11,917 research outputs found
Implications of Spontaneous Glitches in the Mass and Angular Momentum in Kerr Space-Time
The outward-pointing principal null direction of the Schwarzschild Riemann
tensor is null hypersurface-forming. If the Schwarzschild mass spontaneously
jumps across one such hypersurface then the hypersurface is the history of an
outgoing light-like shell. The outward-- pointing principal null direction of
the Kerr Riemann tensor is asymptotically (in the neighbourhood of future null
infinity) null hypersurface-forming. If the Kerr parameters of mass and angular
momentum spontaneously jump across one such asymptotic hypersurface then the
asymptotic hypersurface is shown to be the history of an outgoing light-like
shell and a wire singularity-free spherical impulsive gravitational wave.Comment: 16 pages, TeX, no figures, accepted for publication in Phys. Rev.
Colliding Plane Impulsive Gravitational Waves
When two non-interacting plane impulsive gravitational waves undergo a
head-on collision, the vacuum interaction region between the waves after the
collision contains backscattered gravitational radiation from both waves. The
two systems of backscattered waves have each got a family of rays (null
geodesics) associated with them. We demonstrate that if it is assumed that a
parameter exists along each of these families of rays such that the modulus of
the complex shear of each is equal then Einstein's vacuum field equations, with
the appropriate boundary conditions, can be integrated systematically to reveal
the well-known solutions in the interaction region. In so doing the mystery
behind the origin of such solutions is removed. With the use of the field
equations it is suggested that the assumption leading to their integration may
be interpreted physically as implying that the energy densities of the two
backscattered radiation fields are equal. With the use of different boundary
conditions this approach can lead to new collision solutions.Comment: 21 pages, LaTeX2
How to choose commercial feeds
8 pages: illustrations; 23cm"In the feeding of livestock there are certain fundamentals that must form the basis of the feeder's choice of commercial products to supplement the feeds produced on the farm. It is to emphasize these fundamentals, rather than to discuss the many special cases and exceptions encountered in livestock feeding, that this circular is published." --Page [1
Foreign Bond Markets and Financial Market Development: International Perspectives
The domestic bond markets of the Asia and Pacific region have grown considerably since the Asian financial crisis of 1997, although they remain undeveloped relative to the region's weight in the world economy. This paper proposes that in order to encourage further development of these markets, regulators should make them more accessible to foreign borrowers. To that end we offer insights into the nature and mechanics of foreign bond issuance by investigating the key characteristics of 3,132 foreign bonds issued in 14 countries (other than the United States) between July 1928 and June 2009. We found that the foreign borrowers that tap domestic markets are overwhelmingly of high credit quality and comprise sovereigns, supranationals, and major financial institutions. There is a preference for simple fixed-rate payment structures, which can then be swapped into the currency and coupon type of choice using currency and interest rate derivatives. On the whole, the long-term viability of foreign bond markets appears linked to the presence of highly liquid foreign exchange and derivatives markets that facilitate risk management and transformation, enabling regulation that facilitates cooperation with market participants, the presence of benchmark issues, and competitive pricing between alternate market segments.bond markets; financial market development; foreign bonds
Light-like Signals in General relativity and Cosmology
The modelling of light-like signals in General Relativity taking the form of
impulsive gravitational waves and light-like shells of matter is examined.
Systematic deductions from the Bianchi identities are made. These are based
upon Penrose's hierarchical classification of the geometry induced on the null
hypersurface history of the surface by its imbedding in the space-times to the
future and to the past of it. The signals are not confined to propagate in a
vacuum and thus their interaction with matter (a burst of radiation propagating
through a cosmic fluid, for example) is also studied. Results are accompanied
by illustrative examples using cosmological models, vacuum space-times, the de
sitter univers and Minkowskian space-time.Comment: 21 pages, latex, no figure
Interferometers as Probes of Planckian Quantum Geometry
A theory of position of massive bodies is proposed that results in an
observable quantum behavior of geometry at the Planck scale, . Departures
from classical world lines in flat spacetime are described by Planckian
noncommuting operators for position in different directions, as defined by
interactions with null waves. The resulting evolution of position wavefunctions
in two dimensions displays a new kind of directionally-coherent quantum noise
of transverse position. The amplitude of the effect in physical units is
predicted with no parameters, by equating the number of degrees of freedom of
position wavefunctions on a 2D spacelike surface with the entropy density of a
black hole event horizon of the same area. In a region of size , the effect
resembles spatially and directionally coherent random transverse shear
deformations on timescale with typical amplitude . This quantum-geometrical "holographic noise" in position is not
describable as fluctuations of a quantized metric, or as any kind of
fluctuation, dispersion or propagation effect in quantum fields. In a Michelson
interferometer the effect appears as noise that resembles a random Planckian
walk of the beamsplitter for durations up to the light crossing time. Signal
spectra and correlation functions in interferometers are derived, and predicted
to be comparable with the sensitivities of current and planned experiments. It
is proposed that nearly co-located Michelson interferometers of laboratory
scale, cross-correlated at high frequency, can test the Planckian noise
prediction with current technology.Comment: 23 pages, 6 figures, Latex. To appear in Physical Review
Comparing the yield of Staphylococcus aureus recovery with static versus agitated broth incubation
Given the lack of standardization of methodologies for microbial recovery from built environments, we sought to compare the yield of Staphylococcus aureus with a broth enrichment method when incubated in agitated versus static conditions. Five unique strains of S. aureus at five different concentrations were cultured to compare direct plating, agitated broth enrichment, and static broth enrichment culture methods. All samples were incubated at 35° in ambient air. The lowest concentration recovered across three replicates and five strains did not differ between culture methods (Fisher’s exact test, p=0.50); notably, recovery of S. aureus was equivalent between static and agitated broth incubation. When broth enrichment was used (both static and agitated), the burden of S. aureus growth was higher (by semiquantitative assessment of 4-quadrant streaking) compared to the direct plating culture method. Optimizing strategies for microbial recovery is essential, particularly in areas of lower biomass, given the paucity of research concerning microbial communities of built environments. The results of this study, in conjunction with other experiments investigating microbiomes of built environments, can help inform protocols for standardizing culturing methods within built environments
Models of light-like charges with non-geodesic world lines
Massless particles in General Relativity move with the speed of light, their
trajectories in spacetime are described by null geodesics. This is independent
of the electrical charge of the particle being considered, however, the charged
light-like case is less well understood. Starting with the Maxwell field of a
charged particle having a light-like geodesic world line in Minkowskian
space-time we construct the Maxwell field of such a particle having a
non-geodesic, light-like world line. The necessary geometry in the
neighbourhood of an arbitrary null world line in Minkowskian space-time is
described and properties of the resulting electromagnetic field are discussed.
The electromagnetic field obtained represents a light-like analogue of the
Lienard-Wiechert field, which generalises the Coulomb field of a charge having
a time-like geodesic world line to the field of a charge having an accelerated
world line.Comment: 11 pages, 1 figur
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