A parametrization for dissipative behaviors

The behavioral equivalent of single input single output (SISO) systems are behaviors with two manifest variables. Passive SISO systems can, therefore, be viewed as J-dissipative behaviors with two manifest variables. Here the special matrix J defines a QDF that captures the passivity property of SISO systems. In this paper, we investigate more general QDFs Q_Φs induced by some operator Φ. These QDFs define some relation between the input, the output and their derivatives of a SISO system. We characterize all behaviors that are dissipative with respect to the prescribed QDF Q_Φ. In fact, we parametrize all the behaviors dissipative with respect to Q_Φ in terms of those dissipative with respect to the special QDF Q_J induced by the matrix J. Similar results can also be given for lossless systems.     

A Framework and Lightweight Protocol for Multimedia Network Management

The increasing complexities of modern networks coupled with the popularity of multimedia applications have placed higher demands on network managers. This paper reviews the main requirements and challenges for effective management of multimedia networks, presents a case study of a thin-client-based multimedia system called CSL (Computer-supported Learning System) and proposes a framework for managing such networks. CSL delivers browser-based assessments and other learning materials to thousands of students at the University of Auckland. This type of demand requires more flexible schemes for the management of the network. In the framework proposed, most of the link management information will be kept in a MIB in the network and a very simple MIB will be maintained in the thin client. The MIB in the network is accessible to the network management application, and a lightweight protocol is proposed for updating of the network MIB using an agent at the thin client.     

Structure and properties of some vegetable fibres

The stress-strain curves for pineapple leaf fibre have been analysed. Ultimate tensile strength (UTS), initial modulus (YM), average modulus (AM) and elongation of fibres have been calculated as functions of fibre diameter test length and test speed. UTS, YM, and elongation lie in the range of 362 to 748 MN m^–2, 25 to 36 GN m^–2, and 2.0 to 2.8%, respectively for fibres of diameters ranging from 45 to 205m. UTS Was found to decrease with increasing test lengths in the range 15 to 65 mm. Various mechanical parameters show marginal changes with change in speed of testing in the range of 1 to 50 mm min^–1. The above results are explained on the basis of structural variables of the fibre. Scanning electron microscope studies of the fibres reveal that the failure of the fibres is mainly due to large defect content of the fibre bo1h along the fibre and through the cross-section, The crack is always initiated by the defective cells and further aggravated by the weak bonding material between the cells.     

Fact-oriented modelling for data analysis

Abstract. Although entity-relationship modelling is the most popular means of specifying the conceptual schema for the data perspective of an information system, an alternative design approach known as fact-oriented modelling appears to offer advantages. This paper provides an overview of fact-oriented modelling, including some recent revisions and an evaluation of how the method has coped with large-scale practical applications. One distinguishing feature of the approach is its emphasis on natural verbalization of information examples in terms of elementary facts. This notion of elementarity is clarified to cater for a problematic case involving compositely identified object types. Finally, the algorithm for mapping a conceptual to a relational schema is revised to cater for lazy object types.     

An automatic braking system that stabilizes leukocyte rolling by an increase in selectin bond number with shear

Wall shear stress in postcapillary venules varies widely within and between tissues and in response to inflammation and exercise. However, the speed at which leukocytes roll in vivo has been shown to be almost constant within a wide range of wall shear stress, i.e., force on the cell. Similarly, rolling velocities on purified selectins and their ligands in vitro tend to plateau. This may be important to enable rolling leukocytes to be exposed uniformly to activating stimuli on endothelium, independent of local hemodynamic conditions. Wall shear stress increases the rate of dissociation of individual selectin-ligand tether bonds exponentially (, ) thereby destabilizing rolling. We find that this is compensated by a shear-dependent increase in the number of bonds per rolling step. We also find an increase in the number of microvillous tethers to the substrate. This explains (a) the lack of firm adhesion through selectins at low shear stress or high ligand density, and (b) the stability of rolling on selectins to wide variation in wall shear stress and ligand density, in contrast to rolling on antibodies (). Furthermore, our data successfully predict the threshold wall shear stress below which rolling does not occur. This is a special case of the more general regulation by shear of the number of bonds, in which the number of bonds falls below one.     

低频波动条件下流体平面渗流模型研究

低频振动采油技术已成为一项重要的物理增产、增注措施,但其理论研究水平目前还相对滞后于现场应用.针对这一问题,运用渗流力学、波场传播的基本原理,建立了低频波动条件下地层流体的渗流模型,定量描述了地层、流体参数与振动采油压力波动之间的关系,并利用解析方法分析计算,认为低频波场主要受储层渗透率和振动频率两大因素影响.振动采油现场施工可以通过适当调整振动频率改善施工效果.     

Orally active, hydrolytically stable, semisynthetic, antimalarial trioxanes in the artemisinin family

In only three chemical operations, natural trioxane lactone artemisinin (1) was converted into a series of C-10 carbon-substituted 10-deoxoartemisinin compounds 4-9. The three steps involved lactone reduction, replacement of the anomeric lactol OH by F using diethylaminosulfur trifluoride, and finally boron trifluoride-promoted substitution of F by aryl, heteroaryl, and acetylide nucleophiles. All of these C-10 nonacetal, chemically robust, enantiomerically pure compounds 4-9 have high antimalarial potencies in vitro against Plasmodium falciparum malaria parasites, and furans 5a and 5b and pyrrole 7a are antimalarially potent also in vivo even when administered to rodents orally.     

Cation transport: an example of structural based selectivity

Through the high-resolution structure of the gramicidin A channel in lamellar phase lipids and the characterization of specific ion peptide interactions, fundamental principles for ion channel selectivity and conductance efficiency are illustrated with atomic resolution detail. Delocalized cation binding in the first turn of the helix reduces the unfavorable entropy contribution upon binding. Stepwise dehydration minimizes the energy barrier for cation entry and provides valence selectivity in this channel. Three or more water molecules in the monovalent cation binding site result in flexibility in the cation solvation environment causing weak cation size selectivity. Lack of cation induced structural modification avoids the formation of a significant energy barrier, thus permitting efficient cation transport.     

Adult psychological functioning of individuals born with craniofacial anomalies

This study represents an initial investigation into the adult psychological functioning of individuals born with craniofacial disfigurement. A total of 24 men and women born with a craniofacial anomaly completed paper and pencil measures of body image dissatisfaction, self-esteem, quality of life, and experiences of discrimination. An age- and gender-matched control group of 24 non-facially disfigured adults also completed the measures. As expected, craniofacially disfigured adults reported greater dissatisfaction with their facial appearance than did the control group. Craniofacially disfigured adults also reported significantly lower levels of self-esteem and quality of life. Dissatisfaction with facial appearance, self-esteem, and quality of life were related to self-ratings of physical attractiveness. More than one-third of craniofacially disfigured adults (38 percent) reported experiences of discrimination in employment or social settings. Among disfigured adults, psychological functioning was not related to number of surgeries, although the degree of residual facial deformity was related to increased dissatisfaction with facial appearance and greater experiences of discrimination. Results suggest that adults who were born with craniofacial disfigurement, as compared with non-facially disfigured adults, experience greater dissatisfaction with facial appearance and lower self-esteem and quality of life; however, these experiences do not seem to be universal.