72 research outputs found
Tkachenko waves, glitches and precession in neutron star
Here I discuss possible relations between free precession of neutron stars,
Tkachenko waves inside them and glitches. I note that the proposed precession
period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is
consistent with the period of Tkachenko waves for the spin period 8.4s. Based
on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al.
2007), I propose a simple model, in which long period precession is powered by
Tkachenko waves generated by a glitch. The period of free precession,
determined by a NS oblateness, should be equal to the standing Tkachenko wave
period for effective energy transfer from the standing wave to the precession
motion. A similar scenario can be applicable also in the case of the PSR
B1828-11.Comment: 6 pages, no figures, accepted to Ap&S
Cosmological Black Holes on Branes
We examined analytically a cosmological black hole domain wall system. Using
the C-metric construction we derived the metric for the spacetime describing an
infinitely thin domain wall intersecting a cosmological black hole. We studied
the behaviour of the scalar field describing a self-interacting cosmological
domain wall and find the approximated solution valid for large distances. The
thin wall approximation and the back raection problem were elaborated finding
that the topological kink solution smoothed out singular behaviour of the zero
thickness wall using a core topological and hence thick domain wall. We also
analyze the nucleation of cosmological black holes on and in the presence of a
domain walls and conclude that the domain wall will nucleate small black holes
on it rather than large ones inside.Comment: 13 pages, Revtex, to be published in Phys.Rev. D1
Isothermal Plasma Wave Properties of the Schwarzschild de-Sitter Black Hole in a Veselago Medium
In this paper, we study wave properties of isothermal plasma for the
Schwarzschild de-Sitter black hole in a Veselago medium. We use ADM 3+1
formalism to formulate general relativistic magnetohydrodynamical (GRMHD)
equations for the Schwarzschild de-Sitter spacetime in Rindler coordinates.
Further, Fourier analysis of the linearly perturbed GRMHD equations for the
rotating (non-magnetized and magnetized) background is taken whose determinant
leads to a dispersion relation. We investigate wave properties by using
graphical representation of the wave vector, the refractive index, change in
refractive index, phase and group velocities. Also, the modes of wave
dispersion are explored. The results indicate the existence of the Veselago
medium.Comment: 24 pages, 12 figures, accepted for publication in Astrophys. Space
Sci. arXiv admin note: text overlap with arXiv:1101.0884 and arxiv:1007.285
Relationships of psychosocial factors to dietary intakes of preadolescent girls from diverse backgrounds
Family and personal factors that might be related to the development of food selection and eating patterns have not been well studied in children. The aim of this study was to examine whether such psychosocial factors differ in girls from four culturally diverse Girl Scout troops and how these factors are associated with dietary intakes. The social measures and dietary assessments were all obtained at baseline on subjects who were participating in a small nutrition education programme. The programme enrolled girls and one parent for each girl from four Girl Scout troops in Detroit, Michigan. The social factors assessed included girls’ emotionality and use of food to regulate emotions, their general attitudes about health, eating and body image, and self-perceptions of their competence. Dietary intakes also were assessed in both the girls and their parents. There were large differences between troops in ethnicity and parent education level, and there were differences in dietary intakes as well. The psychosocial factors assessed in this study, however, did not differ significantly by troop. When the psychosocial factors were examined for their relationships to dietary factors, there was an indication that families which reported higher self-competence and academic competence in their daughters also had healthier eating patterns in their daughters. This was a small study, but the data suggest that simple comparisons between ethnic groups may not adequately capture the complexity of family and psychosocial factors contributing to good dietary practices.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73597/1/j.1740-8709.2006.00051.x.pd
Particle Acceleration in Cosmic Sites - Astrophysics Issues in our Understanding of Cosmic Rays
Laboratory experiments to explore plasma conditions and stimulated particle
acceleration can illuminate aspects of the cosmic particle acceleration
process. Here we discuss the cosmic-ray candidate source object variety, and
what has been learned about their particle-acceleration characteristics. We
identify open issues as discussed among astrophysicists. -- The cosmic ray
