Using machine learning algorithms to detect plasma disruptions in fusion reactors

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές

DECOMPOSITION METHOD IN COMPARISON WITH NUMERICAL SOLUTIONS OF BURGERS EQUATION

This paper presents a solution of the one-dimension Burgers equation using Decomposition Method and compares this solution to the analytic solution [Cole] and solutions obtained with other numerical methods. Even though decomposition method is a non-numerical method, it can be adapted for solving nonlinear differential equations. The advantage of this methodology is that it leads to an analytical continuous approximated solution that is very rapidly convergent [2,7,8]. This method does not take any help of linearization or any other simplifications for handling the non-linear terms. Since the decomposition parameter, in general, is not a perturbation parameter, it follows that the non-linearities in the operator equation can be handled easily, and accurate solution may be obtained for any physical problem

PFO size estimation using TCD: Are the measurements gender related?

There is an ongoing interest in using the findings of Transcranial Doppler (TCD) as a diagnostic technique for patent foramen ovale (PFO) determination. The aim of this study was to investigate the sensitivity of TCD for detection of PFO presence and the correlation of PFO size with the detected microbubble signals. The study group comprised of 103 individuals, healthy volunteers and patients with ischemic stroke or other cerebrovascular diseases. TCD was performed on all subjects, while the presence and size of PFO was estimated with Transesophageal Echocardiography (TEE). PFO diagnosis with TCD had a 92.68% sensibility, 89.47% specificity, 86.65% positive predictive value and 94.44% negative predictive value. PFO size was moderately correlated with the number of microembolic signals detected (rs = 0.404, p = 0.026). Further analysis for gender shown a strong correlation for men (rs = 0.781, p = 0.003), but no correlation for women (p = 0.92). Our results show that TCD is a good predictor of PFO in terms of sensibility and specificity. The correlation between the size of PFO on TEE and the number of microembolic signals detected on TCD is gender biased. Further anatomic and physiological studies are required to identify the reasons for this phenomenon

Aligned Magnetic Field Effects on Flow and Heat Transfer of the Upper-Convected Maxwell Fluid over a Stretching/Shrinking Sheet

In this paper, the effect of aligned magnetic field towards the flow and heat transfer of the upper-convected Maxwell (UCM) fluid over a stretching/shrinking sheet is numerically studied. The governing partial differential equations are reduced into a system of ordinary differential equations using a similarity transformation, which are then solved numerically using the shooting method. The skin friction and heat transfer coefficients, the velocity, as well as the temperature profiles of the fluid are presented and discussed. Results indicate that an increase in the aligned angle strengthens the applied magnetic field which decrease the velocity and increase the temperature profiles of the fluid. This implies that an increase in the aligned angle increases the skin friction coefficient and decreases the heat transfer coefficients

Plutonic foundation of a slow-spreading ridge segment : oceanic core complex at Kane Megamullion, 23°30′N, 45°20′W

