9,839 research outputs found
Mass spectrometry in structural and stereochemical problems. Part 178 - The electron-impact promoted fragmentation of 1,2-cyclohexene oxide
Mass spectra of 1,2-cyclohexane oxide and three deuterium labeled analog
Parallel algorithm for determining motion vectors in ice floe images by matching edge features
A parallel algorithm is described to determine motion vectors of ice floes using time sequences of images of the Arctic ocean obtained from the Synthetic Aperture Radar (SAR) instrument flown on-board the SEASAT spacecraft. Researchers describe a parallel algorithm which is implemented on the MPP for locating corresponding objects based on their translationally and rotationally invariant features. The algorithm first approximates the edges in the images by polygons or sets of connected straight-line segments. Each such edge structure is then reduced to a seed point. Associated with each seed point are the descriptions (lengths, orientations and sequence numbers) of the lines constituting the corresponding edge structure. A parallel matching algorithm is used to match packed arrays of such descriptions to identify corresponding seed points in the two images. The matching algorithm is designed such that fragmentation and merging of ice floes are taken into account by accepting partial matches. The technique has been demonstrated to work on synthetic test patterns and real image pairs from SEASAT in times ranging from .5 to 0.7 seconds for 128 x 128 images
Motion detection in astronomical and ice floe images
Two approaches are presented for establishing correspondence between small areas in pairs of successive images for motion detection. The first one, based on local correlation, is used on a pair of successive Voyager images of the Jupiter which differ mainly in locally variable translations. This algorithm is implemented on a sequential machine (VAX 780) as well as the Massively Parallel Processor (MPP). In the case of the sequential algorithm, the pixel correspondence or match is computed on a sparse grid of points using nonoverlapping windows (typically 11 x 11) by local correlations over a predetermined search area. The displacement of the corresponding pixels in the two images is called the disparities to cubic surfaces. The disparities at points where the error between the computed values and the surface values exceeds a particular threshold are replaced by the surface values. A bilinear interpolation is then used to estimate disparities at all other pixels between the grid points. When this algorithm was applied at the red spot in the Jupiter image, the rotating velocity field of the storm was determined. The second method of motion detection is applicable to pairs of images in which corresponding areas can experience considerable translation as well as rotation
ECoG-based short-range recurrent stimulation techniques to stabilize tissue at risk of progressive damage: Theory based on clinical observations
We introduce theoretical concepts based on chaos control to stabilize in acute stroke the tissue at risk of progressive damage by preventing adverse effects of waves of mass neuronal depolarization. Moreover, we present clinical electrocorticography (ECoG) recordings of relevant signals suggested for the feedback control. The recordings are performed in combination with novel subdural opto-electrode technology for simultaneous laser-Doppler flowmetry in patients with aneurysmal subarachnoid haemorrhage (aSAH). In aSAH patients waves of spreading depolarization (SD) have a high incidence and cause hypoxia in tissue at risk, and, importantly, the haemodynamic response is the inverse of that seen in healthy tissue. In previous clinical studies, clusters of prolonged SDs have been measured in aSAH patients in close proximity to structural brain damage as assessed by neuroimaging, and, in theoretical studies, a mechanism was presented, suggesting how a failure of internal feedback could be a putative mechanism of such SD cluster patterns in acute stroke. 

This failing internal feedback control is now suggested to be replaced by ECoG-based short-range recurrent functional stimulation that initiates the normal hyperperfusion haemodynamic response in a demand-controlled way and stabilizes the tissue at risk during the critical phase of SD passage. The suggested method has three key features: (i) it is short-range, i.e., in the order of the distance of the ECoG electrode strip, (ii) it is demand-controlled, and (iii) it uses no prior knowledge of the target state, in particular, it adapts to conditions in the healthy physiological range. On-demand type stimulation provides minimal invasive feedback as the control force is off when the target state is reached, i.e., the tissue at risk is without SD or it is back to the physiological range (out of risk). These last two features (ii-iii) are shared with classical methods of chaos control, where major progress was made in the last years with respect to extensions for spatio-temporal wave patterns. A detailed bifurcation analysis of the nonlinear model is presented, in particular, the SD cluster forming cortical state is suggested to be caused by a delay-induced saddle-node bifurcation.

Prospects For Detecting Dark Matter With GLAST In Light Of The WMAP Haze
Observations by the WMAP experiment have identified an excess of microwave
emission from the center of the Milky Way. It has previously been shown that
this "WMAP Haze" could be synchrotron emission from relativistic electrons and
positrons produced in the annihilations of dark matter particles. In
particular, the intensity, spectrum and angular distribution of the WMAP Haze
is consistent with an electroweak scale dark matter particle (such as a
supersymmetric neutralino or Kaluza-Klein dark matter in models with universal
extra dimensions) annihilating with a cross section on the order of sigma
v~3x10^-26 cm^3/s and distributed with a cusped halo profile. No further exotic
astrophysical or annihilation boost factors are required. If dark matter
annihilations are in fact responsible for the observed Haze, then other
annihilation products will also be produced, including gamma rays. In this
article, we study the prospects for the GLAST satellite to detect gamma rays
from dark matter annihilations in the Galactic Center region in this scenario.
