A software solution for point counting. Petrographic thin section analysis as a case study     

Martín L. Larrea  Silvia M. Castro  Ernesto A. Bjerg 《Arabian Journal of Geosciences》2014,7(8):2981-2989

In the field of geology, as in many other fields, a common problem is the analysis of 2D sections. An example of this is the petrographic study of rock samples, i.e., the quantification of its mineral components and the percentages of each phase present in it. Conventionally, this quantification has been determined by point counting performed on thin sections. Although point counting is very time consuming, it is of common use in several domains including geology, biology, medicine, and materials sciences, among others. Point counting in thin sections is normally conducted through mechanical or electromechanical devices attached to a microscope; such devices are very expensive, offer limited functionality, and are very time consuming. In this contribution, we introduce an interactive visualization application called Rock.AR that reduces the amount of time required to apply this technique and simplify its work flow. It provides visual tools like distortion techniques, overview + detail, and statistics to assist the technique. A comparison between this application and similar tools through users' experiences is provided. We compare the time it takes to complete a session of point counting and the tools' usability.  相似文献   

Can agriculture support climate change adaptation, greenhouse gas mitigation and rural livelihoods? insights from Kenya     

Elizabeth Bryan  Claudia Ringler  Barrack Okoba  Jawoo Koo  Mario Herrero  Silvia Silvestri 《Climatic change》2013,118(2):151-165

Changes in the agriculture sector are essential to mitigate and adapt to climate change, meet growing food demands, and improve the livelihoods of poor smallholder producers. What agricultural strategies are needed to meet these challenges? To what extent are there synergies among these strategies? This paper examines these issues for smallholder producers in Kenya across several agroecological zones. Several practices emerge as triple wins, supporting climate adaptation, greenhouse gas mitigation, and profitability goals. In particular, integrated soil fertility management and improved livestock feeding are shown to provide multiple benefits across all agroecological zones examined. Triple wins of other agricultural practices are limited to specific agroecological zones. Irrigation and soil and water conservation, for example, are essential for adaptation, mitigation, and profitability in arid areas. The results suggest that agricultural investments targeted toward these triple-win strategies will have the greatest payoff in terms of increased resilience of farm and pastoralist households and global climate change mitigation. To reap the benefits of triple-win strategies will require that policymakers, researchers, and practitioners move away from isolated approaches focused on either adaptation or mitigation or rural income generation toward a more holistic assessment of joint strategies as well as their tradeoffs and synergies.  相似文献   

Dust-induced chemical differentiation in dense regions     

Silvia Casu  Cesare Cecchi-Pestellini  Santi Aiello 《Monthly notices of the Royal Astronomical Society》2001,325(2):826-834

Dust grains respond to the physical and chemical conditions of the interstellar region in which they are embedded. The interaction produces an extinction curve which depends on the local environment and on the past history of the dust grains. In this work we present a theoretical study of the effects of radial variations of dust extinction properties on gas-phase chemistry in spherical core–halo clouds. We use observational constraints on the variation range of the extinction curve, and we analyse if the degree of dust environmental processing could be reflected by chemical signatures in the gas-phase molecular concentrations. The results of this work show that significant variations in the photodestruction rates and in the thermal profile of the cloud might induce chemical patterns otherwise excluded in the standard dense-cloud chemistry. Some discrepancies between observations and theoretical provisions are discussed in the light of the present results.  相似文献   

Annual trace element cycles in calcite–aragonite speleothems: evidence of drought in the western Mediterranean 1200–1100 yr BP     

Emily A. McMillan  Ian J. Fairchild  Silvia Frisia  Andrea Borsato  Frank McDermott 《第四纪科学杂志》2005,20(5):423-433

