Models of high velocity impacts into dust-covered ice: Application to Martian northern lowlands

The detection of fresh impact craters with bright floors and ejecta (arising from fresh clean water ice) in the northern lowlands of Mars (Byrne et al., 2009b, Science 325, 1674), together with observations of polygonal structures and evidence from the Phoenix probe, suggests that there are substantial water ice deposits just below the surface over large areas. Specifically in cases of the larger craters observed, the impacts themselves may have raised the temperature and the pressure of the water ice deposits locally to values which allow phase changes. In this paper, we use smoothed particle hydrodynamics to model hyper-velocity impacts. We estimate peak shock pressures in a solid water ice target covered by a layer of loose material, modeled by pre-damaged dunite. In addition, we account for the possibility of a thin layer of sub-surface water ice by using a three-layer model where the ice is surrounded by dunite. We find that the peak shock pressures reached in the simulated events are high enough to produce several 100-1000 kg of liquid water depending upon the impact parameters and the exact shock pressure needed for the phase change. A difficulty remains however in determining whether liquid is generated or whether a type of fluidized ice is produced (or indeed some combination of the two). We also note that the process can become rather complex as the number of layers increases because of reflections of the shock at sub-surface boundaries—a process which should lead to increased fluidization.     

红层泥岩半刚性基床结构动态变形试验研究

高速铁路要为列车的高速行驶提供一个高平顺性和稳定性的轨下基础,而路基作为轨道结构的基础,必须具有强度高、刚度大、稳定性和耐久性好的特性。由于红层泥岩属于软岩,工程稳定性差,以红层泥岩作为基床的填料,其刚度明显不足,所以为了弥补基床表层的不足,在其顶部添加一层水泥稳定级配碎石。为了验证这些措施的效果,以便指导工程设计和施工,通过足尺动态模型试验,模拟在实际荷载条件下基床的动态变形特性,结果表明,采用水泥稳定级配碎石作为基床表层填料,静态变形明显降低,能够大幅降低动荷载作用时的动变形,减少了基床结构的永久变形,增强了轨道结构的稳定性。     

基于细观力学的混凝土劈拉破坏率相关特性研究

提出了一种高效的混凝土细观力学预处理方法,其中包括基于背景网格的骨料投放与细观三组分的识别;建立了颗粒离散元的混凝土细观力学模型。利用该模型对不同应变率下混凝土的劈拉试验进行了数值仿真,仿真结果显示出的混凝土动力强度提高的规律以及不同应变率下混凝土的破坏模式与试验结果吻合较好。研究表明,随着应变率的提高,混凝土破坏时产生更多弥散状分布的裂纹,同时有些裂纹穿过强度较高的骨料,导致混凝土在高应变率破坏过程中消耗更多的能量,是混凝土的动力强度提高的重要原因。此外,在高应变率下,力链产生更多的分叉,空间分布的不均匀性和随机性增加,因此,在高应变率下混凝土动力强度表现出更大的离散性。     

基于PSO-PP的围岩稳定性评价

围岩的稳定性评价是一个复杂的不确定系统问题。结合投影寻踪方法、粒子群算法和逻辑斯谛曲线函数,建立了围岩稳定性评价的粒子群优化投影寻踪(projection pursuit based on particle swarm optimization,PSO-PP)模型。该模型一方面采用粒子群算法优化投影指标函数及逻辑斯谛曲线函数参数,确保了模型的准确性;另一方面利用逻辑斯谛曲线函数建立投影值与经验等级之间的非线性关系。模型的测试结果显示了良好的精度,实例分析结果与实际状态完全一致,表明该模型在围岩稳定性评价中的可行性和有效性。     

国际流行彩色宝石品质分级评估体系的比较及其启示

彩色宝石品质分级标准对彩色宝石市场的形成与发展具有重要意义。彩色宝石品种的多样性和品质影响要素的复杂性,加上不同国家、地区或民族对彩色宝石颜色的偏好不同,在国际市场上要建立一个统一的彩色宝石品质分级评估体系困难重重。通过比较各彩色宝石聚集地（如美国、泰国、中国香港与大陆等）现有的彩色宝石品质分级评估体系,探讨了不同体系对其颜色、净度、切工分级的思想与方法。结果显示,目前国际上不同彩色宝石分级体系在颜色分级术语上强调的要素有一定的差异,对净度分级在思路上有明显的不同,对切工分级则在思路及技术操作上均存在明显差异。因此,要建立统一的国际彩色宝石品质分级体系尚需时日。最后提出,中国可以尝试以宝石的净度和透明度分级为先导,结合颜色、净度与切工分级设计新的彩色宝石二级递进制（时尚首饰级和宝石级）品质评估分级体系。     

