Vibrational properties of nanograins and interfaces in nanocrystalline materials

The vibrational dynamics of nanocrystalline Fe(90)Zr(7)B(3) was studied at various phases of crystallization. The density of phonon states (DOS) of the nanograins was separated from that of the interfaces for a wide range of grain sizes and interface thicknesses. The DOS of the nanograins does not vary with their size and down to 2 nm grains still closely resembles that of the bulk. The anomalous enhancement of the phonon states at low and high energies originates from the DOS of the interfaces and scales linearly to their atomic fraction.     

On the sensitive dynamical system and the transition from the apparently deterministic process to the completely random process

The detailed analysis of the dynamical process of coin tossing is made. Through calculations, it is illustrated how and why the result is extremely sensitive to the initial conditions. It is also shown that, as the initial height of the mass center of the coin increases, the final configuration, i.e. head or tail, becomes more and more sensitive to the initial parameters (the initial velocity angular velocity, and the initial orientation), the coefficient of the air drag, and the energy absorption factor of the surface on which the coin bounces. If we keep the head upward initially but allow a small range for the change of some other initial parameters, the frequency that the final configuration is head, would be 1 if the initial height h of the mass center is sufficiently small, and would be clo to 1/2 if h is sufficiently large. An interesting question is how this frequency changes continuously from 1 to 1/2 as h increases. Detailed calculations show that such a transition is very similar to the transition from laminar to turbulent flows. A basic difference between the transition stage and the completely random stage is indicated: In the completely random stage, the deterministic process of the individual case is extremely sensitive to the initial conditions and the dynamical parameters, out the statistical properties of the ensemble are insensitive to the small changes of the initial conditions and the dynamical parameters. On the contrary, in the transition stage, both the deterministic process of the individual case and the statistical properties of the ensemble are sensitive to the initial conditions and the dynamical parameters. The mechanism for this feature of the transition stage is the existence of the long-train structure in the parameter space. The illuminations of this analysis on some other random phenomena are discussed.     

3-芳亚甲基联氨羰基-5-(对位取代苯基)-吡唑衍生物的 合成、结构和生物活性

以4-取代苯乙酮及草酸二乙酯为起始原料, 设计合成了20个新的3-芳亚甲基联氨羰基-5-(对位取代苯基)-吡唑衍生物, 产率较高. 所合成的化合物经元素分析, IR, 1H NMR对其结构进行了表征, 化合物4b, 4h还通过X-ray单晶衍射进一步确证了其结构. 初步生物活性实验结果表明, 所合成的化合物对绿豆发芽过程有着较好的生长调节作用.     

电感耦合等离子体原子发射光谱分析中光谱干扰校正卡尔曼滤波法研究

本文利用电感耦合等离子体原子发射光谱多色仪的扫描功能,用卡尔曼滤波法对各种光谱干扰进行校正。结果表明,该法能处理各种类型光谱干扰,不需要样品基体匹配,其测定回收率明显优于在峰法和离峰法,具有简便、准确等优点。     

质子交换光波导生长动力学研究

分析了质子交换光波导的生长动力学并给出了波导层厚度与生长时间的计算公式。     

Studies on self-pumped phase conjugation in Cu-doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 crystals

The use of Cu-doped (K_0.5Na_0.5)_0.2(Sr_0.61Ba_0.39)_0.9Nb₂O₆ as self-pumped phase conjugators using internal reflection is reported. Reflectivities as high as 63% at 5145.5 nm and 60% at 632.8 nm were realized. It was found that the photorefractive response changes significantly at different doping concentration. The responses of the crystals to the laser wavelength, incident angle and dopant concentration are studied.     

无人机视角下的林木爆燃火特性研究

森林火灾“爆燃”现象的特征是突然发生的高强度、高蔓延速度的燃烧。目前为止,关于“爆燃火”的原因还没有达成共识。以无人机视角下对林木爆燃火特性研究,以四川木里特大森林火灾为研究对象,通过分析凉山州某森林扑火部队3月31日木里森林火灾当天KWT（科卫泰）无人机航拍火场画面,结合无人机实时影像及实地调研数据,分析了峡谷地形林火蔓延时空特征,探讨了峡谷中风向风速变化时空分布规律,研究了地形变化条件下,不同海拔高度风速特征,建立了无人机倾角测量风速模型（其中为风速m·s-1,为无人机倾角°）。结果表明,高山峻岭特殊地形环境下每天4:00—12:00时间段为静风期,为峡谷林火扑救最佳时期;午后15:00—17:00和晚上20:00—22:00为山谷地形风速活跃期;仿真软件数据显示山顶、谷底与山腰不同海拔位置的风速风向不统一,谷底会产生乱流现象,且风速与海拔不存在正相关关系,小气候在复杂地形中占主导影响地位;在谷口至山谷深处的中间位置会出现气流速度的波峰状态,并易形成乱流,为爆燃火发生提供了客观必要条件。该研究可为复杂地形环境下,森林草原火灾扑救安全提供数据和技术支撑。     

一种可拆装式的脑外科手术用磁共振成像线圈

在临床磁共振成像(MRI)应用中,射频线圈的设计是非常关键的,针对不同的应用目的,合适的线圈能获得质量更好的图像. 有的应用需要线圈提供均匀性较好的射频场,而有的应用则需要线圈在特定区域内提供高的信噪比(SNR). 但是线圈很难同时得到好的射频场（B₁场）、空间均匀性和高的SNR,需要根据实际应用情况进行折衷设计. 针对MRI在脑外科手术中的应用特点,设计并制作了一种新颖的、适用于脑外科手术的MRI接收和发射共用射频线圈. 该线圈采用可分拆式结构,在脑外科手术支架上可以进行反复组装和拆卸,减少了MRI对医生手术的影响. 仿真结果和人体成像实验表明,该线圈能产生均匀的射频场、有较高的SNR和较大的成像范围,满足脑外科手术的需要.