416 research outputs found
Vital and functional outcomes of the first-ever hemispheric stroke, epidemiological comparative study between Kunming (China) and Limoges (France)
AbstractBackgroundClinical outcomes and socioeconomic consequences after a stroke may differ between regions.MethodsOne cohort was established prospectively in Kunming (China) to compare with a cohort of 156 stroke patients included in Limoges (France). During 1 year, patients hospitalized within 48hours for a first-ever hemispheric stroke were included. Demographic data and neurocardiovascular risk factors were registered. Hemiplegia was evaluated. Functional outcome was assessed using the Barthel Index (BI) after 3 months.ResultsOne hundred and eighteen patients were included in Kunming. Patients of Kunming were younger (61.4±13.4 vs 72.3±14.6 years in Limoges, P<0.0001), more involved in professional activity (36.4% vs 12.8%, P<0.0001). Survival analysis indicated that mortality did not differ between cohorts, but independently predicted by coma at the 2nd day (HR=9.33, 95% CI [4.39, 19.78]) and age>70 years (HR=6.29, 95% CI [2.36, 16.59]). Despite a better baseline BI for patients of Kunming (50.0±34.9 vs 37.4±34.2, P=0.0031), after adjustment for confusing, patients in Limoges had a 2.11 OR 95% CI [1.03, 4.31]) to reach a BI>80 at 3 months.ConclusionsFunctional recovery for patients of Kunming was not as good as expected. The socioeconomic consequences of stroke in Kunming are significant as they involved younger subjects who were still in work
The approach to thermalization in the classical phi^4 theory in 1+1 dimensions: energy cascades and universal scaling
We study the dynamics of thermalization and the approach to equilibrium in
the classical phi^4 theory in 1+1 spacetime dimensions. At thermal equilibrium
we exploit the equivalence between the classical canonical averages and
transfer matrix quantum traces of the anharmonic oscillator to obtain exact
results for the temperature dependence of several observables, which provide a
set of criteria for thermalization. We find that the Hartree approximation is
remarkably accurate in equilibrium. The non-equilibrium dynamics is studied by
numerically solving the equations of motion in light-cone coordinates for a
broad range of initial conditions and energy densities.The time evolution is
described by several stages with a cascade of energy towards the ultraviolet.
After a transient stage, the spatio-temporal gradient terms become larger than
the nonlinear term and a stage of universal cascade emerges.This cascade starts
at a time scale t_0 independent of the initial conditions (except for very low
energy density). Here the power spectra feature universal scaling behavior and
the front of the cascade k(t) grows as a power law k(t) sim t^alpha with alpha
lesssim 0.25. The wake behind the cascade is described as a state of Local
Thermodynamic Equilibrium (LTE) with all correlations being determined by the
equilibrium functional form with an effective time dependent temperatureTeff(t)
which slowly decreases as sim t^{-alpha}.Two well separated time scales emerge
while Teff(t) varies slowly, the wavectors in the wake with k < k(t) attain LTE
on much shorter time scales.This universal scaling stage ends when the front of
the cascade reaches the cutoff at a time t_1 sim a^{-1/alpha}. Virialization
starts to set much earlier than LTE. We find that strict thermalization is
achieved only for an infinite time scale.Comment: relevance for quantum field theory discussed providing validity
criteria. To appear in Phys. Rev.
Dressing Up the Kink
Many quantum field theoretical models possess non-trivial solutions which are
stable for topological reasons. We construct a self-consistent example for a
self-interacting scalar field--the quantum (or dressed) kink--using a two
particle irreducible effective action in the Hartree approximation. This new
solution includes quantum fluctuations determined self-consistently and
nonperturbatively at the 1-loop resummed level and allowed to backreact on the
classical mean-field profile. This dressed kink is static under the familiar
Hartree equations for the time evolution of quantum fields. Because the quantum
fluctuation spectrum is lower lying in the presence of the defect, the quantum
kink has a lower rest energy than its classical counterpart. However its energy
is higher than well-known strict 1-loop results, where backreaction and
fluctuation self-interactions are omitted. We also show that the quantum kink
exists at finite temperature and that its profile broadens as temperature is
increased until it eventually disappears.Comment: 13 pages, latex, 3 eps figures; revised with yet additional
references, minor rewordin
Out-of-equilibrium evolution of quantum fields in the hybrid model with quantum back reaction
The hybrid model with a scalar "inflaton" field coupled to a "Higgs" field
with a broken symmetry potential is one of the promising models for inflation
and (p)reheating after inflation. We consider the nonequilibrium evolution of
the quantum fields of this model with quantum back reaction in the Hartree
approximation, in particular the transition of the Higgs field from the
metastable "false vacuum" to the broken symmetry phase. We have performed the
renormalization of the equations of motion, of the gap equations and of the
energy density, using dimensional regularization. We study the influence of the
back reaction on the evolution of the classical fields and of the quantum
fluctuations. We observe that back reaction plays an important role over a wide
range of parameters. Some implications of our investigation for the preheating
stage after cosmic inflation are presented.Comment: 35 pages, 16 eps figures, revtex4; v2: typos corrected and references
added, accepted for publication in Physical Review
Nonequilibrium Evolution of Correlation Functions: A Canonical Approach
We study nonequilibrium evolution in a self-interacting quantum field theory
invariant under space translation only by using a canonical approach based on
the recently developed Liouville-von Neumann formalism. The method is first
used to obtain the correlation functions both in and beyond the Hartree
approximation, for the quantum mechanical analog of the model. The
technique involves representing the Hamiltonian in a Fock basis of annihilation
and creation operators. By separating it into a solvable Gaussian part
involving quadratic terms and a perturbation of quartic terms, it is possible
