1,254 research outputs found
Direct Numerical Simulation of a separated channel flow with a smooth profile
A direct numerical simulation (DNS) of a channel flow with one curved surface
was performed at moderate Reynolds number (Re_tau = 395 at the inlet). The
adverse pressure gradient was obtained by a wall curvature through a
mathematical mapping from physical coordinates to Cartesian ones. The code,
using spectral spanwise and normal discretization, combines the advantage of a
good accuracy with a fast integration procedure compared to standard numerical
procedures for complex geometries. The turbulent flow slightly separates on the
profile at the lower curved wall and is at the onset of separation at the
opposite flat wall. The thin separation bubble is characterized with a reversal
flow fraction. Intense vortices are generated near the separation line on the
lower wall but also at the upper wall. Turbulent normal stresses and kinetic
energy budget are investigated along the channel.Comment: 23 pages, submitted to Journal of Turbulenc
Time to exhaustion at estimated functional threshold power in road cyclists of different performance levels
This study assessed the functional threshold power and the time to exhaustion estimated from the Allen & Coggan test and verify whether performance level has an influence on this parameter
Characteristics of pedaling muscle stiffness among cyclists of different performance levels
Background and Objectives: The aim of the present study was to compare the impact of an incremental exercise test on muscle stiffness in the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and gastrocnemius (GL) among road cyclists of three performance levels. Materials and Methods: The study group consisted of 35 cyclists grouped according to their performance level; elite (n = 10; professional license), sub-elite (n = 12; amateur license), and recreational (n = 13; cyclosportive license). Passive muscle stiffness was assessed using myometry before and after an incremental exercise test. Results: There was a significant correlation between time and category in the vastus lateralis with stiffness increases in the sub-elite (p = 0.001, Cohenâs d = 0.88) and elite groups (p = 0.003, Cohenâs d = 0.72), but not in the recreational group (p = 0.085). Stiffness increased over time in the knee extensors (RF, p < 0.001; VL, p < 0.001), but no changes were observed in the knee flexors (GL, p = 0.63, BF, p = 0.052). There were no baseline differences among the categories in any muscle. Conclusions: Although the performance level affected VL stiffness after an incremental exercise test, no differences in passive stiffness were observed among the main muscles implicated in pedaling in a resting state. Future research should assess whether this marker could be used to differentiate cyclists of varying fitness levels and its potential applicability for the monitoring of training load. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Gain degradation of a linear array due to random deformations
This paper deals with the gain degradation ofa lineararray when the signal spatial
coherence is reduced by the random deformations of the line supporting the array.
When the signal is imperfectly coherent, the gain is reduced by a sa called « gain
degradation factor » which can be evaluated from the signal spatial coherence
function and the array weighting function .
In the case of random deformations of the array, an apparent signal spatial coherencefunction
may be calculated from the stochastic model which characterizes the
deformations. An expression of the gain degradation factor can then be deduced as
a function of some reduced parameters which depend on frequency, array length,
signal direction of arrival and the statistical parameters which characterize the
deformations.Cet article prĂ©sente une mĂ©thode qui permet de calculer la dĂ©gradation de gain d'une antenne linĂ©aire lorsque la cohĂ©rence spatiale du signal se trouve limitĂ©e par les dĂ©formations alĂ©atoires qui peuvent affecter la linĂ©aritĂ© de l'antenne. Lorsqu'on se trouve en prĂ©sence d'un signal imparfaitement cohĂ©rent le gain est rĂ©duit par un certain "facteur de dĂ©gradation" que l'on peut calculer Ă partir de la fonction de cohĂ©rence spatiale du signal et de la fonction de pondĂ©ration de l'antenne. Dans le cas des dĂ©formations alĂ©atoires de l'antenne, une fonction de cohĂ©rence spatiale apparente du signal peut ĂȘtre calculĂ©e Ă partir du modĂšle stochastique qui caractĂ©rise ces dĂ©formation
