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Search Results: 1 - 10 of 1530 matches for " Habib Rostami "
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A Solution for Scalable Routing in Depth Divisions-Based DUSNs via Adding a Scalable Parameter to Control Depth Clusters: Creating an Energy Efficient and Low Delay NI-Independent Communication Protocol  [PDF]
Mohammad Reza Khosravi, Reza Salari, Habib Rostami
Journal of Computer and Communications (JCC) , 2016, DOI: 10.4236/jcc.2016.47008
Abstract: Due to effectiveness of network layer on general performance of networks, designing routing protocols is very important for lifetime and traffic efficiency in wireless sensor networks. So in this paper, we are going to represent an efficient and scalable version of depth-based routing (DBR) protocol that is limited by depth divisions-policy. In fact the new version is a network information independent routing protocol for acoustic communications. Proposed method by use of depth clustering is able to reduce consumed energy and end-to-end delay in dense underwater sensor networks (DUSNs) and this issue is proved by simulation.
Valley Zeeman effect and spin-valley polarized conductance in monolayer MoS$_2$ in a perpendicular magnetic field
Habib Rostami,Reza Asgari
Physics , 2014, DOI: 10.1103/PhysRevB.91.075433
Abstract: We study the effect of a perpendicular magnetic field on the electronic structure and charge transport of a monolayer MoS$_2$ nanoribbon at zero temperature. We particularly explore the induced valley Zeeman effect through the coupling between the magnetic field, $B$, and the orbital magnetic moment. We show that the effective two-band Hamiltonian provides a mismatch between the valley Zeeman coupling in the conduction and valence bands due to the effective mass asymmetry and it is proportional to $B^2$ similar to the diamagnetic shift of exciton binding energies. However, the dominant term which evolves with $B$ linearly, originates from the multi-orbital and multi-band structures of the system. Besides, we investigate the transport properties of the system by calculating the spin-valley resolved conductance and show that, in a low-hole doped case, the transport channels at the edge are chiral for one of the spin components. This leads to a localization of the non-chiral spin component in the presence of disorder and thus provides a spin-valley polarized transport induced by disorder.
Charge compressibility and quantum magnetic phase transition in MoS$_2$
Habib Rostami,Reza Asgari
Physics , 2014, DOI: 10.1103/PhysRevB.91.235301
Abstract: We investigate the ground-state properties of monolayer MoS$_2$ incorporating the Coulomb interaction together with a short-range intervalley interaction between charged particles between two valleys within the Hartree-Fock approximation. We consider four variables as independent parameters, namely homogeneous charge (electron or hole) density, averaged dielectric constant, spin degree of freedom and finally the Hubbard repulsion coefficient which originates mostly from $4d$ orbits of Mo atoms. We find the electronic charge compressibility within the mean-field approximation and show that non-monotonic behavior of the compressibility as a function of carrier density which is rather different from those of the two-dimensional electron gas. We also explore a paramagnetic-to-ferromagnetic quantum phase transition for the wide range of the electron density in the parameter space.
Intrinsic optical conductivity of modified-Dirac fermion systems
Habib Rostami,Reza Asgari
Physics , 2014, DOI: 10.1103/PhysRevB.89.115413
Abstract: We analytically calculate the intrinsic longitudinal and transverse optical conductivities of electronic systems which govern by a modified-Dirac fermion model Hamiltonian for materials beyond graphene such as monolayer MoS$_2$ and ultrathin film of the topological insulator. We analyze the effect of a topological term in the Hamiltonian on the optical conductivity and transmittance. We show that the optical response enhances in the non-trivial phase of the ultrathin film of the topological insulator and the optical Hall conductivity changes sign at transition from trivial to non-trivial phases which has significant consequences on a circular polarization and optical absorption of the system.
Electronic structure and layer-resolved transmission of bilayer graphene nanoribbon in the presence of vertical fields
Habib Rostami,Reza Asgari
Physics , 2013, DOI: 10.1103/PhysRevB.88.035404
Abstract: Electronic properties of bilayer graphene are distinct from both the conventional two dimensional electron gas and monolayer graphene due to its particular chiral properties and excitation charge carrier dispersions. We study the effect of strain on the electronic structure, the edge-states and charge transport of bilayer graphene nanoribbon at zero-temperature. We demonstrate a valley polarized quantum Hall effect in biased bilayer graphene when the system is subjected to a perpendicular magnetic field. In this system a topological phase transition from a quantum valley Hall to a valley polarized quantum Hall phase can occur by tuning the interplanar strain. Furthermore, we study the layer-resolved transport properties by calculating the layer polarized quantity by using the recursive Green's function technique and show that the resulting layer polarized value confirms the obtained phases. These predictions can be verified by experiments and our results demonstrate the possibility for exploiting strained bilayer graphene in the presence of external fields for electronics and valleytronics devices.
