Zugl.: Karlsruhe, University, Diss., 2007.

Stuttgart, Univ., Diss., 2002.

Ulm, Univ. Diss., 2006.

Universiẗat, Diss., 2001--Jena.

Techn. Universiẗat, Diss., 2003--Berlin.

Techn. Universiẗat, Diss., 2003--Berlin.

Techn. Universiẗat, Diss., 2005--Berlin.

THz light has important applications in medical imaging, chemical sensing, industrial quality control, and future wireless communications. However, the widespread adoption of these applications is currently limited by the lack of practical sources of THz radiation that can operate at or near room temperature. Graphene is a promising materials system for basic studies and device applications in THz optoelectronics, with several key functionalities, including photodetection and optical modulation, already demonstrated in recent years. This thesis work is focused on the use of graphene for the THz light emission. In particular, I have demonstrated for the first time the generation of gate-tunable THz radiation from graphene nanoribbons under current injection. The underlying radiation mechanism involves the excitation of graphene plasmonic oscillations by the injected hot carriers and their subsequent radiative decay at the nanoribbon resonance frequency. Combined with suitably designed optical elements, this approach is promising for the development of compact THz sources for imaging and sensing applications. In addition, I have also investigated alternative radiation mechanisms that can provide higher efficiencies but require more complex ultra-high-mobility graphene samples. These mechanisms include Smith-Purcell emission by the graphene electron gas in the vicinity of a periodic grating and interminiband transitions in graphene superlattices produced with a periodic external potential. Finally, I have designed and investigated numerically a graphene-nanoribbon metasurface platform that can provide arbitrary wavefront shaping functionalities for incident THz light, such as beam steering and focusing. Importantly, this device can be actively reconfigured by varying the nanoribbon gate voltages, which makes it particularly attractive for applications in wireless communications beyond 5G.

The pathophysiology, etiology, and treatment of schizophrenia remain elusive, but research is closing the gap. Schizophrenia globally affects less than 1% of the population and presents with positive, negative, and cognitive symptoms. As treatment for schizophrenia is not completely and meaningfully effective at treating all of the symptoms, without eliciting side effects, the current thesis aimed to evaluate a new drug candidate. PAOPA is a novel allosteric modulator that increases dopamine binding to the dopamine D2 receptor. It has previously shown positive findings in preventing and reversing behaviours proposed to model phenotypes of schizophrenia. However, it has not yet been tested to improve cognitive deficits in animal models, nor has its effects on other animals models been investigated. Lastly, its mechanism of action has not yet been comprehensively answered. In three separate studies, PAOPA was tested on ameliorating attentional deficits using the 5-choice serial reaction time task in an amphetamine model, deficits in novel objection recognition memory, sensorimotor gating, social interaction, and locomotor activity using a PCP model, and its effects on proteins regulating G protein-coupled receptors (GRK2 and arrestin-3), downstream signalling (ERK1 and ERK2), and synaptic vesicular control (synapsin II) were investigated. Although the sample sizes were too small to draw valid interpretations, the results suggested that PAOPA partially attenuated deficits in attention, novel object recognition memory, social interaction, sensorimotor gating, but not locomotor. Furthermore PAOPA increased the protein expression of GRK2, arrestin-3, ERK1 and 2, and synapsin IIa in the medial prefrontal cortex, striatum, and the nucleus accumbens. The results suggest that PAOPA influences the dopaminergic system in the striatum to change behaviour via receptor internalization and possibly downstream signalling. The present studies illuminate new insights, and point to future explorations for the potential development of PAOPA as a therapeutic for schizophrenia. / Thesis / Master of Science (MSc)

<p> A simple and relatively inexpensive equalizer has been developed in conjuction with a FSK modulator and demodulator (modem) for the transmission of digital data over time dispersive channels. </p> <p> The transmitter structure consists of a digital modulator followed by two filters, the first of which is a binary transversal filter (BTF), the second a conventional two-stage R-C low-pass filter. </p> <p> In the receiver structure a phaselock loop (PLL) is employed as a discriminator. Synchronization is achieved with a digital phaselock loop (DPLL). Considerable attention is placed on the error rate optimization of the receiving structure. </p> <p> The equalizer uses binary transversal filter comprising a tapped delay line, realized by a long string of metal-oxide semiconductor (MOS) flipflops, with a variable gain circuit associated with each tap in the delay line. The operation of the equalizer is adaptive in that the tap gains are adjusted rom the received data, consequently the tap gains are continually optimized. The algorithm employed for setting the tap gains is simple and can be quite easily implemented using a combination of analog and digital techniques. </p> <p> Experimental results are presented which illustrate the important features of the system implemented under a variety of operating conditions. </p> / Thesis / Master of Engineering (MEngr)