Supernova Remnants in the Magellanic Clouds III: An X-ray Atlas of LMC Supernova Remnants
We have used archival ROSAT data to present X-ray images of thirty-one
supernova remnants (SNRs) in the Large Magellanic Cloud (LMC). We have
classified these remnants according to their X-ray morphologies, into the
categories of Shell-Type, Diffuse Face, Centrally Brightened, Point-Source
Dominated, and Irregular. We suggest possible causes of the X-ray emission for
each category, and for individual features of some of the SNRs.Comment: 27 pages, 6 figures (9 figure files). To appear in the Supplement
Series of the Astrophysical Journal, August 1999 Vol. 123 #
Quasilinear theory of the 2D Euler equation
We develop a quasilinear theory of the 2D Euler equation and derive an
integro-differential equation for the evolution of the coarse-grained
vorticity. This equation respects all the invariance properties of the Euler
equation and conserves angular momentum in a circular domain and linear impulse
in a channel. We show under which hypothesis we can derive a H-theorem for the
Fermi-Dirac entropy and make the connection with statistical theories of 2D
turbulence.Comment: 4 page
Beyond scaling and locality in turbulence
An analytic perturbation theory is suggested in order to find finite-size
corrections to the scaling power laws. In the frame of this theory it is shown
that the first order finite-size correction to the scaling power laws has
following form , where
is a finite-size scale (in particular for turbulence, it can be the Kolmogorov
dissipation scale). Using data of laboratory experiments and numerical
simulations it is shown shown that a degenerate case with can
describe turbulence statistics in the near-dissipation range , where
the ordinary (power-law) scaling does not apply. For moderate Reynolds numbers
the degenerate scaling range covers almost the entire range of scales of
velocity structure functions (the log-corrections apply to finite Reynolds
number). Interplay between local and non-local regimes has been considered as a
possible hydrodynamic mechanism providing the basis for the degenerate scaling
of structure functions and extended self-similarity. These results have been
also expanded on passive scalar mixing in turbulence. Overlapping phenomenon
between local and non-local regimes and a relation between position of maximum
of the generalized energy input rate and the actual crossover scale between
these regimes are briefly discussed.Comment: extended versio
Extented ionized gas emission and kinematics of the compact group galaxies in HCG 16: Signatures of mergers
We report on kinematic observations of Ha emission line from four late-type
galaxies of Hickson Compact Group 16 (H16a,b,c and d) obtained with a scanning
Fabry-Perot interferometer and samplings of 16 km/s and 1". The velocity fields
show kinematic peculiarities for three of the four galaxies: H16b, c and d.
Misalignments between the kinematic and photometric axes of gas and stellar
components (H16b,c,d), double gas systems (H16c) and severe warping of the
kinematic major axis (H16b and c) were some of the peculiarities detected. We
conclude that major merger events have taken place in at least two of the
galaxies group. H16c and d, based on their significant kinematic peculiarities,
their double nuclei and high infrared luminosities. Their Ha gas content is
strongly spatially concentred - H16d contains a peculiar bar-like structure
confined to the inner 1 h^-1 kpc region. These observations are in
agreement with predictions of simulations, namely that the gas flows towards
the galaxy nucleus during mergers, forms bars and fuel the central activity.
Galaxy H16b, and Sb galaxy, also presents some of the kinematic evidences for
past accretion events. Its gas content, however, is very spare, limiting our
ability to find other kinematic merging indicators, if they are present. We
find that isolated mergers, i.e., they show an anormorphous morphology and no
signs of tidal tails. Tidal arms and tails formed during the mergers may have
been stripped by the group potential (Barnes & Hernquist 1992) ar alternatively
they may have never been formed. Our observations suggest that HCG 16 may be a
young compact group in formation throught the merging of close-by objects in a
dense environment.Comment: Accepted for publication in ApJ. 35 pages, 13 figures. tar file
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