Plasma diagnostics and simulation for the SMART-1 mission     

M. Tajmar  J. Gonzlez  G. Saccoccia  G. Noci  H. Laakso 《Planetary and Space Science》2002,50(14-15)

SMART-1 is a technology demonstrator for using primary electric propulsion on interplanetary spacecraft. Hence, studying of the interaction of the plasma emitted by the thruster with the environment and the spacecraft is one of the top priorities during the mission. Two experiments (Electronic propulsion diagnostic package and Spacecraft potential, electron and dust experiment) are available to measure the electron densities and temperatures as well as wave electric fields during the operation of the electric propulsion thruster. Additionally, a retarding potential analyser, a quartz microbalance and a solar-cell sample will analyse data from slow charge-exchange ions which are a potential contamination source. ESTEC is developing a 3D particle-in-cell model in order to study the spacecraft/environment interactions on SMART-1 and interpret the measurements. In the present paper, we will review the contamination effects associated with electric propulsion and how the plasma sensors cover them. We further present preliminary results from the numerical simulation and show how the flight data will be used to validate the modelling code. A successful validation of the simulation will support future interplanetary and commercial missions featuring electric propulsion to reduce the risk of contamination and interference with on board instruments.  相似文献   

Preliminary study on plasma membrane fluidity of Psychrophilic Yeast Rhodotorula sp.NJ298 in low temperature     

唐海田  郑洲  缪锦来  刘均铃  阚光峰 《极地研究(英文版)》2007,18(1):63-72

The ability of cell to modulate the fluidity of plasma membrane was crucial to the survival of microorganism at low temperature. Plasma membrane proteins, fatty acids and carotenoids profiles of Antarctic psychrophilc yeast Rhodotorula sp. NJ298 were investigated at -3 ℃, 0 ℃ and 8 ℃. The results showed that plasma membrane protein content was greater at -3 ℃ than that at 8 ℃, and a unique membrane polypeptide composition with an apparent molecular mass of 94.7 kDa was newly synthesized with SDS-PAGE analysis; GC analysis showed that the main changes of fatty acids were the percentage of unsaturated fatty acids (C18∶ 1 and C18∶ 2) and shorter chain saturated fatty acid (C10∶ 0) increased along with the decrease of the culture temperature from 8 ℃ to -3 ℃; HPLC analysis indicated that astaxanthin was the major functional carotenoids of the plasma membrane, percentage of which increased from 54.6±1.5% at 8 ℃ to 81.9±2.1% at -3 ℃. However the fluidity of plasma membrane which was determined by measuring fluorescence anisotropy was similar at -3 ℃, 0 ℃ and 8 ℃. Hence these changes in plasma membrane's characteristics were involved in the cellular cold-adaptation by which NJ298 could maintain normal plasma membrane fluidity at near-freezing temperature.  相似文献   

Experimental Design for the Laboratory Simulation of Magnetized Astrophysical Jets     

Radu Presura  Stephan Neff  Lucas Wanex 《Astrophysics and Space Science》2007,307(1-3):93-98

Concepts of several experimental configurations for the investigation of magnetized jets and their interaction with magnetized environments are presented. In the planned experiments, the plasma jets will be created by laser ablation of shaped targets, while magnetic and electric fields with the required configurations will be produced independently by a pulsed power generator. In particular, the recently coupled Terawatt laser Tomcat and Terawatt pulsed power generator Zebra will be used for experiments.  相似文献   

Magnetic field rearrangement by accelerated particles near a shock front     

A. Z. Dolginov  N. I. Podol'skaya  I. N. Toptygin 《Astronomy Letters》2004,30(3):169-178

We solve the self-consistent problem of the generation of a static magnetic field by the electric current of accelerated particles near a strong plane MHD shock front. We take into account the back reaction of the field on the particle diffusion tensors and the background plasma parameters near the front. Various states that differ significantly in static magnetic-field strength are shown to be possible near a strong front. If the initial field has a component normal to the front, then its components parallel to the front are suppressed by accelerated particles by several orders of magnitude. Only the component perpendicular to the front remains. This field configuration for uniform particle injection at the front does not lead to the generation of an additional field, and, in this sense, it is stable. If the initial field is parallel to the front, then either its significant enhancement by two or three orders of magnitude or its suppression by several orders of magnitude is possible. The phenomenon under consideration is an example of the self-organization of plasma with a magnetic field in a strongly nonequilibrium system. It can significantly affect the efficiency of particle acceleration by the shock front and the magnetobremsstrahlung of the accelerated particles.  相似文献   

A nonlinear theory of stellar wind with allowance for the influence of relativistic particles     

