13,235 research outputs found
Digital program for dynamics of non-rigid gravity gradient satellites
Digital program for dynamics of nonrigid gravity gradient satellite
Surveying the solar system by measuring angles and times: from the solar density to the gravitational constant
A surprisingly large amount of information on our solar system can be gained
from simple measurements of the apparent angular diameters of the sun and the
moon. This information includes the average density of the sun, the distance
between earth and moon, the radius of the moon, and the gravitational constant.
In this note it is described how these and other quantities can be obtained by
simple earthbound measurements of angles and times only, without using any
explicit information on distances between celestial bodies. The pedagogical and
historical aspects of these results are also discussed briefly.Comment: 12 pges, one figur
Viscous evolution of point vortex equilibria: The collinear state
When point vortex equilibria of the 2D Euler equations are used as initial
conditions for the corre- sponding Navier-Stokes equations (viscous), typically
an interesting dynamical process unfolds at short and intermediate time scales,
before the long time single peaked, self-similar Oseen vortex state dom-
inates. In this paper, we describe the viscous evolution of a collinear three
vortex structure that cor- responds to an inviscid point vortex fixed
equilibrium. Using a multi-Gaussian 'core-growth' type of model, we show that
the system immediately begins to rotate unsteadily, a mechanism we attribute to
a 'viscously induced' instability. We then examine in detail the qualitative
and quantitative evolution of the system as it evolves toward the long-time
asymptotic Lamb-Oseen state, showing the sequence of topological bifurcations
that occur both in a fixed reference frame, and in an appropriately chosen
rotating reference frame. The evolution of passive particles in this viscously
evolving flow is shown and interpreted in relation to these evolving streamline
patterns.Comment: 17 pages, 15 figure
Remarkable symmetries in the Milky Way disk's magnetic field
Using a new, expanded compilation of extragalactic source Faraday rotation
measures (RM) we investigate the broad underlying magnetic structure of the
Galactic disk at latitudes over all longitudes ,
where our total number of RM's in this low-latitude range of the Galactic sky
is comparable to those in the combined Canadian Galactic Plane Survey(CGPS) at
and the Southern Galactic Plane (SGPS)
survey. We report newly revealed, remarkably coherent patterns of RM at
from to and RM()
features of unprecedented clarity that replicate in with opposite sign on
opposite sides of the Galactic center. They confirm a highly patterned
bisymmetric field structure toward the inner disc, an axisymmetic pattern
toward the outer disc, and a very close coupling between the CGPS/SGPS RM's at
("mid-plane") and our new RM's up to ("near-plane").
Our analysis also shows the approximate -height -- the vertical height of
the coherent component of the disc field above the Galactic disc's mid-plane --
to be kpc out to kpc from the Sun. This identifies the
approximate height of the transition layer to the halo field structure. We find
no RM sign change across the plane within in any
longitude range. The prevailing {\it disc} field pattern, and its striking
degree of large scale ordering confirm that our side of the Milky Way has a
very organized underlying magnetic structure, for which the inward spiral pitch
angle is at all up to in
the inner semicircle of Galactic longitudes. It decreases to
toward the anticentre.Comment: 7 pages, 5 figures, Version 3. Accepted 2011 for publication in
Publications of the Astronomical Society of Australia(PASA
Exactly-solvable coupled-channel potential models of atom-atom magnetic Feshbach resonances from supersymmetric quantum mechanics
Starting from a system of radial Schr\"odinger equations with a vanishing
potential and finite threshold differences between the channels, a coupled exactly-solvable potential model is obtained with the help of a
single non-conservative supersymmetric transformation. The obtained potential
matrix, which subsumes a result obtained in the literature, has a compact
analytical form, as well as its Jost matrix. It depends on
unconstrained parameters and on one upper-bounded parameter, the factorization
energy. A detailed study of the model is done for the case: a
geometrical analysis of the zeros of the Jost-matrix determinant shows that the
model has 0, 1 or 2 bound states, and 0 or 1 resonance; the potential
parameters are explicitly expressed in terms of its bound-state energies, of
its resonance energy and width, or of the open-channel scattering length, which
solves schematic inverse problems. As a first physical application,
exactly-solvable atom-atom interaction potentials are constructed,
for cases where a magnetic Feshbach resonance interplays with a bound or
virtual state close to threshold, which results in a large background
scattering length.Comment: 19 pages, 15 figure
Completed cohomology of Shimura curves and a p-adic Jacquet-Langlands correspondence
We study indefinite quaternion algebras over totally real fields F, and give
an example of a cohomological construction of p-adic Jacquet-Langlands
functoriality using completed cohomology. We also study the (tame) levels of
p-adic automorphic forms on these quaternion algebras and give an analogue of
Mazur's `level lowering' principle.Comment: Updated version. Contains some minor corrections compared to the
published versio
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Paediatric gastroenterology evaluation of overweight and obese children referred from primary care for suspected non-alcoholic fatty liver disease.
BackgroundScreening overweight and obese children for non-alcoholic fatty liver disease (NAFLD) is recommended by paediatric and endocrinology societies. However, gastroenterology societies have called for more data before making a formal recommendation.AimTo determine whether the detection of suspected NAFLD in overweight and obese children through screening in primary care and referral to paediatric gastroenterology resulted in a correct diagnosis of NAFLD.MethodsInformation generated in the clinical evaluation of 347 children identified with suspected NAFLD through screening in primary care and referral to paediatric gastroenterology was captured prospectively. Diagnostic outcomes were reported. The diagnostic performance of two times the upper limit of normal (ULN) for alanine aminotransferase (ALT) was assessed.ResultsNon-alcoholic fatty liver disease was diagnosed in 55% of children identified by screening and referral. Liver disease other than NAFLD was present in 18% of those referred. Autoimmune hepatitis was the most common alternative diagnosis. Children with NAFLD had significantly (P < 0.05) higher screening ALT (98 ± 95) than children with liver disease other than NAFLD (86 ± 74). Advanced fibrosis was present in 11% of children. For the diagnosis of NAFLD, screening ALT two times the clinical ULN had a sensitivity of 57% and a specificity of 71%.ConclusionsScreening of overweight and obese children in primary care for NAFLD with referral to paediatric gastroenterology has the potential to identify clinically relevant liver pathology. Consensus is needed on how to value the risk and rewards of screening and referral, to identify children with liver disease in the most appropriate manner
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