共查询到20条相似文献,搜索用时 515 毫秒
1.
Gaurang B. Yodh 《Space Science Reviews》1996,75(1-2):199-212
This paper discusses the properties of using the water Cherenkov technique to detect air showers in the few hundred GeV to 100 TeV energy range. The responses of a 6 m2 2 m deep water Cherenkov counter and that of a 6 m2 10cm thick scintillator-lead sandwich counter to air shower electrons and photons is described. The advantages of water Cherenkov detector is outlined. Its application to do VHE gamma ray astronomy is discussed with particular reference to the MILAGRO telescope currently under construction. Milagro, a water-Cherenkov detector to do gamma ray astronomy above 100 Gev, uses an existing pool 60m × 80m by 8m, located in the Jemez mountains near Los Alamos, NM. The threshold of the MILAGRO detector is comparable to atmospheric Cherenkov detectors, however it has several advantages over these optical detectors. MILAGRO can operate 24 hours a day in all weather conditions and it has an open aperture which allows it to view the entire northern sky every day. These capabilities allow for a systematic all-sky survey to be done for the first time at these energies. MILAGRO will measure the Crab spectrum with high significance over a wide energy range, it will detect and measure the spectra from AGN's such as MRK 421 and it will search for short duration bursts from GRBs and possibly evaporating PBHs. 相似文献
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Pierre Y. Bely Holland C. Ford Richard Burg Larry Petro Rick White John Bally 《Space Science Reviews》1995,74(1-2):101-112
The tropopause, typically at 16 to 18 km altitude at the lower latitudes, dips to 8 km in the polar regions. This makes the cold, dry and nonturbulent lower stratosphere accessible to tethered aerostats. Tethered aerostats can fly as high as 12 km and are extremely reliable, lasting for many years. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recovered for maintenance and adjustment and relaunched in a matter of hours. We propose to use such a platform, located first in the Arctic (near Fairbanks, Alaska) and, potentially, later in the Antarctic, to operate a new technology 6-meter, diluted aperture telescope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (220 K), thermal emission from the optics is of the same order as that of the zodiacal light in the 2 to 3 micron band. Since this wavelength interval is the darkest part of the zodiacal light spectrum from optical wavelengths to 100 microns, the combination of high resolution images and a very dark sky make it the spectral region of choice for observing the redshifted light from galaxies and clusters of galaxies at moderate to high redshifts.Affiliated to the Astrophysics Division, Space Science Department, European Space Agency 相似文献
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P. M. Chadwick J. E. Dickinson M. R. Dickinson N. A. Dipper J. Holder T. J. L. Mccomb K. J. Orford S. M. Rayner I. D. Roberts M. D. Roberts S. P. Tummey K. E. Turver 《Space Science Reviews》1996,75(1-2):153-167
Current approaches to the identification of VHE gamma rays using stereo images of erenkov light flashes are reviewed. The method of analysis developed by the University of Durham group involving a measure of cascade development is described. This method is applied to observations of a burst of VHE gamma rays from AE Aqr and enhancement of the gamma ray signal is demonstrated. 相似文献
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研究了热处理对新研制的定向凝固钴基高温合金DZ40M组织和性能的影响。结果表明 :12 80℃ / 4h固溶处理可完全溶解DZ40M合金中初生碳化物M7C3 和MC ,合金成为单相固溶体。95 0℃和 10 5 0℃时效处理可使DZ40M合金发生硬化 ,以 95 0℃时效硬化效果更为明显 ,相应的峰时效制度为 95 0℃ / 12h和 10 5 0℃ / 2 4h。时效处理引起M2 3 C6沉淀析出。 95 0℃ / 12h时效显著提高DZ40M合金室温强度和高温持久寿命 ,同时也减少了合金塑性 ,但合金仍保持一定的塑性。 10 5 0℃ / 2 4h虽然能增加室温拉伸性能 ,但削弱了高温持久性能 相似文献
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研究热等静压温度对定向层片组织常规铸造 TiAl 合金层片分解程度和室温拉伸性能的影响,以期优选出适于定向层片组织的热等静压温度。结果表明:在1250℃热等静压处理,析出过多的等轴γ晶粒,降低了该合金的室温拉伸强度;在1290℃热等静压处理,发生层片粗化和生成随机取向二次层片,破坏了取向一致性,降低了室温拉伸性能的稳定性。在1270℃等静压处理,等轴γ晶粒析出量较少,且未见明显的层片粗化和二次层片,所得组织保持较好的层片组织完整性和取向一致性,并表现出最佳的室温强度、塑性和性能稳定性。确定适于定向层片组织铸造 TiAl 合金的热等静压温度是1270℃。 相似文献
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煤基喷气燃料代用组分神经网络混合构建方法 总被引:1,自引:1,他引:0
为了建立航空燃料的喷雾模型,用于高保真液雾燃烧数值模拟,提出了基于人工神经网络混合模型的煤基喷气燃料代用组分构建方法.基于这一构建方法,重点针对煤基喷气燃料的雾化特性,利用多组分混合燃料的理化性质数据库对神经网络进行训练,获得了混合燃料理化性质隐式预测模型,结合随机投点优化方法,构建出能够很好地模拟煤基喷气燃料目标理化性质的代用组分.结果表明:该代用组分包含了5种碳氢化合物成分,摩尔分数为11.46%正癸烷、23.29%正十二烷、49.87%正十四烷、6.66%异辛烷和8.72%甲基环己烷.通过雾化特性实验,验证了代用组分对真实燃料雾化性能的模拟效果.该代用组分构建方法可以较好地解决混合燃料模拟过程中的非线性问题,通过改变目标理化性质可构建出相应代用组分. 相似文献
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The international Cassini/Huygens mission consists of the Cassini Saturn
Orbiter spacecraft and the Huygens Titan Probe that is targeted for entry into the atmosphere of Saturn's largest moon, Titan. From launch on October 15, 1997 to arrival
