Sharif Digital Repository

Power quality has become an increasing concern to utilities and customers. The increased concern has resulted in measuring power quality variations and characteristic disturbances for different distribution companies. This paper explains the results of power quality indexes for 50 customer loads at two voltage levels 20kV and 400v. The measurement period is 7 days with 10 minutes intervals. Also this survey has been presented according to IEC61000 and Iranian Power Quality Standard (IPQS). IPQS has some differences from IEC61000, EN50160 and IEEE standards in power quality indexes, which are investigated in this paper. At the end of paper, individual and global power indicators for all... 

In this paper, we propose a new modeling approach for analytical evaluation of normalized throughput and average backoff time for IEEE 802.11 MAC standard in non-saturation mode and with Poisson arrivals. To this end, we map different stages of distributed coordinated function (DCF) onto different components of a closed multi-class BCMP queueing network with arbitrary service time distribution. At the last part of the paper, we illustrate the applicability of the proposed approach by some numerical results in both saturation and non-saturation modes and obtain average backoff time for different arrival rates. © 2007 IEEE  

In this paper we study the structure of some special bases for the null space of the incidence matrix of a graph. Recently it was shown that if G is a graph with no cut vertex, then G has a {-1, 0, 1}-basis. We generalize this result showing that the statement remains valid for every graph with no cut edge. For the null space of any bipartite graph, we construct a {-1, 0, 1}-basis. For any bipartite graph we obtain the support sizes of all elements in the null space of its incidence matrix. Among other things, we prove that for a graph G, there exists a {-1, 1}-vector for the null space of G if and only if the degree of any vertex of G is even and G has an even number of edges. © 2005... 

This paper presents a novel approach to speech recognition using fuzzy modeling. The task begins with conversion of speech spectrogram into a linguistic description based on arbitrary colors and lengths. While phonemes are also described using these fuzzy measures, and recognition is done by normal fuzzy reasoning, a genetic algorithm optimizes phoneme definitions so that to classify samples into correct phonemes. The method is tested over a standard speech data base and the results are presented. © 2005 IEEE  

Nowadays, companies strive to survive in a competitive global environment. Reduction of product development cycle plays a major role in market penetration and cost reduction. To speed up product development/modifications, it is suggested to adopt a collaborative product development approach. Collaborative design and manufacture requires an integrated platform to support related CAx product data models. To integrate CAx product data, a number of solutions are proposed. The most successful solution is adopting the STandard for Exchange of Product Data (STEP). In the course of the STEP standard structure and procedure development, two approaches can be recognised: classical and modular. The... 

In this paper, an algorithm for image coding based on a sparse 3-dimensional Discrete Cosine Transform (3D DCT) is studied. The algorithm is essentially a method for achieving a sufficiently sparse representation using 3D DCT. The experimental results obtained by the algorithm are compared to the 2D DCT (used in JPEG standard) and wavelet db9/7 (used in JPEG2000 standard). It is experimentally shown that the algorithm, that only uses DCT but in 3 dimensions, outperforms the DCT used in JPEG standard and achieves comparable results (but still less than) the wavelet transform. © Springer-Verlag Berlin Heidelberg 2009  

Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS) combined to multivariate curve resolution-alternating least-squares (MCR-ALS) is proposed for the resolution and quantification of very complex mixtures of compounds such as polycyclic aromatic hydrocarbons (PAHs) in heavy fuel oil (HFO). Different GC × GC-TOFMS data slices acquired during the analysis of HFO samples and PAH standards were simultaneously analyzed using the MCR-ALS method to resolve the pure component elution profiles in the two chromatographic dimensions as well as their pure mass spectra. Outstandingly, retention time shifts within and between GC × GC runs were not affecting... 

Axon is an important part of the neuronal cells and axonal microtubules are bundles in axons. In axons, microtubules are coated with microtubule-associated protein tau, a natively unfolded filamentous protein in the central nervous system. These proteins are responsible for cross-linking axonal microtubule bundles. Through complimentary dimerization with other tau proteins, bridges are formed between nearby microtubules creating bundles. Formation of bundles of microtubules causes their transverse reinforcement and has been shown to enhance their ability to bear compressive loads. Though microtubules are conventionally regarded as bearing compressive loads, in certain circumstances during... 

H.264/AVC, the latest video coding standard, achieves better video compression rates since it supports new features such as a large number of intra- and inter-prediction candidate modes. H.264/AVC adopts rate-distortion optimization (RDO) technique to obtain the best intra- and inter-prediction, while maximizing visual quality and minimizing the required bit rate. However, the RDO reduces the encoding speed via the exhaustive evaluation of all candidate modes. In this paper, we decrease the encoding time by reducing the computational complexity of the prediction function and the number of candidate modes. First, we improve Pan's method, by eliminating the DC mode from the candidates. Second,...