Analysis of Asynchronous Band-Limited DS-CDMA with MMSE Multiuser Detector over Generalized-<Emphasis Type="Italic">k</Emphasis> Fading Channels

In this paper, we investigate bit-error-rate (BER) performance of a minimum mean-squared error (MMSE) multiuser receiver for asynchronous band-limited direct- sequence code-division multiple-access (DS-CDMA) systems. We focus on the BER performance in the presence of multitone jamming (MTJ) over frequency-selective multipath fading channels. We consider the generalized-K fading model in our analysis, as it can model a large spectrum of fading-channel characteristics. We also analyze the effects of band- limited pulse shape on the BER performance of the system. Multipath diversity based on the maximal-ratio combining (MRC) scheme is employed to combat fading effects. Our analytical expressions are valid for arbitrary diversity levels and fading parameters. Spectrum raised cosine (SRC) and Beaulieu–Tan–Damen (BTD) pulse shapes are employed for numerical analysis. Numerical results show that in the presence of MTJ and under various channel conditions, the MMSE based receiver gives better BER performance than the one without it. Moreover, the system with BTD pulses outperforms the one with SRC pulses.     

Enhanced Wettability Alteration by Surfactants with Multiple Hydrophilic Moieties

The main production mechanism during water flooding of naturally fractured oil reservoirs is the spontaneous imbibition of water into matrix blocks and resultant displacement of oil into the fracture system. This is an efficient recovery process when the matrix is strongly water-wet. However, in mixed- to oil-wet reservoirs, secondary recovery from water flooding is often poor. Oil production can be improved by dissolving low concentrations of surfactants in the injected water. The surfactant alters the wettability of the reservoir rock, enhancing the spontaneous imbibition process. Our previous study revealed that the two main mechanisms responsible for the wettability alteration are ion-pair formation and adsorption of surfactant molecules through interactions with the adsorbed crude oil components on the rock surface. Based on the superior performance of surfactin, an anionic biosurfactant with two charged groups on the hydrophilic head, it was hypothesized that the wettability alteration process might be further improved through the use of dimeric or gemini surfactants, which have two hydrophilic head groups and two hydrophobic tails. We believe that when ion-pair formation is the dominant wettability alteration mechanism, wettability alteration in oil-wet cores can be improved by increasing the charge density on the head group(s) of the surfactant molecule since the ion-pair formation is driven by electrostatic interactions. At a concentration of 1.0 mmol L⁻¹ a representative anionic gemini surfactant showed oil recoveries of up to 49% original oil-in-place (OOIP) from oil-wet sandstone cores, compared to 6 and 27% for sodium laureth sulfate and surfactin, respectively. These observations are consistent with our hypothesis.     

Morphological,mechanical, and rheological studies of PVC/ABS blends in the presence of maleic anhydride

A novel method of enhancing compatibility in PVC/ABS blends is the use of ABS‐grafted‐(maleic anhydride) (ABS‐g‐MAH) as a compatibilizer. In this study, maleic anhydride was grafted onto ABS (initiated by peroxide) in an internal mixer. Grafting degree was determined by a back‐titration method, and certain amounts of the resultant ABS‐g‐MAH were added to PVC/ABS blends during their melt blending in the mixer. The weight ratio of PVC to ABS was kept at 70:30. Evaluation of compatibilization was accomplished via tensile and notched Izod impact tests, scanning electron microscopy (SEM), and rheological studies. According to the SEM micrographs, better dispersion of the rubber phase and its finer size in properly compatibilized blends were indications of better compatibility. Besides, in the presence of a proper amount [5 parts per hundred parts of PVC (php)] of ABS‐g‐MAH, PVC/ABS blends showed significantly higher impact strengths than uncompatibilized blends. This result, in turn, would be an indication of better compatibility. In the presence of 5 php of compatibilizer, the higher complex viscosity and storage modulus, as well as a lower loss modulus and loss factor in the range of frequency studied, indicated stronger interfacial adhesion as a result of interaction between maleic anhydride and the PVC‐SAN matrix. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

加劲肋对焊缝区域应变模式的影响

通过试验和数值分析对工字形梁和箱形柱焊接连接的性能进行探讨,以获得加劲肋和柱翼缘厚度对连接耗能性能的影响。采用有限元法对试验构件进行了建模和分析,并将结果与全尺试验对比。考虑了各类加劲肋的影响,包括:柱加劲肋、侧向加劲肋、翼缘顶部和底部加劲肋。评测了各种加劲肋在塑性变形控制和连接耗能性能方面的贡献。     

