711 research outputs found
Casimir energy for a scalar field with a frequency dependent boundary condition
We consider the vacuum energy for a scalar field subject to a frequency
dependent boundary condition. The effect of a frequency cut-off is described in
terms of an {\it incomplete} -function. The use of the Debye asymptotic
expansion for Bessel functions allows to determine the dominant (volume, area,
>...) terms in the Casimir energy. The possible interest of this kind of models
for dielectric media (and its application to sonoluminescence) is also
discussed.Comment: 7 pages, RevTeX. Version to appear in PRD (Introduction enlarged,
references added
Pade-related resummations of the pressure of quark-gluon plasma by approximate inclusion of g**6-terms
We perform various resummations of the hot QCD pressure based on the actual
knowledge of the perturbation series which includes the g**6 ln(1/g) and part
of the g**6 terms. Resummations are performed separately for the short- and
long-distance parts. The g**6 term of the short-distance pressure is estimated
on the basis on the known UV cutoff dependence of the long-distance part. The
resummations are of the Pade and Borel-Pade type, using in addition the
(Pade-)resummed expression for the squared screening mass mE**2 and for the
EQCD coupling parameter gE**2. The resummed results depend weakly on the yet
unknown g**6 terms and on the the short-range renormalization scale, at all
temperatures. The dependence on the long-range renormalization scale is
appreciable at low temperatures T < 1 GeV. The resulting dependence of pressure
on temperature T is compatible with the results of the lattice calculations at
low T.Comment: 25 pages, 15 double figures, 4 single figures, revtex4; thoroughly
extended analysis; more figures; conclusions more clearly formulated; new
references added; title slightly changed; accepted for publication in
Phys.Rev.
Thermal nonlocal Nambu--Jona-Lasinio model in the real time formalism
The real-time formalism at finite temperature and chemical potential for the
nonlocal Nambu--Jona-Lasinio model is developed in the presence of a Gaussian
covariant regulator. We construct the most general thermal propagator, by means
of the spectral function. As a result, the model involves the propagation of
massive quasiparticles. The appearance of complex poles is interpreted as a
confinement signal, and in this case we have unstable quasiparticles with a
finite decay width. An expression for the propagator along the critical line,
where complex poles start to appear, is also obtained. A generalization to
other covariant regulators is proposed.Comment: 9 pages, 5 figures, minor changes, to appear in Phys. Rev.
Simulated and observed horizontal inhomogeneities of optical thickness of Arctic stratus
Two-dimensional horizontal fields of cloud optical thickness Ď„ derived
from airborne measurements of solar spectral, cloud-reflected radiance are
compared with semi-idealized large eddy simulations (LESs) of Arctic
stratus performed with the Consortium for Small-scale Modeling
(COSMO) atmospheric model. The measurements were collected during the
Vertical Distribution of Ice in Arctic Clouds (VERDI) campaign carried out in
Inuvik, Canada, in April/May 2012. The input for the LESs is obtained from
collocated airborne dropsonde observations of a persistent Arctic stratus
above the sea-ice-free Beaufort Sea. Simulations are performed for spatial
resolutions of 50 m (1.6 km  ×  1.6 km domain) and 100 m
(6.4 km  ×  6.4 km domain). Macrophysical cloud properties, such as
cloud top altitude and vertical extent, are well captured by the COSMO
simulations. However, COSMO produces rather homogeneous clouds compared to
the measurements, in particular for the simulations with coarser spatial
resolution. For both spatial resolutions, the directional structure of the
cloud inhomogeneity is well represented by the model. Differences between the
individual cases are mainly associated with the wind shear near cloud top and
the vertical structure of the atmospheric boundary layer. AÂ sensitivity study
changing the wind velocity in COSMO by a vertically constant scaling factor
shows that the directional, small-scale cloud inhomogeneity structures can
range from 250 to 800 m, depending on the mean wind speed, if the simulated
domain is large enough to capture also large-scale structures, which then
influence the small-scale structures. For those cases, a threshold wind
velocity is identified, which determines when the cloud inhomogeneity stops
increasing with increasing wind velocity.</p
Pion condensation in quark matter with finite baryon density
The phase structure of the Nambu -- Jona-Lasinio model at zero temperature
and in the presence of baryon- and isospin chemical potentials is investigated.
