Toward a constitutive model for cure dependent modulus of a high temperature epoxy during the cure

A constitutive model, based on Kohlrausch-Williams-Watts (KWW) equations, was developed to simulate the evolution of the dynamic relaxation modulus during the cure of a "high temperature' epoxy. The basic assumption of the modelling methodology proposed is the equivalence of the mechanisms underlying the evolution of the glass transition temperature and the relaxation time shift during the cure, leading to the use of a common potential function. This assumption is verified by the comparison of normalized glass transition data and principal relaxation times, which have been found to follow a single master curve. Results show satisfactory agreement between experimental data and model prediction over the range of chemical conversion considered

Percolation threshold of carbon nanotubes filled unsaturated polyesters

This paper reports on the development of electrically conductive nanocomposites containing multi-walled carbon nanotubes in an unsaturated polyester matrix. The resistivity of the liquid suspension during processing is used to evaluate the quality of the filler dispersion, which is also studied using optical microscopy. The electrical properties of the cured composites are analysed by AC impedance spectroscopy and DC conductivity measurements. The conductivity of the cured nanocomposite follows a statistical percolation model, with percolation threshold at 0.026 wt.% loading of nanotubes. The results obtained show that unsaturated polyesters are a matrix suitable for the preparation of electrically conductive thermosetting nanocomposites at low nanotube concentrations. The effect of carbon nanotubes reaggregation on the electrical properties of the spatial structure generated is discussed

The impact of novel AMP-activated protein kinase (AMPK) activators and glucose variability on pancreatic α-cell function

The physiological maintenance of normal blood glucose levels (euglycaemia) and prevention of hypoglycaemia is controlled by the intricate process of hormone release from the pancreatic islets of Langerhans, including the secretion of glucose-raising hormone (glucagon) from the islet α-cells. The defective control of glucagon release is commonly associated with both hyperglycaemia and recurrent hypoglycaemia in individuals with diabetes mellitus (DM). There is increasing evidence that α-cells, alongside intra-islet and autonomic control, are directly glucose-sensing to control glucagon secretion, This is includes evidence to suggest the activation of a critical energy sensor, AMP-activated protein kinase (AMPK), is at least partly involved in the stimulation of glucagon release. The mechanisms behind how α-cells intrinsically regulate glucagon secretion, and how these defective regulatory mechanisms could contribute toward the pathophysiology of DM are relatively under-explored. Providing greater understanding of α-cell physiology can therefore aid the development of small molecule compounds to pharmacologically boost α-cell glucose sensing and restore the α-cell functionality observed in DM. Here, the overarching aim of this thesis was to characterise the bioenergetic and secretory effects of pharmacological AMPK activation in pancreatic α-cells by using novel small molecules, including R481, O-304 and BI-9774. By doing so, this will widen the current knowledge on α-cell functional dynamics in both physiological and pathophysiological contexts, including recurrent hypoglycaemia. In addition to this, a literature review was conducted to highlight the putative role of AMPK and potential application of small molecule activators as a therapeutic avenue in cystic fibrosis-related diabetes (CFRD). Evidence suggests that, for the first time, AMPK could be a potent modulator of α-cell metabolic function and substrate utilisation in nutrient-depleted conditions. Here, AMPK activator exposure differentially controlled the glucagon secretory response and total glucagon content in α-cells, suggesting a role of AMPK in regulating glucagon granule dynamics and mechanism-of-action of such small molecules. Similarly, novel findings indicated that α-cells exposed to recurrent hypoglycaemic-like conditions (RLG) had intrinsic glycolytic and mitochondrial adaptations during low glucose and upon recovery, possibly to maintain energy status. The dysregulated intra-islet responses to glycaemia are similarly observed in other DM sub-types, such as CFRD, and contribute to worsened glucose tolerance. The author therefore discussed how the defective glucose-sensing in several tissues could contribute towards worsened glycaemia in CF/CFRD and postulated if the therapeutic application for small molecule AMPK activators could alleviate glucose-related complications, including inflammation, associated with CFRD. Altogether, the themes in this thesis explored the complex and wide-ranging metabolic targets of small molecule AMPK activators in the pancreatic α-cell. Furthermore, evidence suggested α-cells metabolically respond and adapt, respectively, to acute and recurrent nutrient depletion, and thereby pose an important therapeutic avenue in restoring glucose homeostasis in DM.Diabetes U

Fractional Consumption of Liquid Hydrogen and Liquid Oxygen During the Space Shuttle Program

The Space Shuttle uses the propellants, liquid hydrogen and liquid oxygen, to meet part of the propulsion requirements from ground to orbit. The Kennedy Space Center procured over 25 million kilograms of liquid hydrogen and over 250 million kilograms of liquid oxygen during the 3D-year Space Shuttle Program. Because of the cryogenic nature of the propellants, approximately 55% of the total purchased liquid hydrogen and 30% of the total purchased liquid oxygen were used in the Space Shuttle Main Engines. The balance of the propellants were vaporized during operations for various purposes. This paper dissects the total consumption of liqUid hydrogen and liqUid oxygen and determines the fraction attributable to each of the various processing and launch operations that occurred during the entire Space Shuttle Program at the Kennedy Space Center

Liquid Hydrogen Consumption During Space Shuttle Program

This slide presentation reviews the issue of liquid hydrogen consumption and the points of its loss in prior to the shuttle launch. It traces the movement of the fuel from the purchase to the on-board quantity and the loss that results in 54.6 of the purchased quantity being on board the Shuttle