Browsing by Subject "Spectrum analysis"
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Item Applications of time-resolved spectroscopy to spectrochemical analysis(1966) Burnett, Harold Morris, 1928-; Not availableItem Characterizing Vs profiles by the SASW method and comparison with other seismic methods(2007-05) Lin, Yin-Cheng, 1972-; 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 Determination of in situ Vs and Gmax using surface wave measurements in cased and uncased boreholes(1998) Kalinski, Michael E. (Michael Edward), 1963-; Stokoe, Kenneth H.The Spectral-Analysis-of-Surface-Waves (SASW) method is a technique in which surface waves are used to determine variations in small-strain shear modulus (G [subscript max]) with depth in layered systems. The SASW method has traditionally been applied to flat systems where the surface is readily accessible, such as soil profiles and pavement systems. However, the research presented herein shows the applicability of the SASW method to characterize materials around cased and uncased boreholes in soil and rock by propagating surface waves along the borehole wall. In cased boreholes, surface wave measurements can be used to determine G [subscript max] of the casing. In many instances, surface wave measurements can be used to determine G [subscript max] of the surrounding material and the quality of the bond between the material and the casing. In these instances, success is limited by the thickness of the casing and the stiffness contrast between the casing and the surrounding material. In uncased boreholes, surface wave measurements were used to identify and delineate zones of disturbance and cracking around cylindrical drilled shafts in rock. In addition, surface wave measurements were used to delineate the extent of affected soil in a large-diameter (42-in. (1.1-m)) borehole treated with a lime slurry. In both cased and uncased boreholes, it was found experimentally that the cylindrical geometry of the borehole significantly affected the dispersive characteristics of the surface wave energy. Furthermore, this geometry-induced dispersion was completely different when propagating in the axial and circumferential directions. Appropriate numerical formulations developed on companion projects were incorporated into the results presented herein to accurately model the experimental surface wave data. The focus of this research was the development of a borehole SASW tool to determine the in situ relationship between G [subscript max] and state of stress in uncased pressurized boreholes in soil. In situ relationships were successfully determined using the borehole SASW tool in unsaturated cohesive and cohesionless soils. These relationships compared favorably to relationships determined from laboratory resonant column testing. At this time, minimization of soil disturbance around the borehole is the single most important issue in advancing this technology, although many other opportunities exist for future researchItem 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 Nonlinear spectroscopic studies of liquids(1995-05) Muller, Laura Jean; Not availableItem On-line drill wear monitoring by higher order spectra for printed circuit board production(1995-05) Sneor, Alon Moshe; Not availableItem 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 Spectroscopic properties of granulation in K-type dwarf stars(2008-05) Ramírez, Iván, 1979-; Prieto, Carlos Allende; Lambert David L.The presence of surface convection in K-type dwarfs is revealed in very high quality spectra (R ≃ 180, 000, S/N &300) of nine bright stars. Relative radial velocities between pairs of spectra of the same object are determined with a mean accuracy of 12 m s−1 , which is necessary for achieving high S/N without distorting the spectral line shapes by coadding individual frames. The observed asymmetries and wavelength shifts of the Fe i absorption line profiles are mainly due to granulation. The bisectors of the strongest Fe i lines have a span of about 100 m s−1 and the central wavelengths of the weakest Fe i lines are shifted by up to −200 m s−1 . The blueshifts decrease for stronger Fe i lines, but they become independent of line strength for equivalent widths larger than about 100 m˚A. The detection of this “plateau” in the velocity shifts of the strongest Fe i lines is necessary to remove the uncertainty introduced by granulation, which is of the order of hundreds of meters per second, in the determination of absolute radial velocities. Line profiles computed using a 3D model atmosphere accurately reproduce the observations. Statistical tests show that the theoretical line asymmetries and wavelength shifts correspond to the observed ones at a 90–95% confidence level, thus validating the 3D model for spectroscopic studies of abundances and fundamental parameters of K-dwarfs. We find that 3D effects reduce the difference in the iron abundance determined separately from Fe ii and Fe i lines, which is about 0.15 dex for 1D models, by two thirds, thus alleviating significantly the iron ionization imbalance problem in K-dwarfs. However, the 3D iron abundances from Fe i lines show a small dependence with excitation potential, similar to the 1D case, possibly due to non-LTE effects that have not been taken into account. We also find that the 3D correction to the effective temperatures of solar metallicity K-dwarfs derived with the infrared flux method is about +30 K. Finally, we show that the 3D spectrum synthesis of molecular bands greatly improves the agreement with the observational data compared to the 1D analysis, which overestimates the abundances derived from molecular features by a factor of 2.