1,804 research outputs found
Equal-time correlation function for directed percolation
We suggest an equal-time n-point correlation function for systems in the
directed percolation universality class which is well defined in all phases and
independent of initial conditions. It is defined as the probability that all
points are connected with a common ancestor in the past by directed paths.Comment: LaTeX, 12 pages, 8 eps figure
On the feasibility of studying vortex noise in 2D superconductors with cold atoms
We investigate the feasibility of using ultracold neutral atoms trapped near
a thin superconductor to study vortex noise close to the
Kosterlitz-Thouless-Berezinskii transition temperature. Alkali atoms such as
rubidium probe the magnetic field produced by the vortices. We show that the
relaxation time of the Zeeman sublevel populations can be conveniently
adjusted to provide long observation times. We also show that the transverse
relaxation times for Zeeman coherences are ideal for studying the vortex
noise. We briefly consider the motion of atom clouds held close to the surface
as a method for monitoring the vortex motion.Comment: 4 pages, 1 figur
Novel method for the measurement of liquid film thickness during fuel spray impingement on surfaces
This paper describes the development and application of a novel optical technique for the measurement of liquid film thickness formed on surfaces during the impingement of automotive fuel sprays. The technique makes use of the change of the light scattering characteristics of a metal surface with known roughness, when liquid is deposited. Important advantages of the technique over previously established methods are the ability to measure the time-dependent spatial distribution of the liquid film without a need to add a fluorescent tracer to the liquid, while the measurement principle is not influenced by changes of the pressure and temperature of the liquid or the surrounding gas phase. Also, there is no need for non-fluorescing surrogate fuels. However, an in situ calibration of the dependence of signal intensity on liquid film thickness is required. The developed method can be applied to measure the time-dependent and two-dimensional distribution of the liquid fuel film thickness on the piston or the liner of gasoline direct injection (GDI) engines. The applicability of this technique was evaluated with impinging sprays of several linear alkanes and alcohols with different thermo-physical properties. The surface temperature of the impingement plate was controlled to simulate the range of piston surface temperatures inside a GDI engine. Two sets of liquid film thickness measurements were obtained. During the first set, the surface temperature of the plate was kept constant, while the spray of different fuels interacted with the surface. In the second set, the plate temperature was adjusted to match the boiling temperature of each fuel. In this way, the influence of the surface temperature on the liquid film created by the spray of different fuels and their evaporation characteristics could be demonstrated
Kinetics of the long-range spherical model
The kinetic spherical model with long-range interactions is studied after a
quench to or to . For the two-time response and correlation
functions of the order-parameter as well as for composite fields such as the
energy density, the ageing exponents and the corresponding scaling functions
are derived. The results are compared to the predictions which follow from
local scale-invariance.Comment: added "fluctuation-dissipation ratios"; fixed typo
On the universality of luminosity-metallicity and mass-metallicity relations for compact star-forming galaxies at redshifts 0 < z < 3
We study relations between global characteristics of low-redshift (0 < z < 1)
compact star-forming galaxies, including absolute optical magnitudes, Hbeta
emission-line luminosities (or equivalently star-formation rates), stellar
masses, and oxygen abundances. The sample consists of 5182 galaxies with
high-excitation HII regions selected from the SDSS DR7 and SDSS/BOSS DR10
surveys adopting a criterion [OIII]4959/Hbeta > 1. These data were combined
with the corresponding data for high-redshift (2 < z < 3) star-forming
galaxies. We find that in all diagrams low-z and high-z star-forming galaxies
are closely related indicating a very weak dependence of metallicity on stellar
mass, redshift, and star-formation rate. This finding argues in favour of the
universal character of the global relations for compact star-forming galaxies
with high-excitation HII regions over redshifts 0 < z < 3.Comment: 13 pages, 10 figures, accepted for publication in MNRA
Searching for metal-deficient emission-line galaxy candidates: the final sample of the SDSS DR12 galaxies
We present a spectroscopic study of metal-deficient dwarf galaxy candidates,
selected from the SDSS DR12. The oxygen abundances were derived using the
direct method in galaxies with the electron temperature-sensitive emission line
[OIII]4363A measured with an accuracy better than 30%. The oxygen abundances
for the remaining galaxies with larger uncertainties of the [OIII]4363A line
fluxes were calculated using a strong-line semi-empirical method by Izotov and
Thuan. The resulting sample consists of 287 low-metallicity candidates with
oxygen abundances below 12+logO/H=7.65 including 23 extremely metal-deficient
(XMD) candidates with 12+log O/H<7.35. Ten out of sixteen XMDs known so far (or
~60%) have been discovered by our team using the direct method. Three XMDs were
found in the present study. We study relations between global parameters of
low-metallicity galaxies, including absolute optical magnitudes, Hbeta
luminosities (or equivalently star formation rates), stellar masses,
mid-infrared colours, and oxygen abundances. Low-metallicity and XMD galaxies
strongly deviate to lower metallicities in L-Z, L(Hbeta)-Z and Mstar-Z diagrams
than in relations obtained for large samples of low-redshift, star-forming
galaxies with non-restricted metallicities. These less chemically evolved
galaxies with stellar masses ~10^6-10^8Msun, Hbeta luminosities ~10^38-10^41
erg/s, SFR~0.01-1.0Msun/yr, and sSFR~50 Gyr^-1 have physical conditions which
may be characteristic of high-redshift low-mass star-forming galaxies which are
still awaiting discovery.Comment: 13 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
On the predictive power of Local Scale Invariance
Local Scale Invariance (LSI) is a theory for anisotropic critical phenomena
designed in the spirit of conformal invariance. For a given representation of
its generators it makes non-trivial predictions about the form of universal
scaling functions. In the past decade several representations have been
identified and the corresponding predictions were confirmed for various
anisotropic critical systems. Such tests are usually based on a comparison of
two-point quantities such as autocorrelation and response functions. The
present work highlights a potential problem of the theory in the sense that it
may predict any type of two-point function. More specifically, it is argued
that for a given two-point correlator it is possible to construct a
representation of the generators which exactly reproduces this particular
correlator. This observation calls for a critical examination of the predictive
content of the theory.Comment: 17 pages, 2 eps figure
The Mg II 2797, 2803 emission in low-metallicity star-forming galaxies from the SDSS
We present 65 Sloan Digital Sky Survey (SDSS) spectra of 62 star-forming
galaxies with oxygen abundances 12 + logO/H ~ 7.5-8.4. Redshifts of selected
galaxies are in the range z~0.36-0.70. This allows us to detect the redshifted
MgII 2797,2803 emission lines. Our aim is to use these lines for the magnesium
abundance determination. The MgII emission was detected in ~2/3 of the
galaxies. We find that the MgII 2797 emission-line intensity follows a trend
with the excitation parameter x= O^{2+}/O that is similar to that predicted by
CLOUDY photoionised HII region models, suggesting a nebular origin of MgII
emission. The Mg/O abundance ratio is lower by a factor ~2 than the solar
ratio. This is probably the combined effect of interstellar MgII absorption and
depletion of Mg onto dust. However, the effect of dust depletion in selected
galaxies, if present, is small, by a factor of ~2 lower than that of iron.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 8
figure
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