10～100 MeV/u能区重离子反应机制的研究

把QMD模型扩展至10～100MeV/A能区，研究了该能区的重离子碰撞，并仔细检验了初始核在基态时传播的稳定性条件。~(40)Ca+~(40)Ca系统，在10 ～ 100MeV/A能区范围内研究了重离子反应机制随入射能量及碰撞参数的演化情况。我们发现，反应机制随能量的变化并不是突然的跃迁，而是一个连续的变化过程，不同的反应机制可以同时存在并发生竞争。在中心碰撞时，反应机制从全融合发展至非全融合，最后演化至碎裂机制。在周连碰撞时，随着入射能量的增加，根据我们提出的关于深部非弹碰撞和参加者－旁观者质量分布的判据，反应机制的可能变化趋势为从非完全融合或深部非弹碰撞到参加者－旁观者，最后发展至碎裂反应。我们知道，目前还没有人用QMD模型来研究过渡能区DIC机制的基本特征，我们还对~(20)(25Mev/A)+~(20)Ne系统周边碰撞时DIC机制的基本特征作了研究，计算结果表明：在中能区，DIC机制仍然存在，同时，在质量分布、旋转效应及能量损失方面具有低能时相同的特征，但与低能DIC的明显差别在于，出射的中间质量碎片已成为质量分布的主要部分，出射的轻粒子数目也相对增多。当碰撞参数小于7fm时，这里存在着不同反应机制的共存及竞争。根据质量分布随时间的演化情况，我们发现，中间质量碎片主要是由动力学过程中平均场涨落引起的动力学不稳定性造成的，统计衰变也贡献较小的一部分。由粗糙估计可以看出，25MeV/A时~(20)Ne+~(20)Ne系统的DIC机制仍然是一个趋向于平衡过程。相又于低能区，中能区的周边碰撞显得相当复杂

Electromechanical influence of crack velocity at bifurcation for poled ferroelectric materials

The piezoelastodynamic field equations are solved to determine the crack velocity at bifurcation for poled ferroelectric materials where the applied electrical field and mechanical stress can be varied. The underlying physical mechanism, however, may not correspond to that assumed in the analytical model. Bifurcation has been related to the occurrence of a pair of maximum circumferential stress oriented symmetrically about the moving crack path. The velocity at which this behavior prevails has been referred to as the limiting crack speed. Unlike the classical approach, bifurcation will be identified with finite distances ahead of a moving crack. Nucleation of microcracks can thus be modelled in a single formulation. This can be accomplished by using the energy density function where fracture initiation is identified with dominance of dilatation in relation to distortion. Poled ferroelectric materials are selected for this study because the microstructure effects for this class of materials can be readily reflected by the elastic, piezoelectic and dielectric permittivity constants at the macroscopic scale. Existing test data could also shed light on the trend of the analytical predictions. Numerical results are thus computed for PZT-4 and compared with those for PZT-6B in an effort to show whether the branching behavior would be affected by the difference in the material microstructures. A range of crack bifurcation speed upsilon(b) is found for different r/a and E/sigma ratios. Here, r and a stand for the radial distance and half crack length, respectively, while E and a for the electric field and mechanical stress. For PZT-6B with upsilon(b) in the range 100-1700 m/s, the bifurcation angles varied from +/-6degrees to +/-39degrees. This corresponds to E/sigma of -0.072 to 0.024 V m/N. At the same distance r/a = 0.1, PZT-4 gives upsilon(b) values of 1100-2100 m/s; bifurcation angles of +/-15degrees to +/-49degrees; and E/sigma of -0.056 to 0.059 V m/N. In general, the bifurcation angles +/-theta(0) are found to decrease with decreasing crack velocity as the distance r/a is increased. Relatively speaking, the speed upsilon(b) and angles +/-theta(0) for PZT-4 are much greater than those for PZT-6B. This may be attributed to the high electromechanical coupling effect of PZT-4. Using upsilon(b)(0) as a base reference, an equality relation upsilon(b)(-) < upsilon(b)(0) < upsilon(b)(+) can be established. The superscripts -, 0 and + refer, respectively, to negative, zero and positive electric field. This is reminiscent of the enhancement and retardation of crack growth behavior due to change in poling direction. Bifurcation characteristics are found to be somewhat erratic when r/a approaches the range 10(-2)-10(-1) where the kinetic energy densities would fluctuate and then rise as the distance from the moving crack is increased. This is an artifact introduced by the far away condition of non-vanishing particle velocity. A finite kinetic energy density prevails at infinity unless it is made to vanish in the boundary value problem. Future works are recommended to further clarify the physical mechanism(s) associated with bifurcation by means of analysis and experiment. Damage at the microscopic level needs to be addressed since it has been known to affect the macrocrack speeds and bifurcation characteristics. (C) 2002 Published by Elsevier Science Ltd.

