382 research outputs found
Phase transitions of quasistationary states in the Hamiltonian Mean Field model
The out-of-equilibrium dynamics of the Hamiltonian Mean Field (HMF) model is
studied in presence of an externally imposed magnetic field h. Lynden-Bell's
theory of violent relaxation is revisited and shown to adequately capture the
system dynamics, as revealed by direct Vlasov based numerical simulations in
the limit of vanishing field. This includes the existence of an
out-of-equilibrium phase transition separating magnetized and non magnetized
phases. We also monitor the fluctuations in time of the magnetization, which
allows us to elaborate on the choice of the correct order parameter when
challenging the performance of Lynden-Bell's theory. The presence of the field
h removes the phase transition, as it happens at equilibrium. Moreover, regions
with negative susceptibility are numerically found to occur, in agreement with
the predictions of the theory.Comment: 6 pages, 7 figure
A dynamical classification of the range of pair interactions
We formalize a classification of pair interactions based on the convergence
properties of the {\it forces} acting on particles as a function of system
size. We do so by considering the behavior of the probability distribution
function (PDF) P(F) of the force field F in a particle distribution in the
limit that the size of the system is taken to infinity at constant particle
density, i.e., in the "usual" thermodynamic limit. For a pair interaction
potential V(r) with V(r) \rightarrow \infty) \sim 1/r^a defining a {\it
bounded} pair force, we show that P(F) converges continuously to a well-defined
and rapidly decreasing PDF if and only if the {\it pair force} is absolutely
integrable, i.e., for a > d-1, where d is the spatial dimension. We refer to
this case as {\it dynamically short-range}, because the dominant contribution
to the force on a typical particle in this limit arises from particles in a
finite neighborhood around it. For the {\it dynamically long-range} case, i.e.,
a \leq d-1, on the other hand, the dominant contribution to the force comes
from the mean field due to the bulk, which becomes undefined in this limit. We
discuss also how, for a \leq d-1 (and notably, for the case of gravity, a=d-2)
P(F) may, in some cases, be defined in a weaker sense. This involves a
regularization of the force summation which is generalization of the procedure
employed to define gravitational forces in an infinite static homogeneous
universe. We explain that the relevant classification in this context is,
however, that which divides pair forces with a > d-2 (or a < d-2), for which
the PDF of the {\it difference in forces} is defined (or not defined) in the
infinite system limit, without any regularization. In the former case dynamics
can, as for the (marginal) case of gravity, be defined consistently in an
infinite uniform system.Comment: 12 pages, 1 figure; significantly shortened and focussed, additional
references, version to appear in J. Stat. Phy
Fine structure splittings of excited P and D states in charmonium
It is shown that the fine structure splittings of the and
excited states in charmonium are as large as those of the state if the
same is used. The predicted mass
GeV appears to be 120 MeV lower that the center of gravity of the
multiplet and lies below the threshold. Our value of
is approximately 80 MeV lower than that from the paper by Godfrey and Isgur
while the differences in the other masses are \la 20 MeV. Relativistic
kinematics plays an important role in our analysis.Comment: 12 page
Protective effect and economic impact of insecticide application methods on barley.
Avalia o efeito protetor de diferentes formas de aplicação de inseticida sobre a transmissão do nanismo amarelo em cultivares de cevada, bem como determina os custos de produção e o lucro líquido destes manejos. Os experimentos foram realizados durante as safras 2011 e 2012, tendo-se utilizado os seguintes manejos nas parcelas principais: T1, tratamento de sementes com inseticida (TS) + inseticida na parte aérea aplicado quinzenalmente; T2, apenas TS; T3, inseticida aplicado à parte aérea, quando foi atingido o nível de controle de afídeos (NC); T4, sem inseticida; e T5, TS + inseticida na parte aérea, quando o NC foi atingido. As subparcelas foram constituídas de diferentes cultivares de cevada: BRS Cauê, BRS Brau e MN 6021. Foram utilizados os inseticidas lambda‑cialotrina (piretroide) e thiametoxam (neonicotinoide). Houve diferenças no índice de doença do nanismo amarelo em ambas as safras para os diferentes manejos, enquanto o dano ao rendimento de grãos foi influenciado pelo ano e pela população de afídeos. Os custos de produção e lucro líquido diferiram entre os tratamentos. Constatou-se que o tratamento de sementes com inseticida é suficiente para reduzir a epidemia do nanismo‑amarelo em anos com baixa pressão populacional de afídeos; porém, em anos com maiores populações, a aplicação de inseticida à parte aérea também se torna necessária
Equilibrium and nonequilibrium properties of systems with long-range interactions
We briefly review some equilibrium and nonequilibrium properties of systems
with long-range interactions. Such systems, which are characterized by a
potential that weakly decays at large distances, have striking properties at
equilibrium, like negative specific heat in the microcanonical ensemble,
temperature jumps at first order phase transitions, broken ergodicity. Here, we
mainly restrict our analysis to mean-field models, where particles globally
interact with the same strength. We show that relaxation to equilibrium
proceeds through quasi-stationary states whose duration increases with system
size. We propose a theoretical explanation, based on Lynden-Bell's entropy, of
this intriguing relaxation process. This allows to address problems related to
nonequilibrium using an extension of standard equilibrium statistical
mechanics. We discuss in some detail the example of the dynamics of the free
electron laser, where the existence and features of quasi-stationary states is
likely to be tested experimentally in the future. We conclude with some
perspectives to study open problems and to find applications of these ideas to
dipolar media.Comment: 8 pages, 14 figures, Procs. of STATPHYS23, to be published on EPJ
Study of a zirconium getter for purification of xenon gas
Oxygen, nitrogen and methane purification efficiencies for a common zirconium
getter are measured in 1050 Torr of xenon gas. Starting with impurity
concentrations near 10^{-6} g/g, the outlet impurity level is found to be less
than 120*10^{-12} g/g for O2 and less than 950*10^{-12} g/g for N2. For methane
we find residual contamination of the purified gas at concentrations varying
over three orders of magnitude, depending on the purifier temperature and the
gas flow rate. A slight reduction in the purifier's methane efficiency is
observed after 13 mg of this impurity has been absorbed, which we attribute to
partial exhaustion of the purifier's capacity for this species. We also find
that the purifier's ability to absorb N2 and methane can be extinguished long
before any decrease in O2 performance is observed, and slower flow rates should
be employed for xenon purification due to the cooling effect that the heavy gas
has on the getter.Comment: 14 pages, 5 figure
Nonperturbative hyperfine contribution to the and meson masses
Due to the nonperturbative contribution to the hyperfine splitting the mass
of the state is strongly correlated with the center of gravity of the multiplet: is less than by about 40 MeV (20 MeV) for the 1P (2P) state. For
the agreement with experiment is reached only if belongs to the
multiplet. The predicted mass of is MeV.
For the isoscalar meson a correlation between the mass of (1170)
and composed from light (strange) quarks also
takes place.Comment: 22 pages RevTe
Quarkonium Suppression
I discuss quarkonium suppression in equilibriated strongly interacting
matter. After a brief review of basic features of quarkonium production I
discuss the application of recent lattice data on the heavy quark potential to
the problem of quarkonium dissociation as well as the problem of direct lattice
determination of quarkonium properties in finite temperature lattice QCD.Comment: Invited plenary talk presented on 4th International Conference on
Physics and Astrophysics of Quark Gluon Plasma (ICPAQGP-2001), November
26-30, 2001, Jaipur; 12 pp, LaTeX, uses pramana.st
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