Browsing by Subject "Spectroscopy"
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Item A co-axially configured submillimeter spectrometer and investigations of hydrogen bound molecular complexes(2009-05-15) McElmurry, Blake AnthonyThe development of a co-axially configured submillimeter spectrometer is reported. The spectrometer has been constructed to observe molecular complexes that exhibit non-covalent interactions with energies much less than that of a traditional covalent bond. The structure of molecular complexes such as those formed between a rare gas and a hydrogen halide, Rg:HX where Rg is a rare gas (Rg=Ne, Ar and Kr) and HX (X=F, Cl, Br and I) can be determined directly and accurately. The center of mass interaction distance, RCM, as well as the angle of the hydrogen halide is determined, along with direct evaluation of the intermolecular vibrations as well as accurate isomerization energies between the hydrogen bound and van der Waals forms. The accuracy of the frequency determination of rovibrational transitions using the submillimeter spectrometer is also evaluated by direct comparison with the state-of-theart pulsed nozzle Fourier transform microwave spectrometer, and this accuracy is estimated to be less than 1 kHz at 300 GHz. The tunneling or geared bending vibration of a dimer of hydrogen bromide or hydrogen iodide has been investigated. The selection rules, nuclear statistics and intensity alternation for transitions observed in these dimmers, which is a consequence of interchanging two identical nuclei in the low frequency geared bending vibration of the molecular complex, are reported. Furthermore, the rotation and quadrupole coupling constants are used to determine a vibrationally averaged structure of the complex. The energy of the low frequency bending vibration can then be compared with ab initio based potential energy surfaces. A study of the multiple isomeric forms of the molecular complex OC:HI is also presented. Multiple isotopic substitutions are used to determine the relevant ground state structures and data reported evidence for an anomalous isotope effect supporting a ground state isotopic isomerization effect. All spectroscopic data that has been reported here has been additionally used to subsequently model and generate vibrationally complete morphed potential energy surfaces that are capable or reproducing the experimentally observed data. The utility of this procedure is evaluated on a predicative basis and comparisons made with newly observed data.Item Building high-energy density lithium-sulfur batteries(2015-08) Zu, Chenxi; Manthiram, Arumugam; Goodenough, John B.; Ferreira, Paulo J.; Yu, Guihua; Hwang, Gyeong S.The increasing consumption of limited fossil fuel resources is exerting much pressure on the modern society. Renewable energies, such as solar and wind, are attracting much attention; however, efficient use of these sustainable energies requires economical and efficient electrical energy storage (EES) systems. Among the various possibilities of EES systems, lithium-sulfur (Li-S) batteries are attracting much attention due to their high energy density and low cost. However, the practicality of Li-S technology is hindered by technical obstacles, such as low sulfur utilization and fast capacity decay, caused by the insulating sulfur and the shuttling of corrosive polysulfides. Much progress has been made in recent years towards enhancing the performance of Li-S batteries, but further understanding on the Li-S battery chemistry is needed to realize its practical use. In this dissertation, three critical aspects of Li-S batteries are discussed. First, the strategy of surface modification is used to control the deposition of sulfur and its reduction products. An interlayer configuration using surface-treated carbon paper is analyzed in the beginning, followed by the introduction of a novel surface-hydroxylated graphene-sulfur nanocomposite cathode with superior high-rate performance. Moreover, the hydroylated graphene-sulfur composite cathode is coupled with a fluorinated ether electrolyte that suppresses polysulfide shuttling. The mechanisms of suppressed polysulfide shuttling and lithium-anode surface chemistry are investigated. Second, Li/polysulfide batteries and protection of lithium-metal anode are presented. Various cathode conductive matrices in Li/polysulfide batteries are compared regarding their polysulfide confinement capability and electrochemical performances. It is further identified that the lithium-anode corrosion is the main obstacle to increase the sulfur content in the cathode. Based on the characterization data, a novel anode-protection mechanism is proposed, which may solve the problem of electrode degradation in the case of high sulfur contents at high rates. Third, the development of an alternative, prelithiated sulfur cathode Li2S is presented. Li2S cathode coupled with a lithium-free anode can avoid the use of unstable lithium-metal anode. However, the insulating nature of Li2S and the lack of flexibility to form nanoparticles prevent its practical applications. To solve these problems, a low-cost activation of Li2S bulk particles is presented.Item Carrier envelope phase stabilization of a femtosecond laser and iodine spectroscopy(Texas A&M University, 2006-10-30) Zhu, FengThe carrier envelope (CE) phase of a femtosecond