3,937 research outputs found
Infrared Photometry and Dust Absorption in Highly Inclined Spiral Galaxies
We present JHK surface photometry of 15 highly inclined, late-type (Sab-Sc)
spirals and investigate the quantitative effects of dust extinction. Using the
(J - H, H - K) two-color diagram, we compare the color changes along the minor
axis of each galaxy to the predictions from different models of radiative
transfer. Models in which scattering effects are significant and those with
more than a small fraction of the light sources located near the edge of the
dust distribution do not produce enough extinction to explain the observed
color gradients across disk absorption features. The optical depth in dust near
the plane as deduced from the color excess depends sensitively on the adopted
dust geometry, ranging from tau = 4 to 15 in the visual band. This suggests
that a realistic model of the dust distribution is required, even for infrared
photometry, to correct for dust extinction in the bulges of nearly edge-on
systems.Comment: Accepted for publication in the March 1996 AJ. LaTex source which
generates 27 pages of text and tables (no figures). Complete (text + figs)
compressed Postscript preprint is also available at
ftp://bessel.mps.ohio-state.edu/pub/terndrup/inclined.ps.Z (854 Mbyte
Mathematical Tools for Calculation of the Effective Action in Quantum Gravity
We review the status of covariant methods in quantum field theory and quantum
gravity, in particular, some recent progress in the calculation of the
effective action via the heat kernel method. We study the heat kernel
associated with an elliptic second-order partial differential operator of
Laplace type acting on smooth sections of a vector bundle over a Riemannian
manifold without boundary. We develop a manifestly covariant method for
computation of the heat kernel asymptotic expansion as well as new algebraic
methods for calculation of the heat kernel for covariantly constant background,
in particular, on homogeneous bundles over symmetric spaces, which enables one
to compute the low-energy non-perturbative effective action.Comment: 71 pages, 2 figures, submitted for publication in the Springer book
(in preparation) "Quantum Gravity", edited by B. Booss-Bavnbek, G. Esposito
and M. Lesc
On the origin of the difference between time and space
We suggest that the difference between time and space is due to spontaneous
symmetry breaking. In a theory with spinors the signature of the metric is
related to the signature of the Lorentz-group. We discuss a higher symmetry
that contains pseudo-orthogonal groups with arbitrary signature as subgroups.
The fundamental asymmetry between time and space arises then as a property of
the ground state rather than being put into the formulation of the theory a
priori. We show how the complex structure of quantum field theory as well as
gravitational field equations arise from spinor gravity - a fundamental spinor
theory without a metric.Comment: 4 page
The Existence of Einstein Static Universes and their Stability in Fourth order Theories of Gravity
We investigate whether or not an Einstein Static universe is a solution to
the cosmological equations in gravity. It is found that only one class
of theories admits an Einstein Static model, and that this class is
neutrally stable with respect to vector and tensor perturbations for all
equations of state on all scales. Scalar perturbations are only stable on all
scales if the matter fluid equation of state satisfies
. This result is remarkably similar to
the GR case, where it was found that the Einstein Static model is stable for
.Comment: Minor changes, To appear in PR
Semiclassical thermodynamics of scalar fields
We present a systematic semiclassical procedure to compute the partition
function for scalar field theories at finite temperature. The central objects
in our scheme are the solutions of the classical equations of motion in
imaginary time, with spatially independent boundary conditions. Field
fluctuations -- both field deviations around these classical solutions, and
fluctuations of the boundary value of the fields -- are resummed in a Gaussian
approximation. In our final expression for the partition function, this
resummation is reduced to solving certain ordinary differential equations.
