Neurotransmitter receptor types mediating the generation of intracellular signals are of two types; ligand-gated ion channels and G protein coupled receptors. The effector enzyme phosphoinositide-specific phospholipase C (PLC) is modulated by stimulation of G protein coupled receptors, leading to an increased breakdown of inositol phospholipids ("Ptdlns breakdown").In recent years, the receptors in the brain coupled to PLC and modulation of such receptor-mediated Ptdlns breakdown have been characterised. One such modulation is the "potassium effect", whereby an increase in the assay [K+] from 6 to 18 mM potentiates the Ptdlns breakdown response to the muscarinic agonist carbachol in the rat brain. It has been speculated that this effect is one way of enhancing the signal :noise ratio of muscarinic neurotransmission. The mechanisms responsible for the potassium effect have been studied in this thesis.Initial methodological studies indicated that the temperature of the Krebs buffer used after tissue dissection was an important factor regulating the Ptdlns response to receptor stimulation. Expressing the Ptdlns breakdown response as a fraction of the total labelled phosphoinositides was more useful than other ways of expressing the data. Acid extraction of the Lipid fraction was also superior to neutral extraction.Miniprismspreparedfrompig striatum and hippocampus showed qualitative (but not quantitative) similarities with the rat with respect to stimulation by carbachol, noradrenaline and the potassium effect. Dopamine also stimulated Ptdlns breakdown, though probably via a noradrenergic mechanism.The enhancing actions of potassium appeared to be selective for muscarinic Ml-type receptors. Thus glutamate, quisqualate and NaF-stimulated Ptdlns breakdown are not affected by raised [K+].The potassium effect is brought about by two mechanisms. In calcium-free Krebs buffer, the effect could be mimicked by the calcium channel agonist BAY K-8644 and partially antagonised by verapamil. At an assay [Ca2*] of 2.52 mM, however, modulation of calcium uptake had little effect on carbachol-stimulated Ptdlns breakdown at either normal or raised [K+]. The synergy between potassium and carbachol at252 mM Ca?+ is not dependent upon tissue depolarisation perse, since other ways of depolarising the tissue did not enhance the response to carbachol. It is suggested that potassium might have a direct effect on the muscarinic Ml-type receptor - G protein - PLC complex.In order to investigate this possibility, the effect of fluoride ions (which activate G proteins via formation of AlF4) on basal and carbachol-stimulated Ptdlns breakdown was investigated. Fluoride ions inhibited the enhanced breakdown response to carbachol found at raised [K+]. However, this effect is secondary to effects of fluoride on PLC substrate availibility rather than on G protein function. / digitalisering@umu

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

The ultimate goal of this study is to examine the feasibility of extracting silicon from silica through electrolysis. The objective of the thesis was to evaluate the physico-chemical properties of a cryolite-lithium fluoride mixture as an electrolyte for the electrolysis process. A study of 86.2wt%Cryolite and13.8wt%Lithium fluoride melt with silica concentration varying from 0-4wt% and temperature range of 900-1000°C was done. Three properties were measured using two sets of experiments: 1) Dissolution Behaviour Determination, to obtain a) solubility limit, b) dissolution rate (mass transfer coefficient) and 2) density using Archimedes’ Principle. The study concluded that solubility and dissolution rate increases with temperature and the addition of LiF to cryolite decreases the solubility limit but increases the rate at which silica dissolves into the melt. With addition of silica, the apparent density of electrolyte first increases up to 2-3wt% and the drops.

