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Precision Mass Measurements of Neutron-Rich Neodymium and Samarium Isotopes and Their Role in Understanding Rare-Earth Peak Formation

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Physical Review Letters 2018年第26期120卷 262702-262702页

作者： R. Orford N. Vassh J. A. Clark G. C. McLaughlin M. R. Mumpower G. Savard R. Surman A. Aprahamian F. Buchinger M. T. Burkey D. A. Gorelov T. Y. Hirsh J. W. Klimes G. E. Morgan A. Nystrom K. S. Sharma Department of Physics McGill University Montréal Québec H3A 2T8 Canada Physics Division Argonne National Laboratory Argonne Illinois 60439 USA Department of Physics University of Notre Dame Notre Dame Indiana 46556 USA Department of Physics and Astronomy University of Manitoba Winnipeg Manitoba R3T 2N2 Canada Department of Physics North Carolina State University Raleigh North Carolina 27695 USA Theoretical Division Los Alamos National Laboratory Los Alamos New Mexico 87545 USA Department of Physics University of Chicago Chicago Illinois 60637 USA Soreq NRC Yavne 81800 Israel

The Canadian Penning Trap mass spectrometer at the Californium Rare Isotope Breeder Upgrade (CARIBU) facility was used to measure the masses of eight neutron-rich isotopes of Nd and Sm. These measurements are the first to push into the region of nuclear masses relevant to the formation of the rare-earth abundance peak at A∼165 by the rapid neutron-capture process. We compare our results with theoretical predictions obtained from “reverse engineering” the mass surface that best reproduces the observed solar abundances in this region through a Markov chain Monte Carlo technique. Our measured masses are consistent with the reverse-engineering predictions for a neutron star merger wind scenario.

关键词： r process 150 ≤ A ≤ 189 metropolis algorithm Radioactive beams Spectrometers & spectroscopic techniques

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Time-of-Flight Measurements as a Possible Method to Observe Anyonic Statistics

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Physical Review Letters 2018年第23期120卷 230403-230403页

作者： R. O. Umucalılar E. Macaluso T. Comparin I. Carusotto Deparment of Physics Mimar Sinan Fine Arts University 34380 Sisli Istanbul Turkey INO-CNR BEC Center and Dipartimento di Fisica Università di Trento 38123 Povo Italy

We propose a standard time-of-flight experiment as a method for observing the anyonic statistics of quasiholes in a fractional quantum Hall state of ultracold atoms. The quasihole states can be stably prepared by pinning the quasiholes with localized potentials and a measurement of the mean square radius of the freely expanding cloud, which is related to the average total angular momentum of the initial state, offers direct signatures of the statistical phase. Our proposed method is validated by Monte Carlo calculations for ν=1/2 and 1/3 fractional quantum Hall liquids containing a realistic number of particles. Extensions to quantum Hall liquids of light and to non-Abelian anyons are briefly discussed.

关键词： Anyons Fractional quantum Hall effect Geometric & topological phases Ultracold gases metropolis algorithm

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Bimeron nanoconfined design

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Physical Review B 2018年第18期97卷 184415-184415页

作者： I. A. Iakovlev O. M. Sotnikov V. V. Mazurenko Theoretical Physics and Applied Mathematics Department Ural Federal University Mira Street 19 Ekaterinburg 620002 Russia

We report on the stabilization of the topological bimeron structures in confined geometries. The Monte Carlo simulations for a ferromagnet with a strong Dzyaloshinskii-Moriya interaction revealed the formation of a mixed skyrmion-bimeron phase at finite temperatures. The vacancy grid created in the spin lattice drastically changes the picture of the observed spin configurations and allows one to choose between the formation of a pure bimeron and skyrmion lattice. We found that the rhombic plaquette provides a natural environment for stabilization of the bimeron structures. Such a rhombic geometry can protect the topological state even in the absence of the magnetic field.

