Adaptive Imaging with a Cylindrical, Time-Encoded Imaging System

Most imaging systems for terrestrial nuclear imaging are static in that the design of the system and the data acquisition protocol are defined prior to the experiment. Often, these systems are designed for general use and not optimized for any specific task. The core concept of adaptive imaging is to modify the imaging system during a measurement based on collected data. This enables scenario specific adaptation of the imaging system which leads to better performance for a given task. This dissertation presents the first adaptive, cylindrical, time-encoded imaging (c-TEI) system and evaluates its performance on tasks relevant to nuclear non-proliferation and international safeguards. We explore two methods of adaptation of a c-TEI system, adaptive detector movements and adaptive mask movements, and apply these methods to three tasks, improving angular resolution, detecting a weak source in the vicinity of a strong source, and reconstructing complex source scenes. The results indicate that adaptive imaging significantly improves performance in each case. For the MATADOR imager, we find that adaptive detector movements improve the angular resolution of a point source by 20% and improve the angular resolution of two point sources by up to 50%. For the problem of detecting a weak source in the vicinity of a strong source, we find that adaptive mask movements achieve the same detection performance as a similar, non-adaptive system in 20%-40% less time, depending on the relative position of the weak source. Additionally, we developed an adaptive detection algorithm that doubles the probability of detection of the weak source at a 5% false-alarm rate. Finally, we applied adaptive imaging concepts to reconstruct complex arrangements of special nuclear material at Idaho National Laboratory. We find that combining data from multiple detector positions improves image uniformity of extended sources by 38% and reduces the background noise by 50%. We also demonstrate 2D (azimuthal and radial) imaging in a crowded source scene. These promising experimental results highlight the potential for adaptive imaging using a c-TEI system and motivate further research toward specific, real-world applications.PHDNuclear Engineering & Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163009/1/nirpshah_1.pd

On Defense: African American Males Making Sense of Racialized Narratives in Mathematics Education

This paper examines how African American male students understand, interpret, and think about the effects of racialized narratives in relation to mathematics learning. Drawing on interviews, the authors argue that racialized narratives exist in relation to one another and are fundamental to the way that young people build their identities, including identities as math learners

Effect of Molecular Crowders on the Activation of Cholera Toxin by Protein Disulfide Isomerase

Cholera toxin (CT) is a classic A-B type protein toxin that has an A subunit (A1 + A2) and a pentameric B subunit. The catalytic A1 domain is linked to the A2 domain via a disulfide linkage. CTA1 must be dissociated from the rest of the toxin to cause a cytopathic effect. Protein disulfide isomerase (PDI) can reduce the CTA1/CTA2 disulfide bond, but disassembly of the reduced toxin requires the partial unfolding of PDI that occurs when it binds to CTA1. This unfolding event allows PDI to push CTA1 away from the rest of the toxin. My research question is whether the efficiency of PDI in disassembling CT would be affected by molecular crowding, where a dense internal cell environment is recreated in vitro by the use of chemical agents such as Ficoll. This will give insight on how CT behaves inside a cell. Our hypothesis was that molecular crowding would make CTA1 disassembly more efficient by recreating the tight packing of macromolecules in cells, which provides an extra nudge to enhance toxin disassembly. We then used enzyme-linked immunosorbent assays (ELISAs), a pull-down assay and a biochemical assay to determine how molecular crowders affect the binding, reduction, and disassembly of CT by PDI. Our results will bring about a deeper understanding of the cellular events that may affect the course of a cholera infection. From the preliminary results, molecular crowders increased PDI\u27s ability to bind to CTA1 and did not prevent PDI from cleaving the CTA1/CTA2 disulfide bond. Based off the disassembly results, molecular crowders reduced PDI\u27s ability to displace CTA1 from the rest of the toxin. This contradicts our original hypothesis. Our new hypothesis is that crowders block PDI unfolding, which is required for CT disassembly. Biophysical experiments using Fourier Transform Infrared Spectroscopy will test this prediction in future work

Evolution of Laser Produced Aluminum Plasma in the Presence of a Transverse Magnetic Field

