A surface acoustic wave (SAW) is a combination of a mechanical wave and a potential wave propagating on the surface of a piezoelectric substrate at the speed of sound. Such waves are widely applied in not only the communication industry, but also in quantum physics research, such as nanoelectronics, spintronics, quantum optics, and even quantum information processing. Here, I focus on low-dimensional electron transport and SAWs in GaAs and ZnO semiconductor heterostructures. The ability to pattern quantum nanostructures using gates has stimulated intense interest in research into mesoscopic physics. We have performed a series of simulations of gate structures, and having with the optimised boundary conditions and we find them to match experimental results, such as the pinch-off voltage of one-dimensional channels and SAW charge transport in induced n-i-n and n-i-p junctions. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software. With the calculated potential, we have modelled the process how a dynamic quantum dot is driven by a SAW and have analysed error mechanisms in SAW-driven quantisation (I=Nef, where N is the number of electrons in each SAW minimum, and f is the SAW resonant frequency). From energy spectroscopy measurements, we probe the electron energy inside a SAW-driven dynamic quantum dot and find that the small addition energy, which is around 3meV, is the main limitation for the SAW quantisation. To increase the confinement of SAW-driven quantum dots, we deposit a thin ZnO film, with a better piezoelectric coupling than GaAs, on a GaAs/AlGaAs heterostructure using high-target-utilisation sputtering (an Al2O3 buffer layer is deposited to protect the 2DEG during sputtering). With the ZnO, the SAW amplitude is greatly improved to 100 meV and the RF power required for pumping electrons using a SAW is greatly reduced. Finally, we have studied low-dimensional electron transport in a MgZnO/ZnO heterostructure. We have developed a technique for patterning gates using a parylene insulator, and used these to create one-dimensional quantum wires and observe electron ballistic transport with conductance quantised in units of 2e2/h The increasing electron effective mass as the 1D electron density decreases indicate that the electron-electron interaction in this MgZnO/ZnO heterostructure is strong. Because of these strong interactions, the 0.7 anomaly is observed just below each quantised plateau, and are much stronger than in GaAs quantum wires. Furthermore, we have also calculated the SAW-modulated spontaneous and piezoelectric polarisation in the ZnO heterostructure, and have observed a sign of this SAW-modulation in 2DEG density, which is different from the classical SAW-pumping mechanism. Our results show that a ZnO heterostructure should provide a good alternative to conventional III-V semiconductors for spintronics and quantum computing as they have less nuclear spins. This paves the way for the development of qubits benefiting from the low scattering of an undoped heterostructure together with potentially long spin lifetimes.

Non-contact manipulation technologies present a useful and powerful means of handling particles or cells. Such techniques are of interest in regenerative medicine applications, and in particular the scalability of these techniques is an area of active research. Optical trapping is a precise and dextrous method of manipulating particles with the forces exerted by a laser beam, while acoustic trapping is a scalable technique capable of exerting a force on particles through standing wave resonance. These complimentary modalities can be utilised in a hybrid system to give a resultant technique that borrows from the strengths of each individual method. In this thesis, methods of force balancing, using optics and acoustics, are explored, both independently and in combination with each other. A technique for 3D acoustic trapping in glass capillaries is shown, utilising the two pairs of opposing channel walls and the air-water interfaces of two air bubbles as acoustic reflectors. Standing waves set up between these surfaces show discrete acoustic trapping sites for varying lengths of fluid cavity. A method of optical radiation force balancing is observed in a 3D potential energy landscape, using similar principles as seen in particle trapping with counter-propagating beams. Tuning of the radiation force balance in this system allows particles to, instead of being pinned to the surface by the radiation force from the optical pattern, become localised at discrete planes of trapping sites throughout the fluid volume. A hybrid force balance separation method using the optical and acoustic forces is devised using a single laser beam as the primary deflection mechanism with acoustic trapping providing both localisation and a force balance with the optics. Separation of different sized particles is observed, with larger scale optical deflection mechanisms and their resultant thermal effects demonstrated.

Mercury (Hg) has always been a serious risk to the environment and human health. It is a very common contamination in petroleum industry, which may lower product quality, threaten operation safety and worker’s health even at a very low concentration. Consequently the detection of mercury is very necessary. Gold is widely used as sensing material of mercury because it has a specific affinity with mercury and the adsorption of mercury changes characteristics of gold such as resistivity and effective mass density. In this thesis, common methods for sensing mercury vapor concentration were summarized and a surface acoustic wave (SAW) sensor utilizing the adsorption of mercury on gold electrodes was proposed for 1 μg/m3 level low concentration mercury vapor detection. The working principle of SAW sensor was studied and finite element method models were built to optimize the sensor design. The influence of several physical structure parameters such as electrode width and pitch on the sensor sensitivity and response time were studied using the simulation model. According to the simulation results a prototype of SAW sensor was designed and fabricated. The sensor was then analyzed with network analyzer and tested with mercury vapor. Preliminary results were presented and analyzed in this work. Finally potential future work was proposed and discussed.

