Showing papers by "University of St Andrews published in 2003"

Bird Song: Biological Themes and Variations

Abstract: Introduction 1. The study of bird song 2. Production and perception 3. How song develops 4. Getting the message across 5. When do birds sing? 6. Recognition and territorial defence 7. Sexual selection and female choice 8. Themes and variations 9. Variation in time and space List of common and scientific names References Index.

Thin plate regression splines

Abstract: discuss the production of low rank smoothers for d greater than or equal to 1 dimensional data, which can be fitted by regression or penalized regression methods. The smoothers are constructed by a simple transformation and truncation of the basis that arises from the solution of the thin plate spline smoothing problem and are optimal in the sense that the truncation is designed to result in the minimum possible perturbation of the thin plate spline smoothing problem given the dimension of the basis used to construct the smoother. By making use of Lanczos iteration the basis change and truncation are computationally efficient. The smoothers allow the use of approximate thin plate spline models with large data sets, avoid the problems that are associated with 'knot placement' that usually complicate modelling with regression splines or penalized regression splines, provide a sensible way of modelling interaction terms in generalized additive models, provide low rank approximations to generalized smoothing spline models, appropriate for use with large data sets, provide a means for incorporating smooth functions of more than one variable into non-linear models and improve the computational efficiency of penalized likelihood models incorporating thin plate splines. Given that the approach produces spline-like models with a sparse basis, it also provides a natural way of incorporating unpenalized spline-like terms in linear and generalized linear models, and these can be treated just like any other model terms from the point of view of model selection, inference and diagnostics

The superconductivity of Sr 2 RuO 4 and the physics of spin-triplet pairing

Abstract: This review presents a summary and evaluation of the experimental properties of unconventional superconductivity in ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ as they were known in the spring of 2002. At the same time, the paper is intended to be useful as an introduction to the physics of spin-triplet superconductivity. First, the authors show how the normal-state properties of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ are quantitatively described in terms of a quasi-two-dimensional Fermi liquid. Then they summarize its phenomenological superconducting parameters in the framework of the Ginzburg-Landau model, and discuss the existing evidence for spin-triplet pairing. After a brief introduction to the vector order parameter, they examine the most likely symmetry of the triplet state. The structure of the superconducting energy gap is discussed, as is the effect of symmetry-breaking magnetic fields on the phase diagram. The article concludes with a discussion of some outstanding issues and desirable future work. Appendixes on additional details of the normal state, difficulty in observing the bulk Fermi surface by angle-resolved photoemission, and the enhancement of superconducting transition temperature in a two-phase ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}\ensuremath{-}\mathrm{Ru}$ system are included.

Dissecting Temporal and Spatial Control of Cytokinesis with a Myosin II Inhibitor

Abstract: Completion of cell division during cytokinesis requires temporally and spatially regulated communication from the microtubule cytoskeleton to the actin cytoskeleton and the cell membrane. We identified a specific inhibitor of nonmuscle myosin II, blebbistatin, that inhibited contraction of the cleavage furrow without disrupting mitosis or contractile ring assembly. Using blebbistatin and other drugs, we showed that exit from the cytokinetic phase of the cell cycle depends on ubiquitin-mediated proteolysis. Continuous signals from microtubules are required to maintain the position of the cleavage furrow, and these signals control the localization of myosin II independently of other furrow components.

Microfluidic sorting in an optical lattice

Abstract: The response of a microscopic dielectric object to an applied light field can profoundly affect its kinetic motion1. A classic example of this is an optical trap, which can hold a particle in a tightly focused light beam2. Optical fields can also be used to arrange, guide or deflect particles in appropriate light-field geometries3,4. Here we demonstrate an optical sorter for microscopic particles that exploits the interaction of particles—biological or otherwise—with an extended, interlinked, dynamically reconfigurable, three-dimensional optical lattice. The strength of this interaction with the lattice sites depends on the optical polarizability of the particles, giving tunable selection criteria. We demonstrate both sorting by size (of protein microcapsule drug delivery agents) and sorting by refractive index (of other colloidal particle streams). The sorting efficiency of this method approaches 100%, with values of 96% or more observed even for concentrated solutions with throughputs exceeding those reported for fluorescence-activated cell sorting5. This powerful, non-invasive technique is suited to sorting and fractionation within integrated (‘lab-on-a-chip’) microfluidic systems, and can be applied in colloidal, molecular and biological research.

