5,570 research outputs found
The chemical evolution of local star forming galaxies: Radial profiles of ISM metallicity, gas mass, and stellar mass and constraints on galactic accretion and winds
The radially averaged metallicity distribution of the ISM and the young
stellar population of a sample of 20 disk galaxies is investigated by means of
an analytical chemical evolution model which assumes constant ratios of
galactic wind mass loss and accretion mass gain to star formation rate. Based
on this model the observed metallicities and their gradients can be described
surprisingly well by the radially averaged distribution of the ratio of stellar
mass to ISM gas mass. The comparison between observed and model predicted
metallicity is used to constrain the rate of mass loss through galactic wind
and accretion gain in units of the star formation rate. Three groups of
galaxies are found: galaxies with either mostly winds and only weak accretion,
or mostly accretion and only weak winds, and galaxies where winds are roughly
balanced by accretion. The three groups are distinct in the properties of their
gas disks. Galaxies with approximately equal rates of mass-loss and accretion
gain have low metallicity, atomic hydrogen dominated gas disks with a flat
spatial profile. The other two groups have gas disks dominated by molecular
hydrogen out to 0.5 to 0.7 isophotal radii and show a radial exponential
decline, which is on average steeper for the galaxies with small accretion
rates. The rates of accretion (<1.0 x SFR) and outflow (<2.4 x SFR) are
relatively low. The latter depend on the calibration of the zero point of the
metallicity determination from the use of HII region strong emission lines.Comment: 19 pages, 17 figure, accepted to MNRA
Local tunneling spectroscopy as signatures of the Fulde-Ferrell-Larkin-Ovchinnikov state in s- and d-wave Superconductors
The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states for two-dimensional s- and
d-wave superconductors (s- and d-SC) are self-consistently studied under an
in-plane magnetic field. While the stripe solution of the order parameter (OP)
is found to have lower free energy in s-SC, a square lattice solution appears
to be energetically more favorable in the case of d-SC. At certain symmetric
sites, we find that the features in the local density of states (LDOS) can be
ascribed to two types of bound states. We also show that the LDOS maps for d-SC
exhibit bias-energy-dependent checkerboard patterns. These characteristics can
serve as signatures of the FFLO states.Comment: 5 pages, 5 figures Type and grammaratic errors corrected. Last figure
replaced by colored one. To appear in PR
Metallicity gradients in local field star-forming galaxies: Insights on inflows, outflows, and the coevolution of gas, stars and metals
We present metallicity gradients in 49 local field star-forming galaxies. We
derive gas-phase oxygen abundances using two widely adopted metallicity
calibrations based on the [OIII]/Hbeta, [NII]/Halpha and [NII]/[OII] line
ratios. The two derived metallicity gradients are usually in good agreement
within +/-0.14 dex/R25 (R25 is the B-band iso-photoal radius), but the
metallicity gradients can differ significantly when the ionisation parameters
change systematically with radius. We investigate the metallicity gradients as
a function of stellar mass (8<log(M*/Msun)<11) and absolute B-band luminosity
(-16 > MB > -22). When the metallicity gradients are expressed in dex/kpc, we
show that galaxies with lower mass and luminosity, on average, have steeper
metallicity gradients. When the metallicity gradients are expressed in dex/R25,
we find no correlation between the metallicity gradients, and stellar mass and
luminosity. We provide a local benchmark metallicity gradient of field
star-forming galaxies useful for comparison with studies at high redshifts. We
investigate the origin of the local benchmark gradient using simple chemical
evolution models and observed gas and stellar surface density profiles in
nearby field spiral galaxies. Our models suggest that the local benchmark
gradient is a direct result of the coevolution of gas and stellar disk under
virtually closed-box chemical evolution when the stellar-to-gas mass ratio
becomes high (>>0.3). These models imply low current mass accretion rates
(<0.3xSFR), and low mass outflow rates (<3xSFR) in local field star-forming
galaxies.Comment: 25 pages, 21 figures, accepted to MNRA
Non-Markovian Quantum Trajectories Versus Master Equations: Finite Temperature Heat Bath
The interrelationship between the non-Markovian stochastic Schr\"odinger
equations and the corresponding non-Markovian master equations is investigated
in the finite temperature regimes. We show that the general finite temperature
non-Markovian trajectories can be used to derive the corresponding
non-Markovian master equations. A simple, yet important solvable example is the
well-known damped harmonic oscillator model in which a harmonic oscillator is
coupled to a finite temperature reservoir in the rotating wave approximation.
The exact convolutionless master equation for the damped harmonic oscillator is
obtained by averaging the quantum trajectories relying upon no assumption of
coupling strength or time scale. The master equation derived in this way
automatically preserves the positivity, Hermiticity and unity.Comment: 19 pages, typos corrected, references adde
A note on Zolotarev optimal rational approximation for the overlap Dirac operator
We discuss the salient features of Zolotarev optimal rational approximation
for the inverse square root function, in particular, for its applications in
lattice QCD with overlap Dirac quark. The theoretical error bound for the
matrix-vector multiplication is derived. We check that
the error bound is always satisfied amply, for any QCD gauge configurations we
have tested. An empirical formula for the error bound is determined, together
with its numerical values (by evaluating elliptic functions) listed in Table 2
as well as plotted in Figure 3. Our results suggest that with Zolotarev
approximation to , one can practically preserve the exact
chiral symmetry of the overlap Dirac operator to very high precision, for any
gauge configurations on a finite lattice.Comment: 23 pages, 5 eps figures, v2:minor clarifications, and references
added, to appear in Phys. Rev.
The mechanism of hole carrier generation and the nature of pseudogap- and 60K-phases in YBCO
In the framework of the model assuming the formation of NUC on the pairs of
Cu ions in CuO plane the mechanism of hole carrier generation is
considered and the interpretation of pseudogap and 60 K-phases in
. is offered. The calculated dependences of hole
concentration in on doping and temperature
are found to be in a perfect quantitative agreement with experimental data. As
follows from the model the pseudogap has superconducting nature and arises at
temperature in small clusters uniting a number of
NUC's due to large fluctuations of NUC occupation. Here and
are the superconducting transition temperatures of infinite and finite
clusters of NUC's, correspondingly. The calculated and
dependences are in accordance with experiment. The area between
and corresponds to the area of fluctuations
where small clusters fluctuate between superconducting and normal states owing
to fluctuations of NUC occupation. The results may serve as important arguments
in favor of the proposed model of HTSC.Comment: 12 pages, 7 figure
A practical implementation of the Overlap-Dirac operator
A practical implementation of the Overlap-Dirac operator
is presented. The implementation exploits
the sparseness of and does not require full storage. A simple application
to parity invariant three dimensional SU(2) gauge theory is carried out to
establish that zero modes related to topology are exactly reproduced on the
lattice.Comment: Y-axis label in figure correcte
The nonabelian tensor square of a Bieberbach group with symmetric point group of order six
Bieberbach groups are torsion free crystallographic groups. In this paper, our focus is given on the Bieberbach groups with symmetric point group of order six. The nonabelian tensor square of a group is a well known homological functor which can reveal the properties of a group. With the method developed for polycyclic groups, the nonabelian tensor square of one of the Bieberbach groups of dimension four with symmetric point group of order six is computed. The nonabelian tensor square of this group is found to be not abelian and its presentation is constructed
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