Sharif Digital Repository

In this article, oxygen barrier properties of nanocomposite films composed of organoclay (OC), high-density polyethylene (HDPE), and ethylene vinyl acetate (EVA) copolymer have been investigated. The nanocomposite films whose EVA forms a dominant fraction were prepared using the solution method. The dispersion of the OC in the HDPE/EVA blend was improved through taking two-step procedure in the preparation of nanocomposite. First, the OC and EVA were dissolved in chloroform. Then, the resulting product, after evaporating most of the solvent, along with HDPE was dissolved in xylene. The obtained nanocomposite films underwent a number of tests in order to examine their barrier properties... 

In this study, Yittria Stabilized Zirconia/Titania powders synthesized via air plasma spray (APS) method such as morphology changes and phase transformations of core-shell structure characterized. Phase analysis of powders was performed by XRD. The crystallite size and lattice strain of YSZ/TiO2 core-shell structure was calculated by Williamson-Hall method. Morphology was observed with scanning electron microscope. EDS and map analysis were used for core-shell characterization. Results revealed that all TiO2 nano particles were melted around YSZ powders with the thickness between 1 up to 5 μm. After spraying the YSZ/TiO2 mixture in water, strain values increased but crystallite size... 

In this study, the properties of poly (vinyl alcohol)(PVA) films incorporated with Zataria multiflora essential oil (ZMO) as a potential antioxidant/antibacterial material was investigated. PVA films were prepared from PVA solutions (2% w/v) containing different concentrations of ZMO. Water solubility, moisture absorption, water swelling, and water vapor permeability for pure PVA films were 57 ± 1.1, 99 ± 3.2%, 337 ± 8%, and 0.453 ± 0.015 g mm/m2 h, respectively. Incorporation of ZMO into PVA films caused a significant decrease in water swelling and moisture absorption and increase in solubility and water vapor permeability. Tensile strength, elastic modulus, and elongation at break for pure... 

Nanocomposite films based on low density polyethylene (LDPE), containing of 2, 3, and 4. wt.% organoclay (OC) and ethylene vinyl acetate (EVA) copolymer as a new compatibilizer were prepared and characterized using rheological tests, X-ray diffraction, differential scanning calorimetry, oxygen permeation measurements, and tensile tests. There was no exfoliation or intercalation of the clay layers in the absence of EVA, while an obvious increase in d-spacing was observed when the samples were prepared with EVA present. This issue was reflected in the properties of nanocomposites. The oxygen barrier properties of the LDPE/EVA/OC film were significantly better than those of the LDPE/OC film.... 

Background: Dynamic knee valgus (DKV) is a common lower extremity movement disorder among females. This study aimed to investigate kinematic couplings between lower extremity joints in female junior athletes with DKV during single and double-leg landing and gait. Methods: Twenty-six physically active female junior athletes (10–14 years old) with DKV were recruited. Kinematic couplings between rearfoot, tibia, knee, and hip were extracted using eight Vicon motion capture cameras and two force plates. Zero-lag cross-correlation coefficient and vector coding were used to calculate kinematic couplings between joints during physical tasks. Paired t-test and Wilcoxon tests were run to find... 

Polyvinyl alcohol (PVA) thin films were reinforced by glutaraldehyde and multiwalled carbon nanotubes (MWCNTs) and then mechanical, water solubility, water swelling, water uptake, water vapor permeability, and antibacterial properties of the films were examined. Cross-linking by glutaraldehyde or incorporation of MWCNT caused a significant increase in tensile strength, decrease in elongation at break, and increase in Young's modulus of the PVA films, while MWCNTs were more effective rather than that of glutaraldehyde. Cross-linking by glutaraldehyde or incorporation of MWCNT caused a significant decrease in water solubility, water swelling and water uptake, with a similar manner.... 

Stay and guide vanes (distributor) are essential parts of a turbine. They are used to control the flow rate and to appropriately transfer the flow momentum to the runner. In this work, flow through the distributor is analyzed. For various Boundary Conditions (BC) and different configurations, threedimensional flows in the distributor of a Francis turbine are evaluated and compared with each other. The numerical simulations were carried out using Fluent software and the results were validated with a GAMM Francis turbine, where the geometry and detailed best efficiency measurements were publically available. In these simulations, the flow was assumed to be steady and the effect of turbulence... 

The aim of the study was to predict disability, psychological wellbeing, and somatic health in multiple sclerosis (MS) patients with the mediating variable of religiosity. A sample of 128 patients was recruited, and were administered the Expanded Disability Status Scale, the World Health Organization-5 Well-Being Index, the Patient Health Questionnaire-15, and a Self-Rating Scale of Religiosity. Religiosity did not predict disability, psychological well-being, or somatic health. Religiosity was positively associated with MS duration and disability, but only in male patients. The predictors for predicting psychological wellbeing were age, disability, and somatic health. Patients with... 

Several methods have been developed in the past for analyzing the porosity and other types of well logs for large-scale porous media, such as oil reservoirs, as well as their permeability distributions. We developed a method for analyzing the porosity logs φ(h) (where h is the depth) and similar data that are often nonstationary stochastic series. In this method one first generates a new stationary series based on the original data, and then analyzes the resulting series. It is shown that the series based on the successive increments of the log y(h)=φ(h+δh)-φ(h) is a stationary and Markov process, characterized by a Markov length scale hM. The coefficients of the Kramers-Moyal expansion for... 

