629 research outputs found
Stellar Velocity Dispersion of the Leo A Dwarf Galaxy
We measure the first stellar velocity dispersion of the Leo A dwarf galaxy,
\sigma = 9.3 +- 1.3 km/s. We derive the velocity dispersion from the radial
velocities of ten young B supergiants and two HII regions in the central region
of Leo A. We estimate a projected mass of 8 +- 2.7 x10^7 solar masses within a
radius of 2 arcmin, and a mass to light ratio of at least 20 +- 6 M_sun/L_sun.
These results imply Leo A is at least ~80% dark matter by mass.Comment: 6 pages, accepted to Ap
The Interaction between the ISM and Star Formation in the Dwarf Starburst Galaxy NGC 4214
We present the first interferometric study of the molecular gas in the
metal-poor dwarf starburst galaxy NGC 4214. Our map of the 12CO(1-0) emission,
obtained at the OVRO millimeter array, reveals an unexpected structural wealth.
We detected three regions of molecular emission in the north-west (NW),
south-east (SE) and centre of NGC 4214 which are in very different and distinct
evolutionary stages (total molecular mass: 5.1 x 10^6 M_sun). These differences
are apparent most dramatically when the CO morphologies are compared to optical
ground based and HST imaging: massive star formation has not started yet in the
NW region; the well-known starburst in the centre is the most evolved and star
formation in the SE complex started more recently. We derive a star formation
efficiency of 8% for the SE complex. Using high--resolution VLA observations of
neutral hydrogen HI and our CO data we generated a total gas column density map
for NGC 4214 (HI + H_2). No clear correlation is seen between the peaks of HI,
CO and the sites of ongoing star formation. This emphasizes the irregular
nature of dwarf galaxies. The HI and CO velocities agree well, so do the
H-alpha velocities. In total, we cataloged 14 molecular clumps in NGC 4214. Our
results from a virial mass analysis are compatible with a Galactic CO-to-H_2
conversion factor for NGC 4214 (lower than what is usually found in metal-poor
dwarf galaxies).Comment: accepted for publication in the AJ (February 2001), full ps file at:
ftp://ftp.astro.caltech.edu/users/fw/ngc4214/walter_prep.p
Giant Conductance Oscillations In Mesoscopic Andreev Interferometers
We analyze the electrical conductance of a two-dimensional, phase
coherent structure in contact with two superconductors, which is known to be an
oscillatory function of the phase difference between the
superconductors. It is predicted that for a metallic sample, the amplitude of
oscillation is enhanced by placing a normal barrier at the interface and that,
by tuning the strength of the barrier, can be orders of magnitude greater than
values observed in recent experiments. Giant oscillations can also be obtained
without a barrier, provided a crucial sum rule is broken. This can be achieved
by disorder induced normal scattering. In the absence of zero phase
inter-channel scattering, the conductance possesses a zero phase minimum.Comment: 4 pages of Revtex, 6 figures available on reques
Sign of the crossed conductances at a FSF double interface
Crossed conductance in hybrid Ferromagnet / Superconductor / Ferromagnet
(FSF) structures results from the competition between normal transmission and
Andreev reflection channels. Crossed Andreev reflection (CAR) and elastic
cotunneling (EC) between the ferromagnets are dressed by local Andreev
reflections, which play an important role for transparent enough interfaces and
intermediate spin polarizations. This modifies the simple result previously
obtained at lowest order, and can explain the sign of the crossed resistances
in a recent experiment [D. Beckmann {\sl et al.}, cond-mat/0404360]. This holds
both in the multiterminal hybrid structure model (where phase averaging over
the Fermi oscillations is introduced ``by hand'' within the approximation of a
single non local process) and for infinite planar interfaces (where phase
averaging naturally results in the microscopic solution with multiple non local
processes).Comment: 9 pages, 7 figure
The tribunal atmosphere: on qualitative barriers to access to justice
This the final version. Available on open access from Elsevier via the DOI in this recordVulnerable groups’ direct experiences and impressions of British courts and tribunals have often been
overlooked by politicians and policy makers (JUSTICE, 2019). This paper takes a geographical,
empirical approach to access to justice to respond to these concerns, paying attention to the atmosphere
of First Tier Immigration and Asylum Tribunal hearings to explore the qualitative aspects of (in)access
to justice during asylum appeals. It draws on 41 interviews with former appellants and 390 observations
of hearings in the First tier immigration and asylum tribunal to unpack the lived experiences of tribunal
users and to identify three ways in which the atmosphere in tribunals can constitute a barrier to access
to justice. First, asylum appellants are frequently profoundly disorientated upon arrival at the tribunal.
