Subsonic Radiation Gas Dynamics in a Laser Plasma Generator Channel

The radiation gasdynamic processes in the channel of an air laser plasma generator operating at atmospheric pressure are analyzed. In the multigroup approximation a numerical radiation gasdynamic model is formulated on the basis of the equations of motion of a viscous heat-conducting gas and the selective thermal radiation transport equation. Laminar and turbulent subsonic generator operation regimes are considered.For the purpose of approximately describing the turbulent gas and plasma mixing the Navier-Stokes equations averaged after Reynolds and the k-ε turbulence model are used. The problem is solved in the time-dependent two-dimensional axisymmetric formulation.Strong radiation-gasdynamic interaction regimes are investigated. In these regimes the energy losses due to radiation from the high-temperature region of the laser plasma and the absorption of its thermal self-radiation by the surrounding plasma and gas layers (radiation reabsorption) appreciably affect the gasdynamic flow structure. Two methods of integrating the selective thermal radiation transport equation in the generator channel are discussed. In one of these the thermal radiation transport is calculated inside the heated volume and in the other the radiation heat fluxes are calculated on the surfaces bounding the volume. The results of calculating the spectral and integral radiation heat fluxes on the inner surface of the generator are given.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 126–143.Original Russian Text Copyright © 2005 by Surzhikov.     

Investigations of Droplet‐Plasma Interaction using Multi‐Dimensional Coupled Model

Recently developed multi‐dimensional coupled fluid‐droplet model is used to investigate the behavior of complex interaction between the liquid precursor droplets and atmospheric pressure plasma (APP). The significance of this droplet‐plasma interaction is not well understood under diverse realm of working conditions in two‐phase flow. In this study, we explain the implication of vaporization of liquid droplets in APP which are subsequently responsible to control major characteristics of surface coating depositions. Coalescence of water droplets is more dominant than Hexamethyldisiloxane (HMDSO) droplets because of its sluggish rate of evaporation. A disparity in the performance of evaporation is identified in two independent mediums, such as gas mixture and discharge plasma using HMDSO precursor. The length of evaporation of droplets is amplified by an increment of gas flow rate indicating with a reduction in the gas temperature and electron mean energy. In particular, the spatio‐temporal density distributions of charged particles show a clear pattern in which the typical nitrogen impurity ions are primarily effective as compared to other helium ionic species along the pulse of droplets in APP. Finally, we contrast the behavior of discharge species in the pure helium and He‐N2 gas mixtures revealing the importance of stepwise and Penning ionization processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A New Scheme for High‐Intensity Laser‐Driven Electron Acceleration in a Plasma

We propose a new approach to high‐intensity relativistic laser‐driven electron acceleration in a plasma. Here, we demonstrate that a plasma wave generated by a stimulated forward‐scattering of an incident laser pulse can be in the longest acceleration phase with injected relativistic beam electrons. This is why the plasma wave has the maximum amplification coefficient which is determined by the acceleration time and the breakdown (overturn) electric field in which the acceleration of the injected beam electrons occurs. We must note that for the longest acceleration phase the relativity of the injected beam electrons plays a crucial role in our scheme. We estimate qualitatively the acceleration parameters of relativistic electrons in the field of a plasma wave generated at the stimulated forward‐scattering of a high‐intensity laser pulse in a plasma. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

From Field Emission to Vacuum Arc Ignition: A New Tool for Simulating Copper Vacuum Arcs

Understanding plasma initiation in vacuum arc discharges can help to bridge the gap between nano‐scale triggering phenomena and the macroscopic surface damage caused by vacuum arcs. We present a new twodimensional particle‐in‐cell tool to simulate plasma initiation in direct‐current (DC) copper vacuum arc discharges starting from a single, strong field emitter at the cathode. Our simulations describe in detail how a sub‐micron field emission site can evolve to a macroscopic vacuum arc discharge, and provide a possible explanation for why and how cathode spots can spread on the cathode surface. Furthermore, the model provides us with a prediction for the current and voltage characteristics, as well as for properties of the plasma like densities, fluxes and electric potentials in a simple DC discharge case, which are in agreement with the known experimental values. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron Temperatures and Electron Densities in Microwave Helium Discharges with Pressures Higher than 0.1 MPa

We adopted laser Thomson scattering for measuring the electron density and the electron temperature of microwave plasmas produced in helium at the pressures higher than the atmospheric pressure. The electron density decreased while we observed the increase in the electron temperature with the pressure. These are reasonable results by considering the decrease in the reduced electric field, the dominant loss of electrons via three‐body recombination with helium as the third body, and the production of electrons with medium energy via heavy particle collisions at the high gas pressure. The temporal variation of the electron temperature had the rise and the fall time constants of approximately 10 ns. The rapid heating and cooling of the electron temperature are due to the fast energy transfer from electrons to helium because of the high collision frequency in the high‐pressure discharge. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Doubly‐Charged Xe Ions Evidenced by Time Resolved RPA Measurement in the Far Field Plume of a Low‐Power HET

