Sharif Digital Repository

The focus of this study is the performance of the relaying network with incremental selective decode-and-forward (ISDF) protocol in non-selective slow Nakagami-m fading channels. To enhance bandwidth efficiency, when the direct transmission is not successful the relay is used to retransmit a clean copy of the source signal. The proposed protocol achieves a significant reduction in the power consumption and an improvement in performance compared to the fixed decode-and-forward (DF). The exact symbol error rate (SER) of M-PSK modulation for the ISDF protocol over general fading channels is derived. However, as the exact SER analysis is very complicated, we provide an approximated SER... 

Insider threat is a significant security risk for organizations and hard to detect. Most introduced detection methods need contextual data entries about users, or preprocessed user activity logs to detect insider threats which it is costly and time-consuming. In this paper, we introduce a behavior analysis method that learns its context and detects multiple types of insider threats from raw logs and network traffic in real-time. This method, named XABA, learns user roles and exclusive behaviors, through analyzing raw logs related to each network session of the user. Then it checks for some abnormal patterns, and if so, triggers the appropriate alert. XABA is implemented on the big-stream... 

In this paper the projected gradient method is applied as an effective gradient-based topology optimization algorithm in order to direct energy propagation through the desired region of composites microstructure. Rayleigh Damping model is also used in order to take the effect of internal damping mechanisms into account and thus, to fill in the gap between the designed layouts and those in reality. The success of the proposed algorithm is illustrated through several numerical experiments by revealing a set of various designed optimal layouts besides their corresponding energy distributions  

We have developed a mathematical programming model for minimizing total flow time of the flow shop sequence dependent group scheduling (FSDGS) problem, typically classified as Fm|fmls, Splk, prmu|∑Cj. As the problem is shown to be strongly NP-hard, a tabu search (TS) algorithm as well as a hybrid ant colony optimization (HACO) algorithm have been developed to heuristically solve the problem. A lower bounding (LB) method based on the Branch-and-Price algorithm is also developed to evaluate the quality of the metaheuristic algorithms. In order to compare the performance of metaheuristic algorithms, random test problems, ranging in size from small, medium, to large are created and solved by... 

Site reactivity of some enol-imines derived from N-aryl formamides with pentachloropyridine under basic conditions in dry CH3CN was investigated. The aromatic nucleophilic substitution of pentachloropyridine with enol-imines occurs at the 4-position of pyridine ring by both oxygen and nitrogen site of enol-imines. Nucleophilic attack by the oxygen of enol-imine gave corresponding oximino compounds as a mixture of E- and Z-isomers. In contrast, nucleophilic attack by the nitrogen of enol-imine gave the unexpected N,N-di-substituted aryl compounds. The structures of all the compounds were confirmed by IR, 1H NMR, 13C NMR and 19F NMR spectroscopy as well as elemental analysis and... 

InAlAs/InGaAs/InP high electron mobility transistors have higher mobility comparing to structures without indium. But existence of indium causes smaller Eg and as a result smaller breakdown voltage. However, increasing percentage of indium results in higher mobility and as a result higher current and transconductance. Therefore decreasing percentage of indium causes higher breakdown voltage at the sometime lower transconductance. One of the most important parameters that limit maximum output power of transistor is breakdown voltage. In this paper, InAIAs/InGaAs/InP HEMTs with different structures are simulated and a structure with a good transconductance and breakdown voltage is introduced  

Background/Objectives: In this paper by utilizing frequency tracking electrical loads are shared on voltage source converters and then by applying a proposed-supplementary control system, frequency changes during changing electrical loads inside network is omitted. Methods/Statistical Analysis: Using decentralized control in Microgrids and sharing loads on power generation units respect to their nominal capacity are unavoidable approaches to have stable and operational network. Droop control in load sharing is known as practical and significant solution. In droop control, units output frequency, changes proportional to output active power that is not preferable. Simulation results in PSCAD... 

A simple platform based on a hairpin oligonucleotide switch and multi-walled carbon nanotubes (MWCNTs) for the ultrasensitive detection of specific DNA sequences has been developed. In this approach, the π-stacking interaction of single-strand DNA-MWCNT was employed to construct an electrochemical DNA biosensor. Changes to the surface conductivity, based on the MWCNT replacement, were monitored by using the electrochemical species [Fe(CN)6]3-/4- as a redox probe. Morphological and voltammetric characterizations of the electrode surface were performed using atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and... 

This paper deals with the issue of economic batch quantity (EBQ) in a single machine system in which defective items are produced in each cycle of production. The accumulated defective items produced in a period, consisting of several equal cycles, are all reworked in the last cycle of this period called the rework cycle. At the end of each period the whole process will start all over again. We assume that there is a limitation on the total defective items. We also do not adopt the restriction that the rework process rate be equal to the normal production rate. In addition we assume that there is a set up time for rework process. Further we assume that the number of rework cycles be as small... 