Assessment of modal pushover analysis and conventional nonlinear static procedure with load distributions of federal emergency management agency for high‐rise buildings

The nonlinear static pushover analysis technique is mostly used in the performance‐based design of structures. However, the pushover analysis with load distributions of Federal Emergency Management Agency (FEMA) loses its accuracy in estimating the seismic responses of long‐period structures where higher mode effects are important. Recently, modal pushover analysis (MPA) has been proposed to consider these effects. Hence, FEMA load patterns and MPA are evaluated in the current study and compared with inelastic response history analysis. These approximate procedures are applied to medium‐rise (10 and 15 stories) and high‐rise (20 and 30 stories) buildings; advantages and limitations of them are elaborated. It is shown that MPA procedure presents significant advantage over FEMA load distributions in predicting story drifts. MPA is able to compute hinge plastic rotations better than FEMA load distributions at upper floor levels of high‐rise buildings due to considering higher mode effects by this procedure, but both are unsuccessful in predicting hinge plastic rotations with acceptable accuracy. Copyright © 2008 John Wiley & Sons, Ltd.     

Photocatalytic degradation of diclofenac using hybrid MIL-53(Al)@TiO2 and MIL-53(Al)@ZnO catalysts

In this work, TiO₂ and ZnO were incorporated successfully into a MIL-53(Al) metal–organic framework (MOF) to form nanocomposites via a facile post-modification technique. The hybrid MIL-53(Al)@TiO₂ and MIL-53(Al)@ZnO were characterized by several characterization tests. The X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and field-emission scanning electron microscopy (FE-SEM) analyses showed evidence of the successful incorporation of TiO₂ and ZnO within the MIL-53(Al) framework. The thermal gravimetric analysis (TGA) analysis demonstrated the excellent thermal stability of MIL-53(Al)@TiO₂ and MIL-53(Al)@ZnO, while diffuse reflectance spectroscopy (DRS) determined the direct optical band gaps of MIL-53(Al)@ZnO and MIL-53(Al)@TiO₂ to be 3.24 and 3.34 eV, respectively. The composites were also tested for the photocatalytic degradation of diclofenac (DCF) as a micropollutant. The DCF degradation efficiency of the photocatalysts was ranked in the following order: MIL-53(Al)@TiO₂ > MIL-53(Al) > TiO₂ > ZnO > MIL-53(Al)@ZnO. The incorporation of TiO₂ enhanced the optical properties of MIL-53 (Al), which was confirmed with the superior photodegradation efficiency of MIL-53(Al)@TiO₂ (>85% in 2 h) as compared to the pristine MIL-53(Al) (around 80% in 2 h). The improvement in the photodegradation of the hybrid-MOF is mostly associated with the possible dual function of the adsorption and photodegradation mechanisms. The reusability of MIL-53(Al) and its composites was inspected over 3 cycles of photodegradation experiments with DCF. The photocatalytic activity of MIL-53(Al)@TiO₂ remained unchanged (>90%), while for MIL-53(Al) and MIL-53(Al)@ZnO a slight drop was observed over three cyclic degradation experiments. Fluorescence measurements revealed that the hydroxyl radical is an important reactive oxygen species produced by all the photocatalysts that aid in the photodegradation of DCF. Furthermore, the kinetic modelling of the photoreaction identified a second-order kinetics for all catalysts. Experiments with scavengers showed that hydroxyl radicals played a major role in the photocatalytic process, and it was found that only 2 h of treatment was sufficient to obtain a considerable chemical oxygen demand (COD) reduction of 58%.     

