This thesis takes a fresh approach to cochlear mechanics. Over the last quarter of a century, we have learnt that the cochlea is active and highly tuned, observations suggesting that something may be resonating. Rather than accepting the standard traveling wave interpretation, here I investigate whether a resonance theory of some kind can be applied to this remarkable behaviour.¶ A historical survey of resonance theories is first conducted, and advantages and drawbacks examined. A corresponding look at the traveling wave theory includes a listing of its short-comings.¶ A new model of the cochlea is put forward that exhibits inherently high tuning. The surface acoustic wave (SAW) model suggests that the three rows of outer hair cells (OHCs) interact in a similar way to the interdigital transducers of an electronic SAW device. Analytic equations are developed to describe the conjectured interactions between rows of active OHCs in which each cell is treated as a point source of expanding wavefronts. Motion of a cell launches a wave that is sensed by the stereocilia of neighbouring cells, producing positive feedback. Numerical calculations confirm that this arrangement provides sharp tuning when the feedback gain is set just below oscillation threshold.¶ A major requirement of the SAW model is that the waves carrying the feedback have slow speed (5-200 mm/s) and high dispersion. A wave type with the required properties is identified - a symmetric Lloyd-Redwood wave (or squirting wave) - and the physical properties of the organ of Corti are shown to well match those required by theory.¶ The squirting wave mechanism may provide a second filter for a primary traveling wave stimulus, or stand-alone tuning in a pure resonance model. In both, cyclic activity of squirting waves leads to standing waves, and this provides a physical rendering of the cochlear amplifier. In keeping with pure resonance, this thesis proposes that OHCs react to the fast pressure wave rather than to bending of stereocilia induced by a traveling wave. Investigation of literature on OHC ultrastructure reveals anatomical features consistent with them being pressure detectors: they possess a cuticular pore (a small compliant spot in an otherwise rigid cell body) and a spherical body within (Hensens body) that could be compressible. I conclude that OHCs are dual detectors, sensing displacement at high intensities and pressure at low. Thus, the conventional traveling wave could operate at high levels and resonance at levels dominated by the cochlear amplifier. ¶ The latter picture accords with the description due to Gold (1987) that the cochlea is an ‘underwater piano’ - a bank of strings that are highly tuned despite immersion in liquid.¶ An autocorrelation analysis of the distinctive outer hair cell geometry shows trends that support the SAW model. In particular, it explains why maximum distortion occurs at a ratio of the two primaries of about 1.2. This ratio also produces near-integer ratios in certain hair-cell alignments, suggesting that music may have a cochlear basis.¶ The thesis concludes with an evaluation and proposals to experimentally test its validity.

Some modern laser applications require continuous wave (CW) high power (>100 W), and diffraction limited performance near 1.064 um. One such laser application with these, and additional, requirements is gravitational wave interferometry. This thesis will report the development of a scalable high power laser for this application. A high-power, single-transverse-mode laser might be produced by intensely pumping the small mode volume within a stable resonator or by using a resonator that has a large transverse mode. Intensely pumping a small volume can lead to crystal fracture and large thermally-induced wavefront aberrations. Using a large transverse mode would also be difficult if using a stable resonator as these are, in general, not suited to fundamental modes that have large cross-sectional areas. Unstable resonators, by comparison, routinely produce fundamental modes that have large cross-sectional areas. They have been used for decades with high-power, high-gain chemical or gas lasers and provide efficient energy extraction, good mode discrimination and beam quality. However, the low gain of Nd:YAG in combination with the high output coupling associated with unstable resonators would limit the efficiency of such a CW laser. One way to utilize the properties of unstable resonators while reducing the output coupling, and thus increase the efficiency, is to use a stable-unstable resonator. These resonators are stable in one plane and unstable in the orthogonal plane, rather than unstable in both planes. The required output coupling can be further reduced without degrading the beam quality by using a Graded Reflectivity Mirror (GRM) as the output coupler. The soft aperturing of the GRM also eliminates diffraction loss associated with scraper mirrors in hard-edged unstable resonators, and enhances mode discrimination. The stable-unstable resonator reported in this thesis is side-pumped by fibre-coupled diode- lasers and side-cooled. It uses a total internal reflection (TIR) zigzag slab geometry, in which the zigzag is co-planar with the pumping and cooling. The resonator is stable in the plane of the zigzag (horizontal) and unstable in the plane orthogonal to the zigzag. In this configuration the strong thermal lensing in the horizontal direction is averaged out by the zigzag. The vertical thermal lens is controlled by Thermo-Electric Coolers (TECs) which are used to adjust the temperature of the bottom and top surfaces of the slab. To test the performance of the side-pumped, side-cooled laser head it was operated initially with a stable resonator. Efficient operation was achieved and will be reported. Control of the refractive index profile (thermal lens) using the TECs on the bottom and top surfaces results in a vertical thermal lens that could be set to any value between 47 mm and 450 mm. The thermal lens encountered by the zigzag mode in the plane of pumping and cooling is weak (horizontal direction) and independent of TEC current. Thus, the thermal lensing in the horizontal and vertical directions is de-coupled, as is necessary for scalability of the mode volume in the vertical direction. A travelling-wave (for ease of injection locking) stable-unstable resonator was investigated using a Fox-Li model, which assumed a greater pump power and mode volume than used for the laser head presented in this thesis. A strip, n=2 super-Gaussian GRM is shown to be the optimum output coupler for the stable-unstable laser. Furthermore, it is shown that the output coupling loss associated with a resonator magnification of -1.3 could be sustained using pump densities below the crystal fracture limit. Useful operation over a realistic range of thermal lens focal lengths is predicted. The validity of the Fox-Li modelling is confirmed using with a standing-wave stable-unstable resonator. The standing-wave resonator was chosen as it suited the available crystal and pump power used for the work in this thesis. The GRM reflectivity profile used the minimum commercially available profile radius. The vertical thermal lens is varied by adjusting the pump power, and then by adjusting the temperature of the bottom and top surfaces at full pump power. This demonstrated CW operation of the standing-wave laser with M=1.3 and good beam quality. Good qualitative agreement with the Fox-Li model of the standing-wave resonator is thus confirmed. Finally, suppression of the multiple longitudinal modes by injection locking is reported. / Thesis (Ph.D.)--Physics and Mathematical Physics, 2001.

