591 research outputs found
Hot ion plasma heating experiments in SUMMA
Initial results are presented for the hot-ion plasma heating experiments conducted in the new SUMMA (superconducting magnetic mirror apparatus) at NASA Lewis Research Center. A discharge is formed by applying a radially inward dc electric field between cylindrical anodes and hallow cathodes located at the peak of the mirrors. Data were obtained at midplane magnetic field strengths from 1.0 to 3.5 tesla. Charge-exchange neutral particle energy analyzer data were reduced to ion temperatures using a plasma model that included a Maxwellian energy distribution superimposed on an azimuthal drift, finite ion orbits, and radial variations in density and electric field. The best ion temperatures in a helium plasma were 5 keV and in hydrogen the H2(+) and H(+) ions were 1.2 keV and 1 keV respectively. Optical spectroscopy line broadening measurements yielded ion temperatures about 50 percent higher than the charge-exchange neutral particle analyzer results. Spectroscopically obtained electron temperature ranged from 3 to 30 eV. Ion temperature was found to scale roughly linearly with the ratio of power input-to-magnetic field strength, P/B
Quantitative Photo-acoustic Tomography with Partial Data
Photo-acoustic tomography is a newly developed hybrid imaging modality that
combines a high-resolution modality with a high-contrast modality. We analyze
the reconstruction of diffusion and absorption parameters in an elliptic
equation and improve an earlier result of Bal and Uhlmann to the partial date
case. We show that the reconstruction can be uniquely determined by the
knowledge of 4 internal data based on well-chosen partial boundary conditions.
Stability of this reconstruction is ensured if a convexity condition is
satisfied. Similar stability result is obtained without this geometric
constraint if 4n well-chosen partial boundary conditions are available, where
is the spatial dimension. The set of well-chosen boundary measurements is
characterized by some complex geometric optics (CGO) solutions vanishing on a
part of the boundary.Comment: arXiv admin note: text overlap with arXiv:0910.250
Reconstruction of a function from its spherical (circular) means with the centers lying on the surface of certain polygons and polyhedra
We present explicit filtration/backprojection-type formulae for the inversion
of the spherical (circular) mean transform with the centers lying on the
boundary of some polyhedra (or polygons, in 2D). The formulae are derived using
the double layer potentials for the wave equation, for the domains with certain
symmetries. The formulae are valid for a rectangle and certain triangles in 2D,
and for a cuboid, certain right prisms and a certain pyramid in 3D. All the
present inversion formulae yield exact reconstruction within the domain
surrounded by the acquisition surface even in the presence of exterior sources.Comment: 9 figure
Inverse Transport Theory of Photoacoustics
We consider the reconstruction of optical parameters in a domain of interest
from photoacoustic data. Photoacoustic tomography (PAT) radiates high frequency
electromagnetic waves into the domain and measures acoustic signals emitted by
the resulting thermal expansion. Acoustic signals are then used to construct
the deposited thermal energy map. The latter depends on the constitutive
optical parameters in a nontrivial manner. In this paper, we develop and use an
inverse transport theory with internal measurements to extract information on
the optical coefficients from knowledge of the deposited thermal energy map. We
consider the multi-measurement setting in which many electromagnetic radiation
patterns are used to probe the domain of interest. By developing an expansion
of the measurement operator into singular components, we show that the spatial
variations of the intrinsic attenuation and the scattering coefficients may be
reconstructed. We also reconstruct coefficients describing anisotropic
scattering of photons, such as the anisotropy coefficient in a
Henyey-Greenstein phase function model. Finally, we derive stability estimates
for the reconstructions
Inverse Diffusion Theory of Photoacoustics
This paper analyzes the reconstruction of diffusion and absorption parameters
in an elliptic equation from knowledge of internal data. In the application of
photo-acoustics, the internal data are the amount of thermal energy deposited
by high frequency radiation propagating inside a domain of interest. These data
are obtained by solving an inverse wave equation, which is well-studied in the
literature. We show that knowledge of two internal data based on well-chosen
boundary conditions uniquely determines two constitutive parameters in
diffusion and Schroedinger equations. Stability of the reconstruction is
guaranteed under additional geometric constraints of strict convexity. No
geometric constraints are necessary when internal data for well-chosen
boundary conditions are available, where is spatial dimension. The set of
well-chosen boundary conditions is characterized in terms of appropriate
complex geometrical optics (CGO) solutions.Comment: 24 page
Thermoacoustic tomography arising in brain imaging
We study the mathematical model of thermoacoustic and photoacoustic
tomography when the sound speed has a jump across a smooth surface. This models
the change of the sound speed in the skull when trying to image the human
brain. We derive an explicit inversion formula in the form of a convergent
Neumann series under the assumptions that all singularities from the support of
the source reach the boundary
Uniqueness of reconstruction and an inversion procedure for thermoacoustic and photoacoustic tomography
The paper contains a simple approach to reconstruction in Thermoacoustic and
Photoacoustic Tomography. The technique works for any geometry of point
detectors placement and for variable sound speed satisfying a non-trapping
condition. A uniqueness of reconstruction result is also obtained
A mathematical model and inversion procedure for Magneto-Acousto-Electric Tomography (MAET)
Magneto-Acousto-Electric Tomography (MAET), also known as the Lorentz force
or Hall effect tomography, is a novel hybrid modality designed to be a
high-resolution alternative to the unstable Electrical Impedance Tomography. In
the present paper we analyze existing mathematical models of this method, and
propose a general procedure for solving the inverse problem associated with
MAET. It consists in applying to the data one of the algorithms of
Thermo-Acoustic tomography, followed by solving the Neumann problem for the
Laplace equation and the Poisson equation.
For the particular case when the region of interest is a cube, we present an
explicit series solution resulting in a fast reconstruction algorithm. As we
show, both analytically and numerically, MAET is a stable technique yilelding
high-resolution images even in the presence of significant noise in the data
Measurement of the neutrino component of an anti-neutrino beam observed by a non-magnetized detector
Two independent methods are employed to measure the neutrino flux of the
anti-neutrino-mode beam observed by the MiniBooNE detector. The first method
compares data to simulated event rates in a high purity \numu induced
charged-current single \pip (CC1\pip) sample while the second exploits the
difference between the angular distributions of muons created in \numu and
\numub charged-current quasi-elastic (CCQE) interactions. The results from
both analyses indicate the prediction of the neutrino flux component of the
pre-dominately anti-neutrino beam is over-estimated - the CC1\pip analysis
indicates the predicted \numu flux should be scaled by , while
the CCQE angular fit yields . The energy spectrum of the flux
prediction is checked by repeating the analyses in bins of reconstructed
neutrino energy, and the results show that the spectral shape is well modeled.
These analyses are a demonstration of techniques for measuring the neutrino
contamination of anti-neutrino beams observed by future non-magnetized
detectors.Comment: 15 pages, 7 figures, published in Physical Review D, latest version
reflects changes from referee comment
Master Equation Study of Hydrogen Relaxation Using Complete Sets of State-to-state Transition Rates
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97096/1/AIAA2012-362.pd
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