D. G. Logunov  I. N. Toptygin 《Astronomy Letters》2002,28(4):241-250

We solve the nonlinear problem of the dynamics of a steady-state, spherically symmetric stellar wind by taking into account particle acceleration to relativistic energies near the shock front. The particles are assumed to be accelerated through the Fermi mechanism, interacting with stellar-wind turbulence and crossing many times the shock front that separates the supersonic and subsonic stellar-wind regions. We take into account the influence of the accelerated particles on hydrodynamic plasma-flow parameters. Our method allows all hydrodynamic parameters of the shock front and plasma in the supersonic region to be determined in a self-consistent way and the accelerated-particle energy spectrum to be calculated. Our numerical and analytic calculations show that the plasma compression ratio at the shock front increases compared to the case where there are no relativistic particles and that the velocity profile in the supersonic region acquires a characteristic kink. The shape of the energy spectrum for the accelerated particles and their pressure near the front are essentially determined by the presumed dependence of the diffusion coefficient on particle energy, which, in turn, depends on the scale distribution of turbulent pulsations and other stellar-wind inhomogeneities.  相似文献   

电感耦合等离子体发射光谱法测定磷矿中有效五氧化二磷     

张会芳 《化工矿产地质》2016,(4):246-249

利用电感耦合等离子体发射光谱测定磷矿中的有效五氧化二磷,样品采用柠檬酸浸提处理,干过滤,滤液引入电感耦合等离子体发射光谱测定。这种方法与传统分光光度法测定有效五氧化二磷相比较,能很好的测定磷矿中有效五氧化二磷,相对标准偏差较低,结果准确。  相似文献   

High‐Precision Measurement of Molybdenum Isotopic Compositions of Selected Geochemical Reference Materials          下载免费PDF全文

Jin Li  Xiang‐kun Zhu  Suo‐han Tang  Kan Zhang 《Geostandards and Geoanalytical Research》2016,40(3):405-415

Here we describe high‐precision molybdenum isotopic composition measurements of geological reference materials, performed using multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS). Purification of Mo for isotopic measurements was achieved by ion exchange chromatography using Bio‐Rad AG^® 1‐X8 anion exchange resin. Instrumental mass bias was corrected using ¹⁰⁰Mo‐⁹⁷Mo double spiking techniques. The precision under intermediate measurement conditions (eighteen measurement sessions over 20 months) in terms of δ^98/95Mo was 0.10‰ (2s). The measurement output was approximately four times more efficient than previous techniques, with no compromise in precision. The Mo isotopic compositions of seven geochemical reference materials, seawater (IAPSO), manganese nodules (NOD‐P‐1 and NOD‐A‐1), copper‐molybdenum ore (HV‐2), basalt (BCR‐2) and shale (SGR‐1b and SCo‐1), were measured. δ^98/95Mo values were obtained for IAPSO (2.25 ± 0.09‰), NOD‐P‐1 (?0.66 ± 0.05‰), NOD‐A‐1 (?0.48 ± 0.05‰), HV‐2 (?0.23 ± 0.10‰), BCR‐2 (0.21 ± 0.07‰), SCo‐1 (?0.24 ± 0.06‰) and SGR‐1b (0.63 ± 0.02‰) by calculating δ^98/95Mo relative to NIST SRM 3134 (0.25‰, 2s). The molybdenum isotopic compositions of IAPSO, NOD‐A‐1 and NOD‐P‐1 obtained in this study are within error of the compositions reported previously. Molybdenum isotopic compositions for BCR‐2, SCo‐1 and SGR‐1b are reported for the first time.  相似文献   

Calcium Carbonate and Phosphate Reference Materials for Monitoring Bulk and Microanalytical Determination of Sr Isotopes          下载免费PDF全文

Michael Weber  Federico Lugli  Klaus Peter Jochum  Anna Cipriani  Denis Scholz 《Geostandards and Geoanalytical Research》2018,42(1):77-89