The need for industrial gas turbines to operate at higher temperatures and/or speeds has resulted in the continual modification of nickel-based superalloys to provide better high-temperature strength and corrosion resistance for components such as hot-section turbine blades. Thermal-Mechanical Fatigue (TMF) cracking, accelerated by the oxidation that forms as a result of the exposure of bare metal during the crack-opening stages, is one of the most common forms of damage experienced by service-run turbine blades. Due to the high costs associated with manufacturing nickel-based superalloy components, damaged turbine blades must be repaired to restore their original mechanical properties. One such method, Activated Diffusion Brazing (ADB), is under development for this purpose, and involves melting a two-part powder mixture into a damaged region. However, the tenacious oxides formed on nickel-based superalloy components provide an obstacle for the repair process, and must be removed. Fluoride-Ion Cleaning (FIC) uses flowing hydrogen and HF gas to remove tenacious oxide scales through a set of chemical reactions, leaving cleaned components free of oxide compounds and depleted of the strong oxide-formers of Al and Ti. GTD111 is a nickel-based superalloy containing the strong oxidizing elements of Al, Ti, and Cr, and is similar in composition to other nickel-based superalloys such as DD8 and Rene95. Literature concerning the oxidation, cleaning, and brazing of this particular alloy is limited, and as such this thesis serves as a comprehensive overview of the chemical effects of each above process on GTD111. The objectives of this project are to determine, through SEM-EDX and element mapping analysis, the oxidation behavior of nickel-based superalloy GTD111, the effects of oxidation and FIC on the chemistry near the surface of this particular alloy, and the effects of mixing ratio and paste viscosity on the quality of repairs made by ADB. Notches of 8 mm depth and 0.25 mm width were made in coupons of GTD111 via wire-EDM and samples were oxidized between 1 and 452 hours at 900°C. Samples oxidized between 96 and 452 hours were sectioned in half and one half of each sample was cleaned via the standard FIC process at Ti-Coating Inc. Notches of 8 mm depth and 1 mm width, also made via wire-EDM, were repaired by the ADB process with a bonding temperature of 1220°C and a holding time of 65 minutes. Time-dependent multi-layer oxide growth was observed on all samples, consisting of an innermost discontinuous aluminum oxide region, followed by a thin continuous band of Ni-W-Ta oxide and a thicker, very dense chromium oxide layer. Some oxidation times exhibited the presence of weak, inconsistent oxide regions rich in Ni and/or Ti. Since the GTD111 alloy does not contain sufficient amount of Al to form a continuous layer – as 5-7% Al is required – oxidation resistance was provided mainly by the formation of the dense chromium oxide layer. A region heavily depleted of Al and Ti and therefore the strengthening gamma prime phase was observed below and surrounding the Al-rich oxide regions. Chemical analysis of cleaned samples showed that the standard FIC process at Ti-Coating Inc. was able to remove all oxide compounds formed during oxidation at 900°C, and that the prior oxidation time had no effect on the chemistry within the surface of the cleaned samples; however, the depths of elemental and gamma prime phase depletion were affected. The elemental depletions of Al and Ti have been observed in past studies, but depletions of Ni and concentrations of Cr near the surfaces of cleaned components have not been previously observed. Preliminary brazing trials made with varying paste viscosities demonstrated the importance of paste pre-placement and maintaining the molten filler metal within the notch, as better pre-placement resulted in higher densities in the braze-repaired region of the brazing trial samples. Although porosity was observed on all samples, the paste pre-placement was found to be more important in reducing porosity than the mixing ratio and paste viscosity, although using an appropriate paste viscosity allowed for better pre-placement.

In our earlier work, silica-based diatom frustules were successfully converted to 3-dimesional F-doped titania-based replicas via shape-preserving gas/solid displacement reactions, and experiments showed that the hydrolysis of organophosphorous ester pesticides, methyl paraoxon (MOX) and methyl parathion (MTH) was significantly faster in the presence of these 3-D titania nanostructures than in the presence of other commercial titania nanoparticles. The enhancement effect of titania frustules appeared to be strongly related to the amount of F-doping on these materials. In this work, a wider range of titania frustule replicas with various F-doping were prepared and characterized, and compared in the hydrolysis of MOX and MTH as well as three carboxylic acids (methyl salicylate, methyl benzoate and methyl 4-(aminomethyl)benzoate). A strong relationship between the amount of F-doping and the enhancement effect on the hydrolysis of organophosphorous esters was still observed. However, such enhancement effect did not occur in the hydrolysis of the carboxylic acids. It was discovered that fluorine-leaching from the titania frustules was significant and yielded high concentration of fluoride ions in the reaction solutions. Dissolved fluoride ions alone could significantly catalyze the hydrolysis of organophosphorous esters but not that of carboxylic acids in the oxide-free systems. It is believed that fluoride ions act as nucleophilic catalysts to accelerate the hydrolysis of organophosphorous esters. Comparison in the hydrolysis product formation from the two potential hydrolysis pathways (i.e., the P-O bond and the C-O bond cleavages) in the studied systems also supports the direct involvement of dissolved fluoride ions in the observed catalytic effect.