Yeh et al. have recently proposed a mutual authentication protocol based on EPC Class-1 Gen.-2 standard. They claim their protocol is secure against adversarial attacks and also provides forward secrecy. In this paper we show that the proposed protocol does not have cited security features properly. A powerful and practical attack is presented on this protocol whereby the whole security of the protocol is broken. Furthermore, Yeh et al.'s protocol does not assure the untraceabilitiy and backwarduntraceabilitiy attributes. We also will propose our revision to safeguard the Yeh et al.'s protocol against cited attacks  

In this paper, we show how time-sharing method may reduce transmission delay in the dynamic index coding scenario. We propose a novel time-shared dynamic index coding transmission scheme that achieves the maximum index coding gain for a complete bi-directional side information graph and formulate a constrained optimization problem to tune the transmission scheme for the minimum transmission delay. A closed-form solution is presented for the special case of two-user. We also use analytical and simulation results to provide graphical intuition for the obtained results  

This paper suggests methods for improving efficiency of a high step up high efficiency converter based on three state commutation cells. A loss analysis has been performed to identify the source of power loss. Based on this analysis, methods are presented to reduce losses in the most power dissipating elements. These methods include replacing some power diodes with large conduction losses with MOSFETs having small on-state resistance. Efficiency improvement up to %1.25 percent is verified in simulation and experimental results  

Locally multipath adaptive routing (LMAR) protocol, classified as a new reactive distance vector routing protocol for MANETs is proposed in this paper. LMAR can find an ad-hoc path without selfish nodes and wormholes using a random search algorithm in polynomial-time. Also when the primary path fails, it discovers an alternative safe path if network graph remains connected after eliminating selfish/malicious nodes. The main feature of LMAR to seek safe route free of selfish and malicious nodes in polynomial time is its searching algorithm and flooding stage that its generated traffic is equiloaded compared to single-path routing protocols but its ability to bypass the attacks is much better... 

von Willebrand factor (VWF) is a naturally collapsed protein that participates in primary haemostasis and coagulation events. The clotting process is triggered by the adsorption and conformational changes of the plasma VWFs localized to the collagen fibres found near the site of injury. We develop coarse-grained models to simulate the adsorption dynamics of VWF flowing near the adhesive collagen fibres at different shear rates and investigate the effect of factors such as interaction and cooperativity of VWFs on the success of adsorption events. The adsorption probability of a flowing VWF confined to the receptor field is enhanced when it encounters an adhered VWF in proximity to the... 

A general regression neural network technique was applied to design optimization of a liquid-liquid coaxial swirl injector. Phase Doppler Anemometry measurements were used to train the neural network. A general regression neural network was employed to predict droplet velocity and Sauter mean diameter at any axial or radial position for the operating range of a liquid-liquid coaxial swirl injector. The results predicted by neural network agreed satisfactorily with the experimental data. A general performance map of the liquid-liquid coaxial swirl (LLCS) injector was generated by converting the predicted result to actual fuel/oxidizer ratios. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA  

Development of Smart Grid and deployment of smart meters in large scale has raised a lot of concerns regarding customers’ privacy. Consequently, several schemes have been proposed to overcome the above mentioned issue. These schemes mainly rely on data aggregation as a method of protecting users’ privacy from the grid operators. However, the main problem with most of these schemes is the fact that they require a large amount of processing power at the meter side. This, together with the fact that smart meters don't usually have a powerful processor, can cause the unavailability of smart meter data at the required time for operators of the grid, and at the same time prevents smart meters from... 

Real-time applications play a significant role in the area of VANET, and are mainly required for these kinds of networks. On the other hand, when the number of messages received by vehicles increases in the network, then the applied computation load becomes extremely high and consequently, delay on the message authentication process significantly increases. This paper is presented with the aim of introducing a novel cooperative message authentication (CMA) scheme for VANET, the main purpose of which is alleviating the computation load on vehicles while verifying messages by using two-part identity-based signature. The scheme enables vehicles to verify only a limited number of the total... 

A general regression neural network technique is applied for design optimization of liquid-liquid coaxial swirl injectors. Phase Doppler Anemometry measurements for velocity and SMD distributions for various Reynolds numbers are used to train the neural network to generate the injector's performance map. Excellent agreement between the predicted values and the measurements is obtained. It is observed that by reducing the number of randomly selected training samples to about one third of the number of prediction points, one may reconstruct the velocity field in the extrapolation regime with an accuracy of 93%. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc.... 

A general regression neural network technique is proposed for design optimization of pressure-swirl injectors. Phase doppler anemometry measurements for velocity distributions are used to train the neural network. An overall optimized value for the width of the probability is determined. The velocity field in the extrapolation regime is reconstructed with an accuracy of 93%. Excellent agreement between the predicted values and the measurements is obtained. The results indicate that the capability of performing designand optimization studies for pressure-swirl injectors with sufficient accuracy exists by applying modest amount of data in conjunction with an overall optimized value for the...