737 research outputs found
Evolving fuzzy CP^n and lattice n-simplex
Generalizing the previous works on evolving fuzzy two-sphere, I discuss
evolving fuzzy CP^n by studying scalar field theory on it. The space-time
geometry is obtained in continuum limit, and is shown to saturate locally the
cosmic holographic principle. I also discuss evolving lattice n-simplex
obtained by `compactifying' fuzzy CP^n. It is argued that an evolving lattice
n-simplex does not approach a continuum space-time but decompactifies into an
evolving fuzzy CP^n.Comment: Typos corrected, 13 pages, no figures, LaTe
Three types of statistics and the entropy bounds
We investigated the entropy bounds of the three types of statistics:
para-Bose, para-Fermi and infinite statistics. We showed that the entropy
bounds of the conventional Bose, Fermi statistics and their generalizations to
parastatistics obey the law, while the entropy bound of infinite
statistics obeys the area law. This suggests a close relationship between
infinite statistics and quantum gravity.Comment: 5 pages, pubished versio
ChromaBlur: Rendering Chromatic Eye Aberration Improves Accommodation and Realism
Computer-graphics engineers and vision scientists want to generate images that reproduce realistic depth-dependent blur. Current rendering algorithms take into account scene geometry, aperture size, and focal distance, and they produce photorealistic imagery as with a high-quality camera. But to create immersive experiences, rendering algorithms should aim instead for perceptual realism. In so doing, they should take into account the significant optical aberrations of the human eye. We developed a method that, by incorporating some of those aberrations, yields displayed images that produce retinal images much closer to the ones that occur in natural viewing. In particular, we create displayed images taking the eye's chromatic aberration into account. This produces different chromatic effects in the retinal image for objects farther or nearer than current focus. We call the method ChromaBlur. We conducted two experiments that illustrate the benefits of ChromaBlur. One showed that accommodation (eye focusing) is driven quite effectively when ChromaBlur is used and that accommodation is not driven at all when conventional methods are used. The second showed that perceived depth and realism are greater with imagery created by ChromaBlur than in imagery created conventionally. ChromaBlur can be coupled with focus-adjustable lenses and gaze tracking to reproduce the natural relationship between accommodation and blur in HMDs and other immersive devices. It may thereby minimize the adverse effects of vergence-accommodation conflicts
Unimodular Supergravity
We present the locally supersymmetric formulation of unimodular gravity
theory in D (1\le D \le 11) dimensions, namely supergravity theory with the
metric tensor whose determinant is constrained to be unity. In such a
formulation, the usual fine-tuning of cosmological constant is no longer
needed, but its value is understood as an initial condition. Moreover, the
zero-ness of the cosmological constant is concluded as the most probable
configuration, based on the effective vacuum functional. We also show that the
closure of supersymmetry gauge algebra is consistent with the unimodular
condition on the metric.Comment: 15 pages, latex, new section 7, two new paragraphs in Introduction
and Conclusion
Reconsidering the black hole final state in Dirac fields
We extend Horowitz and Maldacena's proposal about black hole final state to
Dirac fields and find that if annihilation of the infalling positrons and the
collapsed electrons inside the horizon is considered, then the nonlinear
evolution of collapsing quantum state will be avoided. We further propose that
annihilation also plays the central role in the process of black hole
information escaping in both Dirac and scalar fields. The computation speed of
a black hole is also briefly discussed.Comment: 7pages; Phys. Lett. B 2005 (in press
Computational capacity of the universe
Merely by existing, all physical systems register information. And by
evolving dynamically in time, they transform and process that information. The
laws of physics determine the amount of information that a physical system can
register (number of bits) and the number of elementary logic operations that a
system can perform (number of ops). The universe is a physical system. This
paper quantifies the amount of information that the universe can register and
the number of elementary operations that it can have performed over its
history. The universe can have performed no more than ops on
bits.Comment: 17 pages, TeX. submitted to Natur
Validity of self-reported height and weight and derived body mass index in middle-aged and elderly individuals in Australia
Background: Body mass index (BMI) is an important measure of adiposity. While BMI derived from self-reported data generally agrees well with that derived from measured values, evidence from Australia is limited, particularly for the elderly. Methods: We compared self-reported with measured height and weight in a random sample of 608 individuals aged ≥45 from the 45 and Up Study, an Australian population-based cohort study. We assessed degree of agreement and correlation between measures, and calculated sensitivity and specificity to quantify BMI category misclassification. Results: On average, in males and females respectively, height was overestimated by 1.24cm (95% CI: 0.75-1.72) and 0.59cm (0.26-0.92); weight was underestimated by 1.68kg (-1.99-1.36) and 1.02kg (-1.24-0.80); and BMI based on self-reported measures was underestimated by 0.90kg/m2 (-1.09-0.70) and 0.60 kg/m2 (-0.75-0.45). Underestimation increased with increasing measured BMI. There were strong correlations between self-reported and measured height, weight and BMI (r=0.95, 0.99 and 0.95, respectively, p<0.001). While there was excellent agreement between BMI categories from self-reported and measured data (kappa=0.80), obesity prevalence was underestimated. Findings did not differ substantially between middleaged and elderly participants. Conclusions: Self-reported data on height and weight quantify body size appropriately in middle-aged and elderly individuals for relative measures, such as quantiles of BMI. However, caution is necessary when reporting on absolute BMI and standard BMI categories, based on self-reported data, particularly since use of such data is likely to result in underestimation of the prevalence of obesity
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Cases of advanced visual field loss at referral to glaucoma clinics - more men than women?
