624 research outputs found

### Probing the Equation of State of Nuclear Matter via Neutron Star Asteroseismology

We general relativistically calculate the frequency of fundamental torsional
oscillations of neutron star crusts, where we focus on the crystalline
properties obtained from macroscopic nuclear models in a way depending on the
equation of state of nuclear matter. We find that the calculated frequency is
sensitive to the density dependence of the symmetry energy, but almost
independent of the incompressibility of symmetric nuclear matter. By
identifying the lowest-frequency quasi-periodic oscillation in giant flares
observed from soft gamma-ray repeaters as the fundamental torsional mode and
allowing for the dependence of the calculated frequency on stellar models, we
provide a lower limit of the density derivative of the symmetry energy as
$L\simeq 50$ MeV.Comment: 4 pages, 4 figure

### An Approach to Learning Strategy Training for Groups of Secondary Students

This research was published by the KU Center for Research on Learning, formerly known as the University of Kansas Institute for Research in Learning Disabilities.The purpose of this article is to outline specific instructional procedures that can be used effectively to teach LD adolescents in small-group settings. Specifically, the article covers the following: a brief review of research on 1 earning strategies conducted by the University of Kansas
Institute for Research in Learning Disabilities, (KU-IRLD); a set of instructional procedures for teaching specific learning strategies to groups of LD adolescents; and a set of general principles for teaching learning strategies to groups of students

### Crustal Oscillations of Slowly Rotating Relativistic Stars

We study low-amplitude crustal oscillations of slowly rotating relativistic
stars consisting of a central fluid core and an outer thin solid crust. We
estimate the effect of rotation on the torsional toroidal modes and on the
interfacial and shear spheroidal modes. The results compared against the
Newtonian ones for wide range of neutron star models and equations of state.Comment: 15 page

### Cosmological Perturbations of Quantum-Mechanical Origin and Anisotropy of the Microwave Background

Cosmological perturbations generated quantum-mechanically (as a particular
case, during inflation) possess statistical properties of squeezed quantum
states. The power spectra of the perturbations are modulated and the angular
distribution of the produced temperature fluctuations of the CMBR is quite
specific. An exact formula is derived for the angular correlation function of
the temperature fluctuations caused by squeezed gravitational waves. The
predicted angular pattern can, in principle, be revealed by the COBE-type
observations.Comment: 9 pages, WUGRAV-92-17 Accepted for Publication in Phys. Rev. Letters
(1993

### Quantum teleportation with squeezed vacuum states

We show how the partial entanglement inherent in a two mode squeezed vacuum
state admits two different teleportation protocols. These two protocols refer
to the different kinds of joint measurements that may be made by the sender.
One protocol is the recently implemented quadrature phase approach of
Braunstein and Kimble[Phys. Rev. Lett.{\bf 80}, 869 (1998)]. The other is based
on recognising that a two mode squeezed vacuum state is also entangled with
respect to photon number difference and phase sum. We show that this protocol
can also realise teleportation, however limitations can arise due to the fact
that the photon number spectrum is bounded from below by zero. Our examples
show that a given entanglement resource may admit more than a single
teleportation protocol and the question then arises as to what is the optimum
protocol in the general case

### Discovery of Fast X-ray Oscillations During the 1998 Giant Flare from SGR 1900+14

We report the discovery of complex high frequency variability during the
August 27, 1998 giant flare from SGR 1900+14 using the Rossi X-ray Timing
Explorer (RXTE). We detect an 84 Hz oscillation (QPO) during a 1 s interval
beginning approximately 1 min after the initial hard spike. The modulation
amplitude is energy dependent, reaching a maximum of 26% (rms) for photons
above 30 keV, and is not detected below 11 keV, with a 90% confidence upper
limit of 14% (rms). Remarkably, additional QPOs are detected in the average
power spectrum of data segments centered on the rotational phase at which the
84 Hz signal was detected. Two signals, at 53.5 and 155.1 Hz, are strongly
detected, while a third feature at 28 Hz is found with lower significance.
These QPOs are not detected at other rotational phases. The phenomenology seen
in the SGR 1900+14 flare is similar to that of QPOs recently reported by Israel
et al. from the December 27, 2004 flare from SGR 1806-20, suggesting they may
have a common origin, perhaps torsional vibrations of the neutron star crust.
Indeed, an association of the four frequencies (in increasing order) found in
SGR 1900+14 with l = 2, 4, 7, and 13 toroidal modes appears plausible. We
discuss our findings in the context of this model and show that if the stars
have similar masses then the magnetic field in SGR 1806-20 must be about twice
as large as in SGR 1900+14, broadly consistent with magnetic field estimates
from pulse timing.Comment: 13 Pages, 5 figures, AASTeX, accepted for publication in the
Astrophysical Journal Letter

