2,432 research outputs found
An approach to anomalous diffusion in the n-dimensional space generated by a self-similar Laplacian
We analyze a quasi-continuous linear chain with self-similar distribution of
harmonic interparticle springs as recently introduced for one dimension
(Michelitsch et al., Phys. Rev. E 80, 011135 (2009)). We define a continuum
limit for one dimension and generalize it to dimensions of the
physical space. Application of Hamilton's (variational) principle defines then
a self-similar and as consequence non-local Laplacian operator for the
-dimensional space where we proof its ellipticity and its accordance (up to
a strictly positive prefactor) with the fractional Laplacian
. By employing this Laplacian we establish a
Fokker Planck diffusion equation: We show that this Laplacian generates
spatially isotropic L\'evi stable distributions which correspond to L\'evi
flights in -dimensions. In the limit of large scaled times the obtained distributions exhibit an algebraic decay independent from the initial distribution
and spacepoint. This universal scaling depends only on the ratio of
the dimension of the physical space and the L\'evi parameter .Comment: Submitted manuscrip
Bose-Einstein transition temperature in a dilute repulsive gas
We discuss certain specific features of the calculation of the critical
temperature of a dilute repulsive Bose gas. Interactions modify the critical
temperature in two different ways. First, for gases in traps, temperature
shifts are introduced by a change of the density profile, arising itself from a
modification of the equation of state of the gas (reduced compressibility);
these shifts can be calculated simply within mean field theory. Second, even in
the absence of a trapping potential (homogeneous gas in a box), temperature
shifts are introduced by the interactions; they arise from the correlations
introduced in the gas, and thus lie inherently beyond mean field theory - in
fact, their evaluation requires more elaborate, non-perturbative, calculations.
One illustration of this non-perturbative character is provided by the solution
of self-consistent equations, which relate together non-linearly the various
energy shifts of the single particle levels k. These equations predict that
repulsive interactions shift the critical temperature (at constant density) by
an amount which is positive, and simply proportional to the scattering length
a; nevertheless, the numerical coefficient is difficult to compute. Physically,
the increase of the temperature can be interpreted in terms of the reduced
density fluctuations introduced by the repulsive interactions, which facilitate
the propagation of large exchange cycles across the sample.Comment: two minor corrections, two refs adde
Analysis of repeated high-intensity running performance in professional soccer
The aims of this study conducted in a professional soccer team were two-fold: to characterise repeated high-intensity movement activity profiles in official match-play; b) to inform and verify the construct validity of tests commonly used to determine repeated-sprint ability in soccer by investigating the relationship between the results from a test of repeated-sprint ability and repeated high-intensity performance in competition. High-intensity running performance (movement at velocities >19.8 km/h for a minimum of 1-s duration) in 20 players was measured using computerised time motion analysis. Performance in 80 French League 1 matches was analysed. In addition, 12 out of the 20 players performed a repeated-sprint test on a non-motorized treadmill consisting of 6 consecutive 6s sprints separated by 20s passive recovery intervals. In all players, the majority of consecutive high-intensity actions in competition were performed after recovery durations ≥61s, recovery activity separating these efforts was generally active in nature with the major part of this spent walking, and players performed 1.1±1.1 repeated high-intensity bouts (a minimum of 3 consecutive high-intensity with a mean recovery time ≤20s separating efforts) per game. Players reporting lowest performance decrements in the repeated-sprint ability test performed more high-intensity actions interspersed by short recovery times (≤20s, p<0.01 and ≤30s, p<0.05) compared to those with higher decrements. Across positional roles, central-midfielders performed a greater number of high-intensity actions separated by short recovery times (≤20s) and spent a larger proportion of time running at higher intensities during recovery periods while fullbacks performed the most repeated high-intensity bouts (statistical differences across positional roles from p<0.05 to p<0.001). These findings have implications for repeated high-intensity testing and physical conditioning regimens
Dedicated and industrial robotic arms used as force feedback telerobots at the AREVA-La Hague recycling plant
