2,361 research outputs found
Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3
Tungsten trioxide is a versatile material with widespread applications
ranging from electrochromic and optoelectronic devices to water splitting and
catalysis of chemical reactions. For technological applications, thin films of
WO3 are particularly appealing, taking advantage from high surface-to-volume
ratio and tunable physical properties. However, the growth of stoichiometric,
crystalline thin films is challenging because the deposition conditions are
very sensitive to the formation of oxygen vacancies. In this work, we show how
background oxygen pressure during pulsed laser deposition can be used to tune
the structural and electronic properties of WO3 thin films. By performing X-ray
diffraction and low-temperature transport measurements, we find changes in WO3
lattice volume up to 10%, concomitantly with an insulator-to-metal transition
as a function of increased level of electron doping. We use advanced ab initio
calculations to describe in detail the properties of the oxygen vacancy defect
states, and their evolution in terms of excess charge concentration. Our
results depict an intriguing scenario where structural, electronic, optical,
and transport properties of WO3 single-crystal thin films can all be purposely
tuned by a suited control of oxygen vacancies formation during growth
Superconducting quantum point contact with split gates in the two dimensional LaAlO3/SrTiO3 superfluid
One of the hallmark experiments of quantum transport is the observation of
the quantized resistance in a point contact formed with split gates in
GaAs/AlGaAs heterostructures. Being carried out on a single material, they
represent in an ideal manner equilibrium reservoirs which are connected only
through a few electron mode channel with certain transmission coefficients. It
has been a long standing goal to achieve similar experimental conditions also
in superconductors, only reached in atomic scale mechanically tunable break
junctions of conventional superconducting metals, but here the Fermi wavelength
is so short that it leads to a mixing of quantum transport with atomic orbital
physics. Here we demonstrate for the first time the formation of a
superconducting quantum point contact (SQPC) with split gate technology in a
superconductor, utilizing the unique gate tunability of the two dimensional
superfluid at the LaAlO3/SrTiO3 (LAO/STO) interface. When the constriction is
tuned through the action of metallic split gates we identify three regimes of
transport: (i) SQPC for which the supercurrent is carried only by a few quantum
transport channels. (ii) Superconducting island strongly coupled to the
equilibrium reservoirs. (iii) Charge island with a discrete spectrum weakly
coupled to the reservoirs. Our experiments demonstrate the feasibility of a new
generation of mesoscopic all-superconductor quantum transport devices.Comment: 18 page
Struttura di popolazione di vongola verace (<i>Ruditapes decussatus</i> l.) in due lagune costiere della Sardegna = Population structure of carpet shell clam (<i>Ruditapes decussatus</i> l.) in two coastal lagoons of Sardinia (Italy)
Ruditapes decussatus L. (Bivalvia) is a traditional resource for fishing activity in Sardinia Island. This species is not cultured, but fishermen pick them up from the bottom of brackish areas. The distribution and the population structure of R. decussatus were investigated in two coastal lagoons: S. Giovanni (CA) and Calich (SS). The samplings were performed seasonally from autumn 2008 to summer 2009
Il Lago Omodeo: caratteristiche fisiche e chimiche
The chemical and physical data collected in Lago Omodeo (Central Sardinia) during 1976 are presented. Particulary temperature and oxygen distributions show the influences of the deep water withdrawl.
The high winter nitrate and orthophosphate concentrations and their seasonal changes, the dissolved oxygen depletion in deep waters are importat indices of high eutrophic conditions
Is it possible to compare inhibitory and excitatory intracortical circuits in face and hand primary motor cortex?
