12,690 research outputs found
Quark Number Susceptibility in Hard Thermal Loop Approximation
We calculate the quark number susceptibility in the deconfined phase of QCD
using the hard thermal loop (HTL) approximation for the quark propagator. This
improved perturbation theory takes into account important medium effects such
as thermal quark masses and Landau damping in the quark-gluon plasma. We
explicitly show that the Landau damping part in the quark propagator for
spacelike quark momenta does not contribute to the quark number susceptibility
due to the quark number conservation. We find that the quark number
susceptibility only due to the collective quark modes deviates from that of
free one around the critical temperature but approaches free results at
infinite temperature limit. The results are in conformity with recent lattice
calculations.Comment: 9 pages including four figures and this version is accepted for
publication in Euro. Phys. J.
Recognition of two distinct elements in the RNA substrate by the RNA-binding domain of the T. thermophilus DEAD box helicase Hera
DEAD box helicases catalyze the ATP-dependent destabilization of RNA duplexes. Whereas duplex separation is mediated by the helicase core shared by all members of the family, flanking domains often contribute to binding of the RNA substrate. The Thermus thermophilus DEAD-box helicase Hera (for “heat-resistant RNA-binding ATPase”) contains a C-terminal RNA-binding domain (RBD). We have analyzed RNA binding to the Hera RBD by a combination of mutational analyses, nuclear magnetic resonance and X-ray crystallography, and identify residues on helix α1 and the C-terminus as the main determinants for high-affinity RNA binding. A crystal structure of the RBD in complex with a single-stranded RNA resolves the RNA–protein interactions in the RBD core region around helix α1. Differences in RNA binding to the Hera RBD and to the structurally similar RBD of the Bacillus subtilis DEAD box helicase YxiN illustrate the versatility of RNA recognition motifs as RNA-binding platforms. Comparison of chemical shift perturbation patterns elicited by different RNAs, and the effect of sequence changes in the RNA on binding and unwinding show that the RBD binds a single-stranded RNA region at the core and simultaneously contacts double-stranded RNA through its C-terminal tail. The helicase core then unwinds an adjacent RNA duplex. Overall, the mode of RNA binding by Hera is consistent with a possible function as a general RNA chaperone
Gluon Condensate and Non-Perturbative Quark-Photon Vertex
We evaluate the quark-photon vertex non-perturbatively taking into account
the gluon condensate at finite temperature. This vertex is related to the
previously derived effective quark propagator by a QED like Ward-Takahashi
identity. The importance of the effective vertex for the dilepton production
rate from a quark-gluon plasma is stressed.Comment: 9 pages including two figure
Bid participates in genotoxic drug-induced apoptosis of HeLa cells and is essential for death receptor ligands' apoptotic and synergistic effects
Background: The BH3-only protein Bid is an important component of death receptor-mediated caspase activation. Bid is cleaved by caspase-8 or -10 into t-Bid, which translocates to mitochondria and triggers the release of caspase-activating factors. Bid has also been reported to be cleaved by other proteases. Methodology/Principal Findings: To test the hypothesis that Bid is a central mediator of stress-induced apoptosis, we investigated the effects of a small molecule Bid inhibitor on stress-induced apoptosis, and generated HeLa cells deficient for Bid. Stable knockdown of bid lead to a pronounced resistance to Fas/CD95- and TRAIL-induced caspase activation and apoptosis, and significantly increased clonogenic survival. While Bid-deficient cells were equally sensitive to ER stress-induced apoptosis, they showed moderate, but significantly reduced levels of apoptosis, as well as increased clonogenic survival in response to the genotoxic drugs Etoposide, Oxaliplatin, and Doxorubicin. Similar effects were observed using the Bid inhibitor BI6C9. Interestingly, Bid-deficient cells were dramatically protected from apoptosis when subtoxic concentrations of ER stressors, Etoposide or Oxaliplatin were combined with subtoxic TRAIL concentrations. Conclusions/Significance: Our data demonstrate that Bid is central for death receptor-induced cell death and participates in anti-cancer drug-induced apoptosis in human cervical cancer HeLa cells. They also show that the synergistic effects of TRAIL in combination with either ER stressors or genotoxic anti-cancer drugs are nearly exclusively mediated via an increased activation of Bid-induced apoptosis signalling
Global existence for the spherically symmetric Einstein-Vlasov system with outgoing matter
We prove a new global existence result for the asymptotically flat,
spherically symmetric Einstein-Vlasov system which describes in the framework
of general relativity an ensemble of particles which interact by gravity. The
data are such that initially all the particles are moving radially outward and
that this property can be bootstrapped. The resulting non-vacuum spacetime is
future geodesically complete.Comment: 16 page
Low Mass Dilepton Rate from the Deconfined Phase
We discuss low mass dilepton rates ( GeV) from the deconfined phase of
QCD using both perturbative and non-perturbative models and compare with those
from lattice gauge theory and in-medium hadron gas. Our analysis suggests that
the rate at very low invariant mass ( MeV) using the nonperturbative
gluon condensate in a semiempirical way within the Green function dominates
over the Born-rate and independent of any uncertainty associated with the
choice of the strong coupling in perturbation theory. On the other hand the
rate from interaction in the deconfined phase is important between 200
MeV M\ge 200M\ge 500$ MeV, constraining on the broad resonance structures
in the dilepton rate at large invariant mass. We also discuss the lattice
constraints on the low mass dilepton rate. Furthermore, we discuss a more
realistic way to advocate the quark-hadron duality hypothesis based on the
dilepton rates from QGP and hadron gas than it is done in the literature.Comment: 24 pages, 9 figures; Discussion added, Accepted in Phys. Rev.
Conserved Density Fluctuation and Temporal Correlation Function in HTL Perturbation Theory
Considering recently developed Hard Thermal Loop perturbation theory that
takes into account the effect of the variation of the external field through
the fluctuations of a conserved quantity we calculate the temporal component of
the Euclidian correlation function in the vector channel. The results are found
to be in good agreement with the very recent results obtained within the
quenched approximation of QCD and small values of the quark mass ()
on improved lattices of size at (),
(), and (), where is
the temporal extent of the lattice. This suggests that the results from lattice
QCD and Hard Thermal Loop perturbation theory are in close proximity for a
quantity associated with the conserved density fluctuation.Comment: 16 pages, 4 figures; One para added in introduction, Fig 1 modified;
Accepted in Phys. Rev.
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