A novel heteropolyacid-doped carbon nanotubes/Nafion nanocomposite membrane for high performance proton-exchange methanol fuel cell applications

A novel proton-exchange polymer composite membrane was synthesized using Nafion^®, tetraethoxysilane-modified carbon nanotubes (CNTs) and phosphotungstic acid-modified carbon nanotubes with the aim of using direct methanol fuel cells (DMFCs). Physicochemical properties of the modified CNTs and fabricated composite membranes were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, water uptake, thermogravimetric analysis, ion exchange capacity, proton conductivity and methanol permeability tests. It was demonstrated that chemical surface modification of CNTs and introduction of the phosphotungstic acid (PWA) groups effectively improved the performance of DMFC. It was found that the presence of PWA groups on the surface of CNTs led to the formation of strong electrostatic interactions between the PWA groups and clusters of sulfonic acid in Nafion^® macromolecules. Hence, the incorporation of inorganic phosphotungstic super-acid-doped silicon oxide-covered carbon nanotubes (CNT@SiO₂-PWA) into Nafion^® matrices enhanced the proton conductivity of the prepared membranes. Moreover, the methanol permeability was reduced to 2.63 × 10^?7 cm² s^?1 in comparison with the recast Nafion^® membrane (2.25 × 10^?6 cm² s^?1). Enhancing the proton conductivity and reducing the methanol permeability, the selectivity of the prepared nanocomposite membranes was enhanced to a greater value of 330,700 S s cm^?3 as compared to the value of 38,222 S s cm^?3 for recast Nafion^®.     

Defending Against Flooding Attacks in Mobile Ad-Hoc Networks Based on Statistical Analysis

Wireless Personal Communications - Due to their specific structure and plenty of their utilization, mobile ad-hoc networks are vulnerable to various attacks. An attack which impacts on network...     

Large eddy simulation of thermal stratification effect on convective and turbulent diffusion fluxes concerning gaseous pollutant dispersion around a high-rise model building

In this paper, the large eddy simulation (LES) approach is employed to investigate the role of different thermal stratification conditions (stable, neutral and unstable) in the air flow and gaseous pollutant dispersion processes around a high-rise non-isolated model building with 1:1:2 shape placed within a non-isothermal boundary layer. The simulation results are initially validated with available experimental measurements and then applied to study the characteristics of pollutant dispersion. Predictions show a low-velocity zone behind the model building. The major effect of a stable stratification on flow field is the formation of a weak recirculation flow in the wake region. Results represent an intense temperature gradient close to the sides of the model building for both stable and unstable conditions. Moreover, the convective and turbulent diffusion fluxes are compared under different thermal stratification conditions, and it is shown that the LES approach is capable of predicting the counter-gradient mechanism.     

Anti-mutagenic Properties of Mono- and Dienoic Acid Biohydrogenation Products from Beef Fat

Unsaturated fatty acid biohydrogenation products from beef fat and pure fatty acids were subjected to the Ames Salmonella mutagenicity testing, including monounsaturated fatty acids [MUFA: oleic acid, vaccenic acid, elaidic acid; beef fatty acid fractions rich in trans (t)11/t13‐t14‐18:1 (t11,13,14‐Frac), t10‐18:1 (t10‐Frac)] and dienoic fatty acids [linoleic acid, conjugated linoleic isomers cis (c)9,t11‐18:2 and t10,c12‐18:2, and a mixed beef dienoic fatty acid fraction high in c9,t13‐/t8,c12/t11c15‐18:2 (MD)]. Significantly higher anti‐mutagenic effects of oleic acid, vaccenic acid, t11, 13, 14‐Frac, and t10‐Frac against daunomycin were observed at 2.5 mg. All dienoic acids except MD significantly reduced daunomycin mutagenicity at ≥0.25 mg. Anti‐mutagenicity of oleic and vaccenic acids against 2‐aminoanthracene was found at 2.5 and 0.25 mg, respectively. All dienoic acids significantly reduced 2‐aminoanthracene mutagenicity at ≥0.25 mg. Findings of this study show that unsaturated fatty acids, including trans‐fatty acids commonly found in beef, can act as strong anti‐mutagens.     

Designing fuzzy-genetic learner model based on multi-agent systems in supply chain management

Supply chain requirements and challenges in recent years have made managers to explore new methods in dealing with supply chain management (SCM) problems. Methods with high flexibility which can adapt plans to real conditions help one to make a decision at the right time.In the SCM, distribution and allocation problems are of enormous significance and due to their applications in the cross-functional and final parts of SCM problems, they are in a particular position among the SCM problems.In this paper, by proposing an architecture based up on multi-agent system (MAS), a model is developed to tackle such problems as the nature of supply chain distributions, dynamic distributions systems (DS), uncertain parameters in DS, management of diverse objectives in DS, need for flexibility in DS and other factors considered as challenges and designing requirements in an agile model which can be all found in the SCM. MAS was used in this article owing to their special attributes and features. In MAS, each agent follows up a duty in a self-contained way and is able to adapt it to the environmental changes, after all helping the system to stay alive.     

