Effects of finite pulse width on two-dimensional Fourier transform electron spin resonance

Two-dimensional (2D) Fourier transform ESR techniques, such as 2D-ELDOR, have considerably improved the resolution of ESR in studies of molecular dynamics in complex fluids such as liquid crystals and membrane vesicles and in spin labeled polymers and peptides. A well-developed theory based on the stochastic Liouville equation (SLE) has been successfully employed to analyze these experiments. However, one fundamental assumption has been utilized to simplify the complex analysis, viz. the pulses have been treated as ideal non-selective ones, which therefore provide uniform irradiation of the whole spectrum. In actual experiments, the pulses are of finite width causing deviations from the theoretical predictions, a problem that is exacerbated by experiments performed at higher frequencies. In the present paper we provide a method to deal with the full SLE including the explicit role of the molecular dynamics, the spin Hamiltonian and the radiation field during the pulse. The computations are rendered more manageable by utilizing the Trotter formula, which is adapted to handle this SLE in what we call a "Split Super-Operator" method. Examples are given for different motional regimes, which show how 2D-ELDOR spectra are affected by the finite pulse widths. The theory shows good agreement with 2D-ELDOR experiments performed as a function of pulse width.     

Determination of melissyl alcohol by capillary column gas chromatography

Summary For accurate determination of polar, high-boiling melissyl alcohol in mixtures containing also low-boiling components by capillary column gas chromatography with hot split injection, all experimental paramenters, such as the injection procedure, insert size and design, injector temperature, sample size, solvent and carrier gas nature, etc. must be optimized. Of the factors affecting the quantitation the nature of the insert packing material is of the greatest importance. With the commonly used packing material, quartz wool, in the insert, a much lower than true melissyl alcohol concentration was obtained. Accurate quantitation was only possible when stop-flow injection, together with an insert packed with glass beads was used.     

Theoretical studies of hydrogen storage in binary Ti-Ni,Ti-Cu,and Ti-Fe alloys

Theoretical studies have been carried out to examine hydrogen storage in some binary transition metal alloys which include titanium as one of the alloying elements. Quantum mechanical calculations at the Extended Hückel level of approximation have been performed on numerous clusters of compositions Ti₁₈Ni₁₈, Ti₁₈Ni₁₈H, Ti₁₈Ni₁₈H₁₂, Ti₂₄Ni₁₂, Ti₂₄Ni₁₂H, Ti₂₄Ni₁₂Hi₁₂, Ti₁₆Cu₁₆, Ti₁₆Cu₁₆H, Ti₂₄Cu₂, Ti₁₆Fe₁₆, Ti₁₆Fe₁₆H₉, and Ti₁₆Fe₁₆H₃₂, to yield information on energetics, densities of states, charge distributions, and the effects of hydrogenation on these properties. In addition, ab initio calculations at the split valence level of approximation have been performed on several smaller clusters. The hydrogens have been shown to acquire a partially anionic character in all cases. Another conclusion is that the preference of H for certain types of sites (for example the tetrahedral Ti₄ sites in crystalline TiCu) is more likely to be related not to the intrinsically greater stability of a hydrogen atom located in such a site, but to more general topological and electronic considerations. Qualitative concepts related to the classification, spatial distribution, and sizes and shapes of hole sites which could become occupied by hydrogen atoms, have been shown to correlate with hydrogen storage capacity for crystalline materials. These qualitative concepts have been extended to amorphous materials and corroborate the observations that under optimized conditions amorphous alloys can be found with better reversible hydrogen storage properties than the crystalline or microcrystalline systems. Distorted tetrahedral and octahedral holes have been examined in detail, and parameters (volume, area, tetrahedrality, and octahedrality) have been introduced to describe their sizes and shapes. An algorithmic surveying technique has been introduced, and shown to provide useful information about the limiting amounts of hydrogen uptake.Camille and Henry Dreyfus teacher-scholar     

Sampling onto capillary columns. Difficulties with various types of samples a simple accessory to split injectors for avoidance of discrimination

Summary The quantitation problems arising by discrimination at split sampling onto capillary columns due to selective vaporization from the syringe needle after extrusion of the adjusted volume of the liquid sample into the vaporization chamber and/or due to malfunction of the splitting itself can be avoided by a simple accessory to the common injector constructions in order to arrange for cooling of the entire syringe needle except the tip. It could be proved that the discrimination which is usually observed does not originate from the splitting itself, if the temperature of the split region is not changed appreciably during the sampling procedure. Dedicated to Professor G. Wilke on the occasion of his 60th birthday. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Quantitative aspects of directly coupled supercritical fluid extraction–capillary gas chromatography with a conventional split/splitless injector as interface

