15,797 research outputs found
Extrapolation Method for the No-Core Shell Model
Nuclear many-body calculations are computationally demanding. An estimate of
their accuracy is often hampered by the limited amount of computational
resources even on present-day supercomputers. We provide an extrapolation
method based on perturbation theory, so that the binding energy of a large
basis-space calculation can be estimated without diagonalizing the Hamiltonian
in this space. The extrapolation method is tested for 3H and 6Li nuclei. It
will extend our computational abilities significantly and allow for reliable
error estimates.Comment: 8 pages, 7 figures, PRC accepte
Somatostatin agonist pasireotide inhibits exercise stimulated growth in the male Siberian hamster (Phodopus sungorus)
R.Dumbell was supported by a University of Aberdeen PhD studentship and a research visit grant awarded by the British Society of Neuroendocrinology. Further support was provided by the Scottish Government Rural and Environment Science and Analytical Services Division (Barrett and the German Research Foundation (DFG; STE 331/8-1; Steinlechner lab). We are grateful for technical assistance from Dana Wilson at RINH and Siegried Hiliken at UVMH, and thank Dr Claus-Dieter Mayer of Biomathematics & Statistics Scotland for valuable advice on statistical analysis.Peer reviewedPostprin
Critical dynamics of diluted relaxational models coupled to a conserved density (diluted model C)
We consider the influence of quenched disorder on the relaxational critical
dynamics of a system characterized by a non-conserved order parameter coupled
to the diffusive dynamics of a conserved scalar density (model C). Disorder
leads to model A critical dynamics in the asymptotics, however it is the
effective critical behavior which is often observed in experiments and in
computer simulations and this is described by the full set of dynamical
equations of diluted model C. Indeed different scenarios of effective critical
behavior are predicted.Comment: 4 pages, 5 figure
Does the Isotropy of the CMB Imply a Homogeneous Universe? Some Generalised EGS Theorems
We demonstrate that the high isotropy of the Cosmic Microwave Background
(CMB), combined with the Copernican principle, is not sufficient to prove
homogeneity of the universe -- in contrast to previous results on this subject.
The crucial additional factor not included in earlier work is the acceleration
of the fundamental observers. We find the complete class of irrotational
perfect fluid spacetimes admitting an exactly isotropic radiation field for
every fundamental observer and show that are FLRW if and only if the
acceleration is zero. While inhomogeneous in general, these spacetimes all
possess three-dimensional symmetry groups, from which it follows that they also
admit a thermodynamic interpretation. In addition to perfect fluids models we
also consider multi-component fluids containing non-interacting radiation, dust
and a quintessential scalar field or cosmological constant in which the
radiation is isotropic for the geodesic (dust) observers. It is shown that the
non-acceleration of the fundamental observers forces these spacetimes to be
FLRW. While it is plausible that fundamental observers (galaxies) in the real
universe follow geodesics, it is strictly necessary to determine this from
local observations for the cosmological principle to be more than an
assumption. We discuss how observations may be used to test this.Comment: replaced with final version. Added discusion and ref
Fractal Weyl law behavior in an open, chaotic Hamiltonian system
We numerically show fractal Weyl law behavior in an open Hamiltonian system
that is described by a smooth potential and which supports numerous
above-barrier resonances. This behavior holds even relatively far away from the
classical limit. The complex resonance wave functions are found to be localized
on the fractal classical repeller.Comment: 4 pages, 3 figures. to appear in Phys Rev
The Molecular Interstellar Medium in Ultraluminous Infrared Galaxies
We present CO observations of a large sample of ultraluminous IR galaxies out
to z = 0.3. Most of the galaxies are interacting, but not completed mergers.
All but one have high CO(1-0) luminosities, log(Lco [K-km/s-pc^2]) = 9.92 +/-
0.12. The dispersion in Lco is only 30%, less than that in the FIR luminosity.
The integrated CO intensity correlates Strongly with the 100 micron flux
density, as expected for a black body model in which the mid and far IR
radiation are optically thick. We use this model to derive sizes of the FIR and
CO emitting regions and the enclosed dynamical masses. Both the IR and CO
emission originate in regions a few hundred parsecs in radius. The median value
of Lfir/Lco = 160 Lsun/(K-km/s-pc^2), within a factor of two of the black body
limit for the observed FIR temperatures. The entire ISM is a scaled up version
of a normal galactic disk with densities a factor of 100 higher, making even
the intercloud medium a molecular region. Using three different techniques of
H2 mass estimation, we conclude that the ratio of gas mass to Lco is about a
factor of four lower than for Galactic molecular clouds, but that the gas mass
is a large fraction of the dynamical mass. Our analysis of CO emission reduces
the H2 mass from previous estimates of 2-5e10 Msun to 0.4-1.5e10 Msun, which is
in the range found for molecular gas rich spiral galaxies. A collision
involving a molecular gas rich spiral could lead to an ultraluminous galaxy
powered by central starbursts triggered by the compression of infalling
preexisting GMC's.Comment: 34 pages LaTeX with aasms.sty, 14 Postscript figures, submitted to
ApJ Higher quality versions of Figs 2a-f and 7a-c available by anonymous FTP
from ftp://sbast1.ess.sunysb.edu/solomon/
Radio Astronomy
Contains research objectives and reports on two research projects.National Aeronautics and Space Administration (Grant NsG-250-62)National Aeronautics and Space Administration (Grant NsG-419)U. S. Navy (Office of Naval Research) under Contract Nonr-3963(02)-Task 2Lincoln Laboratory, Purchase Order DDL BB-107U. S. Air Force under Contract AF 19(628)-50
Optically Pumped NMR Measurements of the Electron Spin Polarization in GaAs Quantum Wells near Landau Level Filling Factor nu=1/3
The Knight shift of Ga-71 nuclei is measured in two different electron-doped
multiple quantum well samples using optically pumped NMR. These data are the
first direct measurements of the electron spin polarization,
P(nu,T)=/max, near nu=1/3. The P(T) data at nu=1/3 probe the
neutral spin-flip excitations of a fractional quantum Hall ferromagnet. In
addition, the saturated P(nu) drops on either side of nu=1/3, even in a Btot=12
Tesla field. The observed depolarization is quite small, consistent with an
average of about 0.1 spin-flips per quasihole (or quasiparticle), a value which
does not appear to be explicable by the current theoretical understanding of
the FQHE near nu=1/3.Comment: 4 pages (REVTEX), 5 eps figures embedded in text; minor changes,
published versio
Radio Astronomy
Contains research objectives and reports on three research projects.U. S. Navy (Office of Naval Research) under Contract Nonr- 3963(02)-Task 2National Aeronautics and Space Administration (Grant NsG-264-62)National Aeronautics and Space Administration (Grant NsG-250-62)National Aeronautics and Space Administration (Contract NaSr-l01
Non-commutative geometry and the standard model vacuum
The space of Dirac operators for the Connes-Chamseddine spectral action for
the standard model of particle physics coupled to gravity is studied. The model
is extended by including right-handed neutrino states, and the S0-reality axiom
is not assumed. The possibility of allowing more general fluctuations than the
inner fluctuations of the vacuum is proposed. The maximal case of all possible
fluctuations is studied by considering the equations of motion for the vacuum.
Whilst there are interesting non-trivial vacua with Majorana-like mass terms
for the leptons, the conclusion is that the equations are too restrictive to
allow solutions with the standard model mass matrix.Comment: 21 pages. v2: some comments improve
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