Natural fibers have drawn attention of researchers as an environmentally-friendly alternative to synthetic fibers. Developing natural fiber reinforced bio-composites are a viable alternative to the problems of non-degrading and energy consuming synthetic composites. This study focuses on (i) the application of kenaf fiber as a potential reinforcement and, (ii) determining the tensile properties of the randomly oriented short kenaf fiber composite both experimentally and numerically. Kenaf fiber micro-structure and its Young's modulus with varying gage length (10, 15, 20, and 25.4 mm) were investigated. The variation in tensile strength of kenaf fibers was analyzed using the Weibull probability distribution function. It was observed that the Young's modulus of kenaf fiber increased with increase in gage length. Fabrication of randomly oriented short kenaf fiber using vacuum bagging techniques and hand-lay-up techniques were discussed and the tensile properties of the specimens were obtained experimentally. The tensile modulus of the composite sample at 22% fiber volume fraction was found to be 6.48 GPa and tensile strength varied from 20 to 38 MPa. Numerical models based on the micro mechanics concepts in conjunction with finite element methods were developed for predicting the composite properties. A two-step homogenization procedure was developed to evaluate the elastic constants at the cell wall level and the meso-scale level respectively. Von-Mises Fisher probability distribution function was applied to model the random orientation distribution of fibers and obtain equivalent modulus of composite. The predicted equivalent modulus through numerical homogenization was in good agreement with the experimental results.

Ultrafine particles (UFPs) are present in the ambient atmosphere and are generated from atmospheric gases, pollution sources, and combustion. Candles emit carbonaceous soot particles similar to UFPs present in the ambient atmosphere. With the exception of lead, airborne concentrations of candle emissions have not been shown capable of causing cancer or cardiopulmonary disease during normal use. The purpose of this research is to determine the occupational risk associated with candle emissions. Candle studies employ chambers to measure candle emission exposures and assess public health risk. Chambers used in previous studies did not match normal room conditions. They were affected by turbulence and high temperature, which affected particle distribution and constituent concentrations, while making it difficult to extrapolate the results. The chamber designed for this study sought to avoid the problems noted above. This study also employed a room constructed to closely simulate a normal work environment. Candle suppliers and users were surveyed to determine occupational candle use and settings. Scented, unscented, and church candles were measured in both ventilated and unventilated environments. A condensation nuclei counter was used to measure UFPs from candle emissions. Relative to previous chamber designs, results indicated a reduction in candle soot generation, no significant airborne concentrations of metals, and airborne concentrations of polycyclic aromatic hydrocarbons (PAHs), below occupational limits. Scented candles generated more soot than unscented candles. UFP studies have demonstrated only weak associations between ambient UFP exposures and cardiopulmonary disease. However, ambient UFP exposures were used as a benchmark for candle soot exposures. The lifetime average daily dose (LADD) was calculated from the candle soot measurement data and ambient UFP data. Candle soot generated inside the test room ranged from 5.73 x 109 to 1.86 x 1011 number of candle soot particles inhaled daily compared to the 3.25 x1011 to 2.45 x 1012 soot particles inhaled in the ambient environment. The calculated candle soot dose was nearly an order of magnitude less than the calculated ambient dose. The conclusion is that candle emissions do not pose a health risk under normal occupational use.

The arithmetic operations such as multiplication and division in binary number system are computationally complex in terms of area, delay and power. Logarithmic Number Systems (LNS) offer a viable alternative combining the simplicity of fixed point number systems and the precision of floating point number systems. However, the computations in LNS result in some loss of accuracy and thus, are limited to mostly signal processing applications; where in certain amount of error is tolerable. In LNS, the cost of computations can be tradeoff with the level of accuracy needed. The Mitchell algorithm proposed incite[mitchell], is a simple approach commonly used for logarithmic multiplication. The method involves a high error margin due to a piecewise straight line approximation of the logarithm curve. Thus, several methods have been proposed in the literature for improving the accuracy of Mitchell's algorithm. In this thesis, we propose a new method for improving the accuracy of Mitchell's logarithmic multiplication using operand decomposition. The operand decomposition process decreases the number of bits with the value of '1' in the multiplicands and reduces the amount of approximation. The proposed method brings down the average error percentage of Mitchell's logarithmic multiplication by around 45%. It can be combined with previous methods to further improve the accuracy. Experimental results are presented to show that both the error range and the average error percentage can be significantly improved by using operand decomposition.

