575 research outputs found
Investigation of the use of microwave image line integrated circuits for use in radiometers and other microwave devices in X-band and above
Program results are described in which the use of a/high permittivity rectangular dielectric image waveguide has been investigated for use in microwave and millimeter wavelength circuits. Launchers from rectangular metal waveguide to image waveguide are described. Theoretical and experimental evaluations of the radiation from curved image waveguides are given. Measurements of attenuation due to conductor and dielectric losses, adhesives, and gaps between the dielectric waveguide and the image plane are included. Various passive components are described and evaluations given. Investigations of various techniques for fabrication of image waveguide circuits using ceramic waveguides are also presented. Program results support the evaluation of the image line approach as an advantageous method for realizing low loss integrated electronic circuits for X-band and above
The electrokinetic behavior of calcium oxalate monohydrate in macromolecular solutions
Electrophoretic mobilities were measured for calcium oxalate monohydrate (COM) in solutions containing macromolecules. Two mucopolysaccharides (sodium heparin and chrondroitin sulfate) and two proteins (positively charged lysozyme and negatively charged bovine serum albumin) were studied as adsorbates. The effects of pH, calcium oxalate surface charge (varied by calcium or oxalate ion activity), and citrate concentration were investigated. All four macromolecules showed evidence for chemical adsorption. The macromolecule concentrations needed for reversing the surface charge indicated that the mucopopolysacchrides have greater affinity for the COM surface than the proteins. The amount of proteins that can chemically adsorb appears to be limited to approximately one monomolecular layer. When the surface charge is high, an insufficient number of proteins can chemically adsorb to neutralize or reverse the surface charge. The remaining surface charge is balanced by proteins held near the surface by longer range electrostatic forces only. Citrate ions at high concentrations appear to compete effectively with the negative protein for surface sites but show no evidence for competing with the positively charged protein
Simple bonding technique for high-temperature ceramic coatings
Coatings, consisting of zirconia powder bonded with orthophosphoric acid and a small amount of hydrofluoric acid, are hard, strong, and refractory, resist thermal shock, and provide good thermal protection. After the aqueous coating is applied to a metallic surface, only a 600 deg F cure is required before service
(2n×1) Reconstructions of TiO2(011) Revealed by Noncontact Atomic Force Microscopy and Scanning Tunneling Microscopy
We have used noncontact atomic force microscopy (NC-AFM) and scanning tunneling microscopy (STM) to study the rutile TiO2(011) surface. A series of (2n×1) reconstructions were observed, including two types of (4×1) reconstruction. High resolution NC-AFM and STM images indicate that the (4×1)-α phase has the same structural elements as the more widely reported (2×1) reconstruction. An array of analogous higher order (2n×1) reconstructions were also observed where n = 3-5. On the other hand, the (4×1)-β reconstruction seems to be a unique structure without higher order analogues. A model is proposed for this structure that is also based on the (2×1) reconstruction but with additional microfacets of {111} character
Magneto-optics induced by the spin chirality in itinerant ferromagnet NdMoO
It is demonstrated both theoretically and experimentally that the spin
chirality associated with a noncoplanar spin configuration produces a
magneto-optical effect. Numerical study of the two-band Hubbard model on a
triangle cluster shows that the optical Hall conductivity
is proportional to the spin chirality. The detailed comparative experiments on
pyrochlore-type molybdates MoO with Nd (Ising-like moments)
and Gd (Heisenberg-like ones) clearly distinguishes the two mechanisms,
i.e., spin chirality and spin-orbit interactions. It is concluded that for
=Nd, is dominated by the spin chirality for the dc
() and the incoherent intraband optical transitions between
Mo atoms.Comment: 4 pages, 5 figures. submitted to Phys. Rev.