laser was stabilized. The laser produces an ultra stable comb of frequency spanning the visible region and basically is an optical frequency synthesizer and ready for the frequency domain applications. In this context, the CW stability of the Ti:sapphire laser is discussed to provide a procedure for the femtosecond laser adjustments. In addition, the pulse trains emitted by the femtosecond laser are described analytically to provide a theoretical basis for carrier envelope phase stabilization. An f to 2f interferometer was used to detect the carrier envelope offset frequency, and a fast photo diode was employed to measure the repetition rate. Two similar designed phase lock loops are used to stabilize both the carrier envelope offset frequency and the repetition rate to the respective reference frequencies. The stability reaches 100mHz for the carrier envelope offset frequency and 10mHz for the repetition rate for a period of up to an hour. Doppler free iodine saturation spectroscopy was set up to provide a precise frequency reference to which a CW dye laser can be locked on. The near future goal is to accurately measure this frequency stabilized dye laser with the optical frequency synthesizer.Item Clinical, non-invasive in vivo diagnosis of skin cancer using multimodal Spectral Diagnosis(2013-12) Lim, Liang; Tunnell, James W.The goal of this thesis is to study the potential of optical spectroscopy as a clinical diagnostic tool for melanoma and nonmelanoma skin cancer. Skin cancer is the most common cancer in the United States. Like most cancers, early diagnosis and treatment improves patient prognosis for both melanoma and nonmelanoma skin cancer. However, current “gold standard” for diagnosis is invasive, costly and time-consuming. A diagnostic procedure consists of a clinical examination of the suspicious lesion, followed by biopsy and histopathology, with an additional turnaround time of approximately one week. There is a need for an accurate, objective, noninvasive, and faster method to aid physician in diagnosing cancerous lesions, increasing diagnosis accuracy while preventing unnecessary biopsies. We propose Spectral Diagnosis, a system capable of noninvasive in vivo spectroscopic examination of human skin. The research objectives are: (1) Probe pressure effects on in vivo spectroscopy measurements of human skin, (2) Clinical trial of Spectral Diagnosis, (3) Design, construction, and characterization of a confocal Raman microspectroscope. Spectral Diagnosis utilizes an optical fiber probe that transmits and collects optical spectra in contact with the suspected lesion. We identified short term and light probe pressure effects to be minimal on diagnostic parameters, and should not negatively influence diagnostic performance. We conducted a clinical trial at the University of Texas MD Anderson Cancer Center, and our results show that principal components from three spectroscopy modalities (diffuse reflectance spectroscopy, laser induced fluorescence spectroscopy, and Raman spectroscopy) provide excellent melanoma and nonmelanoma skin cancer diagnosis. We also constructed and characterized a Raman microspectroscope, with the goal of developing a physiological-based fitting model to better understand the analysis of in vivo Raman spectroscopy data from human skin tissue.Item Creating and measuring white dwarf photospheres in a terrestrial laboratory(2014-08) Falcon, Ross Edward; Winget, Donald Earl, 1955-As the ultimate fate of nearly all stars, including our Sun, white dwarfs (WDs) hold rich and informative histories in their observable light. To determine a fundamental parameter of WDs, mass, we perform the first measurement of the average gravitational redshift of an ensemble of WDs. We find a larger mean mass than that determined from the primary and expansive technique known as the spectroscopic method. The potential inaccuracy of this method has broad astrophysical implications, including for our understanding of Type 1a supernova progenitors and for constraining the age of the Universe. This motivates us to investigate the WD atmosphere models used with the spectroscopic method, particularly the input theoretical line profiles, by developing a new experimental platform to create plasmas at WD photospheric conditions (T_e ~ 1 eV, n_e ~ 10^17 cm^-3). Instead of observing WD spectra to infer the plasma conditions at the surface of the star, we set the conditions and measure the emergent spectra in the laboratory. X-rays from a z-pinch dynamic hohlraum generated at the Z Pulsed Power Facility at Sandia National Laboratories irradiate a gas cell to initiate formation of a large (120x20x10 mm or 24 cm^3) plasma. We observe multiple Balmer lines from our plasma in emission and in absorption simultaneously along relatively long (~120 mm) lines of sight perpendicular to the heating radiation. Using a large, radiation-driven plasma aides us to achieve homogeneity along our observed lines of sight. With time-resolved spectroscopy we measure lines at a range of electron densities that spans an order of magnitude, and we do this within one pulsed power shot experiment. Observing our plasma in absorption not only provides the signal-to-noise to measure relative line shapes, it allows us to measure relative line strengths because the lines share the same lower level population. This constrains