Positron annihilation study on thin-film composite pervaporation membranes: Correlation between polyamide fine structure and different interfacial polymerization conditions

To investigate the variation in the fine structure of polyamide thin-film composite (TFC) membranes prepared via two different interfacial polymerization conditions (IP-I and IP-II), experiments on Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), water contact angle, and positron annihilation spectroscopy (PAS) coupled to a slow positron beam were conducted. Polyamide TFC membranes were prepared via the interfacial polymerization reaction between triethylenetetramine (TETA) and trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane. Compared with the polyamide TFC membrane prepared via IP-I, the polyamide layer prepared via IP-II showed a shorter S plateau length (thinner thickness), a higher o-Ps intensity I₃ value (higher free-volume concentration), and a smaller o-Ps lifetime τ₃ value (smaller free-volume size), resulting in higher permeation rate and separation factor obtained from the pervaporative separation of a 70 wt% isopropanol aqueous solution at 25 °C.     

Simulation and Validation of Thin Layer Models for Peanut Drying

Simulations of peanut drying in a trailer-type dryer with thin-layer drying models, Newton model and Henderson-Pabis model, and five equilibrium moisture content (EMC) models in this study. The results show that the match of Henderson-Pabis model using Hummeida K-value model and modified Oswin EMC model can yield the best fit of experimental data, although the error in temperature prediction still exists at the middle layer.     

Tuning the EDCA parameters in WLANs with heterogeneous traffic: A flow-level analysis

The need to support multimedia services in WLANs has motivated the research on traffic differentiation mechanisms at the MAC layer. The most common approach is the tuning of the different MAC parameters of the heterogeneous traffic profiles in order to provide different channel access probabilities. The benefits of these mechanisms in terms of throughput and transmission delay, as well as their traffic differentiation and QoS capabilities, have been thoroughly studied. However, there are very few results on how the tuning of the MAC parameters impacts on the flow-level metrics, such as blocking probability or average flow duration. In this article, several EDCA-based tuning algorithms have been evaluated by comparing their flow-level response in presence of rigid (e.g. VoIP) and elastic (e.g. P2P) flows. Results show that those algorithms which adapt better to the changing WLAN state (number and type of active flows), and that are designed under multiple objectives, provide significantly higher performance and QoS than static and single-objective configurations.     

利用电凝聚-气浮法研究印染废水的脱色性能

自制电解装置,以铁板作为阳极,以NaCl作为电解液,采用电凝聚-气浮法对模拟印染废水偶氮染料活性绿RG19和活性蓝RBu171进行脱色研究,探索废水的pH值、浓度、电凝聚时间、电解质浓度等因素对废水的色度去除率的影响.实验结果显示:染料废水浓度低于300 ppm,电解质NaCl浓度为2g/L,溶液的pH初始值小于7,两种染料RG19和RB171在120 min内,脱色效率均可达到90％.     

Hexavalent chromium removal from near natural water by copper-iron bimetallic particles

The reduction of hexavalent chromium (Cr(VI)) by zero-valent iron (ZVI) is self-inhibiting in near natural groundwater because insulating Fe(III)-Cr(III) (oxy)hydroxide film forms on the ZVI surface during the reaction. This study tries to overcome this deficiency by coating the surface of ZVI with copper to form copper-iron bimetallic particles. The Cr(VI) removal rate by ZVI rose significantly after the copper coating was applied. The copper loading needed for enhancing Cr(VI) removal was much higher than that needed for enhancing removal of chlorinated organic compounds or other oxidative contaminants, because of the higher oxidation potential of Cr(VI). The results of X-ray photoelectron spectroscopy (XPS) indicate that coating copper onto the surface of ZVI can not only increase the deepness of the oxidation film but also increase the oxidation state of iron in the film. This phenomenon means higher Cr(VI) removal capacity per unit weight of ZVI.     

