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Computational Investigation Of Boundary-Layer Transition Mechanisms In A Blunt Cone
No full textIn this study, we have performed two-dimensional steady-state hypersonic CFD and one-and-two-dimensional steady-state heat conduction numerical simulations. We are using them to guide and study hypersonic boundary-layer transition ground testing physical experiments to be performed at Holloman High-Speed Test Track. We use surface heat transfer and fluid flow spot signatures to identify fluid flow regimes using laminar and turbulent numerical simulation solvers to understand boundary-layer transition thermocouple temperatures and fluid flow-forming structures. We have also analyzed the fluid flow in the geometries to be inviscid. We passed the CFD solution into the boundary-layer Harris code developed by NASA to explore the boundary layer for laminar fluid flow correlation predictions developed by PANT and Demetriades. Where analysis has been performed to study these effects under non-dimensional numbers, in this study, ANSYS Fluent and ANSYS Transient Heat Transfer and Python and MATLAB Codes have been used to compute the numerical solution of the Navier-Stokes and the Heat Equation. The coupling between the solvers allows us to perform a complete aero-thermal analysis of a blunt cone for our proposed experiment. The blunt cone numerical simulation has been validated using Stetsonâ??s experiment at Wright-Patterson Air Force Base Ludwig tube. Using this methodology, we can forecast boundary-layer transition for modern nose geometries
Rockets, Rovers, And Rocks, Oh My!
No full textThis body of work undertakes three distinct projects, all with the ultimate goal of improving the future efforts of human space exploration.Chapter 2 is a seismic analysis of rocket launch and landing operations. Being able to identify and understand anthropogenically induced seismic signals in comparison to naturally occurring seismic signals is an important step in characterizing and monitoring both types of signals on the Moon. Relatively few terrestrial studies have been performed to explore this, but there is a growing opportunity to record, discern, and understand the differences between anthropogenic and naturally occurring seismic signals due to the increasing pace of rocket launch activity by governmental agencies and commercial companies around the world. This study analyzes seismic data for launch and landing operations of the New Shepard reusable suborbital rocket system at Blue Originâ??s Launch Site One near Van Horn, Texas. Through the investigation of 14 launch events between October 2020 and August 2024, we were able to use data from existing seismic monitoring networks that captured data during Launch Site One operations to (a) visualize and discern seismic activity from the rocket launch and landing operations; (b) distinguish those signals from naturally occurring seismic signals; and (c) identify and correlate seismic signatures related to critical phases of rocket launch and landing operations. We can consistently identify a variety of seismic signals that correspond to the critical phases of Blue Originâ??s New Shepard flight profile with seismometers 36 km to 74 km away from Launch Site One. Data from seismometers closer to Launch Site One (~8 km) increase our ability to further characterize the seismic signals and to discern signals not evident at farther distances. Our results are an exciting step in the seismic analysis of terrestrial space port operations and launch-and landing operations on the surfaces of the Moon and Mars. Chapter 3 is a concept-of-operations for documenting planetary surface operations. NASA and its commercial partners are taking humanity back to the Moon and then on to Mars with the Artemis program. At present, it is planned for two astronauts to land on the lunar surface during each Artemis mission to conduct extravehicular activities (EVAs) in support of operations, engineering, and science objectives. Each Artemis astronaut is expected to have a video camera embedded into their spacesuit helmets and each be equipped with a handheld camera for still images. These first-person perspective imaging tools, along with the astronautsâ?? voice transmission, are presently all that will be available for the astronauts to document their EVAs and the associated operations, engineering, and science tasks. Motivated by the limitations of the Artemis imaging plan, we conducted a first-of-its-kind test of third-person perspective imaging concepts-of-operations (CONOPS) at the Kilbourne Hole planetary analog site. We utilized four first-person and 17 third-person perspective cameras during a 2-hour 40-minute 17-second analog EVA in which we conducted various Artemis-like geologic tasks, such as sample collection and station characterization. We obtained 19 hours 27 minutes 18 seconds of video and 1,294 still images, with which we demonstrate the value of third-person perspective cameras working in coordination with first-person perspective cameras. We are able to more completely capture the spatial and temporal context of crew activities, crew localization, collected data, and collected samples at multiple scales, as well as create supporting data products that can be used to reconstruct traverses and study sites. We highlight five case studies to demonstrate viable uses of the imaging tools and data at various scales of task execution. We strongly advocate for a camera affixed to a tripod that mounts to the tool cart in its monopod/mast configuration and can be quickly and easily detached, manipulated into its tripod configuration, and deployed to the planetary surface. Chapter 4 is a field geologic mapping and analysis of the distribution of volcanic blocks at Kilbourne Hole, New Mexico. Kilbourne Hole is a maar volcano in the Potrillo Volcanic Field in Southern New Mexico that was explosively formed approximately 24,000 years ago by a phreatomagmatic eruption. A characteristic of Kilbourne Hole that has been largely underexplored is the distribution of the basalt volcanic blocks around the crater rim. This research effort focuses on the spatial distribution of those basalt volcanic blocks to better understand and constrain the explosive and erosive history of this maar volcano. Through field mapping and analysis of high-resolution images, we (a) determine the farthest extent of volcanic blocks ejected during the explosive activity; (b) map the nonuniform abundance of volcanic blocks around the crater rim, including a relative absence of volcanic blocks in the southwest and southeast; and (c) identify and two, distinct populations of volcanic blocks that while lithologically identical, have distinct color appearances owing to their weathering characteristics. We present a conceptual model for the formation and erosional modification of the Kilbourne Hole surge deposits, particularly the burial and exhumation history of ejected blocks of the pre-existing Afton lava flow. This model allows us to constrain the original shape of the explosively-excavated crater to an ellipse, likely the result of multiple smaller explosive eruptions with a migrating explosion center along the Fitzgerald Fault, with later significant erosional modification to form the present-day topography. This research effort not only increases our knowledge of Kilbourne Holeâ??s eruptive and erosional history, but it aids in our understanding of maar volcanology both on and off the Earth, with timely application to Mars surface exploration and resulting imagery obtained by the Perseverance rover in May 2024
