Geometry and Dynamics with Time-Dependent Constraints

We describe how geometrical methods can be applied to a system with explicitly time-dependent second-class constraints so as to cast it in Hamiltonian form on its physical phase space. Examples of particular interest are systems which require time-dependent gauge fixing conditions in order to reduce them to their physical degrees of freedom. To illustrate our results we discuss the gauge-fixing of relativistic particles and strings moving in arbitrary background electromagnetic and antisymmetric tensor fields.Comment: 8 pages, Plain TeX, CERN-TH.7392/94 and MPI-PhT/94-4

The Construction of Sorkin Triangulations

Some time ago, Sorkin (1975) reported investigations of the time evolution and initial value problems in Regge calculus, for one triangulation each of the manifolds $R*S^3$ and $R^4$. Here we display the simple, local characteristic of those triangulations which underlies the structure found by Sorkin, and emphasise its general applicability, and therefore the general validity of Sorkin's conclusions. We also make some elementary observations on the resulting structure of the time evolution and initial value problems in Regge calculus, and add some comments and speculations.Comment: 5 pages (plus one figure not included, available from author on request), Plain Tex, no local preprint number (Only change: omitted "\magnification" command now replaced

Examining error detection capabilities in a novel force production task as a function of athletic experience.

The purpose of this experiment is to determine whether having previous athletic experience in a routine sport (ie. Cheerleading) will affect the participant’s ability to self-report superior error-detection, motor performance, time on target, confidence, and agonist and antagonist co-activation patterns while learning a novel skill compared to non-routine athletes. Participants were required to perform proportions of their maximal isometric elbow flexion (46%) and extension (38%) forces for 5 seconds over 30 acquisition trials on an elbow flexion and extension device. Following each trial, participants will be required to estimate how much force they think they exerted on that trial as well as their confidence on that trial. A feedback screen was provided regarding what their task goal was, their actual performance, and their estimated performance. A no-KR (Knowledge of Results) retention and transfer test was conducted approximately 48-hours after the acquisition period. Meanwhile, we examined the co-activation patterns in the EMG (electromyography) of their biceps and triceps as they performed their isometric contractions. During the acquisition, retention, and transfer periods there were no between group differences for error detection, motor performance, time on target, confidence, nor for muscle co-activation. The present study found that skill level of the participant does not affect error-detection accuracy and decreases muscle co-activation when learning a novel skill

Low Apparent Survival and Heterogeneous Movement Patterns of Invasive Blue Catfish in a Coastal River

Blue Catfish Ictalurus furcatus were purposefully introduced into freshwater tributaries to Chesapeake Bay in the past, and populations have subsequently spread to new areas, negatively impacting native communities and causing concern for resource managers. To aid development of management strategies, we implemented a multiyear (2012-2015) tagging study of invasive Blue Catfish in a 40-km stretch of the Potomac River to estimate survival and assess movement patterns. Blue Catfish (N = 1,237) were captured by electrofishing and double-tagged to allow us to estimate tag retention rates; we used reward tags to increase reporting rates. Recaptured fish (N = 104; 8.4% return rate) were at large for between 2 and 1,208 d. Tag retention rates were 0.88 (SE = 0.045) after 1 year and declined to 0.31 (SE = 0.107) after 2.7 years. The mean minimum distance moved by fish was 24.1 km (range = 0.0-112.6 km). Most (63%) fish displayed downriver movements, but distance moved was unrelated to fish size or days at large. Greater distances were observed among fish that moved downriver (34.4 km) than those that moved upriver (6.7 km). These results suggest high variability in movement behaviors for Blue Catfish inhabiting the tidal Potomac River from freshwater reaches to estuarine habitats. We estimated an annual apparent survival rate of 0.56 (SE = 0.057; Brownie tag-return model) across the study period. This survival rate is lower than survival rates reported from their native range. Long-distance movements of Blue Catfish in the Potomac River indicate that robust, large-scale control measures will be needed to reduce population abundance and minimize negative impacts of this species on native communities

Discrete quantum gravity in the framework of Regge calculus formalism

An approach to the discrete quantum gravity based on the Regge calculus is discussed which was developed in a number of our papers. Regge calculus is general relativity for the subclass of general Riemannian manifolds called piecewise flat ones. Regge calculus deals with the discrete set of variables, triangulation lengths, and contains continuous general relativity as a particular limiting case when the lengths tend to zero. In our approach the quantum length expectations are nonzero and of the order of Plank scale $10^{-33}cm$. This means the discrete spacetime structure on these scales.Comment: LaTeX, 16 pages, to appear in JET