to find the improved vacuum state to any desired order. The correlation
functions for the field theory are then investigated in the Hartree
approximation and those beyond the Hartree approximation are obtained by
finding the improved vacuum state corrected up to . These
correlation functions take into account next-to-leading and
next-to-next-to-leading order effects in the coupling constant. We also use the
Heisenberg formalism to obtain the time evolution equations for the equal-time,
connected correlation functions beyond the leading order. These equations are
derived by including the connected 4-point functions in the hierarchy. The
resulting coupled set of equations form a part of infinite hierarchy of coupled
equations relating the various connected n-point functions. The connection with
other approaches based on the path integral formalism is established and the
physical implications of the set of equations are discussed with particular
emphasis on thermalization.Comment: Revtex, 32 pages; substantial new material dealing with
non-equilibrium evolution beyond Hartree approx. based on the LvN formalism,
has been adde
Quantum dynamics and thermalization for out-of-equilibrium phi^4-theory
The quantum time evolution of \phi^4-field theory for a spatially homogeneous
system in 2+1 space-time dimensions is investigated numerically for
out-of-equilibrium initial conditions on the basis of the Kadanoff-Baym
equations including the tadpole and sunset self-energies. Whereas the tadpole
self-energy yields a dynamical mass, the sunset self-energy is responsible for
dissipation and an equilibration of the system. In particular we address the
dynamics of the spectral (`off-shell') distributions of the excited quantum
modes and the different phases in the approach to equilibrium described by
Kubo-Martin-Schwinger relations for thermal equilibrium states. The
investigation explicitly demonstrates that the only translation invariant
solutions representing the stationary fixed points of the coupled equation of
motions are those of full thermal equilibrium. They agree with those extracted
from the time integration of the Kadanoff-Baym equations in the long time
limit. Furthermore, a detailed comparison of the full quantum dynamics to more
approximate and simple schemes like that of a standard kinetic (on-shell)
Boltzmann equation is performed. Our analysis shows that the consistent
inclusion of the dynamical spectral function has a significant impact on
relaxation phenomena. The different time scales, that are involved in the
dynamical quantum evolution towards a complete thermalized state, are discussed
in detail. We find that far off-shell 1 3 processes are responsible for
chemical equilibration, which is missed in the Boltzmann limit. Finally, we
address briefly the case of (bare) massless fields. For sufficiently large
couplings we observe the onset of Bose condensation, where our scheme
within symmetric \phi^4-theory breaks down.Comment: 77 pages, 26 figure
Formation of topological defects in gauge field theories
When a symmetry gets spontaneously broken in a phase transition, topological
defects are typically formed. The theoretical picture of how this happens in a
breakdown of a global symmetry, the Kibble-Zurek mechanism, is well established
and has been tested in various condensed matter experiments. However, from the
viewpoint of particle physics and cosmology, gauge field theories are more
relevant than global theories. In recent years, there have been significant
advances in the theory of defect formation in gauge field theories, which make
precise predictions possible, and in experimental techniques that can be used
to test these predictions in superconductor experiments. This opens up the
possibility of carrying out relatively simple and controlled experiments, in
which the non-equilibrium phase transition dynamics of gauge field theories can
be studied. This will have a significant impact on our understanding of phase
transitions in the early universe and in heavy ion collider experiments. In
this paper, I review the current status of the theory and the experiments in
which it can be tested.Comment: Review article, 43 pages, 7 figures. Minor changes, some references
added. Final version to appear in IJMP
Full Spectrum Archaeology
Full Spectrum Archaeology (FSA) is an aspiration stemming from the convergence of archaeology’s fundamental principles with international heritage policies and community preferences. FSA encompasses study and stewardship of the full range of heritage resources in accord with the full range of associated values and through the application of treatments selected from the full range of appropriate options. Late modern states, including British Columbia, Canada, nominally embrace de jure heritage policies consonant with international standards yet also resist de facto heritage management practice grounded in professional ethics and local values and preferences. In response, inheritor communities and their allies in archaeology are demonstrating the benefits of FSA and reclaiming control over cultural heritage. Archaeology and heritage management driven by altruistic articulation of communal, educational, scientific and other values further expose shortcomings and vulnerabilities of late modern states as well as public goods in and from FSA
Turbulent Thermalization
We study, analytically and with lattice simulations, the decay of coherent
field oscillations and the subsequent thermalization of the resulting
stochastic classical wave-field. The problem of reheating of the Universe after
inflation constitutes our prime motivation and application of the results. We
identify three different stages of these processes. During the initial stage of
``parametric resonance'', only a small fraction of the initial inflaton energy
is transferred to fluctuations in the physically relevant case of sufficiently
large couplings. A major fraction is transfered in the prompt regime of driven
turbulence. The subsequent long stage of thermalization classifies as free
turbulence. During the turbulent stages, the evolution of particle distribution
functions is self-similar. We show that wave kinetic theory successfully
describes the late stages of our lattice calculation. Our analytical results
are general and give estimates of reheating time and temperature in terms of
coupling constants and initial inflaton amplitude.Comment: 27 pages, 13 figure
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