第十一届全国周培源大学生力学竞赛“理论设计与操作”团体赛命题和竞赛总结

对第十一届全国周培源大学生力学竞赛``理论设计与操作'团体赛的命题思路、竞赛过程进行了总结,并提出了相关的建议。     

铁在高压下的结构与磁性的全势的线性Muffin-tin轨道研究

采用全势的线性Muffin-tin轨道(FP-LMTO)方法对铁在高压下的结构和磁性进行了系统的研 究.对铁存在的三种结构bcc,fcc和hcp分别以三种磁性耦合机理在很宽的体积范围内进行了 计算,得到系统的总能、磁矩随体积变化的关系;导出了压强与体积、体弹性模量与体积的 关系曲线;讨论了各相在不同范围内的稳定性;估算了α→ε相之间的转变压强;并把得到 的结果与实验进行了比较,证明所得到的结果与实验是一致的. 关键词： FP-LMTO Bain转变     

萘普生噻唑衍生物的设计和合成及其环氧合酶-2抑制活性的体外评价

基于环氧合酶-2 (COX-2)与COX-1结构上的差异, 设计了萘普生的噻唑衍生物, 以期利用COX-2的侧面口袋, 增加对COX-2的结合作用. 以萘普生为原料经四步反应合成7个目标化合物, 其结构经核磁共振氢谱、质谱和元素分析(或高分辨质谱)确证. 体外筛选结果表明, 化合物有一定的COX-2抑制活性.     

Stimulated Brillouin scattering by the interaction between different-order optical and acoustical modes in an As_2Se_3 photonic crystal fiber

Brillouin gain spectra(BGS)in an As2Se3 photonic crystal fiber(PCF)are investigated numerically.The profiles of the BGS are simulated by calculating the characteristics of different-order optical and acoustic waves in the PCFs with different core diameters.For the small-core PCF,there are two peaks in BGS,but there is only one peak for the large-core PCF.We also reveal that in the small-core PCF,the difference of Brillouin frequency shift between the LP01 and LP11 modes is obvious,while it is not obvious in the large-core PCF.The Brillouin threshold increases with the core diameter increasing.     

二肽肽酶Ⅳ抑制剂的三维定量构效关系研究

二肽肽酶Ⅳ是一类用于治疗Ⅱ型糖尿病具有潜在价值的关键酶,很多此类酶的抑制剂用于处理此病具有相当好的有效性.一系列N-取代的甘氨酰氰基吡咯烷衍生物对于二肽肽酶具有高的活性和选择性.我们使用比较分子力场分析方法建立DPP-Ⅳ抑制剂--N-取代的甘氨酰氰基吡咯衍生物的三维定量构效关系,该模型为设计用于治疗Ⅱ型糖尿病的高效DPP-Ⅳ抑制剂提供结构信息.CoMFA模型的交叉验证相关系数q2=0.575,非交叉验证相关系数r2=0.981,绝对误差S=0.184,F9.68=388.5.使用七个预测集检验了模型的预测能力.所得的模型解释了已有的构效关系,并对同类化合物有较好的预测能力,该模型可用于指导新型的DPP-Ⅳ抑制剂的设计与优化.     

取向易面各向异性羰基铁粉体的高频磁性研究

研究了取向度对羰基铁粉体复合材料微波磁性的影响.理论上构造了取向片状磁性颗粒磁矩的高斯分布,并通过Landau-Lifshitz-Gilbert方程得到了有取向度的软磁材料复数磁导率的求解方法,模拟计算了羰基铁样品高频复数磁导率随频率的变化.研究发现:随着样品取向角?θ?的变大,高斯分布标准偏差σ减小,取向度f增大;随着片状样品取向度的提高,材料初始有效磁导率的实部值增大.为了对照,利用穆斯堡尔谱得到磁体的取向度,并通过网络分析仪测量了磁体的高频磁导率,所获得的实验结果与理论预期值相符.     

Electronic structures and magnetic couplings of B-, C-, and N-doped BeO

The electronic structures and magnetic properties of B-, C-, and N-doped BeO supercells are investigated by means of ab initio calculations using density functional theory. The magnetic exchange constants of C-doped BeO at different doping levels are also calculated. A phenomenological band structure model based on p-d exchange-like p-p level repulsion between the dopants is proposed to explain the magnetic ground states in B-, C-, and N-doped BeO systems. The evolution from the antiferromagnetic phase to the ferromagnetic phase of C-doped BeO supercell with C concentration decreasing can also be well explained using this model. The findings in this study provide a simple guide for the design of band structure for a magnetic sp-electron semiconductor.     

Spin excitations in a K0.84Fe1.99Se2 superconductor as studied by Mssbauer spectroscopy

Mssbauer spectroscopy was used to probe the site-specific information of a K 0.84 Fe 1.99 Se 2 superconductor. A spin excitation gap,△ E ≈ 5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field (HMF) at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron–selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.     

Discussion on the SIF for points on border of elliptical flat crack inside infinite solid under uniform tension

Using the results of crack surface displacement field in Green-Sneddon’s solution[1] and coordinate transformation, this paper has derived an expression K₁(x₁,z₁,a) for SIF at any point and at any orientation on the border of elliptical flat crack inside infinite solid under uniform tension. As a complement of Irwin’s work[3], it is shown that for any pointed point on the elliptical border the SIF defined on normal plane takes the maximum value. And it should be pointed out that in some works some idea concerning Irvin’s contents is open to question. An expression K₁ in terms of polar angle which is more intuitional than centrifugal angle is proposed for SIF at any point on the elliptical border.     

STRUCTURE AND M?SSBAUER STUDY OF NANOCRYSTALLINE Ni-Zn FERRITE

Ni_1-xZn_xFe₂O₄ (0.0≤x≤1.0) nanoparticles have been prepared by the polyvinyl alcohol (PVA) sol-gel method. The lattice parameter of Ni-Zn ferrite nanoparticles is larger than that of the bulk material. The variation of saturation magnetization (M_s) as a function of x has been studied. The M?ssbauer spectra of the samples at room temperature showed the presence of ultrafine particles, exhibiting superparamagnetic relaxation. At higher annealing temperature, the portion of the ferromagnetic ultrafine particles increased.