5,620 research outputs found
Total focussing method for volumetric imaging in immersion non destructive evaluation
This paper describes the use of a 550 (25x22) element 2MHz 2D piezoelectric composite array in immersion mode to image an aluminum test block containing a collection of artificial defects. The defects included a 1mm diameter side-drilled hole, a collection of 1mm slot defects with varying degrees of skew to the normal and a flat bottomed hole. The data collection was carried out using the full matrix capture; a scanning procedure was developed to allow the operation of the large element count array through a conventional 64-channel phased array controller. A 3D TFM algorithm capable of imaging in a dual media environment was implemented in MATLAB for the offline processing the raw scan data. This algorithm facilitates the creation of 3D images of defects while accounting for refraction effects at material boundaries. In each of the test samples interrogated the defects, and their spatial position, are readily identified using TFM. Defect directional information has been characterized using VTFM for defect exhibiting angles up to and including 45o of skew
A numerical investigation on the vortex formation and flow separation of the oscillatory flow in jet pumps
A two-dimensional computational fluid dynamics model is used to predict the
oscillatory flow through a tapered cylindrical tube section (jet pump) placed
in a larger outer tube. Due to the shape of the jet pump, there will exist an
asymmetry in the hydrodynamic end effects which will cause a time-averaged
pressure drop to occur that can be used to cancel Gedeon streaming in a
closed-loop thermoacoustic device. The performance of two jet pump geometries
with different taper angles is investigated. A specific time-domain impedance
boundary condition is implemented in order to simulate traveling acoustic wave
conditions. It is shown that by scaling the acoustic displacement amplitude to
the jet pump dimensions, similar minor losses are observed independent of the
jet pump geometry. Four different flow regimes are distinguished and the
observed flow phenomena are related to the jet pump performance. The simulated
jet pump performance is compared to an existing quasi-steady approximation
which is shown to only be valid for small displacement amplitudes compared to
the jet pump length.Comment: The following article has been accepted by the Journal of the
Acoustical Society of America. After it is published, it will be found at:
http://scitation.aip.org/JAS
Saturated gain spectrum of VECSELs determined by transient measurement of lasing onset
We describe time-resolved measurements of the evolution of the spectrum of radiation emitted by an optically-pumped continuous-wave InGaAs-GaAs quantum well laser, recorded as lasing builds up from noise to steady state. We extract a fitting parameter corresponding to the gain dispersion of the parabolic spectrum equal to ?79 ± 30 fs2 and ?36 ± 6 fs2 for a resonant and anti-resonant structure, respectively. Furthermore the recorded evolution of the spectrum allows for the calculation of an effective FWHM gain bandwidth for each structure, of 11 nm and 18 nm, respectively
Jet pumps for thermoacoustic applications: design guidelines based on a numerical parameter study
The oscillatory flow through tapered cylindrical tube sections (jet pumps) is
characterized by a numerical parameter study. The shape of a jet pump results
in asymmetric hydrodynamic end effects which cause a time-averaged pressure
drop to occur under oscillatory flow conditions. Hence, jet pumps are used as
streaming suppressors in closed-loop thermoacoustic devices. A two-dimensional
axisymmetric computational fluid dynamics model is used to calculate the
performance of a large number of conical jet pump geometries in terms of
time-averaged pressure drop and acoustic power dissipation. The investigated
geometrical parameters include the jet pump length, taper angle, waist diameter
and waist curvature. In correspondence with previous work, four flow regimes
are observed which characterize the jet pump performance and dimensionless
parameters are introduced to scale the performance of the various jet pump
geometries. The simulation results are compared to an existing quasi-steady
theory and it is shown that this theory is only applicable in a small operation
region. Based on the scaling parameters, an optimum operation region is defined
and design guidelines are proposed which can be directly used for future jet
pump design.Comment: The following article has been accepted by the Journal of the
Acoustical Society of America. After it is published, it will be found at
http://scitation.aip.org/JAS
Study of techniques and applications of satellite imagery to small scale mapping
There are no author-identified significant results in this report
Narratives of therapeutic art-making in the context of marital breakdown: Older women reflect on a significant mid-life experience
This paper explores the narratives of three women aged 65-72 years. They reflected on an episode of therapeutic art-making in midlife, which addressed depression associated with marital crisis and breakdown. The narrative analysis focused upon on the ways in which participants narrated the events leading up to their participation in therapeutic art-making; the aspects of therapeutic art-making that continued to be given significance; the characters given primacy in the stories they told about their journey through therapy and marital breakdown; meanings, symbolic and otherwise, that participants ascribed to their artwork made during this turning point in their lives; and aspects of the narratives that conveyed present-day identities and artistic endeavors. The narratives revealed the complexity of the journey through marital breakdown and depression into health, and showed that therapeutic art-making could best be understood, not as a stand-alone experience, but as given meaning within the context of wider personal and social resources. Participants looked back on therapeutic art-making that occurred two decades earlier and still described this as a significant turning point in their personal development. Art as an adjunct to counselling/therapy was not only symbolically self-expressive but provided opportunity for decision-making, agency and a reformulated self-image
Study of the relationship between solar activity and terrestrial weather
Evidence for some connection between weather and solar related phenomena is presented. Historical data of world wide temperature variations with relationship to change in solar luminosity are examined. Several test methods for estimating the statistical significance of such phenomena are discussed in detail
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