giving them the right to vote as part of a democratic society. 8. While the format may not be the same as the many democracies around the world today, there is no doubt that this was the first step. 9. He also established a council.
Why was Kohoutek referred to as "the comet of the century" ？
A．It was thought to be extremely old.
B．It passes the Earth once a century.
C．Scientists predicted it would be very bright.
D．Scientists have been tracking it for a century.
To: Kenneth Moore
From: KayIa Stewart
Subject: Book reviews
Date: Sep. 24, 2009
Dear Mr. Kenneth Moore,
Allow me to congratulate you again on becoming part of our online magazine writing team. As you learned in an earlier communication, you will be writing reviews of recently published non-fiction books.
By Monday next week, you will receive your first assignment parcel, which will (141) copies of the publications on your assignment list. Instructions for submitting the first draft of each review, in addition to information on the formation of a peer critic group for your work, are located on our website. Essentially, you will be posting your work on our non-fiction book review board, which you can access only (142) an administration-approved user name and password. Since you need a password to log in, your (143) password is: crimson. You can change this password for your convenience after you have logged on to the site.
Welcome again, and we look forward to working with you!
(41)
A．consist
B．constitute
C．contain
D．compose
Unit 4 医学英语名词化结构的翻译作业，请留意标红色字体的地方。 1. In many cases a simple cause may be responsible for failure of the ulcer to heal. 2. Septic thrombosis occurs in adjacent small blood vessels, and the detachment of fragments of infected blood clot accounts for the septic embolism which may complicate a relatively insignificant abscess. 3. The method of making cultures of tissues gives the possibility to observe the formation and development of the living cells. 4. Chemotherapy or endocrine therapy, begun soon after the completion of primary therapy and continued for months or years, delays recurrence in almost all patients and prolongs survival in some. 5. The study of ophthalmology is very hard, and it takes a long time to become an excellent eye specialist. 6. Access to insulin by those who require it is a subject of special concern to international health agencies and national health authorities.
给气体或输气管上可能形成水合物的地段加热，使气体温度高于水合物形成的温度。该法在干线输气管上是不宜采用的，因为它会降低管道的输气能力。在矿场集气或城市配气站中，压降主要消耗在节流上，节流前后，温度下降很多，加热就成了这些地方防止水合物形成的主要方法。Heating a gas or gas pipe where a hydrate may form so that the gas temperature is higher than the temperature of hydrate formation. This method is not suitable for the main pipeline, because it will reduce the capacity of the pipeline. In gas collection or urban distribution stations, the pressure drop is mainly consumed in throttling. Before and after throttling, the temperature drops a lot, and heating becomes the only major method to prevent hydrate formation in these places.
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