Light-cone coordinates based at a geodesic world line

Continuing work initiated in an earlier publication [Phys. Rev. D 69, 084007 (2004)], we construct a system of light-cone coordinates based at a geodesic world line of an arbitrary curved spacetime. The construction involves (i) an advanced-time or a retarded-time coordinate that labels past or future light cones centered on the world line, (ii) a radial coordinate that is an affine parameter on the null generators of these light cones, and (iii) angular coordinates that are constant on each generator. The spacetime metric is calculated in the light-cone coordinates, and it is expressed as an expansion in powers of the radial coordinate in terms of the irreducible components of the Riemann tensor evaluated on the world line. The formalism is illustrated in two simple applications, the first involving a comoving world line of a spatially-flat cosmology, the other featuring an observer placed on the axis of symmetry of Melvin's magnetic universe.Comment: 11 pages, 1 figur

How do we know what works? Evaluating data on the extent and impact of young people’s involvement in English health research

The case for children and young people’s involvement in health research has been well documented, but less attention has been paid to the experiences and impact of involving children and young people rather than adults. This paper explores these issues in relation to a project undertaken for the James Lind Initiative on the availability, quality and reliability of existing data on young people’s involvement in studies supported by the National Institute for Health Research (NIHR). The project found that there was no systematic way of getting reliable and comparable information about which young people are involved in health research in England, what form that involvement may have taken or the impacts of involvement. There is a need to better collate and disseminate evidence on young people’s involvement in research, using both existing systems and processes, and the possible development of new metrics and measures. Not having this information risks children and young people’s involvement continuing to develop in a piecemeal fashion. Further research is needed about how, when and where children and young people are involved in health research, and about the impact of involvement on research and on the children and young people involved

Ten milliparsec-scale structure of the nucleus region in Centaurus A

We present the results of a VLBI Space Observatory Programme (VSOP) observation of the subparsec structure in Centaurus A at 4.9 GHz. Owing to its proximity, our Centaurus A space-VLBI image is one of the highest spatial resolution images of an AGN ever made -- 0.01 pc per beam. The elongated core region is resolved into several components over 10 milli-arcseconds long (0.2 pc) including a compact component of brightness temperature 2.2x10^10K. We analyze the jet geometry in terms of collimation. Assuming the strongest component to be the core, the jet opening angle at ~ 5,000 r_s (Schwarzchild radii) from the core is estimated to be ~ 12 degree, with collimation of the jet to ~ 3 degree continuing out to ~ 20,000 r_s. This result is consistent with previous studies of the jet in M87, which favor MHD disk outflow models. Future space VLBI observations at higher frequencies will probably be able to image the collimation region, within 1,000 r_s of the center of Centaurus A, together with the accretion disk itself.Comment: 12 pages, 6 figures, accepted for publication in PASJ, Vol.57 No.6, VSOP special issu

The Stac Fada “impact ejecta” layer: not what it seems

The Stac Fada Member (SFM) forms part of the Stoer Group of the Torridonian of NW Scotland. The SFM is unique in the Torridonian, being characterized by the presence of greenish altered glass clasts. Its origin has been debated for decades with several hypotheses being proposed but all invoking some connection with volcanic activity in the region. More recently, Amor et al. suggested that the SFM represents “a chord section through the continuous ejecta blanket surrounding an impact crater”. Here, we confirm the presence of shocked material within the SFM and then discuss its origin

Searching for low mass objects around nearby dMe radio stars

Nearby M-dwarfs are best suited for searches of low mass companions. VLBI phase-referencing observations with sensitive telescopes are able to detect radio star flux-densities of tenths of mJy as well as to position the star on the sky with submilliarcsecond precision. We have initiated a long-term observational program, using EVN telescopes in combination with NASA DSN dishes, to revisit the kinematics of nearby, single M dwarfs. The precision of the astrometry allows us to search for possible companions with masses down to 1 Jupiter mass. In this contribution we report preliminary results of the first observation epochs, in which we could detect some of the radio stars included in our program.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros E., Porcas R.W., Lobanov A.P., & Zensus J.A. (eds.), MPIfR, Bonn, Germany, p. 255-258 (2002). 4 pages, 3 figures, needs evn2002.cl

