Restriction techniques for the unit-commitment problem with total procurement costs

Many discrete optimization problems may be solved much easier, if the solution space can be restricted in a convenient way. For a given specific problem, the restriction techniques can be helpful if an available optimization solver, perceived as a black box, is capable of solving quickly only reduced subproblems of a limited size. For the family of hard unit-commitment problems we investigate a hierarchical search algorithm, which is based on decomposition of the problem into two subproblems. The upper-level subproblem is a relatively small decision “kernel” of the problem that can be solved approximately by a search algorithm. We define an appropriate restricted decision space for this subproblem. The lower-level subproblem is an appropriate restriction of the original problem that can be solved efficiently by a dedicated solver. Our approach was analyzed on a set of historical data from the Polish electrical balancing market and the best known solutions were improved by the average of about 2–5%.     

Fatty acid composition and content of tocopherols and carotenoids in raw and extruded grass pea (Lathyrus sativus L)

The effects of adding 140, 180, 220, 260 and 300 g water to 1 kg grass pea seeds and using three levels of extrusion temperature, 90/100/120/100 °C, 120/140/170/160 °C and 140/180/220/200 °C, on concentrations of total lipids, tocopherols, carotenoids and fatty acids in extruded seeds were determined. Extrusion-cooking and a higher moisture content resulted in a lower content of polyenoic fatty acids. The smallest decrease in the content of polyenoic fatty acids in grass pea seeds was observed during extrusion-cooking at 120/140/170/160 °C. Moisturising as well as extrusion lowered significantly the content of the natural antioxidants: α-tocopherol, γ-tocopherol, β-carotene and lutein. © 1999 Society of Chemical Industry     

Effect of saliva viscosity on tribological behaviour of tooth enamel

Employing a special device simulating conditions of the masticatory process, two series tests were conducted involving studies of the tribological behaviour of enamel subjected to two- and three-body tests at different saliva viscosities.The studies showed no significant influences of saliva viscosity on the mean of the friction coefficient. However, below 2.08 mPa s the coefficient was unstable, i.e. scatter was observed. Both higher wear rate and higher scatter were observed for viscosities below of 1.68 mPa s. Comparing the wear results of the three- and two-body tests, no significant differences were obtained for viscosities above 1.68 mPa s, although for lower viscosities the wear rate in the presence of abrasive particles was higher than that obtained with pure saliva.Two regions with different tribological behaviour of enamel were observed in relation to saliva viscosity; the region with stable and low values of the tribological parameters beyond some threshold value, and the other with higher mean values of tribological parameters and their scattering. The author suggests that different concentrations of proteins are possible at the same low saliva viscosity, thus there are qualitatively different interactions between enamel surface and saliva components resulting in different lubrication regimes.     

轮铲式挖掘机新一代驾驶室隔震系统的优化

 提出新一代驾驶室计算机辅助设计的一些观点,重点关注驾驶室隔振系统的原始设计方案,它由挖掘悬臂连同驾驶室悬臂组成。用有限元法对驾驶室动态特性进行了分析,在虚拟模型数值分析的基础上形成一个方案,随后建立一个带有隔振系统的驾驶室原型样模,实体振动测量提供了非常令人满意的结果。     

Scaffold-aided repair of articular cartilage studied by MRI

OBJECTIVE: The objective of the study was to evaluate the ability of the noninvasive magnetic resonance techniques to monitor the scaffold-aided process of articular cartilage repair. MATERIALS AND METHODS: Defects of 4 mm in diameter and 3 mm in depth were created in right knees of 30 adolescent white New Zealand rabbits. Fourteen rabbits were implanted with poly(lactide-co-glycolic acid) (PLGA) scaffold trimmed to match the size and the shape of the defect (PLGA+ group). No procedure was applied to the remaining 16 animals (PLGA- group). Animals were sacrificed sequentially at 4, 12, and 24 weeks after the surgery and magnetic resonance T (2)-weighted images (400 MHz) of the dissected bone plugs at eight different echo times were taken to derive T (2) relaxation time. The images and the T (2) time dependencies versus the tissue depth were statistically analyzed. Histological results of bone plugs were evaluated using semiquantitative histological scales. RESULTS: The results obtained for PLGA repair tissue were evaluated versus the PLGA- group and the healthy tissue harvested from the opposite knee (reference group), and compared with histological results (hematoxylin and eosin staining). The magnetic resonance images and T (2) relaxation time profiles taken 4 weeks after surgery for both the PLGA- and PLGA+ group did not reveal the tissue reconstruction. After 12 weeks of treatment T (2) time dependence indicates a slight reconstruction for PLGA+ group. The T (2) time dependence obtained for PLGA+ samples taken after 24 weeks of treatment resembled the one observed for the healthy cartilage, indicating tissue reconstruction in the form of fibrous cartilage. The tissue reconstruction was not observed for PLGA- samples. CONCLUSION: The study revealed correlation between magnetic resonance and histology data, indicating the potential value of using MRI and spatial variation of T (2) as the noninvasive tools to evaluate the process of articular cartilage repair. It also suggested, that the PLGA scaffold-aided treatment could help to restore the proper architecture of collagen fibrils.     

