Browsing by Subject "Motion"
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Item Decision-making in the primate brain : formation, location, and causal manipulation(2016-05) Katz, Leor Nadav; Huk, Alexander C.; Aldrich, Richard; Cormack, Lawrence K; Hayhoe, Mary; Priebe, Nicholas; Seidmann, EyalInteraction within the environment relies on the ability to accumulate sensory evidence in favor of a decision. Despite the paramount importance of decision-making to survival, the neural instantiations and computational principles governing the process have remained elusive. In this thesis I consider how sensory evidence is accumulated to guide decisions, and where in the primate brain this process takes place. I report the results of three main experiments. In the first, I test whether sensory evidence is accumulated differentially for motion in the frontoparallel plane (i.e. 2D motion; left/right) compared to motion through depth (i.e. 3D motion; towards/away). I show that integration of 3D motion is different than 2D and likely relies on a mechanism that is distinct. In the second experiment, I test an influential theory in cognitive neuroscience: that neurons in the monkey lateral intraparietal (LIP) cortex accumulate sensory information in favor of a decision communicated by an eye-movement. I found that despite strong correlations between LIP responses and decisions, reversible inactivation of neurons in LIP had no measurable impact on decision-making performance. More generally, I show that decision-related activity does not necessarily play a causal role in choices. In the final experiment, I test whether the process of making a decision stands to influence functions that are decision irrelevant. I found that causally manipulating the amount of sensory evidence available to human observers influenced decision-irrelevant oculomotor commands, suggesting that even during non- oculomotor decisions, oculomotor regions of the brain are recruited. Taken together, the experimental findings reported motivate new ideas about evidence accumulation and advance our understanding of the decision-making process in the primate brain.Item Loose bodies(2010-05) Akers, Madeleine Ruth; Howard, Donald Wayne; Lewis, Richard; Stein, LauraMy thesis film for the Master of Fine Arts degree is a 10-minute documentary entitled Loose Bodies. It traces my mom's recovery from knee replacement surgery, meanwhile exploring her relationship to her knees through interviews and archival footage and my own relationship to my body's ability to move. The film contains three animated sequences, using the Renaissance anatomical drawings of Andreas Vesalius. This report is an account of the filmmaking process from initial idea to finished film.Item On the motion of flexible strings and filaments in inertial and viscous regimes(2007-12) Lin, Bisen, 1976-; Ravi-Chandar, K.Study of the dynamics of strings and filaments has broad applications, for instance, macroscopic coil motion in petroleum engineering and microscopic one-armed swimmers in biological science. In this work, we study the motions of flexible strings and thin filaments in two different regimes, inertial and viscous, theoretically and experimentally. Quantitative experiments on the whirling string show that steady motion exists only when the string whirls at its natural frequencies and that whirling motions for other frequencies exhibit rich dynamics. Furthermore, three kinds of response have been observed experimentally for the planar excitation: planar steady oscillation; two-dimensional (2D) to three-dimensional (3D) transient response; 3D steady whirling motion. These phenomena repeat as the driving frequency is increased. The forced response of a string subjected to planar excitation is analyzed through a perturbation technique and multiple time scale method. The steady-state whirling motion of linear elastic filaments under self-weight with rotary excitation at one end and free at the other has been examined; specifically, the effect of bending stiffness has been investigated both theoretically and experimentally. The theoretical predictions have been compared with the experimental results for thin filaments with different bending stiffness to demonstrate the effect of bending stiffness directly. The dynamic response of thin filaments under planar excitation has also been studied experimentally. The two-dimensional dynamics of an Euler elastica in low-Reynolds number regime has been studied. Tension effects have been shown to be either comparable to or dominant over the bending contributions for the microscopic one-armed swimmers. Hence one may change the tension in situ through the externally or internally generated forces, thus changing the effective bending stiffness, and as a consequence controlling the swimming velocity and the propulsion efficiency. Finally, the low-Reynolds-number dynamics of a micro-string has been studied, in order to understand the physics underpinning eukaryotic sperm flagellar swimming. Both linear analysis of small-amplitude swimming and fully numerical simulations show that time-reversal symmetry is broken, which leads to the propulsion. Numerical studies have been performed for different boundary conditions and different forcing levels. Comparison with previous bending model illustrated that, for the same equivalent bending stiffness, the micro-string has higher propulsion efficiency with similar swimming velocity. Excellent agreement between the simulation predictions and