8,179 research outputs found
Scale-invariance in gravity and implications for the cosmological constant
Recently a scale invariant theory of gravity was constructed by imposing a
conformal symmetry on general relativity. The imposition of this symmetry
changed the configuration space from superspace - the space of all Riemannian
3-metrics modulo diffeomorphisms - to conformal superspace - the space of all
Riemannian 3-metrics modulo diffeomorphisms and conformal transformations.
However, despite numerous attractive features, the theory suffers from at least
one major problem: the volume of the universe is no longer a dynamical
variable. In attempting to resolve this problem a new theory is found which has
several surprising and atractive features from both quantisation and
cosmological perspectives. Furthermore, it is an extremely restrictive theory
and thus may provide testable predictions quickly and easily. One particularly
interesting feature of the theory is the resolution of the cosmological
constant problem.Comment: Replaced with final version: minor changes to text; references adde
Cataract prevalence, cataract surgical coverage and barriers to uptake of cataract surgical services in Pakistan: the Pakistan National Blindness and Visual Impairment Survey.
AIM: To estimate the prevalence of visual impairment and blindness caused by cataract, the prevalence of aphakia/pseudophakia, cataract surgical coverage (CSC) and to identify barriers to the uptake of cataract services among adults aged >or=30 years in Pakistan. METHODS: Probability proportional-to-size procedures were used to select a nationally representative sample of adults. Each subject underwent interview, visual acuity measurement, autorefraction, biometry and ophthalmic examination. Those that saw <6/12 in either eye underwent a more intensive examination procedure including corrected visual acuity, slit lamp and dilated fundus examination. CSC was calculated for different levels of visual loss by person and by eye. Individuals with <6/60 in the better eye as a result of cataract were interviewed regarding barriers. RESULTS: 16 507 Adults were examined (95.5% response rate). The crude prevalence of blindness (presenting <3/60 in the better eye) caused by bilateral cataract was 1.75% (95% CI 1.55%, 1.96%). 1317 Participants (633 men; 684 women) had undergone cataract surgery in one or both eyes, giving a crude prevalence of 8.0% (95% CI 7.6%, 8.4%). The CSC (persons) at <3/60, <6/60 and <6/18 were 77.1%, 69.3% and 43.7%, respectively. The CSC (eyes) at <3/60, <6/60 and <6/18 were 61.4%, 52.2% and 40.7%, respectively. Cost of surgery (76.1%) was the main barrier to surgery. CONCLUSION: Approximately 570 000 adults are estimated to be blind (<3/60) as a result of cataract in Pakistan, and 3,560000 eyes have a visual acuity of <6/60 because of cataract. Overall, the national surgical coverage is good but underserved populations have been identified
The physical gravitational degrees of freedom
When constructing general relativity (GR), Einstein required 4D general
covariance. In contrast, we derive GR (in the compact, without boundary case)
as a theory of evolving 3-dimensional conformal Riemannian geometries obtained
by imposing two general principles: 1) time is derived from change; 2) motion
and size are relative. We write down an explicit action based on them. We
obtain not only GR in the CMC gauge, in its Hamiltonian 3 + 1 reformulation but
also all the equations used in York's conformal technique for solving the
initial-value problem. This shows that the independent gravitational degrees of
freedom obtained by York do not arise from a gauge fixing but from hitherto
unrecognized fundamental symmetry principles. They can therefore be identified
as the long-sought Hamiltonian physical gravitational degrees of freedom.Comment: Replaced with published version (minor changes and added references
VOFilter, Bridging Virtual Observatory and Industrial Office Applications
VOFilter is an XML based filter developed by the Chinese Virtual Observatory
project to transform tabular data files from VOTable format into OpenDocument
format. VOTable is an XML format defined for the exchange of tabular data in
the context of the Virtual Observatory (VO). It is the first Proposed
Recommendation defined by International Virtual Observatory Alliance, and has
obtained wide support from both the VO community and many Astronomy projects.
