1,089 research outputs found
Zero-Range Processes with Multiple Condensates: Statics and Dynamics
The steady-state distributions and dynamical behaviour of Zero Range
Processes with hopping rates which are non-monotonic functions of the site
occupation are studied. We consider two classes of non-monotonic hopping rates.
The first results in a condensed phase containing a large (but subextensive)
number of mesocondensates each containing a subextensive number of particles.
The second results in a condensed phase containing a finite number of extensive
condensates. We study the scaling behaviour of the peak in the distribution
function corresponding to the condensates in both cases. In studying the
dynamics of the condensate we identify two timescales: one for creation, the
other for evaporation of condensates at a given site. The scaling behaviour of
these timescales is studied within the Arrhenius law approach and by numerical
simulations.Comment: 25 pages, 18 figure
Three-dimensional modelling of edge-on disk galaxies
We present detailed three-dimensional modelling of the stellar luminosity
distribution for the disks of 31 relatively nearby (<= 110 Mpc) edge-on spiral
galaxies. In contrast to most of the standard methods available in the
literature we take into account the full three-dimensional information of the
disk. We minimize the difference between the observed 2D-image and an image of
our 3D-disk model integrated along the line of sight. Thereby we specify the
inclination, the fitting function for the z-distribution of the disk, and the
best values for the structural parameters such as scalelength, scaleheight,
central surface brightness, and a disk cut-off radius. From a comparison of two
independently developed methods we conclude, that the discrepancies e.g. for
the scaleheights and scalelengths are of the order of ~10%. These differences
are not due to the individual method itself, but rather to the selected fitting
region, which masks the bulge component, the dust lane, or present foreground
stars. Other serious limitations are small but appreciable intrinsic deviations
of real disks compared to the simple input model. In this paper we describe the
methods and present contour plots as well as radial profiles for all galaxies
without previously published surface photometry. Resulting parameters are given
for the complete sample.Comment: LaTeX, 25 pages, 28 figures higher quality figures available at
http://www.astro.ruhr-uni-bochum.de/astro/publications/pub2000.htm
Life-history consequences of divergent selection on egg size in Drosophila melanogaster
Life histories are generally assumed to evolve via antagonistic pleiotropy (negative genetic correlations) among traits, and trade-offs between life-history traits are typically studied using either phenotypic manipulations or selection experiments. We investigated the trade-off between egg size and fecundity in Drosophila melanogaster by examining both the phenotypic and genetic relationships between these traits after artificial selection for large and small eggs, relative to female body size. Egg size responded strongly to selection in both directions, increasing in the large-egg selected lines and decreasing in the small-egg selected lines. Phenotypic correlations between egg size and fecundity in the large-egg selected lines were negative, but no relationship between these traits occurred in either the control or small-egg selected lines. There was no negative genetic correlation between egg size and fecundity. Total reproductive allocation decreased in the small-egg selected lines but did not increase in the large-egg lines. Our results have three implications. First, our selection procedure may have forced females selected for large eggs into a physiological trade-off not reflected in a negative genetic correlation between these traits. Second, the lack of a negative genetic correlation between egg size and number suggests that the phenotypic trade-off frequently observed between egg size and number in other organisms may not evolve over the short term via a direct genetic trade-off whereby increases in egg size are automatically accompanied by decreased fecundity. Finally, total reproductive allocation may not evolve independently of egg size as commonly assumed
Inferior Occipital Gyrus Is Organized along Common Gradients of Spatial and Face-Part Selectivity
The ventral visual stream of the human brain is subdivided into patches with categorical stimulus preferences, like faces or scenes. However, the functional organization within these areas is less clear. Here, we used functional magnetic resonance imaging and vertex-wise tuning models to independently probe spatial and face-part preferences in the inferior occipital gyrus (IOG) of healthy adult males and females. The majority of responses were well explained by Gaussian population tuning curves for both retinotopic location and the preferred relative position within a face. Parameter maps revealed a common gradient of spatial and face-part selectivity, with the width of tuning curves drastically increasing from posterior to anterior IOG. Tuning peaks clustered more idiosyncratically but were also correlated across maps of visual and face space. Preferences for the upper visual field went along with significantly increased coverage of the upper half of the face, matching recently discovered biases in human perception. Our findings reveal a broad range of neural face-part selectivity in IOG, ranging from narrow to “holistic.” IOG is functionally organized along this gradient, which in turn is correlated with retinotopy
Invading the soundscape: exploring the effects of invasive species’ calls on acoustic signals of native wildlife
