Space Science and Microsatellites - A Case Study Observations of the Near-Earth Radiation Environment using the Cosmic-Ray Effects and Dosimetry (CREDO) Payload On-Board UoSAT-3

The University of Surrey\u27s technology demonstration microsatellite: UoSAT-3 launched in January 1990. carries on-board a Cosmic-Ray Effects and Dosimetry (CREDO) payload for characterizing the low-Earth orbit (LEO) radiation environment. Measurements made with this payload are correlated with radiation effects observed in the spacecraft\u27s microelectronics, in particular, the occurrence of single event upsets (SEUs) in solid-state memory devices. The CREDO payload consists of two Sub-systems, the Cosmic Particle Experiment (CPE) and the Total-Dose Experiment (TDE). The CPE houses an array of large-area PIN diode detectors, connected to a pulse-height analysis network. Particles incident on the detector are counted and logged according to their linear-energy transfer (LET). Results are integrated over five minute intervals and the data are stored in the PACSAT Communications Experiment (PCE) memory. The TDE consists of specially manufactured p-channel MOSFETs which are monitored for changes in threshold voltage due to accumulated radiation dose. During the first year\u27s operation, CREDO has provided measurements of the cosmic-ray background, the trapped particle population of the South Atlantic Anomaly (SAA), and has observed a number of large solar proton events - most recently, the major events of June 1991. This paper reviews the results obtained so far and comments on the suitability of microsatellites for this kind of small-scale space science mission

The acyclic group dichotomy

Two extremal classes of acyclic groups are discussed. For an arbitrary group G, there is always a homomorphism from an acyclic group of cohomological dimension 2 onto the maximum perfect subgroup of G, and there is always an embedding of G in a binate (hence acyclic) group. In the other direction, there are no nontrivial homomorphisms from binate groups to groups of finite cohomological dimension. Binate groups are shown to be of significance in relation to a number of important K-theoretic isomorphism conjectures.Comment: To appea

A pulsating white dwarf in an eclipsing binary

White dwarfs are the burnt-out cores of Sun-like stars and are the fate of 97 per cent of the stars in our Galaxy. The internal structure and composition of white dwarfs are hidden by their high gravities, which causes all elements apart from the lightest ones to settle out of their atmospheres. The most direct method of probing the inner structure of stars and white dwarfs in detail is via asteroseismology. Here we present a pulsating white dwarf in an eclipsing binary system, enabling us to place extremely precise constraints on the mass and radius of the white dwarf from the lightcurve, independent of the pulsations. This 0.325-solar-mass white dwarf—one member of the SDSS J115219.99+024814.4 system—will serve as a powerful benchmark with which to constrain empirically the core composition of low-mass stellar remnants and to investigate the effects of close binary evolution on the internal structure of white dwarfs

Embeddings of hyperbolic Kac-Moody algebras into E10\mathbf{E_{10}}}

We show that the rank 10 hyperbolic Kac-Moody algebra $E_{10}$ contains every simply laced hyperbolic Kac-Moody algebra as a Lie subalgebra. Our method is based on an extension of earlier work of Feingold and Nicolai.Comment: 10 pages. to appear in Letters in Mathematical Physic

Double agents: gendered organizational culture, control and resistance

Author's pre-publication draft. Final version of the article published in Sociology; available online on http://online.sagepub.com/This article presents ethnographic data showing how recruitment consultants negotiate managerial attempts to control workforce culture. I suggest the values which senior managers encourage consultants to embody prioritize so-called`masculine' attributes over `feminine' ones. I attempt to demonstrate the limits of cultural control by outlining three ways in which the consultants engage with this imposed culture: defiance, parody and ritual. These activities contain gendered assumptions similar to those embedded in corporate culture. I discuss the potential such practices have for resisting corporate culture and the gender within it, suggesting that one source of ambiguity within workplace `control' and `resistance' practices is that they employ overlapping cultural resources and assumptions

Characterising eclipsing white dwarf M dwarf binaries from multi-band eclipse photometry

With the prevalence of wide-field, time-domain photometric sky surveys, the number of eclipsing white dwarf systems being discovered is increasing dramatically. An efficient method to follow these up will be key to determining any population trends and finding any particularly interesting examples. We demonstrate that multi-band eclipse photometry of binaries containing a white dwarf and an M dwarf can be used to determine the masses and temperatures of the white dwarfs to better than 5 per cent. For the M dwarfs we measure their parameters to a precision of better than 6 per cent with the uncertainty dominated by the intrinsic scatter of the M dwarf mass-radius relationship. This precision is better than what can typically be achieved with low-resolution spectroscopy. The nature of this method means that it will be applicable to LSST data in the future, enabling direct characterisation without follow-up spectroscopy. Additionally, we characterise three new post-common-envelope binaries from their eclipse photometry, finding two systems containing hot helium-core white dwarfs with low-mass companions (one near the brown dwarf transition regime) and a possible detached cataclysmic variable at the lower edge of the period gap

Enhanced generation of VUV radiation by four-wave mixing in mercury using pulsed laser vaporization

The efficiency of a coherent VUV source at 125 nm, based on 2-photon resonant four-wave mixing in mercury vapor, has been enhanced by up to 2 orders of magnitude. This enhancement was obtained by locally heating a liquid Hg surface with a pulsed excimer laser, resulting in a high density vapor plume in which the nonlinear interaction occurred. Energies up to 5 μJ (1 kW peak power) have been achieved while keeping the overall Hg cell at room temperature, avoiding the use of a complex heat pipe. We have observed a strong saturation of the VUV yield when peak power densities of the fundamental beams exceed the GW/cm2 range, as well as a large intensity-dependant broadening (up to ~30 cm-1) of the two-photon resonance. The source has potential applications for high resolution interference lithography and photochemistry

Long-term photometric monitoring and spectroscopy of the white dwarf pulsar AR Scorpii

AR Scorpii (AR Sco) is the only radio-pulsing white dwarf known to date. It shows a broad-band spectrum extending from radio to X-rays whose luminosity cannot be explained by thermal emission from the system components alone, and is instead explained through synchrotron emission powered by the spin-down of the white dwarf. We analysed NTT/ULTRACAM, TNT/ULTRASPEC, and GTC/HiPERCAM high-speed photometric data for AR Sco spanning almost seven years and obtained a precise estimate of the spin frequency derivative, now confirmed with 50-σ significance. Using archival photometry, we show that the spin-down rate of P/P˙=5.6×106 years has remained constant since 2005. As well as employing the method of pulse-arrival time fitting used for previous estimates, we also found a consistent value via traditional Fourier analysis for the first time. In addition, we obtained optical time-resolved spectra with WHT/ISIS and VLT/X-shooter. We performed modulated Doppler tomography for the first time for the system, finding evidence of emission modulated on the orbital period. We have also estimated the projected rotational velocity of the M-dwarf as a function of orbital period and found that it must be close to Roche lobe filling. Our findings provide further constraints for modelling this unique system