9,859 research outputs found
Vacuum fluctuations and the thermodynamics of chiral models
We consider the thermodynamics of chiral models in the mean-field
approximation and discuss the relevance of the (frequently omitted) fermion
vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended
version, we show that the fermion vacuum fluctuations can change the order of
the phase transition in the chiral limit and strongly influence physical
observables. We compute the temperature-dependent effective potential and
baryon number susceptibilities in these models, with and without the vacuum
term, and explore the cutoff and the pion mass dependence of the
susceptibilities. Finally, in the renormalized model the divergent vacuum
contribution is removed using the dimensional regularization.Comment: 9 pages, 5 figure
Digital voltage-controlled oscillator
Digital voltage-controlled oscillator generates a variable frequency signal controlled linearly about a center frequency with high stability and is phase controlled by an applied voltage. Integration ahead of the digital circuitry provides linear operation with control voltage having appreciable noise components
Higher-order ratios of baryon number cumulants
The relevance of higher order cumulants of net baryon number fluctuations for
the analysis of freeze-out and critical conditions in heavy-ion collisions at
LHC and RHIC is addressed. The sign structure of the higher order cumulants in
the vicinity of the chiral crossover temperature might be a sensitive probe and
may allow to elucidate their relation to the QCD phase transition. We calculate
ratios of generalized quark-number susceptibilities to high orders in three
flavor QCD-like models and investigate their sign structure close to the chiral
crossover line.Comment: presented at the International Conference "Critical Point and Onset
of Deconfinement - CPOD 2011", Wuhan, November 7-11, 2011; version to appear
in Cent. Eur. J. Phy
Position paper on the potential of inadvertent weather modification of the Florida Peninsula resulting from neutralization of space shuttle solid rocket booster exhaust clouds
A concept of injecting compounds into the exhaust cloud was proposed to neutralize the acidic nature of the low-level stabilized ground cloud (SGC) was studied. The potential Inadvertent Weather Modification caused by exhaust cloud characteristics from three hours to seven days after launch was studied. Possible effects of the neutralized SGC in warm and cloud precipitation processes were discussed. Based on a detailed climatology of the Florida Peninsula, the risk for weather modification under a variety of weather situations was assessed
Position paper on the potential of inadvertent weather modification of the Florida peninsula resulting from the stabilized ground cloud
Based on the climatology of the Florida Peninsula, we assessed the risk for weather modification. Certain weather situations warrant launch rescheduling because of the risk of possible impact on hurricanes, hail formation and lightning activity, strong wind developments, and intensification of high rainfall rates. The cumulative effects of 40 launches per year on weather modification were found to be insignificant
Empirical evidence for the Birch and Swinnerton-Dyer conjectures for modular jacobians of genus 2 curves
This paper provides empirical evidence for the Birch and Swinnerton-Dyer conjectures for modular Jacobians of genus 2 curves. The second of these conjectures relates six quantities associated to a Jacobian over the rational numbers. One of these six quantities is the size of the Shafarevich-Tate group. Unable to compute that, we computed the five other quantities and solved for the last one. In all 32 cases, the result is very close to an integer that is a power of 2. In addition, this power of 2 agrees with the size of the 2-torsion of the Shafarevich-Tate group, which we could compute
On the appearance of hyperons in neutron stars
By employing a recently constructed hyperon-nucleon potential the equation of
state of \beta-equilibrated and charge neutral nucleonic matter is calculated.
The hyperon-nucleon potential is a low-momentum potential which is obtained
within a renormalization group framework. Based on the Hartree-Fock
approximation at zero temperature the densities at which hyperons appear in
neutron stars are estimated. For several different bare hyperon-nucleon
potentials and a wide range of nuclear matter parameters it is found that
hyperons in neutron stars are always present. These findings have profound
consequences for the mass and radius of neutron stars.Comment: 12 pages, 12 figures, RevTeX4; summary and conclusions are
strengthened, to appear in PR
The Complexity of Drawing Graphs on Few Lines and Few Planes
It is well known that any graph admits a crossing-free straight-line drawing
in and that any planar graph admits the same even in
. For a graph and , let denote
the minimum number of lines in that together can cover all edges
of a drawing of . For , must be planar. We investigate the
complexity of computing these parameters and obtain the following hardness and
algorithmic results.
- For , we prove that deciding whether for a
given graph and integer is -complete.
- Since , deciding is NP-hard for . On the positive side, we show that the problem
is fixed-parameter tractable with respect to .
- Since , both and
are computable in polynomial space. On the negative side, we show
that drawings that are optimal with respect to or
sometimes require irrational coordinates.
- Let be the minimum number of planes in needed
to cover a straight-line drawing of a graph . We prove that deciding whether
is NP-hard for any fixed . Hence, the problem is
not fixed-parameter tractable with respect to unless
Mapping the phase diagram of strongly interacting matter
We employ a conformal mapping to explore the thermodynamics of strongly
interacting matter at finite values of the baryon chemical potential .
This method allows us to identify the singularity corresponding to the critical
point of a second-order phase transition at finite , given information
only at . The scheme is potentially useful for computing thermodynamic
properties of strongly interacting hot and dense matter in lattice gauge
theory. The technique is illustrated by an application to a chiral effective
model.Comment: 5 pages, 3 figures; published versio
- …