Sharif Digital Repository

The present study was an attempt to explore international English-medium publication in humanities and social sciences in Iran. In so doing, 50 PhD students from 8 humanities and social sciences disciplines, who had already published or attempted to publish in English-medium journals, were requested to write reflection guide accounts and to take part in follow-up semi-structured interviews. The reflection guide and interview data were analyzed based on the principles of grounded theory research yielding the four major themes of motivations, hurdles, strategies, and call for support. The results indicated that the Iranian PhD students in the fields of humanities and social sciences are... 

The robots that can move on rough terrains are very important especially in Rescue operation, exploration, etc. In this research, a mechanism is introduced for a ring-like robot with a flexible body. This robot is moved by arms which are placed radially and have Reciprocating motion in this direction. By controlling the contraction and the extension of the arms which contact lhe ground, the robot will be forced to move which is called rolling-creeping motion. The robot is stable in stationary state.; also the maximum angle which it can be stable is determined. Considering the speed of contracted arm is the input parameter, the speed of the extended arm for locomotion of the robot has been... 

The Haptic device is capable of interacting dynamically with the operator by the forces it can exert on human's hand. Controlling the haptic device and constraining it through the desired trajectory is the common task in the most of the training systems. Haptic interface application in virtual Persian handwriting learning system is investigated in this paper. Two different modes of learning is investigated: The full guidance mode, guides the user to follow a prerecorded trajectory by applying proper force to operator's hand; whereas in partial guidance, combination of haptics andvisual feedback guides the operator and prevents deviation from the desired trajectory. © 2009 IEEE  

In this paper, the authors analyze conditions under which they can be certain on the intensity addition of a given device, such as tapped-delay lines, used in digital incoherent all-optical communication systems. A general expression for phase-induced intensity noise that is applicable to all types of semiconductor lasers is derived by defining an optical self-SNR expression that can be used to analyze and measure phase-induced intensity noise. The result shows that in order to have a minimal phase-induced intensity noise in most digital optical incoherent systems, a large optical self-SNR, e.g., 20 dB or more, is needed. This in turn is shown to place a limit on the maximum rate of... 

Microstructural features, thermal stability and crystallization kinetics of various melt spun Al-based alloys containing transition metals (TM = Ni, Cu) and Ce-based rare earth metals (MM: Misch Metal) were investigated via X-ray diffractometry (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). It is shown that the extended topological instability of Egami-Waseda model (λ criterion) is a useful tool to predict the crystallization behavior of the prepared alloys. FCC-Al nanoparticles are formed during the initial crystallization process. Calculation of the apparent activation energy using the Kissinger method indicates that partial replacement of... 

In this paper, the authors analyze conditions under which they can be certain on the intensity addition of a given device, such as tapped-delay lines, used in digital incoherent all-optical communication systems. A general expression for phase-induced intensity noise that is applicable to all types of semiconductor lasers is derived by defining an optical self-SNR expression that can be used to analyze and measure phase-induced intensity noise. The result shows that in order to have a minimal phase-induced intensity noise in most digital optical incoherent systems, a large optical self-SNR, e.g., 20 dB or more, is needed. This in turn is shown to place a limit on the maximum rate of... 

In this study, polypropylene/clay nanocomposites were prepared by melt blending method and their thermal conductivity and the thermal conductivity of polypropylene/multi-wall carbon nanotube (MWCNT) nanocomposites were investigated and modeled. It is found that the thermal conductivity of the PP/Clay and PP/MWCNT nanocomposites is increased with increasing temperature. The thermal conductivity of the nanocomposites is improved due to incorporation of nanoclay and MWCNT compared with pure PP matrix  

In this contribution a new approach to perform spatial integration is presented using a dielectric slab. Our approach is indeed based on the fact that the transmission coefficient of a simple dielectric slab at its mode excitation angle matches the Fourier-Green's function of first-order integration. Inspired by the mentioned dielectric-based integrator, we further demonstrate its graphene-based counterpart. The latter is not only reconfigurable but also highly miniaturized in contrast to the previously reported designs [Opt. Commun. 338, 457 (2015)]. Such integrators have the potential to be used in ultrafast analog computation and signal processing. © 2017 Optical Society of America  

In the present work, fcc-Al nanoparticle development in Al90−xNi10MMx (MM: Ce mischmetal; x=2, 4) amorphous alloys was studied via non-isothermal differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, and nanoindentation test. Results showed that the crystallization of Al88Ni10MM2 alloy occurred by the precipitation of fcc-Al nanoparticles followed by the crystallization of Al11MM3 and Al3Ni phases. Transmission electron microscopy revealed that the aluminum precipitates had an average size of ~12 nm with a round morphology. Increasing the mischmetal content to 4 at% (Al86Ni10MM4 alloy) caused a three-stage crystallization process with a change in the size... 