Exponential stability of impulsive systems with application to uncertain sampled-data systems

We establish exponential stability of nonlinear time-varying impulsive systems by employing Lyapunov functions with discontinuity at the impulse times. Our stability conditions have the property that when specialized to linear impulsive systems, the stability tests can be formulated as Linear Matrix Inequalities (LMIs). Then we consider LTI uncertain sampled-data systems in which there are two sources of uncertainty: the values of the process parameters can be unknown while satisfying a polytopic condition and the sampling intervals can be uncertain and variable. We model such systems as linear impulsive systems and we apply our theorem to the analysis and state-feedback stabilization. We find a positive constant which determines an upper bound on the sampling intervals for which the stability of the closed loop is guaranteed. The control design LMIs also provide controller gains that can be used to stabilize the process. We also consider sampled-data systems with constant sampling intervals and provide results that are less conservative than the ones obtained for variable sampling intervals.     

Low-voltage cross-sectional EBIC for characterisation of GaN-based light emitting devices

Electron beam induced current (EBIC) characterisation can provide detailed information on the influence of crystalline defects on the diffusion and recombination of minority carriers in semiconductors. New developments are required for GaN light emitting devices, which need a cross-sectional approach to provide access to their complex multi-layered structures. A sample preparation approach based on low-voltage Ar ion milling is proposed here and shown to produce a flat cross-section with very limited surface recombination, which enables low-voltage high resolution EBIC characterisation. Dark defects are observed in EBIC images and correlation with cathodoluminescence images identify them as threading dislocations. Emphasis is placed on one-dimensional quantification which is used to show that junction delineation with very good spatial resolution can be achieved, revealing significant roughening of this GaN p-n junction. Furthermore, longer minority carrier diffusion lengths along the c-axis are found at dislocation sites, in both p-GaN and the multi-quantum well (MQW) region. This is attributed to gettering of point defects at threading dislocations in p-GaN and higher escape rate from quantum wells at dislocation sites in the MQW region, respectively. These developments show considerable promise for the use of low-voltage cross-sectional EBIC in the characterisation of point and extended defects in GaN-based devices and it is suggested that this technique will be particularly useful for degradation analysis.     

Webometric analysis of Iranian universities of medical sciences

Introduction  There are many researches have been conducted on webometrics, especially the impacts of websites on each other and the web impact factor. However, there are few studies focusing on the websites of Iranian universities. This study analyzed the websites of Iranian universities of medical sciences according to the webometric indicators. Method and materials  In a cross-sectional study, the number of web pages, inlinks, external inlinks and also the overall and absolute web impact factors for Iranian universities of medical sciences with active exclusive websites were calculated and compared using AltaVista search engine. Finally, the websites were ranked based on these webometric indicators. Results  The results showed that the website of Tehran university of medical sciences with 49,300 web pages and 9860 inlinks was ranked first for the size and number of inlinks, while its impact factor was ranked 38th. Rafsanjan UMS with 15 web pages and 211 links had the highest rank for the web impact factor among Iranian universities of medical sciences. Discussions and conclusions  The study revealed that Iranian universities of medical sciences did not have much impact on the web and were not well known internationally. The major reason relies on linguistic barriers. Some of them also suffer from technical problems in their web design.     

In vitro and in vivo evaluations of phenytoin sodium-loaded electrospun PVA, PCL, and their hybrid nanofibrous mats for use as active wound dressings

In this work, polyvinyl alcohol (PVA), poly(ε-caprolactone) (PCL), and their electrospun PVA/PCL (80/20) hybrid nanofibrous mats were used for the development of active wound dressings. The biocompatibility and therapeutic effects of the developed products were studied by in vitro cell culture and in vivo experimental rat wound model. The release rate measurements by HPLC showed that the PVA nanofibrous sample containing phenytoin sodium (PHT-Na) has a higher level of the drug release compared to the hybrid PVA/PCL (80/20) and PCL nanofibrous mats. A mesenchymal stem cell was seeded on neat as well as drug-loaded PVA nanofibrous mats. The results represented that the mats provide a suitable environment for cell growth and viability. PVA nanofibers containing PHT-Na have a unique performance for fibroblasts and myofibroblasts cells formation and consequently reaching to the remodeling phase and faster healing of the wounds. Also, PHT-Na-loaded electrospun PVA nanofibrous mats showed a remarkable efficiency in wound closure compared with the treatments results from gauze, commercial wound dressing Comfeel^®Plus, and 2 % PHT-Na ointment. Histology analysis showed the formation of epidermis, the lack of necrosis, and accumulation of collagen fibers in dermis for PVA nanofibrous mats containing PHT-Na.