514 research outputs found
Receding-horizon switched linear system design: a semidefinite programming approach with distributed computation
No full textThis dissertation presents a framework for analysis and controller synthesis problems for switched linear systems. These are multi-modal systems whose parameters vary within a finite set according to the state of a discrete time automaton; the switching signal may be unconstrained or may be drawn from a language of admissible switching signals. This model of system dynamics and discrete logic has many applications in a number of engineering contexts. A receding-horizon type approach is taken by designing controllers with access to a finite-length preview of future modes and finite memory of past modes; the length of both preview and memory are taken as design choices. The results developed here take the form of nested sequences of SDP feasibility problems. These conditions are exact in that the feasibility of any element of the sequence is sufficient to construct a suitable controller, while the existence of a suitable controller necessitates the feasibility of some element of the sequence.
Considered first is the problem of controller synthesis for the stabilization of switched systems. These developments serve both as a control problem of interest and a demonstration of the methods used to solve subsequent switched control problems. Exact conditions for the existence of a controller are developed, along with converse results which rule out levels of closed-loop stability based on the infeasibility of individual SDP problems. This permits the achievable closed-loop performance level to be approximated to arbitrary accuracy.
Examined next are two different performance problems: one of disturbance attenuation and one of windowed variance. For each problem, controller synthesis conditions are presented exactly in the form of SDP feasibility problems which may be optimized to determine levels of performance. In both cases, the performance level may be taken as uniform or allowed to vary based on the switching path encountered.
The controller synthesis conditions presented here can grow both large and computationally intensive, but they share a common structural sparsity which may be exploited. The last part of this dissertation examines this structure and presents a distributed approach to solving such problems. This maintains the tractability of these results even at large scales, expanding the scope of systems to which these methods can be applied.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2019-02-05 without embargo termsThe student, Raymond Essick V, accepted the attached license on 2018-10-16 at 21:27.The student, Raymond Essick V, submitted this Dissertation for approval on 2018-10-16 at 21:37.This Dissertation was approved for publication on 2018-10-22 at 15:08.DSpace SAF Submission Ingestion Package generated from Vireo submission #13035 on 2019-02-05 at 11:08:24Made available in DSpace on 2019-02-06T19:32:44Z (GMT). No. of bitstreams: 4
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Previous issue date: 2018-10-2
ORBITAL DECAY OF HOT JUPITERS DUE TO NONLINEAR TIDAL DISSIPATION WITHIN SOLAR-TYPE HOSTS
No full textWe study the orbital evolution of hot Jupiters due to the excitation and damping of tidally driven g-modes within solar-type host stars. Linearly resonant g-modes (the dynamical tide) are driven to such large amplitudes in the stellar core that they excite a sea of other g-modes through weakly nonlinear interactions. By solving the dynamics of large networks of nonlinearly coupled modes, we show that the nonlinear dissipation rate of the dynamical tide is several orders of magnitude larger than the linear dissipation rate. We find stellar tidal quality factors Q[' over *] ≃ 10[superscript 5]–10[superscript 6] for systems with planet mass M[subscript p] ≳ 0.5M[subscript J] and orbital period P ≲ 2\;\mathrm{days},$ which implies that such systems decay on timescales that are small compared to the main-sequence lifetime of their solar-type hosts. According to our results, there are ≃ 10 currently known exoplanetary systems, including WASP-19b and HAT-P-36-b, with orbital decay timescales shorter than a Gyr. Rapid, tidally induced orbital decay may explain the observed paucity of planets with M[subscript p] ≳ M[subscript J] and P < 2 days around solar-type hosts and could generate detectable transit-timing variations in the near future.National Science Foundation (U.S.) (Laser Interferometer Gravitational-Wave Observatory PHY-0757058)United States. National Aeronautics and Space Administration (NNX14AB40G
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The twelve large colour prints of William Blake: a study on techniques, materials and context
No full textThe aim of this thesis is to study in entirety the group of large colour prints which William Blake made between 1795 and 1805. The series of prints represents the single most important and complete development of Blake’s skill as an innovative printmaker. Although they include some of Blake’s best-known images, they have not been studied before in their entirety or from the point of view of analysing the techniques and methods Blake had used. My study will show how Blake executed these truly impressive prints in terms of materials, method and motives. The first half of the thesis deals with the materialistic aspects of Blake’s colour printing. In chapter one tracing the controversial two-pull discussion to the root, I will make clear the focus points as well as revealing the early tradition of experimental criticism on Blake’s colour printing method. Focusing on two important critics, W. Graham Robertson and Ruthven Todd, and the periods they lived, I attempt to reveal the role they played in a wider context. Also I show how the tradition of Blake’s art was inherited directly through the Ancients to the Pre-Raphaelite Brotherhood, which leads to Robertson and Todd. In the second chapter I deal with the development of Blake’s colour printing experiments. It is obvious that the Twelve Large Colour Prints were produced as a result of Blake’s series of colour printing experiments, starting with monocolour simple prints, going through the illuminated books progressing with more colours and higher skills
Impact of the tidal p−g instability on the gravitational wave signal from coalescing binary neutron stars
