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991.
Processes which occur in microwave discharges of dilute mixtures of SF6 and O2 in He have been examined using a flow reactor sampled by a mass spectrometer. Two classes of experiments were performed. In the first set of experiments, mixtures containing 6×1011 cm–3 SF6, 6×1016 cm–3 He, and O2 in the range (0–3.6)×1013 cm–3 were passed through a 20-W 2450-MHz microwave discharge. The gas mixtures arriving at a sample point downstream from the discharge were examined for SF6, SF4, SOF2, SOF4, SO2F2, SO2, F, and O. In the second class of experiments, rate coefficients were measured for the reactions of SF4 with O and O2 and for the reaction of SF with O. The rate coefficient for the reaction of SF with O was found to be (4.2±1.5)×10–11 cm–3 s–1. SF4 was found to react so slowly with both oxygen atoms and oxygen molecules that only upper limits could be placed on the rate coefficients for these reactions. These values were 2×10–14 cm3 s–1 and 5×10–15 cm3 s–1 for reactions with O and O2 respectively. The observed distribution of products from the discharged mixtures is discussed in terms of the measured rate coefficients. 相似文献
992.
相转移催化下双媒质体系对醇类的选择性间接电氧化 总被引:5,自引:0,他引:5
在相转移催化剂(Bu4NHSO4)作用下,用Cr(Ⅵ)/Cr(Ⅲ)及Ag(Ⅱ)/Ag(Ⅰ)双媒质体系对醇类进行间接电氧化,产率为75.4~97.5%,电流效率达60.2~75.8%,双媒质体系可重复使用。 相似文献
993.
994.
Pavla Kaparov Markus Antonietti Helmut Clfen 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):153-162
The synthesis and folding behavior of two different series of double hydrophilic block copolymers based on polyethyleneglycol and short acidic polypeptide blocks are described. The employment of those species in the crystallization of CaCO3 and BaSO4 shows that in contrast to the expectations from biomineral examples, a random conformation of the peptide is more advantageous in mineralization control than an -helical arrangement of the same chain, which is contradictory to the epitaxial adsorption model in biomineralization. Otherwise, the peptide block copolymers support formation of superstructures similar to those already reported, e.g. well-defined spherical, prolate, and dumbbell morphologies are found. 相似文献
995.
本文提出了精确固定节面量子Monte Carlo差值法,这个新算法能够在精确固定节面量子Monte Carlo方法的基础上直接计算两个体系之间的能量差,且使计算结果的统计误差达到10-2
kJ/mol 数量级,获得电子相关能90%以上。我们把这个新算法应用于分子势能面的研究中,使用一个“刚性移动”模型,利用Jacobi变换使分子两个几何构型的能量计算具有很好的正相关性,因而能得到准确的能量差值,于是精确的分子势能面就可以得到。这个新算法已经被使用到BH分子基态势能曲线和H3分子势能面的研究。这个算法还可应用于分子光谱、化学反应能量变化值等领域的研究。 相似文献
996.
A.M. El Sherbini Th.M. El Sherbini H. Hegazy G. Cristoforetti S. Legnaioli V. Palleschi L. Pardini A. Salvetti E. Tognoni 《Spectrochimica Acta Part B: Atomic Spectroscopy》2005,60(12):1573-1579
In quantitative Laser Induced Breakdown Spectroscopy (LIBS) measurements it is essential to account for the effect of self-absorption on the emission lines intensity. In order to quantify this effect, in this paper we propose a simple method for evaluating the ratio between the actual measured line intensity and the intensity expected in absence of self-absorption and, if necessary, correcting the effect of self-absorption on line intensity. The method, based on a homogeneous plasma model, is applicable when the plasma electron density is known and in particular to lines whose Stark broadening parameter is available. 相似文献
997.