Second, appellants become distrustful of the courtroom when they cannot see it as independent of the
state. Third they often experience the courtroom procedures and the interactions that take place as
disrespectful, inhibiting their participation. These insights demonstrate how the concept of ‘atmosphere’
can illuminate legal debates in valuable ways. Additionally we argue that legal policy making must find
better ways to take vulnerable litigants’ experiences into account.Economic and Social Research Council (ESRC)European Commissio
Reflectionless tunneling in ballistic normal-metal--superconductor junctions
We investigate the phenomenon of reflectionless tunneling in ballistic
normal-metal--superconductor (NS) structures, using a semiclassical formalism.
It is shown that applied magnetic field and superconducting phase difference
both impair the constructive interference leading to this effect, but in a
qualitatively different way. This is manifested both in the conductance and in
the shot noise properties of the system considered. Unlike diffusive systems,
the features of the conductance are sharp, and enable fine spatial control of
the current, as well as single channel manipulations. We discuss the
possibility of conducting experiments in ballistic semiconductor-superconductor
structures with smooth interfaces and some of the phenomena, specific to such
structures, that could be measured. A general criterion for the barrier at NS
interfaces, though large, to be effectively transparent to pair current is
obtained.Comment: published versio
Measuring vertebrate telomeres: applications and limitations
Telomeres are short tandem repeated sequences of DNA found at the ends of eukaryotic
chromosomes that function in stabilizing chromosomal end integrity.
In vivo
studies of
somatic tissue of mammals and birds have shown a correlation between telomere length and
organismal age within species, and correlations between telomere shortening rate and
lifespan among species. This result presents the tantalizing possibility that telomere length
could be used to provide much needed information on age, ageing and survival in natural
populations where longitudinal studies are lacking. Here we review methods available for
measuring telomere length and discuss the potential uses and limitations of telomeres as
age and ageing estimators in the fields of vertebrate ecology, evolution and conservation
The star-forming content of the W3 giant molecular cloud
We have surveyed a ~0.9-square-degree area of the W3 giant molecular cloud
and star-forming region in the 850-micron continuum, using the SCUBA bolometer
array on the James Clerk Maxwell Telescope. A complete sample of 316 dense
clumps was detected with a mass range from around 13 to 2500 Msun. Part of the
W3 GMC is subject to an interaction with the HII region and fast stellar winds
generated by the nearby W4 OB association. We find that the fraction of total
gas mass in dense, 850-micron traced structures is significantly altered by
this interaction, being around 5% to 13% in the undisturbed cloud but ~25 - 37%
in the feedback-affected region. The mass distribution in the detected clump
sample depends somewhat on assumptions of dust temperature and is not a simple,
single power law but contains significant structure at intermediate masses.
This structure is likely to be due to crowding of sources near or below the
spatial resolution of the observations. There is little evidence of any
difference between the index of the high-mass end of the clump mass function in
the compressed region and in the unaffected cloud. The consequences of these
results are discussed in terms of current models of triggered star formation.Comment: 13 pages, 8 figures, 1 table (full source table available on
request). Accepted for publication in Monthly Notices of the Royal
Astronomical Society (Main Journal
Software Agents as Facilitators of Coherent Coalition Operations
The University of Edinburgh and research sponsors are authorised to reproduce and distribute reprints and on-line copies for their purposes notwithstanding any copyright annotation hereon. The views and conclusions contained herein are the author’s and shouldn’t be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of other parties.Software agents can be viewed as semi-autonomous entities which help people cope with the complexities of working collaboratively in a distributed information environment. This paper describes the research that DERA is carrying out into Software Agents for use in Command Systems and the collaborative work with the 16 partners of an international Coalition Agents
Experiment. Specifically, the paper aims to show that using software agent-based C2 frameworks is a useful way of dealing with the complexity of real-world problems such as supporting agile and robust Coalition operations and enabling interoperability between legacy or previously incompatible systems. In addition, Agent-enabled 'grids' can be used to rapidly integrate a wide
variety of agents and infrastructures, with domain management services structuring agent
relationships, limiting their behaviours and enforcing Coalition policies
- …