Optimization of peroxidase-catalyzed oxidative coupling process for phenol removal from wastewater using response surface methodology

Hydroxylated aromatic compounds (HACs) are considered to be primary pollutants in a wide variety of industrial wastewaters. Horseradish peroxidase (HRP) is suitable for the removal of these toxic substances. However, development of a mathematical model and optimization of the HRP-based treatment considering the economical issues by novel methods is a necessity. In the present study, optimization of phenol removal from wastewater by horseradish peroxidase (HRP) was carried out using response surface methodology (RSM) and central composite design (CCD). As the initial experimental design, 2(4-1) half-fraction factorial design (H-FFD) is accomplished in triplicate at two levels to select the most significant factors and interactions in the phenol removal procedure. Temperature (degrees C), pH, concentration of enzyme (unit mL(-1)), and H202 (mM) were determined as the most effective independent variables. Finally, a fourfactor-five coded level CCD, 30 runs, was performed in order to fit a second-order polynomial function to the results and calculate the economically optimum conditions of the reaction. The goodness of the model was checked by different criteria including the coefficient of determination (R2 = 0.93), the corresponding analysis of variance ((Pmodel > F) < 0.0001) and parity plot (r = 0.96). These analyses indicated that the fitted model is appropriate for this enzymatic system. With the assumption that the minimum enzyme concentration was 0.26 unit mL(-1), the analysis of the response surface contour and surface plots defined the optimum conditions as follows: pH = 7.12, hydrogen peroxide concentration 1.72 mM, and 10 degrees C. This work improves phenol removal operation economically by applying minimum enzyme concentration and highest removal in comparison with previous studies.     

Simultaneous minimization of total tardiness and waiting time variance on a single machine by genetic algorithms

This paper considers a single machine scheduling problem, with the objective of minimizing a linear combination of total tardiness and waiting time variance in which the idle time is not allowed. Minimizing total tardiness is always regarded as one of the most significant performance criteria in practical systems to avoid penalty costs of tardiness, and waiting time variance is an important criterion in establishing quality of service (QoS) in many systems. Each of these criteria is known to be non-deterministic polynomial-time hard (NP-hard); therefore, the linear combination of them is NP-hard too. For this problem, we developed a genetic algorithm (GA) by applying its general structure that further improves the initial population, utilizing some of heuristic algorithms. The GA is shown experimentally to perform well by testing on various instances.     

A Novel Delay-less Control of Unified Power Quality Conditioner to Enhance Power Quality in Power System

In this article, an analytical and delay-less model for the unified power quality conditioner is proposed to improve electrical power quality in power systems. The designed model includes a shunt active filter, series active filter, and common DC link, which is capable of improving power quality parameters in different conditions. The proposed control is based on a combination of the rotating reference frame theory and least mean square method that (1) can enhance power quality, including reduction of the voltage and current harmonics, voltage flicker, and reactive power of system, and (2) has no delay in the reference current generation. The DC link is also designed in a manner that capacitor voltage has a stabilized voltage in all instants. In addition, fundamental frequency estimation is employed to control frequency changes in the control system. For testing the proposed method in the worst conditions, the electric arc furnace load based on an actual stochastic arc that can generate almost all electrical power quality parameters is taken into account for the power system. The validity of proposed method is analyzed by comparing different existing control methods of the unified power quality conditioner. The simulation results show the accuracy of the control system.     

Effectiveness of Zataria multiflora Boiss essential oil and grape seed extract impregnated chitosan film on ready-to-eat mortadella-type sausages during refrigerated storage

BACKGROUND: The effectiveness of chitosan films containing Zataria multiflora Boiss essential oil (ZEO) (5 and 10 g kg^?1) and grape seed extract (GSE) (10 g kg^?1) on lipid oxidation and microbial (lactic acid bacteria, aerobic mesophiles and inoculated Listeria monocytogenes) characteristics of mortadella sausage at 4 °C for 21 days was evaluated. The release of total phenolics (TPs) into sausage was also assessed. RESULTS: All films exhibited antibacterial activity against L. monocytogenes on agar culture media. Chitosan films containing ZEO were the most effective on the growth of bacteria. The growth of L. monocytogenes was significantly inhibited by ZEO‐GSE containing films especially during storage of the sausages for 6 days. Aerobic mesophiles and lactic acid bacteria were the most sensitive and resistant groups to films by 0.1–1.1 and 0.1–0.7 log cycles reduction, respectively. Sausages wrapped by 10 g kg^?1 GSE + 10 g kg^?1 ZEO films had the lowest degrees of lipid oxidation, which was 23% lower than the control. The TPs of ZEO films decreased to zero after 6 days, whereas TPs of GSE films followed a slight decrease during the storage. CONCLUSION: Antimicrobial/antioxidant chitosan film could be developed by incorporating GSE and ZEO for extending the shelf life of mortadella sausage. Copyright © 2011 Society of Chemical Industry