Sharif Digital Repository

The Graphics Processing Unit (GPU) is the most promising candidate platform for faster rate of improvement in peak processing speed, low latency and high performance. The highly programmable and multithreaded nature of GPUs makes them a remarkable candidate for general purpose computing. However, supporting non-graphics computing on graphics processors requires addressing several architecture challenges. In this paper, we focus on improving performance by better hiding long waiting time to transfer data from the slow global memory. Thereupon study an effective light-overhead prefetching mechanism, which utilizes idle processing elements. Our results show that we can potentially improve... 

In this study, the microstructural and mechanical features of monolithic pure Cu and Cu matrix nanocomposites reinforced with three different fractions (2, 4, and 6. vol%) of SiC nanoparticles (n-SiC) fabricated via a combination of high energy mechanical milling and hot pressing techniques were investigated. The fabricated composites exhibited homogeneous distribution of the n-SiC with few porosities. It was found that the grain refinement, the planar features within the grains, and the lattice strains increase with increase in the n-SiC content. The yield and compressive strengths of the nanocomposites were significantly improved with increases in the n-SiC content up to 4. vol%; then they... 

The interaction of laser pulses of picosecond duration and terawatt to petawatt power accelerated for the very fast undistorted plasma blocks for deuterium DD or deuterium tritium fast ignition is investigated. Based on the direct and instant conversion of laser energy into mechanical motion by nonlinear (ponderomotive) forces, any thermal pressure generation is delayed by the collision process. Following the studying of the classical collision frequency, it is found that the quantum modified collision at higher energies results in a correction by about 15% reduction of the delay  

In spite of earlier experimental and modeling studies, the relative role of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study employs simple analytical and finite element (FE) models of the spine and its surrounding structures to investigate the contribution of IAP to spinal loading and stability. The analytical model includes the abdominal cavity surrounded by muscles, lumbar spine, rib cage and pelvic ring. The intra-abdominal cavity and its surrounding muscles are represented by a thin deformable cylindrical membrane. Muscle activation levels are simulated by changing the Young's modulus of the membrane in the direction of muscle fibers, yielding... 

It is well known that the quantum Zeno effect can protect specific quantum states from decoherence by using projective measurements. Here we combine the theory of weak measurements with stabilizer quantum error correction and detection codes. We derive rigorous performance bounds which demonstrate that the Zeno effect can be used to protect appropriately encoded arbitrary states to arbitrary accuracy while at the same time allowing for universal quantum computation or quantum control  

In this paper a modal coupling procedure is developed to improve residual modal effects based on experimentally generated data. While showing that CraigChangs proposed approximation function for higher frequency modes does not compare well with the exact function, a new procedure is developed in order to re-express the dynamic residuals. For this purpose, all frequency dependent terms of the Maclaurin series in CraigChangs proposed method are replaced by a general compatible function, which includes the neglected higher order terms. However, this function no longer appears in final equation of motion. Results from case studies for the discrete, continuous and experimental models are... 

Aximum coverage location problem is considered in this study. Extension of this problem is investigated for situations that coverage areas are elliptical; these ellipses can locate anywhere on the plane with any angle. Mixed integer nonlinear programming (MINLP) is applied for formulation. This problem can be used in many practical situations such as locating wireless transmitter towers. A heuristic algorithm named MCLPEA for solving this problem was designed. This algorithm can produce very good results in efficient running time. Finally, the comparison of the results for this study was carried done  

The concept of three-dimensional (3D) resolvability of an integral imaging system is thoroughly investigated in this research. The general concept of 3D resolution fails to describe the 3D discrimination completely. Then the concepts of the depth-resolution plane and lateral-resolution plane are introduced to show the difference between the conventional 3D spatial resolution and the newly introduced 3D resolvability. Therefore, the different properties of these planes for differentiating lateral spatial variations and axial variations are analyzed in this paper. The theoretical statements are demonstrated experimentally  

In the present research, different weld layers were deposited on a 1.2714 steel die by gas tungsten arc (GTA) welding with the weld wire of Udimet 520, and effects of welding parameters on microstructure and mechanical properties of Udimet 520 superalloy were investigated. The results showed Udimet 520 weld with cellular-dendritic and rarely dendritic structure including γ matrix rich of Cr, Mo and W, low percentage associated with order morphology and relative uniform distribution of MC type carbides. Udimet 520 alloy showed high resistance against hot cracking during welding and hot cracking occurred only at high input heat values. Also, cracking during welding occurred at the places that... 

Nowadays, gasochromic Pd/WO3 coatings as optically switchable materials have become more applicable for hydrogen sensors and smart windows. In this study, WO3 films were prepared by Pulsed Laser Deposition (PLD) and spin-coating sol-gel techniques. For deposition of Pd, first a layer of PdCl2 was obtained via a simple drop-drying process by dropping PdCl2 solution onto WO3 substrates and drying them at room temperature. Then Pd nanoparticles were synthesized via hydrogen gas exposure that causes reduction of the PdCl2 layer. According to Scanning Electron Microscope (SEM) observations before hydrogen reduction, many individual nanoparticles or fractal-like constructions of palladium were... 

