Abdominal aortic aneurysm follow-up after endovascular repair in a canine model with non-invasive vascular elastography

Le traitement chirurgical des anévrismes de l'aorte abdominale est de plus en plus remplacé par la réparation endovasculaire de l’anévrisme (« endovascular aneurysm repair », EVAR) en utilisant des endoprothèses (« stent-grafts », SGs). Cependant, l'efficacité de cette approche moins invasive est compromise par l'incidence de l'écoulement persistant dans l'anévrisme, appelé endofuites menant à une rupture d'anévrisme si elle n'est pas détectée. Par conséquent, une surveillance de longue durée par tomodensitométrie sur une base annuelle est nécessaire ce qui augmente le coût de la procédure EVAR, exposant le patient à un rayonnement ionisants et un agent de contraste néphrotoxique. Le mécanisme de rupture d'anévrisme secondaire à l'endofuite est lié à une pression du sac de l'anévrisme proche de la pression systémique. Il existe une relation entre la contraction ou l'expansion du sac et la pressurisation du sac. La pressurisation résiduelle de l'anévrisme aortique abdominale va induire une pulsation et une circulation sanguine à l'intérieur du sac empêchant ainsi la thrombose du sac et la guérison de l'anévrisme. L'élastographie vasculaire non-invasive (« non-invasive vascular elastography », NIVE) utilisant le « Lagrangian Speckle Model Estimator » (LSME) peut devenir une technique d'imagerie complémentaire pour le suivi des anévrismes après réparation endovasculaire. NIVE a la capacité de fournir des informations importantes sur l'organisation d'un thrombus dans le sac de l'anévrisme et sur la détection des endofuites. La caractérisation de l'organisation d'un thrombus n'a pas été possible dans une étude NIVE précédente. Une limitation de cette étude était l'absence d'examen tomodensitométrique comme étalon-or pour le diagnostic d'endofuites. Nous avons cherché à appliquer et optimiser la technique NIVE pour le suivi des anévrismes de l'aorte abdominale (AAA) après EVAR avec endoprothèse dans un modèle canin dans le but de détecter et caractériser les endofuites et l'organisation du thrombus. Des SGs ont été implantés dans un groupe de 18 chiens avec un anévrisme créé dans l'aorte abdominale. Des endofuites de type I ont été créés dans 4 anévrismes, de type II dans 13 anévrismes tandis qu’un anévrisme n’avait aucune endofuite. L'échographie Doppler (« Doppler ultrasound », DUS) et les examens NIVE ont été réalisés avant puis à 1 semaine, 1 mois, 3 mois et 6 mois après l’EVAR. Une angiographie, une tomodensitométrie et des coupes macroscopiques ont été réalisées au moment du sacrifice. Les valeurs de contrainte ont été calculées en utilisant l`algorithme LSME. Les régions d'endofuite, de thrombus frais (non organisé) et de thrombus solide (organisé) ont été identifiées et segmentées en comparant les résultats de la tomodensitométrie et de l’étude macroscopique. Les valeurs de contrainte dans les zones avec endofuite, thrombus frais et organisé ont été comparées. Les valeurs de contrainte étaient significativement différentes entre les zones d'endofuites, les zones de thrombus frais ou organisé et entre les zones de thrombus frais et organisé. Toutes les endofuites ont été clairement caractérisées par les examens d'élastographie. Aucune corrélation n'a été trouvée entre les valeurs de contrainte et le type d'endofuite, la pression de sac, la taille des endofuites et la taille de l'anévrisme.

Patient-specific anisotropic model of human trunk based on MR data

There are many ways to generate geometrical models for numerical simulation, and most of them start with a segmentation step to extract the boundaries of the regions of interest. This paper presents an algorithm to generate a patient-specific three-dimensional geometric model, based on a tetrahedral mesh, without an initial extraction of contours from the volumetric data. Using the information directly available in the data, such as gray levels, we built a metric to drive a mesh adaptation process. The metric is used to specify the size and orientation of the tetrahedral elements everywhere in the mesh. Our method, which produces anisotropic meshes, gives good results with synthetic and real MRI data. The resulting model quality has been evaluated qualitatively and quantitatively by comparing it with an analytical solution and with a segmentation made by an expert. Results show that our method gives, in 90% of the cases, as good or better meshes as a similar isotropic method, based on the accuracy of the volume reconstruction for a given mesh size. Moreover, a comparison of the Hausdorff distances between adapted meshes of both methods and ground-truth volumes shows that our method decreases reconstruction errors faster. Copyright © 2015 John Wiley & Sons, Ltd.

