Distributed data structures and the power of topological self-stabilization

In dieser Arbeit betrachten wir Probleme im Bereich verteilter Systeme und lokaler Algorithmen. Wir betrachten verteilte Systeme, die gegeben sind durch bestimmte Topologien miteinander vernetzter Knoten, und stellen die Frage, ob solche Topologien wiederhergestellt werden können, wenn das Netzwerk durch den Ausfall oder Hinzukommen von Knoten oder Kanten verändert wird. Dabei sollen lokale verteilte Algorithmen entwickelt werden, die das Netzwerk von einer beliebigen schwach zusammenhängenden Starttopologie in eine Zieltopologie überführen. Diese Eigenschaft eines Algorithmus nennen wir topologische Selbststabilisierung. Motiviert wird diese Betrachtung durch die zunehmende Nutzung von Peer-to-Peer Systemen und von Cloud Dienstleistern, also Szenarien in denen das System aus Ressourcen besteht, für die Ausfälle nicht mehr kontrolliert werden können. Zur Analyse von topologisch selbststabilisierenden Algorithmen oder Protokollen führen wir geeignete Modelle ein. Wir präsentieren dann für einige bestimme Topologien mit welchen topologisch selbststabilisierenden Protokollen diese erreicht werden können. Wir betrachten dabei als einführendes Beispiel eine sortierte Liste von Knoten und fahren dann mit komplexeren Topologien wie einem Small-World Netzwerk und einem vollständigem Graphen fort. Als nächstes wenden wir die Idee von topologisch selbststabilisierenden Protokollen auf das Konzept von verteilten Hashtabellen an. Dabei zeigen wir, dass eine solche Lösung für bereits existierende verteilte Hashtabellen möglich ist und entwickeln dann eine weitere verteilte Hashtabelle, die heterogene Kapazitäten unterstützt. Zum Schluss betrachten wir, wie verteilte Hashtabellen erweitert werden können, sodass nicht nur exakte Suchanfragen sondern auch Suchanfragen nach ähnlichen Schlüsseln unterstützt werden.This thesis considers problems located in the fields of distributed systems and local algorithms. In particular we consider such systems given by specific topologies of interconnected nodes and want to examine whether these topologies can be rebuilt in case the network is (massively) changed by failing or joining nodes or edges. For this case we search for local distributed algorithms, i.e. the algorithms are executed on every single node and only use local information stored at the nodes like their neighborhood of nodes. By executing these algorithms we will show that the desired goal topologies can be reached from any weakly connected start topology. We call this property of an algorithm topological self-stabilization and motivate it by the increasing usage of peer-to-peer (P2P) systems and of cloud computing. In both cases the user or owner of the data and executed algorithms cannot control the resources and their connectivity. In order to analyze topological self-stabilizing algorithms or protocols we introduce suited models. For some specific topologies we then present and analyze topological self-stabilizing protocols. We consider topologies like a sorted list of nodes, which we use as a simple introductory example. We then proceed with more complex topologies like a specific small-world network and a clique. We then show that the concept of topological self-stabilization can be used for distributed hash tables. In particular we show that for existing distributed hash tables a topological self-stabilizing protocol canbe found. We also construct a new overlay network, that builds a distributed hash table that supports heterogeneous capacities, and a corresponding topological self-stabilizing protocol. At last we leave the concept of topological self-stabilization behind and instead show how to extend the usage of distributed hash tables, in order to answer more than only exact queries.Tag der Verteidigung: 21.05.2015Paderborn, Univ., Diss., 201

Influence of glottal closure on the phonatory process in ex vivo porcine larynges

Many cases of disturbed voice signals can be attributed to incomplete glottal closure, vocal fold oscillation asymmetries, and aperiodicity. Often these phenomena occur simultaneously and interact with each other, making a systematic, isolated investigation challenging. Therefore, ex vivo porcine experiments were performed which enable direct control of glottal configurations. Different pre-phonatory glottal gap sizes, adduction levels, and flow rates were adjusted. The resulting glottal closure types were identified in a post-processing step. Finally, the acoustic quality, aerodynamic parameters, and the characteristics of vocal fold oscillation were analyzed in reference to the glottal closure types. Results show that complete glottal closure stabilizes the phonation process indicated through a reduced left-right phase asymmetry, increased amplitude and time periodicity, and an increase in the acoustic quality. Although asymmetry and periodicity parameter variation covers only a small range of absolute values, these small variations have a remarkable influence on the acoustic quality. Due to the fact that these parameters cannot be influenced directly, the authors suggest that the (surgical) reduction of the glottal gap seems to be a promising method to stabilize the phonatory process, which has to be confirmed in future studies

