Potential policy decisions regarding fly fishing in the Yellowstone National Park Area could severely impact the enjoyment possibilities of many of its users. In order to determine the magnitude of the impact, this paper applies a form of the basic travel cost model developed by Bell and Leeworthy [JEEM. 18,189-205 (1990)] to fishing sites in the Yellowstone National Park Area. Bell and Leeworthy have argued that consumer demand for the time spent at a recreation site is inversely related to on-site cost per day, and may be positively related to travel cost per trip. The paper discusses relevant literature on the method, presents background information on the site, and generates a demand curve for users of the resource. A consumer surplus measurement is then derived from the resulting demand data, which gives an estimate for the value of the resource; the consumer surplus is determined to be roughly $751.88 per day spent at the site. The assumptions of the model are then discussed, and an assessment is made of the potential policy implications. / Graduation date: 1998

Arsenic (As) poses a significant water quality problem and it is a big challenge for all coal-based power plant industries worldwide. Currently most of the researches on the leaching behavior of arsenic from fly ash are based on the titration experiments. In this study a simulation method is used to study on the pH effect on the arsenic separation of coal-based power plants. Both single point and composition survey simulation of the OLI stream analyzer are used in the study. The simulation results of single point calculation indicates that for the fly ash which has high lime weight percent and equilibrium fly ash solution pH is over 11 and between 7 and 9, that is, Type C fly ash, the simulation results for equilibrium pH in fly ash solutions have great accuracy compared to actual experiment results. Based on the results obtained from single point simulation, both acid and base titrations of composition survey are simulated and the output results suggest that for the same type of fly ash, the simulation results proves the general trend of arsenic solubility in fly ash solutions. The solubility of arsenic decreases with the increase of pH value. It is also noted that at the equilibrium pH fly ash solutions, the maximum solid/liquid ratio of arsenic concentration is observed for type C fly ash. For other fly ashes which have low lime weight percent, the simulation results have discrepancy compared to actual experiment results. This work is important in offering an alternative way of analyze the reasonable output species and relative concentrations for type C fly ash in the waste water storage pond under specific pH conditions, which can be of great importance for the power plants to monitor and minimize the environment pollution in order to meet the future federal regulations.

<p>It was hypothesized that South African FA and brine could sequester CO2 through mineral carbonation. A statistical approach was undertaken to optimize the % CaCO3 formed from FA/brine/CO2 interaction with input parameters of temperature, pressure, particle size and solid/liquid ratio (S/L) being varied. The ranges adopted for the input parameters were: temperature of 30 &ordm / C or 90 &ordm / C / pressure of 1 Mpa or 4 Mpa / four particle sizes namely bulk ash, &gt / 150 &mu / m, &lt / 20 &mu / m and 20 &mu / m- 150 &mu / m particle size range / S/L ratios of 0.1, 0.5 or 1. The FA/ brine dispersions were carbonated in a high pressure reactor varying the above mentioned input parameters. The fresh Secunda FA of various size fractions was characterized morphologically using scanning electron microscopy, chemically using X-ray fluorescence and mineralogically using qualitative X-ray diffraction. The carbonated solid residues on the other hand were characterized using quantitative X-ray diffraction, scanning electron microscopy, thermal gravimetic analysis and Chittick tests. The raw brine from Tutuka together with the carbonation leachates were characterized using inductively coupled mass spectrometry and ion chromatography. Total acid digestion was carried out to evaluate the differences in the total elemental content in both the fresh ash and the carbonated solid residues. The results suggested that South African FA from Secunda belongs to class F based on the CaO content as well as the total alumina, silica and ferric oxide content, while the RO brine from Tutuka were classified as NaSO4 waters...</p>

<p>This study evaluated SO4 2- removal from circumneutral mine water (CMW) collected from Middleburg coal mine using coal FA collected from Hendrina power station. The following parameters were investigated: the effect of the amount of FA, the effect of the final pH achieved during treatment, the effect of the initial pH of the mine water and the effect of Fe and Al on SO4 2- removal from mine water. The precipitation of ettringite at alkaline pH was evaluated to further reduce the SO4 2- concentration to below the DWAF limit for potable water. Removal of SO4 2- from mine water was found to be dependent on: the final pH achieved during treatment, the amount of FA used to treat the mine water and the presence of Fe and Al in the mine water. Treatment of CMW using different CMW:FA ratios / 5:1, 4:1, 3:1, and 2:1 resulted in 55, 60, 70 and 71 % SO4 2- removal respectively. Treatment of CMW to pH 8.98, 9.88, 10.21, 10.96, 11.77 and 12.35 resulted in 6, 19, 37, 45, 63 and 71 % SO4 2- removal respectively. When the CMW was modified by adding Fe and Al by mixing with Navigation coal mine AMD and treated to pH 10, 93 % SO4 2- removal was observed. Further studies were done to evaluate the effects of Fe and Al separately. Treatment of simulated Fe containing AMD (Fe-AMD) to pH 9.54, 10.2, 11.8, and 12.1 resulted in 47, 52, 65, and 68 % SO4 2- removal respectively. When Al containing AMD was treated to pH 9.46, 10.3, 11.5 and 12 percentage SO4 2- removal of 39, 51, 55 and 67 % was observed respectively.</p>

