13,672 research outputs found
Data uncertainties in geographic information system
2006-2007 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Calibration of Commercial Eddy Current Instruments for Quantitative NDE
Eddy current testing is typically used in the field to detect defects in a specimen that exceed a set threshold. In most conventional techniques this is done by calibrating the test setup with a reference standard in a way that will correlate the output signal to a known and standard flaw size, such as 10% metal loss due to corrosion thinning in a aircraft skin. However, these standard methods cannot completely characterize a defect in a quantitative manner. In general, reliable quantitative NDE requires quantitative measurements and a theory to interpret them. Theoretical eddy current NDE usually models the test coil’s impedance change (in ohms) as the quantitative measure that varies with specimen and flaw parameters. Specific laboratory instruments such as impedance analyzers are capable of making quantitative measurements that allow researchers to compare experimental data directly to theory. But typical commercial eddy current instruments are not designed to measure probe impedances quantitatively. Rather, they measure relative changes in the coil impedance
Treatment of stiff thoracic scoliosis by thoracoscopic anterior release combined with posterior instrumentation and fusion
Background. Thoracoscopic anterior release has been shown that it can effectively improve spinal flexibility in animal and human cadaveric studies, and has been advocated for use in patients with scoliosis. This prospective case series aims to investigate the improvement of the spinal flexibility and the effectiveness in deformity correction by anterior thoracoscopic release and posterior spinal fusion. Methods. Eleven patients with stiff idiopathic thoracic scoliosis underwent anterior thoracoscopic release followed by posterior instrumentation. The average number of discs excised was five. Spinal flexibility was assessed by the fulcrum bending technique. Cobb angle before and after the anterior release was compared. Results. The patients were followed for an average of 5.6 years (range 2.2 to 8.1 years). Fulcrum bending flexibility was increased from 39% before the thoracoscopic anterior spinal release to 54% after the release. The average Cobb angle before anterior release was 74° on the standing radiograph and 45° with the fulcrum-bending radiograph. This reduced to 34° on the fulcrum-bending radiograph after the release, and highly corresponded to the 31° measured at the post-operative standing radiograph. Conclusion. It was demonstrated in patients with stiff idiopathic thoracic scoliosis that thoracoscopic anterior spinal release can effectively improve the spinal flexibility and increase the correction of the spinal deformity.published_or_final_versio
A Schwarz lemma for K\"ahler affine metrics and the canonical potential of a proper convex cone
This is an account of some aspects of the geometry of K\"ahler affine metrics
based on considering them as smooth metric measure spaces and applying the
comparison geometry of Bakry-Emery Ricci tensors. Such techniques yield a
version for K\"ahler affine metrics of Yau's Schwarz lemma for volume forms. By
a theorem of Cheng and Yau there is a canonical K\"ahler affine Einstein metric
on a proper convex domain, and the Schwarz lemma gives a direct proof of its
uniqueness up to homothety. The potential for this metric is a function
canonically associated to the cone, characterized by the property that its
level sets are hyperbolic affine spheres foliating the cone. It is shown that
for an -dimensional cone a rescaling of the canonical potential is an
-normal barrier function in the sense of interior point methods for conic
programming. It is explained also how to construct from the canonical potential
Monge-Amp\`ere metrics of both Riemannian and Lorentzian signatures, and a mean
curvature zero conical Lagrangian submanifold of the flat para-K\"ahler space.Comment: Minor corrections. References adde
Thickness and Conductivity of Metallic Layers from Pulsed Eddy Current Measurements
Coatings and surface treatments find a wide range of technological applications; they can provide wear resistance, oxidation and corrosion protection, electrical contact or isolation and thermal insulation. Consequently, the ability to determine the thickness of coated metals is important for both process control and in-service inspection of parts. Presently ultrasonic, thermal, and eddy current inspection methods are used, depending on the circumstances. A number of commercial instruments for determining the thickness of nonconducting coatings on metal substrates are based on the fact that the impedance change of the coil decreases exponentially with the distance of the coil from the metal (the lift-off effect). However, these instruments are not suitable for determining the thickness of metal layers on conducting substrates
Power-Law Distributions in a Two-sided Market and Net Neutrality
"Net neutrality" often refers to the policy dictating that an Internet
service provider (ISP) cannot charge content providers (CPs) for delivering
their content to consumers. Many past quantitative models designed to determine
whether net neutrality is a good idea have been rather equivocal in their
conclusions. Here we propose a very simple two-sided market model, in which the
types of the consumers and the CPs are {\em power-law distributed} --- a kind
of distribution known to often arise precisely in connection with
Internet-related phenomena. We derive mostly analytical, closed-form results
for several regimes: (a) Net neutrality, (b) social optimum, (c) maximum
revenue by the ISP, or (d) maximum ISP revenue under quality differentiation.
One unexpected conclusion is that (a) and (b) will differ significantly, unless
average CP productivity is very high
Parity Doubling and the S Parameter Below the Conformal Window
We describe a lattice simulation of the masses and decay constants of the
lowest-lying vector and axial resonances, and the electroweak S parameter, in
an SU(3) gauge theory with and 6 fermions in the fundamental
representation. The spectrum becomes more parity doubled and the S parameter
per electroweak doublet decreases when is increased from 2 to 6,
motivating study of these trends as is increased further, toward the
critical value for transition from confinement to infrared conformality.Comment: 4 pages, 5 figures; to be submitted to PR
Effects of cold water immersion on muscle oxygenation during repeated bouts of fatiguing exercise : a randomized controlled study
2015-2016 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
The particle carriers of field-aligned currents in the Earth's magnetotail during a substorm
Although the particle carriers of field-aligned currents (FACs) in the Earth's magnetotail play an important role in the transfer of momentum and energy between the solar wind, magnetosphere, and ionosphere, the characteristics of the FAC carriers have been poorly understood. Taking advantage of multiinstrument magnetic field and plasma data collected by the four spacecraft of the Cluster constellation as they traversed the northern plasma sheet boundary layer in the magnetotail on 14 September 2004, we identified the species type and energy range of the FAC carriers for the first time. The results indicate that part of tailward FACs is carried by energetic keV ions, which are probably originated from the ionosphere through outflow, and they are not too small (~2 nA/m2) to be ignored. The earthward (tailward) FACs are mainly carried by the dominant tailward (earthward) motion of electrons, and higher-energy electrons (from ~0.5 to 26 keV) are the main carriers
Low Frequency, Pulsed Eddy Currents for Deep Penetration
Using eddy-currents to detect flaws buried deeply in a conducting material has always been a difficult problem. This is due in part to the fact that deep penetration requires low frequencies so that the skin depth is large enough for the eddy-currents to penetrate into the material the depth of the flaw. Also, low frequency eddy-current methods are beset with difficulties in probe design. In order to achieve the large inductance needed to operate at frequencies below 1 kHz, a large number of turns is needed, adding to the resistance of the coil and reducing the energy available to couple into the test piece. One solution is to use pulsed eddy-current methods, which operate efficiently and effectively with low inductance coils.</p
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