15,121 research outputs found
High-performance light-weight electrodes for hydrogen-oxygen fuel cells
High performance light weight electrodes for hydrogen oxygen fuel cell
Numerical solution of the time-dependent compressible Navier-Stokes equations in inlet regions
The results of a study to determine the effects of compressibility on the viscous flow through channels that have straight, parallel walls are presented. Two channel configurations are considered, the flow between two semi-infinite flat plates with uniform flow prescribed at the inlet plane and a cascade of semi-infinite flat plates with uniform flow introduced upstream. The flow field is modeled by using the time dependent, compressible Navier-Stokes equations. Time dependent solutions are obtained by using an explicit finite difference technique which advances the pressure on near field subsonic boundaries such that accurate steady state solutions are obtained. Steady state results at Reynolds number 20 and 150 are presented for Mach numbers between 0.09 and 0.36 and compared with the incompressible solutions of previous studies
Simulations of Spinodal Nucleation in Systems with Elastic Interactions
Systems with long-range interactions quenched into a metastable state near
the pseudospinodal exhibit nucleation that is qualitatively different than the
classical nucleation observed near the coexistence curve. We have observed
nucleation droplets in our Langevin simulations of a two-dimensional model of
martensitic transformations and have determined that the structure of the
nucleating droplet differs from the stable martensite structure. Our results,
together with experimental measurements of the phonon dispersion curve, allow
us to predict the nature of the droplet. These results have implications for
nucleation in many solid-solid transitions and the structure of the final
state
Comparison of Measured and Calculated Specific Resistances of Pd/Pt Interfaces
We compare specific resistances (AR equals area A times resistance R) of
sputtered Pd/Pt interfaces measured in two different ways with
no-free-parameter calculations. One way gives 2AR(Pd/Pt) of 0.29 (0.03)
fohm-m(2) and the other 0.17 (0.13) fohm-m(2). From these we derive a best
estimate of 2AR(Pd/Pt) of 0.28 (0.06) fohm-m(2), which overlaps with
no-free-parameter calculations: 2AR(predicted) of 0.30 (0.04) fohm-m(2) for
flat, perfect interfaces, or 0.33 (0.04) fohm-m(2) for interfaces composed of 2
monolayers of a 50percent-50percent PdPt alloy. These results support three
prior examples of agreement between calculations and measurements for pairs of
metals having the same crystal structure and the same lattice parameter to
within 1 percent. We also estimate the spin-flipping probability at Pd/Pt
interfaces as 0.13 (0.08).Comment: 3 pages, 3 figures, submitted for publication New version has
corrected value of delta(Pd/Pt
Unsupervised decoding of long-term, naturalistic human neural recordings with automated video and audio annotations
Fully automated decoding of human activities and intentions from direct
neural recordings is a tantalizing challenge in brain-computer interfacing.
Most ongoing efforts have focused on training decoders on specific, stereotyped
tasks in laboratory settings. Implementing brain-computer interfaces (BCIs) in
natural settings requires adaptive strategies and scalable algorithms that
require minimal supervision. Here we propose an unsupervised approach to
decoding neural states from human brain recordings acquired in a naturalistic
context. We demonstrate our approach on continuous long-term
electrocorticographic (ECoG) data recorded over many days from the brain
surface of subjects in a hospital room, with simultaneous audio and video
recordings. We first discovered clusters in high-dimensional ECoG recordings
and then annotated coherent clusters using speech and movement labels extracted
automatically from audio and video recordings. To our knowledge, this
represents the first time techniques from computer vision and speech processing
have been used for natural ECoG decoding. Our results show that our
unsupervised approach can discover distinct behaviors from ECoG data, including
moving, speaking and resting. We verify the accuracy of our approach by
comparing to manual annotations. Projecting the discovered cluster centers back
onto the brain, this technique opens the door to automated functional brain
mapping in natural settings
Charge Exchange Spectra of Hydrogenic and He-like Iron
We present H-like Fe XXVI and He-like Fe XXV charge-exchange spectra
resulting from collisions of highly charged iron with N2 gas at an energy of 10
eV/amu in an electron beam ion trap. Although individual high-n emission lines
are not resolved in our measurements, we observe that the most likely level for
Fe25+ --> Fe24+ electron capture is n~9, in line with expectations, while the
most likely value for Fe26+ --> Fe25+ charge exchange is significantly higher.
In the Fe XXV spectrum, the K-alpha emission feature dominates, whether
produced via charge exchange or collisional excitation. The K-alpha centroid is
lower in energy for the former case than the latter (6666 versus 6685 eV,
respectively), as expected because of the strong enhancement of emission from
the forbidden and intercombination lines, relative to the resonance line, in
charge-exchange spectra. In contrast, the Fe XXVI high-n Lyman lines have a
summed intensity greater than that of Ly-alpha, and are substantially stronger
than predicted from theoretical calculations of charge exchange with atomic H.
We conclude that the angular momentum distribution resulting from electron
capture using a multi-electron target gas is significantly different from that
obtained with H, resulting in the observed high-n enhancement. A discussion is
presented of the relevance of our results to studies of diffuse Fe emission in
the Galactic Center and Galactic Ridge, particularly with ASTRO-E2/Suzaku.Comment: 16 pages, 4 figures (3 color), accepted by Ap
Weather, Crime, and Mental Illness
ABSTRACT - A simple count of disturbed incidents in the mentally ill and total radio transmissions of the Minneapolis Police Departmenf were collected daily over a six-month period. These were correlated with calendar time, temperature, humidity, and barometric pressure for the same period. Separate comparisons were made of all these measures for December 1959 with those of other Decembers. All the weather variables correlated linearly and significantly with the behavior v.ariables; temperature and humidity, positively; barometric pressure negatively. Calendar time for the half year correlated linearly and negatively. December 1959 had a higher crime and mental disturbance rate than other Decembers; this was accompanied by higher temperature and humidity
Nuclear forward scattering in particulate matter: dependence of lineshape on particle size distribution
In synchrotron Moessbauer spectroscopy, the nuclear exciton polariton
manifests itself in the lineshape of the spectra of nuclear forward scattering
(NFS) Fourier-transformed from time domain to frequency domain. This lineshape
is generally described by the convolution of two intensity factors. One of them
is Lorentzian related to free decay. We derived the expressions for the second
factor related to Frenkel exciton polariton effects at propagation of
synchrotron radiation in Moessbauer media. Parameters of this Frenkelian shape
depend on the spatial configuration of Moessbauer media. In a layer of uniform
thickness, this factor is found to be a simple hypergeometric function. Next,
we consider the particles spread over a 2D surface or diluted in non-Moessbauer
media to exclude an overlap of ray shadows by different particles. Deconvolving
the purely polaritonic component of linewidths is suggested as a simple
procedure sharpening the experimental NFS spectra in frequency domain. The
lineshapes in these sharpened spectra are theoretically expressed via the
parameters of the particle size distributions (PSD). Then, these parameters are
determined through least-squares fitting of the line shapes.Comment: 13 pages, 12 figure
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