Browsing by Subject "Oxygen"
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Item Classical and quasiclassical trajectory calculations of ozone isotopomer formation in atomic oxygen and molecular oxygen collisions(Texas Tech University, 2002-08) Baker, Thomas A.In the present study, the ozone formation rate is determined using the calculated O3 survival time (ST) distribution explicitly rather than an average lifetime. This approach has the advantage of not constraining the PM dependence of ke6 by any assumptions about the nature of the ST distribution. The present chapter will be confined principally to modeling the absolute rate of ozone formation over the broad range of temperature (T = 130 - 370 K) and density (PM = 10^18 - 10^22 cm^-1 for which experimental information is available[10, 22, 23, 29, 32, 1].Item Measurement of Cerebral Metabolism and Vascular Function with Magnetic Resonance Imaging(2012-08-13) Xu, Feng; Lu, HanzhangThe brain relies on oxidative metabolism to function properly. Cerebral metabolic rate of oxygen (CMRO2) is thus an important marker for brain health. Existing techniques for quantification of CMRO2 with positron emission tomography (PET) or magnetic resonance imaging (MRI) involve special equipment and/or exogenous agents, and may not be suitable for routine clinical studies. To fill this gap, I developed a noninvasive method for quantifying whole brain CMRO2. This method uses the Fick principle of arterio-venous difference for the calculation of CMRO2.and employs phase-contrast MRI for quantitative blood flow measurement and T2-relaxation-under-spin-tagging (TRUST) MRI for venous oxygenation estimation. During this thesis, I conducted several technical development studies. I first optimized TRUST and phase-contrast MR imaging parameters and demonstrated the ability to measure CMRO2 using completely non-invasive procedures. I further performed calibration and validations studies to show that blood oxygenation measured with TRUST reveals an excellent agreement with the gold standard Pulse Oximetry method. A final technical study was to improve the speed and reliability of TRUST MRI by shortening the scan duration by 60% while reducing the measuring error by half. I have also applied this novel CMRO2 method in better understanding brain physiology in younger and older adults. I studied the effect of CO2 inhalation (also known as hypercapnia) on brain metabolism. A reduced CMRO2 was observed and this effect was further supported by findings using functional connectivity MRI and electroencephalography techniques. I also investigated the effect of O2 modulation (hypoxia and hyperoxia) on brain metabolism and showed a dose dependent effect of O2 concentration on brain activity. Finally, I used this method to assess aged-related differences in brain metabolism and blood supply, and demonstrated a paradoxically higher metabolic rate in older adults, which may be associated with lower neural efficiency in elderly individuals.Item Oxygen Deficient Metabolism in Organs: A Link to Combustion Science(2014-12-10) Miller, Jason MathewIn an attempt to better understand and model transport of oxygen, O2, from capillaries to living cells in surrounding tissue, the group combustion (O2 deficient) concept from the field of combustion science in engineering is applied to the biological field of microvascular O2 transport from capillaries to cells immersed in interstitial fluid (IF). The conventional Krogh model represents typical biological models, considering tissue cylinder with uniform oxygen source/sink term (US) (m''', g/s/cm^3) and O2 transport from capillary on axis (COA) towards the surface; engineering models consider cylinders with O2 supplied from the surface of cylinder (COS); in addition, they present i) transport (diffusion) and ii) kinetics limited sink rates and profiles for O2. Diffusion limitation causes m''' to be proportional to local O2 concentration. Thus, the present work modifies COS engineering models for COA cases and considers only diffusion limited transport of O2 to metabolic cells from IF. O2 profiles and resulting specific metabolic rates, SMRs (W/g), are generated for four models: I) COA with oxygen dependent consumption source term (O2) (COA-O2), II) COA-US, III) COS-O2, and IV) COS-US. In order to validate the current approach, the model results are verified with the following different types of experimental data: A) If SMRs (mq W/g) are given by the allometric law, kbmk^kq=am for organ k, then COS models under limiting conditions suggest -1/3Item Oxygen scavenging styrene-butadiene-styrene block copolymer films for barrier applications(2013-08) Tung, Kevin; Paul, Donald