460 research outputs found
Role of interband scattering in neutron irradiated MgB thin films by Scanning Tunneling Spectroscopy measurements
A series of MgB thin films systematically disordered by neutron
irradiation have been studied by Scanning Tunneling Spectroscopy. The c-axis
orientation of the films allowed a reliable determination of local density of
state of the band. With increasing disorder, the conductance peak moves
towards higher voltages and becomes lower and broader, indicating a monotonic
increase of the gap and of the broadening parameter. These results are
discussed in the frame of two-band superconductivity.Comment: The text will be submitted in Latex format, and the corresponding pdf
file should take 6 pages. There are 5 figures (eps files submitted) and 1
tabl
Volatile signals during pregnancy: A possible chemical basis for mother-infant recognition
Human pheromones play a role in regulating relationships and apparently influence partner choice and mother–infant recognition. We analyzed the chemical content of volatiles from sweat patch samples from the para-axillary and nipple–areola regions of women during pregnancy and after childbirth. Solid phase microextraction was used to extract the volatile compounds, which were then characterized and quantified by gas chromatography–mass spectrometry. During pregnancy, women developed a distinctive pattern of five volatile compounds common to the para-axillary and nipple–areola regions (1-dodecanol, 1-1′-oxybis octane, isocurcumenol, α-hexyl-cinnamic aldehyde, and isopropyl myristate). These compounds were absent outside pregnancy and had slightly different patterns in samples from the two body areas. Differentiation of the volatile patterns among pregnant women may help newborns to distinguish their own mothers
Early mapping of industrial tomato in Central and Southern Italy with Sentinel 2, aerial and RapidEye additional data
Timely crop information, i.e. well before harvesting time and at first stages of crop development, can benefit farmers and producer organizations. The current case study documents the procedure to deliver early data on planted tomato to users, showing the potential of Sentinel 2 to map tomato at the very beginning of the crop season, which is a challenging task. Using satellite data, integrated with ground and aerial data, an initial estimate of area planted with tomato and early tomato maps were generated in seven main production areas in Italy. Estimates of the amount of area planted with tomato provided similar results either when derived from field surveys or from remote sensing-based classification. Tomato early maps showed a producer accuracy > 80% in seven cases out of nine, and a user accuracy > 80% in five cases out of nine, with differences attributed to the varying agricultural characteristics and environmental heterogeneity of the study areas. The additional use of aerial data improved producer accuracy moderately. The ability to identify abrupt growth changes, such as those caused by natural hazards, was also analysed: Sentinel 2 detected significant changes in tomato growth between a hailstorm-affected area and a control area. The study suggests that Sentinel 2, with enhanced spectral capabilities and open data policy, represents very valuable data, allowing crop monitoring at an early development stage
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
A sol-gel method for growing superconducting MgB2 films
In this paper we report a new sol-gel method for the fabrication of MgB2
films. Polycrystalline MgB2 films were prepared by spin-coating a precursor
solution of Mg(BH_4)_2 diethyl ether on (001)Al2O3 substrates followed with
annealing in Mg vapor. In comparison with the MgB2 films grown by other
techniques, our films show medium qualities including a superconducting
transition temperature of Tc ~ 37 K, a critical current density of Jc(5 K, 0 T)
~ 5 {\times} 10^6 A cm^{-2}, and a critical field of H_{c2}(0) ~ 19 T. Such a
sol-gel technique shows potential in the commercial fabrication of practically
used MgB2 films as well as MgB2 wires and tapes.Comment: 8 pages, 5 figure
Growth methods of c-axis oriented MgB2 thin films by pulsed laser deposition
High quality MgB2 thin films have been obtained by pulsed laser deposition
both on MgO and on Al2O3 substrates using different methods. In the standard
two-step procedure, an amorphous precursor layer is deposited at room
temperature starting both from stoichiometric target and from boron target:
after this first step, it is annealed in magnesium atmosphere in order to
crystallize the superconducting phase. The so obtained films show a strong
c-axis orientation, evidenced by XRD analysis, a critical temperature up to 38
K and very high critical fields along the basal planes, up to 22T at 15K. Also
an in situ one step technique for the realization of superconducting MgB2 thin
films has been developed. In this case, the presence of an argon buffer gas
during deposition is crucial and we observe a strong dependence of the quality
of the deposited film on the background gas pressure. The influence of the Ar
atmosphere has been confirmed by time and space-resolved spectroscopy
measurements on the emission spectrum of the plume. The Ar pressure modifies
strongly the plasma kinetics by promoting excitation and ionization of the
plume species, especially of the most volatile Mg atoms, increasing their
internal energy.Comment: Paper presented at Boromag Workshop, Genoa 17-19 June 2002, in press
on SUS
Coherent Electron Transport in Superconducting-Normal Metallic Films
We study the transport properties of a quasi-two-dimensional diffusive normal
metal film attached to a superconductor. We demonstrate that the properties of
such films can essentially differ from those of quasi-one-dimensional systems:
in the presence of the proximity induced superconductivity in a sufficiently
wide film its conductance may not only increase but also decrease with
temperature. We develop a quantitative theory and discuss the physical nature
of this effect. Our theory provides a natural explanation for recent
experimental findings referred to as the ``anomalous proximity effect''.Comment: 4 Pages RevTex, 4 Postscript figures; submitted to Phys. Rev. Let
Superconducting gap anisotropy of LuNi2B2C thin films from microwave surface impedance measurements
Surface impedance measurements of LuNi2B2C superconducting thin films as a
function of temperature have been performed down to 1.5 K and at 20 GHz using a
dielectric resonator technique. The magnetic penetration depth closely
reproduces the standard B.C.S. result, but with a reduced value of the energy
gap at low temperature. These data provide evidence for an anisotropic s-wave
character of the order parameter symmetry in LuNi2B2C. From the evaluation of
the real part of complex conductivity, we have observed constructive (type II)
coherence effects in the electromagnetic absorption below Tc.Comment: 15 pages, 4 figure
Quasiparticle Inelastic Lifetime from Paramagnons in Disordered Superconductors
The paramagnon contribution to the quasiparticle inelastic scattering rate in
disordered superconductors is presented. Using Anderson's exact eigenstate
formalism, it is shown that the scattering rate is Stoner enhanced and is
further enhanced by the disorder relative to the clean case in a manner similar
to the disorder enhancement of the long-range Coulomb contribution. The results
are discussed in connection with the possibility of conventional or
unconventional superconductivity in the borocarbides. The results are compared
to recent tunneling experiments on LuNiBC.Comment: 5 pages, no figure
Effect of two bands on critical fields in MgB2 thin films with various resistivity values
Upper critical fields of four MgB2 thin films were measured up to 28 Tesla at
Grenoble High Magnetic Field Laboratory. The films were grown by Pulsed Laser
Deposition and showed critical temperatures ranging between 29.5 and 38.8 K and
resistivities at 40 K varying from 5 to 50 mWcm. The critical fields in the
perpendicular direction turned out to be in the 13-24 T range while they were
estimated to be in 42-57 T the range in ab-planes. In contrast to the
prediction of the BCS theory, we did not observe any saturation at low
temperatures: a linear temperature dependence is exhibited even at lowest
temperatures at which we made the measurements. Moreover, the critical field
values seemed not to depend on the normal state resistivity value. In this
paper, we analyze these data considering the multiband nature of
superconductivity in MgB2 We will show how the scattering mechanisms that
determine critical fields and resistivity can be different.Comment: 17 pages, 3 figure
- …