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Search Results: 1 - 10 of 50601 matches for " Y. Keshavarzi "
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Some geometrical properties of Berger Spheres
Y. Keshavarzi
Mathematics , 2014,
Abstract: Our aim in this paper is to investigate some geometrical properties of Berger Spheres i.e. homogeneous Ricci solitons and harmonicity properties of invariant vector ?fields. We determine all vector ?fields which are critical points for the energy functional restricted to vector ?fields. We also see that do not exist any vector ?fields defining harmonic map, and the energy of critical points is explicitly calculated.
Misleading Communication VS. Effective Aviation Management  [PDF]
Keshavarzi Zahra
Intelligent Information Management (IIM) , 2011, DOI: 10.4236/iim.2011.36029
Abstract: In this paper some of the important problems and issues such as human and communication errors in safety and civil aviation management are presented. The problems arise from misleading information from different sources. To avoid the above problems, a centralization of the information is proposed here. To centralize the information for Air Traffic Management (ATM), a mining data routing system called SCADA (Supervisory Control and Data Acquisition) system is suggested in this study. The utilization of SCADA system will helps to capture air traffic information and aircraft data via satellite technology and transfer it to data mining center and then to central organization. The stored digital data will exchange the information between different organizations and will be used by management systems. The stored reliable information helps to make an appropriate decision in the Air Traffic Management system.
On Conformally flat homogeneous Walker four-manifolds
M. Chaichi,A. Zaeim,Y. Keshavarzi
Mathematics , 2015,
Abstract: In this paper we study the invariant Walker structures over the conformally flat four-dimensional homogeneous manifolds according to the Seger types of the Ricci operator.
On Lorentzian two-symmetric manifolds of dimension four
A. Zaeim,M. Chaichi,Y. Keshavarzi
Mathematics , 2014,
Abstract: We study curvature properties of four-dimensional Lorentzian manifold with two-symmetry property. We then consider Einstein-like metrics, Ricci solitons and homogeneity over these spaces.
Harmonicity and Minimality of vector fields on four-dimensional Lorentzian lie groups
Yadollah Keshavarzi
Mathematics , 2014,
Abstract: We consider four dimensional lie groups equipped with left invariant Lorentzian Einstein metrics, and determine the harmonicity properties of vector fields on these spaces. In some cases, all these vector fields are critical points for the energy functional restricted to vector ?fields. We also classify vector fields defining harmonic maps, and calculate explicitly the energy of these vector fields. Then we study the minimality of critical points for the energy functional.
Uranium Doping and Thermal Neutron Irradiation Flux Pinning Effects in MgB2
T. Silver,J. Horvat,M. Reinhard,Y. Pei,S. Keshavarzi,P. Munroe,S. X. Dou
Physics , 2003,
Abstract: The U/n method is a well-established means of improving flux pinning and critical current performance in cuprate superconductors. The method involves the doping of the superconductor with 235U followed by irradiation with thermal neutrons to promote fission. The resultant columnar damage tracks produced by the energetic fission products pin flux vortices and improve critical current performance in magnetic fields. No such improvement could be observed when the U/n method was applied to MgB2 superconductor. No fission tracks could be observed in TEM, even for samples that were irradiated at the highest fluence. Gamma-ray spectroscopy indicated that fission had occurred in the expected way.
Application of Artificial Neural Network, Kriging, and Inverse Distance Weighting Models for Estimation of Scour Depth around Bridge Pier with Bed Sill  [PDF]
Homayoon Seyed Rahman, Keshavarzi Alireza, Gazni Reza
Journal of Software Engineering and Applications (JSEA) , 2010, DOI: 10.4236/jsea.2010.310112
Abstract: This paper outlines the application of the multi-layer perceptron artificial neural network (ANN), ordinary kriging (OK), and inverse distance weighting (IDW) models in the estimation of local scour depth around bridge piers. As part of this study, bridge piers were installed with bed sills at the bed of an experimental flume. Experimental tests were conducted under different flow conditions and varying distances between bridge pier and bed sill. The ANN, OK and IDW models were applied to the experimental data and it was shown that the artificial neural network model predicts local scour depth more accurately than the kriging and inverse distance weighting models. It was found that the ANN with two hidden layers was the optimum model to predict local scour depth. The results from the sixth test case showed that the ANN with one hidden layer and 17 hidden nodes was the best model to predict local scour depth. Whereas the results from the fifth test case found that the ANN with three hidden layers was the best model to predict local scour depth.
Experimental Study of the Effects of Submerged Dikes on the Energy and Momentum Coefficients in Compound Channel  [PDF]
Alireza Keshavarzi, Mehdi Valizadeh, James Ball
Engineering (ENG) , 2010, DOI: 10.4236/eng.2010.211108
Abstract: This paper aims to understand the flow structure around submerged dike in the main channel and flood plain of a compound cross section. The study undertaken to develop this understanding was carried out in a laboratory flume using a submerged vane installed at a 90 degree angle to the bank. In order to study the flow structures, the flow velocity was measured using a three-dimensional Acoustic Doppler Velocity meter (micro-ADV) with data collection rate of 50 Hz. These flow velocity measurements were taken at 500 points on a regular grid. As the tests were undertaken with turbulent flow, these conditions were subcritical. Furthermore, all the tests were undertaken using a fixed bed. The results obtained showed that the momentum transfer and the kinetic energy reduced in two directions. Also the energy and momentum coefficients decreased significantly with the installation of the submerged vane inside the main channel. Finally, streamlines were found to deviate from the side walls of channel into the main channel.
Systematic Study of Weedy Species of Setaria (L.) P. Beauv. (Poaceae) in Iran
Maryam Keshavarzi,Mahvash Seifali
Pakistan Journal of Biological Sciences , 2007,
Abstract: Weedy species of Setaria (L.) P. Beauv. (Poaceae, Panicoiodeae and Paniceae) compose one of the worst weed groups interfering with world agriculture and in other disturbed and managed habitats. These weed species (S. glauca, S. viridis and S. verticillata) form the foxtail species-group in Iran. In this study 30 populations from different part of Iran were collected. Morphological traits were studied. Some morphological characters as texture of upper lemma, awn color and ligule shape are used to differentiate Setaria species group in Iran. It is believed that these morphological traits have a lot of overlapping. Morphological variations were evaluated by multivariate statistical methods. This study shows the systematic value of different quantitative and qualitative characters in weedy Setaria species native to Iran. An identification key based on studied characters is provided.
Morphological Study of Salicornieae (Chenopodiaceae) Native to Iran
Golshan Zare,Maryam Keshavarzi
Pakistan Journal of Biological Sciences , 2007,
Abstract: The tribe Salicornieae Dum. belonging to the subfamily Salicornioideae Kostel (Chenopodiaceae Vent.) includes halophyte plants. These 5 genera and 6 species are distributed in different habitats of Iran. Members of this tribe have reduced vegetative parts, scale like leaves and articulated stems. In this study quantitative and qualitative morphological characters for 46 accessions of Salicornieae were evaluated. Vegetative characters are not sufficient to distinguish these taxa. Our results indicated that vegetative form, globular buds, plant color, stem base disarticulation and presence of node at the base of inflorescence are diagnostic character in this tribe. Besides floral arrangement in inflorescences, bracts shape, color and shape of seeds are important key features in members of Salicornieae in Iran. Seed coat ornamentations and its hairs and color are found to be helpful in distinguishing these taxa. Quantitative characters show variation too, but as they were not significant, they can not help to resolve the taxonomic problems of this tribe in Iran. Based on studied morphological characters, an identification key for members of this tribe in Iran is provided.
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