This thesis is concerned primarily with the optimization of the current regulation in bi-directional ac-dc power converters through the use of appropriate current control methods. Following a review into prior current control technology, current control methods which attempt to achieve Zero Average Current Error (ZACE) in each switching period are presented. A ZACE controlled converter offers independent real and reactive power flow control with negligible low order current harmonics, a relatively narrow switching frequency band, and relative immunity to power circuit parameter variations, including DC link or AC line voltage harmonics. ZACE and other desirable characteristics in a current control method are discussed. The single phase ac and dc ripple current is characterized.Two new types of ZACE current control techniques for directly controlling the inductor current in switched power converters are introduced in this thesis together with variations for certain applications. Slope-generated hysteresis (SGH), the first to be developed, is a hysteresis method which uses the slopes of the current error signal alone to generate a hysteresis band which will result in a fixed switching frequency. Slope-generated hysteresis-clock (SGHC) is presented as an alternative with a dual clock to force a narrow switching frequency band.Ramptime current control is the second type of ZACE current control presented. Developed as an improvement over SGH, ramptime produces ZACE in each switching period by using the timing of a previous switching instant relative to the coincident previous current error signal excursion time to determine each switching instant. The digital current error polarity signal is the only variable input required to produce a pwm output.Variations of ramptime current control are also presented. Polarized ramptime is a subset of ramptime which maintains a narrow ++ / switching frequency band despite switching delays. Dual ramptime is the final enhancement of ramptime where two polarized ramptime regulators are used together to provide the appropriate choice between full-bridge and half-bridge switching in a single phase current controlled full-bridge voltage source inverter with the ac ripple current minimized without compromising the transient response. Using this technique, excellent fidelity and a narrow switching frequency band are demonstrated.The ZACE current control techniques are applied to a three phase voltage source inverter. A "standing phase" system of control for a three wire, three phase inverter is chosen over individual phase control since only two current regulators are required to control two decoupled current error signals, and the effective switching frequency is reduced by one third.The new ZACE methods are found to compare favourably in simulation to existing linear and hysteresis type current control techniques. SGH current control has equivalent fidelity to any other hysteresis control in delivering the reference current waveform, but is prone to noise in the hysteresis band determination requiring filtering. This, combined with the effect of switching delays compromises the narrowness of the switching frequency band. SGHC current control is also prone to noise in the generation of the hysteresis band, and results in a decrease in the fidelity of reproduction of the reference waveform. Ramptime current control is a robust technique, largely immune to power circuit parameter and voltage variances, with good fidelity and a relatively narrow switching frequency band. Polarized ramptime current control is shown to produce excellent fidelity with a narrow switching frequency band.The operation of the ZACE methods in single and three phase prototype converters is demonstrated. A field installation of a ++ / grid-connected ramptime current controlled converter is shown to source 20 kW of real power onto the grid from a photovoltaic array with a maximum power point tracking control, while independently providing grid voltage support through reactive power control.The effect of the synchronization of the current regulators on the ac and dc current ripple are presented. Synchronized polarized ramptime regulators are shown to produce the minimum ripple current in simulation and in the prototype operation.ZACE current control techniques, and ramptime and polarized ramptime in particular, are presented as a significant contribution to the control of current in power electronic converters.