Human phonation is a complex phenomenon produced by multiphysics interaction of the fluid, tissue and acoustics fields. Despite recent advancement, little is known about the effect of false vocal folds on the fluid dynamics of the glottal flow. Recent investigations have hypothesized that this pair of tissue can affect the laryngeal flow during phonation. This hypothesis was tested both computationally and experimentally in this dissertation. The computations were performed using an incompressible solver developed in fixed Cartesian grid with a second order sharp immersed-boundary formulation while the experiments were carried out in a low-speed wind tunnel with physiologic speeds and dimensions. A parametric study was performed to understand the effect of false vocal folds geometry on the glottal flow dynamics and the flow structures in the laryngeal ventricle. The investigation was focused on three geometric features: the size of the false vocal fold gap, the height between the true and false vocal folds, and the width of the laryngeal ventricle. The computational simulations were used to study the flow structures of the glottal flow and pressure distribution on the surface of the larynx. The experimental pressure data served to validate the computational results and provided extended knowledge over a broad range of Reynolds numbers. It was found that the size of the false vocal fold gap has a significant effect on glottal flow aerodynamics; whereas the height between the true and false vocal folds and the width of the laryngeal ventricle were of lesser importance. Due to lack of appreciation of the effect of real geometry of the larynx in the literature, a framework was discussed to extract the laryngeal geometry from the CT scan images. The image segmentation technique was utilized to extract the laryngeal geometries of a canine and a 45 years old female human larynx. Fully resolved three dimensional simulations of the laryngeal flow were conducted for physological Reynolds numbers in these realistic geometries to gain insight into the evolution of vortical structures in the larynx. It was shown that the glottal jet flow is highly three dimensional. The two and three dimensional computational investigations revealed the presence of the rarely reported secondary vortices in the laryngeal ventricle known as rebound vortical structures. It was found that these vortical structures are formed due to the interaction between the starting vortex ring and the false vocal folds. Therefore, the small size of the false vocal folds gap was identified as an important factor in increasing the intensity of these vortical structures. Finally, a novel high order Cartesian based moving least square finite volume solver was developed in this dissertation to model acoustic wave scattering at low Mach numbers flows. The computational aeroacoustic approach is based on incompressible viscous/acoustic splitting technique. In this solver, linearized perturbed compressible equations are solved on Cartesian grids and the boundaries are treated sharply using ghost fluid approach. The Cartesian grid framework is compatible with the incompressible solver and provides the flexibility of handling complex geometries. The acoustic solver was validated against several benchmark problems for which analytical solution is available.

No description available.

In this thesis, the author proposes and develops novel multilayered Surface Acoustic Wave (SAW) devices with unique attributes for gas sensing applications. The design, simulation, fabrication and gas sensing performance of three multilayered SAW structures has been undertaken. The investigated structures are based on two substrates having high electromechanical coupling coefficient: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3), with a piezoelectric zinc oxide (ZnO) intermediate layer. Sensitivity towards target gas analytes is provided by thin film indium oxide (InOx) or tungsten trioxide (WO3). The high performance of the gas sensors is achieved by adjusting the intermediate ZnO layer thickness. Sensitivity calculations, undertaken with perturbation theory illustrate how the intermediate ZnO layer can be employed to modify the velocity-permittivity product of the supported SAW modes, resulting in highly sensitive conductometric SAW gas sensors. The work contained within this thesis addresses a broad spectrum of issues relating to multilayered SAW gas sensors. Topics include finite-element modelling, perturbation theory, micro-fabrication, metal oxide deposition, material characterisation and experiential evaluation of the layered SAW sensors towards nitrogen dioxide (NO2), hydrogen (H2) and ethanol gas phase analytes. The development of two-dimensional (2D) and three dimensional (3D) finite-element models provides a deep insight and understanding of acoustic wave propagation in layered anisotropic media, whilst also illustrating that the entire surface of the device can and should be used as the active sensing area. Additionally, the unique and distinctive surface morphology of the layered structures are examined by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline structure and orientation of the ZnO and WO3 layers are also examined by X-ray Diffraction Spectroscopy (XRD). The novel multilayered SAW structures a re shown to be highly sensitive, capable of sensing NO2 and ethanol concentration levels in the parts-per-billion and parts-per-million range, respectively, and H2 concentrations below 1.00% in air. The addition of platinum or gold catalyst activator layers on the WO3 sensitive layer is shown to improve sensitivity and dynamic performance, with response magnitudes up to 50 times larger than bare WO3. The gas sensing performance of the investigated structures provide strong evidence that high sensitivity can be achieved utilising multilayered SAW structures for conductometric gas sensing applications.

