共查询到20条相似文献，搜索用时 750 毫秒
1.
Thermal continuum emission from the Pluto-Charon system has been detected at wavelents of 800 and 1300 micrometers, and significant upper limits have been obtained at 450 and 1100 micrometers. After the subtraction of emission from Charon, the deduced surface temperature of much of Pluto is between 30 and 44 kein, probably near 35 to 37 kelvin. This range is significantly cooler than what radiative equilibrium models have suged and cooler than the surface temperature derived by the Infrared Astronomy Satellite. The low temperature indicates that methane cannot be present at the microbar pressure levels indicated by the 1988 stellar occultation measurements and that the methane features in Pluto's spectrum are from solid, not gas-phase, absorptions. This result is evidence that Pluto's atmosphere is dominated by nitrogen or carbon monoxide rather than methane. 相似文献
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Sandel BR Shemansky DE Broadfoot AL Bertaux JL Blamont JE Belton MJ Ajello JM Holberg JB Atreya SK Donahue TM Moos HW Strobel DF McConnell JC Dalgarno A Goody R McElroy MB Takacs PZ 《Science (New York, N.Y.)》1979,206(4421):962-966
Extreme ultraviolet spectral observations of the Jovian planetary system made during the Voyager 2 encounter have extended our knowledge of many of the phenomena and physical processes discovered by the Voyager 1 ultraviolet spectrometer. In the 4 months between encounters, the radiation from Io's plasma torus has increased in intensity by a factor of about 2. This change was accompanied by a decrease in plasma temperature of about 30 percent. The high-latitude auroral zones have been positively associated with the magnetic projection of the plasma torus onto the planet. Emission in molecular hydrogen bands has been detected from the equatorial regions of Jupiter, indicating planetwide electron precipitation. Hydrogen Lyman alpha from the dark side of the planet has been measured at an intensity of about 1 kilorayleigh. An observation of the occultation of alpha Leonis by Jupiter was carried out successfully and the data are being analyzed in detail. 相似文献
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[目的]建立人参细胞中尿苷二磷酸葡萄糖（UDPG）：人参皂苷Rh2葡萄糖基转移酶（UGRh2GT）活性测定体系。[方法]以人参皂苷Rh2为底物,以UDPG为葡萄糖供体,选取合适的温度和pH值,用提取的人参细胞酶液催化Rh2生成Rg3,采用高效液相色谱法（HPLC）测定Rg3的生成量,色谱柱为C18柱（150mm×4.6mm）,流动相为乙腈和水,梯度洗脱。[结果]人参细胞中UGRh2GT活性测定体系的最优pH值是9.3,最优温度是34.1℃。[结论]建立的酶活测定体系能够较好较方便地测定UGRh2GT的比活。 相似文献
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成品油在输送过程中出现油品温度升高的问题，当输送介质为轻质油品且输量增大时，温升可能产生严重的危害，包括油品发生损耗，油品质量降低，污染环境及管道产生很大的热应力等。这是在成品油管道的设计和运行中必须要考虑的问题。 相似文献
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为了高效实时地采集农田信息,实现农业生产的精细管理,设计出一种基于GPS、EDGE和LabVIEW技术的农田信息远程采集与监测系统。该系统采用自行设计的基于单片机、GPS和传感器技术的多参数农田信息采集仪,实现对土壤含水量、土壤温度、土壤电导率、环境温湿度等农田信息的快速定位测量。通过EDGE模块,利用移动EGPRS技术覆盖面广、传输速度快、资费低等特点,将测量所得数据快速实时传送至上位机。该系统的上位机系统把EDGE模块接收的数据存入数据库,并对其进行分析。该系统通过应用多功能信息采集设备和高速网络传输技术,实现对农田信息的实时、高效、精确和低成本采集,对精细农业作业决策具有广泛的应用价值。 相似文献
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When a liquid is cooled below its melting temperature, it usually crystallizes. However, if the quenching rate is fast enough, the system may remain in a disordered state, progressively losing its fluidity upon further cooling. When the time needed for the rearrangement of the local atomic structure reaches approximately 100 seconds, the system becomes "solid" for any practical purpose, and this defines the glass transition temperature Tg. Approaching this transition from the liquid side, different systems show qualitatively different temperature dependencies of the viscosity, and accordingly they have been classified by introducing the concept of "fragility." We report experimental observations that relate the microscopic properties of the glassy phase to the fragility. We find that the vibrational properties of the glass well below Tg are correlated with the fragility value. Consequently, we extend the fragility concept to the glassy state and indicate how to determine the fragility uniquely from glass properties well below Tg. 相似文献
