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Articles 1 - 5 of 5
Full-Text Articles in Physics
Geographic Variations Of Sound Channel Axis In The Global Ocean, Mukunda Kumar Acharya
Geographic Variations Of Sound Channel Axis In The Global Ocean, Mukunda Kumar Acharya
Electronic Theses and Dissertations
Sound signals are used for imaging and communication in the ocean. Underwater sound speed has a minimum at a certain depth that forms a sound channel for long-range underwater sound propagation. The geographic variation of sound channel is crucial in uses of underwater sound in various environments including ocean acoustic tomography and monitoring of global warming. In this work, sound speed and depth of the channel axis in the global ocean are characterized for their variation with the latitude, longitude, and depth.
Manifoldlike Causal Sets, Miremad Aghili
Manifoldlike Causal Sets, Miremad Aghili
Electronic Theses and Dissertations
The content of this dissertation is written in a way to answer the important question of manifold likeness of causal sets. This problem has importance in the sense that in the continuum limit and in the case one finds a formalism for the sum over histories, the result requires to be embeddable in a manifold to be able to reproduce General Relativity. In what follows I will use the distribution of path length in a causal set to assign a measure for manifold likeness of causal sets to eliminate the dominance of nonmanifold like causal sets. The distribution of interval …
Acoustic Radiation Force On A Fluid To Fluid Boundary By Phase Plate Focused Ultrasound, Robert Lee Lirette
Acoustic Radiation Force On A Fluid To Fluid Boundary By Phase Plate Focused Ultrasound, Robert Lee Lirette
Electronic Theses and Dissertations
In this study, the physics and applications of the ultrasonic radiation force at the interface between two immiscible fluids were investigated. These studies were performed using low-profile discrete-stepped lenses to the modify the phase of the incident radiation generating multiple field morphologies. In its first application to acoustics, a fraxicon lens was developed to approximate the field generated by an axicon. This type of lens creates a minimally diffractive Bessel beam and long depth of focus that is useful in ultrasonic imaging, therapy, and non-destructive evaluation techniques. Fields modified by fraxicon, Fresnel, and axicon lenses were characterized experimentally by scanning …
Gravitational Radiation From Superradiant Instabilities Of Rotating Black Holes, Shrobana Ghosh
Gravitational Radiation From Superradiant Instabilities Of Rotating Black Holes, Shrobana Ghosh
Electronic Theses and Dissertations
We use the Teukolsky formalism to calculate the gravitational radiation from a non-axi\-symmetric cloud formed due to superradiant amplification of a spin-0 bosonic field. We focus on the prospects of the future space-based gravitational wave detector, Laser Interferometer Space Antenna (LISA), and the current version of ground-based detector, Advanced Laser Interferometer Gravitational-Wave Observatory (AdLIGO), to detect or constrain scalars with mass in the range $m_s\in [10^{-19},10^{-15}]$ eV and $m_s\in[10^{-14},10^{-11}]$ eV, respectively. Using astrophysical models of black hole populations calibrated to observations we find that, in optimistic scenarios, AdLIGO could detect up to $10^4$ resolvable events in a four-year search if …
Investigation Of Narrow Bipolar Events In Mississippi Thunderstorms, Sampath Asiri Bandara
Investigation Of Narrow Bipolar Events In Mississippi Thunderstorms, Sampath Asiri Bandara
Electronic Theses and Dissertations
In the first part of the study FA and Log-RF data were used to examine low-altitude (<8.0 km) negative NBEs (NNBEs) to see how many -CG flashes were initiated by NNBEs. Out of 686 -CG flashes only 33 (5%) flashes were initiated by an NNBE. These NNBEs occurred at an average altitude of 6.2 km had average amplitude (range-normalized amplitude to 100 km) of 0.4 V/m and had average VHF (Log-RF) power of 130 W. Since the low-altitude NNBEs were substantially weaker than positive NBEs that initiate intracloud (IC) flashes it is hypothesized that -CG flashes are easier to initiate than IC flashes. The second part of the study investigated the properties of 201 positive NBEs (+NBEs). The +NBEs were classified in two ways: into Types A-D [Karunarathne et al. 2015] and into three different groups: Isolated Not-isolated and IC flash-initiator or INBE [Wu et al. 2014]. The average VHF (Log-RF) power of NBEs within the A-D categories were 1.9 4 9.8 and 13.2 kW respectively while the powers for the Isolated Not-isolated and INBE categories were 10.1 4 and 10.1 kW respectively. The third study considered 34 NBEs that occurred close in space and time to each other: 13 pairs of NBEs one group of three +NBEs and one group of five +NBEs. The NBEs were overlaid on radar data of the parent thunderstorms. The data indicate that the individual NBEs in each group initiated in separate intense electric field regions of small extent rather than in a single large-scale electric field region. This dissertation investigates Narrow Bipolar Events (NBEs) which are a type of short-duration (10- 30 µs) lightning discharge. The study primarily used data from NBEs collected in 2016 at seven sensor sites within 50 km of Oxford Mississippi USA. Each sensor site had three electromagnetic antennas called Fast Antenna (FA) dE⁄dt and Log-RF with bandwidths of 0-2.5 MHz 0-1.0 MHz and 186-192 MHz respectively. NBEs are often isolated from other lightning events in thunderclouds but they sometimes initiate negative cloud-to-ground (-CG) and intracloud (IC) lightning flashes or they can occur during these flashes.