This study used electrospinning to fabricate a polyvinylidene fluoride (PVDF) piezoelectric nanofiber harvesting device with interdigitated electrode to capture ambient energy. According to d33 mechanical-electric energy conversion mode, the energy harvesting device can be applied on the low frequency ambient vibration and impact abilities for the transformation mechanical energy into electrical energy effectively. First, the PVDF powder was mixed in acetone solution uniformly and the dimethyl sulfoxide (DMSO) was mixed with multi-walled carbon nanotube (MWCNT) to prepare PVDF macromolecular solution. The mixed solution was filled in a metals needle injector and contacted hundreds of voltage. After the PVDF drop in the needle was subjected to high electric field, the drop overcame surface tension of the solution itself, then extremely fine PVDF fiber was formed and spun out. The electrospun was collected orderly using X-Y digital control stage and the linear diameter of electrospun can be controlled easily by adjusting the travelling speed of the stage. In the spinning process, as affected by stretching strain and electric field at the same time, the PVDF piezoelectric fiber resulted in electric polarization and transformed £] piezoelectric crystal phase, in which the dipoles are oriented in the same direction. Furthermore, MWCNT was added to improve the mechanical properties of fiber and increase £] phase, to enhance the tensile strength and piezoelectric property of PVDF fiber effectively. Finally, the photolithography was used to fabricate interdigitated electrodes with 100£gm gap on the flexible PI substrate. The PVDF fibers, with a length and diameter of approximately 1cm and 700-1000nm, were aligned on interdigitated electrodes and packaged with the PI film. In order to increase the conversion efficiency of piezoelectric fiber in d33 mode, the PVDF fibers were repolarized in a high electric field. The results showed that the PVDF fiber energy harvesting device can generate 15mV open-circuit voltage under low frequency vibration of 4Hz and generate above 30mV open-circuit voltage under 6Hz vibrations. As compared with the piezoelectric fiber not repolarized by interdigitated electrode, its output voltage was increased by1- 2 times.

In this study, a cylindrical near-field electrospining (CNFES) process will be used to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF) piezoelectric fibers, and a piezoelectric fiber harvesting device with parallel electrode was fabricated to capture ambient energy. First, the PVDF powder was mixed in acetone solution uniformly and the dimethyl sulfoxide (DMSO) was mixed with fluorosurfactant to prepare PVDF macromolecular solution. The PVDF macromolecular solution was filled in a metals needle injector and contacted a high power supply, after the PVDF drops in the needle was subjected to high electric field, the drops became a Taylor cone and overcame surface tension of the solution itself, extremely fine PVDF fiber was formed and jetted out. The fibers were collected numerous and quickly by homemade cylindrical collector and the diameter of fiber could be controlled easily by adjusting the rotating speed of the cylinder and the electric field. From the observation of XRD (X-ray diffraction), it reveals a high diffraction peak at 2£c=20.7¢X of piezoelectric crystal £]-phase structure by adjusting PVDF concentrations and DC voltage. By providing 7Hz shake and 0.23% strain, the piezoelectric fiber harvesting device with parallel electrode could generate 76mV; by providing 7Hz shake and 0.14% strain, the device could generate 1.1nA.

In this study, it was aimed to investigate the structural, mechanical and biological properties of nano hydroxyapatite (HA) doped with yttrium and fluoride with different compositions. HAs were synthesized by precipitation method. After sintering at 900oC, 1100oC or 1300oC for 1 hour, the structural properties of HAs were investigated by XRD, FTIR spectroscopy and SEM. High relative densities (above 88 % of relative density) were achieved after sintering. No second phases were observed in XRD measurements. Hexagonal lattice parameters and unit cell volumes of doped HAs decreased indicating the substitutions of ions. Characteristics absorbtion bands of HA and additional bands due to fluoride substitutions were observed in FTIR patterns. SEM images showed that grain sizes decreased with increasing doping amounts and decreasing sintering temperatures. Discs prepared by cold pressing were sintered at 900oC, 1100oC and 1300oC for 1 hour to determine mechanical properties. Mechanical properties of HAs were found to be directly related to the sintering temperatures and amount of dopings. Biocompatibility of pure and doped HA discs was assessed with in vitro cytotoxicity studies. Cell attachment, proliferation and differentiation state of cells were studied using MTT, ALP and calcium assays and SEM. Cell attachment and proliferation were enhanced with dopings and increasing sintering temperatures. The highest ALP production and calcium deposition were observed on HAs sintered at 1100oC. In vitro studies revealed that 1100oC was the sintering temperature for best cell responses. Specifically, 2.5YFHA seemed to be promising as an alternative for pure HA among all doped HAs.

