具有混合隔离策略的非线性计算机病毒传播模型的Hopf分岔研究

建立了考虑潜伏期时滞和临时免疫期时滞的具有混合隔离策略的非线性计算机病毒传播模型,旨在帮助理解计算机病毒在网络中的传播规律。通过计算模型基本再生数,以不同时滞组合为分岔参数,研究了模型的局部渐近稳定性;利用中心流形定理和规范型理论分析了Hopf分岔的方向和周期解的稳定性,并通过数值模拟验证了理论分析的正确性。研究结果可为计算机病毒治理提供理论依据。     

弱正定阵的表征及判定条件

本文利用分块矩阵实正定性的判定，给出了弱正定阵的等价表征，并得到了若于弱正定阵的判定条件。     

两种联苯酚类化合物的太赫兹时域光谱研究

利用太赫兹时域光谱技术获得了295 K时2,2′-二羟基联苯(2,2′-biphenol, 2BP)和4,4′-二羟基联苯(4,4′-biphenol, 4BP)在0.1~1.6 THz波段的光谱. 实验结果显示, 两种同分异构体在太赫兹频率范围内的吸收谱有显著的差异. 结合量子化学计算, 2BP中的两个羟基间能够形成分子内氢键, 在1.45 THz的运动模式初步判断为包含氢键在内的两个苯环的低频摆动.     

Rheological properties of a surfactant-induced gel for the lysozyme–sodium dodecyl sulfate–water system

Rheological properties of isotropic solutions and gel structures of lysozyme–sodium dodecyl sulfate mixtures in water are investigated. Isotropic solutions behave as Newtonian fluids with very low viscosity values. For the lysozyme solutions the intrinsic viscosity and the Huggins coefficient were calculated on the basis of the Mooney equation. Above a certain yield stress value, the viscosity of the gel samples decreases continuously in the whole range of the shear rate. Dynamic rheological experiments show weak gel behavior where the storage modulus and the loss modulus are almost parallel and are frequency-dependent. A belated gel stage with very slow kinetics has been characterized. There is a substantial enhancement of the gel strength by ageing since the belated gel stage manifests a higher yield stress value and a higher storage modulus than the initial gel stage. The gels are stable in the temperature range between 10 and 32 °C.     

AlPxO催化剂的制备、表征及其在邻苯二酚O-单醚化反应中的催化性能

采用沉淀法制备了AlPxO(x=0,0.33,0.5,1.0,1.5,2.0)催化剂,通过XRD,FTIR,固体核磁共振,BET,NH3-TPD和CO2-TPD等手段对催化剂进行了表征,发现n(P)/n(Al)对催化剂结构及表面酸碱性质有很大影响.考察了AlPxO催化剂上以邻苯二酚和甲醇为原料,采用气相法一步合成愈创木酚的反应性能,并研究了催化剂表面酸碱性质对反应活性和选择性的影响.结果表明,催化剂表面同时存在一定量的弱酸和弱碱中心有利于提高愈创木酚的收率.     

Helical racemate architecture based on osmium(II)-polypyridyl complexes: Synthesis and structural characterisation

New polypyridyl osmium(II) complexes [Os(κ³-tptz)(EPh₃)₂Cl]BF₄ (E = P, 1; As, 2) with group 15 donor ligands are reported. Structural studies on the representative complex [Os(κ³-tptz)(PPh₃)₂Cl]BF₄ revealed formation of helical racemates with sidewise stacking of right and left-handed anti-parallel helical strands. Salient structural features and DNA binding studies along with binding constant [6.6 × 10³ M⁻¹] and site size [0.12] of the complex 1 with calf thymus (ct) DNA by absorption spectroscopy are described.     

Al2O3改性CuO/Fe2O3催化剂水煤气变换反应性能

采用分步共沉淀法制备了不同Al₂O₃含量(0%-15% (w))的CuO/Fe₂O₃催化剂, 并进行水煤气变换反应(WGSR)评价测试. 制得的催化剂中含有复合物CuFe₂O₄, 其晶粒尺寸, 氧化还原性质和表面Cu分散通过相应表征手段加以研究. X 射线粉末衍射(XRD), 拉曼(Raman)光谱, N₂物理吸附, N₂O分解和CO₂程序升温脱附(CO₂-TPD)等表征技术说明适量Al₂O₃的加入可以促进尖晶石CuFe₂O₄发生由四方相向立方相的转变, 阻止催化剂中Cu烧结, 增大表面Cu分散, 增加弱碱性位点的数量. 此外, 采用H₂程序升温还原(H₂-TPR)技术探究改性的CuO/Fe₂O₃催化剂的还原性能. 关联结果发现, Al₂O₃掺杂在增大铜物种的耗氢量, 降低其还原温度方面起着重要的作用. 即Al₂O₃的添加促进CuO/Fe₂O₃催化剂中铜铁物种之间的协同作用. 结合活性测试和表征结果,适量的Al₂O₃ (10%(w))改性的催化剂具有较小的Cu颗粒尺寸、较大的Cu分散、较强的还原性能、较多数量的弱碱性位点, 因此具有更好的初始活性和热稳定性.     

Hopf bifurcation analysis of a predator-prey system with Holling type IV functional response and time delay

This paper is concerned with a predator-prey system with Holling type IV functional response and time delay. Our aim is to investigate how the time delay affects the dynamics of the predator-prey system. By choosing the delay as a bifurcation parameter, the local asymptotic stability of the positive equilibrium and existence of local Hopf bifurcations are analyzed. Based on the normal form and the center manifold theory, the formulaes for determining the properties of Hopf bifurcation of the predator-prey system are derived. Finally, to support these theoretical results, some numerical simulations are given to illustrate the results.     

Equivariant Hopf bifurcation for neutral functional differential equations

In this paper we employ an equivariant Lyapunov-Schmidt procedure to give a clearer understanding of the one-to-one correspondence of the periodic solutions of a system of neutral functional differential equations with the zeros of the reduced bifurcation map, and then set up equivariant Hopf bifurcation theory. In the process we derive criteria for the existence and direction of branches of bifurcating periodic solutions in terms of the original system, avoiding the process of center manifold reduction.

     

Hopf bifurcation analysis for a model of genetic regulatory system with delay

This paper deals with a mathematical model that describe a genetic regulatory system. The model has a delay which affects the dynamics of the system. We investigate the stability switches when the delay varies, and show that Hopf bifurcations may occur within certain range of the model parameters. By combining the normal form method with the center manifold theorem, we are able to determine the direction of the bifurcation and the stability of the bifurcated periodic solutions. Finally, some numerical simulations are carried out to support the analytic results.