1,372 research outputs found
Nonequilibrium perturbation theory for spin-1/2 fields
A partial resummation of perturbation theory is described for field theories
containing spin-1/2 particles in states that may be far from thermal
equilibrium. This allows the nonequilibrium state to be characterized in terms
of quasiparticles that approximate its true elementary excitations. In
particular, the quasiparticles have dispersion relations that differ from those
of free particles, finite thermal widths and occupation numbers which, in
contrast to those of standard perturbation theory evolve with the changing
nonequilibrium environment. A description of this kind is essential for
estimating the evolution of the system over extended periods of time. In
contrast to the corresponding description of scalar particles, the structure of
nonequilibrium fermion propagators exhibits features which have no counterpart
in the equilibrium theory.Comment: 16 pages; no figures; submitted to Phys. Rev.
Primary cutaneous anaplastic large cell lymphoma shows a distinct miRNA expression profile and reveals differences from tumor-stage mycosis fungoides
Copyright @ 2012 John Wiley & SonsThe miRNA expression profiles of skin biopsies from 14 primary cutaneous anaplastic large cell lymphoma (C-ALCL) patients were analysed with miRNA microarrays using the same control group of 12 benign inflammatory dermatoses (BID) as previously used to study the miRNA expression profile of tumor-stage mycosis fungoides (MF). We identified 13 differentially expressed miRNAs between C-ALCL and BID. The up-regulation of miR-155, miR-27b, miR-30c and miR-29b in C-ALCL was validated by miRNA-Q-PCR on independent study groups. Additionally, the miRNA expression profiles of C-ALCL were compared with those of tumor-stage MF. Although miRNA microarray analysis did not identify statistically significant differentially expressed miRNAs, miRNA-Q-PCR demonstrated statistically significantly differential expression of miR-155, miR-27b, miR-93, miR-29b and miR-92a between tumor-stage MF and C-ALCL. This study, the first describing the miRNA expression profile of C-ALCL, reveals differences with tumor-stage MF, suggesting a different contribution to the pathogenesis of these lymphomas.This work was funded by grants from
Netherlands Organization for Scientific Research (NWO) (MHV) and the Fondation Rene´ Touraine (MvK), and grants from the Leukaemia and Lymphoma Research (EB) and the Julian Starmer-Smith Memorial Fund (CHL)
Nonequilibrium perturbation theory for complex scalar fields
Real-time perturbation theory is formulated for complex scalar fields away
from thermal equilibrium in such a way that dissipative effects arising from
the absorptive parts of loop diagrams are approximately resummed into the
unperturbed propagators. Low order calculations of physical quantities then
involve quasiparticle occupation numbers which evolve with the changing state
of the field system, in contrast to standard perturbation theory, where these
occupation numbers are frozen at their initial values. The evolution equation
of the occupation numbers can be cast approximately in the form of a Boltzmann
equation. Particular attention is given to the effects of a non-zero chemical
potential, and it is found that the thermal masses and decay widths of
quasiparticle modes are different for particles and antiparticles.Comment: 15 pages using RevTeX; 2 figures in 1 Postscript file; Submitted to
Phys. Rev.
The parasitic worm-derived immunomodulator, ES-62 and its drug-like small molecule analogues exhibit therapeutic potential in a model of chronic asthma
Chronic asthma is associated with persistent lung inflammation and long-term remodelling of the airways that have proved refractory to conventional treatments such as steroids, despite their efficacy in controlling acute airway contraction and bronchial inflammation. As its recent dramatic increase in industrialised countries has not been mirrored in developing regions, it has been suggested that helminth infection may protect humans against developing asthma. Consistent with this, ES-62, an immunomodulator secreted by the parasitic worm Acanthocheilonema viteae, can prevent pathology associated with chronic asthma (cellular infiltration of the lungs, particularly neutrophils and mast cells, mucus hyper-production and airway thickening) in an experimental mouse model. Importantly, ES-62 can act even after airway remodelling has been established, arresting pathogenesis and ameliorating the inflammatory flares resulting from repeated exposure to allergen that are a debilitating feature of severe chronic asthma. Moreover, two chemical analogues of ES-62, 11a and 12b mimic its therapeutic actions in restoring levels of regulatory B cells and suppressing neutrophil and mast cell responses. These studies therefore provide a platform for developing ES-62-based drugs, with compounds 11a and 12b representing the first step in the development of a novel class of drugs to combat the hitherto intractable disorder of chronic asthma
Scaling in high-temperature superconductors
A Hartree approximation is used to study the interplay of two kinds of
scaling which arise in high-temperature superconductors, namely critical-point
scaling and that due to the confinement of electron pairs to their lowest
Landau level in the presence of an applied magnetic field. In the neighbourhood
of the zero-field critical point, thermodynamic functions scale with the
scaling variable , which differs from the variable
suggested by the gaussian approximation.
