2,430 research outputs found
A Compact Approximate Solution to the Friedel-Anderson Impuriy Problem
An approximate groundstate of the Anderson-Friedel impurity problem is
presented in a very compact form. It requires solely the optimization of two
localized electron states and consists of four Slater states (Slater
determinants). The resulting singlet ground state energy lies far below the
Anderson mean field solution and agrees well with the numerical results by
Gunnarsson and Schoenhammer, who used an extensive 1/N_{f}-expansion for a spin
1/2 impurity with double occupancy of the impurity level.
PACS: 85.20.Hr, 72.15.R
Theory of Core-Level Photoemission and the X-ray Edge Singularity Across the Mott Transition
The zero temperature core-level photoemission spectrum is studied across the
metal to Mott insulator transition using dynamical mean-field theory and
Wilson's numerical renormalization group. An asymmetric power-law divergence is
obtained in the metallic phase with an exponent alpha(U,Q)-1 which depends on
the strength of both the Hubbard interaction U and the core-hole potential Q.
For Q <~ U_c/2 alpha decreases with increasing U and vanishes at the transition
(U -> U_c) leading to a symmetric peak in the insulating phase. For Q >~ U_c/2,
alpha remains finite close to the transition, but the integrated intensity of
the power-law vanishes and there is no associated peak in the insulator. The
weight and position of the remaining peaks in the spectra can be understood
within a molecular orbital approach.Comment: 5 pages, 6 figure
Event-Based Visual-Inertial Odometry Using Smart Features
Event-based cameras are a novel type of visual sensor that operate under a unique paradigm, providing asynchronous data on the log-level changes in light intensity for individual pixels. This hardware-level approach to change detection allows these cameras to achieve ultra-wide dynamic range and high temporal resolution. Furthermore, the advent of convolutional neural networks (CNNs) has led to state-of-the-art navigation solutions that now rival or even surpass human engineered algorithms. The advantages offered by event cameras and CNNs make them excellent tools for visual odometry (VO). This document presents the implementation of a CNN trained to detect and describe features within an image as well as the implementation of an event-based visual-inertial odometry (EVIO) pipeline, which estimates a vehicle\u27s 6-degrees-offreedom (DOF) pose using an affixed event-based camera with an integrated inertial measurement unit (IMU). The front-end of this pipeline utilizes a neural network for generating image frames from asynchronous event camera data. These frames are fed into a multi-state constraint Kalman filter (MSCKF) back-end that uses the output of the developed CNN to perform measurement updates. The EVIO pipeline was tested on a selection from the Event-Camera Dataset [1], and on a dataset collected from a fixed-wing unmanned aerial vehicle (UAV) flight test conducted by the Autonomy and Navigation Technology (ANT) Center
A new neutron study of the short range order inversion in FeCr
We have performed new neutron diffuse scattering measurements in
FeCr solid solutions, in a concentration range 0x0.15, where
the atomic distribution shows an inversion of the short range order. By
optimizing the signal-background ratio, we obtain an accurate determination of
the concentration of inversion x =0.110(5). We determine the near neighbor
atomic short range order parameters and pair potentials, which change sign at
x. The experimental results are compared with previous first principle
calculations and atomistic simulations.Comment: 6 pages; 6 figure
Nuclear Pairing: Surface or Bulk ?
We analyse how the spatial localisation properties of pairing correlations
are changing in a major neutron shell of heavy nuclei. It is shown that the
radial distribution of the pairing density depends strongly on whether the
chemical potential is close to a low or a high angular momentum level and has
very little sensitivity to whether the pairing force acts in the surface or in
the bulk. The averaged pairing density over one major shell is however rather
flat, practically independent of the pairing force. Hartree-Fock-Bogoliubov
calculations for the isotopic chain Sn are presented for
demonstration purposes.Comment: 12 pages, 5 figure
Self-energy corrections to anisotropic Fermi surfaces
The electron-electron interactions affect the low-energy excitations of an
electronic system and induce deformations of the Fermi surface. These effects
are especially important in anisotropic materials with strong correlations,
such as copper oxides superconductors or ruthenates. Here we analyze the
deformations produced by electronic correlations in the Fermi surface of
anisotropic two-dimensional systems, treating the regular and singular regions
of the Fermi surface on the same footing. Simple analytical expressions are
obtained for the corrections, based on local features of the Fermi surface. It
is shown that, even for weak local interactions, the behavior of the
self-energy is non trivial, showing a momentum dependence and a self-consistent
interplay with the Fermi surface topology. Results are compared to experimental
observations and to other theoretical results.Comment: 13 pages, 10 figure
Nature of Decoupling in the Mixed Phase of Extremely Type-II Layered Superconductors
The uniformly frustrated layered XY model is analyzed in its Villain form. A
decouple pancake vortex liquid phase is identified. It is bounded by both
first-order and second-order decoupling lines in the magnetic field versus
temperature plane. These transitions, respectively, can account for the
flux-lattice melting and for the flux-lattice depinning observed in the mixed
phase of clean high-temperature superconductors.Comment: 11 pages of PLAIN TeX, 1 postscript figure, published version, many
change
Friedel Oscillations and Charge-density Waves Pinning in Quasi-one-dimensional Conductors: An X-ray Access
We present an x-ray diffraction study of the Vanadium-doped blue bronze
K0.3(Mo0.972V0.028)O3. At low temperature, we have observed both an intensity
asymmetry of the +-2kF satellite reflections relative to the pure compound, and
a profile asymmetry of each satellite reflections. We show that the profile
asymmetry is due to Friedel oscillation around the V substituant and that the
intensity asymmetry is related to the charge density wave (CDW) pinning. These
two effects, intensity and profile asymmetries, gives for the first time access
to the local properties of CDW in disordered systems, including the pinning and
even the phase shift of FOs.Comment: 4 pages REVTEX, 5 figure
Friedel oscillations of Kondo impurities: A comparison
Recently Affleck et al. derived the existence of Friedel oscillations in the
presence of a Kondo impurity. They supported their analytic derivation by
numerical calculations using Wilson's renormalization approach (NRG). In this
paper the size of the Friedel oscillations is calculated with the FAIR method
(Friedel Artificially Inserted Resonance) which has been recently developed.
The results of NRG and FAIR are compared. The development of Friedel
oscillations with a phase shift of pi/2 outside of the Kondo radius is
confirmed
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