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Phase diagram of the one-dimensional anisotropic Kondo-necklace model
, Article Physical Review B - Condensed Matter and Materials Physics ; Volume 77, Issue 2 , 2008 ; 10980121 (ISSN) ; Langari, A ; Sharif University of Technology
2008
Abstract
The one-dimensional anisotropic Kondo-necklace model has been studied by several methods. It is shown that a mean field approach fails to gain the correct phase diagram for the Ising-type anisotropy. We then applied the spin wave theory which is justified for the anisotropic case. We have derived the phase diagram between the antiferromagnetic long range order and the Kondo singlet phases. We have found that the exchange interaction (J) between the itinerant spins and local ones enhances the quantum fluctuations around the classical long range antiferromagnetic order and finally destroy the ordered phase at the critical value Jc. Moreover, our results show that the onset of anisotropy in the...
Investigation of phase diagrams for cylindrical Ising nanotube using cellular automata
, Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 382, Issue 19 , May , 2018 , Pages 1291-1297 ; 03759601 (ISSN) ; Ghaemi, M ; Afzali, K ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Recent developments in the field of applied nanoscience and nanotechnology have heightened the need for categorizing various characteristics of nanostructures. In this regard, this paper establishes a novel method to investigate magnetic properties (phase diagram and spontaneous magnetization) of a cylindrical Ising nanotube. Using a two-layer Ising model and the core-shell concept, the interactions within nanotube has been modelled. In the model, both ferromagnetic and antiferromagnetic cases have been considered. Furthermore, the effect of nanotube's length on the critical temperature is investigated. The model has been simulated using cellular automata approach and phase diagrams were...
Vortex Dynamics in Magnetic Phase Diagram of High Tc Cuprate Oxides
, M.Sc. Thesis Sharif University of Technology ; Khosroabadi, Hossein (Supervisor) ; Akhavan, Mohammad (Supervisor)
Abstract
In the 1950s, Abrikosov predicted the mixed state in superconductors (type II superconductors) which lead to a Noble Prize in 2003 with the experimental verification by shubnikov. Mixed-state is a network of magnetic flux lines with quantized flux (vortices) in superconductors. High-temperature superconductors are of Type II which the existense of vortices in a significant part of the temperature-field phase diagram of them, is an obvious phenomenon. These superconductors provided a proper context for understanding physical phenomena related to vortices and access to experimental data to compare with those provided by statistical mechanics. Vortices can move inside the superconductor by the...
Two-flavor color superconductivity at finite temperature, chemical potential and in the presence of strong magnetic fields
, Article Proceedings of Science ; 2012 , p-3 ; 18248039 (ISSN) ; Sadooghi, N ; Sharif University of Technology
2012
Abstract
Utilizing an extended two-flavor Nambu-Jona Lasinio (NJL) model, we review some of the effects of external magnetic fields on two-flavor color superconducting phase (2SC) at moderate baryon densities in the QCD phase diagram. The effective action of the extended NJL model consists of two mass gaps as functions of three intensive quantities, the temperature, the quark chemical potential and the external magnetic field. The nonzero values of the mass gaps, chiral and diquark condensates, induce spontaneous chiral and color symmetry breaking, respectively, and as a result two different phases of quark matter appear. We find the transition curves between these phases as well as the critical...
Kinetics of chemical ordering in a Ag-Pt nanoalloy particle via first-principles simulations
, Article Journal of Chemical Physics ; Volume 137, Issue 19 , 2012 ; 00219606 (ISSN) ; Taherkhani, F ; Parsafar, G ; Caro, A ; Fortunelli, A ; Sharif University of Technology
2012
Abstract
The energetics and kinetic energy barriers of vacancy/atom exchange in a 37-atom truncated octahedron Ag-Pt binary cluster in the Ag-rich range of compositions are investigated via a first-principles atomistic approach. The energy of the local minima obtained considering various distributions of a single vacancy and a few Pt atoms within the cluster and the energy barriers connecting them are evaluated using accurate density-functional calculations. The effects of the simultaneous presence of a vacancy and Pt atoms are found to be simply additive when their distances are larger than first-neighbors, whereas when they can be stabilizing at low Pt content due to the release of strain by the...