It is shown that in the chiral limit and for a wide range of model parameters
there exist two different phases with pion condensation. In the first, ordinary
phase, quarks are gapped particles. In the second, gapless pion condensation
phase, there is no energy cost for creating only - or both and
quarks, and the density of baryons is nonzero.Comment: 7 pages, 6 figures; two references adde
Massless fermions in a bag at finite density and temperature
We introduce the chemical potential in a system of massless fermions in a bag
by impossing boundary conditions in the Euclidean time direction. We express
the fermionic mean number in terms of a functional trace involving the Green's
function of the boundary value problem, which we study analytically. Numerical
evaluations are made, and an application to a simple hadron model is discussed.Comment: 14 pages, 3 figures, RevTe
The HMW effect in Noncommutative Quantum Mechanics
The HMW effect in non-commutative quantum mechanics is studied. By solving
the Dirac equations on non-commutative (NC) space and non-commutative phase
space, we obtain topological HMW phase on NC space and NC phase space
respectively, where the additional terms related to the space-space and
momentum-momentum non-commutativity are given explicitly.Comment: 8 Latex page
Properties of Quarkonia at T_c
We discuss how the spectral changes of quarkonia at T_c can reflect the
``critical'' behaviour of QCD phase transition. Starting from the temperature
dependencies of the energy density and pressure from lattice QCD calculation,
we extract the temperature dependencies of the scalar and spin 2 gluon
condensates near T_c. We also parameterize these changes into the electric and
magnetic condensate near T_c. While the magnetic condensate hardly changes
across T_c, we find that the electric condensate increases abruptly above T_c.
Similar abrupt change is also seen in the scalar condensate. Using the QCD
second-order Stark effect and QCD sum rules, we show that these sudden changes
induce equally abrupt changes in the mass and width of J/psi, both of which are
larger than 100 MeV at slightly above T_c.Comment: 8 pages, Plenary talk given at Quark Matter 2008, Jaipur Indi
Genotoxic mixtures and dissimilar action: Concepts for prediction and assessment
This article has been made available through the Brunel Open Access Publishing Fund. This article is distributed under the terms of the
creative commons Attribution license which permits any use, distribution, and reproduction in any medium, provided the original author(s)and the source are credited.Combinations of genotoxic agents have frequently been assessed without clear assumptions regarding their expected (additive) mixture effects, often leading to claims of synergisms that might in fact be compatible with additivity. We have shown earlier that the combined effects of chemicals, which induce micronuclei (MN) in the cytokinesis-block micronucleus assay in Chinese hamster ovary-K1 cells by a similar mechanism, were additive according to the concept of concentration addition (CA). Here, we extended these studies and investigated for the first time whether valid additivity expectations can be formulated for MN-inducing chemicals that operate through a variety of mechanisms, including aneugens and clastogens (DNA cross-linkers, topoisomerase II inhibitors, minor groove binders). We expected that their effects should follow the additivity principles of independent action (IA). With two mixtures, one composed of various aneugens (colchicine, flubendazole, vinblastine sulphate, griseofulvin, paclitaxel), and another composed of aneugens and clastogens (flubendazole, doxorubicin, etoposide, melphalan and mitomycin C), we observed mixture effects that fell between the additivity predictions derived from CA and IA. We achieved better agreement between observation and prediction by grouping the chemicals into common assessment groups and using hybrid CA/IA prediction models. The combined effects of four dissimilarly acting compounds (flubendazole, paclitaxel, doxorubicin and melphalan) also fell within CA and IA. Two binary mixtures (flubendazole/paclitaxel and flubendazole/doxorubicin) showed effects in reasonable agreement with IA additivity. Our studies provide a systematic basis for the investigation of mixtures that affect endpoints of relevance to genotoxicity and show that their effects are largely additive.UK Food Standards Agenc
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