694 research outputs found
Inhomogeneous superconductivity induced in a weak ferromagnet
Under certain conditions, the order parameter induced by a superconductor (S)
in a ferromagnet (F) can be inhomogeneous and oscillating, which results e.g.
in the so-called pi-coupling in S/F/S junctions. In principle, the
inhomogeneous state can be induced at T_c as function of the F-layer thickness
d_F in S/F bilayers and multilayers, which should result in a dip-like
characteristic of T_c(d_F). We show the results of measurements on the S/F
system Nb/Cu_{1-x}Ni_x, for Ni-concentrations in the range x = 0.5-0.7, where
such effects might be expected. We find that the critical thickness for the
occurrence of superconductivity is still relatively high, even for these weak
ferromagnets. The resulting dip then is intrinsically shallow and difficult to
observe, which explains the lack of a clear signature in the T_c(d_F) data.Comment: 4 pages, 4 figures. To be publishedin Physica C (proceedings of the
Second Euroconference on Vortex Matter in Superconductors, Crete, 2001
Lambert formula - Bouguer absorption law?
It is shown that the fundamental Bouguer law, which links the fraction of absorbed light to the intensity of the incident light for a constant thickness of absorbing layer, was discovered experimentally and that the Lambert law is in no way related to it. The Lambert formula can be used only to estimate the attenuation (transmission) of light in a homogeneous medium containing scattering heterogeneous particles and with no jumps of the refractive index. The fraction of light absorbed in a layer is shown to depend on the thickness of that layer. © 1998 Plenum Publishing Corporation
The role of the Fraunhofer lines in solar brightness variability
The solar brightness varies on timescales from minutes to decades. A clear
identification of the physical processes behind such variations is needed for
developing and improving physics-based models of solar brightness variability
and reconstructing solar brightness in the past. This is, in turn, important
for better understanding the solar-terrestrial and solar-stellar connections.
We estimate the relative contributions of the continuum, molecular, and
atomic lines to the solar brightness variations on different timescales.
Our approach is based on the assumption that variability of the solar
brightness on timescales greater than a day is driven by the evolution of the
solar surface magnetic field. We calculated the solar brightness variations
employing the solar disc area coverage of magnetic features deduced from the
MDI/SOHO observations. The brightness contrasts of magnetic features relative
to the quiet Sun were calculated with a non-LTE radiative transfer code as
functions of disc position and wavelength. By consecutive elimination of
molecular and atomic lines from the radiative transfer calculations, we
assessed the role of these lines in producing solar brightness variability.
We show that the variations in Fraunhofer lines define the amplitude of the
solar brightness variability on timescales greater than a day and even the
phase of the total solar irradiance variability over the 11-year cycle. We also
demonstrate that molecular lines make substantial contribution to solar
brightness variability on the 11-year activity cycle and centennial timescales.
In particular, our model indicates that roughly a quarter of the total solar
irradiance variability over the 11-year cycle originates in molecular lines.
The maximum of the absolute spectral brightness variability on timescales
greater than a day is associated with the CN violet system between 380 and 390
nm.Comment: 9 pages, 4 figures, accepted for publication in
Astronomy&Astrophysic
Collective dissociative desorption of water molecules from glass produced by IFP-2000 flash tubes
When the radiation from an IFP-2000 lamp interacts with the surface crazed layer of glass, there is a weak spectral absorption not only in the vacuum ultraviolet but also in the range 420 >λ > 290 nm. The adsorbed H2O molecules are desorbed mainly by the dissociation, for the concentration of molecular hydrogen in the products is 80-84%. At intensities E≥600 W/cm2 and E≥4600 W/ cm2, in accordance with the working conditions, the desorption becomes collective. The rate of integral photon absorption then attains 1019 photons/cm2·sec. The transition to collective desorption in the first case (at relatively low intensity) is due to the production of a plasma in the material as a result of a sliding discharge struck at the surface of the glass. © 1981 Plenum Publishing Corporation
Critical temperature of superconductor/ferromagnet bilayers
Superconductor/ferromagnet bilayers are known to exhibit nontrivial
dependence of the critical temperature T_c on the thickness d_f of the
ferromagnetic layer. We develop a general method for investigation of T_c as a
function of the bilayer's parameters. It is shown that interference of
quasiparticles makes T_c(d_f) a nonmonotonic function. The results are in good
agreement with experiment. Our method also applies to multilayered structures.Comment: 4 pages, 2 EPS figures; the style file jetpl.cls is included. Version
2: typos correcte
Effect of annealing on structure and mechanical behavior of an AA2139 alloy
An AA2139 alloy with a chemical composition of Al-4.35Cu-0.46%Mg-0.63Ag-0.36Mn-0.12Ti (in wt.%) and an initial grain size of about 155 μm was subjected to annealing at 430°C for 3 h followed by furnace cooling. This treatment resulted in the formation of a dispersion of coarse particles having essentially plate-like shape. The over-aged alloy exhibits lower flow stress and high ductility in comparison with initial material in the temperature interval 20-450°C. Examination of microstructural evolution during high-temperature deformation showed localization of plastic flow in vicinity of coarse particles. Over-aging leads to transition from ductile-brittle fracture to ductile and very homogeneous ductile fracture at room temperatur
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