Phase diagram of the XXZ ferrimagnetic spin-(1/2, 1) chain in the presence of transverse magnetic field
, Article Journal of Statistical Mechanics: Theory and Experiment ; Volume 2011, Issue 8 , August , 2011 ; 17425468 (ISSN) ; Abouie, J ; Asadzadeh, M. Z ; Rezai, M ; Sharif University of Technology
2011
Abstract
We investigate the phase diagram of an anisotropic ferrimagnetic spin-(1/2, 1) in the presence of a non-commuting (transverse) magnetic field. We find a magnetization plateau for the isotropic case while there is no plateau for the anisotropic ferrimagnet. The magnetization plateau can appear only when the Hamiltonian has the U(1) symmetry in the presence of the magnetic field. The anisotropic model is driven by the magnetic field from the Néel phase for low fields to the spin-flop phase for intermediate fields and then to the paramagnetic phase for high fields. We find the quantum critical points and their dependence on the anisotropy of the aforementioned field-induced quantum phase...
A case study in vapor phase synthesis of Mg-Al alloy nanoparticles by plasma arc evaporation technique
, Article Chemical Engineering Journal ; Volume 259 , 2015 , Pages 918-926 ; 13858947 (ISSN) ; Derakhshan, R ; Mirzaee, O ; Sharif University of Technology
Elsevier
2015
Abstract
Alloy nanoparticles in the Mg-Al system were prepared by plasma arc discharge method from the Mgx to Al (45%
Mode identification of high-amplitude pressure waves in liquid rocket engines
, Article Journal of Sound and Vibration ; Volume 229, Issue 4 , 2000 , Pages 973-991 ; 0022460X (ISSN) ; Mazaheri, K ; Ghafourian, A ; Sharif University of Technology
2000
Abstract
Identification of existing instability modes from experimental pressure measurements of rocket engines is difficult, specially when steep waves are present. Actual pressure waves are often non-linear and include steep shocks followed by gradual expansions. It is generally believed that interaction of these non-linear waves is difficult to analyze. A method of mode identification is introduced. After presumption of constituent modes, they are superposed by using a standard finite difference scheme for solution of the classical wave equation. Waves are numerically produced at each end of the combustion tube with different wavelengths, amplitudes, and phases with respect to each other. Pressure...
Quantum phase diagram of the two-dimensional transverse-field Ising model: Unconstrained tree tensor network and mapping analysis
, Article Physical Review B ; Volume 99, Issue 14 , 2019 ; 24699950 (ISSN) ; Haghshenas, R ; Langari, A ; Sharif University of Technology
American Physical Society
2019
Abstract
We investigate the ground-state phase diagram of the frustrated transverse-field Ising (TFI) model on the checkerboard lattice (CL), which consists of Néel, collinear, quantum paramagnet, and plaquette-valence bond solid (-VBS) phases. We implement a numerical simulation that is based on the recently developed unconstrained tree tensor network ansatz, which systematically improves the accuracy over the conventional methods as it exploits the internal gauge selections. At the highly frustrated region (J2=J1), we observe a second-order phase transition from the plaquette-VBS state to the paramagnet phase at the critical magnetic-field Γc=0.28 with the associated critical exponents ν=1 and...
Investigation of Buckling Phenomenon in Fiber Production Using Direct Electrospinning
, M.Sc. Thesis Sharif University of Technology ; Iraji Zad, Azam (Supervisor)
Abstract
Duringfalling a viscous liquid freely on a surface, the viscous thread bends due to a phenomenon called buckling. The gravity force in this process could be replaced by an electric force in electrospinning process. In the present thesis, we have designed a number of setups in order to investigate the buckling phenomenon in two categories of helical and non-helical buckling by using direct electrospinning process. By making the collector moving, the electrospun fibers show several shapes including coiling, meander, figure of 8 shape, etc. There are three effective forces acting in this process which are viscous force, electric force and inertia. Also there are three distinct regimes defined...
