Hybrid Simulation of Collisionless Shock Formation in Support of Laboratory Experiments at Unr

The problem of producing collisionless shocks in the laboratory is of great interest for space and astrophysical plasmas. One approach is based on the idea of combining strong magnetic field (up to 100 Tesla) created during a Z-pinch discharge with a plasma flow produced in the process of the interaction of a laser pulse with a solid target. In support of laboratory experiments we present hybrid simulations of the interaction of the plasma flow with frozen in it magnetic field, with the spherical obstacle. Parameters of the flow correspond to a laser plasma ablation produced in the laboratory during irradiation of the target by a 3 J laser. Magnetic fields in the plasma flow and around the obstacle are created by the currents produced by the pulse power ZEBRA voltage generator. With the appropriate set of initial conditions imposed on the flow collisionless shocks can be created in such a system. Using independent generators for plasma flow and magnetic field allows for the exploration of a wide range of shock parameters. We present simulations of the formation of supercritical collisionless shock relevant to the experiment, performed with the 2D version of the hybrid code based on the CAM-CL algorithm [Planet. Space Sci. 51, 649, 2003].     

Mass Fractions of Forty‐Six Major and Trace Elements,Including Rare Earth Elements,in Sediment and Soil Reference Materials Used in Environmental Studies

Development of new techniques, enabling simultaneous determination of large numbers of elements in environmental samples, can force analysts to use certified reference materials that do not contain all the elements of interest. In this paper, the mass fractions of forty‐six major and trace elements, including rare earth elements (REE), are presented in one soil (NCS DC 77302 also known as GBW 07410) and five sediment (Metranal‐1, IAEA 405, MESS‐3, NCS DC 73309 also known as GBW 07311 and NCS DC 75301 also known as GBW 07314) certified reference materials determined by high resolution inductively coupled plasma‐mass spectrometry. The selected certified materials represent a spectrum of geological matrices often analysed in environmental studies. Measured elements include certified elements, elements listed with information values as well as new elements absent from certificates, including REEs and some other elements. REE + Y mass fractions in the river sediment reference material Metranal‐1 are reported for the first time. The results obtained are in agreement with available certified or information values.     

Laser Ablation In Situ Silicon Stable Isotope Analysis of Phytoliths

Silicon is a beneficial element for many plants and is deposited in plant tissue as amorphous bio‐opal called phytoliths. The biochemical processes of silicon uptake and precipitation induce isotope fractionation: the mass‐dependent shift in the relative abundances of the stable isotopes of silicon. At the bulk scale, δ³⁰Si ratios span from ?2 to +6‰. To further constrain these variations in situ, at the scale of individual phytolith fragments, we used femtosecond laser ablation multi‐collector inductively coupled plasma‐mass spectrometry (fsLA‐MC‐ICP‐MS). A variety of phytoliths from grasses, trees and ferns were prepared from plant tissue or extracted from soil. Good agreement between phytolith δ³⁰Si ratios obtained by bulk solution MC‐ICP‐MS analysis and in situ isotope ratios from fsLA‐MC‐ICP‐MS validates the method. Bulk solution analyses result in at least twofold better precision for δ³⁰Si (2s on reference materials ≤ 0.11‰) over that found for the means of in situ analyses (2s typically ≤ 0.24‰). We find that bushgrass, common reed and horsetail show large internal variations up to 2‰ in δ³⁰Si, reflecting the various pathways of silicon from soil to deposition. Femtosecond laser ablation provides a means to identify the underlying processes involved in the formation of phytoliths using silicon isotope ratios.     

Effect of the IMF B y component on the ionospheric flow overhead at EISCAT: observations and theory

We have analysed a database of 300 h of tristatic ionospheric velocity measurements obtained overhead at Tromsø (66.3° magnetic latitude) by the EISCAT UHF radar system, for the presence of flow effects associated with the y-component of the IMF. Since it is already known that the flow depends upon IMF B_z, a least-squares multivariate analysis has been used to determine the flow dependence on both IMF B_y and B_z simultaneously. It is found that significant flow variations with IMF B_y occur, predominantly in the midnight sector (2100/0300 MLT), but also pre-dusk (1600/1700 MLT), which are directed eastward for IMF B_y positive and westward for IMF B_y negative. The flows are of magnitude 20/30 m s^–1 nT^–1 in the midnight sector, and smaller, 10/20 m s^–1 nT^–1, pre-dusk, and are thus associated with significant changes of flow of order a few hundred m s^–1 over the usual range of IMF B_y of about ±5 nT. At other local times the IMF B_y-related perturbation flows are much smaller, less than 5 m s^–1 nT^–1, and consistent with zero within the uncertainty estimates. We have investigated whether these IMF B_y-dependent flows can be accounted for quantitatively by a theoretical model in which the equatorial flow in the inner magnetosphere is independent of IMF B_y, but where distortions of the magnetospheric magnetic field associated with a penetrating component of the IMF B_y field changes the mapping of the field to the ionosphere, and hence the ionospheric flow. We find that the principal flow perturbation produced by this effect is an east-west flow whose sense is determined by the north-south component of the unperturbed flow. Perturbations in the north-south flow are typically smaller by more than an order of magnitude, and generally negligible in terms of observations. Using equatorial flows which are determined from EISCAT data for zero IMF B_y, to which the corotation flow has been added, the theory predicts the presence of zonal perturbation flows which are generally directed eastward in the Northern Hemisphere for IMF B_y positive and westward for IMF B_y negative at all local times. However, although the day and night effects are therefore similar in principle, the model perturbation flows are much larger on the nightside than on the dayside, as observed, due to the day-night asymmetry in the unperturbed magnetospheric magnetic field. Overall, the model results are found to account well for the observed IMF B_y-related flow perturbations in the midnight sector, in terms of the sense and direction of the flow, the local time of their occurrence, as well as the magnitude of the flows (provided the magnetic model employed is not too distorted from dipolar form). At other local times the model predicts much smaller IMF B_y-related flow perturbations, and thus does not account for the effects observed in the pre-dusk sector.     

