由结构力学的平面问题例说最小势能原理

最小势能原理作为结构力学的提高部分,很少在该课程中看到关于它的完整介绍。本文以等刚度连续梁为研究对象,在只考虑弯曲变形的情况下,讨论了位移法典型方程的适用条件。在此基础上,分析了势能法和位移法之间的对偶关系。得出：等刚度连续梁在平面载荷与支座反力构成的平衡力系作用下,可能的小位移状态由虚力方程控制。若真实位移还能利用叠加原理进行求解,则可能位移状态下的总势能在真实位移处取极小值。等刚度连续梁弯曲变形的分析验证了最小势能原理,有助于对一般情况下最小势能原理的深刻认识。

     

聚醚醚酮酮等温结晶动力学的研究

聚醚醚酮酮等温结晶动力学的研究陈艳，王军佐，曹俊奎，那辉，吴忠文（吉林大学化学系，长春，１３００２３）关键词聚醚醚酮酮，等温结晶动力学，差示扫描量热法聚醚醚酮酮（ＰＥＥＫＫ）是在聚醚醚酮（ＰＥＥＫ）基础上开发成功的一种耐热高分子材料。它保持了ＰＥＥＫ...     

A new parametric equation of state and quark stars

It is still a matter of debate to understand the equation of state of cold matter with supra-nuclear density in compact stars because of unknown non-perturbative strong interaction between quarks. Nevertheless, it is speculated from an astrophysical view point that quark clusters could form in cold quark matter due to strong coupling at realistic baryon densities. Although it is hard to calculate this conjectured matter from first principles, one can expect that the inter-cluster interaction will share some general features with the nucleon-nucleon interaction successfully depicted by various models. We adopt a two-Gaussian component soft-core potential with these general features and show that quark clusters can form stable simple cubic crystal structure if we assume that the wave function of quark clusters have a Gaussian form. With this parametrization, the Tolman-Oppenheimer-Volkoff equation is solved with reasonably constrained parameter space to give mass-radius relations of crystalline solid quark stars. With baryon number densities truncated at 2_n0 at surface and the range of the interaction fixed at 2 fm we can reproduce similar mass-radius relations to that obtained with bag model equations of state. The maximum mass ranges from 0.5M_⊙ to 3M_⊙. The recently measured high pulsar mass ( 2M_⊙) is then used to constrain the parameters of this simple interaction potential.     

4,4'-二氨基二苯醚二苯酮固化环氧树脂/粘土纳米复合材料的研究

采用离子交换法, 用十六烷基三甲基溴化铵处理钙基蒙脱土(MMT), 使蒙脱土的层间距由1.49 nm扩大到2.21 nm, 制备了环氧树脂/ BADK/MMT纳米复合材料, 并用XRD等手段研究了有机蒙脱土在环氧树脂中的插层及剥离行为. 研究结果表明, 蒙脱土含量及环氧树脂与有机土的混合温度和时间均对固化后复合材料的剥离产生影响, 只有在特定条件下才能得到剥离型纳米复合材料.     

去势手术对大鼠肾上腺中孕烯醇酮、17α-羟孕烯醇酮和脱氢表雄酮代谢的影响

雄激素阻断治疗作为临床上治疗前列腺癌的主要方式,已被证明能够引起肾上腺中CYP17α1基因表达的增强.由于该基因所编码的酶为肾上腺中的肾上腺雄激素合成的关键酶,因此去势后由该酶所催化的甾体激素合成途径中的孕烯醇酮、17a-孕烯醇酮以及脱氢表雄酮的含量应会出现相应变化.本文建立了一种适用于生物组织样品中上述3种激素的Gc...     

纳米氢氧化钴原位修饰碳糊电极固-液微萃取及电化学检测辛硫磷

运用纳米氢氧化钴原位修饰碳糊电极微分脉冲伏安(DPV)法检测了辛硫磷。在外加电位下辛硫磷分子被萃取到电极表面,并与纳米氢氧化钴相互作用形成络合物,在-0.489 V处得到1还原峰,且还原峰电流随扫速线性增长,表明电极上的还原过程受吸附控制。吸附过程满足Temkin等温吸附模型。pH与电位的关系表明辛硫磷的还原过程为1电子1个质子反应。运用交流阻抗方法考察了反应过程,并辅以理论计算,表明反应为自发过程,计算结果与循环伏安法一致。采用该体系检测辛硫磷,其还原峰电流与辛硫磷浓度的对数分别在3.333×10~(-13)～3.333×10~(-8) mol/L和3.333×10~(-8)～3.333×10~(-6) mol/L范围内呈线性关系,检出限(S/N=3)可达3.333×10~(-13) mol/L。该方法具有良好的重现性及选择性,用于菠菜中辛硫磷农药的检测,结果满意。     

Direct measurement of the Chudakov effect

Experimental results for the restricted energy loss of pairs created from 1-178 GeV photons in a thin Au target and subsequently passing a CCD detector are presented. It is shown that pairs--when detected close to the creation vertex--suffer a reduced energy loss due to the internal screening of the charges constituting the pair. Furthermore, the ability to measure directly the energy of the pair by calorimetry enables a comparison with theory as a function of energy. The observed phenomenon is in good qualitative agreement with general expectations from the Chudakov effect but indicates a quantitative disagreement with either of two mutually disagreeing theories.     

Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS

We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.     

Charmonium production in Pb−Pb collisions at 158 <Emphasis Type="Italic">A</Emphasis> GeV

The NA50 experiment at CERN SPS studies charmonia and Drell-Yan production in the μ⁺ μ^? decay channel at 158A GeV. The data collected in Pb?Pb collisions during 1995, 1996 and 1998 run periods show that the J/ψ is anomalously suppressed in central collisions. This observed suppression pattern can be considered as a strong indication of the production of Quark-Gluon Plasma.