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Chondrulelike objects in short-period comet 81P/Wild 2 总被引：1，自引：0，他引：1
Nakamura T Noguchi T Tsuchiyama A Ushikubo T Kita NT Valley JW Zolensky ME Kakazu Y Sakamoto K Mashio E Uesugi K Nakano T 《Science (New York, N.Y.)》2008,321(5896):1664-1667
The Stardust spacecraft returned cometary samples that contain crystalline material, but the origin of the material is not yet well understood. We found four crystalline particles from comet 81P/Wild 2 that were apparently formed by flash-melting at a high temperature and are texturally, mineralogically, and compositionally similar to chondrules. Chondrules are submillimeter particles that dominate chondrites and are believed to have formed in the inner solar nebula. The comet particles show oxygen isotope compositions similar to chondrules in carbonaceous chondrites that compose the middle-to-outer asteroid belt. The presence of the chondrulelike objects in the comet suggests that chondrules have been transported out to the cold outer solar nebula and spread widely over the early solar system. 相似文献
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Hinkov V Haug D Fauqué B Bourges P Sidis Y Ivanov A Bernhard C Lin CT Keimer B 《Science (New York, N.Y.)》2008,319(5863):597-600
Electronic phases with symmetry properties matching those of conventional liquid crystals have recently been discovered in transport experiments on semiconductor heterostructures and metal oxides at millikelvin temperatures. We report the spontaneous onset of a one-dimensional, incommensurate modulation of the spin system in the high-transition-temperature superconductor YBa2Cu3O6.45 upon cooling below approximately 150 kelvin, whereas static magnetic order is absent above 2 kelvin. The evolution of this modulation with temperature and doping parallels that of the in-plane anisotropy of the resistivity, indicating an electronic nematic phase that is stable over a wide temperature range. The results suggest that soft spin fluctuations are a microscopic route toward electronic liquid crystals and that nematic order can coexist with high-temperature superconductivity in underdoped cuprates. 相似文献
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通过多年来对小麦冠层温度和生物性状观测,结果发现自然界存在小麦温度分异现象,可将不同基因型小麦按冠层温度划分为冷型小麦、暖型小麦和中间型小麦等不同类群,这些类群的生物学性状有明显的差异,尤其在叶片输出功能期、根系活力、叶绿素含量、蛋白质氮含量、丙二醛含量、蒸腾速率和净光合速率等方面.冷型小麦在上述诸方面表现较优,即使在严重干旱和连阴雨等灾害性天气下也是如此.通过杂交试验表明,这些性状具有遗传性.又进一步从解剖学角度揭示冷型小麦和暖型小麦各器官在灌浆结实期的结构差异以及在干旱和淹水条件下冷、暖型小麦叶片结构的动态变化特征. 相似文献
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为了研究气候变暖对天水极端温度的影响,利用天水观测站1951年至2013年逐年的极端温度资料,运用气候倾向率、趋势系数、百分位法、滑动T检验等统计方法,分析极端温度对气候变暖的响应特征。结果表明：天水年极端最高（低）温度均呈显著性升高趋势,极端最高气温上升0.2℃/10a,极端最低气温上升0.3℃/10a,都通过了α=0.01的显著性检验;通过百分位法定义了极端温度的阈值,分析发现：极端最高气温与阈值的差值随时间序列的增加逐步增大,极端最低气温与阈值的差值随时间序列的增加逐步减少,对极端最高温度和极端最低温度利用滑动T检验法进行突变检验,在α=0.01显著性水平下,极端最低温度没有发生突变,而极端最高温度在1983年和1993年发生了两次十分明显的突变。 相似文献
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Low temperature wheat genotypes are a group of wheat with a slightly low canopy （plant） temperature, and the research on their biological characters and utilization in wheat breeding has been done at home and abroad for more than 20 years, and has made great progress. The research contents and advances include the following respects： Wheat genotypes with slightly low canopy temperature have been verified to exist in nature; these wheat genotypes, which present cold temperature, are superior to conventional wheat materials in some important biological characters and particularly prominently in metabolic function and cellular structure; when they suffer stresses such as drought, high temperature and overcast and rainy weather, they still retain their superiority in some of their important biological characters and therefore have a wide range of ecological adaptability; slightly low canopy temperatures of these genotypes are closely correlated with low temperatures of their second heat sources and their vigorous plants; since their low canopy temperatures can be inherited, they can exert favorable influence on the temperatures of their offspring while crossing with other wheat materials, and in particular, the discovery of cold-source wheat as a contributor to low temperature, has further formed good conditions for breeding high and stable quality low temperature wheat varieties with a high and stable yield. Thus, low temperature wheat genotypes are of great research importance and have great prospects. 相似文献
