Dissertations / Theses on the topic 'Gas exchange'

This thesis deals with flow measuring techniques applied to steady and pulsating gas flows relevant to gas exchange systems for internal combustion engines. Gas flows in such environments are complex, i.e. they are inhomogeneous, three-dimensional, unsteady, non-isothermal and exhibit significant density changes. While a variety of flow metering devices are available and have been devised for such flow conditions, the performance of these flow metersis to a large extent undocumented when a strongly pulsatile motion is superposed on the already complex flow field. Nonetheless, gas flow meters are commonly applied in such environments, e.g. in the measurement of the air flow to the engine or the amount of exhaust gas recirculation. The aim of the present thesis is therefore to understand and assess, and if possible to improve the performance of various flow meters under highly pulsatile conditions as well as demonstrating the use of a new type of flow meter for measurements of the pulsating mass flow upstream and downstream the turbine of a turbocharger. The thesis can be subdivided into three parts. The first one assesses the flow quality of a newly developed flow rig, designed for measurements of steady and pulsating air flow at flow rates and pulse frequencies typically found in the gas exchange system of cars and smaller trucks. Flow rates and pulsation frequencies achieved and measured range up to about 200 g/s and 80 Hz, respectively. The time-resolved mass flux and stagnation temperature under both steady and pulsating conditions were characterized by means of a combined hot/cold-wire probe which is part of a newly developed automated measurement module. This rig and measurement module were used to create a unique data base with well-defined boundary conditions to be used for the validation of numerical simulations, but in particular, to assess the performance of various flow meters. In the second part a novel vortex flow meter that can measure the timedependent flow rate using wavelet analysis has been invented, verified and extensively tested under various industrially relevant conditions. The newly developed technique was used to provide unique turbine maps under pulsatile conditions through time-resolved and simultaneous measurements of mass flow, temperature and pressure upstream and downstream the turbine. Results confirm that the quasi-steady assumption is invalid for the turbine considered as a whole. In the third and last part of the thesis, two basic fundamental questions that arose during the course of hot/cold-wire measurements in the aforementioned high speed flows have been addressed, namely to assess which temperature a cold-wire measures or to which a hot-wire is exposed to in high speed flows as well as whether the hot-wire measures the product of velocity and density or total density. Hot/cold-wire measurements in a nozzle have been performed to test various hypothesis and results show that the recovery temperature as well as the product of velocity and stagnation density are measured.
QC 20120510

Background: Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations. Methods: Shunt, PaO2 and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (Mtotal). We logarithmically transformed PaO2 (lnPaO2) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range). Results: Mtotal was 768 (715–884) g in sheep and 543 (503–583) g in pigs. Atelectasis was 26 (16–47)% in sheep and 18 (13–23) % in pigs. PaO2 (FiO2 = 1.0) was 242 (106–414) mmHg in sheep and 480 (437–514) mmHg in pigs. Shunt was 39 (29–51)% in sheep and 15 (11–20) % in pigs. Atelectasis correlated closely with lnPaO2 (R2 = 0.78) and shunt (R2 = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO2 (R2 = 0.63) and shunt (R2 = 0.34) was weaker in pigs, but R2 increased to 0.71 for lnPaO2 and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO2 and shunt. Discussion and Conclusion: In lung-healthy sheep, atelectasis correlates closely with lnPaO2 and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis.

Aquatic ecosystems play a substantial role in global cycling of carbon (C), despite covering only about 4% of the earth surface. They emit large amounts of greenhouse gases (GHG) to the atmosphere, comparable to the amount of C stored annually in terrestrial ecosystems. In addition, C can be buried in lake sediments. Headwater systems are located at the interface of the terrestrial and aquatic environment, and are first in line to process terrestrial C and throughout its journey through the aquatic continuum. The uncertainties in global estimates of aquatic GHG emissions are largely related to these headwater systems, as they are highly variable in time and space, and underrepresented in global assessments. The overall aim of this thesis was therefore to study GHG exchange between sediment, water and air in headwater systems, from both an ecosystem perspective and at the small scale of physical drivers of gas exchange. This thesis demonstrates that carbon dioxide (CO2) emission from headwater systems, especially streams, was the main pathway of C loss from surface waters from a lake catchment. Of the total aquatic CO2-emission of the catchment, 65% originated from stream systems that covered only 0.1% of the total catchment area. The gas transfer velocity (k) was the main driver of stream CO2-emission, but there was a high variability in k on small spatial scales (meters). This variability may have implications for upscaling GHG emissions, especially when using scaled k estimates. Lake sediments only contributed 16% to total lake C emission, but in reality, sediment C emission is probably even lower because experimentally determined sediment C flux returns high estimates that are biased since artificially induced turbulence enhances C flux rates beyond in-situ conditions. When sediment C flux is estimated in-situ, in natural bottom water turbulence conditions, flux rates were lower than those estimated experimentally. Conclusively, this thesis shows that GHG emissions from small aquatic ecosystems are dominant over other aquatic C fluxes and that our current knowledge regarding the physical processes controlling gas exchange from different small aquatic systems is limited, implying an inherent uncertainty of GHG emission estimates from small aquatic ecosystems.

Thesis (Ph.D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2000.
Includes bibliographical references (p. 299-312).
by Sean Patrick McKenna.
Ph.D.

