30.
Một vật dao động điều hoà theo phương trình x = - 5cos[5πt - π/6] cm. Biên độ dao động và pha ban đầu của vật là
A. A = 5 cm và φ = - π/6 rad. B. A = - 5 cm và φ = - π/6 rad. C. A = 5 cm và φ = π/3 rad. D. A = 5 cm và φ = 5π/6 rad.
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Một vật dao động điều hòa theo phương trình x = -4cos[5πt – π/3] cm. Biên độ dao động và pha ban đầu của vật là
A.
B.
C.
D.
Một vật dao động điều hoà theo phương trình x = – 5sin[5πt – π/6] cm. Biên độ dao động và pha ban đầu của vật là
A. A = – 5 cm và φ = – π/6 rad.
B. A = 5 cm và φ = – π/6 rad.
C. A = 5 cm và φ = 5π/6 rad.
D. A = 5 cm và φ = π/3 rad.
Đáp án và lời giải
Đáp án:C
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The biologist's role in society as well as his moral and ethical responsibility in the discovery and development of new ideas has led to a reassessment of his social and scientific value systems. A scientist can no longer ignore the consequences of his discoveries; he is as concerned with the possible misuses of his findings as he is with the basic research in which he is involved. This emerging social and political role of the biologist and all other scientists requires a weighing of values that cannot be done with the accuracy or the objectivity of a laboratory balance. As a member of society, it is necessary for a biologist now to redefine his social obligations and his functions, particularly in the realm of making judgments about such ethical problems as man's control of his environment or his manipulation of genes to direct further evolutionary development.
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Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Yoursymptomscould be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can beset offby foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods [read the labels!]. Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who arehyperactivemay benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few oftheseare almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective.
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Scientists do not yet thoroughly understand just how the body of an individual becomes sensitive to a substance that is harmless or even wholesome for the average person. Milk, wheat, and egg, for example, rank among the most healthful and widely used foods. Yet these foods can cause persons sensitive to them to suffer greatly. At first, the body of the individual is not harmed by coming into contact with the substance. After a varying interval of time, usually longer than a few weeks, the body becomes sensitive to it, and an allergy has begun to develop. Sometimes it's hard to figure out if you have a food allergy, since it can show up so many different ways. Yoursymptomscould be caused by many other problems. You may have rashes, hives, joint pains, mimicking arthritis, headaches, irritability, or depression. The most common food allergies are to milk, eggs, seafood, wheat, nuts, seeds, chocolate, oranges, and tomatoes. Many of these allergies will not develop if these foods are not fed to an infant until her or his intestines mature at around seven months. Breast milk also tends to be protective. Migraines can beset offby foods containing tyramine, phenathylamine, monosodium glutamate, or sodium nitrate. Common foods which contain these are chocolate, aged cheeses, sour cream, red wine, pickled herring, chicken livers, avocados, ripe bananas, cured meats, many Oriental and prepared foods [read the labels!]. Some people have been successful in treating their migraines with supplements of B-vitamins, particularly B6 and niacin. Children who arehyperactivemay benefit from eliminating food additives, especially colorings, and foods high in salicylates from their diets. A few oftheseare almonds, green peppers, peaches, tea, grapes. This is the diet made popular by Benjamin Feingold, who has written the book “Why your Child is Hyperactive”. Other researchers have had mixed results when testing whether the diet is effective.
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The three phases of human memory are the sensory memory, the short-term memory, and the long-term memory. This devision of the memory into phases is based on the length of time of the memory.
Sensory memory is instantaneous memory. It is an image or memory that enters your mind only for a short period of time; it comes and goes in under a second. The memory will not last longer than that unless the information enters the short-term memory.
Information can be held in the short-term memory for about twenty seconds or as long as you are actively using it. If you repeat a fact to yourself, that fact will stay in your short-term memory as long as you keep repeating it. Once you stop repeating it, either it is forgotten or it moves into long term memory.
Long-term memory is the huge memory tank that can hold ideas and images for years and years. Information can be added to your long-term memory when you actively try to put it there through memorization or when an idea or image enters your mind on its own.
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