Thermovibrational Instability Of Rayleigh-Marangoni-Benard Convection In Two-Layer Fluid Systems

The thermovibrational instability of Rayleigh-Marangoni-Benard convection in a two-layer system under the high-frequency vibration has been investigated by linear instability analysis in the present paper. General equations for the description of the convective flow and within this framework, the generalized Boussinesq approximation are formulated. These equations are dealt with using the averaging method. The theoretical analysis results show that the high-frequency thermovibrations can change the Marangoni-Benard convection instabilities as well as the oscillatory gaps of the Rayleigh-Marangoni-Benard convection in two-layer liquid systems. It is found that vertical high-frequency vibrations can delay convective instability of this system, and damp the convective flow down. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

有关多层流体对流的研究

简述多层不相混流体系统的研究发展，尤其是在空间材料生长过程中的应用；介绍多层流体系统内流体对流及传热现象，以及利用理论分析、实验研究和数值模拟方法研究二层及三层流体内的自然对流及热毛细对流的成果，并分析探讨覆盖液体层对被覆盖液体的动力控制特性及其系统的稳定性。

Ar~+和He~+离子与C_(60)碰撞后富勒希离子的激发机制

C60 在与重离子作用下的激发机制与入射离子能量、质量及电荷态有关。核阻止主要出现在低能重离子与C60 的碰撞中 ;而高能轻离子作用下 ,电子阻止迅速增强 ,成为主要的激发方式。本文中直接观察到由弹性碰撞引起的C+ 峰 ,及其丰度依赖于入射离子的质量。同时我们还发现电子阻止随入射离子能量 (7～ 2 0keV)增大相应增加 ,这与绝热量子分子动力学计算的结果一致。

An introduction to the trapping of clusters with ion traps and electrostatic storage devices

This paper presents an introduction to the application of ion traps and storage devices for cluster physics. Some experiments involving cluster ions in trapping devices such as Penning traps, Paul traps, quadrupole or multipole linear traps are briefly discussed. Electrostatic ion storage rings and traps which allow for the storage of fast ion beams without mass limitation are presented as well. We also report on the recently developed mini-ring, a compact electrostatic ion storage ring for cluster, molecular and biomolecular ion studies.

High negative ion production yield in 30 keV F2+ + adenine (C5H5N5) collisions

In collisions between slow F2+ ions (30 keV) and molecular targets, adenine, scattered particle production yields have been measured directly by simultaneous detection of neutrals, positive and negative ions. The relative cross-section for a negative ion formation channel was measured to be 1%. Despite a slight decrease compared to a larger target, the fullerene C-60, the measured negative ion formation cross section is still at least one order of magnitude larger than the yield in ion-atom interactions.

Excitation and dissociation of tungsten hexacarbonyl W(CO)(6): Statistical and nonstatistical dissociation processes

We have studied the excitation and dissociation processes of the molecule W(CO)(6) in collisions with low kinetic energy (3 keV) protons, monocharged fluorine, and chlorine ions using double charge transfer spectroscopy. By analyzing the kinetic energy loss of the projectile anions, we measured the excitation energy distribution of the produced transient dications W(CO)(6)(2+). By coincidence measurements between the anions and the stable or fragments of W(CO)(6)(2+), we determined the energy distribution for each dissociation channel. Based on the experimental data, the emission of the first CO was tentatively attributed to a nonstatistical direct dissociation process and the emission of the second or more CO ligands was attributed to the statistical dissociation processes. The dissociation energies for the successive breaking of the W-CO bond were estimated using a cascade model. The ratio between charge separation and evaporation (by the loss of CO+ and CO, respectively) channels was estimated to be 6% in the case of Cl+ impact. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3523347]

The Early Diagenetic Formation of Organic Sulfur in the Sediments of Mangrove Lake, Bermuda

Due to a low mineral content, the sapropelic sediments depositing in Mangrove Lake, Bermuda, provide an excellent opportunity to explore for possible additions of sulfur to organic matter during the early stages of diagenesis. We evaluated early diagenetic organic sulfur transformations by monitoring the concentrations and stable isotopic compositions of a number of inorganic and organic sulfur pools, thereby accounting for all of the sulfur in the sediments. We have identified and quantified the following sulfur pools: porewater sulfate, porewater sulfide, elemental sulfur, pyrite sulfur, hydrolyzable organic sulfur (HYOS), chromium-reducible organic sulfur (CROS), and nonchromium-reducible organic sulfur (Non-CROS). Of the organic sulfur pools, the Non-CROS pool is by far the largest, followed by CROS, and finally HYOS. By 60 cm depth these pools contribute, respectively, to 85, 7.9, and 3.6% of the total solid phase sulfur. The HYOS pool is probably of biological origin and shows no interaction with the sulfur compounds produced during diagenesis. By contrast, CROS is produced, most likely, from the diagenetic addition of polysulfides to functionalized lipids in the upper, H2S-poor, elemental sulfur-rich, region of the sediment. A portion of this sulfur pool is unstable and decomposes on contact with the H2S-rich porewaters. The portion of CROS that remains in the sulfidic waters appears to readily exchange sulfur isotopes with H2S. While some of the Non-CROS pool is of biological origin, some is also formed by the diagenetic addition of sulfur to organic compounds in the upper H2S-poor region of the sediment. By contrast with CROS, Non-CROS is not diagenetically active in the H2S-rich porewaters. Overall, somewhere between 27 and 53 % of the organic sulfur buried in Mangrove Lake sediments is of diagenetic origin, with the remaining organic sulfur derived from biosynthesis. We extrapolate our Mangrove Lake results and calculate that in typical coastal marine sediments between 11 and 29 μmol g−1 of organic sulfur will form during early diagenesis, of which 2–5 μmol g−1 will be chromium reducible.

Natural 13C abundance as a tracer for studies of soil organic matter dynamics

A method for measuring the long- and medium-term turnover of soil organic matter is described. Its principle is based on the variations of 13C natural isotope abundance induced by the repeated cultivations of a plant with a high 13C/12C ratio (C4 photosynthetic pathway) on a soil which has never carried any such plant. The 13C/12C ratio in soil organic matter being about equal to the 13C/12C ratio of plant materials from which it is derived, changing the 13C content of the organic inputs to the soil (by altering vegetation from C3 type into C4 type) is equivalent to a true labelling in situ of the organic matter. Two cases of continuous corn cultivation (Zea mays: δ13C = −12%.) on soils whose initial organic matter average δ13C is −26%. were studied. The quantity of organic carbon originating from corn (that is the quantity which had turned-over since the beginning of continuous cultivation) was estimated using the 13C natural abundance data. After 13 yr, 22% of total organic carbon had turned-over, in the system studied. Particle size fractions coarser than 50μm on the one hand, and finer than 2μm on the other. contained the youngest organic matters. The turnover rate of silt-sized fractions was slower