Performance bounds on matched-field methods for source localization and estimation of ocean environmental parameters

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2001Matched-field methods concern estimation of source location and/or ocean environmental parameters by exploiting full wave modeling of acoustic waveguide propagation. Typical estimation performance demonstrates two fundamental limitations. First, sidelobe ambiguities dominate the estimation at low signal-to-noise ratio (SNR), leading to a threshold performance behavior. Second, most matched-field algorithms show a strong sensitivity to environmental/system mismatch, introducing some biased estimates at high SNR. In this thesis, a quantitative approach for ambiguity analysis is developed so that different mainlobe and sidelobe error contributions can be compared at different SNR levels. Two large-error performance bounds, the Weiss-Weinstein bound (WWB) and Ziv-Zakai bound (ZZB), are derived for the attainable accuracy of matched-field methods. To include mismatch effects, a modified version of the ZZB is proposed. Performance analyses are implemented for source localization under a typical shallow water environment chosen from the Shallow Water Evaluation Cell Experiments (SWellEX). The performance predictions describe the simulations of the maximum likelihood estimator (MLE) well, including the mean square error in all SNR regions as well as the bias at high SNR. The threshold SNR and bias predictions are also verified by the SWellEX experimental data processing. These developments provide tools to better understand some fundamental behaviors in matched-field performance and provide benchmarks to which various ad hoc algorithms can be compared.Financial support for my research was provided by the Office of Naval Research and the WHOI Education Office

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Intrusive memories and trauma-related symptoms in individuals presenting with dental anxiety

Research indicates that between 36-40% of people are afraid to visit the dentist, 20% are highly anxious and 5% avoid dental treatments due to severe anxiety (Lindsay & Jackson, 1993). Dental anxiety is known to be a major barrier to optimal health care with individuals fearful of impending invasive procedures often presenting only when in severe pain. Dental anxiety has been found to be based on past memories of experiences of pain and loss of control in the dental setting.Evidence from the literature suggests that some individuals with dental anxiety also present with additional psychological problems, such as panic disorder. De Jongh, Muris, ter Horst and Duyx (1995) also reported that individuals with dental anxiety also exhibited more catastrophizing thoughts related to dental treatment. A recent study by De Jongh, Aartman & Brand (manuscript submitted for publication) reported that intrusive memories of past distressing dental experiences were associated with trauma-related symptoms. However no structured assessment for Post-Traumatic Stress Disorder (PTSD) was carried out.This study aimed to identify the association between intrusive memories related to dental experiences and trauma-related symptomatology and to investigate differences in psychopathology and frequency of thought content in individuals presenting with and without intrusive memories. The proportion of individuals with intrusive memories who would meet criteria for PTSD was also investigated. Results will be given and conclusions reached

The hypothalamic-pituitary-testicular axis: studies on delayed puberty and infertility

