Dispersion measure variations and their effect on precision pulsar timing

We present an analysis of the variations seen in the dispersion measures (DMs) of 20-ms pulsars observed as part of the Parkes Pulsar Timing Array project. We carry out a statistically rigorous structure function analysis for each pulsar and show that the variations seen for most pulsars are consistent with those expected for an interstellar medium characterized by a Kolmogorov turbulence spectrum. The structure functions for PSRs J1045-4509 and J1909-3744 provide the first clear evidence for a large inner scale, possibly due to ion-neutral damping. We also show the effect of the solar wind on the DMs and show that the simple models presently implemented into pulsar timing packages cannot reliably correct for this effect. For the first time we clearly show how DM variations affect pulsar timing residuals and how they can be corrected in order to obtain the highest possible timing precision. Even with our presently limited data span, the residuals (and all parameters derived from the timing) for six of our pulsars have been significantly improved by correcting for the DM variations. © 2007 RAS

Theorising interprofessional pedagogic evaluation: framework for evaluating the impact of interprofessional CPD on practice change

This paper outlines the development of a conceptual framework to guide the evaluation of the impact of the pedagogy employed in continuing professional development for professionals in education, health and social care. The work is developed as part of the Centre for Excellence in Teaching and Learning: Interprofessional Learning across the Public Sector (CETL: IPPS) at the University of Southampton. The paper briefly outlines the field for pedagogic research and comments on the underpinning theories that have so far been used to guide research into interprofessional learning (IPL). It maps out the development of interprofessional CPD in its specific context as part of the CETL: IPPS with its links to a local authority undergoing service reorganisation and the role of the continuing professional development (CPD) in effecting change. It then brings together a theoretical framework with the potential toexplore, explain and evaluate the essential features of the model of pedagogy used in interprofessional CPD, in which professionals from education have for the first time been included alongside those from health and social care. The framework draws upon elements of situated learning theory, Activity Theory and Dreier’s work (2002, 1999) on trajectories of participation, particularly Personal Action Potency. By combining the resulting analytic framework with an adapted version of an established evaluation model, a theoretically-driven, practicable evaluation matrix is developed. The matrix has potential use in evaluating the impact of pedagogic input on practice change. The paper models a process for developing a conceptual framework to steer pedagogic evaluation. Such a process and the resulting matrix may be of use to other researchers who are similarly developing pedagogic evaluation

Timing stability of millisecond pulsars and prospects for gravitational-wave detection

The analysis of high-precision timing observations of an array of ∼20 millisecond pulsars (a so-called \u27timing array\u27) may ultimately result in the detection of a stochastic gravitational-wave background. The feasibility of such a detection and the required duration of this type of experiment are determined by the achievable rms of the timing residuals and the timing stability of the pulsars involved. We present results of the first long-term, high-precision timing campaign on a large sample of millisecond pulsars used in gravitational-wave detection projects. We show that the timing residuals of most pulsars in our sample do not contain significant low-frequency noise that could limit the use of these pulsars for decade-long gravitational-wave detection efforts. For our most precisely timed pulsars, intrinsic instabilities of the pulsars or the observing system are shown to contribute to timing irregularities on a 5-year time-scale below the 100 ns level. Based on those results, realistic sensitivity curves for planned and ongoing timing array efforts are determined. We conclude that prospects for detection of a gravitational-wave background through pulsar timing array efforts within 5 years to a decade are good. © 2009 RAS

The sensitivity of the Parkes Pulsar Timing Array to individual sources of gravitational waves

We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves (GWs) emitted by individual supermassive black hole binary systems in the early phases of coalescing at the cores of merged galaxies. Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to Laser Interferometer Gravitational-Wave Observatory and Laser Interferometer Space Antenna. We place a sky-averaged constraint on the merger rate of nearby (z \u3c 0.6) black hole binaries in the early phases of coalescence with a chirp mass of 1010 M⊙ of less than one merger every 7 yr. The prospects for future GW astronomy of this type with the proposed Square Kilometre Array telescope are discussed. © 2010 The Authors. Journal compilation © 2010 RAS

