363 research outputs found
Feature combinations and the Bhattacharyya criterion
A procedure for calculating a kxn rank k matrix B for data compression using the Bhattacharyya bound on the probability of error and an iterative construction using Householder transformation was developed. Two sets of remotely sensed agricultural data are used to demonstrate the application of the procedure. The results of the applications gave some indication of the extent to which the Bhattacharyya bound on the probability of error is affected by such transformations for multivariate normal populations
Multi-electrode nerve cuff recording - model analysis of the effects of finite cuff length
The effect of finite cuff length on the signals recorded by electrodes at different positions along the nerve was analysed in a model study. Relations were derived using a one-dimensional model. These were evaluated in a more realistic axially symmetric 3D model. This evaluation indicated that the cuff appeared shorter because of edge effects at the beginning and end of the cuff. The method for velocity selective filtering introduced by Donaldson was subsequently analysed. In this method, velocity selective filtering is achieved by summing the signals of subsequent tripoles after applying time shifts tuned to a certain conduction velocity. It was also found that the optimum electrode distance for a given cuff length for maximum summed RMS of symmetrical tripoles in the cuff is larger than when evaluating peak-peak amplitudes of single fibre action potentials. Velocity selective filtering yields better selectivity when using symmetrical tripoles, but may yield larger signal RMS when using the wider asymmetrical tripoles, potentially allowing for shorter cuffs. It is speculated that application of a multi-electrode reference may improve velocity selectivity for asymmetrical tripoles
Optical and evaporative cooling of cesium atoms in the gravito-optical surface trap
We report on cooling of an atomic cesium gas closely above an evanescent-wave
atom mirror. At high densitities, optical cooling based on inelastic
reflections is found to be limited by a density-dependent excess temperature
and trap loss due to ultracold collisions involving repulsive molecular states.
Nevertheless, very good starting conditions for subsequent evaporative cooling
are obtained. Our first evaporation experiments show a temperature reduction
from 10muK down to 300nK along with a gain in phase-space density of almost two
orders of magnitude.Comment: 8 pages, 6 figures, submitted to Journal of Modern Optics, special
issue "Fundamentals of Quantum Optics V", edited by F. Ehlotzk
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LiDAR mapping of tidal marshes for ecogeomorphological modelling in the TIDE project
The European research project TIDE (Tidal Inlets Dynamics and Environment) is developing and validating coupled models describing the morphological, biological and ecological evolution of tidal environments. The interactions between the physical and biological processes occurring in these regions requires that the system be studied as a whole rather than as separate parts. Extensive use of remote sensing including LiDAR is being made to provide validation data for the modelling.
This paper describes the different uses of LiDAR within the project and their relevance to the TIDE science objectives. LiDAR data have been acquired from three different environments, the Venice Lagoon in Italy, Morecambe Bay in England, and the Eden estuary in Scotland. LiDAR accuracy at each site has been evaluated using ground reference data acquired with differential GPS. A semi-automatic technique has been developed to extract tidal channel networks from LiDAR data either used alone or fused with aerial photography. While the resulting networks may require some correction, the procedure does allow network extraction over large areas using objective criteria and reduces fieldwork requirements. The networks extracted may subsequently be used in geomorphological analyses, for example to describe the drainage patterns induced by networks and to examine the rate of change of networks. Estimation of the heights of the low and sparse vegetation on marshes is being investigated by analysis of the statistical distribution of the measured LiDAR heights. Species having different mean heights may be separated using the first-order moments of the height distribution
Driving the atom by atomic fluorescence: analytic results for the power and noise spectra
We study how the spectral properties of resonance fluorescence propagate
through a two-atom system. Within the weak-driving-field approximation we find
that, as we go from one atom to the next, the power spectrum exhibits both
sub-natural linewidth narrowing and large asymmetries while the spectrum of
squeezing narrows but remains otherwise unchanged. Analytical results for the
observed spectral features of the fluorescence are provided and their origin is
thoroughly discussed.Comment: 13 pages, 5 figures; to be published in Phys. Rev. A Changed title
and conten
Underwater Thruster Saturation Detection and Prevention Considering Battery Voltage Sag
ABSTRACT This paper reports on the development of a control module that detects and effectively prevents thruster saturation for an autonomous underwater vehicle (AUV). A model has been developed to approximate the maximum available thrust, per thruster, as a function of the battery voltage sag. A thruster would be considered to be in saturation if its reference input exceeds its particular output limit. This ratio can be expressed as a scalar value, which can be used to adjust the reference thrust vector that is fed to the thruster control system. This approach can minimize the total error vector in the vehicle kinematics
Quantum-gravity-motivated Lorentz-symmetry tests with laser interferometers
We consider the implications for laser interferometry of the
quantum-gravity-motivated modifications in the laws of particle propagation,
which are presently being considered in attempts to explain puzzling
observations of ultra-high-energy cosmic rays. We show that there are
interferometric setups in which the Planck-scale effect on propagation leads to
a characteristic signature. A naive estimate is encouraging with respect to the
possibility of achieving Planck-scale sensitivity, but we also point out some
severe technological challenges which would have to be overcome in order to
achieve this sensitivity.Comment: 17 pages, 3 figure
Using atomic interference to probe atom-surface interaction
We show that atomic interference in the reflection from two suitably
polarized evanescent waves is sensitive to retardation effects in the
atom-surface interaction for specific experimental parameters. We study the
limit of short and long atomic de Broglie wavelength. The former case is
analyzed in the semiclassical approximation (Landau-Zener model). The latter
represents a quantum regime and is analyzed by solving numerically the
associated coupled Schroedinger equations. We consider a specific experimental
scheme and show the results for rubidium (short wavelength) and the much
lighter meta-stable helium atom (long wavelength). The merits of each case are
then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX
sourc
A new Doubly Special Relativity theory from a quantum Weyl-Poincare algebra
A mass-like quantum Weyl-Poincare algebra is proposed to describe, after the
identification of the deformation parameter with the Planck length, a new
relativistic theory with two observer-independent scales (or DSR theory).
Deformed momentum representation, finite boost transformations, range of
rapidity, energy and momentum, as well as position and velocity operators are
explicitly studied and compared with those of previous DSR theories based on
kappa-Poincare algebra. The main novelties of the DSR theory here presented are
the new features of momentum saturation and a new type of deformed position
operators.Comment: 13 pages, LaTeX; some references and figures added, and terminology
is more precis
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