Background: Obesity is a global and growing public health problem. Bariatric surgery (BS) is indicated in patients with morbid obesity. To our knowledge, the effects of mòrbid obesity and BS on ventilation/perfusion (VA/Q) ratio distributions using the multiple inert gas elimination technique have never before been explored. Methods: We compared respiratory and inert gas (VA/Q ratio distributions) pulmonary gas exchange, breathing both ambient air and 100% oxygen, in 19 morbidly obese women (BMI, 45 ± 1 kg/m2), both before and 1 year after BS, and in eight normal-weight, never smoker, age-matched, healthy women. Results: Before BS, morbidly obese individuals had reduced arterial PO2 (76 ± 2 mm Hg) and an increased alveolar-arterial PO2 difference (27 ± 2 mm Hg) caused by small amounts of shunt (4.3 ± 1.1% of cardiac output), along with abnormally broadly unimodal blood flow dispersion (0.83 ± 0.06). During 100% oxygen breathing, shunt increased twofold in parallel with a reduction of blood flow to low VA/Q units, suggesting the development of reabsorption atelectasis without reversion of hypoxic pulmonary vasoconstriction. After BS, body weight was reduced significantly (BMI, 31 ± 1 kg/m2), and pulmonary gas exchange abnormalities were decreased. Conclusions: Morbid obesity is associated with mild to moderate shunt and VA/Q imbalance. These abnormalities are reduced after BS. Manuscript 2. Postural effects on pulmonary gas exchange abnormalities in severe obesity before and after bariatric surgery Background: We hypothesized that in morbid obesity, pulmonary gas Exchange abnormalities will worsen when supine and that bariatric surgery (BS) will mitigate this effect. Methods: Gas exchange was investigated in 19 morbidly obese and 8 non-obese, age-matched control females, spontaneously breathing ambient air, both upright and supine, before and one year after BS. Results: In control non-obese individuals, no postural changes in arterial blood gases (ABGs) were observed. While obese subjects had more altered PaO2, SaO2 and AaPO2 values than controls (p<0.05 each) when upright, the values unexpectedly remained unchanged when supine. This was also the case in the subset of 6 normoxemic obese but the remaining 13 hypoxemic individuals actually improved ABGs when supine: AaPO2 (by –3.4 ± 1.4 mmHg), SaO2 (by +1.5 ± 0.6 %), pH (by +0.01 ± 0.01); and cardiac output increased (by +0.4 ± 0.2 L·min-1) (p<0.05 each). After BS, PaO2 (from 75.5 ± 2.4 to 89.4 ± 2.4 mmHg) and AaPO2 (from 27.0 ± 2.0 to 15.4 ± 2.1 mmHg) (p<0.05 each) and pulmonary gas exchange were improved compared to before BS when upright, but ABGs worsened when supine (PaO2, by –4.6 ± 1.7 mmHg; AaPO2, by +4.2 ± 1.6 mmHg) (p<0.05 each). Conclusions: Before BS, ABGs are not altered in normoxemic obese subjects moving from upright to supine, even improving in those with hypoxemia when supine. After successful BS, pulmonary gas exchange improved when upright in all subjects but ABGs deteriorated when supine. However, the important clinical observation is the lack of gas Exchange deterioration when supine, which may have implications for critical care and anesthesia settings. Manuscript 3. Lung tissue volume is elevated in obesity and reduced by bariatric surgery Background: Bariatric surgery (BS) in severely obese subjects causes a significant reduction of body weight and improvement in lung function. We have shown previously that abnormalities in pulmonary gas exchange in morbidly obese are substantially improved with BS. These abnormalities were thought to be related to reduced lung volumes as well as to abnormal endothelial function induced by low-grade chronic inflammation linked to perivascular adipose tissue (PVAT). In this study we used computed tomography (CT) to assess whether BS also caused measurable structural changes in the lung. We focused in lung tissue volume (Vtiss) and cross-sectional vessel analysis hypothesizing that these measures could be related to the previously reported lung functional changes. Methods: Pulmonary vessels and lung volumes, including Vtiss, were quantified in thoracic CT scans. We compared findings in 12 obese women before and after BS and in 8 healthy lean women. Results: Vtiss was significantly elevated in obese subjects before BS compared to control subjects and systematically reduced after BS (by 8%); other CT lung volumes or vascular areas were not affected in a consistent manner. No relationship was observed between BS-induced individual changes in Vtiss and pulmonary vessel area. Conclusions: Vtiss is elevated in morbidly obese, compared to lean individuals of similar body height, and is systematically reduced by BS. These effects do not appear related to vascular changes but may be caused by elevated extra-vascular lung water, due to low-grade inflammation, and/or hypertrophic PVAT in severe obesity.