the theoretical reduction factors used to describe ionization potential depression or the occupation probabilities associated with these Balmer lines. We compare our measured line shapes with the theoretical ones used in WD atmosphere models as part of the first fruits of this rich experimental platform.Item The "Curtain Dress" : construction, conservation, and analytical research(2012-08) Villarreal, Nicole; Xu, Bugao; Jay, Cynthia K.This thesis examines the condition of the “Curtain Dress” of Gone With the Wind (GWTW) with the purpose of advising a conservation plan that would allow its exhibit in 2014 as part of the 75th anniversary of the film. The dress has been stored since 1981 in the Harry Ransom Center (HRC) at the University of Texas at Austin as part of the David O. Selznick (DOS) Collection. The project addresses the book, the film, the creation of the dress, and what happened to it after filming was over. A collaborative team was formed including HRC staff, a conservator, and graduate students from the Textiles and Apparel Division at the University of Texas at Austin. The author of this study provided historical context, document analysis, construction evaluation, and fiber testing. A timeline for the book, film, and garment was established; communications from Selznick referencing the dress were analyzed; construction details were photographed and documented for reference; and colorimetry and spectroscopy techniques were used for fiber analysis.Item Defect analysis using resonant ultrasound spectroscopy(2009-05-15) Flynn, Kevin JosephThis thesis demonstrates the practicability of using Resonant Ultrasound Spectroscopy (RUS) in combination with Finite Element Analysis (FEA) to determine the size and location of a defect in a material of known geometry and physical constants. Defects were analyzed by comparing the actual change in frequency spectrum measured by RUS to the change in frequency spectrum calculated using FEA. FEA provides a means of determining acceptance/rejection criteria for Non-Destructive Testing (NDT). If FEA models of the object are analyzed with defects in probable locations; the resulting resonant frequency spectra will match the frequency spectra of actual objects with similar defects. By analyzing many FEA-generated frequency spectra, it is possible to identify patterns in behavior of the resonant frequencies of particular modes based on the nature of the defect (location, size, depth, etc.). Therefore, based on the analysis of sufficient FEA models, it should be possible to determine nature of defects in a particular object from the measured resonant frequency. Experiments were conducted on various materials and geometries comparing resonant frequency spectra measured using RUS to frequency spectra calculated using FEA. Measured frequency spectra matched calculated frequency spectra for steel specimens both before and after introduction of a thin cut. Location and depth of the cut were successfully identified based on comparison of measured to calculated resonant frequencies. However, analysis of steel specimens with thin cracks, and of ceramic specimens with thin cracks, showed significant divergence between measured and calculated frequency spectra. Therefore, it was not possible to predict crack depth or location for these specimens. This thesis demonstrates that RUS in combination with FEA can be used as an NDT method for detection and analysis of cracks in various materials, and for various geometries, but with some limitations. Experimental results verify that cracks can be detected, and their depth and location determined with reasonable accuracy. However, experimental results also indicate that there are limits to the applicability of such a method, the primary one being a lower limit to the size of crack ? especially thickness of the crack - for which this method can be applied.Item Do metal-polluted stars of the ZZ ceti instability strip have a distinct asteroseismic signature?(2015-08) Jumper, Kevin Arthur; Winget, Donald Earl, 1955-; Montgomery, Michael Houston; Sneden, ChrisCooling DA stars that pass through the ZZ instability strip, a region between temperatures of approximately 12,600 K to 11,100 K, tend to experience the driving of g-mode pulsations near their surface layers. These pulsations cause variations in the luminosities of such stars, leading them to be known as DAVs. A fraction of DAVs also have photospheres contaminated by metals, usually thought to be from the tidally disrupted remnants of planetary systems. The high resolution spectroscopy needed to make definite identifications of these metal lines is relatively demanding, whereas it is simple to obtain photometric data on the pulsation periods of DAV stars. Therefore, if known metal-polluted DAVs (DAZVs) have systematic differences in their photometric data compared to that of DAVs that lack such pollution, photometry could provide an easy way to determine which stars are likely to contain metals in their photospheres in the future. However, we find that the known DAZV population is not large enough to permit its behavior to be distinguished from that of the normal DAV population at the present time, though extremely low-mass white dwarfs may help expand the populations and improve the quality of our fits.Item Functional and molecular photoacoustic imaging for the detection