beta-delayed fission of Ac-228

The basic process of an exotic decay mode namely P-delayed fission is simply introduced. The progress status of the study in the world is essentialized. The observation of P-delayed fission of Ac-228 is reported. The radium was radiochemically separated from natural thorium. Thin Ra sources in which Ac-228 was got through Ra-228 ->(beta-) Ac-228 were prepared for observing fission fragments from beta-delayed fission Ac-228. They exposed to the mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2) x 10(-12).

Search for beta-delayed fission of Ac-228

Radium was radiochemically separated from natural thorium. Thin Ra-228 ->beta Ac-228 sources were prepared and exposed to mica fission track detectors, and measured by an HPGe gamma-ray detector. The beta-delayed fission events of Ac-228 were observed and its beta-delayed fission probability was found to be (5 +/- 2)x10(-12).

铅－210、钍－228、钚年代学在滇池、洞庭湖和昆明湖环境问题上的应用

笔者在大量的文献调研基础上，试图利用 ~(210)Pb、~(228)Th 等短半衰期的铀系子体确定某些湖泊沉积物的沉积速率及年代，结合 239，240 pu 在我国内陆湖泊的分布规律，以全球 pu 随时间的分布规律探索其测年的可能性，以多核素方法探讨测年结果的可靠性，建立沉积的时间尺度。同时，利用这些核素作示踪研究沉积物表层的生物扰动所造成的混合效应。通过对沉积物垂直方向上物质成份。矿物成份和元素分析，研究沉积环境的演化及近百年工业污染的历史。根据所选湖泊的纬度差别，研究湖泊沉积环境和沉积物类型对所研究的核素方法的影响。本论文是首次利用多核素方法研究我国一些内陆湖泊的环境问题，对在我国继续开展这方面研究具有重要意义。

旋转流体侵入型异重流实验研究

文中介绍了对旋转系统中侵入型异重流特征的若干实验室观察结果,在Coriolis力作用下,异重流取沿岸(壁)流形式,其宽度与其Rossby变形半径成比例,在实验的参数范围内,这种沿岸流均为不稳定的,在其演化过程中产生出气旋——反气旋涡对,乃至与岸壁分离与再附的大弯曲,本文还初步考察了波长、相对厚度与Frou de数之间的关系。

托卡马克中凯尔文-亥姆霍尔茨不稳定性与密度分布及速度分布的关系

近年来,在托卡马克装置实验中观察到等离子体环的密度及环向速度沿半径都有变化。当反平行中性束注入时,密度分布对应空洞型温度(即中心温度低而外侧高),等离子体的稳定性变坏。本文对密变分布和速度分布对等离子体环的凯尔文-亥姆霍尔茨稳定性的影响分别进行了研究,得出,在托卡马克实验参数范围内,密度沿半径的分布会使凯尔文-亥姆霍尔茨稳定性变坏,从而为反平行注入对等离子体约束有明显破坏提供了一种可能的解释。

柔性弦中弹塑性波的传播

本文用Lagrange方法研究了弦中弹塑性枞波和横波的传播,对不论是强间断或弱间断建立了一般微分关系式.着重讨论了相似问题.对于无滑动冲击的情况,问题是容易求解的;对于滑动冲击的情况,在补充考察了摩擦条件后,问题也可以求解.此外,论证了能量守恒条件;讨论了理想塑性弦的特殊情况.文中指出了文献[1]和[2]的某些错误.

流化床中垃圾与煤混烧的技术经济分析

本文对城市生活垃圾在流化床中与煤的混烧技术进行了分析;根据垃圾热值;讨论了低热值垃圾焚烧中添加煤混烧的必要性;给出了垃圾处置收费和售电价格对于混烧电厂的经济影响。结果表明:对于所给定焚烧项目的垃圾来讲,其垃圾的低位热值近似为 4200 kJ/kg,需要进行混烧,其中煤的比例应小于10～20％;垃圾量的提高,垃圾收费带来的收益九;而垃圾热值的提高,售电价格带来的收益大。增加垃圾收费补贴可鼓励焚烧厂焚烧更多的垃圾。

湍流射流理论与计算

A smoothing technique for discrete delta functions with application to immersed boundary method in moving boundary simulations.

