ACCURACY OF MEASUREMENT OF NATURAL GAMMA RAY SPECTRA BY HD－8004 NaI（T1）GAMMA SPECTROMETER

ＡＣＣＵＲＡＣＹ　ＯＦ　ＭＥＡＳＵＲＥＭＥＮＴ　ＯＦ　ＮＡＴＵＲＡＬ　ＧＡＭＭＡ　ＲＡＹ　ＳＰＥＣＴＲＡ　ＢＹ　ＨＤ－８００４　ＮａＩ（Ｔ１）ＧＡＭＭＡ　ＳＰＥＣＴＲＯＭＥＴＥＲＺｈｕＧｕｏｑｉｎ（朱国钦）ａｎｄＺｈｅｎｇＲｅｎｓｈｕ（郑仁淑）（Ｄｅ...     

大功率InGaAsP/GaAs量子阱半导体激光器的直流和1/f噪声性质

对大功率InGaAsP/GaAs量子阱(QW)半导体激光器(LD)的直流(DC)特性和小注入下的低频噪声(LFN)特性进行了实验研究.DC检测发现,V-J和I dV/dI-I可以对LD的电流泄漏作出判断.LFN检测发现,小注入下的1/f低频电压噪声幅值Bv(I)∝I<'βv>.理论分析和老化实验均表明,电流指数βv与载流子输运和电流泄漏机制之间有很好的相关性,存在电流泄漏和无辐射复合的器件其|βv|较小,可靠性较差.     

PLC在煤气炉电解液控制系统中的应用

在介绍了PLC可编程控制器的结构和工作原理的基础上,阐明了在煤气炉电解液控制系统中利用PLC可编程控制器结构上的优点,可以实现生产过程的集中控制和管理,并且显示了PLC在煤气炉电解液控制系统中具有良好的应用性能和抗干扰能力.该系统的使用达到了降低工人劳动强度、改善劳动条件、提高劳动生产率的目的,并为保证化工生产长周期的稳定运行,提供了有力保障.     

Effect of a sweeping air stream and gas–phase aspect ratio of an isothermal Stefan diffusion column on the experimental estimation of binary gas diffusivities

The Stefan column consists of liquid A evaporating into an inert/stagnant gas B with a sweeping B stream at the top. It was designed to estimate binary gas diffusivities, D_AB’s, but “end effects” such as gas mixing at the top and interfacial curvature have been either ignored or uncorrelated to the operational settings. This study’s hypothesis is that gas mixing at the top and the gas–phase aspect ratio affect D_AB estimation in the acetone (A)-ambient air (B) system at 50?°C. The sweeping stream Reynolds number (Re) and the gas–phase aspect ratio (AR?=?initial gas phase height to column internal diameter) were the variables tested. Isothermal evaporation-diffusion experiments were conducted in which the temporal interfacial descent was tracked. The settings were 492 ≤ Re ≤ 5378 and AR between 5 and 15. A 1D transport model allowed determination of the experimental diffusivity, D_AB,exp, by nonlinear regression. For Re < 600, the D_AB,exp errors relative to D_AB,CE (predicted by the Chapman–Enskog kinetic theory for low-density gases) were small and unrelated to AR, while for Re > 600 the errors increased considerably with Re and were inversely proportional to AR. This study is the first to relate the column’s operational settings to the D_AB estimation errors. The column should be operated at low sweeping gas Re and large AR for accurate D_AB,exp’s. The low Re region deserves further study, while the present transport model may have to be replaced by computational fluid dynamics simulations to account for the multidimensional gas flow patterns.     

Performance Investigation of IEEE 802.11e EDCA Under Non-Saturation Condition Based on the M/G/1/K Model

The IEEE 802.11e network provides different with QoS （Quality of service） guarantee for different traffic streams. The Enhanced distributed channel access （EDCA） in IEEE 802.11e MAC protocol is proposed to support prioritized QoS on the basis of the Distributed coordination function （DCF） in IEEE 802.11. We first build a new Markov chain model for the EDCA. The model takes into account both the idle state that represents that there are no packets to be transmitted and differentiation based on different AIFS-value （Arbitration inter-frame space） for different traffic. We can use the signal transfer function of the generalized Z-transform domain state transition diagram to derive a probability distribution of the MAC layer service time and analyze the performance of EDCA from a non-saturated channel to a saturated medium by using M/G/1/K queuing model. The proposed model is calculated numerically and validated against simulation results, we observed a good match between the analytical model and simulation. Simulation and theoretical results show that despite providing prloritized QoS, the EDCA still can not support strict QoS for real-time application. On the other hand, it is inevitable that there is unfairness of channel access to prloritized traffic due to EDCA.     