Understanding The Factors Associated With The Targeting Of Prison Gangs By Specialized Gang Units (sgus) In The United States
No full textSpecialized gang units (SGUs) are prominent in police departments in the United States with their sole purpose to respond to gang activity across the country. SGUs vary in the types of gangs they target, resources available, officer composition, and the types of enforcement activities they use. SGUs have encountered various controversies such as exaggerating the gang problem in the media, for distorted intelligence in their gang databases, and for racial stereotyping and harassment among Hispanics in particular. Research regarding SGUs is limited in general, but even fewer studies exist on the targeting efforts of prison gangs by SGUs. Prison gang activities often extend beyond the walls of correctional institutions and onto the streets. Prison gang research and official reports from state and federal agencies show that multi-agency collaborations to investigate, surveil, and prosecute prison gangs in the community is common, but no empirical assessments exist on which SGUs are involved in the targeting of prison gangs. The overarching goal of this work is to advance understanding of SGUs in the context of prison gang surveillance and enforcement across the country. To fill this gap in the literature, this thesis examined factors associated with the targeting of prison gangs by SGUs using a national survey of specialized gang units in the United States. I examined a range of theoretically and empirically informed factors expected to differentiate SGUs that target prison gangs from those that do not. Findings showed important differences between SGUs focused on prison gangs from SGUs without this focus across contingency theory, resource dependency theory, and social threat perspective factors. Implications for research, policy, and practice are discussed
Local CEOs and Voluntary Disclosure: Evidence from Non-GAAP Earnings
No full textIn the U.S. CEO labor market, firms are more likely to hire local CEOs than non-local CEOs. We explore the consequences of this hiring practice on voluntary disclosure of firm financial information in the non-GAAP earnings setting. Using a sample of S&P 1500 firms from 2003 to 2020, we show that firms led by local CEOs are less likely to provide non-GAAP earnings than those led by non-local CEOs. This result holds across a battery of robustness tests, including a placebo test, adopting different matching procedures, an instrumental variable approach, various regression specifications, and alternative samples using CEO turnover events. We also find evidence that when non-GAAP earnings are disclosed, the quality of non-GAAP earnings from firms with local CEOs is generally higher than those provided by firms with non-local CEOs. Our results suggest that the hiring bias towards local CEOs shapes firms’ voluntary disclosure practices
Cartel Breakdown: The Impact of Demonopsonization on Market Concentration
No full textThe exogenous removal of labor restrictions mandated by Alston vs. NCAA (National Collegiate Athletic Association) has provided a unique natural experiment for analyzing the impact of demonopsonization on market concentration. Using basketball tournament data between 2003 and 2024 we find evidence of increased concentration in performance among higher-tiered programs. The larger magnitude of estimates for women’s programs likely results from wider dispersion in market demand for participating programs predating the reforms. We also analyze parity in regular-season conference play and fail to detect a relationship between the changes and dispersion for higher-tiered conferences, but we do find a relationship for lower-tiered conferences, a result we attribute to adjustments to increased transfers toward more prominent programs. These findings are crucial not only for measuring the effects of removing mobility barriers but also for offering valuable insights into the broader economic impact as universities adjust to evolving financial realities
A Simple Higher-Order Rational Email-Game Bubble Model and Some Implications for Momentum
No full textWe propose a simple higher-order rational greater-fool bubble model, where the period-1 information structure is motivated by an “information leakage” story, reminiscent of Rubinstein’s (1989) email game. Our nth-order bubble model requires only n + 2 states, and is thus simpler than that in Conlon (2004), which required n^2 + 5n + 5 states. Our model is also related to the two-agent-type case of the Araujo and Doblas-Madrid’s (2022) model, and we argue that our model might therefore not capture “momentum,” though simple extensions of it may be able to
Every Feasibly Computable Reals-to-Reals Function Is Feasibly Uniformly Continuous
No full textIt is known that every computable function is continuous; moreover, it is computably continuous in the sense that for every ε \u3e 0, we can compute δ \u3e 0 such that δ-close inputs lead to ε-close outputs. It is also known that not all functions which are, in principle, computable, can actually be computed: indeed, the computation sometimes requires more time than the lifetime of the Universe. A natural question is thus: can the above known result about computable continuity of computable functions be extended to the case when we limit ourselves to feasible computations? In this paper, we prove that this extension is indeed possible
Why Bernstein Polynomials: Yet Another Explanation
No full textIn many computational situations -- in particular, in computations under interval or fuzzy uncertainty -- it is convenient to approximate a function by a polynomial. Usually, a polynomial is represented by coefficients at its monomials. However, in many cases, it turns out more efficient to represent a general polynomial by using a different basis -- of so-called Bernstein polynomials. In this paper, we provide a new explanation for the computational efficiency of this basis
