Foredune formation at Tugela River mouth.

Thesis (M.Sc.)-University of Natal, Durban, 1998.This study examines foredune evolution along a 2100 m section of coast adjacent to the Tugela River. The foredunes vary in both height and shape along the study area and form the southern most extension of the Tugela foredune-ridge plain. Sand accumulation and erosion was measured at regular intervals over a 30 month period by tacheometric surveys. The foredunes and beaches are comprised of over 99 % sand. The sediment was predominantly composed of quartz and feldspar with subordinate lithic fragments. The quartz grains display conchoidal fractures and mechanical v-shaped pits and curved grooves. The beach and dune sand is well sorted and slightly negatively skewed with a mean grain size of 1.62 ф. The vegetation structure and floristic composition of the foredunes are explored. A range of factors influencing foredune morphology and evolution, including canopy density, height and distribution, wind velocity and a variety of ecological and environmental processes are examined. Ridge and swale morphology as well as alongshore variation in the dunefield could not be related to biological processes. The development of a foredune-ridge topography depends on a large sediment supply from the Tugela River over the long-term. Periods of high discharge introduce a fresh source of sediment to the littoral zone. Reworking of fluvial sediment landwards results in wide beaches. Onshore winds transport the sand from the beaches to the foredunes. Scaevola thunbergii encourages rapid vertical accretion and hummock dunes are formed. Lateral extensive invasion by seedlings may result in the hummock dunes joining to form coast parallel foredunes. Under periods of reduced sediment discharge erosion of the shoreline results in steep narrow beaches. Despite a negative beach budget foredunes continue to accrete vertically. Marine erosion results in either the complete destruction of embryo foredunes or their landward shift. Natural breaks in the dune crestline were attributed to changes in the delivery of sediment to the beaches. The processes operating in the study area conform to Psuty's (1988,1989) sediment budget model of foredune development. Sediment availability to the coastline produces characteristic morphologies

Lossless voltage regulation and control of the resonant switched-capacitor DC-DC converter

Abstract—This paper presents an approach for nom-inally lossless regulation of the output voltage, and for design of tight closed-loop voltage control of a resonant switched-capacitor (ResSC) dc-dc converter. A switching pattern for the ResSC dc-dc converter that enables wide range lossless voltage regulation and zero voltage switching (ZVS) is developed. An appropriate small signal model is derived based on the generalized averaging method. In view of the dynamics of the developed small signal transfer functions, a compensation method based on a minor phase loop is introduced to stabilize the system. The steady state and transient responses of the system are evaluated based on the developed model. The performance of the proposed controller is verified by a switch-based simulation in a design example for on-chip power delivery application. I

Enhanced Viability of Endothelial Colony Forming Cells in Fibrin Microbeads for Sensor Vascularization

Enhanced vascularization at sensor interfaces can improve long-term function. Fibrin, a natural polymer, has shown promise as a biomaterial for sensor coating due to its ability to sustain endothelial cell growth and promote local vascularization. However, the culture of cells, particularly endothelial cells (EC), within 3D scaffolds for more than a few days is challenging due to rapid loss of EC viability. In this manuscript, a robust method for developing fibrin microbead scaffolds for long-term culture of encapsulated ECs is described. Fibrin microbeads are formed using sodium alginate as a structural template. The size, swelling and structural properties of the microbeads were varied with needle gauge and composition and concentration of the pre-gel solution. Endothelial colony-forming cells (ECFCs) were suspended in the fibrin beads and cultured within a perfusion bioreactor system. The perfusion bioreactor enhanced ECFCs viability and genome stability in fibrin beads relative to static culture. Perfusion bioreactors enable 3D culture of ECs within fibrin beads for potential application as a sensor coating

US and European Household Debt and Credit Constraints

This paper uses micro data from four OECD countries (the United States, Spain, Italy, and the Netherlands), to assess the determinants of household debt holding and to investigate whether or not credit constraints are important for household debt holding. We extend the existing literature in important ways. First, we present comparative evidence for four countries at the micro level, where we rely on household panel data for two countries; we are thus able to control for unobserved heterogeneity via individual household effects and to track changes in household behaviour over time. Second, by making data across countries as comparable as possible, we can explore the importance of the differences in institutional settings for debt incidence, debt outstanding and credit constraints. We also explore the implications for debt holding from consumption models, including a numerically solved precautionary savings model. We find that inter-country differences are substantial and remain even after controlling for a host of observable characteristics. This points to institutional differences between the countries being important

