Sharif Digital Repository

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... 

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  

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...