作者:Li, Feng;Cho, Richard W.;Buhl, Lauren Kaye;等 学位:
Li, Feng;Cho, Richard W.;Buhl, Lauren Kaye;等
Synaptic plasticity is a fundamental feature of the nervous system that allows adaptation to changing behavioral environments. Most studies of synaptic plasticity have examined the regulated trafficking of postsynaptic glutamate receptors that generates alterations in synaptic transmission. Whether and how changes in the presynaptic release machinery contribute to neuronal plasticity is less clear. The SNARE complex mediates neurotransmitter release in response to presynaptic Ca[superscript 2+] entry. Here we show that the SNARE fusion clamp Complexin undergoes activity-dependent phosphorylation that alters the basic properties of neurotransmission in Drosophila. Retrograde signaling following stimulation activates PKA-dependent phosphorylation of the Complexin Cterminus that selectively and transiently enhances spontaneous release. Enhanced spontaneous release is required for activity-dependent synaptic growth. These data indicate that SNAREdependent fusion mechanisms can be regulated in an activity-dependent manner and highlight the key role of spontaneous neurotransmitter release as a mediator of functional and structural plasticity.
作者:Filipowicz, Alexandre 学位:
关键词:Belief Updating;Mental Model;...
To make sense of the world, humans build mental models that guide actions and expectations. These mental models need to be receptive to change and updated when they no longer accurately predict observations from an environment. Although ubiquitous in our everyday lives, research is still uncovering the factors that guide mental model building and updating. A significant challenge arises from the need to characterize how mental models can be both robust to noisy, stochastic fluctuations, while also being flexible to environmental changes. The current thesis explores this trade-off by examining some of the main components involved in updating. Chapter 2 proposes a novel task to measure the influence of prior mental models on the way new information is integrated. Chapter 3 tests the role of unexpected, ;;surprising’ events on our ability to detect changes in the environment. Chapter 4 measures the strategies used to explore new mental models, after a change has been detected, and how specific forms of brain damage influence these strategies. The results from this thesis provide novel insights into the behavioural and neural mechanisms that underlie mental model updating. The last chapter situates these results in existing literature, and suggests directions for future research.
作者:Baros, Stefanos, Ilić, Marija D. 学位:
Baros, Stefanos, Ilić, Marija D.
In this work, we propose a distributed control methodology that solves the problem of dispatching and regulating the power outputs of a group of deloaded wind Double- Fed Induction Generators (DFIGs) so that wind farm (WF) power output regulation is attained. Our control methodology guarantees additionally that fair load-sharing among the DFIGs is achieved. In our context, fair load-sharing means that, the ratio defined by the mechanical power over the maximum power from the wind i.e the utilization level, of all DFIGs, is the same in steady state. Dynamic, distributed dispatch and control of the power outputs of DFIGs refers to their ability to self-dispatch and regulate their power outputs under dynamical conditions and through peer-to-peer information exchange. Initially, we propose a leader-follower consensus protocol that DFIGs can adopt into their control system to attain: a) asymptotic consensus on their utilization levels (i.e fair load-sharing), b) total power output regulation. Then, we perform compositional stability analysis of the protocol and design a distributed Control Lyapunov Function (CLF) - based torque controller for the rotor-side converter (RSC) that realizes the protocol. Finally, the performance of our proposed distributed control methodology is evaluated through simulations on the modified IEEE 24-bus RT system.
作者:Sancar, Feyyaz Emre 学位:
关键词:Platoon Merging;Autonomous Highways;...
