4,933 research outputs found

    Effect of Environmental Exposures on the Aramid Fibre Kevlar

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    The effects of exposure of Kevlar 49 fibres to thermal, ultrasonic and chemical environments have been analysed. Both the tensile strength and the tensile modulus deteriorate with thermal exposures . However, the former is more sensitive than the latter. The prominent crystal structural changes induced by thermal exposures are reduction in crystallinity, molecular misalignment about the fibre axis, increase in the inter layer distance, changes in crystallite size and/or microstrain. Thermally induced macro changes include introduction of surface holes, partial hollowness near the core, localised thinning, material loss in the vicinity of surface impurities etc . The structural changes could be satisfactorily correlated with the corresponding changes in tensile properties . All the thermally induced effects are controlled by two parameters, viz ., the temperature (T) and the duration of the cumulative exposure to T, te,,,,,(T). The T-tcam(T) effect leads to the observation of isothermal decomposition of Kevlar over a range of temperatures which include T's, far below the reported decomposition temperature of 500/550 °C. A hitherto unknown direct correlation between X-ray diffraction peak positions and the tensile strength has also been identified . Exposure to ultrasonic waves introduces axial compression, evinced by the formation of kink bands, fibrillation and macro buckling . The unit cell of axially compressed fibres manifests an anisotropic deformation. The process of moisture uptake by Kevlar 49 fibres is controlled by the relative humidity (RH) of ambient atmosphere . The saturation moisture content is, however, determined by structural characteristics such as the degree of crystallinity, molecular alignment etc . The uptake of common organic solvents by Kevlar is dependent on the molar volume of the former

    On the mechanism of Dehydroquinate synthase : a thesis presented to Massey University in partial fulfilment of the requirements for the degree of Master of Science in Chemistry

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    The aim of this thesis is to investigate the influence of fluorine substitution on the second reaction of the shikimate pathway catalysed by the enzyme 3-dehydroquinate synthase. The shikimate pathway is an essential pathway that is required for the synthesis of aromatic compounds in bacteria, microbial eukaryotes and plants. The enzyme, 3-dehydroquinate synthase, catalyses the second step of the shikimate pathway, the conversion of 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) into 3-dehydroquinate (DHQ). Item_03771-1.jpg It has been reported that when (3S)-3-fluoro DAHP (where fluorine occupies the C3 axial position) is treated with the enzyme 3-dehydroquinate synthase, two products, the expected (6S)-6-fluorodehydroquinate (5) and its C1 epimer, (6S)-6-fluoro-1-epideydroquinate (6) are formed in a ratio of 2 : 1. Item_03771-2.jpg The C1 epimer of 3-dehydroquinate was reported to be formed from the natural substrate DAHP in a solution reaction, but not in the enzyme catalysed reaction. Therefore, it has been suggested that fluorine substitution at the axial position on C3 stabilises the fluoroenolpyranose intermediate allowing the intermediate to dissociate from the enzyme and cyclise to complete the formation of (6S)-6-fluoro-1-epideydroquinate free in solution. The results reported in this thesis are from an investigation carried out to understand further the influence of fluorine orientation on the stereochemical outcome of the products in the dehydroquinate synthase reaction. (3S)-3-Fluoro DAHP was synthesised in large amounts using both chemical and enzymatic synthesis. This was achieved by treating the isomers of 3-fluoro phosphoenolpyruvate and D-erythrose 4-phosphate with DAHP synthase, the first enzyme of the shikimate pathway. The erythrose 4-phosphate was prepared by lead tetraacetate oxidation of D-glucose 6-phosphate. The isomers of 3-fluoro phosphoenolpyruvate were prepared from 3-bromo, 3-fluoropyruvic acid by the Perkow reaction. Then (3S)-3-3-fluoro DAHP was purified by anion exchange chromatography. The chemical synthesis of erythrose 4-phosphate and the isomers of 3-fluoro phosphoenolpyruvate and the enzymatic synthesis of (3S)-3- fluoro DAHP and its purification are discussed in Chapter Two. A recombinant Escherichia coli strain (pJB 14) was used to over-express the enzyme dehydroquinate synthase, and partial purification of the enzyme was achieved by anion exchange chromatography. Chapter Three describes the production and purification of the enzyme 3-dehydroquinate synthase. Purified (3S)-3-fluoru DAHP was treated with the E. coli enzyme 3-dehydroquinate synthase. Formation of both (6S)-6-fluorodehydroquinate and its C1 epimer was observed. The reaction was followed at different pH and temperature values. The ratio of products produced in the enzyme-catalysed reaction was monitored by 19 F NMR spectroscopy. No significant change in the ratios was observed with the different conditions employed. The results from these experiments are discussed in Chapter Four. Our results are consistent with the hypothesis that the fluoroenolpyranose intermediate is released to the solution, where it cyclises without the constraint of an enzymatic template. To test this hypothesis unequivocally, further investigations are required and these are discussed in Future Directions. [NB: Mathematical/chemical formulae or equations have been omitted from the abstract due to website limitations. Please read the full text PDF file for a complete abstract.