Objectives: To investigate whether any changes in nasal cavity dimensions or subjective report of nasal symptoms exist after rapid maxillary expansion using two types of expansion appliances, comparing results with an untreated control group. Methods: Subjects were randomly assigned into one of three groups: tooth-borne or bone-anchored expander or untreated control. Acoustic rhinometry was used to measure minimal cross-sectional area and volume of the nasal cavity over three timepionts for treatment subjects and two timepoints for control subjects, taken along with the NOSE Instrument survey. Results: No significant changes in nasal cavity dimension or subjective reports were found in subjects treated with tooth- or bone-anchored appliances compared to control subjects over three timepoints. In addition, non-significant correlation was observed between nasal airway dimensional change and subject symptoms. Conclusions: Rapid maxillary expansion does not result in change of i) nasal airway dimensions or ii) the sensation of nasal symptoms. / Orthodontics

No description available.

Carbonate reservoirs are usually diffcult to map and identify in seismic sections due to their complex structure, lithology and diagenetic frabrics. The Midland Basin, located in the Permian Basin of West Texas, is an excellent example of these complex carbonate structures. In order to obtain a better characterization and imaging of the carbonate buildups, an acoustic impedance inversion is proposed here. The resolution of the acoustic impedance is the same as the input seismic data, which is greatly improved with the addition of the low frequency content extracted from well data. From the broadband volume, high resolution maps of acoustic impedance distributions were obtained, and therefore the locations of carbonate buildups were easily determined. A correlation between acoustic impedance and porosity extracted from well data shows that areas with high acoustic impedance were correlated with low porosity values, whereas high porosities were located in areas of low acoustic impedance. Theoretical analyses were performed using the time-average equation and the Gassmann equation. These theoretical models helped to understand how porosity distributions affect acoustic impedance. Both equations predicted a decrease in acoustic impedance as porosity increases. Inversion results showed that average porosity values are 5% [plus or minus] 5%, typical for densely cemented rocks. Previous studies done in the study area indicate that grains are moderately to well-sorted. This suggests that time-average approximation will overestimate porosity values and the Gassmann approach better predicts the measured data. A comparison between measured data and the Gassmann equation suggests that rocks with low porosities (less than 5%) tend to have high acoustic impedance values. On the other hand, rocks with higher porosities (5% to 10%) have lower acoustic impedance values. The inversion performed on well data also shows that the fluid bulk modulus for currently producing wells is lower than in non-productive wells, (wells with low production rates for brine and hydrocarbons), which is consistent with pore fluids containing a larger concentration of oil. The acoustic impedance inversion was demonstrated to be a robust technique for mapping complex structures and estimating porosities as well. However, it is not capable of differentiating different types of carbonate buildups and their origin.

