1,295 research outputs found
Spectra and Symmetry in Nuclear Pairing
We apply the algebraic Bethe ansatz technique to the nuclear pairing problem
with orbit dependent coupling constants and degenerate single particle energy
levels. We find the exact energies and eigenstates. We show that for a given
shell, there are degeneracies between the states corresponding to less and more
than half full shell. We also provide a technique to solve the equations of
Bethe ansatz.Comment: 15 pages of REVTEX with 2 eps figure
Are X-ray properties of loose groups different from those of compact groups?
We compare the X-ray properties of loose and compact galaxy groups, using a
combined sample of 42 groups. We find that we are unable to separate loose and
compact groups on the luminosity-temperature relation, the luminosity-velocity
dispersion relation or the velocity dispersion-temperature relation using
equally weighted errors. This suggests that the distinction between compact and
loose groups is not a fundamental one, and we argue that a more useful
distinction is that between X-ray bright and X-ray faint systems. Given their
similarity in X-ray properties, we combine the loose and compact subsamples to
derive relations based on the full sample. This provides the highest
statistical quality results to date on the way in which the correlations in
X-ray properties of low mass systems depart from those seen in rich clusters.Comment: 6 pages, 6 figures. Accepted for publication in MNRA
Wide-bandwidth mode-hop-free tuning of extended-cavity GaN diode lasers
We present a new approach for extended-cavity diode-laser tuning to achieve wide mode-hop-free tuning ranges. By using a multiple piezoactuated grating mount, the cavity length and grating angle in the laser can be adjusted independently, allowing mode-hop-free tuning without the need for a mechanically optimized pivot-point mount. Furthermore, synchronized diode injection-current tuning allows diode lasers without antireflection coatings to be employed. In combination these two techniques make the construction of a cheap, efficient, and easily optimized extended-cavity diode laser possible. A theoretical analysis is presented for optimal control of piezoactuator displacements and injection current to achieve the widest possible mode-hop-free tuning ranges, and a comparison is made with measurements. The scheme is demonstrated for blue and violet GaN lasers operating at similar to 450 nm and similar to 410 nm, for which continuous tuning ranges exceeding 90 GHz have been achieved. Examples of applications of these lasers are also given
The Anisotropic Distribution of M 31 Satellite Galaxies: A Polar Great Plane of Early-Type Companions
The highly anisotropic distribution and apparent alignment of the Galactic
satellites in polar great planes begs the question how common such
distributions are. The satellite system of M31 is the only nearby system for
which we currently have sufficiently accurate distances to study the
three-dimensional satellite distribution. We present the spatial distribution
of the 15 presently known M31 companions in a coordinate system centered on M31
and aligned with its disk. Through a detailed statistical analysis we show that
the full satellite sample describes a plane that is inclined by -56 deg with
respect to the poles of M31 and that has an r.m.s. height of 100 kpc. With 88%
the statistical significance of this plane is low and it is unlikely to have a
physical meaning. The great stellar stream found near Andromeda is inclined to
this plane by 7 deg. There is little evidence for a Holmberg effect. If we
confine our analysis to early-type dwarfs, we find a best-fit polar plane
within 5 deg to 7 deg from the pole of M31. This polar great plane has a
statistical significance of 99.3% and includes all dSphs (except for And II),
M32, NGC 147, and PegDIG. The r.m.s. distance of these galaxies from the polar
plane is 16 kpc. The nearby spiral M33 has a distance of only about 3 kpc from
this plane, which points toward the M81 group. We discuss the anisotropic
distribution of M31's early-type companions in the framework of three
scenarios, namely as remnants of the break-up of a larger progenitor, as tracer
of a prolate dark matter halo, and as tracer of collapse along large-scale
filaments. (Abridged)Comment: 14 pages, 5 figures, accepted for publication in the Astronomical
Journa
NuSTAR Hard X-ray Observation of the Gamma-ray Binary Candidate HESS J1832-093
We present a hard X-ray observation of the TeV gamma-ray binary candidate
HESS J1832-093 coincident with supernova remnant (SNR) G22.7-0.2 using the
Nuclear Spectroscopic Telescope Array (NuSTAR). Non-thermal X-ray emission from
XMMU J183245-0921539, the X-ray source associated with HESS J1832-093, is
detected up to ~30 keV and is well-described by an absorbed power-law model
with the best-fit photon index . A re-analysis of archival
Chandra and XMM-Newton data finds that the long-term X-ray flux increase of
XMMU J183245-0921539 is % (90% C.L.), much less than previously
reported. A search for a pulsar spin period or binary orbit modulation yields
no significant signal to a pulse fraction limit of fp < 19% in the range 4 ms <
P < 40 ks. No red noise is detected in the FFT power spectrum to suggest active
accretion from a binary system. While further evidence is required, we argue
that the X-ray and gamma-ray properties of XMMU J183245-0921539 are most
consistent with a non-accreting binary generating synchrotron X- rays from
particle acceleration in the shock formed as a result of the pulsar and stellar
wind collision. We also report on three nearby hard X-ray sources, one of which
may be associated with diffuse emission from a fast-moving supernova fragment
interacting with a dense molecular cloud.Comment: ApJ in press. 9 page
Fluctuating Hemiparesis Secondary to Moyamoya Phenomenon in a Child with Down Syndrome: a case report
Moyamoya phenomenon is a term used to describe extensive collateralization of the circle of Willis arteries associated with severe unilateral or bilateral internal carotid artery stenosis or occlusion in the presence of certain conditions. Down syndrome is among these conditions. A case is reported of a young girl with Down syndrome who presented with fluctuating right-sided weakness and facial droop found to have cerebral ischemia. Subsequent investigations disclosed characteristic "puff of smoke" patterns on angiographic studies consistent with moyamoya phenomenon. The patient was initially treated with aspirin and eventually underwent an encephalomyosynangiosis. This young patient with Down syndrome and moyamoya phenomenon serves as a reminder of the association between these two conditions
Could the photon dispersion relation be non-linear ?
