Browsing by Subject "Spectrum analysis"
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Item A method for correction of experimental inner Bremsstrahlung spectra(Texas Tech University, 1964-05) Adams, James D.The purpose of this thesis is to present an improved method of comparing experimental inner bremsstrahlung (internal bremsstrahlung) spectra with the results of theories predicting the shape and intensity distributions of these spectra, by correcting the experimental data for various effects due to the efficiency and resolution of the detection equipment. A computer program for correcting the experimental data for efficiency of the detector, resolution, and Compton scattering in the crystal is included in the Appendix* The corrected experimental spectrum can then be compared directly with the spectrum predicted by theory. Experimenters (e.g., reference 1) have usually attempted to alter the theoretical spectrum in the same way that the detector does, and then compared the experimental data with this changed theoretical spectrum. Since comparing a theory to the original (pre-detection) spectrum is the ultimate goad, it seems that the method to be described in this paper is the more desirable.Item A study of certain molecular emission spectra produced by a radio-frequency plasma generator(Texas Tech University, 1969-05) Wendel, Carlton TyrusNot availableItem An Atlas of Arc and Geissler Tube Spectra of Seventy-Four of the Elements(Texas Tech University, 1938-08) Hurmence, Howard HenryNot Available.Item Item Bispectral density computation and its application to time series analysis(Texas Tech University, 1995-08) Dey, Aswini KumarPrediction and simulation are the main purposes of the time series data analysis. In order to obtain good results, one needs to fitting of an appropriate model for the given time series data. Early time series model fittings were concerned with the fitting of linear type models, namely, ARMA models. But in many cases, time series come from some non-linear process. Consequently, linear models fail to produce satisfactory results. In recent years, neural network approaches are used satisfactorily to deal with almost all type of time series. Spectral density also plays an important role in time series analysis. Particularly, when the data emerges from a linear and Gaussian process, it contains all the necessary and useful information about the series. However, in order to deal with non-linear and non-Gaussian processes, we need to consider higher order spectra. The simplest higher order spectra is bispectra. In this thesis, we have computed bispectral density and have used it in testing the linearity and Gaussianity properties of the time series for ECG and WIND data. Based on the outcome of this test appropriate models are fitted for the data sets considered. The fitted model is then used for one point prediction and simulation of the original series. It is found that Multistep prediction collapses within a few steps. This is not the case in neural network approach.Item Characterizing Vs profiles by the SASW method and comparison with other seismic methods(2007) Lin, Yin-Cheng; Stokoe, Kenneth H.The shear wave velocity (VS) profile has been used as an important parameter in characterizing geotechnical sites and performing earthquake designs. The SpectralAnalysis-of-Surface-Wave (SASW) method, one of the VS profiling methods, was developed in the early 1980s. This method is a non-intrusive test which uses Rayleigh waves, one kind of surface wave, to explore the subsurface. The SASW method has been widely used in geotechnical earthquake engineering to profile soil and rock sites. All equipment required to conduct the SASW test is deployed on the ground surface and no boreholes are needed. In this study, the SASW method was used to measure shear wave velocity profiles in four different geographic regions. These four regions are: (1) Imperial Valley, CA, (2) Taiwan, (3) Hanford, WA and (4) Yucca Mountain, NV. The SASW tests performed at these locations were for different purposes. At the Imperial Valley and Taiwan sites, the SASW tests were carried out at the locations of strong motion recorders (SMR) to obtain VS profiles of the top 30 m (VS,30). At the Hanford and Yucca Mountain sites, deeper profiling (>300 m) was required to obtain VS values of the geotechnical structure around or beneath critical facilities associated with the handling, treatment and/or storage of high-level radioactive waste. The VS,30 values determined by the SASW method were used to classify the test sites based on the International Building Code (IBC-2006) provisions. Available downhole and suspension logging measurements at/near the SASW test sites were also used to determine VS,30. In addition, deeper VS profiles determined by the SASW, downhole and suspension logging methods were compared. By doing so, the consistency between the three seismic surveys methods and the reliability of the SASW method were studied. Finally, sensitivity studies of the SASW method were conducted to investigate: (1) the impact on the final VS profile of changing assumed parameters in the SASW data reduction process, and (2) the capability of the SASW method to detect relatively soft layers sandwiched between stiffer layers.Item Characterizing Vs profiles by the SASW method and comparison with other seismic methods(2007-05) Lin, Yin-Cheng, 1972-; Stokoe, Kenneth H.Item Design of miniature flow through optical absorbance detectors(Texas Tech University, 1998-05) Bellamy, Harvey S.Several novel flow through optical absorbance detectors have been developed which combine small size, low power requirements, simplicity of manufacture, low cost, and unique capabilities. The employment of optical fibers to connect the light emitting and detecting elements to the flow through cell enable separation of the cell and the detector electronics, allowing cell