<p>The role of intrinsic hydrodynamic instability of the premixed flame (known as Landau-Darrieus instability) in various flame phenomena is studied by means of direct numerical simulations of the complete system of hydrodynamic equations. Rigorous study of flame dynamics and effect of Landau-Darrieus instability is essential for all premixed combustion problems where multidimensional effects cannot be disregarded.</p><p>The present thesis consists of three parts. The first part deals with the fundamental problem of curved stationary flames propagation in tubes of different widths. It is shown that only simple "single-hump" slanted stationary flames are possible in wide tubes, and "multi-hump" flames in a laminar flow are possible in wide tubes only as a non-stationary mode of flame propagation. The stability limits of curved stationary flames in wider tubes are obtained, together with the dependence of the velocity of the stationary flame on the tube width. The flame dynamics in wider tubes is shown to be governed by a large-scale stability mechanism resulting in a highly slanted flame front.</p><p>The second part of the thesis is dedicated to studies of acceleration and fractal structure of outward freely propagating flames. It is shown that in direct numerical simulation the development of Landau-Darrieus instability results in the formation of fractal-like flame front structure. The fractal excess for radially expanding flames in cylindrical geometry is evaluated. Two-dimensional simulation of radially expanding flames in cylindrical geometry displays a radial growth with 1.25 power law temporal behavior after some transient time. It is shown that the fractal excess for 2D geometry obtained in the numerical simulation is in good agreement with theoretical predictions. The difference in fractal dimension between 2D cylidrical and three-dimensional spherical radially expanding flames is outlined. Extrapolation of the obtained results for the case of spherical expanding flames gives a radial growth power law that is consistent with temporal behavior obtained in the survey of experimental data.</p><p>The last part of the thesis concerns the role of Landau-Darrieus instability in the transition from deflagration to detonation. It is found that in sufficiently wide channels Landau-Darrieus instability may invoke nucleation of hot spots within the folds of the developing wrinkled flame, triggering an abrupt transition from deflagrative to detonative combustion. It is found that the mechanism of the transition is the temperature increase due to the influx of heat from the folded reaction zone, followed by autoignition. The transition occurs when the pressure elevation at the accelerating reaction front becomes high enough to produce a shock capable of supporting detonation.</p>

Στην παρούσα διδακτορική διατριβή παρουσιάζεται µία µελέτη τυπωµένων κεραιών γεωµετρίας φράκταλ για ασύρµατες τερµατικές συσκευές, µε έµφαση στις εφαρµογές των κινητών επικοινωνιών και των ασύρµατων τοπικών δικτύων. Η ραγδαία εξέλιξη των ασύρµατων επικοινωνιών είχε ως αποτέλεσµα την σηµαντική µείωση των διαστάσεων των τερµατικών συσκευών, την ολοκλήρωση διαφορετικών υπηρεσιών διαφορετικών συχνοτήτων λειτουργίας στην ίδια συσκευή και την ανάγκη πολλαπλών κεραιών για την αντιµετώπιση του φαινοµένου της διάλειψης και της διασυµβολικής παρεµβολής του ασύρµατου καναλιού. Αυτές οι εξελίξεις έθεσαν καινούργιες απαιτήσεις στην σχεδίαση της κεραίας οδηγώντας στην ανάγκη κεραιών εξαιρετικά µικρών διαστάσεων, πολυσυχνοτικών, χαµηλού κόστους, υψηλής απόδοσης και επιθυµητών χαρακτηριστικών ακτινοβολίας κατά περίπτωση. Στα πλαίσια της διατριβής διερευνήθηκε η ικανότητα σµίκρυνσης και παραγωγής πολυσυχνοτικής συµπεριφοράς που παρουσιάζουν τα σχήµατα γεωµετρίας φράκταλ αν χρησιµοποιηθούν σαν κεραίες. Αρχικά προτείνεται µία καινούργια κατηγορία κεραιών, οι τυπωµένες µονοπολικές κεραίες γεωµετρίας φράκταλ και συγκρίνονται διάφορες γεωµετρίες φράκταλ τόσο ως προς την ικανότητα σµίκρυνσης όσο και ως προς τα χαρακτηριστικά εµπέδησης και ακτινοβολίας που παρουσιάζουν. Εξετάζεται