Each of two calcitic stalagmites from Grotte de Clamouse, Herault, southern France, displays a discrete aragonite layer dated at around 1100 yr BP. The layer of fanning aragonite ray crystals is immediately preceded by calcite with Mg and Sr compositions that are uniquely high for the past 3 kyr. Trace element compositions close to the boundary between original aragonite and calcite are consistent with quasi‐equilibrium partitioning of trace elements between the phases. Study of modern dripwaters demonstrates that pronounced covariation of Mg/Ca and Sr/Ca ratios in dripwater occurs owing to large amounts of calcite precipitation upflow of the drips that fed the stalagmites. Trace element to Ca ratios are enhanced during seasonally dry periods. Ion microprobe data demonstrate a pronounced covariation of trace elements, including Mg and Sr in calcite, and Sr, U and Ba in aragonite. The mean peak spacing is close to the long‐term mean of annual growth rates determined by differences in U‐series ages and so the trace element peaks are interpreted as annual. The trace element chemistry of the stalagmites on annual to inter‐annual scales thus directly reflects the amounts of prior calcite precipitation, interpreted as an index of aridity. The longer‐term context is a multi‐decadal period of aridity (1200–1100 yr BP) possibly correlated with an analogous episode in Central America. The arid period culminated in the nucleation of aragonite, but within a decade was followed by a return to precursor conditions. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Concentration and subcellular distribution of trace elements in liver of small cetaceans incidentally caught along the Brazilian coast     

Kunito T  Nakamura S  Ikemoto T  Anan Y  Kubota R  Tanabe S  Rosas FC  Fillmann G  Readman JW 《Marine pollution bulletin》2004,49(7-8):574-587

Concentrations of trace elements (V, Cr, Mn, Fe, Co, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Sb, Cs, Ba, T-Hg, Org-Hg, Tl and Pb) were determined in liver samples of estuarine dolphin (Sotalia guianensis; n = 20), Franciscana dolphin (Pontoporia blainvillei; n = 23), Atlantic spotted dolphin (Stenella frontalis; n = 2), common dolphin (Delphinus capensis; n = 1) and striped dolphin (Stenella coeruleoalba; n = 1) incidentally caught along the coast of Sao Paulo State and Parana State, Brazil, from 1997 to 1999. The hepatic concentrations of trace elements in the Brazilian cetaceans were comparable to the data available in literature on marine mammals from Northern Hemisphere. Concentrations of V, Se, Mo, Cd, T-Hg and Org-Hg increased with increasing age in liver of both estuarine and Franciscana dolphins. Very high concentrations of Cu (range, 262-1970 microg/g dry wt.) and Zn (range, 242-369 microg/g dry wt.) were observed in liver of sucklings of estuarine dolphin. Hepatic concentrations of V, Se, T-Hg, Org-Hg and Pb were significantly higher in estuarine dolphin, whereas Franciscana dolphin showed higher concentrations of Mn, Co, As and Rb. Ratio of Org-Hg to T-Hg in liver was significantly higher in Franciscana dolphin than estuarine dolphin, suggesting that demethylation ability of methyl Hg might be lower in liver of Franciscana than estuarine dolphins. High hepatic concentrations of Ag were found in some specimens of Franciscana dolphin (maximum, 20 microg/g dry wt.), and 17% of Franciscana showed higher concentrations of Ag than Hg. These samples with high Ag concentration also exhibited elevated hepatic Se concentration, implying that Ag might be detoxified by Se in the liver. Higher correlation coefficient between (Hg+0.5 Ag) and Se than between Hg and Se and the large distribution of Ag in non-soluble fraction in nuclear and mitochondrial fraction of the liver also suggests that Ag might be detoxified by Se via formation of Ag2Se in the liver of Franciscana dolphin.  相似文献   

The Geochemistry of Lake Joyce, McMurdo Dry Valleys, Antarctica     

Joseph A. Shacat  William J. Green  Eric H. Decarlo  Silvia Newell 《Aquatic Geochemistry》2004,10(3-4):325-352