A redox-stable efficient anode for solid-oxide fuel cells.

Abstract: Solid-oxide fuel cells (SOFCs) promise high efficiencies in a range of fuels. Unlike lower temperature variants, carbon monoxide is a fuel rather than a poison, and so hydrocarbon fuels can be used directly, through internal reforming or even direct oxidation. This provides a key entry strategy for fuel-cell technology into the current energy economy. Present development is mainly based on the yttria-stabilized zirconia (YSZ) electrolyte. The most commonly used anode materials are Ni/YSZ cermets, which display excellent catalytic properties for fuel oxidation and good current collection, but do exhibit disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels, and poor redox cycling causing volume instability. Here, we report a nickel-free SOFC anode, La0.75Sr0.25Cr0.5Mn0.5O3, with comparable electrochemical performance to Ni/YSZ cermets. The electrode polarization resistance approaches 0.2 Omega cm2 at 900 degrees C in 97% H2/3% H2O. Very good performance is achieved for methane oxidation without using excess steam. The anode is stable in both fuel and air conditions, and shows stable electrode performance in methane. Thus both redox stability and operation in low steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes.

A new metric for probability distributions

Abstract: We introduce a metric for probability distributions, which is bounded, information-theoretically motivated, and has a natural Bayesian interpretation. The square root of the well-known /spl chi//sup 2/ distance is an asymptotic approximation to it. Moreover, it is a close relative of the capacitory discrimination and Jensen-Shannon divergence.

Homogeneous Catalysis--New Approaches to Catalyst Separation, Recovery, and Recycling

Abstract: Homogeneous catalysts have many attractive properties, such as high selectivities. However, many homogeneous catalytic systems cannot be commercialized because of difficulties associated with separating the products from the catalyst. Recent approaches to tackling this problem are reviewed and compared.

Explaining the excess of rare species in natural species abundance distributions.

Abstract: The observation that a few species in ecological communities are exceptionally abundant, whereas most are rare, prompted the development of species abundance models Nevertheless, despite the large literature on the commonness and rarity of species inspired by these pioneering studies, some widespread empirical patterns of species abundance resist easy explanation Notable among these is the observation that in large assemblages there are more rare species than the log normal model predicts Here we use a long-term (21-year) data set, from an estuarine fish community, to show how an ecological community can be separated into two components Core species, which are persistent, abundant and biologically associated with estuarine habitats, are log normally distributed Occasional species occur infrequently in the record, are typically low in abundance and have different habitat requirements; they follow a log series distribution These distributions are overlaid, producing the negative skew that characterizes real data sets

The formation of a star cluster: predicting the properties of stars and brown dwarfs

Abstract: We present results from the largest numerical simulation of star formation to resolve the fragmentation process down to the opacity limit. The simulation follows the collapse and fragmentation of a large-scale turbulent molecular cloud to form a stellar cluster and, simultaneously, the formation of circumstellar discs and binary stars. This large range of scales enables us to predict a wide variety of stellar properties for comparison with observations. The calculation clearly demonstrates that star formation is a highly-dynamic and chaotic process. Star formation occurs in localized bursts within the cloud via the fragmentation both of dense molecular cloud cores and of massive circumstellar discs. Star-disc encounters form binaries and truncate discs. Stellar encounters disrupt bound multiple systems. We find that the observed statistical properties of stars are a natural consequence of star formation in such a dynamical environment. The cloud produces roughly equal numbers of stars and brown dwarfs, with masses down to the opacity limit for fragmentation (5 Jupiter masses). The initial mass function is consistent with a Salpeter slope (Γ = -1.35) above 0.5 M O ., a roughly flat distribution (r = 0) in the range 0.006-0.5 M O ., and a sharp cut-off below 0.005 M O .. This is consistent with recent observational surveys. The brown dwarfs form by the dynamical ejection of low-mass fragments from dynamically unstable multiple systems before the fragments have been able to accrete to stellar masses. Close binary systems (with separations ≤10 au) are not formed by fragmentation in situ. Rather, they are produced by hardening of initially wider multiple systems through a combination of dynamical encounters, gas accretion, and/or the interaction with circumbinary and circumtriple discs. Finally, we find that the majority of circumstellar discs have radii less than 20 au due to truncation in dynamical encounters. This is consistent with observations of the Orion Trapezium cluster and implies that most stars and brown dwarfs do not form large planetary systems.

