Orientadores: Luiz Carlos Barbosa, Cristiano Monteiro de Barros Cordeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T15:49:21Z (GMT). No. of bitstreams: 1 FerenczJunior_JulioAlbertoPeres_M.pdf: 3491630 bytes, checksum: 5d5b5385cd23f50e9a3c39e9e55705e2 (MD5) Previous issue date: 2013 / Resumo: Devido à crescente necessidade de troca de informações, cada vez mais é necessário o desenvolvimento e criação de meios para torna-la mais rápida e eficaz, e é necessário que esta tecnologia seja comercial. Uma alternativa seria utilizar fibras ópticas como um meio para a informação quântica. Para tal, vidros teluritos e nanocristais de diamante apresentam propriedades desejáveis. Neste trabalho foi sintetizado e caracterizado um sistema de vidros teluritos frente algumas propriedades térmicas, ópticas e estruturais, em relação à dopagem por CsCl. Após esta caracterização, foi adicionado nanocristais de diamante na composição vítrea mais adequada e verificado que o método utilizado foi eficaz. Observou-se uma maior estabilidade térmica do sistema, menor densidade, maior janela de transparência óptica e menor índice de refração linear com o incremento da concentração de CsCl na matriz vítrea. Além disso, verificamos por microscopia eletrônica de transmissão que os nanocristais de diamante estão presentes na estrutura do material, quando utilizamos nosso método / Abstract: Due to the growing needed for exchange information it is necessary to develop and create ways being a technology faster, more effective and commercial. An alternative option is the use of fiber optics as a media for quantum information. In order to do it, tellurite glasses and diamond nanocrystals exhibit desirable properties. In this work, we synthesized and characterized a system of tellurite glasses forward some thermal, optical and structural properties towards doping CsCl. After this characterization, we added diamond nanocrystals in glass composition more suitable and we verified if the method was effective. We showed a higher thermal stability, lower density, higher optical transparency window and lower linear refractive index with increasing concentration of CsCl in the vitreous system. Furthermore, by transmission electron microscopy was checked that diamond nanocrystals are present inside the structure of the material, when we use this method / Mestrado / Física / Mestre em Física

Hazelnuts are mostly non-dormant at harvest but develop seed dormancy after a few days of storage. The seeds have been classified as recalcitrant since they cannot be stored for more than one year under ambient conditions. Cryopreservation has not been satisfactory so an alternative protocol is required. To test for recalcitrance, chilled non-dormant seeds (control) were compared with gibberellic acid (GA3) treated seeds during 6 weeks storage at 5°C or at ambient temperature. Control seed moisture content (MC) was 14-15% compared with 20% for GA3 treated seeds. No change in viability was noted until the end of 6 weeks at ambient temperature, when infection proliferated. Reduced germinability, associated with increased leachate conductivity, was noted on all treatments and controls, with ambient temperature storage most harmful for seed viability. This supports classification of hazel seeds as recalcitrant. However, orthodox behaviour could be induced by reducing seed moisture to <6%, showing survival for more than 3 years at -20°C with acceptable germinability and producing healthy seedlings. Pathogen tests show that 6 weeks chilling to break seed dormancy may activate the seeds’ internal protective mechanisms, thereby reducing infection and enabling germination and healthy seedling establishment. The link between seed viability and protection from free radicals and pathogens was examined. Antioxidant activity in hazelnut seed associates (such as endocarp, funiculus and testa) was found to be much higher than in the seed embryo, perhaps indicating that hazel seeds have natural protective mechanisms within the pericarp. Antioxidant activity of seed associates increased during chilling, indicating their role in protecting the seed. Nevertheless, TTC test revealed that seeds acclimatised to ii < 6% MC and stored at 5°C for 45 weeks showed viability loss due to damage of the embryonic axes, probably caused by free radicals. Initial tests to stabilise seed moisture content showed that reduction in seed moisture did not impose dormancy and seed moisture content (MC) stabilisation resulted in > 80% germination but many abnormal seedlings. Dormancy reversibility was tested by treatments T1 (one period at 15°C) and T2 (two periods at 15°C), designed following a consideration of the natural environment. Both resulted in reduced germination, delayed seedling emergence, increased abnormal seedlings, reduced seedling height and decreased internode numbers. To test the role of temperature in reduced seed performance, non-dormant hazelnuts were held at either 5°C or at ambient temperature for up to 6 weeks. Seeds from both sets exhibited high viability, but germinability was significantly decreased in the ambient temperature set, associated with increases in leachate conductivity and infection. Work in this thesis has confirmed that dormancy was broken by chilling, with gradually increasing germination as chilling time was increased. Germination increased with increase in chilling and reduction in infection. No infection was recoreded after 6 weeks chilling. It is most likely that protective agents are produced causing suppression of infection. In these experiments it was observed that not all germinated seeds produced healthy seedlings, suggesting that germination tests without observation of seedlings may give an incomplete assessment of germination success. Assessment using the Tetrazolium test (TTC) was found to be much more dependable and it was also possible to detect damage to specific tissues that might result in unhealthy seedlings.

