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911.
Numerous measurements of CO2 degassing from the soil, carried out with the accumulation chamber method, indicate that in the period April–July 1995 the upper part of the Fossa cone released a total output of 200 t d–1 of CO2, which corresponds to approximately 1000 t d–1 of steam. These large amounts of fluids are of the same order of magnitude as those released by the high temperature fumarolic
field located inside the crater. The spatial distribution of soil gas fluxes shows that the main structures releasing CO2 are the inner slopes of the crater and a NW–SE line, located NE of the crater rim, which correspond to the main direction
of Vulcano Island active faults. The comparison of the φCO2 maps with the soil temperature distribution, derived from both direct measurements and airborne infrared images, indicates
the occurrence of extensive condensation of fumarolic steam within the upper part of the Fossa cone, whose total amount is
comparable to the rainfall budget. Part of the condensate which originates from this process contributes to the recharge of
the phreatic aquifer of Porto Plain, modifying the chemical and isotopic composition of the groundwater.
Received: 1 September 1995 / Accepted: 8 January 1996 相似文献
912.
Comet 81P/Wild 2 was observed in the thermal infrared over 6 months during its 1997 perihelion passage. The comet was most active in late February, about 3 months preperihelion; dust production declined by a factor of 3 between February and August. For the GIOTTO Halley dust size distribution, maximum dust production rate was ∼2 × 106 g/s. The comet displayed a 10-μm silicate feature about 25% above the continuum, similar to several other Jupiter-family comets, but much lower than that seen in a number of Oort cloud comets.NASA’s STARDUST sample return mission will encounter P/Wild 2 98 days postperihelion in January 2004. Based on our observations at a similar point in the orbit and the Halley size distribution, we predict that the mass fluence on the spacecraft for a 150 km miss distance will be about 8 × 10−6 g/cm2 for particles up to 1 cm in radius. The corresponding areal coverage will be about 10−4. 相似文献
913.
914.
E. L. Wright 《New Astronomy Reviews》2003,47(11-12):877
The Wilkinson Microwave Anisotropy Probe (WMAP) science team has released results from the first year of operation at the Earth–Sun L2 Lagrange point. The maps are consistent with previous observations but have much better sensitivity and angular resolution than the COBE DMR maps, and much better calibration accuracy and sky coverage than ground-based and balloon-borne experiments. The angular power spectra from these ground-based and balloon-borne experiments are consistent within their systematic and statistical uncertainties with the WMAP results. WMAP detected the large angular-scale correlation between the temperature and polarization anisotropies of the CMB caused by electron scattering since the Universe became reionized after the “Dark Ages”, giving a value for the electron scattering optical depth of 0.17 ± 0.04. The simplest ΛCDM model with n=1 and Ωtot=1 fixed provides an adequate fit to the WMAP data and gives parameters which are consistent with determinations of the Hubble constant and observations of the accelerating Universe using supernovae. The time-ordered data, maps, and power spectra from WMAP can be found at http://lambda.gsfc.nasa.gov along with 13 papers by the WMAP science team describing the results in detail. 相似文献
915.
916.
基于我国武汉超导重力仪1985年11月23日至1994年12月31日(3326d共79824h整点读数值)的长周期序列重力潮汐观测数据,利用国际上通用的资料分析方法和计算机软件系统研究了重力场潮汐变化特征,精密测定了地球潮汐常数,几个主要潮波的振幅因子测定精度达0.04%。对采用不同引潮位展开、是否考虑加权滤波、做气压改正、删除错误数据以及规定数据段均方差上限等方式对提高资料分析精度的影响问题进行了讨论。利用Schwiderski全球模型对重力潮汐观测分析结果进行了海潮负荷改正,较系统地研究了观测重力残差和台站气压变化之间的相关性,在时间和频率域内测定了相应的大气重力导纳值。与Wahr-Dehant标准地球潮汐模型相比较,潮汐振幅因子的平均偏差分别是0.4%(O1波)和0.2%(M2波)。 相似文献
917.
R. J. Ivison T. R. Greve J. S. Dunlop J. A. Peacock E. Egami Ian Smail E. Ibar E. van Kampen I. Aretxaga T. Babbedge A. D. Biggs A. W. Blain S. C. Chapman D. L. Clements K. Coppin D. Farrah M. Halpern D. H. Hughes M. J. Jarvis T. Jenness J. R. Jones A. M. J. Mortier S. Oliver C. Papovich P. G. Pérez-González A. Pope S. Rawlings G. H. Rieke M. Rowan-Robinson R. S. Savage D. Scott M. Seigar S. Serjeant C. Simpson J. A. Stevens M. Vaccari J. Wagg C. J. Willott 《Monthly notices of the Royal Astronomical Society》2007,380(1):199-228
918.
We report Arecibo observations of 55 main-belt asteroids (MBAs) during 1999-2003. Most of our targets had not been detected previously with radar, so these observations more than double the number of radar-detected MBAs. Our bandwidth estimates constrain our targets' pole directions in a manner that is geometrically distinct from optically derived constraints. We present detailed statistical analyses of the disk-integrated properties (radar albedo and circular polarization ratio) of the 84 MBAs observed with radar through March 2003; all of these observations are summarized in the online supplementary information. Certain conclusions reached in previous studies are strengthened: M asteroids have higher mean radar albedos and a wider range of albedos than do other MBAs, suggesting that both metal-rich and metal-poor M-class objects exist; and C- and S-class MBAs have indistinguishable radar albedo distributions, suggesting that most S-class objects are chondritic. Also in accord with earlier results, there is evidence that primitive asteroids from outside the C taxon (F, G, P, and D) are not as radar-bright as C and S objects, but a convincing statistical test must await larger sample sizes. In contrast with earlier work, we find S-class MBAs to have higher circular polarization ratios than other MBAs, indicating greater near-surface structural complexity at decimeter scales, due to different mineralogy (material strength or loss tangent), a different impactor population, or both. 相似文献
919.
920.
Boudewijn F. Roukema 《Monthly notices of the Royal Astronomical Society》2001,325(1):138-142
The inner product provides a conceptually and algorithmically simple method for calculating the comoving distance between two cosmological objects given their redshifts, right ascension and declination, and arbitrary constant curvature. The key to this is that just as a distance between two points 'on' the surface of the ordinary 2-sphere 2 is simply an arc-length (angle multiplied by radius) in ordinary Euclidean 3-space ℰ3 , the distance between two points 'on' a 3-sphere 3 (a 3-hyperboloid ℋ3 ) is simply an 'arc-length' in Euclidean 4-space ℰ4 (Minkowski 4-space ℳ4 ), i.e. an 'hyper-angle' multiplied by the curvature radius of the 3-sphere (3-hyperboloid). 相似文献