The truncated and evolving inner accretion disc of the black hole GX 339-4

The nature of accretion onto stellar mass black holes in the low/hard state remains unresolved, with some evidence suggesting that the inner accretion disc is truncated and replaced by a hot flow. However, the detection of relativistic broadened Fe emission lines, even at relatively low luminosities, seems to require an accretion disc extending fully to its innermost stable circular orbit. Modelling such features is however highly susceptible to degeneracies, which could easily bias any interpretation. We present the first systematic study of the Fe line region to track how the inner accretion disc evolves in the low/hard state of the black hole GX 339$-$4. Our four observations display increased broadening of the Fe line over two magnitudes in luminosity, which we use to track any variation of the disc inner radius. We find that the disc extends closer to the black hole at higher luminosities, but is consistent with being truncated throughout the entire low/hard state, a result which renders black hole spin estimates inaccurate at these stages of the outburst. Furthermore, we show that the evolution of our spectral inner disc radius estimates corresponds very closely to the trend of the break frequency in Fourier power spectra, supporting the interpretation of a truncated and evolving disc in the hard state.Comment: Accepted for publication in A&A. Some typos corrected from version

UAS ANALYSIS OF WAVE RUNUP AT COASTAL CALIFORNIA EPHEMERAL RIVERS

Dynamical interactions between small-scale ephemeral river plumes and neighboring littoral regions directly affect sediment transport, nearshore morphology, bathymetry, and beach topography. Research into wave runup and river breaching events directly influences coastal engineering planning, and if current and accurate, can inform naval operational planning. Consistent and reliable data collection for these processes is challenging due to the active nature of both the surf and swash zones, and the rapid decay of data accuracy. This research expands previous wave runup and river breach studies, while simultaneously assessing the viability of using small commercially available unmanned aerial systems (UAS) as a nearshore research tool that is easily employable, low in cost, yet accurate. Existing empirical runup models have historically shown high predictive skill for gradually sloping smooth beaches; however, in many cases, do not account for rocky bottoms or surf-zone variations such as sand bars. Research sites were selected based on their distinct features related to alongshore profile, bathymetry, and bottom type. The main result was that models do not predict runup accurately in complex coastal regions that include rocky bottoms, river mouths, or sandbars. The UAS imagery analysis reinforced limitations of utilizing these models and demonstrated a means to identify unique surf-zone features, and accurately capture runup excursions at diverse beaches.NSFOutstanding ThesisLieutenant, United States NavyApproved for public release. Distribution is unlimited

Revealing accretion onto black holes: X-ray reflection throughout three outbursts of GX 339-4

Understanding the dynamics behind black hole state transitions and the changes they reflect in outbursts has become long-standing problem. The X-ray reflection spectrum describes the interaction between the hard X-ray source (the power-law continuum) and the cool accretion disc it illuminates, and thus permits an indirect view of how the two evolve. We present a systematic analysis of the reflection spectrum throughout three outbursts (500+ observations) of the black hole binary GX 339-4, representing the largest study applying a self-consistent treatment of reflection to date. Particular attention is payed to the coincident evolution of the power-law and reflection, which can be used to determine the accretion geometry. The hard state is found to be distinctly reflection weak, however the ratio of reflection to power-law gradually increases as the source luminosity rises. In contrast the reflection is found dominate the power-law throughout most of the soft state, with increasing supremacy as the source decays. We discuss potential dynamics driving this, favouring inner disc truncation and decreasing coronal height for the hard and soft states respectively. Evolution of the ionisation parameter, power-law slope and high-energy cut-off also agree with this interpretation.Comment: Accepted for publication in MNRA

Study of an engine flow diverter system for a large scale ejector powered aircraft model

Requirements were established for a conceptual design study to analyze and design an engine flow diverter system and to include accommodations for an ejector system in an existing 3/4 scale fighter model equipped with YJ-79 engines. Model constraints were identified and cost-effective limited modification was proposed to accept the ejectors, ducting and flow diverter valves. Complete system performance was calculated and a versatile computer program capable of analyzing any ejector system was developed

Pressures measured in flight on the aft fuselage and external nozzle of a twin-jet fighter