The aim of this study was to investigate the microstructure and mechanical properties of pure and Mg2+ and F- doped nano-calcium phosphate (CaP) powders, which were synthesized by precipitation method. After the drying and calcination processes, the samples were sintered at 1100&ordm / C for 1 hour. High densities were achieved except for the 7.5 % mole Mg doped samples. Microstructure of the CaPs were investigated by X- ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Due to the Mg substitution, &amp / #946 / -TCP phase was detected besides HAp, resulting in the formation of HAp/ &amp / #946 / -TCP biphasic composites with different compositions. The substitutions of the ions have been verified by the decrease in the hexagonal unit cell volumes of the doped CaPs. FTIR spectra revealed the characteristic absorption bands of HAp, &amp / #946 / -TCP and the ones that were resulted from the F-OH bonds and substitution of the Mg2+ ions. The SEM results revealed the grain sizes in the range of ~197 nm-740 nm. In general, the micro hardness and diametral tensile strength tests revealed that Mg2+ ions in large amounts (7.5 % mole) had negative effects on the mechanical properties of the samples, while substitution of the F- ions had a positive effect on their mechanical properties.

This study aimed synthesizing hydroxylapatite (HA) and Zn2+, F- and Cl- doped HA by solution precipitation method. The synthesized compounds were sintered at 1100&deg / C for 1h. For structural characterization, density of the samples were measured by Archimedes&rsquo / method. It was observed that Zn2+ addition increased the density significantly whereas F- caused a decrease and Cl- increased the density with a little amount. XRD was applied to the samples and it was found that co-doping of Zn2+ and F- ions decreased the unit cell volume of HA with F- addition. Other compositions gave fluctuated results in terms of unit cell volumes. HA phase and a little amount of CaO phase were detected in some samples. FTIR spectroscopy was used to detect whether Zn2+, F- and Cl- ions were incorporated to the HA structure or not by observing the bands corresponding to the bonds in the molecules. The amount of addition was also detected by FTIR. Results showed that ion incorporation to the HA structure was done successfully. SEM images were v analyzed and grain sizes of samples were calculated by Rietvelt analysis. Grain sizes of the samples increased by Cl- addition and decreased by Zn2+ and/or F- addition. For mechanical characterization, Vickers microhardness test was applied. Fracture toughness was calculated from Vickers microhardness results. According to the results, the highest microhardness values were found for F- and Zn2+ co-doped samples. It was also shown that fracture toughness decreased by Zn2+ addition. However, Zn2+ and F- co-doped samples gave higher fracture toughness results when compared with pure HA. Cl- addition also decreased the fracture toughness. The best compositions in terms of structural and mechanical properties was chosen as Zn2+ and F- co-doped samples and biological characterization was applied to these samples. Saos-2 cell line was used in biological examinations. For biological characterizations, Alamar Blue&trade / assay to detect viability and alkaline phosphatase activity (ALP) assay to detect differentiation were done. It was observed that 2 mol.% Zn2+ addition increased the cell viability and alkaline phosphatase activity. 1 mol.% F- addition also improved cell viability and alkaline phosphatase activiy. SEM images were analyzed to observe the morphology of the cells on HA and selected doped HA discs. In accordance with Alamar Blue&trade / assay and alkaline phosphatase activity assay, cells showed dendritic shapes on 2 Zn and 2 Zn 1 F sample which was the indicator of good material-cell interaction. Dissolution test was also applied by immersing the samples in simulated body fluid (SBF). pH change and SEM images for Ca2+ deposition were investigated. Increase in pH change with time was observed. F- included samples gave the lowest pH change results, especially 2 Zn 1 F. Dissolution pits and some apatitic formations were observed in SEM images.