考虑微观结构特征长度演化的内变量黏塑性本构模型

在金属晶体材料高应变率大应变变形过程中,存在强烈的位错胞尺寸等微观结构特征长度细化现象,势必对材料加工硬化、宏观塑性流动应力产生重要影响。基于宏观塑性流动应力与位错胞尺寸成反比关系,提出了一种新型的BCJ本构模型。利用位错胞尺寸参数,修正了BCJ模型的流动法则、内变量演化方程,引入了考虑应变率和温度相关性的位错胞尺寸演化方程,建立了综合考虑微观结构特征长度演化、位错累积与湮灭的内变量黏塑性本构模型。应用本文模型,对OFHC铜应变率在10-4~103 s-1、温度在298~542 K、应变在0~1的实验应力-应变数据进行了预测。结果表明:在较宽应变率、温度和应变范围内,本文模型的预测数据与实验吻合很好;与BCJ模型相比,对不同加载条件下实验数据的预测精度均有较大程度的提高,最大平均相对误差从9.939%减小为5.525%。     

Determination of carbamates and organophosphorus pesticides by SDME–GC in natural water

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. Analytical methods with low quantification limits are necessary. The application of a new extraction technique, solvent drop microextraction (SDME), followed by gas chromatography with a nitrogen-phosphorus detector, was assessed for determining carbamates and organophosphorus pesticides in natural water. Experimental parameters which control the performance of SDME such as selection of microextraction solvent, optimization of organic drop volume, effects of sample stirring, salt addition, and, finally, sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity (r ²>0.99), precision (<13%), and detection limits (0.2 to 5 μg/L), plus matrix effects were evaluated (no matrix effects were found). SDME is a dynamic technique able to extract pesticides from water in 14 min; the use of organic solvents and water samples for SDME is negligible compared to other extraction techniques.     

Investigation of wavelength division multiplexing ring network topology to enhance the system capacity

In this paper, we have investigated the wavelength division multiplexed (WDM) system using ring network topology. This network is used to increase the capacity with eight optical add/drop multiplexers (OADMs) by using dispersion compensating fiber and semiconductor optical amplifier (SOA) to achieve a distance up to 1600 km. It is observed that network shows the acceptable results at 15 Gbps data rate with 100 GHz channel spacing. The OADM nodes are also varied to investigate the network performance in the term of BER and Q-factor.     

固相萃取-大体积程序升温进样气相色谱-三重四极杆串联质谱测定饮用水中3种挥发性N-亚硝胺

建立了固相萃取大体积程序升温进样气相色谱-三重四极杆质谱联用（GC-QqQ-MS/MS）同时测定饮用水中N-亚硝基二甲胺、N-亚硝基甲基乙基胺及N-亚硝基二乙基胺的分析方法。用椰壳活性炭固相萃取小柱萃取水样中待测物组分，少量二氯甲烷洗脱、无水硫酸钠脱水，大体积程序升温进样，气相色谱-三重四极杆质谱联用仪进行多反应监测（MRM）模式检测，外标法定量。3种N-亚硝胺在1~50 ng/L范围内线性关系良好，相关系数（r²）均大于0.999，在饮用水中进行10、20和50 ng/L水平的添加，3种待测物平均加标回收率为94.8%~109%，相对标准偏差（RSD）为4.44%~8.10%（n=5），定量限（LOQ）为0.08~0.7 ng/L。该法灵敏、准确、简单、可靠，适用于饮用水中3种N-亚硝胺组分的痕量检测。     

一类非线性的经济系统控制模型的稳定性分析

用边界比较法讨论了以CE S生产函数作为反馈的定常经济系统控制模型的稳定性,该模型为含有非局部条件的分布参数系统.并且证明了非定常模型的平衡解是全局渐进稳定的.     

Refreshable mercury film silver based electrode for determination of chromium(VI) using catalytic adsorptive stripping voltammetry

The refreshable mercury film silver based electrode Hg(Ag)FE applied for determination of Cr(VI) traces using catalytic adsorptive striping voltammetry (CAdSV) will be presented. The film electrode is characterized by its very good surface reproducibility (not less than 2%) and long-term stability (1500–2000 measurement cycles). The mechanical refreshing of mercury film is realized in the specially constructed device, in a time shorter than 1–2 s.

In the paper, it will be proved that a mechanically weak hanging mercury drop electrode (HMDE) may be substituted by mercury film Hg(Ag)FE electrode with a surface area adjustable from 1.5 to 12 mm². For the electrode surface 4 mm² the detection limit obtained for Cr(VI) was 0.19 nM, while the linearity range measured for a 20 s accumulation time was between 0.5 and 50 nM. The relative standard deviation (R.S.D.) in determination of Cr(VI) varied from 1 to 5%. The influence of the excess of Cr(III) on determination of Cr(VI) was analyzed using samples from the Dobczyce reservoir spiked with known amounts of Cr(VI) and Cr(III).     

Comparison of the thermal performances of two nanofluids at low temperature in a plate heat exchanger

The objective of this study is to compare experimentally the thermal performances of two types of commercial nanofluids. The first is composed of oxides of alumina (γAl₂O₃) dispersed in water and the second one is aqueous suspensions of nanotubes of carbons (CNTs). The viscosity of the nanofluids is measured as a function of the temperature between 2 and 10 °C. An experimental device, containing three thermal buckles controlled in temperature and greatly instrumented permits to study the thermal convective transfers. The evolution of the convective coefficient permits to study the convective thermal transfers. The evolution of the convective coefficient is presented according to the Reynolds number, at low temperature from 0 to 10 °C and for the two aforementioned nanofluids. An assessment of the pressure drops in the circuit as well as of the powers of the circulator and outputs is dealt with.     

饱和多孔弹性Timoshenko梁的大挠度分析

基于微观不可压饱和多孔介质理论和弹性梁的大挠度变形假设,考虑梁剪切变形效应,在梁轴线不可伸长和孔隙流体仅沿轴向扩散的限定下,建立了饱和多孔弹性Timoshenko梁大挠度弯曲变形的非线性数学模型.在此基础上,利用Galerkin截断法,研究了两端可渗透简支饱和多孔Timoshenko梁在突加均布横向载荷作用下的拟静态弯曲,给出了饱和多孔 Timoshenko梁弯曲变形时固相挠度、弯矩和孔隙流体压力等效力偶等随时间的响应.比较了饱和多孔Timoshenko梁非线性大挠度和线性小挠度理论以及饱和多孔 Euler-Bernoulli梁非线性大挠度理论的结果,揭示了他们间的差异,指出当无量纲载荷参数q>l0时,应采用饱和多孔Timoshenko梁或Euler-Bernoulli梁的大挠度数学模型进行分析,特别的,当梁长细比λ<30时,应采用饱和多孔Timoshenko梁大挠度数学模型进行分析.     

Large Deviation Theorems for Gaussian Processes and Their Applications in Information Theory

We discuss on the large deviation theorems for stationary Gaussian processes and their applications in information theory. The topics investigated here include error probability of string matching, error probabilities for random codings, and a conditional limit theorem which justifies the maximum entropy principle.