Surface erosion of plasma-facing components is a very important problem in fusion reactors. In order to make fusion reactors economically viable the lifetime of plasma-facing components must be extended. My research entails using magnetic field interactions with plasma in order to determine how the plasma moves through the field, and if it can be stopped by using a certain orientation of magnetic field. A magnetic field should be able to alter the path of evolving plasma due to the interaction of the magnetic field with the charged particles in the plasma. The optimal orientation for slowing the evolution of the plasma is hypothesized to be perpendicular to the magnetic field. Also it is anticipated that the higher the magnetic field the greater the stopping of the plasma. This experiment consisted of designing a magnetic trap and creating laser produced plasma with and without a magnetic field. Intensified CCD was used to image the plasma plume expansion with and without a transverse magnetic field. An aluminum target was used to generate the plasma using laser pulse energies of 50 mJ, 100 mJ, and 150 mJ. It was found that with no magnetic field the plume expanded freely, with larger velocities for higher laser pulse energy. With magnetic field the plasma was confined and this confinement was more pronounced at higher energies. This experiment can be extended by gathering spectroscopic data in order to determine the temperature and the levels of ionization inside the plasmas at different laser energies and magnetic orientations

Collimation Effects on Magnetically Confined Laser Produced Plasmas

Tokamaks for fusion research are extremely complex and are still limited by inherent instabilities such as material erosion from plasma instabilities. Due to the lack of data and high demand of resources, simulations to portray Tokamaks are essential. A Particle-In-Cell (PIC) simulation for plasma erosion on materials within the Tokamak is to be benchmarked using the experimental data obtained in these experiments. The effects of an axial magnetic field (magnetic field lines are along the plasma propagation direction) on an expanding laser produced plasma plume are investigated. A Continuum Surelite Nd:YAG laser system at 1064 nm wavelength and 6 ns full width half max (FWHM) is used to ablate carbon, aluminum, and boron nitride surfaces in the presence of a magnetic field (~.6T) at 50 mJ, 100 mJ, and 150 mJ under vacuum. The resulting plasma plume is studied using fast photography by employing an intensified charge coupled device (ICCD). The effect of the axial magnetic field changes with the target material. Carbon plume undergoes the creation of side wings that expand perpendicular to the field and curve back into the field after the primary plume has expanded and dissipated. Both aluminum and boron nitride exhibit significant focusing at the center of the magnetic field with no evidence of wings formation. Further work using optical emission spectroscopy is in progress to obtain temperature, electron density, and ionization rate of the laser produced plasma plumes to better understand the mechanism of wing formation as well as plume focusing in different materials

Exploring different theoretical frontiers – A symposium

Providing for a praxis of uncertainty, theoretical traditions that undercover how knowledge, power, and identity are interwoven and constituted in and through socio-cultural and -political discourses characterize the sociopolitical-turn moment in mathematics education research. Researchers who work in the sociopolitical-turn moment pull from a variety of theoretical perspectives most often located in the emancipate and/or deconstruct paradigms of inquiry. In this symposium, panelists discuss how different theoretical traditions available to researchers in the sociopolitical-turn moment provide new productive ways to think and rethink mathematics teaching and learning

Distribution of Hyperpolarized Xenon in the Brain Following Sensory Stimulation: Preliminary MRI Findings

In hyperpolarized xenon magnetic resonance imaging (HP 129Xe MRI), the inhaled spin-1/2 isotope of xenon gas is used to generate the MR signal. Because hyperpolarized xenon is an MR signal source with properties very different from those generated from water-protons, HP 129Xe MRI may yield structural and functional information not detectable by conventional proton-based MRI methods. Here we demonstrate the differential distribution of HP 129Xe in the cerebral cortex of the rat following a pain stimulus evoked in the animal's forepaw. Areas of higher HP 129Xe signal corresponded to those areas previously demonstrated by conventional functional MRI (fMRI) methods as being activated by a forepaw pain stimulus. The percent increase in HP 129Xe signal over baseline was 13–28%, and was detectable with a single set of pre and post stimulus images. Recent innovations in the production of highly polarized 129Xe should make feasible the emergence of HP 129Xe MRI as a viable adjunct method to conventional MRI for the study of brain function and disease

