24,870 research outputs found
Anisotropy, disorder, and superconductivity in CeCu2Si2 under high pressure
Resistivity measurements were carried out up to 8 GPa on single crystal and
polycrystalline samples of CeCu2Si2 from differing sources in the homogeneity
range. The anisotropic response to current direction and small uniaxial
stresses was explored, taking advantage of the quasi-hydrostatic environment of
the Bridgman anvil cell. It was found that both the superconducting transition
temperature Tc and the normal state properties are very sensitive to uniaxial
stress, which leads to a shift of the valence instability pressure Pv and a
small but significant change in Tc for different orientations with respect to
the tetragonal c-axis. Coexistence of superconductivity and residual
resistivity close to the Ioffe-Regel limit around 5 GPa provides a compelling
argument for the existence of a valence-fluctuation mediated pairing
interaction at high pressure in CeCu2Si2.Comment: 12 pages, 7 figure
A flight evaluation of a trailing anemometer for low-speed calibrations of airspeed systems on research aircraft
Research airspeed systems on three low-speed general aviation airplanes were calibrated by the trailing anemometer method. Each airplane was fitted with an NASA pitot-static pressure tube mounted on either a nose or wing boom. The uncalibrated airspeed systems contained residual static-pressure position errors which were too large for high-accuracy flight research applications. The trailing anemometer calibration was in agreement with the tower flyby calibration for the one aircraft for which the comparison was made. The continuous deceleration technique for the trailing anemometer method offers reduced test time with no appreciable loss of accuracy for airspeed systems with pitot-static system lag characteristics similar to those described
Overdamped Stress Relaxation in Buckled Rods
We present a comprehensive theoretical analysis of the stress relaxation in a
multiply but weakly buckled incompressible rod in a viscous solvent. In the
bulk two interesting regimes of generic self--similar intermediate asymptotics
are distinguished, which give rise to two classes of approximate and exact
power--law solutions, respectively. For the case of open boundary conditions
the corresponding non--trivial boundary--layer scenarios are derived by a
multiple--scale perturbation (``adiabatic'') method. Our results compare well
with -- and provide the theoretical explanation for -- previous results from
numerical simulations, and they suggest new directions for further fruitful
numerical and experimental investigations.Comment: 20 pages, 12 figure
Quantifying Spatiotemporal Chaos in Rayleigh-B\'enard Convection
Using large-scale parallel numerical simulations we explore spatiotemporal
chaos in Rayleigh-B\'enard convection in a cylindrical domain with
experimentally relevant boundary conditions. We use the variation of the
spectrum of Lyapunov exponents and the leading order Lyapunov vector with
system parameters to quantify states of high-dimensional chaos in fluid
convection. We explore the relationship between the time dynamics of the
spectrum of Lyapunov exponents and the pattern dynamics. For chaotic dynamics
we find that all of the Lyapunov exponents are positively correlated with the
leading order Lyapunov exponent and we quantify the details of their response
to the dynamics of defects. The leading order Lyapunov vector is used to
identify topological features of the fluid patterns that contribute
significantly to the chaotic dynamics. Our results show a transition from
boundary dominated dynamics to bulk dominated dynamics as the system size is
increased. The spectrum of Lyapunov exponents is used to compute the variation
of the fractal dimension with system parameters to quantify how the underlying
high-dimensional strange attractor accommodates a range of different chaotic
dynamics
A transient heat transfer and thermodynamic analysis of the Apollo service module propulsion system. Vol. I, phase I - Transient thermal analysis Final report, 28 Jul. 1964 - 28 Jul. 1965
Transient heat transfer and thermodynamic behavior analysis for Apollo service module propulsion system - fuel cell effect on overheatin
Minimality of planes in normed spaces
We prove that a region in a two-dimensional affine subspace of a normed space
has the least 2-dimensional Hausdorff measure among all compact surfaces
with the same boundary. Furthermore, the 2-dimensional Hausdorff area density
admits a convex extension to . The proof is based on a (probably)
new inequality for the Euclidean area of a convex centrally-symmetric polygon.Comment: 10 pages, v2: minor changes according to referees' comments, to
appear in GAF
Gravitational wave recoil in Robinson-Trautman spacetimes
We consider the gravitational recoil due to non-reflection-symmetric
gravitational wave emission in the context of axisymmetric Robinson-Trautman
spacetimes. We show that regular initial data evolve generically into a final
configuration corresponding to a Schwarzschild black-hole moving with constant
speed. For the case of (reflection-)symmetric initial configurations, the mass
of the remnant black-hole and the total energy radiated away are completely
determined by the initial data, allowing us to obtain analytical expressions
for some recent numerical results that have been appeared in the literature.
Moreover, by using the Galerkin spectral method to analyze the non-linear
regime of the Robinson-Trautman equations, we show that the recoil velocity can
be estimated with good accuracy from some asymmetry measures (namely the first
odd moments) of the initial data. The extension for the non-axisymmetric case
and the implications of our results for realistic situations involving head-on
collision of two black holes are also discussed.Comment: 9 pages, 6 figures, final version to appear in PR
“I Control What I Eat and I'm Sensible with What I Eat, Apart from School” – A Qualitative Study of Adolescents’ Food Choices and the School Environment
Objectives
Adolescent obesity is a significant issue in the UK, with 36% of 11 to 15 year olds classified as overweight or obese. Schools are seen as a sound setting to address this phenomenon. Mandatory School Food Standards have endeavoured to improve the nutritional profile of school food provision. However students often choose micronutrient poor, energy dense options. This study aimed to explore how and why secondary school students make their food choices within the school environment.
Methods
Seven focus group interviews were conducted with students (n = 28) aged 13–14 years in a school in Northern England. Development of the focus group schedule was informed by the socio-ecological model and food choice process model. Question topics included school food provision, students’ food choices and the role of friends and family in students’ food choices. Discussions were audio-recorded, transcribed verbatim and analysed using an inductive thematic approach: an iterative process of reading and re-reading transcripts, coding of nodes and grouping of nodes into unique themes. NVivo12 software was used to facilitate data management.
Results
Six initial themes emerged; (1) home environment, (2) food knowledge, (3) food choice factors, (4) food autonomy struggle, (5) social influences and (6) home versus school. Findings suggest that adolescents juxtapose the school and home food environments, in terms of food provision, food choices, as well as food-related rules and customs. Students identified food choices at home as being a structured and clearly defined process, with parents and caregivers acting as nutritional gatekeepers. In contrast, students depicted school food choices as being less straight-forward, determined by factors including social influences and school food choice parameters (e.g., time, queues, cost). Students reported choosing less “healthy” items at school than at home, and justified this by reportedly adopting perceived healthier choices/behaviours at home.
Conclusions
Both the school and home environment (in)directly influence adolescents’ school food choices. Further research is needed to understand these contrasting environmental influences, and how adolescents manage and integrate their food choice behaviours in different environments
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