No full textRecent studies suggest that coalescing neutron stars are subject to a fluid instability involving the nonlinear coupling of the tide to p modes and g modes. Its influence on the inspiral dynamics and thus the gravitational wave signal is, however, uncertain because we do not know precisely how the instability saturates. Here we construct a simple, physically motivated model of the saturation that allows us to explore the instability’s impact as a function of the model parameters. We find that for plausible assumptions about the saturation, current gravitational wave detectors might miss >70% of events if only point particle waveforms are used. Parameters such as the chirp mass, component masses, and luminosity distance might also be significantly biased. On the other hand, we find that relatively simple modifications to the point particle waveform can alleviate these problems and enhance the science that emerges from the detection of binary neutron stars.United States. National Aeronautics and Space Administration (ATP Grant NNX14AB40G)National Science Foundation (U.S.)Laser Interferometer Gravitational Wave Observator
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Variation in the autism candidate gene GABRB3 modulates tactile sensitivity in typically developing children
No full textBackground: Autism spectrum conditions have a strong genetic component. Atypical sensory sensitivities are one of the core but neglected features of autism spectrum conditions. GABRB3 is a well-characterised candidate gene for autism spectrum conditions. In mice, heterozygous Gabrb3 deletion is associated with increased tactile sensitivity. However, no study has examined if tactile sensitivity is associated with GABRB3 genetic variation in humans. To test this, we conducted two pilot genetic association studies in the general population, analysing two phenotypic measures of tactile sensitivity (a parent-report and a behavioural measure) for association with 43 SNPs in GABRB3.
Findings: Across both tactile sensitivity measures, three SNPs (rs11636966, rs8023959 and rs2162241) were nominally associated with both phenotypes, providing a measure of internal validation. Parent-report scores were nominally associated with six SNPs (P <0.05). Behaviourally measured tactile sensitivity was nominally associated with 10 SNPs (three after Bonferroni correction).
Conclusions: This is the first human study to show an association between GABRB3 variation and tactile sensitivity. This provides support for the evidence from animal models implicating the role of GABRB3 variation in the atypical sensory sensitivity in autism spectrum conditions. Future research is underway to directly test this association in cases of autism spectrum conditions
Job’s Gethsemane: tradition and imagination in William Blake’s illustrations for the book of job
No full textBlake created two versions of his Illustrations of the Book of Job, and it is now agreed that about twenty years separates his first watercolour series and the final engraved set of plates. The first chapter is biographical and technical: it establishes that the Butts series of water-colours was the product of the tumultuous and creative years 1805-10, following a time wh6n Blake experienced a strong sense of vision and Christian regeneration; whereas the engraved set was produced 1821-1826, at the end of his life. It also reviews all Blake's treatments of the Job theme. The friends-turned-accusers seem to have been a central pre-occupation. Blake's illustrations contain important elements which are not found in the Old Testament text. I have followed Bo Lindberg's principle that explanation should be sought in the artistic tradition, and in the work itself The second chapter concentrates on the tradition available to Blake, following and supplementing Lindberg's examination of the influence of the apocryphal Testament of Job, and of the artistic tradition of seeing Job as alter Christus and as Christian. Chapters three to five, interpreting Blake's imaginative use of this material, are new both in focussing on the Butts set, and in exploring the importance to Blake of St.Teresa, Fenelon, Mme. Guyon, Hervey and other people of prayer. Also discussed are Joseph Hallett's radical biblical commentary, of which Blake owned a copy, variant proofs discovered by Robert Essick of the first and last engraved plates, and the thirteenth century Job wall- paintings discovered in 1800 in St. Stephen's Chapel, Westminster. Blake's Job was unique in the corpus of his work. Previous studies have followed Wicksteed in concentrating on the engraved set, and no one has explored the implications of the earlier dating now agreed for the watercolour series. The thesis is essentially concerned with Blake's Christocentric theme, and Job's inner journey of prayer, in these illustrations. Conclusions drawn differ substantially from Wicksteed's
Orbital Decay of Hot Jupiters due to Weakly Nonlinear Tidal Dissipation
No full textWe study tidal dissipation in hot Jupiter host stars due to the nonlinear damping of tidally driven g -modes, extending the calculations of Essick & Weinberg to a wide variety of stellar host types. This process causes the planet’s orbit to decay and has potentially important consequences for the evolution and fate of hot Jupiters. Previous studies either only accounted for linear dissipation processes or assumed that the resonantly excited primary mode becomes strongly nonlinear and breaks as it approaches the stellar center. However, the great majority of hot Jupiter systems are in the weakly nonlinear regime in which the primary mode does not break but instead excites a sea of secondary modes via three-mode interactions. We simulate these nonlinear interactions and calculate the net mode dissipation for stars that range in mass from 0.5 M _⊙ ≤ M _⋆ ≤ 2.0 M _⊙ and in age from the early main sequence to the subgiant phase. We find that the nonlinearly excited secondary modes can enhance the tidal dissipation by orders of magnitude compared to linear dissipation processes. For the stars with M _⋆ ≲ 1.0 M _⊙ of nearly any age, we find that the orbital decay time is ≲100 Myr for orbital periods P _orb ≲ 1 day. For M _⋆ ≳ 1.2 M _⊙ , the orbital decay time only becomes short on the subgiant branch, where it can be ≲10 Myr for P _orb ≲ 2 days and result in significant transit time shifts. We discuss these results in the context of known hot Jupiter systems and examine the prospects for detecting their orbital decay with transit timing measurements
William Blake and the visionary poetry of the law.
