BFKL Physics in Jet Production at e+e- colliders

Virtual photon scattering in $e^+e^-$ collisions can result in events with the electron-positron pair at large rapidity separation with hadronic activity in between. The BFKL equation resums large logarithms that dominate the cross section for this process. We report here on a Monte Carlo method for solving the BFKL equation that allows kinematic constraints to be taken into account and show results for $e^+e^-$ collisions.Comment: 3 pages, Latex, talk presented at the 2000 Meeting of the Division of Particles and Fields of the APS, Columbus, OH, August 9--12, 200

An Optical Spectroscopic Study of T Tauri Stars. I. Photospheric Properties

Measurements of masses and ages of young stars from their location in the HR diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux calibrated optical spectra to measure accurate spectral types and extinctions of 283 nearby T Tauri stars. The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are 1-2 subclasses later than literature spectral types for the original members of the TWA and are discrepant with literature values for some well known Taurus CTTSs. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than nIR measurements, likely the result of methodological differences and the presence of nIR excesses in most CTTSs. As an illustration of the impact of accretion, SpT, and extinction uncertainties on the HR diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.Comment: Accepted by ApJ. 30 pages plus 12 pages of Tables and Reference

Empirical Isochrones for Low Mass Stars in Nearby Young Associations

Absolute ages of young stars are important for many issues in pre-main sequence stellar and circumstellar evolution but are long recognized as difficult to derive and calibrate. In this paper, we use literature spectral types and photometry to construct empirical isochrones in HR diagrams for low-mass stars and brown dwarfs in the eta Cha, epsilon Cha, and TW Hya Associations and the beta Pic and Tuc-Hor Moving Groups. A successful theory of pre-main sequence evolution should match the shapes of the stellar loci for these groups of young stars. However, when comparing the combined empirical isochrones to isochrones predicted from evolutionary models, discrepancies lead to a spectral type (mass) dependence in stellar age estimates. Improved prescriptions for convection and boundary conditions in the latest models of pre-main sequence models lead to a significantly improved correspondence between empirical and model isochrones, with small offsets at low temperatures that may be explained by observational uncertainties or by model limitations. Independent of model predictions, linear fits to combined stellar loci of these regions provide a simple empirical method to order clusters by luminosity with a reduced dependence on spectral type. Age estimates calculated from various sets of modern models that reproduce Li depletion boundary ages of the beta Pic Moving Group also imply a ~4 Myr age for the low mass members of the Upper Sco OB Association, which is younger than the 11 Myr age that has been recently estimated for intermediate mass members.Comment: Accepted by ApJ, 18 page

Progress Towards a Generator for BFKL Physics

In certain regions of phase space in jet production, large logarithms can arise which are resummed by the BFKL equation. Linear colliders can potentially be excellent places to study BFKL effects in jet production. We discuss an approach to BFKL calculations which incorporates kinematic effects explicitly and can be implemented in an event generator.Comment: 4 pages including 2 figures, Latex, uses epsfig, aipproc.sty; talk presented at Linear Collider Workshop 2000, Fermilab, Batavia, IL, Oct. 24--28, 200

Good places for ageing in place : development of objective built environment measures for investigating links with older people's wellbeing

Background: There is renewed interest in the role of the built environment in public health. Relatively little research to date investigates its impact on healthy ageing. Ageing in place has been adopted as a key strategy for coping with the challenges of longevity. What is needed is a better understanding of how individual characteristics of older people’s residential environments (from front door to wider neighbourhood) contribute to their wellbeing, in order to provide the basis for evidence-based housing/urban design and development of interventions. This research aimed to develop a tool to objectively measure a large range of built environment characteristics, as the basis for a preliminary study of potential relationships with a number of ‘place-related’ functional, emotional and social wellbeing constructs. Methods: Through a review of urban design literature, design documents, and existing measures, a new tool, the NeDeCC (Neighbourhood Design Characteristics Checklist) was developed. It was piloted, refined, and its reliability validated through inter-rater tests. A range of place-related wellbeing constructs were identified and measured through interviews with 200 older people living in a wide variety of rural-urban environments and different types of housing in England. The NeDeCC was used to measure the residential environment of each participant, and significant bivariate relationships with wellbeing variables were identified. Results: The NeDeCC was found to have convincing face and construct validity and good inter-rater and test/ retest reliability, though it would benefit from use of digital data sources such as Google Earth to eliminate the need for on-site survey. The significant relationships found in the study suggest that there may be characteristics of residential environments of potential relevance for older people’s lives that have been overlooked in research to date, and that it may be worthwhile to question some of the assumptions about where and how older people want to live (e.g. villages seem to be positive). They also point to the importance of considering non-linear relationships. Conclusions: The NeDeCC provides the basis for generation of evidence-based design guidance if it is used in prospective controlled studies or ‘natural experiments’ in the future. Ultimately, this will facilitate the creation of better places for ageing in place