Theoretical Analysis of Acoustic Emission Spectra

Frequency analysis of acoustic emission spectra has been done by our group and others for several years now. Lloyd Graham presented some of the results in a previous paper. One would like, of course, to extract as much information as possible from these spectra. We hope, for example, that at least some fracture or failure processes, microscopic failure processes, will have distinctive frequency signatures: perhaps certain kinds of phase transformations or, as has been discussed, microcrack initiation by brittle fracture of intermetallic particles

Half-Space Radiation by EMAT\u27s

A Green\u27s function calculation of the far field radiation patterns of EMAT\u27s is presented. The approach is based upon (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMAT, which react to produce the driving Lorentz forces and (b) a Green\u27s function derived from the steepest descent approximation to the far field response of an arbitary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMAT\u27s and horizontally polarized shear waves as radiated by the latter

Sensors for Carbonization Control

Phase I of “Research on Intelligent Processing of Carbon-Carbon Composites” is a two year program to develop enabling technologies for real time control of the carbonization process for resin matrix composites. The research has three related foci: in situ material property sensors; process models; and intelligent control architecture. The research has, to date, 1) developed control strategies at three levels of sophistication that use sensors and models to complete carbonization more rapidly while still reducing losses; 2) developed a control architecture that integrates those sensors and models; 3) conducted successful in situ tests of chemical and physical property sensors; 4) developed a high temperature eddy current sensor (not yet tested in situ); 5) developed considerable kinetic data on the carbonization reactions, described the basic reaction paths and their relation to physical properties qualitatively, and developed a kinetic equation for the lowest temperature family of carbonization reactions, the production of water from hydroxyl groups; 6) defined the modeling strategy for calculating gas pressure and the experimental strategy for developing models for matrix strength. In the following, we describe the general problem and the issues in modeling and control to provide a context for the sensor results

Direct Regulation of Striated Muscle Myosins by Nitric Oxide and Endogenous Nitrosothiols

, both through activation of guanylyl cyclase and through modification of cysteines in proteins to yield S-nitrosothiols. While NO affects the contractile apparatus directly, the identities of the target myofibrillar proteins remain unknown. Here we report that nitrogen oxides directly regulate striated muscle myosins..These data show that nitrosylation signaling acts as a molecular “gear shift” for myosin—an altogether novel mechanism by which striated muscle and cellular biomechanics may be regulated

Feedback Inhibition in the PhoQ/PhoP Signaling System by a Membrane Peptide

The PhoQ/PhoP signaling system responds to low magnesium and the presence of certain cationic antimicrobial peptides. It regulates genes important for growth under these conditions, as well as additional genes important for virulence in many gram-negative pathogens. PhoQ is a sensor kinase that phosphorylates and activates the transcription factor PhoP. Since feedback inhibition is a common theme in stress-response circuits, we hypothesized that some members of the PhoP regulon may play such a role in the PhoQ/PhoP pathway. We therefore screened for PhoP-regulated genes that mediate feedback in this system. We found that deletion of mgrB (yobG), which encodes a 47 amino acid peptide, results in a potent increase in PhoP-regulated transcription. In addition, over-expression of mgrB decreased transcription at both high and low concentrations of magnesium. Localization and bacterial two-hybrid studies suggest that MgrB resides in the inner-membrane and interacts directly with PhoQ. We further show that MgrB homologs from Salmonella typhimurium and Yersinia pestis also repress PhoP-regulated transcription in these organisms. In cell regulatory circuits, feedback has been associated with modulating the induction kinetics and/or the cell-to-cell variability in response to stimulus. Interestingly, we found that elimination of MgrB-mediated feedback did not have a significant effect on the kinetics of reporter protein production and did not decrease the variability in expression among cells. Our results indicate MgrB is a broadly conserved membrane peptide that is a critical mediator of negative feedback in the PhoQ/PhoP circuit. This new regulator may function as a point of control that integrates additional input signals to modulate the activity of this important signaling system