136879 research outputs found
Sort by
Dry Cell Radiation Field Characterization at the Texas A&M University Nuclear Engineering and Science Center
No full textThe Nuclear Engineering and Science Center at the Texas A&M Engineering Experiment Station routinely conducts experiments involving neutron and gamma irradiations with a 1-MW TRIGA research reactor. The Center is equipped with a dry irradiation cell, which can be used for experiments requiring a mixed neutron/gamma field. However, in recent years the dry irradiation cell has not been utilized and there exists no surviving information on the radiation environment inside the cell during operation. To resolve this, a full characterization of the neutron and gamma radiation environment inside the cell has been completed.
To fully characterize the neutron flux environment inside the dry irradiation cell, neutron activation analysis has been performed on two different configurations: one with shielding and one without shielding. The program STAYSL PNNL was employed to unfold the full neutron spectrum using the experimental results of the neutron activation analysis. Furthermore, thermoluminescent dosimetry has been utilized to calculate the absorbed gamma dose rates of silicon and tissue inside the cell for each configuration. Each technique has been utilized according to industry standard practices.
The results of this work have shown that adding shielding material to the dry irradiation cell window will have a significant impact on the quantity and energy of radiation which enters the cell. With no shielding present in the window, 50-kW reactor operation produces a neutron flux of 2.59E+09 and a gamma dose rate 50.84 krad/hr in silicon. When 8 inches of high-density polyethylene shielding and 0.8 inches of lead shielding are installed in the window, the neutron flux drops to 4.81E+07 while the gamma dose rate falls to 13.45 krad/hr in silicon
Allocation of Peptidoglycan Resources Between the Rod System and Class-A Penicillin-Binding Proteins in Myxococcus xanthus
No full textPeptidoglycan (PG) is a polymer scaffolding surrounding the cell membrane of bacteria and is key to survival as it aids in preserving cell structure and protects against harmful stresses. It is composed of alternating N-acetylglucosamine and N-acetylmuramic acid strands that are crosslinked through peptide chains. The synthesis of PG is a highly dynamic and tightly regulated process, spanning across the cytoplasm, inner membrane, and periplasm in gram-negative bacteria. PG synthesis is vital for cell survival and remodeling of the sacculus is required during cell elongation and division as well as during PG repair. PG synthesis has been heavily studied, however, it is still unknown how the allocation of PG precursors are portioned between the two PG synthase systems of the class-A penicillin-binding proteins and the Rod system. Here we take advantage of the monomer-dimer characteristic of the phospho-MurNAc-pentapeptide translocase protein, MraY, as a proxy for PG precursor usage of PG synthases. Using single particle tracking photoactivatable localization microscopy, we show that the Rod system is the main synthase system active in vegetative growth while aPBP���s are responsible for PG repair. This study aims to further understand the properties of PG synthesis and how the cell divides its resources during vegetative growth and repair
The Role of Auditors in Classification of Debt Securities: Evidence From Banks
No full textFirms that hold debt securities can exploit the discretion in security classification and classify securities as held-to-maturity when the classification provides a more favorable accounting treatment (hereby referred to as security classification shifting). In this study, I utilize the banking industry to examine whether auditors are associated with their clients��� security classification shifting strategies. I find a positive association between a bank-client���s security classification shifting and the classification shifting at other bank-clients audited by the same audit office. This finding is consistent with auditors influencing their clients��� security classification strategies. The effect of auditors is concentrated in banks engaging an audit office with a greater emphasis on bank-specific non-audit services and in smaller banks which suggests that auditors are more likely to influence their clients��� financial reporting strategies when the auditor has a greater proclivity to provide advice and when clients have a greater need for financial reporting expertise. Finally, I find evidence suggesting that industry-expert auditors limit security classification shifting in resource-constrained banks; however, non-expert auditors do not appear to have a similar effect
Anger-Induced Early Childhood Respiratory Sinus Arrhythmia and Parenting Style: Predictors of Toddler Externalizing Behavior Problems and School Readiness
No full textEarly childhood emotional regulation has been linked to favorable academic, behavioral and socioemotional outcomes. Respiratory sinus arrhythmia (RSA) in response to an emotion induction has been studied as an indicator of emotional regulation. This study investigated children���s dynamic RSA change in response to a negative-affect evoking laboratory episode, and how RSA relates to behavior problems and school readiness. The sample consisted of 58 typically developing children (males = 24, mean age = 3.1, SD = .02) and their parents (mothers = 56, mean age = 35.04, SD = 5.25) in the Bryan-College Station area. Greater RSA suppression during the anger induction was associated with lower externalizing behavioral problem scores and higher school readiness scores. Children of authoritarian parents had the highest school readiness scores across levels of RSA suppression but the highest externalizing problems for those with low emotional regulation. Girls showed more pronounced patterns of RSA suppression whereas boys��� RSA levels remained comparatively flat over the anger induction. My study contributes to the emotion regulation literature from a family study perspective while employing multi-method assessments of child temperament. The findings shed further insight to the relationship between emotion regulation and cognitive performance. This research has implications for preschool readiness, cognition and behavioral interventions
Sequential Decision-Making Under Uncertainty in Multi-Robot Target Tracking Application
No full textA significant advance in robotics and automation is making robots handle uncertainty, a prerequisite to deploying robots outside the lab. To interact with a stochastic environment, the significant effort of evaluating possible conditions challenges the robotic system���s reaction and functionality. For example, how to meet the typical 1 Hz decision frequency with online planning to accommodate uncertainties in a multi-robot system, combined by robots maintaining multiple robotic layers in a single-board computer.
