Browsing by Subject "Resolution"
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Item Anisotropic hybrid turbulence modeling with specific application to the simulation of pulse-actuated dynamic stall control(2015-12) Haering, Sigfried William; Moser, Robert deLancey; Murthy, Jayathi; Bogard, David G; Ezekoye, Ofodike A; Oliver, ToddExperimental studies have shown pulse actuated dynamic stall control may provide a simple means to significantly increase the performance of lifting surfaces and expand their flight envelope. However, precise information of the complex boundary layer reattachment mechanisms are inaccessible to experimental measurements. Therefore, simulations are necessary to fully understand, optimize, and apply this method. Due to the inherent shortcomings of RANS, computational expense of LES, and deficiencies in current hybrid modeling approaches, a new hybrid modeling framework has been developed. Based in using the two-point second-order structure function to drive a local equilibrium between resolved and modeled turbulence, the new approach addresses issues associated with inhomogeneous and anisotropic grids as well as the treatment of the RANS/LES interface in hybrid simulations. Numerical studies using hybrid RANS/LES modeling approaches of a stalled airfoil with spanwise-uniform actuation regions experiencing single pulse actuated flow reattachment have been performed. The mechanism responsible for reattachment has been identified as a repeating wall-vortex interaction process. The new hybrid framework and anisotropic SGS models developed here are anticipated to be of great benefit well beyond the focus of this work with application to many challenging flow situations of pressing engineering interest.Item Development of a variable-temperature ion mobility/ time-of-flight mass spectrometer for separation of electronic isomers(Texas A&M University, 2005-08-29) Verbeck, Guido FridolinThe construction of a liquid nitrogen-cooled ion mobility spectrometer coupled with time-of-flight mass spectrometry was implemented to demonstrate the ability to discriminate between electronic isomers. Ion mobility allows for the separation of ions based on differing cross-sections-to-charge ratio. This allows for the possible discrimination of species with same mass if the ions differ by cross-section. Time-offlight mass spectrometry was added to mass identify the separated peak for proper identification. A liquid nitrogen-cooled mobility cell was employed for a two-fold purpose. First, the low temperatures increase the peak resolution to aid in resolving the separated ions. This is necessary when isomers may have similar cross-sections. Second, low temperature shortens the mean free path and decreases the neutral buffer gas speeds allowing for more interactions between the ions and the drift gas. Kr2+ study was performed to verify instrument performance. The variable-temperature ion mobility spectrometer was utilized to separate the distonic and conventional ion forms of CH3OH, CH3F, and CH3NH2 and to discriminate between the keto and enol forms of the acetone radical cation. Density functional theory and ab initio calculations were employed to aid in proper identification of separating isomers. Monte Carlo integration tools were also developed to predict ion cross-section and resolution within a buffer gas.Item Improving resolution of NMO stack using shaping regularization(2016-05) Regimbal, Kelly Alaine; Fomel, Sergey B.; Zahm, Chris; Spikes, KyleCommon midpoint (CMP) stacking is one of the major steps in seismic data processing. Traditional CMP stacking sums a combination of normal moveout (NMO) corrected traces across a CMP gather to produce a single trace with a higher signal-to-noise (S/N) ratio than that of individual traces within the gather. Several problems arise with the assumptions and principles of conventional NMO and stack. NMO correction causes undesirable distortions of signals on a seismic trace known as "NMO stretch", which lowers the frequency content of the corrected reflection event at far offsets. This violates the assumption of a uniform distribution of phase and frequency of seismic reflections across the corrected gather. Common procedures to eliminate this stretching effect involve muting all of the samples with severe distortions. This causes a decrease in fold and can destroy useful far-offset information essential for amplitude variation with