The technique of �open throat� is a pedagogical concept transmitted through the oral tradition of singing. This thesis explored the pedagogical perceptions and practices of �open throat� using empirical methodologies to assess technical skill and associated vocal quality. In the first study (Mitchell, Kenny, Ryan, & Davis, 2003), we assessed the degree of consensus amongst singing pedagogues regarding the definition of, and use in the singing studio of the technique called �open throat.� Results indicated that all fifteen pedagogues described �open throat� technique as fundamental to singing training and were positive about the sound quality it achieved, especially in classical singing. It was described as a way of maximising pharyngeal space or abducting the false vocal folds. Hypotheses generated from pedagogical beliefs expressed in this first study were then tested acoustically (Mitchell & Kenny, 2004a, 2004b). Six advanced singing students sang in two conditions: �optimal� (O), using maximal open throat, �sub-optimal� (SO), using reduced open throat and loud sub-optimal (LSO) to control for the effect of loudness. From these recordings, acoustic characteristics of vibrato (Mitchell & Kenny, 2004b) and energy distribution (Mitchell & Kenny, 2004a) were examined. Subsequent investigations of the vibrato parameters of rate, extent and onset, revealed that extent was significantly reduced and onset increased when singers did not use the technique. As inconsistent vibrato is considered indicative of poor singing, it was hypothesized that testing the energy distribution in these singers� voices in each condition would identify the timbral changes associated with open throat. Visual inspection of long term average spectra (LTAS) confirmed differences between O and SO, but conventional measures applied to long term average spectra (LTAS), comparing energy peak height [singing power ratio (SPR)] and peak area [energy ratio (ER)] were not sensitive to the changes identified through visual inspection of the LTAS. These results were not consistent with the vibrato findings and suggest that conventional measures of SPR and ER are not sufficiently sensitive to evaluate LTAS. In the fourth study, fifteen expert listeners consistently and reliably identified the presence of open throat technique with 87% accuracy (Mitchell & Kenny, in press). In the fifth study, LTAS measurements were examined with respect to the perceptual ratings of singers. There was no relationship between perceptual rankings of vocal beauty and acoustic rankings of vocal quality (Kenny & Mitchell, 2004, in press). There is a vast literature of spectral energy definitions of good voice but the studies in this thesis have indicated that current acoustic methods are limited in defining vocal quality. They also suggest that current work in singing has not sufficiently incorporated perceptual ratings and descriptions of sound quality or the relationship between acoustic and perceptual factors with pedagogical practices.

<p>Tidigare forskning har visat att människor överskattar chanserna för att positiva händelser ska inträffa dem och underskattar riskerna för att negativa händelser ska inträffa dem jämfört med genomsnittet. Detta kallas orealistisk optimism (OO). En faktor som påverkar detta är grad av upplevd kontroll. Studiens huvudsakliga syfte var att undersöka sambanden mellan upplevd kontroll och OO. I en enkätstudie undersöktes OO och upplevd kontroll för diverse händelser. Deltagarna fick t ex svara på hur sannolikt det är att de utsattes för vissa händelser jämfört med genomsnittet. Händelserna var bl a hälsorelaterade. Deltagarna var studenter från en högskola i Mellansverige, 18 män och 109 kvinnor. OO uppstod för alla händelser utom två. Det fanns vissa samband mellan OO och upplevd kontroll. Nytt med studien är att vissa händelser som i tidigare undersökningar skattats som okontrollerbara i själva verket kan upplevas som delvis kontrollerbara. Sambanden mellan OO och upplevd kontroll bör vidare undersökas.</p>

<p>This study aim at investigating whether income inequality ceteris paribus is a determinant of population health measured by infant mortality rate and average expected lifetime. Earlier research has found results pointing in different directions but the income inequality hypothesis suggests that income inequality alone is something bad for the population. The study uses data on income distribution from the Luxembourg Income Study (LIS) and the World Income Inequality Database (WIID). Data on economic development and health indicators comes from the OECD database. An econometric model which applies country fixed effects is specified and the results indicates no effect from income inequality on infant mortality rate but some indications of a negative effect on average expected lifetime.</p>