of lymph node metastasis(2013-12) Luke, Geoffrey Patrick; Emelianov, Stanislav Y.Accurate detection of the spread of cancer is critical for planning the best treatment strategy for a patient. Currently, an invasive sentinel lymph node biopsy is commonly used to detect metastases after a primary tumor is detected. This procedure results in patient morbidity, requires weeks of waiting, and is prone to sampling error. This dissertation presents new developments in an emerging biomedical imaging modality – photoacoustic imaging – and their application to improving the detection of metastases in the lymphatic system in a metastatic mouse model of squamous cell carcinoma of the oral cavity. Label-free spectroscopic photoacoustic imaging is demonstrated to detect hypoxia that results from the development of sub-millimeter cancer foci in the lymph node. In order to improve the sensitivity to micrometastases, molecularly-activated plasmonic nanosensers which are targeted to the epidermal growth factor receptor are introduced. The nanosensors are demonstrated to detect metastases consisting of only a few tens of cells. Improvements to spectroscopic photoacoustic imaging are then demonstrated by selecting imaging wavelengths based on the spectral properties of the optical absorbers. Finally, a new contrast agent – silica-coated gold nanoplates – are used to map the sentinel lymph node with high contrast. The final result is a set of tools that can be used to noninvasively detect micrometastases and improve molecular photoacoustic imaging.Item Generation of Core/shell Nanoparticles with Laser Ablation(2012-10-19) Jo, Young KyongTwo types of core/shell nanoparticles (CS-NPs) generation based on laser ablation are developed in this study, namely, double pulse laser ablation and laser ablation in colloidal solutions. In addition to the study of the generation mechanism of CS-NPs in each scheme, the optical properties of designed CS-NPs are determined with UV-VIS-NIR spectroscopy and EM field simulation. In the first scheme, which is double pulse laser ablation, two laser beams are fired in a sequence on two adjacent targets with different material. We have successfully demonstrated the generation of Sn/Glass, Zn/Glass, Zn/Si, Ge/Si, and Cu/Zn CS-NPs. Key factors affecting the generation of CS-NPs are (1) surface tensions of the constructing materials affecting the associated Gibbs free energy of CS-NPs, (2) physical properties of selected background gases (i.e., He and Ar), (3) delay time between two laser pulses, and (4) the amount of laser energy. The second scheme examined for the generation of CS-NPs is through laser ablation of solid targets in colloidal solutions. Compared to the double pulse laser ablation, this second approach provides better control of the size and shape of the resulting CS-NPs. Two colloidal solutions, namely, Au and SiO2 colloidal solution are applied in the second scheme. Key factors affecting the formation of CS-NPs with the second scheme and are (a) the adhesion energy between the shell and the core material, (b) the diameter of the core and (c) the laser ablation time and the laser energy. Red shift of absorption peaks are measured in both SiO2/Au and SiO2/Ag colloids compared with pure nanoparticles (NPs). The amount of red-shift is very sensitive to the shell thickness of the CS-NPs. The same red shift is reproduced with the corresponding full wave analysis. The observed red shift can be attributed to the additional surface plasmon resonance at the interface of metal/dielectric of the CS-NPs compared with pure nanoparticles. Through adjusting the material and size combination, the absorption peak of the CS-NPs can be tuned in a limit range around the intrinsic absorption peak of the metal of the CS-NPs. The freedom of adjusting the absorption peak makes CS-NPs is favorable in bio and optical applications.Item Ground-based Technologies for Cotton Root Rot Control(2013-04-24) Cribben, Curtis DThe overall goal of this research is to develop ground-based technologies for disease detection and mapping which can maximize the effectiveness and efficiency of cotton root rot (CRR) treatments. Accurately mapping CRR could facilitate a much more economical solution than treating entire fields. Three cotton fields around CRR-prone areas of Texas have been the sites for three years of data collection. A complete soil apparent electrical conductivity (ECa) survey was conducted for each field with an EM38DD sensor. Multiple linear regression was used to relate physical and chemical soil properties to the ECa values obtained from the EM38DD. The variability in soil ECa measurements can be best accounted for using calcium carbonate levels as well as clay and sand contents in the soil. T-tests were used to determine that soil pH, clay, sand, and inorganic carbon content were significantly related to CRR incidence as determined by aerial images of each location. Spectral data were obtained for freshly picked cotton leaves from healthy, disease-stressed, and dying or dead plants using an ASD VisNIR spectroradiometer. The leaf spectra were evaluated using linear discriminant analysis (LDA), the receiver operator characteristic, and wavelet analysis to relate them to classifications of infection level. It was determined that healthy and infected leaves can be correctly classified 85% of the time