3,802 research outputs found
Properties of pedestrians walking in line: Stepping behavior
In human crowds, interactions among individuals give rise to a variety of
self-organized collective motions that help the group to effectively solve the
problem of coordination. However, it is still not known exactly how humans
adjust their behavior locally, nor what are the direct consequences on the
emergent organization. One of the underlying mechanisms of adjusting individual
motions is the stepping dynamics. In this paper, we present first quantitative
analysis on the stepping behavior in a one-dimensional pedestrian flow studied
under controlled laboratory conditions. We find that the step length is
proportional to the velocity of the pedestrian, and is directly related to the
space available in front of him, while the variations of the step duration are
much smaller. This is in contrast with locomotion studies performed on isolated
pedestrians and shows that the local density has a direct influence on the
stepping characteristics. Furthermore, we study the phenomena of
synchronization -walking in lockstep- and show its dependence on flow
densities. We show that the synchronization of steps is particularly important
at high densities, which has direct impact on the studies of optimizing
pedestrians flow in congested situations. However, small synchronization and
antisynchronization effects are found also at very low densities, for which no
steric constraints exist between successive pedestrians, showing the natural
tendency to synchronize according to perceived visual signals.Comment: 8 pages, 5 figure
Spontaneous symmetry breaking in a two-lane model for bidirectional overtaking traffic
First we consider a unidirectional flux \omega_bar of vehicles each of which
is characterized by its `natural' velocity v drawn from a distribution P(v).
The traffic flow is modeled as a collection of straight `world lines' in the
time-space plane, with overtaking events represented by a fixed queuing time
tau imposed on the overtaking vehicle. This geometrical model exhibits platoon
formation and allows, among many other things, for the calculation of the
effective average velocity w=\phi(v) of a vehicle of natural velocity v.
Secondly, we extend the model to two opposite lanes, A and B. We argue that the
queuing time \tau in one lane is determined by the traffic density in the
opposite lane. On the basis of reasonable additional assumptions we establish a
set of equations that couple the two lanes and can be solved numerically. It
appears that above a critical value \omega_bar_c of the control parameter
\omega_bar the symmetry between the lanes is spontaneously broken: there is a
slow lane where long platoons form behind the slowest vehicles, and a fast lane
where overtaking is easy due to the wide spacing between the platoons in the
opposite direction. A variant of the model is studied in which the spatial
vehicle density \rho_bar rather than the flux \omega_bar is the control
parameter. Unequal fluxes \omega_bar_A and \omega_bar_B in the two lanes are
also considered. The symmetry breaking phenomenon exhibited by this model, even
though no doubt hard to observe in pure form in real-life traffic, nevertheless
indicates a tendency of such traffic.Comment: 50 pages, 16 figures; extra references adde
PALAEONTOLOGICAL (RADIOLARIAN) LATE JURASSIC AGE CONSTRAINT FOR THE STEPANAVAN OPHIOLITE (LESSER CAUCASUS, ARMENIA)
Η χρονολόγηση με βάση μικροπαλαιοντολογικά δεδομένα, των ιζηματογενών καλυμμάτων των οφιολίθων είναι ιδιαίτερης σημασίας για την κατανόηση της παλαιογεωγραφικής και γεωδυναμικής εξέλιξης των περιοχών της Τηθύος. Η οφιολιθική ακολουθία του Stepanavan στη Βόρεια Αρμενία συνίσταται από περιδοτίτες, γάββρους, πλαγιογρανίτες και λάβες και ιζηματογενή καλύματα ραδιολαριτών. Θεωρείται ως η βόρεια επέκταση της οφιολιθικής ζώνης Sevan Akera και η ανατολική επέκταση της ζώνης Izmir-Ankara. Αντιπροσωπεύει κατάλοιπο μιας βραδέως εκτεινόμενης μεσο-ωκεάνιας ράχης, που ήταν ενεργή μεταξύ της Ευρασίας και του νότιου Αρμενικού τεμάχους γκοντβανικής προέλευσης. Τα ραδιολάρια που εξετάστηκαν από τους ραδιολαρίτες στην περιοχή της οφιολιθικής ακολουθίας του Stepanavan πιστοποιούν για πρώτη φορά ηλικία Ανώτερου Ιουρασικού (ανώτερο Κιμμερίδιο έως κατώτερο Τιθώνιο) προσδίδοντας ηλικία για αυτό το τμήμα του ωκεάνιου φλοιού της Τηθύος που παρατηρείται στο Lesser Caucasus.Micropalaeontological age evidence for the sedimentary cover of ophiolites is important to understand the palaeogeographic and geodynamic evolution of Tethyan realms. The Stepanavan ophiolitic suite of Northern Armenia consists of peridotites, gabbros, plagiogranite and lavas with a radiolarite sedimentary cover. It is regarded as the northern extension of the Sevan Akera ophiolitic zone and may be considered as the eastern extension of the Izmir-Ankara suture zone. It represents the relics of a slow-spreading mid oceanic ridge that was active between Eurasia and the South-Armenian Block of Gondwanian origin. Radiolaria extracted from radiolarites of the Stepanavan ophiolite provide for the first time a Late Jurassic (late Kimmeridgian to early Tithonian) age constraint for this part of Tethyan oceanic crust preserved in Lesser Caucasus
Entrapment and traumatic neuropathies of the elbow and hand: An imaging approach