The free photon dispersion relation is a reference quantity for high
precision tests of Lorentz Invariance. We first outline theoretical approaches
to a conceivable Lorentz Invariance Violation (LIV). Next we address
phenomenological tests based on the propagation of cosmic rays, in particular
in Gamma Ray Bursts (GRBs). As a specific concept, which could imply LIV, we
then focus on field theory in a non-commutative (NC) space, and we present
non-perturbative results for the dispersion relation of the NC photon.Comment: 9 pages, 5 figures, talk presented at the 4. EU RTN Workshop on
"Constituents, Fundamental Forces and Symmetries of the Universe" in Varna,
Sept. 2008. References adde
From planning the port/city to planning the port-city : exploring the economic interface in European port cities
In last three decades, planning agencies of most ports have institutionally evolved into a (semi-) independent port authority. The rationale behind this process is that port authorities are able to react more quickly to changing logistical and spatial preferences of maritime firms, hence increasing the competitiveness of ports. Although these dedicated port authorities have proven to be largely successful, new economic, social, and environmental challenges are quickly catching up on these port governance models, and particularly leads to (spatial) policy ‘conflicts’ between port and city. This chapter starts by assessing this conflict and argue that the conflict is partly a result of dominant—often also academic—spatial representations of the port city as two separate entities. To escape this divisive conception of contemporary port cities, this chapter presents a relational visualisation method that is able to analyse the economic interface between port and city. Based on our results, we reflect back on our proposition and argue that the core challenge today for researchers and policy makers is acknowledging the bias of port/city, being arguably a self-fulfilling prophecy. Hence, we turn the idea of (planning the) port/city conflicts into planning the port-city’s strengths and weaknesses
Positron Annihilation in the Galaxy
The 511 keV line from positron annihilation in the Galaxy was the first γ-ray line detected to originate from outside our solar system. Going into the fifth decade since the discovery, the source of positrons is still unconfirmed and remains one of the enduring mysteries in γ-ray astronomy. With a large flux of ∼10−3 γ/cm2/s, after 15 years in operation INTEGRAL/SPI has detected the 511 keV line at >50σ and has performed high-resolution spectral studies which conclude that Galactic positrons predominantly annihilate at low energies in warm phases of the interstellar medium. The results from imaging are less certain, but show a spatial distribution with a strong concentration in the center of the Galaxy. The observed emission from the Galactic disk has low surface brightness and the scale height is poorly constrained, therefore, the shear number of annihilating positrons in our Galaxy is still not well know. Positrons produced in β+-decay of nucleosynthesis products, such as 26Al, can account for some of the annihilation emission in the disk, but the observed spatial distribution, in particular the excess in the Galactic bulge, remains difficult to explain. Additionally, one of the largest uncertainties in these studies is the unknown distance that positrons propagate before annihilation. In this paper, we will summarize the current knowledge base of Galactic positrons, and discuss how next-generation instruments could finally provide the answers.Non peer reviewedFinal Accepted Versio
Falsifiable predictions from semiclassical quantum gravity
Quantum gravity is studied in a semiclassical approximation and it is found
that to first order in the Planck length the effect of quantum gravity is to
make the low energy effective spacetime metric energy dependent. The
diffeomorphism invariance of the semiclassical theory forbids the appearance of
a preferred frame of reference, consequently the local symmetry of this
energy-dependent effective metric is a non-linear realization of the Lorentz
transformations, which renders the Planck energy observer independent. This
gives a form of deformed or doubly special relativity (DSR), previously
explored with Magueijo, called the rainbow metric. The general argument
determines the sign, but not the exact coefficient of the effect. But it
applies in all dimensions with and without supersymmetry, and is, at least to
leading order, universal for all matter couplings.
A consequence of DSR realized with an energy dependent effective metric is a
helicity independent energy dependence in the speed of light to first order in
the Planck length. However, thresholds for Tev photons and GZK protons are
unchanged from special relativistic predictions. These predictions of quantum
gravity are falsifiable by the upcoming AUGER and GLAST experiments.Comment: 9 page
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