13,095 research outputs found
Thermodynamics of (2+1)-flavor QCD: Confronting Models with Lattice Studies
The Polyakov-quark-meson (PQM) model, which combines chiral as well as
deconfinement aspects of strongly interacting matter is introduced for three
light quark flavors. An analysis of the chiral and deconfinement phase
transition of the model and its thermodynamics at finite temperatures is given.
Three different forms of the effective Polyakov loop potential are considered.
The findings of the (2+1)-flavor model investigations are confronted to
corresponding recent QCD lattice simulations of the RBC-Bielefeld, HotQCD and
Wuppertal-Budapest collaborations. The influence of the heavier quark masses,
which are used in the lattice calculations, is taken into account. In the
transition region the bulk thermodynamics of the PQM model agrees well with the
lattice data.Comment: 13 pages, 7 figures, 3 tables; minor changes, final version to appear
in Phys. Rev.
Rating of electrical wires in vacuum environments
Electric conductors used in vacuum environments have smaller cross sections. This report provides data on the correct size wire for a required current load in free-air, low-pressure oxygen, and vacuum environments
Noise generated by quiet engine fans. 3: Fan C
A family of fans designed with low noise features was acoustically evaluated, and noise results are documented for a 1.6-pressure-ratio, 472-m/sec (155-ft/sec) tip speed fan. The fan is described and some aerodynamic operating data are given. Far field noise around the fan was measured over a range of operating conditions for a variety of configurations having different arrangements of sound absorbing material in the flow ducts. Complete results of 1.3 octave band analysis of the data are presented in tabular form. Included also are acoustic power spectra and sideline perceived noise levels. Representative 1/3 octave band data are presented graphically, and sample graphs of continuous narrow band spectra are also provided
Noise generated by quiet engine fans. 2: Fan A
A significant effort within the NASA Quiet Engine Program has been devoted to acoustical evaluation at the Lewis Research Center noise test facility of a family of full-scale fans. This report, documents the noise results obtained with fan A - a 1.5-pressure-ratio, 1160-ft/sec-tip-speed fan. The fan is described and some aerodynamic operating data are given. Far-field noise around the fan was measured for a variety of configurations pertaining to acoustical treatment and over a range of operating conditions. Complete results of 1/3-octave band analysis of the data are presented in tabular form. Included also are power spectra and sideline perceived noise levels. Some representative 1/3-octave band data are presented graphically, and sample graphs of continuous narrow-band spectra are also provided
QCD critical region and higher moments for three flavor models
One of the distinctive feature of the QCD phase diagram is the possible
emergence of a critical endpoint. The critical region around the critical point
and the path dependency of the critical exponents is investigated within
effective chiral (2+1)-flavor models with and without Polyakov-loops. Results
obtained in no-sea mean-field approximations where a divergent vacuum part in
the fermion-loop contribution is neglected, are confronted to the renormalized
ones. Furthermore, the modifications caused by the back-reaction of the matter
fluctuations on the pure Yang-Mills system are discussed. Higher order,
non-Gaussian moments of event-by-event distributions of various particle
multiplicities are enhanced near the critical point and could serve as a probe
to determine its location in the phase diagram. By means of a novel derivative
technique higher order generalized quark-number susceptibilities are calculated
and their sign structure in the phase diagram is analyzed.Comment: 12 pages, 11 figures. Final PRD version (references and one more
equation added
Discovery of the 2010 Eruption and the Pre-Eruption Light Curve for Recurrent Nova U Scorpii
We report the discovery by B. G. Harris and S. Dvorak on JD 2455224.9385
(2010 Jan 28.4385 UT) of the predicted eruption of the recurrent nova U Scorpii
(U Sco). We also report on 815 magnitudes (and 16 useful limits) on the
pre-eruption light curve in the UBVRI and Sloan r' and i' bands from 2000.4 up
to 9 hours before the peak of the January 2010 eruption. We found no
significant long-term variations, though we did find frequent fast variations
(flickering) with amplitudes up to 0.4 mag. We show that U Sco did not have any
rises or dips with amplitude greater than 0.2 mag on timescales from one day to
one year before the eruption. We find that the peak of this eruption occurred
at JD 2455224.69+-0.07 and the start of the rise was at JD 2455224.32+-0.12.
From our analysis of the average B-band flux between eruptions, we find that
the total mass accreted between eruptions is consistent with being a constant,
in agreement with a strong prediction of nova trigger theory. The date of the
next eruption can be anticipated with an accuracy of +-5 months by following
the average B-band magnitudes for the next ~10 years, although at this time we
can only predict that the next eruption will be in the year 2020+-2.Comment: Astronomical Journal submitted, 36 pages, 3 figures, full table
Towards finite density QCD with Taylor expansions
Convergence properties of Taylor expansions of observables, which are also
used in lattice QCD calculations at non-zero chemical potential, are analyzed
in an effective N_f = 2+1 flavor Polyakov-quark-meson model. A recently
developed algorithmic technique allows the calculation of higher-order Taylor
expansion coefficients in functional approaches. This novel technique is for
the first time applied to an effective N_f = 2+1 flavor Polyakov-quark-meson
model and the findings are compared with the full model solution at finite
densities. The results are used to discuss prospects for locating the QCD phase
boundary and a possible critical endpoint in the phase diagram.Comment: 11 pages, 6 figures; minor clarifying changes, version to be
published in Phys. Lett.
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
Susceptibilities near the QCD (tri)critical point
Based on the proper-time renormalization group approach, the scalar and the
quark number susceptibilities in the vicinity of possible critical end points
of the hadronic phase diagram are investigated in the two-flavor quark-meson
model. After discussing the quark-mass dependence of the location of such
points, the critical behavior of the in-medium meson masses and quark number
density are calculated. The universality classes of the end points are
determined by calculating the critical exponents of the susceptibilities. In
order to numerically estimate the influence of fluctuations we compare all
quantities with results from a mean-field approximation. It is concluded that
the region in the phase diagram where the susceptibilities are enhanced is more
compressed around the critical end point if fluctuations are included.Comment: 14 pages, 19 figures; v3 typos and minor changes, references adde
The Phase Structure of the Polyakov--Quark-Meson Model
The relation between the deconfinement and chiral phase transition is
explored in the framework of an Polyakov-loop-extended two-flavor quark-meson
(PQM) model. In this model the Polyakov loop dynamics is represented by a
background temporal gauge field which also couples to the quarks. As a novelty
an explicit quark chemical potential and N_f-dependence in the Polyakov loop
potential is proposed by using renormalization group arguments. The behavior of
the Polyakov loop as well as the chiral condensate as function of temperature
and quark chemical potential is obtained by minimizing the grand canonical
thermodynamic potential of the system. The effect of the Polyakov loop dynamics
on the chiral phase diagram and on several thermodynamic bulk quantities is
presented.Comment: 13 pages, 12 figures, RevTex4; discussion of mu-dependence extended,
references added, version to be published in PR
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