The transmission and reception of sound, both between conspecifics and among individuals of different species, play a crucial role in individual fitness, because correct interpretation of meaning encoded in acoustic signals enables important context-appropriate behaviours, such as predator avoidance, foraging, and mate location and identification. Novel noise introduced into a soundscape can disrupt the processes of receiving and recognising sounds. When species persist in the presence of novel noise, it may mask the production and reception of sounds important to fitness, and can reduce population size, species richness, or relative abundances, and thus influence community structure. In the past, most investigations into the effects of novel noise have focused on noises generated by anthropogenic sources. The few studies that have explored the effects of calls from invasive species suggest native species alter behaviours (particularly their vocal behaviour) in the presence of noise generated by invasive species. These effects may differ from responses to anthropogenic noises, because noises made by invasive species are biotic in origin, and may therefore be more spectrally similar to the calls of native species, and occur at similar times. Thus, in some cases, negative fitness consequences for native species, associated with noises generated by invasive species, may constitute interspecific competition. Possible negative consequences of invasive species calls represent an overlooked, and underappreciated, class of competitive interactions. We are far from understanding the full extent of the effects of invasive species on native ones. Further investigation of the contribution of noise interference to native species’ decline in the presence of invasive species will significantly increase our understanding of an important class of interactions between invasive and native species
Non-gapped Fermi surfaces, quasiparticles and the anomalous temperature dependence of the near- electronic states in the CMR oxide LaSrMnO with
After years of research into colossal magnetoresistant (CMR) manganites using
bulk techniques, there has been a recent upsurge in experiments directly
probing the electronic states at or near the surface of the bilayer CMR
materials LaSrMnO using angle-resolved photoemission
or scanning probe microscopy. Here we report new, temperature dependent, angle
resolved photoemission data from single crystals with a doping level of
. The first important result is that there is no sign of a pseudogap in
the charge channel of this material for temperatures below the Curie
temperature . The second important result concerns the temperature
dependence of the electronic states. The temperature dependent changes in the
Fermi surface spectra both at the zone face and zone diagonal regions in
-space indicate that the coherent quasiparticle weight disappears for
temperatures significantly above , and that the -dependence of the
T-induced changes in the spectra invalidate an interpretation of these data in
terms of the superposition of a `universal' metallic spectrum and an insulating
spectrum whose relative weight changes with temperature. In this sense, our
data are not compatible with a phase separation scenario.Comment: 6 pages, 4 figure
Epidemic spreading in evolving networks
A model for epidemic spreading on rewiring networks is introduced and
analyzed for the case of scale free steady state networks. It is found that
contrary to what one would have naively expected, the rewiring process
typically tends to suppress epidemic spreading. In particular it is found that
as in static networks, rewiring networks with degree distribution exponent
exhibit a threshold in the infection rate below which epidemics die
out in the steady state. However the threshold is higher in the rewiring case.
For no such threshold exists, but for small infection rate
the steady state density of infected nodes (prevalence) is smaller for rewiring
networks.Comment: 7 pages, 7 figure
Criticality and Condensation in a Non-Conserving Zero Range Process
The Zero-Range Process, in which particles hop between sites on a lattice
under conserving dynamics, is a prototypical model for studying real-space
condensation. Within this model the system is critical only at the transition
point. Here we consider a non-conserving Zero-Range Process which is shown to
exhibit generic critical phases which exist in a range of creation and
annihilation parameters. The model also exhibits phases characterised by
mesocondensates each of which contains a subextensive number of particles. A
detailed phase diagram, delineating the various phases, is derived.Comment: 15 pages, 4 figure, published versi
Fall-experiments on Merapi basaltic andesite and constraints on the generation of pyroclastic surges
International audienceWe have performed fall-experiments with basaltic andesite rock samples from Merapi volcano, using an apparatus designed to analyze samples heated up to 850°C. Relative pressure changes during impact and fragmentation of the samples were measured by a pressure transducer. From 200°C, dynamic pressure waves were formed on impact and fragmentation. Peak and duration of the pressure signal, and degree of fragmentation were found to strongly increase with increasing temperature of rock samples. The pressure waves are most likely generated by sudden heating of air forcing it to expand. We propose that the observed pressure changes are analogues to pyroclastic surges that may be generated on impact and fragmentation of large blocks during passage of a pyroclastic flow over a steep cliff. We infer that rock temperatures of ca. 400°C are sufficient for this process to occur, a temperature common in pyroclastic flows even in distal reaches
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