172 research outputs found
Celestial Bodies
No full textCelestial Bodies
Jared C. White
ABSTRACT
The following is a collection of original poetry written over a span of three years while attending the University of South Florida. The poetry is divided into five numbered sections, marking the major thematic divisions. Preceding the poetry is a critical introduction to the work that outlines the author\u27s developing thematic ideology
A methodology for the concurrent design of products and their assembly sequence
No full textThis thesis reports on the development of a Two-Tier methodology that provides
support for assembly sequence construction, validation and evaluation in parallel with
the design. This facilitates the production of products that are optimised for
assemblability. The proposed approach diverges significantly from many of the
sequence generation methods developed to date, which assume that assembly
planning starts at the conclusion of the design process. It is believed that the latter
approach misses an important opportunity to concurrently implement design and
sequence improvements that would result in products inherently suited to assembly.
The industrial assembly planning process was found to be completely different from
the automatic sequence generation approach. The Two-Tier methodology has its
foundations in this manual process, which uses a breadth-first, depth-second search. A
constraint-based method is used to interactively validate the sequence. In direct
contrast to traditional sequence generators, the hard and soft constraints are invoked
throughout the process. A novel approach to sequence evaluation allows the user to
quantitatively determine the suitability of the sequence at any time during the
construction process.
However, designers are rarely assembly experts and it is unreasonable to expect
practical sequences to be generated without assistance. Thus, a set of generic
assembly planning rules was identified from industrial surveys by the author. These
were collaboratively implemented into an Expert Assembler, which currently consists
of two mini advisors. Support is available to identify the most suitable base
component and the most appropriate component to add next.
The Two-Tier methodology has been implemented into a computer-based system
called SPADE (Sequence Planning And Design Environment). A four-layer model
holds the product data that underpins this implementation. The methodology and
SPADE have been successfully tested using representative case studies and the results
are reported as part of this thesis
The nonlinear future stability of the FLRW family of solutions to the Euler–Einstein system with a positive cosmological constant
No full textOriginal manuscript January 24, 2012In this article, we study small perturbations of the family of Friedmann–Lemaître–Robertson–Walker cosmological background solutions to the 1 + 3 dimensional Euler–Einstein system with a positive cosmological constant. These background solutions describe an initially uniform quiet fluid of positive energy density evolving in a spacetime undergoing accelerated expansion. Our nonlinear analysis shows that under the equation of state p=c[2 over s]ρ, 0 < c[2 over s] < 1/3 , the background solutions are globally future-stable. In particular, we prove that the perturbed spacetime solutions, which have the topological structure [0,∞) × T[superscript 3], are future-causally geodesically complete. These results are extensions of previous results derived by the author in a collaboration with I. Rodnianski, in which the fluid was assumed to be irrotational. Our novel analysis of a fluid with non-zero vorticity is based on the use of suitably defined energy currents.National Science Foundation (U.S.). All-Institutes Postdoctoral Fellowship (Mathematical Sciences Research Institute (Berkeley, Calif.) Grant DMS-0441170
Birthplace effects on the development of female athletic talent
No full textThis study examined the extent to which an athlete's place of birth can influence the likelihood of playing professional sport. Information regarding the birthplace of all American female athletes in the Ladies Professional Golf Association and Women's United Soccer Association was gathered from official league websites. Monte Carlo simulations were used to determine if the birthplace of these professional athletes differed in any systematic way from official census population distributions. Odds-ratios were determined for cities within specific population ranges to ascertain if the likelihood of playing professional sport was influenced in any systematic way by city size. The analyses revealed that female professional soccer players born in cities of less than 1,000,000 were over-represented, as were female professional golfers born in cities of less than 250,000. Results are consistent with those of male professional athletes in suggesting that areas of lower population provide conditions more conducive to the development of expertise than do larger city environments
On the questions of local and global well-posedness for the hyperbolic PDEs occurring in some relativistic theories of gravity and electromagnetism
No full textThe two hyperbolic systems of PDEs we consider in this work are the source-free Maxwell-Born-Infeld (MBI) field equations and the Euler-Nordstr??m system for gravitationally self-interacting fluids. The former system plays a central role in Kiessling's recently proposed self-consistent model of classical
electrodynamics with point charges, a model that does not suffer from the infinities found in the classical Maxwell-Maxwell model with point charges. The latter system is a scalar gravity caricature of the incredibly more complex Euler-Einstein system. The primary original contributions of the thesis can be summarized as follows:
1) We give a sharp non-local criterion for the formation of singularities in plane-symmetric solutions to the source-free MBI field equations. We also use a domain of dependence argument to show that 3-d initial data agreeing with certain plane-symmetric data on a large enough ball lead to solutions that form singularities in finite time. This work is an extension of a theorem of Brenier, who studied singularity formation in periodic plane-symmetric solutions.