A low power Hall Effect Thruster (HET), based on a permanent magnet circuit, was investigated in the GREMI laboratory facility. The thruster operated in the working range between 50 and 300 W and the previously measured thrust is between 4 and 16 mN for an anodic efficiency respectively between 15% and 27%. The pulsed character of the thruster current is an important feature of this HET. The ion current's bursts are recorded at 30 and 70 cm from the exit plane in the thruster plume and are time‐resolved, which lead to a preliminary analysis of the time of flight (TOF) phenomena. This paper presents a detailed study of these bursts of ion current in the plume. The total ion current is shown to be a superposition of 2 distinct contributions of charged species. In complement, a controlled single current interruption in stable anodic current condition leads to exactly the same features than in oscillating mode. This crucial verification garantees the validity of the time of flight origine of the two distinct contributions. Then, the slower one is the more intense and is proportional to the ion Xe+ current whereas the faster one could be attributed either to doubly‐charged Xe⁺⁺ or to superfast Xe⁺. The work presents a way to determine unambiguously the nature of the fast contribution by recording the Retardated Potential Analyser (RPA) signals at various repelling grid potentials with respect to time. The energy distribution of the 2 wellseparated contributions are reconstructed and confirms the contribution of doubly‐charged xenon ions (Xe⁺⁺) in the plume. This way of RPA collecting data and interpretation presents the main advantage tobe an easy way for the identification of the nature of the charged species in the plume. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Si/Ge/Si异质横向SPiN二极管固态等离子体解析模型

采用横向表面PiN(SPiN)二极管构造的硅基可重构天线具有众多优于传统天线的独特优势, 是实现天线小型化和提升雷达与微波通信系统性能的有效技术途径. 本文提出一种Si/Ge/Si异质横向SPiN二极管, 并基于双极扩散模型与Fletcher型边界条件, 在大注入条件下建立了二极管结电压、电流密度与本征区固态等离子体浓度分布解析模型, 并数值模拟分析了本征区长度、P⁺与N⁺区掺杂浓度、外加电压对所建模型的影响. 结果表明, 固态等离子体浓度随本征区长度的增加下降, 随外加电压的增加而指数上升, 随P⁺与N⁺区掺杂浓度的提高而上升, 电流密度随外加电压的增加而指数上升. 同等条件下, 异质SPiN二极管的固态等离子体浓度相比同质二极管提高近7倍以上. 本文所建模型为硅基可重构天线的设计与应用提供有效的参考.     

Decrease of dynamic range of proteins in human plasma by ampholine immobilized polymer microspheres

A novel protein sample pretreatment method based on ampholine immobilized polymer microsphere (ampholine@PM) was developed for the fractionation of intact proteins prior to protein digestion and peptide analysis to reduce the dynamic range of human plasma proteome. After incubation with our prepared ampholine@PM, the captured plasma proteins were successively desorbed by 2 M NaCl, 100 mM glycine-hydrochloric acid, and 30% (v/v) acetonitrile with 0.1% (v/v) trifluoroacetic acid. The SDS-PAGE results showed the protein dynamic range in such three fractions was obviously reduced as compared with the native plasma. On-particle digestion was ultimately performed to release all proteins retained on ampholine@PM. Followed by MuPIT analysis, the number of identified proteins in plasma was improved by 75% after ampholine@PM treatment. Furthermore, the spectral count of 9 high abundance proteins was decreased by 37.6–97.2%, and the identified low abundance protein (<100 ng mL⁻¹) number was increased from 4 to 17. These results demonstrated that the fractionation by ampholine@PM could efficiently decrease the protein dynamic range in abundance, beneficial to achieve the deep coverage identification of human plasma proteome.     

Direct determination of mercury in cosmetic samples by isotope dilution inductively coupled plasma mass spectrometry after dissolution with formic acid

A new method was proposed for the accurate determination of mercury in cosmetic samples based on isotopic dilution (ID)-photochemical vapor generation (PVG)-inductively coupled plasma mass spectrometry (ICP MS) measurement. Cosmetic samples were directly dissolved in formic acid solution and subsequently subjected to PVG for the reduction of mercury into vapor species following by ICP MS detection. Therefore, the risks of analyte contamination and loss were avoided. Highly enriched ²⁰¹Hg isotopic spike is added to cosmetics and the isotope ratios of ²⁰¹Hg/²⁰²Hg were measured for the quantitation of mercury. With ID calibration, the influences originating from sample matrixes for the determination of mercury in cosmetic samples have been efficiently eliminated. The effects of several experimental parameters, such as the concentration of the formic acid, and the flow rates of carrier gas and sample were investigated. The method provided good reproducibility and the detection limits were found to be 0.6 pg mL⁻¹. Finally, the developed method was successfully applied for the determination of mercury in six cosmetic samples and a spike test was performed to verify the accuracy of the method.     

Picomole‐level Formaldehyde Determination in Gaseous and Beer Samples Using Flow Injection Chemiluminescence Analysis

Based on the linear enhancement of formaldehyde (FA) within 7.0 ～ 1000 pmol l^?1 on luminol—bovine serum albumin (BSA) chemiluminescence (CL) system, FA determination in air and beer samples using CL with flow injection (FI) was proposed. The detection limit was 2.5 pmol l^?1 (3σ) and the relative standard deviations were less than 4.5% (n = 7). At a flow rate of 2.0 mL min^?1, a whole analysis from sampling to washing only needed 32 s, offering a sample throughput of 112 h^?1. This proposed method was successfully utilized to determine FA vapor pressure in liquid (121.8 ± 3.8 Pa), FA content in real air sample (8.93 ± 0.03 mg m^?3), and FA levels in beer (199.5 ± 5.6 ～ 225.2 ± 3.5 mg l^?1), giving determination recoveries from 90.7% to 109.3%. The mechanism of BSA—FA interaction was also investigated, showing FA binding to BSA was a spontaneous process mainly through hydrogen bonding and van der Waals force by FI‐CL, with binding constant K of 1.89 × 10⁶ l mol^?1 and the number of binding sites n of 0.86. Molecular docking analysis further revealed FA could enter into the pocket at subdomain IIA of BSA, with K of 1.71 × 10⁵ l mol^?1 and ΔG of ‐29.68 kJ mol^?1.