基于NOAA/POES卫星观测的磁层相对论电子起源的初探

本文利用低高度极轨卫星NOAA/POES的观测数据,并结合ACE卫星和Polar卫星的观测结果,研究分析了磁层相对论电子的起源. NOAA/POES卫星对于不同地磁活动时期相对论电子的分布和起源进行了较为详细观测, 分析结果表明（1） 亚暴期间注入磁层的能量电子可以为与磁暴相关的磁层高能电子暴提供种子电子;（2）太阳质子事件期间太阳风中的能量电子也可以为磁层中的相对论电子提供所需要的源.     

Report on the physical characteristics of Vaidya-Tikekar's exact relativistic model for a superdense star

We report here the results of our examination of the physical properties of Vaidya-Tikekar's model for a relativistic star. Full details will be published elsewhere. The analysis yields a strong indication that the model is stable with respect to infinitesimal radial oscillations. We find that the adiabatic speed of sound is smaller than the speed of light everywhere inside the fluid sphere if the radius of the sphere is larger than 1.46 times its Schwarzschild radius. We also find that the fluid must necessarily be supraluminal somewhere if the speed of sound is decreasing outwards close to the center. We further find that the strong energy condition is fulfilled everywhere if it is fulfilled at the center. Since the ratio of the pressure p and the density ⋅ is decreasing outwards, this indicates that the temperature gradient is negative. We also find that the relativistic adiabatic index is larger than two. Demanding the fluid to be causal, and taking the pressure and the density to be somewhere given by 7.4 ⋅ 10³³ dynes/cm³ and 5.1 ⋅ 10¹⁴ g/cm³, we calculate the maximum mass of the fluid sphere to be 3 solar masses.     

风尘堆积常见的同沉积和沉积后改造特征及其环境意义

黄土堆积作为气下沉积,任何一个深度都曾经暴露于地表,因而必然受到相关地表过程的作用.由于这些过程均发生于特定的环境条件下,形成的特征多数具有明确的环境意义;而黄土在沉积后也可能受到各种地质过程的改造,从而对研究中常用的气候代用指标有一定影响.文章基于野外、微形态等分析,结合前人成果,对我国北方新近纪风尘堆积中常见的同沉积和沉积后改造特征、形成过程及环境意义进行研究.由于一些特征在黄土堆积中具有普遍性,可作为识别风成堆积的标志和环境事件研究的指标,并有助于全面理解常用的替代指标的环境意义.     

Spatial patterns of groundwater‐lake exchange – implications for acid neutralization processes in an acid mine lake

Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (?2.5 to 5.8 L m^‐2 d^‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (?1.8 to 8.1 L m^‐2 d^‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g^‐1 d^‐1) compared to alternating sites (<220 nmol g^‐1 d^‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.     

Raindrop‐impact‐induced erosion processes and prediction: a review

Raindrop‐impact‐induced erosion is initiated when detachment of soil particles from the surface of the soil results from an expenditure of raindrop energy. Once detachment by raindrop impact has taken place, particles are transported away from the site of the impact by one or more of the following transport processes: drop splash, raindrop‐induced flow transport, or transport by flow without stimulation by drop impact. These transport processes exhibit varying efficiencies. Particles that fall back to the surface as a result of gravity produce a layer of pre‐detached particles that provides a degree of protection against the detachment of particles from the underlying soil. This, in turn, influences the erodibility of the eroding surface. Good understanding of rainfall erosion processes is necessary if the results of erosion experiments are to be properly interpreted. Current process‐based erosion prediction models do not deal with the issue of temporal variations in erodibility during a rainfall event or variabilities in erodibility associated with spatial changes in dominance of the transport processes that follow detachment by drop impact. Although more complex erosion models may deal with issues like this, their complexity and high data requirement may make them unsuitable for use as general prediction tools. Copyright © 2005 John Wiley & Sons, Ltd.     

