The initial value problem of a Fokker-Planck equation with a bistable potential

The initial value problem of a Fokker-Planck equation with a bistable potential is solved by a new approach which suggests two time regions, the initial time region when the linearization of the drift force is valid and the second (final) time region in which the Ω-expansion of the Green function is applicable, instead of the three time regions of the scaling theory.     

Neutron diffraction investigation of the cationic distribution in the structure of the spinel-type solid solutions Li2−2xM1+xCl4 (M = Mg, V): Correlation with the ionic conductivity and NMR data

The structure of the spinel-type solid solutions Li_2?2xMin1+xCl₄ M = Mg, V has been studied by neutron diffraction. The cationic distribution in the stoichiometric phases Li₂MgC1₄ and Li₂ VCl₄ is inverse at room temperature, but some vacancies tend to appear in the tetrahedral 8(a) sites. With increasing temperature a gradual migration of the Li⁺ ions from the 8(a) positions into the octahedral 16(c) ones has been established for Li₂MgCl₄. The extra vacancies in the highly deficient spinels LiMgCl₃ and LiVCl₃ ($\text{x =}\text{1}\text{3}$) have been found to be located in the tetrahedral 8(a) sites only. The correlation between the thermal evolutiomn of the cationic dustribution and the corresponding conductivity and NMR data gives a satisfying interpretation of the jump mechanisms responsible for the high ionic mobility in these materials.     

Influence of the TEGa flow on the optical and structural properties of InGaN/GaN multiple quantum wells grown by MOCVD

We have investigated the influence of the TEGa flow on the optical and structural properties of InGaN/GaN multiple quantum wells (MQWs) with an indium composition around 20%. The samples with five-pairs InGaN/GaN MQWs were grown on sapphire substrates by metalorganic chemical vapor deposition. Photoluminescence spectra at 8 K showed that the MQWs grown with a low amount of TEGa flow gave a strong single peak and a higher emission energy. High-resolution X-ray diffraction measurements showed a deterioration of the InGaN/GaN interfaces in the sample grown with the large TEGa flow. The luminescence thermal quenching characteristics suggested that more structural defects acting as non-radiative recombination centers formed in the MQWs when the TEGa flow increased. The results indicate that decreasing the TEGa flow help to build up a new growth balance during the growth of InGaN wells, leading to less structural defects, more homogeneous indium distribution and the abrupt MQWs interfaces.     

斜入射分层线性各向异性等离子体电磁散射时域有限差分方法分析

提出了斜入射分层线性各向异性等离子体电磁散射的时域有限差分(FDTD)方法,通过将二维麦克斯韦方程等价地转换为一维麦克斯韦方程,避免了用二维时域有限差分方法分析该散射问题,极大地提高了计算效率.分析推导了TEz和TMz波斜入射线性分层各向异性等离子体电磁散射的FDTD方法,然后通过该方法计算不同入射角的各向异性等离子板的电磁波反射系数,并与其解析解进行比较,结果表明该方法的准确性和有效性.最后,将该算法应用于计算涂覆分层各向异性等离子体金属板在不同入射角下的反射系数,分析了不同入射角对反射系数的影响.     

最近邻耦合网络的时空混沌同步研究

本文进行了最近邻网络的时空混沌同步研究.以时空混沌系统作为网络的节点,基于Lyapunov稳定性定理,通过确定网络的最大Lyapunov指数,得到了实现网络完全同步的条件.采用Fisher-Kolmogorov时空混沌系统作为网络节点实例进行了仿真模拟,获得了理想的同步效果.进一步研究了有界噪声影响下网络的同步性能,结果显示它具有较强的抗干扰能力.     

正压Rossby波扰动能量

利用Fourier变换方法,研究准地转近似下beta平面上绝热、无摩擦、无强迫耗散的正压大气Rossby波扰动能量在有限时段内的快速发展和衰减情形.给出线性正压位势涡度方程扰动流函数的解析解,并进一步分析扰动能量与东西波数、南北波数、基流切变和黏性系数之间的关系.     

槽道湍流的展向振荡电磁力壁面减阻

采用直接数值模拟方法,对槽道湍流的展向振荡电磁力的减阻效果和减阻机理进行了研究,讨论了电磁力强度和振荡频率对湍流猝发事件以及壁面减阻率的影响.结果表明,电磁力强度或振荡频率变化时,湍流猝发频率和猝发强度的变化趋势是相反的,所以存在最优参数使得减阻效果最好.等价壁面展向速度可以很好地描述电磁力强度和振荡频率的变化对减阻效果的综合效应。     

固体炸药的磁驱动准等熵压缩实验研究

较宽压力范围内未反应炸药的本构关系和状态方程对于深入和精确认识压缩波作用下炸药组分间相互作用的力学过程和起爆热点的形成机制具有重要意义。较之冲击压缩,磁驱动准等熵压缩加载(无冲击压缩)是获取较宽压力范围内未反应炸药的动态压缩力学特性更有效的手段。基于大电流产生的电磁力作用原理,在国内率先实现了炸药的磁驱动无冲击压缩实验技术。通过对负载电极、炸药样品参数的优化设计和安装工艺的控制,实现了5 GPa载荷内JO-9159炸药的磁驱动准等熵压缩加载。基于激光位移干涉测量技术和Lagrange数据处理方法,获得了JO-9159炸药的速度响应历史和准等熵压缩线。所得结果与文献数据进行了比较,结果表明,在实验压力范围内,JO-9159炸药的等熵压缩线与PBX9501炸药的等熵压缩线一致。     

V替代Mn对La_(0.45)Ca_(0.55)MnO_3电荷有序相及自旋玻璃态的影响

用固相反应法制备了La0.45Ca0.55Mn1-xVxO3(x=0.00,0.10)多晶样品.通过X射线衍射谱、质量磁化强度-温度曲线、电子自旋共振谱,研究了V5+替代Mn3+/Mn4+对La0.45Ca0.55MnO3电荷有序相和自旋玻璃态的影响.实验结果表明,当x=0.10时,不仅母体的电荷有序相基本破坏,而且母体在40K左右出现的自旋玻璃态也被融化.电荷有序相被破坏的主要原因是用V5+替代Mn3+/Mn4+后,增加了Mn3+与Mn4+的比例,使铁磁双交换作用优于反铁磁超交换作用;自旋玻璃态的融化是由于V替代Mn后破坏了反铁磁背景下有少量铁磁成分的自旋玻璃态的形成条件.     

微带型光导开关的电压转换效率

采用微带测试电路对光导开关电压转换效率进行了测试。依据传输线理论,考虑微带传输电路的端点反射,计算给出了光导开关导通电阻不为0的情况下,微带测试电路电压转换效率的解析结果。计算表明:对窄脉宽的线性电脉冲输出,电压转换效率将小于50%;对lock-on模式下的宽脉冲输出,电压转换效率可以超过50%,在理想情况下达到100%;在临界状态下,形成双峰电脉冲输出。结果表明,存在端点反射且光导开关产生电脉冲脉宽达到一定值时,微带线可以起到倍压传输线的作用。