1,224 research outputs found
Rate statistics for radio noise from lightning
Radio frequency noise from lightning was measured at several frequencies in the HF - VHF range at the Kennedy Space Center, Florida. The data were examined to determine flashing rate statistics during periods of strong activity from nearby storms. It was found that the time between flashes is modeled reasonably well by a random variable with a lognormal distribution
High Frequency Scattering from Arbitrarily Oriented Dielectric Disks
Calculations have been made of electromagnetic wave scattering from dielectric disks of arbitrary shape and orientation in the high frequency (physical optics) regime. The solution is obtained by approximating the fields inside the disk with the fields induced inside an identically oriented slab (i.e. infinite parallel planes) with the same thickness and dielectric properties. The fields inside the disk excite conduction and polarization currents which are used to calculate the scattered fields by integrating the radiation from these sources over the volume of the disk. This computation has been executed for observers in the far field of the disk in the case of disks with arbitrary orientation and for arbitrary polarization of the incident radiation. The results have been expressed in the form of a dyadic scattering amplitude for the disk. The results apply to disks whose diameter is large compared to wavelength and whose thickness is small compared to diameter, but the thickness need not be small compared to wavelength. Examples of the dependence of the scattering amplitude on frequency, dielectric properties of the disk and disk orientation are presented for disks of circular cross section
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
Polaronic state and nanometer-scale phase separation in colossal magnetoresistive manganites
High resolution topographic images obtained by scanning tunneling microscope
in the insulating state of Pr0.68Pb0.32MnO3 single crystals showed regular
stripe-like or zigzag patterns on a width scale of 0.4 - 0.5 nm confirming a
high temperature polaronic state. Spectroscopic studies revealed inhomogeneous
maps of zero-bias conductance with small patches of metallic clusters on length
scale of 2 - 3 nm only within a narrow temperature range close to the
metal-insulator transition. The results give a direct observation of polarons
in the insulating state, phase separation of nanometer-scale metallic clusters
in the paramagnetic metallic state, and a homogeneous ferromagnetic state
High-Pressure Phase Diagram in the Manganites: a Two-site Model Study
The pressure dependence of the Curie temperature in manganites,
recently studied over a wide pressure range, is not quantitatively accounted
for by the quenching of Jahn-Teller distortions, and suggests the occurrence of
a new pressure-activated localizing processes. We present a theoretical
calculation of based on a two-site double-exchange model with
electron-phonon coupling interaction and direct superexchange between the core spins. We calculate the pressure dependence of and compare
it with the experimental phase diagram. Our results describe the experimental
behavior quite well if a pressure-activated enhancement of the
antiferromagnetic superexchange interaction is assumed
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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