21,889 research outputs found
Does Inflation Provide Natural Initial Conditions for the Universe?
If our universe underwent inflation, its entropy during the inflationary
phase was substantially lower than it is today. Because a low-entropy state is
less likely to be chosen randomly than a high-entropy one, inflation is
unlikely to arise through randomly-chosen initial conditions. To resolve this
puzzle, we examine the notion of a natural state for the universe, and argue
that it is a nearly-empty spacetime. If empty space has a small vacuum energy,
however, inflation can begin spontaneously in this background. This scenario
explains why a universe like ours is likely to have begun via a period of
inflation, and also provides an origin for the cosmological arrow of time.Comment: Submitted to Gravity Research Foundation Essay Competition; based on
hep-th/041027
The development of a new sport-specific classification of coping and a meta-analysis of the relationship between different coping strategies and moderators on sporting outcomes
There is an ever growing coping and sports performance literature, with researchers using many different methods to assess performance and different classifications of coping. As such, it makes it difficult to compare studies and therefore identify how coping is related to performance. Furthermore, there are no quantitative syntheses of the results from these studies. A quantitative synthesis would facilitate a more comprehensive understanding of how coping is associated with athletic performance. In order to accurately compare studies, our first aim was to develop a new coping classification that would make this possible. Firstly, we reviewed the strengths and limitations of the different coping classifications and then identified the commonalities and differences between such classifications. We opted for a three-factor classification of coping, because the evidence suggests that a three-factor classification provides a superior model fit to two-factor approaches. Our new classification of coping was based on an existing model from the developmental literature, which received an excellent model fit. We made some adaptations, however, as our classification was intended for an athletic population. As such, we classified coping as mastery (i.e., controlling the situation and eliminating the stressor), internal regulation (i.e., managing internal stress responses), or goal withdrawal (i.e., ceasing efforts towards goal attainment). Undertaking a meta-analysis, our second aim was to identify which coping strategies correlated with sports performance and whether this relationship varied according to moderator variables. Articles were sourced from online electronic databases and manual journal searches. PRISMA guidelines were used to search, select, and synthesize relevant studies. Random effects meta-analyses were performed to identify associations between coping classification and sport performance. Q, I2, and R2 values assessed heterogeneity. Eighteen published investigations, including 3900 participants and incorporating fifty-nine correlations, indicated an overall positive effect for mastery coping, a negligible negative effect for internal regulation coping, and a negative effect for goal withdrawal strategies. The findings of this meta-analysis could be used by sports practitioners to help them deliver effective coping interventions. In order to maximize performance, practitioners could encourage the use of mastery coping, but advise their athletes not to use goal withdrawal strategies
The adaptive observer
The simple generation of state from available measurements, for use in systems for which the criteria defining the acceptable state behavior mandates a control that is dependent upon unavailable measurement is described as an adaptive means for determining the state of a linear time invariant differential system having unknown parameters. A single input output adaptive observer and the reduced adaptive observer is developed. The basic ideas for both the adaptive observer and the nonadaptive observer are examined. A survey of the Liapunov synthesis technique is taken, and the technique is applied to adaptive algorithm for the adaptive observer
Matrix elements of atomic interaction operators for d sup n configurations
Tabulation of matrix elements of atomic interaction operators for various configuration
Abnormalities of the ventilatory equivalent for carbon dioxide in patients with chronic heart failure
Introduction. The relation between minute ventilation (VE) and carbon dioxide production (VCO2) can be characterised by the instantaneous ratio of ventilation to carbon dioxide production, the ventilatory equivalent for CO2 (VEqCO2). We hypothesised that the time taken to achieve the lowest VEqCO2 (time to VEqCO2 nadir) may be a prognostic marker in patients with chronic heart failure (CHF). Methods. Patients and healthy controls underwent a symptom-limited, cardiopulmonary exercise test (CPET) on a treadmill to volitional exhaustion. Results. 423 patients with CHF (mean age 63±12 years; 80% males) and 78 healthy controls (62% males; age 61±11 years) were recruited. Time to VEqCO2 nadir was shorter in patients than controls (327±204 s versus 514±187 s; P=0.0001). Univariable predictors of all-cause mortality included peak oxygen uptake (X 2 =53.0), VEqCO2 nadir (X 2 =47.9), and time to VEqCO2 nadir (X 2 =24.0). In an adjusted Cox multivariable proportional hazards model, peak oxygen uptake (X 2 =16.7) and VEqCO2 nadir (X 2 =17.9) were the most significant independent predictors of all-cause mortality. Conclusion. The time to VEqCO2 nadir was shorter in patients with CHF than in normal subjects and was a predictor of subsequent mortality. © 2012 Lee Ingle et al
Anisotropic Cosmological Constant and the CMB Quadrupole Anomaly
There are evidences that the cosmic microwave background (CMB) large-angle
anomalies imply a departure from statistical isotropy and hence from the
standard cosmological model. We propose a LCDM model extension whose dark
energy component preserves its nondynamical character but wield anisotropic
vacuum pressure. Exact solutions for the cosmological scale factors are
presented, upper bounds for the deformation parameter are evaluated and its
value is estimated considering the elliptical universe proposal to solve the
quadrupole anomaly. This model can be constructed from a Bianchi I cosmology
with cosmological constant from two different ways: i) a straightforward
anisotropic modification of the vacuum pressure consistently with
energy-momentum conservation; ii) a Poisson structure deformation between
canonical momenta such that the dynamics remain invariant under scale factors
rescalings.Comment: 8 pages, 2 columns, 1 figure. v2: figure improved, added comments on
higher eccentricity powers and references. v3: typos corrected, version to
appear in PR
Ground-based measurements of O3, NO2, OClO, and BrO during the 1987 Antarctic ozone depletion event
Near-ultraviolet absorption spectroscopy in the wavelength range from 330 to 370 nm was used to measure O3, NO2, OClO, and BrO at McMurdo Station (78S) during 1987. Visible absorption measurements of O3, NO2, and OClO were also obtained using the wavelength range from about 403 to 453 nm. These data are described and compared to observations obtained in 1986. It is shown that comparisons of observations in the two wavelength ranges provide a sensitive measure of the altitude where the bulk of atmospheric absorption takes place
Non-linear enhancement of laser generated ultrasonic Rayleigh waves by cracks
Laser generated ultrasound has been widely used for detecting cracks, surface and sub-surface defects in
many different materials. It provides a non-contact wideband excitation source which can be focused into
different geometries. Previous workers have reported enhancement of the laser generated Rayleigh wave
when a crack is illuminated by pulsed laser beam irradiation. We demonstrate that the enhancement
observed is due to a combination of source truncation, the free boundary condition at the edge of the crack
and interference effects. Generating a Rayleigh wave over a crack can lead to enhancement of the
amplitude of the Rayleigh wave signal, a shift in the dominant frequency of the wideband Rayleigh wave
and strong enhancement of the high frequency components of the Rayleigh wave
Nonlocal Cosmology
We explore nonlocally modified models of gravity, inspired by quantum loop
corrections, as a mechanism for explaining current cosmic acceleration. These
theories enjoy two major advantages: they allow a delayed response to cosmic
events, here the transition from radiation to matter dominance, and they avoid
the usual level of fine tuning; instead, emulating Dirac's dictum, the required
large numbers come from the large time scales involved. Their solar system
effects are safely negligible, and they may even prove useful to the black hole
information problem.Comment: Expanded(!) version, to appear in Phys. Rev. Letter
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