基于直流供电技术的电压暂降保护系统研究

变频器在软启动、变频调速、优化设计、经济运行等方面具有明显优势,得到广泛应用。在电压暂降期间,变频器会因低压保护而跳闸,造成连续性生产企业非计划停运,带来巨大的经济损失和事故。根据变频器交-直-交的特性,结合电力电子技术,研究开发了两种基于直流供电技术的电压暂降保护系统。两种保护系统分别利用电网残压和蓄电池组作为能量来源,通过Boost DC/DC变换器,输出恒定的直流电压,为变频器直流母线提供恒定的直流电。实验数据和现场应用表明,该两种电压暂降保护系统可以确保变频器在电压暂降期间正常运行,大大提高了供电可靠性,为用户避免了大量的经济损失。     

Time dependence of the mechanical properties of GICs in simulated physiological conditions

The mechanical properties of glass-ionomer cements (GICs) have been satisfactory for dental applications and have shown their potential in orthopedic surgery. Because the physiological environment in orthopedics is different from dentistry by unavoidable contamination with blood and other fluids such as normal saline used during an operation, the determination of GICs for orthopedic applications should be performed in an appropriate environment. The properties of a novel resin-modified GIC, S430, for orthopedic applications were evaluated in simulated orthopedic conditions by an early exposure to and long-term storage in normal saline. An early exposure to normal saline caused 20–60% reduction of its compressive and flexural properties, whereas long-term storage in normal saline showed slight changes of its mechanical properties. The effects were probably due to the disturbance of the cross-linking formation in the acid-base reaction and also the reduction of electrostatic interactions of the cross-linking polymeric chain of hydroxyethyl methacrylate (HEMA) in resin-modified GIC.     

Determination of trace isoflavone phytoestrogens in biological materials by capillary electrochromatography

Capillary electrochromatography using a specialty monolithic matrix was utilized in developing a rapid and highly efficient separation of isoflavones in biological materials. Without a preconcentration technique, it is relatively easy to reach ppm-ppb concentrations of these compounds in soy-based foods and verify them structurally using a photodiode array detector. With on-column preconcentration, we were able to measure low-ppb levels in human serum. Using blood samples from human volunteers, whose diet was supplemented by a soy-based product, the method has been validated for high-throughput screening of isoflavones in clinical studies.     

Photoelastic and acousto-optical properties of Cs2HgCl4 crystals

We use a Mach-Zehdner interferometric technique to study the piezo-optical properties of Cs2HgCl4 crystals at room temperature. All piezo-optical (pi(mn)) and photoelastic (p(in)) tensor constants are obtained. A substantial photoelastic effect and low ultrasonic velocities in these crystals determine a relatively high figure of merit M2 for isotropic diffraction (for a certain geometry of acousto-optical interactions, M2 approximately 110 x 10(-15) s3/kg). The new material may be considered, therefore, a candidate for applications in acousto-optical devices. The dependence of the acoustic walk-off angle on the direction of sound propagation is calculated for the principal crystallographic planes.     

Structure of an edge-dislocation wave originating in plane-wave diffraction by a half-plane

A new treatment of the well-known Sommerfeld solution of the problem of plane-wave diffraction from a perfectly conducting half-plane is reported. We show, in both theory and experiment, that the diffraction field (E-polarization) can be represented as a superposition of real physically existing waves, in contrast to geometrical and boundary waves postulated in Sommerfeld's representation. Our representation includes two pairs of wave components: one pair propagates along the direction of the incident wave, and the other in a mirror-reflected direction. Each wave pair consists of a plane-wave component with an amplitude half that of the incident wave and a nearly plane-wave component with an infinitely extended edge dislocation. On the basis of the proposed interpretation, all features of the half-plane diffraction are explained.     