Primer artículo (First Manuscript). Anomalías de las distribuciones ventilación-perfusión en la obesidad grave, antes y después de cirugía bariátrica En la actualidad, la obesidad es un grave problema de salud pública a escala mundial. La cirugía bariátrica (CB) es un tratamiento efectivo de la obesidad grave. No existen Trabajos previos sobre los efectos de la obesidad grave y la pérdida ponderal inducida por CB sobre el intercambio gaseoso pulmonar, específicamente en la distribución de las relaciones ventilación-perfusión (VA/Q) con el empleo de la técnica de gases inertes múltiples (TEGIM). Métodos: Se investigó el intercambio gaseoso pulmonar mediante la TEGIM en 19 mujeres obesas graves (índice de masa corporal [IMC] 45 ± 1kg/m2) antes y después CB y, también en 8 mujeres con peso normal, no fumadoras, de la misma edad. Resultados: Antes de la CB, las mujeres obesas tenían una PaO2 reducida (76 ± 2 mm Hg) y un gradiente alveolo-arterial de oxígeno aumentado (27 ± 2 mm Hg) secundarios a un aumento discreto del shunt intrapulmonar (4 ± 1% del gasto cardiaco) y de la dispersión de la distribución de la perfusión pulmonar (Log SDQ, 0,83 ± 0,06 [valores normales ≤0,60]) (aire ambiente). Tras respirar oxígeno al 100%, el shunt se duplicó sin cambios acompañantes en la dispersión de la perfusión pulmonar (Log SDQ), todo ello sugestivo del desarrollo de atelectasias de reabsorción sin reversión de la vasoconstricción pulmonar hipóxica. Después de la CB, tanto el peso corporal (IMC, 31 ± 1 kg/m2) como las alteracions del intercambio gaseoso pulmonar se redujeron significativamente. Conclusiones: La obesidad mórbida se asocia con la presencia de shunt intrapulmonar discreto asociado a un desequilibro leve-moderado de las relaciones VA/Q. Estas anomalies se reducen tras CB. Segundo artículo (Second Manuscript). Efecto de los cambios posturales sobre las anomalías del intercambio gaseoso pulmonar en la obesidad grave, antes y después de cirugía bariátrica Introducción: En este trabajo se planteó la hipótesis de que las alteraciones del intercambio gaseoso pulmonar empeorarían en posición supina en la obesidad grave, hallazgo que debería mejorar tras cirugía bariátrica (CB). Métodos: Se investigó el intercambio gaseoso pulmonar (aire ambiente) en los dos grupos de mujeres, obesas graves y peso normal, en posición sentada y supina, antes y después de la CB. Resultados: No se observaron cambios gasométricos posturales en el grupo control. Mientras que todas las mujeres obesas tenían valores de PaO2, SaO2 y AaPO2 más alterados que las controles (p<0,05, respectivamente) en posición sentada, no se observaron cambios en supino. El mismo comportamiento gasométrico se observó en las mujeres obesas normoxémicas (PaO2≥80 mmHg). Por contra, la oxigenación arterial mejoró (AaPO2, –3,4 ± 1,4 mmHg; SaO2, +1,5 ± 0,6 %; pH, +0,01 ± 0,01) y el gasto cardiaco aumentó (+0,4 ± 0,2 L·min-1) (p<0,05, respectivamente) en supino en las 13 obesas hipoxémicas (PaO2<80 mmHg). Tras CB , la PaO2 (de 75,5 ± 2,4 a 89,4 ± 2,4 mmHg) y el AaPO2 (de 27,0 ± 2,0 a 15,4 ± 2,1 mmHg) (p<0,05, respectivamente) y en general el conjunto del intercambio gaseoso mejoraron en la población obesa en posición sentada, si bien la gasometría arterial (PaO2, –4,6 ± 1,7 mmHg; AaPO2, +4,2 ± 1,6 mmHg; p<0,05, respectivamente) empeoró en supino. Conclusiones: Antes de CB, la gasometría arterial no varió con los cambios posturales en las mujeres obesas normoxémicas e incluso mejoró en las hipoxémicas en supino. Tras una CB exitosa en todos los casos, el intercambio gaseoso pulmonar mejoró en posición sentada si bien la gasometría arterial empeoró en supino. El interés clínico de estos hallazgos radica en la ausencia de un deterioro del intercambio gaseoso en posición supina, lo que puede conllevar connotaciones prácticas en medicina intensiva y anestesiología. Tercer artículo (Third Manuscript). Aumento del volumen de tejido pulmonar en la obesidad grave y su reducción tras cirugía bariátrica. Introducción: En este tercer estudio, se empleó la tomografía computarizada (TC) toràcica para valorar si la cirugía bariátrica (CB) es capaz de provocar cambios estructurales a nivel pulmonar, para centrarnos en el análisis del volumen de tejido pulmonar (Vtiss) y el área de corte de los pequeños vasos pulmonares. Nuestra hipótesis fue que estos parámetros podrían correlacionarse con los cambios funcionales pulmonares descritos previamente. Métodos: Se cuantificaron mediante TC los volúmenes pulmonares, incluido el volumen de tejido pulmonar (Vtiss) y el área de los vasos pulmonares, en un subgrupo de 12 mujeres obesas mórbidas, antes y después de CB, así como en las 8 mujeres del grupo control ya referidas en los dos artículos previos. Resultados: Los valores de Vtiss estaban aumentados en las mujeres obesas antes de CB, en comparación con el grupo control, y se redujeron (en un 8%) sistemáticamente un año después. No se observaron cambios en el resto de volúmenes pulmonares o en áreas vasculares. No se observó ninguna asociación entre los cambios inducidos por la CB en las áreas vasculares pulmonares ni en el Vtiss. Conclusiones: El volumen de tejido pulmonar (Vtiss) está aumentado en las personas+ obesas graves antes de CB, en comparación con el de mujeres de peso normal y se reduce de forma sistemática tras CB. Estos efectos sobre el Vtiss no se relacionan con cambios vasculares pulmonares, pero podrían estar influidos con el aumento de agua pulmonar extravascular inducido por la inflamación sistémica y/o la hipertrofia del tejido adiposo perivascular subyacentes.

