QuEChERS-液相色谱-串联质谱法测定植物性食品中30种氨基甲酸酯类农药残留

基于欧洲标准化委员会标准方法(EN 15662)对食品基质的分类,选择6种代表性植物性食品作为基质,系统优化了QuEChERS样品前处理方法;在此基础上,建立了30种氨基甲酸酯类农药的液相色谱-串联质谱分析方法。实验结果表明,除涕灭威砜的线性范围为2~100 μg/kg,其他29种氨基甲酸酯类农药的线性范围均为1~100 μg/kg;6种样品基质在3个添加水平(5、20、100 μg/kg)下的回收率为56.13%~127.6%,相对标准偏差为0.47%~16%;以信噪比(S/N)≥10计,30种农药的定量限(LOQ)为0.041~1.9 μg/kg。本文方法灵敏、有效,适用于植物性食品基质中30种氨基甲酸酯类农药残留的测定。     

On Mixed Pressure-Velocity Regularity Criteria to the Navier-stokes Equations in Lorentz Spaces,Part Ⅱ:The Non-slip Boundary Value Problem

This paper is a continuation of the authors recent work [Beir?o da Veiga, H.and Yang, J., On mixed pressure-velocity regularity criteria to the Navier-Stokes equations in Lorentz spaces, Chin. Ann. Math., 42(1), 2021, 1–16], in which mixed pressure-velocity criteria in Lorentz spaces for Leray-Hopf weak solutions of the three-dimensional NavierStokes equations, in the whole space R~3 and in the periodic torus T~3, are established. The purpose of the present work is to extend the result of mentio...     

浅海环境中矢量水听器角度谱特性

为探明远场舰船噪声和近场平台噪声声能流相互作用的机制对矢量水听器角度谱特性的影响,基于简正波矢量场理论,构建舰船平台噪声声场模型,获得与海上实验结果相符的声能流角度谱特性,声能流方向均随频率变化。对远场舰船噪声声能流和近场平台噪声声能流相互作用进行仿真,两者声能流强度的此消彼长使角度谱出现4种条纹,与海上实验获得的角度谱特性一致,导致目标方位估计出现误差,且不同频带上的结果不一致。说明两个声能流相互作用时,影响合成能流角度谱特性的主要因素是两者的声压级之差,为浅海中同时存在多个声源时的目标方位估计提供参考。     

采用可见光源和分划板快速装调激光光路

 分析了激光测量光路的特点和装校要求,给出了采用可见光源、分划板装校激光光路的原理。以预放测量模块为例,介绍了装校的流程及装校中的注意事项,分析了装校所能达到的精度,并用内调焦望远镜进行了装校精度检查。结果表明,采用可见光源、分划板装校的激光光路透镜光轴正过心的偏心极限误差小于等于0.07 mm,光轴倾斜极限误差小于等于25″。     

基于多分辨分析的沪深股市相关性分析

为了有效地揭示沪深股市不同交易周期股票交易的相关性,本文采用极大重叠离散小波变换,将上证指数和深圳成指高频收益率分解在不同的交易周期上,对各个周期的收益率采用semi-GPD模型作为其边缘分布分别进行拟合,在此基础上采用Copula函数方法建立同周期收益率的联合分布,度量了沪深两市同周期交易的相关性.实证表明,不同交易周期所表现出的相关性存在明显差异,并且随着交易期的增长,沪深两市非对称结构逐步明显。     

COMPONENT ALLEE EFFECTS AND STAGE‐SPECIFIC PREDATION: A BRIEF INSIGHT INTO CONSERVATION AND BIOLOGICAL CONTROL ISSUES

In this paper, we propose a two‐stage structured population model subject to component Allee effects in fecundity and maturation, and with two disturbances (predation only and harvest and predation) acting on both stages. It is shown that this combination leads to a demographic Allee effect—a characteristic that could be exploited in pest biological control, but on the other hand, it represents a bane in conservation biology. The analysis is performed for disturbances with functional responses type 2 and 3, and the models show that they yield qualitatively similar results. This characteristic is discussed from the species conservation and biological control point of view, together with possible extensions of this work.     

Measurement of the e + e − → ηπ+π− cross section in the \sqrt s = 1.04–1.38-GeV energy range with a spherical neutral detector at the VEPP-2M collider

The e ⁺ e ^? → ηπ⁺π^? cross section in the η → 2γ channel has been measured in the $ \sqrt s $ = 1.04- to 1.38-GeV energy range. The data with a total integrated luminosity of 9.05 pb^?1 were collected on a spherical neutral detector at the VEPP-2M collider. The results are consistent with the BaBar and CMD2 data and have a higher statistical accuracy.     

Observation of B --> K(+/-) pi(0) and B --> (K)0 pi(0), and evidence for B --> pi(+)pi(-)

We have studied charmless hadronic decays of B mesons into two-body final states with kaons and pions and observe three new processes with the following branching fractions: beta(B-->pi(+)pi(-)) = (4.3(+1. 6)(-1.4)+/-0.5)x10(-6), beta(B-->K(0)pi(0)) = (14.6(+5.9+2.4)(-5.1-3. 3))x10(-6), and beta(B-->K(+)/-pi(0)) = (11.6(+3.0+1.4)(-2.7-1.3))x10(-6). We also update our previous measurements for the decays B-->K(+)/-pi(-/+) and B+/--->K(0)pi(+/-).     

全局特征及弱尺度融合策略的小样本语音情感识别

语音是一种短时平稳时频信号,因此大多数的研究者都通过分帧来提取情感特征。然而,分帧后提取的特征为局部特征,无法准确反应情感语音动态特性,故单纯采用局部特征往往无法构建鲁棒的情感识别系统。针对这个问题,先在不分帧的语音信号里通过多尺度最优小波包分解提取语句级全局特征,分帧后再提取384维的语句级局部特征,并利用Fisher准则进行降维,最后提出一种弱尺度融合策略来将这两种语句级特征进行融合,再利用SVM进行情感分类。基于柏林情感库的实验结果表明本文方法较单纯使用语句级局部特征最后识别率提高了4.2%到13.8%,特别在小样本的情况下,语音情感识别率波动较小。     

Equivalent properties of single event burnout induced by different sources

The experimental results of single event burnout induced by heavy ions and 252Cf fission fragments in power MOSFET devices have been investigated. It is concluded that the characteristics of single event burnout induced by 252Cf fission fragments is consistent to that in heavy ions. The power MOSFET in the ＂turn-off＂ state is more susceptible to single event burnout than it is in the ＂turn-on＂ state. The thresholds of the drain-source voltage for single event burnout induced by 173 MeV bromine ions and ^252Cf fission fragments are close to each other, and the burnout cross section is sensitive to variation of the drain-source voltage above the threshold of single event burnout. In addition, the current waveforms of single event burnouts induced by different sources are similar. Different power MOSFET devices may have different probabilities for the occurrence of single event burnout.