906 research outputs found
The "zeroth law" of turbulence: Isotropic turbulence simulations revisited
The dimensionless kinetic energy dissipation rate C_epsilon is estimated from
numerical simulations of statistically stationary isotropic box turbulence that
is slightly compressible. The Taylor microscale Reynolds number Re_lambda range
is 20 < Re_lambda < 220 and the statistical stationarity is achieved with a
random phase forcing method. The strong Re_lambda dependence of C_epsilon
abates when Re_lambda approx. 100 after which C_epsilon slowly approaches
approx 0.5 a value slightly different to previously reported simulations but in
good agreement with experimental results. If C_epsilon is estimated at a
specific time step from the time series of the quantities involved it is
necessary to account for the time lag between energy injection and energy
dissipation. Also, the resulting value can differ from the ensemble averaged
value by up to +-30%. This may explain the spread in results from previously
published estimates of C_epsilon.Comment: 7 pages, 7 figures. Submitted to Phys. Rev.
Using built environment characteristics to predict walking for exercise
Background: Environments conducive to walking may help people avoid sedentary lifestyles and associated diseases. Recent studies developed walkability models combining several built environment characteristics to optimally predict walking. Developing and testing such models with the same data could lead to overestimating one's ability to predict walking in an independent sample
of the population. More accurate estimates of model fit can be obtained by splitting a single study population into training and validation sets (holdout approach) or through developing and
evaluating models in different populations. We used these two approaches to test whether built
environment characteristics near the home predict walking for exercise. Study participants lived in western Washington State and were adult members of a health maintenance organization. The physical activity data used in this study were collected by telephone interview and were selected for their relevance to cardiovascular disease. In order to limit confounding by prior health conditions, the sample was restricted to participants in good self-reported health and without a
documented history of cardiovascular disease.
Results: For 1,608 participants meeting the inclusion criteria, the mean age was 64 years, 90 percent were white, 37 percent had a college degree, and 62 percent of participants reported that they walked for exercise. Single built environment characteristics, such as residential density or connectivity, did not significantly predict walking for exercise. Regression models using multiple built environment characteristics to predict walking were not successful at predicting walking for
exercise in an independent population sample. In the validation set, none of the logistic models had a C-statistic confidence interval excluding the null value of 0.5, and none of the linear models
explained more than one percent of the variance in time spent walking for exercise. We did not detect significant differences in walking for exercise among census areas or postal codes, which
were used as proxies for neighborhoods.
Conclusion: None of the built environment characteristics significantly predicted walking for exercise, nor did combinations of these characteristics predict walking for exercise when tested
using a holdout approach. These results reflect a lack of neighborhood-level variation in walking for exercise for the population studied.University of Washington Royalty Research fund award; by contracts R01-HL043201, R01-HL068639, and T32-HL07902 from the National Heart, Lung, and Blood Institute; and by grant R01-AG09556 from the National Institute on Aging
Football Banning Orders: The Highly Effective Cornerstone of a Preventative Strategy?
The chapter examines the development, use and effectiveness of football banning orders in the UK, comparing their use in England to address issues of football 'hooliganism' with their distinct evolution in Scotland to address concerns around sectarian disorder
Magnetic fluctuations in the classical XY model: the origin of an exponential tail in a complex system
We study the probability density function for the fluctuations of the
magnetic order parameter in the low temperature phase of the XY model of finite
size. In two-dimensions this system is critical over the whole of the low
temperature phase. It is shown analytically and without recourse to the scaling
hypothesis that, in this case, the distribution is non-Gaussian and of
universal form, independent of both system size and critical exponent .
An exact expression for the generating function of the distribution is
obtained, which is transformed and compared with numerical data from high
resolution molecular dynamics and Monte Carlo simulations. The calculation is
extended to general dimension and an exponential tail is found in all
dimensions less than four, despite the fact that critical fluctuations are
limited to D=2. These results are discussed in the light of similar behaviour
observed in models of interface growth and for dissipative systems driven into
a non-equilibrium steady state.Comment: 32 pages, 13 figures, 1 table. Few changes. To appear in Phys. Rev.
