633 research outputs found
PIRATE: A Remotely-Operable Telescope Facility for Research and Education
We introduce PIRATE, a new remotely-operable telescope facility for use in
research and education, constructed from 'off-the-shelf' hardware, operated by
The Open University. We focus on the PIRATE Mark 1 operational phase where
PIRATE was equipped with a widely- used 0.35m Schmidt-Cassegrain system (now
replaced with a 0.425m corrected Dall Kirkham astrograph). Situated at the
Observatori Astronomic de Mallorca, PIRATE is currently used to follow up
potential transiting extrasolar planet candidates produced by the SuperWASP
North experiment, as well as to hunt for novae in M31 and other nearby
galaxies. It is operated by a mixture of commercially available software and
proprietary software developed at the Open University. We discuss problems
associated with performing precision time series photometry when using a German
Equatorial Mount, investigating the overall performance of such 'off-the-shelf'
solutions in both research and teaching applications. We conclude that PIRATE
is a cost-effective research facility, and also provides exciting prospects for
undergraduate astronomy. PIRATE has broken new ground in offering practical
astronomy education to distance-learning students in their own homes.Comment: Accepted for publication in PASP. 14 pages, 11 figure
Discovery of disc precession in the M31 dipping X-ray binary Bo 158
We present results from three XMM-Newton observations of the M31 low mass
X-ray binary XMMU J004314.4+410726.3 (Bo 158), spaced over 3 days in 2004,
July. Bo 158 was the first dipping LMXB to be discovered in M31. Periodic
intensity dips were previously seen to occur on a 2.78-hr period, due to
absorption in material that is raised out of the plane of the accretion disc.
The report of these observations stated that the dip depth was anti-correlated
with source intensity. However, our new observations do not favour a strict
intensity dependance, but rather suggest that the dip variation is due to
precession of the accretion disc. This is to be expected in LMXBs with a mass
ratio <~ 0.3 (period <~ 4 hr), as the disc reaches the 3:1 resonance with the
binary companion, causing elongation and precession of the disc. A smoothed
particle hydrodynamics simulation of the disc in this system shows retrograde
rotation of a disc warp on a period of ~11 P_orb, and prograde disc precession
on a period of ~29 P_orb. This is consistent with the observed variation in the
depth of the dips. We find that the dipping behaviour is most likely to be
modified by the disc precession, hence we predict that the dipping behaviour
repeats on a 81+/-3 hr cycle.Comment: 9 pages, 6 figures, accepted for publication by MNRAS, changed
conten
Hydrodynamic modelling of accretion flows
In the proceedings of this, and of several recent close binary conferences,
there have been several contributions describing smoothed particle
hydrodynamics simulations of accretion disks. It is apposite therefore to
review the numerical scheme itself with emphasis on its advantages for disk
modelling, and the methods used for modelling viscous processes.Comment: 3 pages, to appear in proceedings of IAU Colloquium 194: Compact
binaries in the galaxy and beyon
Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB
We aim to understand how stellar parameters such as mass and rotation impact the distribution of star-spots on the stellar surface. To this purpose, we have used Doppler imaging to reconstruct the surface brightness distributions of three fully convective M dwarfs with similar rotation rates. We secured high cadence spectral time series observations of the 5.5 au separation binary GJ 65, comprising GJ 65A (M5.5V, Prot = 0.24 d) and GJ 65B (M6V, Prot = 0.23 d). We also present new observations of GJ 791.2A (M4.5V, Prot = 0.31 d). Observations of each star were made on two nights with UVES, covering a wavelength range from 0.64 - 1.03μm. The time series spectra reveal multiple line distortions that we interpret as cool star-spots and which are persistent on both nights suggesting stability on the time-scale of 3 d. Spots are recovered with resolutions down to 8.3° at the equator. The global spot distributions for GJ 791.2A are similar to observations made a year earlier. Similar high latitude and circumpolar spot structure is seen on GJ 791.2A and GJ 65A. However, they are surprisingly absent on GJ 65B, which instead reveals more extensive, larger, spots concentrated at intermediate latitudes. All three stars show small amplitude latitude-dependent rotation that is consistent with solid body rotation. We compare our measurements of differential rotation with previous Doppler imaging studies and discuss the results in the wider context of other observational estimates and recent theoretical predictions
Microfluidic chromatography for early stage evaluation of biopharmaceutical binding and separation conditions
Optimization of separation conditions for biopharmaceuticals requires evaluation of a large number of process variables. To miniaturize this evaluation a microfluidic column (1.5 mu L volume and 1cm height) was fabricated and packed with a typical process scale resin. The device was assessed by comparison to a protein separation at conventional laboratory scale. This was based upon measurement of the quality of packing and generation of breakthrough and elution curves. Dynamic binding capacities from the microfluidic column compared well with the laboratory scale. Microfluidic scale gradient elution separations also equated to the laboratory column three orders of magnitude larger in scale
ULTRACAM observations of the black hole X-ray transient XTE J1118+480 in quiescence
We present high time-resolution multicolour observations of the quiescent