The lifetime prediction of a rotary screw compressor of a liquid cooler subjected to high pressure and high frequency loads

The estimation of the lifetime of high pressure and high frequency loaded components by testing is very costly and time-consuming. The simulation of fatigue life is an important design step in the fast moving and competitive automotive industry, where the steady rise of engineering components and the demand for lightweight construction concurred with enhanced reliability require an optimized dimensioning process. The paper presents the chosen problems of 3D numerical strength and fatigue simulation of a rotary screw compressor of a liquid cooler. The presented results of the FEM mechanical calculation based on a real components. The fatigue analysis were executed using the criterion of critical plane. Local multi-axial state of stresses and deformation has been calculated based on Hooke’s law with simultaneous consideration of kinematics hardening rule of material according to Jiang’s model.     

Optimization of the technological parameters of epoxidation of allyl alcohol by hydrogen peroxide over Ti–BETA catalyst

The influence of the technological parameters on the epoxidation of allyl alcohol by a 30 wt% hydrogen peroxide in the medium of methanol over the Ti–BETA catalyst in the direction of glycidol has been presented. The experimental conditions were established on the basis of preliminary experiments and through the applications of statistical experimental design methods (rotatable uniform design). The results of the particular experiments were described by the following functions: the yield of glycidol in relation to allyl alcohol introduced into the reactor, the selectivity of transformation to glycidol in relation to allyl alcohol and hydrogen peroxide reacted, and the degree of conversion of allyl alcohol and H₂O₂. The optimal values of each function were established. The courses of functions corresponding to the parameters were plotted in the system of two variable parameters. The optimum parameters of the epoxidation process were established after the analysis of the layer drawings. The obtained results were confirmed by a series of verifying syntheses. Copyright © 2004 Society of Chemical Industry     

Modelling of residual stresses developed in steel cylinders subjected to surface-layer deposition by welding

A new model for the determination of the residual stress–strain and microstructural state of a cylinder subjected to layer deposition by welding is developed. The growing body of theory and unified the Bodner–Partom viscoplastic theory generalized for the case of coupled thermomechanic processes are involved to describe the mechanical behavior of the material. Continuous cooling transformation (CCT) diagrams are used to account for microstructural transformation. The concept of eigenstrains and temperature state is utilized to satisfy the boundary conditions on the growing surface. A time-stepping procedure and a finite-element technique are used to simulate both the instantaneous and the residual stress–strain and microstructural state of a deposited cylinder. The influence of initial temperature on the residual stress–strain and the structural states of the cylinder deposited by austenitic and martensitic steel layers is investigated. It is discovered that martensite and bainite shares in the heat-affected zone can be effectively controlled by the initial temperature of the cylinder. Numerical and experimental results are compared.     

Changes to polyphenols in the process of production of must and wines from blackcurrants and cherries. Part I. Total polyphenols and phenolic acids

The effect of pulp treatment on the qualitative and quantitative changes to polyphenol compounds exhibiting antioxidant properties, in musts and wines from blackcurrants and cherries was investigated. The following variants of pulp treatment were used: hot maceration, hot maceration and pulp pectinolysis with Rohapect MA Plus and Pektopol PM preparations, and also pulp pectinolysis with Rohapect and Pektopol preparations. Blackcurrant musts contained from 4800 to 6600 mg l^-1 of total polyphenols and cherry musts from 3060 to 3920 mg l^-1. The fermentation process caused a decrease in polyphenols content of approximately 25%. In production of fruit wines, the pulp treatment method had a considerable effect on the total content of polyphenols. In blackcurrant wines the highest extraction of polyphenols was obtained after pectinolysis with a Rohapect preparation. In the case of cherry wines the highest content of these compounds was extracted during pectinolysis with a Pektopol preparation. In musts and wines the presence of the following compounds, derivatives of hydroxycinnamic acid, was determined: neochlorogenic, chlorogenic, caffeic, p-coumaric and ferulic acids. The content of neochlorogenic acid was the highest both in musts and wines from blackcurrants and cherries and amounted to 41.7-126.3 mg l^-1, and 24.7-35.3 mg l^-1 respectively for blackcurrants and 74.3-87.7 mg l^-1and 44.5-71.4 mg l^-1 respectively for cherries. The enzymatic preparation Pektopol PM contained an enzyme acting as depsidase. It broke down chlorogenic acid and other compounds to simple phenolic acids (caffeic acid, p-coumaric acid).     

Radioluminescence and photoluminescence of hafnia-based Eu-doped phosphors

Crystal structures of hafnia are discussed and it is shown that addition of about 7 at.% of Lu to the HfO₂ host lattice enforces the mixed composition to crystallize in cubic structure even at room temperature. Without Lu HfO₂ crystallizes in monoclinic structure. Luminescence and luminescence excitation spectra of Hf_0.93Lu_0.07O_1.965 are presented and discussed for powders prepared at different temperatures (600–1000 °C) and with different content of Eu. It is shown that decay of the 595.4 nm luminescence is longer (2.5 ms) than the 610 nm (1.6 ms). Radioluminescence efficiency of the cubic Hf_0.93Lu_0.07O_1.965 is low and does not exceed 10% of the commercial Gd₂O₂S:Eu.