This thesis focuses on such trade-offs between computation and optimality in the world of uncertainty. We formalize planning tasks as Partial Observation Markov Decision Process (POMDP) as it models uncertainties in a horizon-based mathematical model.
The first topic is to plan under time-dependent stochastic constraints, specifically traffic signals. The vehicle���s pass at the intersection depends on the stochastic fixed-pattern traffic signal, introducing the time dimension to the planning space. We propose a spatial horizon-based search to avoid such a curse of additional dimensionality in the planning. Furthermore, the uncertainty of the future signal is overcome by the event of an initial signal change, after which the problem is no longer stochastic. With probabilistic modeling of traffic signal dynamics, we define such planning as an MDP and obtain the solution.
Uncertainty needs tackling in partially observable environments and multi-agent systems. Our second topic, multi-sensor active target tracking, involves interacting with objects of interest (OOI) in a multi-robot system. The objective is to deploy multiple robots with a limited field of view (FoV) to maximize the system-wise target tracking performance. We formulate the problem as a POMDP and apply the approximate dynamic programming (ADP) method to generate the receding horizon control policy for the POMDP. Planning horizon incorporates the estimation of OOIs to handle tricky target-tracking scenarios such as divergent OOI trajectories. On the other hand, extending the horizon increases resilience to the uncertainty of the world model, such as the unknown object of occlusion to the sensing.
The multi-agent aspect injects other robots��� actions, which become a consideration in the uncertainty of the ego agent. Agent-by-agent planning reduces the complexity of planning, and we found the performance boundary of such sequential decision-making based on the locally Greedy algorithm. Since the original locally Greedy algorithm does not consider agents��� policies, which are not updated, adding the intention of those agents shows improvement based on our empirical studies. From implementing multi-agent planning based on receding horizon and objective optimization, we observe the emergent behaviors of cooperation. We show the consistency between planning algorithms��� optimality and the frequency of cooperative behavior in active target-tracking scenarios.
In summary, this dissertation mainly includes algorithmic research in robotic planning in an environment with various uncertainties: sensing, world model, and other agents��� decisions. It also contributes to the eco-driving and multi-robot sensing system application in the problem statement, algorithm design, behavior analysis, and simulation
Feasibility of Mixed-Integer Linear Programming for Onboard Planning in Distributed Earth Observation Satellite Systems
No full textPlanning is traditionally completed on the ground, which limits swift response to events of interest. As a result, there is an expanding need for onboard planning for satellites. This sparks exploration of the feasibility of reactive Earth observation using optimization for onboard, edge processing of plans. Reactive Earth observation lowers response time to events of interest, such as tropical storms or the formation of algal blooms.
This thesis compares a global optimization method, mixed-integer linear programming (MILP), with two less computationally expensive local optimization methods: greedy and forward search algorithms. This planning problem models a satellite constellation operating within an inland water quality remote sensing mission over a 24-hour simulation period. The water quality mission poses a challenge due to the small swath of relevant onboard instruments used to observe the large quantity of water bodies.
Two respective cases of 5- and 10-satellite constellations are applied to investigate scalability of the problem. On average, the local optimization methods achieve 64% of MILP performance. Smaller 1- to 2-hour planning horizons generally have little effect on MILP performance. Additionally, the MILP successfully solves problem sets of up to 580,000 variables for the 5-satellite problem and up to 900,000 variables for the 10-satellite problem. The MILP achieves these metrics in planning horizons of up to 8-hours for the 5-satellite problem and in planning horizons up to 4-hours in the 10-satellite problem.
A Raspberry Pi was employed to characterize the feasibility of using MILP for onboard planning. The Raspberry Pi could solve problems that did not exceed its memory capacity and was able to solve at least half as many problems as the PC was able to solve, depending on the size of the problem set.
