150,185 research outputs found
Ethnic minority business in the uk: a review of research and policy development
Part of a series produced to support a ESRC/CRE/DTI/emda workshop on ethnic minority entrepreneurship. This paper comprised a review of research literature on ethnic minority enterprise and an overview of UK policy developments
Production of Millisecond Dips in Sco X-1 Count Rates by Dead Time Effects
Chang et al. (2006) reported millisecond duration dips in the X-ray intensity
of Sco X-1 and attributed them to occultations of the source by small
trans-Neptunian objects (TNOs). We have found multiple lines of evidence that
these dips are not astronomical in origin, but rather the result of high-energy
charged particle events in the RXTE PCA detectors. Our analysis of the RXTE
data indicates that at most 10% of the observed dips in Sco X-1 could be due to
occultations by TNOs, and, furthermore, we find no positive or supporting
evidence for any of them being due to TNOs. We therefore believe that it is a
mistake to conclude that any TNOs have been detected via occultation of Sco
X-1.Comment: Submitted to ApJ; uses emulateapj.cls, 8 pages with 8 figure
Photodetection in silicon beyond the band edge with surface states
Silicon is an extremely attractive material platform for integrated optics at
telecommunications wavelengths, particularly for integration with CMOS
circuits. Developing detectors and electrically pumped lasers at telecom
wavelengths are the two main technological hurdles before silicon can become a
comprehensive platform for integrated optics. We report on the generation of
free carriers in unimplanted SOI ridge waveguides, which we attribute to
surface state absorption. By electrically contacting the waveguides, a
photodetector with a responsivity of 36 mA/W and quantum efficiency of 2.8% is
demonstrated. The photoconductive effect is shown to have minimal falloff at
speeds of up to 60 Mhz
Virtual audio reproduced in a headrest
When virtual audio reproduction is simultaneously required in many seats, such as in aircraft or
cinemas, it may be convenient to use loudspeakers mounted inside each seat's headrest. In
this preliminary study, the feasibility of virtual audio reproduction in the headrest of a single seat
is explored using an inversion technique to compensate for crosstalk and the synthesis of head
related transfer functions. Although large changes in the magnitude of the signals reproduced
at the listener's ears are observed as the listener moves their head within the headrest, informal
listening tests indicate that the reproduced acoustic images are surprisingly stable in about an
eighth of an arc either side of the loudspeaker positions. Not surprisingly, frontal images are
more difficult to reproduce with headrest loudspeakers
Photon Frequency Mode Matching using Acousto-Optic Frequency Beam Splitters
It is a difficult engineering task to create distinct solid state single
photon sources which nonetheless emit photons at the same frequency. It is also
hard to create entangled photon pairs from quantum dots. In the spirit of
quantum engineering we propose a simple optical circuit which can, in the right
circumstances, make frequency distinguishable photons frequency
indistinguishable. Our circuit can supply a downstream solution to both
problems, opening up a large window of allowed frequency mismatches between
physical mechanisms. The only components used are spectrum analysers/prisms and
an Acousto-Optic Modulator. We also note that an Acousto-Optic Modulator can be
used to obtain Hong-Ou-Mandel two photon interference effects from the
frequency distinguishable photons generated by distinct sources.Comment: 4 pages, 4 figure
Hot Electrons and Cold Photons: Galaxy Clusters and the Sunyaev-Zel'dovich Effect
The hot gas in clusters of galaxies emits thermal bremsstrahlung emission
that can be probed directly through measurements in the X-ray band with
satellites like ROSAT and ASCA. Another probe of this gas comes from its effect
on the cosmic microwave background radiation (CMBR): the hot cluster electrons
inverse Compton scatter the CMBR photons and thereby distort the background
radiation from its blackbody spectral form. In the last few years, the
development of sensitive new instruments for measuring this distortion, called
the Sunyaev-Zel'dovich (SZ) effect, has sparked a revolution in the field.
Current radio interferometric arrays can now detect and map the SZ effect in
even distant (z ~ 1) clusters. It is well known that one of the purposes of
conducting such measurements is to determine the Hubble constant. In this
review I report on the progress that has been made in this area, quote the
current best estimate of Ho from the SZ effect of 8 galaxy clusters (44 - 64
km/s/Mpc +/- 17%), discuss important systematic uncertainties, and highlight
what else has been learned about galaxy clusters from these investigations.Comment: 4 pages, including 2 postscript figs, LaTeX. To appear in the
proceedings of IAU Symposium 188 "The Hot Universe" (held August 26-30, 1997,
Kyoto, Japan
Deep learning extends de novo protein modelling coverage of genomes using iteratively predicted structural constraints
The inapplicability of amino acid covariation methods to small protein
families has limited their use for structural annotation of whole genomes.
Recently, deep learning has shown promise in allowing accurate residue-residue
contact prediction even for shallow sequence alignments. Here we introduce
DMPfold, which uses deep learning to predict inter-atomic distance bounds, the
main chain hydrogen bond network, and torsion angles, which it uses to build
models in an iterative fashion. DMPfold produces more accurate models than two
popular methods for a test set of CASP12 domains, and works just as well for
transmembrane proteins. Applied to all Pfam domains without known structures,
confident models for 25% of these so-called dark families were produced in
under a week on a small 200 core cluster. DMPfold provides models for 16% of
human proteome UniProt entries without structures, generates accurate models
with fewer than 100 sequences in some cases, and is freely available.Comment: JGG and SMK contributed equally to the wor
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