Carbon-sensitive pedotransfer functions for plant available water

Currently accepted pedotransfer functions show negligible effect of management-induced changes to soil organic carbon (SOC) on plant available water holding capacity (θAWHC), while some studies show the ability to substantially increase θAWHC through management. The Soil Health Institute\u27s North America Project to Evaluate Soil Health Measurements measured water content at field capacity using intact soil cores across 124 long-term research sites that contained increases in SOC as a result of management treatments such as reduced tillage and cover cropping. Pedotransfer functions were created for volumetric water content at field capacity (θFC) and permanent wilting point (θPWP). New pedotransfer functions had predictions of θAWHC that were similarly accurate compared with Saxton and Rawls when tested on samples from the National Soil Characterization database. Further, the new pedotransfer functions showed substantial effects of soil calcareousness and SOC on θAWHC. For an increase in SOC of 10 g kg–1 (1%) in noncalcareous soils, an average increase in θAWHC of 3.0 mm 100 mm–1 soil (0.03 m3 m–3) on average across all soil texture classes was found. This SOC related increase in θAWHC is about double previous estimates. Calcareous soils had an increase in θAWHC of 1.2 mm 100 mm–1 soil associated with a 10 g kg–1 increase in SOC, across all soil texture classes. New equations can aid in quantifying benefits of soil management practices that increase SOC and can be used to model the effect of changes in management on drought resilience

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity

Cardiovascular response to beta-hydroxy thujaplicin and gamma-thujaplicin.

An Investigation was undertaken to determine the effects of beta-hydroxy thujaplicin and gamma-thujaplicin, used as the sodium salts, on blood pressure and heart rate in the rat. Attempts were made to discover the sites and modes of action of these two compounds. Gamma-thujaplicin 30mg/kg. produced either a vasopressor or a vasodepressor response in anesthetized rats. The pressor response was usually more pronounced, than the vasodepressor response. Tachycardia occurred with either blood pressure response. To determine whether the central nervous system was necessary for the vasopressor and tachycardiac response, pithed rats were used. In these preparations gamma-thujaplicin produced only a fall in blood pressure and a decrease in heart rate. The effect of adrenergic blocking drugs on the response to gamma-thujaplicin was investigated. In the anesthetized rat the vasopressor response was reduced significantly by both phenoxybenzamine and pronethalol; however, the heart rate was unaffected. In the pithed rat the vasodepressor response produced by gamma-thujaplicin was not affected by pronethalol; however, gamma-thujaplicin produced a significantly greater decrease in heart rate after treatment with pronethalol. To determine whether gamma-thujaplicin had adrenergic alpha-receptor or beta-receptor blocking properties its effect on blood pressure responses to noradrenaline and isoproterenol was investigated. Gamma-thujaplicin was found to reduce the vasopressor effect of intravenous noradrenaline 0.5ug/kg. but had no effect on the vasopressor response produced by isoproterenol 0.25ug/kg. The pressor response to intravenous physostigmine salicylate 40ug/kg. was unaffected by gamma-thujaplicin. The increase in heart rate and blood pressure produced by gamma-thujaplicin, with injections repeated every fifteen minutes, was greatly reduced after the second dose. It is concluded that in the anesthetized rats the vasopressor and tachycardiac response produced by gamma-thujaplicin were of central origin while the vasodepressor effect was a result of direct action on vascular smooth muscle. The vasopressor response could involve the stimulation, via sympathetic nerves, of alpha-adrenergic receptors of vascular smooth muscle. Gamma-thujaplicin can produce alpha-adrenergic receptor, blockade to exogenous noradrenaline, but not to endogenously released noradrenaline since the response to intravenous physostigmine was not affected by the tropolone. Beta-hydroxy thujaplicin 10mg/kg. caused a vasopressor response in all anesthetized and pithed rats tested. The vasopressor response was abolished by phenoxybenzamine in both anesthetized and pithed rats. Beta-hydroxy thujaplicin did not alter isoproterenol induced tachycardia or the vasopressor response produced by physostigmine salicylate. It is concluded that beta-hydroxy thujaplicin caused its vasopressor effect in rats by acting directly on the alpha-adrenergic receptors of vascular smooth muscle.Medicine, Faculty ofAnesthesiology, Pharmacology and Therapeutics, Department ofGraduat