On understanding multi-instrument Rosetta data of the innermost dust and gas coma of comet 67P/Churyumov-Gerasimenko - results, strengths, and limitations of models

Numerical models are powerful tools for understanding the connection between the emitted gas and dust from the surface of comets and the subsequent expansion into space where remote sensing instruments can perform measurements. We will present such a predictive model which can provide synthetic measurements for multiple instruments on board ESA's Rosetta mission to comet 67P/Churyumov-Gerasimenko (hereafter 67P). We will demonstrate why a multi instrument approach is essential and how models can be used to constrain the gas and dust source distribution on the surface

Μη επιβλεπόμενη κατάτμηση τριδιάστατων (3Δ) πολυγωνικών πλεγμάτων

In this thesis we deal with the problem of unsupervised 3D mesh segmentation. Undoubtedly, 3D mesh segmentation is a difficult and important problem. Semantic analysis of 3D content is strongly related to the parts each object consists of. Due to this reason there is a clear trend in literature towards part-based algorithms. However, current mesh segmentation algorithms are often restricted in a limited range of types of objects, use prior knowledge of the object's class, or human interaction. We review previous approaches and discuss the various existing evaluation frameworks. A novel mesh segmentation algorithm is proposed, which is based on a spectral framework. We introduce a new graph Laplacian based on an heterogeneous graph, which comprises two types of nodes, namely faces and patches. Furthermore, we deal with the problem of partitioning the 3D mesh from the eigenvectors of the aforementioned Laplacian. The proposed approach is motivated by the observation that individual eigenvectors highlight different segments. The nodal sets and nodal domains are used to extract segments from each eigenvector separately, while multiple eigenvectors are combined in a hierarchical manner to produce the final segmentation. Experimental results indicate that the proposed methodology achieves improved performance compared to current unsupervised approaches, while it generates results with error equivalent to the ground truth of the very popular Princeton segmentation benchmark. In addition, we use the segmentation produced by the proposed approach, and show how a part-based representation can be used to retrieve similar objects under the premise that objects of the same class will consist of the same parts. This study further supports the experimental results of the segmentation algorithm. The parts produced for each object are used to construct a graph, where nodes represent parts and adjacency between parts is represented by edges in the graph. A novel matching scheme is proposed, which uses a graph cut algorithm to find a correspondence between parts of one object to the other. The matching scheme penalizes parts (nodes) as well as pairs of parts (edges) without a counterpart. We perform experiments in diverse datasets, which show superior performance of the part-based approach in the case of articulated objects, while being competitive with respect to the state-of-the-art in other datasets.Οι εφαρμογές τριδιάστατων (3Δ) γραφικών χρησιμοποιούνται ευρέως από τα τέλη του 20ου αιώνα. Κινηματογραφικές ταινίες, βιντεοπαιχνίδια, εκπαιδευτικές εφαρμογές, μηχανολογικά και αρχιτεκτονικά εργαλεία, ψηφιοποιήσεις πολιτιστικής κληρονομιάς, ιατρικές εφαρμογές κ.α. γίνονται όλο και πιο δημοφιλή λόγω της αμεσότητας και της διαδραστικότητας που μπορεί να προσφέρει το τριδιάστατο περιεχόμενο. Η αυξανόμενη ευκολία με την οποία μπορεί να παραχθεί τριδιάστατο περιεχόμενο, όπως τριδιάστατοι σαρωτές, ανακατασκευή 3Δ αντικειμένων από κάμερες, αλγόριθμοι δημιουργίας 3Δ μοντέλων κτλ. έχουν συμβάλει στην έκρηξη της διαθεσιμότητας των 3Δ δεδομένων. Σε αυτό το πλαίσιο, η ανάπτυξη αλγορίθμων επεξεργασίας 3Δ μοντέλων γίνεται επιτακτική ανάγκη, τόσο για την ανάπτυξη εφαρμογών Όρασης Υπολογιστών, όσο για την αποδοτική ανάκτηση και οργάνωση 3Δ περιεχομένου σε μεγάλες βάσεις δεδομένων. Η ανάλυση 3Δ περιεχομένου από σημασιολογικής σκοπιάς έχει άμεση σχέση με την εξαγωγή τμημάτων των αντικειμένων, και υπάρχει μία σαφής τάση στη βιβλιογραφία για ανάπτυξη αλγορίθμων ανάλυσης αντικειμένων με βάση τα τμήματα. Αυτό οφείλεται στο ότι η καθαρά γεωμετρική αναπαράσταση δεν είναι αρκετή για να αποτυπώσει τις ιδιότητες των αντικειμένων, ενώ η αναπαράσταση με βάση τα τμήματα αποτελεί μία υψηλότερου επιπέδου αναπαράσταση που επιτρέπει την καλύτερη κατανόηση του αντικειμένου. Στη βιβλιογραφία υπάρχουν αρκετοί αλγόριθμοι που χρησιμοποιούν κατατμήσεις από ανθρώπους ώστε να εκπαιδεύσουν κάποιο μοντέλο κατάτμησης, το οποίο επιτυγχάνει πολύ καλά αποτελέσματα σε αντικείμενα της ίδιας κατηγορίας. Το μεγαλύτερο πρόβλημα αυτής της προσέγγισης είναι η απουσία κατατμημένων αντικειμένων από ανθρώπους. Παράλληλα, οι υπάρχοντες αλγόριθμοι κατάτμησης που δεν χρησιμοποιούν αρχική γνώση για τα αντικείμενα προς κατάτμηση (μη επιβλεπόμενοι) δεν έχουν φτάσει σε ικανοποιητικό επίπεδο απόδοσης, με συγκεκριμένους αλγορίθμους κατάτμησης να επιτυγχάνουν ικανοποιητικά αποτελέσματα σε ένα περιορισμένο εύρος τύπων αντικειμένων, ή με ιδιαίτερη συνεισφορά του ανθρώπινου χρήστη. Η μη επιβλεπόμενη κατάτμηση συνεπώς, μολονότι έχει πολλές εφαρμογές, βρίσκεται ακόμα μακριά από το να λυθεί. Στην παρούσα διατριβή παρουσιάζουμε μία νέα προσέγγιση όσον αφορά την κατάτμηση 3Δ αντικειμένων, όπως αναπαρίστανται από τριδιάστατα τριγωνικά πλέγματα

