65 research outputs found
Odd-parity perturbations of self-similar Vaidya spacetime
We carry out an analytic study of odd-parity perturbations of the
self-similar Vaidya space-times that admit a naked singularity. It is found
that an initially finite perturbation remains finite at the Cauchy horizon.
This holds not only for the gauge invariant metric and matter perturbation, but
also for all the gauge invariant perturbed Weyl curvature scalars, including
the gravitational radiation scalars. In each case, `finiteness' refers to
Sobolev norms of scalar quantities on naturally occurring spacelike
hypersurfaces, as well as pointwise values of these quantities.Comment: 28 page
General existence proof for rest frame systems in asymptotically flat space-time
We report a new result on the nice section construction used in the
definition of rest frame systems in general relativity. This construction is
needed in the study of non trivial gravitational radiating systems. We prove
existence, regularity and non-self-crossing property of solutions of the nice
section equation for general asymptotically flat space times. This proves a
conjecture enunciated in a previous work.Comment: 14 pages, no figures, LaTeX 2
Uniqueness of the compactly supported weak solutions of the relativistic Vlasov-Darwin system
We use optimal transportation techniques to show uniqueness of the compactly
supported weak solutions of the relativistic Vlasov-Darwin system. Our proof
extends the method used by Loeper in J. Math. Pures Appl. 86, 68-79 (2006) to
obtain uniqueness results for the Vlasov-Poisson system.Comment: AMS-LaTeX, 21 page
Charmonium suppression at RHIC and SPS: a hadronic baseline
A kinetic equation approach is applied to model anomalous J/psi suppression
at RHIC and SPS by absorption in a hadron resonance gas which successfully
describes statistical hadron production in both experiments. The puzzling
rapidity dependence of the PHENIX data is reproduced as a geometric effect due
to a longer absorption path for J/psi production at forward rapidity.Comment: 16 pages, 6 figures, final version accepted for publication in Phys.
Lett.
Predictions of polarized dust emission from interstellar clouds: spatial variations in the efficiency of radiative torque alignment
Polarization carries information about the magnetic fields in interstellar
clouds. The observations of polarized dust emission are used to study the role
of magnetic fields in the evolution of molecular clouds and the initial phases
of star-formation. We study the grain alignment with realistic simulations,
assuming the radiative torques to be the main mechanism that spins the grains
up. The aim is to study the efficiency of the grain alignment as a function of
cloud position and to study the observable consequences of these spatial
variations. Our results are based on the analysis of model clouds derived from
MHD simulations. The continuum radiative transfer problem is solved with Monte
Carlo methods to estimate the 3D distribution of dust emission and the
radiation field strength affecting the grain alignment. We also examine the
effect of grain growth in cores. We are able to reproduce the results of Cho &
Lazarian using their assumptions. However, the anisotropy factor even in the 1D
case is lower than their assumption of , and thus we get less
efficient radiative torques. Compared with our previous paper, the polarization
degree vs. intensity relation is steeper because of less efficient grain
alignment within dense cores. Without grain growth, the magnetic field of the
cores is poorly recovered above a few . If grain size is doubled in
the cores, the polarization of dust emission can trace the magnetic field lines
possibly up to magnitudes. However, many of the prestellar
cores may be too young for grain coagulation to play a major role. The
inclusion of direction dependent radiative torque efficiency weakens the
alignment. Even with doubled grain size, we would not expect to probe the
magnetic field past a few magnitudes in .Comment: 12 pages, 15 figures, submitted to A&A 19.12.2008; 09.01.2009:
Corrected the name of Juvela; 24.04.2009: revised, added content, 13 pages,
16 figures; 18.06.2009: Language edited, print versio
Where Is More Important Than How in Coastal and Marine Ecosystems Restoration
Restoration is considered an effective strategy to accelerate the recovery of biological communities at local scale. However, the effects of restoration actions in the marine ecosystems are still unpredictable. We performed a global analysis of published literature to identify the factors increasing the probability of restoration success in coastal and marine systems. Our results confirm that the majority of active restoration initiatives are still concentrated in the northern hemisphere and that most of information gathered from restoration efforts derives from a relatively small subset of species. The analysis also indicates that many studies are still experimental in nature, covering small spatial and temporal scales. Despite the limits of assessing restoration effectiveness in absence of a standardized definition of success, the context (degree of human impact, ecosystem type, habitat) of where the restoration activity is undertaken is of greater relevance to a successful outcome than how (method) the restoration is carried out. Contrary to expectations, we found that restoration is not necessarily more successful closer to protected areas (PA) and in areas of moderate human impact. This result can be motivated by the limits in assessing the success of interventions and by the tendency of selecting areas in more obvious need of restoration, where the potential of actively restoring a degraded site is more evident. Restoration sites prioritization considering human uses and conservation status present in the region is of vital importance to obtain the intended outcomes and galvanize further actions
Author Correction: Future response of global coastal wetlands to sea-level rise.
