Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Development of the translaminar circuits in the mouse cortex(2020) Deng, Rongkang; Kanold, Patrick O; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The elaborated connections among cortical neurons form the cortical circuits, which are essential mechanisms underlying various cortical functions such as sensory perception, motor control, and other cognitive functions. The cortical circuits are composed of excitatory neurons and GABAergic interneurons. Excitatory neurons send excitatory connections to cortical neurons, while inhibitory neurons send inhibitory connections. Building the neural circuits is no easy task involving complex genetic programs and the influence of the environment through sensation. Malformation of the cortical circuits during development is implicated in causing neurological disorders, but our knowledge about the developmental process is scarce. The work in this dissertation uses in vitro electrophysiology in brain slices from transgenic mice to investigate how the excitatory connections onto GABAergic interneurons in the primary auditory cortex develop during the first two postnatal weeks. Furthermore, this dissertation explores the mechanisms that could regulate the early development of the cortical circuits by testing the requirement of sensory epithelium and N-methyl-D-aspartate receptors (NMDARs) in the early postnatal development of the neural circuits in the primary sensory cortex and temporal association cortex (TeA), respectively. Results from these studies fill crucial gaps in our understanding of how GABAergic interneurons are integrated into the cortical circuits and highlight the importance of sensory epithelium in the normal development of excitatory connections onto cortical GABAergic interneurons. My results also showed impaired development of GABAergic connections onto excitatory neurons lacking functional NMDARs in the TeA, suggesting an essential role of NMDARs for the early development of inhibitory circuits in the cortex.Item High power microwave interference effects on analog and digital circuits in IC's(2008-01-17) Kim, Kye Chong; Iliadis, Agis A.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microwave or electromagnetic interference (EMI) can couple into electronic circuits and systems intentionally from high power microwave (HPM) sources or unintentionally due to the proximity to general electromagnetic (EM) environments, and cause "soft" reversible upsets and "hard" irreversible failures. As scaling-down of device feature size and bias voltage progresses, the circuits and systems become more susceptible to the interference. Thus, even low power interference can disrupt the operation of the circuits and systems. Furthermore, it is reported that even electronic systems under high level of shielding can be upset by intentional electromagnetic interference (IEMI), which has been drawing a great deal of concern from both the civil and military communities, but little has been done in terms of systematic study and investigation of these effects on IC circuits and devices. We have investigated the effects of high power microwave interference on three levels, (a) on fundamental single MOSFET devices, (b) on basic CMOS IC inverters and cascaded inverters, and (c) on a representative large IC timer circuit for automotive applications. We have studied and identified the most vulnerable static and dynamic parameters of operation related to device upsets. Fundamental upset mechanisms in MOSFETs and CMOS inverters and their relation to the characteristics of microwave interference (power, frequency, width, and period) and the device properties such as size, mobility, dopant concentration, and contact resistances, were investigated. Critical upsets in n-channel MOSFET devices resulting in loss of amplifier characteristics, were identified for the power levels above 10dBm in the frequency range between 1 and 20 GHz. We have found that microwave interference induced excess charges are responsible for the upsets. Upsets in the static operation of CMOS inverters such as noise margins, output voltages, power dissipation, and bit-flip errors were identified using a load-line characteristic analysis. We developed a parameter extraction method that can predict the dynamic operation of inverters under microwave interference from DC load-line characteristics. Using the method, the effects of microwave interference on propagation delays, output voltage swings, and output currents as well as their relation to device scaling, were investigated. Two new critical hard error sources in MOSFETs and CMOS inverters regarding power dissipation and power budget disruption were found. EMI hardened design for digital circuits has been proposed to mitigate the stress on the devices, the contacts, and the interconnects. We found important new bit-flip and latch-up errors under pulsed microwave interference, which demonstrated that the excess charge effects are due to electron-hole pair generation under microwave interference. We proposed a theory of excess charge effects and obtained good agreement of our excess charge model with our experimental results. Further work is proposed to improve the vulnerabilities of integrated circuits.