Improved performances of a two-step passivated heterojunction bipolar transistor

An interesting InGaP/GaAs heterojunction bipolar transistor (HBT) with a two-step passivated (ledge structure and sulfur treatment) process on the base surface has been fabricated and studied. Based on the two-step passivation, improved transistor characteristics including the specific contact resistances ρ_C, sheet resistances R_sh, base surface recombination current density J_SR, base current ideality factor n_B, and microwave performances are obtained. Furthermore, the device with two-step passivation reveals the better thermal stability on ρ_C, R_sh, and n_B than the devices with and without ledge structure. Therefore, the two-step passivation method can be employed for high-temperature and low-power electronics applications.     

Fuzzy weighted support vector regression with a fuzzy partition.

The problem of the traditional support vector regression (SVR) approach, referred to as the global SVR approach, is the incapability of interpreting local behavior of the estimated models. An approach called the local SVR approach was proposed in the literature to cope with this problem. Although the local SVR approach can indeed model local behavior of models better than the global SVR approach does, the local SVR approach still has the problem of boundary effects, which may generate a large bias at the boundary and also need more time to calculate. In this paper, the fuzzy weighted SVR with a fuzzy partition is proposed. Because the concept of locally weighted regression is not used in the proposed approach, the boundary effects will not appear. The proposed method first employs the fuzzy c-mean clustering algorithm to split training data into several training subsets. Then, the local-regression models (LRMs) are independently obtained by the SVR approach for each training subset. Finally, those LRMs are combined by a fuzzy weighted mechanism to form the output. Experimental results show that the proposed approach needs less computational time than the local SVR approach and can have more accurate results than the local/global SVR approaches does.     

Schottky diode performance of an Au/Pd/GaAs device fabricated by deposition of monodisperse palladium nanoparticles over a p-type GaAs substrate

Au/Pd/p-GaAs Schottky diodes were fabricated by simple assembly of monodisperse Pd nanoparticles on a p-type GaAs semiconductor. Monodisperse 5-nm Pd nanoparticles were synthesized via reduction of palladium(II) acetylacetonate in oleylamine using a borane tert-butylamine complex. The Au/Pd/p-GaAs Schottky diodes provided a barrier height of 0.68 eV, which is higher than room-temperature values reported in the literature. A double distribution was observed for the barrier height for the Schottky diodes from I–V–T measurements. A decrease in temperature lowered the zero-bias barrier height and increased the ideality factor. These observations were ascribed to barrier height inhomogeneities at the interface that altered the barrier height distribution. Values of the series resistance obtained by the Norde method decreased with increasing temperature. Understanding the temperature dependence of the current–voltage characteristics of Au/Pd/p-GaAs devices might be helpful in improving the quality of Pd deposited on GaAs for future device technologies.     

Triple-shape memory properties of thermoplastic polyurethane/olefin block copolymer/polycaprolactone blends

Thermoplastic polyurethane (TPU)/olefin block copolymer (OBC)/polycaprolactone (PCL) blends (70/20/10 and 50/30/20) were melt-blended to form the first environmental OBC-based triple-shape memory polymer blends. In this work, PCL with low crystalline temperature (switching phase), OBC with medium crystalline temperature (switching phase), and TPU with high crystalline temperature (fixed phase) could form an alternative triple-shape memory polymer (TSMP). Two compatibilizers, OBC-g-glycidyl methacrylate (OBC-g-GMA) and dicumyl peroxide, were confirmed to show a synergistic effect in enhancing the compatibility further through the morphological observation. Crystallinity of both OBC and PCL in the blends with or without modification decreased in comparison with that of pure resin. For dual-shape behaviors, the shape fixing ratio (R_f) and shape recovery ratio (R_r) were up to 96.3% and 91.2% for the GMA and peroxide-modified blends (50/30/20). The higher amount of TPU didn’t give higher recovery ratio, but instead slightly lower R_r due to the morphology difference. For triple-shape behaviors, both TPU/OBC/PCL blend compositions with or without GMA or peroxide modifications gave high R_f(C→B) values in the first fixing stage, but slightly lower values R_f(B→A) in the second fixing stage, especially for (70/20/10) case. On the other hand, a reverse trend was observed for two recovery stages. To enhance the R_f(B→A) in the second fixing stage, higher deformation temperatures were considered, and a measurable increment on R_f(B→A) was attained. Through this subtle adjustment on the temperature difference between high and low deformation temperatures, the theoretical multi-shape memory shape could be readily tailored to meet different applications.