Thermal desorption of CH4 retained in CO2 ice

CO₂ ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density, refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that CO₂ traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH₄ in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of several retaining mechanisms related to the structure of CO₂ ice.     

双向土工格栅加筋土回弹模量试验研究

利用双向土工格栅对源自强风化红砂岩的粉砂土进行加筋,对压实度分别为90 %,95 %,100 %以及加筋层数分别为0,1,2,3,5的数组土样完成了室内回弹模量试验工作。总结并分析了双向土工格栅加筋层的布设位置、加筋层数、土的压实度等对回弹模量的影响规律。试验结果表明,在合适的加筋方式和加筋层数以及较高的压实度下,可以获得较高的回弹模量。这表明利用双向土工格栅加筋技术实现公路桥台台背与桥头路堤间刚柔的平顺过渡,从而达到控制桥头跳车的目的是可能的。     

Vesiculation and crystallization under instantaneous decompression: Numerical study and comparison with laboratory experiments

Vesiculation and crystallization in ascending magmas are key processes that control the eruption behavior, and they interplay each other through the water exsolution process. We conducted a numerical study in order to quantitatively understand the water exsolution and crystallization processes in natural eruptions (decompression history is unknown) and in laboratory experiments (the amount of decompression is constant with time). The numerical results, which take into account homogeneous or heterogeneous nucleation and growth of bubbles with varying diffusivity of water, viscosity, and the amount of decompression, provide a quantitative understanding of their control on bubble formation and water exsolution in the constant amount of decompression. The bubble nucleation in the homogeneous nucleation can be divided into two regimes – the diffusion control regime and viscosity control regime – depending on the modified Peclet number and the effective supersaturation. In the cases of both homogeneous and heterogeneous nucleations, the bubble growth is controlled by diffusion or viscosity, depending on the modified Peclet number and bubble number density. The water exsolution rate, which is controlled by the modified Peclet number in the viscosity control regime and by the bubble number density and diffusive driving force in the diffusion control regime, acts as an effective cooling rate in a decompression-induced crystallization process. A comparison of the numerical results with the results of laboratory experiments suggests that water exsolution proceeds by the diffusion-limited growth of bubbles under disequilibrium vesiculation through the heterogeneous nucleation of bubbles, and this in turn controls the crystallization kinetics of microlite with the homogeneous nucleation of microlite and the diffusion-limited growth of crystal. The several orders of variation of microlite number density with the amount of decompression in laboratory experiments can be interpreted as the effect of the amount of decompression on the driving force for the diffusive bubble growth that controls the water exsolution rate.     

煤层煤质参数测井解释模型

摘　 要　 以确定煤质参数的体积模型法为基础‚结合煤样实验室分析资料‚利用概率模型法 （多元线性回归） 确定煤质参数的测井解释模型。经 F 检验‚说明建立的方程组有效‚线性关 系显著。实际解释结果表明‚解释模型估算的煤质参数与煤样实验室分析的煤质参数之间一 致性好‚解释精度高。     

Summary findings of the fourth international radiocarbon intercomparison (FIRI)(1998–2001)

Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the ¹⁴C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with ‘good practice’. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques. Copyright © 2002 John Wiley & Sons, Ltd.     

CTD温度实验室校准结果不确定度的分析

文章分析了CTD温度实验室校准不确定度来源项,按不确定度的评定方法,以实例形式分析评定了CTD温度实验室校准结果的不确定度。     

新型消暖雾催化剂与传统吸湿性催化剂消雾性能的室内对比试验

为了研究一种新的环保型消暖雾催化剂RC／XW的消雾性能,同时选取无水氯化钙（CaCl2）和氯化钠（NaCl）2种吸湿性物质作为对比物,对它们进行室内试验研究。其中RC／XW粒子直径主要集中在12um;将无水氯化钙和氯化钠分别粉碎成10um、15um、20um和30um4个不同的直径。结果表明：不同种类的催化剂、同种类不同尺度的催化剂之间消雾效果都存在很大差异。消雾效果与播撒剂量直接相关。RC／XW适用于消除含水量在0．3g·m^-3以上的严重影响视程的暖雾,且播撒剂量要〉1g·m^-3。     

列车振动荷载作用下南京细砂动强度变化规律研究

以南京细砂为研究对象,采用空心圆柱扭剪仪模拟列车振动荷载作用对应的土体单元所受应力路径,考虑试样围压、加载幅值和排水条件,研究列车振动荷载作用下土体动强度的变化规律。试验结果分析表明:在模拟列车振动荷载作用对土体竖向应变的影响时,采用椭圆应力路径来代替心形应力路径是切实可行的,能克服试验仪器高频加载时无法有效模拟心形应力路径的缺点;其次,当围压和加载幅值都较小时南京细砂主要表现为在振动初期强度强化特征,当振动次数达到一定数量后强度也达到一个稳定阶段;当试验围压较大时,随振动次数增加,南京细砂的强度变化主要以强度弱化阶段为主;同时,排水条件对其强度变化的主要影响表现为对其振动前期强度强化阶段的影响,对其强度弱化阶段的影响并不明显。     

Pyrite-hydrocarbon Interaction under Hydrothermal Conditions: an Alternative Origin of H2S and Organic Sulfur Compounds in Sedimentary Environments

Sulfate rocks and organic sulfur from sedimentary organic matter are conventionally assumed as the original sulfur sources for hydrogen sulfide(H_2S) in oil and gas reservoirs. However,a few recent experiments preliminarily indicate that the association of pyrite and hydrocarbons may also have implications for H_2S generation,in which water effects and natural controls on the evolution of pyrite sulfur into OSCs and H_2S have not been evaluated. In this study,laboratory experiments were conducted from 200 to 450° C to investigate chemical interactions between pyrite and hydrocarbons under hydrothermal conditions. Based on the experimental results,preliminary mechanism and geochemical implications were tentatively discussed. Results of the experiments showed that decomposition of pyrite produced H_2S and thiophenes at as low as 330°C in the presence of water and n-pentane. High concentrations of H_2S were generated above 450°C under closed pyrolysis conditions no matter whether there is water in the designed experiments. However,much more organic sulfur compounds(OSCs) were formed in the hydrous pyrolysis than in anhydrous pyrolysis. Generally,most of sulfur liberated from pyrite at elevated temperatures was converted to H_2S. Water was beneficial to breakdown of pyrite and to decomposition of alkanes into olefins but not essential to formation of large amounts of H_2S,given the main hydrogen source derived from hydrocarbons. In addition,cracking of pyrite in the presence of 1-octene under hydrous conditions was found to proceed at 200°C,producing thiols and alkyl sulfides. Unsaturated hydrocarbons would be more reactive intermediates involved in the breakdown of pyrite than alkanes. The geochemistry of OSCs is actually controlled by various geochemical factors such as thermal maturity and the carbon chain length of the alkanes. This study indicates that the scale of H_2S gas generated in deep buried carbonate reservoirs via interactions between pyrite and natural gas should be much smaller than that of thermochemical sulfate reduction(TSR) due to the scarcity of pyrite in carbonate reservoirs and the limited amount of long-chained hydrocarbons in natural gas. Nevertheless,in some cases,OSCs and/or low contents of H_2S found in deep buried reservoirs may be associated with the deposited pyrite-bearing rock and organic matters(hydrocarbons),which still needs further investigation.