Sharif Digital Repository

By going to millimeter wave (mmWave) we can use large scale MIMO due to short mmWave wavelength to overcome path loss by using beamforming to focus power of signal to the receiver. System structure of mmWave band is different with conventional MIMO because of large scale MIMO which is leading to use many RF-chains. For this reason Hybrid structure have been proposed for large Scale MIMO. By going to Hybrid structure a new issue has been created with phase shifter constraint. In this paper we propose a novel solution to make a hybrid precoding and combing to reach high spectral efficiency. Our problem includes a maximizing Frobenius norm of multiplying five complex matrices. As constraints,... 

Users often have very specific visual content in mind that they are searching for. The most natural way to communicate this content to an image search engine is to use key-words that specify various properties or attributes of the content. A naive way of dealing with such multi-attribute queries is the following: train a classifier for each attribute independently, and then combine their scores on images to judge their fit to the query. We argue that this may not be the most effective or efficient approach. Conjunctions of attribute often correspond to very characteristic appearances. It would thus be beneficial to train classifiers that detect these conjunctions as a whole. But not all... 

In this paper, Ti-6Al-4V/TiC composite was fabricated by VIM furnace and graphite crucible. X-ray diffraction analysis and EDS techniques were used to identify the phases in the material. Microstructure characteristics of the Ti-6Al-4V/TiC composite were evaluated by means of optical microscopy. The tensile test was performed at room temperature after hot-rolling of the samples in the beta phase field. The results revealed that at different melting times, three kinds of precipitates are formed in the microstructure including grain boundary, eutectic and transgranular precipitates. The size of transgranular precipitates was significantly larger than that of the other two types of carbides and... 

Fetching Lexico-Syntactic patterns from text rely on pairs of words (positive instances) that represent the target relation, and finding their simultaneous occurrence in text corpus. Due to existence of WordNet thesaurus (which contains the semantic relationship between words), collecting positive instances is easy. In non-english languages, it's hard to collect large number of positive instances in various contexts. We investigated some new ideas for collecting them in Persian language and finally run the best one and collected approximately 6,000 positive instances  

In order to study the effect of boron addition on the microstructure and tensile properties of titanium matrix composites, two Ti-6Al-4V/10. Vol% TiC ingots with and without boron were fabricated by VIM furnace and hot rolling. The microstructures of composites were examined using optical microscopy (OM). The X-ray diffraction (XRD) was used to identify the phases present in the composites. Addition of boron resulted in the formation of needle shaped TiB in the matrix that was followed by the refinement of grain size. Compared with Ti-6Al-4V/TiC composite, the composite containing boron content exhibited a significantly higher ductility and lower strength. It was caused by the effects of... 

Information extraction and refinement systems rely on a set of extraction patterns in pattern based approaches in order to construct taxonomies and finding instances of concepts in a corpus. Pattern based methods have high precision and suffer from low recall. Pattern generalization and modeling techniques can increase matching power and decrease GAP between training and test data  

The out-of-pack cementation method was applied to coat the Nickel-based super alloy IN738LC with Si-modified aluminide. Different mixtures of the pack containing pure Al, Si, alumina powders as an inert filler, and NH4Cl as a halide salt activator were used for co-deposition at 950 and 1,050°C. The results showed although the amount of subhalide vapour pressures of Al and Si were equal at 1,050°C, Al atoms diffused only after Si atoms had been deposited. Before heat treatment, the coating thickness formed by the pack containing 2.3 wt.% Al was 6 μm more than that containing 3.5 wt.% Al. After heat treatment, thickening coatings formed within the pack containing 2.3 wt.% Al was less than that... 

Alumina-zirconia nanostructured coatings were formed on 7075 Al alloy through Plasma Electrolytic Oxidation (PEO) operated in aDC potentiostatic mode. The composite coatings were produced in the range of 425-500 V in an alkaline electrolyte containing 4 g/LK2ZrF6. Tribological properties of coatings were investigated using dry sliding wear test against WC balls with a pin-on-disc tribometer. Wear rates were evaluated using optical profilometer. It was shown that the nanostructured alumina-zirconia composite coatings can be formed at voltages 450 V. The coating thickness and roughness were in the range of 15.2-24.2 μm and 0.68-2.35 μm, respectively. The distribution of Al, Zr and O in the... 