placement in hazardous or inaccessible locations without jeopardizing operator safety. Two spectrometer designs are also presented which include the above advantages and allow visible wavelength spectra to be obtained for fluids passing through the cell without flow interruption. This is achieved without the use of any moving parts.Item Effect of pressure on hydrocarbon emission spectra in an induction-coupled plasma(Texas Tech University, 1967-08) Wendel, Carlton TyrusNot availableItem Emission spectra of simple hydrocarbons excited in a radio-frequency plasma(Texas Tech University, 1965-08) Mercer, Howard NicholasBeginning with an elementary discussion of the theory of atomic and molecular spectra and continuing with a discussion of the plasma state and other methods of excitation, a description of the apparatus used as well as the procedure followed in obtaining the results is given. The results of the analysis of the spectra will be introduced In tabular form. Generally, these results will be discussed In terms of the various methods of excitation.Item Explorations of electrothermal vaporization inductively coupled plasma time-of-flight mass spectrometry for isotopic analysis(2008-12) Rowland, Adam Michael, 1982-; Holcombe, James A.The application of inductively coupled plasma time-of-flight mass spectrometers (ICP-TOFMS) coupled to electrothermal vaporization (ETV) presents several unique analytical opportunities for isotopic analysis. This dissertation explores several subjects that utilize these characteristics in specific analytical applications. The viability of using the thermal programming abilities of the ETV in order to separate Rb and Sr is explored. These elements are isobaric at m/z 87, and must normally be separated prior to analysis for isotopic studies. Their disparate thermal properties allow them to be separated in time by the ETV allowing for simpler, faster isotope ratio analysis with less opportunity for contamination. A test case using standard potassium feldspar is found to produce moderately accurate and precise results. TOF instruments are of interest for isotope ratio analysis due to inherent isotope ratio precision. However, it has been observed that when operated in the analog data collection mode the isotope ratios observed possess a previously uncharacterized inaccuracy. This bias is rooted in variable detection efficiency of arriving ions, which can be corrected for with an algorithm described within. A method of determining the effective detector efficiency as a function of signal is presented, as well as an evaluation of the effectiveness of ratio correction. The use of ETV with TOF for isotope dilution analysis is explored. Correction of transient signals for efficiency effects is discussed, as well as the viability of using the autosampler for mixing of the solution and spike. A final study presents explores the combination of the ETV and TOF for analysis of a large number of elements from a brief transient signal. A library of peptide covered beads is analyzed for binding capacity to a variety of metals. Solutions containing metals stripped from the beads are analyzed to determine the binding capacity and specificity of the peptide sequence. The beads themselves are also analyzed for metal content using the ETV as an indicator of the efficiency of metal stripping off of the beads.Item Linear and nonlinear optical spectroscopies of SiGe interfaces and Si nanocrystals(2002) Jiang, Yingying; Downer, Michael CoffinLinear and nonlinear optical spectroscopies are used to study SiGe alloy films and Si nanocrystals (NCs). With spectroscopic ellipsometry (SE), a bulk-sensitive linear optical probe, we demonstrate in-situ monitoring and control of compositionally graded SiGe films grown on Si(001) by chemical vapor deposition. Feedback control is achieved by comparing the Ge composition of the most recently deposited layer determined from SE to the set values, then adjusting the flow of disilane gas accordingly. Second harmonic generation (SHG), a surface/interfacesensitive nonlinear optical probe, complements SE greatly in monitoring film growth. We develop a real-time SHG technique by tracking surface Ge composition with the peak of the SHG spectrum (E1 resonance) using a 15 femtosecond broad bandwidth laser. Data acquisition is much faster than traditional SHG spectroscopy, in which a 100 femtosecond narrow bandwidth laser must be tuned. Using broadband SHG and SE, we also explore the strain effect caused by adding a small amount of C into SiGe alloys. SHG studies are extended from the planar surface/interface such as SiGe/Si to the sharply curved Si/SiO2 interfaces of Si NCs embedded in SiO2. We observe SHG from 3-dimensional distributions of spherical Si NCs prepared by ionimplantation into glass, which have applications in photonic and light-emitting devices. The results suggest that SHG originates microscopically from Si/SiO2 interfaces states, which are passivated by hydrogen annealing of NC samples, and macroscopically in part from fluctuations in NC size, shape and density. We also study SHG from dense (1010 or 6×1011 cm−2 ) 2-dimensional layers of Si NC (5 or 8 nm average diameter) prepared by chemical vapor deposition of Si precursor gases onto an oxidized Si wafer, and subsequently embedded in SiO2. Such Si NC layers act as a controllable planar charge storage layer in flash-memory devices. Time-dependent SHG measures the electrostatic charging and discharging of the NC layer in real-time. By polarization-dependent and frequency-domain interferometric SHG (FDISH) spectroscopy, SHG intensity and phase spectra of Si NCs are distinguished from contributions of the Si substrate, and reveal a NC-size-dependent blue-shift of the E1 resonance, consistent with quantum confinement, that can be used as an in-situ size diagnostic. Although these results were obtained ex-situ, they show that SHG can probe