Climate change and habitat destruction: a deadly anthropogenic cocktail.

Abstract: Climate change and habitat destruction are two of the greatest threats to global biodiversity. Lattice models have been used to investigate how hypothetical species with different characteristics respond to habitat loss. The main result shows that a sharp threshold in habitat availability exists below which a species rapidly becomes extinct. Here, a similar modelling approach is taken to establish what determines how species respond to climate change. A similar threshold exists for the rate of climate change as has been observed for habitat loss-patch occupancy remains high up to a critical rate of climate change, beyond which species extinction becomes likely. Habitat specialists, especially those of relatively poor colonizing ability are least able to keep pace with climate change. The interaction between climate change and habitat loss might be disastrous. During climate change, the habitat threshold occurs sooner. Similarly, species suffer more from climate change in a fragmented habitat.

Electrophysiology and brain imaging of biological motion

Abstract: The movements of the faces and bodies of other conspecifics provide stimuli of considerable interest to the social primate. Studies of single cells, field potential recordings and functional neuroimaging data indicate that specialized visual mechanisms exist in the superior temporal sulcus (STS) of both human and non-human primates that produce selective neural responses to moving natural images of faces and bodies. STS mechanisms also process simplified displays of biological motion involving point lights marking the limb articulations of animate bodies and geometrical shapes whose motion simulates purposeful behaviour. Facial movements such as deviations in eye gaze, important for gauging an individual's social attention, and mouth movements, indicative of potential utterances, generate particularly robust neural responses that differentiate between movement types. Collectively such visual processing can enable the decoding of complex social signals and through its outputs to limbic, frontal and parietal systems the STS may play a part in enabling appropriate affective responses and social behaviour.

Linking bees and flowers: how do floral communities structure pollinator communities?

Abstract: Pollinators provide essential ecosystem services, and declines in some pollinator communities around the world have been reported. Understanding the fundamental components defining these communities is essential if conservation and restoration are to be successful. We examined the structure of plant-pollinator communities in a dynamic Mediterranean landscape, comprising a mosaic of post-fire regenerating habitats, and which is a recognized global hotspot for bee diversity. Each community was characterized by a highly skewed species abundance distribution, with a few dominant and many rare bee species, and was consistent with a log series model indicating that a few environmental factors govern the community. Floral community composition, the quantity and quality of forage resources present, and the geographic locality organized bee communities at various levels: (1) The overall structure of the bee community (116 species), as revealed through ordination, was dependent upon nectar resource diversity (defined as the variety of nectar volume-concentration combinations available), the ratio of pollen to nectar energy, floral diversity, floral abundance, and post-fire age. (2) Bee diversity, measured as species richness, was closely linked to floral diversity (especially of annuals), nectar resource diversity, and post-fire age of the habitat. (3) The abundance of the most common species was primarily related to post-fire age, grazing intensity, and nesting substrate availability. Ordination models based on age-characteristic post-fire floral community structure explained 39-50% of overall variation observed in bee community structure. Cluster analysis showed that all the communities shared a high degree of similarity in their species composition (27-59%); however, the geographical location of sites also contributed a smaller but significant component to bee community structure. We conclude that floral resources act in specific and previously unexplored ways to modulate the diversity of the local geographic species pool, with specific disturbance factors, superimposed upon these patterns, mainly affecting the dominant species.

