1,617 research outputs found
The multi-parameter remote measurement of rainfall
The measurement of rainfall by remote sensors is investigated. One parameter radar rainfall measurement is limited because both reflectivity and rain rate are dependent on at least two parameters of the drop size distribution (DSD), i.e., representative raindrop size and number concentration. A generalized rain parameter diagram is developed which includes a third distribution parameter, the breadth of the DSD, to better specify rain rate and all possible remote variables. Simulations show the improvement in accuracy attainable through the use of combinations of two and three remote measurables. The spectrum of remote measurables is reviewed. These include path integrated techniques of radiometry and of microwave and optical attenuation
Robustness of the transition against compositional and structural ageing in S/F/S heterostructures
We have studied the temperature induced thermodynamic transition in
Nb/PdNi/Nb Superconductor/Ferromagnetic/Superconductor (SFS) heterostructures
by microwave measurements of the superfluid density. We have observed a shift
in the transition temperature with the ageing of the heterostructures,
suggesting that structural and/or chemical changes took place. Motivated by the
electrodynamics findings, we have extensively studied the local structural
properties of the samples by means of X-ray Absorption Spectroscopy (XAS)
technique, and the compositional profile by Time-of-Flight Secondary Ion Mass
Spectrometry (ToF-SIMS). We found that the samples have indeed changed their
properties, in particular for what concerns the interfaces and the composition
of the ferromagnetic alloy layer. The structural and compositional data are
consistent with the shift of the transition toward the behaviour of
heterostructures with different F layers. An important emerging indication to
the physics of SFS is the weak relevance of the ideality of the interfaces:
even in aged samples, with less-than-ideal interfaces, the temperature-induced
transition is still detectable albeit at a different critical F
thickness.Comment: 11 pages, 9 figures, accepted for publication on Phys. Rev. B,
http://journals.aps.org/prb
Microwave properties of Nb/PdNi/Nb trilayers. Observation of flux flow in excess of Bardeen-Stephen theory
We combine wideband (1-20 GHz) Corbino disk and dielectric resonator (8.2
GHz) techniques to study the microwave properties in Nb/PdNi/Nb trilayers,
grown by UHV dc magnetron sputtering, composed by Nb layers of nominal
thickness =15 nm, and a ferromagnetic PdNi layer of thickness = 1, 2,
8 and 9 nm. We focus on the vortex state. Magnetic fields up to were
applied. The microwave resistivity at fixed increases with ,
eventually exceeding the Bardeen Stephen flux flow value.Comment: 6 pages. Submitted to Journal of Superconductivity and Novel
Magnetis
Structural dichroism in the antiferromagnetic insulating phase of V_2O_3
We performed near-edge x-ray absorption spectroscopy (XANES) at V K edge in
the antiferromagnetic insulating (AFI) phase of a 2.8% Cr-doped V_2O_3 single
crystal. Linear dichroism of several percent is measured in the hexagonal plane
and found to be in good agreement with ab-initio calculations based on multiple
scattering theory. This experiment definitively proves the structural origin of
the signal and therefore solves a controversy raised by previous
interpretations of the same dichroism as non-reciprocal. It also calls for a
further investigation of the role of the magnetoelectric annealing procedure in
cooling to the AFI phase.Comment: 4 pages 3 figures. To be published in Phys. Rev. B (2005
Pressure effects on charge, spin, and metal-insulator transitions in narrow bandwidth manganite PrCaMnO
Pressure effects on the charge and spin states and the relation between the
ferromagnetic and metallic states were explored on the small bandwidth
manganite PrCaMnO (x = 0.25, 0.3, 0.35). Under pressure,
the charge ordering state is suppressed and a ferromagnetic metallic state is
induced in all three samples. The metal-insulator transition temperature
(T) increases with pressure below a critical point P*, above which
T decreases and the material becomes insulating as at the ambient
pressure. The e electron bandwidth and/or band-filling mediate the
pressure effects on the metal-insulator transition and the magnetic transition.
In the small bandwidth and low doping concentration compound (x = 0.25), the
T and Curie temperature (T) change with pressure in a reverse way
and do not couple under pressure. In the x = 0.3 compound, the relation of
T and T shows a critical behavior: They are coupled in the range
of 0.8-5 GPa and decoupled outside of this range. In the x = 0.35
compound, T and T are coupled in the measured pressure range where
a ferromagnetic state is present
Stability of Jahn-Teller distortion ordering in LaMn1-x ScxO3
We have investigated the role of Mn3+ Jahn-Teller distortion in driving ferromagnetism in the LaMn1-xScxO3 series. The replacement of Mn by Sc in LaMnO3 decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the LaScO3 sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in LaMnO3 into a nearly regular one in LaScO3. Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc K edges reveal the stability of both Jahn-Teller distorted MnO6 octahedron and nearly regular ScO6 octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted MnO6 octahedra spatially ordered as in LaMnO3 and nearly regular ScO6 octahedra. This result contrasts with the pseudocubic phase and the appearance of regular MnO6 octahedra in LaMn1-xGaxO3 for x>0.5. Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the Mn3+ atom is allocated. Besides, a ferromagnetic ground state is observed for x>0.5 in both series independently of the presence (or not) of Jahn-Teller distortions around Mn3+, which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in LaMn1-xBxO3 (B=Sc or Ga).The authors thank ESRF, ALBA, and Elettra Synchrotrons for granting beam time. Financial support from the Spanish MINECO (Projects No. MAT2012-38213-C02-01 and No. MAT2011-23791) and the Diputacion General de Aragón (CAMRADS) are acknowledged.Peer Reviewe
Gauge factor of thick film resistors: outcomes of the variable range hopping model
Despite a large amount of data and numerous theoretical proposals, the
microscopic mechanism of transport in thick film resistors remains unclear.
However, recent low temperature measurements point toward a possible variable
range hopping mechanism of transport. Here we examine how such a mechanism
affects the gauge factor of thick film resistors. We find that at sufficiently
low temperatures , for which the resistivity follows the Mott's law
, the gauge factor GF is proportional to
. Moreover, the inclusion of Coulomb gap effects leads to at lower temperatures. In addition, we study a simple
model which generalizes the variable range hopping mechanism by taking into
account the finite mean inter-grain spacing. Our results suggest a possible
experimental verification of the validity of the variable range hopping in
thick film resistors.Comment: 7 pages, 3 eps figures, submitted to Journal of Applied Physic
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