<p>This thesis presents the mechanical design and dimensioning of a pressure vessel, which is to be used as housing for a marine substation in a wave power park. A concept for generation of electricity from ocean waves is being developed at the Division of electricity at Uppsala University. The concept is based on the use of a permanent magnet linear generator, placed on the seabed, connected via a line to a buoy at the surface. The generated electricity from a group of generators is transmitted in sea cables to a marine substation where conversion and transformation takes place before the electricity is transmitted to shore. To reduce the risk of water leakage, the gas pressure inside the marine substation is larger than the surrounding water pressure. The substation can be pressurized before submersion, which requires the housing to be designed as a pressure vessel. The pressure vessel has been dimensioned with formula based methods according to EN 13445, the European standard for unfired pressure vessels. The construction has been based on modifying a standard pressure tank. The housing has been designed for installation and sealing of a large number of electrical connectors. The connectors have been placed in a way that allows for future cable coupling with remotely operated vehicles and simplifies maintenance of the substation. Another design consideration has been to facilitate submersion by reducing the buoyancy of the substation.</p>

The eventual deployment of wave energy converters (WECs) on a commercial scale will necessitate the grouping of devices into arrays or "wave farms," in order to minimize overhead costs of mooring, maintenance, installation, and electrical cabling for shoreward power delivery. Closely spaced WECs will interact hydrodynamically through diffracted and radiated waves. Recent research has focused on the WEC wave field and used its structures to design constructive WEC arrays as well as to describe the means of WEC energy absorption. In this study, the WEC wave field is investigated for a single WEC and a five WEC array with linear wave theory and experimental results. Both regular waves and spectral seas are considered. Computational results are produced with the linear boundary-element-method (BEM) hydrodynamic software WAMIT for a simple WEC geometry. Experimental data comes from WEC array tests that took place at Oregon State University over the winter of 2010-11 [1]. The experimental measurements help validate the computational modeling, and the computational models serve as an aid to interpreting the experimental data. Results reveal two universal WEC wave field features - partially standing waves and a wave shadow, both of which are the result of the coherent interaction of the planar incident wave with the circular generated wave, composed of the diffracted and radiated waves. The partial standing waves in the offshore are seen qualitatively in experimental data but could not be exactly reproduced computationally, because the computational model is only a simple representation of the physical model. In the lee of the WEC, the measured longshore structure of the wave shadow is in good agreement with theoretical expectations as well as computational results. It is believed that the agreement is because the formation of the wave shadow is dominated by energy extraction, which was approximately the same for both the computational and physical models. A study of the linear WEC wave field in regular waves and spectral seas reveals patterns such as the wave shadow that have also been found in experimental data. The positions and magnitudes of the offshore partially standing waves are very sensitive to wavelength, and WEC geometry, motions and location, and in spectral seas, they are smoothed when considering significant wave height. All of which suggest that it may be difficult to use them advantageously in the design of WEC arrays. The wave shadow is a dominant feature of the WEC wave field for both regular waves and spectral seas. It appears to be fairly generic and to be based on power absorption. In the design of WEC arrays, rather than attempting constructive interference by using standing wave crests, perhaps the best one can do is to avoid destructive interference of the wave shadow. / Graduation date: 2013

Thesis (Ph. D.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 222-232). Also available on the World Wide Web.