A system dynamic model for the assessment of different exposure routes in aquatic ecosystems

With the exception of a limited number of highly persistent lipophilic pollutants, waterborne exposure is considered the most relevant exposure route for aquatic organisms, and even the only relevant exposure route in lower tier assessment, while the potential for bioaccumulation is only evaluated as secondary poisoning for birds and mammals. In addition, some evaluations consider that only the dissolved fraction is bioavailable for pelagic organisms. The lack of easy and cost-effective assessment methods is probably the main reason to disregard the contribution of other routes. This paper presents a system dynamics model that estimates the time-dependent accumulation of toxic chemicals through the food chain, and has also the potential to include the exposure from sediment. The generic ecosystem includes a primary producer and three levels of consumers, represented by unicellular algae, cladoceran invertebrates, cladoceran-eating fish and fish-eating fish, respectively. Nevertheless, the model, built using Microsoft Excel software, allows any number of levels and ecological-exposure relationships. The results obtained for four illustrative pollutants demonstrate that factors such as the binding to algae and other edible particles or food chain exposure for lipophilic non-persistent chemicals may constitute significant exposure routes. The current low tier European ecological risk assessment guidelines do not cover these aspects, and therefore may under estimate the real risk for both aquatic organisms and their predators. The model includes a simplified worst-case alternative that normally can be calculated using the existing information. Under a tiered approach, the simplified alternative is proposed to trigger the need of the toxicokinetics assays required to perform the complete time-dependent calculation.     

An improvement in the hygienic instruction of workers in dairy industry enterprises

The article presents the experience of the work on the sanitary education of the workers of the milk industry plants in Moscow and Moscow Province. The Institute's specialists had worked out basing on the studied experience the program of the full-time and external differential sanitary education of the workers of the milk industry which was approved by the Department of the State Sanitary Control of the Ministry of Health of Russia the April 22, 1998. "An exercise book for the sanitary education of the workers of the milk industry plants" was also prepared and published in 1999.     

LROC analysis of detector-response compensation in SPECT

Localization ROC (LROC) observer studies examined whether detector response compensation (DRC) in ordered-subset, expectation-maximization (OSEM) reconstructions helps in the detection and localization of hot tumors. Simulated gallium (Ga-67) images of the thoracic region were used in the study. The projection data modeled the acquisition of attenuated 93- and 185-keV photons with a medium-energy parallel-hole collimator, but scatter was not modeled. Images were reconstructed with five strategies: 1) OSEM with no DRC; 2) OSEM preceded by restoration filtering; 3) OSEM with iterative DRC; 4) OSEM with an ideal DRC; and 5) filtered backprojection (FBP) with no DRC. All strategies included attenuation correction. There were four LROC studies conducted. In a study using a single tumor activity, the ideal DRC offered the best performance, followed by iterative DRC, restoration filtering, OSEM with no DRC, and FBP. Statistical significance at the 5% level was found between all pairs of strategies except for restoration filtering and OSEM with no DRC. A similar ranking was found for a more realistic study using multiple tumor activities. Additional studies considered the effects of OSEM iteration number and tumor activity on the detection improvement that iterative DRC offered with respect to OSEM with no DRC.     

Interfacial bond strength of electrophoretically deposited hydroxyapatite coatings on metals

Hydroxyapatite (HAp) coatings were deposited onto substrates of metal biomaterials (Ti, Ti6Al4V, and 316L stainless steel) by electrophoretic deposition (EPD). Only ultra-high surface area HAp powder, prepared by the metathesis method 10Ca(NO₃)₂ + 6(NH₄)₂HPO₄ + 8NH₄OH), could produce dense coatings when sintered at 875–1000°C. Single EPD coatings cracked during sintering owing to the 15–18% sintering shrinkage, but the HAp did not decompose. The use of dual coatings (coat, sinter, coat, sinter) resolved the cracking problem. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) inspection revealed that the second coating filled in the valleys in the cracks of the first coating. The interfacial shear strength of the dual coatings was found, by ASTM F1044-87, to be 12 MPa on a titanium substrate and 22 MPa on 316L stainless steel, comparing quite favorably with the 34 MPa benchmark (the shear strength of bovine cortical bone was found to be 34 MPa). Stainless steel gave the better result since -316L (20.5 m mK^-1) > -HAp (14 m mK^-1), resulting in residual compressive stresses in the coating, whereas -titanium (10.3 m mK^-1) < -HAp, resulting in residual tensile stresses in the coating. © 1999 Kluwer Academic Publishers