Thermochemical investigations of nearly ideal binary solvents. I. Standard heats and volume changes of solution in methanol-isopropanol mixtures at 25°C

Standard heats and volume changes of solution of acetone,n-butanol, chloroform, and water in methanol, isopropanol, and mixtures of the two are reported. In every case, the value of a measured property in a mixture is more negative than the mole-fraction average of the values measured in the pure solvents. Equations relating the heat of solution in a binary mixture to the heats of solution in the pure solvents and the excess enthalpy of the binary mixture are developed from equations for the excess enthalpy of simple ternary systems. Heats of solution ofn-butanol agree fairly well with predicted values. Combination of standard heats of solution with standard volume changes of solution allow estimation of standard energy changes of solution at constant volume.     

Kinetic Modeling and Parameter Estimation in a Tower Bioreactor for Bioethanol Production

In this work, a systematic method to support the building of bioprocess models through the use of different optimization techniques is presented. The method was applied to a tower bioreactor for bioethanol production with immobilized cells of Saccharomyces cerevisiae. Specifically, a step-by-step procedure to the estimation problem is proposed. As the first step, the potential of global searching of real-coded genetic algorithm (RGA) was applied for simultaneous estimation of the parameters. Subsequently, the most significant parameters were identified using the Placket–Burman (PB) design. Finally, the quasi-Newton algorithm (QN) was used for optimization of the most significant parameters, near the global optimum region, as the initial values were already determined by the RGA global-searching algorithm. The results have shown that the performance of the estimation procedure applied in a deterministic detailed model to describe the experimental data is improved using the proposed method (RGA–PB–QN) in comparison with a model whose parameters were only optimized by RGA.     

A Variant of Newton's Method for the Computation of Traveling Waves of Bistable Differential-Difference Equations

We consider a variant of Newton's method for solving nonlinear differential-difference equations arising from the traveling wave equations of a large class of nonlinear evolution equations. Building on the Fredholm theory recently developed by Mallet-Paret we prove convergence of the method. The utility of the method is demonstrated with a series of examples.     

C-H bond dissociation enthalpies in norbornane. An experimental and computational study

Gas-phase C-H bond dissociation enthalpies (BDEs) in norbornane were determined by quantum chemistry calculations and the C2-H BDE was experimentally obtained for the first time by time-resolved photoacoustic calorimetry. CBS-Q and CBS-QB3 methods were used to derive the values DH degrees (C1-H) = 449 kJ mol-1, DH degrees (C7-H) = 439 kJ mol-1, and DH degrees (C2-H) = 413 kJ mol-1. The experimental result DH degrees (C2-H) = 414.6 +/- 5.4 kJ mol-1 is in excellent agreement with the theoretical value. The trend DH degrees (C1-H) > DH degrees (C7-H) > DH degrees (C2-H) is discussed.     

cis‐μ‐Chloro‐μ‐p‐toluene­thiol­ato‐bis­[chloro­(triethyl­phos­phine)­palladium]

The title compound, cis‐[Pd₂Cl₃(C₇H₇S)(C₆H₁₅P)₂], has bridging chloro and aryl­thiol­ato groups, with the phosphines being trans to the bridging chloro group. The four‐membered metallocyclic Pd₂ClS ring is unexpectedly non‐planar, with a dihedral angle of 133.8 (1)° between the PdCl₂SP coordination planes. Principal dimensions include Pd—Cl_t 2.316 (3) and 2.329 (3), Pd—Cl_b 2.442 (3) and 2.432 (3), Pd—S 2.280 (3) and 2.282 (3), and Pd—P 2.233 (3) and 2.236 (3) Å (where Cl_t and Cl_b are terminal and bridging chloro ligands, respectively).     

Longitudinal, multimodal functional imaging of microvascular response to photothermal therapy

Although studies have shown that photothermal therapy can coagulate selectively abnormal vasculature, the ability of this method to achieve consistent, complete removal of the vasculature is questionable. We present the use of multimodal, wide-field functional imaging to study, in greater detail, the biological response to selective laser injury. Specifically, a single-platform instrument capable of coregistered fluorescence imaging and laser speckle imaging was utilized to monitor vascular endothelial growth factor gene expression and blood flow, respectively, in a transgenic rodent model. Collectively, the longitudinal, in vivo data collected with our instrument suggest that the biological response to selective laser injury involves early-stage redistribution of blood flow, followed by increased vascular endothelial growth factor promoter activity to stimulate pro-angiogenic events.     

Local-scaling transformation version of density functional theory

The local-scaling transformation version of density functional theory (LS-DFT ) is reviewed. It is shown that in the context of LS-DFT it is possible to construct N-representable energy density functionals and that the theory provides systematic ways for calculating strict upper bounds to the exact energies. The importance of the concept of “orbit” in LS-DFT is indicated and several approaches leading to intraorbit and interorbit optimization are discussed. Results of the application of these optimization procedures to the determination of upper bounds for the ground-state energy of the beryllium atom are given. Also, numerical results are reported on the use of local scaling transformations for the direct solution of the Kohn-Sham equations via the density-constrained minimization of the kinetic energy of a noninteracting system. © 1995 John Wiley & Sons, Inc.     

Etching of GaAs (100) with gaseous H/CH3 mixtures

GaAs (100) wafers were etched in mixtures of hydrogen atoms and methyl radicals. The atoms were formed in a remote hydrogen plasma, and a fraction of these were converted into methyl radicals by introducing methane into the flow system upstream from the semiconductor surface. The flux of hydrogen atoms into the reaction chamber was determined by isothermal calorimetry. The methyl radical flux passing over the substrate was then calculated using previously determined rate parameters for the reaction between atomic hydrogen and methane, and a simple modeling program. The GaAs etch rates were about an order of magnitude faster when methyl radicals were present in the hydrogen atom stream, and were found to follow a first-order dependence on the partial pressure of methyl radicals. Absolute rate constants were determined and an Arrhenius activation energy of 1.2 kcal mol^?1 was calculated. The values of k and E_a are consistent with a diffusion-controlled process. SEM photographs of the surface revealed small crystallographic features that made the surface appear very rough. XPS analysis indicated that these surfaces were arsenic deficient. A mechanism is proposed for the etching of GaAs by a combination of methyl radicals and hydrogen atoms. © 1994 John Wiley & Sons, Inc.