Sharif Digital Repository

HF radar systems are widely used for the measurement of ocean surface currents and wave parameters. Theoretical analysis of high frequency radio wave backscattering from the sea has been derived in the past. Also, the relationship between Bragg frequencies and surface currents is determined and has been proved by HF radars. It is known that when surface currents are present, the Bragg frequencies move to new frequencies. Their movement is proportional to the surface current in the direction toward radar. In addition, it is observed that sea surface current changes the second order part of the spectrum of radar reflection from the sea surface. In this paper, a theoretical analysis of... 

In this study, SiC/Ti–Cu nanocomposite was fabricated by mechanical alloying and sintering process. Effects of SiC nano-reinforcement on phase transformation, microstructure and tribological and antibacterial properties Ti–Cu intermetallic alloy were studied. The microstructure of the powders and sintered materials was investigated using X-ray diffraction, and scanning/transmission electron microscopy. The results exhibited the formation of major TiCu and TiCu 4 , and minor Ti 2 Cu and Ti 2 Cu 3 nanocrystalline phases in the sintered Ti–Cu and SiC/Ti–Cu samples. With the addition of the nanoparticles, the amount of TiCu 4 phase increased. Reinforcing Ti–Cu intermetallic alloy by SiC... 

The demands for high-performance biomaterials are driving the development of new metallic alloys with improved mechanical and biological responses. In this study, a nanocrystalline Ti-Cu intermetallic alloy was prepared by a powder metallurgy route, and its application as an orthopedic material was evaluated by the microstructural, mechanical, corrosion, antibacterial, cytotoxicity and osseointegration examinations. Microstructural characterization revealed the formation of TiCu and Ti2Cu3 as major phases with 23 nm grain size in the structure of the alloy. The synthesized alloy exhibited ultra-high hardness of 10 GPa, acceptable toughness of 8.14 MPam1/2, a ∼98 % anti-bacterial rate against... 

Effects of SiC nanoparticles addition on synthesis and antibacterial properties of TiCu nanocrystalline powder prepared through high energy mechanical milling were studied. The results showed that the synthesis of TiCu powder in the presence of the nanoparticles was accelerated and after mechanical alloying for 20 h, a TiCu/SiC nanocrystalline powder with the crystallite size <5 nm, and 3.3% lattice micro-strain obtained. Further milling resulted in fully amorphous TiCu intermetallic alloy with more uniform distribution of SiC nanoparticles. The antibacterial activity of the synthesized powders was investigated by disk diffusion test. The TiCu/SiC nanocomposites showed enhanced antibacterial... 

In this paper, ultra-small CuO nanoparticles (NPs) were synthesized through a mechanochemical method using two different Cu-containing precursors (i.e. CuSO4·5H2O and CuCl2·2H2O), and their structure and antibacterial activity were studied. From the microstructural studies, it was observed that CuO NPs have a spherical morphology and a narrow size distribution with 7 and 14 nm median particle sizes for CuCl2·2H2O and CuSO4.5H2O precursors, respectively. The CuCl2·2H2O derived nanoparticles showed more antibacterial activity than CuSO4.5H2O derived nanoparticles. The minimum inhibitory concentration (MIC) of the synthesized nanoparticles (derived from both precursors) against E. coli and... 

This paper considers the Gaussian multichannel binary detection problem. A multichannel generalized likelihood ratio (GLR) is presented using a model-based approach where the signal and its amplitude are known and additive noise is characterized by autoregressive (AR) vector processes which can be a suitable model for ground clutter in most scenarios involving airborne surveillance phased array radar. The detector can use secondary vectors to improve its performance. Although, in our model, the amplitude of signal must be known, but according to its excellent performance, an approximation of GLR on the amplitude is also presented. The detector performance in various conditions and the result... 

In this research, Linear Amplitude Sweep (LAS) test was conducted on several asphalt binders modified by different percentages of gilsonite and Styrene-Butadiene-Styrene (SBS) polymer. Asphalt mixtures were also made from some of the study binders and tested for fatigue resistance using Four-point Bending Beam (FBB) fatigue test. The results showed that a strong correlation exists between LAS and FBB rankings at all the tested strain levels. Also, SHRP binder fatigue index (G∗sinδ), as a traditional binder fatigue index, was evaluated which did not show a strong correlation with either LAS or FBB tests. It was concluded that LAS test seems to be an effective binder fatigue test in predicting... 

This study focused on the synthesis of TiO2-Zeolite nanocomposite through a sol-gel approach. The decrease in the size of the nanocomposite is considered a primary parameter to improve photocatalytic activity. In this regard, fabricated samples were exposed to laser irradiation (532 nm) for four different time intervals in order to investigate the size variation of the nanocomposite. FTIR, UV-Vis, XRD, DLS, SEM and EDX analyses were applied to characterize and determine the size of the products. An optimized nanocomposite sample, in term of the particle size, was used for photodegradation of 2,4-D herbicide from aqueous solution. Photodegradation was carried out under UV irradiation (12 W)... 

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  

Dynamic index coding is a practical generalization of conventional index coding that deals with real dynamic traffic streams. We identify the code-constrained capacity region of a dynamic index coding problem with a complete bi-directional side information graph and introduce the performance metric of dynamic index coding gain to measure how dynamic index coding reduces the required data transmissions. A greedy dynamic index coding scheme is proposed that achieves the maximum coding gain almost everywhere in the identified capacity region. Although the greedy scheme attains the maximum coding gain, its selfish nature may unacceptably increase transmission delay. To address this issue, a... 

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....