The quantitative measurement of organizational culture in health care: A review of the available instruments

Abstract: Health system reforms have until recently tended to focus primarily on structural change. The introduction of managed care in the United States (Miller and Luft 1997), the establishment of standard-setting bodies such as the National Institute for Clinical Excellence (Department of Health 1998) in the United Kingdom, the development of medical error reporting systems in Australia (Wilson et al. 1995), and the restructuring of primary care in the United Kingdom and Canada (Hutchison, Abelson, and Lavis 2001) are examples of this approach. However, recent studies show that structural changes alone do not deliver anticipated improvements in quality and performance in health care (Le Grand, May, and Mulligan 1998; Shortell, Bennett, and Byck 1998). As a result, we hear calls for “cultural transformation” to be wrought alongside structural change in order to deliver improvements in quality and performance. This call has been prominent in the United States (Institute of Medicine 2001) and also as a central component of the recent reforms of the National Health Service (NHS) in the United Kingdom (Department of Health 2000; 2002). A theory of organizational culture emerges from a combination of organizational psychology, social psychology, and social anthropology. The development of organizational culture as a subject of study can be seen as an elaboration of the human relations (Roethlisberger and Dickson 1939) and social systems approaches (Parsons 1977); which in turn developed as correctives to the scientific management techniques of Frederick Winslow (“Speedy”) Taylor, and his successor Frank B. Gilbreth. The study of organizations has been conducted from within various different theories or paradigms (Burrell and Morgan 1979). The term “organizational culture” first appeared in the academic literature in an article in Administrative Science Quarterly by Pettigrew (Pettigrew 1979; Hofstede et al. 1990)—though Jacques refers to the culture of a factory as early 1952 (Jacques 1952). Its constituent themes can be traced to earlier literature on organizational analysis. Pettigrew's own empirical study of a private British boarding school appears strongly influenced by Burton Clarke (Clarke 1970). Both trace the influence of the strong, idiosyncratic individuals who founded the organizations. This concern with the role of leaders and leadership in turn underlines the influence of Selznick's Leadership in Administration (Selznick 1957). Selznick distinguishes between two ideal types of enterprise: on the one hand, a rational instrumental organization and, on the other hand, the value-infused institution. According to Selznick, the term “organisation” suggests a technical instrument to harness human energies and direct them towards set aims, while the term “institution” suggests an organic social entity, or culture. Organizational culture has been variously defined (Ott 1989; Schein 1990; Davies, Nutley, and Mannion 2000). It denotes a wide range of social phenomena, including an organization's customary dress, language, behavior, beliefs, values, assumptions, symbols of status and authority, myths, ceremonies and rituals, and modes of deference and subversion; all of which help to define an organization's character and norms. Unsurprisingly in view of this diverse array of phenomena, little agreement exists over a precise definition of organizational culture, how it should be observed or measured, or how different methodologies can be used to inform routine administration or organizational change. While some commentators see the task in terms of specific and measurable variables, traits or processes, others see it as a global challenge to capture culture as an intrinsic property of the social milieu that forms whenever people are brought together in common enterprise. A third approach sees organizational culture as an anthropological metaphor or a paradigm (Burrell and Morgan 1979; Burrell 1996) to analyze organizations as microsocieties (Morgan, Frost, and Pondy 1983; Smircich 1983; Morgan 1986). According to Edgar Schein, Organizational culture is the pattern of shared basic assumptions—invented, discovered, or developed by a given group as it learns to cope with its problems of external adaptation and internal integration—that has worked well enough to be considered valid and, therefore, to be taught to new members as the correct way to perceive, think, and feel in relation to those problems (Schein 1985a). This definition captures one of the basic challenges faced by any culture to reconcile the often divergent aims and actions of its members. It also points to the difficulty of addressing that challenge. Its emphasis on the role of shared basic assumptions influencing beliefs and behavior suggests that organizational culture denotes much more than just “the way things are done around here” (Davies, Nutley, and Mannion 2000). Changing the way things are done appears, on the functional level of systems redesign, relatively easy. Attempting to understand why things are done in their distinctive ways, the factors underlying resistance to change attempts, and the extent to which new practices are sustained is far more challenging. To successfully engender change in organizational behavior we need to understand the collective thought processes informing that behavior at both conscious and unconscious levels. This is where a deeper analysis and understanding of organizational culture may be productive. Advocates of strategic cultural change typically make a number of implicit assumptions. First, health organizations possess discernible cultures, which affect quality and performance. Second, although cultures may be resistant to change, they are to some extent malleable and manageable. Third, it is possible to identify particular cultural attributes that facilitate or inhibit good performance and it should therefore be feasible for managers to design strategies for cultural change. Finally, it is assumed that any benefits accruing from the change will outweigh any dysfunctional consequences. Although there is as yet little empirical evidence to support these assumptions, some academics and many policymakers are showing renewed interest in the quantitative measurement of organizational culture in order to determine its relationship with performance and quality of care (Davies, Nutley, and Mannion 2000; Shortell et al. 2000; Shortell et al. 2001). A range of tools designed to measure organizational culture have been developed and applied in industrial, educational, and health care settings over the last two decades. In this paper we describe the results of an extensive review of these instruments and examine their usefulness for health service researchers. The review forms part of a larger study into the relationship between organizational culture and the performance of health organizations (Scott et al. 2001, In press).

