Investigation of Concurrent Energy Harvesting from Ambient Vibrations and Wind

In recent years, many new concepts for micro-power generation have been introduced to harness wasted energy from the environment and maintain low-power electronics including wireless sensors, data transmitters, controllers, and medical implants. Generally, such systems aim to provide a cheap and compact alternative energy source for applications where battery charging or replacement is expensive, time consuming, and/or cumbersome. Within the vast field of micro-power generation, utilizing the piezoelectric effect to generate an electric potential in response to mechanical stimuli has recently flourished as a major thrust area. Based on the nature of the ambient excitation, piezoelectric energy harvesters are divided into two major categories: the first deals with harvesting energy from ambient vibrations; while the second focuses on harvesting energy from aerodynamic flow fields such as wind or other moving fluids. This Dissertation aims to investigate the potential of integrating both sources of excitation into a single energy harvester. To that end, the Dissertation presents reduced-order models that can be used to capture the nonlinear response of piezoelectric energy harvesters under the combination of external base and aerodynamic excitations; and provides approximate analytical solutions of these models using perturbation theory. The analytical solutions are used, subsequently, to identify the important parameters affecting the response under the combined loading and to develop an understanding of the conditions under which the combined loading can be used to enhance efficacy and performance. As a platform to achieve these goals, the Dissertation considers two energy harvesters; the first consisting of a piezoelectric cantilever beam rigidly attached to a bluff body at the free end to permit galloping-type responses, while the second consists of a piezoelectric cantilever beam augmented with an airfoil at its tip. The airfoil is allowed to plunge and pitch around an elastic axis to enable flutter-type responses. Theoretical and experimental studies are presented with the goal of comparing the performance of a single integrated harvester to two separate devices harvesting energy independently from the two available energy sources. It is demonstrated that, under some clearly identified conditions, using a single piezoelectric harvester for energy harvesting under the combined loading can improve its transduction capability and the overall power density. Even when the wind velocity is below the cut-in wind speed of the harvester, i.e. galloping or flutter speed, using the integrated harvester amplifies the influence of the base excitation which enhances the output power as compared to using one aeroelastic and one vibratory energy harvesters. When the wind speed is above the cut-in wind speed, the performance of the integrated harvester becomes dependent on the excitation\u27s frequency and its magnitude with maximum improvements occurring near resonance and for large base excitation levels

A diallel analysis of cellular membrane thermostability in common bean (Phaseolus vulgaris L.)

Call number: LD2668 .T4 1986 X8Master of ScienceHorticulture, Forestry, and Recreation Resource

Measuring Acoustic Nonlinearity of Elastic Materials Using Thermal Modulation of Ultrasonic Waves

Nonlinear acoustic techniques have been used to determine the nonlinear properties of materials. Existing methods either require complex equipment to measure absolute nonlinear coefficients or can only be used on laboratory-sized specimens. A recently developed thermal modulation method addresses the limitations of existing methods, but further theoretical analysis and validation are required. In this dissertation, theoretical analyses were first conducted to study the mechanically and thermally induced acoustoelastic effect. Beginning with the wave equation, the relationship of the ultrasonic wave velocity with respect to mechanical strain and the thermal strain was derived in detail. These analyses provided theoretical support for subsequent validation experiments and applications. Mechanical and thermal modulation tests on aluminum and concrete were performed to validate the theory of thermally induced acoustoelasticity. The stretching technique was applied in calculating ultrasonic wave velocity changes, helping reach a high resolution and accuracy in measuring small wave velocity changes. Acoustoelastic coefficients obtained from the mechanical and thermal modulation methods showed good agreement. Owing to the simple test setup and high measurement sensitivity, the thermal modulation test is a potential experimental method to determine absolute acoustic nonlinearity parameters. The thermal modulation method was then applied to evaluating nonlinear parameters in different materials, and the values were consistent with those from the literature. In addition, the acoustoelastic coefficient, obtained using the thermal modulation method, was used to evaluate stress change in a full-scale prestressed concrete girder. The predicted stress change was verified by direct strain measurement. Adviser: Jinying Zh

DNA Double-Strand Breaks and Telomeres Play Important Roles in Trypanosoma brucei Antigenic Variation