基于GIS与水动力模型融合技术的山洪沟溃堤风险分析

为加强洪灾预防与应对措施建设,融合GIS和一、二维水动力数值计算方法,建立了具有实际地形的山洪沟溃堤风险分析精细化仿真模型,并将其应用于宁夏贺兰山东麓小峰沟溃堤洪水演进模拟。采用非结构化网格与内边界处理技术合理优化了复杂边界与线状地物阻挡水效果,精确模拟了小峰沟遭遇100年一遇洪水导洪堤溃决造成的淹没风险,基于GIS分析了洪水演进不同时刻的风险分布特征与影响情况,实现了GIS与水动力数值模型的有机融合。计算结果基本合理可靠,可为该地区沟道治理、风险管理与灾防决策提供参考。     

Short communication: The effect of delayed colostrum feeding on plasma concentrations of glucagon-like peptide 1 and 2 in newborn calves

Glucagon-like peptide (GLP)-1 is involved in glucose homeostasis via its role in stimulating insulin secretion, whereas GLP-2 increases mucosal growth of the small intestine. To our knowledge, the effect of delayed colostrum feeding on plasma GLP-1 and GLP-2 in neonatal calves has not been evaluated. To investigate the effect of delayed colostrum feeding on plasma concentrations of GLP-1 and GLP-2 in newborn calves, we randomly assigned 27 Holstein bull calves to 1 of 3 treatment groups: those fed colostrum within 1 h after birth (control), 6 h after birth (6H), and 12 h after birth (12H; n = 9 for each treatment). Blood samples were obtained before the colostrum feeding and every 3 h after each colostrum feeding for a 36-h period, and plasma concentrations of GLP-1, GLP-2, insulin, and glucose were measured. Plasma GLP-1 concentration at 12 h after colostrum feeding was lower in 12H than in control calves. In addition, plasma insulin concentration was lower in the 6H and 12H calves than in the controls. Plasma glucose and GLP-2 concentrations were, however, not affected by treatment. These results indicate that delayed colostrum feeding can decrease plasma GLP-1 and insulin concentrations without affecting glucose or GLP-2 concentration.     

Effect of Polyethylene Molecular Architecture on the Dynamic Viscoelastic Behavior of Polyethylene/Polyhexene-1 Blends and Its Correlation with Morphology

In the present work, the rheology, morphology, and interfacial interaction of polyethylene/polyhexane-1 (PE/PH-1) blends with various polyethylene types with different molecular architectures are investigated. The scanning electron microscopy (SEM) images showed a droplet-matrix morphology in all percentage of PH-1 for all blend systems and the size of droplets increased proportionally with PH-1 content. The minimum droplet size is observed for high-density polyethylene (HDPE)/PH-1 blends. The homogeneity of the blends at various compositions is assessed by using viscoelastic parameters determined by dynamic oscillation rheometry in the linear viscoelastic region. A distinct Newtonian plateau at low frequencies is perceived and the variations of complex viscosity (η*) versus angular frequency (ω) for all blend systems are in good agreement with Carreau-Yasuda model. The complex viscosity of samples at various percentages of PH-1 showed the negative deviation from mixing rule in low and high frequencies for all blend systems. The Cole-Cole plots deviated from semi-circular shape at higher percentages of PH-1 than 10wt% in the blends of low-density polyethylene (LDPE)/PH-1 and linear low-density polyethylene (LLDPE)/PH-1. By using emulsion theoretical model, the lowest interfacial tension is found for HDPE/PH-1 blends comparing with its counterparts based on LDPE and LLDPE and the best fitting with experimental data was observed for this blends system.