In infertile patients, an inverse relationship between FSH and sperm count or the severity of germ cell depletion in testicular biopsies was confirmed. The application of FSH measurements to the assessment of 100 infertile patients was evaluated. Elevated FSH in those with sperm density under 5 million /ml indicated severe germ cell atrophy. The use of GnRH stimulation and multiple measurements of basal gonadotrophins and testosterone conferred no advantage. In patients with elevated FSH, circulating oestradiol, oestrone and oestrone sulphate were significantly raised. There was preliminary evidence that the oestrogen excess resulted from testicular secretions of oestradiol. Oestrone sulphate was not secreted by the testis, being derived from unconjugated precursors - oestradiol and oestrone. The pathophysiological significance of these findings in male infertility and their relevance to normal intratesticular control mechanisms were discussed.In conclusion, the development and control of adult testicular functions are dependent on a background of pulsatile LH stimulation against which the complex interactions between FSH, Sertoli and Leydig cells ensure a continuous maturation of spermatogonia and the optimal production of testicular steroids.The functional characteristics and control mechanisms of the hypothalamic-pituitary-testicular axis were explored by examining the patterns of pituitary and testicular hormone secretion in pubertal subjects and in adults with impaired spermatogenesis. The overnight hormone profile and the pituitary response to repeated GnRH stimulation were studied on 1-4 occasions in 16 patients (mean age 16.3 ± 2.7 years) with delayed sexual development while their clinical progress was followed for a mean duration of 22.4 ± 8.5 months. Changes in testis and genital size were confirmed to be the two physical markers which correlated best with the hormonal patterns. The earliest detectable evidence of pubertal onset was an increase in frequency and amplitude of pulsatile LH secretion during nocturnal sleep. Further progress in puberty was characterized by quantitative and qualitative changes in the pattern of LH secretion resulting from the combined effects of changing frequency of hypothalamic GnRH pulses, of gonadal feedback and possibly other ill-defined central mechanisms. Heightened pituitary responsiveness to GnRH could account for the pubertal rise in LH. Since the estimated amplitude of GnRH pulsatile secretion remained constant, the increase in GnRH pulse frequency was considered to be the prime mover in the activation of pituitary- testicular functions at the onset of puberty. Thus the hypothalamic GnRH frequency modulation of the pituitary provides the basic mechanism for the neuroendocrine control of sexual maturation. The pituitary response to GnRH may be helpful in the endocrine assessment of patients with delayed puberty. In response to a single 10 pg bolus of GnRH, an LH rise of 5 u/l or more was associated with well- defined nocturnal pulsatile LH secretion in subjects who subsequently progressed through puberty spontaneously. However, in those where the GnRH- induced LH rise was under 5 u /1, it was not possible to differentiate between constitutional delayed puberty and hypogonadotrophic hypogonadism. The pubertal development of testicular functions was more closely related to the progressive increase in amplitude rather than frequency of pulsatile LH secretion. The roles of FSH and prolactin were less obvious. Exogenous GnRHinduced pulsatile LH secretion failed to stimulate testo- sterone production above the maximal levels in the morning. This implied that the pubertal Leydig cells normally function near to their maximal steroidogenïc capacity

Mathematical Models of Fluid Flows in the Human Eye

Fluids in the eye have many important functions, such as regulating the intraocular pressure, delivering nutrients to the avascular intraocular tissue of the cornea and the lens, and contributing to adhesion forces between the sensory retina and the retinal pigment epithelium. Failure of these functions may lead to a number of pathological conditions. Studying fluid flows in the eye is therefore relevant to improve our understanding of the physiology of the organ and to prevent or treat certain eye diseases. This thesis consists of two main parts. In the first part we propose mathematical models of the dynamics of the aqueous humour in the anterior segment of the eye. The problems considered are in the area of fluid mechanics and our approaches are based on the use of lubrication theory that is applicable for flows in thin domains. The second part is related to fluid transport across the retinal pigment epithelium and it concerns a multiphysics problem, which couples fluid and ion transport

Testing the nature of dark compact objects: a status report

Very compact objects probe extreme gravitational fields and may be the key to understand outstanding puzzles in fundamental physics. These include the nature of dark matter, the fate of spacetime singularities, or the loss of unitarity in Hawking evaporation. The standard astrophysical description of collapsing objects tells us that massive, dark and compact objects are black holes. Any observation suggesting otherwise would be an indication of beyond-the-standard-model physics. Null results strengthen and quantify the Kerr black hole paradigm. The advent of gravitational-wave astronomy and precise measurements with very long baseline interferometry allow one to finally probe into such foundational issues. We overview the physics of exotic dark compact objects and their observational status, including the observational evidence for black holes with current and future experiments.Comment: 76 pages + references. Invited review article for Living Reviews in Relativity. v3: Overall improvements and references added, a few typos corrected. Version to appear in LR

The physicist's guide to one of biotechnology's hottest new topics: CRISPR-Cas

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas) constitute a multi-functional, constantly evolving immune system in bacteria and archaea cells. A heritable, molecular memory is generated of phage, plasmids, or other mobile genetic elements that attempt to attack the cell. This memory is used to recognize and interfere with subsequent invasions from the same genetic elements. This versatile prokaryotic tool has also been used to advance applications in biotechnology. Here we review a large body of CRISPR-Cas research to explore themes of evolution and selection, population dynamics, horizontal gene transfer, specific and cross-reactive interactions, cost and regulation, non-immunological CRISPR functions that boost host cell robustness, as well as applicable mechanisms for efficient and specific genetic engineering. We offer future directions that can be addressed by the physics community. Physical understanding of the CRISPR-Cas system will advance uses in biotechnology, such as developing cell lines and animal models, cell labeling and information storage, combatting antibiotic resistance, and human therapeutics.Comment: 75 pages, 15 figures, Physical Biology (2018