Sancar, Feyyaz Emre
As low-cost reliable sensors are introduced to market, research efforts in autonomous driving are increasing. Traffic congestion is a major problem for nearly all metropolis;;. Assistive driving technologies like cruise control and adaptive cruise control are widely available today. While these control systems ease the task of driving, the driver still needs to be fully alert at all times. While these existing structures are helpful in alleviating the stress of driving to a certain extent, they are not enough to improve traffic flow. Two main causes of congestion are slow response of drivers to their surroundings, and situations like highway ramp merges or lane closures. This thesis will address both of these issues.A modified version of the widely available adaptive cruise control systems, known as cooperative adaptive cruise control, can work at all speeds with additional wireless communication that improves stability of the controller. These structures can tolerate much smaller desired spacing and can safely work in stop and go traffic. This thesis proposes a new control structure that combines conventional cooperative adaptive cruise control with rear end collision check. This approach is capable of avoiding rear end collisions with the following car, as long as it can still maintain the safe distance with the preceding vehicle. This control structure is mainly intended for use with partially automated highways, where there is a risk of being rear-ended while following a car with adaptive cruise control. Simulation results also shows that use of bidirectional cooperative adaptive cruise control also helps to strengthen the string stability of the platoon. Two different control structures are used to accomplish this task: MPC and PD based switching controller.Model predictive control (MPC) structure works well for the purpose of bidirectional platoon control. This control structure can adapt to the changes in the plant with the use of a parameter estimator. Constraints are set to make sure that the controller outputs are always within the boundaries of the plant. Also these constraints assures that a certain gap will always be kept with the preceding vehicle. PD based switching controller offers an alternative to the MPC structure. Main advantage of this control structure is that it is designed to be robust to certain level of sensor noise. Both these control structures gave good simulation results.The thesis makes use of the control structures developed in the earlier chapters to continue developing structures to alleviate traffic congestions. Two merging schemes are proposed to find a solution to un-signaled merging and lane closures. First problem deals with situations where necessary levels of communication is not present to inform surrounding drivers of merging intention. Second structure proposes a merging protocol for cases where two platoons are approaching a lane closure. This structure makes use of the modified cooperative adaptive cruise control structures proposed earlier in the thesis.
作者:Azhari, Amir 学位:
Additive manufacturing (AM) introduces a new era for the fabrication of 3D structures. AM, as an emerging and disruptive manufacturing technology, has the potential to be employed for fabrication of polymeric, metallic, and ceramic structures. Although AM is now being used for commercial applications, there are still many challenges in incorporating high-performance materials into these techniques and employing them to fabricate practical devices. For instance, reduced graphene oxide (RGO) has interesting properties such as high specific surface area and lattice defects with tunable functional groups which make it ideal for different applications. However, there is still a substantial need to introduce reliable manufacturing techniques for RGO-based devices while attaining the utmost performance of graphene-based materials. In this study, a binder-jetting powder-bed AM technique has been employed to fabricate graphene-based structures and devices for energy storage and sensing applications.First, 3D structures of graphene/hydroxyapatite (Hap) based composite with potential applications in bone-implantation were fabricated using AM technique. Hap suffers from lack of sufficient mechanical strength which has limited its application for practical use. The compressive strength of the 3D printed structures were tested and the printing parameters were optimized to improve the mechanical behavior of the specimens.It was shown that at a layer thickness of 125 μm and core binder saturation level of 400%, the mechanical strength of HG4 structures with only 0.4 wt.% of graphene oxide were 70 times more than that of HG0 structures.Our next goal was to print pure graphene-based structures for energy and sensing applications. Hence, graphene oxide was first synthesized through Hummer’s method and then reduced it through thermal and chemical methods to compare their performance for energy applications. The as-obtained thermally and chemically reduced graphene-oxide based powder were both 3D printed and studied accordingly. It was revealed that the gravimetric capacitance of thermally reduced graphene oxide (TRGO) 3D printed electrodes were 3-4 times higher than that of chemically reduced powder. Therefore, TRGO powder was selected for further studies and optimization. In order to improve the performance of 3D printed TRGO based electrodes, a nano palladium dispersion was synthesized and injected into the electrodes after printing. TRGO based decorated with nano palladium particles showed an impressive capacitance of 265 F/g and 700 mF/cm2 at 5 mV/s. This study can introduce a new potential application of AM for the fabrication of graphene-based supercapacitor devices.In addition, a graphene-based humidity sensing devices was also fabricated using powder-bed AM technique. The results obtained from this device were promising and demonstrated a great potential for the use of AM for manufacturing of graphene-based sensor devices.
作者:Mohammadi, Fatemeh 学位:
关键词:3D optical metrology;Digital moiré;...
