Galactomannan esters—A simple, cost-effective method of preparation and characterization

Acetate, succinate and octenylsuccinate derivatives of galactomannans were prepared in anhydrous reaction conditions carried out at slightly elevated temperature (40–60 °C) using solid NaHCO₃ as a mild base catalyst. Prior surface wetting of the reactants with 5% absolute ethyl alcohol gave derivatives with a higher degree of substitution, although it decreased the slurry viscosity. Use of NaHCO₃ significantly minimized high pH-induced degradative reactions, and its quantitative removal later was easily accomplished by repeated washings with aqueous ethyl alcohol. FT-IR, ¹³C-NMR, HPSEC and SEM data provided additional structural information. These derivatives are useful as functional food ingredients.     

Development and evaluation of Zigbee node module for USN

This study aims at securing technology to develop a multisensor and complex position-tracking Zigbee node module for USN (ubiquitous sensor network). In a concrete way, it aims at developing military (invader detection module and system) and industrial (transformer-tracking and thermo-measurement module and system) Zigbee telecommunication node module, and developing wireless monitoring and tracking technology based on such modules. In addition, it aims at building up the foundation of interface test for various sensors (thermo sensors, pressure sensors, vibration sensors and vision sensors) and the foundation of a comprehensive interlocking device to which GIS (Geographic Information System) and GPS (Global Positioning System) were applied, for industrial devices are mostly installed in mountains. Moreover, it aims at developing a roaming-type variable Zigbee node module to the end that it stands against unfavorable conditions (extreme temperatures, dust, winds, electromagnetism, noise, etc.). In case such aims are achieved, Zigbee communications will not be limited to normal and stable conditions (home networks, building automation, etc.) but will be applied to the industrial field under noises and unfavorable conditions. In such a case, the application of Zigbee node modules is expected to be unlimited.     

高压定向喷射灌浆构筑防渗板墙技术的研究

根据坝基帷幕防渗技术的要求,在高压旋喷桩和帷幕灌浆设备的基础上,研制、组装成高压喷射灌浆专用设备,研究提出了高压定向喷射灌浆构筑防渗板墙技术工艺。通过多次进行板墙、围井试验,以及在坝基砂砾层构筑防渗板墙的工程实践,证明该项技术能够构筑厚度均匀、致密连续的板墙。板体之间、板与基岩之间接触牢固,符合防渗要求。施工速度快,且比较经济合理。这项技术可用于低水头坝基砂砾层止水防渗、截潜流等工程。已取得的工艺参数,可供设计、施工因地制宜选用。     

Electrolyte optimization for a Li ion battery by charge profile analysis

Electrolyte design for Li ion batteries was approached by means of comparison of faradaic and non-faradaic currents. The faradaic current by the movement of Li⁺ ions was dependent on the composition of the electrolyte and was related to the battery capacity; the higher the capacity, the greater the current by the faradaic reaction. The open circuit potential of the electrode with a greater faradaic current decreased at a slower rate than that of the electrode with a smaller faradaic current. This analysis method can be used to prepare an optimal electrolyte of an actual Li ion battery, especially when developing batteries with excellent high-rate discharge capabilities and low temperature discharge properties.     

万变的网络,永恒的安全--谈网络安全体系的构建

本文阐述了构建安全体系结构的意义,以及安全体系结构所包括的主要内容.重点以企业网为例介绍了应当如何根据自身实际,以安全体系为指导,构建其安全防护体系.     

On the compression and streaming of concentric mosaic data for free wandering in a realistic environment over the Internet

In this paper, we describe a system for wandering in a realistic environment over the Internet. The environment is captured by the concentric mosaic, compressed via the reference block coder (RBC), and accessed and delivered over the Internet through the virtual media (Vmedia) access protocol. One of the key contributions of the paper is the proposal of the RBC concentric mosaic coder. The RBC coder not only compresses the huge dataset of the concentric mosaic very efficiently, but also produces a well-organized bitstream that can be accessed just-in-time (JIT). To reconstruct a virtual view, only a portion of the RBC bitstream needs to be accessed and decoded. This greatly reduces the memory and computation requirement of the viewer compared with first decoding the entire concentric mosaic data set and then rendering from the decoded data. Our second contribution is the employment of the Vmedia protocol to deliver the compressed concentric mosaic bitstream just-in-time over the Internet. Only the bitstream segments corresponding to the current view are streamed over the Internet. The delivered bitstream segments are managed by a local Vmedia cache, so that frequently used bitstream segments do not need to be streamed over the Internet repeatedly, and a RBC bitstream larger than the memory capacity can be easily handled. Combining RBC and Vmedia, a concentric mosaic interactive browser is developed through which the user can freely wander in a realistic environment, e.g., rotate around, walk forward/backward, and sidestep, even under a tight bandwidth.     

A fracture criterion for three-dimensional crack problems

A criterion for predicting the growth of three-dimensional cracks is developed on the basis of the strain energy density concept which has been used successfully for treating two-dimensional crack problems. Fracture is assumed to initiate from the nearest neighbor element located by a set of spherical coordinates (r, θ, φ) attached to the crack border. The new fracture surface is described by a locus of these elements whose locations correspond to the strain energy function, dW/dV, being a minimum. The function dW/dV is found to be singular of the type 1/r and is of quadratic form in the three stress intensity factors k₁, k₂ and k₃ expressed through the strain energy density factor S. It is postulated that unstable crack propagation initiates from a region where S reaches a critical value S_cr = r₀(dW/dV)_cr. The locations of failure lying on the fracture surface is determined by holding (dW/dV)_cr = S_min/r₀ constant. The quantity S_min stands for the value of S minimized with respect to θ and φ and r₀ is a radial distance measured from the crack border.

An example of failure prediction for an embedded elliptical crack subjected to both normal and shear loads is presented. According to the S-criterion, fracture initiation takes place at the ends of the minor axis. An unexpected result is that for a narrow elliptical crack and Poisson's ratio of 1/3 the lowest failure load occurs when the uniaxial tensile load makes an angle of approximately 60° with the crack surface and is in the plane of the major axis. This is in contrast to the expectation that the lowest critical load occurs when the uniaxial tension is perpendicular to the crack surface. In the limit as the elliptical crack becomes increasingly narrower, the result reduces to the two dimensional line crack case of Mode I and III loading. The S-criterion is also applied to the failure prediction of three dimensional cracks under compressive loads.     

Optimized microwave dielectric properties of Co- and Ca-substituted Mg0.6Zn0.4TiO3

The system of (1 − y)(Mg_0.6Zn_0.4)_1−xCo_xTiO₃-yCaTiO₃ was investigated to optimize its microwave dielectric properties by adopting appropriate contents of Co and Ca and by controlling sintering conditions. The effect of Co substitution was to enhance densification and Qf value, while the addition of CaTiO₃ resulted in increases of dielectric constant and TCF. As an optimal compositions, 0.93(Mg_0.6Zn_0.4)_0.95Co_0.05TiO₃-0.07CaTiO₃ successfully demonstrated a dielectric constant of 23.04, a Qf of 79,460 GHz and a TCF value of +1.4 ppm/°C after firing at a relatively lower sintering temperature of 1200 °C. The increase of sintering temperature beyond 1200 °C tended to degrade overall microwave dielectric properties presumably due to Zn volatilization as evidenced by the presence of a Zn-deficient phase (MgTi₂O₅) at 1400 °C. An attempt to establish the correlation between microstructure characteristics and dielectric properties was made in this dielectric system where the extensive range of firing temperature up to 1400 °C was evaluated.