The Walking Behaviour of Pedestrian Social Groups and Its Impact on Crowd Dynamics

Human crowd motion is mainly driven by self-organized processes based on local interactions among pedestrians. While most studies of crowd behaviour consider only interactions among isolated individuals, it turns out that up to 70% of people in a crowd are actually moving in groups, such as friends, couples, or families walking together. These groups constitute medium-scale aggregated structures and their impact on crowd dynamics is still largely unknown. In this work, we analyze the motion of approximately 1500 pedestrian groups under natural condition, and show that social interactions among group members generate typical group walking patterns that influence crowd dynamics. At low density, group members tend to walk side by side, forming a line perpendicular to the walking direction. As the density increases, however, the linear walking formation is bent forward, turning it into a V-like pattern. These spatial patterns can be well described by a model based on social communication between group members. We show that the V-like walking pattern facilitates social interactions within the group, but reduces the flow because of its “non-aerodynamic” shape. Therefore, when crowd density increases, the group organization results from a trade-off between walking faster and facilitating social exchange. These insights demonstrate that crowd dynamics is not only determined by physical constraints induced by other pedestrians and the environment, but also significantly by communicative, social interactions among individuals.     

Impact of Admission and Cache Replacement Policies on Response Times of Jobs on Data Grids

Caching techniques have been used widely to improve the performance gaps of storage hierarchies in computing systems. Little is known about the impact of policies on the response times of jobs that access and process very large files in data grids, particularly when data and computations on the data have to be co-located on the same host. In data intensive applications that access large data files over wide area network environment, such as data-grids, the combination of policies for job servicing (or scheduling), caching and cache replacement can significantly impact the performance of grid jobs. We present preliminary results of a simulation study that combines an admission policy with a cache replacement policy when servicing jobs submitted to a storage resource manager.The results show that, in comparison to a first come first serve policy, the response times of jobs are significantly improved, for practical limits of disk cache sizes, when the jobs that are back-logged to access the same files are taken into consideration in scheduling the next file to be retrieved into the disk cache. Not only are the response times of jobs improved, but also the metric measures for caching policies, such as the hit ratio and the average cost per retrieval, are improved irrespective of the cache replacement policy used. Ekow Otoo is research staff scientist with the scientific data management group at Lawrence Berkeley National Laboratory, University of California, Berkeley. He received his B.Sc. degree in Electrical Engineering from the University of Science and Technology, Kumasi, Ghana and a post graduate diploma in Computer Science from the University of Ghana, Legon. In 1977, he received his M.Sc. degree in Computer Science from the University of Newcastle Upon Tyne in Britain and his Ph.D. degree in Computer Science from McGill University, Montreal, Canada in 1983. He joined the faculty of the School of Computer Science, Carleton University, in 1983 and from 1987 to 1999, he was a tenured faculty member of the School of Computer Science, Carleton University, Ottawa, Canada. He has served as research consultant to Bell Northern Research, Ottawa, Canada, and as a research project consultant to the GIS Division, Geomatics Canada, Natural Resources Canada, from 1990 to 1998. Ekow Otoo is a member of the ACM and IEEE. His research interests include database management systems, data structures and algorithms, parallel I/O for high performance computing, parallel and distributed computing. Doron Rotem is currently a senior staff scientist and a member of the Data Management group at the Lawrence Berkeley National Lab. His research interests include Grid Computing, Workflow, Scientific Data Management and Paralled and Distributed Computing and Algorithms. He has published over 80 papers in international journals and conferences in these areas. Prior to that, Dr Rotem co-founded and served as a CTO of a startup company, called CommerceRoute, that made software products in the area of workflow and data integration and before that, he was an Associate Professor in the Department of Computer Science, University of Waterloo, Canada. Dr. Rotem holds a B.Sc degree in Mathematics and Statistics from the Hebrew University, Jerusalem, Israel and a Ph.D. in Computer Science from the University of the Witwatersrand, Johannesburg, South Africa. Arie Shoshani is a senior staff scientist at Lawrence Berkeley National Laboratory. He joined LBNL in 1976. He heads the Scientific Data Management Group. He received his Ph.D. from Princeton University in 1969. From 1969 to 1976, he was a researcher at System Development Corporation, where he worked on the Network Control Program for the ARPAnet, distributed databases, database conversion, and natural language interfaces to data management systems. His current areas of work include data models, query languages, temporal data, statistical and scientific database management, storage management on tertiary storage, and grid storage middleware. Arie is also the director of a Scientific Data Management (SDM) Integrated Software Infrastructure Center (ISIC), one of seven centers selected by the SciDAC program at DOE in 2001. In this capacity, he is coordinating the work of collaborators from 4 DOE laboratories and 4 universities (see: http://sdmcenter.lbl.gov). Dr. Shoshani has published over 65 technical papers in refereed journals and conferences, chaired several workshops, conferences, and panels in database management; and served on numerous program committees for various database conferences. He also served as an associate editor for the ACM Transactions on Database Systems. He was elected a member of the VLDB Endowment Board, served as the Publication Board Chairperson for the VLDB Journal, and as the Vice-President of the VLDB Endowment. His home page is http://www.lbl.gov/arie.     

