7,671 research outputs found
Vortex spectrum in superfluid turbulence: interpretation of a recent experiment
We discuss a recent experiment in which the spectrum of the vortex line
density fluctuations has been measured in superfluid turbulence. The observed
frequency dependence of the spectrum, , disagrees with classical
vorticity spectra if, following the literature, the vortex line density is
interpreted as a measure of the vorticity or enstrophy. We argue that the
disagrement is solved if the vortex line density field is decomposed into a
polarised field (which carries most of the energy) and an isotropic field
(which is responsible for the spectrum).Comment: Submitted for publication
http://crtbt.grenoble.cnrs.fr/helio/GROUP/infa.html
http://www.mas.ncl.ac.uk/~ncfb
Using a Gridded Global Dataset to Characterize Regional Hydroclimate in Central Chile
Central Chile is facing dramatic projections of climate change, with a consensus for declining precipitation, negatively affecting hydropower generation and irrigated agriculture. Rising from sea level to 6000 m within a distance of 200 km, precipitation characterization is difficult because of a lack of long-term observations, especially at higher elevations. For understanding current mean and extreme conditions and recent hydroclimatological change, as well as to provide a baseline for downscaling climate model projections, a temporally and spatially complete dataset of daily meteorology is essential. The authors use a gridded global daily meteorological dataset at 0.25° resolution for the period 1948–2008, adjusted by monthly precipitation observations interpolated to the same grid using a cokriging method with elevation as a covariate. For validation, daily statistics of the adjusted gridded precipitation are compared to station observations. For further validation, a hydrology model is driven with the gridded 0.25° meteorology and streamflow statistics are compared with observed flow. The high elevation precipitation is validated by comparing the simulated snow extent to Moderate Resolution Imaging Spectroradiometer (MODIS) images. Results show that the daily meteorology with the adjusted precipitation can accurately capture the statistical properties of extreme events as well as the sequence of wet and dry events, with hydrological model results displaying reasonable agreement with observed streamflow and snow extent. This demonstrates the successful use of a global gridded data product in a relatively data-sparse region to capture hydroclimatological characteristics and extremes
Global gyrokinetic simulations of ITG turbulence in the configuration space of the Wendelstein 7-X stellarator
We study the effect of turbulent transport in different magnetic
configurations of the Weldenstein 7-X stellarator. In particular, we performed
direct numerical simulations with the global gyrokinetic code GENE-3D, modeling
the behavior of Ion Temperature Gradient turbulence in the Standard,
High-Mirror, and Low-Mirror configurations of W7-X. We found that the
Low-Mirror configuration produces more transport than both the High-Mirror and
the Standard configurations. By comparison with radially local simulations, we
have demonstrated the importance of performing global nonlinear simulations to
predict the turbulent fluxes quantitatively
Polarization of superfluid turbulence
We show that normal fluid eddies in turbulent helium II polarize the tangle
of quantized vortex lines present in the flow, thus inducing superfluid
vorticity patterns similar to the driving normal fluid eddies. We also show
that the polarization is effective over the entire inertial range. The results
help explain the surprising analogies between classical and superfluid
turbulence which have been observed recently.Comment: 3 figure
Homothetic Wyman Spacetimes
The time-dependent, spherically symmetric, Wyman sector of the Unified Field
Theory is shown to be equivalent to a self-gravitating scalar field with a
positive-definite, repulsive self-interaction potential. A homothetic symmetry
is imposed on the fundamental tensor, and the resulting autonomous system is
numerically integrated. Near the critical point (between the collapsing and
non-collapsing spacetimes) the system displays an approximately periodic
alternation between collapsing and dispersive epochs.Comment: 15 pages with 6 figures; requires amsart, amssymb, amsmath, graphicx;
formatted for publication in Int. J. Mod. Phys.
Quantification of finite-temperature effects on adsorption geometries of -conjugated molecules
The adsorption structure of the molecular switch azobenzene on Ag(111) is
investigated by a combination of normal incidence x-ray standing waves and
dispersion-corrected density functional theory. The inclusion of non-local
collective substrate response (screening) in the dispersion correction improves
the description of dense monolayers of azobenzene, which exhibit a substantial
torsion of the molecule. Nevertheless, for a quantitative agreement with
experiment explicit consideration of the effect of vibrational mode
anharmonicity on the adsorption geometry is crucial.Comment: 12 pages, 3 figure
Examining the profound effects of COVID19 on mental health: A comprehensive systematic review on anxiety and depression
The COVID-19 pandemic has presented challenges to humanity, economically and in health and wellbeing. The associated limited social isolation and lifestyle changes has increased the risk for mental health services, especially among vulnerable people. This highlights the need for mental health services, burden that already stretch the health systems. This review presents an exposition on COVID-19 and mental health, and ways to minimise, and possibly prevent, their effect on the psychological well-being of those people. We searched four databases (Academic Search Complete, CINAHL Plus, PsycINFO and PsycARTICLES) using specific search terms and eligibility criteria. Of the 33 included studies, 31 were quantitative, and one qualitative and mixed method each. The studies were analysed using thematic narrative synthesis that resulted in three main themes: (a) the internal and external influences on COVID-19 behaviour, (b) the impact of COVID-19 on health and well-being and (c) the coping strategies used. Since COVID-19 will exist for the foreseeable future, understanding its impact on health and mental well-being and the coping techniques to be adopted are important now than ever. This study contributes to such an understanding along with suggestions regarding ways to minimise the impact of COVID-19 on mental health using context-appropriate strategies
Quantum turbulence at finite temperature: the two-fluids cascade
To model isotropic homogeneous quantum turbulence in superfluid helium, we
have performed Direct Numerical Simulations (DNS) of two fluids (the normal
fluid and the superfluid) coupled by mutual friction. We have found evidence of
strong locking of superfluid and normal fluid along the turbulent cascade, from
the large scale structures where only one fluid is forced down to the vorticity
structures at small scales. We have determined the residual slip velocity
between the two fluids, and, for each fluid, the relative balance of inertial,
viscous and friction forces along the scales. Our calculations show that the
classical relation between energy injection and dissipation scale is not valid
in quantum turbulence, but we have been able to derive a temperature--dependent
superfluid analogous relation. Finally, we discuss our DNS results in terms of
the current understanding of quantum turbulence, including the value of the
effective kinematic viscosity
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