1,477 research outputs found

    Function-based Intersubject Alignment of Human Cortical Anatomy

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    Making conclusions about the functional neuroanatomical organization of the human brain requires methods for relating the functional anatomy of an individual's brain to population variability. We have developed a method for aligning the functional neuroanatomy of individual brains based on the patterns of neural activity that are elicited by viewing a movie. Instead of basing alignment on functionally defined areas, whose location is defined as the center of mass or the local maximum response, the alignment is based on patterns of response as they are distributed spatially both within and across cortical areas. The method is implemented in the two-dimensional manifold of an inflated, spherical cortical surface. The method, although developed using movie data, generalizes successfully to data obtained with another cognitive activation paradigm—viewing static images of objects and faces—and improves group statistics in that experiment as measured by a standard general linear model (GLM) analysis

    Experimental Investigations of Millimeter Wave Beamforming

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    The millimeter wave (mmW) band, commonly referred to as the frequency band between 30 GHz and 300 GHz, is seen as a possible candidate to increase achievable rates for mobile applications due to the existence of free spectrum. However, the high path loss necessitates the use of highly directional antennas. Furthermore, impairments and power constraints make it difficult to provide full digital beamforming systems. In this thesis, we approach this problem by proposing effective beam alignment and beam tracking algorithms for low-complex analog beamforming (ABF) systems, showing their applicability by experimental demonstration. After taking a closer look at particular features of the mmW channel properties and introducing the beamforming as a spatial filter, we begin our investigations with the application of detection theory for the non-convex beam alignment problem. Based on an M-ary hypothesis test, we derive algorithms for defining the length of the training signal efficiently. Using the concept of black-box optimization algorithms, which allow optimization of non-convex algorithms, we propose a beam alignment algorithm for codebook-based ABF based systems, which is shown to reduce the training overhead significantly. As a low-complex alternative, we propose a two-staged gradient-based beam alignment algorithm that uses convex optimization strategies after finding a subregion of the beam alignment function in which the function can be regarded convex. This algorithm is implemented in a real-time prototype system and shows its superiority over the exhaustive search approach in simulations and experiments. Finally, we propose a beam tracking algorithm for supporting mobility. Experiments and comparisons with a ray-tracing channel model show that it can be used efficiently in line of sight (LoS) and non line of sight (NLoS) scenarios for walking-speed movements

    Transducer Arrays for 3D Ultrasound Computed Tomography

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    Die Ultraschall-Computertomographie (USCT) ist ein vielversprechendes medizinisches Bildgebungsverfahren zur FrĂŒherkennung von Brustkrebs. Am Karlsruher Institut fĂŒr Technologie wird derzeit ein GerĂ€t der dritten Generation (3D-USCT-III) fĂŒr 3D-Aufnahmen entwickelt. Unter den kritischsten und technologisch anspruchsvollsten Komponenten dieses GerĂ€ts sind die Schallwandlerarrays. Diese mĂŒssen eine pseudozufĂ€llige Positionierung einzelner Wandler ermöglichen, hohe Bandbreiten, große Öffnungswinkel und eine isotrope Schallabstrahlung aufweisen sowie den Vorschriften fĂŒr Medizinprodukte genĂŒgen. In dieser Arbeit wird die Realisierung neuer Schallwandlerarrays (TAS-III) fĂŒr die 3D-USCT-Bildgebung umfassend vorgestellt. Dies beinhaltet die Definition von Anforderungen, Systemdesign, automatisierte Fertigung, Charakterisierung und Entwurfsoptimierung. Kernelement des TAS-III-Designs sind Scheiben aus piezoelektrischen Verbundwerkstoffen, die 18 in Polymer eingebettete, rĂ€umlich verteilte piezokeramische Fasern enthalten. ZusĂ€tzliche Scheiben zur akustischenAnpassung und DĂ€mpfung werden auf beiden Seiten angebracht, um die Arrays zu finalisieren. FĂŒr die Herstellung der benötigten 256 TAS-III wurde ein teilautomatisierter Fertigungsprozess entwickelt. Quantitative QualitĂ€tsprĂŒfungen ergaben, dass mehr als 96% der produzierten Wandler voll funktionsfĂ€hig waren. Die Amplitude und der Phasenwinkel des akustischen Feldes von 54 Wandlern wurden gemessen und ausgewertet. Die meisten der definierten Anforderungen wurden erfĂŒllt. Es wurde eine mittlere Mittenfrequenz von 2,6 MHz, mit einer fraktionellen Bandbreite von 134% bei -10 dB ermittelt. Die Bandbreite resultiert dabei aus zwei unterschiedlichen Schwingungsmoden. Messungen in 3D zeigten isotrope Abstrahlcharakteristiken mit einem mittleren Öffnungswinkel von 42,8°. FĂŒr die Analyse und Optimierung des Designs wurden verschiedene ModellierungsansĂ€tze entwickelt. GeringfĂŒgige Änderungen der LĂ€nge und des Durchmessers der piezoelektrischen Fasern sowie eine höhere laterale DĂ€mpfung konnten die Leistung in gewissem Maße verbessern. Der Umfang weiterer möglicher Verbesserungen zeigte jedoch, dass das TAS-III Design nahe am erreichbaren Optimum liegt. Alternative Wandlertechnologien wurden untersucht, umdie grundsĂ€tzlichen Grenzen von Verbundwerkstoffen bestehend aus piezoelektrischen Fasern in Bezug auf Öffnungswinkel und Bandbreite zu ĂŒberwinden. Der Ersatz der Fasern durch einkristalline piezoelektrische Materialien verspricht eine Erhöhung der Bandbreite um 35%, erfordert jedoch umfangreiche Anpassungen in den Herstellungsprozessen. Die Charakterisierung von mikromechanischen Ultraschallwandlern ergab eine signifikante VergrĂ¶ĂŸerung des Öffnungswinkels, aber geringere erzeugte SchalldrĂŒcke. Dennoch machen die Eigenschaften und die verfĂŒgbare Designfreiheit diese Schallwandlertechnologie sehr vielversprechend fĂŒr zukĂŒnftige 3D-USCT- Generationen. Die entworfenen und realisierten TAS-III erwiesen sich als rundum geeignet fĂŒr den vorgesehenen Einsatz und wurden in zwei 3D-USCT-III-GerĂ€ten integriert. AusfĂŒhrliche klinische Tests werden in naher Zukunft durchgefĂŒhrt, um die SensitivitĂ€t und SpezifitĂ€t dieser neuartigen 3D-Ultraschallbildgebungsmethode zu bewerten

