A study of model deflection measurement techniques applicable within the national transonic facility

Moire contouring, scanning interferometry, and holographic contouring were examined to determine their practicality and potential to meet performance requirements for a model deflection sensor. The system envisioned is to be nonintrusive, and is to be capable of mapping or contouring the surface of a 1-meter by 1-meter model with a resolution of 50 to 100 points. The available literature was surveyed, and computations and analyses were performed to establish specific performance requirements, as well as the capabilities and limitations of such a sensor within the geometry of the NTF section test section. Of the three systems examined, holographic contouring offers the most promise. Unlike Moire, it is not hampered by limited contour spacing and extraneous fringes. Its transverse resolution can far exceed the limited point sampling resolution of scanning heterodyne interferometry. The availability of the ruby laser as a high power, pulsed, multiple wavelength source makes such a system feasible within the NTF

A pair of gigantic bipolar dust jets close to the solar system

We report the discovery of two adjacent jet candidates with a length of about 9 degrees each -- 10 times longer than the largest known jets -- detected by us on 60 and 100 micron IRAS maps, but not observed at any other wavelength. They are extremely collimated (length-to-width ratios 20--50), curved, knotty, and end in prominent bubbles. Their dust temperatures are 25 K and 30 K, respectively. Both harbour faint stars, one having a high proper motion (0.23 arcsec/yr) and being very red, suggesting a distance of about 60 pc. At this distance, the total mass of both jet candidates is about about 1 solar mass. We suspect that these gigantic (9 pc length respectively) jets are of fossil type and have a common origin, due to the decay of a system of evolved stars. They are the first examples of jets radiating in the far IR and might, because of their closeness, be of interest for further studies of the acceleration and collimation processes of astrophysical jets.Comment: 4 pages, 4 figures in reduced quality, accepted by Astronomy & Astrophysics (Letter) february 10, 2004. See http://astro.uibk.ac.at/dustjets/ for the full resolution and color version of the image

The exact solution of shear-lag problems in flat panels and box beams assumed rigid in the transverse direction

A mathematical procedure is herein developed for obtaining exact solutions of shear-lag problems in flat panels and box beams: the method is based on the assumption that the amount of stretching of the sheets in the direction perpendicular to the direction of essential normal stresses is negligible. Explicit solutions, including the treatment of cut-outs, are given for several cases and numerical results are presented in graphic and tabular form. The general theory is presented in a from which further solutions can be readily obtained. The extension of the theory to cover certain cases of non-uniform cross section is indicated. Although the solutions are obtained in terms of infinite series, the present developments differ from those previously given in that, in practical cases, the series usually converge so rapidly that sufficient accuracy is afforded by a small number of terms. Comparisons are made in several cases between the present results and the corresponding solutions obtained by approximate procedures devised by Reissner and by Kuhn and Chiarito

Resolving velocity space dynamics in continuum gyrokinetics

Many plasmas of interest to the astrophysical and fusion communities are weakly collisional. In such plasmas, small scales can develop in the distribution of particle velocities, potentially affecting observable quantities such as turbulent fluxes. Consequently, it is necessary to monitor velocity space resolution in gyrokinetic simulations. In this paper, we present a set of computationally efficient diagnostics for measuring velocity space resolution in gyrokinetic simulations and apply them to a range of plasma physics phenomena using the continuum gyrokinetic code GS2. For the cases considered here, it is found that the use of a collisionality at or below experimental values allows for the resolution of plasma dynamics with relatively few velocity space grid points. Additionally, we describe implementation of an adaptive collision frequency which can be used to improve velocity space resolution in the collisionless regime, where results are expected to be independent of collision frequency.Comment: 20 pages, 11 figures, submitted to Phys. Plasma

Observation of infinite-range intensity correlations above, at and below the 3D Anderson localization transition

We investigate long-range intensity correlations on both sides of the Anderson transition of classical waves in a three-dimensional (3D) disordered material. Our ultrasonic experiments are designed to unambiguously detect a recently predicted infinite-range C0 contribution, due to local density of states fluctuations near the source. We find that these C0 correlations, in addition to C2 and C3 contributions, are significantly enhanced near mobility edges. Separate measurements of the inverse participation ratio reveal a link between C0 and the anomalous dimension \Delta_2, implying that C0 may also be used to explore the critical regime of the Anderson transition.Comment: 13 pages, 11 figures (main text plus supplemental information). Updated version includes an improved introductory paragraph, minor text revisions, a revised title and additional supplemental information on the experimental detail

Inversion of Eddy Current Data Using Holographic Principles

It has proven possible to convert eddy current data associated with flaws to images of these flaws using holographic principles [2,3] because electromagnetic waves propagate in metals [1] and because these waves have subsonic velocities at eddy current frequencies. The purpose of this paper is to review and clarify the physical and mathematical basis for this method of analyzing eddy current data

Mapping Residual Stress Fields by Ultrasonic Tomography

It is well known that the velocity of sound in a solid is affected by stress. This phenomenon is a third order effect, and has been used primarily as a research tool to determine the Lame and Murnaghan elastic constants for various materials. A few preliminary attempts to use it for stress analysis have also been made. In this paper we describe the first attempt to combine this effect with the newly revived mathematical technique known as Computerized Axial Tomography (CAT) to provide quantitative maps of velocity within thick metal sections. From these maps , it is possible to infer the state of residual stress within the material. The technique requires that time-of-flight profiles through a section of the solid be made in a number of angular directions. This is equivalent to measuring the velocity through the solid from many different directions in a single plane. The computer takes the set of data so gathered and inverts it to produce a cross-sectional plot of velocity versus position. We have succeeded in mapping velocity anomalies as low as 0.21% and estimate that 0.5% is technically feasible. This kind of sensitivity should allow us to map stress anomalies as low as 1000 psi/inch in steel. We will also describe an experiment with a mild steel section in which we inserted an oversized pin by shrink fitting. The reconstruction clearly shows the high compressive stress within the pin, and the tensile .stress in the metal surrounding the pin

Mapping of Materials Stress with Ultrasonic Tomography

It is known that internal stress concentrations can give rise to microcracks which then grow when the structure is subjected to external forces. It has also been found that the velocity of sound is altered as it propagates through a region of stress. In this paper we discuss a technique called Computer Assisted Tomography (CAT) and describe an application that provides pictures of stress fields. We report the results of both simulated and experimental models used to evaluate the technique. We conclude that the CAT approach has great potential for locating and mapping residual stress in metals