Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 24 for “"time averaging"”.
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Time-Averaging and Morphology: Variability in Modern Populations and Fossil Assemblages of Mercenaria (Bivalvia)
… studies. However, many fossil assemblages are time-averaged; that is, many generations of non-contemporaneous organisms are mixed into the same fossil bed. Assemblages of robust mollusk shells deposited in nearshore marine environments are often time-averaged over 100's to 1000's of years. …
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Quantitative Estimates of Time-Averaging in Brachiopod Shell Accumulations from a Holocene Tropical Shelf (SW Brazil)
Time-averaging, the mixing of fossils of different ages within a single bed, defines the limit of temporal resolution of the fossil record. Quantitative estimates of this resolution threshold have not been acquired for any group other than mollusks. This study provides the first quantitative …
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Modeling and control of zero-voltage transition three-phase PWM boost rectifier
… for the three-phase boost rectifier using the time-averaging equivalent circuit approach. The small signal model is derived from the average model. The small signal characteristics are compared to the corresponding characteristics without ZVT. A model is also developed for the independent …
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Ecological, Evolutionary, and Taphonomic Comparisons of Brachiopods and Bivalves at Multiple Spatial and Temporal Scales
… tropical shelf and quantifies the magnitude of time averaging (temporal mixing) for these two different organisms. This is accomplished by dating a suite of shells from each site using amino acid racemization calibrated with several radiocarbon dates. By studying the age distributions for each …
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Analysis of single event transients in arbitrary waveforms using statistical window analysis
… processing to detect transient events or for time-averaging of frequency spectra. A generalized window function is demonstrated using the Ionizing Radiation Effects Spectroscopy (IRES) technique to enhance the measurement of transient anomalies within arbitrary waveforms. The IRES filter …
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Fault detection in rotating machines by vibration signal processing techniques
… a range of techniques including synchronous time averaging, Hilbert transform-based demodulation, continuous wavelet transform, Wigner-Ville distribution and spectral correlation density function. The detection and the diagnostic capability of these techniques are discussed and compared on …
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A Problem From Hamiltonian Mechanics With Time -Periodic Coefficients, Small Noise, and Degeneracy
… weakly dissipative dynamical system with time-periodic co-efficients. Their time average is governed by a degenerate Hamiltonian whose set of critical points has an interior. The dynamics of the system is studied in the presence of three time scales. The periodic fluctuations of the …
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Longer Time Steps for Molecular Dynamics
… because stability severely limits the length of time steps relative to the total length needed for simulations---time steps are in the order of femtoseconds (10-15 seconds) whereas simulations of a few microseconds (10-6 seconds) up to one second are most desired. This situation also holds for …
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Morphometric Characterization of a <i>Mercenaria</i> spp. (Bivalvia) Hybrid Zone: Paleontological and Evolutionary Implications
… in morphological intermediates at ecological time scales (dimorphism, ecophenotypy, and geographic variation). Four alternative causal explanations of morphological intermediates through geological time (primary intergradation, uncoupled genetic and morphological divergence, time-averaged …
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Surface wave, internal wave, and source motion effects on matched field processing in a shallow water waveguide
… on actual sea surface statistics and 2) short time averaging of the measured signal, with times on the order of the period of the surface waves. Mismatch due to internal waves can also result in a large degradation of the estimator. Averaging over the same time period as surface waves provides …
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Hábitos de vida dos trilobitas das formações Maecuru e Ererê (Devoniano), Bacia do Amazonas
… complete specimen, described here, at the first time) – presents a fixed conterminant hypostome, medium size eyes, glabella moderately inflated, glabellar frontal lobe differentiated from the others and glabellar furrows deeper than morphotype I; morphotype III – “Malvinela” australis and …
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Taphonomy, palaeoecology and taxonomy of an ophiuroid-stylophoran obrution deposit from the Lower Devonian Bokkeveld Group, South Africa
… bed reflects a complex history with significant time-averaging. This unique assemblage provides a taphonomic window into the marine ecosystems of the Early Devonian, including the structure of an unusual, echinoderm-dominated benthic community that forms part of a much wider fossil biota from the …
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Evaluating the Capability of ICON-MIGHTI to Detect Plasma Bubbles in the Ionosphere
… The evolution of the ionosphere in the time between the two instruments' measurements is accounted for using seasonal medians of expected behavior. Co-located measurements where the two MIGHTI imagers disagreed significantly were found, filtering out disagreements in measurement not …
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Characterizing Exoplanet Atmospheres: From Light-curve Observations to Radiative-Transfer Modeling
… for estimating parameter uncertainties. The time-averaging and the wavelet-based likelihood methods improve the uncertainty estimations, being within 20 - 50% of the expected value. Chapter 5 describes the open-source Bayesian Atmospheric Radiative Transfer (BART) code to characterize …
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The response of wetlands to sea level rise: Ecologic, paleoecologic, and taphonomic models
… thanatocoenosis. This is due to the effects of time averaging over an otherwise harsh and patchy chemical environment. During rapid sea-level rise, fresh marsh sediments become inundated with brackish to salt water. This tends to raise the pH and Eh, enhancing preservation. The thanatocoenoses …
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Unsteady flows in cantilever compressor stator tip clearances and the effect of real tip geometry
… classical tip leakage vortex is a consequence of time-averaging and does not exist in the true unsteady flow. The tip leakage flow is shown to be truly unsteady and poorly represented by a mean flow and added perturbation. Despite the complexity of the tip leakage flow, the flow within the tip gap …
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Unsteady adjoint analysis for output sensitivity and mesh adaptation
… small-scale output unsteadiness when solved with time-inaccurate iterative solvers. It is demonstrated that unconverged steady flow calculations, even with small output unsteadiness, can lead to significant variability in the estimated output sensitivity due to the arbitrary choice of unconverged …
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Error behavior and optimal discretization of chaotic differential equations
… states) and sampling error due to finite-time averaging of trajectories on the attractor. In this work, we first propose an error model to describe the expected absolute errors on the attractor of a chaotic ordinary differential equation system. This model for the error implies optimal …
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Simulating Bluff-body Flameholders: On the Use of Proper Orthogonal Decomposition for Combustion Dynamics Validation
… reproduce the size, shape, amplitude, and timescale of various dynamic modes which exist the experiment, some of which are dwarfed by the other flow features and are not apparent using time-averaging approaches or by inspection of instantaneous snapshots of the flow.
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Numerical Analysis for Data-Driven Reduced Order Model Closures
… investigation of the closure term's role in long-time integration. We theoretically prove and numerically show that there is energy exchange from the most energetic modes to the least energetic modes in closure terms in a long time averaging. One of the promising contributions of this dissertation …
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