Lake Joyce is one of the least studied lakes of the McMurdo Dry Valleys. Similar to other lakes in this region, Lake Joyce is a closed-basin, permanently ice-covered, meromictic lake. We present here a detailed investigation of major ions, nutrients, and dissolved trace elements for Lake Joyce. Specifically, we investigate the role of iron and manganese oxides and hydrous oxides in trace metal cycling.Lake Joyce is characterized by fresh, oxic waters overlying an anoxic brine, primarily Na–Cl. Surface waters have a maximum nitrate concentration of 26M with a molar dissolved inorganic nitrogen to phosphorus ratio of 477. The supply of nitrogen is attributed to atmospheric deposition, possibly from polar stratospheric clouds. Dissolved phosphorus is scavenged by hydrous iron oxides. The pH is highest (10.15) just beneath the 7-m thick ice cover and decreases to a minimum of 7.29 in the redox transition zone. Dissolved Al exceeds 8M in surface waters, and appears to be controlled by equilibrium with gibbsite. In contrast, concentrations of other trace elements in surface waters are quite low (e.g., 5.4nM Cu, 0.19nM Co, <20pM La). Dissolved Fe, Mn, Ni and Cd were below our detection limits of 13 nM, 1. 8 nM, 4.7 nM and 15pM (respectively) in surface waters. There was a 6-m vertical separation in the onset of Mn and Fe reduction, with dissolved Mn appearing higher in the water column than Fe. Based on thermodynamic calculations, dissolved Mn appears to be controlled by equilibrium with hausmannite (Mn3O4). Co tracks the Mn profile closely, suggesting Co(III) is bound in the lattice of Mn oxides, whereas the Ce profile is similar, yet the Ce anomaly suggests oxidative scavenging of Ce. Release of Cu, Ni, Cd and trivalent REE appears to be controlled by pH-induced desorption from Fe and Mn oxides, although Cu (and perhaps Ni) may be scavenged by organic matter in surface waters.  相似文献   

Nickel, Copper, Zinc and Cadmium Cycling with Manganese in Lake Vanda (Wright Valley, Antarctica)     

William J. Green  Brian R. Stage  Bonnie Jo Bratina  Shannon Wagers  Adam Preston  Kevin O’bryan  Joseph Shacat  Silvia Newell 《Aquatic Geochemistry》2004,10(3-4):303-323

Lake Vanda is a closed-basin, permanently ice-covered lake located in the Wright Valley of Antarctica. The lakes more important geochemical features include the fact that it is fed by a single glacial melt water stream for only 6–8weeks out of the year; that it has remained stratified for more than a millennium; and that, like other lakes in the region, it is remote from anthropogenic influence. These, together with the fact that it is among the least biologically productive lakes in the world, make it an ideal system for examining the transport, cycling and fate of trace metals in the aquatic environment. Like others before us, we view this lake as a natural geochemical laboratory, a flask in the desert. This paper presents the first set of closely spaced, vertical, profiles for dissolved and particulate Mn, Fe, Ni, Cu, Zn and Cd in the water column. Despite the absence of an outflow, metals in the fresh upper waters of the lake have extremely low concentrations, in the pico-molar to nano-molar range, and are partitioned largely into dissolved rather than particulate phases. Efficient metal scavenging by particles from these oxygen-rich waters is indicated. Significant increases in metal concentrations begin to appear at depth, between 57 and 60m, and these increases coincide with the onset of manganese oxide dissolution in oxic, but lower pH waters. Vertical profiles suggest that the entire suite of trace metals (Ni, Cu, Zn, and Cd) is being released from manganese oxide carrier phases. Thermodynamic analysis indicates that Mn3O4 (i.e., the mineral hausmannite) may be important in metal sequestration and recycling in the deeper waters of Lake Vanda. Manganese-reducing organisms reported by Bratina etal. (1998) are active in the zone of metal release and these could also contribute to the observed cycling.  相似文献   

1999年欧洲圣诞节风暴数值模拟分析     

Claudio Cassardo  ;Nicola Loglisci  ;Min Wei Qian  ;Silvia Ferrarese  ;Arnaldo Longhetto  ;Gianpaolo Balsamo 《气象与减灾研究》2008,31(2):6-13