Negative workplace behaviour: temporal associations with cardiovascular outcomes and psychological health problems in Australian police

Negative workplace behaviour, such as workplace bullying, is emerging as an important work-related psychosocial hazard with the potential to contribute to employee ill health. We examined the risk of two major health issues (poor mental and cardiovascular health) associated with current and past exposure to negative behaviour in the workplace. Data from 251 police officers, who completed an anonymous mail survey at two time-points spaced 12 months apart, support the potential role of exposure to negative workplace behaviour in the development of physical disease and psychological illness. Specifically, we saw significant effects associated with past exposure to such behaviour on indicators of poor cardiovascular health, and a significant effect of current exposure on the indicator of mental health problems. Our findings reinforce the need to continue to study links between employee health and both negative workplace behaviour and more severe cases of bullying, particularly the mechanisms involved to strengthen theory in this area, and to protect against employee ill health (specifically cardiovascular outcomes and psychological problems) by preventing negative behaviour at work. Copyright (C) 2010 John Wiley & Sons, Ltd

Tracking Decadal Changes in Striped Bass Recruitment: A Calibration Study of Seine Surveys in Chesapeake Bay

In this study we estimated calibration factors necessary to maintain the long‐term integrity of the juvenile striped bass surveys in the Chesapeake Bay region. These surveys provide annual indices of recruitment (estimated as juvenile fish abundance in summer) and are used by fisheries managers in Virginia and Maryland to inform adjustments of annual harvest limits for striped bass from the commercial and recreational fisheries in Chesapeake Bay. During the multi‐decadal history of the survey, a potentially influential change occurred: VIMS deployed a net (the VA net) with a mesh material that differed from the standard net that MD DNR continued to deploy (the MD net). More recently, another change was necessitated when neither the standard net material nor the net material recently used by VIMS was available for construction of replacement nets. Hence, a net using new mesh material was constructed and experimentally deployed in 2015 (new net). Paired net hauls (n=144) were completed in Maryland and Virginia nursery areas during summer 2015 to permit estimation of calibration factors: 70 pairs with the VA‐MD nets, 42 pairs with the MD‐New nets, and 32 pairs with the VA‐new nets. Not all paired hauls captured a given target species, however. Three sets of calibration factors were estimated from using beta‐binomial models that accounted for differences in capture efficiencies and variation in the relative capture success of the nets. We considered the effects of several environmental covariates (e.g., temperature, salinity, and turbidity) as well as deployment characteristics (e.g., bottom type, calendar day, and maximum net extension) on the relative efficiency of nets and on the variation in the probability of capture among paired hauls. More..

Radiotherapy students' perceptions of support provided by clinical supervisors

Aim: The aim of this study was to explore the experiences of radiotherapy students on clinical placement, specifically focussing on the provision of well-being support from clinical supervisors. Materials and methods: Twenty-five students from the University of the West of England and City University of London completed an online evaluation survey relating to their experiences of placement, involving Likert scales and open-ended questions. Results: The quantitative results were generally positive; however, the qualitative findings were mixed. Three themes emerged: (1) provision of information and advice; (2) an open, inclusive and supportive working environment; and (3) a lack of communication, understanding, and consistency. Findings: Students' experiences on placement differed greatly and appeared to relate to their specific interactions with different members of staff. It is suggested that additional training around providing well-being support to students may be of benefit to clinical supervisors

Regge calculus in the canonical form

(3+1) (continuous time) Regge calculus is reduced to Hamiltonian form. The constraints are classified, classical and quantum consequences are discussed. As basic variables connection matrices and antisymmetric area tensors are used supplemented with appropriate bilinear constraints. In these variables the action can be made quasipolinomial with $\arcsin$ as the only deviation from polinomiality. In comparison with analogous formalism in the continuum theory classification of constraints changes: some of them disappear, the part of I class constraints including Hamiltonian one become II class (and vice versa, some new constraints arise and some II class constraints become I class). As a result, the number of the degrees of freedom coincides with the number of links in 3-dimensional leaf of foliation. Moreover, in empty space classical dynamics is trivial: the scale of timelike links become zero and spacelike links are constant.Comment: 24 pages,Plain LaTeX,BINP 93-4