共查询到20条相似文献，搜索用时 15 毫秒
1.
Shapley D 《Science (New York, N.Y.)》1977,196(4291):745
Due to an editing error, the capacities of two nuclear plants were incorrectly described in the 25 March issue, p. 1312. The Millstone 1 plant has a capacity of 630, not 830 megawatts, and Millstone 3 will have a capacity of 1150, not 1000 megawatts. 相似文献
2.
Cool Water, the world's first commercial-scale, integrated coal gasification combined cycle power plant, has been operating successfully since May 1984 near Barstow, California. The 100-megawatt plant, which was completed ahead of schedule and under budget, is probably the cleanest coal-fired power generating facility now in commercial operation. An ongoing demonstration program at Cool Water shows that future baseload power plants that use this technology can be built modularly in increments of a few hundred megawatts and compete economically with much larger, conventional coal-fired power plants equipped for flue gas desulfurization. 相似文献
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The amplification of laser light to generate powers large enough to affect the nucleus has been the desire of scientists since the invention of the laser 40 years ago. Many lasers, including tabletop varieties, now have pulse powers greater than the electrical power generated by all the world's power plants combined. When this power is focused to dimensions of a few microns, laser-driven nuclear phenomena can occur. Here we review the developments in this research field and describe the potential of laser produced proton, neutron, and heavy ion beams, together with isotope and isomer production. 相似文献
4.
Koziol K Vilatela J Moisala A Motta M Cunniff P Sennett M Windle A 《Science (New York, N.Y.)》2007,318(5858):1892-1895
With their impressive individual properties, carbon nanotubes should form high-performance fibers. We explored the roles of nanotube length and structure, fiber density, and nanotube orientation in achieving optimum mechanical properties. We found that carbon nanotube fiber, spun directly and continuously from gas phase as an aerogel, combines high strength and high stiffness (axial elastic modulus), with an energy to breakage (toughness) considerably greater than that of any commercial high-strength fiber. Different levels of carbon nanotube orientation, fiber density, and mechanical properties can be achieved by drawing the aerogel at various winding rates. The mechanical data obtained demonstrate the considerable potential of carbon nanotube assemblies in the quest for maximal mechanical performance. The statistical aspects of the mechanical data reveal the deleterious effect of defects and indicate strategies for future work. 相似文献
5.
Amo A Pigeon S Sanvitto D Sala VG Hivet R Carusotto I Pisanello F Leménager G Houdré R Giacobino E Ciuti C Bramati A 《Science (New York, N.Y.)》2011,332(6034):1167-1170
A quantum fluid passing an obstacle behaves differently from a classical one. When the flow is slow enough, the quantum gas enters a superfluid regime, and neither whirlpools nor waves form around the obstacle. For higher flow velocities, it has been predicted that the perturbation induced by the defect gives rise to the turbulent emission of quantized vortices and to the nucleation of solitons. Using an interacting Bose gas of exciton-polaritons in a semiconductor microcavity, we report the transition from superfluidity to the hydrodynamic formation of oblique dark solitons and vortex streets in the wake of a potential barrier. The direct observation of these topological excitations provides key information on the mechanisms of superflow and shows the potential of polariton condensates for quantum turbulence studies. 相似文献
6.
[目的]测定彩色棉色素含量.[方法]对不同浓度天然彩色棉纤维色素粗提液扫描分析.[结果]绿色棉纤维色素提取液在252 nm附近吸收峰随色素浓度减小向短波长方向小幅度移动,棕色棉纤维色素吸收峰随浓度减小向紫外短波长方向移动幅度较大.对色素粗提液200～700 nm所有吸收值与相对浓度的相关系数进行筛选,选择最大相关系数对应波长为定量分析特征波长,确定绿色棉纤维提取液定量分析特征波长为417 nm,棕色棉纤维提取液定量分析特征波长为613 nm,并且建立直线回归方程,回归方程分别为:C绿=0.053 5 A,R~2=0.996 5;C_棕=0.021 7 A,R~2=0.987 8.相关系数均达到0.99以上.[结论]彩色棉纤维色素吸收值对相对浓度的回归方程有明确意义. 相似文献
7.