The phase behaviour and the formation/gas exchange kinetics of methane hydrates have been studied at elevated pressures and low temperatures, conditions under which naturally occurring hydrates exist or synthetic gas hydrates are formed during exploration operations and transportations. To this end, experimental measurements of hydrate phase equilibria for the binary methane and water mixture were made in mesoporous and macroporous silica, a stirred slurry reactor was used to study hydrate formation kinetics under various driving forces and water-based media, and a new Raman imaging technique was devised to study the exchange kinetics of methane hydrates with carbon dioxide under reservoir conditions. The formation kinetics of methane hydrates were measured using a high-pressure low-temperature autoclave system with a special focus on (a) the physical state of the water phase from which hydrate is formed and (b) the effect of available gas-water interfacial area for mass transfer and reaction during gas hydrate formation. The initial formation rate of methane hydrates in an agitated binary methane and water system was shown to have a universal exponential dependence on the driving chemical potential difference at temperatures between 276.5 K and 283.5 K and pressures between 5 MPa and 10.5 MPa. The hydrate formation rate was also studied for a methane-micronised ice particle system and a methane-‘Dry Water’ system consisting of a nanoparticle-stabilised high internal volume ‘dry’ water emulsion. The results indicated that the large differences in reactive surface area and gas diffusion rates for these three different pre-cursor systems resulted in pronounced effects on the initial formation rate of methane hydrates. Physical mechanisms were proposed to rationalize the observed behavior; it is anticipated that the results could be used to predict the hydrate formation rate for different combinations of water precursor state, reaction geometry and agitation conditions. As a model for natural gas hydrates formed in porous mineral sediments, the phase equilibrium behaviour of synthetic methane hydrates were measured, using high-pressure differential scanning micro-calorimetry, in mesoporous and macroporous silica that had controlled pore sizes ranging from 8.5 nm to 195.7 nm. The effect of pore surface chemistry was also qualified by studying the phase equilibrium in surface functionalised porous media. An oscillating dynamic method was used to essentially fully convert the ice/water pre-cursor into hydrates followed by slow heating in the micro-DSC to determine the decomposition conditions of methane hydrates in the porous silica over a wider range of pressures and pore sizes than previous studies. Significant shifts in dissociation temperatures with pore size were observed and rationalised using a modified Gibbs-Thomson equation. The experimental data up to 50 MPa indicated that the confinement effect in porous media showed a significant pressure dependency, most likely due to the interfacial energy. The effects of interfacial energy on the phase equilibria were investigated quantitatively by grafting different chemical groups onto the silica surface. The dissociation temperatures of methane hydrates in hydrophilic and hydrophobically-modified silica pores were significantly different; hydrates in strongly hydrophobic porous silica tended to behave like bulk methane hydrates regarding the melting temperature, with no significant effect of confinement. The measured phase equilibria, interfacial energy and enthalpy data can be used as parameters in gas hydrate simulation models. For the Raman studies, a high-pressure low-temperature optical reactor was designed, commissioned and applied. The cell accommodated samples to be analyzed over a temperature range of 288 K to 353 K and at pressures up to 50 MPa. Fast temperature response (up to 5 K/s), and stable temperature control (± 20 mK) were facilitated by using four Peltier elements. A large optical path allowed the acquisition of in-situ 3D Raman images to reveal the molecular structure and (CH4-CO2) exchange kinetics of gas hydrates in both single crystal and polycrystalline methane hydrates. An oscillating dynamic method was used to form polycrystalline hydrates at pressures up to 15 MPa and by contrast single crystal hydrates were formed under a small thermal driving force (around 3 K) at pressures up to 14 MPa. The polycrystalline hydrates exhibited a much faster CH4-CO2 exchange rate compared to the single crystal hydrates; defects and crystal imperfections also had a significant effect on this rate. The morphology of methane hydrates hence plays a critical role in the exchange process, which helps to explain the discrepancy of exchange rates for similar conditions reported in the literature. These time-resolved Raman results indicated a diffusion-controlled guest molecule substitution process. The Raman spectra were also used to quantify the exchange kinetics and the cage occupancy of the methane hydrates. This work has provided new insight and data for the rate of methane hydrate formation, their phase behavior under confinement and rates of gas exchange as a function of hydrate physical state under pressure and temperature conditions relevant to natural gas hydrate systems and their potential exploitation. The research represents a significant step forward in our fundamental understanding of the way gas hydrates are formed and behave. The collected data and derived parameters offer valuable inputs to process simulators concerning field exploration/production and potential uses in gas transportation and separation. Areas in which the research could be usefully extended have been identified.

