Observation of the Purcell effect in high-index-contrast micropillar

We have fabricated pillar microcavity samples with Bragg mirrors consisting of alternate layers of GaAs and Aluminium Oxide. Compared to the more widely studied GaAs/AlAs micropillars these mirrors can achieve higher reflectivities with fewer layer repeats and reduce the mode volume. We have studied a number of samples containing a low density of InGaAs/GaAs self assembled quantum dots in a cavity and here report observation of a three fold enhancement in the radiative lifetime of a quantum dot exciton state due to the Purcell effect

Oxide-apertured microcavity single-photon emitting diode

We have developed a microcavity single-photon source based on a single quantum dot within a planar cavity in which wet-oxidation of a high-aluminium content layer provides lateral confinement of both the photonic mode and the injection current. Lateral confinement of the optical mode in optically pumped structures produces a strong enhancement of the radiative decay rate. Using microcavity structures with doped contact layers, we demonstrate a single-photon emitting diode where current may be injected into a single dot

The Las Campanas Infra-red Survey. V. Keck Spectroscopy of a large sample of Extremely Red Objects

(Abridged) We present deep Keck spectroscopy, using the DEIMOS and LRIS spectrographs, of a large and representative sample of 67 ``Extremely Red Objects'' (EROs) to H=20.5, with I-H>3.0, in three of the Las Campanas Infrared Survey fields. Spectroscopic redshifts are determined for 44 sources, of which only two are contaminating low mass stars. When allowance is made for incompleteness, the spectroscopic redshift distribution closely matches that predicted earlier on the basis of photometric data. Our spectra are of sufficient quality that we can address the important question of the nature and homogeneity of the z>0.8 ERO population. A dominant old stellar population is inferred for 75% of our spectroscopic sample; a higher fraction than that seen in smaller, less-complete samples with broader photometric selection criteria (e.g. R-K). However, only 28% have spectra with no evidence of recent star formation activity, such as would be expected for a strictly passively-evolving population. More than ~30% of our absorption line spectra are of the `E+A' type with prominent Balmer absorption consistent, on average, with mass growth of 5-15% in the past Gyr. We use our spectroscopic redshifts to improve earlier estimates of the spatial clustering of this population as well as to understand the significant field-to-field variation. Our spectroscopy enables us to pinpoint a filamentary structure at z=1.22 in the Chandra Deep Field South. Overall, our study suggests that the bulk of the ERO population is an established population of clustered massive galaxies undergoing intermittent activity consistent with continued growth over the redshift interval 0.8<z<1.6.Comment: 27 pages, including 14 figures and appendix of spectra (at low resolution). Full resolution paper can be found at http://www.ast.cam.ac.uk/~md . To appear in MNRA

The status of traditional Scottish animal breeds and plant varieties and the implications for biodiversity

The aim of this scoping study was to evaluate the effects on Scottish biodiversity of changes in the use of traditional breeds and varieties. The overall objectives were: a) The evaluation of the importance of genetic loss from the reduction in use of these breeds and varieties, for example, the loss of unusual characteristics that might have been of particular local use. b) An assessment of the impacts of reduction in the ability to conduct further breeding or research on rare and traditional varieties and breeds. c) Identification of the loss of certain farming techniques associated with particular varieties and breeds. d) An assessment of possible losses of biodiversity associated with reduction in the use of these breeds and varieties and the farming systems associated with them

Inspecting absorption in the spectra of extra-galactic gamma-ray sources for insight into Lorentz invariance violation

We examine what the absorbed spectra of extra-galactic TeV gamma-ray sources, such as blazars, would look like in the presence of Lorentz invariance violation (LIV). Pair-production with the extra-galactic background light modifies the observed spectra of such sources, and we show that a violation of Lorentz invariance would generically have a dramatic effect on this absorption feature. Inspecting this effect, an experimental task likely practical in the near future, can provide unique insight on the possibility of LIV.Comment: Published in Phys. Rev.

Shift in the LHC Higgs diphoton mass peak from interference with background

The Higgs diphoton amplitude from gluon fusion at the LHC interferes with the continuum background induced by quark loops. I investigate the effect of this interference on the position of the diphoton invariant mass peak used to help determine the Higgs mass. At leading order, the interference shifts the peak towards lower mass by an amount of order 150 MeV or more, with the precise value dependent on the methods used to analyze and fit the data.Comment: 10 pages. v2: comments on scale variation added, reference adde

Preliminary study of creep thresholds and thermomechanical response in Haynes 188 at temperatures in the range 649 to 871 C

The following conclusions were drawn from this study of creep thresholds and thermomechanical response: (1) creep threshold can be determined using the latest electrohydraulic test equipment, providing that test durations are short and relatively large accumulations of creep strain are used in defining the threshold; (2) significant creep strains were measured under monotonic loading as stress levels as low as 4 ksi at temperatures predicted for solar receiver service; and (3) the material exhibited creep ratchetting during simulated service cycles, a result not predicted by analysis using current constitutive models for Haynes 188

Low-Energy Theorems for QCD at Finite Temperature and Chemical Potential

The low-energy theorems for QCD are generalized to finite temperature. and chemical potential, including non-zero quark masses.Comment: 6 pages late