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Delamination-Indicating Thermal Barrier Coatings

Luminescent sublayers reveal previously hidden coating damage. The risk of premature failure of thermal barrier coatings (TBCs), typically composed of yttria-stabilized zirconia (YSZ), compromises the reliability of TBCs used to provide thermal protection for turbine engine components. Unfortunately, TBC delamination proceeds well beneath the TBC surface and cannot be monitored by visible inspection. Nondestructive diagnostic tools that could reliably probe the subsurface damage state of TBCs would alleviate the risk of TBC premature failure by indicating when the TBC needs to be replaced before the level of TBC damage threatens engine performance or safety. To meet this need, a new coating design for thermal barrier coatings (TBCs) that are self-indicating for delamination has been successfully implemented by incorporating a europium- doped luminescent sublayer at the base of a TBC composed of YSZ. The luminescent sublayer has the same YSZ composition as the rest of the TBC except for the addition of low-level europium doping and therefore does not alter TBC performance.

Posted in: Physical Sciences, Briefs

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Criterion for Identifying Vortices in High-Pressure Flows

This criterion could enable appropriate comparisons between experiments and simulations. A study of four previously published computational criteria for identifying vortices in high-pressure flows has led to the selection of one of them as the best. This development can be expected to contribute to understanding of high-pressure flows, which occur in diverse settings, including diesel, gas turbine, and rocket engines and the atmospheres of Jupiter and other large gaseous planets.

Posted in: Physical Sciences, Briefs

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Photometric Calibration of Consumer Video Cameras

In imaging of point sources, dynamic ranges can be extended beyond saturation levels. Equipment and techniques have been developed to implement a method of photometric calibration of consumer video cameras for imaging of objects that are sufficiently narrow or sufficiently distant to be optically equivalent to point or line sources. Heretofore, it has been difficult to calibrate consumer video cameras, especially in cases of image saturation, because they exhibit nonlinear responses with dynamic ranges much smaller than those of scientific-grade video cameras. The present method not only takes this difficulty in stride but also makes it possible to extend effective dynamic ranges to several powers of ten beyond saturation levels. The method will likely be primarily useful in astronomical photometry. There are also potential commercial applications in medical and industrial imaging of point or line sources in the presence of saturation.

Posted in: Physical Sciences, Briefs

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Composite Pulse Tube

Axial leakage of heat is reduced. A modification of the design of the pulse tube in a pulse-tube cryocooler reduces axial thermal conductance while preserving radial thermal conductance. It is desirable to minimize axial thermal conductance in the pulse-tube wall to minimize leakage of heat between the warm and cold ends of the pulse tube. At the same time, it is desirable to maximize radial thermal conductance at the cold end of the pulse tube to ensure adequate thermal contact between (1) a heat exchanger in the form of a stack of copper screens inside the pulse tube at the cold end and (2) the remainder of the cold tip, which is the object to which the heat load is applied and from which heat must be removed. The modified design yields a low-heat-leak pulse tube that can be easily integrated with a cold tip.

Posted in: Physical Sciences, Briefs

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Calligraphic Poling of Ferroelectric Material

Arbitrary patterns can be written relatively easily and inexpensively. Calligraphic poling is a technique for generating an arbitrary, possibly complex pattern of localized reversal in the direction of permanent polarization in a wafer of LiNbO3 or other ferroelectric material. The technique is so named because it involves a writing process in which a sharp electrode tip is moved across a surface of the wafer to expose the wafer to a polarizing electric field in the desired pattern. The technique is implemented by use of an apparatus, denoted a calligraphic poling machine (CPM), that includes the electrode and other components as described in more detail below.

Posted in: Physical Sciences, Briefs

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Blackbody Cavity for Calibrations at 200 to 273 K

Care must be taken to ensure high emissivity to minimize error. A laboratory blackbody cavity has been designed and built for calibrating infrared radiometers used to measure radiant temperatures in the range from about 200 to about 273 K. In this below-room- temperature range, scattering of background infrared radiation from room-temperature surfaces could, potentially, contribute significantly to the spectral radiance of the blackbody cavity, thereby contributing a significant error to the radiant temperature used as the calibration value. The spectral radiance error at wavelength λ is given by [l – ε(λ)][B(Tc,λ) + B(Ta,λ)], where ε(λ) is the effective spectral emissivity of the cavity, B(T,λ) is the ideal spectral radiance of a body at absolute temperature T according to Planck’s radiation law, Tc is the temperature in the cavity, and Ta is the ambient temperature. Examining the above expression shows that by making ε(λ) as close as possible to unity, one can minimize the spectral-radiance error and the associated radiant-temperature error. For example, it has been calculated that to obtain a radiant-temperature error of 1 K or less at a cavity temperature of 200 K, ambient temperature of 300 K, and wavelength of 6 μm, one has ε(λ)>0.999 (see Figure 1). A 1 K radiant-temperature error is more than sufficient for atmospheric and cloud studies, which is a common application of infrared radiometers.

Posted in: Physical Sciences, Briefs

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An Automated Flying-Insect Detection System

Real-time monitoring and early detection networks detect harmful flying insects. An automated flying-insect detection system (AFIDS) was developed as a proof-of-concept instrument for real-time detection and identification of flying insects. This type of system has use in public health and homeland-security decision support, agriculture and military pest management, and/or entomological research.

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