The quantitative aspects of on-line supercritical fluid extractioncapillary gas chromatography (SFE-GC) with a split/splitless injector as interface were investigated. Special attention was paid to the discrimination behavior and the reproducibility of the split/splitless interface. A simple experimental set-up is proposed that allows accurate quantitation in on-line SFE-split GC. The results obtained in on-line SFE-GC compare favorably with those from conventional GC with split injection. Discrimination was found to be absent when working at sufficiently high interface temperatures. Finally, the effects of the carbon dioxide flow rate, interface temperature and split ratio on both discrimination and reproducibility were studied.     

Split‐Ugi Reaction with Chiral Compounds: Synthesis of Piperazine‐ and Bispidine‐Based Peptidomimetics

A simple, one‐step, stereoconservative synthesis of diamine‐based peptidomimetics is described, by split‐Ugi multicomponent reaction, involving chiral N‐protected amino acids and α‐substituted isocyanoacetate. In particular, piperazine and bispidine (3,7‐diazabicyclo[3.3.1]nonane) are exploited as diamine components, bispidine being the first example of a sterically demanding bicyclic system employed in a split‐Ugi reaction.     

Split and balanced colorings of complete graphs

An (r, n)-split coloring of a complete graph is an edge coloring with r colors under which the vertex set is partitionable into r parts so that for each i, part i does not contain K_n in color i. This generalizes the notion of split graphs which correspond to (2, 2)-split colorings. The smallest N for which the complete graph K_N has a coloring which is not (r, n)-split is denoted by ƒ_r(n). Balanced (r,n)-colorings are defined as edge r-colorings of KN such that every subset of [N/r] vertices contains a monochromatic K_n in all colors. Then g_r(n) is defined as the smallest N such that K_N has a balanced (r, n)-coloring. The definitions imply that f_r(n) g_r(n). The paper gives estimates and exact values of these functions for various choices of parameters.     

基于时延估计的分裂阵时域波束形成技术

大孔径拖曳线列阵受舰艇横向机动、洋流影响和水动力影响时会产生一定的阵形畸变,阵形畸变使得波束形成时阵列流型失配,进而降低了目标方位分辨率和阵处理的增益。在无法进行阵形估计时,基于时延估计的分裂阵时域波束形成技术将大孔径拖曳线阵分为左右两个子阵分别做波束形成,通过加权广义相关时延估计算法估算对应波束的时延差,再依据估算时延差对左右两个波束进行延时求和得到最终的波束信号。仿真和海试数据证明,相对于全阵直接做波束形成的方法,基于时延估计的分裂阵的时域波束形成技术有效提高了目标方位分辨率和阵处理的增益。     

PMMA材料的动态压缩力学特性及应变率相关本构模型研究

利用INSTRON万能试验机和分离式Hopkinson压杆(SHPB)对PMMA试件在较宽应变率范围内进行了单轴压缩实验,研究加载应变率对PMMA材料力学性能的影响.利用扫描电子显微镜对回收的试样进行了显微观察,重点分析不同加载应变率下PMMA的微观损伤破坏模式.结果表明:随着应变率的增大,PMMA的流动应力显著地增加,且冲击加载条件下,峰值应力的应变率敏感性明显高于准静态;在准静态加载条件下,PMMA试样呈现明显的延性破坏特征,在动态加载条件下则表现为脆性破坏.最后,对PMMA材料的ZWT粘弹性本构模型参数进行了拟合,拟合结果与实验结果吻合较好,表明该本构模型能够较好地描述较宽应变率范围内PMMA材料的应力应变关系.     

The role of a split injection strategy in the mixture formation and combustion of diesel spray: A large-eddy simulation

The role of a split injection in the mixture formation and combustion characteristics of a diesel spray in an engine-like condition is investigated. We use large-eddy simulations with finite rate chemistry in order to identify the main controlling mechanism that can potentially improve the mixture quality and reduces the combustion emissions. It is shown that the primary effect of the split injection is the reduction of the mass of the fuel-rich region where soot precursors can form.Furthermore, we investigate the interaction between different injections and explain the effects of the first injection on the mixing and combustion of the second injection. Results show that the penetration of the second injection is faster than that of the first injection. More importantly, it is shown that the ignition delay time of the second injection is much shorter than that of the first injection. This is due to the residual effects of the ignition of the first injection which increases the local temperature and maintains a certain level of combustion some intermediates or radical which in turn boosts the ignition of the second injection.