Properties of high k gate dielectric gadolinium oxide deposited on Si(100) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.

Fracture behavior of axisymmetrical bars under high triaxial stress and large strain cyclic loading

Axisymmetric notched bars with notch roots of large and small radii were tested under large strain cyclic loading. The main attention is focused on the fracture behaviour of steels having cycles to failure within the range 1-100. Our study shows that a gradual transition from a static ductile nature to one of fatigue cleavage can be observed and characterized by the Coffin-Manson formula in a generalized form. Both the triaxial tensile stress within the central region of specimens and static damage caused by the first increasing load have effects on the final failure event. A generalized cyclic strain range parameter DELTAepsilon is proposed as a measure of the numerous factors affecting behaviour. Fractographs are presented to illustrate the behaviour reported in the paper.

Heat Transfer of Aviation Kerosene at Supercritical Conditions

The heat transfer characteristics of China no. 3 kerosene were investigated experimentally and analytically under conditions relevant to a regenerative cooling system for scramjet applications. A test facility developed for the present study can handle kerosene in a temperature range of 300-1000 K, a pressure range of 2.6-5 MPa, and a mass How rate range of 10-100 g/s. In addition, the test section was uniquely designed such that both the wall temperature and the bulk fuel temperature were measured at the same location along the flowpath. The measured temperature distributions were then used to analytically deduce the local heat transfer characteristics. A 10-component kerosene surrogate was proposed and employed to calculate the fuel thermodynamic and transport properties that were required in the heat transfer analysis. Results revealed drastic changes in the fuel flow properties and heat transfer characteristics when kerosene approached its critical state. Convective heat transfer enhancement was also found as kerosene became supercritical. The heat transfer correlation in the relatively low-fuel-temperature region yielded a similar result to other commonly used jet fuels, such as JP-7 and JP-8, at compressed liquid states. In the high-fuel-temperature region, near and beyond the critical temperature, heat transfer enhancement was observed; hence, the associated correlation showed a more significant Reynolds number dependency.

The effects of fresh and decomposed Microcystis aeruginosa on cladocerans from a subtropic Chinese Lake

We studied in the laboratory the population growth rates of four cladocerans fed both with decomposed Microcystis aeruginosa and with a mixture of fresh colonial M. aeruginosa and Scenedesmus obliquus. The neonates of Diqphanosoma brachyurum and Daphnia carinata were able to develop into adults when they were fed with <64mum decomposed M. aeruginosa, while those of Moina micrura could not use decomposed M. aeruginosa. The population growth rate of the largest species, D. carinata, was less affected by the presence of fresh colonial M. aeruginosa than the other three species. D. carinata obtained the highest growth rate at a biomass level of 10 mg L-1 fresh colonial M. aeruginosa, indicating that, to some extent, it can use colonial M. aeruginosa at a size range of 64-112mum. The population growth rate of M. micrura was negatively correlated with fresh colonial M. aeruginosa within a range of 10-100 mg L-1. The population growth rates of D. brachyurum and Ceriodaphnia cornuta were remarkably decreased by fresh colonial M. aeruginosa, although no significant difference was found within the M. aeruginosa biomass range of 10-100 mg L-1 for either cladoceran. At a biomass level of 50 mg L-1 M. aeruginosa, the population growth rates of the four cladocerans positively correlated with S. obliquus biomass within a range of 0.1-5.0 mg L-1. Our results indicate that the zooplankton community under bloom condition is shaped by the quantity of both M. aeruginosa and other edible algae.

Properties of high k gate dielectric gadolinium oxide deposited on Si(100) by dual ion beam deposition (DIBD)

Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.

Generation of 10 GHz, 1.9 ps optical pulse train using semiconductor optical amplifier and silica-based highly nonlinear fiber

We propose a simple approach to generate a high quality 10 GHz 1.9 ps optical pulse train using a semiconductor optical amplifier and silica-based highly nonlinear fiber. An optical pulse generator based on our proposed scheme is easy to set up with commercially available optical components. A 10 GHz, 1.9 ps optical pulse train is obtained with timing jitter as low as 60 fs over the frequency range 10 Hz-1 MHz. With a wavelength tunable CW laser, a wide wavelength tunable span can be achieved over the entire C band. The proposed optical pulse generator also can operate at different repetition rates from 3 to 10 GHz.

Fabrication and characterization of SERS-active silver clusters on glassy carbon

In this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4-aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS-based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80-100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 x 10(4) relative to silver colloid, which might have resulted from the presence of 'hot-spots' at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 x 10(7) by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface.

