291 research outputs found
Non-perturbative effects in a rapidly expanding quark-gluon plasma
Within first-order phase transitions, we investigate the pre-transitional
effects due to the nonperturbative, large-amplitude thermal fluctuations which
can promote phase mixing before the critical temperature is reached from above.
In contrast with the cosmological quark-hadron transition, we find that the
rapid cooling typical of the RHIC and LHC experiments and the fact that the
quark-gluon plasma is chemically unsaturated suppress the role of
non-perturbative effects at current collider energies. Significant supercooling
is possible in a (nearly) homogeneous state of quark gluon plasma.Comment: LaTeX, 7 pages with 7 Postscript figures. Figures added, discussions
added. Version to appear in Phys. Rev.
Dependence of energy loss of jets on the initial thermodynamic state of deconfined matter at RHIC
The dependence of the radiative energy loss of fast partons on the initial
thermodynamic parameters is studied for deconfined matter to be expected at
RHIC. We demonstrate that the specific QCD radiation pattern with a quadratic
dependence of the energy loss on the propagated distance leads to a strong
increase of the energy loss with increasing initial entropy of deconfined
matter supposed its life-time is less than the average time to pass through the
medium. This is in contrast to a parameterization with constant energy loss per
unit length of propagation. For a sufficiently high initial temperature a
two-regime behavior of the energy loss as a function of the initial parton
momentum occurs. The angular structure of the energy loss of hard jets with
respect to the initial temperature is also discussed for RHIC conditions.Comment: 10 pages with fig
Coronary revascularisation in stable patients after an acute coronary syndrome: a propensity analysis of early invasive versus conservative management in a register-based cohort study
OBJECTIVES: To compare the effectiveness of in-hospital medical therapy versus coronary revascularisation added to medical therapy in patients who stabilised after an acute coronary syndrome (ACS).
DESIGN: Propensity score-matched cohort study from the database of the Tampere ACS registry.
SETTING: A single academic hospital in Finland.
PARTICIPANTS: 1149 patients with a recent ACS, but no serious coexisting conditions: recurrent ischaemic episodes despite adequate medical therapy, haemodynamic instability, overt congestive heart failure and serious ventricular arrhythmias. PRIMARY AND SECONDARY OUTCOME MEASURES: The composite endpoint of major acute cardiovascular events (MACEs): unstable angina requiring rehospitalisation, stroke, myocardial infarction and all-cause mortality, at 6-month follow-up.
RESULTS: Compared with standard medical treatment, revascularisation was associated with a lower rate of MACEs at 6 months in patients of the first quintile (HR 0.81; 95% CI 0.66 to 0.99), but a higher rate of MACEs in the fifth quintile (HR 4.74, CI 1.36 to 16.49; p=0.014). There were no significant differences in the rates of MACEs in the remaining three quintiles. Patients of the first quintile were the oldest (79.7\ub18.3 years) and had a more significant (p<0.001) history of prior myocardial infarction (37%) and poor renal function (creatine, \ub5mol/l: 114.9\ub170.7). They also showed the highest C reactive protein (7.3\ub19.5 mg/l) levels.
CONCLUSIONS: Our findings suggest that in-hospital coronary revascularisation did not lead to any advantage with signal of possible harm in the great majority of patients who stabilised after an ACS. An early invasive management strategy may be best reserved for elderly patients having high-risk clinical features and biochemical evidence of a strong inflammatory activity
Gluon Shadowing in DIS off Nuclei
Within a light-cone quantum-chromodynamics dipole formalism based on the
Green function technique, we study nuclear shadowing in deep-inelastic
scattering at small Bjorken xB < 0.01. Such a formalism incorporates naturally
color transparency and coherence length effects. Calculations of the nuclear
shadowing for the \bar{q}q Fock component of the photon are based on an exact
numerical solution of the evolution equation for the Green function, using a
realistic form of the dipole cross section and nuclear density function. Such
an exact numerical solution is unavoidable for xB > 0.0001, when a variation of
the transverse size of the \bar{q}q Fock component must be taken into account.