offset (AVO) analysis. Inaccuracy in stretch muting with residual "stretching" effects produces a lower amplitude and lower resolution stack. I present two methods that eliminate the effects of "NMO stretch" and restore a wider frequency band by replacing conventional NMO and stack with a regularized inversion to zero offset. The resulting stack is a model that best fits the data using additional constraints imposed by the method of shaping regularization. Shaping regularization implies a mapping of the input model to a space of acceptable models. The shaping operator is integrated in an iterative inversion algorithm and provides an explicit control on the estimated stack. I use shaping regularization to achieve a stack that has a denser time sampling and contains higher frequencies than the conventional stack. In the first approach, I define the backward operator of shaping regularization using the principles of conventional NMO correction and stack. In the second approach, I introduce a recursive stacking scheme using plane-wave construction in the backward operator of shaping regularization. The advantage of using recursive stacking along local slopes in the application to NMO and stack is that it avoids "stretching" effects caused by NMO correction and is insensitive to non-hyperbolic moveout in the data. Numerical tests demonstrate each algorithm's ability to attain a higher frequency stack with a denser temporal sampling interval compared to those of the conventional stack and to minimize stretching effects caused by NMO correction. I apply both methods to two 2-D marine datasets from the North Sea and achieve noticeable resolution improvements in the stacked sections compared with that of conventional NMO and stack. By treating NMO and stack as an iterative inversion using shaping regularization, resolution is enhanced by utilizing signal from different offsets and minimizing stretching effects to reconstruct a high resolution stack.Item n-3 PUFA and Curcumin Modulate the Resolution of Murine Intestinal Inflammtion(2011-07-30) Jia, Qian 1980-Bioactive food components containing n-3 polyunsaturated fatty acids (PUFA) and curcumin modulate multiple determinants that link inflammation to cancer initiation and progression. In this dissertation, both transgenic and dietary mouse models were used to elucidate the effect of n-3 PUFA and curcumin treatment on murine intestinal inflammation. Specifically, fat-1 transgenic mice, which convert endogenous n-6 PUFA to n-3 PUFA in multiple tissues, exhibited a reduced number of colonic adenocarcinomas per mouse (1.05 plus/minus 0.29 versus 2.12 plus/minus 0.51, P = 0.033), elevated apoptosis (P = 0.03), and a decrease in n-6 PUFA?derived eicosanoids compared with wild-type (wt) mice in an azoxymethane (AOM) - dextran sodium sulfate (DSS) model. Following a 2-week recovery period after 5 days of DSS exposure, colonic inflammation and ulceration scores returned to pretreatment levels only in fat-1 mice. In addition, fat-1 vs wt mice exhibited decreased (P < 0.05) levels of CD3 , CD4 T helper, and macrophage cell numbers in the colon. The ability of n-3 PUFA to favorably modulate the resolution of intestinal inflammation in fat-1 mice was linked to an enhancement (P < 0.05) in the percentage of colonic lamina propria (cLP) CD4 FoxP3 cells and a decrease in both splenic and cLP Th17 cells (0.8 vs 1.2 percent in spleen, 1.4 vs 1.7 percent in colon) (P < 0.05) in fat-1 mice compared to wt. These results suggest that the antitumorigenic effect of n-3 PUFA may be mediated via its anti-inflammatory properties. The combined effect of n-3 PUFA and curcumin on DSS induced colitis was assessed in C57BL/6 mice. Addition of fish oil (FO) and/or curcumin to a corn oil (CO) based diet increased animal mortality compared to CO alone (P < 0.05). Consistently, following 1 or 2 cycles of DSS treatment, both dietary FO and curcumin promoted mucosal injury/ulceration compared to CO. However, compared to other diets, FO and curcumin combined feeding enhanced the resolution of chronic inflammation and suppressed (p < 0.05) a key inflammatory mediator, NF-kB, in colon mucosa. Mucosal microarray analysis revealed that dietary FO and curcumin differentially modulated the expression of genes induced by DSS treatment. These results suggest that dietary lipids and curcumin interact to regulate mucosal homeostasis and the resolution of chronic inflammation in the colon.