Cytoskeletal Dependence of Insulin Granule Movement Dynamics in INS-1 Beta-Cells in Response to Glucose

For pancreatic β-cells to secrete insulin in response to elevated blood glucose, insulin granules retained within the subplasmalemmal space must be transported to sites of secretion on the plasma membrane. Using a combination of super-resolution STORM imaging and live cell TIRF microscopy we investigate how the organization and dynamics of the actin and microtubule cytoskeletons in INS-1 β-cells contribute to this process. GFP-labeled insulin granules display 3 different modes of motion (stationary, diffusive-like, and directed). Diffusive-like motion dominates in basal, low glucose conditions. Upon glucose stimulation no gross rearrangement of the actin cytoskeleton is observed but there are increases in the 1) rate of microtubule polymerization; 2) rate of diffusive-like motion; and 3) proportion of granules undergoing microtubule-based directed motion. By pharmacologically perturbing the actin and microtubule cytoskeletons, we determine that microtubule-dependent granule transport occurs within the subplasmalemmal space and that the actin cytoskeleton limits this transport in basal conditions, when insulin secretion needs to be inhibited.     

Groups on Groups: Some Dynamics and Possible Resolution of the Units of Selection Debates in Evolutionary Biology

David Hull's analysis of conceptual change in science, as presentedin his book, Science as a Process (1988), provides a useful framework for understanding one of the scientific controversies in which he actively and constructively intervened, the units of selectiondebates in evolutionary biology. What follows is a brief overview ofthose debates and some reflections on them.     

Disentangling Woodland Caribou Movements in Response to Clearcuts and Roads across Temporal Scales

Although prey species typically respond to the most limiting factors at coarse spatiotemporal scales while addressing biological requirements at finer scales, such behaviour may become challenging for species inhabiting human altered landscapes. We investigated how woodland caribou, a threatened species inhabiting North-American boreal forests, modified their fine-scale movements when confronted with forest management features (i.e. clearcuts and roads). We used GPS telemetry data collected between 2004 and 2010 on 49 female caribou in a managed area in Québec, Canada. Movements were studied using a use – availability design contrasting observed steps (i.e. line connecting two consecutive locations) with random steps (i.e. proxy of immediate habitat availability). Although caribou mostly avoided disturbances, individuals nonetheless modulated their fine-scale response to disturbances on a daily and annual basis, potentially compromising between risk avoidance in periods of higher vulnerability (i.e. calving, early and late winter) during the day and foraging activities in periods of higher energy requirements (i.e. spring, summer and rut) during dusk/dawn and at night. The local context in which females moved was shown to influence their decision to cross clearcut edges and roads. Indeed, although females typically avoided crossing clearcut edges and roads at low densities, crossing rates were found to rapidly increase in greater disturbance densities. In some instance, however, females were less likely to cross edges and roads as densities increased. Females may then be trapped and forced to use disturbed habitats, known to be associated with higher predation risk. We believe that further increases in anthropogenic disturbances could exacerbate such behavioural responses and ultimately lead to population level consequences.     

