On partitioning the overlap charge density in self-consistent charge molecular-orbital calculations

Alternatives to the Mulliken method of partitioning the overlap charge density in self-consistent charge molecular-orbital calculations are examined. It is found that more realistic methods may lead to significantly different self-consistent charges, and different ordering of the electronic energy levels.     

Multidimensional quantum trajectories: applications of the derivative propagation method

In a previous publication [J. Chem. Phys. 118, 9911 (2003)], the derivative propagation method (DPM) was introduced as a novel numerical scheme for solving the quantum hydrodynamic equations of motion (QHEM) and computing the time evolution of quantum mechanical wave packets. These equations are a set of coupled, nonlinear partial differential equations governing the time evolution of the real-valued functions C and S in the complex action, S=C(r,t) + iS(r,t)/Planck's over 2pi, where Psi(r,t)=exp(S). Past numerical solutions to the QHEM were obtained via ensemble trajectory propagation, where the required first- and second-order spatial derivatives were evaluated using fitting techniques such as moving least squares. In the DPM, however, equations of motion are developed for the derivatives themselves, and a truncated set of these are integrated along quantum trajectories concurrently with the original QHEM equations for C and S. Using the DPM quantum effects can be included at various orders of approximation; no spatial fitting is involved; there is no basis set expansion; and single, uncoupled quantum trajectories can be propagated (in parallel) rather than in correlated ensembles. In this study, the DPM is extended from previous one-dimensional (1D) results to calculate transmission probabilities for 2D and 3D wave packet evolution on coupled Eckart barrier/harmonic oscillator surfaces. In the 2D problem, the DPM results are compared to standard numerical integration of the time-dependent Schrodinger equation. Also in this study, the practicality of implementing the DPM for systems with many more degrees of freedom is discussed.     

Stereogenic Propargylic Centers via Base-Mediated Terminal Allene Isomerization

A study of alkali metal amide-mediated isomerizations of terminal allenes is described. The isomerizations of substituted ethenylidenecyclohexanes to form diastereomeric mixtures of terminal alkynes have been conducted to determine factors which may influence the stereochemistry at the newly formed propargylic centers. An initial base screen revealed that potassium N-methylbutylamide (KMBA) exhibits the highest level of equatorial to axial alkyne diastereoselectivity. With the severely hindered terminal allene 26, the use of potassium 3-aminopropylamide is required to effect isomerization. A general synthesis of deuterated terminal allenes has also been achieved, and a mechanistic study using d(2)-allenes 18a,b has revealed the involvement of a propargylic anion in the course of the KMBA-mediated isomerizations.     

Empirical model of slow pyrolysis of hardwood chips

Applied Biochemistry and Biotechnology - The thermal decomposition of mixed hardwood chips was investigated by pyrolyzing 1-kg samples at atmospheric pressure in an electrically-heated batch...     

Micellar affinity gradient focusing: a new method for electrokinetic focusing

This report describes a new method for the concentration and separation of neutral and/or hydrophobic analytes based on a combination of the analytes' electrophoretic mobility, and affinity for partitioning into a micellar phase. Micellar affinity gradient focusing (MAGF) works by creating a gradient in the micellar retention factor. An electric field is applied along the channel to cause the (negatively charged) micelles to move from the region of high retention to the region of low retention, and the mobile phase is forced to move from the region of low retention to the region of high retention. Consequently, the analyte moves into the gradient region from both directions where it is concentrated at a point where its total velocity is zero. Different analytes, which interact differently with the micelles, will have zero total velocity at different points along the gradient, and will thereby be simultaneously concentrated and separated.     

最小化碳排放的共享单车迁移问题

本文考虑共享单车迁移问题, 它可看作是经典旅行售货商问题的一个新颖变形, 不同的是其目标函数为最小化碳排放。其中, 碳排放利用单车负载与其行驶路程的乘积进行刻画。我们提出了两个启发式算法：贪心和基于TSP的算法, 每个算法的核心思想均是优先减少单车负载。从理论上证明算法的可行性并给出数据实验以验证算法的实际性能。数据实验结果表明贪心算法优于基于TSP的算法, 这为共享单车企业进行日常单车分配提供了理论依据。     

Multidimensional reactive scattering with quantum trajectories: dynamics with Morse vibrational modes

The reactive scattering of a wave packet is studied by the quantum trajectory method for a model system with up to 25 Morse vibrational modes. The equations of motion are formulated in curvilinear reaction path coordinates with the restriction to a planar reaction path. Spatial derivatives are evaluated by the least squares method using contracted basis sets. Dynamical results, including trajectory evolution and time-dependent reaction probabilities, are presented and analyzed. For the case of one Morse vibrational mode, the results are in good agreement with those derived through direct numerical integration of the time-dependent Schrodinger equation.     

Sub-10 fs pulse characterization using spatially encoded arrangement for spectral phase interferometry for direct electric field reconstruction

We demonstrate an extremely accurate method for measuring ultrabroadband, sub-10 fs pulses even if they exhibit a highly modulated spectrum, space-time coupling, or both. The method uses a spatially encoded arrangement for spectral phase interferometry for direct electric field reconstruction, which allows a zero additional phase measurement to be performed with a relatively low signal-to-noise ratio in real time and single shot.     

Studies of microwave-enhanced Suzuki-Miyaura vinylation of electron-rich sterically hindered substrates utilizing potassium vinyltrifluoroborate

The Suzuki-Miyaura cross-coupling of sterically hindered and electron-rich ortho,ortho′-substituted aryl halides with potassium vinyltrifluoroborate utilizing microwave irradiation has been conducted while adjusting solvent ratio, irradiation time, and catalyst loading to find optimal conditions. Coupling of benzyl 3,5-bis(benzyloxy)-4-bromobenzoate leads to a mixture of the desired styrene derivative and the reduced product. 4-Bromo-1,3,5-trimethoxybenzene, methyl 4-bromo-3,5-dimethoxybenzoate, and mesitylene bromide were also coupled to test the breadth and scope of this methodology. Of these substrates tested only 4-bromo-1,3,5-trimethoxybenzene was not vinylated successfully, which is believed to be due to the electron-rich nature of this system.