MQFD: A Model for Synergizing TPM and QFD

This thesis presents the methodology of linking Total Productive Maintenance (TPM) and Quality Function Deployment (QFD). The Synergic power ofTPM and QFD led to the formation of a new maintenance model named Maintenance Quality Function Deployment (MQFD). This model was found so powerful that, it could overcome the drawbacks of TPM, by taking care of customer voices. Those voices of customers are used to develop the house of quality. The outputs of house of quality, which are in the form of technical languages, are submitted to the top management for making strategic decisions. The technical languages, which are concerned with enhancing maintenance quality, are strategically directed by the top management towards their adoption of eight TPM pillars. The TPM characteristics developed through the development of eight pillars are fed into the production system, where their implementation is focused towards increasing the values of the maintenance quality parameters, namely overall equipment efficiency (GEE), mean time between failures (MTBF), mean time to repair (MTIR), performance quality, availability and mean down time (MDT). The outputs from production system are required to be reflected in the form of business values namely improved maintenance quality, increased profit, upgraded core competence, and enhanced goodwill. A unique feature of the MQFD model is that it is not necessary to change or dismantle the existing process ofdeveloping house ofquality and TPM projects, which may already be under practice in the company concerned. Thus, the MQFD model enables the tactical marriage between QFD and TPM.First, the literature was reviewed. The results of this review indicated that no activities had so far been reported on integrating QFD in TPM and vice versa. During the second phase, a survey was conducted in six companies in which TPM had been implemented. The objective of this survey was to locate any traces of QFD implementation in TPM programme being implemented in these companies. This survey results indicated that no effort on integrating QFD in TPM had been made in these companies. After completing these two phases of activities, the MQFD model was designed. The details of this work are presented in this research work. Followed by this, the explorative studies on implementing this MQFD model in real time environments were conducted. In addition to that, an empirical study was carried out to examine the receptivity of MQFD model among the practitioners and multifarious organizational cultures. Finally, a sensitivity analysis was conducted to find the hierarchy of various factors influencing MQFD in a company. Throughout the research work, the theory and practice of MQFD were juxtaposed by presenting and publishing papers among scholarly communities and conducting case studies in real time scenario.

Studies on Chaos and Synchronization in ac-driven Josephson junctions

The main goal of this thesis is to study the dynamics of Josephson junction system in the presence of an external rf-biasing.A system of two chaotically synchronized Josephson junction is studied.The change in the dynamics of the system in the presence of at phase difference between the applied fields is considered. Control of chaos is very important from an application point of view. The role Of phase difference in controlling chaos is discussed.An array of three Josephson junctions iS studied for the effect of phase difference on chaos and synchronization and the argument is extended for a system of N Josephson junctions. In the presence of a phase difference between the external fields, the system exhibits periodic behavior with a definite phase relationship between all the three junctions.Itdeals with an array of three Josephson junctions with a time delay in the coupling term. It is observed that only the outer systems synchronize while the middle system remain uncorrelated with t-he other two. The effect of phase difference between the applied fields and time-delay on system dynamics and synchronization is also studied. We study the influence of an applied ac biasing on a serniannular Josephson junction. It is found the magnetic field along with the biasing induces creation and annihilation of fluxons in the junction. The I-V characteristics of the junction is studied by considering the surface loss term also in the model equation. The system is found to exhibit chaotic behavior in the presence of ac biasing.

Dissipation in quasistatically driven disordered systems

This work presents an analysis of hysteresis and dissipation in quasistatically driven disordered systems. The study is based on the random field Ising model with fluctuationless dynamics. It enables us to sort out the fraction of the energy input by the driving field stored in the system and the fraction dissipated in every step of the transformation. The dissipation is directly related to the occurrence of avalanches, and does not scale with the size of Barkhausen magnetization jumps. In addition, the change in magnetic field between avalanches provides a measure of the energy barriers between consecutive metastable states

Finite-size scaling analysis of the avalanches in the three-dimensional Gaussian random-field Ising model with metastable dynamics

A numerical study is presented of the third-dimensional Gaussian random-field Ising model at T=0 driven by an external field. Standard synchronous relaxation dynamics is employed to obtain the magnetization versus field hysteresis loops. The focus is on the analysis of the number and size distribution of the magnetization avalanches. They are classified as being nonspanning, one-dimensional-spanning, two-dimensional-spanning, or three-dimensional-spanning depending on whether or not they span the whole lattice in different space directions. Moreover, finite-size scaling analysis enables identification of two different types of nonspanning avalanches (critical and noncritical) and two different types of three-dimensional-spanning avalanches (critical and subcritical), whose numbers increase with L as a power law with different exponents. We conclude by giving a scenario for avalanche behavior in the thermodynamic limit.