对1999年圣诞期间发生在欧洲中西部的圣诞节风暴进行了分析,认为4个主要的低气压系统中的第二个给法国北部带来了强风暴雨,巴黎的Orly机场阵风速度〉47m／s;第四个低压系统沿法国西海岸产生相似的恶劣天气,并在西班牙的北部海岸及地中海沿岸国家造成了毁灭性的破坏。在法国中部风暴最剧烈的时候,最大阵风〉41m／s;在法国和德国之间的区域,达55m／s。圣诞节风暴造成欧洲国家大约140人死亡,其他损失包括树木、街道和房屋被毁,电力系统和电话中断时间长达数天,受影响的人数大约为1000万,财产损失大约为80亿美元。由于风暴的极端强度和快速发展速度,欧洲大多数国家的数值预报中心没有对这次剧烈天气提供足够的预警。为此,利用中尺度数值预报系统（RAMS）模拟圣诞节风暴,并与ECMWF分析资料以及实况观测资料进行了对比分析。结果表明,RAMS模式能够准确模拟风暴的主要特性、低气压的演变和位置移动、发展的关键时间点、风暴演化期间的平均风场;模拟的平均风场和气象观测网的观测结果相一致;模拟的风暴移动时间和主要新闻媒体的报道相吻合;模式计算的一些特定地区平均风速的时间趋势显示,在阿尔卑斯山脉地区,无论是上风区还是下风区,风暴的时间都被准确地预测;模拟的第一次风暴最低气压值较实际值偏低。  相似文献   

The gravitational wave background from star–massive black hole fly-bys     

Silvia Toonen  Clovis Hopman  Marc Freitag 《Monthly notices of the Royal Astronomical Society》2009,398(3):1228-1234

Stars on eccentric orbits around a massive black hole (MBH) emit bursts of gravitational waves (GWs) at periapse. Such events may be directly resolvable in the Galactic Centre. However, if the star does not spiral in, the emitted GWs are not resolvable for extragalactic MBHs, but constitute a source of background noise. We estimate the power spectrum of this extreme mass ratio burst background (EMBB) and compare it to the anticipated instrumental noise of the Laser Interferometer Space Antenna (LISA). To this end, we model the regions close to an MBH, accounting for mass segregation, and for processes that limit the presence of stars close to the MBH, such as GW inspiral and hydrodynamical collisions between stars. We find that the EMBB is dominated by GW bursts from stellar mass black holes, and the magnitude of the noise spectrum  ( fS _GW)^1/2  is at least a factor of ∼10 smaller than the instrumental noise. As an additional result of our analysis, we show that LISA is unlikely to detect relativistic bursts in the Galactic Centre.  相似文献   

Hydrostatic gas distributions: global estimates of temperature and abundance     

Luca Ciotti  Silvia Pellegrini 《Monthly notices of the Royal Astronomical Society》2008,387(2):902-914

Estimating the temperature and metal abundance of the intracluster and the intragroup media is crucial to determine their global metal content and to determine fundamental cosmological parameters. When a spatially resolved temperature or abundance profile cannot be recovered from observations (e.g. for distant objects), or deprojection is difficult (e.g. due to a significant non-spherical shape), only global average temperature and abundance are derived. After introducing a general technique to build hydrostatic gaseous distributions of prescribed density profile in potential wells of any shape, we compute the global mass-weighted and emission-weighted temperature and abundance for a large set of barotropic equilibria and an observationally motivated abundance gradient. We also compute the spectroscopic-like temperature that is recovered from a single temperature fit of observed spectra. The derived emission-weighted abundance and temperatures are higher by 50 to 100 per cent than the corresponding mass-weighted quantities, with overestimates that increase with the gas mean temperature. Spectroscopic temperatures are intermediate between mass and luminosity-weighted temperatures. Dark matter flattening does not lead to significant differences in the values of the average temperatures or abundances with respect to the corresponding spherical case (except for extreme cases).  相似文献