Change history: In Fig. 2b of this Letter, 'Relative wetland change (km2)' should have read 'Relative wetland change (%)' and equations (2) and (3) have been changed from 'RSLRcrit = (m à TRe) à Sed + i' and 'Sedcrit = (RSLR - i)/(m à TRe)', respectively. The definition of the variables in equation (2) has been updated. These errors have been corrected online
Asymptotic behavior of solutions to the -Yamabe equation near isolated singularities
-Yamabe equations are conformally invariant equations generalizing
the classical Yamabe equation. In an earlier work YanYan Li proved that an
admissible solution with an isolated singularity at to the
-Yamabe equation is asymptotically radially symmetric. In this work
we prove that an admissible solution with an isolated singularity at to the -Yamabe equation is asymptotic to a radial
solution to the same equation on . These results
generalize earlier pioneering work in this direction on the classical Yamabe
equation by Caffarelli, Gidas, and Spruck. In extending the work of Caffarelli
et al, we formulate and prove a general asymptotic approximation result for
solutions to certain ODEs which include the case for scalar curvature and
curvature cases. An alternative proof is also provided using
analysis of the linearized operators at the radial solutions, along the lines
of approach in a work by Korevaar, Mazzeo, Pacard, and Schoen.Comment: 55 page
CHAMPION: Chalmers Hierarchical Atomic, Molecular, Polymeric & Ionic Analysis Toolkit
We present CHAMPION: a software developed to automatically detect
time-dependent bonds between atoms based on their dynamics, classify the local
graph topology around them, and analyze the physicochemical properties of these
topologies by statistical physics. In stark contrast to methodologies where
bonds are detected based on static conditions such as cut-off distances,
CHAMPION considers pairs of atoms to be bound only if they move together and
act as a bound pair over time. Furthermore, the time-dependent global bond
graph is possible to split into dynamically shifting connected components or
subgraphs around a certain chemical motif and thereby allow the physicochemical
properties of each such topology to be analyzed by statistical physics.
Applicable to condensed matter and liquids in general, and electrolytes in
particular, this allows both quantitative and qualitative descriptions of local
structure, as well as dynamical processes such as speciation and diffusion. We
present here a detailed overview of CHAMPION, including its underlying
methodology, implementation and capabilities.Comment: 11 pages, 8 figure
Future response of global coastal wetlands to sea-level rise.
The response of coastal wetlands to sea-level rise during the twenty-first century remains uncertain. Global-scale projections suggest that between 20 and 90 per cent (for low and high sea-level rise scenarios, respectively) of the present-day coastal wetland area will be lost, which will in turn result in the loss of biodiversity and highly valued ecosystem services1-3. These projections do not necessarily take into account all essential geomorphological4-7 and socio-economic system feedbacks8. Here we present an integrated global modelling approach that considers both the ability of coastal wetlands to build up vertically by sediment accretion, and the accommodation space, namely, the vertical and lateral space available for fine sediments to accumulate and be colonized by wetland vegetation. We use this approach to assess global-scale changes in coastal wetland area in response to global sea-level rise and anthropogenic coastal occupation during the twenty-first century. On the basis of our simulations, we find that, globally, rather than losses, wetland gains of up to 60 per cent of the current area are possible, if more than 37 per cent (our upper estimate for current accommodation space) of coastal wetlands have sufficient accommodation space, and sediment supply remains at present levels. In contrast to previous studies1-3, we project that until 2100, the loss of global coastal wetland area will range between 0 and 30 per cent, assuming no further accommodation space in addition to current levels. Our simulations suggest that the resilience of global wetlands is primarily driven by the availability of accommodation space, which is strongly influenced by the building of anthropogenic infrastructure in the coastal zone and such infrastructure is expected to change over the twenty-first century. Rather than being an inevitable consequence of global sea-level rise, our findings indicate that large-scale loss of coastal wetlands might be avoidable, if sufficient additional accommodation space can be created through careful nature-based adaptation solutions to coastal management.Personal research fellowship of Mark Schuerch (Project Number 272052902) and by the Cambridge Coastal Research Unit (Visiting Scholar Programme). Furthermore, this work has partly been supported by the EU research project RISES-AM- (FP7-ENV-693396)
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