Spin Chirality Fluctuation and Anomalous Hall Effect in Itinerant Ferromagnets
The anomalous Hall effect due to the spin chirality order and fluctuation is
studied theoretically in a Kondo lattice model without the relativistic
spin-orbit interaction. Even without the correlations of the localized spins,
can emerge depending on the lattice structure and the spin
anisotropy. We reveal the condition for this chirality-fluctuation driven
mechanism for . Our semiquantitative estimates for a pyrochlore
oxide NdMoO give a finite \sigma_{xy} \sim 10 \Ohm^{-1} \cm^{-1}
together with a high resistivity \rho_{xx} \sim 10^{-4}-10^{-3} \Ohm \cm, in
agreement with experiments.Comment: 5 pages, including 4 figure
Studies of the Anomalous Hall Effect and Magnetic Structure of Nd2Mo2O7 -Test of the Chirality Mechanism-
Neutron scattering studies have been carried out under the magnetic fields
H//[0_11] and H//[001] on a single crystal of Nd2Mo2O7, whose Hall
resistivity(rhoH) exhibits quite unusual H- and temperature(T)-dependences.
Material parameters such as the single ion anisotropies of the Mo- and Nd-
moments and exchange coupling constants among the Mo-Mo, Mo-Nd and Nd-Nd
moments, have been determined to reproduce various kinds of experimental data
taken as a function of H and T. For example, the neutron Bragg intensities,
magnetization curves and the magnetic specific heats have been reproduced by
the common parameters. By using the magnetic structure reproduced by these
parameters, the spin chirality (chi) of Mo spins or the fictitious magnetic
flux Phi proportional to chi has been calculated as a function of H and T by
using equation chi=, where the bracket means the statistical
average. (Note that we do not use the equation chi=x, because the
local nature of the chirality should be correctly considered.) Comparing the
calculated results with the observed rhoH, we can conclude that the unusual
behavior of rH cannot be understood consistently only by the chirality
mechanism.Comment: 16 pages, 12 fiures, submitted to J. Phys. Soc. Jp
Fate of Quasiparticle at Mott Transition and Interplay with Lifshitz Transition Studied by Correlator Projection Method
Filling-control metal-insulator transition on the two-dimensional Hubbard
model is investigated by using the correlator projection method, which takes
into account momentum dependence of the free energy beyond the dynamical
mean-field theory. The phase diagram of metals and Mott insulators is analyzed.
Lifshitz transitions occur simultaneously with metal-insulator transitions at
large Coulomb repulsion. On the other hand, they are separated each other for
lower Coulomb repulsion, where the phase sandwiched by the Lifshitz and
metal-insulator transitions appears to show violation of the Luttinger sum
rule. Through the metal-insulator transition, quasiparticles retain nonzero
renormalization factor and finite quasi-particle weight in the both sides of
the transition. This supports that the metal-insulator transition is caused not
by the vanishing renormalization factor but by the relative shift of the Fermi
level into the Mott gap away from the quasiparticle band, in sharp contrast
with the original dynamical mean-field theory. Charge compressibility diverges
at the critical end point of the first-order Lifshitz transition at finite
temperatures. The origin of the divergence is ascribed to singular momentum
dependence of the quasiparticle dispersion.Comment: 24 pages including 10 figure
Microscopic Calculation of Spin Torques in Disordered Ferromagnets
Effects of conduction electrons on magnetization dynamics, represented by
spin torques, are calculated microscopically in the first order in spatial
gradient and time derivative of magnetization. Special attention is paid to the
so-called -term and the Gilbert damping, , in the presence of
electrons' spin-relaxation processes, which are modeled by quenched magnetic
(and spin-orbit) impurities. The obtained results such as
hold for localized as well as itinerant ferromagnetism.Comment: 4 page
Phase transition between the quantum spin Hall and insulator phases in 3D: emergence of a topological gapless phase
Phase transitions between the quantum spin Hall and the insulator phases in
three dimensions are studied. We find that in inversion-asymmetric systems
there appears a gapless phase between the quantum spin Hall and insulator
phases in three dimensions, which is in contrast with the two-dimensional case.
Existence of this gapless phase stems from a topological nature of gapless
points (diabolical points) in three dimensions, but not in two dimensions.Comment: 16 pages, 5 figure
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