Abdo AA Ackermann M Ajello M Allafort A Baldini L Ballet J Barbiellini G Bastieri D Bechtol K Bellazzini R Berenji B Blandford RD Bloom ED Bonamente E Borgland AW Bouvier A Brandt TJ Bregeon J Brez A Brigida M Bruel P Buehler R Buson S Caliandro GA Cameron RA Cannon A Caraveo PA Casandjian JM Çelik Ö Charles E Chekhtman A Cheung CC Chiang J Ciprini S Claus R Cohen-Tanugi J Costamante L Cutini S D'Ammando F Dermer CD de Angelis A de Luca A de Palma F Digel SW do Couto e Silva E Drell PS 《Science (New York, N.Y.)》2011,331(6018):739-742
A young and energetic pulsar powers the well-known Crab Nebula. Here, we describe two separate gamma-ray (photon energy greater than 100 mega-electron volts) flares from this source detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 and lasted approximately 16 days. The second flare was detected in September 2010 and lasted approximately 4 days. During these outbursts, the gamma-ray flux from the nebula increased by factors of four and six, respectively. The brevity of the flares implies that the gamma rays were emitted via synchrotron radiation from peta-electron-volt (10(15) electron volts) electrons in a region smaller than 1.4 × 10(-2) parsecs. These are the highest-energy particles that can be associated with a discrete astronomical source, and they pose challenges to particle acceleration theory. 相似文献
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金寨毛竹纤维形态及化学成分 总被引：2，自引：0，他引：2
通过离析法制取毛竹纤维,观察并记录纤维长度和宽度,计算纤维长宽比,按照国家标准分别测定化学成分质量分数,以此对3~5年生金寨毛竹不同竹干高度、径向的纤维形态和化学成分进行研究。结果表明:3~5年生金寨毛竹平均纤维长度均大于1500μm,且随着竹龄的增加而增加,而在高度上变异规律不明显;平均纤维长宽比均大于100,在竹干高度为5.5 m处达到最大值;灰分质量分数随竹龄的增加而减小,随竹干高度的增加而增加;综纤维素质量分数随竹龄的增加而增加,随竹干高度的增加趋于稳定;苯醇抽提物和纤维素质量分数随竹龄增加先减小再增加。综上可知,金寨毛竹是优良的造纸原料。 相似文献
9.
高抗性淀粉粳稻新品系稻米淀粉链长分布与主要品质特征差异 总被引：5，自引：1，他引：4
【目的】通过对水稻抗性淀粉性状的遗传研究,为高抗性淀粉水稻资源创新与育种提供理论和实践依据。【方法】以抗性淀粉含量有显著差异的粳稻品系为材料,比较分析高低抗性淀粉粳稻品系类型间的支链淀粉链长分布、稻米RVA谱特性值、膳食纤维和直链淀粉含量等主要品质特性的差异及其相关性。【结果】高低抗性淀粉水稻品系间支链淀粉链长分布差异显著,高抗性淀粉水稻品系的支链淀粉中短链部分即聚合度为5～12所占的相对百分比率显著低于低抗性淀粉类型品系,而长链尤其是聚合度为13以上的长链比率明显高于低抗性淀粉类型品系。膳食纤维和直链淀粉含量,高抗性淀粉品系显著高于低抗性淀粉品系,最高黏度值、最终黏度值、热浆黏度值和崩解值等,高抗性淀粉品系均显著或极显著低于低抗性淀粉类型品系。抗性淀粉含量与支链淀粉短链聚合度（DP≤12）呈极显著负相关,但与支链淀粉的中长链聚合度（12＜DP≤36）呈极显著正相关,与直链淀粉含量和膳食纤维含量呈极显著正相关。【结论】水稻中支链淀粉的链长分布、直链淀粉含量和稻米RVA谱特性值与稻米抗性淀粉含量关系密切,在育种实践中可作为育种选择指标之一。 相似文献
10.
温度对棉纤维干物质积累动态变化的影响 总被引：11，自引：1，他引：11
随温度降低，棉纤维干物质积累减慢，终值降低，在增长高峰期内干重增加量减少，纤维干重占全铃重百分比值呈现“先降后升”趋势；随温度降低，单粒子纤维干重显著降低，并使每毫米纤维干重出现“负增长”现象。温度对棉纤维干物质积累的影响高于棉铃其它组分，14．8℃日温是棉纤维干物质积累停止增长的临界温度。果枝部位对棉纤维干物质积累的影响不显著。 相似文献
11.
