Improved ultrasonic standard reference blocks

A program to improve the quality, reproducibility and reliability of nondestructive testing through the development of improved ASTM-type ultrasonic reference standards is described. Reference blocks of aluminum, steel, and titanium alloys were considered. Equipment representing the state-of-the-art in laboratory and field ultrasonic equipment was obtained and evaluated. Some RF and spectral data on ten sets of ultrasonic reference blocks were taken as part of a task to quantify the variability in response from nominally identical blocks. Techniques for residual stress, preferred orientation, and microstructural measurements were refined and are applied to a reference block rejected by the manufacturer during fabrication in order to evaluate the effect of metallurgical condition on block response

Acoustic Emission Source Characterization Through Direct Time-Domain Deconvolution

While detected acoustic emission (AE) signals contain potentially useful information about the deformation source mechanisms of a structure under load, signal processing techniques such as threshold counting, RMS recording, energy measurement, peak detection, and spectral analysis often fail to extract such information unambiguously. The difficulty lies both in the inherent complexity of the deformation mechanism and in the lack of understanding of the source mechanism, the wave propagation details, and the physics of the sensor\u27s mechanical-to-electrical conversion process. Instead of taking an empirical approach to establish the correlations between the detected AE and the observed possible deformation mechanism, we approach the problem by constructing a simple test system which consists of three main ingredients: a true displacement sensor (capacitive transducer), a simple structure (either a large block or a plate), and known theoretical impulse-response functions for specific sensor-source relative locations. We first establish the validity of these ingredients by testing with simulated AE of known step-function time dependency generated by breaking glass capillaries. Unknown sources are then introduced, one at a time, into the system for determination of their time functions. The time function at the source is determined by a deconvolution process from the known impulse response and the detected displacement. Furthermore, we show the existence of the inverse of the impulse-response function with respect to convolution for at least two extreme cases. Consequently, the source function can be obtained simply by convolving the detected signal with the inverse function. Applications to AE system calibration, sensor characterization, wave propagation studies, and brittle crack opening signature analysis will be demonstrated

Ultrasonic Reference Blocks and Characterized Fatigue Cracks

The National Bureau of Standards initiated an identifiable program in nondestructive testing about a year and a half ago. Up until that time there was significant effort in areas affecting NDT, but the focus of these efforts was not nondestructive testing. I will describe only a couple of the facets of the current NOT program at NBS. The program is growing, and by now is approaching the size of about 3/4 of a million dollars per year. The aim of the program is to bring direct impact on nondestructive activities through better test methods, through standards, and through measurement services and interpretive methodologies. I will describe progress on an activity aimed at near term improvements in ASTM type reference blocks and also on an effort aimed at producing characterized flaws. I will also very briefly touch on some work we are doing towards establishing measurement techniques for determining the characteristics of ultrasonic and acoustic emission transducers. The ASTM reference block work is supported by the Air Force, NASA and the Army, and the work on characterized flaws and transducers is supported by in-house funding

A Basis for Traceable NDE Standards

The National Bureau of Standards (NBS) is beginning to provide a mechanism for traceability for a number of NDE measurement procedures, an activity that is expected to have a significant, positive impact on the reproducibility and accuracy of NDE measurements. Much of the NDE standards activity has been in ultrasonics and acoustic emission, this effort leading to calibration services for ultrasonic reference blocks and ultrasonic and acoustic emission transducers. Additional NDE standards are also available or are being developed in radiography, eddy currents, magnetic particles, liquid penetrants and visual testing

Improved ultrasonic standard reference blocks

A program to improve the quality, reproducibility and reliability of nondestructive testing through the development of improved ASTM-type ultrasonic reference standards is described. Reference blocks of aluminum, steel, and titanium alloys are to be considered. Equipment representing the state-of-the-art in laboratory and field ultrasonic equipment was obtained and evaluated. RF and spectral data on ten sets of ultrasonic reference blocks have been taken as part of a task to quantify the variability in response from nominally identical blocks. Techniques for residual stress, preferred orientation, and micro-structural measurements were refined and are applied to a reference block rejected by the manufacturer during fabrication in order to evaluate the effect of metallurgical condition on block response. New fabrication techniques for reference blocks are discussed and ASTM activities are summarized

The Rho GDI Rdi1 regulates Rho GTPases by distinct mechanisms

© 2008 by The American Society for Cell Biology. Under the License and Publishing Agreement, authors grant to the general public, effective two months after publication of (i.e.,. the appearance of) the edited manuscript in an online issue of MBoC, the nonexclusive right to copy, distribute, or display the manuscript subject to the terms of the Creative Commons–Noncommercial–Share Alike 3.0 Unported license (http://creativecommons.org/licenses/by-nc-sa/3.0).The small guanosine triphosphate (GTP)-binding proteins of the Rho family are implicated in various cell functions, including establishment and maintenance of cell polarity. Activity of Rho guanosine triphosphatases (GTPases) is not only regulated by guanine nucleotide exchange factors and GTPase-activating proteins but also by guanine nucleotide dissociation inhibitors (GDIs). These proteins have the ability to extract Rho proteins from membranes and keep them in an inactive cytosolic complex. Here, we show that Rdi1, the sole Rho GDI of the yeast Saccharomyces cerevisiae, contributes to pseudohyphal growth and mitotic exit. Rdi1 interacts only with Cdc42, Rho1, and Rho4, and it regulates these Rho GTPases by distinct mechanisms. Binding between Rdi1 and Cdc42 as well as Rho1 is modulated by the Cdc42 effector and p21-activated kinase Cla4. After membrane extraction mediated by Rdi1, Rho4 is degraded by a novel mechanism, which includes the glycogen synthase kinase 3β homologue Ygk3, vacuolar proteases, and the proteasome. Together, these results indicate that Rdi1 uses distinct modes of regulation for different Rho GTPases.Deutsche Forschungsgemeinschaf