Preparation and Measurement of Cassiterite for Sn Isotope Analysis

Increased interest in the fractionation of Sn isotopes has led to the development of several techniques for preparing cassiterite (SnO₂, the primary ore of Sn) for isotopic analysis. Two distinct methods have been applied in recent isotopic studies of cassiterite: (a) reduction to tin metal with potassium cyanide (KCN) at high temperature (800 °C), with subsequent dissolution in HCl, and (b) reduction to a Sn solution with hydriodic acid (HI) at low temperature (100 °C). This study compares the effectiveness and accuracy of these two methods and contributes additional methodological details. The KCN method consistently yielded more Sn (> 70% in comparison with < 5%), does not appear to fractionate Sn isotopes at high temperatures over a 2‐hour period and produced consistent Sn isotope values at flux mass ratios of ≥ 4:1 (flux to mineral) with a minimum reduction time of 40 min. By means of a distillation experiment, it was demonstrated that HI could volatilise Sn, explaining the consistently low yields by this method. Furthermore, the distillation generated Sn vapour, which is up to 0.38‰ per mass unit different from the starting material, the largest induced Sn fractionation reported to date. Accordingly, the HI method is not recommended for cassiterite preparation for Sn isotopic analysis.     

液态水含量和冰晶浓度对闪电频数影响的数值模拟研究

假定在软雹和冰晶碰撞的非感应起电机制为主要的起电机制成立的条件下，数值模拟研究了国际上公认的Fletcher和H—M冰晶产生机制以及云中的液态水含量对雷暴云放电过程（区分了云闪和地闪）的影响。结果表明，随着气压和温度的变化，在两种冰晶产生机制假定下，冰晶浓度分布有很大差异，这直接导致了雷暴云内电活动的差异。液态水含量的增加将使得首次放电时间延迟，同时将引起放电位置的下降和闪电频数的减少。     

Next-generation robotic planetary reconnaissance missions: A paradigm shift

A fundamentally new scientific mission concept for remote planetary surface and subsurface reconnaissance will soon replace the engineering and safety constrained mission designs of the past, allowing for optimal acquisition of geologic, paleohydrologic, paleoclimatic, and possible astrobiologic information of Mars and other extraterrestrial targets. Traditional missions have performed local ground-level reconnaissance through rovers and immobile landers, or global mapping performed by an orbiter. The former is safety and engineering constrained, affording limited detailed reconnaissance of a single site at the expense of a regional understanding, while the latter returns immense datasets, often overlooking detailed information of local and regional significance. A “tier-scalable” paradigm integrates multi-tier (orbitatmosphereground) and multi-agent (orbiterblimpsrovers/sensorwebs) hierarchical mission architectures, not only introducing mission redundancy and safety, but enabling and optimizing intelligent, unconstrained, and distributed science-driven exploration of prime locations on Mars and elsewhere, allowing for increased science return, and paving the way towards fully autonomous robotic missions.     

Three dimensional analysis of slope stability

A 3-D mathematical approach to slope stability, which is based on limiting equilibrium and variational analysis, is presented. In the initial formulation there are three unknown functions: the slip surface, the normal stress and the shear stress direction over this surface. The minimum factor of safety is sought through variational extremization. The analysis indicates that the factor of safety is independent of the normal stress distribution over the critical slip surface. It also indicates that the direction of the elementary shear force over the slip surface depends on the slip surface function, but not on the normal stress function. The analysis yields a non-linear first order partial differential equation, relating the slip surface and its first partial derivatives. By limiting the analysis to symmetrical problems an ordinary differential equation, governing the slip surface path on the plane of symmetry, is derived. This equation enables the development of a numerical procedure to determine the minimal factor of safety of symmetrical 3-D slopes. Two possible failure modes are determined for homogeneous slopes. One mode consists of finite 3-D sliding body and the second represents cylindrical failure. Numerical analyses for some simple cases, of homogencous slopes are presented.     

On the Relevance of $$\ln (z_{0} /z_{0T})= kB^{-1}$$

The assumption that the roughness Reynolds number \(( Re_{*})\) can be used as a basis for quantifying the boundary-layer property \({ kB}^{-1} (= \ln (z_{0}/z_{0T}))\) as in some modern numerical models is questioned. While \({ Re}_{*}\) is a useful property in studies of pipe flow, it appears to have only marginal applicability in the case of treeless terrain, as studied in the two experimental situations presented here. For both the daytime and night-time cases there appears to be little correlation between \({ kB}^{-1}\) and \({ Re}_{*}\). For daytime, the present studies indicate that the assumption \({ kB}^{-1} \approx 2\) is acceptable, while for night-time, the scatter involved in relating \({ kB}^{-1}\) to \({ Re}_{*}\) suggests there is little reason to assume a direct relationship. However, while the scatter affecting all of the night-time results is large, there remains a significant correlation between the heat and momentum fluxes upon which an alternative methodology for describing bulk air–surface exchange at night could be constructed. The friction coefficient (\(C_{f}\)) and the turbulent Stanton number \(({ St}_{*})\) are discussed as possible alternatives for describing bulk properties of the air layer adjacent to the surface. While describing the surface roughness in terms of the friction coefficient provides an attractive simplification relative to the conventional methodologies based on roughness length and stability considerations, use of the Stanton number shares many of uncertainties that affect \({ kB}^{-1}\). The transitions at dawn and dusk remain demanding situations to address.     

