On comparison of approximate solutions in vector optimization problems

The problem of comparison of approximations (approximate solutions to a vector optimization problem) obtained using different numerical methods is considered. In the absence of a priori information about the set of weakly efficient vectors, a scalar function is introduced that enables pair-wise comparison of approximations and establishes a binary preference relation according to which the approximations close (in the sense of the Hausdorff distance) to the set containing all possible efficient vectors are preferable to other approximations.     

Analysis of van der Waals loops in the adsorption isotherms of porous systems

The properties of the van der Waals loops for isotherms of the adsorbate located in the slit-shaped and cylindrical pores of different width were analyzed. The adsorbate molecules are modeled by spherical Lennard-Jones type particles. The calculation was based on the latticegas model in the quasichemical approximation for intermolecular interactions. The accuracy of calculations of the adsorption hysteresis loops increases due to the use of distributed models, which reflect the spatial inhomogeneity of the distribution of molecules along the normal to the pore wall. The effect of the adsorbate-adsorbent interaction potential and pore width on the pattern of adsorption isotherms is considered. Taking into account the inhomogeneity of the spatial distribution of molecules changes the course of the spinodal sections of the adsorption isotherms.     

W4 theory for computational thermochemistry: In pursuit of confident sub-kJ/mol predictions

In an attempt to improve on our earlier W3 theory [A. D. Boese et al., J. Chem. Phys. 120, 4129 (2004)] we consider such refinements as more accurate estimates for the contribution of connected quadruple excitations (T4), inclusion of connected quintuple excitations (T5), diagonal Born-Oppenheimer corrections (DBOC), and improved basis set extrapolation procedures. Revised experimental data for validation purposes were obtained from the latest version of the Active Thermochemical Tables thermochemical network. The recent CCSDT(Q) method offers a cost-effective way of estimating T4, but is insufficient by itself if the molecule exhibits some nondynamical correlation. The latter considerably slows down basis set convergence for T4, and anomalous basis set convergence in highly polar systems makes two-point extrapolation procedures unusable. However, we found that the CCSDTQ-CCSDT(Q) difference converges quite rapidly with the basis set, and that the formula 1.10[CCSDT(Q)cc-pVTZ+CCSDTQcc-pVDZ-CCSDT(Q)cc-pVDZ] offers a very reliable as well as fairly cost-effective estimate of the basis set limit T4 contribution. The T5 contribution converges very rapidly with the basis set, and even a simple double-zeta basis set appears to be adequate. The largest T5 contribution found in the present work is on the order of 0.5 kcal/mol (for ozone). DBOCs are significant at the 0.1 kcal/mol level in hydride systems. Post-CCSD(T) contributions to the core-valence correlation energy are only significant at that level in systems with severe nondynamical correlation effects. Based on the accumulated experience, a new computational thermochemistry protocol for first- and second-row main-group systems, to be known as W4 theory, is proposed. Its computational cost is not insurmountably higher than that of the earlier W3 theory, while performance is markedly superior. Our W4 atomization energies for a number of key species are in excellent agreement (better than 0.1 kcal/mol on average, 95% confidence intervals narrower than 1 kJ/mol) with the latest experimental data obtained from Active Thermochemical Tables. Lower-cost variants are proposed: the sequence W1-->W2.2-->W3.2-->W4lite-->W4 is proposed as a converging hierarchy of computational thermochemistry methods. A simple a priori estimate for the importance of post-CCSD(T) correlation contributions (and hence a pessimistic estimate for the error in a W2-type calculation) is proposed.     

Crystal Structures of a New Polymorph of N-tert-butyl-2-thioimidazole,and Its 1,4-Diiodotetrafluorobenzene,Tetraiodoethylene, and Iodine Cocrystals

Journal of Chemical Crystallography - A new polymorph of N-tert-butyl-2-thioimidazole (1), along with its cocrystals with 1,4-diiodotetrafluorobenzene (2), tetraiodoethylene (3), and molecular...     

On boundary integral operators for diffraction problems on graphs with finitely many exits at infinity

We consider a diffraction problem in a multi-connected domain ?² \ Γ, where Γ is an oriented graph with finitely many edges some of which are infinite. The problem is described by the Helmholtz equation (1) $\mathcal{H}u(x) = \rho (x)\nabla \cdot \rho ^{ - 1} (x)\nabla u(x) + k^2 (x)u(x) = 0,x \in \mathbb{R}^2 \backslash \Gamma ,$ where ρ and k are functions bounded together with all derivatives, and by the transmission conditions (2) $u_ + (t) - u_ - (t) = 0,t \in \Gamma \backslash \mathcal{V},$ (3) $a_ + (t)(\partial u/\partial n_t )_ + (t) - a_ - (t)(\partial u/\partial n_t )_ - (t) + a_0 (t)u(t) = f(t),t \in \Gamma \backslash \mathcal{V},$ where V is the set of vertices, a _± and a ₀ are functions bounded on Γ, slowly oscillating discontinuous at the vertices in V, and slowly oscillating at infinity, and f ∈ L ²(Γ). Using Green’s function for the Helmholtz operator H, we introduce simple- and double-layer potentials and reduce the diffraction problem (1)–(3) to a boundary integral equation. The main objective of the paper is to study the essential spectrum, the Fredholm property, and the index of boundary operators on Γ associated with the problem (1)–(3).     

Generation and optical properties of monodisperse wurtzite-type ZnS microspheres

Monodisperse wurtzite-type ZnS microspheres have been prepared by using glutathione (GSH) as a sulfur source at low reaction temperatures ranging from 160 to 210 degrees C. The diameter of the ZnS microspheres can be tuned from approximately 254 to approximately 597 nm by changing the reaction parameters such as temperature, molar ratio of reactants (GSH/Zn2+), and reaction medium (ethylenediamine or ammonia). Our results demonstrate that monodentate amines (ammonia) play the same role as that of bidentate amines (ethylenediamine) in the formation of the wurtzite-type ZnS microspheres. The formation process of the monodisperse ZnS microspheres consists of a GSH-dominated nucleation process and an amine-dominated assembly process. The as-synthesized monodisperse ZnS microspheres readily self-assemble into ordered hexagonal patterns and thus have potential applications as colloidal crystalline materials. Blue fluorescence emission peaks at 415 and 466 nm in wavelength, attributed to deep-trap emission, are observed at room temperature.     

Atomic force microscopy measurement of the elastic properties of the kidney epithelial cells

Direct interaction force measurements using atomic force microscopy (AFM) were carried out between a silicon nitride tip and renal epithelial cells (Madin-Darby Canine Kidney-MDCK and proximal tubular epithelial cells derived from pig kidneys, LLC-PK1). The approaching (extending) portion of the force/distance curves is considered, and repulsive forces in the long range of 2-3 microm were seen in both MDCK as well as LLC-PK1 cells growing under normal conditions. The repulsive force in the shorter distance range of 50-200 nm was also observed, when cells were damaged exposing the underlying basal membrane. LLC-PK1 cells were more prone to damage than the MDCK cells, hence short-range forces were common in the former and long-range forces in the latter cells. The functional dependence of repulsive force on the indentation depth changes, at small indentation depth the force increases linearly, while at larger indentations the force is a quadratic function of the distance, which is attributed to the elasticity of the membrane and the solid-like response of cells, respectively. The oxalate treatment of cells for 2-4 h gives rise to an increase in the elastic modulus of the cells.