Purpose
In many medical conditions ‘late presentation’ of disease is more of a problem for men than women. Risk of sight loss from glaucoma is certainly greater in those detected with advanced disease. We performed a retrospective study to test the hypothesis that men are more likely than women to have advanced visual field loss at referral to glaucoma clinics.
Methods
We used 152 918 Humphrey visual fields from 32 147 patients from three regionally different hospitals in England; no other clinical data were made available apart from patient's age, sex and examination dates. The study population was defined as patients with measureable visual field loss in at least one eye at referral to glaucoma clinics. Cases of advanced visual field loss as defined by the Enhanced Glaucoma Severity Staging method at the first visit to secondary care were used as a proxy measure for late presentation of glaucoma. Age-adjusted relative risk (RR) was calculated as the ratio of the proportion of men to women with this proxy measure.
Results
Median (interquartile range) age and MD (worse eye) for 3733 men and 4264 women was 72 (63, 79) and 74 (64, 81) years and −6.4 (−11.7, −3.8) and −6.3 (−11.0, −3.8) dB respectively. Overall proportion of patients with advanced visual field loss at referral to glaucoma clinics was slightly higher in men (25.0%) than in women (22.3%); this difference was statistically significant (p < 0.01). Overall age-standardised RR was statistically significant (1.16; p < 0.001); a person with late presentation of glaucoma is 16% (95% confidence interval: 7–25%) more likely to be a man than a woman.
Conclusions
A large number of patients with glaucomatous visual field defects are estimated to have advanced loss in at least one eye on referral to secondary care in England; risk for men more likely presenting with late disease is slightly greater than for women
Revalidation Technique on Landslide Susceptibility Modelling: An Approach to Local Level Disaster Risk Management in Kuala Lumpur, Malaysia
Landslide susceptibility modelling in tropical climates is hindered by incomplete inventory due to rapid development and natural processes that obliterate field evidence, making validation a challenge. Susceptibility modelling was conducted in Kuala Lumpur, Malaysia using a new spatial partitioning technique for cross-validation. This involved a series of two alternating east-west linear zones, where the first zone served as the training dataset and the second zone was the test dataset, and vice versa. The results show that the susceptibility models have good compatibility with the selected landslide conditioning factors and high predictive accuracy. The model with the highest area under curve (AUC) values (SRC = 0.92, PRC = 0.90) was submitted to the City Council of Kuala Lumpur for land use planning and development control. Rainfall-induced landslides are prominent within the study area, especially during the monsoon period. An extreme rainfall event in December 2021 that triggered 122 landslides provided an opportunity to conduct retrospective validation of the model; the high predictive capability (AUC of PRC = 0.93) was reaffirmed. The findings proved that retrospective validation is vital for landslide susceptibility modelling, especially where the inventory is not of the best quality. This is to encourage wider usage and acceptance among end users, especially decision-makers in cities, to support disaster risk management in a changing climate
Incompressible Fluids of the de Sitter Horizon and Beyond
There are (at least) two surfaces of particular interest in eternal de Sitter
space. One is the timelike hypersurface constituting the lab wall of a static
patch observer and the other is the future boundary of global de Sitter space.
We study both linear and non-linear deformations of four-dimensional de Sitter
space which obey the Einstein equation. Our deformations leave the induced
conformal metric and trace of the extrinsic curvature unchanged for a fixed
hypersurface. This hypersurface is either timelike within the static patch or
spacelike in the future diamond. We require the deformations to be regular at
the future horizon of the static patch observer. For linearized perturbations
in the future diamond, this corresponds to imposing incoming flux solely from
the future horizon of a single static patch observer. When the slices are
arbitrarily close to the cosmological horizon, the finite deformations are
characterized by solutions to the incompressible Navier-Stokes equation for
both spacelike and timelike hypersurfaces. We then study, at the level of
linearized gravity, the change in the discrete dispersion relation as we push
the timelike hypersurface toward the worldline of the static patch. Finally, we
study the spectrum of linearized solutions as the spacelike slices are pushed
to future infinity and relate our calculations to analogous ones in the context
of massless topological black holes in AdS.Comment: 27 pages, 8 figure
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