A multilayer back propagation learning algorithm was used as an artificial neural network tool to predict the mechanical properties of porous NiTi shape memory alloys fabricated by press/sintering of the mixed powders. Effects of green porosity, sintering time and the ratio of the average Ti to Ni particle sizes on properties of the product were investigated. Hardness and tensile strength of the compacts were determined by hardness Rockwell B method and shear punch test. Three-fourths of 36 pairs of experimental data were used for training the network within the toolbox of the MATLAB software. Porosity, sintering time and particle size ratios were defined as the input variables of the model.... 

In this research we have proposed a new definition for three-dimensional (3-D) integral imaging resolution. The general concept of two-dimensional (2-D) resolution used also for 3-D is failed to describe the 3-D resolvability completely. Thus, the researches focused on resolution improvement in 3-D integral imaging systems, didn't investigate thoroughly the effect of their method on the 3-D quality. The effect has only been shown on the 2-D resolution of each lateral reconstructed image. The newly introduced 3-D resolution concept has been demonstrated based on ray patterns, the cross-section between them and the sampling points. Consequently the effect of resulting sampling points in 3-D... 

Washing the corpse and dressing the body prior to burial is an act of love and necessity in many religions. Applying robotics and automation technologies for the washing and preparation of a deceased Muslim in accordance with the Islamic Shari'at laws has been the challenging foundation of this research. With an increasing annual population growth resulting in an increase in the number of deaths (historically and/or immediately after a national disaster), automating part of this procedure to increase the speed of operation, reducing the health risks to the personnel of washing rooms "Ghassalkhaneh™ at the cemeteries and enhancing their quality of life have been the primary objectives of this... 

A sonochemistry-based synthesis method was used to produce nanocrystalline nickel oxide powder with ∼20 nm average crystallite diameter from Ni(OH)2 precursor. Ultrasound waves were applied to the primary solution to intensify the Ni(OH)2 precipitation. Dried precipitates were calcined at 320 °C to form nanocrystalline NiO particles. The morphology of the produced powder was characterized by transmission electron microscopy. Using sonochemical waves resulted in lowering of the size of the nickel oxide crystallites. FT-IR spectroscopy and X-ray diffraction revealed high purity well-crystallized structure of the synthesized powder. Photoluminescence spectroscopy confirmed production of a wide... 

Hydrothermal synthesis of CuO nanoparticles under near-critical and supercritical conditions was investigated from two different standpoints in the current study. The first standpoint was optimization of "yield", "purity", and "size of the nanoparticles" that were optimized at T = 500 °C, time = 2 h, [Cu(NO3)2] = 0.1 mol dm-3, and pH 3. This was achieved by undertaking an orthogonal experiment design methodology and performing different instrumental analyses, such as X-ray diffractometry, inductively coupled plasma spectrometry, and transmission electron microscopy, along with treatment of the data by analysis of variance (ANOVA). The second goal of the study was elucidation of the... 

Adsorption and recovery of uranium by nanoporous MCM-41 from aqueous solutions (synthetic solution and uranium conversion facility liquid waste) were investigated by use of a fixed-bed column (1.2 cm diameter and 3.0 cm height). Adsorption was carried out at flow rates 0.2 and 0.5 mL min-1, which correspond to retention times of 10 and 6 min. The maximum breakthrough capacity for uranium ions was achieved by use of nanoporous MCM-41 at the optimum pH of 3.6 and flow rate 0.2 mL min-1 (61.95 μg g-1). The Thomas and Yan models were applied to the experimental data, by use of linear regression, to determine the characteristics of the column for process design. The breakthrough curves calculated... 

In this article, droplet size and its distribution along a pulsed liquid-liquid extraction column, is studied where SiO2 nanoparticles with concentrations of 0.01, 0.05 and 0.1vol.% and different hydrophobicities are applied to the dispersed phase. Using ultrasonication, nanoparticles were dispersed in kerosene as the base fluid. Nanofluids' stability was ensured using a UV-vis spectrophotometer. Some 22,000 droplets were measured by photographic technique and results were compared with systems containing no-nanoparticles (Water-Acetic acid-Kerosene). Addition of nanoparticles changed the droplet shape from ellipsoidal to spherical. Also, there was a marked influence on droplet breakage and... 

The electromagnetic wave propagation prediction in smooth homogenous earth is studied. This estimation employs Fourier Split-Step algorithm. The process of how parabolic equation and Fourier Split Step algorithm achieved, is investigated. Error resulted from this approximation is studied. Source modeling is analyzed. Simulations based on this method are illustrated on different values of frequency, range and antenna height  

The instability of large diameter single-walled carbon nanotubes (SWCNTs) conveying fluid is investigated based on the molecular mechanics. Using the modal expansion for structural displacements, the governing equations of coupled fluid-structural dynamics of SWCNTs are derived. The natural frequencies and mode shape of the SWCNTs are obtained based on the molecular structural mechanics to account for the effect of chirality and discrete nature of SWCNTs. The results show that the vibrational behavior of large diameter SWCNTs conveying fluid is size dependent, but the effect of chirality is negligible. The obtained results are compared with the equivalent continuum-based model in the... 

In this study, the steady-state operation of the brushless doubly-fed machine (BDFM) in various modes is physically elaborated and the active power flow and torque analysis are presented for each operating mode alongside confirmatory experimental results on a 4/8 pole D160 size machine. The machine behaviour in asynchronous operating modes is described similar to the conventional induction machines with corresponding pole numbers. Moreover, its performance in synchronous mode is shown to be similar to synchronous machines. On the basis of the above, the BDFM performance is further analysed under two possible fault conditions: first, a controller or converter fault leading to loss of...