Browsing by Subject "Resolution"

Now showing 1 - 4 of 4

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, Todd
Experimental 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.
Characterizing the depth dependence of resolution and signal strength for two-photon microscopy
(2018-05-03) Olin, Katherine Elizabeth; Dunn, Andrew Kenneth, 1970-
Two-photon (2P) microscopy is a useful tool for studying structure and function of biological samples. As optical optimizations occur in 2P systems that allow imaging at deeper depths, there is a need to characterize the resolution and the signal interactions with tissue at these depths. Here, we discuss processes to determine the resolution of a 2P microscope using sub-resolution sized micro-spheres to mimic point spread functions. Through this process, the resolution of the microscope was determined to be about 0.942 μm in vitro and about 1.08 μm in vivo, values that did not change with respect to depth. Additionally, we investigated the relationship between contrast, background intensity, and noise with depth in vivo. From this study, contrast decreased with depth, while background intensity and noise both increased. These results suggest that the decrease in resolving power at deep depths is likely due to the inability to differentiate signal from background and not due to a decrease in the overall resolution of the system.
Improving resolution of NMO stack using shaping regularization
(2016-05) Regimbal, Kelly Alaine; Fomel, Sergey B.; Zahm, Christopher Kent; Spikes, Kyle
Common 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.
Trajectory patterns of ethnic identity among Mexican-origin female adults : the role of age of arrival to the U.S.
(2023-04-24) Tse, Hin Wing; Kim, Su Yeong
Extant research on ethnic identity have primarily focused on adolescence, overlooking the development of ethnic identity in adulthood, which is a critical gap in the literature from a lifespan perspective. Additionally, past research has shown that age of arrival to a host country may determine the overall exposure to sociocultural contexts, which could trigger a variation of trajectory patterns in ethnic identity at later stage of life (e.g., during adulthood). Using a three-wave longitudinal dataset of 596 Mexican-born female adults, three independent growth mixture models were estimated to identify variation in trajectory patterns of ethnic identity exploration, resolution, and centrality. Two distinct trajectories were found in each component of ethnic identity. Associations between linear/quadratic effect of age of arrival to the U.S. and trajectory patterns of ethnic identity exploration, resolution, and centrality were examined, controlling for demographics, including age, income, and education at Wave 1. Results indicated that age of arrival to the U.S. (linear and quadratic terms) were not significant predictors of trajectory patterns of ethnic identity. Study findings add to our understanding of the contemporary lifespan model of ethnic identity development and show that ethnic identity continues to evolve beyond young adulthood. This study may also provide insights for future research on how different trajectory patterns of individual ethnic identity component may be linked to psychological and sociocultural adaptation outcomes in adult immigrant populations.