The surface composition of Trojan asteroids: constraints set by scattering theory     

J.P. Emery  R.H. Brown 《Icarus》2004,170(1):131-152

We present the results of spectral modeling of 17 Trojan asteroids. The surface composition of this group of objects (located just beyond the main belt, trapped in Jupiter's stable Lagrange points) remains uncertain due to an absence of diagnostic absorption features in their spectra. We quantitatively analyze spectra of these objects covering the range 0.3-4.0 μm using the formulation for scattering in a particulate medium developed by Hapke. Since the widest spectral range possible is desired to provide the most robust results, recently measured near-IR spectra are combined with previously published visible and near-IR data. These composite spectra are converted to and modeled in terms of geometric albedo to provide the additional constraint of the absolute brightness of the asteroids. It is important that this modeling is performed for a large number of objects, and results are derived based on trends among best-fit models. Under this rigorous examination, we find that it is unlikely that the red spectral slope is a result of organics on the surfaces, due mainly to the lack of absorptions in the L-band. Instead, anhydrous silicates adequately describe the spectral characteristics of this group of objects. A significant fraction of carbonaceous material is also likely present, but is not responsible for the red spectral slope in these models. Also, using these models, we estimate that these surfaces contain at most a few wt% of H₂O ice and no more than 10-30 wt% of hydrated silicates.  相似文献   

关联指数误差和样本容量     

吴云  周硕愚  孙建中 《大地测量与地球动力学》1994,(1)

根据关联指数的定义，推导了ＧＰ法计算关联指数时的观测数据误差与关联指数误差的关系，导出了任意两个嵌入空间维上关联指数之差的表达式，并提出了一种确定样本容量限的方法。  相似文献   

Partial redistribution effects on line polarization in the presence of velocity fields     

K. N. Nagendra 《Solar physics》1996,164(1-2):67-78

Velocity fields in line formation regions strongly affect the line polarization. The conventionally used observer's frame method of solving the polarized transfer equation becomes expensive and inaccurate for partial redistribution problems, when large amplitude velocity fields have to be considered in the observer's frame. An alternative method of solution is the comoving frame method. Partial redistribution problems are solved using comoving frame formalism for line polarization caused by resonance scattering.  相似文献   

浅论经济增长与物价水平的关系     

文华  李少宇 《成都信息工程学院学报》1997,(4)

从交易方程出发，初步分析了经济增长与物价水平的关系，得到了一些有益的结果。  相似文献   

Room-temperature equation of state of Li<Subscript>2</Subscript>VOSiO<Subscript>4</Subscript> up to 8.5 GPa     

Serena C. Tarantino  Michele Zema  Tiziana Boffa Ballaran  Paolo Ghigna 《Physics and Chemistry of Minerals》2008,35(2):71-76

High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li₂VOSiO₄, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature. Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V ₀ and K ₀ using the data weighted by the uncertainties in V. The bulk modulus is K ₀ = 99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K ₀(c) = 49.7 ± 0.5 GPa) approximately four times more compressible than the a axis (K ₀(a) = 195 ± 3 GPa).  相似文献   

云环境下改进TLBO算法的图像边缘检测     

杨晓红  杨娟  陈韬  张清扬 《测绘科学》2017,42(11)

针对TLBO算法在解决复杂高维问题时,表现容易陷入局部最优,多样性丢失过快等不足的问题,提出了一种基于云计算环境下改进的TLBO算法(ITLBO),并将其应用到图像边缘检测中。通过对基本TLBO算法中的‘教’与‘学’阶段进行改进,引入一种新的种群更新方法,提高算法的迭代寻优能力。利用云环境下将该方法应用到图像边缘检测中进行实际性能验证,实验仿真结果表明,该方法提取图像的边缘信息的有效性。本文研究可为智慧城市的建设提供关键技术参考。  相似文献   

GPS CORS系统中NTRIP传输技术的应用研究     

徐建民 《现代测绘》2008,(4)

