11,116 research outputs found
Fish evacuate smoothly respecting a social bubble
Crowd movements are observed among different species and on different scales,
from insects to mammals, as well as in non-cognitive systems, such as motile
cells. When forced to escape through a narrow opening, most terrestrial animals
behave like granular materials and clogging events decrease the efficiency of
the evacuation. Here, we explore the evacuation behavior of macroscopic,
aquatic agents, neon fish, and challenge their gregarious behavior by forcing
the school through a constricted passage. Using a statistical analysis method
developed for granular matter and applied to crowd evacuation, our results
clearly show that, unlike crowds of people or herds of sheep, no clogging
occurs at the bottleneck. The fish do not collide and wait for a minimum
waiting time between two successive exits, while respecting a social distance.
When the constriction becomes similar to or smaller than their social distance,
the individual domains defined by this cognitive distance are deformed and fish
density increases. We show that the current of escaping fish behaves like a set
of deformable 2D-bubbles, their 2D domain, passing through a constriction.
Schools of fish show that, by respecting social rules, a crowd of individuals
can evacuate without clogging, even in an emergency situation.Comment: 7 pages, 4 figure
Cluster algebras of type
In this paper we study cluster algebras \myAA of type . We solve
the recurrence relations among the cluster variables (which form a T--system of
type ). We solve the recurrence relations among the coefficients of
\myAA (which form a Y--system of type ). In \myAA there is a
natural notion of positivity. We find linear bases \BB of \myAA such that
positive linear combinations of elements of \BB coincide with the cone of
positive elements. We call these bases \emph{atomic bases} of \myAA. These
are the analogue of the "canonical bases" found by Sherman and Zelevinsky in
type . Every atomic basis consists of cluster monomials together
with extra elements. We provide explicit expressions for the elements of such
bases in every cluster. We prove that the elements of \BB are parameterized
by \ZZ^3 via their --vectors in every cluster. We prove that the
denominator vector map in every acyclic seed of \myAA restricts to a
bijection between \BB and \ZZ^3. In particular this gives an explicit
algorithm to determine the "virtual" canonical decomposition of every element
of the root lattice of type . We find explicit recurrence relations
to express every element of \myAA as linear combinations of elements of
\BB.Comment: Latex, 40 pages; Published online in Algebras and Representation
Theory, springer, 201
Monitoramento de um Argissolo Vermelho sob produção de eucalipto de treze e vinte anos.
bitstream/item/30417/1/boletim-71.pd
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
Detection of major coronary artery anomalies in a pediatric and adult population: A prospective echocardiographic study
Effect of a gap on the decoherence of a qubit
We revisit the problem of the decoherence and relaxation of a central spin
coupled to a bath of conduction electrons. We consider both metallic and
semiconducting baths to study the effect of a gap in the bath density of states
(DOS) on the time evolution of the density matrix of the central spin. We use
two weak coupling approximation schemes to study the decoherence. At low
temperatures, though the temperature dependence of the decoherence rate in the
case of a metallic bath is the same irrespective of the details of the bath,
the same is not true for the semiconducting bath. We also calculate the
relaxation and decoherence rates as a function of external magnetic fields
applied both on the central spin and the bath. We find that in the presence of
the gap, there exists a certain regime of fields, for which surprisingly, the
metallic bath has lower rates of relaxation and decoherence than the
semiconducting bath.Comment: 9 pages, 9 figure
Protective activity of propofol, Diprivan and intralipid against active oxygen species.
We separately studied the antioxidant properties of propofol (PPF), Diprivan (the commercial form of PPF) and intralipid (IL) (the vehicle solution of PPF in Diprivan) on active oxygen species produced by phorbol myristate acetate (10(-6) M)-stimulated human polymorphonuclear leukocytes (PMN: 5 x 10(5) cells/assay), human endothelial cells (5 x 10(5) cells/assay) or cell-free systems (NaOCl or H2O2/peroxidase systems), using luminol (10(-4) M)-enhanced chemiluminescence (CL). We also studied the protective effects of Diprivan on endothelial cells submitted to an oxidant stress induced by H2O2/MPO system: cytotoxicity was assessed by the release of preincorporated 51Cr. Propofol inhibited the CL produced by stimulated PMN in a dose dependent manner (until 5 x 10(-5) M, a clinically relevant concentration), while Diprivan and IL were not dose-dependent inhibitors. The CL produced by endothelial cells was dose-dependently inhibited by Diprivan and PPF, and weakly by IL (not dose-dependent). In cell free systems, dose-dependent inhibitions were obtained for the three products with a lower effect for IL. Diprivan efficaciously protected endothelial cells submitted to an oxidant stress, while IL was ineffective. By HPLC, we demonstrated that PPF was not incorporated into the cells. The drug thus acted by scavenging the active oxygen species released in the extracellular medium. IL acted in the same manner, but was a less powerful antioxidant
Fcc-bcc transition for Yukawa interactions determined by applied strain deformation
Calculations of the work required to transform between bcc and fcc phases
yield a high-precision bcc-fcc transition line for monodisperse point Yukawa
(screened-Couloumb) systems. Our results agree qualitatively but not
quantitatively with previously published simulations and phenomenological
criteria for the bcc-fcc transition. In particular, the bcc-fcc-fluid triple
point lies at a higher inverse screening length than previously reported.Comment: RevTex4, 9 pages, 6 figures. Discussion of phase coexistence
extended, a few other minor clarifications added, referencing improved.
Accepted for publication by Physical Review
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