20,575 research outputs found
New camera tube improves ultrasonic inspection system
Electron multiplier, incorporated into the camera tube of an ultrasonic imaging system, improves resolution, effectively shields low level circuits, and provides a high level signal input to the television camera. It is effective for inspection of metallic materials for bonds, voids, and homogeneity
Shock enhancement and control of hypersonic mixing and combustion
The possibility that shock enhanced mixing can
substantially increase the rate of mixing between
coflowing streams of hydrogen and air has been
studied in experimental and computational investigations.
Early numerical computations indicated that
the steady interaction between a weak shock in air
with a coflowing hydrogen jet can be well approximated
by the two-dimensional time-dependent interaction
between a weak shock and an initially circular
region filled with hydrogen imbedded in air. An experimental
investigation of the latter process has been
carned out in the Caltech 17 Inch Shock Tube in experiments
in which the laser induced fluorescence of
byacetyl dye is used as a tracer for the motion of the
helium gas after shock waves have passed across the
helium cylinder. The flow field has also been studied
using an Euler code computation of the flow field.
Both investigations show that the shock impinging
process causes the light gas cylinder to split into two
parts. One of these mixes rapidly with air and the
other forms a stably stratified vortex pair which mixes
more slowly; about 60% of the light gas mixes rapidly
with the ambient fluid. The geometry of the flow field
and the mixing process and scaling parameters are
discussed here. The success of this program encouraged
the exploration of a low drag injection system in
which the basic concept of shock generated streamwise
vorticity could be incorporated in an injector for
a Scramjet combustor at Mach numbers between 5
and 8. The results of a substantial computational
program and a description of the wind tunnel model and preliminary experimental results obtained in the
High Reynolds Number Mach 6 Tunnel at NASA Langley
Research Center are given here
Healthiness from Duality
Healthiness is a good old question in program logics that dates back to
Dijkstra. It asks for an intrinsic characterization of those predicate
transformers which arise as the (backward) interpretation of a certain class of
programs. There are several results known for healthiness conditions: for
deterministic programs, nondeterministic ones, probabilistic ones, etc.
Building upon our previous works on so-called state-and-effect triangles, we
contribute a unified categorical framework for investigating healthiness
conditions. We find the framework to be centered around a dual adjunction
induced by a dualizing object, together with our notion of relative
Eilenberg-Moore algebra playing fundamental roles too. The latter notion seems
interesting in its own right in the context of monads, Lawvere theories and
enriched categories.Comment: 13 pages, Extended version with appendices of a paper accepted to
LICS 201
Accuracy of Approximate Eigenstates
Besides perturbation theory, which requires, of course, the knowledge of the
exact unperturbed solution, variational techniques represent the main tool for
any investigation of the eigenvalue problem of some semibounded operator H in
quantum theory. For a reasonable choice of the employed trial subspace of the
domain of H, the lowest eigenvalues of H usually can be located with acceptable
precision whereas the trial-subspace vectors corresponding to these eigenvalues
approximate, in general, the exact eigenstates of H with much less accuracy.
Accordingly, various measures for the accuracy of the approximate eigenstates
derived by variational techniques are scrutinized. In particular, the matrix
elements of the commutator of the operator H and (suitably chosen) different
operators, with respect to degenerate approximate eigenstates of H obtained by
some variational method, are proposed here as new criteria for the accuracy of
variational eigenstates. These considerations are applied to that Hamiltonian
the eigenvalue problem of which defines the "spinless Salpeter equation." This
(bound-state) wave equation may be regarded as the most straightforward
relativistic generalization of the usual nonrelativistic Schroedinger
formalism, and is frequently used to describe, e.g., spin-averaged mass spectra
of bound states of quarks.Comment: LaTeX, 14 pages, Int. J. Mod. Phys. A (in print); 1 typo correcte
Finite element analysis of gradient coil deformation and vibration in NMR microscopy
Resolution degradation due to gradient coil deformation and vibration in NMR microscopy is investigated using finite element analysis. From the analysis, deformations due to the Lorentz force can be as large as 1-10 μm depending on the gradient strength and coil frame material. Thus, these deformations can be one of the major resolution limiting factors in NMR microscopy. Coil vibration, which depends on the input current waveform and resolution degradation due to time-variant deformation and time-invariant deformation are investigated by numerical simulations
Digital Three-Dimensional Atlas of Quail Development Using High-Resolution MRI
We present an archetypal set of three-dimensional digital atlases of the quail embryo based on microscopic magnetic resonance imaging (µMRI). The atlases are composed of three modules: (1) images of fixed ex ovo quail, ranging in age from embryonic day 5 to 10 (e05 to e10); (2) a coarsely delineated anatomical atlas of the µMRI data; and (3) an organ system–based hierarchical graph linked to the anatomical delineations. The atlas is designed to be accessed using SHIVA, a free Java application. The atlas is extensible and can contain other types of information including anatomical, physiological, and functional descriptors. It can also be linked to online resources and references. This digital atlas provides a framework to place various data types, such as gene expression and cell migration data, within the normal three-dimensional anatomy of the developing quail embryo. This provides a method for the analysis and examination of the spatial relationships among the different types of information within the context of the entire embryo
Pure phase-encoded MRI and classification of solids
Here, the authors combine a pure phase-encoded magnetic resonance imaging (MRI) method with a new tissue-classification technique to make geometric models of a human tooth. They demonstrate the feasibility of three-dimensional imaging of solids using a conventional 11.7-T NMR spectrometer. In solid-state imaging, confounding line-broadening effects are typically eliminated using coherent averaging methods. Instead, the authors circumvent them by detecting the proton signal at a fixed phase-encode time following the radio-frequency excitation. By a judicious choice of the phase-encode time in the MRI protocol, the authors differentiate enamel and dentine sufficiently to successfully apply a new classification algorithm. This tissue-classification algorithm identifies the distribution of different material types, such as enamel and dentine, in volumetric data. In this algorithm, the authors treat a voxel as a volume, not as a single point, and assume that each voxel may contain more than one material. They use the distribution of MR image intensities within each voxel-sized volume to estimate the relative proportion of each material using a probabilistic approach. This combined approach, involving MRI and data classification, is directly applicable to bone imaging and hard-tissue contrast-based modeling of biological solids
Increased cognitive problem reporting after information about chemotherapy-induced cognitive decline:The moderating role of stigma consciousness
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