2,964 research outputs found
Aerosol light absorption in the North Atlantic: trends and seasonal characteristics during the period 1989 to 2003
Aerosol light attenuation on quartz fibre filters has been measured since February 1989 at the Mace Head Atmospheric Research station near Carna, Co. Galway, Ireland, using an Aethalometer. <P style='line-height: 20px;'> The frequency of occurrence of the hourly averaged aerosol absorption data is found to be bimodally distributed. The two modes result from clean marine air and anthropogenically polluted continental air both being advected to the station dependent on the prevailing wind direction. The hourly averages of the marine portion of the aerosol light absorption are found to follow closely a lognormal distribution with a geometric mean of 0.310 Mm<sup>-1</sup>. The hourly averages of continental sector aerosol absorption are neither normally nor lognormally distributed and have an arithmetic mean of 6.36 Mm<sup>-1</sup>, indicating the presence of anthropogenic sources for BC east of the Mace Head station. <P style='line-height: 20px;'> The time series of the monthly averaged attenuation coefficient σ<sub>att</sub> of both marine and continental sector aerosol shows an increase from 1989 to 1997 and a levelling off thereafter. <P style='line-height: 20px;'> The monthly maximum of marine sector σ<sub>att</sub> is found in May. Trend and seasonal characteristics of the clean marine aerosol attenuation coefficients observed at Mace Head appear to be driven by meteorological factors, as indicated by rainfall data and by trends in the North Atlantic Oscillation (NAO) indices. The observed increasing trends of the continental sector σ<sub>att</sub> from 1989 up to 1997 are possibly related to changes in BC emissions over Ireland, calculated from UNSTAT (2002) fuel consumption data
Schr\"odinger operators with complex potential but real spectrum
Several aspects of complex-valued potentials generating a real and positive
spectrum are discussed. In particular, we construct complex-valued potentials
whose corresponding Schr\"odinger eigenvalue problem can be solved
analytically.Comment: 10, pages, LaTeX 2.09, 6 Postscript figures, uses amsfont, figures
available at http://faupt100.physik.uni-erlangen.de/junker/papers95-99.ht
A Precise Determination of the Pion-Nuclear Coupling Parameter from Weak Processes in
We utilize precise weak interaction experiments on atomic muon capture and beta decay in the A = 3 nuclei, and take into account the effects of nuclear "anomalous thresholds" to extract the pseudoscalar pi-^3He-^3H coupling parameter, G^{eff}(m_\pi^2) = 45.8+- 2.4. This is an order of magnitude improvement in precision over that from the use of pion-nuclear scattering data and dispersion relations
Binary Black Hole Coalescence in Semi-Analytic Puncture Evolution
Binary black-hole coalescence is treated semi-analytically by a novel
approach. Our prescription employs the conservative Skeleton Hamiltonian that
describes orbiting Brill-Lindquist wormholes (termed punctures in Numerical
Relativity) within a waveless truncation to the Einstein field equations [G.
Faye, P. Jaranowski and G. Sch\"afer, Phys. Rev. D {\bf 69}, 124029 (2004)]. We
incorporate, in a transparent Hamiltonian way and in Burke-Thorne gauge
structure, the effects of gravitational radiation reaction into the above
Skeleton dynamics with the help of 3.5PN accurate angular momentum flux for
compact binaries in quasi-circular orbits to obtain a Semi-Analytic Puncture
Evolution to model merging black-hole binaries. With the help of the TaylorT4
approximant at 3.5PN order, we perform a {\it first-order} comparison between
gravitational wave phase evolutions in Numerical Relativity and our approach
for equal-mass binary black holes. This comparison reveals that a modified
Skeletonian reactive dynamics that employs flexible parameters will be required
to prevent the dephasing between our scheme and Numerical Relativity, similar
to what is pursued in the Effective One Body approach. A rough estimate for the
gravitational waveform associated with the binary black-hole coalescence in our
approach is also provided.Comment: 16 pages, 5 figure
An energy-based material model for the simulation of shape memory alloys under complex boundary value problems
Shape memory alloys are remarkable 'smart' materials used in a broad spectrum
of applications, ranging from aerospace to robotics, thanks to their unique
thermomechanical coupling capabilities. Given the complex properties of shape
memory alloys, which are largely influenced by thermal and mechanical loads, as
well as their loading history, predicting their behavior can be challenging.
Consequently, there exists a pronounced demand for an efficient material model
to simulate the behavior of these alloys. This paper introduces a material
model rooted in Hamilton's principle. The key advantages of the presented
material model encompass a more accurate depiction of the internal variable
evolution and heightened robustness. As such, the proposed material model
signifies an advancement in the realistic and efficient simulation of shape
memory alloys
Improved approximate inspirals of test-bodies into Kerr black holes
We present an improved version of the approximate scheme for generating
inspirals of test-bodies into a Kerr black hole recently developed by
Glampedakis, Hughes and Kennefick. Their original "hybrid" scheme was based on
combining exact relativistic expressions for the evolution of the orbital
elements (the semi-latus rectum p and eccentricity e) with approximate,
weak-field, formula for the energy and angular momentum fluxes, amended by the
assumption of constant inclination angle, iota, during the inspiral. Despite
the fact that the resulting inspirals were overall well-behaved, certain
pathologies remained for orbits in the strong field regime and for orbits which
are nearly circular and/or nearly polar. In this paper we eliminate these
problems by incorporating an array of improvements in the approximate fluxes.
Firstly, we add certain corrections which ensure the correct behaviour of the
fluxes in the limit of vanishing eccentricity and/or 90 degrees inclination.
Secondly, we use higher order post-Newtonian formulae, adapted for generic
orbits. Thirdly, we drop the assumption of constant inclination. Instead, we
first evolve the Carter constant by means of an approximate post-Newtonian
expression and subsequently extract the evolution of iota. Finally, we improve
the evolution of circular orbits by using fits to the angular momentum and
inclination evolution determined by Teukolsky based calculations. As an
application of the improved scheme we provide a sample of generic Kerr
inspirals and for the specific case of nearly circular orbits we locate the
critical radius where orbits begin to decircularise under radiation reaction.
These easy-to-generate inspirals should become a useful tool for exploring LISA
data analysis issues and may ultimately play a role in source detection.Comment: 25 pages, 14 figures, some typos corrected, short section on
conservative corrections added, minor changes for consistency with published
versio
More on coupling coefficients for the most degenerate representations of SO(n)
We present explicit closed-form expressions for the general group-theoretical
factor appearing in the alpha-topology of a high-temperature expansion of
SO(n)-symmetric lattice models. This object, which is closely related to
6j-symbols for the most degenerate representation of SO(n), is discussed in
detail.Comment: 9 pages including 1 table, uses IOP macros Update of Introduction and
Discussion, References adde
Phase Coherence and Superfluid-Insulator Transition in a Disordered Bose-Einstein Condensate
We have studied the effects of a disordered optical potential on the
transport and phase coherence of a Bose-Einstein condensate (BEC) of 7Li atoms.
At moderate disorder strengths (V_D), we observe inhibited transport and
damping of dipole excitations, while in time-of-flight images, random but
reproducible interference patterns are observed. In-situ images reveal that the
appearance of interference is correlated with density modulation, without
complete fragmentation. At higher V_D, the interference contrast diminishes as
the BEC fragments into multiple pieces with little phase coherence.Comment: 4 pages, 5 figures, distortions in figures 1 and 4 have been fixed in
version 3. This paper has been accepted to PR
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