In this paper, a novel concept is presented for automatic microsampling and continuous monitoring of metal ions in soils with minimum disturbance of the sampling site. It involves a hollow-fiber microdialyser that is implanted in the soil body as a miniaturized sensing device. The idea behind microdialysis in this application is to mimic the function of a passive sampler to predict the actual, rather than potential, mobility and bioavailability of metal traces. Although almost quantitative dialysis recoveries were obtained for lead ( 98%) from aqueous model solutions with sufficiently long capillaries (l 30 mm, 200 m i.d.) at perfusion rates of 2.0 L min–1, the resistance of an inert soil matrix was found to reduce metal uptake by 30%. Preliminary investigation of the potential of the microdialysis analyser for risk assessment of soil pollution, and for metal partitioning studies, were performed by implanting the dedicated probe in a laboratory-made soil column and hyphenating it with electrothermal atomic absorption spectrometry (ETAAS), so that minute, well-defined volumes of clean microdialysates were injected on-line into the graphite furnace. A noteworthy feature of the implanted microdialysis-based device is the capability to follow the kinetics of metal release under simulated natural scenarios or anthropogenic actions. An ancillary flow set-up was arranged in such a way that a continuous flow of leaching solution — mild extractant (10–2 mol L–1 CaCl2), acidic solution (10–3 mol L–1 HNO3), or chelating agent (10–4 or 10–2 mol L–1 EDTA) — was maintained through the soil body, while the concentration trends of inorganic (un-bound) metal species at the soil-liquid interface could be monitored at near real-time. Hence, relevant qualitative and quantitative information about the various mobile fractions is obtained, and metal-soil phase associations can also be elucidated. Finally, stimulus-response schemes adapted from neurochemical applications and pharmacokinetic studies are to be extended to soil research as an alternative means of local monitoring of extraction processes after induction of a chemical change in the outer boundary of the permselective dialysis membrane. 相似文献
998.
根据Redebaugh相位分析理论,建立了双向进气对于G-M型脉冲管制冷机性能影响的数学模型,在此基础上提出了制冷机性能优化的若干措施。同时建立了单级G-M型脉冲管制冷机性能实验系统,通过改进小孔阀的开度,优化旋转阀的进气频率和双向进气的开度,使系统性能得到了明显的改善。 相似文献
999.
《Journal of computational chemistry》2018,39(12):711-720
The function of protein, RNA, and DNA is modulated by fast, dynamic exchanges between three‐dimensional conformations. Conformational sampling of biomolecules with exact and nullspace inverse kinematics, using rotatable bonds as revolute joints and noncovalent interactions as holonomic constraints, can accurately characterize these native ensembles. However, sampling biomolecules remains challenging owing to their ultra‐high dimensional configuration spaces, and the requirement to avoid (self‐) collisions, which results in low acceptance rates. Here, we present two novel mechanisms to overcome these limitations. First, we introduce temporary constraints between near‐colliding links. The resulting constraint varieties instantaneously redirect the search for collision‐free conformations, and couple motions between distant parts of the linkage. Second, we adapt a randomized Poisson‐disk motion planner, which prevents local oversampling and widens the search, to ultra‐high dimensions. Tests on several model systems show that the sampling acceptance rate can increase from 16% to 70%, and that the conformational coverage in loop modeling measured as average closeness to existing loop conformations doubled. Correlated protein motions identified with our algorithm agree with those from MD simulations. © 2018 Wiley Periodicals, Inc. 相似文献
1000.
New A2Fe(Mn0.5W0.5)O6 (A = Ca, Sr, Ba) double perovskite oxides have been prepared by ceramic techniques. X-ray diffraction (XRD) complemented with neutron powder diffraction (NPD) indicate a structural evolution from monoclinic (space group P21/n) for A = Ca to cubic (Fm-3m) for A = Sr and finally to hexagonal (P63/mmc) for A = Ba as the perovskite tolerance factor increases with the A2+ ionic size. The three oxides present different tilting schemes of the FeO6 and (Mn,W)O6 octahedra. NPD data also show evidence in all cases of a considerable anti-site disordering, involving the partial occupancy of Fe positions by Mn atoms, and vice-versa. Magnetic susceptibility data show magnetic transitions below 50 K characterized by a strong irreversibility between ZFC and FC susceptibility curves. The A = Ca perovskite shows a G-type magnetic structure, with weak ordered magnetic moments due to the mentioned antisite disordering. Interesting magnetostrictive effects are observed for the Sr perovskite below 10 K. 相似文献