Fast, accurate three dimensional (3D) optical metrology has diverse applications in object and environment modelling. Structured-lighting techniques allow non-contacting 3D surface-shape measurement by projecting patterns of light onto an object surface, capturing images of the deformed patterns, and computing the 3D surface geometry from the captured 2D images. However, motion artifacts can still be a problem with high-speed surface-motion especially with increasing demand for higher measurement resolution and accuracy. To avoid motion artifacts, fast 2D image acquisition of projected patterns is required. Fast multi-pattern projection and minimization of the number of projected patterns are two approaches for dynamic object measurement. To achieve a higher rate of switching frames, fast multi-pattern projection techniques require costly projector hardware modification or new designs of projection systems to increase the projection rate beyond the capabilities of off-the-shelf projectors. Even if these disadvantages were acceptable (higher cost, complex hardware), and even if the rate of acquisition achievable with current systems were fast enough to avoid errors, minimization of the number of captured frames required will still contribute to reduce further the effect of object motion on measurement accuracy and to enable capture of higher object dynamics. Development of an optical 3D metrology method that minimizes the number of projected patterns while maintaining accurate 3D surface-shape measurement of objects with continuous and discontinuous surface geometry has remained a challenge. Capture of a single image-frame instead of multiple frames would be advantageous for measuring moving or deforming objects. Since accurate measurement generally requires multiple phase-shifted images, imbedding multiple patterns into a single projected composite pattern is one approach to achieve accurate single-frame 3D surface-shape measurement. The main limitations of existing single-frame methods based on composite patterns are poor resolution, small range of gray-level intensity due to collection of multiple patterns in one image, and degradation of the extracted patterns because of modulation and demodulation processes on the captured composite pattern image. To benefit from the advantages of multi-pattern projection of phase-shifted fringes and single-frame techniques, without combining phase-shifted patterns into one frame, digital moiré was used. Moiré patterns are generated by projecting a grid pattern onto the object, capturing a single frame, and in a post-process, superimposing a synthetic grid of the same frequency as in the captured image. Phase-shifting is carried out as a post-process by digitally shifting the synthetic grid across the captured image. The useful moiré patterns, which contain object shape information, are contaminated with a high-frequency grid lines that must be removed. After performing grid removal, computation of a phase map, and phase-to-height mapping, 3D object shape can be computed. The advantage of digital moiré provides an opportunity to decrease the number of projected patterns. However, in previous attempts to apply digital phase-shifting moiré to perform 3D surface-shape measurement, there have been significant limitations.To address the limitation of previous system-calibration techniques based on direct measurement of optical-setup parameters, a moiré-wavelength based phase-to-height mapping system-calibration method was developed. The moiré-wavelength refinement performs pixel-wise computation of the moiré wavelength based on the measured height (depth). In measurement of a flat plate at different depths, the range of root-mean-square (RMS) error was reduced from 0.334 to 0.828 mm using a single global wavelength across all pixels, to 0.204 to 0.261 mm using the new pixel-wise moiré-wavelength refinement.To address the limitations of previous grid removal techniques (precise mechanical grid translation, multiple-frame capture, moiré-pattern blurring, and measurement artifacts), a new grid removal technique was developed for single-frame digital moiré using combined stationary wavelet and Fourier transforms (SWT-FFT). This approach removes high frequency grid both straight and curved lines, without moiré-pattern artifacts, blurring, and degradation, and was an improvement compared to previous techniques.To address the limitations of the high number of projected patterns and captured images of temporal phase unwrapping (TPU) in fringe projection, and the low signal-to-noise ratio of the extended phase map of TPU in digital moiré, improved methods using two-image and three-image TPU in digital phase-shifting moiré were developed. For measurement of a pair of hemispherical objects with true radii 50.80 mm by two-image TPU digital moiré, least-squares fitted spheres to the measured 3D point clouds had errors of 0.03 mm and 0.06 mm, respectively (sphere fitting standard deviations 0.15 mm and 0.14 mm), and the centre-to-centre distance measurement between hemispheres had an error of 0.19 mm. The number of captured images required by this new method is one third that for three-wavelength heterodyne temporal phase unwrapping by fringe projection techniques, which would be advantageous in measuring dynamic objects, either moving or deforming.