History and evolution of the arctic flora: in the footsteps of Eric Hulten

Abstract: A major contribution to our initial understanding of the origin, history and biogeography of the present-day arctic flora was made by Eric Hulten in his landmark book Outline of the History of Arctic and Boreal Biota during the Quarternary Period, published in 1937. Here we review recent molecular and fossil evidence that has tested some of Hulten's proposals. There is now excellent fossil, molecular and phytogeographical evidence to support Hulten's proposal that Beringia was a major northern refugium for arctic plants throughout the Quaternary. In contrast, most molecular evidence fails to support his proposal that contemporary east and west Atlantic populations of circumarctic and amphi-Atlantic species have been separated throughout the Quaternary. In fact, populations of these species from opposite sides of the Atlantic are normally genetically very similar, thus the North Atlantic does not appear to have been a strong barrier to their dispersal during the Quaternary. Hulten made no detailed proposals on mechanisms of speciation in the Arctic; however, molecular studies have confirmed that many arctic plants are allopolyploid, and some of them most probably originated during the Holocene. Recurrent formation of polyploids from differentiated diploid or more low-ploid populations provides one explanation for the intriguing taxonomic complexity of the arctic flora, also noted by Hulten. In addition, population fragmentation during glacial periods may have lead to the formation of new sibling species at the diploid level. Despite the progress made since Hulten wrote his book, there remain large gaps in our knowledge of the history of the arctic flora, especially about the origins of the founding stocks of this flora which first appeared in the Arctic at the end of the Pliocene (approximately 3 Ma). Comprehensive analyses of the molecular phylogeography of arctic taxa and their relatives together with detailed fossil studies are required to fill these gaps.

The radiosensitivity of the human oocyte.