The present study provides the first description of the calls of a multi-species ensiferan assemblage in a tropical evergreen forest of the Indian subcontinent. I have identified and described the calls of twenty ensiferan species constituting the nocturnal acoustic community of a tropical evergreen forest in KNP. I found that the multi-species ensiferan assemblage consisted of diverse taxa representing subfamilies of the families Gryllidae, Tettigoniidae and Anostostomatidae. Eight acoustically communicating species of the family Gryllidae were found. Two species belonged to the family Mogoplistidae. Interestingly, each subfamily was mostly represented by only one genus. In the tettigoniids, representative species were found only from subfamilies Pseudophyllinae, Phaneropterinae and Mecopodinae. The species richness of the acoustically communicating cricket assemblage in the tropical evergreen forest of Kudremukh was found to be low. This study did not include non-calling and ultrasonic species of crickets. The gryllid and tettigoniid species analyzed exhibited different frequency (both narrow and broadband) and temporal patterns. Species belonging to the family Gryllidae had narrow band calls (with bandwidths not greater than 1 kHz) and had dominant frequencies mainly between 3 and 7 kHz. The calls of tettigoniids covered a wide spectral range reaching far into the ultrasound in species of the genus Mecopoda. Interestingly, of nine tettigoniid species, the calls of four (Onomarchus sp., Phyllomimus sp., Brochopeplus sp. and ‘15 kHz’) were narrow band and in the audible range, similar to those of gryllids. Although there was a high overlap of call frequencies between 3 to 7 kHz, gryllid species separated in their syllable repetition rate, which varied from six syllables per second in Landreva to 60 syllables/second in Gryllitara. Species with overlapping syllable repetition rates of 10 – 20 syllables per second separated along the frequency axis. There were species such as those of Phaloria and Gryllitara, Scapsipedus, Xabea and Callogryllus that overlapped both in the spectral and syllable repetition rates. These species however, differed in the other temporal features such as call duration, call period and number of syllables per call. This study also provides the first description of the calls and stridulatory structures of an Indian weta species (Family Anostostomatidae). Both males and females of this species were found to stridulate. The calls of the two sexes had similar spectral features. Male calls consisted of four syllables each, while female calls were bisyllabic. Stridulatory structures were similar between the sexes. I also quantitatively validated the reliability of human listener - based psychoacoustic sampling as a technique to monitor species richness and relative abundance of acoustically communicating ensiferan species that are within the human hearing range. I have shown using controlled psychoacoustic tests in the laboratory that a trained listener is capable of identifying the species as well as the number of individuals of Ensifera with high accuracy. This study suggests that trained listener - based psychoacoustic sampling may be preferable to carry out rapid assessments and species inventories of gryllids and low frequency katydid species in tropical forests. My study also suggests that acoustic monitoring of Orthoptera should be done using both the trained listener - based spot sampling and ambient noise recordings using ultrasound detectors for accurately estimating species richness and relative abundance in an area. Using focal animal sampling, I have shown that most species in the tropical forest ensiferan assemblage of Kudremukh National Park did not move more than a metre in a span of half an hour. The acoustic sampling should be designed in such a way as to cause minimal disturbance to the calling animals and could be limited to ten minutes to avoid re-counting individuals and counter the problem of pseudoreplication. I also investigated the spatial dispersion of calling sites in the vertical dimension. This study revealed vertical stratification of the calling heights of the twenty ensiferan species. Calling heights of both gryllid and tettigoniid species ranged from the ground to the canopy, although more gryllid than tettigoniid species occupied the ground and herb layer. Post hoc comparisons and cluster analysis indicated the presence of discrete calling height layers corresponding to the canopy, understorey, herb and ground layer. These clusters emerged from the raw data of calling heights of individuals of each species without a priori distinction of layers. This is in contrast to other studies on vertical stratification in arthropods and bats where baits, traps and mist nets are placed at different vertical layers, thereby demarcating the layers beforehand. Previous studies on crickets, cicadas and frogs have shown preference for the height of calling sites qualitatively. To my knowledge, this is the first study to quantitatively establish vertical stratification in calling heights in an ensiferan assemblage of an evergreen forest. No correlation between the calling heights and mean dominant frequencies of the species were found. Cricket species with relatively low frequency calls (3–4 kHz) occupied both the ground layer (Callogryllus sp. and Scapsipedus sp.) and the canopy (Xabea sp. and Onomarchus sp) suggesting that these narrow-band, relatively low frequency signals may be optimal for sound transmission in the cluttered habitat of the forest floor (due to leaf litter) and the canopy (due to high leaf density). Species with high frequencies such as Brochopeplus sp. and ‘15 kHz’ called mainly from vegetation in the understorey. Species with broadband calls (Mecopoda sp., Pirmeda sp. and Elimaea sp.) called just above the ground layer and from the understorey suggesting that calls with higher frequencies and bandwidths may be used in the somewhat less-cluttered microhabitat of the understorey. Calling height stratification in the ensiferan assemblages of tropical forests could also be due to other ecological factors such as predation by spiders, mantises, bats, birds or primates. The wide range of duty cycles, presence of high duty cycle callers (such as Mecopoda) and the lack of correlation of duty cycle with calling height found in our study site are interesting. Studies on acoustic transmission in different microhabitats at different heights and on predation pressure on the ensiferan species will provide further insight into the selective forces influencing calling height stratification. The multi-species assemblage constituting the nocturnal acoustic community was found to be calling in the same time period between evening to midnight and no species was found to have a unique calling time that is different from that of another species. There was no diel partitioning of calling time between the acoustically communicating ensiferan species. Frogs and cicadas that can be considered as acoustic competitors of the ensiferan assemblage appeared to be separating from crickets on a seasonal and diel scale respectively. This study has quantified the amount of masking interference in three dimensions viz. temporal, fine temporal and spectral, between sixteen species belonging to the nocturnal acoustic ensiferan assemblage of an evergreen forest. Frequency histograms of overlap, bar graphs of overlap on a species by other species and Mantel’s test results on matrix correlation suggest negative relations between the temporal, fine-temporal and spectral overlaps. Species with high overlap in one dimension had very low levels of overlap in any of the other two dimensions, suggesting acoustic resource partitioning in the ensiferan assemblage of the evergreen forest. I also tried to quantify the extent of spatial overlap between species based on calling intensity and inter-specific distances. However, spatial overlap could not be analysed further as there were some species pairs for which I did not have the inter-individual distances despite carrying out the field work for six months. The procedure of estimating spatial overlap between species pairs and the result along with missing gaps is presented in appendix 2. It will be interesting to investigate the extent of spatial overlap between species pairs as the fourth dimension in which species could separate to avoid acoustic competition. It is also important to estimate the relative abundance of species in the evergreen forest to obtain a realistic representation of masking interference between species. Partitioning of acoustic resources among ensiferan assemblage could also be better explained by analysing all the dimensions.