ISBN: 978-1-4244-6635-1/10International audienceCEA LIST and AREVA have been developing remote operations devices, also called telerobotics for 15 years. These tools were designed for interventions in the AREVA nuclear spent fuel facilities hot cells. From these 15 years of joint research and development, several technological bricks have been industrialized and used at the AREVA La Hague facilities. This article presents some of these bricks and their industrial developments. The “TAO2000” CEA LIST telerobotics generic software controller will be first discussed. This controller has been used to teleoperate dedicated slave arms like the MT200 TAO (an evolution of the conventional wall-transmission mechanical telemanipulator (MSM)) as well as industrial robotic arms like the Stäubli RX robots. Both the MT200 TAO and Stäubli RX TAO telerobotics systems provide force-feedback and are now ready to be used as telemaintenance tools at the AREVA La Hague facilities. Two recent maintenance operations using these tools will be detailed at the end of this pape
Isotope effects in underdoped cuprate superconductors: a quantum phenomenon
We show that the unusual doping dependence of the isotope effects on
transition temperature and zero temperature in - plane penetration depth
naturally follows from the doping driven 3D-2D crossover, the 2D quantum
superconductor to insulator transition (QSI) in the underdoped limit and the
change of the relative doping concentration upon isotope substitution. Close to
the QSI transition both, the isotope coefficient of transition temperature and
penetration depth approach the coefficient of the relative dopant
concentration, and its divergence sets the scale. These predictions are fully
consistent with the experimental data and imply that close to the underdoped
limit the unusual isotope effect on transition temperature and penetration
depth uncovers critical phenomena associated with the quantum superconductor to
insulator transition in two dimensions.Comment: 6 pages, 3 figure
X-Ray Scattering at FeCo(001) Surfaces and the Crossover between Ordinary and Normal Transitions
In a recent experiment by Krimmel et al. [PRL 78, 3880 (1997)], the critical
behavior of FeCo near a (001) surface was studied by x-ray scattering. Here the
experimental data are reanalyzed, taking into account recent theoretical
results on order-parameter profiles in the crossover regime between ordinary
and normal transitions. Excellent agreement between theoretical expectations
and the experimental results is found.Comment: 9 pages, Latex, 1 PostScript figure, to be published in Phys.Rev.
Molecular evidence for increased regulatory conservation during metamorphosis, and against deleterious cascading effects of hybrid breakdown in Drosophila
<p>Abstract</p> <p>Background</p> <p>Speculation regarding the importance of changes in gene regulation in determining major phylogenetic patterns continues to accrue, despite a lack of broad-scale comparative studies examining how patterns of gene expression vary during development. Comparative transcriptional profiling of adult interspecific hybrids and their parental species has uncovered widespread divergence of the mechanisms controlling gene regulation, revealing incompatibilities that are masked in comparisons between the pure species. However, this has prompted the suggestion that misexpression in adult hybrids results from the downstream cascading effects of a subset of genes improperly regulated in early development.</p> <p>Results</p> <p>We sought to determine how gene expression diverges over development, as well as test the cascade hypothesis, by profiling expression in males of <it>Drosophila melanogaster</it>, <it>D. sechellia</it>, and <it>D. simulans</it>, as well as the <it>D. simulans </it>(♀) × <it>D. sechellia </it>(♂) male F1 hybrids, at four different developmental time points (3rd instar larval, early pupal, late pupal, and newly-emerged adult). Contrary to the cascade model of misexpression, we find that there is considerable stage-specific autonomy of regulatory breakdown in hybrids, with the larval and adult stages showing significantly more hybrid misexpression as compared to the pupal stage. However, comparisons between pure species indicate that genes expressed during earlier stages of development tend to be more conserved in terms of their level of expression than those expressed during later stages, suggesting that while Von Baer's famous law applies at both the level of nucleotide sequence and expression, it may not apply necessarily to the underlying overall regulatory network, which appears to diverge over the course of ontogeny and which can only be ascertained by combining divergent genomes in species hybrids.</p> <p>Conclusion</p> <p>Our results suggest that complex integration of regulatory circuits during morphogenesis may lead to it being more refractory to divergence of underlying gene regulatory mechanisms - more than that suggested by the conservation of gene expression levels between species during earlier stages. This provides support for a 'developmental hourglass' model of divergence of gene expression in <it>Drosophila </it>resulting in a highly conserved pupal stage.</p
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