辐射-导热耦合换热边界元算法

本文提出了一种求解辐射-导热耦合换热问题的边界单元算法(BEM),该方法将两种传热方式通过辐射热源耦合起来.首先,采用BEM对辐射传热方程、辐射热源方程和含有辐射热源的热传导方程进行离散;其次,利用辐射传热方程消除辐射热源方程中的辐射热流项;然后,根据Stefan-Boltzmann定律形成含有温度四次方以及热流密度表示的非线性代数方程组.出现在所有积分方程中的域积分由径向积分法转换成边界积分,形成了对于参与性介质问题也只需在边界上划分单元的纯边界元算法.最后,用Newton-Raphson迭代法对方程组进行求解.提供的数值算例将表明本文所介绍方法的正确性与有效性.     

电场调控下合金凝固过程枝晶形貌演变同步辐射原位成像

由于金属合金的不透明性, 研究者们无法实时捕捉到金属合金凝固过程中枝晶生长的动态行为, 也无法直接观察到电流对枝晶生长行为的动态调控过程. 采用同步辐射X 射线成像技术, 实时观察到了电流对枝晶生长形貌演变的动态调控过程. 成像结果表明, 直流电流能够显著抑制枝晶生长, 并促使枝晶尖端变平,随着电流增加, 枝晶尖端发生分裂现象, 这归因于枝晶尖端的电流拥挤以及溶质富集. 脉冲电流能够显著细化枝晶臂间距并影响其凝固进程, 主要原因是周期性的脉冲电流对液固界面产生了循环的热冲击和振荡扰动所致.     

Serum levels of perfluorinated compounds in the general population in Shenzhen, China

Perfluorinated compounds (PFCs) have been detected in many environmental matrices, biota, and nonoccupationally exposed populations in China recently. However, little is known about the distribution and levels of various PFCs in the general population living in areas where there is PFC exposure. In the present study, the levels and prevalence of ten target PFCs were determined in 227 serum samples from a population of nonoccupationally exposed individuals in Shenzhen, China. Results indicated that human exposure to PFCs was prevalent in Shenzhen. Perfluorooctanoate (PFOA) was the dominant PFC contaminant in the serum samples, with a median concentration of 6.72 ng/mL, followed by perfluorooctane sulfonate (PFOS) with a median concentration of 2.07 ng/mL. Other PFCs were detected at much lower concentrations, with median concentrations ranging from 0.02 to 0.87 ng/mL. Statistically, no significant (P>0.05) gender differences were observed for any of the PFCs. Significant (P<0.01) positive correlations were found between age and serum concentrations of the target PFCs, except for perfluorobutane sulfonate (R = 0.16, P = 0.01), perfluorohexanoic acid (R = 0.08, P = 0.22), and perfluoroheptanoic acid (R = 0.11, P = 0.10). Based on the one-compartment pharmacokinetic model, the total daily intakes of PFOA and PFOS for the general population in Shenzhen were calculated as 0.63 and 0.20 ng/kg body weight/day, respectively.     

The determination of atmospheric phosphine in Ny-lesund

Phoshpine (PH3), a volatile and toxic gas, has been proved to commonly exist in the environment.The determination of gaseous phosphine and its emission fluxes in Ny-lesund is reported in this paper.Results showed that gaseous phosphine exist in Arctic atmosphere commonly and the concentration of phosphine ranged from 16.3-600.2 ng/m3, with the maximum concentration of phosphine in tundra areas and the minimum in surface air of ocean.The concentration of phosphine ranged from 65.79-1259 ng/m3 in colliery at...     

电化学修形齿轮齿面微观形貌与摩擦学特性

以电化学修形前后的齿面微观不平度高度的特性和形状特性进行了分析和测算，研究了电化学表面平滑化对齿面摩擦，齿面闪温及润滑状态的影响；证明电化学修形能延长齿轮的使用寿命。     

钢轨气压焊试验研究

对碳钢钢轨气压焊进行了试验研究。探讨了焊接工艺过程对气压焊焊接接头显微组织及强度的影响。     

冷连轧过程线性化动态模型的研究

以多机架四辊冷连轧机为背景，研究了冷连忆过程的动态模型，建立了冷连轧过程的工作点线性化状态空间模型，实验仿真结果说明了这一动态模型的有效性。     

关于P-Laplace方程解的梯度HOlder连续性的一个注记

对文献〔１—３〕中的结果：ｕｔ＝ｄｉｖ（｜ｕ｜ｐ－２ｕ）在ΩＴ＝Ω×（０，Ｔ）上弱解的空间梯度是Ｈｌｄｅｒ连续的做一个补充．在这个注记里，本文作者讨论条件Ｐ＞ｍａｘ｛１，２ＮＮ＋２｝是怎样由ｕ的性质所确定的．属于ＬＮｌｏｃ（ΩＴ）空间解的梯度是Ｈｌｄｅｒ连续的条件仅仅是Ｐ＞１．     

冷库温度自动记录仪

本文介绍广西计算中心和广西区防疫站合作研制的冷库温度自动记录录仪，文中着重介绍其软硬件设计和主要功能。该记录仪性能／价格比优于国外同类产品，可以用来代替进口产品。     

Atomic and efficient e-cash transaction protocol

Atomicity is necessary for reliable and secure electronic commerce transaction and to guarantee the participants' interests. An atomic and efficient e-cash (electronic cash) transaction protocol based on the classical e-cash scheme is presented. The delivery of digital goods is incorporated into the process of payment in the protocol. Apart from ensuring all three levels of atomicity, the novel protocol features high efficiency and practicability with unfavorable strong assumption removed. Furthermore, the proposed protocol provides non-repudiation proofs for any future disputes. At last, analysis of the atomicity and efficiency is illustrated.