281 research outputs found
Vacancy-assisted domain-growth in asymmetric binary alloys: a Monte Carlo study
A Monte Carlo simulation study of the vacancy-assisted domain-growth in
asymmetric binary alloys is presented. The system is modeled using a
three-state ABV Hamiltonian which includes an asymmetry term, not considered in
previous works. Our simulated system is a stoichiometric two-dimensional binary
alloy with a single vacancy which evolves according to the vacancy-atom
exchange mechanism. We obtain that, compared to the symmetric case, the
ordering process slows down dramatically. Concerning the asymptotic behavior it
is algebraic and characterized by the Allen-Cahn growth exponent x=1/2. The
late stages of the evolution are preceded by a transient regime strongly
affected by both the temperature and the degree of asymmetry of the alloy. The
results are discussed and compared to those obtained for the symmetric case.Comment: 21 pages, 9 figures, accepted for publication in Phys. Rev.
Classical and quantum properties of a 2-sphere singularity
Recently Boehmer and Lobo have shown that a metric due to Florides, which has
been used as an interior Schwarzschild solution, can be extended to reveal a
classical singularity that has the form of a two-sphere. Here the singularity
is shown to be a scalar curvature singularity that is both timelike and
gravitationally weak. It is also shown to be a quantum singularity because the
Klein-Gordon operator associated with quantum mechanical particles approaching
the singularity is not essentially self-adjoint.Comment: 10 pages, 1 figure, minor corrections, final versio
Classical approach in quantum physics
The application of a classical approach to various quantum problems - the
secular perturbation approach to quantization of a hydrogen atom in external
fields and a helium atom, the adiabatic switching method for calculation of a
semiclassical spectrum of hydrogen atom in crossed electric and magnetic
fields, a spontaneous decay of excited states of a hydrogen atom, Gutzwiller's
approach to Stark problem, long-lived excited states of a helium atom recently
discovered with the help of Poincar section, inelastic
transitions in slow and fast electron-atom and ion-atom collisions - is
reviewed. Further, a classical representation in quantum theory is discussed.
In this representation the quantum states are treating as an ensemble of
classical states. This approach opens the way to an accurate description of the
initial and final states in classical trajectory Monte Carlo (CTMC) method and
a purely classical explanation of tunneling phenomenon. The general aspects of
the structure of the semiclassical series such as renormgroup symmetry,
criterion of accuracy and so on are reviewed as well. In conclusion, the
relation between quantum theory, classical physics and measurement is
discussed.Comment: This review paper was rejected from J.Phys.A with referee's comment
"The author has made many worthwhile contributions to semiclassical physics,
but this article does not meet the standard for a topical review"
Mantle deformation beneath the Chicxulub impact crater
Accepted versio
Agricultura familiar, multifuncionalidade da agricultura e ruralidade: interfaces de uma realidade complexa.
Nas últimas décadas, assistimos à revitalização do debate em torno da agricultura familiar pela incorporação das discussões sobre as múltiplas funções da agricultura num rural que não pode mais ser visto como domínio exclusivo da atividade agrícola e dos agricultores. No contexto brasileiro, acreditamos que essa discussão deva ser permeada pela análise de como processos diferenciados de distribuição fundiária e desenvolvimento econômico e o tipo de agricultura resultante geram ruralidades específicas com características como, no caso da agricultura familiar, a manutenção de práticas sociais e de trabalho marcadas pelas relações de parentesco e vizinhança presentes numa sociedade de interconhecimento. Partindo desse princípio, este trabalho analisa a agricultura familiar de um bairro rural do município de Ouro Fino - MG, sua herança histórica e sua participação na criação de uma paisagem natural e humana que muito contribui para a atratividade da região
CABARET in the ocean gyres
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Ocean Modelling 30 (2009): 155-168, doi:10.1016/j.ocemod.2009.06.009.A new high-resolution Eulerian numerical method is proposed for modelling quasigeostrophic ocean
dynamics in eddying regimes. The method is based on a novel, second-order non-dissipative and lowdispersive
conservative advection scheme called CABARET. The properties of the new method are
compared with those of several high-resolution Eulerian methods for linear advection and gas
dynamics. Then, the CABARET method is applied to the classical model of the double-gyre ocean
circulation and its performance is contrasted against that of the common vorticity-preserving Arakawa
method. In turbulent regimes, the new method permits credible numerical simulations on much coarser
computational grids.Supports from the Royal Society of London and from the Mary Sears Visitor Grant are
acknowledged by SK with gratitude. The work of VG was supported by the Russian Foundation for
Basic Research (RFBR), grant 06-01-00819a. Funding for PB was provided by the NSF grant 0725796
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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