Modification of Surfaces to Meet Bioadhesive Design Goals: A Review

The modern range of medical devices presents contrasting requirements for adhesion in biological environments. Strong bioadhesion is desired in many circumstances to assure device retention and immobility. Minimal adhesion is absolutely essential in others, where thrombosis or bacterial adhesion would destroy the utility of the implants. A brief review is given of some analytical approaches, based in adhesion science, most useful in addressing these needs. Familiar correlating parameters, such as the critical surface tension, are surprisingly good in predicting bioadhesive outcomes such as tissue integration. The example of dental implants is given to illustrate this correlation. In every case, primary attention must be given to the qualities of the first interfacial conditioning films of bio-macromolecules deposited from the living systems. For instance, fibrinogen deposits from blood may assume different configurations on surfaces of different initial energies, and thus trigger different physiological events. Standard surface modification techniques, such as siliconization, when properly quality controlled can yield improved blood-compatible devices like substitute blood vessels and artificial heart sacs. Promising extensions to new areas of biotechnology are forecast.     

An analog method for detecting superimposed power line voltagedisturbances

Power line monitoring has become increasingly important during the past few years as many failures in sensitive electronic equipment are due to various types of power line disturbances. An analog, low-cost solution for multichannel power line disturbance analyzers which performs a triggering function that detects changes in the voltage waveform is described. The method may also be used for other applications where deviations from a repetitive waveform must be detected. Examples of transient disturbances measured in the field are presented and described     

Variations in the vitamin D-binding protein (Gc locus) are associated with oral glucose tolerance in nondiabetic Pima Indians

Electrophoretic variants of the vitamin D-binding protein (DBP) have been associated with type 2 diabetes as well as with metabolic characteristics that predispose to type 2 diabetes in several populations. The Gc gene that encodes DBP maps to chromosome 4q12, a region that has recently been found to be potentially linked to plasma glucose and insulin concentrations in Pima Indians. Therefore, the gene that encodes DBP was analyzed as a candidate gene for our linkage findings in the Pima Indians. Sequence analysis of the coding exons identified two previously described missense polymorphisms at codons 416 and 420, which are the genetic basis for the three common electrophoretic variants of DBP (Gc1f, Gc1s, and Gc2). These variants in DBP were associated with differences in oral glucose tolerance in nondiabetic Pima Indians.     

Solution structure of human intestinal fatty acid binding protein: implications for ligand entry and exit

The human intestinal fatty acid binding protein (I-FABP) is a small (131 amino acids) protein which binds dietary long-chain fatty acids in the cytosol of enterocytes. Recently, an alanine to threonine substitution at position 54 in I-FABP has been identified which affects fatty acid binding and transport, and is associated with the development of insulin resistance in several populations including Mexican-Americans and Pima Indians. To investigate the molecular basis of the binding properties of I-FABP, the 3D solution structure of the more common form of human I-FABP (Ala54) was studied by multidimensional NMR spectroscopy. Recombinant I-FABP was expressed from E. coli in the presence and absence of 15N-enriched media. The sequential assignments for non-delipidated I-FABP were completed by using 2D homonuclear spectra (COSY, TOCSY and NOESY) and 3D heteronuclear spectra (NOESY-HMQC and TOCSY-HMQC). The tertiary structure of human I-FABP was calculated by using the distance geometry program DIANA based on 2519 distance constraints obtained from the NMR data. Subsequent energy minimization was carried out by using the program SYBYL in the presence of distance constraints. The conformation of human I-FABP consists of 10 antiparallel beta-strands which form two nearly orthogonal beta-sheets of five strands each, and two short alpha-helices that connect the beta-strands A and B. The interior of the protein consists of a water-filled cavity between the two beta-sheets. The NMR solution structure of human I-FABP is similar to the crystal structure of rat I-FABP. The NMR results show significant conformational variability of certain backbone segments around the postulated portal region for the entry and exit of fatty acid ligand.     

Simulation of the uplink of JD-CDMA mobile radio systems with coherent receiver antenna diversity

Due to time variant multipath propagation, both intersymbol interference and multiple access interference occur at CDMA receivers. These degrading effects can be combatted by joint detection (JD) techniques. In order to reduce the performance impairments resulting from time variance, coherent receiver antenna diversity (CRAD) can be used. In the present paper, a system model of CDMA mobile radio systems using various JD techniques in combination with CRAD shall be considered. This system model is an evolution of the pan-European GSM and takes important real world aspects such as imperfect channel estimation, nonlinear amplification and D/A and A/D conversion into account. The viability of JD with CRAD shall be demonstrated by bit error rate simulations of this system model. It is shown that by using JD with two receiver antennas in bad urban areas,E _b/N₀ < 8 dB per antenna is sufficient for a bit error rate of 10^–2, andE _b/N₀ < 11 dB per antenna is required for a bit error rate of 10^–3.List of Abbreviations AWGN Additive white Gaussian noise - A/D Analog-to-digital - BU Bad urban - CDMA Code division multiple access - COST European Co-operation in the Field of Scientific and Technical Research - CRAD Coherent receiver antenna diversity - cdf Cumulative distribution function - DMF Decorrelating matched filter - DMF-BDFE Decorrelating matched filter block decision feedback equalizer - D/A Digital-to-analog - EGC Equal-gain combining - FDMA Frequency division multiple access - GMSK Gaussian minimum shift keying - GSM Global System for Mobile Communications - ISI Intersymbol interference - JD Joint detection - JDC Japanese Digital Cellular - JD-CDMA Joint detection code division multiple access - MA Multiple access - MAI Multiple access interference - MMSE-BLE Minimum mean square error block linear equalizer - MMSE-BDFE Minimum mean square error block decision feedback equalizer - MRC Maximal-ratio combining - RA Rural area - SC Selection combining - SNR Signal-to-noise ratio - TDMA Time division multiple access - TU Typical urban - WSSUS Wide sense stationary uncorrelated scattering - ZF-BLE Zero forcing block linear equalizer - ZF-BDFE Zero forcing block decision feedback equalizer     

卫星姿态控制反作用轮的最佳安装结构

本文讨论卫星姿态控制反作用轮的最佳安装结构.文中例举十种安装结构,用统一准则 (动量、功耗和可靠度)对这些安装结构控制性能的分析证明,斜装轮是最佳安装结构.