On the peak level of tearing instability in an ion-scale current sheet: The effects of ion temperature anisotropy

We have systematically surveyed the effects of the ion temperature anisotropy on the peak reconnected flux level of the tearing instability excited in a thick current sheet (its half-thickness D equal to the ion inertial length). A series of two- and three-dimensional (2-D and 3-D) simulations have been performed for a magnetotail-like situation, where the ion perpendicular temperature is fixed to balance the magnetic pressure of the lobe while the ion parallel temperature can be varied to give rise to the temperature anisotropy α_i=T_i,perp/T_i,para. Focusing on the behavior of the fastest growing mode (wavelength λ=12D), the results are summarized as follows: (1) The peak levels are larger when the initial α_i is larger and lobe reconnection is obtained only when α_i>1.5. (2) 3-D effects do speed-up the reconnection process but do not change the peak level substantially. (3) The time-scale of gas pressure build-up at the center of magnetic islands relative to the time-scale of reconnected flux growth is identified to be the key issue in determining the peak level. Based on these results for the fastest growing mode with λ=12D, discussion is given on the larger-scale development, that is, what happens when longer wavelength modes are allowed to develop.     

Preconcentration of trace multi-elements in water samples using Dowex 50W-x8 and Chelex-100 resins prior to their determination using inductively coupled plasma atomic emission spectrometry (ICP-OES)

This work presents a solid phase extraction (SPE) method for simultaneous preconcentration of trace elements in water samples prior to their ICP-OES determination. Dowex 50W-x8 and Chelex-100 resins were used as SPE sorbent materials for preconcentration of trace Cd, Co, Cr, Cu, Fe, Ni, Pb and Zn. The optimum sample pH, eluent concentration and sample flow rates were found to 6, 3.0 mol L⁻¹ and 3.0 mL min⁻¹, respectively. In terms of multi-element preconcentration capabilities, Dowex 50W-x8 appeared to be a better sorbent. The recoveries for all the tested analytes were >95%. However, Chelex-100 showed a better performance in terms of recovery (>95%) towards Cu, Fe and Zn. Under optimized conditions using Dowex 50W-x8, the relative standard deviations for different metals were <3%. The limits of detection and limits of quantification ranged from 0.01–0.39 μg L⁻¹ and 0.05–0.1.3 μg L⁻¹, respectively. The accuracy of the preconcentration method was confirmed by spike recovery test and the analysis of certified reference materials. The SPE method was applied for preconcentration of the analyte ions in tap water, bottled water and wastewater samples.     

Theoretical and experimental study of time domain-induced polarization in water-saturated sands

A theoretical model of spectral-induced polarization (IP) of sand is presented. In the proposed model, contacts of sand grains and intergrain solution-filled space are considered as electrical current passages of varying thickness, which differ in values of ion transport number. Ion-selective narrow passages are considered as active zones, large passages as passive. The proposed model describes spectral IP characteristics for the medium where the length of passive zones is much greater than the length of active ones. The model is called short narrow pores (SNP) model. The SNP model predicts a growth of IP time constant with increase of length of ion-selective zone. Both the time domain and frequency domain parameters are described. The parameters of Cole–Cole model corresponding to the SNP model were also found.The behaviour of model parameters is compared with experimental data obtained on natural and sieved sands using time domain technique. The natural sand spectra correspond neither to the simple SNP model nor simple Cole–Cole model with single time constant because the lengths of ion-selective zones vary, reflecting the grain-size distribution.The spectra of sieved sand compared with the theoretical SNP spectra reveal close correspondence between experimental data and theoretical parameters. For four sieved sands, both the theoretical and experimental data show that the time constant of the IP is proportional to the square of the average grain size.     

电离层极风的EISCAT-VHF雷达观测

极风现象从理论上提出已20多年了,实验上一直没有充分地证实这种现象的存在,以及它的形成区域位于高纬顶部电离层中.我们利用欧洲非相干散射协会（EISCAT）的VHF雷达（在挪威Tromsφ）,对H+离子极风进行了首次实验研究,结果表明,实验期间观测到H+离子在顶部电离层中的运动速度始终向上,且随高度的增加而增大,从而证实在高纬顶部电离层中确实存在着一个永久向上的H+离子流,即H+离子极风,其速度在1000km 高度上达到1km/s,其通量在此高度上接近于饱和,达到1012ms（-1）,而温度小于0.26eV.在我们的探测高度上仍未发展成超声速极风.     