吉林延边地区浅成热液金(铜)矿床的~(40)Ar/~(39)Ar激光探针测年与成矿时代讨论

延边地区是中国东北部陆缘浅成热液金铜矿床发育的地区之一,广泛发育着浅成热液金矿床、中温热液金(铜)矿床和中深成中高温热液富金铜矿床(类斑岩型);富金铜矿床的成矿时代发生在105～102 Ma,为了进一步确定浅成热液金矿床与中深成中高温热液富金铜矿床的成矿动力学背景,采用流体包裹体的~(40)Ar/~(39)Ar激光探针定年法,对该区典型浅成热液金矿床进行了精细的年代学测定,获得刺猬沟金矿床、五星山金矿床和杜荒岭金矿床的脉石矿物石英流体包裹体的~(40)Ar/~(39)Ar等时线年龄分别为(141±7)Ma、(123±7)Ma和(107±6)Ma,其中刺猬沟金矿床((141±7)Ma)和五星山金矿床((123±7)Ma)的脉石矿物石英流体包裹体含有过剩放射性成因~(40)Ar,而杜荒岭金矿床((107±6)Ma)的脉石矿物石英流体包裹体几乎不含或含极少量过剩放射性成因~(40)Ar。结合最新获得的相关地质体的精细年代学成果,认定该区浅成热液金矿床成矿作用均发生在早白垩世晚期,或发生在早白垩世晚期火山喷发、浅成岩浆就位之后,其形成环境与富金铜矿床一致,为古太平洋板块向亚洲大陆正北向俯冲转入Izanagi-Farallon板块西向俯冲的构造转换期。     

城市元胞自动机扩展邻域效应的测量与校准研究

城市元胞模型由于在定量分析与预测城市动态的潜力而受到众多研究者的持续关注.邻域规则是主导城市元胞模型模拟过程的关键组件.研究表明,不同土地利用组合间存在显著的邻域效应,且邻域效应具有惯性、排斥和吸引等影响.然而,传统城市元胞模型主要考虑的是特定分辨率下较小窗口的邻域范围.本文尝试刻画更大窗口的邻域效应及其对元胞模型的影响.基于测量的扩展邻域因子,应用粒子群优化算法校准大窗口邻域规则,并创建了考虑扩展邻域效应的城市元胞模型.为验证模型有效性,将其应用于模拟厦门市1995-2010年期间的城市扩张动态.与3×3摩尔邻域的逻辑回归模型相比较,1995-2010年期间的建设用地模拟精度从80.7％提高到83.9％,总体精度从87.8％提高到89.6％,Kappa系数从70.0％提高到74.5％,表明考虑扩展邻域效应的城市模型取得了更好的模拟效果.     

Geospatial spreadsheets with microscale air quality visualization and synchronization for supporting multiple-scenario visual collaboration

A major obstacle of the interdisciplinary communications for decision-making is that each participant prefers the solution from their own area because current collaboration systems cannot effectively mediate among many alternatives. If a visual collaboration system could display multiple alternatives in a single visual presentation, users would be able to compare alternatives with only a few variables, where all other parameters are fixed, at least from a visual perspective. In this study, we developed a visualization tool to support a microscale air quality (MSAQ) management group, the members of which often need to compare the effects of many alternative control methods. The main achievements of this study are: (1) three-dimensional (3D) visualization of the MSAQ using a 3D city model and (2) development of a geospatial spreadsheet (GS) to facilitate visual comparisons, thereby improving decision-making by making it easy to compare differences based on realistic visual display items. A questionnaire-based survey showed that use of the GS could generate a shared perspective and provide a spatiotemporal context for the participants, thereby making it easy to compare, mediate and reach decisions when confronted with many alternatives.     

Research on the critical conditions for clay particle release during saline aquifer freshening process

Water sensitivity phenomenon occurs during saline aquifer freshening process in seawater intrusion area, and clay particles released in the phenomenon can damage the infiltration capacity of the aquifer. In order to find out the factors and mechanisms for clay particle release, laboratory column infiltration experiments simulating saline aquifer freshening process were designed to measure the critical conditions(critical flow velocity, critical salt concentration and critical ionic strength) and force analysis for clay particle according to DLVO electric double layer theory was employed to illustrate the mechanisms for particle release. The research results showed that critical flow velocity for clay particle release is influenced by salt concentration of injecting solution. When salt concentration of injecting solution is very high, clay particles are not released, indicating that there does not exist a critical flow velocity in this situation. As salt concentration of injecting solution decreases, particles start to be released. The critical salt concentration for clay particle release is 0.052 mol L-1 in our work, which was determined by a constant-flux experiment for stepwise displacement of high concentration Na Cl solution. The critical ionic strength for clay particle release decreases as Ca2+ molar content percentage of the mixed solution of Na Cl and Ca Cl2 increases following the first-order exponential decay equation y = 0.0391e-0.266 x + 0.0015.     

湛江地区一次冷锋型海雾微物理特征

利用2010年3月31日—4月2日冷锋天气系统影响下湛江海雾综合观测资料,分析了海雾的微物理特征及海雾过程中气溶胶粒子谱的演变特征。结果表明,海雾的生消与风场密切相关,海雾生成和发展与较强的ESE气流相联系,而弱的NE气流则会促使海雾减弱或消散。湛江海雾的雾滴数浓度为100~102cm-3,液态含水量为0.001~0.232 g·m-3,雾滴平均半径小于10μm,雾滴峰值半径多位于1.4μm。海雾雾滴谱分布以单调递减谱为主,谱宽超过20μm,且雾发展过程中雾滴谱谱宽存在突然增宽和迅速减小的现象。海雾过程中雾滴数浓度的变化主要是由半径小于5μm的雾滴数密度变化引起的。海雾过程对气溶胶粒子的湿清除效果并不显著,雾过程中粒径小于0.1μm和大于4μm的气溶胶粒子数密度显著减少,但在雾消散后又迅速恢复到雾发生前的水平。