Geometry and complexity of O'Hara's algorithm

In this paper we analyze O'Hara's partition bijection. We present three type of results. First, we show that O'Hara's bijection can be viewed geometrically as a certain scissor congruence type result. Second, we obtain a number of new complexity bounds, proving that O'Hara's bijection is efficient in several special cases and mildly exponential in general. Finally, we prove that for identities with finite support, the map of the O'Hara's bijection can be computed in polynomial time, i.e. much more efficiently than by O'Hara's construction.Comment: 20 pages, 4 figure

Investigation of prediction methods for the loads and stresses of Apollo type spacecraft parachutes. Volume 1: Loads

An analysis was conducted with the objective of upgrading and improving the loads, stress, and performance prediction methods for Apollo spacecraft parachutes. The subjects considered were: (1) methods for a new theoretical approach to the parachute opening process, (2) new experimental-analytical techniques to improve the measurement of pressures, stresses, and strains in inflight parachutes, and (3) a numerical method for analyzing the dynamical behavior of rapidly loaded pilot chute risers

Insights from Avian Diversification Patterns in the Guineo-Congolian Tropical Lowland Forests

The biogeographical history of the Afro-tropical Guineo-Congolian lowland forests during the Plio-Pleistocene is characterized by pervasive fragmentation-coalescence cycling due to global climatic oscillations. Vicariance scenarios driven by forest fragmentation have long been hypothesized as major mechanisms for the creation and maintenance of Afro-tropical avian diversity. However, the timing and center of diversification events remains unclear. Additionally, the current paradigm within the field regards the Guineo-Congolian forests as regions of little importance in creating genetic diversity patterns. The goal of this dissertation is to address, using multiple levels of evidence, potential avian diversification patterns across Sub-Saharan lowland tropical forests. Utilizing molecular data from 75 avian species, we undertook a combination of molecular and biogeographic methods to construct time-calibrated phylogenies, ancestral area estimations, haplotype networks, and diversification rate estimations. We found substantial, geographically discrete genetic structuring in the majority of sampled avian species, much of it dating to the Pleistocene epoch. Additionally, ancestral area estimations reconstruct the lowland forests as the area of origin the ancestor of our two highest sampled genera. Diversification rates estimated for three genera recovered increasing diversification rates throughout the Plio-Pleistocene. Our results strongly indicate that lowland tropical forests are potentially harboring much more cryptic avian genetic diversity than previously hypothesized. The prevailing view of the Guineo-Congolian forests as regions that have been responsible for the creation of genetic diversity does not appear to be appropriate for many of the avian species sampled here. Specifically, understory taxa, which are heavily tied to the dark, dense parts of the lowland tropical forests showed the most substantial levels of genetic distance between geographic regions. These results highlight the importance of considering behavioral ecology when studying the biogeographic history of forest taxa. Overall, the data from this study signals that climate-induced forest fragmentation in the Plio-Pleistocene undoubtedly played a substantial role in the cyclical creation of new avian diversity in the Guineo-Congolian forests of Africa

Determination of residual stress distributions in autofrettaged thick cylinders

High pressure vessels such as gun barrels are autofrettaged in order to increase their operating pressure and fatigue life. Autofrettage causes plastic expansion of the inner section of the cylinder – setting up residual compressive stresses at the bore after relaxation. Subsequent application of pressure has to overcome these compressive stresses before tensile stresses can be developed, thereby increasing its fatigue lifetime and safe working pressure. A series of Finite Element (FE) models of hydraulic autofrettage were created, to establish the correct boundary conditions required and means of developing accurate but computationally efficient models. Close agreement was observed between the solutions obtained from the developed models and those from existing analytical and numerical models. These initial models used a simplistic bi- linear stress-strain material representation; this deficiency was then addressed through the development of two means of creating radial position dependent non-linear material behaviour within FE, crucial for accurate prediction of residual stresses. The first utilised a method of altering the elastic properties of the material to achieve nonlinear stress-strain response. This provided accurate results that compared well with existing methods, but was unable to be used in simulation of swage autofrettage due to its elastic nature. The second method achieved non- linear behaviour through direct manipulation of the stress and plastic strain states of the FE model at a fundamental level. This was hence suitable for arbitrary loading procedures, including swage autofrettage. A swage-like model that applied deformation via a band of pressure was developed, to investigate the influence of localised loading and shear stresses that result on the residual stress field. A full model of swage autofrettage was then developed, which was optimised on the basis of accuracy and solution effort. It was then used to investigate the effects of various mandrel and contact parameters on the creation of residual stresses. The model is suitable for use in future optimisation studies of the swage autofrettage procedure.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An ordered probit analysis of transaction stock prices

"Latest revision: January 1991."Includes bibliographical references (p. 27-28).Supported by the Batterymarch Fellowship, the Geewax-Terker Investments Research Fund and the Q Group. Supported by the National Science Foundation. SES-8618769 SES-8821583by Jerry Hausman, Andrew W. Lo, and A. Craig MacKinlay

Static and modal analysis of wind turbine towers.

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN049921 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Conceptual design of thermal energy storage systems for near term electric utility applications. Volume 1: Screening of concepts

Over forty thermal energy storage (TES) concepts gathered from the literature and personal contacts were studied for their suitability for the electric utility application of storing energy off-peak discharge during peak hours. Twelve selections were derived from the concepts for screening; they used as storage media high temperature water (HTW), hot oil, molten salts, and packed beds of solids such as rock. HTW required pressure containment by prestressed cast-iron or concrete vessels, or lined underground cavities. Both steam generation from storage and feedwater heating from storage were studied. Four choices were made for further study during the project. Economic comparison by electric utility standard cost practices, and near-term availability (low technical risk) were principal criteria but suitability for utility use, conservation potential, and environmental hazards were considered

Reflecting the instant : information, image, architecture

Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 2005.Includes bibliographical references.A response to the growing importance of designing in an environment that is composed both of physical and non-physical characteristics, this thesis explores a process whereby information is given a visual form through image so that it can be rendered as a site for architectural design. Sited in Times Square, the proposed building responds to the unseen forces of the site, forces which are latent in its physical and visual form, and which are embedded in our experience of the site, but can only be directly grasped in their totality through an armature information. The project is directed by my interpretation of Henri Bergson's notion of virtuality- that is, a notion of the totality of possibility as something that surrounds the actual, but is accessible to our minds as mere fragments. The initial stage of the project uses this notion to translate information about the physical site into virtual images: images which depict a full range of potentials simultaneously, graphically retaining a rich complexity akin to real experience. Emerging out of this process, the proposed building is a mechanism for visualizing virtual characteristics of Times Square in the form of image.by Carl A. Solander.M.Arch