电感耦合等离子体发射光谱法直接测定地质试样中铀

采用电感耦合等离子体发射光谱对地质试样中高低含量的铀的直接测定方法进行了研究，选择了仪器的最佳工作条件，考察了共存元素对测定的干扰情况。选定条件下，方法的检出限在λＵ３８５．９５８ｎｍ和４０９．０１４ｎｍ分别０．６μｇ／ｇ和０．７μｇ／ｇ，检测范围可以在ω（Ｕ）１０＾－６－１０＾－２水平。     

流动注射—电感耦合等离子体质谱应用现状及进展

从样品引入、在线稀释、在线同位素稀释、在线气体发生、在线分离预浓集和其他在线处理手段等方面对流动注射－电感耦合等离子体质谱的应用进行了描述，对其发展进行了展望。引用文献91篇。     

Lightning-generated waves escaping out through plasma holes in the nightside Venus ionosphere

The plasma waves in the Venus ionosphere measured by OEFD aboard PVO are analysed. It is shown that these waves are generated by lightning like cloud-to-cloud discharges anywhere in the Venus ionosphere-surface waveguide. The theoretical minimum attenuation for waveguide mode propagation at 5.4 kHz is consistent with the maximum occurrence rate at this frequency. The lightning-generated and globally-propagating signals when encountered with plasma holes or ion-trough structures escape out partially and are detected by the OEFD aboard PVO. The 100 Hz signals can propagate upwards in whistler mode. Even the localized electrostatic mode waves would be converted into electromagnetic waves in the plasma holes and ion-trough regions.     

电感耦合等离子体发射光谱法间接测定煤中氯

拟定了高压氧弹燃烧处理煤样品，电感耦合等离子体发射光谱法间接测定煤中氯含量的方法。方法经国家一级煤标准物质分析验证，结果与标准值相符，11次测定的相对标准偏差＜5％。     

全谱直读等离子体发射光谱法测定高纯金中的杂质元素

用新型号的全谱直读等离子体发射光谱仪测定了高纯金中的杂质元素，进行了分析谱线的选择，功率、气体流量等工作条件的优化，选用内标法校正标准溶液与样品溶液基体不同的影响。取样量为0．5g时，方法的测定下限为0．02～4．67μg/g，回收率在90％～101％，当待测元素含量大于5μg/g时，分析结果的相对标准偏差小于5％。方法用于实际样品的分析，结果与其他方法相符。     

Accurate quantification of melt inclusion chemistry by LA-ICPMS: a comparison with EMP and SIMS and advantages and possible limitations of these methods

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) has recently emerged as a powerful in situ microanalytical technique for major to trace elements in heterogeneous samples such as fluid and melt inclusions. Here, a rigorous comparison of melt inclusion (MI) data acquired by electron microprobe (EMP), ion microprobe (the secondary ion mass spectrometry, SIMS) and LA-ICPMS is used to evaluate the applicability and advantages/drawbacks of these approaches. We are specifically interested in determining if LA-ICPMS data on entire, unexposed, crystallized MI that cannot be homogenized in the lab are accurate and of a useful precision.

Quantification of LA-ICPMS MI signals requires the use of an internal standard, i.e., the concentration of one element, or an element ratio, at the time of MI entrapment must be known independently, in order to derive the pure MI composition from the MI plus host mixed signal. Analysis of plagioclase-hosted glassy MI of a mid-ocean ridge basalt (MORB) sample from the East Pacific Rise illustrates that melt inclusion chemistry can be accurately quantified by LA-ICPMS, including the correction for postentrapment sidewall crystallisation of the host mineral without prior reheating in the lab.

The LA-ICPMS data obtained on crystallized MI demonstrate agreement with the EMP and SIMS data on exposed glassy MI at the 1 standard deviation uncertainty level except for a few elements close to their limits of detection. LA-ICPMS data reduction schemes include the quantification of analytical uncertainty on each element of single MI. Therefore, weighted average element concentrations can be obtained for MI assemblages, at precisions that compare well with those of average element concentrations obtained by EMP and SIMS.

Simple sample preparation minimizing inclusion loss through polishing combined with the analytical efficiency of 50 inclusions plus neighbouring host mineral at up to 40 elements per day enable the collection of statistically relevant datasets by LA-ICPMS. These allow to recognize nonrepresentative MI (e.g., heterogeneous entrapment). Application to individual clinopyroxene crystals from the AD79 pumice horizon of Mt. Somma-Vesuvius reveals chemical variability that exceeds the analytical precision on single melt inclusions. This variability was not obvious from the limited data set obtained by SIMS and EMP.

The largest source of nonquantifiable error for EMP and SIMS data stems from the requirement of reheating the melt inclusions in the lab in order to reverse postentrapment crystallisation onto inclusion walls or growth of crystallites. For LA-ICPMS analysis of unexposed MI, the reliability with which the internal standard (IS) element concentration is known determines the quality of the data. LA-ICPMS, however, cannot analyse H₂O, F, S and Cl reliably, has higher limits of detection (LODs) than SIMS for some elements for MI below 25 μm, has lower spatial resolution than both EMP and SIMS and consumes much more sample per analysis. Therefore, EMP, SIMS and LA-ICPMS are complementary in MI research, and the type of application will determine the analytical method or methods of choice.