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You searched for subject:(Doppler Shifts). Showing records 1 – 3 of 3 total matches.

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Virginia Tech

1. Yin, Xiaoyan. The Role of Actively Created Doppler shifts in Bats Behavioral Experiments and Biomimetic Reproductions.

Degree: PhD, Mechanical Engineering, 2021, Virginia Tech

Bats are well-known for their intricate biosonar system that allow the animals to navigate even the most complex natural environments. While the mechanism behind most of these abilities remains unknown, an interesting observation is that some bat species produce fast movements of their ears when actively exploring their surroundings. By moving their pinna, the bats create a time-variant reception characteristic and very little research has been directed at exploring the potential benefits of such behavior so far. One hypothesis is that the speed of the pinna motions modulates the received biosonar echoes with Doppler-shift patterns that could convey sensory information that is useful for navigation. This dissertation intends to explore this hypothetical dynamic sensing mechanism by building a soft-robotic biomimetic receiver to replicate the dynamics of the bat pinna. The experiments with this biomimetic pinna robot demonstrate that the non-rigid ear motions produce Doppler signatures that contain information about the direction of a sound source. However, these patterns are difficult to interpret because of their complexity. By combining the soft-robotic pinna with a convolutional neural network for processing the Doppler signatures in the time-frequency domain, I have been able to accurately estimate the source direction with an error margin of less than one degree. This working system, composed of a soft-robotic biomimetic ear integrated with a deep neural net, demonstrates that the use of Doppler signatures as a source of sensory information is a viable hypothesis for explaining the sensory skills of bats. Advisors/Committee Members: Mueller, Rolf (committeechair), Socha, John (committee member), Leonessa, Alexander (committee member), Abaid, Nicole Teresa (committee member), Roan, Michael J. (committee member).

Subjects/Keywords: Bats; Biosonar; Pinna Motions; Doppler Shifts; Direction finding; Biomimetics; Deep Learning

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APA (6th Edition):

Yin, X. (2021). The Role of Actively Created Doppler shifts in Bats Behavioral Experiments and Biomimetic Reproductions. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/101965

Chicago Manual of Style (16th Edition):

Yin, Xiaoyan. “The Role of Actively Created Doppler shifts in Bats Behavioral Experiments and Biomimetic Reproductions.” 2021. Doctoral Dissertation, Virginia Tech. Accessed February 28, 2021. http://hdl.handle.net/10919/101965.

MLA Handbook (7th Edition):

Yin, Xiaoyan. “The Role of Actively Created Doppler shifts in Bats Behavioral Experiments and Biomimetic Reproductions.” 2021. Web. 28 Feb 2021.

Vancouver:

Yin X. The Role of Actively Created Doppler shifts in Bats Behavioral Experiments and Biomimetic Reproductions. [Internet] [Doctoral dissertation]. Virginia Tech; 2021. [cited 2021 Feb 28]. Available from: http://hdl.handle.net/10919/101965.

Council of Science Editors:

Yin X. The Role of Actively Created Doppler shifts in Bats Behavioral Experiments and Biomimetic Reproductions. [Doctoral Dissertation]. Virginia Tech; 2021. Available from: http://hdl.handle.net/10919/101965


Louisiana State University

2. Rashid, Mohammed. Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar.

Degree: MSEE, Signal Processing, 2018, Louisiana State University

Bistatic passive radar (BPR) system does not transmit any electromagnetic signal unlike the active radar, but employs an existing Illuminator of opportunity (IO) in the environment, for instance, a broadcast station, to detect and track the targets of interest. Therefore, a BPR system is comprised of two channels. One is the reference channel that collects only the IO signal, and the other is the surveillance channel which is used to capture the targets' reflected signals. When the IO signal reflected from multiple targets is captured in the surveillance channel (SC) then estimating the delays and Doppler shifts of all the observed targets is a challenging problem. For BPR system, the signal processing algorithms developed so far models the IO waveform as a deterministic process and discretizes the delays and Doppler shifts parameters. In this thesis, we deal with the problem of jointly estimating the delays and Doppler shifts of multiple targets in a BPR system (i.e., a two channel system) when the unknown IO signal is modeled as a correlated stochastic process. Unlike the previous work, we take all the delays and Doppler shifts as continuous-valued parameters to avoid straddle loss due to discretization and propose a computationally efficient Expectation-Maximization (EM) based algorithm that breaks up the complex multidimensional maximum likelihood optimization problem into multiple separate optimization problems. The EM algorithm jointly provides the estimates of all the delays and Doppler shifts of the targets along with the estimate of each target's component signal in the SC and the estimate of the unknown IO signal. We also derive the Cramer-Rao lower bound for the considered multitarget estimation problem with stochastic IO signal. Numerical simulations are presented where we compare our proposed EM-based multi-target estimator with the widely used conventional cross correlation estimator under different multitarget environments.

