Characterization of Cracks From Ultrasonic Scattering Data

1987 ◽  
Vol 54 (4) ◽  
pp. 754-760 ◽  
Author(s):  
J. D. Achenbach ◽  
D. A. Sotiropoulos ◽  
H. Zhu
Keyword(s):  
Scattered Field ◽  
Inverse Method ◽  
Crack Opening ◽  
Elastic Solid ◽  
Scattering Data ◽  
Crack Plane ◽  
Ultrasonic Scattering ◽  
Low Frequencies ◽  
Planar Crack

An inverse method for ultrasonic scattering data is proposed, to characterize a planar crack of general shape contained in an elastic solid. The method is based on an integral representation for the scattered field in the frequency domain. For a given scattered field the inverse problem has been formulated as a nonlinear optimization problem. At low frequencies its solution gives the location of the crack, the orientation of the crack-plane, and the crack-opening volumes. In addition the Mode I stress-intensity factor is obtained for a related static stress state corresponding to service loads.

scholarly journals In Vitro Characterization of the Antibacterial Spectrum of Novel Bacterial Type II Topoisomerase Inhibitors of the Aminobenzimidazole Class

2006 ◽  
Vol 50 (4) ◽  
pp. 1228-1237 ◽  
Author(s):  
Nagraj Mani ◽  
Christian H. Gross ◽  
Jonathan D. Parsons ◽  
Brian Hanzelka ◽  
Ute Müh ◽  
...  
Keyword(s):  
Bacterial Resistance ◽  
Wide Spectrum ◽  
Dna Gyrase ◽  
Antibacterial Activities ◽  
Mechanisms Of Action ◽  
Fluoroquinolone Resistance ◽  
Topoisomerase Iv ◽  
Low Frequencies

ABSTRACT Antibiotics with novel mechanisms of action are becoming increasingly important in the battle against bacterial resistance to all currently used classes of antibiotics. Bacterial DNA gyrase and topoisomerase IV (topoIV) are the familiar targets of fluoroquinolone and coumarin antibiotics. Here we present the characterization of two members of a new class of synthetic bacterial topoII ATPase inhibitors: VRT-125853 and VRT-752586. These aminobenzimidazole compounds were potent inhibitors of both DNA gyrase and topoIV and had excellent antibacterial activities against a wide spectrum of problematic pathogens responsible for both nosocomial and community-acquired infections, including staphylococci, streptococci, enterococci, and mycobacteria. Consistent with the novelty of their structures and mechanisms of action, antibacterial potency was unaffected by commonly encountered resistance phenotypes, including fluoroquinolone resistance. In time-kill assays, VRT-125853 and VRT-752586 were bactericidal against Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, and Haemophilus influenzae, causing 3-log reductions in viable cells within 24 h. Finally, similar to the fluoroquinolones, relatively low frequencies of spontaneous resistance to VRT-125853 and VRT-752586 were found, a property consistent with their in vitro dual-targeting activities.

scholarly journals Diffraction of plane elastic waves by a crack, with application to a problem of brittle fracture

1963 ◽  
Vol 3 (3) ◽  
pp. 325-339 ◽  
Author(s):  
M. Papadopoulos
Keyword(s):  
Elastic Waves ◽  
Scattered Field ◽  
Velocity Potential ◽  
Elastic Solid ◽  
Step Function ◽  
Free Surface Waves ◽  
Dependent Variables ◽  
Smooth Plane ◽  
New Feature ◽  
Set Up

AbstractA crack is assumed to be the union of two smooth plane surfaces of which various parts may be in contact, while the remainder will not. Such a crack in an isotropic elastic solid is an obstacle to the propagation of plane pulses of the scalar and vector velocity potential so that both reflected and diffracted fields will be set up. In spite of the non-linearity which is present because the state of the crack, and hence the conditions to be applied at the surfaces, is a function of the dependent variables, it is possible to separate incident step-function pulses into either those of a tensile or a compressive nature and the associated scattered field may then be calculated. One new feature which arises is that following the arrival of a tensile field which tends to open up the crack there is necessarily a scattered field which causes the crack to close itself with the velocity of free surface waves.

Uncertainty Characterization of the CrCOD Circumferential Crack Opening Displacement Module for xLPR

2015 ◽  
Author(s):  
Richard Olson ◽  
Paul Scott
Keyword(s):  
Crack Opening Displacement ◽  
Crack Opening ◽  
Opening Displacement ◽  
Crack Face ◽  
Pipe Surface ◽  
Circumferential Crack ◽  
The Us ◽  
Experimental Values ◽  
Metal Weld

The US NRC/EPRI xLPR (eXtremely Low Probability of Rupture) probabilistic pipe fracture analysis program uses deterministic modules as the foundation for the calculation of the probability of pipe leak or rupture as a consequence of active degradation mechanisms, vibration or seismic loading. The circumferential crack opening displacement module, CrCOD, estimates crack opening displacement (COD) at the inside pipe surface, at the mid-wall thickness location, and at the outside pipe surface using a combined tension/crack face pressure/bending GE/EPRI-like solution. Each module has an uncertainty beyond the uncertainty of the xLPR data inputs. This paper documents the uncertainty for CrCOD. Using 36 pipe fracture experiments, including: base metal, similar metal weld, and dissimilar metal weld experiments; bend only and pressure and bend loading; static and dynamic load histories; cracks that range from short to long, the uncertainty of the CrCOD methodology is characterized. Module uncertainty is presented in terms mean fit and standard deviation between prediction and experimental values.

scholarly journals Variable-Temperature Noise Characterization of N-MOSFETs Using an In-Situ Broadband Amplifier

2021 ◽  
Author(s):  
Kenji Ohmori ◽  
Shuhei Amakawa
Keyword(s):  
Shot Noise ◽  
Printed Circuit Board ◽  
Noise Figure ◽  
Variable Temperature ◽  
Low Noise ◽  
Broadband Noise ◽  
Circuit Board ◽  
Low Frequencies ◽  
Cryogenic Chamber

Characterization of broadband noise of MOSFETs from room temperature down to 120 K in fine temperature steps is presented. A MOSFET is mounted on a reusable printed circuit board vehicle with a built-in low-noise amplifier, and the vehicle is loaded into a cryogenic chamber. The vehicle allows noise measurement in the frequency range from 50 kHz to 100 MHz. At low frequencies, it enables extraction of activation energies associated with electron trapping sites. At high frequencies, as has been suggested by noise figure measurements, the white noise of MOSFETs is shown to be dominated by the shot noise, which has much weaker temperature dependence than the thermal noise. The shot noise will be a problematic noise source in broadband RF CMOS circuits operating at cryogenic temperatures.<div><br></div>

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