Nonlinear Dynamics of the Movement of the Venus Flytrap

The Venus flytrap has long been regarded as one of the most amazing examples of movement in the plant kingdom. The trapping ability of the flytrap consists of three unique features. First, trap closure represents one of the fastest movements in the plant kingdom. Second, a decision-making stage allows the plant to "decide" whether to completely close or open the trap, based on stimuli provided from the trapped object. Finally, the Venus flytrap contains a "memory function" that requires two mechanical stimuli within about 30 seconds to initiate trap closure. The movement involved in trap closure consists of nonlinear dynamics that have not been well understood. By understanding the movement, through nonlinear dynamics analysis, it will be possible to better understand this biological process. A mathematical model describing the movement of the Venus flytrap was first proposed by the authors in Yang et?al., Plant Signal. Behav. 5(8), 968-978 (2010). In the current work, the earlier research has been advanced and an in-depth nonlinear and control analysis of the dynamic process has been provided.     

Disentangling Membrane Dynamics and Cell Migration; Differential Influences of F-actin and Cell-Matrix Adhesions

Cell migration is heavily interconnected with plasma membrane protrusion and retraction (collectively termed “membrane dynamics”). This makes it difficult to distinguish regulatory mechanisms that differentially influence migration and membrane dynamics. Yet such distinctions may be valuable given evidence that cancer cell invasion in 3D may be better predicted by 2D membrane dynamics than by 2D cell migration, implying a degree of functional independence between these processes. Here, we applied multi-scale single cell imaging and a systematic statistical approach to disentangle regulatory associations underlying either migration or membrane dynamics. This revealed preferential correlations between membrane dynamics and F-actin features, contrasting with an enrichment of links between cell migration and adhesion complex properties. These correlative linkages were often non-linear and therefore context-dependent, strengthening or weakening with spontaneous heterogeneity in cell behavior. More broadly, we observed that slow moving cells tend to increase in area, while fast moving cells tend to shrink, and that the size of dynamic membrane domains is independent of cell area. Overall, we define macromolecular features preferentially associated with either cell migration or membrane dynamics, enabling more specific interrogation and targeting of these processes in future.     

Involvement of Ethylene in Picloram-induced Leaf Movement Response

The relationship of root-applied 4-amino-3,5,6-trichloropicolinic acid (picloram) to ethylene production and the leaf movement response in honey mesquite (Prosopis juliflora [Swartz] DC. var. glandulosa [Torr.] Cockerell) and huisache (Acacia farnesiana [L.] Willd.) was studied in detail. The threshold and saturation levels of exogenous ethylene and root-applied picloram necessary to inhibit leaf movement were determined. Internal levels of ethylene in excess of those necessary to saturate the leaf movement inhibition response occurred in tops of treated plants before and after symptom expression. These internal levels of ethylene, while averages for the entire plant tops, probably occur at the specific site of action and thus account for the action of picloram in inhibition of leaf movement and related responses. Quantitative differences in the leaf movement response of both species to picloram and ethylene were observed. In huisache alone, a very small change in ethylene levels was necessary to produce a major blockage of the leaf movement response, suggesting that the gas may have a natural function in that species.     

Dynamics in Polysaccharide Glasses and Their Impact on the Stability of Encapsulated Flavors

The aim of this work is to examine the correlation between measured instability of model flavor compounds in glassy matrices with the calorimetric relaxation times of the matrices. Spray-dried carbohydrate matrices were chosen as the model compounds for this study. Enthalpy relaxation times were determined for spray-dried carbohydrate matrices using differential and isothermal calorimetric methods. The losses of the volatile methyl acetate, ethyl acetate and limonene, as well as formation of limonene oxidation products, were measured by gas chromatography. Storage conditions were 30 and 40 °C, with samples equilibrated with 11, 23, 33 and 43 % RH at each temperature. A comparison of the relaxation times for temperatures below Tg was made using Modulated DSC (MDSC) and a Thermal Activity Monitor (TAM). TAM yields significantly lower values for relaxation times implying that it is capturing some of the faster dynamics as well as dynamics that are activated near Tg. However, plots of relaxation times as determined by both techniques versus temperature appear to converge at Tg. An increase in the relative humidity results in moderately higher loss of volatiles (methyl acetate, ethyl acetate and limonene) and greater oxidation rates. In general, there is a good correlation between relaxation time and stability, with greater enthalpy relaxation time associated with better stability. Enthalpy relaxation time appears to be a useful predictor of stability for both loss of volatiles and oxidation of limonene.     

