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251.
Two populations of minor bodies in the outer Solar System remain particularly elusive: Scattered Disk Objects and Sedna-like objects. These populations are important dynamical tracers, and understanding the details of their spatial- and size-distributions will enhance our understanding of the formation and on-going evolution of the Solar System. By using newly-derived limits on the maximum heliocentric distances that recent pencil-beam surveys for trans-neptunian objects were sensitive to, we determine new upper limits on the total numbers of distant SDOs and Sedna-like objects. While generally consistent with populations estimated from wide-area surveys, we show that for magnitude-distribution slopes of α ? 0.7-1.0, these pencil-beam surveys provide stronger upper limits than current estimates in literature. 相似文献
252.
We present a new parameter retrieval algorithm for Mars Global Surveyor Thermal Emission Spectrometer data. The algorithm uses Newtonian first-order sensitivity functions of the infrared spectrum in response to variations in physical parameters to fit a model spectrum to the data at 499, 1099, and 1301 cm−1. The algorithm iteratively fits the model spectrum to data to simultaneously retrieve dust extinction optical depth, effective radius, and surface temperature. There are several sources of uncertainty in the results. The assumed dust vertical distribution can introduce errors in retrieved optical depth of a few tens of percent. The assumed dust optical constants can introduce errors in both optical depth and effective radius, although the systematic nature of these errors will not affect retrieval of trends in these parameters. The algorithm does not include the spectral signature of water ice, and hence data needs to be filtered against this parameter before the algorithm is applied. The algorithm also needs sufficient dust spectral signature, and hence surface-to-atmosphere temperature contrast, to successfully retrieve the parameters. After the application of data filters the algorithm is both relatively accurate and very fast, successfully retrieving parameters, as well as meaningful parameter variability and trends from tens of thousands of individual spectra on a global scale (Elteto, A., Toon, O.B. [2010]. Icarus, this issue). Our results for optical depth compare well with TES archive values when corrected by the single scattering albedo. Our results are on average 1–4 K higher in surface temperatures from the TES archive values, with greater differences at higher optical depths. Our retrieval of dust effective radii compare well with the retrievals of Wolff and Clancy (Wolff, M.J., Clancy, R.T. [2003]. J. Geophys. Res. 108 (E9), 5097) for the corresponding data selections from the same orbits. 相似文献
253.
We present a novel method of constructing streamlines to derive wind speeds within jovian vortices and demonstrate its application to Oval BA for 2001 pre-reddened Cassini flyby data, 2007 post-reddened New Horizons flyby data, and 1998 Galileo data of precursor Oval DE. Our method, while automated, attempts to combine the advantages of both automated and manual cloud tracking methods. The southern maximum wind speed of Oval BA does not show significant changes between these data sets to within our measurement uncertainty. The northern maximum does appear to have increased in strength during this time interval, which likely correlates with the oval’s return to a symmetric shape. We demonstrate how the use of closed streamlines can provide measurements of vorticity averaged over the encircled area with no a priori assumptions concerning oval shape. We find increased averaged interior vorticity between pre- and post-reddened Oval BA, with the precursor Oval DE occupying a middle value of vorticity between these two. 相似文献
254.
An obstacle to the asteroid mass determination lies in the difficulty in isolating the gravitational perturbation exerted by a single asteroid on the planets, being strongly correlated and mixed up with those of many other asteroids. This hindrance may be avoided by the method of analysis presented here: an asteroid mass is estimated in correspondence with its close encounters with Mars where the acceleration it induces on the planet can be sufficiently disentangled from those generated by the remaining asteroid masses to calculate. We test this technique in the analysis of range observations to Mars Global Surveyor and Mars Express performed from 1999 to 2007. For this purpose, we adopt the dynamical model of the planetary ephemeris INPOP06 (Fienga et al., 2008), which includes the gravitational influences of the 300 most perturbing asteroids of the Martian orbit. We obtain the solutions of 10 asteroid masses that have the largest effects on this orbit over the period examined: they are generally in good agreement with determinations recently published. 相似文献
255.
结合输变电设施周围电磁环境特点,对其电磁辐射环境影响评价方法进行探讨,提出相应的电磁辐射污染防治措施与建议,消除公众疑虑。在此基础上,总结当前电磁辐射环评工作中存在的问题,以期为后续同类问题深入研究提供思路。 相似文献
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258.
多金属成矿区深地震反射剖面数据处理技术实验研究——以庐枞矿集区为例 总被引:2,自引:1,他引:1
针对庐枞多金属矿集区地震资料特点及浅、深多重探测目标,对深地震反射数据进行了处理技术实验研究。在区域长剖面上,为了获得矿集区地壳与上地幔结构的精细图像,解释成矿深部过程,开展了循序渐进的常规处理技术实验和精细处理技术实验。在矿区剖面,为了获得了浅层精细结构,针对变观测系统接收等特点,进一步开展了特殊处理实验。经过区域剖面与矿区剖面的多重处理实验,集成了一套矿集区深地震反射剖面数据处理方法与处理技术流程,为我国进一步的深部探测积累了技术与经验。 相似文献
259.
本文通过对中国赏石文化的历史、理念、人文、艺术和学术的探讨,试图从中发掘中国赏石文化的内涵,把古代"瘦漏透皱"和现代"形质纹色"的相石标准,提升到"道魂气韵"的赏石意境。 相似文献
260.
Riparian vegetation provides important wildlife habitat in the southwestern United States, but limited distributions and spatial complexity often leads to inaccurate representation in maps used to guide conservation. We test the use of data conflation and aggregation on multiple vegetation/land-cover maps to improve the accuracy of habitat models for the threatened western yellow-billed cuckoo (Coccyzus americanus occidentalis). We used species observations (n = 479) from a state-wide survey to develop habitat models from 1) three vegetation/land-cover maps produced at different geographic scales ranging from state to national, and 2) new aggregate maps defined by the spatial agreement of cover types, which were defined as high (agreement = all data sets), moderate (agreement ≥ 2), and low (no agreement required). Model accuracies, predicted habitat locations, and total area of predicted habitat varied considerably, illustrating the effects of input data quality on habitat predictions and resulting potential impacts on conservation planning. Habitat models based on aggregated and conflated data were more accurate and had higher model sensitivity than original vegetation/land-cover, but this accuracy came at the cost of reduced geographic extent of predicted habitat. Using the highest performing models, we assessed cuckoo habitat preference and distribution in Arizona and found that major watersheds containing high-probably habitat are fragmented by a wide swath of low-probability habitat. Focus on riparian restoration in these areas could provide more breeding habitat for the threatened cuckoo, offset potential future habitat losses in adjacent watershed, and increase regional connectivity for other threatened vertebrates that also use riparian corridors. 相似文献