Automatic cell segmentation has various applications in different parts of science. The development of automated methods for cell segmentation, remains challenging in situations where there are touching cells. In this paper we propose a new method for separating touching cells. As the first step, we use a combination of graph segmentation algorithm and thresholding for segmenting foreground objects and producing a binary image. Next, boundary points of separation zone are selected by using a corner detection algorithm. Finally, the marker controller watershed transform is applied to separate touching cells at selected points. © 2008 IEEE  

Stable control of water level of drum is of great importance for economic operation of power plant steam generator systems. In this paper, a linear model of the boiler unit with time varying parameters is used for simulation. Two transfer functions between drum water level (output variable) and feed-water and steam mass rates (input variables) are considered. Variation of model parameters may be arisen from disturbances affecting water level of drum, model uncertainties and parameter mismatch due to the variant operating conditions. To achieve a perfect tracking of the desired drum water level, two sliding mode controllers are designed separately. Results show that the designed controllers... 

Studying the reliability of cracked structures under different types of failure modes such as a mixture of Mode I and Mode II loadings has been of great importance in many applications. The purpose of this study is to evaluate the effects of different modes of loading, i.e. pure Mode I, pure Mode II and Mixed mode I/II loadings on the reliability of cracked structures via three typical case studies including 1st: through crack in a very wide plate, 2nd: cracked pressurized fuselage and 3rd: cracked fastener holes under actual geometries and loading conditions using the FORM, the fracture toughness and the equivalent SIF for Mixed mode I/II loading which is extracted by the Energy release... 

In this paper, two online path planning methods are presented for SURENA III humanoid robot by using model predictive control scheme. The methods are general control schemes which can generate the online motions for walking of a humanoid robot. For lowering computational costs a three dimensional linear inverted pendulum model is used instead of the full dynamical model of the robot. The generated trajectories are then used for computing the zero-moment point (ZMP) of the robot and the joint torques. The resulted joint torques of the two methods are compared to torques obtained from Genetic Algorithm (GA) path planning method presented for SURENA III humanoid robot in previous studies. The... 

Cavitation phenomenon is defined as the process of rupturing any liquid by a decrease in pressure at nearly constant temperature. The cavities driven by the flow in a region of high pressure will implode and generate high pressure pulses leading eventually to erosion and vibration. But in supercavitation the bubbles produced by cavitation combine to form a large, stable bubble region around the supercavitating object. This phenomenon decreases the drag on the supercavitating body. Experimental testsware performed at 2-D unsteady flow for two wedge shaped bodies made before in laboratory and cavitation inception and its development were captured by a high speed camera. Then this cavitation... 

Effective diffusion coefficient is an important parameter which needs to be determined in different fields of study, such as cathode catalyst layers of PEM fuel. For this purpose, a Loschmidt diffusion cell can be used. When a porous medium is placed in Loschmidt apparatus, the effective gas diffusion coefficient (EGDC) of this section must be correlated by diffusion coefficient in absence of a porous medium. In the previous researches studying the Loschmidt diffusion cell, a simplifying infinite-length assumption was used in the analytical solution. Therefore, the solution is only applicable for a short time range, and this can result in high error. In order to overcome this challenge, the... 

Simulating signal transduction in cellular signaling networks provides predictions of network dynamics by quantifying the changes in concentration and activity-level of the individual proteins. Since numerical values of kinetic parameters might be difficult to obtain, it is imperative to develop non-parametric approaches that combine the connectivity of a network with the response of individual proteins to signals which travel through the network. The activity levels of signaling proteins computed through existing non-parametric modeling tools do not show significant correlations with the observed values in experimental results. In this work we developed a non-parametric computational... 

A signaling pathway is a sequence of proteins and passenger molecules that transmits information from the cell surface to target molecules. Understanding signal transduction process requires detailed description of the involved pathways. Several methods and tools resolved this problem by incorporating genomic and proteomic data. However, the difficulty of obtaining prior knowledge of complex signaling networks limited the applicability of these tools. In this study, based on the simulation of signal flow in signaling network, we introduce a method for determining dominant pathways and signal response to stimulations. The model uses topology-weighted transit compartment approach and comprises... 

One of the main applications of citation is to find articles that are relevant to a particular article. However, not all citations are equally relevant to the target article. This paper presents an approach to identify the most relevant citation(s). To this end, the Normalized Similarity Index (NSI) is proposed to quantify the similarity between the source and target of a citation base on the co-citations and references shared by them. To validate the method, NSI was calculated for five citation networks and was compared with the peer review grades for the relevancy between the source and the target articles. The results showed a significant correlation between the NSI ranks and those of... 

In this paper, we analyze the performance of code acquisition system in atmospheric optical code division multiple access (OCDMA) communications using optical orthogonal codes. Memory introduced by temporal correlation of optical fading process precludes us from using the Markov chain model for a code acquisition analysis. By considering this issue, we discuss how to extend the applicability of the Markov chain model to the atmospheric OCDMA communications. We analyze and compare the performance of correlator and chip level detector (CLD) structures in the acquisition system. In our analysis, we consider the effects of free space optical channel impairments, multiple access interference, and...