拟随机选择法

本文针对通常的随机选择法在求Riemann问题基本解上遇到的困难,提出采用拟特征线形式下的各独立标量方程形式,求其简单的Riemann问题组以代替原Riemann问题的解。这样,使方法基本保持了随机选择法的特点,又使方法的实现、应用和推广更加容易,而且可以设计并行算法。最后用激波管和溃坝问题为例作了实算。结果与已知的结果相比也是满意的。     

闭壳层金掺杂钛氧团簇阴离子解离氢分子研究

Dissociation of molecular hydrogen (H₂) is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H₂ dissociation by Au₁-doped closed-shell titanium oxide cluster anions AuTi₃O₇^- and AuTi₃O₈^- has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and massselected to react with H₂ in an ion trap reactor. In the reaction of AuTi₃O₈^- with H₂, the ion pair Au⁺-O₂^2- rather than Au⁺-O^2- is the active site to promote H₂ dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H₂ dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H₂ activation and dissociation.     

白蚁菌圃上小白球菌和炭角菌的生态关系初报

通过人工调节pH, CO:分压、温湿度以及有机氮等条件,探讨了白蚁巢内两种优势真菌的生态关系.结果表明:小白球菌和炭角菌除对温湿度要求相似外,不同之处在于小白球菌适应于高浓度COZ、低pH值(3.8一4.2),低浓度有机氮,以及对酵母浸膏也有一定的要求。而炭角菌要求低浓度CO, ,高pH值(5.0- 6.3),又需要高浓度有机氮.根据这些实验,我们初步认为白蚁的存在产生了丰富的有机酸和高浓度CO z,可能给小白球菌造成了特定的pH环境,成为蚁巢菌圃上优势真菌的主要选择因子,在“废巢”菌圃上,有机酸和COZ浓度的降低,炭角菌分泌的代谢物质引起菌圃pH值的上升,可能是炭角菌成为优势种的原因。     

黄河三角洲盐生草甸白茅(Imperata cylindrica var. major)群落季节性动态的研究

采用定位研究的方法研究了生长季白茅(Imperata cylidrica var. major)群落的主要特征和动态。群落的种类组成较简单,其盖度一般在七月中旬达到100％。群落的高增长及地上生产量符合逻辑斯蒂增长模型(Logistic model),并主要受环境中水分和温度因子的影响。群落的最大高度为59cm,出现在八月中旬;地上生产量最大值为干重563g/m~2,出现在九月中旬。     

对a_LiIO_3的离子迁移极化现象的进一步讨论

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Transverse spin correlations in a random anisotropy system: Amorphous ErCo2

We provide a coherent interpretation of early small angle scattering experiments performed by some of us on amorphous ErCo₂ [9]. At low temperature the zero field transverse spin-spin correlation function is found to fit a simple exponential for large length scales (l >l_c), supporting the lower critical dimensionality d_c=4. For shorter length scales (l<l_c) the correlation function is of the Ornstein-Zernike type. These results are physically understood in terms of the breaking of ferromagnetism into Imry and Ma domains.A further physical interpretation leads us to consider the localization of ferromagnetic spin waves within Imry and Ma domains in zero field, and their delocalization by application of an external field.     

Co离子注入TiO2薄膜的显微结构和磁性研究

利用直流磁控溅射技术在玻璃衬底上沉积了TiO₂薄膜,并对其进行了Co离子注入,最后在真空中500 ℃退火50 min,得到系列薄膜样品. 利用剥离-分散方法制备了薄膜的透射电镜样品,并用扫描电镜(SEM)、X射线能量散射谱(EDX)和高分辨透射电镜(HRTEM)对样品做了近似原位观察,研究了薄膜样品中不同Co离子注入深度的成分分布和显微结构. 结果表明,薄膜呈锐钛矿结构,Co元素主要分布在薄膜表层,Co离子的注入使TiO₂薄膜的晶粒被部分破坏,并形成CoO,而5 关键词： 2薄膜')" href="#">Co注入TiO₂薄膜 电镜原位观察 室温铁磁性     

Lyapunov exponent calculation of a two-degree-of-freedom vibro-impact system with symmetrical rigid stops

A two-degree-of-freedom vibro-impact system having symmetrical rigid stops and subjected to periodic excitation is investigated in this paper. By introducing local maps between different stages of motion in the whole impact process, the Poincar'e map of the system is constructed. Using the Poincar'e map and the Gram-Schmidt orthonormalization, a method of calculating the spectrum of Lyapunov exponents of the above vibro-impact system is presented. Then the phase portraits of periodic and chaotic attractors for the system and the corresponding convergence diagrams of the spectrum of Lyapunov exponents are given out through the numerical simulations. To further identify the validity of the aforementioned computation method, the bifurcation diagram of the system with respect to the bifurcation parameter and the corresponding largest Lyapunov exponents are shown.     

Orientation dependence of structural transition in fcc Al driven under uniaxial compression by atomistic simulations

By molecular dynamics simulations employing an embedded atom method potential,we have investigated structural transformations in single crystal Al caused by uniaxial strain loading along the [001],[011] and [111] directions. We find that the structural transition is strongly dependent on the crystal orientations. The entire structure phase transition only occurs when loading along the [001] direction,and the increased amplitude of temperature for [001] loading is evidently lower than that for other orientations. The morphology evolutions of the structural transition for [011] and [111] loadings are analysed in detail. The results indicate that only 20% of atoms transit to the hcp phase for [011] and [111] loadings,and the appearance of the hcp phase is due to the partial dislocation moving forward on {111} fcc family. For [011] loading,the hcp phase grows to form laminar morphology in four planes,which belong to the {111} fcc family; while for [111] loading,the hcp phase grows into a laminar structure in three planes,which belong to the {111} fcc family except for the (111) plane. In addition,the phase transition is evaluated by using the radial distribution functions.