Subjects/Keywords: stochastic IO signal; passive radar; multiple target localization; EM algorithm; delays and Doppler shifts estimation; optimization

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APA (6th Edition):

Rashid, M. (2018). Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar. (Masters Thesis). Louisiana State University. Retrieved from https://digitalcommons.lsu.edu/gradschool_theses/4678

Chicago Manual of Style (16th Edition):

Rashid, Mohammed. “Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar.” 2018. Masters Thesis, Louisiana State University. Accessed February 28, 2021. https://digitalcommons.lsu.edu/gradschool_theses/4678.

MLA Handbook (7th Edition):

Rashid, Mohammed. “Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar.” 2018. Web. 28 Feb 2021.

Vancouver:

Rashid M. Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar. [Internet] [Masters thesis]. Louisiana State University; 2018. [cited 2021 Feb 28]. Available from: https://digitalcommons.lsu.edu/gradschool_theses/4678.

Council of Science Editors:

Rashid M. Multitarget Joint Delay and Doppler Shift Estimation in Bistatic Passive Radar. [Masters Thesis]. Louisiana State University; 2018. Available from: https://digitalcommons.lsu.edu/gradschool_theses/4678

3. Reep, Jeffrey. Evidence for Impulsive Heating of Active Region Coronal Loops.

Degree: MS, Natural Sciences, 2013, Rice University

We present observational and numerical evidence supporting the theory of impulsive heating of the solar corona. We have run numerical simulations solving the hydrodynamic equations for plasma confined to a magnetic flux tube, for the two distinct cases of steady and impulsive heating. We find that steady heating cannot explain the observed amount of low-temperature plasma in active regions on the sun. The results for impulsive heating closely match those of the observations. The ratio of heating time to cooling time predominantly determines the observed temperature distribution of the plasma. We have also identified an observational bias in calculating intensities of spectral lines in previous studies, which causes an under-estimation of low-temperature plasma. We predict Doppler shifts in the observed line emission that are in agreement with observations, and which may serve as a diagnostic of the strength of heating. We conclude that impulsive heating of active region coronal loops is more likely than steady heating. Advisors/Committee Members: Bradshaw, Stephen (advisor), Alexander, David (committee member), Ecklund, Karl (committee member).

Subjects/Keywords: Solar physics; Coronal physics; Solar atmosphere; Coronal heating; Coronal loops; Active regions; Impulsive heating; Emission measure; Doppler shifts; Corona; Rice University; Astrophysics

…simulations 5-8 The temperature at which the lines switch from red- to blue- 105 shifts versus… …the loop cooling time for the 20 simulations 5-9 Doppler shift velocities versus… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Reep, J. (2013). Evidence for Impulsive Heating of Active Region Coronal Loops. (Masters Thesis). Rice University. Retrieved from http://hdl.handle.net/1911/71685

Chicago Manual of Style (16th Edition):

Reep, Jeffrey. “Evidence for Impulsive Heating of Active Region Coronal Loops.” 2013. Masters Thesis, Rice University. Accessed February 28, 2021. http://hdl.handle.net/1911/71685.

MLA Handbook (7th Edition):

Reep, Jeffrey. “Evidence for Impulsive Heating of Active Region Coronal Loops.” 2013. Web. 28 Feb 2021.

Vancouver:

Reep J. Evidence for Impulsive Heating of Active Region Coronal Loops. [Internet] [Masters thesis]. Rice University; 2013. [cited 2021 Feb 28]. Available from: http://hdl.handle.net/1911/71685.

Council of Science Editors:

Reep J. Evidence for Impulsive Heating of Active Region Coronal Loops. [Masters Thesis]. Rice University; 2013. Available from: http://hdl.handle.net/1911/71685

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