Invention activities challenge students to tackle problems that superficially appear unrelated to the course material but illustrate underlying fundamental concepts that are fundamental to material that will be presented. During our invention activities in a first-year biology class, students were presented with problems that are parallel to those that living cells must solve, in weekly sessions over a 13-wk term. We compared students who participated in the invention activities sessions with students who participated in sessions of structured problem solving and with students who did not participate in either activity. When faced with developing a solution to a challenging and unfamiliar biology problem, invention activity students were much quicker to engage with the problem and routinely provided multiple reasonable hypotheses. In contrast the other students were significantly slower in beginning to work on the problem and routinely produced relatively few ideas. We suggest that the invention activities develop a highly valuable skill that operates at the initial stages of problem solving.

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Dialkylglycine decarboxylase (DGD) is an unusual pyridoxal phosphate dependent enzyme that catalyzes decarboxylation in the first and transamination in the second half-reaction of its ping-pong catalytic cycle. Directed evolution was employed to alter the substrate specificity of DGD from 2-aminoisobutyrate (AIB) to 1-aminocyclohexane-1-carboxylate (AC6C). Four rounds of directed evolution led to the identification of several mutants, with clones in the final rounds containing five persistent mutations. The best clones show ~2.5-fold decrease in KM and ~2-fold increase in kcat, giving a modest ~5-fold increase in catalytic efficiency for AC6C. Additional rounds of directed evolution did not improve catalytic activity toward AC6C. Only one (S306F) of the five persistent mutations is close to the active site. S306F was observed in all 33 clones except one, and the mutation is shown to stabilize the enzyme toward denaturation. The other four persistent mutations are near the surface of the enzyme. The S306F mutation and the distal mutations all have significant effects on the kinetic parameters for AIB and AC6C. Molecular dynamics simulations suggest that the mutations alter the conformational landscape of the enzyme, favoring a more open active site conformation that facilitates the reactivity of the larger substrate. We speculate that the small increases in kcat/KM for AC6C are due to two constraints. The first is the mechanistic requirement for catalyzing oxidative decarboxylation via a concerted decarboxylation/proton transfer transition state. The second is that DGD must catalyze transamination at the same active site in the second half-reaction of the ping-pong catalytic cycle.

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The use of models to simulate inspections has played a key role in UT NDE R&D efforts. Over the years, a series of wave propagation models, flaw response models, and microstructural backscatter models have been developed at CNDE to address inspection problems of interest. One use of the combined models is the estimation of signal-to-noise ratios (S/N) in circumstances where backscattered echoes from the microstructure (grain noise) act to mask sonic echoes from internal defects. Such S/N models have been used to address questions of inspection reliability, such as how to optimize the choices of transducer properties and inspection design to insure that critical defects are reliably detected. Under the sponsorship of the National Science Foundation's Industry/University Cooperative Research Center at ISU, an effort was initiated in 2015 to repackage existing research-grade software into user friendly tools for the rapid estimation of S/N for ultrasonic inspections of metals.This presentation provides an overview of the ongoing modeling effort, with emphasis on recent developments. The software can now treat both normal and oblique-incidence immersion inspections of curved metal components having equiaxed microstructures in which the grain size varies with depth. Both longitudinal and shear-wave inspections are treated. The model transducer can either be planar, spherically-focused, or bi-cylindricallyfocused. A calibration (or reference) signal is required, and is used to deduce the measurement system efficiency function. This can be "invented" by the software using center frequency and bandwidth information specified by the user, or, alternatively, a measured calibration signal can be used. Defect types include flat-bottomed-hole (FBH) reference reflectors, and spherical pores and inclusions. Simulation outputs include estimated defect signal amplitudes, RMS grain noise amplitudes, and S/N ratios as functions of the depth of the defect within the metal component. At any particular depth, the user can view a simulated A-scan displaying the superimposed defect and grain-noise waveforms. The realistic grain noise signals used in the A-scans are generated from a set of measured "universal" noise signals whose strengths and spectral characteristics are altered to match predicted noise characteristics for the simulation at hand. Examples are presented comparing measured and predicted A-scan signals for FBHs in Nickel-alloy components. We also discuss efforts currently underway to generate a simulated C-scans (including grain noise speckle) corresponding to inspections in which the model transducer is scanned above the defect. As will be demonstrated as part of this poster presentation, the software typically requires only a few seconds to complete a simulation when running on a typical laptop computer.