General Relativistic Instability Supernova of a Supermassive Population III Star

The formation of supermassive Population III stars with masses $\gtrsim$ 10,000 Msun in primeval galaxies in strong UV backgrounds at $z \sim$ 15 may be the most viable pathway to the formation of supermassive black holes by $z \sim$ 7. Most of these stars are expected to live for short times and then directly collapse to black holes, with little or no mass loss over their lives. But we have now discovered that non-rotating primordial stars with masses close to 55,000 Msun can instead die as highly energetic thermonuclear supernovae powered by explosive helium burning, releasing up to 10$^{55}$ erg, or about 10,000 times the energy of a Type Ia supernova. The explosion is triggered by the general relativistic contribution of thermal photons to gravity in the core of the star, which causes the core to contract and explosively burn. The energy release completely unbinds the star, leaving no compact remnant, and about half of the mass of the star is ejected into the early cosmos in the form of heavy elements. The explosion would be visible in the near infrared at $z \lesssim$ 20 to {\it Euclid} and the Wide-Field Infrared Survey Telescope (WFIRST), perhaps signaling the birth of supermassive black hole seeds and the first quasars.Comment: 23 pages, 4 figures (accepted to ApJ

Analysis of Palatal and Upper Airway Dimensions in Patients with Excessive Daytime Sleepiness: A Retrospective Cone-Beam Computed Tomography Study

Excessive Daytime Sleepiness (EDS) is the measure of ones propensity to fall asleep during normal daily activities. It has been reported in 20%-50% of adults in the United States and is the most frequent symptom of patients presenting to sleep clinics. EDS is the result of both primary hypersomnias such as narcolepsy and idiopathic hypersomnia and, more commonly, secondary hypersomnias such as sleep deprivation, psychiatric conditions, medications, illegal substances, and obstructive sleep apnea (OSA). The etiology of OSA is multifactorial. Collapsibility of the upper airway is influenced by both neuromuscular tone and craniofacial anatomy. Common predisposing factors for small airways include obesity, bony anatomical structures that reduce and impede the airway, and in children, oversized tonsils and adenoids. Maxillary dimensions have been shown to have a relationship with upper airway dimensions. Craniofacial growth and development relies on nasal breathing to produce a continuous pressure for the lateral growth of maxilla and for downward palatal growth, however, in mouth breathers this stimulus is lost and ultimately results in altered craniofacial growth that is observed extra-orally as long lower facial height (adenoid face), lip incompetence, and constricted alar base. Intraorally, the findings typically include a narrow maxillary arch associated with a deep palatal vault. Some studies have shown that patients presenting with a narrow maxilla also exhibit constricted nasopharyngeal dimensions and altered respiratory function and other studies showed that there is a strong relationship between airway obstruction and a high palatal vault. Reducing the high number of undiagnosed patients with OSA ultimately relies on health care providers taking a multidisciplinary approach to screen for patients who exhibit the signs and symptoms of OSA and refer these patients for proper diagnosis and treatment. Orthodontists are trained to treat dental and facial skeletal discrepancies and, therefore, play a large role in identifying patients who have or may develop breathing problems. In 2019, the American Academy of Orthodontists released a White Paper regarding the role of orthodontists in the management of OSA and strongly suggested that orthodontists screen for OSA during an initial exam by assessing various risk factors such as body mass index, nasal obstruction, excessive daytime sleepiness and refer at-risk patients for diagnostic evaluation. This study aimed at gaining a deeper understanding of some of the common risk factors for obstructive sleep apnea in order to help health care providers more accurately detect breathing disorders during a routine exam. Level of daytime sleepiness, palatal dimensions, airway dimensions, gender, age, ethnicity and body mass index from 253 patients were compared to corroborate and expand on the findings in the current literature. The data from this study showed significant differences between sleepiness and palatal width, sleepiness and ethnicity, age and airway dimensions, gender and palatal width and airway dimensions, ethnicity and palatal dimensions, body mass index and airway volume, and significant correlations between palatal depth and airway minimum cross-sectional area, palatal depth and airway volume, airway volume and airway minimum cross-sectional area. These findings showed both similarities and differences with the current literature. Future studies are needed to expand on these relationships and their importance in clinical applications for the identification of breathing related sleep disturbances

Spherical microphone array processing for acoustic parameter estimation and signal enhancement

In many distant speech acquisition scenarios, such as hands-free telephony or teleconferencing, the desired speech signal is corrupted by noise and reverberation. This degrades both the speech quality and intelligibility, making communication difficult or even impossible. Speech enhancement techniques seek to mitigate these effects and extract the desired speech signal. This objective is commonly achieved through the use of microphone arrays, which take advantage of the spatial properties of the sound field in order to reduce noise and reverberation. Spherical microphone arrays, where the microphones are arranged in a spherical configuration, usually mounted on a rigid baffle, are able to analyze the sound field in three dimensions; the captured sound field can then be efficiently described in the spherical harmonic domain (SHD). In this thesis, a number of novel spherical array processing algorithms are proposed, based in the SHD. In order to comprehensively evaluate these algorithms under a variety of conditions, a method is developed for simulating the acoustic impulse responses between a sound source and microphones positioned on a rigid spherical array placed in a reverberant environment. The performance of speech enhancement algorithms can often be improved by taking advantage of additional a priori information, obtained by estimating various acoustic parameters. Methods for estimating two such parameters, the direction of arrival (DOA) of a source (static or moving) and the signal-to-diffuse energy ratio, are introduced. Finally, the signals received by a microphone array can be filtered and summed by a beamformer. A tradeoff beamformer is proposed, which achieves a balance between speech distortion and noise reduction. The beamformer weights depend on the noise statistics, which cannot be directly observed and must be estimated. An estimation algorithm is developed for this purpose, exploiting the DOA estimates previously obtained to differentiate between desired and interfering coherent sources.Open Acces