differential intensity spectrum is a rather smooth power-law spectrum, with two
kinks at the "knee" (~10^15 eV) and at the "ankle" (~3 10^18 eV). It is unclear
if these kinks are related to boundaries between different dominating sources,
or rather related to characteristics of cosmic-ray propagation. We believe that
Galactic sources dominate up to 10^17 eV or even above, and the extragalactic
origin of cosmic rays at highest energies merges rather smoothly with Galactic
contributions throughout the 10^15--10^18 eV range. Pulsars and supernova
remnants are among the prime candidates for Galactic cosmic-ray production,
while nuclei of active galaxies are considered best candidates to produce
ultrahigh-energy cosmic rays of extragalactic origin. Acceleration processes
are related to shocks from violent ejections of matter from energetic sources
such as supernova explosions or matter accretion onto black holes. Details of
such acceleration are difficult, as relativistic particles modify the structure
of the shock, and simple approximations or perturbation calculations are
unsatisfactory. This is where laboratory plasma experiments are expected to
contribute, to enlighten the non-linear processes which occur under such
conditions.Comment: accepted for publication in EPJD, topical issue on Fundamental
physics and ultra-high laser fields. From review talk at "Extreme Light
Infrastructure" workshop, Sep 2008. Version-2 May 2009: adjust some wordings
and references at EPJD proofs stag
Energy and Flux Measurements of Ultra-High Energy Cosmic Rays Observed During the First ANITA Flight
The first flight of the Antarctic Impulsive Transient Antenna (ANITA)
experiment recorded 16 radio signals that were emitted by cosmic-ray induced
air showers. For 14 of these events, this radiation was reflected from the ice.
The dominant contribution to the radiation from the deflection of positrons and
electrons in the geomagnetic field, which is beamed in the direction of motion
of the air shower. This radiation is reflected from the ice and subsequently
detected by the ANITA experiment at a flight altitude of 36km. In this paper,
we estimate the energy of the 14 individual events and find that the mean
energy of the cosmic-ray sample is 2.9 EeV. By simulating the ANITA flight, we
calculate its exposure for ultra-high energy cosmic rays. We estimate for the
first time the cosmic-ray flux derived only from radio observations. In
addition, we find that the Monte Carlo simulation of the ANITA data set is in
agreement with the total number of observed events and with the properties of
those events.Comment: Added more explanation of the experimental setup and textual
improvement
Studies of Neutron Stars at Optical/IR Wavelengths
In the last years, optical studies of Isolated Neutron Stars (INSs) have expanded from the more classical rotation-powered ones to other categories, like the Anomalous X-ray Pulsars (AXPs) and the Soft Gamma-ray Repeaters (SGRs), which make up the class of the magnetars, the radio-quiet INSs with X-ray thermal emission and, more recently, the enigmatic Compact Central Objects (CCOs) in supernova remnants. Apart from 10 rotation-powered pulsars, so far optical/IR counterparts have been found for 5 magnetars and for 4 INSs. In this work we present some of the latest observational results obtained from optical/IR observations of different types of INSs
The Projection Method for Reaching Consensus and the Regularized Power Limit of a Stochastic Matrix
In the coordination/consensus problem for multi-agent systems, a well-known
condition of achieving consensus is the presence of a spanning arborescence in
the communication digraph. The paper deals with the discrete consensus problem
in the case where this condition is not satisfied. A characterization of the
subspace of initial opinions (where is the influence matrix) that
\emph{ensure} consensus in the DeGroot model is given. We propose a method of
coordination that consists of: (1) the transformation of the vector of initial
opinions into a vector belonging to by orthogonal projection and (2)
subsequent iterations of the transformation The properties of this method
are studied. It is shown that for any non-periodic stochastic matrix the
resulting matrix of the orthogonal projection method can be treated as a
regularized power limit of Comment: 19 pages, 2 figure
The Antarctic Impulsive Transient Antenna Ultra-high Energy Neutrino Detector Design, Performance, and Sensitivity for 2006-2007 Balloon Flight
We present a detailed report on the experimental details of the Antarctic
Impulsive Transient Antenna (ANITA) long duration balloon payload, including
the design philosophy and realization, physics simulations, performance of the
instrument during its first Antarctic flight completed in January of 2007, and
expectations for the limiting neutrino detection sensitivity. Neutrino physics
results will be reported separately.Comment: 50 pages, 49 figures, in preparation for PR
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