13,391 research outputs found
Radiating sources in higher-dimensional gravity
We study a time-dependent 5D metric which contains a static 4D sub-metric
whose 3D part is spherically symmetric. An expansion in the metric coefficient
allow us to obtain close-to Schwarzschild approximation to a class of
spherically-symmetric solutions. Using Campbell's embedding theorem and the
induced-matter formalism we obtain two 4D solutions. One describes a source
with the stiff equation of state believed to be applicable to dense
astrophysical objects, and the other describes a spherical source with a radial
heat flow.Comment: Latex, 20 pages, no figures. to appear in J. Math. Phy
The discovery circumstances of Earth-approaching asteroids
The discovery circumstances are analyzed for all Earth-approaching asteroids detected in the last twenty-four years. In particular, topocentric angular velocities, opposition distance, geocentric and heliocentric distances, phase angle, and lunar phase at discover were calculated in an effort to separate any selection effects between chance and purposeful (i.e., as the result of a systematic search) discoveries. Another motivation was the possibility of discerning useful clues how to search more efficiently for such objects. There are 60 minor planets in the sample. The principal result is that the discovery of Earth-approaching asteroids is dominated by serendipity. Therefore, searching for them at the current relatively bright limits at less than a very high rate seems pointless
Cyber-pseudepigraphy: A New Challenge for Higher Education Policy and Management
There is no lack of critical literature dealing with cyber-plagiarism and the implications for assessment in higher education. The practice of the selling of academic papers through the Internet is generally included under the category of plagiarism, although it is suggested that this ought to be considered under the separate category of cyber-pseudepigraphy. Pseudepigraphy is defined in this essay as the deliberate ascription of false authorship to a piece of writing, and cyber-pseudepigraphy is defined as using the Internet to have another person write an academic essay or paper, without this authorship being acknowledged. It is suggested that cyber-pseudepigraphy has widespread implications, and five critical issues are discussed. The essay finally raises the prospect of a return to some form of unseen examination as a method of student assessment as a way of dealing with this problem
Scalar field localization on a brane with cosmological constant
We address the localization of a scalar field, whose bulk-mass M is
considered in a wide range including the tachyonic region,on a three-brane. The
brane with non-zero cosmological constant is embedded in five
dimensional bulk space. We find in this case that the trapped scalar could have
mass which has an upper bound and expressed as with the calculable numbers . We point
out that this result would be important to study the stability of the brane and
cosmological problems based on the brane-world.Comment: 14 pages, 5 figure
The Wilsonian Renormalization Group in Randall-Sundrum 1
We find renormalization group transformations for the compactified
Randall-Sundrum scenario by integrating out an infinitesimal slice of
ultraviolet degrees of freedom near the Planck brane. Under these
transformations the coefficients of operators on the Planck brane experience RG
evolution. The extra-dimensional radius also scales, flowing to zero in the IR.
We find an attractive fixed point in the context of a bulk scalar field theory.
Calculations are simplified in the low energy effective theory as we
demonstrate with the computation of a loop diagram.Comment: 19 pages, typos adde
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Environmental sampling to assess the bioburden of Mycobacterium avium subspecies paratuberculosis in drylot pens on California dairies.
Mycobacterium avium subspecies paratuberculosis (MAP) is a bacterium that can cause substantial economic losses in infected dairy herds due to reduced milk production and increased cow-replacement costs. In order to control MAP in dairies with drylot pens, a standardized environmental sampling protocol to quantify MAP in fecal slurry was developed based on an existing protocol for freestall pens. Specifically, following a 24 h hold of the flush, a grab sample of approximately 10 ml of fecal slurry was collected every 1 m along the flush lane of the drylot pens, avoiding individual cow fecal pats. To determine the reliability and repatability of the new environmental sampling protocol for estimation of MAP bioburden at the pen level, two collectors simultaneously collected fecal slurry samples every day for 3 days from six drylot cow pens on two Central California dairies. During the study period no cow movement between pens was allowed with the exception of sick cows. The study herds had MAP seroprevalence of 5.8% and 3.2%, respectively, based on whole pen serum ELISA results. Variance components models for quantitative real-time PCR (qPCR) results showed samples collected from different pens on different dairies accounted for greater variablitiy in MAP concentration (65%), while samples collected by different collectors had the least variability (0.1%). In contrast, variability in MAP concentration in environmental samples collected on different days had 25% variability. The intraclass correlation coefficient showed high reliability (93%) of environmental sampling simultaneously by different collectors. In contrast, the reliability of environmental sampling at different days was 65%, which was similar to the reliability for sampling by different collectors on different days. Investigators can expect high reliability when employing the new environmental sampling protocol along with qPCR testing of environmental samples from drylot pens
Observations and asteroseismic analysis of the rapidly pulsating hot B subdwarf PG 0911+456
The principal aim of this project is to determine the structural parameters
of the rapidly pulsating subdwarf B star PG 0911+456 from asteroseismology. Our
work forms part of an ongoing programme to constrain the internal
characteristics of hot B subdwarfs with the long-term goal of differentiating
between the various formation scenarios proposed for these objects. First
comparisons of asteroseismic values with evolutionary theory look promising,
however it is clear that more targets are needed for meaningful statistics to
be derived. The observational pulsation periods of PG 0911+456 were extracted
from rapid time-series photometry using standard Fourier analysis techniques.
Supplemented by spectroscopic estimates of the star's mean atmospheric
parameters, they were used as a basis for the "forward modelling" approach in
asteroseismology. The latter culminates in the identification of one or more
"optimal" models that can accurately reproduce the observed period spectrum.
This naturally leads to an identification of the oscillations detected in terms
of degree l and radial order k, and infers the structural parameters of the
target. From the photometry it was possible to extract 7 independent pulsation
periods in the 150-200 s range with amplitudes between 0.05 and 0.8 % of the
star's mean brightness. An asteroseismic search of parameter space identified
several models that matched the observed properties of PG 0911+456 well, one of
which was isolated as the "optimal" model on the basis of spectroscopic and
mode identification considerations. All the observed pulsations are identified
with low-order acoustic modes with degree indices l=0,1,2 and 4, and match the
computed periods with a dispersion of only ~0.26 %.Comment: accepted for publication in A&A, 14 pages, 13 figure
Vector field localization and negative tension branes
It is shown that negative tension branes in higher dimensions may lead to an
effective lower dimensional theory where the gauge-invariant vector fields
associated with the fluctuations of the metric are always massless and
localized on the brane. Explicit five-dimensional examples of this phenomenon
are provided. Furthermore, it is shown that higher dimensional gauge fields can
also be localized on these configurations with the zero mode separated from the
massive tower by a gap.Comment: 16 pages, LaTeX style; to appear in Phys. Rev.
Ideally embedded space-times
Due to the growing interest in embeddings of space-time in higher-dimensional
spaces we consider a specific type of embedding. After proving an inequality
between intrinsically defined curvature invariants and the squared mean
curvature, we extend the notion of ideal embeddings from Riemannian geometry to
the indefinite case. Ideal embeddings are such that the embedded manifold
receives the least amount of tension from the surrounding space. Then it is
shown that the de Sitter spaces, a Robertson-Walker space-time and some
anisotropic perfect fluid metrics can be ideally embedded in a five-dimensional
pseudo-Euclidean space.Comment: layout changed and typos corrected; uses revtex
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