based on the spectral data. The results from this study suggest that differences in soil characteristics may not be pronounced enough to accurately map CRR in the soil; however, the precision treatment of CRR may possible using an optoelectronic sensor to diagnose infected plants based on leaf reflectance.Item Hyper-spectral diffuse reflectance spectroscopy imaging towards the identification of non-melanoma skin cancers(2013-05) Bish, Sheldon Floyd; Tunnell, James W.Non-melanoma skin cancer is the most prevalent malignancy in the world, with over a million annual positive diagnoses in the United States. If left untreated, these cancers cause morbidity and in rare cases, can become life threatening. The key to identifying and characterizing these tumors in the earliest stages, where they are most treatable lie in margin delineation in order to prevent recurrence. The visual obscurity of tumor morphology and physiology can make early detection a difficult task for dermatologists, particularly in the initial stages of cancer development. Tumor resection is a common course of action once they are discovered; however, there is a high recurrence rate due to incomplete removal of the malignant tissue. This dissertation presents an imaging system that can capture the spectral signatures correlating with morphological and physiological changes that accompany skin dysplasia. With this system, we may improve tumor margin delineation, reducing the number of incomplete tumor biopsies and false negative screenings. As an initial step of this process, we begin with a non-contact point sampling diffuse reflectance probe that mitigates the adverse effects of traditional contact probing. Validation of this probe is performed using tissue simulating phantoms spanning a biologically relevant range of optical and physiological properties to ensure that the non-contact format will not hinder performance relative to the contact probe. Cross polarization and auto-focus mechanisms were included in the design to reduce specular reflections and movement artifacts from in vivo measurements. This non-contact design was further developed into a platform for investigating the role of sampling geometry on diffuse reflectance measurements with the addition of a DMD spatial filter. Finally, we developed a hyperspectral DRSi system for the acquisition of wide-field maps of optical and physiological properties that is currently being tested on patients undergoing skin cancer screenings. The spectral output of this system has been validated for scattering and absorption across biologically relevant ranges using tissue simulating phantoms. The DRSi system was optimized for portability, ergonomics and resolution.Item Identification of biomolecules by mechanical modulation Raman microscopy(2011-12) Hinko, Kathleen Ann; Florin, Ernst-LudwigRaman microscopy is a tool used by physicists to collect molecular information from a wide variety of samples. Biophysicists have increasingly made use of Raman microscopy in combination with optical tweezers to identify the molecular makeup of structures inside cells. There are high levels of background and noise in Raman spectra from cells, however, that obscure low intensity scattering peaks and prevent complete molecular characterization. We have designed and built a Mechanical Modulation Raman Microscope(MMRM) that is capable of background subtraction and noise reduction for Raman spectra from cells in vivo. There are two mechanisms of modulation: (1) three-axis stage modulation for objects fixed to the coverslip and (2) separate optical trap modulation for objects in solution. In both cases, objects of interest are modulated in and out of the Raman excitation volume while spectra are collected. Difference spectra are created by subtracting the spectrum without the object from the spectrum including the object. These difference spectra are averaged over the number of cycles of modulation. With the mechanical modulation technique, the background in Raman spectra is removed, and the signal-to-noise ratio is improved by two orders of magnitude. This technique was applied to fission yeast cells. Mechanical modulation Raman spectra of exponentially growing cells and starved cells were collected in three dimensions, and spatial differences were observed in the molecular composition for different metabolic states of individual yeast cells.Item Investigating the Roles of Vacuoles in Iron Trafficking in Saccharomyces cerevisiae(2013-11-27) Cockrell, Allison LeighTransition metals play essential roles in biological systems, but Fe can also be toxic to cells. In order to maintain this balance between necessity and toxicity mechanisms are employed for regulating and storing intracellular Fe. In Saccharomyces cerevisiae, vacuoles are responsible for sequestering, storing, and supplying Fe to the cytosol. Many of the proteins and regulatory pathways involved in Fe trafficking and storage in S. cerevisiae have been identified, but the forms of Fe which are involved in these processes have not been fully characterized. In these studies, biophysical and bioanalytical techniques were used to study intracellular Fe distributions in S. cerevisiae cells and organelles. Ultimately, Fe-containing species were biophysically characterized and absolute Fe concentrations in cells and organelles were quantified. The