香港保安产品业“商”聚一“会”掠影

[本刊讯] 7月27日，保安产品业“商”聚一“会”在香港会议展览中心召开。会议由香港贸易发展局客户服务部主管黎清雄先生主持，有36名代表列席了这次圆桌论坛会议，资料与产品展示也同时举行，亚洲防伪协会等11家企业和协会参加了这次展示会。     

油气层中常见微粒的运移程度及其与ζ电位关系的研究

微粒运移是造成油气层损害最严重和最普遍的因素之一。要防止油气层中的微粒运移，就必须先弄清楚油气层中常见微粒的运移情况和影响微粒运移的主要因素。因此，通过对国内外大量微粒分析资料的统计分析，选定了油气层中常见的地层微粒作为研究对象，用新建立的、较完善的实验方法研究了这些微粒的运移程度，对这些微粒的ζ电位进行测定，发现其运移程度与其ζ电位的大小有关。一般地说，微粒ζ电位值越大，其运移程度也越大。     

地面目标图像识别技术研究

本文以数学图像处理为重点，较详细地论述了地面目标图像识别技术中从图像分割、边界跟踪、噪声去除、边界点直线拟合到目标识别的主要过程，并以机场跑道为例，深入探讨了目标特征选取的方法。     

微悬浮氯醋共聚树脂的合成及影响因素的研究

用微悬浮聚合法合成了不同醋酸乙烯酯含量的氯醋共聚物，研究了各种影响因素对聚合反应速及粒径大小和分布的影响，用扫描电镜观察了共聚物的颗粒形态。结果表明，醋酸乙烯酯共聚单体的引入对共聚合反应速率及粒径大小和分布影响不大，由此推出微悬浮氯醋共聚反应了与氯乙烯均聚反应具有类似的成核过程。     

CT features of calcifications in abdominal malignant fibrous histiocytoma

Driven by the need for a readily available, non-immunological tissue that possesses many of the characteristics of normal human skin, tissue-engineered skin has been developed. For over a decade, laboratory grown or processed skin has been under investigation and, in some cases, available as an alternative to autologous grafts. Apligraf, derived from neonatal foreskin and bovine type I collagen, is the first bi-layered living skin equivalent approved in the US and other countries for use in venous ulcers. Apligraf is effective both in the treatment of refractory venous ulcers and for acute wounds such as surgical excision sites and split thickness donor sites. Apligraf is safe and is not clinically rejected. Its ultimate fate is not known, so it may well work to aid healing in a variety of ways including graft 'take' and as a stimulus for healing.     

The adsorption of lithium onto alumina from solutions of mixed chlorides: Effects of temperature and electrolyte control

The effects of temperature, type and concentration of electrolyte on the adsorption of lithium into amorphous hydroxide have been investigated. As a consequence of this phase change lithium was desorbed. In the presence of NaCl and, more particularly, of MgCl₂ both the processes of lithium adsorption and the alumina phase change can be considerably modified.     

Studies of a thermomechanically treated Al-Zn-Mg alloy

The influence of subgrain structure on the precipitation process in an Al-4.2 wt% Zn-1.6 wt% Mg alloy was studied and correlated with its mechanical properties for ageing temperatures of 110, 142 and 165° C.     

Sliding mode controller with sliding perturbation observer based on gain optimization using genetic algorithm

The Stewart platform manipulator is a closed-kinematics chain robot manipulator that is capable of providing high structural rigidity and positional accuracy. However, this is a complex and nonlinear system, so the control performance of the system is not so good. In this paper, a new robust motion control algorithm is proposed. The algorithm uses partial state feedback for a class of nonlinear systems with modeling uncertainties and external disturbances. The major contribution is the design of a robust observer for the state and the perturbation of the Stewart platform, which is combined with a variable structure controller (VSC). The combination of controller and observer provides the robust routine called sliding mode control with sliding perturbation observer (SMCSPO). The optimal gains of SMCSPO, which is determined by nominal eigenvalues, are easily obtained by genetic algorithm. The proposed fitness function that evaluates the gain optimization is to put sliding function. The control performance of the proposed algorithm is evaluated by the simulation and experiment to apply to the Stewart platform. The results showed high accuracy and good performance.     

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目前,由于缺少直接测量水力裂缝长度及导流能力等重要参数的手段,而地下水力裂缝的存在总要反映到油气井压力与产量的变化上来,特别是压力与产量随时间的变化速度与水力裂缝的长短、导流能力的大小等参数有直接关系。在常规压裂井试井分析过程中,所使用的数据主要是停泵后的压降数据,而岩石发生破裂到停泵前这一段压裂施工压力数据则没有得到有效利用;同时,在压裂施工作业过程中也不能对裂缝的延伸状况进行动态监测。文章提供了裂缝模型的诊断技术,通过对岩石发生破裂到停泵前这一段压裂施工压力数据进行分析,确定裂缝参数随压裂时间的变化关系。这样,就可以实时地知道裂缝发育、发展和闭合的过程,对于正确指导压裂施工作业以及获得优质裂缝具有十分重要的意义。     

Distributed Construction of Connected Dominating Set in Wireless Ad Hoc Networks

Connected dominating set (CDS) has been proposed as virtual backbone or spine of wireless ad hoc networks. Three distributed approximation algorithms have been proposed in the literature for minimum CDS. In this paper, we first reinvestigate their performances. None of these algorithms have constant approximation factors. Thus these algorithms cannot guarantee to generate a CDS of small size. Their message complexities can be as high as O(n ²), and their time complexities may also be as large as O(n ²) and O(n ³). We then present our own distributed algorithm that outperforms the existing algorithms. This algorithm has an approximation factor of at most 8, O(n) time complexity and O(nlogn) message complexity. By establishing the (nlogn) lower bound on the message complexity of any distributed algorithm for nontrivial CDS, our algorithm is thus message-optimal.