Interferometric and Holographic Imaging of Surface-Breaking Cracks

Two advanced nondestructive evaluation systems are developed for imaging surface-breaking cracks in aerospace materials. The systems use scanning heterodyne interferometry and frequency-translated holography principles to image ultrasonic displacement fields on material surfaces with high resolution and sensitivity. Surface-breaking cracks are detected and characterized by visualizing near-field ultrasonic scattering processes, which in turn results in local intensification of ultrasonic displacement fields in the immediate vicinity of a crack. The local intensification permits cracks to be easily distinguished from background levels, and creates unique displacement field images that follow the contours and morphology of the cracks with microscopic precision. The interferometric and holographic imaging approaches each provide noncontact and near optical-diffraction-limited measurement capabilities that are essential for probing ultrasonic displacement fields in the immediate vicinity of cracks. Several representative crack-imaging results are provided, along with detailed descriptions of both experimental techniques, and the capabilities and limitations of each method. The resulting systems provide simple yet very powerful tools for evaluating surface-breaking cracks in detail

Recent Decisions

Comments on recent decisions by L. D. Wichmann, Lawrence James Bradley, John F. Beggan, John A. Slevin, Robert P. Mone, and F. James Kane

Identification of Acidic pH-Dependent Ligands of Pentameric C-reactive Protein

C-reactive protein (CRP) is a phylogenetically conserved protein; in humans, it is present in the plasma and at sites of inflammation. At physiological pH, native pentameric CRP exhibits calcium-dependent binding specificity for phosphocholine. In this study, we determined the binding specificities of CRP at acidic pH, a characteristic of inflammatory sites. We investigated the binding of fluid-phase CRP to six immobilized proteins: complement factor H, oxidized low-density lipoprotein, complement C3b, IgG, amyloid β, and BSA immobilized on microtiter plates. At pH 7.0, CRP did not bind to any of these proteins, but, at pH ranging from 5.2 to 4.6, CRP bound to all six proteins. Acidic pH did not monomerize CRP but modified the pentameric structure, as determined by gel filtration, 1-anilinonaphthalene-8-sulfonic acid-binding fluorescence, and phosphocholine-binding assays. Some modifications in CRP were reversible at pH 7.0, for example, the phosphocholine-binding activity of CRP, which was reduced at acidic pH, was restored after pH neutralization. For efficient binding of acidic pH-treated CRP to immobilized proteins, it was necessary that the immobilized proteins, except factor H, were also exposed to acidic pH. Because immobilization of proteins on microtiter plates and exposure of immobilized proteins to acidic pH alter the conformation of immobilized proteins, our findings suggest that conformationally altered proteins form a CRP-ligand in acidic environment, regardless of the identity of the protein. This ligand binding specificity of CRP in its acidic pH-induced pentameric state has implications for toxic conditions involving protein misfolding in acidic environments and favors the conservation of CRP throughout evolution

Towards better utilization of NEXRAD data in hydrology: An overview of hydro-NEXRAD

With a very modest investment in computer hardware and the open-source local data manger (LDM) software from UCAR\u27s Unidata Program Center, an individual researcher can receive a variety of NEXRAD Level III gridded rainfall products, and the unprocessed Level II data in real-time from most NEXRAD radars. Additionally, the National Climatic Data Center has vast archives of these products and Level II data. Still, significant obstacles remain in order to unlock the full potential of the data. One set of obstacles is related to effective management of multi-terabyte data sets: storing, compressing, and backing up. A second set of obstacles, for hydrologists and hydrometeorologists in particular, is that the NEXRAD Level III products are not well suited for application in hydrology. There is a strong need for the generation of high-quality products directly from the Level II data with well-documented steps that include quality control, removal of false echoes, rainfall estimation algorithms with variety of corrections, coordinate conversion and georeferencing, conversion to a convenient data format(s), and integration with GIS. For hydrologists it is imperative that these procedures are basin-centered as opposed to radar-centered. Thirdly, the amount of data present in a multi-year, multi-radar dataset is such that simple cataloging and indexing of the data is not sufficient. Rather, sophisticated metadata extraction and management techniques are required. The authors describe and discuss the Hydro-NEXRAD software system that addresses the above three challenges. With support from the National Science Foundation through its ITR program, the authors are developing a basin-centered framework for addressing all these issues in a comprehensive manner, tailored specifically for use of NEXRAD data in hydrology and hydrometeorology. Through a flexible web interface users can search a large metadata database base, managed by a relational database, for subsets of interest. Well-chosen and documented defaults are provided for the flow from unprocessed NEXRAD data to basin-centered rainfall estimates at a desired space-time resolution. In addition to the web interface, there are web services that provide access to scripts and compiled programs. © 2007 ASCE

Microcalibrator system for chemical signature and reagent delivery.

Networked systems of low-cost, small, integrable chemical sensors will enable monitoring of Nonproliferation and Materials Control targets and chemical weapons threats. Sandia-designed prototype chemical sensor systems are undergoing extended field testing supported by DOE and other government agencies. A required surety component will be verification of microanalytical system performance, which can be achieved by providing a programmable source of chemical signature(s) for autonomous calibration of analytical systems. In addition, such a controlled chemical source could be used to dispense microaliquots of derivatization reagents, extending the analysis capability of chemical sensors to a wider range of targets. We have developed a microfabricated system for controlled release of selected compounds (calibrants) into the analytical stream of microsensor systems. To minimize pumping and valve requirements of microfluidic systems, and to avoid degradation issues associated with storage of dilute solutions, we have utilized thermally labile organic salts as solid-phase reservoir materials. Reproducible deposition of tetrapropyl ammonium hydroxide onto arrays of microfabricated heating elements can provide a pair of calibration marker compounds (one fast and one slow-eluting compound) for GC analyses. The use of this microaliquot gas source array for hydrogen generation is currently under further development. The goal of the latter effort will be to provide a source of high-pressure, low viscosity GC carrier gas for Sandia's next-generation microfabricated gas-phase chemical analysis systems