3,352 research outputs found
Dileptons in High-Energy Heavy-Ion Collisions
The current status of our understanding of dilepton production in
ultrarelativistic heavy-ion collisions is discussed with special emphasis on
signals from the (approach towards) chirally restored and deconfined phases. In
particular, recent results of the CERN-SPS low-energy runs are compared to
model predictions and interpreted. Prospects for RHIC experiments are given.Comment: Invited talk at ICPAQGP, Jaipur, India, Nov. 26-30, 2001; 1 Latex and
9 eps-/ps-files Reoprt No.: SUNY-NTG-02-0
Signatures of Thermal Dilepton Radiation at RHIC
The properties of thermal dilepton production from heavy-ion collisions in
the RHIC energy regime are evaluated for invariant masses ranging from 0.5 to 3
GeV. Using an expanding thermal fireball to model the evolution through both
quark-gluon and hadronic phases various features of the spectra are addressed.
In the low-mass region, due to an expected large background, the focus is on
possible medium modifications of the narrow resonance structures from
and mesons, whereas in the intermediate-mass region the old idea of
identifying QGP radiation is reiterated including effects of chemical
under-saturation in the early stages of central Au+Au collisions.Comment: 17 pages ReVTeX including 16 figure
Hadro-Chemistry and Evolution of (Anti-) Baryon Densities at RHIC
The consequences of hadro-chemical freezeout for the subsequent hadron gas
evolution in central heavy-ion collisions at RHIC and LHC energies are
discussed with special emphasis on effects due to antibaryons. Contrary to
naive expectations, their individual conservation, as implied by experimental
data, has significant impact on the chemical off-equilibrium composition of
hadronic matter at collider energies. This may reflect on a variety of
observables including source sizes and dilepton spectra.Comment: 4 pages ReVTeX incl. 3 ps-figs, submitted to PR
The hydrological regime of a forested tropical Andean catchment.
The hydrology of tropical mountain catchments plays a central role in ecological function, geochemical and biogeochemical cycles, erosion and sediment production, and water supply in globally important environments. There have been few studies quantifying the seasonal and annual water budgets in the montane tropics, particularly in cloud forests. We investigated the water balance and hydrologic regime of the Kosñipata catchment (basin area: 164.4 km2) over the period 2010â2011. The catchment spans over 2500 m in elevation in the eastern Peruvian Andes and is dominated by tropical montane cloud forest with some high-elevation puna grasslands. Catchment-wide rainfall was 3112 ± 414 mm yrâ1, calculated by calibrating Tropical Rainfall Measuring Mission (TRMM) 3B43 rainfall with rainfall data from nine meteorological stations in the catchment. Cloud water input to streamflow was 316 ± 116 mm yrâ1 (9.2% of total inputs), calculated from an isotopic mixing model using deuterium excess (Dxs) and ÎŽD of waters. Field streamflow was measured in 2010 by recording height and calibrating to discharge. River run-off was estimated to be 2796 ± 126 mm yrâ1. Actual evapotranspiration (AET) was 688 ± 138 mm yrâ1, determined using the Priestley and TaylorâJet Propulsion Laboratory (PT-JPL) model. The overall water budget was balanced within 1.6 ± 13.7%. Relationships between monthly rainfall and river run-off follow an anticlockwise hysteresis through the year, with a persistence of high run-off after the end of the wet season. The size of the soil and shallow groundwater reservoir is most likely insufficient to explain sustained dry-season flow. Thus, the observed hysteresis in rainfallârun-off relationships is best explained by sustained groundwater flow in the dry season, which is consistent with the water isotope results that suggest persistent wet-season sources to streamflow throughout the year. These results demonstrate the importance of transient groundwater storage in stabilising the annual hydrograph in this region of the Andes
Nuclear Saturation with in-Medium Meson Exchange Interactions
We show that the assumption of dropping meson masses together with
conventional many-body effects, implemented in the relativistic Dirac-Brueckner
formalism, explains nuclear saturation. We use a microscopic model for
correlated exchange and include the standard many-body effects on the
in-medium pion propagation, which initially increase the attractive
nucleon-nucleon () potential with density. For the vector meson exchanges
in both the and sector, we assume Brown-Rho scaling which---in
concert with `chiral' contact interactions---reduces the attraction at
higher densities.Comment: 5 pages REVTeX, 2 eps-figures included, submitted to Phys. Rev. Let
Transcriptome Analysis of Targeted Mouse Mutations Reveals the Topography of Local Changes in Gene Expression.
