11,988 research outputs found
Finite-size scaling and the deconfinement transition in gauge theories
We introduce a new method for determining the critical indices of the
deconfinement transition in gauge theories. The method is based on the finite
size scaling behavior of the expectation value of simple lattice operators,
such as the plaquette. We test the method for the case of SU(3) pure gauge
theory in (2+1) dimensions and obtain a precise determination of the critical
index , in agreement with the prediction of the Svetitsky-Yaffe
conjecture.Comment: 6 pages. Several comments and one reference added, results unchange
Electromechanical wavelength tuning of double-membrane photonic crystal cavities
We present a method for tuning the resonant wavelength of photonic crystal
cavities (PCCs) around 1.55 um. Large tuning of the PCC mode is enabled by
electromechanically controlling the separation between two parallel InGaAsP
membranes. A fabrication method to avoid sticking between the membranes is
discussed. Reversible red/blue shifting of the symmetric/anti-symmetric modes
has been observed, which provides clear evidence of the electromechanical
tuning, and a maximum shift of 10 nm with < 6 V applied bias has been obtained.Comment: 9 pages, 3 figure
Mapping isoprene emissions over North America using formaldehyde column observations from space
We present a methodology for deriving emissions of volatile organic compounds (VOC) using space-based column observations of formaldehyde (HCHO) and apply it to data from the Global Ozone Monitoring Experiment (GOME) satellite instrument over North America during July 1996. The HCHO column is related to local VOC emissions, with a spatial smearing that increases with the VOC lifetime. Isoprene is the dominant HCHO precursor over North America in summer, and its lifetime (≃1 hour) is sufficiently short that the smearing can be neglected. We use the Goddard Earth Observing System global 3-D model of tropospheric chemistry (GEOS-CHEM) to derive the relationship between isoprene emissions and HCHO columns over North America and use these relationships to convert the GOME HCHO columns to isoprene emissions. We also use the GEOS-CHEM model as an intermediary to validate the GOME HCHO column measurements by comparison with in situ observations. The GEOS-CHEM model including the Global Emissions Inventory Activity (GEIA) isoprene emission inventory provides a good simulation of both the GOME data (r2 = 0.69, n = 756, bias = +11%) and the in situ summertime HCHO measurements over North America (r2 = 0.47, n = 10, bias = −3%). The GOME observations show high values over regions of known high isoprene emissions and a day-to-day variability that is consistent with the temperature dependence of isoprene emission. Isoprene emissions inferred from the GOME data are 20% less than GEIA on average over North America and twice those from the U.S. EPA Biogenic Emissions Inventory System (BEIS2) inventory. The GOME isoprene inventory when implemented in the GEOS-CHEM model provides a better simulation of the HCHO in situ measurements than either GEIA or BEIS2 (r2 = 0.71, n = 10, bias = −10%)
Do long-duration GRBs follow star formation?
We compare the luminosity function and rate inferred from the BATSE long
bursts peak flux distribution with those inferred from the Swift peak flux
distribution. We find that both the BATSE and the Swift peak fluxes can be
fitted by the same luminosity function and the two samples are compatible with
a population that follows the star formation rate. The estimated local long GRB
rate (without beaming corrections) varies by a factor of five from 0.05
Gpc^(-3)yr^(-1) for a rate function that has a large fraction of high redshift
bursts to 0.27 Gpc^(-3)yr^(-1) for a rate function that has many local ones. We
then turn to compare the BeppoSax/HETE2 and the Swift observed redshift
distributions and compare them with the predictions of the luminosity function
found. We find that the discrepancy between the BeppoSax/HETE2 and Swift
observed redshift distributions is only partially explained by the different
thresholds of the detectors and it may indicate strong selection effects. After
trying different forms of the star formation rate (SFR) we find that the
observed Swift redshift distribution, with more observed high redshift bursts
than expected, is inconsistent with a GRB rate that simply follows current
models for the SFR. We show that this can be explained by GRB evolution beyond
the SFR (more high redshift bursts). Alternatively this can also arise if the
luminosity function evolves and earlier bursts were more luminous or if strong
selection effects affect the redshift determination.Comment: 15 pages, 8 figures, accepted for publication in JCA
The spectrum of screening masses near T_c: predictions from universality
We discuss the spectrum of screening masses in a pure gauge theory near the
deconfinement temperature from the point of view of the dimensionally reduced
model describing the spontaneous breaking of the center symmetry. Universality
arguments can be used to predict the values of the mass ratios in the scaling
region of the deconfined phase when the transition is of second order. One such
prediction is that the scalar sector of the screening spectrum in SU(2) pure
gauge theory contains a bound state of the fundamental excitation,
corresponding through universality to the bound state found in the 3D Ising
model and phi^4 theory in the broken symmetry phase. A Monte Carlo evaluation
of the screening masses in the gauge theory confirms the validity of the
prediction. We briefly discuss the possibility of using similar arguments for
first order deconfinement transitions, and in particular for the physically
relevant case of SU(3).Comment: 12 pages, 3 figures. Some changes in the discussion, added
references, results unchanged. Version to appear in Phys. Rev.
Unbraiding the braided tensor product
We show that the braided tensor product algebra
of two module algebras of a quasitriangular Hopf algebra is
equal to the ordinary tensor product algebra of with a subalgebra of
isomorphic to , provided there exists a
realization of within . In other words, under this assumption we
construct a transformation of generators which `decouples' (i.e.
makes them commuting). We apply the theorem to the braided tensor product
algebras of two or more quantum group covariant quantum spaces, deformed
Heisenberg algebras and q-deformed fuzzy spheres.Comment: LaTex file, 29 page
Exclusive quasielastic production of dijets at hadronic colliders
We critically re-examine the calculation of central production of dijets in
quasi-elastic hadronic collisions. We find that the process is not dominated by
the perturbative contribution, and discuss several sources of uncertainties in
the calculation.Comment: 4 pages, talk given at Diffraction-2008, La Londe-les-Maures, France,
9-14 Sept 200
The Equilibrium Photoionized Absorber in 3C351
We present two ROSAT PSPC observations of the radio-loud, lobe-dominated
quasar 3C 351, which shows an `ionized absorber' in its X-ray spectrum. The
factor 1.7 change in flux in the 2~years between the observations allows
a test of models for this ionized absorber.
The absorption feature at ~0.7 keV (quasar frame) is present in both spectra
but with a lower optical depth when the source intensity - and hence the
ionizing flux at the absorber - is higher, in accordance with a simple,
single-zone, equilibrium photoionization model. Detailed modeling confirms this
agrement quantitatively. The maximum response time of 2 years allows us to
limit the gas density: n_e > 2 x 10^4 cm^{-3}; and the distance of the ionized
gas from the central source R < 19 pc. This produces a strong test for a
photoionized absorber in 3C~351: a factor 2 flux change in ~1 week in this
source must show non-equilibrium effects in the ionized absorber.Comment: 10 pages, 3 figures, accepted by Ap
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