Electroluminescence model of bipolar resonant tunnelling diode

An electroluminescence model of a bipolar resonant tunnelling diode is carried out. The current is the sum of the electron and hole current. The electron and hole density at the resonant level of a quantum well are related to the electron and hole current, respectively. A radiative recombination rate formula is derived from the matrix element, electron and hole distribution. The results show that a large on-off ratio of light output can be achieved by the bipolar resonant tunnelling diode.     

Identification of the Phenol Functionality in Deprotonated Monomeric and Dimeric Lignin Degradation Products via Tandem Mass Spectrometry Based on Ion–Molecule Reactions with Diethylmethoxyborane

Conversion of lignin into smaller molecules provides a promising alternate and sustainable source for the valuable chemicals currently derived from crude oil. Better understanding of the chemical composition of the resulting product mixtures is essential for the optimization of such conversion processes. However, these mixtures are complex and contain isomeric molecules with a wide variety of functionalities, which makes their characterization challenging. Tandem mass spectrometry based on ion–molecule reactions has proven to be a powerful tool in functional group identification and isomer differentiation for previously unknown compounds. This study demonstrates that the identification of the phenol functionality, the most commonly observed functionality in lignin degradation products, can be achieved via ion–molecule reactions between diethylmethoxyborane (DEMB) and the deprotonated analyte in the absence of strongly electron-withdrawing substituents in the ortho- and para-positions. Either a stable DEMB adduct or an adduct that has lost a methanol molecule (DEMB adduct-MeOH) is formed for these ions. Deprotonated phenols with an adjacent phenol or hydroxymethyl functionality or a conjugated carboxylic acid functionality can be identified based on the formation of DEMB adduct-MeOH. Deprotonated compounds not containing the phenol functionality and phenols containing an electron-withdrawing ortho- or para-substituent were found to be unreactive toward diethylmethoxyborane. Hence, certain deprotonated isomeric compounds with phenol and carboxylic acid, aldehyde, carboxylic acid ester, or nitro functionalities can be differentiated via these reactions. The above mass spectrometry method was successfully coupled with high-performance liquid chromatography for the analysis of a complex biomass degradation mixture.

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Synthesis of tripeptides containing a very crowded α,α-disubstituted glycine with pyridine rings by solid-phase Ugi reaction

Tripeptides containing a novel α,α-disubstituted glycine with two pyridine rings, α,α-di(2-pyridyl)glycine (2Dpy), were synthesized by the solid-phase Ugi reaction using di(2-pyridyl)methanimine attached directly to a Rink amide resin. Thereby, yields of the tripeptides, Z-AA₁-2Dpy-AA₃-OMe (AA₁ and AA₃ = Gly or Aib), were markedly improved, compared with yields by the solution method.     

Thermoelectric Converters Based on Ionic Conductors

Thermoelectric materials represent a new paradigm for harvesting low-grade heat, which would otherwise be dissipated to the environment uselessly. Relative to conventional thermoelectric materials generally composed of semiconductors or semi-metals, ionic thermoelectric materials are rising as an alternative choice which exhibit higher Seebeck coefficient and lower thermal conductivity. The ionic thermoelectric materials own a completely different thermoelectric conversion mechanism, in which the ions do not enter the electrode but rearrange on the electrode surface to generate a voltage difference between the hot and cold electrodes. This unique character has inspired worldwide interests on the design of ionic-type thermoelectric converters with attractive advantages of high flexibility, low cost, limited environmental pollution, and self-healing capability. Referring to the categories of ionic thermoelectric conversion, some representative ionic thermoelectric materials with their respective characteristics are summarized in this minireview. In addition, examples of applying ionic thermoelectric materials in supercapacitors, wearable devices, and fire warning system are also discussed. Insight into the challenges for the further development of ionic thermoelectric materials is finally provided.     

New perturbation bounds and condition numbers for the hyperbolic QR factorization

Using the modified matrix-vector equation approach, the technique of Lyapunov majorant function and the Banach fixed point theorem, we obtain some new rigorous perturbation bounds for R factor of the hyperbolic QR factorization under normwise perturbation. These bounds are always tighter than the one given in the literature. Moreover, the optimal first-order perturbation bounds and the normwise condition numbers for the hyperbolic QR factorization are also presented.     

带多重右边的不定最小二乘问题的条件数

本文研究了带多重右边的不定最小二乘问题的条件数,给出了范数型、混合型及分量型条件数的表达式,同时,也给出了相应的结构条件数的表达式.所考虑的结构矩阵包含Toeplitz 矩阵、Hankel矩阵、对称矩阵、三对角矩阵等线性结构矩阵与Vandermonde矩阵、Cauchy矩阵等非线性结构矩阵.数值例子显示结构条件数总是紧于非结构条件数.     

液相色谱-串联质谱法测定人血浆中的维拉帕米

维拉帕米（Verapamil,Ver）是第一代钙离子拮抗剂,临床上主要用于心律失常、心绞痛和高血压的治疗。有关生物样品中Ver的分析方法报道较多,主要有高效液相色谱（HPLC）-紫外检测法、HPLC-荧光检测法和高效毛细管电泳法,但色谱分析时间均大于8min。最近有文献报道采用液相色谱-串联质谱法（LC—MS／MS）测定人血浆中Ver及其活性代谢物去甲维拉帕米的对映异构体。本文旨在建立一种专属、快速、灵敏的LC—MS／MS用于测定人血浆中的Ver,以研究该药在体内的药代动力学特点。     

Determination of terrestrial γ-radiation dose rate and soil radon concentration in a river region of Southern China

Journal of Radioanalytical and Nuclear Chemistry - To monitor the natural radiation level in a River region in Southern China, an investigation was conducted into the terrestrial γ dose rate...     

双钻头打孔机作业的优化模型

对于双钻头打孔机的孔群加工问题分为两部分解决.首先建立刀具转换次数最少的优化模型.将钻头A和钻头B每阶段使用某一刀具的状态设为0-1变量建立模型,用LINGO程序求解.另外根据10种孔型所需刀具及加工次序,将整个双钻头打孔作业任务分成3个阶段,在每一阶段,以打孔个数较多的钻头刀具作为基准刀具,使用贪心算法遍历打孔;另一个刀具以两钻头距离大于3cm为约束,确定可行点集合,在可行点集合中制定最优打孔路线,进而可求打孔作业总时间,作业总成本.