Thesis (Ph. D.)--Ohio State University, 1980. / Includes bibliographical references (leaves 77-79). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

In this thesis, we present a theoretical investigation of reactive processes involving the HeH$^+$ molecular ion, with applications in laboratory and astrophysical plasma physics. We consider in particular two processes, which are the charge transfer in H + He$^+$ collisions at low energy from a molecular approach and the photodissociation of HeH$^+$. At the molecular level, the cross section is the basic quantity that has to be determined in order to achieve an understanding of reactive processes. Its calculation will be based on the description of the reactions using an emph{ab initio}, quantum mechanical approach. In this work, we will rely on the Born-Oppenheimer approximation, which allows the molecular motion to be separated into an electronic and a nuclear motion. The evaluation of cross sections then follows two steps. The first is the determination of the electronic structure of the molecule. We will calculate the adiabatic potential energy curves of the excited electronic states as well as the dipole matrix elements between these states. The non-adiabatic radial and rotational couplings, which result from the breakdown of the Born-Oppenheimer approximation, are also estimated. The second step is to solve the nuclear motion, which we achieve using a time-dependent method based on the propagation of wave packets on the coupled electronic states. A particular emphasis will be put on the importance of the excited states and of the non-adiabatic couplings in the description of reactive processes. In the treatment of the charge transfer reaction between H and He$^+$ in excited states, it is well known that the non-adiabatic radial couplings cannot be neglected. However, we will show that the inclusion of the non-adiabatic rotational couplings is also necessary in order to obtain accurate state-to-state cross sections. In the description of the photodissociation of HeH$^+$ from its ground state, we will show the influence of the excited states on the rate constant and the role of the non-adiabatic radial couplings in the determination of partial cross sections. We will also consider the possible astrophysical applications of the first triplet state of HeH$^+$. We will show that this state is metastable by evaluating its lifetime, and calculate the cross sections and rate constants for the photodissociation and radiative association of HeH$^+$ in this state.

In this study, the most part is acquainted with the effect of elbow pipe to the guided wave. Elbow pipes were most seen feature in work environment. It was difficult for inspection that the anti-symmetric of signal increased when it passed the elbow pipe by happening mode conversion. The study content includes the using modal solution of the finite element method to solve the dispersion curve of four different bend radius of elbow pipe, they were : 1.0 m, 0.6 m, 0.4 m and 0.2 m. Therefore, by using simulation of wave propagation and experiment to verify dispersion curve of bend pipe were accuracy. This study reveals that, the dispersion curve of elbow pipe is similar to that of straight pipe, and T(0,1) mode in the elbow pipe is most similar with it in straight pipe. Thus, the dispersion curve in elbow pipe and straight pipe were similar, but the effect of geometry of elbow pipe will make the symmetrical incident signal time delay and wave front will distortion, and then it will cause mode conversion. According to the experiment of this study, although the signal of feature behind the elbow pipe caused by mode conversion will make anti-symmetry of reflection signal increase, it still won¡¦t make shift between reflection signal location and real feature location. It is very difficult and complex for inspecting the particular geometry pipe. If we can use the modal analysis of finite element method to solve the dispersion curve of particular geometry pipe, the inspection can be improve.

Generalized modal analysis techniques for the characterization and modeling of dissipationless planar waveguide structures and discontinuities encountered in microwave and optical integrated circuits, as well as of quantum waveguide structures and devices, are presented. The frequency-dependent transmission properties of the curved microstrip bend are derived by utilizing a second-order perturbation analysis of the equivalent modified curved waveguide model and a mode-matching method which includes the higher order modes. An extension of the mode-matching method for characterization of microstrip right-angle bends and T junctions having a rectangular notch is formulated. The modal solutions for an arbitrary graded-index dielectric slab waveguide are derived by applying the generalized telegraphist's equations to the equivalent inhomogeneous parallel-plate waveguide model with electric or magnetic walls. These modal solutions are employed in a mode-matching procedure to calculate the transmission properties of a step discontinuity in typical diffused optical dielectric slab waveguides. Power loss calculations for an abrupt offset in a diffused optical waveguide show a smooth increase in radiation loss whereas a sharp transition from almost zero to nearly total radiation loss is found for an abrupt change in diffusion depth. In the analysis of quantum waveguide structures, the modal expansions of the wave function together with a mode-matching technique are utilized. The computed generalized scattering matrices (GSMs) of junctions and uniform waveguide sections are combined via an extended GSM technique to obtain the scattering parameters of composite quantum waveguide structures. Results for cascaded right-angle bends and periodic multi-waveguide structures in a split-gate configuration are presented assuming hard wall confinement. For the multisection structures, strong resonant behavior similar to that in resonant tunneling diodes is found. Calculated current-voltage characteristics for a double constriction in GaAs are shown, exhibiting a region of negative differential resistance for temperatures up to approximately 60K with a maximum peak-to-valley ratio of over 80:1. Finally, a uniform narrow constriction with an assumed parabolic - like lateral potential confinement is analyzed by utilizing the modal expansion techniques developed for dielectric waveguides. / Graduation date: 1991