On Thermodynamics and Phase Space of Near Horizon Extremal Geometries
, Ph.D. Dissertation Sharif University of Technology ; Sheikh-Jabbari, Mohammad Mehdi (Supervisor) ; Golshani, Mehdi (Co-Advisor)
Abstract
Near Horizon Extremal Geometries (NHEG), are geometries which may appear in the near horizon region of the extremal black holes. These geometries have SL(2;R)U(1)n isometry, and constitute a family of solutions to the theory under consideration. In the first part of this report,their thermodynamic properties are reviewed, and their three universal laws are derived. In addition, at the end of the first part, the role of these laws in black hole thermodynamics is presented. In the second part of this thesis, we review building their classical phase space in the Einstein-Hilbert theory. The elements in the NHEG phase space manifold are built by appropriately chosen coordinate transformations of...
prediction of Polymeric Membrane Morphology Based on Phase Diagrams for MBR Applications
, M.Sc. Thesis Sharif University of Technology ; Sayf Kordi, Ali Akbar (Supervisor) ; Hemmati, Mahmoud (Supervisor) ; Rekabdar, Fatemeh (Co-Advisor)
Abstract
In this research, we have tried to predict the morphology of the membranes that were prepared by phase inversion method. In this research Polyvinylinedifluoride (PVDF) and dimethylacetamide (DMAc) was used as the polymer and solvent. The affect of titanium oxide (TiO2 ) and polyvinylpyrolidene (PVP) which are respectively an inorganic and an organic additive, on the morphology of the membranes was investigated. Ternary and Quadratic phase diagrams were drawn based on the Flory Huggins theory. The interaction between components was determined and the effect of interactions and molar volumes of polymer, solvent, non-solvent and additives on the binodal line was investigated. To predict...
Ambient temperature effect on single-bubble sonoluminescence in different concentrations of sulfuric acid solutions
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 85, Issue 1 , January , 2012 ; 15393755 (ISSN) ; Bemani, F ; Silatani, M ; Sadighi Bonabi, R ; Sharif University of Technology
2012
Abstract
The effect of ambient temperature on the parameters of the single-bubble sonoluminescence in sulfuric acid (SA) diluted in water is studied. Using a hydrochemical model, three dominant instabilities of shape, Bjerknes, and diffusion are considered. The phase diagrams of the bubble in the (R 0 - P a) space are presented, and the parametric dependence of the light intensity is discussed. In contrast to water, the calculated thermal-bremsstrahlung mechanism of light emission at the fixed degassing condition of high SA concentrations shows that, with increasing the temperature of aqueous SA solutions, the light intensity increases. However, at diluted SA solutions similar to water, the light...
New phase transitions in optimal states for memory channels
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 79, Issue 3 , 2009 ; 10502947 (ISSN) ; Meghdadi, Z ; Memarzadeh, L ; Sharif University of Technology
2009
Abstract
We investigate the question of optimal input ensembles for memory channels and construct a rather large class of Pauli channels with correlated noise, which can be studied analytically with regard to the entanglement of their optimal input ensembles. In a more detailed study of a subclass of these channels, the complete phase diagram of the two-qubit channel, which shows three distinct phases, is obtained. While increasing the correlation generally changes the optimal state from separable to maximally entangled states, this is done via an intermediate region where both separable and maximally entangled states are optimal. A more concrete model, based on random rotations of the error...
Phase diagram and thermal Hall conductivity of the spin-liquid Kekulé-Kitaev model
, Article Physical Review B ; Volume 101, Issue 11 , March , 2020 , Pages: 11-15 ; Kargarian, M ; Langari, A ; Sharif University of Technology
American Physical Society
2020
Abstract
In this work we study the phase diagram of the Kekulé-Kitaev model. The model is defined on a honeycomb lattice with bond-dependent anisotropic exchange interactions, making it exactly solvable in terms of Majorana representation of spins, in close analogy to the Kitaev model. However, the energy spectrum of Majorana fermions has a multiband structure characterized by Chern numbers 0, ±1, and ±2. We obtained the phase diagram of the model in the plane of exchange couplings and in the presence of a magnetic field and found chiral topological and trivial spin-liquid ground states. In the absence of magnetic field most of the phase diagram is a trivial gapped phase continuously connected to an...