We find that by studying only the inner 0.1 degrees around the Galactic Center,
GLAST will be able to detect dark matter annihilating to heavy quarks or gauge
bosons over astrophysical backgrounds with 5sigma (3sigma) significance if they
are lighter than approximately 320-500 GeV (500-750 GeV). If the angular window
is broadened to study the dark matter halo profile's angular extension (while
simultaneously reducing the astrophysical backgrounds), WIMPs as heavy as
several TeV can be identified by GLAST with high significance. Only if the dark
matter particles annihilate mostly to electrons or muons will GLAST be unable
to identify the gamma ray spectrum associated with the WMAP Haze.Comment: 10 pages, 6 figure
Simulations of cosmic ray propagation
We review numerical methods for simulations of cosmic ray (CR) propagation on
galactic and larger scales. We present the development of algorithms designed
for phenomenological and self-consistent models of CR propagation in kinetic
description based on numerical solutions of the Fokker-Planck equation. The
phenomenological models assume a stationary structure of the galactic
interstellar medium and incorporate diffusion of particles in physical and
momentum space together with advection, spallation, production of secondaries
and various radiation mechanisms. The self-consistent propagation models of CRs
include the dynamical coupling of the CR population to the thermal plasma. The
CR transport equation is discretized and solved numerically together with the
set of magneto-hydrodynamic (MHD) equations in various approaches treating the
CR population as a separate relativistic fluid within the two-fluid approach or
as a spectrally resolved population of particles evolving in physical and
momentum space. The relevant processes incorporated in self-consistent models
include advection, diffusion and streaming well as adiabatic compression and
several radiative loss mechanisms.
We discuss applications of the numerical models for the interpretation of CR
data collected by various instruments. We present example models of
astrophysical processes influencing galactic evolution such as galactic winds,
the amplification of large-scale magnetic fields and instabilities of the
interstellar medium.Comment: 99 pages, 13 figures, to be published in the Living Reviews of
Computational Astrophysic
Diffuse Gamma Rays: Galactic and Extragalactic Diffuse Emission
"Diffuse" gamma rays consist of several components: truly diffuse emission
from the interstellar medium, the extragalactic background, whose origin is not
firmly established yet, and the contribution from unresolved and faint Galactic
point sources. One approach to unravel these components is to study the diffuse
emission from the interstellar medium, which traces the interactions of high
energy particles with interstellar gas and radiation fields. Because of its
origin such emission is potentially able to reveal much about the sources and
propagation of cosmic rays. The extragalactic background, if reliably
determined, can be used in cosmological and blazar studies. Studying the
derived "average" spectrum of faint Galactic sources may be able to give a clue
to the nature of the emitting objects.Comment: 32 pages, 28 figures, kapproc.cls. Chapter to the book "Cosmic
Gamma-Ray Sources," to be published by Kluwer ASSL Series, Edited by K. S.
Cheng and G. E. Romero. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Recommended from our members
A culture of silence: modes of objectification and the silencing of disabled bodies
Throughout history different practices have attempted to silence the experiences of disabled people. In this paper we explore some of these practices including the medical, familial, and self-subjugating practices English-speaking Canadian polio survivors experienced throughout their lives. We analyze participant’s experiences of silence and silencing through a Foucauldian lens, drawing on the three modes of objectification to explain the institutional and cultural discourses around polio subjects that acted upon and through the polio body to silence it. Participants’ oral history accounts demonstrate how sociocultural and medical practices effectively silenced survivors from speaking about their polio experiences. However, the trope of silence is also uprooted within oral history traditions. We will demonstrate how participants broke their silence and shifted their perspectives on polio and disability, and how this process contributed to their resistance of hegemonic conceptualizations of disability as defective
The Distance to the Soft Gamma Repeater SGR 1627-41
We report millimeter observations of the line of sight to the recently
discovered Soft Gamma Repeater, SGR 1627-41, which has been tentatively
associated with the supernova remnant SNR G337.0-0.1 Among the eight molecular
clouds along the line of sight to SGR 1627-41, we show that SNR G337.0-0.1 is
probably interacting with one of the most massive giant molecular clouds (GMC)
in the Galaxy, at a distance of 11 kpc from the sun. Based on the high
extinction to the persistent X-ray counterpart of SGR 1627-41, we present
evidence for an association of this new SGR with the SNR G337.0-0.1; they both
appear to be located on the near side of the GMC. This is the second SGR
located near an extraordinarily massive GMC. We suggest that SGR 1627-41 is a
neutron star with a high transverse velocity (~ 1,000 \kms) escaping the young
(~ 5,000 years) supernova remnant G337.0-0.1Comment: 17 pages, including 2 figures. Accepted for publication in the
Astrophysical Journal Letter
Propagation of cosmic-ray nucleons in the Galaxy
We describe a method for the numerical computation of the propagation of
primary and secondary nucleons, primary electrons, and secondary positrons and
electrons. Fragmentation and energy losses are computed using realistic
distributions for the interstellar gas and radiation fields, and diffusive
reacceleration is also incorporated. The models are adjusted to agree with the
observed cosmic-ray B/C and 10Be/9Be ratios. Models with diffusion and
convection do not account well for the observed energy dependence of B/C, while
models with reacceleration reproduce this easily. The height of the halo
propagation region is determined, using recent 10Be/9Be measurements, as >4 kpc
for diffusion/convection models and 4-12 kpc for reacceleration models. For
convection models we set an upper limit on the velocity gradient of dV/dz < 7
km/s/kpc. The radial distribution of cosmic-ray sources required is broader
than current estimates of the SNR distribution for all halo sizes. Full details
of the numerical method used to solve the cosmic-ray propagation equation are
given.Comment: 15 pages including 23 ps-figures and 3 tables, latex2e, uses
emulateapj.sty (ver. of 11 May 1998, enclosed), apjfonts.sty, timesfonts.sty.
To be published in ApJ 1998, v.509 (December 10 issue). More details can be
found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.html Some references
are correcte
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