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q05014, doi:10.1029/2007GC001645.We mapped the Kane megamullion, an oceanic core complex on the west flank of the Mid-Atlantic Ridge exposing the plutonic foundation of a ∼50 km long, second-order ridge segment. The complex was exhumed by long-lived slip on a normal-sense detachment fault at the base of the rift valley wall from ∼3.3 to 2.1 Ma (Williams, 2007). Mantle peridotites, gabbros, and diabase dikes are exposed in the detachment footwall and in outward facing high-angle normal fault scarps and slide-scar headwalls that cut through the detachment. These rocks directly constrain crustal architecture and the pattern of melt flow from the mantle to and within the lower crust. In addition, the volcanic carapace that originally overlay the complex is preserved intact on the conjugate African plate, so the complete internal and external architecture of the paleoridge segment can be studied. Seafloor spreading during formation of the core complex was highly asymmetric, and crustal accretion occurred largely in the footwall of the detachment fault exposing the core complex. Because additions to the footwall, both magmatic and amagmatic, are nonconservative, oceanic detachment faults are plutonic growth faults. A local volcano and fissure eruptions partially cover the northwestern quarter of the complex. This volcanism is associated with outward facing normal faults and possible, intersecting transform-parallel faults that formed during exhumation of the megamullion, suggesting the volcanics erupted off-axis. We find a zone of late-stage vertical melt transport through the mantle to the crust in the southern part of the segment marked by a ∼10 km wide zone of dunites that likely fed a large gabbro and troctolite intrusion intercalated with dikes. This zone correlates with the midpoint of a lineated axial volcanic high of the same age on the conjugate African plate. In the central region of the segment, however, primitive gabbro is rare, massive depleted peridotite tectonites abundant, and dunites nearly absent, which indicate that little melt crossed the crust-mantle boundary there. Greenschist facies diabase and pillow basalt hanging wall debris are scattered over the detachment surface. The diabase indicates lateral melt transport in dikes that fed the volcanic carapace away from the magmatic centers. At the northern edge of the complex (southern wall of the Kane transform) is a second magmatic center marked by olivine gabbro and minor troctolite intruded into mantle peridotite tectonite. This center varied substantially in size with time, consistent with waxing and waning volcanism near the transform as is also inferred from volcanic abyssal-hill relief on the conjugate African plate. Our results indicate that melt flow from the mantle focuses to local magmatic centers and creates plutonic complexes within the ridge segment whose position varies in space and time rather than fixed at a single central point. Distal to and between these complexes there may not be continuous gabbroic crust, but only a thin carapace of pillow lavas overlying dike complexes laterally fed from the magmatic centers. This is consistent with plate-driven flow that engenders local, stochastically distributed transient instabilities at depth in the partially molten mantle that fed the magmatic centers. Fixed boundaries, such as large-offset fracture zones, or relatively short segment lengths, however, may help to focus episodes of repeated melt extraction in the same location. While no previous model for ocean crust is like that inferred here, our observations do not invalidate them but rather extend the known diversity of ridge architecture.NSF Grants OCE-0118445, OCE-0624408 and OCE-0621660 supported this research. B. Tucholke was also supported by the Henry Bryant Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution

Interaction between transform faults and rift systems: A combined field and experimental approach

We present a detailed field structural survey of the area of interaction between the active NW-striking transform Husavik-Flatey Fault (HFF) and the N–S Theystareykir Fissure Swarm (TFS), in North Iceland, integrated by analog scaled models. Field data contribute to a better understanding of how transform faults work, at a much higher detail than classical marine geophysical studies. Analog experiments are conducted to analyse the fracture patterns resulting from different possible cases where transform faulting accompanies or postpones the rift motions. Different tectonic block configurations are also considered and results are compared with field data in order to study as thoroughly as possible the interaction between the HFF and the TFS as well as the possible prolongation of the HFF into the TFS. West of the intersection between the transform fault (HFF) and the rift zone (TFS), the former splays with a gradual bending giving rise to a leading extensional imbricate fan. The westernmost structure of the rift, the N–S Gudfinnugja Fault (GF), is divided into two segments: the southern segment makes a junction with the HFF and is part of the imbricate fan; north of the junction instead, the northern GF appears right-laterally offset by about 20 m. Southeast of the junction, along the possible prolongation of the HFF across the TFS, the strike of the rift faults rotates in an anticlockwise direction, attaining a NNW–SSE orientation. Moreover, the TFS faults north of the HFF prolongation are fewer and have smaller offsets than those located to the south. Through the comparison between the structural data collected in the field at the HFF–TFS connection zone and a set of scaled experiments, we confirm a prolongation of the HFF through the rift, although here the transform fault has a much lower slip-rate than west of the junction. Our data suggest that transform fault terminations may be more complex than previously known, and propagate across a rift through a modification of the rift pattern

