4,717 research outputs found
Break-up fragments excitation and the freeze-out volume
We investigate, in microcanonical multifragmentation models, the influence of
the amount of energy dissipated in break-up fragments excitation on freeze-out
volume determination. Assuming a limiting temperature decreasing with nuclear
mass, we obtain for the Xe+Sn at 32 MeV/nucleon reaction [J. D. Frankland et
al., Nucl. Phys. A689, 905 (2001); A689, 940 (2001)] a freeze-out volume almost
half the one deduced using a constant limiting temperature.Comment: 11 pages, 6 figure
Kinetic energy spectra for fragments and break-up density in multifragmentation
We investigate the possibility, in nuclear fragmentation, to extract
information on nuclear density at break-up from fragment kinetic energy spectra
using a simultaneous scenario for fragment emission. The conclusions we derive
are different from the recently published results of Viola et al. [Phys. Rev.
Lett. 93, (2004), 132701] assuming a sequential fragment emission and claiming
that the experimentally observed decrease of peak centroids for kinetic energy
spectra of fragments with increasing bombarding energy is due to a monotonic
decrease of the break-up density.Comment: 6 pages, 3 figure
Near IR diffraction-limited integral-field SINFONI spectroscopy of the Circinus galaxy
Using the adaptive optics assisted near infrared integral field spectrometer
SINFONI on the VLT, we have obtained observations of the Circinus galaxy on
parsec scales. The morphologies of the H_2(1-0)S(1) 2.12um and Br_gamma 2.17um
emission lines are only slightly different, but their velocity maps are similar
and show a gradient along the major axis of the galaxy, consistent with
rotation.Since V_rot/sigma is approximately 1 suggests that random motions are
also important, it is likely that the lines arise in a rotating spheroid or
thickened disk around the AGN. Comparing the Br_gamma flux to the stellar
continuum indicates that the star formation in this region began almost 10^8 yr
ago. We also detect the [SiVI] 1.96um,[AlIX] 2.04um and [CaVIII] 2.32um coronal
lines. In all cases we observe a broad blue wing, indicating the presence of
two or more components in the coronal line region. A correlation between the
ionisation potential and the asymmetry of the profiles was found for these high
excitation species.Comment: 6 pages, 5 figures, Submitted to the Proceedings of the IFS Workshop,
Jul 4-8 2005, Durham, Englan
Scaling Behavior of the Landau Gauge Overlap Quark Propagator
The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations are done on three lattices with different lattice spacings and
similar physical volumes to explore the approach of the quark propagator
towards the continuum limit. We have calculated the nonperturbative
momentum-dependent wavefunction renormalization function and the
nonperturbative mass function for a variety of bare quark masses and
extrapolate to the chiral limit.
We find the behavior of and are in good agreement for the
two finer lattices in the chiral limit. The quark condensate is also
calculated.Comment: 3 pages, Lattice2003(Chiral fermions
Advancement in the understanding of multifragmentation and phase transition for hot nuclei
Recent advancement on the knowledge of multifragmentation and phase
transition for hot nuclei is reported. It concerns i) the influence of radial
collective energy on fragment partitions and the derivation of general
properties of partitions in presence of such a collective energy, ii) a better
knowledge of freeze-out properties obtained by means of a simulation based on
all the available experimental information and iii) the quantitative study of
the bimodal behaviour of the heaviest fragment charge distribution for
fragmenting hot heavy quasi-projectiles which allows, for the first time, to
estimate the latent heat of the phase transition.Comment: 9 pages, Proceedings of IWM09, November 4-7, Catania (Italy
Infinite Volume and Continuum Limits of the Landau-Gauge Gluon Propagator
We extend a previous improved action study of the Landau gauge gluon
propagator, by using a variety of lattices with spacings from to
0.41 fm, to more fully explore finite volume and discretization effects. We
also extend a previously used technique for minimizing lattice artifacts, the
appropriate choice of momentum variable or ``kinematic correction'', by
considering it more generally as a ``tree-level correction''. We demonstrate
that by using tree-level correction, determined by the tree-level behavior of
the action being considered, it is possible to obtain scaling behavior over a
very wide range of momenta and lattice spacings. This makes it possible to
explore the infinite volume and continuum limits of the Landau-gauge gluon
propagator.Comment: 24 pages RevTex, 18 figures; Responses to referee comments, minor
