Lane Formation Research Articles

Lane formation in colloidal mixtures driven by an external field

The influence of an external field on a binary colloidal mixture performing Brownian dynamics in a solvent is investigated by nonequilibrium computer simulations and simple theory. In our model, one half of the particles are pushed into the field direction while the other half of them are pulled into the opposite direction. For increasing field strength, we show that the system undergoes a nonequilibrium phase transition from a disordered state to a state characterized by lane formation parallel to the field direction. The lanes are formed by the same kind of particles moving collectively with the field. Lane formation accelerates particle transport parallel to the field direction but suppresses massively transport perpendicular to the field. We further show that lane formation also occurs in a time-dependent oscillatory field. If the frequency of the external field exceeds a critical value, however, the system exhibits a transition back to the disordered state. Our results can be experimentally verified in binary colloidal suspensions exposed to external fields under nonequilibrium conditions.

Relationship between Jovian hectometric attenuation lanes and Io volcanic activity

Within the Galileo plasma wave instrument data a narrow (in frequency) attenuation band is seen in the hectometric (HOM) emission that varies in frequency with system III longitude. This attenuation lane is believed to be the result of near‐grazing incidence or coherent scattering of radio emission near the outer edge of the Io torus, i.e., when the ray path is nearly tangent to an L shell containing the Io flux tube [Gurnett et al., 1998]. Such a process should, therefore, be enhanced when the Io volcanic activity is increased and the Io flux tube has enhanced density. We have performed a systematic study of the existing Galileo radio emission data in an effort to determine the phenomenology and frequency of occurrence of the attenuation lanes and the association, if any, with published volcanic activity of Io. Our results indicate that the attenuation lanes are present almost all of the time but are enhanced on occasion. The best examples of attenuation lanes occur when Galileo is within ∼65 RJ of Jupiter and thus are probably more apparent because of the increased signal‐to‐noise ratio of the radio receivers. The lack of continuous monitoring of Io activity and the lack of known activity on the anti‐Earthward side of Io are problematic and make detailed correlation with radio emission very difficult at this time. Nevertheless, if the data are displayed for periods when the spacecraft is within 65 RJ (i.e., for each perijove pass), then the highest‐contrast lanes occur on most passes when the Io volcanic activity is also high for that pass. These results support our current understanding of attenuation lane formation and suggest that future efforts can be made to better understand the interaction of HOM emission with the Io flux tube.

Simulation of pedestrian dynamics using a two-dimensional cellular automaton

We propose a two-dimensional cellular automaton model to simulate pedestrian traffic. It is a v max=1 model with exclusion statistics and parallel dynamics. Long-range interactions between the pedestrians are mediated by a so-called floor field which modifies the transition rates to neighbouring cells. This field, which can be discrete or continuous, is subject to diffusion and decay. Furthermore it can be modified by the motion of the pedestrians. Therefore, the model uses an idea similar to chemotaxis, but with pedestrians following a virtual rather than a chemical trace. Our main goal is to show that the introduction of such a floor field is sufficient to model collective effects and self-organization encountered in pedestrian dynamics, e.g. lane formation in counterflow through a large corridor. As an application we also present simulations of the evacuation of a large room with reduced visibility, e.g. due to failure of lights or smoke.

Nonlocal Continuous-Space Microscopic Simulation of Pedestrian Flows with Local Choice Behavior

Compared with vehicular traffic, pedestrian flow operations are very complex. This is why vehicular flow simulation modeling approaches are generally not applicable to the description of pedestrian flows. Gaining insights into pedestrian flow operations is important in, for instance, the planning and geometric design of pedestrian infrastructural facilities. Additionally, management of pedestrian flows requires knowledge of pedestrian flow behavior. Motivated by the need for accurate pedestrian flow models, a microscopic pedestrian flow model is presented. The model is characterized by pedestrian interaction behavior, based on stimulus-response mechanisms. Moreover, local route-choice behavior is included, which describes how pedestrians choose their direction on the basis of, among other things, their destination and local pedestrian flow conditions. The choice behavior is based on the concept of subjective utility maximization. Moreover, the model features parallel updating, comparable with recently developed cellular automata models for pedestrian flows. However, contrary to these models, pedestrian locations are not bounded to discrete cells. The model can therefore easily describe multidirectional pedestrian flows (e.g., unidirectional, bidirectional, and crossing). Application of the model to a simple hallway is discussed. Besides speed-density relations, self-organizing phenomena are studied in pedestrian flows (dynamic lane formation and clustering) from the microscopic pedestrian flow model.

Early to mid‐Viséan shallow water platform buildups, north Co. Dublin, Ireland

AbstractA number of carbonate buildups in north Co. Dublin, long assigned to the late Viséan (Asbian), are shown on the basis of coral, foraminiferal and algal evidence to be early to mid‐Viséan (late Chadian to Holkerian) in age. They are equivalent in age to beds ranging from the upper part of the Lane Formation to the top of the Holmpatrick Formation.The buildups are poorly exposed and relatively small, probably only a few tens of metres across at most. Buildup sediments are massive to crudely bedded and dominated by peloidal, clotted and dense uniform micrites displaying lime mudstone and bioclastic wackestone textures. Dasycladacean algae are common in the buildups and cryptalgal fabrics are locally important. Cavities in the buildups are generally small (< 5 cm) and lined with inclusion‐rich radiaxial calcite cements. Micritization of bioclasts and cements is ubiquitous. Enclosing off‐buildup limestones are skeletal and intraclastic grainstones possessing sedimentary structures indicative of deposition in moderate to high energy environments. Fossil and petrographic evidence from the buildups also indicate a shallow water origin for the north Co. Dublin buildups.Compared with the slightly older Tournaisian (Courceyan to early Chadian) Waulsortian buildups which developed extensively in the Dublin Basin, these younger platform buildups are smaller and more isolated and possess a diverse suite of algal components and cryptalgal fabrics. Nevertheless, components in the north Co. Dublin buildups most closely resemble the shallowest phase D Waulsortian buildups, particularly in the presence of abundant peloids and micritized cements.The north Co. Dublin buildups developed on a carbonate platform (the Milverton Platform), adjacent to the Dublin Basin, whereas the Waulsortian developed in a deeper ramp setting. Following the demise of the Waulsortian in early Chadian time carbonate buildups established themselves on the shallow platforms. It is suggested that the microbial communities responsible for these buildups may have ‘evolved’ from older phase D Waulsortian communities and that he north Co. Dublin platform buildups represent the shallow water end of a spectrum of Viséan buildups.