3D-FV-FE Aeroacoustic Larynx Model for Investigation of Functional Based Voice Disorders

For the clinical analysis of underlying mechanisms of voice disorders, we developed a numerical aeroacoustic larynx model, called simVoice, that mimics commonly observed functional laryngeal disorders as glottal insufficiency and vibrational left-right asymmetries. The model is a combination of the Finite Volume (FV) CFD solver Star-CCM+ and the Finite Element (FE) aeroacoustic solver CFS++. simVoice models turbulence using Large Eddy Simulations (LES) and the acoustic wave propagation with the perturbed convective wave equation (PCWE). Its geometry corresponds to a simplified larynx and a vocal tract model representing the vowel /a/. The oscillations of the vocal folds are externally driven. In total, 10 configurations with different degrees of functional-based disorders were simulated and analyzed. The energy transfer between the glottal airflow and the vocal folds decreases with an increasing glottal insufficiency and potentially reflects the higher effort during speech for patients being concerned. This loss of energy transfer may also have an essential influence on the quality of the sound signal as expressed by decreasing sound pressure level (SPL), Cepstral Peak Prominence (CPP), and Vocal Efficiency (VE). Asymmetry in the vocal fold oscillations also reduces the quality of the sound signal. However, simVoice confirmed previous clinical and experimental observations that a high level of glottal insufficiency worsens the acoustic signal quality more than oscillatory left-right asymmetry. Both symptoms in combination will further reduce the quality of the sound signal. In summary, simVoice allows for detailed analysis of the origins of disordered voice production and hence fosters the further understanding of laryngeal physiology, including occurring dependencies. A current walltime of 10 h/cycle is, with a prospective increase in computing power, auspicious for a future clinical use of simVoice

Geometry of the Vocal Tract and Properties of Phonation near Threshold: Calculations and Measurements

In voice research, analytically-based models are efficient tools to investigate the basic physical mechanisms of phonation. Calculations based on lumped element models describe the effects of the air in the vocal tract upon threshold pressure (Pth) by its inertance. The latter depends on the geometrical boundary conditions prescribed by the vocal tract length (directly) and its cross-sectional area (inversely). Using Titze’s surface wave model (SWM) to account for the properties of the vocal folds, the influence of the vocal tract inertia is examined by two sets of calculations in combination with experiments that apply silicone-based vocal folds. In the first set, a vocal tract is constructed whose cross-sectional area is adjustable from 2.7 cm2 to 11.7 cm2. In the second set, the length of the vocal tract is varied from 4.0 cm to 59.0 cm. For both sets, the pressure and frequency data are collected and compared with calculations based on the SWM. In most cases, the measurements support the calculations; hence, the model is suited to describe and predict basic mechanisms of phonation and the inertial effects caused by a vocal tract

Impulse dispersion of aerosols during playing the recorder and evaluation of safety measures

Introduction Group musical activities using wind instruments have been restricted during the CoVID19 pandemic due to suspected higher risk of virus transmission. It was presumed that the aerosols exhaled through the tubes while playing would be ejected over larger distances and spread into the room due to jet stream effects. In particular, the soprano recorder is widely used as an instrument in school classes, for beginners of all age groups in their musical education, in the context of leisure activities and in professional concert performances. Understanding the aerosol impulse dispersion characteristics of playing the soprano recorder could assist with the establishment of concepts for safe music-making. Methods Five adult professionally trained soprano recorder players (4 female, 1 male) played four bars of the main theme of L. van Beethoven’s “Ode to Joy” in low and in high octaves, as well as with 3 different potential protection devices in the high octave. For comparison they spoke the corresponding text by F. Schiller. Before each task, they inhaled .5 L of vapor from an e-cigarette filled with base liquid. The vapor cloud escaping during speaking or playing was recorded by cameras and its spread was measured as a function of time in the three spatial dimensions. The potential safety devices were rated for practicability with a questionnaire, and their influence on the sound was compared, generating a long-term average spectrum from the audio data. Results When playing in the high octave, at the end of the task the clouds showed a median distance of 1.06 m to the front and .57 m diameter laterally (maxima: x: 1.35 m and y: .97 m). It was found that the clouds’ expansion values in playing the recorder with and without safety measures are mostly lower when compared to the ordinary, raised speaking voice of the same subjects. The safety devices which covered the instrument did not show clear advantages and were rated as unpractical by the subjects. The most effective reduction of the cloud was reached when playing into a suction funnel. Conclusion The aerosol dispersion characteristics of soprano recorders seem comparable to clarinets. The tested safety devices which covered holes of the instrument did not show clear benefits