The eikonal approximation, used so far in most other models, can be applied
only at high energies, when xB < 0.0001 and the transverse size of the \bar{q}q
Fock component is "frozen" during propagation through the nuclear matter. At xB
< 0.01 we find quite a large contribution of gluon suppression to nuclear
shadowing, as a shadowing correction for the higher Fock states containing
gluons. Numerical results for nuclear shadowing are compared with the available
data from the E665 and NMC collaborations. Nuclear shadowing is also predicted
at very small xB corresponding to LHC kinematical range. Finally the model
predictions are compared and discussed with the results obtained from other
models.Comment: 29 pages including 7 figures; Fig.7 modified, some references and
corresponding discussion adde
Correlations and Fluctuations in High-Energy Nuclear Collisions
Nucleon correlations in the target and projectile nuclei are shown to reduce
significantly the fluctuations in multiple nucleon-nucleon collisions, total
multiplicity and transverse energy in relativistic heavy-ion collisions, in
particular for heavy projectile and target. The interplay between cross-section
fluctuations, from color transparency and opacity, and nuclear correlations is
calculated and found to be able to account for large fluctuations in transverse
energy spectra. Numerical implementation of correlations and cross-section
fluctuations in Monte-Carlo codes is discussed.Comment: 30 pages, in Revtex, plus 4 figures. Figures and preprint can be
obtained by mailing address to: [email protected]
Transport Theoretical Description of Collisional Energy Loss in Infinite Quark-Gluon Matter
We study the time evolution of a high-momentum gluon or quark propagating
through an infinite, thermalized, partonic medium utilizing a Boltzmann
equation approach. We calculate the collisional energy loss of the parton,
study its temperature and flavor dependence as well as the the momentum
broadening incurred through multiple interactions. Our transport calculations
agree well with analytic calculations of collisional energy-loss where
available, but offer the unique opportunity to address the medium response as
well in a consistent fashion.Comment: 12 pages, updated with additional references and typos correcte
Variation of jet quenching from RHIC to LHC and thermal suppression of QCD coupling constant
We perform a joint jet tomographic analysis of the data on the nuclear
modification factor from PHENIX at RHIC and ALICE at LHC. The
computations are performed accounting for radiative and collisional parton
energy loss with running coupling constant. Our results show that the observed
slow variation of from RHIC to LHC indicates that the QCD coupling
constant is suppressed in the quark-gluon plasma produced at LHC.Comment: 9 pages, 2 figure
Quantum kinetics and thermalization in an exactly solvable model
We study the dynamics of relaxation and thermalization in an exactly solvable
model with the goal of understanding the effects of off-shell processes. The
focus is to compare the exact evolution of the distribution function with
different approximations to the relaxational dynamics: Boltzmann, non-Markovian
and Markovian quantum kinetics. The time evolution of the distribution function
is evaluated exactly using two methods: time evolution of an initially prepared
density matrix and by solving the Heisenberg equations of motion. There are two
different cases that are studied in detail: i) no stable particle states below
threshold of the bath and a quasiparticle resonance above it and ii) a stable
discrete exact `particle' state below threshold. For the case of quasiparticles
in the continuum (resonances) the exact quasiparticle distribution
asymptotically tends to a statistical equilibrium distribution that differs
from a simple Bose-Einstein form as a result of off-shell processes. In the
case ii), the distribution of particles does not thermalize with the bath. We
study the kinetics of thermalization and relaxation by deriving a non-Markovian
quantum kinetic equation which resums the perturbative series and includes
off-shell effects. A Markovian approximation that includes off-shell
contributions and the usual Boltzmann equation are obtained from the quantum
kinetic equation in the limit of wide separation of time scales upon different
coarse-graining assumptions. The relaxational dynamics predicted by the
non-Markovian, Markovian and Boltzmann approximations are compared to the exact
result of the model. The Boltzmann approach is seen to fail in the case of wide
resonances and when threshold and renormalization effects are important.Comment: 49 pages, LaTex, 17 figures (16 eps figures
Poor long-term outcome in acute coronary syndrome in a real-life setting: Ten-year outcome of the TACOS study
Background: Long-term outcome of the three categories of acute coronary syndrome (ACS) in real-life patient cohorts is not well known. The objective of this study was to survey the 10-year outcome of an ACS patient cohort admitted to a university hospital and to explore factors affecting the outcome.Methods: A total of 1188 consecutive patients (median age 73 years) with ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI) or unstable angina pectoris (UA) in 2002–2003 were included and followed up for ≥ 10 years.Results: Mortality for STEMI, NSTEMI and UA patients during the follow-up period was 52.5%, 69.9% and 41.0% (p < 0.001), respectively. In multivariable Cox regression analysis, only age and creatinine level at admission were independently associated with patient outcome in all the three ACS categories when analyzed separately.Conclusions: All the three ACS categories proved to have high mortality rates during long-term followup in a real-life patient cohort. NSTEMI patients had worse outcome than STEMI and UA patients during the whole follow-up period. Our study results indicate clear differences in the prognostic significance of various demographic and therapeutic parameters within the three ACS categories
STAR results on medium properties and response of the medium to energetic partons
We report new STAR results on the consequences of highly energetic partons
propagating through the medium formed in heavy ion collisions using
correlations as an experimental probe. The recent results providing insights
about color factor effects and path length dependence of parton energy loss,
system size dependence of di-hadron fragmentation functions, conical emission
and ridge formation in heavy ion collisions are presented.Comment: STAR Plenary talk at QM2008. Manuscript for the Proceedings of Quark
Matter 2008, Jaipur, Indi
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