Kyoto University (京都大学)
0048
新制・課程博士
博士(農学)
甲第10254号
農博第1326号
新制||農||866(附属図書館)
学位論文||H15||N3775(農学部図書室)
UT51-2003-H675
京都大学大学院農学研究科地域環境科学専攻
(主査)教授 谷 誠, 教授 櫻谷 哲夫, 教授 森本 幸裕
学位規則第4条第1項該当

Thesis (Ph. D.)--Joint Program in Marine Chemistry and Geochemistry, Massachusetts Institute of Technology/Woods Hole Oceanographic Institution, 1998.
Includes bibliographical references (p. 251-266).
by Eda Maria Hood.
Ph.D.

The purpose of this investigation was to examine the change in pulmonary ventilation (V_E), ventilatory equivalent of oxygen (VE_O_2) and lactic acid (LA) in relation to oxygen uptake (V_O_2) as predictors of the lactate threshold (LT). Eight healthy male (21.9 ± 3.0 years) subjects conducted three incremental-load tests. In each test the initial work rate consisted of 4 minutes of unloaded pedaling ("0" load) followed by incremental-load work of 360 Kgm • min^-1 at 60 rpm for trial I and trial II, while during trial III the work rate consisted of 540 Kgm • min^-1 of incremental-load work at 90 rpm. Work load was increased every third minute until the subject reached voluntary exhaustion. Blood samples from a forearm vein were collected during trial II (60 rpm) and trial III (90 rpm) and analyzed for lactic acid. In our subjects the measured (x̄ ± SD) lowest VE_O_2 for O_2 in relation to V_O_2 for trial I of 22.9 ± 1.9 occurred at a V_O_2 of 1.27 ± 0.8 L • min^-1. For trial II the VE_O_2 of 22.4 ± 1.3 occurred at a V_O_2 of 1.30 ± 0.09 L • min^-1, while for trial III a VE_O_2 of 24.4 ± 2.5 occurred at a V_O_2 of 1.84 ± 0.15 L • min^-1. The lowest VE_O_2 and onset of LA accumulation as calculated from individual exponential equations relating V_E to V_O_2 yielded V_O_2 values at 1.77 ± 0.18 L • min^-1 and 1.74 ± 0.25 L • min^-1 for trial II, and 1.83 ± 0.19 L • min^-1 and 2.02 ± 0.53 during trial III. Utilizing ln[LA]-ln V_O_2 equations, the LT occurred at a V_O_2 of 1.30 ± 0.07 L • min^-1 during trial II and 1.85 ± 0.12 L • min^-1 during trial III. It was concluded that during the 60 rpm test that the lactate threshold was best predicted by measured lowest VE_O_2 and the plot of the In[LA] to In V_O_2 relationship. The methods used in this study provide a valid and reliable estimate of the lactate threshold and support the use of measured lowest VE_O_2 , a respiratory gas exchange measure, as an indirect measure of the lactate threshold.

Blood gas exchange across synthetic membranes is primarily used in blood oxygenators for short-term (1-3 hours) cardiopulmonary bypass procedures. Long term applications (6 hours - i4 days) of membrane oxygenators include treatment of acute respiratory failure or acute liver failure. There are several types of membranes used in these devices: (1) microporous membranes which have high gas permeabilities but have problems of pore wetting if employed in long-term therapies and (2) homogeneous membranes, e.g. silicone rubber which have lower permeability characteristics but are non-wettable and (3) composite membranes which a very thin homogeneous membrane is mechanically supported by a micro porous layer.