LIMITS ON ANISOTROPY AND INHOMOGENEITY FROM THE COSMIC BACKGROUND RADIATION,

We consider directly the equations by which matter imposes anisotropies on freely propagating background radiation, leading to a new way of using anisotropy measurements to limit the deviations of the Universe from a Friedmann-Robertson-Walker (FRW) geometry. This approach is complementary to the usual Sachs-Wolfe approach: the limits obtained are not as detailed, but they are more model-independent. We also give new results about combined matter-radiation perturbations in an almost-FRW universe, and a new exact solution of the linearised equations.Comment: 18 pages Latex

‘Can you dig it?’ Developing an approach to validly assessing diverse skills in an archaeological context

This paper outlines a case study of an assessment development process which contrasts with more recent ‘top-down’ trends in assessment which tend to leave assessment development processes opaque to users. This paper describes the processes of a collaborative, multi-agency project which set out to develop an assessment framework which would appropriately recognise the various skills present in the Higher Education Field Academy; a widening participation programme aiming to boost the educational aspirations, enthusiasm and attainment of secondary school students through their engagement in archaeological excavation. The case study describes the stages of building an assessment framework that was sympathetic to the intentions of a learning programme whilst providing robust observation-based outcomes that avoided heavy assessment processes that could corrupt learning relationships. The challenges involved in this development process have important parallels with vocational assessment; not least in providing an example of a localised development of an observation-based assessment model which can be used in diverse settings. The insights gained from this case study are useful for others who are engaged in localised assessment development processes

Understanding Galaxy Formation and Evolution

The old dream of integrating into one the study of micro and macrocosmos is now a reality. Cosmology, astrophysics, and particle physics intersect in a scenario (but still not a theory) of cosmic structure formation and evolution called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to explain the origin of galaxies. In these lecture notes, I first present a review of the main galaxy properties, highlighting the questions that any theory of galaxy formation should explain. Then, the cosmological framework and the main aspects of primordial perturbation generation and evolution are pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation, presenting a review on LCDM halo assembling and properties, and on the main candidates for non-baryonic dark matter. It is shown how the nature of elemental particles can influence on the features of galaxies and their systems. Finally, the complex processes of baryon dissipation inside the non-linearly evolving CDM halos, formation of disks and spheroids, and transformation of gas into stars are briefly described, remarking on the possibility of a few driving factors and parameters able to explain the main body of galaxy properties. A summary and a discussion of some of the issues and open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf). Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005 (submitted to the Editors on March 15, 2006

Search for supersymmetry with a dominant R-parity violating LQDbar couplings in e+e- collisions at centre-of-mass energies of 130GeV to 172 GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQDbar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m_0=500 GeV/c^2 and tan(beta)=sqrt(2) charginos with masses smaller than 81 GeV/c^2 and neutralinos with masses smaller than 29 GeV/c^2 are excluded at the 95% confidence level for any generation structure of the LQDbar coupling.Comment: 32 pages, 30 figure

Characterization of optical properties and surface roughness profiles: The Casimir force between real materials

The Lifshitz theory provides a method to calculate the Casimir force between two flat plates if the frequency dependent dielectric function of the plates is known. In reality any plate is rough and its optical properties are known only to some degree. For high precision experiments the plates must be carefully characterized otherwise the experimental result cannot be compared with the theory or with other experiments. In this chapter we explain why optical properties of interacting materials are important for the Casimir force, how they can be measured, and how one can calculate the force using these properties. The surface roughness can be characterized, for example, with the atomic force microscope images. We introduce the main characteristics of a rough surface that can be extracted from these images, and explain how one can use them to calculate the roughness correction to the force. At small separations this correction becomes large as our experiments show. Finally we discuss the distance upon contact separating two rough surfaces, and explain the importance of this parameter for determination of the absolute separation between bodies.}Comment: 33 pages, 14 figures, to appear in Springer Lecture Notes in Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni, David Roberts, and Felipe da Ros