<p>Fly ash and AMD samples were characterised by standard analytical methods for selection of the test materials. Active treatment by means of mixing fly ash with AMD in beakers and a large tank at pre-determined ratios have shown that fly ash is capable of neutralising AMD and increasing the pH beyond neutral values, which optimises the removal of heavy metals and ions. The trend was: the more fly ash added the quicker was the reaction time and higher the pH values achieved. Iron was reduced by as much 99 % in beaker scale experiments via Fe(OH)3 precipitation at pH values &gt / 4.0. A 99 % decrease in aluminium concentration was observed which was attributed to the precipitation of primarily gibbsite and various other mineral phases at pH values &gt / 5.5. As the pH increases, sulphate is adsorbed via Fe(OH)3 and gypsum precipitation at elevated pH. Sulphate attenuation with fly ash was excellent, achieving 98 % attenuation with beaker scale experiments and 1:1 fly ash:AMD ratio. Sulphate attenuation with fly ash was comparable to membrane and ion exchange systems and exceeded the performance of limestone treatment. Except for the larger volumes of fly ash needed to neutralise the AMD, fly ash proved to be a feasible and cost efficient alternative to limestone treatment. Fly ash produced competing results to limestone concerning acidity removal and sulphate attenuation. The comparison highlighted the advantages of utilising fly ash in comparison to limestone and demonstrated its cost effectiveness. The results of this study have shown that fly ash could be successfully applied for the neutralisation of acid mine drainage (AMD) and effectively attenuate the sulphate load in the treated water. The critical parameters to this technology are the variations of chemical composition and mineralogy of fly ash, which could influence the pH, contact time of the neutralisation reaction, and the same is true if the AMD quality varies.</p>

This thesis proposes a novel driving circuit of the RGB light emitting diodes (LEDs) for the back-light source of the liquid crystal display. In stead of employing three dc-to-dc converters, a fly-back converter with three secondary windings is used to drive RGB-LED light bars. By adjusting the duty-ratio, the fly-back converter provides compromised voltages to RGB-LEDs in accordance with the operating modes of dimming control, so as to retain current magnitudes within the acceptable values. LEDs of three colors are dimmed by regulating the duty-ratios of three active power switches individually. By changing the ratio of the average currents of the three primary color LEDs, the color temperature range of driving can reach the requests of dimming control. As compared with a consumer product using the conventional driving circuit, the proposed circuit is obviously much simpler with less components and a higher efficiency.