Dynamics of the Microbiota in Response to Host Infection

Longitudinal studies of the microbiota are important for discovering changes in microbial communities that affect the host. The complexity of these ecosystems requires rigorous integrated experimental and computational methods to identify temporal signatures that promote physiologic or pathophysiologic responses in vivo. Employing a murine model of infectious colitis with the pathogen Citrobacter rodentium, we generated a 2-month time-series of 16S rDNA gene profiles, and quantitatively cultured commensals, from multiple intestinal sites in infected and uninfected mice. We developed a computational framework to discover time-varying signatures for individual taxa, and to automatically group signatures to identify microbial sub-communities within the larger gut ecosystem that demonstrate common behaviors. Application of this model to the 16S rDNA dataset revealed dynamic alterations in the microbiota at multiple levels of resolution, from effects on systems-level metrics to changes across anatomic sites for individual taxa and species. These analyses revealed unique, time-dependent microbial signatures associated with host responses at different stages of colitis. Signatures included a Mucispirillum OTU associated with early disruption of the colonic surface mucus layer, prior to the onset of symptomatic colitis, and members of the Clostridiales and Lactobacillales that increased with successful resolution of inflammation, after clearance of the pathogen. Quantitative culture data validated findings for predominant species, further refining and strengthening model predictions. These findings provide new insights into the complex behaviors found within host ecosystems, and define several time-dependent microbial signatures that may be leveraged in studies of other infectious or inflammatory conditions.     

The Impact of Aminoglycosides on the Dynamics of Translation Elongation

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Highlights? Combined single-molecule, structural, and biochemical studies on aminoglycoside action ? Aminoglycosides disrupt translation through inhibiting the dynamics of elongation ? Apramycin blocks translocation in translation elongation ? Paromomycin and gentamicin disrupt ribosomal rotation and translocation     

Social Networks and the Formation and Maintenance of River Otter Groups

Many studies have evaluated why male mammals form social groups; few however have investigated how these groups are formed and maintained. We observed behavioral interactions of 15 male river otters ( Lontra canadensis ) captured in Prince William Sound (PWS), Alaska, and held in captivity for 10 mo. Because the otters were captured in various areas and differed in age and relatedness, we were able to test how kinship and age influenced social interactions. We also explored how kinship, age and social interactions in captivity related to geographic spacing after the otters were released back in PWS. In 284 h of observations, the otters exhibited more positive than negative interactions. Social network models indicated that in the early stage of captivity, there were more links among individuals than in the late stage. In the late-stage period, older animals that had higher testosterone levels exhibited increased social distance and lower information centrality (a network connectivity metric). Social distance was not related to genetic distance, nor did it relate directly to age, although both social distance and age were correlated with post-release geographic distance. Thus, the formation of male groups in coastal river otters is largely influenced by familiarity and past experience, rather than kinship. The maintenance of groups, especially during the mating season, is a function of reproductive status and age, with older animals withdrawing from the social network during that time. What other phenotypic characters may contribute to the formation and maintenance of river otter groups merit future exploration.     

Impact of Directed Movement on Invasive Spread in Periodic Patchy Environments

To address the effect of taxis of invasive animals on their spreading speed in heterogeneous environments, we deal with an advection-diffusion-reaction equation (ADR) in a periodic patchy environment. Two-types of advection that spatially vary depending on environmental heterogeneity are taken into consideration: a stepwise taxis function and a saw-like taxis function. We first analyze the ADR with the stepwise taxis advection, and derive an invasion criterion. When the invasion criterion holds, an initially localized population evolves to a traveling periodic wave (TPW). The asymptotic speed of the TPW is found to be equal to the minimal speed of the TPW analytically derived. Thus, we examine how the minimal speed is influenced by the taxis. The major results are: (1)?As the magnitude of the taxis toward favorable patches increases, invasion becomes more feasible. However, the spreading speed increases at first, and then decreases to show a one-humped curve against the magnitude of the taxis; (2)?As the scale of fragmentation in the patchy environment is increased, the spreading speed increases when the magnitude of the taxis is small, while it decreases when the magnitude of the taxis becomes sufficiently large. These characteristic features qualitatively apply to the ADR model with the saw-like taxis function.     

