4,554 research outputs found
Superconductivity and charge carrier localization in ultrathin bilayers
/ (LSCO15/LCO) bilayers
with a precisely controlled thickness of N unit cells (UCs) of the former and M
UCs of the latter ([LSCO15\_N/LCO\_M]) were grown on (001)-oriented {\slao}
(SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and
reciprocal space map (RSM) studies confirmed the epitaxial growth of the
bilayers and showed that a [LSCO15\_2/LCO\_2] bilayer is fully strained,
whereas a [LSCO15\_2/LCO\_7] bilayer is already partially relaxed. The
\textit{in situ} monitoring of the growth with reflection high energy electron
diffraction (RHEED) revealed that the gas environment during deposition has a
surprisingly strong effect on the growth mode and thus on the amount of
disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15
containing one plane each). For samples grown in pure
gas (growth type-B), the first LSCO15 UC next to the SLAO
substrate is strongly disordered. This disorder is strongly reduced if the
growth is performed in a mixture of and gas
(growth type-A). Electric transport measurements confirmed that the first UC of
LSCO15 next to the SLAO substrate is highly resistive and shows no sign of
superconductivity for growth type-B, whereas it is superconducting for growth
type-A. Furthermore, we found, rather surprisingly, that the conductivity of
the LSCO15 UC next to the LCO capping layer strongly depends on the thickness
of the latter. A LCO capping layer with 7~UCs leads to a strong localization of
the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity.
The magneto-transport data suggest a similarity with the case of weakly hole
doped LSCO single crystals that are in a so-called {"{cluster-spin-glass
state}"
LHCb Preshower Front-End Electronics Board. Qualification of the final prototype
This note describes the tests performed on the final prototypes of the SPD/Preshower Front-End electronics boards
LHCb Preshower Front-End Electronics Board
This note describes the digital part of the fully synchronous solution developped for the lhcb preshower detector Front-End electronics. The general design and the main features of this board are given including trigger part
Dual formulation of classical W-algebras
By extending the concept of \mc, I introduce a dual formulation of
(classical) nonlinear extensions of the \vir\ algebra. This dual formulation is
closely related to three dimensional actions which are analogous to a \cs\
action. I present an explicit construction in terms of superfields of the
super \wfour.Comment: (only change is an added reference), 9 pages, USC--92/01
Learning and interaction in groups with computers: when do ability and gender matter?
In the research reported in this paper, we attempt to identify the background and process factors influencing the effectiveness of groupwork with computers in terms of mathematics learning. The research used a multi-site case study design in six schools and involved eight groups of six mixed-sex, mixed-ability pupils (aged 9-12) undertaking three research tasks – two using Logo and one a database. Our findings suggest that, contrary to other recent research, the pupil characteristics of gender and ability have no direct influence on progress in group tasks with computers. However, status effects – pupils' perceptions of gender and ability – do have an effect on the functioning of the group, which in turn can impede progress for all pupils concerned
A narrow, edge-on disk resolved around HD 106906 with SPHERE
HD~106906AB is so far the only young binary system around which a planet has
been imaged and a debris disk evidenced thanks to a strong IR excess. As such,
it represents a unique opportunity to study the dynamics of young planetary
systems. We aim at further investigating the close (tens of au scales)
environment of the HD~106906AB system. We used the extreme AO fed, high
contrast imager SPHERE recently installed on the VLT to observe HD~106906. Both
the IRDIS imager and the Integral Field Spectrometer were used. We discovered a
very inclined, ring-like disk at a distance of 65~au from the star. The disk
shows a strong brightness asymmetry with respect to its semi-major axis. It
shows a smooth outer edge, compatible with ejection of small grains by the
stellar radiation pressure. We show furthermore that the planet's projected
position is significantly above the disk's PA. Given the determined disk
inclination, it is not excluded though that the planet could still orbit within
the disk plane if at a large separation (2000--3000 au). We identified several
additional point sources in the SPHERE/IRDIS field-of-view, that appear to be
background objects. We compare this system with other debris disks sharing
similarities, and we briefly discuss the present results in the framework of
dynamical evolution.Comment: 7 pages, 6 figures, accepted by Astronomy & Astrophysic
Study of multianode photomultipliers for the electomagnetic calorimeter preshower read out of the LHCb experiment
First light of the VLT planet finder SPHERE. I. Detection and characterization of the sub-stellar companion GJ 758 B
GJ758 B is a brown dwarf companion to a nearby (15.76 pc) solar-type,
metal-rich (M/H = +0.2 dex) main-sequence star (G9V) that was discovered with
Subaru/HiCIAO in 2009. From previous studies, it has drawn attention as being
the coldest (~600K) companion ever directly imaged around a neighboring star.
We present new high-contrast data obtained during the commissioning of the
SPHERE instrument at the VLT. The data was obtained in Y-, J-, H-, and Ks-bands
with the dual-band imaging (DBI) mode of IRDIS, providing a broad coverage of
the full near-infrared (near-IR) range at higher contrast and better spectral
sampling than previously reported. In this new set of high-quality data, we
report the re-detection of the companion, as well as the first detection of a
new candidate closer-in to the star. We use the new 8 photometric points for an
extended comparison of GJ758 B with empirical objects and 4 families of
atmospheric models. From comparison to empirical object, we estimate a T8
spectral type, but none of the comparison object can accurately represent the
observed near-IR fluxes of GJ758 B. From comparison to atmospheric models, we
attribute a Teff = 600K 100K, but we find that no atmospheric model can
adequately fit all the fluxes of GJ758 B. The photometry of the new candidate
companion is broadly consistent with L-type objects, but a second epoch with
improved photometry is necessary to clarify its status. The new astrometry of
GJ758 B shows a significant proper motion since the last epoch. We use this
result to improve the determination of the orbital characteristics using two
fitting approaches, Least-Square Monte Carlo and Markov Chain Monte Carlo.
Finally, we analyze the sensitivity of our data to additional closer-in
companions and reject the possibility of other massive brown dwarf companions
down to 4-5 AU. [abridged]Comment: 20 pages, 15 figures. Accepted for publication in A&
Monitoring water vapour penetration using a contactless technique
Some layers of thin film photovoltaic modules maybe critically sensitive to moisture. In this study we present a new tool for monitoring the effect of moisture using a particular Transparent Conductive Oxide (TCO) as a sensor. The moisture content of the encapsulant was determined by Fourier Transform Infra Red (FTIR) spectroscopic measurements. The TCO resistivity was measured using an inductive method. The different spectroscopic results show that the diffusion of water vapour in the encapsulant used in this study is in good agreement with Fick’s law and correlate well with the increase of resistivity of the TCO. However, the transport measurements bring evidence for a degradation of the TCO resistivity undetectable by conventional FTIR measurements
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