change
Quark propagator in a covariant gauge
Using mean--field improved gauge field configurations, we compare the results
obtained for the quark propagator from Wilson fermions and Overlap fermions on
a \3 lattice at a spacing of fm.Comment: 5 pages, 8 figures, talk given by F.D.R. Bonnet at LHP 2001 workshop,
Cairns, Australi
The FLIC Overlap Quark Propagator
FLIC overlap fermions are a variant of the standard (Wilson) overlap action,
with the FLIC (Fat Link Irrelevant Clover) action as the overlap kernel rather
than the Wilson action. The structure of the FLIC overlap fermion propagator in
momentum space is studied, and a comparison against previous studies of the
Wilson overlap propagator in quenched QCD is performed. To explore the scaling
properties of the propagator for the two actions, numerical calculations are
performed in Landau Gauge across three lattices with different lattice spacing
and similar physical volumes. We find that at light quark masses the acti
ons agree in both the infrared and the ultraviolet, but at heavier masses some
disagreement in the ultraviolet appears. This is attributed to the two action s
having different discretisation errors with the FLIC overlap providing superior
performance in this regime. Both actions scale reasonably, but some scaling
violations are observed
Diversidade e distribuição espacial de bromeliáceas epifíticas do Altíssimo Rio Tibagi - Paraná - Brasil.
O presente estudo teve como objetivo caracterizar a diversidade e a distribuição espacial das bromeliáceas epifíticas na região do altíssimo rio Tibagi, considerando os fatores geomorfológicos, pedológicos, climáticos e vegetacionais. A avaliação fitossociológica das bromeliáceas foi realizada mediante instalação de parcelas em número variável nas três áreas de estudo. O levantamento florístico foi complementado por observações nas áreas adjacentes às parcelas, respeitando a compartimentação geomorfológica, pedológica e vegetacional. Foram registradas onze espécies de bromeliáceas no total, tendo sido sete delas observadas na área da cabeceira do rio Tibagi, oito no cânion e nove na floresta da foz do rio Bugio. A riqueza foi relacionada, principalmente, com as condições macro e microclimáticas. A umidade fornecida pelas nuvens e chuvas formadas na cuesta do segundo planalto, assim como, em microescala, a umidade atmosférica gerada pelas cachoeiras existentes no cânion e originada da evaporação da água dos Organossolos, é o fator climático fundamental na definição dos padrões encontrados. Considerando a distribuição horizontal das espécies, a diminuição de bromeliáceas da porção mais próxima ao canal para a mais distante está atrelada ao gradiente microclimático, formado pela redução em umidade relativa associada à diminuição em luminosidade
Modeling seismic wave propagation and amplification in 1D/2D/3D linear and nonlinear unbounded media
To analyze seismic wave propagation in geological structures, it is possible
to consider various numerical approaches: the finite difference method, the
spectral element method, the boundary element method, the finite element
method, the finite volume method, etc. All these methods have various
advantages and drawbacks. The amplification of seismic waves in surface soil
layers is mainly due to the velocity contrast between these layers and,
possibly, to topographic effects around crests and hills. The influence of the
geometry of alluvial basins on the amplification process is also know to be
large. Nevertheless, strong heterogeneities and complex geometries are not easy
to take into account with all numerical methods. 2D/3D models are needed in
many situations and the efficiency/accuracy of the numerical methods in such
cases is in question. Furthermore, the radiation conditions at infinity are not
easy to handle with finite differences or finite/spectral elements whereas it
is explicitely accounted in the Boundary Element Method. Various absorbing
layer methods (e.g. F-PML, M-PML) were recently proposed to attenuate the
spurious wave reflections especially in some difficult cases such as shallow
numerical models or grazing incidences. Finally, strong earthquakes involve
nonlinear effects in surficial soil layers. To model strong ground motion, it
is thus necessary to consider the nonlinear dynamic behaviour of soils and
simultaneously investigate seismic wave propagation in complex 2D/3D geological
structures! Recent advances in numerical formulations and constitutive models
in such complex situations are presented and discussed in this paper. A crucial
issue is the availability of the field/laboratory data to feed and validate
such models.Comment: of International Journal Geomechanics (2010) 1-1
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