the experimentally observed flagellar wave-forms has been obtained. With this theoretical model, observations of swimming characteristics of the sperm of different species are reconciled into a single scaling relationship, characterized by the so-called \string sperm number". Our results imply that tension plays a crucial role in flagellar elasticity and provides impetus for studying a different model underlying the physics of flagellar swimming. For example, it is possible to postulate alternate hypotheses for active force generation by the dynein motors; it also enables the formulation of a different role to the micro-filaments in general, one based on tension rather than one based on bending.Item Seasonal air and water mass redistribution and its effect on satellite and polar motion(1990-12) Gutiérrez, Roberto, 1951-; Wilson, Clark R.The laser geodetic satellites Lageos and Starlette exhibit residual orbital motion with an unexplained seasonal component. In addition, recognized polar motion excitation sources do not account for a large portion of observed polar motion. It is hypothesized that air and ocean mass redistribution is the primary source of seasonal perturbations in satellite motion, and that wind-driven ocean mass redistribution is a major source for polar motion excitation. Average monthly variations in zonal spherical harmonic geopotential coefficients are estimated from NMC air pressure for 1958 through 1973, and from variations in continental water storage predicted by a global hydrologic model. These coefficients are used to predict average monthly perturbations in the longitude of the ascending node ([Omega]) for Lageos and Starlette, and in the eccentricity vector ([Psi]) for Starlette. WMO monthly air pressures and twice-daily Navy sea level pressures are used to predict time series of [Omega] and [Psi] perturbations for Lageos during 1976 through 1985, and for Starlette during 1980 through 1983. In addition, the Hellerman and Rosenstein wind stress field for world oceans and the Gill-Niiler bottom pressure equation are used to estimate annual and semi-annual ocean mass redistribution, and to predict polar motion excitation vectors and Lageos [Omega] perturbations. Comparison of predicted [Omega] and [Psi] perturbations with observed Lageos and Starlette behavior indicate that air pressure may be responsible for much of the unmodeled seasonal variation in the Earth's geopotential. In contrast, the water storage contribution is very small. Year-to-year variability in the observed Lageos and Starlette [Omega] times series is well matched by predicted perturbations. Even after the removal of annual and semi-annual components, significant coherence remains between predicted and observed [Omega] time series for both Lageos and Starlette at periods of less than one year. Comparison of predicted polar motion with ILS observations suggest that the effect of ocean mass redistribution is significant, and second only to air pressure in magnitude. Lageos [Omega] perturbations predicted from ocean mass redistribution indicate that non-isostatic sea level fluctuations should be readily observable by satellite laser ranging.Item Stories that weave, type that zooms, things that fade away(2003) Molloy, Ryan Benjamin; Olsen, Daniel M., 1963-I do not deny that I am fascinated by type that zooms across the screen, animated characters, fast paced video games, mouse-overs that make objects dance, and images that appear and disappear. It is not just me. The allure and the appeal of the moving image is making the visual language of motion commonplace, whether on-line, in television advertisements, or in movie-title sequences. From this initial attraction, my work delves into two areas of personal interest. The first is story telling: what is the relationship between traditional narratives and the visual language of new media? The digital narratives are the manifestation of a working methodology that questions the result of combining labyrinthine structures, algorithmic controlled objects, video games, three-dimensional spaces, film, and motion for the sake of motion. The second is the transforming translation of the visual language of new media into printed formats. Motion and interactivity dramatically change the way narratives are communicated; multiplicity and malleability become fundamental elements of writing in an inherently static medium. Reading becomes necessarily both spatial and participatory.Item The effects of wave groups on the nonlinear simulation of ship motion in random seas(Texas A&M University, 2006-04-12) Richer, Jeffrey A.Historically, the analysis of ship motion and loading responses has been performed in the frequency domain with both linear response amplitude operators and wave energy density spectra. This method, therefore, did not account for the nonlinear nature of waves. A more precise method is to obtain the response in the time domain, processing non-linear wave data with a linear response amplitude operator. Since the input is non-linear, even though the system is linear, the output will also be non-linear. This resultant data can then be used to generate a more accurate design of seaworthy vessels. Furthermore the linear frequency domain method does not account for the presence or effects of wave groups. This study shows the improved accuracy in the response obtained by accounting for non-linearities and furthermore indicates that wave groups affect the vertical relative motion of a moored ship (zero-speed).