In situ laser ablation analyses rely on the microanalytical homogeneity of reference materials (RMs) and a similar matrix and mass fraction between unknown samples and RMs to obtain reliable results. Suitable carbonate and phosphate RMs for determination of Sr isotope ratios in such materials are limited. Thus, we determined ⁸⁷Sr/⁸⁶Sr ratios of several carbonate (JCt‐1, JCp‐1, MACS‐1, MACS‐3) and phosphate (MAPS‐4, MAPS‐5, NIST SRM 1400, NIST SRM 1486) international RMs using dissolved samples and two different multi‐collector inductively coupled plasma‐mass spectrometers (MC‐ICP‐MS). Our Sr isotope data are in agreement with published data and have an improved measurement precision for some RMs. For MACS‐1, we present the first ⁸⁷Sr/⁸⁶Sr value. We tested the suitability of these materials for microanalytical analyses by LA‐MC‐ICP‐MS, with two different laser ablation systems: a conventional nanosecond laser and a state‐of‐the‐art femtosecond laser. We investigated the RMs micro‐homogeneity and compared the data with our solution data. Both laser ablation systems yielded identical ⁸⁷Sr/⁸⁶Sr ratios within uncertainty to the solution data for RMs with low interferences of REEs. Therefore, these carbonate and phosphate RMs can be used to achieve accurate and precise results for in situ Sr isotope investigations by LA‐MC‐ICP‐MS of similar materials.  相似文献   

不同温度真空热处理对FeCrMoCBY非晶合金涂层组织结构与摩擦学性能的影响研究          下载免费PDF全文

李润杰  章昕怡  康嘉杰  岳文  梁健  付志强  朱丽娜  张然 《探矿工程》2021,48(S1):61-69

深部地质钻探过程中,复杂的井下工况对钻具的钻探性能以及可靠性提出了苛刻的要求。钻具钢体表面涂覆具有耐磨耐蚀性的非晶涂层可以有效提高其服役寿命。其中Fe基非晶合金涂层因其优异的耐腐蚀抗磨损性能、较强的非晶形成能力等优势,具有重要的应用价值和较好的经济效益。本文通过大气等离子喷涂技术（Air Plasma Spray, APS）在35CrMo基体上制备得到成分为Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ （at.%）的非晶合金涂层,并对其进行不同温度的真空热处理,探究了不同温度热处理对涂层基本性能和磨损失效机制的影响。结果表明：涂层经过真空热处理之后,生成的大量硬质相和成分均匀化使得涂层抗磨损性能提高;且随着热处理温度的提高,涂层磨损率逐渐减小。与未经热处理和750 ℃热处理的涂层相比,经过850 ℃热处理之后的涂层具有最佳的抗磨损性能,磨损率仅为未经热处理的Fe基非晶涂层的16.7%。热处理前后涂层的失效机制均为粘着磨损、磨粒磨损、疲劳磨损和氧化磨损。  相似文献   

Fine structure of decametric type II radio bursts     

G. P. Chernov  A. A. Stanislavsky  A. A. Konovalenko  E. P. Abranin  V. V. Dorovsky  G. O. Rucker 《Astronomy Letters》2007,33(3):192-202

We have performed a comparative analysis of the fine structure of two decametric type II bursts observed on July 17 and August 16, 2002, with the 1024-channel spectrograph of the UTR-2 radio telescope in the frequency range 18.5–29.5 MHz and with the IZMIRAN spectrograph in the frequency range 25–270 MHz. The August 16 burst was weak, ～2–5 s.f.u., but exhibited an unusual fine structure in the form of broadband fibers (Δf _e > 250–500 kHz) that drifted at a rate characteristic of type II bursts and consisted of regular narrow-band fibers (Δf _e > 50–90 kHz at 24 MHz) resembling a rope of fibers. The July 17 burst was three orders of magnitude more intense (up to 4500 s.f.u. at 20 MHz) and included a similar fiber structure. The narrow fibers were irregular and shorter in duration. They differed from an ordinary rope of fibers by the absence of absorption from the low-frequency edge and by slow frequency drift (slower than that of a type II burst). Both type II bursts were also observed in interplanetary space in the WIND/WAVES RAD2 spectra, but without any direct continuation. Analysis of the corresponding coronal mass ejections (CMEs) based on SOHO/LASCO C2 data has shown that the radio source of the type II burst detected on August 16 with UTR-2 was located between the narrow CME and the shock front trailing behind that was catching up with the CME. The July 17 type II fiber burst also occurred at the time when the shock front was catching up with the CME. Under such conditions, it would be natural to assume that the emission from large fibers is related to the passage of the shock front through narrow inhomogeneities in the CME tail. Resonant transition radiation may be the main radio emission mechanism. Both events are characterized by the possible generation of whistlers between the leading CME edge and the shock front. The whistlers excited at shock fronts manifest themselves only against the background of enhanced emission from large fibers (similar to the continuum modulation in type IV bursts). The reduction in whistler group velocity inside inhomogeneities to 760 km s^?1 may be responsible for the unusually low drift rate of the narrow fibers. The magnetic field inside inhomogeneities determined from fiber parameters at 24 MHz is ～0.9 G, while the density should be increased by at least a factor of 2.  相似文献