High temperature, low cycle fatigue of a hybrid particulate/fiber aluminum metal-matrix composite

The effect of shot particles on the high temperature, low cycle fatigue of a hybrid fiber/particulate metal-matrix composite (MMC) was studied. Two hybrid composites with the general composition A356/35%SiC particle/5%Fiber (one without shot) were tested. It was found that shot particles acting as stress concentrators had little effect on the fatigue performance. It appears that fibers with a high silica content were more likely to debond from the matrix. Final failure of the composite was found to occur preferentially in the matrix. SiC particles fracture progressively during fatigue testing, leading to higher stress in the matrix, and final failure by matrix overload. A continuum mechanics based model was developed to predict failure in fatigue based on the tensile properties of the matrix and particles. By accounting for matrix yielding and recovery, composite creep and particle strength distribution, failure of the composite was predicted

A deep learning approach to estimate replicative lifespans from yeast cell images

The budding yeast Saccharomyces cerevisiae is an important model organism for cellular aging. A common metric for determining the lifespan of budding yeast cells is the replicative lifespan (RLS), how many times a mother cell divides in its lifetime. Traditionally, determining the RLS of yeast cells is a tedious manual process. To address this challenge, our long-term goal is to develop an automated RLS estimation process. Recently microfluidics-based methods have been developed, which generate time- series of images of individual cells. This work is focused on classifying these images into categories which can be used to estimate the RLS. We test three different deep learning models and found that all of the models have diverse and complementary errors, so we developed an ensemble of models that combine the best single models which led to high overall accuracy, precision and recall

An Epidemiological and Pharmacokinetic-pharmacodynamic Investigation into the Impact of Carbapenem-resistant Enterobacterales

Background: According to the 2019 CDC Antibiotic Resistance Threats Report, more than 2.8 million antibiotic-resistant infections occur in the United States each year, leading to more than 35,000 deaths. Among the most urgent threats identified by the CDC are carbapenem-resistant Enterobacterales (CRE). Despite efforts to control the spread of these organisms, the number of estimated cases between 2012 and 2017 remained stable. In 2017, an estimated 13,100 hospitalized cases of CRE led to approximately 1,100 deaths and $130 million attributable healthcare costs. This dissertation seeks to address this issue from both a pharmacokinetic/pharmacodynamic and epidemiological perspective. Methods: We evaluated the susceptibility of 140 CRE clinical isolates against novel agents eravacycline and plazomicin using techniques standardized by the Clinical and Laboratory Standards Institute. We performed in-vitro static time-kill assays in 8 Verona Integron-encoded metallo-beta-lactamase (VIM)-producing CRE using single and combination exposures of cefepime, meropenem, piperacillin/tazobactam, amikacin, and plazomicin along with aztreonam and aztreonam/avibactam. Additionally, we performed a 10-year, inverse probability of treatment weighting adjusted retrospective cohort study comparing the risk in observing a composite outcome of all-cause mortality or discharge to hospice in patients having CRE vs. carbapenem-susceptible Enterobacterales (CSE) infections after 14 and 30 days. In this cohort, we also reported on the prevalence of CRE across the decade. Additionally, we compared the organism composition and susceptibilities of isolates cultured in both the CRE and CSE groups. Results: Plazomicin showed higher susceptibility than eravacycline against our CRE isolates. In time kill studies, plazomicin was bactericidal against 5/8 isolates as monotherapy. Meropenem/amikacin or meropenem/plazomicin were bactericidal in all experiments, except for one isolate which regrew against meropenem/plazomicin. Aztreonam/avibactam was bactericidal in all experiments tested. Neither cefepime nor piperacillin/tazobactam improved the activity of plazomicin against our isolates. Cefepime with amikacin showed inconsistent activity. In the retrospective cohort study, the overall incidence of CRE infections was 1.8%. CRE isolates exhibited higher resistance across all routinely tested antimicrobials classes compared to CSE. The CRE population appeared to be largely non-carbapenemase-producing given the high susceptibility of meropenem and the high prevalence of E. cloacae, a known AmpC-producer. Overall, the risk of composite outcome only appeared to be increased among patients with a bloodstream infection on the index date and could only be assessed when utilizing an exposure of carbapenem-non-susceptible Enterobacterales (CNSE) due to insufficient sample size. However, the results were inconclusive as they were not statistically significant. Conclusions: Novel antimicrobial agents plazomicin and aztreonam/avibactam were highly active against a collection of CRE including both Klebsiella pneumoniae carbapenemase (KPC) and VIM. Aztreonam/avibactam, meropenem/amikacin, and meropenem/plazomicin all exhibited comparably bactericidal activity. Furthermore, at an academic medical center in a non-endemic region for CRE, it appears that CRE infection may have increased the risk of experiencing the composite outcome after both 14 and 30 days, but definitive conclusions may not be drawn given the lack of statistical significance and imprecision in the estimation of the effect. The difficulties in drawing definitive conclusions from this study owing to limited sample size in the CRE or CNSE group stresses the importance of developing novel strategies and performing larger, multicenter studies when investigating highly resistant infections with low prevalence

