254,811 research outputs found
Time-resolved ferromagnetic resonance in epitaxial Fe1-xCox films
Magnetodynamics in epitaxial Fe1-xCox films on GaAs (100) are studied using
time-resolved ferromagnetic resonance, in which the free precession of the
magnetization after an impulsive excitation is measured using the polar Kerr
effect. The sample is rotated with respect to the static and pulsed field
directions, providing a complete mapping of the free energy surface and
characteristic relaxation times. The magnetic response can be simulated with a
simple coherent rotation model except in the immediate vicinity of switching
fields. Bulk and surface anisotropies are identified, and unusual dynamics
associated with the coexistence of cubic and uniaxial anisotropies are
observed.Comment: PDF - 4 figure
Phase-Control of Photoabsorption in Optically Dense Media
We present a self-consistent theory, as well as an illustrative application
to a realistic system, of phase control of photoabsorption in an optically
dense medium. We demonstrate that, when propagation effects are taken into
consideration, the impact on phase control is significant. Independently of the
value of the initial phase difference between the two fields, over a short
scaled distance of propagation, the medium tends to settle the relative phase
so that it cancels the atomic excitation. In addition, we find some rather
unusual behavior for an optically thin layer.Comment: 5 pages, 3 figures, submitted to PR
Single-growth embedded epitaxy AlGaAs injection lasers with extremely low threshold currents
A new type of strip-geometry AlGaAs double-heterostructure laser with an embedded optical waveguide has been developed. The new structure is fabricated using a single step of epitaxial growth. Lasers with threshold currents as low as 9.5 mA (150 µm long) were obtained. These lasers exhibit operation in a single spatial and longitudinal mode, have differential quantum efficiencies exceeding 45%, and a characteristic temperature of 175° C. They emit more than 12 mW/facet of optical power without any kinks
Thermal Diagnostics with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory: A Validated Method for Differential Emission Measure Inversions
We present a new method for performing differential emission measure (DEM)
inversions on narrow-band EUV images from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO). The method yields positive
definite DEM solutions by solving a linear program. This method has been
validated against a diverse set of thermal models of varying complexity and
realism. These include (1) idealized gaussian DEM distributions, (2) 3D models
of NOAA Active Region 11158 comprising quasi-steady loop atmospheres in a
non-linear force-free field, and (3) thermodynamic models from a
fully-compressible, 3D MHD simulation of AR corona formation following magnetic
flux emergence. We then present results from the application of the method to
AIA observations of Active Region 11158, comparing the region's thermal
structure on two successive solar rotations. Additionally, we show how the DEM
inversion method can be adapted to simultaneously invert AIA and XRT data, and
how supplementing AIA data with the latter improves the inversion result. The
speed of the method allows for routine production of DEM maps, thus
facilitating science studies that require tracking of the thermal structure of
the solar corona in time and space.Comment: 21 pages, 18 figures, accepted for publication in Ap
Comment on "Superconducting gap anisotropy vs. doping level in high-T_c cuprates" by C. Kendziora et al, PRL 77, 727 (1996)
In a recent paper Kendziora et al concluded that the superconducting gap in
overdoped Bi-2212 is isotropic. From data obtained from electronic Raman
scattering measurements, their conclusion was based on the observation that
pair breaking peaks occured at approximately the same frequency in different
scattering geometries and that the normalized scattering intensity at low
energies was strongly depleted. We discuss a different interpretation of the
raw data and present new data which is consistent with a strongly anisotropic
gap with nodes. The spectra can be successfully described by a model for Raman
scattering in a d_{x^{2}-y^{2}} superconductor with spin fluctuations and
impurity scattering included.Comment: 1 page revtex plus 1 postscript figur
Orbital Order and Spontaneous Orthorhombicity in Iron Pnictides
A growing list of experiments show orthorhombic electronic anisotropy in the
iron pnictides, in some cases at temperatures well above the spin density wave
transition. These experiments include neutron scattering, resistivity and
magnetoresistance measurements, and a variety of spectroscopies. We explore the
idea that these anisotropies stem from a common underlying cause: orbital order
manifest in an unequal occupation of and orbitals, arising
from the coupled spin-orbital degrees of freedom. We emphasize the distinction
between the total orbital occupation (the integrated density of states), where
the order parameter may be small, and the orbital polarization near the Fermi
level which can be more pronounced. We also discuss light-polarization studies
of angle-resolved photoemission, and demonstrate how x-ray absorption linear
dichroism may be used as a method to detect an orbital order parameter.Comment: Orig.: 4+ pages; Rev.: 4+ pages with updated content and reference
Determination of Frequency and Distribution of Hessian Fly (Diptera: Cecidomyiidae) Biotypes in the Northeastern Soft Wheat Region
Fifteen collections of Hessian flies from the northern soft winter wheat region of the United States were used to determine the composition and frequency of biotypes. The wheat cultivars \u27Seneca\u27 (H7Hs), \u27Monon\u27 (H3), \u27Knox 62\u27 (~, H7Hg), and \u27Abe\u27 (Hs) were used as differentials. Biotypes J and L replaced biotype B as the prevalent biotype in Indiana, since wheat cultivars having the Hs and the H6 genes have been grown. Biotype GP, the least virulent of any Hessian fly biotypes, was still present in New York indicating that wheat cuItivars with no genes for resistance are still being grown there. The genetic variability of Hessian fly biotypes that enables them to overcome the resistance in wheat cultivars is discussed
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