In this study, the corrosion resistance of three different stainless steels (304, 316 and 309) towards eutectic chloride salts is investigated. The performances of two materials to reduce the corrosion of the steels are examined: zirconium as sacrificial anode and an Al2O3 coating deposited by flame spraying. Samples are submitted to a 24 hours corrosion test at 700°C in air. The samples are characterised by weight analysis, SEM observations and EDX analysis of their surface and cross-section. The corrosion resistance of the stainless steels is not improved by adding Zr rods in direct contact with the steel, rather decreased in the areas where the rod laid. However, in these conditions, stainless steel 316 has the best resistance to highly corrosive chloride salts. The Al2O3 coating is too porous and penetrated by the salt, the steel underneath is corroded. Nevertheless, some alumina remains intact after the corrosion test, because of the high inertness of the ceramic. The presence of O2 most certainly accelerated the corrosion mechanism studied here.

Master of Science / Food Science Institute / Sara E. Gragg / Leafy greens have been recognized as vehicles for transmission of foodborne pathogens and an effective pre-harvest intervention to control them is currently lacking. After harvest, lettuce is often subjected to chlorinated water to reduce the microbial load in the water and on the lettuce tissue. While moderately effective, there is also a need for improved postharvest interventions. The purpose of Objective I was to 1) determine potassium bisulfate efficacy at reducing populations of Escherichia coli (E. coli) and Listeria innocua (L. innocua) when applied pre-harvest to lettuce, and 2) assess the impact on product quality at harvest. Potassium bisulfate reduced E. coli populations on inoculated lettuce by 1.32 log₁₀ CFU/g (P=0.0002) and L. innocua by 1.18 log₁₀ CFU/g (P=0.0017). No detectable differences were observed in color (P>0.05); however, brown spots were observed on various leaves sprayed with potassium bisulfate. The purpose of Objective II was to employ a blend of benzalkonium chloride, acetic acid, and methyl paraben (BAM) as a postharvest wash on romaine and iceberg lettuce and to 1) determine efficacy at reducing populations of Listeria monocytogenes (L. monocytogenes), E. coli O157:H7 and Salmonella, 2) measure changes in aerobic bacteria throughout the shelf life, and 3) quantify benzalkonium chloride and methyl paraben residues post-washing. To quantify efficacy of BAM reducing pathogenic bacterial populations, fresh-cut romaine and iceberg lettuce were inoculated with L. monocytogenes, E. coli O157:H7, or Salmonella and washed in BAM at concentrations of 0%, 1%, 2% or 3% for one or five minutes. When plated on recovery media, contact time and wash concentration was not significant (P>0.05) for Salmonella on either product. Concentration was significant (P=0.0189) for L. monocytogenes on romaine; however, the greatest reduction observed was <1.0 log₁₀ CFU/g. The 3% wash significantly reduced E. coli O157:H7 on romaine by 1.75 log₁₀ CFU/g, which is 0.66 log₁₀ CFU/g better than the 0% wash. Following washing, wash water was analyzed and data demonstrate that all wash concentrations significantly (P≤0.05) reduced each foodborne pathogen by >2.0 log₁₀ CFU/g in the wash water. To quantify benzalkonium chloride and methyl paraben residues, as well as changes in aerobic bacteria and product quality, fresh-cut romaine and iceberg lettuce were subjected to a 1 minute wash in BAM at concentrations of 0%, 1%, 2%, or 3% and immediately sampled to determine aerobic populations and product quality. Concentrations 0% and 2% were also packaged into retail storage bags and sampled on days 0, 3, 5, and 7. Residues were quantified on these days as well. On day 0, aerobic populations did not vary according to wash concentration (P>0.05). With regards to shelf-life data, the 2% wash significantly reduced (P=0.0203) aerobic bacteria on romaine lettuce; however, no significant difference was observed on iceberg lettuce (P=0.0819). With regards to overall visual appearance of romaine or iceberg lettuce, no significant difference was detected between 0% and 2% BAM washes for each day throughout the shelf-life study (P>0.05). Methyl paraben and benzalkonium chloride residues were <5.0 and <10.0 ppm, respectively, on both products on each sampling day.