Thesis (MSc)--University of Stellenbosch, 2005.
ENGLISH ABSTRACT: Physiological diversity in insects was investigated in terms of gas exchange patterns and metabolic rate. Since the majority of hypotheses that propose to explain the occurrence of Discontinuous Gas Exchange Cycles (DGCs) are adaptive, the possibility of adaptation was explored in two ways. First, since repeatability is one of the three prerequisites for natural selection, and rarely tested in insects, the repeatability of gas exchange characteristics and metabolic rate were tested in a Perisphaeria sp. cockroach. Four major gas exchange patterns were recognized and these patterns were found to be extremely variable within this species. However, repeatability was still generally high for the majority of the gas exchange characteristics and metabolic rate. Moreover, between individual variability generally accounted for a large proportion of the variance, supporting the repeatability findings. Therefore, both metabolic rate and gas exchange patterns might indeed be adaptive traits in this Perisphaeria sp. cockroach. Second, the distribution of the three gas exchange patterns (DGCs, cyclic and continuous) across the insect phylogeny was investigated. Data were extracted from the literature and gas exchange patterns for eight insect orders, representing mainly the endopterygotes, were measured. Using standard respirometry techniques, data for a total of ten additional orders were added, which represented both apterygote orders, six exopterygote orders and two endopterygote orders that were previously uninvestigated. In addition, four of the five adaptive hypotheses were tested by investigating the occurrence of DGCs in winged or wingless insects, subterranean and non-subterranean insects, and insects from mesic and xeric environments. Results indicate that DGC has evolved at least five times in the insects and that the cyclic gas exchange pattern is likely to be basal. No support was found for the chthonic, hybrid and oxidative damage hypotheses, while DGCs were associated with xeric environments. This analysis provides some support for the hygric hypothesis. In addition the prediction of the fractal network model for metabolic scaling which states that both intra- and interspecific scaling coefficients should be identical and equal to 0.75, was tested. Three species of polymorphic worker ants were used to determine the intraspecific scaling coefficient. Data from the literature were added to provide metabolic rate information on 42 species of the Formicidae. The interspecific scaling coefficient was determined in several ways: the traditional method (Ordinary Least Squares regression models), with the two respirometry techniques analyzed separately or in combination (e.g. open and closed system), and using phylogenetic independent contrasts with the same sets of data. Intraspecific coefficients were significantly different from 0.75. The slope of the interspecific regression obtained using Ordinary Least Squares regression models was not significantly different from 0.75. However, when phylogenetic relatedness was accounted for the slope differed significantly from 0.75. Therefore, the fractal network model was not supported by these findings, since slope values are not equal and also not statistically equivalent to 0.75. Overall, variability of both metabolic rate and gas exchange patterns in insects is higher than generally suggested by the literature. These findings provide much scope for future work.
AFRIKAANSE OPSOMMING: Hier word die fisiologiese diversiteit van insekte ondersoek in terme van hul gaswisselings patrone asook hul metaboliese tempo. Die oorgrote meerderheid van die hipoteses wat voorgestel is om die onstaan en bestaan van Diskontinue Gaswisseling in insekte te verklaar, is op ‘n evolusionêre grondslag gebaseer. Vir hierdie rede word die moontlikheid van Diskontinue Gaswisseling as ‘n aanpassing op twee maniere ondersoek. Herhaalbaarheid is een van die voorvereistes van aanpassing (in terme van evolusie) en dit is tot dusver slegs ‘n paar keer in insekte getoets is. Daarom word die herhaalbaarheid van die gaswisselings komponente, asook die metaboliese tempo hier in ‘n Perisphaeria sp. kokkerot ondersoek. Vier hoof gaswisselings patrone is geidentifiseer en die bevinding was dat die patrone geweldig kan varieer binne hierdie spesie. Ten spyte hiervan was die herhaalbaarheid steeds hoog vir die oorgrote meerderheid van die gaswisselings komponente asook vir die metaboliese tempo. Verder het die variasie tussen individue tot ‘n groot proporsie van die totale variasie bygedra, wat die betekenisvolheid van die hoë herhaalbaarheid beklemtoon. Dus, beide metaboliese tempo sowel as gaswisselings komponente kan moontlik as ‘n aanpassing beskou word in hierdie kokkerot. Tweedens, die verspreiding van die drie gaswisselings patrone (Diskontinue Gaswisseling, siklies en kontinu) in die insekte is ondersoek. Gaswisselings patrone vir agt van die dertig insek ordes is vanuit die literatuur verkry, alhoewel dit meestal verteenwoordigend van die Endopterygota is. Data vir tien additionele ordes wat nog nooit voorheen ondersoek is nie is bygevoeg, insluitende beide die ordes van Apterygota en ses ordes van die Exopterygota, asook twee ordes van die Endopterygota. Verder is vier van die vyf hipoteses met betrekking tot aanpassing ondersoek deur die teenwoordigheid van Diskontinue Gaswisseling in gevleuelde en ongevleuelde insekte, ondergrondse en bogrondse insekte, asook insekte van gematigde en droeë omgewings te ondersoek. Resultate dui aan dat Diskontinue Gaswisseling ten minste vyf keer onafhanklik in insekte onstaan het en dat die sikliese patroon heel moontlik basaal is. Die resultate bied geen ondersteuning vir die hipoteses wat gegrond is op gaswisseling in ondergrondse omgewing of oksidasie beskerming nie. Daar is wel ondersteuning vir die hipotese aangaande die rol van water verlies in die onstaan en onderhoud van Diskontinue Gaswisseling. Additioneel is daar ondersoek ingestel na die verwagting wat deur die fraktale netwerk model vir metaboliese glyskale gestel word, wat lui dat beide die binne- sowel as tussen-spesies koëffisiënte identies aan mekaar en gelyk aan 0.75 sal wees. Drie polimorfiese mier spesies is gebruik om die binne-spesies koëffisiënt te bepaal. Data vanuit die literatuur is hier bygevoeg en sodoende was informasie vir 42 mier spesies van die Formicidae beskikbaar. Verskillende metodes is gebruik om die tussen-spesies koëffisiënt te bepaal: die tradisionele metode (sg. “OLS”-regressie), met die twee tegnieke om metaboliese tempo te bepaal (bv. oop en geslote sisteem metodes) apart asook saam, en deur gebruik te maak van filogeneties onafhanklike vergelykings vir dieselfde datastelle. Die binne-spesies koëffisiënte was almal betekenisvol verskillend van 0.75. Die tussen-spesies regressie waar gebruik gemaak is van ‘n “OLS”-regressie model was nie betekensivol verskillend van 0.75 nie. Met filogenetiese verwantskappe egter in ag geneem, het die koëffisiënt wel betekenisvol verskil van 0.75. Dus word die fraktale netwerk model nie ondersteun deur hierdie studie nie, aangesien die koëffisiënte nie indenties aan mekaar is nie, en ook statisties verskil van 0.75. In die algemeen is die variasie in metaboliese tempo sowel as gaswisselings patrone aansienlik hoër as wat afgelei kan word uit die literatuur. Hierdie bevindinge stel ‘n basis vir heelwat verdere werk in die toekoms.