soft X-ray transient XTE J1118+480 obtained with ULTRACAM. Superimposed on the
double-humped continuum g' and i'-band lightcurves are rapid flare events which
typically last a few minutes. The power density spectrum of the lightcurves can
be described by a broken power-law model with a break frequency at ~2 mHz or a
power-law model plus a broad quasi-periodic oscillation (QPO) at ~2 mHz. In the
context of the cellular-automaton we estimate the size of the quiescent
advection-dominated flow (ADAF) region to be ~10^4 Schwarzschild radii, similar
to that observed in other quiescent black hole X-ray transients, suggesting the
same underlying physics. The similarites between the low/hard and quiescent
state PDS suggest a similar origin for the optical and X-ray variability, most
likely from regions at/near the ADAF.Comment: 9 pages, 6 figures, accepted by MNRA
Phosphomolybdenum Blue Detection – A Review of Characteristics, Achievements, Challenges and Future Prospects
Phosphate detection in the environment (especially, water bodies) is very essential in view of its consequent pollution effects on eutrophication. Continuous monitoring of phosphate concentration (and phosphorus compounds in general) in water samples has been based on phosphomolybdenum blue formation coupled with spectrophotometric detection. ContinuÂous flow injection analyses (FIA) are well known to present numerous advantages over batch methods. Furthermore, the development of on-chip micro-channel analytical (ÎĽFIA) systems begun and have gained much attention within the last two decades in view of the striking advantages over conventional FIA techniques. This paper reviews published information on detection of phosphomolybdenum blue in conventional systems as well as on micro-chip. It reports on the challenges encountered (interference from other complex anions), the achieveÂments made so far (intereference removal by electrokinetic separation) and what the future holds (simultaneous determination)
Examining stress and response to stress in medical students and new medical graduates
MOST MEMBERS OF THE MEDICAL PROFESSION feel stressed at some time. If stress is ongoing, impairment may occur (defined as being unable to safely or reliably perform one’s role). A continuum appears to exist between functioning well, being distressed and becoming impaired, with external (environment-related) and internal (personalrelated) stressors determining where an individual will lie on the continuum. We are conducting a study which aims to determine whether distress in new medical graduates can be predicted before the graduates become impaired and unable to safely or reliably perform their role. Study commencement Our study, which commenced in 1997, initially looked at predictors for “troubled” and “troublesome” interns. Hospital- based focus groups comprising interns (postgraduate Year 1), resident medical officers (postgraduate Year 2 and above), ward-based nursing staff and medical administrators reported on internal and external stressors for junior medical staff. Residents and nurses reported similar external stressors, whereas the internal stressors reported by the two groups were quite different (Box 1). Residents tended to report issues relating to “troubled” interns (eg, poor support, few outside interests), whereas nurses identified factors relating more to “troublesome” interns (eg, poor attitude, unprofessionalism). In other words, resident staff seemed to be able to identify their stressed and at-risk peers before effects on performance were observed (Box 1)
Discovery and modelling of disc precession in the M31 X-ray binary Bo 158?
The low mass X-ray binary (LMXB) associated with the M31 globular cluster Bo
158 is known to exhibit intensity dips on a ~2.78 hr period. This is due to
obscuration of the X-ray source on the orbital period by material on the outer
edge of the accretion disc. However, the depth of dipping varied from <10% to
\~83% in three archival XMM-Newton observations of Bo 158. Previous work
suggested that the dip depth was anticorrelated with the X-ray luminosity.
However, we present results from three new XMM-Newton observations that suggest
that the evolution of dipping is instead due to precession of the accretion
disc. Such precession is expected in neutron star LMXBs with mass ratios <0.3
(i.e. with orbital periods <4 hr), such as the Galactic dipping LMXB 4U
1916-053. We simulated the accretion disc of Bo 158 using cutting-edge 3D
smoothed particle hydrodynamics (SPH), and using the observed parameters. Our
results show disc variability on two time-scales. The disc precesses in a
prograde direction on a period of 81+/-3 hr. Also, a radiatively-driven disc
warp is present in the inner disc, which undergoes retrograde precesson on a
\~31 hr period. From the system geometry, we conclude that the dipping
evolution is driven by the disc precession. Hence we predict that the dipping
behaviour repeats on a ~81 hr cycle.Comment: 6 pages, 4 figures, to appear in proceedings "The X-ray Universe
2005", San Lorenzo de El Escoriale (Madrid, Spain), 26-30 September 200
Regulation of Chromatin Remodeling by Inositol Polyphosphates
Chromatin remodeling is required for efficient transcription of eukaryotic genes. In a genetic selection for budding yeast mutants that were defective in induction of the phosphate-responsive PHO5 gene, we identified mutations inARG82/IPK2, which encodes a nuclear inositol polyphosphate kinase. In arg82 mutant strains, remodeling ofPHO5 promoter chromatin is impaired, and the adenosine triphosphate–dependent chromatin-remodeling complexes SWI/SNF and INO80 are not efficiently recruited to phosphate-responsive promoters. These results suggest a role for the small molecule inositol polyphosphate in the regulation of chromatin remodeling and transcription
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