Interactions of two distinct shapes of the pulses namely positive/negative chirped pulse and fast/slow rising-edge pulse with plasma are studied using particle-in-cell simulation. It is found that, for a pulse duration of 34 fs and intensity a0 = 12, proton acceleration could be enhanced by asymmetric pulses with either pulse envelope or pulse frequency modification. The number of accelerated protons, as well as the proton energy cut-off, is increased by asymmetric pulses. In this work, for positive chirped pulse, electrostatic field at the rear side of the target is improved by about 30%, which in turns leads to an increase in the proton energy cut-off more than 40%. Moreover, in contrary... 

The effect of pulse shaping on the intense laser-driven proton beam produced through radiation pressure acceleration as a highly efficient mechanism is investigated. In this regard, the interaction of pulses with modified frequencies, including positive and negative chirped pulses with plasma, is simulated using particle-in-cell code. The simulation results indicate that the proton acceleration could be significantly enhanced for both negative and positive chirped pulses. As a consequence of the acceleration time extension as well as the electron heating suppression, a sharper and narrower proton beam could be achieved for negative chirped pulses. The same trend is observed for all negative... 

Comprehensive numerical analyses are conducted to simulate and capture “Buzz” phenomenon in a supersonic mixed compression air inlet. The buzz is an unsteady self-sustained feature that occurs in supersonic inlets, especially when operating in their subcritical condition. In such a situation, the shock waves oscillate along the inlet and cause mass flow fluctuations inside the inlet that will deteriorate the engine performance significantly. An axisymmetric unsteady numerical simulation was used to solve the Navier–Stokes equations combined with the URANS SST k–ω turbulence model. The simulations for two different free-stream Mach numbers of M∞=2.0 and 2.2 and at two specific subcritical... 

We derive exact expressions for the forces and torques between biaxial molecules interacting via the RE-squared potential, a recent variant of the Gay-Berne potential. Moreover, efficient routines have been provided for rigid body MD simulations, resulting in 1.6 times speedup compared to the two-point finite difference approach. It has also been shown that the time cost of a MD simulation will be almost equal to a similar MC simulation, making use of the provided routines. © 2006 Elsevier Inc. All rights reserved  

Gas sparging and back-flushing treatments were compared as a means to tackle the problem of fouling in yeast microfiltration. Based on the feed and membrane characteristics, it was shown that either of these techniques could be superior to the other in order to overcome the problem. At more concentrated feed streams the main cause of flux decline was cake formation. In this condition gas sparging showed greater efficiency in flux enhancement. On the other hand at lower feed concentration the relative importance of internal fouling due to pore blockage, increased. In this case back-flushing was more effective. © 2007  

For large and complex reacting systems, computational efficiency becomes a critical issue in process simulation, optimization and model-based control. Mechanism simplification is often a necessity to improve computational speed. We present a novel approach to simplification of reaction networks that formulates the model reduction problem as an optimization problem and solves it using genetic algorithm (GA).The aim of simplification kinetics modeling is to derive the simplest reaction system, which retains the essential features of the full system. Numerical results for H2/O2 combustion reaction mechanism illustrate the potential and proficiency of this approach  

With the growing rate of network attacks, intelligent methods for detecting new attacks have attracted increasing interest. The RT-UNNID system, introduced in this paper, is one such system, capable of intelligent real-time intrusion detection using unsupervised neural networks. Unsupervised neural nets can improve their analysis of new data over time without retraining. In previous work, we evaluated Adaptive Resonance Theory (ART) and Self-Organizing Map (SOM) neural networks using offline data. In this paper, we present a real-time solution using unsupervised neural nets to detect known and new attacks in network traffic. We evaluated our approach using 27 types of attack, and observed... 

We have proposed an efficient parametrization method for a recent variant of the Gay Berne potential for dissimilar and biaxial particles [Phys. Rev. E 67, 041710 (2003)] and demonstrated it for a set of small organic molecules. Compared with the previously proposed coarse-grained models, the new potential exhibits a superior performance in close contact and large distant interactions. The repercussions of thermal vibrations and elasticity have been studied through a statistical method. The study justifies that the potential of mean force is representable with the same functional form, extending the application of this coarse-grained description to a broader range of molecules. Moreover, the... 

A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO4 in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO2 system for silylation of alcohols in the presence of amine and phenolic hydroxy groups. © 2005 Elsevier B.V. All rights reserved  

A comprehensive model for pervaporation in thin membrane channels was developed to study the effect of changing temperature and concentration on mass flux. This model consists of momentum, energy and species mass balances along and across the membrane in the flow channel. A computational fluid dynamics (CFD) code was written in C++ programming language to solve the coupled non-linear transport equations in the channel by finite volume method. The Semi-Implicit Pressure Link Equation (SIMPLE) CFD algorithm is used to modify the dependent variables in each of the iterations. The effect of variation of temperature and concentration on transport and thermodynamic properties were considered by... 

The employment of tissue engineering scaffolds in the reconstruction of the damaged bone tissues has shown remarkable promise since they significantly facilitate the healing process. Fabrication of highly porous biocompatible scaffolds with sufficient mechanical strength is still challenging. In this regard, polymers have been widely utilized to construct three-dimensional (3D) porous scaffolds due to their excellent processability and biocompatibility. However, insufficient mechanical strength and inappropriate degradation rate of the monophasic polymer scaffolds in the bone regeneration process, as the main challenges, limit their extensive clinical application. The incorporation of...