296 research outputs found
Observed development of the vertical structure of the marine boundary layer during the LASIE experiment in the Ligurian Sea
In the marine environment, complete datasets describing the surface layer and the vertical structure of the Marine Atmospheric Boundary Layer (MABL), through its entire depth, are less frequent than over land, due to the high cost of measuring campaigns. During the seven days of the Ligurian Air-Sea Interaction Experiment (LASIE), organized by the NATO Undersea Research Centre (NURC) in the Mediterranean Sea, extensive in situ and remote sensing measurements were collected from instruments placed on a spar buoy and a ship. Standard surface meteorological measurements were collected by meteorological sensors mounted on the buoy ODAS Italia1 located in the centre of the Gulf of Genoa. The evolution of the height (<I>z<sub>i</sub></I>) of the MABL was monitored using radiosondes and a ceilometer on board of the N/O Urania. <br><br> Here, we present the database and an uncommon case study of the evolution of the vertical structure of the MABL, observed by two independent measuring systems: the ceilometer and radiosondes. Following the changes of surface flow conditions, in a sequence of onshore – offshore – onshore wind direction shifting episodes, during the mid part of the campaign, the overall structure of the MABL changed. Warm and dry air from land advected over a colder sea, induced a stably stratified Internal Boundary Layer (IBL) and a consequent change in the structure of the vertical profiles of potential temperature and relative humidity
Control of Multi-level Voltage States in a Hysteretic SQUID Ring-Resonator System
In this paper we study numerical solutions to the quasi-classical equations
of motion for a SQUID ring-radio frequency (rf) resonator system in the regime
where the ring is highly hysteretic. In line with experiment, we show that for
a suitable choice of of ring circuit parameters the solutions to these
equations of motion comprise sets of levels in the rf voltage-current dynamics
of the coupled system. We further demonstrate that transitions, both up and
down, between these levels can be controlled by voltage pulses applied to the
system, thus opening up the possibility of high order (e.g. 10 state),
multi-level logic and memory.Comment: 8 pages, 9 figure
Switching between dynamic states in intermediate-length Josephson junctions
The appearance of zero-field steps (ZFS’s) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hill’s equation which predicts how the number, locations, and widths of the instability regions depend on the junction parameters. A numerical integration of the PSGE in terms of truncated series of time-dependent Fourier spatial modes verifies that the parametrically excited instabilities of the MCB evolve into the fluxon oscillations characteristic of the ZFS’s. An approximate analysis of the Fourier mode equations in the presence of a small magnetic field yields a field-dependent Hill’s equation which predicts that the major effect of such a field is to reduce the widths of the instability regions. Experimental measurements on Nb-NbxOy-Pb junctions of intermediate length, performed at different operating temperatures in order to vary the junction parameters and for various magnetic field values, verify the physical existence of switching from the MCB to the ZFS’s. Good qualitative, and in many cases quantitative, agreement between analytic, numerical, and experimental results is obtained
Superconductivity enhanced conductance fluctuations in few layer graphene nanoribbons
We investigate the mesoscopic disorder induced rms conductance variance
in a few layer graphene nanoribbon (FGNR) contacted by two
superconducting (S) Ti/Al contacts. By sweeping the back-gate voltage, we
observe pronounced conductance fluctuations superimposed on a linear background
of the two terminal conductance G. The linear gate-voltage induced response can
be modeled by a set of inter-layer and intra-layer capacitances.
depends on temperature T and source-drain voltage .
increases with decreasing T and . When lowering , a
pronounced cross-over at a voltage corresponding to the superconducting energy
gap is observed. For |V_{sd}|\ltequiv \Delta the fluctuations are
markedly enhanced. Expressed in the conductance variance of one
graphene-superconducutor (G-S) interface, values of 0.58 e^2/h are obtained at
the base temperature of 230 mK. The conductance variance in the sub-gap region
are larger by up to a factor of 1.4-1.8 compared to the normal state. The
observed strong enhancement is due to phase coherent charge transfer caused by
Andreev reflection at the nanoribbon-superconductor interface.Comment: 15 pages, 5 figure
Kink propagation in a two-dimensional curved Josephson junction
We consider the propagation of sine-Gordon kinks in a planar curved strip as
a model of nonlinear wave propagation in curved wave guides. The homogeneous
Neumann transverse boundary conditions, in the curvilinear coordinates, allow
to assume a homogeneous kink solution. Using a simple collective variable
approach based on the kink coordinate, we show that curved regions act as
potential barriers for the wave and determine the threshold velocity for the
kink to cross. The analysis is confirmed by numerical solution of the 2D
sine-Gordon equation.Comment: 8 pages, 4 figures (2 in color
Promoting health and welfare in organic laying hens. Recommendations to ensure hen health and welfare in organic husbandry
In the HealthyHens project we investigated laying hen health and welfare in organic poultry systems in eight European countries. This leaflet presents our findings and recommendations. Most of our recommendations are also relevant for conventional poultry systems
Subharmonic Shapiro steps and assisted tunneling in superconducting point contacts
We analyze the current in a superconducting point contact of arbitrary
transmission in the presence of a microwave radiation. The interplay between
the ac Josephson current and the microwave signal gives rise to Shapiro steps
at voltages V = (m/n) \hbar \omega_r/2e, where n,m are integer numbers and
\omega_r is the radiation frequency. The subharmonic steps (n different from 1)
are a consequence of the ocurrence of multiple Andreev reflections (MAR) and
provide an unambiguous signature of the peculiar ac Josephson effect at high
transmission. Moreover, the dc current exhibits a rich subgap structure due to
photon-assisted MARs.Comment: Revtex, 4 pages, 4 figure
Isotope Effect in the Presence of Magnetic and Nonmagnetic Impurities
The effect of impurities on the isotope coefficient is studied theoretically
in the framework of Abrikosov-Gor'kov approach generalized to account for both
potential and spin-flip scattering in anisotropic superconductors. An
expression for the isotope coefficient as a function of the critical
temperature is obtained for a superconductor with an arbitrary contribution of
spin-flip processes to the total scattering rate and an arbitrary degree of
anisotropy of the superconducting order parameter, ranging from isotropic
s-wave to d-wave and including anisotropic s-wave and mixed (s+d)-wave as
particular cases. It is found that both magnetic and nonmagnetic impurities
enhance the isotope coefficient, the enhancement due to magnetic impurities
being generally greater than that due to nonmagnetic impurities. From the
analysis of the experimental results on La-Sr-Cu-M-O high temperature
superconductor, it is concluded that the symmetry of the pairing state in this
system differs from a pure d-wave.Comment: 4 pages, 3 figure
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