Rate coefficients and kinetic isotope effects of the abstraction reaction of H atoms from methylsilane

ABSTRACT

Thermal rate constants for chemical reactions using improved canonical variational transition state theory (ICVT) with small-curvature tunnelling (SCT) contributions in a temperature range 180–2000 K are reported. The general procedure is used with high-quality ab initio computations and semi-classical reaction probabilities along the minimum energy path (MEP). The approach is based on a vibrational adiabatic reaction path and is applied to the multiple-channel hydrogen abstraction reaction H + SiH₃CH₃ → products and its isotopically substituted variants. All the degrees of freedom are optimised and harmonic vibrational frequencies and zero-point energies are calculated at the MP2 level with the cc-pVTZ basis set. Single-point energies are calculated at a higher level of theory; CCSD(T)-F12a/VTZ-F12. ICVT/SCT rate constants show that the quantum tunnelling contributions at low temperatures are relatively important and the H-abstraction channel from SiH₃ group of SiH₃CH₃ is the major pathway. The total rate constants are given by the following expression: k_tot(ICVT/SCT) = 2.29 10^?18 T^2.42 exp(?350.9/T) cm³ molec^?1 s^?1. These calculated rates are in agreement with the available experiments. The ICVT/SCT method is further exploited to predict primary and secondary kinetic isotope effects, respectively).     

Nanoparticle‐Driven Orientation Transition and Soft‐Shear Alignment in Diblock Copolymer Films via Dynamic Thermal Gradient Field

Sharp dynamic thermal gradient (∇T ≈ 45 °C mm⁻¹) field‐driven assembly of cylinder‐forming block copolymer (c‐BCP) films filled with PS‐coated gold nanoparticles (AuNPs; d_NP ≈ 3.6 nm, φ_NP ≈ 0–0.1) is studied. The influence of increasing AuNP loading fraction on dispersion and assembly of AuNPs within c‐BCP (PS‐PMMA) films is investigated via both static and dynamic thermal gradient fields. With φ_NP increasing, a sharp transition from vertical to random in‐plane horizontal cylinder orientation is observed due to enrichment of AuNPs at the substrate side and favorable interaction of PMMA chains with gold cores. Furthermore, a detachable capping elastomer layer can self‐align these random oriented PMMA microdomains into unidirectional hybrid AuNP/c‐BCP nanolines, quantified with an alignment order parameter, S.

     

Optimization of an Externally Modulated RF Photonic Link

Abstract

The noise figure and sub-octave spurious-free dynamic range of a carrier-suppressed analog RF photonic link are examined. Expressions for noise figure and dynamic range are derived as a function of the modulator bias angle. A closed form expression for the bias angle that optimizes link noise figure and spurious-free dynamic range is also derived. Experimental results are presented and shown to agree with calculations. These experimental results include some of the lowest noise figure and highest dynamic range results published to date for an RF photonic link incorporating a standard Mach-Zehnder modulator: 6 dB and 122 dB·Hz^2/3, respectively.     

Vector Lattice Powers: f-Algebras and Functional Calculus

Let s ∈ {2.3,…} and E be an Archimedean vector lattice. We prove that there exists a unique pair (E ^? ,?), where E ^? is an Archimedean vector lattice and ?:E× ··· ×E (s times) → E ^? is a symmetric lattice s-morphism, such that for every Archimedean vector lattice F and every symmetric lattice s-morphism T:E × ··· × E (s times) → F, there exists a unique lattice homomorphism T ^? :E ^?  → F such that T = T ^? ○?. We give two approaches to construct (E ^? ,?) based on f-algebras and functional calculus, respectively, provided that E is also uniformly complete.     

The phase transition behaviors of Li1−xMn0.5Fe0.5PO4 during lithium extraction studied by in situ X-ray absorption and diffraction techniques

How the structural changes take place in LiMn_yFe_1−yPO₄-type cathode materials during lithium extraction/insertion is an important issue, especially on if they go through the single-phase reaction (i.e., solid solution reaction) or the two-phase reaction regions. Here we report the studies on the phase transition behaviors of a carbon coated Li_1−xMn_0.5Fe_0.5PO₄ (CLi₁₋xMn_0.5Fe0_.5PO₄, 0.0  x  1.0) sample during the first charge using in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) techniques. The combination of in situ XAS and XRD results clearly identify two two-phase coexistence regions at two voltage plateaus of 3.6 (Fe²⁺/Fe³⁺) and 4.2 V (Mn²⁺/Mn³⁺) and a narrow intermediate region which proceeds via single-phase reaction in between two two-phase regions. In addition, simultaneous redox reactions of Fe²⁺/Fe³⁺ and Mn²⁺/Mn³⁺ in the narrow single-phase region are reported and discussed for the first time.     

二阶非线性脉冲积分-微分方程的边值问题

本文利用单调迭代技术给出了Banach空间中含有非线性一阶微分项x′的二阶脉冲积分-微分方程边值问题存在最大最小解的充分条件;作为主要结论的应用,我们给出了一个无限系统的例子.     

A characterization of complex lattice homomorphisms

In this paper we discuss the problem of how to recognize a complex lattice homomorphism on the complexification of a real vector lattice L from its behavior on a small subset of .      

瑞利型非简并四波混频:一种研究超快过程的新方法

文章提出了用瑞利型非简并四波混频来研究物质的超快过程，与传统的时间领域技术不同，瑞利型非简并四波混频是一种频率领域的光谱学方法，它的时间分辨率与激光的脉冲宽度无关。     

Milnor K-Groups and Finite Field Extensions

Let E/F be a finite separable field extension and let m denote the integral part of log₂ [E : F]. David Leep recently showed that if char(F) 2, then for n m the nth power of the fundamental ideal in the Witt ring of E satisfies the equality I ⁿ E = I ^n–m F · I ^m E. The aim of this note is to prove the analogous equality for the Milnor K-groups, that is K _n E = K _n–m F · K _m E for n m. In either of these equalities one may not replace m by m – 1, as examples of certain m-quadratic extensions indicate.     

Diffraction by an Acoustic Grating Perturbed by a Bounded Obstacle

An original approach to solve 2D time harmonic diffraction problems involving locally perturbed gratings is proposed. The propagation medium is composed of a periodically stratified half-space and a homogeneous half-space containing a bounded obstacle. Using Fourier and Floquet transforms and integral representations, the diffraction problem is formulated as a coupled problem of Fredholm type with two unknowns: the trace of the diffracted field on the interface separating the two half-spaces on one hand, and the restriction of the diffracted field to a bounded domain surrounding the obstacle, on the other hand.