2) We prove well-posedness for the Euler-Nordstr??m system with a cosmological constant k (EN_k) for initial data that are an H^N perturbation (not necessarily small) of a uniform, quiet fluid, for N [greater than]= 3. The method of proof relies on the framework of energy currents that has been recently developed by Christodoulou. We turn to this method out of necessity: two common frameworks for showing well-posedness in H^N, namely symmetric hyperbolicity and strict hyperbolicity, do not apply to the EN_k system, while Christodoulou's techniques apply to all hyperbolic systems derivable from a Lagrangian, of which the EN_k system is an example.
3) We insert the speed of light c as a parameter into the EN_k system (and designate the family of systems EN_k^c) in order to study the non-relativistic limit c to infinity. Taking the formal limit in the equations gives the Euler-Poisson system with a cosmological constant (EP_k). Using energy currents, we prove that for fixed initial data, as c goes to infinity, the solutions to the EN_k^c system converge uniformly on a spacetime slab [0,T] x R^3 to the solution of the EP_k system.Ph.D.Includes bibliographical references (p. 140-143)
Energy Harvesting with Piezoelectric Grass for Autonomous Self-Sustaining Sensor Networks.
No full textThe primary objective of this research is to develop a deploy-and-forget energy harvesting device for use in low velocity, highly turbulent, and unpredictable fluid flow environments. The work presented in this dissertation focuses on a novel, lightweight, highly robust, energy harvester design referred to as piezoelectric grass. This biologically inspired design consists of an array of cantilevers, constructed with piezoelectric material. When exposed to a wide range of flow conditions, these cantilevers experience vigorous persistent vibration.
Included in this work is an experimentally validated theoretical analysis of the piezoelectric grass harvester generalized for the case of a single cantilever in turbulent cross-flow. A brief parameter optimization study is presented using this distributed parameter model. Two high-sensitivity pressure probes were needed to perform spatiotemporal measurements within various turbulent flows. Measurements with these probes are used to develop a turbulent fluid forcing function. This function is then combined with an analytical structural dynamics model such that not only the modal RMS displacements, but also the modal displacement power spectral density trends are predicted for a given structure. Pressure probe design, turbulence measurement techniques, and both statistical and analytical models are validated with experimental results.
An experimental investigation on the energy harvesting potential of large harvester arrays containing up to 112 flexible piezoelectric structures is presented. Experimental results show that a given array will experience large amplitude, waving, resonant-type vibration over a large range of velocities, and is unaffected by large-scale turbulence upstream of the array. These dynamic characteristics make large arrays of flexible piezoelectric structures ideal for many energy harvesting applications.
Lastly, this dissertation presents the first documented investigation of a flow-induced vibration phenomenon referred to as dual cantilever flutter (DCF). At a particular combination of flow velocity and distance between two adjacent beams, aeroelastic coupling between the beams causes them to become unstable and undergo limit cycle oscillations. An attractive feature of DCF for energy harvesting is that it provides robust flow-induced excitation over a large range of flow velocities. An experimentally validated lumped parameter model for DCF is presented. Results include CFD simulations that were setup and executed using ANSYS-CFX.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107068/1/jdhobeck_1.pd
Residual thermal effects in macro fiber composite actuators exposed to persistent temperature cycling
No full textIn this letter, the authors present results of an experimental investigation demonstrating how extreme persistent thermal cycling influences the performance of piezoelectric macro fiber composite (MFC) actuators. More specifically, this research shows how repeated temperature cycling ranging from −60 °C to 90 °C and from −50 °C to 150 °C affects an MFCs ability to actuate while being driven at frequencies of 60 Hz to 90 Hz with a voltage of 20 Vpp. Experimental results show that thermal cycling causes MFC actuation characteristics to drift and eventually stabilize after approximately 20 cycles. In two cases presented here, thermal cycling alone caused a residual increase in actuation amplitude that exceeded the initial amplitude by 70%. This apparent thermal memory effect of MFCs may significantly impact the design and analysis of active structures where MFCs are used for vibration or displacement control in transient extreme temperature environments such as those encountered by aerospace structures, industrial equipment, automobiles, and civil infrastructure
YOU GOT GIS: GEOSPATIAL DATA, SIMPLIFIED FOR 501(c)3 NONPROFITS
No full textabstract: The contemporary world is motivated by data-driven decision-making. Small 501(c)3 nonprofit organizations are often limited in their reach due to their size, lack of funding, and a lack of data analysis expertise. In an effort to increase accessibility to data analysis for such organizations, a Founders Lab team designed a product to help them understand and utilize geographic information systems (GIS) software. This product – You Got GIS – strikes the balance between highly technical documentation and general overviews, benefiting 501(c)3 nonprofits in their pursuit of data-driven decision-making. Through the product’s use of case studies and methodologies, You Got GIS serves as a thought experiment platform to start answering questions regarding GIS. The product aims to continuously build partnerships in an effort to improve curriculum and user engagement. (abstract
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