Microanatomic Morphometric Characteristics of the Third Ventricle Floor

Background: Endoscopic third ventriculostomy (ETV) is an effective treatment for hydrocephalus. The in-depth understanding of microanatomy is essential for accurate diagnosis, treatment and complications prevention. The aim of this study is to supplement the knowledge gap regarding the microanatomical metrics and correlations for which the literature includes only scarce mentions at best. Methods: This is a descriptive microanatomical study including 25 cadaver brains. Specimens from donors with neurological, psychiatric disorders or alcohol abuse were excluded. Surgical loops were used for harvesting. High-precision tools were employed to dissect and measure the anatomical landmarks under a surgical microscope. Each measurement was performed in three consecutive attempts and outliers were rejected. RStudio was used for statistical analysis. Distribution was evaluated employing the Shapiro–Wilk test. Normally distributed values were presented as mean and standard deviation, and others as median and interquartile range. Results: The age of the donors was 61.72 (±10.08) years. The distance from the anterior aspect of the foramen of Monro to the anterior margin of the mamillary body was 16.83 (±1.04) mm, and to the posterior margin was 16.76 (±1.9) mm. The distance from the anterior mamillary body margin to the infundibulum was 6.39 (±1.9) mm, to the optic recess was 8.25 (±1.84) mm, and to the apex of the vertebral artery was 5.05 (±1.62) mm. The distance from the anterior commissure to the brain aqueduct was 22.46 (±2.29) mm, and to the infundibulum was 13.93 (±2.54) mm. The mamillary body diameter was 4.91 (±0.34) mm in the anteroposterior and 4.21 (±0.48) mm in the cranio-caudal plane. The intraventricular segment was protruding by 1.63 (±0.46) mm. The diameter of the hypothalamus on the anterior margin of mamillary bodies was 1.37 (±0.75) mm, of the Liliequist membrane was 0.19 (±0.07) mm and of the lamina terminalis was 0.35 (±0.32) mm. Conclusion: The presented microanatomical measurements and correlations are expected to contribute to the improvement of ETV safety

Multi-instrument Rosetta data and model comparison for the innermost coma of 67P for the period around equinox (May 2015)