Controlled synthesis of 2D Au nanostructure assembly with the assistance of sulfonated polyaniline nanotubes

A wet chemical approach is used successfully to produce nanostructured Au material by the reduction of sulfonated polyaniline (SPANI) nanotubes. The Au nanostructures obtained are composed of single crystal Au nanoplates, which are aggregated layer-by-layer into stacks or edge-on-face into clusters at various conditions. The Au nanoplate diameter and thickness can be conveniently controlled in the range of 100 nm to 2 mu m and 10 to 30 nm, respectively, with no accompanying single Au nanoparticles being observed. The formation of the Au nanostructures was controlled by the degradation of SPANI. The gradually and slowly released segments of SPANI served as the reductant during the growth of the 2D Au nanostructures.

The electrical and magnetic properties of lanthanide alkaline-earth transition-metal oxides

Five Ln(2)SrMCuO(6.5) oxides (M = Co, Ln = Y and Ho; M = Fe, Ln = Y, Ho, and Dy) were synthesized, and their crystal structures, IR spectra, and physical properties were studied. They have almost the same structure and crystallize in orthorhombic systems. Below room temperature, Y2SrFeCuO6.5, a known layered oxide, shows antiferromagnetic behavior, but the four new oxides are paramagnetic. Y2SrFeCuO6.5 fits the Curie-Weiss law in the temperature range 300-100 K, but Y2SrCoCuO6.5 shows complex magnetic behavior because of the disproportion of some Co+3 to Co+2 and Co+4 The five oxides are all p-type semiconductors in the measured temperature range and have large electrical resistivities at room temperature.

The encysted dormant embryo proteome of Artemia sinica

The possibility of the brine shrimp Artemia to produce dormant embryo (cysts) in diapause is a key feature in its life history. In the present study, we obtained a proteomic reference map for the diapause embryo of Artemia sinica using two-dimensional gel electrophoresis with a pH range of 4-7 and a molecular weight range of 10-100 kDa. Approximately 233 proteins were detected, and 60 of them were analyzed by capillary liquid chromatography tandem mass spectrometry (LC-MS/MS). Of these, 39 spots representing 33 unique proteins were identified, which are categorized into functional groups, including cell defense, cell structure, metabolism, protein synthesis, proteolysis, and other processes. This reference map will contribute toward understanding the state of the diapause embryo and lay the basis and serve as a useful tool for further profound studies in the proteomics of Artemia at different developmental stages and physiological conditions.

Using oxidized carbon nanotubes as matrix for analysis of small molecules by MALDI-TOF MS

Oxidized carbon nanotubes are tested as a matrix for analysis of small molecules by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS). Compared with nonoxidized carbon nanotubes, oxidized carbon nanotubes facilitate sample preparation because of their higher solubility in water. The matrix layer of oxidized carbon nanotubes is much more homogeneous and compact than that of nonoxidized carbon nanotubes. The efficiency of desorption/ionization for analytes and the reproducibility of peak intensities within and between sample spots are greatly enhanced on the surface of oxidized carbon nanotubes. The advantage of the oxidized carbon nanotubes in comparison with alpha-cyano-4-hydroxycinnamic acid (CCA) and carbon nanotubes is demonstrated by MALDI-TOF-MS analysis of an amino acid mixture. The matrix is successfully used for analysis of synthetic hydroxypropyl P-cyclodextrin, suggesting a great potential for monitoring reactions and for product quality control. Reliable quantitative analysis of jatrorrhizine and palmatine with a wide linear range (1-100 ng/mL) and good reproducibility of relative peak areas (RSD less than 10 %) is achieved using this matrix. Concentrations of jatrorrhizine (8.65 mg/mL) and palmatine (10.4 mg/mL) in an extract of Coptis chinensis Franch are determined simultaneously using the matrix and a standard addition method. (c) 2005 American Society for Mass Spectrometry.

ADI方法求解Navier-Stokes方程的一个改进格式

ADI方法常被用来计算不可压缩Navier-Stokes方程。在处理涡度方程的非线性项和涡度在壁面上的条件时,通常采用滞后的方法对涡度方程和流函数方程分别求解。然而,非线性项的滞后破坏了ADI方法的完全二阶精度;涡度方程和流函数方程分别求解减弱了两个方程的耦合性;涡度壁面条件的滞后则破坏了方法的完全隐式。本文在应用ADI方法求解涡度方程和流函数方程时应用了一种交替线性化的技术,对涡度方程和流函数方程耦合求解,内点和边界点上的涡度和流函数值同时求出。因此,ADI方法保持了完全的二阶精度,避免了上面所提到的问题。作者应用这一方法计算了雷诺数R_θ等于1,10,100,500,1000时的二维方腔流动(空间步长h=1/20)。计算结果表明:这一方法保持了通常ADI方法的优点,可以应用大的时间步长。最后补充计算了雷诺数R_θ=2000的二维方腔流动。