Social Influence and the Collective Dynamics of Opinion Formation

Social influence is the process by which individuals adapt their opinion, revise their beliefs, or change their behavior as a result of social interactions with other people. In our strongly interconnected society, social influence plays a prominent role in many self-organized phenomena such as herding in cultural markets, the spread of ideas and innovations, and the amplification of fears during epidemics. Yet, the mechanisms of opinion formation remain poorly understood, and existing physics-based models lack systematic empirical validation. Here, we report two controlled experiments showing how participants answering factual questions revise their initial judgments after being exposed to the opinion and confidence level of others. Based on the observation of 59 experimental subjects exposed to peer-opinion for 15 different items, we draw an influence map that describes the strength of peer influence during interactions. A simple process model derived from our observations demonstrates how opinions in a group of interacting people can converge or split over repeated interactions. In particular, we identify two major attractors of opinion: (i) the expert effect, induced by the presence of a highly confident individual in the group, and (ii) the majority effect, caused by the presence of a critical mass of laypeople sharing similar opinions. Additional simulations reveal the existence of a tipping point at which one attractor will dominate over the other, driving collective opinion in a given direction. These findings have implications for understanding the mechanisms of public opinion formation and managing conflicting situations in which self-confident and better informed minorities challenge the views of a large uninformed majority.     

The Impact of Perceived Social Power and Dangerous Context on Social Attention

Past research has shown that position in a social hierarchy modulates one''s social attention, as in the gaze cueing effect. While studies have manipulated the social status of others with whom the participants interact, we believe that a sense of one''s own social power is also a crucial factor affecting gaze following. In two experiments, we primed the social power of participants, using different approaches, to investigate the participants'' performance in a subsequent gaze cueing task. The results of Experiment 1 showed a stronger gaze cueing effect among participants who were primed with low social power, compared to those primed with high social power. Our predicted gender difference (i.e., women showing a stronger gaze cueing effect than men) was confirmed and this effect was found to be dominated by the lower social power condition. Experiment 2 manipulated the level of danger in the context and replicated the joint impact of gender and one''s perceived social power on gaze cueing effect, especially in the low danger context, in comparison to the high danger context. These findings demonstrate that one''s perceived social power has a concerted effect on social attention evoked by gaze, along with other factors such as gender and characteristics of the environment, and suggest the importance of further research on the complex relationship between an individual''s position in the social hierarchy and social attention.     

Response of Cat Cortical Neurons to Position and Movement of the Femur

The contribution of joint afferents to the response of cortical neurons in area 3a to mechanical stimulation of the contralateral hindlimb was evaluated in cats anesthetized with sodium pentobarbital and paralyzed with pancuronium bromide. The hindlimb projection to the pericruciate cortex was established by recording the evoked potentials to electrical stimulation of the sciatic nerve and some of its branches, the biceps-semitendinosus and the quadratus femoris

Out of 169 neurons, 63 responded exclusively to cutaneous stimuli (superficial), whereas the others could be activated by local pressure of hindlimb muscles and/or by joint rotation (deep). Deep neurons were classified as slowly adapting (SA) or rapidly adapting (RA) units. In the neurons responding exclusively to joint rotation, the site of the receptive field could not be identified with certainty. In 13 deep neurons, their firing was affected by rotation of multiple joints of the contralateral hindlimb

In an attempt to identify the source of activation of cortical neurons, partial denervations and muscle disconnections were performed in five animals to isolate and stimulate the hip capsule. In these preparations, in 14 of 15 cortical neurons the source of activation was localized in the periarticular muscles, with no response to mechanical stimulation of the joint capsule. Only one neuron (S A) could be selectively excited by punctate pressure on the hip capsule

Our results suggest that in neurons of area 3a of the cat, the information about the position of the femur relies mainly on muscle afferents     

The Impact of the Allee Effect in Dispersal and Patch-Occupancy Age on the Dynamics of Metapopulations

In this paper, we introduce a Levins-type metapopulation model with empty and occupied patches, and dispersing population. We structure the proportion of occupied patches according to the patch-occupancy age. We observe that patch-occupancy age may destabilize the metapopulation, leading to persistent oscillations. We also allow for the dispersal rate to vary with the proportion of empty patches in a monotone or unimodal way. The unimodal dependence leads to multiple non-trivial equilibria and bistability when the reproduction number of the metapopulation < 1 but greater than a lower critical value ^*. We show that the metapopulation will persist independently of its initial status if > 1.