R.; Freeman, B. D. (Benny D.)This dissertation discusses the oxidation behavior of reactive membranes that were produced by solution casting and by melt extrusion. These films, containing styrene-butadiene-styrene (SBS) block copolymer that undergoes catalytic oxidation, are of potential use as an oxygen scavenging polymer (OSP) for barrier applications. A thin film kinetic model was developed to ascertain reaction parameters that were used to describe thick film oxidation behavior. Ultimately complex structures containing these scavengers need to be produced via melt-extrusion. Therefore, processing conditions were established to ensure that melt-processed films have the same oxidation kinetics and capacity as those prepared by solution casting. Blends containing a non-reactive styrene phase and an oxygen-scavenging SBS phase were extruded and, by uptake and permeation experiments, their oxidation behaviors were monitored. The flux behavior and time lag extension as a function of oxygen pressure, film thickness, SBS scavenger and photoinitator contents were measured and compared to the theoretical model. The permeation behavior of the reactive blend films containing SBS showed that time lags can be extended via an oxidative mechanism and barrier properties be improved compared to traditional packaging membrane of native polystyrene.Item Photodetachment as a discharge control mechanism in gases containing oxygen(Texas Tech University, 1985-05) Thurmond, Leo ErasmusInterest in high voltage switches for pulsed power applications has increased significantly in the last several years. Inductive energy storage has space and weight advantages over capacitive energy storage, but requires the use of a high power opening switch. Opening switch technology has only recently started to be developed, and several concepts for opening switches are being studied. One of these concepts is the diffuse discharge switch, which shows several advantages over other types of opening switches. One major advantage of the diffuse discharge switch is that it may be controlled externally by an electron beam or by optical means. There are several processes possible for optical control of a diffuse discharge, one of which is photodetachment. In this paper, three experiments are presented which study the possibility of using photodetachment as a discharge control mechanism in gases containing 02 are presented. The first experiment shows the effect of photodetachment outside the discharge and the dependence of the effect on laser energy flux density. The second experiment demonstrates the feedback effect of photodetachment on a glow discharge. Operating conditions for the largest effect are presented. The last experiment simulates the conditions in a high power switching device, and the preliminary results of this study are given.Item The Role of Particulate Matter in the Development of Hypoxia on the Texas-Louisiana Shelf(2013-07-31) Cochran, Emma MaryIn the northern Gulf of Mexico, hypoxia occurs annually during the summer on the Texas-Louisiana shelf. This study examines the distribution of particulate and dissolved components relative to hydrography, to better understand the processes controlling the development of hypoxia. Particulate matter on the Texas-Louisiana Shelf has three major sources ? river plumes, primary production, and resuspended sediments. The sources and processes controlling distribution and transport of particles are investigated using optical proxies (backscattering, chlorophyll fluorescence, Colored Dissolved Organic Matter fluorescence (CDOM)), temperature, salinity, dissolved oxygen (DO), and in-situ sampling during June and August 2011 cruises of the Mechanisms Controlling Hypoxia program (hypoxia.tamu.edu). Discrete samples of particulate matter (PM) and particulate organic carbon (POC) concentration were obtained for analysis and calibration of optical instruments interfaced with a profiling CTD, a towed undulating CTD (Acrobat), and the ship?s flow-through system along the shelf from south of Galveston, Texas, to east of the Mississippi delta. The results of this study support a previously hypothesized concept of three primary areas of organic and inorganic particle composition and processes that dominate those areas ? river-dominated water, highly productive surface waters, and clear, nutrient-poor low-productivity surface waters. The distribution and bulk composition of particulate matter in the northern Gulf of Mexico, plus the distribution of chlorophyll fluorescence and CDOM suggest that subpycnocline primary production plays a role in determining oxygen concentration in subpycnocline waters away from the river-dominated water.