Generalised quadratic forms and the u-invariant

The u-invariant of a field is the supremum of the dimensions of anisotropic quadratic forms over the field. We define corresponding u-invariants for hermitian and generalised quadratic forms over a division algebra with involution in characteristic 2 and investigate the relationships between them. We also investigate these invariants in the case of a quaternion algebra and in particular when this quaternion algebra is the unique quaternion division algebra over a field.Comment: 20 page

Cyclical Flow: Spatial Synthesis Sound Toy as Multichannel Composition Tool

This paper outlines and discusses an interactive system designed as a playful ‘sound toy’ for spatial composition. Proposed models of composition and design in this context are discussed. The design, functionality and application of the software system is then outlined and summarised. The paper concludes with observations from use, and discussion of future developments

The Charge Transfer Efficiency and Calibration of WFPC2

A new determination of WFPC2 photometric corrections is presented, using HSTphot reduction of the WFPC2 Omega Centauri and NGC 2419 observations from January 1994 through March 2000 and a comparison with ground-based photometry. No evidence is seen for any position-independent photometric offsets (the "long-short anomaly"); all systematic errors appear to be corrected with the CTE and zero point solution. The CTE loss time dependence is determined to be very significant in the Y direction, causing time-independent CTE solutions (Stetson 1998; Saha, Lambert, & Prosser 2000) to be valid only for a small range of times. On average, the present solution produces corrections similar to Whitmore, Heyer, & Casertano (1999), although with an improved functional form that produces less scatter in the residuals and determined with roughly a year of additional data. In addition to the CTE loss characterization, zero point corrections are also determined as functions of chip, gain, filter, and temperature. Of interest, there are chip-to-chip differences of order 0.01-0.02 magnitudes relative to the Holtzman et al. (1995) calibrations, and the present study provides empirical zero point determinations for the non-standard filters such as the frequently-used F450W, F606W, and F702W.Comment: 30 pages, 10 figures Accepted for publication in October 2000 PAS

A Revised Characterization of the WFPC2 CTE Loss

Charge-transfer loss on the Wide Field Planetary Camera 2 (WFPC2) onboard the Hubble Space Telescope is a primary source of uncertainty in stellar photometry obtained with this camera. This effect, discovered shortly after the camera was installed, has grown over time and can dim stars by several tenths of a magnitude (or even more, in particularly bad cases). The impact of CTE loss on WFPC2 stellar photometry was characterized by several studies between 1998 and 2000, but has received diminished attention since ACS became HST's primary imager. After the failure of ACS in January 2007, WFPC2 once again became the primary imaging instrument onboard HST, restoring the importance of ensuring accurate CTE corrections. This paper re-examines the CTE loss of WFPC2, with three significant changes over previous studies. First, the present study considers calibration data obtained through 2007, thus increasing the confidence in the reliability of the CTE corrections when applied to recent observations. Second, the change in CTE loss during readout is accounted for analytically. Finally, a reanalysis of the CTE dependencies on counts, background, and observation date was made. The resulting correction is significantly more accurate than that provided in the WFPC2 Instrument Handbook (Dolphin 2002 and updates through 2004), resulting in photometry that can be enhanced by over 5% in certain circumstances.Comment: 30 pages, 11 figures. PASP in pres

With an easing of fiscal policy off the cards, George Osborne’s only hope for growth may lie with another round of quantitative easing.

Last week saw the release of low quarterly growth figures from the Office for National Statistics. Tony Dolphin argues that the government has done little to prevent the current period of mild stagflation and, if it is unwilling to increase spending or reduce VAT, the only action that can be taken to encourage growth is further quantitative easing.

If the economic outlook continues to worsen, George Osborne will have to relax the pace of deficit reduction and take measures to increase demand in the economy.

Yesterday saw the Chancellor’s autumn statement. Tony Dolphin argues that the measures announced in this ‘mini-budget’ are not a real plan for growth. If increased demand is not generated – and only the government is in a position to do this – then unemployment and public sector borrowing will continue to rise in excess of previous predictions.

The Star Formation Histories of Two Northern LMC Fields

Ground-based UBV photometry of two fields in the northern disk of the LMC are presented. A distance modulus of (m-M)_0 = 18.41 +/- 0.04 and an extinction of A_V = 0.30 +/- 0.05 has been calculated for these fields. The measurable star formation history of the LMC began no more than 12 Gyr ago with a strong star forming episode with [Fe/H] = -1.63 +/- 0.10 that accounted for approximately half (by mass) of the LMC's total star formation in the first 3 Gyr. The data does not give accurate star formation rates during intermediate ages, but there appears to have been a recent increase in the star formation rate in these fields, beginning approximately 2.5 Gyr ago, with the current metallicity in the region being [Fe/H] = -0.38 +/- 0.10. The two fields have had very similar star formation rates until 200 Myr ago, at which point one shows a large increase.Comment: 8 pages, 11 figures Accepted for publication in MNRA