3,942 research outputs found
Transition to turbulence in slowly divergent pipe flow
The results of a combined experimental and numerical study of the flow in
slowly diverging pipes are presented. Interestingly, an axisymmetric conical
recirculation cell has been observed. The conditions for its existence and the
length of the cell are simulated for a range of diverging angles and expansion
ratios. There is a critical velocity for the appearance of this state. When the
flow rate increases further, a subcritical transition for localized turbulence
arises. The transition and relaminarization experiments described here quantify
the extent of turbulence. The findings suggest that the transition scenario in
slowly diverging pipes is a combination of stages similar to those observed in
sudden expansions and in straight circular pipe flow.Comment: 8 pages, 5 figure
Lyapunov analysis captures the collective dynamics of large chaotic systems
We show, using generic globally-coupled systems, that the collective dynamics
of large chaotic systems is encoded in their Lyapunov spectra: most modes are
typically localized on a few degrees of freedom, but some are delocalized,
acting collectively on the trajectory. For globally-coupled maps, we show
moreover a quantitative correspondence between the collective modes and some of
the so-called Perron-Frobenius dynamics. Our results imply that the
conventional definition of extensivity must be changed as soon as collective
dynamics sets in.Comment: 4 pages, 4 figures; small changes, mostly stylistic, made in v
Extensive and Sub-Extensive Chaos in Globally-Coupled Dynamical Systems
Using a combination of analytical and numerical techniques, we show that
chaos in globally-coupled identical dynamical systems, be they dissipative or
Hamiltonian, is both extensive and sub-extensive: their spectrum of Lyapunov
exponents is asymptotically flat (thus extensive) at the value
given by a single unit forced by the mean-field, but sandwiched between
sub-extensive bands containing typically exponents whose
values vary as with .Comment: 4 pages, 4 figures; minor changes made and 2 figure panels adde
Phenotypic diversity of farmerâs traditional maize (Zea mays L) varieties in Cote dâIvoire
Primitive cultivars and their wild relatives are an invaluable heritage for humanity. They must be preserved, stud- ied and used to increase agricultural production. This study aims at assessing the phenotypic diversity of 118 maize (Zea mays L) accessions collected CĂŽte dâIvoire. The test was conducted in FerkessĂ©dougou (north of CĂŽte dâIvoire) during the 2013/2014 and 2014/2015 rainy seasons. It was implanted in a square lattice design 11 x 11, repeated three times. Twenty-two quantitative variables were measured. From the results, it appeared that there was significant morphological variability among accessions. The multivariate analyses (Principal Components Analysis and Hierarchical Cluster Analysis) enabled to structure this diversity into five groups. Days to 50 % silk- ing and to 50 % tasselling, ear insertion height, plant height, number of leaves below the uppermost ear, and ear parameters are those that best explain the agro-morphological diversity. The different groups obtained can serve as a starting point for the definition of a core collection. They offer a wide possibility of choice of breeding lines for the creation of improved maize varieties adapted to the different agro-climatic zones of CĂŽte dâIvoir
Effects of photoperiod extension on clock gene and neuropeptide RNA expression in the SCN of the Soay sheep
In mammals, changing daylength (photoperiod) is the main synchronizer of seasonal functions. The photoperiodic information is transmitted through the retino-hypothalamic tract to the suprachiasmatic nuclei (SCN), site of the master circadian clock. To investigate effects of day length change on the sheep SCN, we used in-situ hybridization to assess the daily temporal organization of expression of circadian clock genes (Per1, Per2, Bmal1 and Fbxl21) and neuropeptides (Vip, Grp and Avp) in animals acclimated to a short photoperiod (SP; 8h of light) and at 3 or 15 days following transfer to a long photoperiod (LP3, LP15, respectively; 16h of light), achieved by an acute 8-h delay of lights off. We found that waveforms of SCN gene expression conformed to those previously seen in LP acclimated animals within 3 days of transfer to LP. Mean levels of expression for Per1-2 and Fbxl21 were nearly 2-fold higher in the LP15 than in the SP group. The expression of Vip was arrhythmic and unaffected by photoperiod, while, in contrast to rodents, Grp expression was not detectable within the sheep SCN. Expression of the circadian output gene Avp cycled robustly in all photoperiod groups with no detectable change in phasing. Overall these data suggest that synchronizing effects of light on SCN circadian organisation proceed similarly in ungulates and in rodents, despite differences in neuropeptide gene expression
Absorbing states and elastic interfaces in random media: two equivalent descriptions of self-organized criticality
We elucidate a long-standing puzzle about the non-equilibrium universality
classes describing self-organized criticality in sandpile models. We show that
depinning transitions of linear interfaces in random media and absorbing phase
transitions (with a conserved non-diffusive field) are two equivalent languages
to describe sandpile criticality. This is so despite the fact that local
roughening properties can be radically different in the two pictures, as
explained here. Experimental implications of our work as well as promising
paths for future theoretical investigations are also discussed.Comment: 4 pages. 2 Figure
Entrainment transition in populations of random frequency oscillators
The entrainment transition of coupled random frequency oscillators is
revisited. The Kuramoto model (global coupling) is shown to exhibit unusual
sample-dependent finite size effects leading to a correlation size exponent
. Simulations of locally coupled oscillators in -dimensions
reveal two types of frequency entrainment: mean-field behavior at , and
aggregation of compact synchronized domains in three and four dimensions. In
the latter case, scaling arguments yield a correlation length exponent
, in good agreement with numerical results.Comment: published versio
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