不同施氮肥水平对白菜硝酸盐积累的影响 总被引：5，自引：0，他引：5
利用农田试验研究不同施氮肥水平对白菜生产期硝酸盐积累的影响。白菜生长期间两次施氮肥体内形成两个硝酸盐积累峰值。第一个峰值在施氮肥后 8～ 15 d左右 ,积累峰值较高。第一个峰值在第二次施肥后 2 0～ 30 d左右 ,但峰值较低且有的不明显。随着白菜的成熟 ,硝酸盐积累逐渐降低。总体上看 ,抗病高产的晚熟品种“龙协白 1号”各个生长期间硝酸盐的积累量都低于品质优良的中熟品种“东农 90 1”。采收后的白菜窖贮一个月后 ,较低施肥水平白菜体内硝酸盐含量有所减少 ,但高施肥水平 6 75 kg· hm- 2 的白菜有所回升。其机理有待于进一步研究 相似文献
12.
以30棵一年生人工林69杨(Populus deltoids Bartr. cv. ''Lux'' (I-69/55))为研究对象，在生长季节将其中的15棵苗木人工倾斜45°，将直立生长和倾斜生长的苗木分别平均分成5组（每组3棵），分别施加0、5、20、50和100 mg·kg-1的Cd(NO3)2，记为C0、C1、C2、C3和C4。苗木生长8个月后开始取样，树干按其纵向上的高度分为顶部、中部和基部，倾斜生长分应拉区和对应区对其解剖特性进行测定分析。结果表明：（1）随着土壤中重金属Cd浓度的增加，直立生长下的杨树的纤维长度在C0、C1、C2浓度下大于倾斜生长，C3、C4浓度下则小于倾斜生长；在倾斜生长下，C0与C4浓度下应拉区纤维长度小于对应区，而C1、C2、C3则相反。在树干纵向分布上，纤维长度为基部＞中部＞顶部。方差分析表明，不同Cd浓度对纤维长度的影响显著，不同区域上影响不显著。（2） 导管长度上，直立生长大于倾斜生长，应拉区的导管长度大于对应区；纵向分布上，在倾斜生长下导管长度为基部＞中部＞顶部。方差分析表明，不同Cd浓度和不同区域对导管长度的影响显著。（3）双壁厚上，C0、C1为直立生长小于倾斜生长， C2、C3、C4则与此相反。方差分析表明，不同Cd浓度对双壁厚的影响显著，不同生长方式和高度上影响不显著。（4）微纤丝角上， C0、C1、C2浓度下直立生长大于倾斜生长，C3、C4浓度下则相反；倾斜生长下的应拉区微纤丝角小于对应区。方差分析表明不同Cd浓度和不同区域对微纤丝角的影响显著。（5）结晶度上，倾斜生长下应拉区结晶度大于对应区；在纵向分布上，结晶度为基部＞中部＞顶部。方差分析表明，不同Cd浓度和不同区域对结晶度的影响显著。 相似文献
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采用木材离析方法对2个邓恩桉Eucalyptus dunnii种源木材纤维特性进行了测定分析。结果表明:邓恩桉胸径生长与纤维长度、纤维宽度之间相关关系不显著;纤维长度大致成正态分布,种源A和种源B纤维长度均值分别为986.44μm与908.91μm,种源A长度在700~1 700μm的纤维数量占纤维数的97.11%,种源B为86.67%。在个体水平上分布范围较广,为纤维长度的改良提供可能,纤维长度呈自髓心向外逐渐增加。种源A和种源B纤维宽度均值分别为25.71μm与19.30μm,纤维宽度径向上种源A自髓心向外增长,种源B自髓心向外减小。种源A和种源B纤维长宽比均值为42.94和47.13,纤维双壁厚均值分别为13.44μm和9.40μm,达到纸浆材要求。纤维壁腔比均值大于1,但个体水平上有些壁腔比小于1。 相似文献
15.
