一种广义旁瓣相消的超声成像算法

针对最小方差和相干系数结合算法在超声成像对比度、分辨率和对噪声的鲁棒性方面存在的不足, 提出一种广义旁瓣相消的成像算法. 首先基于最小方差准则, 构造广义旁瓣相消器, 获得自适应与非自适应两部分加权向量, 然后根据接收信号的协方差矩阵构建特征阈值信号子空间, 并将获得的加权向量投影到此特征信号子空间的左奇异矢量空间中, 获得新的加权矢量. 通过Field II点目标和吸声斑仿真结果表明: 该方法获得的超声图像在对比度、分辨率和对噪声的鲁棒性上均优于传统延时叠加算法及最小方差和相干系数结合算法, 同时将广义旁瓣相消算法获得的加权向量与符号相干系数结合, 还能进一步提高超声图像质量. 最后通过geabr_0实验数据进行测试, 结果表明: 提出算法的分辨率和对比度及对噪声的鲁棒性上均优于传统延时叠加算法及最小方差和相干系数结合算法.     

欠叠异质栅纳米碳管场效应管的量子输运特性（英文）

采用量子力学模型,对欠叠栅对传统单质栅碳纳米管场效应管(简称C-CNTFET)和异质栅碳纳米管场效应管(简称HMG-CNTFET)电学特性的影响进行理论研究,该模型基于二维非平衡格林函数(NEGF)泊松方程自洽求解.仿真结果表明,C-CNTFET的截止频率可高达THz量级,另外,通过比较C-和HMG-CNTFET可以看出,CCNTFET增加欠叠栅后能够提高器件的开关速度,但不利于提高器件的开关电流比.在HMG-CNTFET中,欠叠栅的采用不仅能够同时改善亚阈值特性和开关电流比,还能降低输出电导.     

Au纳米薄膜的熔化机理及其结构演变的分子动力学模拟

利用分子动力学模拟详细研究了不同厚度的Au纳米薄膜的熔化机理和结构演变. 模拟结果表明所有Au纳米薄膜的熔化行为分为两个阶段,即表面预熔和均相熔化. 只有最外层原子出现了预熔化行为, 其他内层原子在均相熔化之前始终保持稳定的固态,这与零维的Au纳米团簇和一维的Au纳米线的预熔化行为是不同的. 同时Au纳米薄膜的熔化温度随着薄膜厚度的增加而升高. 在预熔化过程中,在原子水平上发现了所有的Au纳米薄膜的f100g晶面向f111g晶面转变的表面重建过程. 对于最薄的L2纳米薄膜,当温度低于500 K 时表面应力不能诱导这样的表面重建. 然而一维的Au纳米线在更低温度下就能够观察到了由表面应力诱导的表面重建过程. 这主要是因为Au纳米线具有更高的比表面积所导致的. 另外研究结果还表明当模拟温度达到某一特定值时,由双原子层组成的Au纳米薄膜能够分裂成一维的纳米线.     

Multi-mycotoxin analysis of animal feed and animal-derived food using LC–MS/MS system with timed and highly selective reaction monitoring

Mycotoxins have the potential to enter the human food chain through carry-over of contaminants from feed into animal-derived products. The objective of the study was to develop a reliable and sensitive method for the analysis of 30 mycotoxins in animal feed and animal-derived food (meat, edible animal tissues, and milk) using liquid chromatography–tandem mass spectrometry (LC–MS/MS). In the study, three extraction procedures, as well as various cleanup procedures, were evaluated to select the most suitable sample preparation procedure for different sample matrices. In addition, timed and highly selective reaction monitoring on LC–MS/MS was used to filter out isobaric matrix interferences. The performance characteristics (linearity, sensitivity, recovery, precision, and specificity) of the method were determined according to Commission Decision 2002/657/EC and 401/2006/EC. The established method was successfully applied to screening of mycotoxins in animal feed and animal-derived food. The results indicated that mycotoxin contamination in feed directly influenced the presence of mycotoxin in animal-derived food.

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Graphical abstract Multi-mycotoxin analysis of animal feed and animal-derived food using LC-MS/MS

     

Calcium Carbonate Mineralized Nanoparticles as an Intracellular Transporter of Cytochrome c for Cancer Therapy

A new intracellular delivery system based on an apoptotic protein‐loaded calcium carbonate (CaCO₃) mineralized nanoparticle (MNP) is described. Apoptosis‐inducing cytochrome c (Cyt c) loaded CaCO₃ MNPs (Cyt c MNPs) were prepared by block copolymer mediated in situ CaCO₃ mineralization in the presence of Cyt c. The resulting Cyt c MNPs had a vaterite polymorph of CaCO₃ with a mean hydrodynamic diameter of 360.5 nm and exhibited 60 % efficiency for Cyt c loading. The Cyt c MNPs were stable at physiological pH (pH 7.4) and effectively prohibited the release of Cyt c, whereas, at intracellular endosomal pH (pH 5.0), Cyt c release was facilitated. The MNPs enable the endosomal escape of Cyt c for effective localization of Cyt c in the cytosols of MCF‐7 cells. Flow cytometry showed that the Cyt c MNPs effectively induced apoptosis of MCF‐7 cells. These findings indicate that the CaCO₃ MNPs can meet the prerequisites for delivery of cell‐impermeable therapeutic proteins for cancer therapy.     

Rheological properties of lightly crosslinked carboxy copolymers in aqueous solutions

The rheological properties of a series of lightly crosslinked carboxy copolymers in aqueous solutions have been evaluated in steady shear and dynamic oscillatory modes. Viscosity profiles and the behavior of storage modulus are related to the chemical composition of the copolymers and their crosslinking density. A maximum in viscosity and in storage modulus which depends on the type of crosslinking agent used is explained by a combination of a chain entanglement mechanism and a closely-packed spheres model. The recovery of viscosity and storage modulus after shearing is very fast and is related to the very fast rearrangement of the microgel structure as a function of time.     

Numerical solution of natural convection flow past a non-isothermal vertical flat plate

The problem of natural convection over a semi-infinite flat plate with non-uniform wall temperature is studied by using a numerical method. The local rates of heat transfer as a function of the distance along the plate are tabulated for a range of Prandtl numbers (0.01 to 100) and for a few cases of wall temperature distributions. Such tabulations serve as a reference against which other approximate solutions can be compared in the future.     

临界非线性椭圆系统的正解［英文］

本文我们借助全空间中无穷远处的方程组,结临界非线性椭圆系统建立一个整体紧性定理.利用此抽象结果及熟知的山路定理证明该系统的正解存在性.     

直馏柴油中硫化物甲基锍盐合成及电喷雾-高分辨质谱分析

在四氟硼酸银的催化作用下,以碘甲烷对直馏柴油进行甲基衍生化反应,使其中的有机硫化物转变成极性较强的锍盐,再用电喷雾-傅立叶变换离子回旋共振质谱仪进行检测。结合气相色谱-脉冲火焰光度检测器(GC-PFPD)分析,研究不同类型的硫化物甲基衍生化反应的选择性和转化率。结果表明:柴油中硫化物在室温条件下容易与碘甲烷发生甲基化反应,大部分硫化物转化为锍盐,总转化率超过80%,苯并噻吩类比二苯并噻吩类更易发生甲基衍生化反应,转化率也相应较高。烷基二苯并噻吩不同取代位异构体间反应选择性存在较大差异,高分辨质谱分析结果表明,直馏柴油中存在环状硫醚类化合物。