Long‐term effects of revegetation on soil hydrological processes in vegetation‐stabilized desert ecosystems

Planting of sand‐binding vegetation in the Shapotou region on the southeastern edge of the Tengger Desert began in 1956. The revegetation programme successfully stabilized formerly mobile dunes in northern China, permitting the operation of the Baotou‐Lanzhou railway. Long‐term monitoring has shown that the revegetation programme produced various ecological changes, including the formation of biological soil crusts (BSCs). To gain insight into the role of BSCs in both past ecological change and current ecological evolution at the revegetation sites, we used field measurements and HYDRUS‐1D model simulations to investigate the effects of BSCs on soil hydrological processes at revegetated sites planted in 1956 and 1964 and at an unplanted mobile dune site. The results demonstrate that the formation of BSCs has altered patterns of soil water storage, increasing the moisture content near the surface (0–5 cm) while decreasing the moisture content in deeper layers (5–120 cm). Soil evaporation at BSC sites is elevated relative to unplanted sites during periods when canopy coverage is low. Rainfall infiltration was not affected by BSCs during the very dry period that was studied (30 April to 30 September 2005); during periods with higher rainfall intensity, differences in infiltration may be expected due to runoff at BSC sites. The simulated changes in soil moisture storage and hydrological processes are consistent with ongoing plant community succession at the revegetated sites, from deep‐rooted shrubs to more shallow‐rooted herbaceous species. Copyright © 2009 John Wiley & Sons, Ltd.     

An inexpensive and portable drill rig for bedrock groundwater studies in headwater catchments

Bedrock groundwater dynamics in headwater catchments are poorly understood and poorly characterized. Here, we present an inexpensive and portable bedrock drilling system designed for use in remote locations. Our system is capable of drilling bedrock wells up to 11 m deep and 38 mm in diameter in a wide range of bedrock types. The drill consists of a lawn mower engine adapted to rotate a diamond tipped coring bit, a small water pump to cool and flush the drill bit and a scaffolding platform for stable footing on steep slopes. The complete drilling assembly costs under $ 2000 USD. Here, we show proof‐of‐concept of our approach with 40 successful wells drilled in different geological substrates, including a conglomerate at the Maimai experimental catchment in New Zealand, volcanic breccias at the HJ Andrews experimental watershed in Oregon, USA, sandstone and siltstone at the Alsea watershed in Oregon, USA, and basalt at the Los Gavilanes experimental watershed in Veracruz, Mexico. We also present a transparent comparison between our design and other portable bedrock drilling systems and outline the strengths and weaknesses of each system. Copyright © 2011 John Wiley & Sons, Ltd.     

On-line estimation of nonlinear physical systems

Recursive algorithms for estimating states of nonlinear physical systems are presented. Orthogonality properties are rediscovered and the associated polynomials are used to linearize state and observation models of the underlying random processes. This requires some key hypotheses regarding the structure of these processes, which may then take account of a wide range of applications. The latter include streamflow forecasting, flood estimation, environmental protection, earthquake engineering, and mine planning. The proposed estimation algorithm may be compared favorably to Taylor series-type filters, nonlinear filters which approximate the probability density by Edgeworth or Gram-Charlier series, as well as to conventional statistical linearization-type estimators. Moreover, the method has several advantages over nonrecursive estimators like disjunctive kriging. To link theory with practice, some numerical results for a simulated system are presented, in which responses from the proposed and extended Kalman algorithms are compared.     

渤海陆缘地震的力学特征和成因

渤海陆缘是华北强震活动区,如1966年的邢台震群,1967年的河间地震,1969年的渤海地震,1975年的海城地震,1976年的唐山震群和1983年的菏泽地震,都是在该区发生的。显然,深入研究该地区的构造运动和地震成因是有重要科学意义的。本文拟从应力场角度进行研究。     

物理过程和分辨率对西南涡演变的中尺度模拟影响

本文运用PSU/NCAR中尺度模式第四改进型(MM_4),对“81.7”四川暴雨期西南涡的演变进行了一系列96和72小时数值模拟;其目的在于研究模式物理过程和空间分辨率以及行星边界层(PBL)参数化对西南涡生成和发展模拟的影响。96小时的控制试验(方案Ⅰ)结果表明:水平分辨率160km和总体PBL的10层MM_4对西南涡发展模拟得较好,但对其生成只有初步模拟的能力;各种物理过程主要影响西南涡演变的强度,而对其位置影响较小;去掉潜热释放会显著影响西南涡在后期的发展;没有地面通量将使西南涡的生成和发展强度明显减弱;于试验不能模拟出西南涡在整个暴雨期的发展,且使其移速略快,无摩擦试验指出,地面摩擦对西南涡的生成是不重要的。提高模式空间分辨率和采用高分辨PBL模式,能使西南涡生成和发展位置的模拟有明显改进,但其强度一般偏强于实况。事实表明,进一步完善模式物理过程、改进PBL参数化和提高模式空间分辨率将是十分必要的。