<p>The production of biodiesel (methyl esters) from vegetable oils represents analternative means of producing liquid fuels from biomass, and one which is growing rapidly in commercial importance and relevance due to increase in petroleum prices and the environmental advantages the process offers. Commercially, biodiesel is produced from vegetable oils, as well as from waste cooking oils and animal fats. These oils are typically composed of C14-C20 fatty acid triglycerides. In order to produce a fuel that is suitable for use in diesel engines, these triglycerides are usually converted into the respective mono alkyl esters by base-catalyzed transesterification with short chain alcohol, usually methanol. In the first part of this study, the transesterification reactions of three different vegetable oils / sunflower (SFO), soybean (SBO) and waste cooking oil (WCO) with methanol was studied using potassium hydroxide as catalyst in a conventional batch process. The production of biodiesel from waste cooking oil was also studied via continuous operation systems (employing the use of low frequency ultrasonic technology and the jet loop reactor). The characterisation of the feedstock used and the methyl ester products were determined by different analytical techniques such as gas chromatography (GC), high performance liquid chromatography (HPLC) and thin layer chromatography (TLC). The effects of different reaction parameters (catalyst amount, methanol to oil ratio, reaction temperature, reaction time) on methyl ester/FAME yield were studied and the optimum reaction conditions of the different process systems were determined. The optimum reaction conditions for production of methyl esters via the batch process with the fresh oil samples (SFO and SBO) were established as follows: a reaction time of 60 min at 60 &ordm / C with a methanol: oil ratio of 6:1 and 1.0 KOH % wt/wt of oil / while the optimum reaction conditions for the used oil (WCO) was observed at a reaction time of 90 min at 60 &ordm / C, methanol: oil ratio of 6:1 and 1.5% KOH wt/wt of oil. The optimum reaction conditions for the transesterification of the WCO via ultrasound technology applied in a continuous system in this study were: a reaction time of 30 min, 30 &ordm / C, 6:1 methanol/oil ratio and a 0.75 wt% (KOH) catalyst concentration. The ultrasound assisted transesterification reactions performed at optimum conditions on the different oil samples led to higher yields of methyl esters (96.8, 98.32 and 97.65 % for WCO, SFO and SBO respectively) compared to methyl esters yields (90, 95 and 96 % for WCO, SFO and SBO respectively) obtained when using conventional batch procedures. A considerable increase in yields of the methyl esters in the ultrasound assisted reaction process were obtained at room temperature, in a remarkably short time span (completed in 30 min) and with a lower amount of catalyst (0.75 wt % KOH) while the results from the continuous jet loop process system showed even better results, at an optimum reaction condition of 25 min of reaction, a methanol: oil ratio of 4:1 and a catalyst amount of 0.5 wt%. This new jet loop process allowed an added advantage of intense agitation for an efficient separation and adequate purification of the methyl esters phase at a reduced time of 30 min. The use of homogeneous catalysts in conventional processes poses many disadvantages / heterogeneous catalysts on the other hand are attractive on the basis that their use could enable the biodiesel production to be more readily performed as a continuous process resulting in low production costs. Consequently, a solid base catalyst (KNO3/FA) prepared from fly ash (obtained from Arnot coal power station, South Africa) and a new zeolite, FA/Na-X synthesized from the same fly ash were used as solid base catalysts in the transesterification reactions in the conversion of a variety of oil feedstock with methanol to methyl esters. Since fly ash is a waste product generated from the combustion of coal for power generation, its utilization in this manner would allow for its beneficiation (as a catalytic support material and raw material for zeolite synthesis) in an environmentally friendly way aimed at making the transesterification process reasonably viable. Arnot fly ash (AFA) was loaded with potassium (using potassium nitrate as precursor) via a wet impregnation method while the synthesized zeolite FA/Na-X was ion exchanged with potassium (using potassium acetate as precursor) to obtain the KNO3/FA and FA/K-X catalysts respectively. Several analytical techniques were applied for characterization purposes. The results of the XRD and XRF showed that the AFA predominantly contained some mineral phases such as quartz, mullite, calcite and lime. The high concentration of CaO in AFA was apparent to be beneficial for the use of fresh fly ash as a support material in the heterogeneous catalysed transesterification reactions. XRD characterisation of KNO3/FA results indicated that the structure of KNO3/FA gradually changed with the increase in KNO3 loading. The catalyst function was retained until the loading of KNO3 was over 10 %. IR spectra showed that the KNO3 was decomposed to K2O on the fly ash support during preparation at a calcination temperature of 500 &ordm / C. The CO2-TPD of the KNO3/FA catalysts showed that two basic catalytic sites were generated which were responsible for high catalytic abilities observed in the transesterification reactions of sunflower oil to methyl esters. On the other hand, XRD results for the as- received zeolite synthesized from AFA showed typical diffraction peaks of zeolite NaX. SEM images of the FA /NaX showed nano platelets unique morphology different from well known pyramidal octahedral shaped crystal formation of faujasite zeolites and the morphology of the FA /KX zeolite did not show any significant difference after ion exchange. The fly ash derived zeolite NaX (FA /NaX) exhibited a high surface area of 320 m2/g. The application of the KNO3/FA catalysts in the conversion reactions to produce methyl esters (biodiesel) via transesterification reactions revealed methyl ester yield of 87.5 % with 10 wt% KNO3 at optimum reaction conditions of methanol: oil ratio of 15:1, 5 h reaction time, catalyst amount of 15 g and reaction temperature 160 &deg / C, while with the use of the zeolite FA/K-X catalyst, a FAME yield of 83.53 % was obtained for 8 h using the ion exchanged Arnot fly ash zeolite NaX catalyst (FA/KX) at reaction conditions of methanol: oil ratio of 6:1, catalyst amount of 3 % wt/wt of oil and reaction temperature of 65 &ordm / C. Several studies have been carried out on the production of biodiesel using different heterogeneous catalysts but this study has been able to uniquely demonstrate the utilization of South African Class F AFA both as a catalyst support and as a raw material for zeolite synthesis / these catalyst materials subsequently applied sucessfully as solid base catalysts in the production of biodiesel.</p>

