37,863 research outputs found
The NWRA Classification Infrastructure: Description and Extension to the Discriminant Analysis Flare Forecasting System (DAFFS)
A classification infrastructure built upon Discriminant Analysis has been
developed at NorthWest Research Associates for examining the statistical
differences between samples of two known populations. Originating to examine
the physical differences between flare-quiet and flare-imminent solar active
regions, we describe herein some details of the infrastructure including:
parametrization of large datasets, schemes for handling "null" and "bad" data
in multi-parameter analysis, application of non-parametric multi-dimensional
Discriminant Analysis, an extension through Bayes' theorem to probabilistic
classification, and methods invoked for evaluating classifier success. The
classifier infrastructure is applicable to a wide range of scientific questions
in solar physics. We demonstrate its application to the question of
distinguishing flare-imminent from flare-quiet solar active regions, updating
results from the original publications that were based on different data and
much smaller sample sizes. Finally, as a demonstration of "Research to
Operations" efforts in the space-weather forecasting context, we present the
Discriminant Analysis Flare Forecasting System (DAFFS), a near-real-time
operationally-running solar flare forecasting tool that was developed from the
research-directed infrastructure.Comment: J. Space Weather Space Climate: Accepted / in press; access
supplementary materials through journal; some figures are less than full
resolution for arXi
Segregation by membrane rigidity in flowing binary suspensions of elastic capsules
Spatial segregation in the wall normal direction is investigated in
suspensions containing a binary mixture of Neo-Hookean capsules subjected to
pressure driven flow in a planar slit. The two components of the binary mixture
have unequal membrane rigidities. The problem is studied numerically using an
accelerated implementation of the boundary integral method. The effect of a
variety of parameters was investigated, including the capillary number,
rigidity ratio between the two species, volume fraction, confinement ratio, and
the number fraction of the more floppy particle in the mixture. It was
observed that in suspensions of pure species, the mean wall normal positions of
the stiff and the floppy particles are comparable. In mixtures, however, the
stiff particles were found to be increasingly displaced towards the walls with
increasing , while the floppy particles were found to increasingly
accumulate near the centerline with decreasing . The origins of this
segregation is traced to the effect of the number fraction on the
localization of the stiff and the floppy particles in the near wall region --
the probability of escape of a stiff particle from the near wall region to the
interior is greatly reduced with increasing , while the exact opposite
trend is observed for a floppy particle with decreasing . Simple model
studies on heterogeneous pair collisions involving a stiff and a floppy
particle mechanistically explain this observation. The key result in these
studies is that the stiff particle experiences much larger cross-stream
displacement in heterogeneous collisions than the floppy particle. A unified
mechanism incorporating the wall-induced migration of deformable particles and
the particle fluxes associated with heterogeneous and homogeneous pair
collisions is presented.Comment: 19 Pages, 16 Figure
Achieving Consistent Doppler Measurements from SDO/HMI Vector Field Inversions
NASA's Solar Dynamics Observatory is delivering vector field observations of
the full solar disk with unprecedented temporal and spatial resolution;
however, the satellite is in a highly inclined geostationary orbit. The
relative spacecraft-Sun velocity varies by ~km/s over a day which
introduces major orbital artifacts in the Helioseismic Magnetic Imager data. We
demonstrate that the orbital artifacts contaminate all spatial and temporal
scales in the data. We describe a newly-developed three stage procedure for
mitigating these artifacts in the Doppler data derived from the Milne-Eddington
inversions in the HMI Pipeline. This procedure was applied to full disk images
of AR11084 to produce consistent Dopplergrams. The data adjustments reduce the
power in the orbital artifacts by 31dB. Furthermore, we analyze in detail the
corrected images and show that our procedure greatly improve the temporal and
spectral properties of the data without adding any new artifacts. We conclude
that this new and easily implemented procedure makes a dramatic improvement in
the consistency of the HMI data and in its usefulness for precision scientific
studies.Comment: 58 pages, 19 figures, submitted to Ap
Energy-level pinning and the 0.7 spin state in one dimension: GaAs quantum wires studied using finite-bias spectroscopy
We study the effects of electron-electron interactions on the energy levels
of GaAs quantum wires (QWs) using finite-bias spectroscopy. We probe the energy
spectrum at zero magnetic field, and at crossings of opposite-spin-levels in
high in-plane magnetic field B. Our results constitute direct evidence that
spin-up (higher energy) levels pin to the chemical potential as they populate.
We also show that spin-up and spin-down levels abruptly rearrange at the
crossing in a manner resembling the magnetic phase transitions predicted to
occur at crossings of Landau levels. This rearranging and pinning of subbands
provides a phenomenological explanation for the 0.7 structure, a
one-dimensional (1D) nanomagnetic state, and its high-B variants.Comment: 6 pages, 4 figure
Dynamics of a two-level system strongly coupled to a high-frequency quantum oscillator
Recent experiments on quantum behavior in microfabricated solid-state systems
suggest tantalizing connections to quantum optics. Several of these experiments
address the prototypical problem of cavity quantum electrodynamics: a two-level
system coupled to a quantum harmonic oscillator. Such devices may allow the
exploration of parameter regimes outside the near-resonance and weak-coupling
assumptions of the ubiquitous rotating-wave approximation (RWA), necessitating
other theoretical approaches. One such approach is an adiabatic approximation
in the limit that the oscillator frequency is much larger than the
characteristic frequency of the two-level system. A derivation of the
approximation is presented and the time evolution of the two-level-system
occupation probability is calculated using both thermal- and coherent-state
initial conditions for the oscillator. Closed-form evaluation of the time
evolution in the weak-coupling limit provides insight into the differences
between the thermal- and coherent-state models. Finally, potential experimental
observations in solid-state systems, particularly the Cooper-pair
box--nanomechanical resonator system, are discussed and found to be promising.Comment: 16 pages, 11 figures; revised abstract; some text revisions; added
two figures and combined others; added references. Submitted to Phys. Rev.
Minimax studies
Effect of nonzero initial conditions on selection of minimax controllers for large launch vehicles and extremal bounded amplitude bounded rate inputs to linear system
Coarse Brownian Dynamics for Nematic Liquid Crystals: Bifurcation Diagrams via Stochastic Simulation
We demonstrate how time-integration of stochastic differential equations
(i.e. Brownian dynamics simulations) can be combined with continuum numerical
bifurcation analysis techniques to analyze the dynamics of liquid crystalline
polymers (LCPs). Sidestepping the necessity of obtaining explicit closures, the
approach analyzes the (unavailable in closed form) coarse macroscopic
equations, estimating the necessary quantities through appropriately
initialized, short bursts of Brownian dynamics simulation. Through this
approach, both stable and unstable branches of the equilibrium bifurcation
diagram are obtained for the Doi model of LCPs and their coarse stability is
estimated. Additional macroscopic computational tasks enabled through this
approach, such as coarse projective integration and coarse stabilizing
controller design, are also demonstrated
Transport airplane flight deck development survey and analysis: Report and recommendations
Results of a survey and analysis of research and development work related to improving transport airplane flight deck equipment and aircrew performance is reported. Research and development related to flight deck advancement in general, as well as that concerned directly with terminal area operations, is described and discussed
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