Fuselage, boundary layer, and nozzle pressures were measured in flight for a twin jet fighter over a Mach number range from 0.60 to 2.00 at test altitudes of 6100, 10,700, and 13,700 meters for angles of attack ranging from 0 deg to 7 deg. Test data were analyzed to find the effects of the propulsion system geometry. The flight variables, and flow interference. The aft fuselage flow field was complex and showed the influence of the vertical tail, nacelle contour, and the wing. Changes in the boattail angle of either engine affected upper fuselage and lower fuselage pressure coefficients upstream of the nozzle. Boundary layer profiles at the forward and aft locations on the upper nacelles were relatively insensitive to Mach number and altitude. Boundary layer thickness decreased at both stations as angle of attack increased above 4 deg. Nozzle pressure coefficient was influenced by the vertical tail, horizontal tail boom, and nozzle interfairing; the last two tended to separate flow over the top of the nozzle from flow over the bottom of the nozzle. The left nozzle axial force coefficient was most affected by Mach number and left nozzle boattail angle. At Mach 0.90, the nozzle axial force coefficient was 0.0013

Results of an aqueous source term model for a radiological risk assessment of the Drigg LLW Site, U.K.

A radionuclide source term model has been developed which simulates the biogeochemical evolution of the Drigg low level waste (LLW) disposal site. The DRINK (DRIgg Near field Kinetic) model provides data regarding radionuclide concentrations in groundwater over a period of 100,000 years, which are used as input to assessment calculations for a groundwater pathway. The DRINK model also provides input to human intrusion and gaseous assessment calculations through simulation of the solid radionuclide inventory. These calculations are being used to support the Drigg post closure safety case. The DRINK model considers the coupled interaction of the effects of fluid flow, microbiology, corrosion, chemical reaction, sorption and radioactive decay. It represents the first direct use of a mechanistic reaction-transport model in risk assessment calculations

Bounded analysis of constrained dynamical systems: a case study in nuclear arms control

We introduce a simple dynamical system that describes key features of a bilateral nuclear arms control regime. The evolution of each party's beliefs and declarations under the regime are represented, and the e ects of inspection processes are captured. Bounded analysis of this model allows us to explore { within a nite horizon { the consequences of changes to the rules of the arms control process and to the strategies of each party, bounded scope invariants for variables of interest, and dynamics for initial states containing strict uncertainty. Together these would potentially enable a decision support system to consider cases of interest irrespective of unknowns. We realize such abilities by building a Python package that draws on the capabilities of a Satis ability Modulo Theory (SMT) solver to explore particular scenarios and to optimize measures of interest { such as the belief of one nation in the statements made by another, or the timing of an unscheduled inspection such that it has maximum value. We show that these capabilities can in principle support the design or assessment of future bilateral arms control instruments by applying them to a set of representative and relevant test scenarios with realistic nite horizons

Hyperacute Corticosteroid Treatment of Optic Neuritis at the Onset of Pain May Prevent Visual Loss: A Case Series

Aim. To show that high-dose corticosteroids may prevent visual loss in patients with optic neuritis (ON) treated at the prodromal, hyperacute, phase of retrobulbar pain. Method. Prospective case series: patients were recruited with a history of ON associated with pain. The patients were advised to report immediately to the investigators should the pain recur in either eye. Where possible, orbital magnetic resonance imaging (MRI) was performed to confirm a recurrence of ON and treatment with high-dose corticosteroids was commenced. Visual function and the patient's subjective account were monitored. Results. Eight patients (including cases of MS, CRION and NMO) presented in the hyperacute phase. MRI confirmed optic nerve inflammation in 5/5. Treatment was commenced immediately, and, in all cases, no visual loss ensued. Conclusion. MRI can be used to confirm acute optic neuritis prior to visual loss in the hyperacute phase. We suggest that treatment with high-dose corticosteroids may abort the attack and prevent loss of vision in patients with ON who are treated at the onset of pain. This has potential implications for the management of acute ON and also for our understanding of the pathogenesis and potential therapeutic targets in the neuroinflammatory conditions associated with ON