    Energy efficient 5G networks

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    For a greener tomorrow, an important step today will be the energy efficient designs in any aspect. The 5G networks which is most awaited by all, though proposes better data rates, but also speaks about the energy efficiency in its agenda. A broad study of different techniques for energy efficiency reveals that beamforming plays a crucial role. Thus leading to this thesis mainly concentrating on the aspects of beamforming. Beamforming though has been into existence for more than over a decade, continuous improvements in the methodology keeps it ahead of many other technologies used for the common goal. This thesis work is done with the concept called multi-beam beamforming. An interesting concept of amplitude tapering is tailed to keep a check on the magnitude of power supplied at the antenna terminals. Using these, the thesis compares the gain values of both the desired and undesired users which will aid in estimating the amount of power required for covering a set of users using different tapering methods. This works also includes the effect of increasing number of antennas and the users and the effect on the gain values for both desired and undesired users. This develops a scope to introduce a new metric called “potential power improvement” for different tapering methods. Also, a framework has been developed to expand and evaluate the cases mentioned above to a multi-cell scenario in both general antenna configuration and Massive MIMO configuration

    Physically Informed Subtraction of a String's Resonances from Monophonic, Discretely Attacked Tones : a Phase Vocoder Approach

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    A method for the subtraction of a string's oscillations from monophonic, plucked- or hit-string tones is presented. The remainder of the subtraction is the response of the instrument's body to the excitation, and potentially other sources, such as faint vibrations of other strings, background noises or recording artifacts. In some respects, this method is similar to a stochastic-deterministic decomposition based on Sinusoidal Modeling Synthesis [MQ86, IS87]. However, our method targets string partials expressly, according to a physical model of the string's vibrations described in this thesis. Also, the method sits on a Phase Vocoder scheme. This approach has the essential advantage that the subtraction of the partials can take place \instantly", on a frame-by-frame basis, avoiding the necessity of tracking the partials and therefore availing of the possibility of a real-time implementation. The subtraction takes place in the frequency domain, and a method is presented whereby the computational cost of this process can be reduced through the reduction of a partial's frequency-domain data to its main lobe. In each frame of the Phase Vocoder, the string is encoded as a set of partials, completely described by four constants of frequency, phase, magnitude and exponential decay. These parameters are obtained with a novel method, the Complex Exponential Phase Magnitude Evolution (CSPME), which is a generalisation of the CSPE [SG06] to signals with exponential envelopes and which surpasses the nite resolution of the Discrete Fourier Transform. The encoding obtained is an intuitive representation of the string, suitable to musical processing

    Multi-Scale Vector-Ridge-Detection for Perceptual Organization Without Edges

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    We present a novel ridge detector that finds ridges on vector fields. It is designed to automatically find the right scale of a ridge even in the presence of noise, multiple steps and narrow valleys. One of the key features of such ridge detector is that it has a zero response at discontinuities. The ridge detector can be applied to scalar and vector quantities such as color. We also present a parallel perceptual organization scheme based on such ridge detector that works without edges; in addition to perceptual groups, the scheme computes potential focus of attention points at which to direct future processing. The relation to human perception and several theoretical findings supporting the scheme are presented. We also show results of a Connection Machine implementation of the scheme for perceptual organization (without edges) using color

    Plausible reconstruction ans rendering of semi-procedural landscapes

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    We present a new method for the reconstruction of tree crowns from a single photograph, as well as an efficient representation to render them. The obtained model is used in our terrain viewer application to navigate through large forests with several thousands of trees in real time
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