Lowest-Landau-level (LLL) scaling occurs in a region of high field surrounding
the upper critical field line but not in the vicinity of the zero-field
transition. For YBaCuO in particular, a field of at least 10 T is needed to
observe LLL scaling. These results are consistent with a range of recent
experimental measurements of the magnetization, transport properties and,
especially, the specific heat of high- materials.Comment: 22 pages + 1 figure appended as postscript fil
Critical Casimir Effect in 3He-4He films
Universal aspects of the thermodynamic Casimir effect in wetting films of
3He-4He mixtures near their bulk tricritical point are studied within suitable
models serving as representatives of the corresponding universality class. The
effective forces between the boundaries of such films arising from the
confinement are calculated along isotherms at several fixed concentrations of
3He. Nonsymmetric boundary conditions impose nontrivial concentration profiles
leading to repulsive Casimir forces which exhibit a rich behavior of the
crossover between the tricritical point and the line of critical points. The
theoretical results agree with published experimental data and emphasize the
importance of logarithmic corrections.Comment: 12 pages, 4 figures, submitted to the Phys. Rev. Let
Relaxation and Kinetics in Scalar Field Theories
A new approach to the dynamics of relaxation and kinetics of thermalization
in a scalar field theory is presented that incorporates the relevant time
scales through the resummation of hard thermal loops. An alternative derivation
of the kinetic equations for the ``quasiparticle'' distribution functions is
obtained that allows a clear understanding of the different ``coarse graining''
approximations usually involved in a kinetic description. This method leads to
a systematic perturbative expansion to obtain the kinetic equations including
hard-thermal loop resummation and to an improvement including renormalization,
off-shell effects and contributions that change chemical equilibrium on short
time scales. As a byproduct of these methods we establish the relation between
the relaxation time scale in the linearized equation of motion of the
quasiparticles and the thermalization time scale of the quasiparticle
distribution function in the ``relaxation time approximation''. Hard thermal
loop resummation dramatically modifies the scattering rate for long wavelength
modes as compared to the usual (semi) classical estimate. Relaxation and
kinetics are studied both in the unbroken and broken symmetry phases of the
theory. The broken symmetry phase also provides the setting to obtain the
contribution to the kinetic equations from processes that involve decay of a
heavy scalar into light scalar particles in the medium.Comment: 28 pages, revtex 3.0, two figures available upon reques
Crossover from Isotropic to Directed Percolation
Percolation clusters are probably the simplest example for scale--invariant
structures which either are governed by isotropic scaling--laws
(``self--similarity'') or --- as in the case of directed percolation --- may
display anisotropic scaling behavior (``self--affinity''). Taking advantage of
the fact that both isotropic and directed bond percolation (with one preferred
direction) may be mapped onto corresponding variants of (Reggeon) field theory,
we discuss the crossover between self--similar and self--affine scaling. This
has been a long--standing and yet unsolved problem because it is accompanied by
different upper critical dimensions: for isotropic, and
for directed percolation, respectively. Using a generalized
subtraction scheme we show that this crossover may nevertheless be treated
consistently within the framework of renormalization group theory. We identify
the corresponding crossover exponent, and calculate effective exponents for
different length scales and the pair correlation function to one--loop order.
Thus we are able to predict at which characteristic anisotropy scale the
crossover should occur. The results are subject to direct tests by both
computer simulations and experiment. We emphasize the broad range of
applicability of the proposed method.Comment: 19 pages, written in RevTeX, 12 figures available upon request (from
[email protected] or [email protected]), EF/UCT--94/2, to be
published in Phys. Rev. E (May 1994
Critical and Tricritical Hard Objects on Bicolorable Random Lattices: Exact Solutions
We address the general problem of hard objects on random lattices, and
emphasize the crucial role played by the colorability of the lattices to ensure
the existence of a crystallization transition. We first solve explicitly the
naive (colorless) random-lattice version of the hard-square model and find that
the only matter critical point is the non-unitary Lee-Yang edge singularity. We
then show how to restore the crystallization transition of the hard-square
model by considering the same model on bicolored random lattices. Solving this
model exactly, we show moreover that the crystallization transition point lies
in the universality class of the Ising model coupled to 2D quantum gravity. We
finally extend our analysis to a new two-particle exclusion model, whose
regular lattice version involves hard squares of two different sizes. The exact
solution of this model on bicolorable random lattices displays a phase diagram
with two (continuous and discontinuous) crystallization transition lines
meeting at a higher order critical point, in the universality class of the
tricritical Ising model coupled to 2D quantum gravity.Comment: 48 pages, 13 figures, tex, harvmac, eps
Quantum Rolling Down out of Equilibrium
In a scalar field theory, when the tree level potential admits broken
symmetry ground states, the quantum corrections to the static effective
potential are complex. (The imaginary part is a consequence of an instability
towards phase separation and the static effective potential is not a relevant
quantity for understanding the dynamics). Instead, we study here the equations
of motion obtained from the one loop effective action for slow rollover out of
equilibrium.
We considering the case in which a scalar field theory undergoes a rapid
phase transition from to . We find that, for slow rollover
initial conditions (the field near the maximum of the tree level potential),
the process of phase separation controlled by unstable long-wavelength
fluctuations introduces dramatic corrections to the dynamical evolution of the
field. We find that these effects slow the rollover even furtherComment: 33 pages, Latex,LPTHE-PAR 92-33 PITT 92-0
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