空气冲旋钻头牙齿失效分析与新材料实验研究

针对目前空气冲旋钻头钻进中牙齿频繁断裂、脱落以及磨损严重，导致破岩效率低、使用寿命短等问题，采用纳米改型技术，在硬质合金中掺杂纳米Al₂O₃制备出Al₂O₃/WC Co纳米/微米复合材料，对其性能、组织结构进行分析，对其耐磨性、耐冲击性进行实验研究，结果表明：加入3%的纳米Al₂O₃并添加适量的抑制剂和稀土元素能明显改善Al₂O₃/WC Co纳米/微米复合材料的组织结构、细化晶粒，复合材料的耐磨性和耐冲击性能得到大幅提高，较硬质合金YG8提高4～8倍。为大幅度提高钻头破岩效率，延长钻头使用寿命提供了可能性。     

Optimal portfolio of safety-first models

The purpose of this article is to study Kataoka's safety-first (KSF) model, which is a representative of safety-first models of most popular models in portfolio selection of modern finance. We obtain conditions that guarantee that the KSF model has a finite optimal solution without normality assumption. When short-sell is allowed, we provide an explicit analytical solution of the KSF model in two cases. When short-sell is not allowed, we propose an iterating algorithm for finding the optimal portfolios of the KSF model. We also investigate a KSF model with constraint of mean return and obtain the explicit analytical expression of the optimal portfolio.     

3,4-二氯甲苯的合成

以对氯甲苯为原料,经直接氯化合成3,4-二氯甲苯。选择AlCl_3/S_2Cl_2为催化剂,经正交试验得最佳反应条件为:反应温度100℃、催化剂浓度2.O％、主辅催化剂配比1:0.5,此时3,4-二氯甲苯在二氯甲苯中的选择性达51％,单程收率为41.5％。     

二苯基乙炔及双二茂铁基乙炔与Fe_3(CO)_(12)的反应性研究

本文以十二羰基三铁Fe3(CO)12作为催化剂前体,研究了Fe3(CO)12分别与两种炔烃的反应性能。结果表明,当炔烃为二苯基乙炔时,可以同时得到四苯基环戊二烯酮化合物(1)和具有铁碳五元环状结构的双核铁羰基配合物(2);而与双二茂铁基乙炔反应时,仅获得了一个产物四二茂铁取代环戊二烯酮羰基铁配合物(3)。这类反应产物种类繁多,通过设计该类反应,可为合成不同取代基的环戊二烯酮类化合物提供一条新的途径。     

会计电算化专业工学结合人才培养模式的建设——以商丘职业技术学院为例

本文提出了会计电算化"3+1+1+1"工学结合的人才培养模式,并指出只有通过加强教学团队、课程体系、ⅱ实训基地等教学环节的具体建设,才能实现培养人才的目标.     

Positive quadrant dependence tests for copulas

In this paper the interest is in testing the null hypothesis of positive quadrant dependence (PQD) between two random variables. Such a testing problem is important since prior knowledge of PQD is a qualitative restriction that should be taken into account in further statistical analysis, for example, when choosing an appropriate copula function to model the dependence structure. The key methodology of the proposed testing procedures consists of evaluating a “distance” between a nonparametric estimator of a copula and the independence copula, which serves as a reference case in the whole set of copulas having the PQD property. Choices of appropriate distances and nonparametric estimators of copula are discussed, and the proposed methods are compared with testing procedures based on bootstrap and multiplier techniques. The consistency of the testing procedures is established. In a simulation study the authors investigate the finite sample size and power performances of three types of test statistics, Kolmogorov–Smirnov, Cramér–von‐Mises, and Anderson–Darling statistics, together with several nonparametric estimators of a copula, including recently developed kernel type estimators. Finally, they apply the testing procedures on some real data. The Canadian Journal of Statistics 38: 555–581; 2010 © 2010 Statistical Society of Canada     

浅论明初朱元璋废相的原因

先秦尚无正式相制,军政合一,政务尚简.自军政分立,国政繁琐,辅政职务越发重要,秦设丞相总领百官辅政,汉武帝时以中官夺相权,隋唐宋时相职以多散权,元朝则独设中书省,家天下的朝政导致私利和公权交杂,而明太祖废相制,以天子亲政朱批政务.历朝治乱循环均无法从制度层面解决家天下的稳定传承,相权演变也是皇权变化的外在表现.本文试图从相权的演变中探讨明初废相的原因和动机.     

3G时代电信运营商营运模式分析

3G时代电信市场发生了深刻的变化,从原来以追求垄断为主的电信运营商竞争转变成为以追求更大客户价值的合作创造市场的产业链竞争。与2G产业链相比,3G产业链具有产业链的构成发生重大变化、链中环节被重新定义且协同试发生变化,不同产业的关联性加强等特点。电信运营商在建立有效、成功的3G产业链时要关注用户需求,扩大原用户群,注重市场营销战略,还要正确地选择营运模式,在有效的模式选择中展开竞争,以提升随之带来的各种增值业务的经济效益。     

不同致惊药物对小鼠不同脑区~3H-GABA与GABA_A受体结合的影响

用放射配体受体结合分析法,测定致惊药物红藻氨酸(kainic,KA)和印防己毒素(picrotoxin,Pic)对小白鼠下丘脑、大脑皮层、海马、小脑四个脑区~3H-GA-BA 和 GABA_A 受体结合的影响。结果显示,KA、Pic 均能明显降低各脑区~3H-GABA和 GABA_A 受体的结合量,除 Pic 对下丘脑无显著差异外,其余均有显著性差异(P<0.05或 P<0.01)。实验结果提示:KA 和 Pic 均能降低 GABA_A 受体的结合量,但是它们是通过不同的途径间接或直接地影响 GABA 能系统活动的。