5,321 research outputs found
Constraints on the Growth and Spin of the Supermassive Black Hole in M32 From High Cadence Visible Light Observations
We present 1-second cadence observations of M32 (NGC221) with the CHIMERA
instrument at the Hale 200-inch telescope of the Palomar Observatory. Using
field stars as a baseline for relative photometry, we are able to construct a
light curve of the nucleus in the g-prime and r-prime band with 1sigma=36
milli-mag photometric stability. We derive a temporal power spectrum for the
nucleus and find no evidence for a time-variable signal above the noise as
would be expected if the nuclear black hole were accreting gas. Thus, we are
unable to constrain the spin of the black hole although future work will use
this powerful instrument to target more actively accreting black holes. Given
the black hole mass of (2.5+/-0.5)*10^6 Msun inferred from stellar kinematics,
the absence of a contribution from a nuclear time-variable signal places an
upper limit on the accretion rate which is 4.6*10^{-8} of the Eddington rate, a
factor of two more stringent than past upper limits from HST. The low mass of
the black hole despite the high stellar density suggests that the gas liberated
by stellar interactions was primarily at early cosmic times when the low-mass
black hole had a small Eddington luminosity. This is at least partly driven by
a top-heavy stellar initial mass function at early cosmic times which is an
efficient producer of stellar mass black holes. The implication is that
supermassive black holes likely arise from seeds formed through the coalescence
of 3-100 Msun mass black holes that then accrete gas produced through stellar
interaction processes.Comment: 8 pages, 3 figures, submitted to the Astrophysical Journal, comments
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Polio survivorsâ perceptions of the meaning of quality of life and strategies used to promote participation in everyday activities
This article is made available through the Brunel Open Access Publishing Fund.Introduction: The term âpost-polio syndromeâ (PPS) is used to describe new and late manifestations of poliomyelitis that occur later in life. Research in this area has focused upon health status rather than its effect on quality of life. Aim: To gain an in-depth understanding of the meaning of quality of life for polio survivors and to determine the type of strategies that are used by people with PPS and the support that they consider as important to facilitate participation in everyday life activities that have an impact on their quality of life. Method: Six focus groups were conducted with 51 participants from two regions in England. Data were audio-taped and analysed using thematic analysis. Results: Our research found that polio survivors used terms used to describe quality of life which could be associated with that of happiness. Our research has identified resolvable factors that influence quality of life namely inaccessible environments, attitudes of health-care professionals and societal attitudes. Polio survivors have tried alternative therapies, chiefly acupuncture and massage, and found them to be effective in enhancing their quality of life. Conclusion: It is suggested that health-care professionals should consider factors which influence happiness and implement a person-centred approach with the views of the polio survivor being listened to. The three factors that influenced quality of life could be resolved by health-care professionals and by society. With regard to strategies used, we suggest that polio survivors should have access to the treatments that they perceive as important, although further research is required to design optimal interventions for this client group
Can remote STI/HIV testing and eClinical Care be compatible with robust public health surveillance?
In this paper we outline the current data capture systems for human immunodeficiency virus (HIV) and sexually transmitted infection (STI) surveillance used by Public Health England (PHE), and how these will be affected by the introduction of novel testing platforms and changing patient pathways. We outline the Chlamydia Online Clinical Care Pathway (COCCP), developed as part of the Electronic Self-Testing for Sexually Transmitted Infections (eSTI(2)) Consortium, which ensures that surveillance data continue to be routinely collected and transmitted to PHE. We conclude that both novel diagnostic testing platforms and established data capture systems must be adaptable to ensure continued robust public health surveillance
Source population synthesis and the Galactic diffuse gamma-ray emission
Population synthesis is used to study the contribution from undetected
sources to the Galactic ridge emission measured by EGRET. Synthesized source
counts are compared with the 3rd EGRET catalogue at low and high latitudes. For
pulsar-like populations, 5-10% of the emission >100 MeV comes from sources
below the EGRET threshold. A steeper luminosity function can increase this to
20% without violating EGRET source statistics. Less luminous populations can
produce much higher values without being detected. Since the unresolved source
spectrum is different from the interstellar spectrum, it could provide an
explanation of the observed MeV and GeV excesses above the predictions, and we
give an explicit example of how this could work.Comment: Astrophysics and Space Science, in press. (Proceedings of Conference
'The multi-messenger approach to high-energy gamma-ray sources', Barcelona,
2006). Minor changes for accepted version, updated reference
Lattice Relaxation and Charge-Transfer Optical Transitions Due to Self-Trapped Holes in Non-Stoichiometric LaMnO Crystal
We use the Mott-Littleton approach to evaluate polarisation energies in
LaMnO lattice associated with holes localized on both Mn cation and
O anion. The full (electronic and ionic) lattice relaxation energy for a
hole localized at the O-site is estimated as 2.4 eV which is appreciably
greater than that of 0.8 eV for a hole localized at the Mn-site, indicating on
the strong electron-phonon interaction in the former case. Using a Born-Haber
cycle we examine thermal and optical energies of the hole formation associated
with electron ionization from Mn, O and La ions in
LaMnO lattice. For these calculations we derive a phenomenological value
for the second electron affinity of oxygen in LaMnO lattice by matching the
optical energies of La and O hole formation with maxima of binding
energies in the experimental photoemission spectra. The calculated thermal
energies predict that the electronic hole is marginally more stable in the
Mn state in LaMnO host lattice, but the energy of a hole in the