It is known that, in addition to corrosion processes, the electrochemical noise (EN) can be generated by some other disturbances such as mass transfer and flow turbulence. In this study the influence of both laminar and turbulent flow on the characteristics of electrochemical noise (EN) has been studied using a carbon steel rotating cylinder electrode (RCE) in aerated neutral (pH=7) 0.1 M NaCl and 0.1 M NaCl+0.1 M NaNO2 solutions. The RCE has a set of four graphite brushes for electrical connection. The supplied cathodic current was applied through the top two graphite brushes and measured the specimen potential through the bottom two to eliminate any expected cyclic variations in the measured potential.Prior to the measurement of EN, calibration of the mass transport properties of the electrode was performed by measuring the limiting current density for oxygen reduction as a function of rotation speed in order to estimate the transition from laminar to turbulent flow regime. EN experiments have been performed in free corrosion conditions (uninhibited and inhibited solutions), and with applied cathodic polarisation in the regions of hydrogen evolution and oxygen reduction processes. In the case of oxygen reduction and hydrogen evolution cathodic reactions it has been found that laminar flow had a negligible effect on the noise produced but a significant increase in the amplitude of the noise was observed in turbulent flow. On the other hand in free corrosion conditions in uninhibited solution the influence of flow was relatively insignificant and that was attributed to the low impedance of the corroding electrode. It is claimed that flow has a negligible effect in inhibited solutions due to the passivity of the system, which is responsible for the low rate of both anodic and cathodic reactions. Finally spectral analysis showed that the noise produced by turbulent flow had power at significantly higher frequencies than is normal for corrosion-related noise.

Hyperkalemic periodic paralysis (HEPP) is an inherited, autosomal disorder characterized by myotonia and periodic paralysis in skeletal muscle. The hallmark of the disease is a severe sensitivity to the K+-induced force depression, the cause of the paralysis. Previous studies have provided evidence that the sensitivity to the K+-induced force depression can be alleviated when the Cl- conductance (GCl) is lowered. However, those studies were carried out at non-physiological temperatures (25°-30°C) and few stimulation frequencies. The overarching goal of this study was to examine whether manipulating GCl pharmacologically was a viable target for treating HEPP. This work sought to document the interactive effect of K+ and Cl- on force development in mouse skeletal muscle at 37°C, over a wide range of stimulation frequencies. Secondly, experiments were undertaken to determine if a reduction in GCl could protect against the severe K+ sensitivity in HEPP. The results show that in wildtype muscle, a reduction in GCl improved force generation at high [K+]e at stimulation frequencies that naturally occur in vivo for mouse EDL and soleus. While the effect in wildtype muscles was proof of principle that a reduction in GCl may be a potential approach to treat HEPP patients, the effects of reduced GCl at high [K+]e was quite variable in HEPP muscles. In a few cases, lowering GCl did improve force generation at high [K+]e. However, in most cases the decrease in GCl exacerbated the force depression at high [K+]e, suggesting that more studies will be necessary to understand the variability in the Cl- effect to conclude whether a decrease in GCl is a viable approach to treat HEPP patients.