Carbon plays a major role in physical and biogeochemical processes in the atmosphere, the biosphere, and the ocean. CO2 and CH4 are two of the most common carbon-containing compounds in the atmosphere, also recognized as major greenhouse gases. The exchange of CO2 and CH4 between the ocean and the atmosphere is an essential part of the global carbon cycle. The exchange is controlled by the air–sea concentration gradient and by the efficiency of the transfer processes. The lack of knowledge about the forcing mechanisms affecting the exchange of these climate-relevant gases is a major source of uncertainty in the estimation of the global oceanic contributions. Quantifying and understanding the air–sea exchange processes is essential to constrain the estimates and to improve our knowledge about the current and future climate. In this thesis, the mechanisms controlling the air–sea gas exchange in the Baltic Sea are investigated. The viability of micrometeorological techniques for CH4 monitoring in a coastal environment is evaluated. One year of semi-continuous measurements of air–sea CH4 fluxes using eddy covariance measurements suggests that the method is useful for CH4 flux estimations in marine environments. The measurements allow long-term monitoring at high frequency rates, thus, capturing the temporal variability of the flux. The region off Gotland is a net source of CH4, with both the air–sea concentration gradient and the wind as controlling mechanisms. A sensitivity analysis of the gas transfer velocity is performed to evaluate the effect of the forcing mechanisms controlling the air–sea CO2 exchange in the Baltic Sea. This analysis shows that the spatio-temporal variability of CO2 fluxes is strongly modulated by water-side convection, precipitation, and surfactants. The effect of these factors is relevant both at regional and global scales, as they are not included in the current budget estimates.

An orbital dependent local spin density-functional (LSD) scheme with a generated exchange, the LSD GX scheme, has been developed based on the correct normalization conditions of an electron gas. This scheme contains no adjustable parameters; the B$ sb1$, B$ sb2$ and $ alpha sp lim$ are constant for all atoms once the shape of the Fermi hole is chosen. These parameters are rigorously calculated using an unspecified Fermi hole correlation factor and they give an exchange density which reduces exactly to the homogeneous free electron gas one at the high electron density limit.
The LSD GX exchange density is corrected for self-interaction (SI) by splitting the total Fermi hole correlation factor into pure-exchange and self-interaction holes.
These new LSD and SI corrected schemes are compared to each other. They also compare very well theoretically and numerically (total energies and eigenvalues) with other local schemes current in the literature.
New equations for the IP and electronegativities of the atoms in these local schemes are derived which give good results.

This thesis deals with the estimation of plant-atmosphere trace gas exchange and isotopic discrimination from atmospheric concentration measurements. Two space scales were investigated: canopy and regional. The canopy-scale study combined a Lagrangian model of turbulent dispersal with ecophysiological principles to infer vertical profiles of fluxes of CO2, H2O and heat as well as carbon and oxygen isotope discrimination during CO2 assimilation, from concentration measurements within a forest. The regional-scale model used a convective boundary layer budget approach to infer average regional isotopic discrimination and fluxes of CO2 and sensible and latent heat from the evolution during the day of boundary layer height and mean concentrations of CO2 and H2O, temperature and carbon and oxygen isotope composition of CO2. For the canopy study, concentrations of five scalar quantities, CO2, 13CO2, C18O16O, H2O and temperature, were measured at up to nine heights within and above a mixed fir and spruce forest in central Siberia over several days just after snow melt in May 2000. Eddy covariance measurements of CO2, H2O and heat fluxes were made above the canopy over the same period, providing independent verification of the model flux estimates. Photosynthesis, transpiration, heat exchange and isotope discrimination during CO2 assimilation were modelled for sun and shade leaves throughout the canopy through a combination of inversion of the concentration data and principles of biochemistry, plant physiology and energy balance. In contrast to the more usual inverse modelling concept where fluxes are inferred directly from concentrations, in this study the inversion was used to predict unknown parameters within a process-based model of leaf gas and energy exchange. Parameters relating to photosynthetic capacity, stomatal conductance, radiation penetration and turbulence structure were optimised by the inversion to provide the best fit of modelled to measured concentration profiles of the five scalars. Model results showed that carbon isotope discrimination, stomatal conductance and intercellular CO2 concentration were depressed due to the low temperatures experienced during snow melt, oxygen isotope discrimination was positive and consistent with other estimates, radiation penetrated further than simple theoretical predictions because of leaf clumping and penumbra, the turbulence coherence was lower than expected and stability effects were important in the morning and evening. For the regional study, five flights were undertaken over two days in and above the convective boundary layer above a heterogeneous pine forest and bog region in central Siberia. Vertical profiles of CO2 and H2O concentrations, temperature and pressure were obtained during each flight. Air flask samples were taken at various heights for carbon and oxygen isotopic analysis of CO2. Two budget methods were used to estimate regional surface fluxes of CO2 and plant isotopic discrimination against 13CO2 and C18O16O, with the first method also used to infer regional sensible and latent heat fluxes. Flux estimates were compared to ground-based eddy covariance measurements. Model results showed that afternoon estimates for carbon and oxygen isotope discrimination were close to those expected from source water isotopic measurements and theory of isotope discrimination. Estimates for oxygen isotope discrimination for the morning period were considerably different and could be explained by contrasting influences of the two different ecosystem types and non-steady state evaporative enrichment of leaf water.