motivation for these studies stemmed from previous studies which revealed that the majority of the whole-cell Fe is a non-heme, high-spin (NHHS) form of Fe^(3+). This Fe is not localized to the mitochondria. The purpose of these studies was to determine if the vacuoles contained this NHHS Fe^(3+). A large-scale isolation procedure was developed to obtain purified vacuoles from S. cerevisiae and to investigate the Fe in these organelles. M?ssbauer and EPR analysis revealed that the primary form of Fe in vacuoles is a mononuclear, NHHS Fe^(3+) species. A second form of Fe was also observed as superparamagnetic ferric phosphate nanoparticles (NP). By investigating model compounds of Fe and polyphosphate we determined that a shift in vacuolar pH induces the conversion between NHHS Fe^(3+) and NP. These results showed that there are at least two forms of Fe in vacuoles, and that the ratio of these two forms is dependent upon the pH of these organelles. Biophysical analyses of whole cells also revealed the presence of low concentrations of a non-heme, high-spin Fe^(2+) species. The goal of these next projects was to determine if this NHHS Fe^(2+) species was localized to the cytosol. Genetic strains lacking or over-expressing the vacuolar Fe import protein Ccc1p were studied by M?ssbauer spectroscopy (?CCC1 and CCC1-up, respectively). ?CCC1 cells showed low vacuolar Fe (NHHS Fe3+ and NP), and increased NHHS Fe^(2+). We hypothesize that this NHHS Fe^(2+) is cytosolic Fe. We also propose that this NHHS Fe^(2+) is involved in the regulating intracellular Fe levels. CCC1-up cells accumulated more Fe than wild-type (WT) cells, and showed elevated levels of vacuolar Fe (NHHS Fe^(3+) and NP). These cells also accumulated high levels of NHHS Fe^(2+). The CCC1-up cells exhibited an adenine deficient phenotype, where the cells developed a red color during growth. With excess adenine the levels of NHHS Fe^(2+) declined, which indicated that this Fe accumulation was related to adenine deficiency. We conclude that adenine deficiency leads to the accumulation of a sequestered (possibly vacuolar) form of NHHS Fe^(2+). Overall, we have identified two separate pools of NHHS Fe^(2+) in ?CCC1 and CCC1-up cells. In ?CCC1 cells the NHHS Fe^(2+) pool is localized to the cytosol and is sensed by the cell. In CCC1-up cells the NHHS Fe^(2+) is sequestered from the Fe regulatory mechanism- possibly in the vacuoles. These data have helped us better understand the roles of vacuoles in Fe trafficking and the dynamics of vacuolar Fe trafficking.Item Midlife body mass index and cerebral metabolism(2011-08) Gonzales, Mitzi Michelle; Haley, Andreana P.; Schallert, TimothyObesity is a pervasive condition associated with increased risk of dementia, cognitive impairment, and cerebral atrophy in later life. Given that the pathophysiology underlying obesity’s impact on the central nervous system is poorly understood, the current study examined the association between body mass index (BMI) and five cerebral metabolites of neurobiological significance: N-acetyl-aspartate (NAA), a marker of neuronal viability; choline-containing compounds, free choline, phosphocholine and glycerophosphocholine (Cho), markers of membrane breakdown and turn over; creatine (Cr), a marker of energy metabolism; myo-inositol (mI), an organic osmolyte and substrate for the synthesis of the secondary messenger, inositol triphosphate; and glutamate (Glu), a marker of excitatory neurotransmission and synaptic integrity. Fifty-five participants, aged 40-60 years, underwent neuropsychological testing, health screen and proton magnetic resonance spectroscopy (1H MRS) of the occipitoparietal grey matter. Concentrations of NAA, Cho, mI, and Glu were calculated as a ratio over Cr and examined in relation to BMI using multivariate multiple regression. Higher BMI was associated with elevations in mI/Cr (F(5,47)=3.583, p=0.008, ß=0.387, p=0.006), independent of age, sex, fasting glucose levels, and systolic blood pressure. The current study found that higher BMI is related to increased concentrations of the organic osmoltye and glial marker myo-inositol, potentially implicating plasma hypertonicity and neuroinflammation as mechanisms underlying obesity-related brain dysfunction. With validation and absolute quantification, studies of neurometabolites may improve identification of the pathological mechanisms underlying obesity’s consequences on cognition.Item Multiscalar line measurements in nonisobaric high-pressure underexpanded supersonic jets using rotational-vibrational raman spectroscopy(2009-05-15) Cohen, Benjamin NathanThis work describes the development of a Raman spectroscopy system for measuring aerothermochemistry in high-speed jets and flames. A transmissive grating spectrometer was newly developed for capturing pure rotational Raman and rotationalvibrational Raman with a single CCD camera. Previous state-of-the-art experiments applied line imagining in known flowfields of constant pressure. The system described herein is designed to provide local measurement of pressure, with full thermochemistry, along a line. In every point, temperature will be measured by examining the Boltzmann decay of the rotational spectrum, while molar fraction will be measured from the vibrational Raman spectrum. The temperature and concentrations will then be combined to obtain partial pressure measurements via the equation of state. This work examines the phenomenology of rotational and vibrational Raman scattering and proposes algorithms that can be used for data extraction.Item Novel tools for ultrafast spectroscopy(2011-12) Jarvis, Thomas William; Li, Elaine; Fink, Manfred; Keto, John; Lim, Sang-Hyun; Shih, Chih-Kang; Sitz, GregExciton dynamics in semiconductor nanostructures are dominated by the effects of many-body physics. The application of coherent spectroscopic tools, such as two-dimensional Fourier transform spectroscopy (2dFTS), to the study of these systems can reveal signatures of these effects, and in combination with sophisticated theoretical modeling, can lead to more complete understanding of the behaviour of these systems. 