6,292 research outputs found
Dilepton production at HADES: theoretical predictions
Dileptons represent a unique probe for nuclear matter under extreme
conditions reached in heavy-ion collisions. They allow to study meson
properties, like mass and decay width, at various density and temperature
regimes. Present days models allow generally a good description of dilepton
spectra in ultra-relativistic heavy ion collision. For the energy regime of a
few GeV/nucleon, important discrepancies between theory and experiment, known
as the DLS puzzle, have been observed. Various models, including the one
developed by the T\"{u}bingen group, have tried to address this problem, but
have proven only partially successful. High precision spectra of dilepton
emission in heavy-ion reactions at 1 and 2 GeV/nucleon will be released in the
near future by the HADES Collaboration at GSI. Here we present the predictions
for dilepton spectra in C+C reactions at 1 and 2 GeV/nucleon and investigate up
to what degree possible scenarios for the in-medium modification of vector
mesons properties are accessible by the HADES experiment.Comment: 12 pages, 4 figures; submitted to Phys.Lett.
Low mass dimuons within a hybrid approach
We analyse dilepton emission from hot and dense hadronic matter using a
hybrid approach based on the Ultrarelativistic Quantum Molecular Dynamics
(UrQMD) transport model with an intermediate hydrodynamic stage for the
description of heavy-ion collisions at relativistic energies. Focusing on the
enhancement with respect to the contribution from long-lived hadron decays
after freeze-out observed at the SPS in the low mass region of the dilepton
spectra (often referred to as "the excess"), the relative importance of the
emission from the equilibrium and the non-equilibrium stages is discussed.Comment: Proceedings of Hot Quarks 2010, 21-26 June 2010 Las Londe Les Maures;
v2: Corrected typos and added a commen
A phylogenomic perspective on the radiation of ray-finned fishes based upon targeted sequencing of ultraconserved elements
Ray-finned fishes constitute the dominant radiation of vertebrates with over
30,000 species. Although molecular phylogenetics has begun to disentangle major
evolutionary relationships within this vast section of the Tree of Life, there
is no widely available approach for efficiently collecting phylogenomic data
within fishes, leaving much of the enormous potential of massively parallel
sequencing technologies for resolving major radiations in ray-finned fishes
unrealized. Here, we provide a genomic perspective on longstanding questions
regarding the diversification of major groups of ray-finned fishes through
targeted enrichment of ultraconserved nuclear DNA elements (UCEs) and their
flanking sequence. Our workflow efficiently and economically generates data
sets that are orders of magnitude larger than those produced by traditional
approaches and is well-suited to working with museum specimens. Analysis of the
UCE data set recovers a well-supported phylogeny at both shallow and deep
time-scales that supports a monophyletic relationship between Amia and
Lepisosteus (Holostei) and reveals elopomorphs and then osteoglossomorphs to be
the earliest diverging teleost lineages. Divergence time estimation based upon
14 fossil calibrations reveals that crown teleosts appeared ~270 Ma at the end
of the Permian and that elopomorphs, osteoglossomorphs, ostarioclupeomorphs,
and euteleosts diverged from one another by 205 Ma during the Triassic. Our
approach additionally reveals that sequence capture of UCE regions and their
flanking sequence offers enormous potential for resolving phylogenetic
relationships within ray-finned fishes
How Sensitive are Di-Leptons from Rho Mesons to the High Baryon Density Region?
We show that the measurement of di-leptons might provide only a restricted
view into the most dense stages of heavy ion reactions. Thus, possible studies
of meson and baryon properties at high baryon densities, as e.g. done at
GSI-HADES and envisioned for FAIR-CBM, might observe weaker effects than
currently expected in certain approaches. We argue that the strong absorption
of resonances in the high baryon density region of the heavy ion collision
masks information from the early hot and dense phase due to a strong increase
of the total decay width because of collisional broadening. To obtain
additional information, we also compare the currently used approaches to
extract di-leptons from transport simulations - i.e. shining, only vector
mesons from final baryon resonance decays and instant emission of di-leptons
and find a strong sensitivity on the method employed in particular at FAIR and
SPS energies. It is shown explicitly that a restriction to rho meson (and
therefore di-lepton) production only in final state baryon resonance decays
provide a strong bias towards rather low baryon densities. The results
presented are obtained from UrQMD v2.3 calculations using the standard set-up.Comment: 8 pages, 6 figures, expanded versio
Modeling post-fire water erosion mitigation strategies
Abstract. Severe wildfires are often followed by significant increase in runoff and erosion, due to vegetation damage and changes in physical and chemical soil properties. Peak flows and sediment yields can increase up to two orders of magnitude, becoming dangerous for human lives and the ecosystem, especially in the wildlandâurban interface. Watershed post-fire rehabilitation measures are usually used to mitigate the effects of fire on runoff and erosion, by protecting soil from splash and shear stress detachment and enhancing its infiltration capacity. Modeling post-fire erosion and erosion mitigation strategies can be useful in selecting the effectiveness of a rehabilitation method. In this paper a distributed model based on the Revised Universal Soil Loss Equation (RUSLE), properly parameterized for a Mediterranean basin located in Sardinia, is used to determine soil losses for six different scenarios describing both natural and post-fire basin condition, the last also accounting for the single and combined effect of different erosion mitigation measures. Fire effect on vegetation and soil properties have been mimed by changing soil drainage capacity and organic matter content, and RUSLE factors related to soil cover and protection measures. Model results, validated using measured data on erosion rates from the literature and in situ field campaigns, show the effect of the analyzed rehabilitation treatments in reducing the amount of soil losses with the peculiar characteristics of the spatial distribution of such changes. In particular, the mulching treatment substantially decreases erosion both in its mean value (â75%) and in the spatially distribution of the erosion levels over the burned area . On the contrary, the breaking up of the hydrophobic layer decreases post-fire mean soil losses of about the 14%, although it strongly influences the spatial distribution of the erosion levels
Automation and sectoral reallocation
Empirical evidence in Dauth et al. (J Eur Econ Assoc, 2021) suggests that industrial robot adoption in Germany has led to a sectoral reallocation of employment from manufacturing to services, leaving total employment unaffected. We rationalize this evidence through the lens of a general equilibrium model with two sectors, matching frictions and endogenous participation. Automation induces firms to create fewer vacancies and job seekers to search less in the automatable sector (manufacturing). The service sector expands due to the sectoral complementarity in the production of the final good and a positive wealth effect for the household. Analysis across steady states shows that the reduction in manufacturing employment can be offset by the increase in service employment. The model can also replicate the magnitude of the decline in the ratio of manufacturing employment to service employment in Germany between 1994 and 2014
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