Influence of the driving mechanism on the response of systems with athermal dynamics: The example of the random-field Ising model

We investigate the influence of the driving mechanism on the hysteretic response of systems with athermal dynamics. In the framework of local mean-field theory at finite temperature (but neglecting thermally activated processes), we compare the rate-independent hysteresis loops obtained in the random field Ising model when controlling either the external magnetic field H or the extensive magnetization M. Two distinct behaviors are observed, depending on disorder strength. At large disorder, the H-driven and M-driven protocols yield identical hysteresis loops in the thermodynamic limit. At low disorder, when the H-driven magnetization curve is discontinuous (due to the presence of a macroscopic avalanche), the M-driven loop is reentrant while the induced field exhibits strong intermittent fluctuations and is only weakly self-averaging. The relevance of these results to the experimental observations in ferromagnetic materials, shape memory alloys, and other disordered systems is discussed.

Chaotic dynamics of electric-field domains in periodically driven superlattices

Self-sustained time-dependent current oscillations under dc voltage bias have been observed in recent experiments on n-doped semiconductor superlattices with sequential resonant tunneling. The current oscillations are caused by the motion and recycling of the domain wall separating low- and high-electric-field regions of the superlattice, as the analysis of a discrete drift model shows and experimental evidence supports. Numerical simulation shows that different nonlinear dynamical regimes of the domain wall appear when an external microwave signal is superimposed on the dc bias and its driving frequency and driving amplitude vary. On the frequency-amplitude parameter plane, there are regions of entrainment and quasiperiodicity forming Arnold tongues. Chaos is demonstrated to appear at the boundaries of the tongues and in the regions where they overlap. Coexistence of up to four electric-field domains randomly nucleated in space is detected under ac+dc driving.

Agent Based Evacuation Simulation Using Leader-Follower Model

Agent based simulation is a widely developing area in artificial intelligence.The simulation studies are extensively used in different areas of disaster management. This work deals with the study of an agent based evacuation simulation which is being done to handle the various evacuation behaviors.Various emergent behaviors of agents are addressed here. Dynamic grouping behaviors of agents are studied. Collision detection and obstacle avoidances are also incorporated in this approach.Evacuation is studied with single exits and multiple exits and efficiency is measured in terms of evacuation rate, collision rate etc.Net logo is the tool used which helps in the efficient modeling of scenarios in evacuation

Integrating TPM and QFD for improving quality in maintenance engineering

To provide maintenance engineering community with a model named “Maintenance quality function deployment” (MQFD) for nourishing the synergy of quality function deployment (QFD) and total productive maintenance (TPM) and enhancing maintenance quality of products and equipment.The principles of QFD and TPM were studied. MQFD model was designed by coupling these two principles. The practical implementation feasibility of MQFD model was checked in an automobile service station.Both QFD and TPM are popular approaches and several benefits of implementing them have been reported worldwide. Yet the world has not nourished the synergic power of integrating them. The MQFD implementation study reported in this paper has revealed its practical validity

Effect of market-driven minigrids on the frequency stabilization process of isolated middle-sized power grids

Neueste Entwicklungen in Technologien für dezentrale Energieversorgungsstrukturen, erneuerbare Energien, Großhandelsenergiemarkt, Mini- und Mikronetze, verteilte Intelligenz, sowie Informations- und Datenübertragungstechnologien werden die zukünftige Energiewelt maßgeblich bestimmen. Die derzeitigen Forschungsbemühungen zur Vernutzung aller dieser Technologien bilden die Voraussetzungen für ein zukünftiges, intelligentes Stromnetz. Dieses neue Konzept gründet sich auf die folgenden Säulen: Die Versorgung erfolgt durch dezentrale Erzeugungsanlagen und nicht mehr durch große zentrale Erzeuger; die Steuerung beeinflusst nicht mehr allein die Versorgung sondern ermöglich eine auch aktive Führung des Bedarf; die Eingabeparameter des Systems sind nicht mehr nur mechanische oder elektrische Kenngrößen sondern auch Preissignale; die erneuerbaren Energieträger sind nicht mehr nur angeschlossen, sondern voll ins Energienetz integriert. Die vorgelegte Arbeit fügt sich in dieses neue Konzept des intelligenten Stromnetz ein. Da das zukünftige Stromnetz dezentral konfiguriert sein wird, ist eine Übergangsphase notwendig. Dieser Übergang benötigt Technologien, die alle diese neue Konzepte in die derzeitigen Stromnetze integrieren können. Diese Arbeit beweist, dass ein Mininetz in einem Netzabschnitt mittlerer Größe als netzschützende Element wirken kann. Hierfür wurde ein neues Energiemanagementsystem für Mininetze – das CMS (englisch: Cluster Management System) – entwickelt. Diese CMS funktioniert als eine von ökonomischorientierte Betriebsoptimierung und wirkt wie eine intelligente Last auf das System ein, reagierend auf Preissignale. Sobald wird durch eine Frequenzsenkung eine Überlastung des Systems bemerkt, ändert das Mininetz sein Verhalten und regelt seine Belastung, um die Stabilisierung des Hauptnetzes zu unterstützen. Die Wirksamkeit und die Realisierbarkeit des einwickelten Konzept wurde mit Hilfe von Simulationen und erfolgreichen Laborversuchen bewiesen.