2dFTS has previously been applied to the study of GaAs quantum well samples. In this thesis, we outline a precis of the technique before describing our own experiments using 2dFTS in a partially collinear geometry. This geometry has previously been used to study chemical systems, but we believe these experiments to be the first such performed on semiconductor samples. We extend this technique to a reflection mode 2dFTS experiment, which we believe to be the first such measurement. In order to extend the techniques of coherent spectroscopy to structured systems, we construct an experimental apparatus that permits us to control the beam geometry used to perform four-wave mixing reflection measurements. To isolate extremely weak signals from intense background fields, we extend a conventional lock-in detection scheme to one that treats the optical fields exciting the sample on an unequal footing. To the best of our knowledge, these measurements represent a novel spectroscopic tool that has not previously been described.Item Numerical simulation and interpretation of neutron-induced gamma-ray spectroscopy measurements(2015-12) Ajayi, Oyinkansola Modupe; Torres-Verdín, Carlos; Peters, Ekwere J; Preeg, William E; Schneider, Erich A; Sepehrnoori, KamyNeutron-induced spectroscopy measurements are commonly used to quantify in-situ elemental and mineral compositions of rocks from the processing of measured gamma-ray energy spectra. However, geometrical effects on measured spectroscopy logs, such as thin beds, dipping beds, and deviated well trajectories, can cause shoulder-bed averaging that compromises the assessment of true layer elemental and mineral compositions. Traditional methods of interpreting neutron-induced gamma-ray spectroscopy measurements typically neglect such shoulder-bed averaging effects in the estimation of elemental and mineral compositions. Monte Carlo methods accurately reproduce borehole and formation geometrical effects on spectroscopy measurements but are extremely time consuming and impractical for use in routine interpretation. Reliable measurement interpretation must therefore begin with the development of a fast and accurate forward simulation method that explicitly incorporates measurement physics, borehole, tool, and formation geometry. This dissertation introduces a new algorithm to rapidly simulate elemental and mineral compositions from neutron induced spectroscopy measurements. The algorithm utilizes neutron-gamma ray spatial sensitivity functions to account for environmental and three-dimensional (3D) effects of formation porosity, fluids, dipping beds, thin beds, and arbitrary well trajectories. Simulations assume a logging-while-drilling (LWD) spectroscopy tool furbished with a 14-MeV pulsed-neutron source in the interpretation of gamma ray spectra obtained from high energy inelastic neutron scattering and thermal neutron capture. Results obtained with the rapid simulation method are benchmarked against rigorous Monte Carlo spectroscopy calculations for synthetic conventional and unconventional thinly-bedded reservoirs penetrated by vertical and high angle/horizontal (HA/HZ) wells. The fast simulation method yields calculations in approximately 1e6 the time required by Monte Carlo simulations, with an average difference below 5% between Monte Carlo and fast simulated logs. An inversion-based interpretation method is next introduced to accurately evaluate mineral concentrations from measured spectroscopy elemental logs based on the analytical relationship between elements and minerals through their chemical formulas. In the presence of geometrical effects, spectroscopy elemental and mineral logs are corrected for shoulder-bed averaging by the inclusion of spatial sensitivity maps, which account for such geometrical effects, in the inversion-based interpretation. Calculations are performed with both inelastic and capture gamma-ray spectroscopy measurements which arise from high-energy inelastic neutron scattering and low-energy thermal neutron capture, respectively. This strategy provides two sets of data that can ascertain chemical elements or minerals detectable in only one measurement mode and also independently validates estimated elemental and mineral compositions. In laminated formations, where layer thicknesses are below the vertical resolution of the tool, it is impossible to quantify layer properties with inversion methods. An additional interpretation method based on a new spectroscopy mixing law is therefore developed to estimate elemental and mineral compositions within individual laminae. The new