Patent foramen ovale detection and size estimation using transcranial doppler

The aim of the present dissertation is the study of the patent foramen ovale (PFO) with the use of contrast transcranial doppler (cTCD). The primary goal was to investigate whether there is any correlation between the findings on the intracranial arterial blood flow and the size of the PFO. The secondary goal was to re-assess the sensitivity, specificity and prognostic value of cTCD, which I consider to be a first line screening method for ruling out the existence of a PFO in patients with relevant clinical indications. The technique used consisted of carrying out bilateral monitoring of the middle cerebral arteries by the TCD for the detection of high intensity transient signals (HITS) and the simultaneous intravenous infusion of normal saline with microbubbles on patients with a known history of PFO. The existence of PFO was verified by transesophageal echocardiogram (TEE), which is the gold standard for the detection of this condition and is described in detail in the general part of my thesis. TEE also provided us with a measurement of the PFO’s actual size, whereas patients with known PFO and no size measurement were used only in estimating the sensitivity of cTCD. The results of my thesis verify the excellent sensitivity of cTCD in detecting PFO as well as a strong correlation between HITS characteristics and actual PFO size, especially in males.Σκοπός της παρούσας διατριβής είναι η μελέτη του ανοικτού ωοειδούς τρήματος (ΑΩΤ) με τη μέθοδο του διακρανιακού υπερηχογραφήματος με σκιαγραφικό. Πρωτίστως έγινε προσπάθεια να διερευνηθεί η πιθανή συσχέτιση των επιμέρους υπερηχογραφικών χαρακτηριστικών της αιματικής ροής των ενδοκρανιακών αρτηριών με την παρουσία και το μέγεθος του ΑΩΤ, σε συνάρτηση με διάφορες δημογραφικές παραμέτρους. Δευτερευόντως εκτιμήθηκε η ευαισθησία, η ειδικότητα και η προγνωστική αξία του διακρανιακού υπερηχογραφήματος, το οποίο και προτείνω στην παρούσα διατριβή ως παρακλινική μέθοδο πρώτης επιλογής στην αρχική διερεύνηση ύπαρξης ΑΩΤ, εφ’ όσον υφίστανται κλινικές ενδείξεις. Η τεχνική που χρησιμοποιήθηκε περιλαμβάνει τη διενέργεια διακρανιακού υπερηχογραφήματος (ΔΚΥ) αμφοτερόπλευρης συνεχούς καταγραφής των μέσων εγκεφαλικών αρτηριών για την ανίχνευση εμβολικών σημάτων (HITS) με την ταυτόχρονη ενδοφλέβια χορήγηση σκιαγραφικού (αναδευθέντος φυσιολογικού ορού), σε άτομα στα οποία ήταν γνωστή με βεβαιότητα η ύπαρξη ΑΩΤ. Η επιβεβαίωση της παρουσίας ή απουσίας ΑΩΤ στους ασθενείς της διατριβής έγινε με την χρήση διοισοφαγείου υπερηχοκαρδιογραφήματος, η οποία είναι η πλέον ενδεδειγμένη τεχνική για τον σκοπό αυτό και περιγράφεται εκτενώς στο γενικό μέρος της παρούσας διατριβής. Επιπροσθέτως, χάρη στην υπερηχογραφική απεικόνισης της καρδιάς, στην περίπτωση της παρουσίας ΑΩΤ, ήταν δυνατός ο υπολογισμός της μέγιστης τιμής της διαμέτρου του τρήματος. Τα άτομα στα οποία ήταν γνωστή η ύπαρξη ΑΩΤ, αλλά δεν υπήρχε μέτρηση του μεγέθους του, χρησιμοποιήθηκαν μόνο για τις αναλύσεις που σχετίζονταν με την παρουσία ή απουσία του. Τα αποτελέσματα αυτής της διατριβής επιβεβαιώνουν την εξαιρετική ευαισθησία του ΔΚΥ στην ανίχνευση του ΑΩΤ, καθώς και τη συσχέτιση του πλήθους και της έντασης των καταγραφομένων HITS με το μέγεθος του ΑΩΤ, κυρίως στους άνδρες

Hyperstructures associated with binary relations

AbstractIn this paper, we deal with the partial hyperoperation <ÕR> introduced and studied by Corsini [1]. Various characterizations of the relations R, so that (H, ÕR) is a hypergroupoid, are given by means of the associated Boolean matrices. All hypergroupoids (H, ÕR) obtained from the set H, card H=2, 3, 4 are calculated