NTRIP是一种播发实时差分定位改正信息的IP协议。本文讨论了NTRIP的组成、工作原理,并给出一个应用实例。  相似文献   

干旱区水资源约束下的生态退耕空间优化及权衡分析——以奇台县为例   总被引：1，自引：0，他引：1  

许尔琪  李婧昕 《地理研究》2021,40(3):627-642

干旱区耕地大规模扩张导致水资源超载、生态问题频发,亟须退地还水。因此,探索水资源约束下的生态退耕空间优化方案,不仅有助于解决干旱区面临的问题,还可为土地利用规划和决策提供参考。目前对退耕方案多效益矛盾的研究尚量化不足,有鉴于此,本文建立生态退耕空间优化配置及权衡分析模型,以新疆奇台县为研究区进行模型应用,构建了水资源约束下的生态退耕方案群,并设计保有耕地优先和保护生态优先等两种情景,利用蚁群优化算法实现了生态退耕的空间配置模拟与优化。结果表明：耕地面积在保有耕地优先情景将减至9.94万hm²,保护生态优先情景则为6.96万hm²;在此退耕过程中,河道内生态用水占水资源总量的比例从10%增加到30%,防固沙量由713.22万t增加至816.59万t,经济效益则由34.86亿元下降至24.75亿元。通过比较单位经济效益的减少比例可产生的生态效益增加比例,确定耕地面积退至8.35万hm²时是权衡生态和经济效益下的生态退耕最优方案。退耕还草主要发生在奇台县耕地集中区的东北、西北及西南部边缘,将有利于北部的沙漠化防控和南部的水源保护。本研究实现了干旱区水资源约束下生态退耕方案空间模拟和优化,对农业经营和生态保护具有重要参考意义。  相似文献   

An optimized baseflow separation method for assessment of seasonal and spatial variability of baseflow and the driving factors     

SUN Jiaqi  WANG Xiaojun  Shamsuddin SHAHID  LI Hongyan 《地理学报(英文版)》2021,31(12):1873-1894

Baseflow is an important component of river or streamflow. It plays a vital role in water utilization and management. An improved Eckhardt recursive digital filter(IERDF) is proposed in this study. The key filter parameter and maximum baseflow index(BFImax) were estimated using the minimum smoothing method to improve baseflow estimation accuracy. The generally considered BFImax of 0.80, 0.50 and 0.25 according to the drainage basin's predominant geological characteristics often leads to significant errors in the regions that have complex subsurface and hydrologic conditions. The IERDF improved baseflow estimation accuracy by avoiding arbitrary parameter values. The proposed method was applied for baseflow separation in the upstream of Yitong River, a tributary of the Second Songhua River, and its performance was evaluated by comparing the results obtained using isotope-tracer data. The performance of IERDF was also compared with nine baseflow separation techniques belonging to filter, BFI and HYSEP methods. The IERDF was also applied for baseflow separation and calculation of rainfall infiltration recharge coefficient at different locations along the Second Songhua River's mainstream for the period 2000–2016. The results showed that the minimum smoothing method significantly improved BFImax estimation accuracy. The baseflow process line obtained using IEDRF method was consistent with that obtained using isotope 18 O. The IERDF estimated baseflow also showed stability and reliability when applied in the mainstream of the Second Songhua River. The BFI alone in the river showed an increase from the upstream to the downstream. The proportion of baseflow to total flow showed a decrease with time. The intra-annual variability of BFI was different at different locations of the river due to varying climatic conditions and subsurface characteristics. The highest BFI was observed at the middle reaches of the river in summer due to a water surplus from power generation. The research provided valuable information on baseflow characteristics and runoff mode determination, which can be used for water resources assessment and optimization of economic activity distribution in the region.  相似文献   

改进的自适应遗传算法在遥感图像分割中的应用     

张京钊  江涛  程凤菊 《测绘科学》2008,(Z1)

为了自动确定遥感图像分割的最佳阈值,本文提出了一种改进的自适应遗传算法,并利用该算法对二维Otsu图像阈值分割函数进行了全局优化,提高了分割闻值的求解速度。该算法能够根据个体适应度大小和群体的分散程度自动调整遗传控制参数,从而能够在保持群体多样性的同时加快收敛速度,克服基本遗传算法的收敛性差、易早熟问题。实验结果表明,该算法具有良好的收敛速度和稳定性,达到较好的图像分割效果,大大缩短了计算时间。  相似文献