O state is only higher by a small amount, 0.75 eV, rather suggesting that
both possibilities should be treated seriously. We examine the energies of a
number of fundamental optical transitions, as well as those involving
self-trapped holes of Mn and O in LaMnO lattice. The reasonable
agreement with experiment of our predicted energies, linewidths and oscillator
strengths leads us to plausible assignments of the optical bands observed. We
deduce that the optical band near 5 eV is associated with O(2p) - Mn(3d)
transition of charge-transfer character, whereas the band near 2.3 eV is rather
associated with the presence of Mn and/or O self-trapped holes in
non-stoichiometric LaMnO compound.Comment: 18 pages, 6 figures, it was presented partially at SCES-2001
conference in Ann Arbor, Michiga
CHIMERA: a wide-field, multi-colour, high-speed photometer at the prime focus of the Hale telescope
The Caltech HIgh-speed Multi-colour camERA (CHIMERA) is a new instrument that has been developed for use at the prime focus of the Hale 200-inch telescope. Simultaneous optical imaging in two bands is enabled by a dichroic beam splitter centred at 567 nm, with Sloan uâČ and gâČ bands available on the blue arm and Sloan râČ, iâČ and z_s bands available on the red arm. Additional narrow-band filters will also become available as required. An electron multiplying CCD (EMCCD) detector is employed for both optical channels, each capable of simultaneously delivering sub-electron effective read noise under multiplication gain and frame rates of up to 26 fps full frame (several 1000 fps windowed), over a fully corrected 5 Ă 5 arcmin field of view. CHIMERA was primarily developed to enable the characterization of the size distribution of sub-km Kuiper Belt Objects via stellar occultation, a science case that motivates the frame-rate, the simultaneous multi-colour imaging and the wide field of view of the instrument. In addition, it also has unique capability in the detection of faint near-Earth asteroids and will be used for the monitoring of short-duration transient and periodic sources, particularly those discovered by the intermediate Palomar Transient Factory (iPTF), and the upcoming Zwicky Transient Facility (ZTF)
Galactic populations of radio and gamma-ray pulsars in the polar cap model
We simulate the characteristics of the Galactic population of radio and
-ray pulsars using Monte Carlo techniques. At birth, neutron stars are
spatially distributed in the Galactic disk, with supernova-kick velocities, and
randomly dispersed in age back to years. They are evolved in the
Galactic gravitational potential to the present time. From a radio luminosity
model, the radio flux is filtered through a selected set of radio-survey
parameters. -ray luminosities are assigned using the features of recent
polar cap acceleration models invoking space-charge-limited flow, and a pulsar
death valley further attenuates the population of radio-loud pulsars. Assuming
a simple emission geometry with aligned radio and -ray beams of 1
steradian solid angle, our model predicts that EGRET should have seen 7
radio-loud and 1 radio-quiet, -ray pulsars. With much improved
sensitivity, GLAST, on the other hand, is expected to observe 76 radio-loud and
74 radio-quiet, -ray pulsars of which 7 would be identified as pulsed
sources. We also explore the effect of magnetic field decay on the
characteristics of the radio and -ray pulsar populations. Including
magnetic field decay on a timescale of 5 Myr improves agreement with the radio
pulsar population and increases the predicted number of GLAST detected pulsars
to 90 radio-loud and 101 radio-quiet (9 pulsed) -ray pulsars. The lower
flux threshold allows GLAST to detect -ray pulsars at larger distances
than those observed by the radio surveys used in this study.Comment: 38 pages, 11 figures, accepted for publication v565 n1 Ap
A new beamline for laser spin-polarization at ISOLDE
A beamline dedicated to the production of laser-polarized radioactive beams
has been constructed at ISOLDE, CERN. We present here different simulations
leading to the design and construction of the setup, as well as technical
details of the full setup and examples of the achieved polarizations for
several radioisotopes. Beamline simulations show a good transmission through
the entire line, in agreement with observations. Simulations of the induced
nuclear spin-polarization as a function of atom-laser interaction length are
presented for Na, [1] and for Ar, which is studied in this
work. Adiabatic spin rotation of the spin-polarized ensemble of atoms, and how
this influences the observed nuclear ensemble polarization, are also performed
for the same nuclei. For Ar, we show that multiple-frequency pumping
enhances the ensemble polarization by a factor 1.85, in agreement with
predictions from a rate equations model.
[1] J. Phys. G: Nucl. Part. Phys./174408400
Magnetic Photon Splitting: the S-Matrix Formulation in the Landau Representation
Calculations of reaction rates for the third-order QED process of photon
splitting in strong magnetic fields traditionally have employed either the
effective Lagrangian method or variants of Schwinger's proper-time technique.
Recently, Mentzel, Berg and Wunner (1994) presented an alternative derivation
via an S-matrix formulation in the Landau representation. Advantages of such a
formulation include the ability to compute rates near pair resonances above
pair threshold. This paper presents new developments of the Landau
representation formalism as applied to photon splitting, providing significant
advances beyond the work of Mentzel et al. by summing over the spin quantum
numbers of the electron propagators, and analytically integrating over the
component of momentum of the intermediate states that is parallel to field. The
ensuing tractable expressions for the scattering amplitudes are satisfyingly
compact, and of an appearance familiar to S-matrix theory applications. Such
developments can facilitate numerical computations of splitting considerably
both below and above pair threshold. Specializations to two regimes of interest
are obtained, namely the limit of highly supercritical fields and the domain
where photon energies are far inferior to that for the threshold of
single-photon pair creation. In particular, for the first time the
low-frequency amplitudes are simply expressed in terms of the Gamma function,
its integral and its derivatives. In addition, the equivalence of the
asymptotic forms in these two domains to extant results from effective
Lagrangian/proper-time formulations is demonstrated.Comment: 19 pages, 3 figures, REVTeX; accepted for publication in Phys. Rev.
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