We tested two interlinked hypotheses concerning forest responses to hydraulic stress using data collected at a through-fall exclusion (artificial droughting) experiment at Caxiuana in Eastern Amazonia. First, we tested the ‘isohydric’ hypothesis, that stomatal conductance, in water stressed conditions, operates to maintain leaf water potential above a certain critical threshold limit. We used the soil-plant-atmosphere (SPA) model to predict the expected ecophysiological behaviour of the trees, and tested these predictions against intensive diurnal cycle measurements of leaf water potential, stomatal conductance, sap flow and stem water potential. The data and the model predictions were largely consistent, indicating that the isohydric stomatal control may be the prevailing mechanism controlling water use of rain forest trees in drought stressed conditions. The model was parameterised using independent measurements of ecosystem properties and as such required no fitted parameters. The implication of this is that the response of rain forest ecosystems to drought may be predicted using soil, rooting and vegetation properties. The SPA model is both computationally and data requirement intensive. We assimilated the model and produced a set of empirical equations which replicate the daily modelled gas exchange predictions from daily model inputs. We extrapolated this model 100 years into the future using the latest Amazonian climate predictions and found that after -50 years, a threshold was reached when all the rainfall falling on the plot was evaporated (by interception, soil surface evaporation or evapotranspiration) and none was drained away into stream flow. The response of the forest in the first 50 years was modulated strongly by soil hydraulic properties and rooting depth, and we conclude that increased field measurements of these properties are necessary if the response of Amazonian forests to anticipated drying is to be accurately predicted.

The objectives of this research were to study the gas transport properties of proton exchange membranes (PEM), namely disulfonated poly(arylene ether sulfone) (BPSH-35), post sulfonated diels-alder poly(phenylene) (SDAPP), and poly(perfluoro sulfonic acid) (Nafion). The O2 gas permeabilities were found to be lower in BPSH and SDAPP as compared to poly(perfluoro sulfonic acid) because of difference in Tg (TgBSPH= 250 oC, TgSDAPP= 330 oC versus TgNafion=150 oC). Higher Tg polymers have a more rigid, inflexible polymer segments causing a reduction in gas permeability. In comparison to SDAPP, BPSH has a lower O2 gas permeability because of the bulky side groups in the SDAPP backbone. O2 sorption measurements were carried out both under non-humidified and humidified conditions as a function of relative humidity and temperature at a normal PEM operating pressure of 1 atm. Under non-humidified conditions, BPSH, SDAPP, and Nafion 112 exhibited Henryâ s Law sorption, consistent with dilute dissolution of O2 into the polymer matrix. The enthalpies of sorption were calculated to determine the interaction of O2 with each membrane. The sorption enthalpies in BPSH and SDAPP increased with increasing pressure indicating the formation of more O2-O2 interactions. The enthalpies in Nafion 112 were relatively constant with increasing pressure. In the presence of moisture, the sorption behavior changed from Henryâ s Law to Type IV sorption behavior, which is common in hydrophilic polymers. The SDAPP membrane was found to have the highest percent wet O2 mass uptake because of a higher number of sulfonic acid groups interacting with the water/O2 system. Finally the O2 sorption for various porous catalyst powders, consisting of platinum supported on carbon was measured in the non-humidified and humidified state. The catalysts were found to have Knudsen diffusion in the non-humidified state with 20 wt% Pt-C having the largest O2 sorption. In the humidified state, the highest O2 mass uptake was achieved with 40 wt% Pt-C. These results are explained in terms of the trade-off between catalyst dispersion and catalyst size. Furthermore, O2 sorption measurements were utilized for membrane electrode assemblies containing 40 wt% Pt-C and hot pressed at 210 oC for BPSH-35 (25 and 80K) and Nafion 112 membranes. The same sorption behavior occurred in the MEAs as in the neat membrane, but at a lower capacity. This is because the electrode introduces a more tortuous path to the gas molecules permeating across the membrane.
Ph. D.

Total charge exchange and excitation cross-sections are presented for collisions between He(^2+) ions and helium atoms, the laboratory frame collision energy being in the range 16-800keV. Cross-sections from the helium ground state and the He(ls2s(^1)S) and He(ls2s(^3)S) metastable states are calculated. The calculations were performed using the semiclassical impact parameter model where wave-functions are expressed as an expansion of two-electron atomic basis states. Transfer channels included plane-wave translation factors. The transition He(^+)(n = 4) → He(^+)(n = 3) results in the emission of visible light (468.5nm) which is observed in the JET fusion device. Helium beam injection into the JET device introduces some of the atoms in initially excited states. Even a small fraction of metastable helium effects the observed 468.5nm spectrum significantly because of the very large charge exchange cross-sections. Accurate charge exchange cross-sections to the He(^+)(n = 4) states are required to analyse the spectroscopic data used in the diagnosis of the plasma. The cross-sections produced are therefore also presented in a form suitable for direct inclusion into the plasma analysis database. Where possible the current results are compared to previous calculations. Total charge exchange cross-sections from the He(ls2s(^1)S) state are in good agreement with the previous one-electron calculation. Charge exchange cross-sections from the triplet state are found to differ with those from the singlet. The results are discussed in the context of their usefulness in the diagnosis of fusion plasmas. Suggestions for further work are made.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 26, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Peter Pfeifer. Vita. Includes bibliographical references.