等离子体片边界层内静电离子束流-密度漂移不稳定性

本文研究了地球磁尾等离子体片边界层内由离子束流和等离子体密度梯度联合作用产生的静电不稳定性.模型等离子体由向尾流动的冷离子束流、向地球流动的暖离子束流和背景暖电子组成,等离子体密度是非均匀的,等离子体β（热压强与磁压强之比值）很小,电子等离子体频率与电子退旋频率之比。ωe/Ωe》1.结果表明,斜传播的静电快、慢离子束流-密度漂移模能够被激发。     

Pore water evolution in oilfield sandstones: constraints from oxygen isotope microanalyses of quartz cement

Oxygen isotope microanalyses of authigenic quartz, in combination with temperatures of quartz precipitation constrained by fluid inclusion microthermometry and burial history modelling, are employed to trace the origin and evolution of pore waters in three distinct reservoirs of the Brae Formation in the Miller and Kingfisher Fields (North Sea). Oxygen isotope ratios of quartz cements were measured in situ in nine sandstone thin sections with a Cameca ims-4f ion microprobe. In conjunction with quartz cement paragenesis in the reservoirs, constrained from textural and cathodoluminescence (CL) microscopy studies, pore water evolution was reconstructed from the time of deposition of the sandstones in the Upper Jurassic until the present.CL photomicrographs of quartz overgrowths in the Brae Formation sandstones show three cement zones (A, B and C) which can be related to different oxygen isotope compositions: (1) the earliest, and thinnest, zone A (homogeneous CL pattern with probable δ¹⁸O values between +23‰ and +26‰—direct measurements were not possible) precipitated in the sandstones at temperatures <60 °C; (2) the second zone B (complex CL pattern and directly measured δ¹⁸O values between +15‰ and +18‰) precipitated in the sandstones most likely between 70 and 90 °C; (3) the third zone C (homogeneous CL pattern and directly measured δ¹⁸O values between +16‰ and +22‰) precipitated in the sandstones most likely at temperatures >90 °C. Calculated oxygen isotope compositions of pore waters show that zone A quartz cements, and enclosing concretionary calcite, precipitated from a meteoric-type fluid (∼−7‰) during shallow burial (<1.5 km). Zone B quartz cements precipitated from fluids which evolved in composition from a meteoric-type fluid (δ¹⁸O −7‰) to a more ¹⁸O-enriched fluid (δ¹⁸O −4‰) as burial continued to ∼3.0 km. Data from zone C quartz cements are consistent with further fluid evolution from δ¹⁸O −4‰ to basinal-type fluids with δ¹⁸O similar to the present-day formation water oxygen isotope composition (+0.6‰ at 4.0 km burial). A similar pore water evolution can be derived for all three reservoirs studied, indicating that hydrogeologic evolution was similar across sandstones of the whole Brae Formation.The quartz cement zones observed in the Brae Formation sandstones, and the pore water history derived for the area studied, is analogous to published petrographic and pore water evolution data from the nearby Brent Group reservoirs and from reservoirs located in the Haltenbanken area on the Atlantic margin offshore Norway. Considering quartz cement is a major porosity-occluding phase in many reservoir sandstones, and because pore waters both dissolve quartz and carry the dissolved silica to cementation sites, the data presented are valuable for improving the understanding and prediction of reservoir quality development in sandstones globally.     

连续流动分析法测定污水中阴离子表面活性剂、总氮、总磷、挥发酚、氰化物、硫化物的方法及实例

快速同时测定排污口样品中阴离子表面活性剂、总氮、总磷、挥发酚、氰化物、硫化物的分析方法。采用连续流动分析法,确定最佳实验方案。经多次试验验证,呈良好线性关系;质量控制样品测定值均在保证值范围内,样品回收率在95．2％～104％之间,RSD小于2％。     

硼特效树脂离子交换法分离B的研究

本文对Amberlite IRA 743 硼特效树脂交换分离B的特征及其影响因素进行了研究。它适用于各种地质样品中B的分离提取，特别是在B同位素地球化学研究时必须进行B纯化的场合。     

New perspectives on radium behavior within a subterranean estuary

Over the past decade, radium isotopes have been frequently applied as tracers of submarine groundwater discharge (SGD). The unique radium signature of SGD is acquired within the subterranean estuary, a mixing zone between fresh groundwater and seawater in coastal aquifers, yet little is known about what controls Ra cycling in this system. The focus of this study was to examine controls on sediment and groundwater radium activities within permeable aquifer sands (Waquoit Bay, MA, USA) through a combination of field and laboratory studies. In the field, a series of sediment cores and corresponding groundwater profiles were collected for analysis of the four radium isotopes, as well as dissolved and sediment associated manganese, iron, and barium. We found that in addition to greater desorption at increasing salinity, radium was also closely tied to manganese and iron redox cycling within these sediments. A series of laboratory adsorption/desorption experiments helped elucidate the importance of 1) contact time between sediment and water, 2) salinity of water in contact with sediment, 3) redox conditions of water in contact with sediment, and 4) the chemical characteristics of sediment on radium adsorption/desorption. We found that these reactions are rapid (on the order of hours), desorption increases with increasing salinity and decreasing pH, and the presence of Fe and Mn (hydr)oxides on the sediment inhibit the release of radium. These sediments have a large capacity to sorb radium from fresh water. Combined with these experimental results, we present evidence from time series groundwater sampling that within this subterranean estuary there are cyclic periods of Ra accumulation and release controlled by changing salinity and redox conditions.