Cognitive demands of face monitoring: Evidence for visuospatial overload
Young children perform difficult communication tasks better face to face than when they cannot see one another (e.g., Doherty-Sneddon & Kent, 1996). However, in recent studies, it was found that children aged 6 and 10 years, describing abstract shapes, showed evidence of face-to-face interference rather than facilitation. For some communication tasks, access to visual signals (such as facial expression and eye gaze) may hinder rather than help children’s communication. In new research we have pursued this interference effect. Five studies are described with adults and 10- and 6-year-old participants. It was found that looking at a face interfered with children’s abilities to listen to descriptions of abstract shapes. Children also performed visuospatial memory tasks worse when they looked at someone’s face prior to responding than when they looked at a visuospatial pattern or at the floor. It was concluded that performance on certain tasks was hindered by monitoring another person’s face. It is suggested that processing of visual communication signals shares certain processing resources with the processing of other visuospatial information
Focusing and Compression of Ultrashort Pulses through Scattering Media
Light scattering in inhomogeneous media induces wavefront distortions which
pose an inherent limitation in many optical applications. Examples range from
microscopy and nanosurgery to astronomy. In recent years, ongoing efforts have
made the correction of spatial distortions possible by wavefront shaping
techniques. However, when ultrashort pulses are employed scattering induces
temporal distortions which hinder their use in nonlinear processes such as in
multiphoton microscopy and quantum control experiments. Here we show that
correction of both spatial and temporal distortions can be attained by
manipulating only the spatial degrees of freedom of the incident wavefront.
Moreover, by optimizing a nonlinear signal the refocused pulse can be shorter
than the input pulse. We demonstrate focusing of 100fs pulses through a 1mm
thick brain tissue, and 1000-fold enhancement of a localized two-photon
fluorescence signal. Our results open up new possibilities for optical
manipulation and nonlinear imaging in scattering media
Pathogenesis of bovine spongiform encephalopathy in sheep
The pathogenesis of bovine spongiform encephalopathy (BSE) in sheep was studied by immunohistochemical detection of scrapie-associated prion protein (PrPSc) in the gastrointestinal, lymphoid and neural tissues following oral inoculation with BSE brain homogenate. First accumulation of PrPSc was detected after 6 months in the tonsil and the ileal Peyer’s patches. At 9 months postinfection, PrPSc accumulation involved all gut-associated lymphoid tissues and lymph nodes as well as the spleen. At this time point, PrPSc accumulation in the peripheral neural tissues was first seen in the enteric nervous system of the caudal jejunum and ileum and in the coeliac-mesenteric ganglion. In the central nervous system, PrPSc was first detected in the dorsal motor nucleus of the nervus Vagus in the medulla oblongata and in the intermediolateral column in the spinal cord segments T7–L1. At subsequent time points, PrPSc was seen to spread within the lymphoid system to also involve all non-gut-associated lymphoid tissues. In the enteric nervous system, further spread of PrPSc involved the neural plexi along the entire gastrointestinal tract and in the CNS the complete neuraxis. These findings indicate a spread of the BSE agent in sheep from the enteric nervous system through parasympathetic and sympathetic nerves to the medulla oblongata and the spinal cord
Interface localisation-delocalisation transition in a symmetric polymer blend: a finite-size scaling Monte Carlo study
Using extensive Monte Carlo simulations we study the phase diagram of a
symmetric binary (AB) polymer blend confined into a thin film as a function of
the film thickness D. The monomer-wall interactions are short ranged and
antisymmetric, i.e, the left wall attracts the A-component of the mixture with
the same strength as the right wall the B-component, and give rise to a first
order wetting transition in a semi-infinite geometry. The phase diagram and the
crossover between different critical behaviors is explored. For large film
thicknesses we find a first order interface localisation/delocalisation
transition and the phase diagram comprises two critical points, which are the
finite film width analogies of the prewetting critical point. Using finite size
scaling techniques we locate these critical points and present evidence of 2D
Ising critical behavior. When we reduce the film width the two critical points
approach the symmetry axis of the phase diagram and for we encounter a tricritical point. For even smaller film thickness the
interface localisation/delocalisation transition is second order and we find a
single critical point at .
Measuring the probability distribution of the interface position we determine
the effective interaction between the wall and the interface. This effective
interface potential depends on the lateral system size even away from the
critical points. Its system size dependence stems from the large but finite
correlation length of capillary waves. This finding gives direct evidence for a
renormalization of the interface potential by capillary waves in the framework
of a microscopic model.Comment: Phys.Rev.
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