The blended-wing-body (BWB) configuration appears as a promising contender for the next generation of large transport aircraft. The idea of blending the wing with the fuselage and eliminating the tail is not new, it has long been known that tailless aircraft can suffer from stability and control problems that must be addressed early in the design. This thesis is concerned with identifying and then evaluating the flight dynamics, stability, flight controls and handling qualities of a generic BWB large transport aircraft concept. Longitudinal and lateral-directional static and dynamic stability analysis using aerodynamic data representative of different BWB configurations enabled a better understanding of the BWB aircraft characteristics and identification of the mechanisms that influence its behaviour. The static stability studies revealed that there is limited control power both for the longitudinal and lateral-directional motion. The solution for the longitudinal problem is to limit the static margins to small values around the neutral point, and even to use negative static margins. However, for the directional control problem the solution is to investigate alternative ways of generating directional control power. Additional investigation uncovered dynamic instability due to the low and negative longitudinal and directional static stability. Furthermore, adverse roll and yaw responses were found to aileron inputs. The implementation of a pitch rate command/attitude hold flight control system (FCS) improved the longitudinal basic BWB characteristics to satisfactory levels, or Level 1, flying and handling qualities (FHQ). Although the lateral-directional command and stability FCS also improved the BWB flying and handling qualities it was demonstrated that Level 1 was not achieved for all flight conditions due to limited directional control power. The possibility to use the conventional FHQs criteria and requirements for FCS design and FHQs assessment on BWB configurations was also investigated. Hence, a limited set of simulation trials were undertaken using an augmented BWB configuration. The longitudinal Bandwidth/Phase delay/Gibson dropback criteria, as suggested by the military standards, together with the Generic Control Anticipation Parameter (GCAP) proved possible to use to assess flying and handling qualities of BWB aircraft. For the lateral-directional motion the MIL-F-8785C criteria were used. Although it is possible to assess the FHQ of BWB configuartions using these criteria, more research is recommended specifically on the lateral-directional FHQs criteria and requirements of highly augmented large transport aircraft.

On-the-fly laser drilling provides a highly productive method for producing hole clusters (pre-defined groups of holes to be laser drilled) on freeform surfaced parts, such as gas turbine combustion chambers. Although the process is capable of achieving high throughputs, current machine tool controllers are not equipped with appropriate trajectory functions that can take full advantage of the achievable laser drilling speeds. While the problem of contour following has received previous attention in time-optimal trajectory generation literature, on-the-fly laser drilling presents different technological requirements, needing a different kind of trajectory optimization solution, which has not been studied prior to this thesis. The duration between consecutive hole locations, which corresponds to the laser pulsing period, has to be kept constant, ideally throughout the part program. However, the toolpath between the holes is not fixed and can be optimized to enable the shortest possible segment duration. To preserve the dynamic beam positioning accuracy and avoid inducing excessive vibrations on the laser optics, the axis velocity, acceleration, and jerk profiles need to be limited. Furthermore, to ensure that hole elongation does not violate the given part tolerances, the orthogonal component of part velocity relative to the laser beam needs to be capped. All of these requirements have been fulfilled in the trajectory optimization algorithm developed in this thesis. The hole locations are provided as pre-programmed sequences by the Computer Aided Design/Manufacturing software (CAD/CAM). A time-optimized trajectory for each sequence is planned through a series of time-scaling and unconstrained optimization operations, which guarantees a feasible solution. The initial guess for this algorithm is obtained by minimizing the integral square of the fourth time derivative (i.e. ‘snap’). The optimized trajectories for each cluster are then joined together or looped onto themselves (for repeated laser shots) using a time-optimized looping/stitching (optimized/smooth toolpath to repeat/loop a cluster or connect/stitch between consecutive clusters) algorithm. This algorithm also minimizes the integral square of jerk in the faster axes. The effectiveness of the overall solution has been demonstrated in simulations and preliminary experimental results for on-the-fly laser drilling of a hole pattern for a gas turbine combustion chamber panel. It is shown that the developed algorithm improves the cycle time for a single pass by at least 6% (from kinematic analysis of the motion duration), and more importantly reduces the integral square of jerk by 56%, which would enable the process speed to be pushed up further.

Arsenic and selenium distributions in coal-fired plant samples are studied. This research includes arsenic and selenium concentrations in samples of coal, fly ash, bottom ash, economizer ash, Flue Gas Desulfurization (FGD) slurry and flue gas taken from four power plants with the goal being to examine the distribution of these metals in these materials and calculate a materials balance for the system. All samples were analyzed using ICP-ES. This research shows that 60-80% of the arsenic in coal-fired plant samples will be associated with the fly ash. Approximately 35-55% of the selenium will be associated with the fly ash and approximately 30-40% will be associated with the FGD slurry materials. The amount of arsenic and selenium present in the flue gases escaping the stack is very little, 6-7% or less. Hopefully, research in this area will be helpful when setting emissions limits, identifying and disposing of hazardous wastes and improving air pollution control devices for maximum metal removal.