222 research outputs found
The causal exposure model of vascular disease
Primary prevention of cardiovascular disease is governed at present by the risk factor model for cardiovascular events, a model which is widely accepted by physicians and professional associations, but which has important limitations: most critically, that effective treatment to reduce arterial damage is often delayed until the age at which cardiovascular events become common. This delay means that many of the early victims of vascular disease will not be identified in time. This delay also allows atherosclerosis to develop and progress unchecked within the arterial tree with the result that the absolute effectiveness of preventive therapy is limited by the time it is eventually initiated. The causal exposure model of vascular disease is an alternative to the risk factor model for cardiovascular events. Whereas the risk factor model aims to identify and treat those at markedly increased risk of vascular events within the next decade, the causal exposure model of vascular disease aims to prevent events by treating the causes of the disease when they are identified. In the risk factor model, age is an independent non-modifiable risk factor and the predictive power of age far outweighs that of the other risk factors. In the causal exposure model, age is the duration of time the arterial wall is exposed to the causes of atherosclerosis: apoB (apolipoprotein B) lipoproteins, hypertension, diabetes and smoking. Preventing the development of advanced atherosclerotic lesions by treating the causes of vascular disease is the simplest, surest and most effective way to prevent clinical events
Bounding the graviton mass with binary pulsar observations
By comparing the observed orbital decay of the binary pulsars PSRB1913+16 and
PSRB1534+12 to that predicted by general relativity due to gravitational-wave
emission, we are able to bound the mass of the graviton to be less than
at 90% confidence. This is the first such
bound to be derived from dynamic gravitational fields. It is approximately two
orders of magnitude weaker than the static-field bound from solar system
observations, and will improve with further observations.Comment: 9 pages, 1 figure. Presented at Fourth Edoardo Amaldi Conference on
Gravitational Waves, Perth, 200
Private information via the Unruh effect
In a relativistic theory of quantum information, the possible presence of
horizons is a complicating feature placing restrictions on the transmission and
retrieval of information. We consider two inertial participants communicating
via a noiseless qubit channel in the presence of a uniformly accelerated
eavesdropper. Owing to the Unruh effect, the eavesdropper's view of any encoded
information is noisy, a feature the two inertial participants can exploit to
achieve perfectly secure quantum communication. We show that the associated
private quantum capacity is equal to the entanglement-assisted quantum capacity
for the channel to the eavesdropper's environment, which we evaluate for all
accelerations.Comment: 5 pages. v2: footnote deleted and typos corrected. v3: major
revision. New capacity (single-letter!) theorem and implicit assumption
lifte
Non-linear instability of Kerr-type Cauchy horizons
Using the general solution to the Einstein equations on intersecting null
surfaces developed by Hayward, we investigate the non-linear instability of the
Cauchy horizon inside a realistic black hole. Making a minimal assumption about
the free gravitational data allows us to solve the field equations along a null
surface crossing the Cauchy Horizon. As in the spherical case, the results
indicate that a diverging influx of gravitational energy, in concert with an
outflux across the CH, is responsible for the singularity. The spacetime is
asymptotically Petrov type N, the same algebraic type as a gravitational shock
wave. Implications for the continuation of spacetime through the singularity
are briefly discussed.Comment: 11 pages RevTeX, two postscript figures included using epsf.st
Violation of CPT and Quantum Mechanics in the K0--K0bar System
We reconsider the model of quantum mechanics violation in the \ko--\kob
system, due to Ellis, Hagelin, Nanopoulos, and Srednicki, in which \cp- and
\cpt-violating signatures arise from the evolution of pure states into mixed
states. We present a formalism for computing time-dependent asymmetries in this
model and show that present data constrains its parameters significantly. In
the future, this model will be put to very stringent tests at a factory.
We present the theory of these tests and show the relation between particular
decay correlations and the parameters of quantum mechanics violation.Comment: 50 pages, uses PHYZZX, one figure available on request. This revised
version contains minor corrections, improved bounds on the parameters which
measure violation of quantum mechanics, and a more complete set of formula
Spinors, Inflation, and Non-Singular Cyclic Cosmologies
We consider toy cosmological models in which a classical, homogeneous, spinor
field provides a dominant or sub-dominant contribution to the energy-momentum
tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a
field were to exist, appropriate choices of the spinor self-interaction would
generate a rich variety of behaviors, quite different from their widely studied
scalar field counterparts. We first discuss solutions that incorporate a stage
of cosmic inflation and estimate the primordial spectrum of density
perturbations seeded during such a stage. Inflation driven by a spinor field
turns out to be unappealing as it leads to a blue spectrum of perturbations and
requires considerable fine-tuning of parameters. We next find that, for simple,
quartic spinor self-interactions, non-singular cyclic cosmologies exist with
reasonable parameter choices. These solutions might eventually be incorporated
into a successful past- and future-eternal cosmological model free of
singularities. In an Appendix, we discuss the classical treatment of spinors
and argue that certain quantum systems might be approximated in terms of such
fields.Comment: 12 two-column pages, 3 figures; uses RevTeX
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