29,335 research outputs found
Universal charge transport of the Mn oxides in the high temperature limit
We have found that various Mn oxides have the universal resistivity and
thermopower in the high temperature limit. The resistivities and thermopowers
of all the samples go toward constant values of 71 mcm and
3 V/K, which are independent of carrier density and crystal
structures. We propose that the electric conduction occurs in a highly
localized way in the high temperature limit, where the exchange of entropy and
charge occurs in the neighboring Mn and Mn ions.Comment: 4 pages, 4 eps figures, to be published in J. Appl. Phy
Structure-related transport properties of A-site ordered perovskite Sr3ErMn4-xGaxO10.5-d
We report x-ray diffraction, resistivity, thermopower, and magnetization of
Sr3ErMn4-xGaxO10.5-d, in which A-site ordered tetragonal phase appears above
x=1, and reveal that the system exhibits typical properties seen in the
antiferromagnetic insulator with Mn3+. We succeed in preparing both A-site
ordered and disordered phases for x=1 in different preparation conditions, and
observe a significant decrease of the resistivity in the disordered phase. We
discuss possible origins of the decrease focusing on the dimensionality and the
disordered effect.Comment: 4 pages, 6 figure
Restrictions of generalized Verma modules to symmetric pairs
We initiate a new line of investigation on branching problems for generalized
Verma modules with respect to complex reductive symmetric pairs (g,k). Here we
note that Verma modules of g may not contain any simple module when restricted
to a reductive subalgebra k in general.
In this article, using the geometry of K_C orbits on the generalized flag
variety G_C/P_C, we give a necessary and sufficient condition on the triple
(g,k, p) such that the restriction X|_k always contains simple k-modules for
any g-module lying in the parabolic BGG category O^p attached to a
parabolic subalgebra p of g.
Formulas are derived for the Gelfand-Kirillov dimension of any simple
k-module occurring in a simple generalized Verma module of g. We then prove
that the restriction X|_k is multiplicity-free for any generic g-module X \in O
if and only if (g,k) is isomorphic to a direct sum of (A_n,A_{n-1}), (B_n,D_n),
or (D_{n+1},B_n). We also see that the restriction X|_k is multiplicity-free
for any symmetric pair (g, k) and any parabolic subalgebra p with abelian
nilradical and for any generic g-module X \in O^p. Explicit branching laws are
also presented.Comment: 31 pages, To appear in Transformation Group
Doppler radar with multiphase modulation of transmitted and reflected signal
A microwave radar signal is generated and split by a circulator. A phase shifter introduces a series of phase shifts into a first part of the split signal which is then transmitted by antenna. A like number of phase shifts is introduced by the phase shifter into the return signal from the target. The circulator delivers the phase shifted return signal and the leakage signal from the circulator to a mixer which generates an IF signal output at the Doppler frequency. The IF signal is amplified, filtered, counted per unit of time, and the result displayed to provide indications of target sense and range rate. An oscillator controls rate of phase shift in the transmitted and received radar signals and provides a time base for the counter. The phase shift magnitude increases may be continuous and linear or discrete functions of time
Doppler radar having phase modulation of both transmitted and reflected return signals
A microwave radar signal is generated for transmission through an antenna. Before transmission, the signal is phase modulated by 0 deg or 90 deg amounts during each alternate half-cycles of an intermediate frequency (IF) clock signal. After transmission and return, the signal is again phase modulated the same amounts during each alternate half-cycles. The return phase modulated signal is mixed with a leakage signal component of the microwave signal, leaving an IF Doppler. The IF Doppler signal may then be amplified, removing any requirement that direct current level signals be amplified and also removing the effect of detector noise from the Doppler signal
Modeling Grain Boundaries using a Phase Field Technique
We propose a two dimensional frame-invariant phase field model of grain
impingement and coarsening. One dimensional analytical solutions for a stable
grain boundary in a bicrystal are obtained, and equilibrium energies are
computed. We are able to calculate the rotation rate for a free grain between
two grains of fixed orientation. For a particular choice of functional
dependencies in the model the grain boundary energy takes the same analytic
form as the microscopic (dislocation) model of Read and Shockley.Comment: 4 pages, 2 figure
Co-NMR Knight Shift of NaxCoO2 \dot yH2O Studied in Both Superconducting Regions of the Tc-nuQ3 Phase Diagram Divided by the Nonsuperconducting Phase
In the temperature (T)-nuQ3 phase diagram of NaxCoO2 \dot yH2O, there exist
two superconducting regions of nuQ3 separated by the nonsuperconducting region,
where nuQ3 is usually estimated from the peak position of the 59Co-NQR spectra
of the 5/2-7/2 transition and well-approximated here as nuQ3~3nuQ,nuQ being the
interaction energy between the nuclear quadrupole moment and the electric field
gradient. We have carried out measurements of the 59Co-NMR Knight shift (K) for
a single crystal in the higher-nuQ3 superconducting phase and found that K
begins to decrease with decreasing T at Tc for both magnetic field directions
parallel and perpendicular to CoO2-planes. The result indicates together with
the previous ones that the superconducting pairs are in the spin-singlet state
in both phases, excluding the possibility of the spin-triplet superconductivity
in this phase diagram. The superconductivity of this system spreads over the
wide nuQ3 regions, but is suppressed in the narrow region located at the middle
point of the region possibly due to charge instability.Comment: 8 pages, 5 figures, submitted to J. Phys. Soc. Jp
Method and apparatus for measuring distance
The invention employs a continuous wave radar technique and apparatus which can be used as a distance measuring system in the presence of background clutter by utilizing small passive transponders. A first continuous electromagnetic wave signal S sub 1 at a first frequency f sub 1 is transmitted from a first location. A transponder carried by a target object positioned at a second (remote) location receives the transmitted signal, phase-coherently divides the f sub 1 frequency and its phase, and re-transmits the transmitted signal as a second continuous electromagnetic wave signal S sub 2 at a lower frequency f sub 2 which is a subharmonic of f sub 1. The re-transmitted signal is received at the first location where a measurement of the phase difference is made between the signals S sub 1 and S sub 2, such measuremnt being indicative of the distance between the first and second locations
Unitarization of monodromy representations and constant mean curvature trinoids in 3-dimensional space forms
We present a theorem on the unitarizability of loop group valued monodromy
representations and apply this to show the existence of new families of
constant mean curvature surfaces homeomorphic to a thrice-punctured sphere in
the simply-connected 3-dimensional space forms , \bbS^3 and \bbH^3.
Additionally, we compute the extended frame for any associated family of
Delaunay surfaces.Comment: 18 pages, revised versio
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