Bridging the gap: rewritable electronics using real-time light-induced dielectrophoresis on lithium niobate

In the context of micro-electronics, the real-time manipulation and placement of components using optics alone promises a route towards increasingly dynamic systems, where the geometry and function of the device is not fixed at the point of fabrication. Here, we demonstrate physically reconfigurable circuitry through light-induced dielectrophoresis on lithium niobate. Using virtual electrodes, patterned by light, to trap, move, and chain individual micro-solder-beads in real-time via dielectrophoresis, we demonstrate rewritable electrical contacts which can make electrical connections between surface-bound components. The completed micro-solder-bead bridges were found to have relatively low resistances that were not solely dominated by the number of interfaces, or the number of discrete beads, in the connection. Significantly, these connections are formed without any melting/fusing of the beads, a key feature of this technique that enables reconfigurability. Requiring only a low-power (~3.5 mW) laser source to activate, and without the need for external power supply or signal generation, the all-optical simplicity of virtual-electrodes may prove significant for the future development of reconfigurable electronic systems

Master of Science

thesisSpectrographic observations were made for copper projectiles impacting into copper targets in various controlled atmospheres. Atomic copper lines are the predominant feature of the impact flash of copper-to-copper impacts in a medium of argon. Since a copper line with a 7.1 ev excitation energy is excited in an argon atmosphere, an energy of at least this magnitude is available for excitation of copper atoms. Results indicate that in argon, the flash is produced by micron-size copper particles ejected from the target, some with velocities no less than 6-7 km/sec and heated by the medium. A collision process between copper atoms evaporated from the heated spray particles and atoms of the argon atmosphere can account for the observed copper lines. In a medium of hydrogen, the impact flash is dimmer by at least two orders of magnitude, giving a smooth spectral contour with no detectable line structure. However, no obvious black body temperature is obtainable from the contour of this light emission in hydrogen. 5516 relative velocity between copper atoms and hydrogen molecules required to produce copper lines is greater than 20 km/sec in a collision process. The reduced size of the flash in hydrogen indicates that the particles responsible for the flash are smaller than those producing the flash in argon. It appears that the size of the particles that produce the flash in each gas are of the order of magnitude of the mean free path of the molecules in that gas

Baseline sensitivities of Corynespora cassiicola to thiophanate-methyl, iprodione and fludioxonil

Corynespora cassiicola, causal agent of Corynespora leaf spot, causes severe epidemics in African violet production facilities. Recent concerns over loss of fungicide efficacy has led to this investigation of baseline sensitivity distributions to thiophanate-methyl, iprodione and fludioxonil fungicides and temperature sensitivity study to evaluate fitness of high and low sensitivity groups. During a disease outbreak, 325 single lesion isolates were collected and 40 isolates were selected randomly for an in vitro assay to determine EC[Subscript50] (the point at which 50% of mycelial growth was inhibited) values on potato dextrose agar (PDA) or PDA amended with thiophanate-methyl, iprodione and fludioxonil. EC[Subscript50] values for iprodione and thiophanate-methyl ranged from 0.0833 to 0.6478 [Mu]g/ml and 0.0157 to 0.1539 [Mu]g/ml with mean values of 0.2828 [Mu]g/ml (Figure 1-1, see Chapter 2 appendix) and 0.0553 [Mu]g/ml (Figure 1-2), respectively.Fludioxonil EC[Subscript50] values ranged from 0.0013 to 0.0103 [Mu]g/ml and the mean value was 0.0075 [Mu]g/ml (Figure 1-3). A resistance factor for each fungicide was calculated by dividing the least sensitive isolate\u27s EC[Subscript50] value to the mean EC[Subscript50] for that fungicide. A lower resistance factor for fludioxoni-amended plates (1.37) than for iprodione (2.39) or thiophanate-methyl (2.78) (Table 1-1) indicates a tendency toward less insensitivity to this fungicide in this population. Correlation coefficients were calculated to determine cross-sensitivity between fungicides. Of the three fungicides, iprodione and fludioxonil had a moderately significant correlation (r = 0.38686) (P = 0.0125) (Table 1-2), indicating moderate cross-resistance.To determine fitness ranges of isolates to each fungicide, three isolates least sensitive to each fungicide along with three isolates most sensitive to each fungicide were used with mean radial growth area recorded every three days for twelve days across 10, 15, 20, 25, 30 and 35° C temperatures. Across all fungicide sensitivity groups, growth did not occur at 10° C and was very limited at 35° C. Optimum growth for all isolates within sensitivity groups was 25° C (Figure 2-1 to Figure 2-3, see Chapter 3 appendix) across all fungicide and observation times. Differences in growth area (mm²) between the least and most sensitive isolate groups did not differ for the thiophanate-methyl isolate group (P = 0.2246), the iprodione isolate group (P = 0.0512), or the fludioxonil isolate group (P = 0.6070) based on linear mixed model analysis.Even though significant differences did not exist in this analysis, temperature sensitivity information is an important part of fungicide resistance management. Developing baseline and temperature sensitivity data is the first step in determining fungal population sensitivity shifts for better resistance management strategies