1,590 research outputs found
Image normalization : a basic requirement for computer-based automatic diagnostic applications
Surface electrical properties experiment, part 1
The work is reported which was performed on the Surface Electrical Properties Experiment Data Acquisition System. Areas discussed include: data handling and processing, installation and external signal application, operation of the equipment, and digital output. Detailed circuit descriptions are included
Temperature dependence of the resistance of metallic nanowires (diameter 15 nm): Applicability of Bloch-Gr\"{u}neisen theorem
We have measured the resistances (and resistivities) of Ag and Cu nanowires
of diameters ranging from 15nm to 200nm in the temperature range 4.2K-300K with
the specific aim to assess the applicability of the Bloch-Gr\"{u}neisen formula
for electron phonon resistivity in these nanowires. The wires were grown within
polymeric templates by electrodeposition. We find that in all the samples the
resistance reaches a residual value at T=4.2K and the temperature dependence of
resistance can be fitted to the Bloch-Gr\"{u}neisen formula in the entire
temperature range with a well defined transport Debye temperature
(). The value of Debye temperature obtained from the fits lie
within 8% of the bulk value for Ag wires of diameter 15nm while for Cu
nanowires of the same diameter the Debye temperature is significantly lesser
than the bulk value. The electron-phonon coupling constants (measured by
or ) in the nanowires were found to have the same
value as that of the bulk. The resistivities of the wires were seen to increase
as the wire diameter was decreased. This increase in the resistivity of the
wires may be attributed to surface scattering of conduction electrons. The
specularity p was estimated to be about 0.5. The observed results allow us to
obtain the resistivities exactly from the resistance and gives us a method of
obtaining the exact numbers of wires within the measured array (grown within
the template).Comment: 9 pages, 10 figure
Professional boundaries: crossing a line or entering the shadows?
This article explores the professional boundaries guidance for social workers. It presents research findings from the formal literature, from agency codes of practice, from telephone interviews with regulatory and professional bodies and from an exercise using ‘snowballing techniques’ in which informants responded to brief scenarios illustrating boundary dilemmas. The findings suggest that formal research plays little part in the guidance that individuals use to help them determine professional boundaries. Similarly, only 10–15 per cent of informants made regular reference to regulatory and professional codes of practice, with an even smaller percentage quoting specific sections from these codes. A slightly larger group (15–20 per cent) made fairly regular reference to their agency's policy documents. However, a clear majority relied on their own sense of what is appropriate or inappropriate, and made their judgements with no reference to any formal guidance. Agency guidance tended to ignore the ambiguous areas of practice and seemed to act as an insurance policy, brought out and dusted off when something goes awry. The authors caution against ever-increasing bullet points of advice and prescription, and advance a notion of ethical engagement in which professionals exercise their ethical senses through regular discussion of professional boundary dilemmas
A natural formation scenario for misaligned and short-period eccentric extrasolar planets
Recent discoveries of strongly misaligned transiting exoplanets pose a
challenge to the established planet formation theory which assumes planetary
systems to form and evolve in isolation. However, the fact that the majority of
stars actually do form in star clusters raises the question how isolated
forming planetary systems really are. Besides radiative and tidal forces the
presence of dense gas aggregates in star-forming regions are potential sources
for perturbations to protoplanetary discs or systems. Here we show that
subsequent capture of gas from large extended accretion envelopes onto a
passing star with a typical circumstellar disc can tilt the disc plane to
retrograde orientation, naturally explaining the formation of strongly inclined
planetary systems. Furthermore, the inner disc regions may become denser, and
thus more prone to speedy coagulation and planet formation. Pre-existing
planetary systems are compressed by gas inflows leading to a natural occurrence
of close-in misaligned hot Jupiters and short-period eccentric planets. The
likelihood of such events mainly depends on the gas content of the cluster and
is thus expected to be highest in the youngest star clusters.Comment: 7 pages, 4 figures. Accepted for publication in MNRAS. Updated to
match published versio
The role of a central actor in increasing platform stickiness and stakeholder profitability: Bridging the gap between value creation and value capture in the sharing economy
Physics of Eclipsing Binaries: Modelling in the new era of ultra-high precision photometry
Recent ultra-high precision observations of eclipsing binaries, especially data acquired by the Kepler satellite, have made accurate light curve modelling increasingly challenging but also more rewarding. In this contribution, we discuss low-amplitude signals in light curves that can now be used to derive physical information about eclipsing binaries but that were unaccessible before the Kepler era. A notable example is the detection of Doppler beaming, which leads to an increase in flux when a star moves towards the satellite and a decrease in flux when it moves away. Similarly, Rømer delays, or light travel time effects, also have to taken into account when modelling the supreme quality data that is now available. The detection of offsets between primary and secondary eclipse phases in binaries with extreme mass ratios, and the observation of Rømer delays in the signals of pulsators in binary stars, have allowed us to determine the orbits of several binaries without the need for spectroscopy. A third example of a small-scale effect that has to be taken into account when modelling specific binary systems, are lensing effects. A new binary light curve modelling code, PHOEBE 2.0, that takes all these effect into account is currently being developed
The spin-orbit alignment of the transiting exoplanet WASP-3b from Rossiter-McLaughlin observations
We present an observation of the Rossiter-McLaughlin effect for the planetary
system WASP-3. Radial velocity measurements were made during transit using the
SOPHIE spectrograph at the 1.93m telescope at Haute-Provence Observatory. The
shape of the effect shows that the sky-projected angle between the stellar
rotation axis and planetary orbital axis (lambda) is small and consistent with
zero within 2 sigma; lambda = 15 +10/-9 deg. WASP-3b joins the ~two-thirds of
planets with measured spin-orbit angles that are well aligned and are thought
to have undergone a dynamically-gentle migration process such as planet-disc
interactions. We find a systematic effect which leads to an anomalously high
determination of the projected stellar rotational velocity (vsini = 19.6
+2.2/-2.1 km/s) compared to the value found from spectroscopic line broadening
(vsini = 13.4 +/- 1.5 km/s). This is thought to be caused by a discrepancy in
the assumptions made in the extraction and modelling of the data. Using a model
developed by Hirano et al. (2009) designed to address this issue, we find vsini
to be consistent with the value obtained from spectroscopic broadening
measurements (vsini = 15.7 +1.4/-1.3 km/s).Comment: 7 pages, 3 figures, published in MNRAS 405 (2010) 1867-1872. Update
includes discussion on differential rotaation and correction of typo
The spin-orbit angle of the transiting hot jupiter CoRoT-1b
We measure the angle between the planetary orbit and the stellar rotation
axis in the transiting planetary system CoRoT-1, with new HIRES/Keck and
FORS/VLT high-accuracy photometry. The data indicate a highly tilted system,
with a projected spin-orbit angle lambda = 77 +- 11 degrees. Systematic
uncertainties in the radial velocity data could cause the actual errors to be
larger by an unknown amount, and this result needs to be confirmed with further
high-accuracy spectroscopic transit measurements.
Spin-orbit alignment has now been measured in a dozen extra-solar planetary
systems, and several show strong misalignment. The first three misaligned
planets were all much more massive than Jupiter and followed eccentric orbits.
CoRoT-1, however, is a jovian-mass close-in planet on a circular orbit. If its
strong misalignment is confirmed, it would break this pattern. The high
occurence of misaligned systems for several types of planets and orbits favours
planet-planet scattering as a mechanism to bring gas giants on very close
orbits.Comment: to appear in in MNRAS letters [5 pages
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