Abstract: BACKGROUND: We determined the best model available for natural follicle decline in healthy women and used this to calculate the radiosensitivity of the human oocyte. METHODS: Ovarian failure was diagnosed in six patients with a median age of 13.2 years (range 12.5-16.0) who were treated with total body irradiation (14.4 Gy) at 11.5 years of age (4.9-15.1). We previously estimated the dose of radiation required to destroy 50% of the oocytes (LD 50 ) to be <4 Gy. This estimate is an oversimplification, because decay represents an instantaneous rate of temporal change based upon the remaining population pool, expressed as a differential equation: dy/dx = -y[0.0595 + 3716/ (11780 + y)], with initial value y(0) = 701 200. RESULTS: Solving the differential equation, we have estimated the number of follicles left after irradiation given as sol(51 - s + r), where r equals age at treatment, s equals age at diagnosis of ovarian failure, and 51 years is the average age of menopause. The surviving fraction of oocytes as a percentage is 100 times this value divided by sol(r). The mean surviving fraction for the six cases is 0.66%. We obtain a function, g(z), which decreases in value from 100% at zero dosage to mean value at dosage z = 14.4 Gy. We have g(z) = 10 mx+c , where c = log 10 100 = 2, and m = [log 10 (0.66) - c]/14.4. Solving g(z) = 50 gives an LD 50 of 1.99. CONCLUSIONS: Based on new data and a revised mathematical model of natural oocyte decline, we have determined the surviving fraction of oocytes following irradiation and estimate the LD 50 of the human oocyte to be <2 Gy.

Two-dimensional Radiative Transfer in Protostellar Envelopes. I. Effects of Geometry on Class I Sources

Abstract: We present two-dimensional radiation transfer models of class I protostars and show the effect of including more realistic geometries on the resulting spectral energy distributions and images. We begin with a rotationally flattened infalling envelope as our comparison model and add a flared disk and bipolar cavity. The disk affects the spectral energy distribution most strongly at edge-on inclinations, causing a broad dip at about 10 lm (independent of the silicate feature) due to high extinction and low scattering albedo in this wavelength region. The bipolar cavities allow more direct stellar+disk radiation to emerge into polar directions and more scattering radiation to emerge into all directions. The wavelength-integrated flux, often interpreted as luminosity, varies with viewing angle, with pole-on viewing angles seeing 2–4 times as much flux as edge-on, depending on geometry. Thus, observational estimates of luminosity should take into account the inclination of a source. The envelopes with cavities are significantly bluer in near-IR and mid-IR color-color plots than those without cavities. Using one-dimensional models to interpret Class I sources with bipolar cavities would lead to an underestimate of envelope mass and an overestimate of the implied evolutionary state. We compute images at near-, mid-, and far-IR wavelengths. We find that the mid-IR colors and images are sensitive to scattering albedo and that the flared disk shadows the midplane on large size scales at all wavelengths plotted. Finally, our models produce polarization spectra that can be used to diagnose dust properties, such as albedo variations due to grain growth. Our results of polarization across the 3.1 l mi ce feature agree well with observations for ice mantles covering 5% of the radius of the grains. Subject headings: circumstellar matter — dust, extinction — polarization — radiative transfer — stars: formation — stars: pre–main-sequence

Mechanism of Electrochemical Activity in Li2MnO3

Abstract: Lithium intercalation compounds based on lithium manganese oxides are of great importance as positive electrodes for rechargeable lithium batteries. It is widely accepted that Li+ may be extracted (deintercalated) from such lithium manganese oxides accompanied by oxidation of Mn up to a maximum oxidation state of +4. However, it has been suggested recently that further Li+ removal may be possible. Among the mechanisms that have been proposed to charge balance the removal of Li+ are Mn oxidation beyond +4 or loss of O2-. To investigate this phenomenon we have selected Li2MnO3, a layered compound Li[Li1/3Mn2/3]O2 with a ready supply of mobile Li+ ions but with all Mn already in the +4 oxidation state. We show that a substantial quantity of Li (at least 1.39 Li) may be removed. At 55 °C this occurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3. The presence of H+ between the oxide layers results in a change of the layer stac...

