Effect of tin fluoride content on the structure and properties of phosphate glass – polyamide 11 hybrids

This research investigates tin-fluoride phosphate glasses as liquid-phase fillers in polyamide 11. Optimizing the tin-fluoride content was shown to reduce the glass-transition temperature of the glass down to 106oC and enable both constituents of the composite to be fluid during processing. During extrusion, the phosphate glass was elongated into threads and ultimately broken up into droplets. The interaction parameter between the phosphate and polyamide was found to be - 0.012 due to molecular interactions and enhanced solubility of the ultrafine glass particles. All hybrids showed limited ductility due to the inability of the pinned polymer chains to be drawn into an expanding stable neck. However, there were major increases in both the Young's modulus and flexural modulus owing to the strengthening of molecular bonds by the phosphate-polyamide interactions

Process control for thermal-spray deposition of thermoset coatings using computer simulation

Thermal spraying is a green solvent-free process with the potential of applying polymer coatings to large components in-house or on-site without the need for prolonged drying. Almost no systematic research has been undertaken on thermally spraying thermoset coatings owing to the complexity and difficulty of managing the curing process. An adequately cured thermoset coating could not be deposited by thermal spraying owing to insufficient cumulative time above the cure temperature. Preheating and post-heating the substrate under a constant heat source were not successful as they led to non-uniform curing, residual stress and the risk of overheating. This study develops and validates a computer model that simulates the deposition of thermoset coatings on metal substrates using thermal spraying and high-energy infrared irradiation. The model uses readily-available commercial software and enables precise control of the coating process to improve energy efficiency and coating quality. Further research showed that evenly cured coatings could be achieved by using variable heat fluxes and controlled utilization of inward conduction from the outer surface layers. Self curing during cooling was significant and maybe employed to increase energy efficiency. The thickness of the metal substrate was shown to be an important variable as it acts as a heat sink and, for heavy sections, can substantially increase energy consumption. The results indicate a need for sufficiently accurate process control and provide a suitable methodology for the deposition of thermoset coatings

Effect of composition on the mechanical properties of 3d printed polymer nanocomposites

Fused filament fabrication (FFF) is one of the most widely employed techniques in additive manufacturing. Despite its ease of use and environmentally friendly nature, FFF has only demonstrated a narrow range of applications due to the limited number of materials compatible with the technique. Furthermore, FFF printed parts exhibit inferior mechanical properties compared to those of their conventionally manufactured counterparts. An approach for tailoring the properties of printing materials and extending the applicability of FFF is the addition of nanoparticles to the polymer, such as organo-modified nanoclays. To date, there has been only limited research using this approach but some improvement in properties has been obtained. This research concerns polylactide-nanoclay composites and investigates the effect of the clay type and content on the 3D printed product. This is the first systematic study on the mechanical properties of 3D printed PLA/clay samples by an extrusion-based technique. The introduction of clays to the PLA matrix was found to improve the modulus of elasticity of the 3D printed PLA/clay samples. However, this behaviour was accompanied by a decrease in the ultimate tensile strength and elongation at break, while the flexural properties exhibited similar trend to the tensile properties. The quality of the printed filament was related to the non-uniform dispersion of clays in the polymer matri

Consequences of converting graded to action potentials upon neural information coding and energy efficiency

Information is encoded in neural circuits using both graded and action potentials, converting between them within single neurons and successive processing layers. This conversion is accompanied by information loss and a drop in energy efficiency. We investigate the biophysical causes of this loss of information and efficiency by comparing spiking neuron models, containing stochastic voltage-gated Na+ and K+ channels, with generator potential and graded potential models lacking voltage-gated Na+ channels. We identify three causes of information loss in the generator potential that are the by-product of action potential generation: (1) the voltage-gated Na+ channels necessary for action potential generation increase intrinsic noise and (2) introduce non-linearities, and (3) the finite duration of the action potential creates a ‘footprint’ in the generator potential that obscures incoming signals. These three processes reduce information rates by ~50% in generator potentials, to ~3 times that of spike trains. Both generator potentials and graded potentials consume almost an order of magnitude less energy per second than spike trains. Because of the lower information rates of generator potentials they are substantially less energy efficient than graded potentials. However, both are an order of magnitude more efficient than spike trains due to the higher energy costs and low information content of spikes, emphasizing that there is a two-fold cost of converting analogue to digital; information loss and cost inflation

Gray matter imaging in multiple sclerosis: what have we learned?

At the early onset of the 20th century, several studies already reported that the gray matter was implicated in the histopathology of multiple sclerosis (MS). However, as white matter pathology long received predominant attention in this disease, and histological staining techniques for detecting myelin in the gray matter were suboptimal, it was not until the beginning of the 21st century that the true extent and importance of gray matter pathology in MS was finally recognized. Gray matter damage was shown to be frequent and extensive, and more pronounced in the progressive disease phases. Several studies subsequently demonstrated that the histopathology of gray matter lesions differs from that of white matter lesions. Unfortunately, imaging of pathology in gray matter structures proved to be difficult, especially when using conventional magnetic resonance imaging (MRI) techniques. However, with the recent introduction of several more advanced MRI techniques, the detection of cortical and subcortical damage in MS has considerably improved. This has important consequences for studying the clinical correlates of gray matter damage. In this review, we provide an overview of what has been learned about imaging of gray matter damage in MS, and offer a brief perspective with regards to future developments in this field

Microporosity and delamination mechanisms in thermally sprayed borosilicate glass coatings

Conventional enamelling requires both the feedstock powder and the substrate component to be heated one or more times in a furnace at 800–900 °C. The process can degrade the substrate and limit the size of the component to the furnace dimensions, which are serious restrictions on the technology. This study concerns the use of combustion- flame spraying as an alternative technique for enamelling. In this process, the heat source (the flame) is separated from the substrate, which enables much lower substrate temperatures and avoids thermal damage. It also removes the need for furnace treatment and opens up the possibility of on-site enamelling and repair. However, experimental trials showed that thick flame-spray coatings delaminated during cooling and had high microporosities due to quenching stresses at the glass-steel interface and inadequate splat flow of small feedstock particles. The research shows that these adverse mechanisms could be overcome by pre-heating the substrate surface to the dilatometric softening temperature and removing fines from the feedstock powder. The control of these two parameters was found to double the adhesion strength, provide coatings of very similar hardness and fracture toughness to conventional enamel aswell as deposit coatings of over 1mmin thickness for heavy-duty corrosion protection. Thermal spraying is well established for ceramic and metal coatings but the fundamentally different structure of glasses requires a different approach. An advantage of combustion flame spraying shown up by this research is that the high energy of the flame accelerates the particles to a high velocity and the resulting impact forces promote the flow of the glass. As a result, lower substrate temperatures may be used with reduced risk of degradation or higher viscosity glasses may be deposited with enhanced properties. The influence of the type of thermal-spray technique on coating quality is also discusse