Many-body optimization using an ab initio monte carlo method

Advances in computing power have made it possible to study solvated molecules using ab initio quantum chemistry. Inclusion of discrete solvent molecules is required to determine geometric information about solute/solvent clusters. Monte Carlo methods are well suited to finding minima in many-body systems, and ab initio methods are applicable to the widest range of systems. A first principles Monte Carlo (FPMC) method was developed to find minima in many-body systems, and emphasis was placed on implementing moves that increase the likelihood of finding minimum energy structures. Partial optimization and molecular interchange moves aid in finding minima and overcome the incomplete sampling that is unavoidable when using ab initio methods. FPMC was validated by studying the boron trifluoride-water system, and then the method was used to examine the methyl carbenium ion in water to demonstrate its application to solvation problems.     

Condensed matter chemistry under ‘extreme’ high pressure–high temperature conditions

Improved techniques for high-pressure experiments have led to new studies of the structure and physical properties of materials compressed to extremely high densities. Now we must fully enable the field of condensed matter chemistry under extreme high-pressure conditions. This will require development of strategies for the analysis and control of the chemical composition during reactions between solid, liquid and fluid phases. Such approaches already exist within the fields of experimental geochemistry and petrology, and they can be readily adapted to the wider area of chemistry. The first consideration is the manipulation and determination of stable and metastable pressure–temperature phase diagrams, illustrated here for the one-component system Si. Next, relationships between P, T and the chemical composition, X, expressed in terms of the chemical potential (μ) or the activity–composition relations, can be used to constrain and determine components within the system. This is illustrated by examples drawn from our recent work on high-pressure syntheses of boron suboxides (B₆O_1???δ) and (Si, Ge)₃N₄ nitride spinels.     

Independent sets of maximal size in tensor powers of vertex‐transitive graphs

Let G be a connected, nonbipartite vertex‐transitive graph. We prove that if the only independent sets of maximal cardinality in the tensor product G × G are the preimages of the independent sets of maximal cardinality in G under projections, then the same holds for all finite tensor powers of G, thus providing an affirmative answer to a question raised by Larose and Tardif (J Graph Theory 40(3) (2002), 162–171). © 2009 Wiley Periodicals, Inc. J Graph Theory 60: 295‐301, 2009     

Effect of successive sprays on liquid distribution in fluidized beds

In processes such as Fluid Coking^?,agglomerate formation should be minimized since it reduces the yield of valuable products,and degrades operability because of the fouling of internals.An experimental model,consisting of an aqueous solution of gum arabic with a dye,has been successfully developed to simulate the formation of agglomerates in the Fluid Coking^?process,where bitumen is sprayed into a fluidized bed of coke particles The particles wetted by a spray could be predicted by assuming that all the particles in the wake of bubbles formed from the tip of the spray jet have been wetted by the injected liquid.The transfer of liquid from particles wetted with the spray to dry bed particles was relatively ineffective,as the number of wet particles increased by only 50%.With successive liquid injections,the proportion of the liquid trapped in agglomerates increases in latter injections:large agglomerates from earlier injections accumulate above the grid and are carried by gas bubbles into the spray jet cavity,where they seed fresh agglomerates.     

Equivalent Conditions for the Solvability of Nonstandard and Singular LQ-Problems with Application to Parabolic Equations

We consider an optimal control problem with indefinite cost for an abstract model, which covers, in particular, parabolic systems in a general bounded domain. Necessary and sufficient conditions are given for the synthesis of the optimal control, which is given in terms of the Riccati operator arising from a nonstandard Riccati equation. The theory extends also a finite-dimensional frequency theorem to the infinite-dimensional setting. Applications include the heat equation with Dirichlet and Neumann controls, as well as the strongly damped Euler–Bernoulli and Kirchhoff equations with the control in various boundary conditions.     

Characterization of heterologous and native enzyme activity profiles in metabolically engineered Zymomonas mobilis strains during batch fermentation of glucose and xylose mixtures

Zymomonas mobilis has been metabolically engineered to broaden its substrate utilization range to include d-xylose and l-arabinose. Both genomically integrated and plasmid-bearing Z. mobilis strains that are capable of fermenting the pentose d-xylose have been created by incorporating four genes: two genes encoding xylose utilization metabolic enzymes (xylA/xylB) and two genes encoding pentose phosphate pathway enzymes (talB/tktA). We have characterized the activities of the four newly introduced enzymes for xylose metabolism, along with those of three native glycolytic enzymes, in two different xylose-fermenting Z. mobilis strains. These strains were grown on glucose-xylose mixtures in computer-controlled fermentors. Samples were collected and analyzed to determine extracellular metabolite concentrations as well as the activities of several intracellular enzymes in the xylose and glucose uptake and catabolism pathways. These measurements provide new insights on the possible bottlenecks in the engineered metabolic pathways and suggest methods for further improving the efficiency of xylose fermentation.     

Magnetism and superconductivity in ErNi2B2C

We have performed a series of neutron diffraction experiments from the magnetic order and the vortex lattice in single crystal ErNi₂B₂C. The incommensurate magnetic structure develops additional even harmonics below the ‘ferromagnetic’ ordering temperature, T _F of 2.3 K. This feature and the existence of rods of diffuse scattering suggest the development of ferromagnetic microdomain walls. The magnetic structure is very sensitive to the application of a magnetic field with changes in modulation vector and harmonic content. Studies of the vortex lattice show the presence of a 45° reorientation transition and a distorted hexagonal to square transition as a function of applied field. Further distortions of the vortex lattice occur at T _N, but no changes are seen at T _F.     

High-performance liquid chromatographic method for the analysis of Oltipraz in human serum and urine.

A rapid, sensitive procedure for the analysis of Oltipraz in serum and urine using high-performance liquid chromatography was developed. The proposed method illustrates recovery of Oltipraz from biological fluids was greater than 80%. Detection and separation of Oltipraz required as little as 1 ml of serum or urine. Oltipraz was detectable when 2 ng or more of drug was present in 1 ml of serum or urine; the method is highly reproducible when 5 ng/ml or more Oltipraz is present in the biological fluid.     

An x-ray study of aerothionin from aplysina fistularis (pallas)

The structure of aerothionin, a tyrosine-derived brominated compound from the sponge $\text{Aplysina fistularis}$ (Pallas), is confirmed by X-ray data, which with CD data assign its absolute configuration.     

Molecular structure of isolongifolene epoxide

An X-ray analysis on isolongifolene epoxlde definitely settles the dispute over the stereochemistry in favor of the $\text{endo}$-formulation.