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Our world has never been so small or so flat, thanks to technologies that have altered our relationship with time and space in ways that would startle even Albert Einstein.
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To be effective in the 21st century, educational institutions will have to become truly cosmopolitan.
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We’re at the mercy of fluctuating gas prices all too often; we pump too many greenhouse gases into the air.
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What we need, then, is a smart transportation system equal to the needs of the 21st century.
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This high-speed rail system is not some fanciful, pie-in-the-sky vision of the future.
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More people travel between those cities by rail than by car and airplane combined.
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By making investments across the country, we’ll lay a new foundation for our economic competitiveness and contribute to smart urban and rural growth.
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We’ll create highly-skilled construction and operating jobs, and generate demand for technology that gives a new generation of innovators and entrepreneurs the opportunity to step up and lead the way in the 21st century.
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The Electron Microscope
The general layout of the illumination system and lenses of the electron microscope corresponds to the layout of the light microscope. The electrons are accelerated by a high-voltage potential (usually 40, 000 to 100, 000 volts), and pass through a condenser lens system usually composed of two magnetic lenses. The system concentrates the beam on to the specimen, and the objective lens provides the primary magnification. The final image in the electron microscope must be projected on to a phosphor-coated screen so that it can be seen. For this reason, the lenses that are the equivalent of the eyepiece in an optical microscope are called “projector“ lenses.
Normally, the electron microscope is upside-down when compared with the light microscope, with the electron gun at the top of the column and the fluorescent screen at the bottom. The screen is viewed through a window let into the front. The column of the microscope is held under high vacuum to prevent the electrons passing through it from striking air molecules and being scattered.
The strength of an electron lens depends on the current passing through the coil that produces the magnetic field. The strength of the lens can be varied by altering the current. In the electron microscope, therefore, the lenses are fixed, and adjustments are made to magnification and focus by altering the current passing through the lens coils. The condenser lens focuses the beam of electrons on to the specimen and affects the amount of illumination on the screen; the objective lens focuses the image; and the projector lenses alter the magnification.
Magnetic lenses suffer from the same defects (chromatic and spherical aberration) in the same way as glass lenses. But the same methods of correction cannot be used, because there is no “negative“ electron lens.
A very small lens aperture is employed to correct spherical aberration, but this severely limits the final resolution. Chromatic aberration is reduced by using electrons of a single wavelength. To produce such electrons, the accelerating voltage must be kept very steady because the wavelength of the beam is related to the accelerating voltage.
Electron-microscope lenses suffer from the further aberration of astigmatism, which affects light-microscope lenses to a far lesser degree. Astigmatism is caused by the lens having two focal planes for axes at right angles to each other .
Nothing can be done about astigmatism in an optical microscope. But in an electron microscope it can be corrected. Astigmatism in the electron microscope arises from two sources: from the lenses themselves, and from dirty apertures ( which are only 25 to 50 microns in diameter) in the objective lens. In both cases the astigmatism can be corrected by a skilled operator. In effect, the electron microscope achieves its superior resolution more in spite of, than because of, its lenses.
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Electric Traction
It is generally held that the most efficient method of railway operation, and ultimately the most economical, given a reasonably cheap electricity supply, is with electricity as the motive power. The electric locomotive is not dependent, like its steam counterpart, on the competence of driving and firing or the quality of the fuel burned. On the other hand, the speeds that will be possible with any given load are completely predictable and apart from signal or permanent way checks, or other delay-producing casualties, exact observance of schedule times can be guaranteed within narrow limits. With such accurate timetable observance trains can be operated with shorter turnaround times at terminals, which means that more intensive use can be made of rolling stock than is generally possible with steam power.
In suburban areas the rapid acceleration afforded by electric motors from rest and in recovery from speed restrictions makes it possible to work trains with very frequent stops at higher speeds and a closer headway than with steam locomotives. Multiple-unit working, which brings the motors of two or more sets of passenger stock, or two of more locomotives, under the control of one motorman in the leading driving cabin, would be impossible with steam, for each steam locomotive must be manned by its own driver and fireman. Moreover, except on the fastest and heaviest passenger and freight duties, on which it is advisable to have a second man at the head end to assist in the observation of signals and, if necessary, to attend to the electrical equipment, the equivalent of the steam locomotive fireman is unnecessary; thus the great majority of electric trains have a driver only, which makes for considerable economies in staffing.
So much for the credit side of the ledger with electric operation. On the debit side is the extremely high cost of providing all the line equipment for supplying current to the trains, and of the sub-stations for feeding the current to the line conductors, hitherto this has been the chief obstacle to more widespread electrification. There is also the obvious disadvantage that, unlike the steam or diesel or diesel-electric locomotive, the electric motive-power unit cannot run anywhere beyond the line or lines equipped with conductors. Concentration of the power supply in large power-stations, also, means that any serious breakdown in the supply can have very widespread effects, bringing a large number of trains to a stand, though with the help of the modern grid system of current distribution in a country like Britain alternative sources of supply can generally be made available without much delay. There is the final disadvantage that in hard winter conditions icing of the conductors, which hinders the picking up of the current, may cause serious delays to trains, as has often been the case on winter mornings on the suburban lines round London; but such trouble is confined mainly to the railways on which the current is picked up from a third rail rather than from overhead conductors. These lines have to be provided with de-icing trains, which patrol them in the early mornings when icing conditions are severe, spreading certain liquid compounds on the rails in order to melt ice formations.
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单位GDP能耗同比下降4．2％，碳排放强度下降5％左右，是多年来降幅最大的。
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我们支持推动传统经济转型升级，挖掘绿色经济、蓝色经济、互联网经济等发展前景良好的新经济形态，走绿色、循环、低碳和高效发展之路。
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稀土作为不可再生的战略资源，在新能源、新材料、节能环保、航空航天及电子信息等领域的应用日益广泛。
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在新能源、信息及节能减排领域，具有自主创新能力的中小企业发生了巨大变化。
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据统计，将有近10万名科技人员进入企业、进入农村、进入各行各业，帮助中小企业渡过难关，帮助中小企业进行产品创新和技术改进。
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随着总量扩大，经济增长的就业容量扩大了，对波动的容忍度也提高了。
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稳增长是为了保就业，调控的下限是比较充分的就业。
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我们更加关注结构调整等长期问题，不随单项指标的短期小幅波动而起舞。
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中国经济有巨大韧性、潜力和回旋余地。
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我们采取的措施既利当前、更惠长远，有能力防范出现大的起伏，更不会发生“硬着陆”。