Performance results build an argument to use small planning horizons to create plans in a reasonable amount of time. Raspberry Pi results suggest that smaller problem sets that do not exceed memory capacity during solving ensure that onboard planning is feasible for MILP. Overall, results suggest that MILP is a great method for satellite planning for relatively small problems
Complex Fluids Formed from Surfactant-Based Dynamic Binary Complexes
No full textThis work attempts to study the rheological properties and corresponding morphologies associated with complex fluids formed by novel surfactant-based dynamic binary complexes. Dynamic binary complexes refer to non-covalent supramolecular assemblies of surfactants and an appropriate complexing agent, giving rise to the potential for stimuli-responsiveness. The fundamental mechanisms that constitute viscosity modifier systems are an important point of discussion as well. Such chemistries are capable of interesting nanoarchitectures in aqueous suspension, that can have wide-ranging implications in several multi-billion dollar industries such as pharmaceuticals, personal care and the energy sector.
We examined an aqueous system of zwitterionic surfactant stearyl betaine with diethylenetriamine as the complexing agent, which displayed pH-responsive rheological properties and morphological changes. The surfactant was synthesized via a straightforward condensation reaction and then mixed with diethylenetriamine in an aqueous suspension at 2wt% to formulate the system. Notably, acidic conditions exhibited substantial steady-shear viscosities (up to 160 Pa.s) and viscoelastic behavior, decreasing with rising pH. A temperature analysis using zero-shear viscosities and differential scanning calorimetry unveiled thermodynamic transitions. Morphological insights from AFM and SAXS revealed distinctive bilayer nanotubules at low pH, transforming into bilayer sheets and then vesicles with increasing pH.
We then studied a system comprising of ��-cyclodextrin (��-CD) with three sulfonic surfactants: sodium hexadecylsulfate, sodium dodecylbenzenesulfonate, and myristyl sulfobetaine. Optimal axial growth and high viscosities in the suspensions were achieved with a ��-CD:surfactant ratio of 2:1. The complexation processes exhibited nanostructural phase behaviors and rheological properties sensitive to the molecular structure of sulfonic surfactants. DIC microscopy provided visual insights into the microstructure regarding sulfonate molecular architecture. Additionally, surface tension measurements, along with FTIR and NMR spectroscopies, deepened the understanding of interactions leading to complexation and nanostructural features. The proposed mechanics aimed to correlate supramolecular morphologies with rheological properties
Optimizing Infectious Disease Control: Strategies for Social Separation and Vaccine Allocation with Equity Consideration
No full textAs global threats from infectious diseases intensify, as highlighted by the COVID-19 pandemic, the urgency to enhance control measures becomes evident. Strategies such as social separation and vaccine allocation are pivotal in disease management. However, despite extensive research, many models still fall short. They rely on oversimplified assumptions such as population homogeneity and a single-wave pattern of infection spread. Current research still lacks comprehensive approaches in addressing the effective and equitable implementation of these strategies in more complex, realistic scenarios.
To address these gaps, we explore various models for social separation and vaccine distribution, considering individual-specific factors and the multi-wave nature of pandemics observed in reality. Focusing on efficiency and equity in disease mitigation, we uncover key components of an optimal infectious disease control strategy. These insights help us to formulate effective algorithms, understanding the trade-offs between efficacy, costs, and fairness. Our work also leads to the development of an efficient, fair clustering algorithm that not only performs well in our disease mitigation context but also excels across various datasets.
Case studies underscore the advantages of strategies tailored to specific individual information and dynamic behavior. Such approaches are more effective, cost-efficient, and equitable than traditional disease control measures. The fair clustering algorithm we developed further demonstrates its advantages over benchmark algorithms
John Bickham field notebook: Mamm_AK201-AK300.pdf
No full textEach page/AK number corresponds to a karyotype slide data and/or unique specimen.Data pages for Mamm_AK201-AK300 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
���Let the Storm Begin!���: Ethnic Politics, German Americans, and the Mass Lynching of Eleven Italians in New Orleans, 1830-1899
No full textThis thesis argues elite German New Orleanians used the anti-Italian hysteria in New Orleans following Police Chief David Hennessy���s death in 1890 to promote their precarious social status among the elite White New Orleans native-born community. 1890 is only one year in the German community���s long endeavor to prove their status as members of elite White New Orleans society. Upon their arrival in the 1830s, German immigrants navigated anti-immigrant sentiment directed towards them. Not until after the Civil War did the German New Orleanians��� social status begin to shift within the southern socio-racial hierarchy. This thesis will demonstrate that German New Orleanians benefitted directly from the expansion of the definition of whiteness in the late nineteenth century as they participated in the racialization of the city���s Italian community. Sources for this study came largely from the city���s local English-language and German-language presses