Critical behavior in an evolutionary Ultimatum Game

Experimental studies have shown the ubiquity of altruistic behavior in human societies. The social structure is a fundamental ingredient to understand the degree of altruism displayed by the members of a society, in contrast to individual-based features, like for example age or gender, which have been shown not to be relevant to determine the level of altruistic behavior. We explore an evolutionary model aiming to delve how altruistic behavior is affected by social structure. We investigate the dynamics of interacting individuals playing the Ultimatum Game with their neighbors given by a social network of interaction. We show that a population self-organizes in a critical state where the degree of altruism depends on the topology characterizing the social structure. In general, individuals offering large shares but in turn accepting large shares, are removed from the population. In heterogeneous social networks, individuals offering intermediate shares are strongly selected in contrast to random homogeneous networks where a broad range of offers, below a critical one, is similarly present in the population.Comment: 13 pages, 7 figure

The Fertility Problem Inventory and Infertility-Related Stress: A Case Study

More than seven million people of childbearing age in the United States experience infertility. Oftentimes, for women, the experience of infertility is stressful. The Fertility Problem Inventory (FPI) has been used to quantitatively measure women’s experience of infertility-related stress. However, the construct of infertility-related stress is poorly described in existing literature. The purpose of this case study was to understand how women experience the FPI as a measure of infertility-related stress. To address this issue, women who were undergoing infertility treatment completed the FPI and participated in unstructured interviews. Archival documents were also retrieved to corroborate findings and satisfy saturation. Results indicated that the FPI is lacking in structure and organization to describe women’s experiences of infertility-related stress. Specifically, women described feeling infertility having an influence upon their identity and their coping

Solution of the Bohr hamiltonian for soft triaxial nuclei

The Bohr-Mottelson model is solved for a generic soft triaxial nucleus, separating the Bohr hamiltonian exactly and using a number of different model-potentials: a displaced harmonic oscillator in $\gamma$, which is solved with an approximated algebraic technique, and Coulomb/Kratzer, harmonic/Davidson and infinite square well potentials in $\beta$, which are solved exactly. In each case we derive analytic expressions for the eigenenergies which are then used to calculate energy spectra. Here we study the chain of osmium isotopes and we compare our results with experimental information and previous calculations.Comment: 13 pages, 9 figure

The Contribution of Adult Learning to Health and Social Capital

Objectives and methods • The aim of this research is to investigate the effects of adult learning upon a range of measures of health and social capital and cohesion. • The study has a broad scope. We estimate effects of adult learning on a wide range of outcomes. We break down participation in learning in a number of ways, and we assess the different impacts of participation on different groups. The primary objective is to assess the nature and extent of wider effects of adult learning. More detailed findings relating to specific outcomes, types of courses taken and groups of learners are extremely interesting and indicate directions for further research. • The National Child Development Study is the database used for analyses. We use data relating to almost 10,000 adults born in Britain in 1958, focusing upon changes in their lives between the ages of 33 (in 1991) and 42 (in 2000). • The effects of participation in learning between the ages of 33 and 42 are estimated. Participation in learning is broken down according to the type of course taken – courses resulting in academic and vocational qualifications, work-related training and leisure courses. • Previous, closely related research on the effects of adult learning focused on wage effects only and neglected non-accredited learning of the kind considered here. The current project is, therefore, a timely reminder that many learners take courses in adult learning that are not accredited and for reasons other than wage returns. A proper assessment of the value of adult learning must take these wider benefits into account. • The outcomes considered are changes between age 33 and 42 in social and political attitudes, civic participation, health behaviours (smoking, alcohol consumption and exercise), self-reported life satisfaction and onset and recovery from depression. • Effects of participation upon these outcomes are estimated for the whole sample. In addition, the different effects of participation are separately estimated for men and women, and for those without Level 2 qualifications at age 33. • We restrict selection bias by exploiting the fact that our data are longitudinal. We attempt to consider effects on individuals as they change over time, making before and after comparisons. We also control for a wide range of life-course background, achievement and developmental factors

Low frequency VLBI in space using GAS-Can satellites: Report on the May 1987 JPL Workshop

Summarized are the results of a workshop held at JPL on May 28 and 29, 1987, to study the feasibility of using small, very inexpensive spacecraft for a low-frequency radio interferometer array. Many technical aspects of a mission to produce high angular resolution images of the entire sky at frequencies from 2 to 20 MHz were discussed. The workshop conclusion was that such a mission was scientifically valuable and technically practical. A useful array could be based on six or more satellites no larger than those launched from Get-Away-Special canisters. The cost of each satellite could be $1-2M, and the mass less than 90 kg. Many details require further study, but as this report shows, there is good reason to proceed. No fundamental problems have been discovered involving the use of untraditional, very inexpensive spacecraft for this type of mission