Two-dimensional radiative transfer in protostellar envelopes. ii. an evolutionary sequence

Abstract: We present model spectral energy distributions (SEDs), colors, polarization, and images for an evolutionary sequence of a low-mass protostar from the early collapse stage (Class 0) to the remnant disk stage (Class III). We find a substantial overlap in colors and SEDs between protostars embedded in envelopes (Class 0–I) and T Tauri disks (Class II), especially at mid-IR wavelengths. Edge-on Class I–II sources show double-peaked SEDs, with a short-wavelength hump due to scattered light and a long-wavelength hump due to thermal emission. These are the bluest sources in mid-IR color-color diagrams. Since Class 0 and I sources are diffuse, the size of the aperture over which fluxes are integrated has a substantial effect on the computed colors, with larger aperture results showing significantly bluer colors. Viewed through large apertures, the Class 0 colors fall in the same regions of mid-IR color-color diagrams as Class I sources and are even bluer than Class II–III sources in some colors. It is important to take this into account when comparing color-color diagrams of star formation regions at different distances or different sets of observations of the same region. However, the near-IR polarization of the Class 0 sources is much higher than the Class I–II sources, providing a means to separate these evolutionary states. We varied the grain properties in the circumstellar envelope, allowing for larger grains in the disk midplane and smaller grains in the envelope. In comparing with models with the same grain properties throughout, we find that the SED of the Class 0 source is sensitive to the grain properties of the envelope only—that is, grain growth in the disk in Class 0 sources cannot be detected from the SED. Grain growth in disks of Class I sources can be detected at wavelengths greater than 100 lm. Our image calculations predict that the diffuse emission from edge-on Class I and II sources should be detectable in the mid-IR with the Space Infrared Telescope Facility (SIRTF) in nearby star-forming regions (out to several hundred parsecs). Subject headings: circumstellar matter — dust, extinction — polarization — radiative transfer — stars: formation — stars: pre–main-sequence

Tradeoffs and the evolution of thermal reaction norms

Abstract: Tradeoffs have played a prominent role in the development of theories describing the evolution of reaction norms Different classes of tradeoffs are known to constrain the evolution of phenotypes, but current theories incorporate only a subset of these tradeoffs Consequently, these theories cannot account for some of the variation in reaction norms that has been observed within and among species Empirical studies of thermal reaction norms for physiological and life historical traits have shown that different proximate mechanisms can produce similar reaction norms As a consequence, certain tradeoffs can be circumvented when the fitness costs imposed by these tradeoffs are severe We argue that a unified theory that includes all classes of tradeoffs would provide a better understanding of the mechanisms that drive the evolution of reaction norms

From Knowing to Doing: A Framework for Understanding the Evidence-into-Practice Agenda

Abstract: The past decade has witnessed widespread interest in the development of policy and practice that is better informed by evidence. Enthusiasm has, however, been tempered by recognition of the difficulties of devising effective strategies to ensure that evidence is integrated into policy and utilized in practice. There is already a rich but diverse and widely dispersed literature that can be drawn upon to inform such strategies. This article offers a guide to this literature by focusing on six main interrelated concerns: (1) the types of knowledge relevant to understanding research utilization/evidence-based practice (RU/EBP) implementation; (2) the ways in which research knowledge is utilized; (3) models of the process of utilization; (4) the conceptual frameworks that enable us to understand the process of RU/EBP implementation; (5) the main ways of intervening to increase evidence uptake and the effectiveness of these; (6) different ways of conceptualizing what RU/EBP means in practice.

