Continuity and Fréchet-differentiability of Nemytskij operators in Hölder spaces

The paper is devoted to superposition operators acting between Hölder spaces, for which we prove continuity properties and Fréchet-differentiability under assumptions being weaker than those so far known in the literature.     

Experimental realization of one-way quantum computing with two-photon four-qubit cluster states

We report an experimental realization of one-way quantum computing on a two-photon four-qubit cluster state. This is accomplished by developing a two-photon cluster state source entangled both in polarization and spatial modes. With this special source, we implemented a highly efficient Grover's search algorithm and high-fidelity two-qubit quantum gates. Our experiment demonstrates that such cluster states could serve as an ideal source and a building block for rapid and precise optical quantum computation.     

Investigating directed cortical interactions in time-resolved fMRI data using vector autoregressive modeling and Granger causality mapping

We present a framework aimed to reveal directed interactions of activated brain areas using time-resolved fMRI and vector autoregressive (VAR) modeling in the context of Granger causality. After describing the underlying mathematical concepts, we present simulations helping to characterize the conditions under which VAR modeling and Granger causality can reveal directed interactions from fluctuations in BOLD-like signal time courses. We apply the proposed approach to a dynamic sensorimotor mapping paradigm. In an event-related fMRI experiment, subjects performed a visuomotor mapping task for which the mapping of two stimuli (“faces” vs “houses”) to two responses (“left” or “right”) alternated periodically between the two possible mappings. Besides expected activity in sensory and motor areas, a fronto-parietal network was found to be active during presentation of a cue indicating a change in the stimulus-response (S-R) mapping. The observed network includes the superior parietal lobule and premotor areas. These areas might be involved in setting up and maintaining stimulus-response associations. The Granger causality analysis revealed a directed influence exerted by the left lateral prefrontal cortex and premotor areas on the left posterior parietal cortex.     

In vivo mapping of functional domains and axonal connectivity in cat visual cortex using magnetic resonance imaging

Noninvasive cognitive neuroimaging studies based on functional magnetic resonance imaging (fMRI) are of ever-increasing importance for basic and clinical neurosciences. The explanatory power of fMRI could be greatly expanded, however, if the pattern of the neuronal circuitry underlying functional activation could be made visible in an equally noninvasive manner. In this study, blood oxygenation level-dependent (BOLD)-based fMRI and diffusion tensor imaging (DTI) were performed in the same cat visual cortex, and the foci of fMRI activation utilized as seeding points for 3D DTI fiber reconstruction algorithms, thus providing the map of the axonal circuitry underlying visual information processing. The methods developed in this study will lay the foundation for in vivo neuroanatomy and the ability for noninvasive longitudinal studies of brain development.     

Nonuniform-channel MOS device

This paper presents a novel technology of lateral profile engineering addressing nonuniform-channel MOS devices. For the first time MOS devices with highly nonuniform 2-D doping profiles are achieved by post-processing implantation of channel doping peaks. By reducing the thermal budget to a single anneal/activation step, any unintentional broadening or washout of the doping profiles is avoided. We demonstrate the feasibility of this scheme in terms of trap generation and damage, and the appropriateness of this approach to explore nonuniform-channel MOS devices. As predicted by simulations, the I_on/I_off ratio of MOS devices is greatly improved by the introduction of peaking channel dopings. These devices are much less prone to hot-carrier degradation due to reduced electric fields, are less affected by drain induced barrier lowering (DIBL) and exhibit improved resistance to punch through, thus being easier to scale into the ultra-deep-submicron regime. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +43-1/58801-36291, E-mail: alois.lugstein@tuwien.ac.at