From August 2014 to September 2016 ESA's Rosetta spacecraft escorted comet 67P/Chury-umov-Gerasimenko (hereafter 67P) on its journey into the inner solar system and out again. The mission provides, via various dust and gas instruments, unprecedented data on the nature of cometary activity. The determination of the activity distribution on the surface of a comet is a key goal of any mission to investigate the interaction of the comet with the Sun. As the ice sublimates the gas expands into space it fills the near-nucleus environment. Individual sources of activity have been observed on the surface but it remains uncertain where the bulk of the mass is lost and how the processes that are involved work in detail. There are several reasons for this. First, imaging experiments use the dust as a proxy for the gas activity. Because the optical depth of the dust is orders of magnitude below 1 in all but a few cases, it is not possible to trace dust filament back to the source against the backdrop of the illuminated surface. Second, remote sensing instruments detecting gas emission (i.e. infrared and sub-mm spectrometers) may suffer with limited spatial and temporal resolution. In addition, the spectra lines may be optically thick and the line-of-sight direction usually cuts through inhomogeneous coma (in density or temperature) which further complicates their interpretation considerably. However, as we will show, with good a-priori estimates of coma structures spectral lines can be accurately inverted to provide constraints of the gas coma down to a few hundreds of meters above the surface (e.g. MIRO). The in-situ instruments (e.g. ROSINA, or GIADA) must consider possible biases due to the spacecraft position relative to the nucleus and respective illumination conditions on the surface. For instance, the frequent use of terminator orbits by Rosetta introduced a significant problem because the measured local densities are at points remote from what we assume to be the main direction of outflow, namely near the sunward direction. In addition, the possible inhomogeneities of the outgassing at the surface cannot be detected due to the fact that the rapid gas expansion smoothens the coma. Therefore, measurements taken tens of kilometers above the nucleus surface are rather insensitive and provide only ambiguous results. The difficulties described above show the need for predictive models that can reproduce multiple measurements in one self-consistent framework. We will present results from our study of diverse Rosetta data sets (including OSIRIS, VIRTIS, MIRO, and ROSINA), constraining the gas emission into the coma and to establish whether the data enable us to reach appropriate conclusions on the activity distribution on the nucleus surface. The models can be used on the one hand to constrain certain properties of the activity and on the other hand they provide clues on the limits of the interpretations of some of the available datasets. We focus here on the time around May 2015 (equinox). While this period is a few months prior to perihelion, the spacecraft was close to the comet, providing a relatively high spacial resolution of the remote sensing observations such that, in principle, they can be more easily linked with the in-situ measurements

On understanding multi-instrument Rosetta data of the innermost dust and gas coma of comet 67P/Churyumov-Gerasimenko - results, strengths, and limitations of models

Numerical models are powerful tools for understanding the connection between the emitted gas and dust from the surface of comets and the subsequent expansion into space where remote sensing instruments can perform measurements. We will present such a predictive model which can provide synthetic measurements for multiple instruments on board ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko (hereafter 67P). We will demonstrate why a multi instrument approach is essential and how models can be used to constrain the gas and dust source distribution on the surface

RACE Project 2116 TOMQAT

: The TOMQAT project enchances the concept of Dynamic Total Quality Management in the context of IBC networks, and investigates the resulting performance benefits. The present deliverable analyses the requirements to be fulfilled by Total Quality Management, and suggests an approach to meet such requirements, including QoS parameters to be managed and appropriate management mechanisms. Keywords: Total Quality Management, QoS parameters, TQM Requirements, TQM Approach Deliverable 5 Page 2 RACE Project R2116 - TOMQAT (c) l994 by the TOMQAT Consortium. Organizations in the TOMQAT consortium are: ALPHA SYSTEMS ANALYSIS INTEGRATION LTD., ALCATEL ISR SA, CRAY COMMUNICATIONS LTD, GMD-FOKUS, INTRACOM SA, NATIONAL TECHNICAL UNIVERSITY OF ATHENS, TECHNICAL UNIVERSITY BERLIN, TELMAT COMMUNICATIONS, WANDEL & GOLTERMANN Deliverable 5 Page 3 RACE Project R2116 - TOMQAT xecutive Summary The main objective of project TOMQAT is to enhance the Total Quality Management (TQM) concept and adapt/ap..