Solids, Liquids, and Gases

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The familiar compound H2O provides the evidence that substances occur in three different physical classes called states. At room temperature, H2O is a dense fluid called a liquid. When that liquid is chilled to 0º C, it changes to a rigid solid. If the liquid is heated to 100º C, however, it abruptly expands to a tenuous fluid called vapor or gas. Almost all substances can exist in two or three of the fundamental states. These states have different properties because they have distinct structures on the atomic or molecular scale. In a solid, the atoms are strongly bonded to the surrounding atoms so that each is in a fixed position; if the solid structure has a regular pattern that is repeated throughout the solid, it is described as a crystalline structure. The atoms or molecules in a liquid are less strongly bonded than in a solid of the same chemical composition, and consequently, they may shift their positions. The bonds in a liquid are, nevertheless, strong enough so that the atoms stay in contact with surrounding atoms. In a gas, the bonding between individual molecules is so weak that individual molecules may move in all directions, and the absence of cohesive forces allows the vapor to expand throughout any container.

3. Navigation Systems for Unmanned Aerial Vehicles

The work presents a study of variants of navigation microsystems based on primary measuring elements of various physical nature. The authors analyze the possibility of constructing reference systems basing on inertial, pyrometrical and optical sensors, as well as their performance abilities, and describe methods of enhancing their accuracy. The authors also study the advantages and disadvantages of the systems and analyze the possibility of applying them in various types of UAVs. Navigation systems present an integral part of aerial vehicles automatic control systems, including those used in UAVs. Navigation systems are intended for measuring the course angle, roll angle and pitch angle. Small UAVs navigation systems are of special interest, as they are based on microsystem sensitive elements.

Задание 4. Проанализируйте данный отрывок из научно-популярного текста. Чем он отличается от научно-технического текста?

The humorist Robert Benchley said that there are two classes of people in the world: those who divide the people of the world into two classes, and those who do not. In Chapter 2, when I asked why the mind keeps track of individuals, I took it for granted that the mind forms categories. But the habit of categorizing deserves scrutiny as well. People put things and other people into mental boxes, give each box a name, and thereafter treat the contents of a box the same. But if our fellow humans are as unique as their fingerprints and no two snowflakes are alike, why the urge to classify? Psychology textbooks typically give two explanations, neither of which makes sense. One is that memory cannot hold all the events that bombard our senses; by storing only their categories, we cut down on the load. But the brain, with its trillion synapses, hardly seems short of storage space. It’s reasonable to say that entities cannot fit in memory when the entities are combinatorial—English sentences, chess games, all shapes in all colors and sizes at all locations—because the numbers from combinatorial explosions can exceed the number of particles in the universe and overwhelm even the most generous reckoning of the brain’s capacity. But people live for a paltry two billion seconds, and there is no known reason why the brain could not record every object and event we experience if it had to. (S.Pinker)

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