Calcium-activated chloride channels (CaCCs) are ubiquitously expressed in a plethora of cell types and, consequently, are involved in numerous cellular processes as diverse as epithelial secretion, regulation of cardiac excitability and smooth muscle contraction. Current pharmacology of CaCCs is limited to compounds with low potency and poor selectivity. The lack of knowledge surrounding the molecular identity of the CaCC has greatly hindered the development of more specific drugs and has impaired our understanding of the channel physiology and biophysics. The recent discovery that the TMEM16A gene codes for CaCCs has offered hope for new developments in these areas. CaCCs have been suggested as possible targets to treat a variety of conditions including asthma as well as pulmonary and systemic hypertension. Due to the ubiquitous expression of CaCCs and the ability of the channel to interact with a number of pharmacological compounds with diverse chemical structures however, it was hypothesised that TMEM16A could be a possible source for off-target drug effects and may represent a concern for safety pharmacology. The principal aim of this thesis was to assess the functional significance of TMEM16A in the cardiovascular system, as this is one of the major systems of concern for safety pharmacology and accounts for the largest number of post-market drug withdrawals. The main findings of this study can be summarised as follows: 1) RT-PCR analysis revealed a ubiquitous expression of TMEM16A in tissues of the rat and human cardiovascular systems, including systemic and pulmonary arteries as well as cardiac tissue. Analysis also revealed the presence of multiple TMEM16A splice variants in all rat tissues examined, in addition to a number of other TMEM16x family members. 2) Myography experiments using the “classical” CaCC blocker niflumic acid and newly identified TMEM16A blockers confirmed a functional role for TMEM16A in phenylephrine-induced vascular smooth muscle contraction. 3) The suitability of currently available Cl- channel blockers for use as pharmacological tools for TMEM16A research was assessed using conventional whole-cell patch clamp and high-throughput electrophysiology techniques to respectively compare their potencies and selectivity over other cardiovascular ion channels. Of the compounds tested, DIDS and T16Ainh-A01 appeared the most suitable blockers; however all compounds had a degree of non-selectivity, raising concerns for their use in functional studies. In conclusion, these findings provide evidence for the ubiquitous expression and functional significance of TMEM16A within the cardiovascular system and support the hypothesis that TMEM16A is a concern for safety pharmacology and should be included into future pre-clinical safety assays. The inadequacy of current inhibitors however highlights the urgency for the development of novel potent and selective channel modulators for future TMEM16A research.

It has been the purpose of this PhD program to determine whether current laboratory-based methods of investigating Atmospherically-Induced Stress Corrosion Cracking (AISCC) of austenitic Stainless Steels (SS) are adequate in modelling realistic corrosion processes within a marine aerosol environment. Results obtained throughout the study have sought to address three key aims. Mainly, to understand the nature and behaviour of primary marine aerosol containing organic matter present within oceanic surface waters, the interfacial interactions of such aerosol droplets deposited on to austenitic stainless steels and, ultimately, their impact upon AISCC processes. Based upon the work conducted during this research, several conclusions may be deduced. The presence of primary organic components within a sea-salt aerosol leads to a reduction in surface tension at the liquid-vapour interface; highlighting the surface-active nature of algal exudates. Surface-active constituents also have the potential to aggregate at the liquid-solid interface. The inclusion of exudates, therefore, has the potential to maintain an electrolytic environment on an austenitic steel substrate for an elongated time period under ambient conditions. Following subsequent evaporation, organically-enriched seawater droplets typically produce an organic surface film. The results of these interfacial studies have informed AISCC measurements using U-bend specimens, which demonstrate a correlation between cracking and droplet size. Furthermore, the limiting factor for AISCC may not be a function of deposition density as previously thought but rather of droplet surface area.

M.Sc. (Chemistry) / The fabrication of multiwalled carbon nanotube/polyvinyl chloride (PVC) composites and a study of their thermal, fire retardancy and mechanical properties are reported. Triphenylphosphine linked - multiwalled carbon nanotube (TPP-MWCNT) and pristine MWCNT were used. The MWCNT were embedded in the polymer matrix through melt blending and solvent casting. The phosphorylation of the MWCNT and their dispersion in the PVC matrix was characterized by scanning electron microscopy and Raman spectroscopy. Thermal analysis of the nanocomposites by thermal gravimetric analysis (TGA) in both solvent casting and melt bending processes, showed different results when compared with the neat PVC. The modulus of the MWCNTs / PVC nanocomposites synthesized via melt blending increased, whilst there was a reduction in their tensile strength, indicating a decrease in polymer toughness. The tensile modulus and strength of MWCNTs / PVC nanocomposite synthesized via Solvent casting decreased whilst there was an increase in Tpp-MWCNT/PVC nanocomposite when compared with its counterpart MWCNTs / PVC nanocomposite, indicating an increase in stiffness and strength. The limited oxygen index (LOI) fire retardant tests of all the neat PVC and its nanocomposites showed no value difference.

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Industrial Engineering))--University of Pretoria, 2006. / Industrial and Systems Engineering / unrestricted