at Saturn in July 2004, Cassini/Huygens will travel over three billion kilometers. Once in orbit about Saturn, Huygens is released from the orbiter and enters Titan's atmosphere. The Probe descends by parachute and measures the properties of the atmosphere. If the landing is gentle, the properties of the surface
will be measured too. Then the orbiter commences a four-year tour of the Saturnian system with 45 flybys of Titan and multiple encounters with the icy moons. The
rings, the magnetosphere and Saturn itself are all studied as well as the interactions among them.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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正十七烷与正十八烷对航空煤油理化性能及液滴平均直径的影响 总被引:2,自引:1,他引:1
讨论了正十七烷与正十八烷(C17,C18)对燃料运动黏度、密度、表面张力理化性能的影响,探究了直链烷烃对SMD(Sauter mean diameter)的影响.将Key's混合规律、Tat混合规律和多项式拟合应用于密度公式的拟合,并将Key's混合规律与对数拟合应用于运动黏度公式的拟合,得出的理化性能拟合公式精度较高;通过测量纯煤油及C17,C18混合油雾化的SMD,实验发现随着直链烷烃的质量分数的增加,混合油的运动黏度增加,SMD也随之增加,雾化效果与纯航空煤油的相比较差,而C18混合油的SMD要比C17混合油要大,并且利用密度、运动黏度的拟合公式对SMD进行预测的偏差小于0.3%. 相似文献
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Ulysses measurements yield reliable in-situdetection of large dust particles which stem from the interstellar medium (ISM) and which
are not observed in interstellar extinction data. Both current models of large grains in the ISM: core-mantle grains as well
as composite grains, are in agreement with dust properties implied by the Ulysses results. However, the size of particles detected by Ulysses still exceeds the size of the large grains that are predicted for the ISM.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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F. Curtis Michel 《Space Science Reviews》1979,24(4):381-406
We compare the properties of Jupiter with those of radio pulsars and find a number of parallels insofar as the magnetic field, energization, and radio emission properties (pulsed, coherent, and microstructured), as well as a number of important presumed differences such as the Io modulation. Now that we can directly explore Jupiter's magnetosphere (but are yet uncertain as to the exact source of its radio emissions) what we learn may help us understand pulsars and other inaccessible astrophysical objects.Proceedings of the NASA JPL Workshop on the Physics of Planetary and Astrophysical Magnetospheres. 相似文献
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为研究杂质Fe元素对2219铝合金及其焊接接头的组织、性能以及电化学腐蚀性能等的影响,采用力学拉伸、焊接试验以及金相和扫描电镜等分析测试方法,对0.15%(w)至0.01%(w)等不同Fe元素含量的2219铝合金锻件进行实验研究和分析。研究表明:2219铝合金中经热变形加工存在网络状Al_2Cu变成颗粒状和纤维状的Al_7Cu_2(Fe,Mn)相,随着Fe含量由0.15%(w)降低至0.01%(w),合金固溶时效后的Al_7Cu_2(Fe,Mn)相显著减少,锻件强度和塑性显著提高;合金焊接接头断口由脆性断裂逐渐转变为韧窝尺寸细小的韧性断裂,尤其对于延伸率,提高至近1.4倍,强度和塑性显著提高;合金的自腐蚀电流逐渐减小,单位面积上的线性极化电阻增大,合金焊接接头的耐腐蚀性能显著提高。 相似文献
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Edward F. Guinan 《Space Science Reviews》1989,49(3-4):35-49
The properties of the eclipsing binaries Algol, Beta Lyrae, and W Serpentis are discussed and new results are presented. The physical properties of the components of Algol are now well determined. High resolution spectroscopy of the H-alpha feature by Richards et al. and by Gillet et al. and spectroscopy of the ultraviolet resonance lines with the International Ultraviolet Explorer satellite reveal hot gas around the BBV primary. Gas flows also have been detected apparently originating from the low mass, cooler secondary component and flowing toward the hotter star through the Lagrangian L1 point. Analysis of 6 years of multi-bandpass photoelectric photometry of Beta Lyrae indicates that systematic changes in light curves occur with a characteristic period of -275 ± 25 days. These changes may arise from pulsations of the B8II star or from changes in the geometry of the disk component. Hitherto unpublished u, v, b, y, and H-alpha index light curves of W Ser are presented and discussed. W Ser is a very complex binary system that undergoes complicated, large changes in its light curves. The physical properties of W Ser are only poorly known, but it probably contains one component at its Roche surface, rapidly transfering matter to a component which is embedded in a thick, opaque disk. In several respects, W Ser resembles an upscale version of a cataclysmic variable binary system. 相似文献
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Eberhard Grün 《Space Science Reviews》1991,56(1-2):105-108
In situ observations of comet Halley yielded information on the nucleus and its environment. These measurements are related to properties of and processes at the nucleus by theoretical modelling and by simulation experiments in the laboratory. The objective of the KOSI (Kometensimulation) experiments is to study in detail processes which occur near the surface of ice-dust mixtures under irradiation by light, like heat transport into the sample, chemical fractionation of sample material, emission of gases, and others. The KOSI experiments are carried out at the large space simulation chamber in Köln. By providing an in-depth understanding of potential cometary processes the results from the KOSI experiments are relevant to any comet nucleus sample return mission. 相似文献