Andreev reflection in monolayer MoS2
Leyla Majidi,Habib Rostami,Reza Asgari
Physics , 2013, DOI: 10.1103/PhysRevB.89.045413
Abstract: Andreev reflection in a monolayer molybdenum disulfide superconducting-normal (S/N) hybrid junction is investigated. We find, by using a modified-Dirac Hamiltonian and the scattering formalism, that the perfect Andreev reflection happens at normal incidence with $p$-doped S and N regions. The probability of the Andreev reflection and the resulting Andreev conductance, in this system, are demonstrated to be large in comparison with corresponding gapped graphene structure. We further investigate the effect of a topological term ($\beta)$ in the Hamiltonian and show that it results in an enhancement of the Andreev conductance with $p$-doped S and N regions, while in the corresponding structure with $n$-doped S region it is strongly reducible in comparison. This effect can be explained in terms of the dependence of the Andreev reflection probability on the sign of $\beta$ and the chemical potential in the superconducting region.
Effective lattice Hamiltonian for monolayer MoS2 : Tailoring electronic structure with perpendicular electric and magnetic fields
Habib Rostami,Ali G. Moghaddam,Reza Asgari
Physics , 2013, DOI: 10.1103/PhysRevB.88.085440
Abstract: We propose an effective lattice Hamiltonian for monolayer MoS$_2$ in order to describe the low-energy band structure and investigate the effect of perpendicular electric and magnetic fields on its electronic structure. We derive a tight-binding model based on the hybridization of the $d$ orbitals of molybdenum and $p$ orbitals of sulfur atoms and then introduce a modified two-band continuum model of monolayer MoS$_2$ by exploiting the quasi-degenerate partitioning method. Our theory proves that the low-energy excitations of the system are no longer massive Dirac fermions. It reveals a difference between electron and hole masses and provides trigonal warping effects. Furthermore, we predict a valley degeneracy breaking effect in the Landau levels. Besides, we also show that applying a gate voltage perpendicular to the monolayer modifies the electronic structure including the band gap and effective masses.
Valley polarized transport in strained graphene based Corbino disc
Zahra Khatibi,Habib Rostami,Reza Asgari
Physics , 2013, DOI: 10.1103/PhysRevB.88.195426
Abstract: We study analytically and numerically the magnetotransport of strained graphene in a Corbino geometry gating in the presence of an external perpendicular magnetic field. The conductance of the Corbino disc of deformed graphene with a uniaxial and an inhomogeneous strain is calculated by using the Landauer-B\"{u}ttiker method. We show that the oscillation period of the conductance as a function of the magnetic flux depends on uniaxial strain and the conductance sharply drops along the direction of graphene stretching. The conductance amplitude, on the other hand, can be manipulated by induced pseudomagnetic flux. A valley polarized regime, caused by the inhomogeneous strain, is obtained and in addition we find a wide energy interval in which the system is fully valley polarized.
Edge modes in zigzag and armchair ribbons of monolayer MoS$_2$
Habib Rostami,Reza Asgari,Francisco Guinea
Physics , 2015,
Abstract: We explore the electronic structure, orbital character and topological aspect of a monolayer MoS$_2$ nanoribbon using tight-binding (TB) and low-energy (${\bm k}\cdot{\bm p} $) models. We obtain a mid-gap edge mode in the zigzag ribbon of monolayer MoS$_2$, which can be traced back to the topological properties of the bulk band structure. Monolayer MoS$_2$ can be considered as a valley Hall insulator. The boundary conditions at armchair edges mix the valleys, and a gap is induced in the edge modes. The spin-orbit coupling in the valence band reduces the hybridization.
MRF-Based Multispectral Image Fusion Using an Adaptive Approach Based on Edge-Guided Interpolation  [PDF]
Mohammad Reza Khosravi, Mohammad Sharif-Yazd, Mohammad Kazem Moghimi, Ahmad Keshavarz, Habib Rostami, Suleiman Mansouri
Journal of Geographic Information System (JGIS) , 2017, DOI: 10.4236/jgis.2017.92008
Abstract: In interpretation of remote sensing images, it is possible that some images which are supplied by different sensors become incomprehensible. For better visual perception of these images, it is essential to operate series of pre-processing and elementary corrections and then operate a series of main processing steps for more precise analysis on the images. There are several approaches for processing which are depended on the type of remote sensing images. The discussed approach in this article, i.e. image fusion, is the use of natural colors of an optical image for adding color to a grayscale satellite image which gives us the ability for better observation of the HR image of OLI sensor of Landsat-8. This process with emphasis on details of fusion technique has previously been performed; however, we are going to apply the concept of the interpolation process. In fact, we see many important software tools such as ENVI and ERDAS as the most famous remote sensing image processing tools have only classical interpolation techniques (such as bi-linear (BL) and bi-cubic/cubic convolution (CC)). Therefore, ENVI- and ERDAS-based researches in image fusion area and even other fusion researches often don’t use new and better interpolators and are mainly concentrated on the fusion algorithm’s details for achieving a better quality, so we only focus on the interpolation impact on fusion quality in Landsat-8 multispectral images. The important feature of this approach is to use a statistical, adaptive, and edge-guided interpolation method for improving the color quality in the images in practice. Numerical simulations show selecting the suitable interpolation techniques in MRF-based images creates better quality than the classical interpolators.
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