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

Non-diffusive resonant acceleration of electrons in the radiation belts

International audienceWe describe a mechanism of resonant electron acceleration by oblique high-amplitude whistlerwaves under conditions typical for the Earth radiation belts. We use statistics of spacecraftobservations of whistlers in the Earth radiation belts to obtain the dependence of the angle hbetween the wave-normal and the background magnetic field on magnetic latitude k. According tothis statistics, the angle h already approaches the resonance cone at k 15 and remains close to itup to k 30–40 on the dayside. The parallel component of the electrostatic field of whistlerwaves often increases around k 15 up to one hundred of mV/m. We show that due to thisincrease of the electric field, the whistler waves can trap electrons into the potential well via waveparticle resonant interaction corresponding to Landau resonance. Trapped electrons then move withthe wave to higher latitudes where they escape from the resonance. Strong acceleration is favoredby adiabatic invariance along the increasing magnetic field, which continuously transfers theparallel energy gained to perpendicular energy, allowing resonance to be reached and maintained.The concomitant increase of the wave phase velocity allows for even stronger relative accelerationat low energy <50 keV. Each trapping-escape event of electrons of 10 keV to 100 keV results inan energy gain of up to 100 keV in the inhomogeneous magnetic field of the Earth dipole. Forelectrons with initial energy below 100 keV, such rapid acceleration should hasten their drop intothe loss-cone and their precipitation into the atmosphere. We discuss the role of the consideredmechanism in the eventual formation of a trapped distribution of relativistic electrons for initialenergies larger than 100 keV and in microbursts precipitations of lower energy particles

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

Chaotic properties of systems with Markov dynamics

We present a general approach for computing the dynamic partition function of a continuous-time Markov process. The Ruelle topological pressure is identified with the large deviation function of a physical observable. We construct for the first time a corresponding finite Kolmogorov-Sinai entropy for these processes. Then, as an example, the latter is computed for a symmetric exclusion process. We further present the first exact calculation of the topological pressure for an N-body stochastic interacting system, namely an infinite-range Ising model endowed with spin-flip dynamics. Expressions for the Kolmogorov-Sinai and the topological entropies follow.Comment: 4 pages, to appear in the Physical Review Letter

Frozen shuffle update for an asymmetric exclusion process on a ring

We introduce a new rule of motion for a totally asymmetric exclusion process (TASEP) representing pedestrian traffic on a lattice. Its characteristic feature is that the positions of the pedestrians, modeled as hard-core particles, are updated in a fixed predefined order, determined by a phase attached to each of them. We investigate this model analytically and by Monte Carlo simulation on a one-dimensional lattice with periodic boundary conditions. At a critical value of the particle density a transition occurs from a phase with `free flow' to one with `jammed flow'. We are able to analytically predict the current-density diagram for the infinite system and to find the scaling function that describes the finite size rounding at the transition point.Comment: 16 page

Chorus source region localization in the Earth's outer magnetosphere using THEMIS measurements

Discrete ELF/VLF chorus emissions, the most intense electromagnetic plasma waves observed in the Earth's radiation belts and outer magnetosphere, are thought to propagate roughly along magnetic field lines from a localized source region near the magnetic equator towards the magnetic poles. THEMIS project Electric Field Instrument (EFI) and Search Coil Magnetometer (SCM) measurements were used to determine the spatial scale of the chorus source localization region on the day side of the Earth's outer magnetosphere. We present simultaneous observations of the same chorus elements registered onboard several THEMIS spacecraft in 2007 when all the spacecraft were in the same orbit. Discrete chorus elements were observed at 0.15–0.25 of the local electron gyrofrequency, which is typical for the outer magnetosphere. We evaluated the Poynting flux and wave vector distribution and obtained chorus wave packet quasi-parallel propagation to the local magnetic field. Amplitude and phase correlation data analysis allowed us to estimate the characteristic spatial correlation scale transverse to the local magnetic field to be in the 2800–3200 km range

Multiple primary cancers in the Vaud Cancer Registry, Switzerland, 1974-89.

Data collected by the Cancer Registry of the Swiss Canton of Vaud (whose population in 1980 was about 530,000 inhabitants) were used to estimate the incidence of second metachronous primary cancers following any specific neoplasm. Among 34,615 cases of incident neoplasms registered between 1974 and 1989 and followed through integrated active follow-up to the end of 1989, for a total of 118,241 person-years at risk, there were 2,185 second primaries (1,280 males, 905 females). For both sexes, the standardised incidence ratios (SIR) were significantly elevated by about 20%. Overall significantly elevated ratios were registered for cancers of the oral cavity and pharynx (SIR = 1.6 for males, 2.0 for females), oesophagus in males (SIR = 1.5), lung in males (SIR = 1.4), skin melanoma (SIR = 1.7 for males, 1.5 for females), non-melanomatous skin cancers (SIR = 1.6 for males, 1.5 for females), female breast (SIR = 1.3), kidney (SIR = 1.5 for males, 1.9 for females), and thyroid in males (SIR = 2.4). When specific first cancer sites were considered, the SIR following a cancer of the oral cavity and pharynx was around 3 in both sexes, mainly on account of a substantial excess of second primaries of the oral cavity, oesophagus, larynx and lung. The overall SIR following laryngeal cancer was 3.0, and significant excesses were observed for oral cavity and pharynx, oesophagus and lung. After lung cancer, the overall SIR was 1.7 for males and 2.6 for females, and significantly elevated SIRs were observed for oral cavity, lung and oesophagus. Following non-melanomatous skin cancers, elevated SIRs were observed in both sexes for skin melanoma and non-melanomas. The incidence of any cancer after breast cancer was significantly elevated (SIR = 1.2), mainly on account of an elevated risk of subsequent breast cancer (SIR = 1.7). With reference to cervical cancer, there was a significant excess for any subsequent primary (SIR = 1.6), and for lung cancer (SIR = 7.8). Significantly elevated SIRs were observed for kidney following bladder cancer, and for bladder after kidney cancer. In both sexes, the incidence of cancers of any site was elevated following leukaemias (SIR = 1.7 for males, 2.5 for females), and a significant excess was registered for lung in males and non-melanomatous skin cancers in both sexes.(ABSTRACT TRUNCATED AT 400 WORDS