MgO/MCM-22催化苯与草酸二乙酯烷基化合成乙苯的研究

实验以MgO/MCM-22为催化剂,在气相连续流动固定床反应器上催化苯与草酸二乙酯(DEO)烷基化,合成乙苯(EB)。考察了MgO负载量变化和工艺条件的影响。以硝酸镁为前驱体通过等体积浸渍法制备了MgO/MCM-22催化剂,并以低温N_2吸附脱附、X射线衍射、NH_3-TPD、吡啶吸附IR等,对催化剂进行了表征。实验结果表明:随MgO负载量的增加,苯的转化率逐渐下降,而乙苯的选择性明显提高,这主要是由于负载MgO后催化剂的酸性位数量下降引起的。以MCM-22为催化剂,在最佳反应条件下:温度653 K,空速为2 h~(-1),原料配比n(苯):n(DEO)=4:1,苯的转化率为37.5%,乙苯选择性为80.3%。     

热处理工艺对22Cr双相不锈钢组织的影响

研究了热处理工艺(固溶处理、固溶处理 时效处理)对22Cr双相不锈钢板材显微组织、脆性析出相形态的影响.结果表明:22Cr轧制板材在1 150℃以下固溶处理后,组织为由典型的α、γ两相组成的条状组织;经1 150℃固溶处理后,γ相已基本变成块状分布;在950～1 150℃固溶时,α、γ两相含量随固溶温度呈良好的直线关系.经1 050℃固溶处理后,在850℃进行时效处理,从α相中析出脆性相,随着时效时间的延长,脆性相含量增加.     

The anti-tumor effects of cordycepin-loaded liposomes on the growth of hepatoma 22 tumors in mice and human hepatoma BEL-7402 cells in culture

Liposomes have successfully been used for decades to encapsulate and protect drugs that are prone to deactivation in the body. The present study aimed to demonstrate the use of liposomes to encapsulate cordycepin, an adenosine analog that quickly loses its activity in vivo. The cordycepin-loaded liposomes were prepared by the ammonium sulfate gradient approach, and its in vitro and in vivo antitumour activities were evaluated using BEL-7402 cells and hepatocellular carcinoma H22 transplanted tumors, respectively. An MTT assay was used to observe the cytotoxicity of cells treated with cordycepin and cordycepin-loaded liposomes in vitro. High-content screening (HSC) was carried out using Hoechst 33342 to detect apoptotic cells and the ratio of cells in different cell cycle stages. The data demonstrated that both the cordycepin and the cordycepin-loaded liposomes resulted in clear cytotoxicity with IC50 values of 18.97 and 29.39?μg/mL, respectively. The latter showed significantly strong inhibitory effects on H22 tumor growth in mice, while the former did not show any inhibitory effects on tumor growth. In addition, the HSC assay showed that the cordycepin-loaded liposomes resulted in a higher rate of apoptosis than the cordycepin alone in BEL-7402 cells. Further data analysis revealed that the cells treated with cordycepin-loaded liposomes were predominately arrested at the G2/M phase (p?p?in vivo anti-tumor activity of cordycepin.     

绿色环保混合制冷剂

介绍了环保混合制冷剂R-404A、R-407C、R-410A、R-413A和R-417A的性能、用途及我国目前的研究状况。     

煤矿液压支架大流量技术改造

通过简要分析煤矿液压支架大流量技术改造的必要性及理论依据,并确定液压支架大流量技术合理方案及工艺的改造,以煤矿BC480-22/42型液压支架为例,最后对煤矿液压支架大流量改造前后控制进行对比。     

多项式矩阵的无穷秩与广义微分算子系统的无穷行为（下）

多项式矩阵的无穷秩与广义微分算子系统的无穷行为（下）程学建，丁立刚（数学教研室）２广义微分算子多项式矩阵系统能控（观）的ＰＢＨ型条件考虑系统（１）。记定理２．１广义微分算子多项式矩阵系统（１）（１）Ｒ—能控有限；（２）脉冲能控；（３）强能控，有限及证...     

冷藏车层叠式蒸发器应用R404A与R22和R134a的比较

采用分布参数法对层叠式蒸发器建立数学模型，并对蒸发器采用R404A，R22和R134a时的换热和流动性能进行模拟比较。结果表明，在空调工况范围内，新型中低温混合制冷剂R404A具有R134a换热性能好和R22压降小的特点，能够很好地适用于冷藏车系统空调侧层叠式蒸发器。     

Leaving home,returning home: Migration as a labor market choice for Alaska Natives

We investigate determinants of the pattern of recent migration of Alaska Natives between rural homelands and urban areas. A review of the literature on moving in the North American North suggests that economic opportunities draw migrants, although such opportunities must be viewed in the context of the mixed subsistence-cash economy prevailing in rural areas of the region. Consequently, we model Native migration as a simultaneous decision with labor market participation in a mixed economy. Estimated equations explaining individual Alaska Native migration choices using the U.S. Census Public Use Microdata Sample (PUMS) are consistent with the model, and also suggest that perceived opportunities differ between women and men.The authors acknowledge financial support from the National Science Foundation, grant OPP-9521459. An earlier version of this paper was presented to the 1998 annual meeting of the Western Regional Science Association