inversion-based interpretation methods are successfully implemented in diverse synthetic and field cases with varying lithology types and well trajectories including vertical and HA/HZ wells. Results show that the developed methods reduce shoulder-bed averaging effects on measured spectroscopy logs by as much as 0.4 yield fraction, 0.17 weight fraction, and 0.34 mineral volume fraction. Finally, a new spectroscopy-based petrophysical interpretation method is introduced that utilizes estimated mineralogy to overcome the common assumption of homogeneous lithology in measured porosity logs, thereby improving the estimation of porosity and water saturation. Inclusion of shoulder-bed averaging effects on spectroscopy mineral logs also increases the accuracy of spectroscopy-based petrophysical interpretation.Item Polarization modulation infrared reflection absorption spectroscopy for heterogeneous catalytic applications at elevated pressures(Texas A&M University, 2005-08-29) Ozensoy, EmrahThis dissertation focuses on bridging the pressure and complexity gap between heterogeneous catalysis and surface science by introducing new instrumental tools that can operate under catalytically relevant conditions (i.e. atmospheric pressures and temperatures higher than room temperature). Thus, some of the few detailed examples of the polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) as an in situ vibrational spectroscopic tool for the elevated-pressure investigation of gas/solid interfaces on planar single crystal model catalyst systems were presented in this work. Furthermore, for the first time in the literature, PM-IRAS technique was applied to study complex multi-component model catalyst structures exhibiting three dimensional morphologies such as metal nanoparticles deposited on a metal-oxide thin film. In order to achieve a molecular understanding of the properties of CO+NO catalytic reaction at elevated temperatures and pressures on Pd based catalysts, adsorption trends of each of the reactant molecules were studied separately on Pd (111). The adsorption properties of CO/Pd (111) and NO/Pd (111) systems both under UHV conditions and at elevated pressures were discussed in a comparative manner to highlight the pressure dependent behavioral differences between these two probe molecules by emphasizing the risks of extrapolating UHV trends to elevated pressure regimes. CO+NO reaction mechanism and kinetics was also studied on Pd (111) by in situ PM-IRAS. Factors affecting the conversion and the selectivity of the Pd (111) model catalyst towards CO+NO reaction at elevated pressures were discussed. Formation of isocyanate containing species?? was also observed and the catalytic implications of this observation was elaborated. Finally, design and characterization of a complex model catalyst composed of supported Pd nano-particles was investigated using CO adsorption at elevated pressures. Catalytic activity of the defect sites on the supported Pd nano-particles towards CO dissociation was demonstrated and compared with Pd (111) to elucidate the significance of the surface morphology of the active sites in a catalytic reaction.Item Spectro-electrochemical studies of [conjugated] polymer single-molecules, nanoparticles, and thin films(2009-12) Chang, Ya-Lan, 1980-; Barbara, P. F. (Paul F.), 1953-; Rossky, Peter J.; Stevenson, Keith J.; Makarov, Dmitrii E.; Korgel, Brian A.Conjugated polymers are widely used and rapidly developed in practical polymer-based light-emitting electronic devices. Understanding the electrochemical reaction of conjugated polymer has become essential in the design and operation of devices such as electrochemical light-emitting diodes. In particular, we have studied the dynamics and kinetics of oxidation/reduction behavior of conjugated polymer single-molecules and nanoparticles in order to obtain the molecular level properties of deeply trapped holes in organic semiconductor devices. Theoretical calculations suggest the penetration of ions and solvent molecules effectively stabilizes the injected charges, which allows homogeneous charge distribution and further hole injection. The formation and decay of deep traps have been explored by changing the charging rate and duration. We found that the laser excitation significantly promotes the untrapping of deep holes. Electrogenerated chemiluminescence of single nanoparticles has been investigated to unravel the effects due to particle heterogeneity, which are masked in bulk electrochemical studies of nanoparticles. Bigger particles showed more intense light and longer duration time than smaller ones. Co-reactant, tripropylamine can facilitate the formation of electrogenerated chemiluminescence as well as alleviate the polymer oxidation and following irreversible electrochemical reaction. Electrochemically generated light waves from the conjugated polymer thin films have been visualized to obtain microscopic level understanding on the complex reaction mechanism. Electrochemical reaction occurs at local defects and propagates isotropically over macroscopic distances with a sharp wave front. The initially injected holes (oxidized polymers) drag counter-ions into the film, thereby induce a phase-transition-like swelling that enhances transport of ions and solvent and move forward the double layer and corresponding propagation of the wave.