Investigations of eddy coherence in jet flows

In turbulent shear flow the term coherent structures refers to eddies which are both spatially coherent, i.e., large eddies, aand also temporally coherent, i.e., they retain their identities for times which are long compared with their time scales in fixed point measurements. In transitional flows, the existence of such structures is evident from flow visualizations. In many other flows, such structures are not so evident. The reasons for the existence of these two classes of flows are discussed and attention is focused upon the more difficult flows, where coherent structures are not so evident. Techniques by which the existence (or nonexistence) of such structures in these flows can be established from point measurements, are also discussed. A major problem is shown to be the need to discriminate between real losses in eddy coherence and apparent losses in coherence introduced by phase scrambling effects which 'smear' multipoint correlations. The analysis of multiprobe time dependent data in cold and reacting round turbulent jets is described and it is shown how evidence of strong eddy coherence can be extracted from data

Express: a web-based technology to support human and computational experimentation

Experimental cognitive psychology has been greatly assisted by the development of general computer-based experiment presentation packages. Typically, however, such packages provide little support for running participants on different computers. It is left to the experimenter to ensure that group sizes are balanced between conditions and to merge data gathered on different computers once the experiment is complete. Equivalent issues arise in the evaluation of parameterized computational models, where it is frequently necessary to test a model's behavior over a range of parameter values (which amount to between-subjects factors) and where such testing can be speeded up significantly by the use of multiple processors. This article describes Express, a Web-based technology for coordinating "clients" (human participants or computational models) and collating client data. The technology provides an experiment design editor, client coordination facilities (e.g., automated randomized assignment of clients to groups so that group sizes are balanced), general data collation and tabulation facilities, a range of basic statistical functions (which are constrained by the specified experimental design), and facilities to export data to standard statistical packages (such as SPSS). We report case studies demonstrating the utility of Express in both human and computational experiments. Express may be freely downloaded from the Express Web site (http://express.psyc.bbk.ac.uk/)

College Students’ Perceptions of Barriers to Bystander Intervention

Sexual violence is a major problem on college campuses and is associated with a range of negative health consequences for victims. Teaching students to intervene as prosocial bystanders has become a common element of sexual assault prevention efforts; although these programs have demonstrated positive effects on participants’ beliefs and knowledge, their impact on actual behavior is weaker. Understanding the factors that inhibit intervening in risky situations may enhance the effectiveness of bystander programs by identifying material that addresses these barriers. A sample of 281 first-year college students indicated whether they had encountered 10 situations that may present elevated risk of sexual or physical assault since arriving on campus, and if so, whether they had done something to intervene. If they had not intervened, they were asked to identify the barriers that had inhibited them. Participants also completed measures of two factors proposed to predict bystander behavior, self-efficacy and emotion regulation. A majority of participants intervened in most of the situations, but only 27% of participants intervened in every situation they encountered. Men and women differed in the barriers they identified most frequently across situations, with men endorsing Perceived Responsibility more often than women, and women reporting Skill Deficits more often than men. Neither men nor women perceived Audience Inhibition to be a significant barrier; it was salient in only one of the 10 situations. Students higher in global bystander self-efficacy were more likely to intervene and less likely to report barriers related to skill deficits and perceived responsibility. These results suggest that existing bystander intervention programs efforts can be improved by fostering a greater sense of collective responsibility in students and teaching specific intervention behaviors

Caregiver Behaviors Associated With Emotion Regulation in High-Risk Preschoolers

Children who witness violence are at risk for developing a range of developmental problems, including deficits in understanding and regulating. The ability to adaptively manage emotions is associated with children’s mental health and their social and academic competence; however, little is known about how parents of at-risk youth can foster the healthy development of emotion regulation. The current study aimed to identify specific parenting practices associated with adaptive emotion regulation in at-risk preschoolers. Multimethod, multi-informant data were collected from 124 caregiver-child dyads from Head Start programs. Results indicated that interparental aggression was negatively associated with caregivers’ and children’s emotion regulation, but there were specific caregiver behaviors that moderated the association between interparental aggression and children’s emotion regulation. Specifically, care- givers’ sensitivity to children’s emotions during play, listening effectively to children’s expression of sadness, and their own capacity for emotion regulation buffered the association between exposure to interparental aggression and children’s emotion regulation. These findings provide practical insight into how parents can promote resilience in children exposed to violence by fostering healthy emotional regulation

Vaporization of droplets in premixing chambers

Detailed measurements were made of the structures of turbulent fuel sprays vaporizing in heated airstreams. The measurements show the size dependent vaporization and dispersion of the droplets and the important influence of the large eddies in the turbulence. The measurements form a data base for the development of models of fuel spray vaporization. Two laser techniques were specially developed for the investigation. A laser tomography technique converts line-of-sight light scattering measurements into time averaged 'point' measurements of droplet size distribution and volume concentration. A laser anemometer particle sizing technique was further developed to permit accurate measurements of individual particle sizes and velocities, with backscatter collection of light. The experiments are combined with heat transfer models to analyze the performance of miniature thermocouples in liquid sprays

Statistics of Lead Changes in Popularity-Driven Systems

We study statistical properties of the highest degree, or most popular, nodes in growing networks. We show that the number of lead changes increases logarithmically with network size N, independent of the details of the growth mechanism. The probability that the first node retains the lead approaches a finite constant for popularity-driven growth, and decays as N^{-phi}(ln N)^{-1/2}, with phi=0.08607..., for growth with no popularity bias.Comment: 4 pages, 4 figures, 2 column revtex format. Minor changes in response to referee comments. For publication in PR