Forty eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance

Abstract: We have conducted a programme to determine the fundamental parameters of a substantial number of eclipsing binaries of spectral types O and B in the Small Magellanic Cloud (SMC). New spectroscopic data, obtained with the two- degree- field (2dF) multi- object spectrograph on the 3.9- m Anglo- Australian Telescope, have been used in conjunction with photometry from the Optical Gravitational Lens Experiment (OGLE- II) data base of SMC eclipsing binaries. Previously we reported results for 10 systems; in this second and concluding paper we present spectral types, masses, radii, temperatures, surface gravities and luminosities for the components of a further 40 binaries. The uncertainties are typically +/- 10 per cent on masses, +/- 4 per cent on radii and +/- 0.07 on log L. The full sample of 50 OB- type eclipsing systems is the largest single set of fundamental parameters determined for high- mass binaries in any galaxy. We find that 21 of the systems studied are in detached configurations, 28 are in semidetached post- mass- transfer states, and one is a contact binary.The overall properties of the detached systems are consistent with theoretical models for the evolution of single stars with SMC metal abundances (Z similar or equal to 0.004); in particular, observed and evolutionary masses are in excellent agreement. Although there are no directly applicable published models, the overall properties of the semidetached systems are consistent with them being in the slow phase of mass transfer in case A. About 40 per cent of these semidetached systems show photometric evidence of orbital- phase- dependent absorption by a gas stream falling from the inner Lagrangian point on the secondary star towards the primary star. This sample demonstrates that case- A mass transfer is a common occurrence amongst high- mass binaries with initial orbital periods P less than or similar to 5 d, and that this slow phase has a comparable duration to the detached phase preceding it.Each system provides a primary distance indicator. We find a mean distance modulus to the SMC of 18.91 +/- 0.03 +/- 0.1 (internal and external uncertainties; D = 60.6 +/- 1.0 +/- 2.8 kpc). This value represents one of the most precise available determinations of the distance to the SMC.

Implementing culture change in health care: theory and practice.

Abstract: Objectives. To review some of the key debates relating to the nature of organizational culture and culture change in health care organizations and systems. Methods. A literature review was conducted that covered both theoretical contributions and published studies of the processes and outcomes of culture change programmes across a range of health and non-health care settings. Results. There is little consensus among scholars over the precise meaning of organizational culture. Competing claims exist concerning whether organizational cultures are capable of being shaped by external manipulation to beneficial effect. A range of culture change models has been developed. A number of underlying factors that commonly attenuate culture change programmes can be identified. Key factors that appear to impede culture change across a range of sectors include: inadequate or inappropriate leadership; constraints imposed by external stakeholders and professional allegiances; perceived lack of ownership; and subcultural diversity within health care organizations and systems. Conclusions. Managing organizational culture is increasingly viewed as an essential part of health system reform. To transform the culture of a whole health system such as the UK National Health Service would be a complex, multi-level, and uncertain process, comprising a range of interlocking strategies and supporting tactics unfolding over a period of years.

The hierarchical formation of a stellar cluster

Abstract: Recent surveys of star-forming regions have shown that most stars, and probably all massive stars, are born in dense stellar clusters. The mechanism by which a molecular cloud fragments to form several hundred to thousands of individual stars has remained elusive. Here, we use a numerical simulation to follow the fragmentation of a turbulent molecular cloud, and the subsequent formation and early evolution of a stellar cluster containing more than 400 stars. We show that the stellar cluster forms through the hierarchical fragmentation of a turbulent molecular cloud. This leads to the formation of many small subclusters, which interact and merge to form the final stellar cluster. The hierarchical nature of the cluster formation has serious implications in terms of the properties of the new-born stars. The higher number-density of stars in subclusters, compared to a more uniform distribution arising from a monolithic formation, results in closer and more frequent dynamical interactions. Such close interactions can truncate circumstellar discs, harden existing binaries and potentially liberate a population of planets. We estimate that at least one-third of all stars, and most massive stars, suffer such disruptive interactions.

The Physics of Plasmas

Abstract: The Physics of Plasmas provides a comprehensive introduction to the subject, illustrating the basic theory with examples drawn from fusion, space and astrophysical plasmas. A particular strength of the book is its discussion of the various models used to describe plasma physics and the relationships between them. These include particle orbit theory, fluid equations, ideal and resistive magnetohydrodynamics, wave equations and kinetic theory. The reader will gain a firm grounding in the fundamentals, and develop this into an understanding of some of the more specialised topics. Throughout the text, there is an emphasis on the physical interpretation of plasma phenomena. Exercises are provided throughout. Advanced undergraduate and graduate students of physics, applied mathematics, astronomy and engineering will find a clear but rigorous explanation of the fundamental properties of plasmas with minimal mathematical formality. This book will also appeal to research physicists, nuclear and electrical engineers.