The 3-dimensional oscillon equation

On a bounded three-dimensional smooth domain, we consider the generalized oscillon equation with Dirichlet boundary conditions, with time-dependent damping and time-dependent squared speed of propagation. Under structural assumptions on the damping and the speed of propagation, which include the relevant physical case of reheating phase of inflation, we establish the existence of a pullback global attractor of optimal regularity, and finite-dimensionality of the kernel sections

Time-Dependent Attractor for the Oscillon Equation

We investigate the asymptotic behavior of the nonautonomous evolution problem generated by the Klein-Gordon equation in an expanding background, in one space dimension with periodic boundary conditions, with a nonlinear potential of arbitrary polynomial growth. After constructing a suitable dynamical framework to deal with the explicit time dependence of the energy of the solution, we establish the existence of a regular, time-dependent global attractor. The sections of the attractor at given times have finite fractal dimension.Comment: to appear in Discrete and Continuous Dynamical System

PRODUCTIVITY AND LAND ENHANCING TECHNOLOGIES IN NORTHERN ETHIOPIA: HEALTH, PUBLIC INVESTMENTS, AND SEQUENTIAL ADOPTION

The adoption of more efficient farming practices and technologies that enhance agricultural productivity and improve environmental sustainability is instrumental for achieving economic growth, food security and poverty alleviation in sub-Saharan Africa. Our research examines the interaction between public investments, community health, and adoption of productivity and land enhancing technologies by households in the northern Ethiopian state of Tigray. Agricultural technology adoption decisions are modeled as a sequential process where the timing of choices can matter. We find that time spent sick and opportunity costs of caring for sick family members are significant factors in adoption. Sickness, through its impact on household income and labor allocation decisions for healthcare and other activities, significantly reduces the likelihood of technology adoption. Our findings suggest that agencies working to improve agricultural productivity and land resource conservation should consider not only the financial status of potential adopters, but also their related health situation.Research and Development/Tech Change/Emerging Technologies,

A preliminary survey of the concentration of selected ions in some California native plants growing in serpentine and non-serpentine soil

Do the peculiar ion concentrations of serpentine soils appear in the tissues of plants growing on those soils? To what extent are the same species of plants growing in serpentine and non-serpentine soil similar in ionic concentrations? This work was an attempt to answer these questions

Master of Science

thesisA crushed, secondary sulfide copper ore was provided by a large mining company. The agglomeration of the ore was studied in three phases. In phase one, a series of scoping experiments were conducted to characterize agglomerates produced in terms of agglomerate size distribution, electrical conductivity, hydraulic conductivity, and a test of binding strength. Using these tools and visual appearance, optimum agglomeration conditions were determined to be 13.0% moisture determined on a wet basis, 60 g/L H2SO4, 30% critical speed, and 3 minute agglomeration time. Upon determination of agglomeration conditions, the study entered a second phase where agglomerates were subjected to leaching in order to determine the relation of leaching behavior to agglomeration conditions. Acid concentration was found to be important for the initial week of leaching. None of the agglomeration conditions affected copper recovery at 90 days of leaching. Following leaching, acid-resistant agglomeration aids were evaluated to identify those with a potential to improve agglomerate stability and potentially, leaching behavior. Two cationic polymers were selected from an assortment of potential binders. Both polymers greatly improved agglomerate strength and hydraulic conductivity when used during agglomeration at a dosage of 0.5 kg polymer per tonne of ore

A method for determining mixed mode stress intensity factors using strain gage data

An experimental method for determining mixed mode stress intensity factors, crack tip location, and crack tip orientation using strain gage data near the crack tip is developed. From the strain gage data and the relative location of the strain gages to each other the location of the crack tip and its orientation relative to the strain gages is derived along with the mixed mode stress intensity factors. The method is based on an iterative linear least squares fit to generalized Westergaard equations that describe the strain field near a crack tip;The method is applied to numerical data generated from finite element models of a compact tension specimen and a mixed mode specimen. The method is also applied to experimental data from the same specimens. Theoretical, numerical, and experimental results are compared. Limits on the applicability and accuracy of the method are developed

The effects of different burning regimes on grassland phytodiversity

Bibliography: leaves 144-163.The southern African grassland biome has a diverse flora including many rare and endangered species deserving a high conservation priority. With less than two percent currently conserved, proper management of this biome is crucial to maintaining its diversity. Fire, in particular, is important and although there has been extensive research into the grazeable component of the sward, little attention has been paid to the effects of burning on forbs or the overall phytodiversity. The aim of this study was examine the effects of different burning regimes on grassland phytodiversity. To do this, three long-term burning trials, widely located across the biome and consisting of a range of treatments randomly allocated to plots in replicated block designs, were sampled. Manipulated according to the frequency and season of burn, with fire protection controls, diversity was sampled at different scales across a range of treatments. In addition, a range of sward attributes was sampled in an attempt to explain diversity patterns

Conceptual modelling of Work Systems using ABC notation

This paper seeks to extend the Work System Method WSM of Steven Alter by means of a modelling notation and mechanism called ABC. It does so because it is often necessary to know (or at least to conjecture) how things, processes and events interrelate. Our contention, which we support by literature primarily derived from cybernetics, is that we must discern conceptual models, so as to understand and, potentially, to improve by design, active models – specifically, the information systems which support work systems. We do this in order to regulate work systems, whether actively by explicit control or implicitly by aiding learning, understanding and self-control by modellers and participants. This paper is not a definitive statement concerning ABC. Instead, it sufficiently introduces the modelling approach to enable the reader to understand some examples of the approach as applied to work systems. It can also serve in a tutorial approach to the ABC modelling of work systems

What is the contribution of personal information management systems (PIMS) to the Working Model and personal work system of knowledge workers?

The thesis reports research into a phenomenon which it calls the personal working model of an individual knowledge worker. The principal conjecture addressed in this thesis is that each of us has a personal working model which is supported by a personal work system enabled by a personal information management system. For some people, these are well defined; for most they are not even explicit. By means of structured self-reflection aided by conceptual knowledge modelling within the context of a process of action learning they can be improved. That personal working model is predicted by Ashby's law of requisite variety and by the good regulator theorem of Conant and Ashby. The latter theorem states that the only good regulator of a system is a model of that system. The thesis and the work it reports result from a systemic approach to identifying the personal information management system and personal work system which together contribute to the personal working model. Starting with abductive conjecture, the author has sought to understand what models are and to explore ways in which those models can themselves be expressed. The thesis shows how a new approach to the conceptual modelling of aspects of the personal knowledge of knowledge worker was designed, built and then used. Similarly, the actual data used by a knowledge worker had to be stored, and for this purpose a personal information management system was also designed. Both these artefacts are evaluated in accordance with principles drawn from the literature of design science research. The research methodology adopted in the first phase of the research now ending also included a relatively novel approach in which the PhD student attempted to observe himself over the last five years of his PhD research – this approach is sometimes called autoethnography. This autoethnographic element is one of a number of methods used within an overall framework grounded by the philosophical approach called critical realism. The work reported in the thesis is initial exploratory research which, it is planned, will continue in empirical action research involving mentored action learning undertaken by professional knowledge workers

Pessimistic portfolio allocation and Choquet expected utility

Recent developments in the theory of choice under uncertainty and risk yield a pessimistic decision theory that replaces the classical expected utility criterion with a Choquet expectation that accentuates the likelihood of the least favorable outcomes. A parallel theory has recently emerged in the literature on risk assessment. It is shown that a general form of pessimistic portfolio optimization based on the Choquet approach may be formulated as a problem of linear quantile regression.