    Women in Aerospace in India: Aerowoman

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    The main objective of the seminar was to bring together the Indian women in the field of aerospace and identify their scientific and technical contributions. In this context, the seminar was perhaps the first of its kind held in India. It was also aptly conducted in the x2018;Womenx2019;s Empowerment Year x2013; 2001x2019; declared by the Govt. of India.13

    The role of Follistatin-like 3 (Fstl3) in cardiac hypertrophy and remodelling

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    Follistatins are extracellular inhibitors of TGF-β family ligands like activin A, myostatin and bone morphogenetic proteins. Follistatin-like 3 (Fstl3) is a potent inhibitor of activin signalling and antagonises the cardioprotective role of activin A in the heart. The expression of Fstl3 is elevated in patients with heart failure and upregulated by hypertrophic stimuli in cardiomyocytes. However its role in cardiac remodelling is largely unknown. The aim of this thesis was to analyse the function of Fstl3 in the myocardium in response to hypertrophic stimuli using both in vivo and in vitro approaches. To explore the role of Fstl3 in cardiac hypertrophy, cardiac-specific Fstl3 knock-out mice (Fstl3 KO) were subjected to pressure overload induced by trans-aortic constriction. They showed attenuated cardiac hypertrophy and improved cardiac function compared to wild type littermate control mice. Knock-out of Fstl3 specifically from cardiomyocytes was sufficient to reduce the total expression of Fstl3 in the heart following pressure overload, implying that cardiomyocytes are the major source of Fstl3 in the heart after TAC. Fstl3 KO mice also showed reduced expression of typical hypertrophic markers including ANP, BNP, α-skeletal actin and β-MHC. Similarly, treatment of neonatal rat cardiomyocytes with Fstl3 resulted in hypertrophy as measured by increased cell size and protein synthesis. This was also accompanied by activation of p38 and JNK signalling pathways. Microarray analysis of ventricular samples from these mice indicated reduced expression of genes involved in protein binding and extracellular matrix. Verification by quantitative real-time RT-PCR revealed reduced expression of collagens and TGF- β1 in the myocardium, indicating reduced fibrosis. This was supported by histological analysis showing reduced interstitial fibrosis. As an in vitro model of pressure overload, cardiomyocytes were subjected to mechanical stretch, which elevated the expression of Fstl3. In order to explore the role of cardiomyocyte-derived Fstl3 in modulating fibroblast function, cardiac fibroblasts were treated with the conditioned medium from stretched cardiomyocytes and collagen synthesis was measured. Fstl3 was found to be necessary for conditioned medium to induce an increase in collagen synthesis in fibroblasts. Fstl3 was also shown to induce low levels of cell death in cardiac fibroblasts. In order to identify stretched cardiomyocyte derived factors necessary for Fstl3 action on fibroblast collagen synthesis, a yeast two hybrid analysis was undertaken. Results indicated that Fstl3 may act, at least in part, through binding to proteins of the extracellular matrix as well as pro-fibrotic factors, including connective tissue growth factor (CTGF). While CTGF did not affect fibroblast collagen synthesis in the presence of Fstl3, it inhibited Fstl3 induced cell death, indicating a protective role. In summary, data presented in this thesis demonstrates that Fstl3 is upregulated after cardiac injury and functions by activating the pro-hypertrophic and pro-fibrotic responses in the myocardium, making it an attractive therapeutic target for intervention of cardiac pathologies

    A Robot Operating System (ROS) based humanoid robot control

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    This thesis presents adapting techniques required to enhance the capability of a commercially available robot, namely, Robotis Bioloid Premium Humanoid Robot (BPHR). BeagleBone Black (BBB), the decision-making and implementing (intelligence providing) component, with multifunctional capabilities is used in this research. Robot operating System (ROS) and its libraries, as well as Python Script and its libraries have been developed and incorporated into the BBB. This fortified BBB intelligence providing component is then transplanted into the structure of the Robotis Bioloid humanoid robot, after removing the latter’s original decision-making and implementing component (controller). Thus, this study revitalizes the Bioloid humanoid robot by converting it into a humanoid robot with multiple features that can be inherited using ROS. This is a first of its kind approach wherein ROS is used as the development framework in conjunction with the main BBB controller and the software impregnated with Python libraries is used to integrate robotic functions. A full ROS computation is developed and a high level Application Programming Interface (API) usable by software utilizing ROS services is also developed. In this revised two-legged-humanoid robot, USB2Dynamixel connector is used to operate the Dynamixel AX-12A actuators through the Wi-Fi interface of the fortified BBB. An accelerometer sensor supports balancing of the robot, and updates data to the BBB periodically. An Infrared (IR) sensor is used to detect obstacles. This dynamic model is used to actuate the motors mounted on the robot leg thereby resulting in a swing-stance period of the legs for a stable forward movement of the robot. The maximum walking speed of the robot is 0.5 feet/second, beyond this limit the robot becomes unstable. The angle at which the robot leans is governed by the feedback from the accelerometer sensor, which is 20 degrees. If the robot tilts beyond a specific degree, then it would come back to its standstill position and stop further movement. When the robot moves forward, the IR sensors sense obstacles in front of the robot. If an obstacle is detected within 35 cm, then the robot stops moving further. Implementation of ROS on top of the BBB (by replacing CM530 controller with the BBB) and using feedback controls from the accelerometer and IR sensor to control the two-legged robotic movement are the novelties of this work
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