Newton trajectories for the tilted Frenkel–Kontorova model

ABSTRACT

Newton trajectories are used for the Frenkel–Kontorova model of a finite chain with free-end boundary conditions. We optimise stationary structures, as well as barrier breakdown points for a critical tilting force were depinning of the chain happens. These special points can be obtained straight forwardly by the tool of Newton trajectories. We explain the theory and add examples for a finite-length chain of a fixed number of 2,?3,?4,?5 and 23 particles.     

Lower bound for the ratios of eigenvalues of Schrödinger with nonpositive single‐barrier potentials

Horváth and Kiss (Proc. Amer. Math. Soc., 2005) proved the upper bound estimate for Dirichlet eigenvalue ratios of the Schrödinger problem ?y^′′ + q(x)y = λy with nonnegative and single‐well potential q. In this paper, we prove that if q(x) is a nonpositive, continuous, and single‐barrier potential, then for λ_n > λ_m≥ ? 2q^?, where . In particular, if q(x) satisfies the additional condition , then λ₁ > 0 and for n > m ≥ 1. For this result, we develop a new approach to study the monotonicity of the modified Prüfer angle function.     

Kinetic Studies of the Thermal cis-to-trans Isomerization of Dioxaphospholanes

By following a previously reported method,¹ the synthesis of r-2-alkoxy-cis-4-cis-5-dimethyl-1,3,2-λ³-dioxaphospholanes ligands (1 and 3) was carried out. The purpose of this work is the kinetic study of the inversion barrier at phosphorus for 1 and 3 and the comparison with the already informed dioxaphospholane 2. The kinetic measurements of the thermal isomerization cis-to-trans were performed by ³¹P NMR spectroscopy, observing a first order kinetics for both compounds. The energy of activation (E_a) for the epimerization of compounds cis-1 and cis-3 was calculated to be 16.0 ± 0.6 and 11.8 ± 0.8 kcal/mol, respectively. The values of the thermodynamic parameters of the transition state (Δ H^≠, Δ S^≠, Δ G^≠) suggest that the inversion at phosphorus not only depends on the spatial requirements of the alkoxy substituent but also on entropic effects. The thermodynamic parameters Δ H°, Δ S°, and Δ G° were also evaluated and they show that the cis isomers are preferred from enthalpic point of view, but entropic effects dominate the equilibrium trans ? cis leading to the entropically favored trans isomers. Furthermore, the results are supported by density functional theory calculations of 1–4 at the B3LYP/6-31G** level.     

A NEW SYSTEM EXHIBITING A HIGH BARRIER TO ROTATION ABOUT THE P—N BOND. SYNTHESES AND SPECTRAL STUDIES OF 1,3,2-DIAZAPHOSPHETIDIN-4-ONE DERIVATIVES

Abstract

1,3,2-Diazaphosphetidin-4-one derivatives were synthesized. Their ¹H NMR signals at ambient temperature displaed a broad doublet which eventually coalesced before becoming sharp upon warming, and the ¹³C NMR spectra also showed that the α-and β-carbons of the dialkylamino group were non-equivalent. The phenomena were ascribed to restricted rotation about the exocyclic P—N bond.     

Functions of Acyclic Poly(ethylene Oxide) Homologs: Acceleration of Nucleophilic Reactions and Selective Ion Transport through Membranes

The acceleration effect of poly(ethylene oxide) on nucleophilic reactions was investigated. The enhancement of the reaction rate was interpreted by the cooperative solvation of alkali metal ions with ethereal oxygens of PEO resulting in active nucleophilic anions. In relation to the complex formation of alkali metal ions with PEO, the oligo(ethylene oxide) derivatives were prepared as the synthetic ionophores, which were able to transport alkali metal ions selectively through a liquid membrane against the alkali metal ion concentration.     

Cross‐linked Multilayer Polymer‐Clay Nanocomposites and Permeability Properties

Abstract

Electrostatically layered aluminosilicate nanocomposites have been prepared by the sequential deposition of poly(allylamine hydrochloride)/poly(acrylic acid)/poly(allylamine hydrochloride)/saponite (PAH/PAA/PAH/saponite)₁₀ on poly(ethylene terephtalate) (PET) film. Exfoliated saponite nanoplatelets were obtained by extensive shaking, sonication, and centrifugation of a water suspension. To minimize permeability and improve the mechanical integrity, cross‐linking of composite films was carried out at different temperatures. The formation of amide linkage induced through heating was observed by Fourier Transform Infrared (FT‐IR) and x‐ray photoelectron spectroscopy (XPS). The cross‐linking of nanocomposites (PAH/PAA/PAH/saponite)₁₀ showed 60% decrease in permeability of oxygen when compared with the pristine PET substrate film. In contrast, water permeability of the nanocomposite membrane was not affected by heating temperature and deposition cycles.     

量子态选择的分子离子解离动力学：阈值光电子-光离子符合成像技术的应用

阈值光电子一光离子符合速度成像技术通过对光电子和符合的光离子同时进行速度聚焦控制,大幅提高了电子和离子的收集效率和离子平动能分辨率,成为开展气相分子光电离和光电离．解离动力学研究的有效工具．利用该技术,我们精确地测量了分子的电离能、离子出现势等重要参数,并且开展了若干具有量子态或内能选择的离子解离动力学研究,描绘了相关势能面存在浅势阱等重要动力学特征,讨论了不同振动态和电子态的激发对解离机理和产物通道的重要影响．     

High Temperature Corrosion Resistance of Coatings Deposited by Hvof for Application in Steam Turbines

The geothermal steam turbines are exposed to mechanisms of corrosion/erosion that weakens its components and reduces their useful life. Due to this problem work has been done in application and characterization of coating in solid state by means of the technique of high-velocity Oxygen Fuel (HVOF), evaluating the corrosion rate (V_corr) at high temperature of MCrAlY and Diamalloy 4006 coatings deposited on stainless steel SS304. Test was performance in an Autoclave at 170 ⁰C using a modified geothermal fluid as electrolyte. Open circuit potential was monitoring during 24 hours until the system reached the equilibrium. After that, Polarization and Impedance Spectroscopy techniques were used to evaluate the specimens. For microstructure characterization; X–ray Diffraction (XRD), electron sweep microscope (SEM) and Optical microscope were applied. Results show that both coatings (Diamalloy 4006 and MCrAlY), have low current density compare with the substrate, which is an indicative of a lower corrosion rate due to the passive behavior of the species deposited on the Surface of the coating.