The unintended consequences of gene targeting in mouse models have not been thoroughly studied and a more systematic analysis is needed to understand the frequency and characteristics of off-target effects. Using RNA-seq, we evaluated targeted and neighboring gene expression in tissues from 44 homozygous mutants compared with C57BL/6N control mice. Two allele types were evaluated: 15 targeted trap mutations (TRAP); and 29 deletion alleles (DEL), usually a deletion between the translational start and the 3' UTR. Both targeting strategies insert a bacterial beta-galactosidase reporter (LacZ) and a neomycin resistance selection cassette. Evaluating transcription of genes in +/- 500 kb of flanking DNA around the targeted gene, we found up-regulated genes more frequently around DEL compared with TRAP alleles, however the frequency of alleles with local down-regulated genes flanking DEL and TRAP targets was similar. Down-regulated genes around both DEL and TRAP targets were found at a higher frequency than expected from a genome-wide survey. However, only around DEL targets were up-regulated genes found with a significantly higher frequency compared with genome-wide sampling. Transcriptome analysis confirms targeting in 97% of DEL alleles, but in only 47% of TRAP alleles probably due to non-functional splice variants, and some splicing around the gene trap. Local effects on gene expression are likely due to a number of factors including compensatory regulation, loss or disruption of intragenic regulatory elements, the exogenous promoter in the neo selection cassette, removal of insulating DNA in the DEL mutants, and local silencing due to disruption of normal chromatin organization or presence of exogenous DNA. An understanding of local position effects is important for understanding and interpreting any phenotype attributed to targeted gene mutations, or to spontaneous indels
Correlations of Heavy Quarks Produced at Large Hadron Collider
We study the correlations of heavy quarks produced in relativistic heavy ion
collisions and find them to be quite sensitive to the effects of the medium and
the production mechanisms. In order to put this on a quantitative footing, as a
first step, we analyze the azimuthal, transverse momentum, and rapidity
correlations of heavy quark-anti quark () pairs in
collisions at (). This sets the stage for the
identification and study of medium modification of similar correlations in
relativistic collision of heavy nuclei at the Large Hadron Collider. Next we
study the additional production of charm quarks in heavy ion collisions due to
multiple scatterings, {\it viz.}, jet-jet collisions, jet-thermal collisions,
and thermal interactions. We find that these give rise to azimuthal
correlations which are quite different from those arising from prompt initial
production at leading order and at next to leading order.Comment: 26 pages, 15 figures. Three new figures added, comparison to
experimental data included, abstract and discussion expande
A Diagrammatic Approach to Crystalline Color Superconductivity
We present a derivation of the gap equation for the crystalline color
superconducting phase of QCD which begins from a one-loop Schwinger-Dyson
equation written using a Nambu-Gorkov propagator modified to describe the
spatially varying condensate. Some aspects of previous variational calculations
become more straightforward when rephrased beginning from a diagrammatic
starting point. This derivation also provides a natural base from which to
generalize the analysis to include quark masses, nontrivial crystal structures,
gluon propagation at asymptotic densities, and nonzero temperature. In this
paper, we analyze the effects of nonzero temperature on the crystalline color
superconducting phase.Comment: 15 pages. 2 eps figure
QCD at small non-zero quark chemical potentials
We study the effects of small chemical potentials associated with the three
light quark flavors in QCD. We use a low-energy effective field theory that
solely relies on the symmetries of the QCD partition function. We find three
different phases: a normal phase, a pion superfluid phase and a kaon superfluid
phase. The two superfluid phases are separated by a first order phase
transition, whereas the normal phase and either of the superfluid phases are
separated by a second order phase transition. We compute the quark-antiquark
condensate, the pion condensate and the kaon condensate in each phase, as well
as the isospin density, the strangeness density, and the mass spectrum.Comment: 14 pages, 5 figure
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