Moreover, we show that it is renormalizable with the usual 1-loop counterterms.Comment: 24 pages, 5 postscript figure
Buckfast : laat de bijen het maar vertellen
De Buckfast-bijen danken hun ontstaan aan Broeder Adam (1 898-1 996). In het Benedictijner klooster Buckfast te Buckfastleigh in Devon werd hij in 1919 het hoofd van de klooster-imkerij. Het inheemse Engelse ras was toen vrijwel heel uitgestonren als gevolg van de tracheeën-mijt. De bijen die op de Buckfast Abdij waren overgebleven bestonden uit Ligurische bijen (Ligustica) en kruisingen daarvan met darren van de Engelse bij. In 1930 werd een een kruising uitgevoerd tussen Franse koninginnen en darren van het toenmalige Buckfast-kunstras. Na 10 jaar van strenge selectie werd het kruisingsresultaat toegevoegd aan de Buckfast-bij
Correlated Binomial Models and Correlation Structures
We discuss a general method to construct correlated binomial distributions by
imposing several consistent relations on the joint probability function. We
obtain self-consistency relations for the conditional correlations and
conditional probabilities. The beta-binomial distribution is derived by a
strong symmetric assumption on the conditional correlations. Our derivation
clarifies the 'correlation' structure of the beta-binomial distribution. It is
also possible to study the correlation structures of other probability
distributions of exchangeable (homogeneous) correlated Bernoulli random
variables. We study some distribution functions and discuss their behaviors in
terms of their correlation structures.Comment: 12 pages, 7 figure
Environmental pollutants in blood donors: The multicentre Norwegian donor study
Objectives - The aim of this study was to measure blood concentrations of environmental pollutants in Norwegian donors and evaluate the risk of pollutant exposure through blood transfusions.
Background - Transfused blood may be a potential source of exposure to heavy metals and organic pollutants and presents a risk to vulnerable patient groups such as premature infants.
Methods/Materials - Donors were randomly recruited from three Norwegian blood banks: in Bergen, TromsĂž and Kirkenes. Selected heavy metals were measured in whole blood using inductively coupled plasma mass spectrometry (ICPâMS), and perfluoroalkyl substances (PFAS) were measured in serum by ultrahighâpressure liquid chromatography coupled with a tripleâquadrupole mass spectrometer (UHPLCâMS/MS).
Results - Almost 18% of blood donors had lead concentrations over the limit suggested for transfusions in premature infants (0.09âÎŒmol/L). About 11% of all donors had mercury concentrations over the suggested limit of 23.7 nmol/L. Cadmium was higher than the limit, 16ânmol/L, in 4% of donors. Perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) concentrations were over the suggested limit of 0.91âng/mL in 68% and 100% of the donors, respectively. PFAS concentrations and heavy metal concentrations increased with donor's age.
Conclusion - A considerable percentage of donors had lead, PFOS and PFOA concentrations over the suggested limits. In addition, at each study site, there were donors with high mercury and cadmium concentrations. Selecting young donors for transfusions or measurements of pollutants in donor blood may be a feasible approach to avoid exposure through blood transfusions to vulnerable groups of patients such as premature infants
Does gravitational wave propagate in the five dimensional space-time with Kaluza-Klein monopole?
The behavior of small perturbations around the Kaluza-Klein monopole in the
five dimensional space-time is investigated. The fact that the odd parity
gravitational wave does not propagate in the five dimensional space-time with
Kaluza-Klein monopole is found provided that the gravitational wave is constant
in the fifth direction.Comment: 10 @ages, LATE
Hin-mediated DNA knotting and recombining promote replicon dysfunction and mutation
<p>Abstract</p> <p>Background</p> <p>The genetic code imposes a dilemma for cells. The DNA must be long enough to encode for the complexity of an organism, yet thin and flexible enough to fit within the cell. The combination of these properties greatly favors DNA collisions, which can knot and drive recombination of the DNA. Despite the well-accepted propensity of cellular DNA to collide and react with itself, it has not been established what the physiological consequences are.</p> <p>Results</p> <p>Here we analyze the effects of recombined and knotted plasmids in <it>E. coli </it>using the Hin site-specific recombination system. We show that Hin-mediated DNA knotting and recombination (i) promote replicon loss by blocking DNA replication; (ii) block gene transcription; and (iii) cause genetic rearrangements at a rate three to four orders of magnitude higher than the rate for an unknotted, unrecombined plasmid.</p> <p>Conclusion</p> <p>These results show that DNA reactivity leading to recombined and knotted DNA is potentially toxic and may help drive genetic evolution.</p
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