This thesis addresses the mechanisms involved in cellulosedegradation in general and Totally Chlorine Free (TCF) bleachingof pulp in particular. The thesis shows that the cellulosedegradation during high consistency ozone bleaching is explainedby free radical chain reactions. By simulation, it has been shown that the number, weight andviscosity average of liner polymer chain length can be used tocalculate the number of random scissions in a linear polymer ofany molecular weight distribution, provided that there is acalibrated Mark-Houwink equation. A model describing partialdegradation of molecular weight distributions of linear polymersmeasured with viscometry was developed and verifiedexperimentally. The model predicts viscometric measurement ofchemical cellulose degradation by a rapidly reacting reagent tobe strongly dependent on cellulose accessibility. The role of free radical reactions in cellulose degradationwas studied by varying the amount of ferrous ions and ozone addedto the cotton linters. The result was compared to the resultsobtained from cellulose of lower crystallinity (cellulose beads)by measuring average chain length. When a ferryl ion reacted withcotton linters in the presence of ozone, the very formation ofone glycosidic radical was more significant to degradation thanthe final step of forming one oxidised glycoside. The inefficientdegradation observed of the oxidation step is explainable by theamount of accessible glycosides being too small to influenceviscometry. The efficient degradation observed in associationwith the glycosidic radical formation is explained by initiationof free radical chain reactions that are propagated as long asthere is ozone in the system. As none of these phenomena werefound in the less crystalline cellulose, cellulose structureappears to be important for how free radical mediated cellulosedegradation develops. The theory of free radical chain reactions coupled withdiffusion suggests a concentric expansion of the chain reactionsoutwards from the initial site of radical formation duringozonation of carbohydrates. This was confirmed by demonstratingfree radical chain reactions spreading from a spot of initiationoutwards during ozonation of a filter paper, using a pH-indicatorto monitor acid formation. Furthermore, the interior and exteriorof cellulose fibres doped with initiator were shown to bepermeated by small holes after ozonation. Ethylene glycol was shown to improve the selectivity duringozone bleaching of oxygen bleached kraft pulp at pH 3. Optimalconditions were obtained at pH 3 for 25 wt% ethylene glycol. Theinfluence of ethylene glycol on selectivity is explained by aproportion of the free radical chain reactions being carried bythe ethylene glycol instead of the cellulose during ozonebleaching. The observations were summarised in the form of amodel where the observed degradations for pulp, bleached pulp andcotton fibres during both ozone bleaching and ethylene glycolassisted ozone bleaching were shown to agree with each other. From g-irradiation of ozonised aqueous solutions of alcohol,the rate constant of superoxide formation from the peroxylradical of methanol was estimated to be 10 s-1. Rate constants of the reactions between ozone andalkylperoxyl radicals were determined to be around 104M-1s-1. The possibility of the reaction betweenalkylperoxyl radicals and ozone contributing significantly tofree radical chain reactions during ozonation of carbohydratesand alcohols could therefore be ruled out. Cellulose, degradation, free radical, ozone, selectivity,ethylene glycol, alcohol, bleaching, kraft pulp, cotton linters,delignification, fibre, fibril, crystallinity, ferryl ion, freeradical chain reactions, TCF, viscometry, molecular weightdistributions, random scissions.

This dissertation presents adaptation techniques that can achieve high spectral efficiency for single user multiple-input multiple-output (MIMO) systems. Two types of adaptation techniques, adaptive modulation and adaptive powe allocation, are employed to adapt the rate and the transmit power to fading channels. We start by investigating the adaptive modulation subject to a certain bit-error-ratio (BER) constraint, either instantaneous BER constraint or average BER constraint. The resulting average spectral efficiencies are obtained in closed-form expressions. It turns out that, by employing the average BER constraint, we can achieve the optimal average spectra efficiency at the cost of prohibitive computational complexity. On the other hand, instantaneous BER constraint leads to inferior performance with little computational complexity. In order to achieve comparable performance to the average BER constraint with limited complexity, a non-linear optimization method is proposed. To further enhance the average spectra efficiency, adaptive power allocation schemes are considered to adjust the transmit power across the temporal domain or the spatial domain, depending on the specific situation. Provided the closed-form expressions of the average spectral efficiency, the optimal MIMO coding scheme that offers the highest average spectral efficiency under the same circumstances can be identified. As we take into account the effect of imperfect channel estimation, the adaptation techniques are revised to tolerate interference introduced by the channel estimation errors. As a result, the degradation with respect to the average spectral efficiency is in proportion to signal-to-noise ratio (SNR). In order to facilitate fast development and verification of the adaptation schemes proposed for various MIMO systems, a reconfigurable Link Layer Simulator (LiLaS) which accommodates a variety of wireless/wireline applications is designed in the environment of MATLAB/OCTAVE. The idea of the simulator is originated from Software Defined Radio (SDR) and evolved to suit Cognitive Radio (CR) applications. For the convenience of modification and reconfiguration, LiLaS is functionally divided into generic blocks and all blocks are parameterized. / QC 20100812

This study aim at investigating whether income inequality ceteris paribus is a determinant of population health measured by infant mortality rate and average expected lifetime. Earlier research has found results pointing in different directions but the income inequality hypothesis suggests that income inequality alone is something bad for the population. The study uses data on income distribution from the Luxembourg Income Study (LIS) and the World Income Inequality Database (WIID). Data on economic development and health indicators comes from the OECD database. An econometric model which applies country fixed effects is specified and the results indicates no effect from income inequality on infant mortality rate but some indications of a negative effect on average expected lifetime.