Model Calculations and Implementation of Filters and Hybrid Green VCSELs based on Optical Thin Film Stacks

This work introduced the novel conception of complex coupled hybrid VCSELs for the first time. Alternating organic and inorganic layers in the lasers provide periodic variation of refractive index and optical gain, which enable single mode operation and low threshold of the VCSELs. Model calculations revealed great reduction of the lasing threshold with factors over 30, in comparison with the existing micro-cavity lasers. Tunable green VCSEL has been also designed, implemented and analyzed taking advantage of the broad photoluminescence spectra of the organics. Free standing optical thin films without compressive stress are technologically implemented. Multiple membrane stacks with air gap in between have been fabricated for the implementation of complex coupled VCSEL structures. Complex coupled hybrid VCSEL is a very promising approach to fill the gaps in the green spectral range of the semiconductor lasers.

Konzeption von Entwicklungspfaden für Zulieferparks in der Automobilindustrie

Die Automobilindustrie reagiert mit Modularisierungsstrategien auf die zunehmende Produktkomplexität, getrieben durch die wachsenden Individualisierungsanforde-rungen auf der Kundenseite und der Modellpolitik mit neuen Fahrzeuganläufen. Die Hersteller verlagern die Materialbereitstellungskomplexität durch Outsourcing an die nächste Zulieferebene, den First Tier Suppliern, die seit Beginn der 90er Jahre zunehmend in Zulieferparks in unmittelbarer Werknähe integriert werden. Typische Merkmale eines klassischen Zulieferparks sind: Bereitstellung einer Halleninfrastruktur mit Infrastrukturdienstleistungen, Anlieferung der Teileumfänge im JIS-Verfahren (Just-in-Sequence = reihenfolgegenaue Synchronisation), lokale Wertschöpfung (Vormontagen, Sequenzierung) des Zulieferers, Vertragsbindung der First Tier Zulieferer für die Dauer eines Produktlebenszyklus und Einbindung eines Logistikdienstleisters. Teilweise werden zur Finanzierung Förderprojekte des öffent-lichen Sektors initiiert. Bisher fehlte eine wissenschaftliche Bearbeitung dieses Themas "Zulieferpark". In der Arbeit werden die in Europa entstandenen Zulieferparks näher untersucht, um Vor- und Nachteile dieses Logistikkonzeptes zu dokumentieren und Entwicklungs-trends aufzuzeigen. Abgeleitet aus diesen Erkenntnissen werden Optimierungs-ansätze aufgezeigt und konkrete Entwicklungspfade zur Verbesserung der Chancen-Risikoposition der Hauptakteure Automobilhersteller, Zulieferer und Logistikdienst-leister beschrieben. Die Arbeit gliedert sich in vier Haupteile, einer differenzierten Beschreibung der Ausgangssituation und den Entwicklungstrends in der Automobilindustrie, dem Vorgehensmodell, der Dokumentation der Analyseergebnisse und der Bewertung von Zulieferparkmodellen. Im Rahmen der Ergebnisdokumentation des Analyseteils werden vier Zulieferparkmodelle in detaillierten Fallstudien anschaulich dargestellt. Zur Erarbeitung der Analyseergebnisse wurde eine Befragung der Hauptakteure mittels strukturierten Fragebögen durchgeführt. Zur Erhebung von Branchentrends und zur relativen Bewertung der Parkmodelle wurden zusätzlich Experten befragt. Zur Segmentierung der Zulieferparklandschaft wurde die Methode der Netzwerk-analyse eingesetzt. Die relative Bewertung der Nutzenposition basiert auf der Nutzwertanalyse. Als Ergebnisse der Arbeit liegen vor: · Umfassende Analyse der Zulieferparklandschaft in Europa, · Segmentierung der Parks in Zulieferparkmodelle, Optimierungsansätze zur Verbesserung einer Win-Win-Situation der beteiligten Hauptakteure, · Relative Nutzenbewertung der Zulieferparkmodelle, · Entwicklungspfade für klassische Zulieferparks.