No full textPhDThis dissertation examines the meaning of law in Blake's work. I argue that Blake's poetry
intersects with contemporaneous challenges to the traditional model of the ancient constitution,
a debate which I present as a conflict between custom and code. Blake's support for the French
Revolution's overthrow of the customary systems of the ancien regime is countered by his
nervousness about the rights-based discourse advanced by leading radical intellectuals such as
Thomas Paine, a belief that the new systems which they proposed merely re-stated those which
they sought to replace within an even narrower compass.
Law is also a contested ground within radical political discourse of this period; although the
dominant proposals advocated the enshrinement of fundamental rights and the codification of
law, there was also a tendency towards a more enthusiastic radicalism These millenarian
groups, emerging from antinomian heresy, rejected the notion of life being framed within a set
of moral laws. I argue that Blake cannot easily be placed in either group; his work exhibits a
fidelity to the redemptive potential of law, coupled with a real concern that to define freedoms
in legal terms serves to limit rather than to liberate.
Blake's work thus engages with a problem of the period: how to understand the new
discourses of law. The customary account of the ancient English conunon law is predicated on
the idea that it is codified, yet not written down; secular, though grounded in divine principle.
These ambivalences are exploited by Blake in his poetic exploration of the law in the 1790s. In
his nineteenth-century epics, Blake finds increasing help in dissenting religion's reconstruction
of a radicalized Jesus. Through this radical prophetic voice, Blake is able to construct a
redemptive legality founded on a deinstitutio-nalized Christianity, a constitutionalism that is
also recovered from the conventional customary account
Constraining the p-Mode-g-Mode Tidal Instability with GW170817
No full textWe analyze the impact of a proposed tidal instability coupling p modes and g modes within neutron stars on GW170817. This nonresonant instability transfers energy from the orbit of the binary to internal modes of the stars, accelerating the gravitational-wave driven inspiral. We model the impact of this instability on the phasing of the gravitational wave signal using three parameters per star: An overall amplitude, a saturation frequency, and a spectral index. Incorporating these additional parameters, we compute the Bayes factor (lnB!pgpg) comparing our p-g model to a standard one. We find that the observed signal is consistent with waveform models that neglect p-g effects, with lnB!pgpg=0.03-0.58+0.70 (maximum a posteriori and 90% credible region). By injecting simulated signals that do not include p-g effects and recovering them with the p-g model, we show that there is a ≃50% probability of obtaining similar lnB!pgpg even when p-g effects are absent. We find that the p-g amplitude for 1.4 MâŠneutron stars is constrained to less than a few tenths of the theoretical maximum, with maxima a posteriori near one-Tenth this maximum and p-g saturation frequency ∼70 Hz. This suggests that there are less than a few hundred excited modes, assuming they all saturate by wave breaking. For comparison, theoretical upper bounds suggest a103 modes saturate by wave breaking. Thus, the measured constraints only rule out extreme values of the p-g parameters. They also imply that the instability dissipates a1051 erg over the entire inspiral, i.e., less than a few percent of the energy radiated as gravitational waves
Inferior alveolar nerve injury following orthognathic surgery: a review of assessment issues: INFERIOR ALVEOLAR NERVE INJURY
No full textThe sensory branches of the trigeminal nerve encode information about facial expressions, speaking and chewing movements, and stimuli that come into contact with the orofacial tissues. Whatever the cause, damage to the inferior alveolar nerve negatively affects the quality of facial sensibility as well as the patient's ability to translate patterns of altered nerve activity into functionally meaningful motor behaviours. There is no generally accepted, standard method of estimating sensory disturbances in the distribution of the inferior alveolar nerve following injury. Assessment of sensory alterations can be conducted using three types of measures: (i) objective electrophysiological measures of nerve conduction, (ii) sensory testing (stimulus) measures and (iii) patient report. Each type of measure with advantages and disadvantages for use are reviewed
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