Face muscles are important in a variety of different functions, such as feeding, speech and communication of non-verbal affective states, which require quite different patterns of activity from those of a typical hand muscle. We ask whether there are differences in their neurophysiological control that might reflect this. Fifteen healthy individuals were studied. Standard single- and paired-pulse transcranial magnetic stimulation (TMS) methods were used to compare intracortical inhibitory (short interval intracortical inhibition (SICI); cortical silent period (CSP)) and excitatory circuitries (short interval intracortical facilitation (SICF)) in two typical muscles, the depressor anguli oris (DAO), a face muscle, and the first dorsal interosseous (FDI), a hand muscle. TMS threshold was higher in DAO than in FDI. Over a range of intensities, resting SICF was not different between DAO and FDI, while during muscle activation SICF was stronger in FDI than in DAO (P = 0.012). At rest, SICI was stronger in FDI than in DAO (P = 0.038) but during muscle contraction, SICI was weaker in FDI than in DAO (P = 0.034). We argue that although many of the difference in response to the TMS protocols could result from the difference in thresholds, some, such as the reduction of resting SICI in DAO, may reflect fundamental differences in the physiology of the two muscle groups
Balanced electron-hole transport in spin-orbit semimetal SrIrO3 heterostructures
Relating the band structure of correlated semimetals to their transport
properties is a complex and often open issue. The partial occupation of
numerous electron and hole bands can result in properties that are seemingly in
contrast with one another, complicating the extraction of the transport
coefficients of different bands. The 5d oxide SrIrO3 hosts parabolic bands of
heavy holes and light electrons in gapped Dirac cones due to the interplay
between electron-electron interactions and spin-orbit coupling. We present a
multifold approach relying on different experimental techniques and theoretical
calculations to disentangle its complex electronic properties. By combining
magnetotransport and thermoelectric measurements in a field-effect geometry
with first-principles calculations, we quantitatively determine the transport
coefficients of different conduction channels. Despite their different
dispersion relationships, electrons and holes are found to have strikingly
similar transport coefficients, yielding a holelike response under field-effect
and thermoelectric measurements and a linear, electronlike Hall effect up to 33
T.Comment: 5 pages, 4 figure
Influence of thermal boundary conditions on the current-driven resistive transition in VO 2
Design and Optimization of an Active Leveling System Actuator for Lunar Lander Application
This work proposes a systematic methodology for designing an active leveling system
(ALS) actuator for lunar landing application. The ALS actuator is integrated into an inverted
tripod leg layout, exploiting a honeycomb crushable damper as a shock absorber. The proposed ALS
actuator is fitted within the leg’s primary strut and features a custom permanent-magnet synchronous
machine rigidly coupled with a lead screw. The actuator aims to both provide proper leg deployment
functioning and compensate for the different shock absorber deformations during landing. The leg
dynamic behavior is simulated through a parameterized multi-body model to investigate different
landing scenarios. First, a parametric sensitivity approach is used to optimize the transmission system
and the electric machine characteristics. Then, the electric motor model is numerically validated and
optimized through electromagnetic finite element analysis. To validate the proposed ALS design
methodology, a virtual test bench is used to assess the ALS performances under different load
scenarios. It is found that the proposed methodology is able to yield a compact, well-sized actuator
which is numerically validated with the EL3 platform as a case study
Bimodal Phase Diagram of the Superfluid Density in LaAlO3/SrTiO3 Revealed by an Interfacial Waveguide Resonator
We explore the superconducting phase diagram of the two-dimensional electron
system at the LaAlO3/SrTiO3 interface by monitoring the frequencies of the
cavity modes of a coplanar waveguide resonator fabricated in the interface
itself. We determine the phase diagram of the superconducting transition as a
function of temperature and electrostatic gating, finding that both the
superfluid density and the transition temperature follow a dome shape, but that
the two are not monotonically related. The ground state of this 2DES is
interpreted as a Josephson junction array, where a transition from long- to
short-range order occurs as a function of the electronic doping. The synergy
between correlated oxides and superconducting circuits is revealed to be a
promising route to investigate these exotic compounds, complementary to
standard magneto-transport measurements.Comment: 5 pages, 4 figures and 10 pages of supplementary materia
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