通过应用Cosgrove方法研究了Kaup-Kupershmidt-Parker-Dye方程的相应的四维行波系统,得到了一些新的确切显式紧孤子、非紧孤子、周期解和非周期解.同时对一些已知平衡点的局部动力学行为进行了讨论. 相似文献
16.
The geothermal heat flux is an important factor in the dynamics of ice sheets; it affects the occurrence of subglacial lakes, the onset of ice streams, and mass losses from the ice sheet base. Because direct heat flux measurements in ice-covered regions are difficult to obtain, we developed a method that uses satellite magnetic data to estimate the heat flux underneath the Antarctic ice sheet. We found that the heat flux underneath the ice sheet varies from 40 to 185 megawatts per square meter and that areas of high heat flux coincide with known current volcanism and some areas known to have ice streams. 相似文献
17.
Physico-Chemical Properties of Flour, Starch, and Modified Starch of Two Rice Varieties 总被引：1，自引：0，他引：1
LIN Qin-lu XIAO Hua-xi FU Xiang-jin TIAN Wei LI Li-hui YU Feng-xiang 《中国农业科学(英文版)》2011,10(6):960-968
The physical and chemical properties of the flours, starches, and modified starches of indics rice and japonica rice were investigated in this paper. Results showed that the swelling powers of flour, starch, and phosphate starch [substitution degree (DS)=0.065] of japonica rice were significantly higher than those (DS=0.065) of indics rice. The transmittance of modified starches was highest; and that of flours was lowest. The pasting property investigated with rapid visco analyzer (RVA) indicated that the peak viscosity and breakdown value of paste with high swelling power were high. Furthermore, the effect of protein and amylose content on pasting property were investigated. The results of rheological properties determined using rheological rheometer showed that at the same temperature, the storage modulus (G') of flour, starch, and modified starch of indica rice was higher than that of japonica rice. For each variety, the G' of flour was the highest, while the G' of modified starch was the lowest. 相似文献
18.
针对红松和白松特征相似,容易被冒充的现象,提出了采用光纤液滴分析技术对两者进行树种识别的方法。采用高压反应釜对白松和红松木屑进行了液化,由光纤液滴分析仪实验装置得到了相应的光纤液滴指纹图。比较了两者指纹图的形状,提取了液滴总周期、光纤信号的平均值、光纤信号的波谷值、光纤信号的波峰值等9个特征,结果表明:二者的指纹图在形状上有明显的差异,9个特征值中,3个特征值的相对差异小于10%,1个特征值的相对差异超过了10%,5个特征值的相对差异超过了50%。运用方差分析对两个树种的特征值差异性进行了检验,得出两个树种的特征值差异性显著(P值为0.002 887)。说明光纤液滴分析技术具备识别红松和白松树种的能力。 相似文献
19.
Byer RL 《Science (New York, N.Y.)》1988,239(4841):742-747
Diode laser-pumped solid-state lasers are efficient, compact, all solid-state sources of coherent optical radiation. Major advances in solid-state laser technology have historically been preceded by advances in pumping technology. The helical flash lamps used to pump early ruby lasers were superseded by the linear flash lamp and arc lamp now used to pump neodymium-doped yttrium-aluminum-garnet lasers. The latest advance in pumping technology is the diode laser. Diode laser-pumped neodymium lasers have operated at greater than 10 percent electrical to optical efficiency in a single spatial mode and with linewidths of less than 10 kilohertz. The high spectral power brightness of these lasers has allowed frequency extension by harmonic generation in nonlinear crystals, which has led to green and blue sources of coherent radiation. Diode laser pumping has also been used with ions other than neodymium to produce wavelengths from 946 to 2010 nanometers. In addition, Q-switched operation with kilowatt peak powers and mode-locked operation with 10-picosecond pulse widths have been demonstrated. Progress in diode lasers and diode laser arrays promises all solid-state lasers in which the flash lamp is replaced by diode lasers for average power levels in excess of tens of watts and at a price that is competitive with flash lamp-pumped laser systems. Power levels exceeding 1 kilowatt appear possible within the next 5 years. Potential applications of diode laser-pumped solid-state lasers include coherent radar, global sensing from satellites, medical uses, micromachining, and miniature visible sources for digital optical storage. 相似文献
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