key material and electrical properties of Si NCs sensitively without contacting the sample, and thus can be transferred readily to in-situ, real-time monitoring of the deposition of Si NCs.Item Liquid-liquid equilibrium in the system acetonitrile-water-salt by infrared spectroscopy(Texas Tech University, 1969-05) Cannon, Stephen LeeThis investigation was concerned with the development of an infrared analysis technique by which liquid-liquid equilibrium in the system acetonitrile-water-salt could be obtained. The method developed utilized sample bottles which constituted a completely closed system from initiation to termination of each determination. The calibration curve procedure proved to be an effective method for obtaining binodal curve data in that each point was determined independently as contrasted to the well known cloud-point technique. It was found that the analysis technique was usable for samples containing less than five weight per cent salt and i t was proposed that the method might be extended for any salt composition if the dilution by a known amount technique was used. The previously hard-to-determine acetonitrile-rich end point could be easily and accurately determined, and the location of the plait point could be closely bracketed by employing this technique.Item Microwave spectroscopic studies of ethyl mercaptan(Texas Tech University, 1974-05) Schmidt, Ronald ENot availableItem Paramagnetic resonance and optical spectra of some divalent group I-B metal pyridine complexes(Texas Tech University, 1966-08) Frazier, John PedenNot availableItem Quantitative spectrographic analysis(Texas Tech University, 1941-06) Glass, King IrwinNot AvailableItem Reactions and photochemistry of samarium(II) complexes(Texas Tech University, 2003-12) Knettle, Brian WesleyOver the previous twenty years, divalent lanthanide reagents have become reagents of choice for organic functional group transformations. Samarium diiodide has made a particularly impressive impact on the way synthetic chemists perform reductions, reductive couplings of multiple 7t-bonds, and coupling of alkyl halides to ;i-bonds. It has been shown that the rate of reduction and the reducing ability of samarium(II) complexes can be influenced by the coordinating ligands and solvent medium. The most common additive is HMPA, which accelerates many reactions, and can also alter the stereoselectivity of products. This is due to the electron donating ability of HMPA to the divalent cation (increasing the reducing power) and the increased steric bulk about the samarium reductant. The first portion of this research focused on the behavior of samarium(II) complexes towards imines. It was found that substitution of Sml2 (which does not mediate imine reductions) with SmBr2, Sm[N(SiMe3)2]2, or a mixture of Sml2-Et3N-H20 allowed for imine reduction. However, the study showed that profound differences in reactivity could be related to the choice of ligand. SmBr2 and Sm[N(Si(CH3)3)2]2 were both effective at reduction of ketimines to amines. Sm[N(Si(CH3)3)2]2 was also able to reductively couple certain aldimines in a stereoselective manner. The Sml2-Et3N-H20 mixture was found to be effective at coupling both aldimines and ketimines. It had been previously shown that illumination of Sml2 increased its reducing power. To further examine this phenomenon, photochemical quenching experiments were performed upon Sml2 solutions containing a quencher molecule. Experimental rate constants were calculated for quenching by the N-benzyl imine of acetophenone, styrene, 1-chlorobutane, 2-butanone, and 4-toludine, and were found to be in good agreement with theoretical rates derived from Marcus theory. This indicates that the electron transfer is an outer sphere process. Lastly, a spectroscopic study of several samarium(II) reagents was performed. Relative quantum yields for Sml2 and SmBr2 were found to be 0.13 and 0.011, respectively. Molar extinction coefficients were also found for these complexes and clearly showed that Sml2 is more efficient in the photon absorption process.Item Second-harmonic generation and reflecance-anisotropy spectroscopy of vicinal Si(001)(2006) Kwon, Jinhee; Downer, Michael CoffinSpectroscopic second-harmonic generation (SHG) and reflectance-anisotropy spectroscopy (RAS) of native-oxidized vicinal Si(001) with off-cut angles ζ = 0o , 4o , 6o , 8o and 10o from (001) toward [110] are performed. The SHG spectra are first decomposed using the macroscopic Fourier analysis. As a common microscopic analysis for SHG and RAS, we use a simplified bond hyperpolarizability model. The description of the expanded bond model and the result of the calculation are presented. The derived complex hyperpolarizability spectra are compared with the corresponding inverted real and imaginary parts using nonlinear Kramers-Kronig relations, thus confirming the consistency of the developed bond model. RAS and SHG spectra from clean and selectively H2 adsorbed reconstructed vicinal Si(001):6o surfaces are obtained and analyzed in a similar way.Item Spectral estimation: synthesis of methods(Texas Tech University, 1988-12) Vogel, Jay DixonThis paper examines two publications; each presents a method of spectral estimation. The first paper provides an iterative scheme for the estimation of the power spectrum of a time series. The latter paper details the use of the Yule-Walker equations to estimate the power spectrum. A process whereby the two methods are combined is examined. An initial estimate of the spectrum is obtained from the Yule-Walker method. This initial estimate is used as the first step in the iterative process. The results for this new process are not encouraging. Some possible sources of error are examined to explain the poor results.Item Spectral properties of [Greek letter alpha]-ketoacetates in the cyclohexanone series(Texas Tech University, 1968-05) Tabachnick, MurrayNot availabl