Towards a Clinically Applicable Computational Larynx Model

The enormous computational power and time required for simulating the complex phonation process preclude the effective clinical use of computational larynx models. The aim of this study was to evaluate the potential of a numerical larynx model, considering the computational time and resources required. Using Large Eddy Simulations (LES) in a 3D numerical larynx model with prescribed motion of vocal folds, the complicated fluid-structure interaction problem in phonation was reduced to a pure flow simulation with moving boundaries. The simulated laryngeal flow field is in good agreement with the experimental results obtained from authors’ synthetic larynx model. By systematically decreasing the spatial and temporal resolutions of the numerical model and optimizing the computational resources of the simulations, the elapsed simulation time was reduced by 90% to less than 70 h for 10 oscillation cycles of the vocal folds. The proposed computational larynx model with reduced mesh resolution is still able to capture the essential laryngeal flow characteristics and produce results with sufficiently good accuracy in a significant shorter time-to-solution. The reduction in computational time achieved is a promising step towards the clinical application of these computational larynx models in the near future

Self-stabilizing Overlays for high-dimensional Monotonic Searchability

We extend the concept of monotonic searchability for self-stabilizing systems from one to multiple dimensions. A system is self-stabilizing if it can recover to a legitimate state from any initial illegal state. These kind of systems are most often used in distributed applications. Monotonic searchability provides guarantees when searching for nodes while the recovery process is going on. More precisely, if a search request started at some node $u$ succeeds in reaching its destination $v$, then all future search requests from $u$ to $v$ succeed as well. Although there already exists a self-stabilizing protocol for a two-dimensional topology and an universal approach for monotonic searchability, it is not clear how both of these concepts fit together effectively. The latter concept even comes with some restrictive assumptions on messages, which is not the case for our protocol. We propose a simple novel protocol for a self-stabilizing two-dimensional quadtree that satisfies monotonic searchability. Our protocol can easily be extended to higher dimensions and offers routing in $\mathcal O(\log n)$ hops for any search request

Bilateral Functional Electrical Stimulation for the Treatment of Presbyphonia in a Sheep Model

Objectives: The aim of the study was to increase muscle volume and improve phonation characteristics of the aged ovine larynx by functional electrical stimulation (FES) using a minimally invasive surgical procedure. Methods: Stimulation electrodes were placed bilaterally near the terminal adduction branch of the recurrent laryngeal nerves (RLN). The electrodes were connected to battery powered pulse generators implanted subcutaneously at the neck region. Training patterns were programmed by an external programmer using a bidirectional radio frequency link. Training sessions were repeated automatically by the implant every other day for 1 week followed by every day for 8 weeks in the awake animal. Another group of animals were used as sham, with electrodes positioned but not connected to an implant. Outcome parameters included gene expression analysis, histological assessment of muscle fiber size, functional analysis, and volumetric measurements based on three-dimensional reconstructions of the entire thyroarytenoid muscle (TAM). Results: Increase in minimal muscle fiber diameter and an improvement in vocal efficiency were observed following FES, compared with sham animals. Conclusion: This is the first study to demonstrate beneficial effects in the TAM of FES at molecular, histological, and functional levels. FES of the terminal branches of the RLN reversed the effects of age-related changes and improved vocal efficiency

Resource discovery for distributed computing systems: A comprehensive survey

Large-scale distributed computing environments provide a vast amount of heterogeneous computing resources from different sources for resource sharing and distributed computing. Discovering appropriate resources in such environments is a challenge which involves several different subjects. In this paper, we provide an investigation on the current state of resource discovery protocols, mechanisms, and platforms for large-scale distributed environments, focusing on the design aspects. We classify all related aspects, general steps, and requirements to construct a novel resource discovery solution in three categories consisting of structures, methods, and issues. Accordingly, we review the literature, analyzing various aspects for each category