关键词： Magnetism Skyrmions Vacancies Disordered systems Magnetic systems Nanoclusters Heisenberg model metropolis algorithm Monte Carlo methods

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Ni2C surface carbide to catalyze low-temperature graphene growth

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Physical Review B 2018年第20期97卷 205431-205431页

作者： Rafael Martinez-Gordillo Céline Varvenne Hakim Amara Christophe Bichara Aix Marseille Université–CNRS CINaM Campus de Luminy 13288 Marseille France Laboratoire d'Etudes des Microstructures ONERA-CNRS Boîte Postale 72 92322 Châtillon Cedex France

The possibility to grow a graphene layer using the chemical-vapor-deposition technique over a Ni2C/Ni(111) substrate has been identified experimentally, with the advantage of having a lower processing temperature (T<500∘C), compared to standard growth over a Ni(111) surface. To understand the role of the metal carbide/metal catalyst, we first perform a static study of the Ni2C/Ni(111) structure and of the binding and removal of a carbon atom at the surface, using both a tight-binding (TB) energetic model and ab initio calculations. Grand-canonical Monte Carlo TB simulations then allow us (i) to determine the thermodynamic conditions to grow graphene and (ii) to separate key reaction steps in the growth mechanism explaining how the Ni2C/Ni(111) substrate catalyzes graphene formation at low temperature.

关键词： Adhesion Chemical bonding Growth Interface & surface thermodynamics Semiconductors Surface reconstruction Carbon-based materials Graphene Nanostructures metropolis algorithm Monte Carlo methods Tight-binding model

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Size effects in finite systems with long-range interactions

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Physical Review E 2018年第3期97卷 032103-032103页

作者： E. S. Loscar C. M. Horowitz Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA) UNLP CCT La Plata-CONICET Sucursal 4 Casilla de Correo 16 (1900) La Plata Argentina

Small systems consisting of particles interacting with long-range potentials exhibit enormous size effects. The Tsallis conjecture [Tsallis, Fractals 3, 541 (1995)], valid for translationally invariant systems with long-range interactions, states a well-known scaling relating different sizes. Here we propose to generalize this conjecture to systems with this symmetry broken, by adjusting one parameter that determines an effective distance to compute the strength of the interaction. We apply this proposal to the one-dimensional Ising model with ferromagnetic interactions that decay as 1/r1+σ in the region where the model has a finite critical temperature. We demonstrate the convenience of using this generalization to study finite-size effects, and we compare this approach with the finite-size scaling theory.

关键词： Classical statistical mechanics Critical phenomena Phase transitions Classical spin models Equilibrium lattice models Finite-size scaling metropolis algorithm

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Emergence of collective propulsion through cell-cell adhesion

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Physical Review E 2018年第4期97卷 042413-042413页

作者： Katsuyoshi Matsushita Department of Biological Sciences Osaka University Toyonaka Osaka Japan

The mechanisms driving the collective movement of cells remain poorly understood. To contribute toward resolving this mystery, a model was formulated to theoretically explore the possible functions of polarized cell-cell adhesion in collective cell migration. The model consists of an amoeba cell with polarized cell-cell adhesion, which is controlled by positive feedback with cell motion. This model cell has no persistent propulsion and therefore exhibits a simple random walk when in isolation. However, at high density, these cells acquire collective propulsion and form ordered movement. This result suggests that cell-cell adhesion has a potential function, which induces collective propulsion with persistence.

关键词： Cell communication Cell migration Cell polarity Cells metropolis algorithm Monte Carlo methods

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Ordering kinetics in the q-state clock model: Scaling properties and growth laws

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Physical Review E 2018年第3期98卷 032109-032109页

作者： S. Chatterjee S. Puri R. Paul Indian Association for the Cultivation of Science Kolkata 700032 India School of Physical Sciences Jawaharlal Nehru University New Delhi 110067 India

We present a comprehensive Monte Carlo study of the ordering kinetics in the d=2 ferromagnetic q-state clock model with nonconserved Glauber dynamics. In agreement with previous studies we find that q≥5 is characteri... 详细信息

关键词： Growth processes Nonequilibrium statistical mechanics Phase transitions metropolis algorithm Monte Carlo methods

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Effects of Ga doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2: Ab initio and Monte Carlo approaches

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Physical Review B 2018年第17期98卷 174403-174403页

作者： Ahmed Albaalbaky Yaroslav Kvashnin Renaud Patte Raymond Frésard Denis Ledue Normandie Université UNIROUEN INSA Rouen CNRS GPM 76800 Saint Étienne du Rouvray France Department of Physics and Astronomy Division of Materials Theory Uppsala University Box 516 SE-75120 Uppsala Sweden Normandie Université UNICAEN ENSICAEN CNRS CRISMAT 14050 Caen France