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Climate models with enhanced greenhouse gas concentrations have projected temperature increases of 2 degrees to 4 degrees C, winter precipitation increases of up to 15 percent, and summer precipitation decreases of 5 to 10 percent in the central United States by the year 2030. An analysis of the climate record over the past 95 years for this region was undertaken in order to evaluate these projections. Results indicate that temperature has increased and precipitation decreased both during winter and summer, and that the ratio of winter-to-summer precipitation has decreased. The signs of some trends are consistent with the projections whereas others are not, but none of the changes is statistically significant except for maximum and minimum temperatures, which were not among the parameters predicted by the models. Statistical models indicate that the greenhouse winter and summer precipitation signal could have been masked by natural climate variability, whereas the increase in the ratio of winter-to-summer precipitation and the higher rates of temperature change probably should have already been detected. If the models are correct it will likely take at least another 40 years before statistically significant precipitation changes are detected and another decade or two to detect the projected changes of temperature. 相似文献
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我国两系法杂交水稻研究的形势,任务和发展前景 总被引：35，自引：0，他引：35
从育种上讲，杂交水稻育种可以分为三系法、两系法和一系法三个发展阶段；从利用杂种优势水平来看，杂交水稻育种可以分为品种间、亚种间和远缘杂种优势利用三个发展阶段。与三系法比较，两系法具有配组自由、种子生产成本低、无不育细胞质负效应、易转育新不育系等优点。迄今为止，我国已育成２０多个通过省级鉴定的实用光温敏核不育系，７个通过省级审定的两系法杂交稻组合，解决了低温敏不育系繁殖产量低而不稳的难题，实施了光温 相似文献
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为在烤烟烘烤期间利用太阳能替代部分燃煤,以达到节能减排的目的,对现有的密集烤房进行太阳能改造,在屋顶加装太阳能加热室,吸收太阳能并加热太阳能加热室内空气,高温空气通过内循环管道与烤房的加热室、装烟室连通,提供辅助热源。太阳能循环风机由温差控制器控制。对改造的太阳能密集烤房进行烘烤效应研究,结果表明密集型烤房的太阳能改造简单易行,经济实用,节能效果明显;太阳能提供的热量可满足烟叶烘烤前期的需要,每千克干烟耗能比改造前降低20%~24%,烘烤烟叶质量与普通密集烤房所烤烟叶质量相当,社会效益与经济效益明显,在光照好的烟区具有一定的推广价值。 相似文献
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Ott A 《Science (New York, N.Y.)》1969,164(3877):297
Isotopic enrichment of several percent has been obtained in liquid lithium metal by applying a temperature gradient over a single-stage separation column. For other metals the method should have the highest eficiency, if these have low melting points and are liquids over a wide temperature range. 相似文献
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Nanowires are conventionally assumed to grow via the vapor-liquid-solid process, in which material from the vapor is incorporated into the growing nanowire via a liquid catalyst, commonly a low-melting point eutectic alloy. However, nanowires have been observed to grow below the eutectic temperature, and the state of the catalyst remains controversial. Using in situ microscopy, we showed that, for the classic Ge/Au system, nanowire growth can occur below the eutectic temperature with either liquid or solid catalysts at the same temperature. We found, unexpectedly, that the catalyst state depends on the growth pressure and thermal history. We suggest that these phenomena may be due to kinetic enrichment of the eutectic alloy composition and expect these results to be relevant for other nanowire systems. 相似文献
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本研究以吉化炼油厂６５ｔ燃油供汽锅炉运行系统为对象，参数全部采用其运行工艺参数，从给水，过热蒸汽温度两大部分探讨与论证了控制方案，以微机为核心，具有优良的控制功能和丰富的运算功能的单回路调节器代替常规调节仪表实现控制，给水控制系统采用的是三冲量给水控制系统，它依据水位，同时参照蒸汽流量和给水流量的变化控制给水阀。 相似文献
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饲料环模制粒机在挤压加工苜蓿草颗粒成型过程中会对环模产生严重的磨损,为探究环模失效的磨损机理,新设计了一种三体磨料磨损试验机,模拟制粒工况.该试验机具有加热及相应的控制系统,温度偏差小于2%,可用于100℃左右温度条件下草粉等磨料与不同金属试样的磨损试验. 相似文献