### Oscillations of rapidly rotating relativistic stars

Non-axisymmetric oscillations of rapidly rotating relativistic stars are
studied using the Cowling approximation. The oscillation spectra have been
estimated by Fourier transforming the evolution equations describing the
perturbations. This is the first study of its kind and provides information on
the effect of fast rotation on the oscillation spectra while it offers the
possibility in studying the complete problem by including spacetime
perturbations. Our study includes both axisymmetric and non-axisymmetric
perturbations and provides limits for the onset of the secular bar mode
rotational instability. We also present approximate formulae for the dependence
of the oscillation spectrum from rotation. The results suggest that it is
possible to extract the relativistic star's parameters from the observed
gravitational wave spectrum.Comment: this article will be published in Physical Review

### Maximum elastic deformations of relativistic stars

We present a method for calculating the maximum elastic quadrupolar
deformations of relativistic stars, generalizing the previous Newtonian,
Cowling approximation integral given by [G. Ushomirsky et al., Mon. Not. R.
Astron. Soc. 319, 902 (2000)]. (We also present a method for Newtonian gravity
with no Cowling approximation.) We apply these methods to the m = 2 quadrupoles
most relevant for gravitational radiation in three cases: crustal deformations,
deformations of crystalline cores of hadron-quark hybrid stars, and
deformations of entirely crystalline color superconducting quark stars. In all
cases, we find suppressions of the quadrupole due to relativity compared to the
Newtonian Cowling approximation, particularly for compact stars. For the crust
these suppressions are up to a factor ~6, for hybrid stars they are up to ~4,
and for solid quark stars they are at most ~2, with slight enhancements instead
for low mass stars. We also explore ranges of masses and equations of state
more than in previous work, and find that for some parameters the maximum
quadrupoles can still be very large. Even with the relativistic suppressions,
we find that 1.4 solar mass stars can sustain crustal quadrupoles of a few
times 10^39 g cm^2 for the SLy equation of state or close to 10^40 g cm^2 for
equations of state that produce less compact stars. Solid quark stars of 1.4
solar masses can sustain quadrupoles of around 10^44 g cm^2. Hybrid stars
typically do not have solid cores at 1.4 solar masses, but the most massive
ones (~2 solar masses) can sustain quadrupoles of a few times 10^41 g cm^2 for
typical microphysical parameters and a few times 10^42 g cm^2 for extreme ones.
All of these quadrupoles assume a breaking strain of 0.1 and can be divided by
10^45 g cm^2 to yield the fiducial "ellipticities" quoted elsewhere.Comment: 21 pages, 11 figures, version accepted by PRD, including the
corrected maximum hybrid star quadrupoles (from the erratum to the shear
modulus calculation) and the corrected binding energy computatio

### A Model for Conducting Research with Learning Disabled Adolescents and Young Adults

This research was published by the KU Center for Research on Learning, formerly known as the University of Kansas Institute for Research in Learning Disabilities.Issues from the field of learning disabilities and the field of education in general which impact the learning disabled individual are discussed as they relate to research with learning disabled adolescents and young adults . Based on this knowledge of the context in which the LD adolescent is required to function, a research model that allows a commitment to programmatic research leading to the validation of interventions as well as the generation and investigation of new research questions is presented. Critical questions within the three research areas of the Institute epidemiology, intervention, and generalization-- are discussed as they relate to this research model

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