OpenOffice.org is a mature, open source, front office applications suite with
the advantage of native support of industrial standard OpenDocument XML file
format. Using the VOFilter, VOTable files can be loaded in OpenOffice.org Calc,
a spreadsheet application, and then displayed and analyzed as other spreadsheet
files. Here, the VOFilter acts as a connector, bridging the coming VO with
current industrial office applications. Virtual Observatory and technical
background of the VOFilter are introduced. Its workflow, installation and usage
are presented. Existing problems and limitations are also discussed together
with the future development plans.Comment: Accepted for publication in ChJAA (9 pages, 2 figures, 185KB
Baryon Current Matrix Elements in a Light-Front Framework
Current matrix elements and observables for electro- and photo-excitation of
baryons from the nucleon are studied in a light-front framework. Relativistic
effects are estimated by comparison to a nonrelativistic model, where we use
simple basis states to represent the baryon wavefunctions. Sizeable
relativistic effects are found for certain transitions, for example, to radial
excitations such as that conventionally used to describe to the Roper
resonance. A systematic study shows that the violation of rotational covariance
of the baryon transition matrix elements stemming from the use of one-body
currents is generally small.Comment: 32 pages, LaTeX, 10 postscript figures, uses epsf.sty; figures
uuencoded with uufiles (or available by request in .ps or hardcopy form
Reducing space-time to binary information
We present a new description of discrete space-time in 1+1 dimensions in terms of a set of elementary geometrical units that represent its independent classical degrees of freedom. This is achieved by means of a binary encoding that is ergodic in the class of space-time manifolds respecting coordinate invariance of general relativity. Space-time fluctuations can be represented in a classical lattice gas model whose Boltzmann weights are constructed with the discretized form of the Einstein–Hilbert action. Within this framework, it is possible to compute basic quantities such as the Ricci curvature tensor and the Einstein equations, and to evaluate the path integral of discrete gravity. The description as a lattice gas model also provides a novel way of quantization and, at the same time, to quantum simulation of fluctuating space-time
Confronting the trans-Planckian question of inflationary cosmology with dissipative effects
We provide a class of QFTs which exhibit dissipation above a threshold
energy, thereby breaking Lorentz invariance. Unitarity is preserved by coupling
the fields to additional degrees of freedom (heavy fields) which introduce the
rest frame. Using the Equivalence Principle, we define these theories in
arbitrary curved spacetime. We then confront the trans-Planckian question of
inflationary cosmology. When dissipation increases with the energy, the quantum
field describing adiabatic perturbations is completely damped at the onset of
inflation. However it still exists as a composite operator made with the
additional fields. And when these are in their ground state, the standard power
spectrum obtains if the threshold energy is much larger that the Hubble
parameter. In fact, as the energy redshifts below the threshold, the composite
operator behaves as if it were a free field endowed with standard vacuum
fluctuations. The relationship between our models and the Brane World scenarios
studied by Libanov and Rubakov displaying similar effects is discussed. The
signatures of dissipation will be studied in a forthcoming paper.Comment: 30 pages, 1 Figure, to appear in CQ
Einstein gravity as a 3D conformally invariant theory
We give an alternative description of the physical content of general
relativity that does not require a Lorentz invariant spacetime. Instead, we
find that gravity admits a dual description in terms of a theory where local
size is irrelevant. The dual theory is invariant under foliation preserving
3-diffeomorphisms and 3D conformal transformations that preserve the 3-volume
(for the spatially compact case). Locally, this symmetry is identical to that
of Horava-Lifshitz gravity in the high energy limit but our theory is
equivalent to Einstein gravity. Specifically, we find that the solutions of
general relativity, in a gauge where the spatial hypersurfaces have constant
mean extrinsic curvature, can be mapped to solutions of a particular gauge
fixing of the dual theory. Moreover, this duality is not accidental. We provide
a general geometric picture for our procedure that allows us to trade foliation
invariance for conformal invariance. The dual theory provides a new proposal
for the theory space of quantum gravity.Comment: 27 pages. Published version (minor changes and corrections
The Effects of Body Tempering on Force Production, Flexibility and Muscle Soreness in Collegiate Football Athletes
There has been limited research to explore the use of body tempering and when the use of this modality would be most appropriate. This study aimed to determine if a body tempering intervention would be appropriate pre-exercise by examining its effects on perceived soreness, range of motion (ROM), and force production compared to an intervention of traditional stretching. The subjects for this study were ten Division 1 (D1) football linemen from Sacred Heart University (Age: 19.9 ± 1.5 years, body mass: 130.9 ± 12.0 kg, height: 188.4 ± 5.1 cm, training age: 8.0 ± 3.5 years). Subjects participated in three sessions with the first session being baseline testing. The second and third sessions involved the participants being randomized to receive either the body tempering or stretching intervention for the second session and then receiving the other intervention the final week. Soreness using a visual analog scale (VAS), ROM, counter movement jump (CMJ) peak force and jump height, static jump (SJ) peak force and jump height, and isometric mid-thigh pull max force production were assessed. The results of the study concluded that body tempering does not have a negative effect on muscle performance but did practically reduce perceived muscle soreness. Since body tempering is effective at reducing soreness in athletes, it can be recommended for athletes as part of their pre-exercise warmup without negatively effecting isometric or dynamic force production
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