Detection and Characterization of Boric Acid and Borate Ion Binding to Cytochrome c Using Multiple Quantum Filtered NMR

The application of multiple quantum filtered (MQF) NMR to the identification and characterization of the binding of ligands containing quadrupolar nuclei to proteins is demonstrated. Using relaxation times measured by MQF NMR multiple binding of boric acid and borate ion to ferri and ferrocytochrome c was detected. Borate ion was found to have two different binding sites. One of them was in slow exchange, k_diss = 20 ± 3 s⁻¹ at 5°C and D₂O solution, in agreement with previous findings by ¹H NMR (G. Taler et al., 1998, Inorg. Chim. Acta 273, 388–392). The triple quantum relaxation of the borate in this site was found to be governed by dipolar interaction corresponding to an average B–H distance of 2.06 ± 0.07 Å. Other, fast exchanging sites for borate and boric acid could be detected only by MQF NMR. The binding equilibrium constants at these sites at pH 9.7 were found to be 1800 ± 200 M⁻¹ and 2.6 ± 1.5 M⁻¹ for the borate ion and boric acid, respectively. Thus, detection of binding by MQF NMR proved to be sensitive to fast exchanging ligands as well as to very weak binding that could not be detected using conventional methods.     

多点多媒体通信服务的研究与实现

随着数字技术在通信领域的发展,多媒体技术应用越来越广泛。本文介绍了多点多媒体通信平台的服务功能及其标准协议,并重点介绍了其设计与实现的方案。     

时隙式随机争用多址系统分析方法研究

本文给出一种新的平均周期分析方法,并对时隙式随机争用多址系统进行了分析,得到了系统的信息分组发送成功的平均长度公式、信息分组发生碰撞的平均长度公式和空闲时隙的平均长度公式,并在讨论了系统的冲突分解特性后,给出了系统的吞吐量。     

一种特殊DBF—PD米波雷达体制下的多目标检测方法

提出了一种特殊米波雷达体制下的多目标检测方法。该方法借助数字波束形成（ＤＢＦ）、脉冲多普勒（ＰＤ）和单脉冲技术在空域、时域、频域内完成目标测量。文中给出了系统框图、检测算法和仿真结果     

亚精胺诱导DNA凝聚的有序性的AFM研究

观察生物体内ＤＮＡ凝聚参与物—亚精胺对ＤＮＡ的凝缩作用将有利于深入理解ＤＮＡ在体内的紧密存储机制。本文采用原子力显微镜（ＡＦＭ）研究了在不同的ＤＮＡ浓度下亚精胺—ＤＮＡ凝聚体的形态变化。研究表明：随着体系中ＤＮＡ浓度的变化,亚精胺将诱导ＤＮＡ形成两种类型的凝聚物（类型Ⅰ和类型Ⅱ）。当λ－ＤＮＡ浓度低于１ｎｇ／μｌ,亚精胺可诱导λ－ＤＮＡ形成一种特殊的结构—环形凝聚体,其体积与单个λ－ＤＮＡ的体积近似（类型Ⅰ）;当λ－ＤＮＡ浓度介于１ｎｇ／μｌ和１０ｎｇ／μｌ之间,可观察到由许多小颗粒堆积而成的多分子凝聚的环状体（类型Ⅱ）。对类型Ⅱ的高度分析表明它可能具有分层结构,统计表明其组成颗粒在粒径上和单个类型Ⅰ凝聚体相近。这些观察暗示了亚精胺诱导ＤＮＡ凝聚可能是一个分级自组装过程。     

时分双工环境下的分组预约多址(PRMA/TDD)协议及其性能

在分析标准分组预约多址（PRMA／FDD）协议的基础上,提出了时分双工环境下的分组预约多址（PRMA／TDD）协议,理论分析和计算机仿真均表明,PRMA／TDD与PRMA／FDD的性能相近,可以较大幅度地提高系统的容量。     

考查一维随机分布表面高次散射程度的随机分布闪耀光栅近似法

本文提出了将Ｇａｕｓｓ－起伏,Ｇａｕｓｓ－相关的一维随机粗糙散射表面近似成连续三角槽型的面型分布的数值分析方法;通过粗糙度值、高度概率密度分布函数及相关函数等诸参量的模拟统计分析,验证了此方法的可靠性;给出了此方法在解决起伏剧烈的大粗糙度随机表面上形成的散射场分布之数值模拟计算方面的应用前景。     

On the Existence and Stability of Positive Solutions for Some Pairs of Differential Equations

In this paper, we are concerned with the existence and stability of the positive solutions of a semilinear elliptic system - Δu(x) = a(x)v^6(x) + e(x) - Δv(x) = b(x}u^μ(x) + m(x) \qquad in Ω u = v = 0 \qquad\qquad on ∂Ω where Ω ⊂ R^N is a bounded domain with smooth boundary ∂Ω. It is shown that under the suitable conditions on \delta, μ, there exist a stable and an unstable positive solutions for this system if e and m are sufficiently small in L^∞.     

Predicting Homoclinic Bifurcations in Planar Autonomous Systems

An analytical method to predict the homoclinic bifurcation in a planar autonomous self-excited weakly nonlinear oscillator is presented. The method is mainly based on the collision between the periodic orbit undergoing the homoclinic bifurcation and the saddle fixed point. To illustrate the analytical predictive criteria, two typical examples are investigated. The results obtained in this work are then compared to Melnikov's technique and to a previous criterion based on the vanishing of the frequency. Numerical simulations are also provided.     

服从正态分布的强度变量在多个独立应力作用下的结构可靠性估计

本文讨论了服从正态分布的强度变量在(分布不一定相同的)多个独立应力作用下的结构可靠性估计.在假设应力参数已知,强度参数部分未知或全部未知的条件下,给出了结构可靠度的点估计和置信下限.