Theoretical investigation of the enhanced solubility of perfluorobenzene in the supercritical carbon dioxide as a function of temperature and density by Monte Carlo simulation
, Article Chemical Physics Letters ; Volume 444, Issue 1-3 , 2007 , Pages 48-55 ; 00092614 (ISSN) ; Khanlarkhani, A ; Sharif University of Technology
2007
Abstract
The absolute free energy of solvation of benzene and perfluorobenzene was measured in supercritical carbon dioxide using the expanded-ensemble method in the context of Monte Carlo (MC) Simulations. The MC calculations were carried out at 12 state points on the solvent phase diagram: (ρr = 0.5, 1.0, 1.5, 2.0; Tr = 1.01, 1.10, and 1.20). These conditions were chosen to address the accurance of specific molecular interactions between CO2 and fluorine. The greater stability of perfluorobenzene observed over all states investigated in this study attributed to the greater solvent accessible surface area and 25-30% increase in the strength of the interaction of this molecule with CO2 in the...
Spin ladder with anisotropic ferromagnetic legs in a transverse magnetic field
, Article Journal of Physics Condensed Matter ; Volume 19, Issue 7 , 2007 ; 09538984 (ISSN) ; Langari, A ; Mahdavifar, S ; Sharif University of Technology
2007
Abstract
We have studied the ground-state phase diagram of a two-leg spin ladder with anisotropic ferromagnetic leg couplings under the influence of a symmetry-breaking transverse magnetic field by the exact diagonalization technique. In the case of antiferromagnetic coupling between legs we identified two phase transitions in the plane of magnetic field versus interchain coupling strength. The first corresponds to the transition from the gapped rung-singlet phase to the gapped stripe-ferromagnetic phase. The second represents the transition from the gapped stripe-ferromagnetic phase into the fully polarized ferromagnetic phase. © IOP Publishing Ltd
Development of the Electron and Photon Transport Code for Dose Calculations on GPU and Benchmarking with EGSnrc Simulation for Radiotherapy
, M.Sc. Thesis Sharif University of Technology ; Sohrabpour, Mostafa (Supervisor)
Abstract
Almost half of all cancer patients receive radiation therapy as main or part of the treatment process. Before performing radiation therapy, first it is necessary to determine the patient’s treatment plan and estimate the outcome of it based on the dose distribution. The quality of treatment is dependent on the accuracy of dosimetry calculations that lies in Monte Carlo algorithms. Unfortunately, most of the computation time is long and not suitable for clinical applications. On the other hand, a real treatment planning will be possible if all aspects of radiation therapy should be considered. The radiation source that is obtained from a medical linear accelerator head is one of these...
A Study of the Phase Diagram of the Hubbard Model Using Modern Numerical Methods
, M.Sc. Thesis Sharif University of Technology ; Vaezi, Mir Abolhassan (Supervisor)
Abstract
The Hubbard model is one of the simplest interacting models in theoretical physics, especially condensed matter physics which despite its simplicity, its solutions are highly nontrivial and intractable. After 5 decades since its introduction, its phase diagram is not fully understood and whether or not, it has a high-temperature superconducting phase. In this thesis, we aim to employ the recent advances in machine learning and GPU programming to accelerate the QMC method. By accelerated QMC methods, we can explore the Hubbard model's phase diagram more efficiently. Using massive parallelization of the GPUs can speed up the measuring process by several times. The self-learning quantum...
The Effect of Rotation on the Magnetic Dual Chiral Density Wave Phase
, M.Sc. Thesis Sharif University of Technology ; Sadooghi, Néda (Supervisor)
Abstract
The theoretical and experimental investigation of quantum chromodynamics phase diagrams is one of the most important subjects in elementary particle physics. Some properties of this diagram are the existence of the hadron phase at low temperatures and chemical potentials, color superconductivity at low temperatures and high chemical potentials, and quark-gluon plasma at high temperatures and chemical potentials. In recent years, the main focus was on the study of quark matter at very high chemical potentials. In particular, the formation of magnetic dual chiral density wave was investigated using the Nambu–Jona-Lasinio effective model. In this thesis, we study, in particular, the phase...