Racial Discourse in Mathematics and its Impact on Student Learning, Identity, and Participation

Discussions of race in educational research have focused primarily on performance gaps and differential access to advanced coursework. Thus, very little is known about how race mediates the learning process, particularly with respect to classroom participation and student identity formation. This dissertation examines mathematics learning as a context for illuminating the racial dynamics of learning in everyday classroom activity.Although mathematics and race may seem strange bedfellows, a poststructural analysis reveals specific linkages between them that suggest that their discourses are actually well aligned. To conceptualize this alignment, this dissertation introduces the theoretical frame of racial-mathematical discourse, which establishes the groundwork for the empirical investigation reported here. Observations took place in four mathematics classrooms at a racially diverse high school over the course of a school year. Interviews (n=35) were conducted with students from the focal classrooms. Data were analyzed to explore how students make sense of racial-mathematical discourse, and to gauge the discourse's impact on learning.Findings indicate that racial-mathematical narratives were central to students' sense making. All students reported awareness of the "Asians are good at math" narrative, as part of a web of racial ideology. Importantly, students linked it to narratives about other groups' mathematical inferiority (e.g., "Blacks are bad at math"). They also connected racial-mathematical narratives to broader racialized discourses outside mathematics (e.g., perceptions of intelligence). Students observed the presence of these narratives in locations outside the school setting, such as media imagery and international comparisons. Data further suggest that racial-mathematical discourse is not a static belief system. Rather, it emerges and is reified as students engage in typical classroom practices, such as noting which classmates get asked for help. This is consequential for learning, in that the deployment of racial narratives in social interaction frames students' opportunities to build identities as capable learners. This dissertation develops a framework leveraging insights from sociocultural and poststructural theory to trace the impact of racialized classroom episodes on students' identity formation. It highlights critical issues that need to be taken into account in the design of equitable learning environments, especially for students of color from persistently marginalized backgrounds

Mechanism of tamoxifen resistance in breast cancer

Acquired tamoxifen resistance develops in the majority of hormone responsive breast cancers and frequently involves overexpression of the PI3K/AKT axis. Here, breast cancer cells, with elevated endogenous AKT or overexpression of activated AKT exhibited tamoxifen-stimulated cell proliferation and enhanced cell motility. To gain mechanistic insight on AKT-induced endocrine resistance, gene expression profiling was performed to determine the transcripts that are differentially expressed post-tamoxifen therapy under conditions of AKT overexpression. Consistent with the biological outcome, many of these transcripts function in cell proliferation and cell motility networks and were quantitatively validated in a larger panel of breast cancer cells. Moreover, ribonucleotide reductase M2 (RRM2) was revealed as a key contributor to AKT-induced tamoxifen resistance. Inhibition of RRM2 by RNAi-mediated approaches significantly reversed the tamoxifen-resistant cell growth, inhibited cell motility, and activated pro-apoptotic pathways. In addition, treatment of tamoxifen-resistant breast cancer cells with the small molecule RRM2 inhibitor Didox significantly reduced cell growth in vitro and in vivo. To further establish a functional association between RRM2 expression and tamoxifen resistance in breast cancer cells, gain of function studies were performed by overexpressing RRM2 in MCF-7 cells. Overexpression of RRM2 profoundly reduced tamoxifen sensitivity and down-regulated ER-&agr; in otherwise tamoxifen sensitive breast cancer cells. Furthermore, breast cancer cells with high RRM2 had elevated Her-2 and EGFR expression, modulated ER-&agr; signaling and NFκB expression. These findings also indicate that it may be possible to use RRM2 as a prognostic factor in breast cancer patients under tamoxifen therapy, and can be considered a potential therapeutic target in tumors that have acquired resistance to tamoxifen. Finally, inhibition of RRM2 by drug Didox effectively eradicates the tamoxifen resistant population, revealing a potential beneficial effect of combination therapy that includes RRM2 inhibition to delay or abrogate tamoxifen resistance. In conclusion, the findings of this work delineate the important role of RRM2 in Akt induced and acquired tamoxifen resistance in breast cancer. It also provides a preclinical rationale for evaluating tamoxifen in combination with Didox for breast cancer treatment