17,421 research outputs found
Atmospheric densities from Explorer 17 density gauges and a comparison with satellite drag data
Atmospheric density data from Explorer XVII GAUGES and satellite drag dat
Quantum-state tomography for spin-l systems
We show that the density matrix of a spin-l system can be described entirely
in terms of the measurement statistics of projective spin measurements along a
minimum of 4l+1 different spin directions. It is thus possible to represent the
complete quantum statistics of any N-level system within the spherically
symmetric three dimensional space defined by the spin vector. An explicit
method for reconstructing the density matrix of a spin-1 system from the
measurement statistics of five non-orthogonal spin directions is presented and
the generalization to spin-l systems is discussed.Comment: 10 pages, including 2 tables, minor modifications in section II,
final version for publication in Phys. Rev.
Improved bounds on the set A(A+1)
For a subset A of a field F, write A(A + 1) for the set {a(b + 1):a,b\in A}.
We establish new estimates on the size of A(A+1) in the case where F is either
a finite field of prime order, or the real line.
In the finite field case we show that A(A+1) is of cardinality at least
C|A|^{57/56-o(1)} for some absolute constant C, so long as |A| < p^{1/2}. In
the real case we show that the cardinality is at least C|A|^{24/19-o(1)}. These
improve on the previously best-known exponents of 106/105-o(1) and 5/4
respectively
From Microscales to Macroscales in 3D: Selfconsistent Equation of State for Supernova and Neutron Star Models
First results from a fully self-consistent, temperature-dependent equation of
state that spans the whole density range of neutron stars and supernova cores
are presented. The equation of state (EoS) is calculated using a mean-field
Hartree-Fock method in three dimensions (3D). The nuclear interaction is
represented by the phenomenological Skyrme model in this work, but the EoS can
be obtained in our framework for any suitable form of the nucleon-nucleon
effective interaction. The scheme we employ naturally allows effects such as
(i) neutron drip, which results in an external neutron gas, (ii) the variety of
exotic nuclear shapes expected for extremely neutron heavy nuclei, and (iii)
the subsequent dissolution of these nuclei into nuclear matter. In this way,
the equation of state is calculated across phase transitions without recourse
to interpolation techniques between density regimes described by different
physical models. EoS tables are calculated in the wide range of densities,
temperature and proton/neutron ratios on the ORNL NCCS XT3, using up to 2000
processors simultaneously.Comment: 6 pages, 11 figures. Published in conference proceedings Journal of
Physics: Conference Series 46 (2006) 408. Extended version to be submitted to
Phys. Rev.
Influence of viscoelasticity and interfacial slip on acoustic wave sensors
Acoustic wave devices with shear horizontal displacements, such as quartz crystal microbalances (QCM) and shear horizontally polarised surface acoustic wave (SH-SAW) devices provide sensitive probes of changes at solid-solid and solid- liquid interfaces. Increasingly the surfaces of acoustic wave devices are being chemically or physically modified to alter surface adhesion or coated with one or more layers to amplify their response to any change of mass or material properties. In this work, we describe a model that provides a unified view of the modification in the shear motion in acoustic wave systems by multiple finite thickness loadings of viscoelastic fluids. This model encompasses QCM and other classes of acoustic wave devices based on a shear motion of the substrate surface and is also valid whether the coating film has a liquid or solid character. As a specific example, the transition of a coating from liquid to solid is modelled using a single relaxation time Maxwell model. The correspondence between parameters from this physical model and parameters from alternative acoustic impedance models is given explicitly. The characteristic changes in QCM frequency and attenuation as a function of thickness are illustrated for a single layer device as the coating is varied from liquid-like to that of an amorphous solid. Results for a double layer structure are given explicitly and the extension of the physical model to multiple layers is described
Levinson's Theorem for Non-local Interactions in Two Dimensions
In the light of the Sturm-Liouville theorem, the Levinson theorem for the
Schr\"{o}dinger equation with both local and non-local cylindrically symmetric
potentials is studied. It is proved that the two-dimensional Levinson theorem
holds for the case with both local and non-local cylindrically symmetric cutoff
potentials, which is not necessarily separable. In addition, the problems
related to the positive-energy bound states and the physically redundant state
are also discussed in this paper.Comment: Latex 11 pages, no figure, submitted to J. Phys. A Email:
[email protected], [email protected]
Efficacy of crustal superfluid neutrons in pulsar glitch models
In order to assess the ability of purely crust-driven glitch models to match
the observed glitch activity in the Vela pulsar, we conduct a systematic
analysis of the dependence of the fractional moment of inertia of the inner
crustal neutrons on the stiffness of the nuclear symmetry energy at saturation
density . We take into account both crustal entrainment and the fact that
only a fraction of the core neutrons may couple to the crust on the
glitch-rise timescale. We use a set of consistently-generated crust and core
compositions and equations-of-state which are fit to results of low-density
pure neutron matter calculations. When entrainment is included at the level
suggested by recent microscopic calculations and the core is fully coupled to
the crust, the model is only able to account for the Vela glitch activity for a
1.4 star if the equation of state is particularly stiff MeV.
However, an uncertainty of about 10\% in the crust-core transition density and
pressure allows for the Vela glitch activity to be marginally accounted for in
the range MeV consistent with a range of experimental results.
Alternatively, only a small amount of core neutrons need be involved. If less
than 50\% of the core neutrons are coupled to the crust during the glitch, we
can also account for the Vela glitch activity using crustal neutrons alone for
EOSs consistent with the inferred range of . We also explore the possibility
of Vela being a high-mass neutron star, and of crustal entrainment being
reduced or enhanced relative to its currently predicted values.Comment: 10 pages, 6 figure
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