Understanding the role of local safety groups in managing safety practices between micro construction firms and principal contractors

Construction projects incorporate the input of a range of tradesmen and different sized firms, ranging from micro to large organisations. Working practices of micro construction firms are carried out in an informal manner while larger organisations tend to adopt more formal on-site management techniques. Many micro firms seek to develop long-term relationships with large principal contractors and a major strain on their relationships stem from the difference in safety management techniques they employ. Faced with a fundamental shift in their style of safety management, workers of micro construction firms must successfully negotiate this challenge. Against this background, records from the Health and Safety Executives show year on year reductions in accident and incident rates in the East Midlands, an indication that the safety practices on projects are being implemented more effectively. Some of this success has been attributed to the efforts of local safety groups, such as Nottinghamshire Occupational Safety and Health Association (NOSHA). As such, it is important that the interdependencies between large principal contractors and micro firms, and the role that safety groups such as NOSHA play in managing this relationship are better understood. This paper presents interviews conducted with some members of NOSHA. This is the first of two phases of empirical work. The roles that the members of the local safety group perform have been found to go beyond simply promoting safety awareness and safety knowledge on site. They have been found to help in conflict resolution among the various construction parties. Such practices help create a harmonious working environment and subsequently lead to long-term working relations

Fuelling Active Galactic Nuclei

We suggest that most nearby active galactic nuclei are fed by a series of small--scale, randomly--oriented accretion events. Outside a certain radius these events promote rapid star formation, while within it they fuel the supermassive black hole. We show that the events have a characteristic time evolution. This picture agrees with several observational facts. The expected luminosity function is broadly in agreement with that observed for moderate--mass black holes. The spin of the black hole is low, and aligns with the inner disc in each individual feeding event. This implies radio jets aligned with the axis of the obscuring torus, and uncorrelated with the large--scale structure of the host galaxy. The ring of young stars observed about the Galactic Centre are close to where our picture predicts that star formation should occur.Comment: MNRAS, in pres

Detecting adaptive evolution in phylogenetic comparative analysis using the Ornstein-Uhlenbeck model

Phylogenetic comparative analysis is an approach to inferring evolutionary process from a combination of phylogenetic and phenotypic data. The last few years have seen increasingly sophisticated models employed in the evaluation of more and more detailed evolutionary hypotheses, including adaptive hypotheses with multiple selective optima and hypotheses with rate variation within and across lineages. The statistical performance of these sophisticated models has received relatively little systematic attention, however. We conducted an extensive simulation study to quantify the statistical properties of a class of models toward the simpler end of the spectrum that model phenotypic evolution using Ornstein-Uhlenbeck processes. We focused on identifying where, how, and why these methods break down so that users can apply them with greater understanding of their strengths and weaknesses. Our analysis identifies three key determinants of performance: a discriminability ratio, a signal-to-noise ratio, and the number of taxa sampled. Interestingly, we find that model-selection power can be high even in regions that were previously thought to be difficult, such as when tree size is small. On the other hand, we find that model parameters are in many circumstances difficult to estimate accurately, indicating a relative paucity of information in the data relative to these parameters. Nevertheless, we note that accurate model selection is often possible when parameters are only weakly identified. Our results have implications for more sophisticated methods inasmuch as the latter are generalizations of the case we study.Comment: 38 pages, in press at Systematic Biolog

Why Low-Mass Black-Hole Binaries Are Transient

We consider transient behavior in low-mass X-ray binaries. In short-period neutron-star systems (orbital period less than ~ 1d) irradiation of the accretion disk by the central source suppresses this except at very low mass transfer rates. Formation constraints however imply that a significant fraction of these neutron star systems have nuclear-evolved main-sequence secondaries and thus mass transfer rates low enough to be transient. But most short-period low-mass black-hole systems will form with unevolved main-sequence companions and have much higher mass transfer rates. The fact that essentially all of them are nevertheless transient shows that irradiation is weaker, as a direct consequence of the fundamental black-hole property - the lack of a hard stellar surface.Comment: 13 pages (including 3 figures); accepted for publication in Ap