The effects of complex boundary conditions on flows are represented by a volume force in the immersed boundary methods. The problem with this representation is that the volume force exhibits non-physical oscillations in moving boundary simulations. A smoothing technique for discrete delta functions has been developed in this paper to suppress the non-physical oscillations in the volume forces. We have found that the non-physical oscillations are mainly due to the fact that the derivatives of the regular discrete delta functions do not satisfy certain moment conditions. It has been shown that the smoothed discrete delta functions constructed in this paper have one-order higher derivative than the regular ones. Moreover, not only the smoothed discrete delta functions satisfy the first two discrete moment conditions, but also their derivatives satisfy one-order higher moment condition than the regular ones. The smoothed discrete delta functions are tested by three test cases: a one-dimensional heat equation with a moving singular force, a two-dimensional flow past an oscillating cylinder, and the vortex-induced vibration of a cylinder. The numerical examples in these cases demonstrate that the smoothed discrete delta functions can effectively suppress the non-physical oscillations in the volume forces and improve the accuracy of the immersed boundary method with direct forcing in moving boundary simulations.

High Order Multi-Moment Constrained Finite Volume Method. Part I: Basic Formulation

A new high-order finite volume method based on local reconstruction is presented in this paper. The method, so-called the multi-moment constrained finite volume (MCV) method, uses the point values defined within single cell at equally spaced points as the model variables (or unknowns). The time evolution equations used to update the unknowns are derived from a set of constraint conditions imposed on multi kinds of moments, i.e. the cell-averaged value and the point-wise value of the state variable and its derivatives. The finite volume constraint on the cell-average guarantees the numerical conservativeness of the method. Most constraint conditions are imposed on the cell boundaries, where the numerical flux and its derivatives are solved as general Riemann problems. A multi-moment constrained Lagrange interpolation reconstruction for the demanded order of accuracy is constructed over single cell and converts the evolution equations of the moments to those of the unknowns. The presented method provides a general framework to construct efficient schemes of high orders. The basic formulations for hyperbolic conservation laws in 1- and 2D structured grids are detailed with the numerical results of widely used benchmark tests. (C) 2009 Elsevier Inc. All rights reserved.

飞行目标红外多光谱高效识别算法

随着新型诱饵的快速发展,在日益复杂的目标环境中探测识别真假目标是红外探测识别系统最难解决的技术问题之一.通过分析天空背景下红外小目标,干扰物,噪音及背景的光谱特性,利用人造飞行目标光谱辐射强度高且相邻波段光谱辐射强度连续性特点,提出了一种以多光谱辐射强度和梯度相组合的目标识别高效算法.就此给出了相应的仿真算例,验证了算法在获取的红外图像信噪比很低,背景高亮度,多个诱饵干扰的条件下也能准确识别目标,具有更强的自适应性,更高的识别率和更为快捷的处理能力.

Beam splitter entangler for light fields

We propose an experimentally feasible scheme to generate various types of entangled states of light fields by using beam splitters and single-photon detectors. Two beams of light fields are incident on two beam splitters respectively with each beam being asymmetrically split into two parts in which one part is supposed to be so weak that it contains at most one photon. We let the two weak output modes interfere at a third beam splitter. A conditional joint measurement on both weak output modes may result in an entanglement between the other two output modes. The conditions for the maximal entanglement are discussed based on the concurrence. Several specific examples are also examined.

Generation of near-field hexagonal array illumination with a phase grating

A hexagonal array not only is a nature-preferred pattern but also is widely used in optoelectronical materials and devices. We report a simple method of hexagonal array illumination based on the Talbot effect that has a theoretical efficiency of 100%. An experimental efficiency of 90.6% with a binary phase (0, pi) hexagonal grating is given. This method should be highly interesting for applications of hexagonal array illumination in optical devices as well as in other hexagonal cells. (C) 2002 Optical Society of America.