弹弓效应原理简析

文章用速度变换和矢量图对"弹弓效应"的加速原因做出了较为简洁直观的解释,以关于"弹弓效应"的一个简例.分析"弹弓效应"中的加速条件,得出能使入射物体被加速的偏转角范围.与通常所采用的两体碰撞理论相比较,此方法更能凸显"弹弓效应"的加速机理,且能有效避免冗繁的数学运算.将"弹弓效应"与粒子散射问题对照分析,得出两者之间的可类比性.因而可由散射问题中的散射角关于瞄准距离的公式类比推出"弹弓效应"中偏转角与瞄准距离之间的关系.文章还将"弹弓效应"的思想推广到了一般尺度上的两体问题.     

自制三种物理实验装置及演示

1演示超重现象 取透明塑料瓶一个，截去瓶底，并改用一张白纸封住底部（可用细线捆扎）．再取一段橡皮筋，一端和一柱形金属重物连结，并将重物放入瓶中，橡皮筋另一端固定在瓶口处．静止时重物不和白纸接触，约保持1cm距离．整个装置如图1所示．     

Enhancement of water permeation across nanochannels by partial charges mimicked from biological channels

In biological water channel aquaporins （AQPs）, it is believed that the bipolar orientation of the single-file water molecules inside the channel blocks proton permeation but not water transport. In this paper, the water permeation and particularly the water-selective behaviour across a single-walled carbon nanotube （SWNT） with two partial charges adjacent to the wall of the SWNT are studied by molecular dynamics simulations, in which the distance between the two partial charges is varied from 0.14 nm to 0.5 nm and the charges each have a quantity of 0.5 e. The two partial charges are used to mimic the charge distribution of the conserved non-pseudoautosomal （NPA） （asparagine/proline/alanine） regions in AQPs. Compared with across the nanochannel in a system with one ＋1 ε charge, the water permeation across the nanochannel is greatly enhanced in a system with two ＋0.5 e charges when charges are close to the nanotube, i.e. the two partial charges permit more rapid water diffusion and maintain better bipolar order along the water file when the distance between the two charges and the wall of SWNT is smaller than about 0.05 nm. The bipolar orientation of the single-file water molecules is crucial for the exclusion of proton transfer. These findings may serve as guidelines for the future nanodevices by using charges to transport water and have biological implications because membrane water channels share a similar single-file water chain and positive charged region at centre and provide an insight into why two residues are necessitated in the central region of water channel protein.     

微型数据采集器及其在加速器周围辐射场实时监测中的应用

各种类型加速器周围的辐射场变化是很复杂的,只有对其进行连续的实时监测才能准确地掌握全面资料.以往的数据采集系统用的是模拟信号长距离传输方式,采集器体积较大,存储技术上也显落后,已不能适应当今的需求.为辐射场实时监测研制的微型数据采集器采用了先进的设计理念,具有体积小、通讯能力强、数据存储量大且断电数据不丢失的特点,可运行于局域网环境.它既可利用局域网远距离向控制计算机传递数据,也可用便携式PC通过串口就近读取数据.所以它不但适于固定场所的连续监测,也可灵活地用于临时测量场所.介绍了它的主要性能和在各类型加速器周围所做测量的结果.     

距离-边数拓扑指数: 饱和链烃类化合物的结构/性质相关性研究

本文提出一种新的拓扑指数——距离-边数拓扑指数S_q,并用于研究饱和链烃类化合物的理化性质,获得比较满意的结果.与其它已有的拓扑指数比较,该指数结构选择性和相关性好,并且计算更加简便.     

Distance—Stability of Nonlinear Discrete Systems

In this paper,the distance-sability of nonlinear discrete system is investigated by meansof the Gauss-Seidel iteration method.Some algebric criteria of the distance-stability are ob-tained.Construction of Lyapunov function is avoided.     

哈勃常数——一个难有确定值的重要参量

 何常同志的文章(《哈勃常数战和宇宙命运》,本刊1994年第4期11-14页)介绍了测定河外星系的几种方法、哈勃常数50与100之争,以及哈勃常数与宇宙命运的关系。本文旨在向读者介绍哈勃常数值演变的历史、近年来用不同方法测定的哈勃常数值以及对此问题的几点小结。     

Talagrand＇s T2-transportation Inequality w.r.t, a Uniform Metric for Diffusions

Using the method of Girsanov transformation, we establish the Talagrand‘s T2-inequality for diffusion on the path space C([0, N], R^d) with respect to a uniform metric, with the constant independent of N. This improves the known results for the L2-metric.     

天体距离的测量方法

天体测量在天文研究中占有重要地位,在不同时代、对不同天体有不同的测量方法,随着科学技术的发展,天体测量的手段也越来越先进。由于宇宙空间广袤无垠,所使用的距离单位与通常表示距离的单位也有所不同,表示天体距离的单位有天文单位(AU)、光年(ly)和秒差距(pc)。太阳与地球间     

甾族化合物~(13)CNMR谱化学位移定量构谱关系的研究

利用原子电性距离矢量(Atomic Electro-negativity Distance Vector,AEDV)和原子杂化状态指数(Atomic Hybridization State Index,AHSI)对203个甾族化合物中4434个碳原子进行结构表征并与其核磁共振碳谱(13CNMR)建立多元线性定量结构波谱相关(QSSR)模型,同时运用逐步回归结合统计检测对模型变量进行筛选,最后采用内部及外部双重验证的办法对所得模型稳定性能进行深入分析和检验,建模计算值、留一法(leave-one-out,LOO)交互校验(cross-validation,CV)预测值和外部样本预测值的复相关系数(R)分别为0.9574、0.9571和0.9537.其结果表明,AEDV,AHSI与13CNMR谱化学位移显著相关.