AbstractUltrasound and magnetic resonance imaging currently offer a detailed analysis of the peripheral nerves. Compressive and traumatic nerve injuries are the two main indications for imaging investigation of nerves with several publications describing the indications, technique and diagnostic capabilities of imaging signs. Investigation of entrapment neuropathies has three main goals, which are to confirm neuronal distress, search for the cause of nerve compression and exclude a differential diagnosis on the entire nerve. For traumatic nerve injuries, imaging, predominantly ultrasound, occasionally provides essential information for management including the type of nerve lesion, its exact site and local extension
Eye lens β-crystallins are predicted by native ion mobility-mass spectrometry and computations to form compact higher-ordered heterooligomers
Eye lens crystallin proteins maintain the refractive properties of the lens but are not replaced after denucleation. Rolland et al. use native ion mobility-mass spectrometry, kinetics experiments, and computations to reveal that b-crystallins form heterodimers. These likely assemble into compact heterooligomers that enable the very high protein concentrations found in lens tissue
Bethe Ansatz for the Weakly Asymmetric Simple Exclusion Process and phase transition in the current distribution
The probability distribution of the current in the asymmetric simple
exclusion process is expected to undergo a phase transition in the regime of
weak asymmetry of the jumping rates. This transition was first predicted by
Bodineau and Derrida using a linear stability analysis of the hydrodynamical
limit of the process and further arguments have been given by Mallick and
Prolhac. However it has been impossible so far to study what happens after the
transition. The present paper presents an analysis of the large deviation
function of the current on both sides of the transition from a Bethe ansatz
approach of the weak asymmetry regime of the exclusion process.Comment: accepted to J.Stat.Phys, 1 figure, 1 reference, 2 paragraphs adde
Calibration of the LIGO displacement actuators via laser frequency modulation
We present a frequency modulation technique for calibration of the
displacement actuators of the LIGO 4-km-long interferometric gravitational-wave
detectors. With the interferometer locked in a single-arm configuration, we
modulate the frequency of the laser light, creating an effective length
variation that we calibrate by measuring the amplitude of the frequency
modulation. By simultaneously driving the voice coil actuators that control the
length of the arm cavity, we calibrate the voice coil actuation coefficient
with an estimated 1-sigma uncertainty of less than one percent. This technique
enables a force-free, single-step actuator calibration using a displacement
fiducial that is fundamentally different from those employed in other
calibration methods.Comment: 10 pages, 5 figures, submitted to Classical and Quantum Gravit
Long range correlations and phase transition in non-equilibrium diffusive systems
We obtain explicit expressions for the long range correlations in the ABC
model and in diffusive models conditioned to produce an atypical current of
particles.In both cases, the two-point correlation functions allow to detect
the occurrence of a phase transition as they become singular when the system
approaches the transition
On the decay of turbulence in plane Couette flow
The decay of turbulent and laminar oblique bands in the lower transitional
range of plane Couette flow is studied by means of direct numerical simulations
of the Navier--Stokes equations. We consider systems that are extended enough
for several bands to exist, thanks to mild wall-normal under-resolution
considered as a consistent and well-validated modelling strategy. We point out
a two-stage process involving the rupture of a band followed by a slow
regression of the fragments left. Previous approaches to turbulence decay in
wall-bounded flows making use of the chaotic transient paradigm are
reinterpreted within a spatiotemporal perspective in terms of large deviations
of an underlying stochastic process.Comment: ETC13 Conference Proceedings, 6 pages, 5 figure
Protein Shape Sampled by Ion Mobility Mass Spectrometry Consistently Improves Protein Structure Prediction
Ion mobility (IM) mass spectrometry provides structural information about protein shape and size in the form of an orientationally-averaged collision cross-section (CCSIM). While IM data have been used with various computational methods, they have not yet been utilized to predict monomeric protein structure from sequence. Here, we show that IM data can significantly improve protein structure determination using the modelling suite Rosetta. We develop the Rosetta Projection Approximation using Rough Circular Shapes (PARCS) algorithm that allows for fast and accurate prediction of CCSIM from structure. Following successful testing of the PARCS algorithm, we use an integrative modelling approach to utilize IM data for protein structure prediction. Additionally, we propose a confidence metric that identifies near native models in the absence of a known structure. The results of this study demonstrate the ability of IM data to consistently improve protein structure prediction
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