Crowdsourcing a cyclist perspective on suggested recreational paths in real-world networks

ABSTRACT

Routing and navigation services for leisure activities are conditioned by special needs and trade-offs. The advent of online communities and large crowdsourced datasets offers opportunities to improve the adoption of a user’s perspective in these suggested paths. This paper focuses on achieving two goals. First, the presented methodology analyses a dataset of 190,610 historical GPS traces to gain insights into the appreciation or attractiveness of each edge in a real-world network for a specific leisure activity (i.e. road cycling). Second, as literature on these leisure activities is still sparse, we want to create a thorough understanding of the activities at hand for future work. An appreciation model is proposed and the spread of this score is analyzed in shortest-path alternatives of popular routing engines for this activity. This analysis successfully discriminates these shortest paths based on the scoring value and three morphological parameters of the path. However, the robustness of the model should be improved to ensure the viability of the proposed approach in future work. More specifically, further research on the local optimality of the route choices will be imperative.     

Vegetation and climate of the last glacial-interglacial cycle in Southern Illinois,USA

Raymond Basin and Bald Knob Basin, Montgomery County, Illinois, formed as kettles during Illinoian time. Fossil pollen from these basins provides information on vegetation and climate during the last glacial-interglacial cycle. The pollen profile at Raymond Basin contains an expanded Sangamonian section and an early Wisconsinan section, but both are missing the late Wisconsinan. The ages for the following pollen zones are estimated by correlation with the deep-sea ¹⁸O record.In the late Illinoian,Picea-Pinus pollen zone 1, dating from about 150–130 ka, represents an apparently closed boreal coniferous forest indicating a cold late-glacial climate. The Sangamonian includes three major pollen zones ranging from about 130–75 ka. The early Sangamonian is represented byQuercus-Ulmus-Carya-Fagus dominance in zone 2, indicating vegetation comparable to the modern deciduous forest and climate that was warm and moist. The middle Sangamonian in zone 3, which is characterized byAmbrosia-Poaceae-Cupressaceae-Quercus pollen, suggests a savanna vegetation and a warm, dry climate. The late Sangamonian is subdivided into aQuercus-Ulmus-Carya subzone (4a) that indicates a mesic forest and greater precipitation; aQuercus-Ambrosia subzone (4b) that suggests drier climate and savanna conditions; and aQuercus-Liquidambar-Carya subzone (4c), containing the southeastern forest element,Liquidambar, suggesting the peak in warmth and moisture. The early Wisconsinan is represented by a transitionalPicea-Chenopodiineae zone (5). This unusual assemblage suggests a cool prairie-like vegetation, perhaps with scatteredPicea trees at the end of that depositional interval. The Middle Wisconsinan is marked by the return of high percentages ofPicea andPinus pollen in zone 6. The latest pollen zone (7) is dominated by Chenopodiineae pollen and is absent at Raymond Basin. It is most likely Holocene in age, and probably represents prairie conditions and warm, dry climate.Apparent surface-temperature and apparent effective-moisture curves were derived from the first detrended correspondence analysis (DCA) axis of the pollen data. The first axis correlates well with the normalized deep-sea ¹⁸O curve of sea surface temperature, and the second is controlled mainly by precipitation. The interglacial vegetation differs from that predicted by models driven by orbitally-induced insolation curves.This is the 9th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994; at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.     

Sub-regional snow cover distribution across the southern Appalachian Mountains

Abstract

Snowfall in the Southern Appalachian Mountain region of the eastern US is characterized by much spatiotemporal variability. Annual snowfall totals vary by up to 75 cm, and variations in snowfall intensity can lead to large differences in the local snowfall distribution. Research has shown that the synoptic pattern associated with the snowfall strongly influences the regional-scale distribution of snow cover. However, topographic variability results in locally complex snow cover patterns that are not well understood or documented. In this study, we characterize the snow covered area (SCA) and fractional snow cover associated with different synoptic patterns in 14 individual sub-regions. We analyze 63 snow events using Moderate-resolution Imaging Spectroradiometer standard snow cover products to ascertain both qualitative and quantitative differences in snow cover across sub-regions. Among sub-regions, there is significant variation in the snow cover pattern from individual synoptic classes. Furthermore, the percent SCA follows the regional snowfall climatology, and sub-regions with the highest elevations and northerly latitudes exhibit the greatest variability. Results of the sub-regional analysis provide valuable guidance to forecasters by contributing a deeper understanding of local snow cover patterns and their relationship to synoptic-scale circulation features.