CMMI is a unified model for software and system engineering in organizations. The initial CMM has been designed for software development. According to its successes, different models were developed by different groups such as: SECM, SACMM, IPDCMM, and FAAICMM. CMM Integration was introduced due to some problems such as lack of uniformity, overlapping, and incompatibility of mentioned models. Current paper is a research on CMMI, especially on configuration management process. We believe that accepting all change requests lead to ad-hoc versions and rejecting them lead to customer dissatisfaction. Therefore a Change-Request buffer is needed in configuration management process based on CMMI... 

In this paper, we evaluate the capacity of Multiple-Input Multiple-Output (MIMO) systems using directional antennas in non-isotropic scattering environments. Our analytical analysis approach results in closed-form approximate formulas in low Signal to Noise Ratio (SNR) regime (in contrast to previous research works which have investigated the same problem by employing experimental or simulation frameworks). We propose an upper bound for the introduced approximate error. Our results show that MIMO systems equipped with directional antennas may have much higher capacity in nonisotropic scattering environments compared to MIMO systems equipped with omni-directional antennas. We also evaluate... 

This paper addresses dynamic cell formation problem (DCFP) which has been explored vastly for several years. Although a considerable body of literature in this filed, two remarkable aspects have been significantly ignored so far, as uncertainty and human-related issues. In order to compensate such a shortage, this paper develops a bi-objective stochastic model. The first objective function of the developed model seeks to minimize total cost of machine procurement, machine relocation, inter-cell moves, overtime utilization, worker hiring/laying-off, and worker moves between cells; while the second objective function maximizes labor utilization of the cellular manufacturing system. In the... 

In this paper, trace locality of reference (LoR) is identified as a mechanism to predict the behavior of a variety of systems. If two objects were accessed nearby in the past and the first one is accessed again, trace LoR predicts that the second one will be accessed in near future. To capture trace LoR, trace graph is introduced. Although trace LoR can be observed in a variety of systems, but the focus of this paper is to characterize it for data accesses in memory management systems. In this field, it is compared with recency-based prediction (LRU stack) and it is shown that not only the model is much simpler, but also it outperforms recency-based prediction in all cases. The paper... 

It is now known that at least 10% of samples with pancreatic cancers (PC) contain a causative mutation in the known susceptibility genes, suggesting the importance of identifying cancer-associated genes that carry the causative mutations in high-risk individuals for early detection of PC. In this study, we develop a statistical pipeline using a new concept, called gene-motif, that utilizes both mutated genes and mutational processes to identify 4211 3-nucleotide PC-associated gene-motifs within 203 significantly mutated genes in PC. Using these gene-motifs as distinguishable features for pancreatic cancer subtyping results in identifying five PC subtypes with distinguishable phenotypes and... 

This paper has been prepared, based on reports regarding extraordinary induced ac voltage on buried gas pipelines in residential and industrial areas of the capital city of Tehran, especially in densely populated central areas. Also, some reports are considered on the existence of ac induced voltage in buried gas pipelines under the overhead transmission lines, for example, one case located 80 Km to the west of Tehran, in an agricultural region of the town of Abyek. In this paper, the results of an extensive theoretical, experimental and practical investigation and implementation of methods carried out during the last two years are introduced. Furthermore, this paper includes evaluation of... 

The axial turbine is one of the most challenging components of gas turbines for industrial and aerospace applications. With the ever-increasing requirement for high-aerodynamic performance blades, three-dimensional aerodynamic shape optimization is of great importance. In this research, the rear part of a gas turbine consisting of a one-stage axial turbine is optimized numerically. A useful optimization algorithm is presented to improve the efficiency and/or pressure ratio of the axial turbine with two different objective functions. The three-dimensional blade-shape optimization is employed to study the effects of the turbine stator and rotor lean and sweep angles on the turbine performance....