Human-infecting microbial pathogens all face a serious problem of elimination by the host immune response. Antigenic variation is an effective immune evasion mechanism where the pathogen regularly switches its major surface antigen. In many cases, the major surface antigen is encoded by genes from the same gene family, and its expression is strictly monoallelic. Among pathogens that undergo antigenic variation, Trypanosoma brucei (a kinetoplastid), which causes human African trypanosomiasis, Plasmodium falciparum (an apicomplexan), which causes malaria, Pneumocystis jirovecii (a fungus), which causes pneumonia, and Borrelia burgdorferi (a bacterium), which causes Lyme disease, also express their major surface antigens from loci next to the telomere. Except for Plasmodium, DNA recombination-mediated gene conversion is a major pathway for surface antigen switching in these pathogens. In the last decade, more sophisticated molecular and genetic tools have been developed in T. brucei, and our knowledge of functions of DNA recombination in antigenic variation has been greatly advanced. VSG is the major surface antigen in T. brucei. In subtelomeric VSG expression sites (ESs), VSG genes invariably are flanked by a long stretch of upstream 70-bp repeats. Recent studies have shown that DNA double-strand breaks (DSBs), particularly those in 70-bp repeats in the active ES, are a natural potent trigger for antigenic variation in T. brucei. In addition, telomere proteins can influence VSG switching by reducing the DSB amount at subtelomeric regions. These findings will be summarized and their implications will be discussed in this review

Electromechanical Modeling and Analysis of a Self-excited Micro-power Generator

Micro-power generators (MPGs) are compact, scalable, and low-maintenance energy harvesting devices that capture and transform wasted ambient energy into electricity. Such devices, which are currently being researched as a possible replacement for batteries, can act as a power source to maintain and allow autonomous operations of remote low-power consumption sensors. This thesis introduces a novel MPG which transforms wind energy into electricity via wind-induced self-excited oscillations of piezoelectric cantilever beams. The operation concept of the device is simple: similar to music-playing harmonica that create tones via oscillations of reeds when subjected to air blow, the proposed device uses flow-induced self-excited oscillations of a piezoelectric beam embedded within a cavity to generate electric power. When the volumetric flow rate of air past the beam exceeds a certain threshold, the energy pumped into the structure via nonlinear pressure forces offsets the intrinsic damping in the system setting the beam into self-sustained limit-cycle oscillations as a result of a Hopf bifurcation. The vibratory energy is then converted into electricity through principles of piezoelectricity. The objectives of this thesis are two folds: The first investigates the development of an analytical aero-electromechanical model to describe the response behavior of the device, and the second deals with understanding the influence of the design parameters on its cut-on wind speed and the generated power. To achieve the first objective, we obtain a mathematical model describing the dynamic evolution of the four essential system\u27s parameters. These are the spatial and temporal dynamics of the beam deflection, the temporal dynamics of the voltage developed across the electric load, the temporal evolution of the exciting pressure on the surface of the beam, and the flow rate through the aperture between the beam and the support. The modeling is carried out at three successive levels. First, we employ Hamilton\u27s principle in combination with the nonlinear Euler-Bernoulli\u27s beam theory and the linear constitutive equations of piezoelectricity to obtain the nonlinear partial differential equation relating the flexural dynamics of the beam to the output voltage and the exciting pressure. Second, we use basic electric circuits theories to obtain the nonlinear ordinary differential equation relating the output voltage of the harvester to the strain rate in the piezoelectric layer. Third, assuming that the flow rate through the aperture is irrotational, two dimensional, and steady; we utilize the steady Bernoulli\u27s equation in conjunction with the continuity equation to relate the exciting pressure on the surface of the beam to the in- and outflow rates of air. Subsequently, we use a Galerkin expansion to discretize the partial differential equation into a set of nonlinearly-coupled ordinary differential equations. We carry a convergence analysis and determine that a single-mode reduced-order mode can predict the static, linear, and nonlinear dynamic responses of the device. Additionally, we study the influence of neglecting the beam\u27s geometric and inertia nonlinearities on the response behavior showing that such nonlinearities can be safely ignored within the operation range of the device. We validate the resulting reduced-order model against experimental data demonstrating good agreement for two different configurations. To achieve the second objective, we utilize the resulting analytical model to understand the influence of the design parameters (e.g., beam\u27s thickness, length, chamber\u27s volume, aperture\u27s width, and electric load) on the device\u27s response with the goal of minimizing the cut-on wind speed and maximizing the output power of the MPG. Results indicate that for a beam of a given thickness and length, there exists an optimal volume that minimizes the cut-on wind speed of the device. This optimal volume is inversely proportional to the beam\u27s first modal frequency. Results also indicate that the cut-on wind speed can be decreased significantly as the aperture\u27s width is decreased. However, it is observed that minimizing the cut-on wind speed does not always correspond to an increase in the output power. As such, we use the resulting model to construct design charts that aid in designing a MPG with optimal design parameters for a given known average wind speed. Finally, in an attempt to increase the output power of the device, we explore the prospect of designing the harvester such that the Hopf bifurcation responsible for the onset of the beam\u27s oscillation is sub-critical. Towards that end, we utilize the method of multiple scales to obtain the bifurcation\u27s normal form, then use it to demonstrate that the resulting bifurcation will always be super-critical