The effects of nonmagnetic impurity doping on magnetic and ferroelectric properties of multiferroic delafossite CuCrO2 are investigated by means of density functional theory calculations and Monte Carlo simulations. Density functional theory calculations show that replacing up to 30% of Cr3+ ions by Ga3+ ones does not significantly affect the remaining Cr-Cr superexchange interactions. Monte Carlo simulations show that CuCr1−xGaxO2 preserves its magnetoelectric properties up to x≃0.15 with a spiral ordering, while it becomes disordered at higher fractions. Antiferromagnetic transition shifts towards lower temperatures with increasing x and eventually disappears at x≥0.2. Our simulations show that Ga3+ doping increases the Curie-Weiss temperature of CuCr1−xGaxO2, which agrees well with experimental observations. Moreover, our results show that the incommensurate ground-state configuration is destabilized by Ga3+ doping under zero applied field associated with an increase of frustration. Finally, coupling between noncollinear magnetic ordering and electric field is reported for x≤0.15 through simulating P−E hysteresis loops, which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model.

关键词： Exchange interaction Ferroelectricity Magnetic order Magnetism Specific heat Transition temperature Antiferromagnets Multiferroics Density functional theory metropolis algorithm Monte Carlo methods

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Using experimental data to test an n-body dynamical model coupled with an energy-based clusterization algorithm at low incident energies

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Physical Review C 2018年第3期97卷 034624-034624页

作者： Rohit Kumar Rajeev K. Puri Department of Physics Panjab University Chandigarh - 160014 India

Employing the quantum molecular dynamics (QMD) approach for nucleus-nucleus collisions, we test the predictive power of the energy-based clusterization algorithm, i.e., the simulating annealing clusterization algorithm (SACA), to describe the experimental data of charge distribution and various event-by-event correlations among fragments. The calculations are constrained into the Fermi-energy domain and/or mildly excited nuclear matter. Our detailed study spans over different system masses, and system-mass asymmetries of colliding partners show the importance of the energy-based clusterization algorithm for understanding multifragmentation. The present calculations are also compared with the other available calculations, which use one-body models, statistical models, and/or hybrid models.

关键词： Low & intermediate energy heavy-ion reactions Models & methods for nuclear reactions Nuclear fragmentation Nuclear reactions metropolis algorithm

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First-principles-based strain and temperature-dependent ferroic phase diagram of SrMnO3

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Physical Review Materials 2018年第10期2卷 104409-104409页

作者： Alexander Edström Claude Ederer Materials Theory ETH Zürich Wolfgang-Pauli-Strasse 27 8093 Zürich Switzerland

Perovskite structure SrMnO3 is a rare example of a multiferroic material where strain tuning and/or cation substitution could lead to coinciding magnetic and ferroelectric ordering temperatures, which would then promise strong magnetoelectric coupling effects. Here, we establish the temperature- and strain-dependent ferroic phase diagram of SrMnO3 using first-principles-based effective Hamiltonians. All parameters of these Hamiltonians are calculated using density functional theory, i.e., no fitting to experimental data is required. Temperature-dependent properties are then obtained from Monte Carlo and molecular dynamics simulations. We observe a sequence of several magnetic transitions under increasing tensile strain, with a moderate variation of the corresponding critical temperatures. In contrast, the ferroelectric Curie temperature increases strongly after its onset around 2.5% strain, and indeed crosses the magnetic transition temperature just above 3% strain. Our results indicate pronounced magnetoelectric coupling, manifested in dramatic changes of the magnetic ordering temperatures and different magnetic ground states as function of the ferroelectric distortion. In addition, coexisting ferroelectric and ferromagnetic order is obtained for strains above 4%. Our calculated phase diagram suggests the possibility to control the magnetic properties of SrMnO3 through an applied electric field, significantly altering the magnetic transition temperatures, or even inducing transitions between different magnetic states.

关键词： Exchange interaction Ferroelectricity Magnetism Magnetoelectric effect Ferroelectrics Magnetic systems Multiferroics Perovskites Density functional calculations metropolis algorithm Molecular dynamics

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