191 research outputs found
Testing imaginary vs. real chemical potential in finite-temperature QCD
One suggestion for determining the properties of QCD at finite temperatures
and densities is to carry out lattice simulations with an imaginary chemical
potential whereby no sign problem arises, and to convert the results to real
physical observables only afterwards. We test the practical feasibility of such
an approach for a particular class of physical observables, spatial correlation
lengths in the quark-gluon plasma phase. Simulations with imaginary chemical
potential followed by analytic continuation are compared with simulations with
real chemical potential, which are possible by using a dimensionally reduced
effective action for hot QCD. We find that for imaginary chemical potential the
system undergoes a phase transition at |mu/T| \approx pi/3, and thus
observables are analytic only in a limited range. However, utilising this
range, relevant information can be obtained for the real chemical potential
case.Comment: 14 pages. Some clarifications and references added, figures modified.
To appear in PL
One-variable word equations in linear time
In this paper we consider word equations with one variable (and arbitrary
many appearances of it). A recent technique of recompression, which is
applicable to general word equations, is shown to be suitable also in this
case. While in general case it is non-deterministic, it determinises in case of
one variable and the obtained running time is O(n + #_X log n), where #_X is
the number of appearances of the variable in the equation. This matches the
previously-best algorithm due to D\k{a}browski and Plandowski. Then, using a
couple of heuristics as well as more detailed time analysis the running time is
lowered to O(n) in RAM model. Unfortunately no new properties of solutions are
shown.Comment: submitted to a journal, general overhaul over the previous versio
Endorectal magnetic resonance imaging of prostatic cancer: comparison between fat-suppressed T2-weighted fast spin echo and three-dimensional dual-echo, steady-state sequences
Peer reviewe
Lattice Artefacts In The Non-Abelian Debye Screening Mass In One Loop Order
We compute the electric screening mass in lattice QCD with Wilson fermions at
finite temperature and chemical potential to one-loop order, and show that
lattice artefacts arising from a finite lattice spacing result in an
enhancement of the screening mass as compared to the continuum. We discuss the
magnitude of this enhancement as a function of the temperature and chemical
potential for lattices with different number of lattice sites in the temporal
direction that can be implemented in lattice simulations. Most of the
enhancement is found to be due to the fermion loop contribution.Comment: 23 pages, 8 figures, LaTe
Static correlation lengths in QCD at high temperatures and finite densities
We use a perturbatively derived effective field theory and three-dimensional
lattice simulations to determine the longest static correlation lengths in the
deconfined QCD plasma phase at high temperatures (T\gsim 2 Tc) and finite
densities (\mu\lsim 4 T). For vanishing chemical potential, we refine a
previous determination of the Debye screening length, and determine the
dependence of different correlation lengths on the number of massless flavours
as well as on the number of colours. For non-vanishing but small chemical
potential, the existence of Debye screening allows us to carry out simulations
corresponding to the full QCD with two (or three) massless dynamical flavours,
in spite of a complex action. We investigate how the correlation lengths in the
different quantum number channels change as the chemical potential is switched
on.Comment: 34 pages; references, clarifications and a note on recent literature
added; to appear in Nucl.Phys.
The Nonabelian Debye Mass at Next-to-Leading Order
It is shown that after a resummation of leading high-temperature
contributions, a complete and gauge-independent result for the nonabelian Debye
screening mass at next-to-leading order can be extracted from the static gluon
propagator. In contrast to previous, incomplete results, the correction to the
Debye mass is found to be logarithmically sensitive to the nonperturbative
magnetic mass and positive, in accordance with recent high-statistics results
from lattice calculations.Comment: 8 pages, REVTEX v3.0, BI-TP 93/42 (minor corrections in text and
references
The Impact of Bdnf Gene Deficiency to the Memory Impairment and Brain Pathology of APPswe/PS1dE9 Mouse Model of Alzheimer's Disease
Peer reviewe
HX600, a synthetic agonist for RXR-Nurr1 heterodimer complex, prevents ischemia-induced neuronal damage
Ischemic stroke is amongst the leading causes of death and disabilities. The available treatments are suitable for only a fraction of patients and thus novel therapies are urgently needed. Blockage of one of the cerebral arteries leads to massive and persisting inflammatory reaction contributing to the nearby neuronal damage. Targeting the detrimental pathways of neuroinflammation has been suggested to be beneficial in conditions of ischemic stroke. Nuclear receptor 4A-family (NR4A) member Nurr1 has been shown to be a potent modulator of harmful inflammatory reactions, yet the role of Nurr1 in cerebral stroke remains unknown. Here we show for the first time that an agonist for the dimeric transcription factor Nurr1/retinoid X receptor (RXR), HX600, reduces microglia expressed proinflammatory mediators and prevents inflammation induced neuronal death in in vitro co-culture model of neurons and microglia. Importantly, HX600 was protective in a mouse model of permanent middle cerebral artery occlusion and alleviated the stroke induced motor deficits. Along with the anti-inflammatory capacity of HX600 in vitro, treatment of ischemic mice with HX600 reduced ischemia induced Iba-1, p38 and TREM2 immunoreactivities, protected endogenous microglia from ischemia induced death and prevented leukocyte infiltration. These anti-inflammatory functions were associated with reduced levels of brain lysophosphatidylcholines (lysoPCs) and acylcarnitines, metabolites related to proinflammatory events. These data demonstrate that HX600 driven Nurr1 activation is beneficial in ischemic stroke and propose that targeting Nurr1 is a novel candidate for conditions involving neuroinflammatory component.Peer reviewe
Connection between Chiral Symmetry Restoration and Deconfinement
We propose a simple explanation for the connection between chiral symmetry
restoration and deconfinement in QCD at high temperature. In the Higgs
description of the QCD vacuum both spontaneous chiral symmetry breaking and
effective gluon masses are generated by the condensate of a color octet
quark-antiquark pair. The transition to the high temperature state proceeds by
the melting of this condensate. Quarks and gluons become (approximately)
massless at the same critical temperature. For instanton-dominated effective
multiquark interactions and three light quarks with equal mass we find a first
order phase transition at a critical temperature around 170 MeV.Comment: New section on vortices,33 pages,LaTe
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