ο καθοριστικός ρόλος του επιπέδου γείωσης αυτής της κατηγορίας κεραιών και εξάγονται γενικά συµπεράσµατα για την εκµετάλλευσή του µε τον βέλτιστο δυνατό τρόπο. Επιπλέον διερευνήθηκε η χρήση των σχηµάτων φράκταλ για την µείωση των διαστάσεων των µικροταινιακών κεραιών. Η φράκταλ ορθογώνια καµπύλη προτείνεται για εφαρµογές γραµµικής και κυκλικής πόλωσης, η οποία παρουσιάζει σηµαντική ικανότητα σµίκρυνσης και προσφέρει πολλούς σχεδιαστικούς βαθµούς ελευθερίας που µπορούν να χρησιµοποιηθούν είτε για περαιτέρω µείωση του µεγέθους της είτε για την διατήρηση του εύρους ζώνης της σε ικανοποιητικά επίπεδα. Λόγω του συµπαγούς σχήµατος και των επιθυµητών χαρακτηριστικών των τυπωµένων µονοπολικών και µικροταινιακών κεραιών φράκταλ, µελετάται περαιτέρω η χρησιµοποίησή τους για την υλοποίηση συστηµάτων πολλαπλών κεραιών µε σκοπό την βελτίωση της ποιότητας του λαµβανοµένου σήµατος. Ακόµη µελετάται η ικανότητα παραγωγής πολυσυχνοτικής συµπεριφοράς της µονοπολικής κεραίας Sierpinski και προτείνεται µία τροποποίηση η οποία µειώνει σηµαντικά το µέγεθος της κεραίας και καθίσταται δυνατόν να τυπωθεί σε ασύρµατες συσκευές µικρού µεγέθους. Επιπλέον, διερευνώνται διάφορες τεχνικές για να ελεγχθούν οι συχνότητες συντονισµού της κεραίας και να συµπέσουν µε τις εκάστοτε επιθυµητές µπάντες λειτουργίας. Τέλος εξετάζεται η επίδραση των διαστάσεων του επιπέδου γείωσης στα χαρακτηριστικά εµπέδησης του συστήµατος. / This Ph.D. thesis presents a comprehensive study on printed fractal antennas for wireless terminal devices, with emphasis on mobile and wireless local area network applications. The rapid evolution of wireless communications resulted in a decrease of terminal devices’ dimensions, in the integration of different services, operating in different spectra, in the same device and finally in the deployment of multiple antenna systems to mitigate the phenomena of fading and intersymbol interference of wireless channel. These evolutions, in turn, set new demands on antenna’s design leading to the necessity of exceptionally small, multiband and low cost radiators possessing high efficiency and desirable radiation characteristics. In the context of the present work, the miniaturization and multiband ability of fractal shaped antennas is examined. Initially a new antenna type is proposed, that of printed fractal monopole antennas, and several innovative fractal shaped monopoles are compared with respect to their miniaturization ability, input impedance and radiation characteristics. The important role of the ground plane is also investigated and general conclusions are drawn to exploit its effects in the most appropriate way. The application of fractals on microstrip antennas was further studied with the fractal rectangular curve (frc) microstrip antenna being proposed for linear and circular polarization applications. The frc microstrip antenna proved to possess a noticeable miniaturization ability and a geometry with several degrees of freedom that can be used either to reduce further its size, or to keep the bandwidth to a satisfactory level. Due to the compact size and desirable electrical characteristics of printed monopole and microstrip fractal antennas, they were further considered for the implementation of multi element antenna systems in order to improve the SNR of the received signal. Finally, the multiband ability of the Sierpinski monopole antenna is investigated and a modification is proposed to decrease the overall antenna height making it feasible to be printed in small terminal devices. Several techniques to allocate the desirable bands of interest are also discussed along with the effect the ground plane dimension’s on the system’s input impedance.

For correct specification human’s physiological state, it is very important to evaluate the changes of main human organism systems. Fractal dimensions of the parameters of the human organism, according to proposed model which includes three functional elements – periphery, regulation and supplying systems were analyzed. The parameters that characterize the function of those systems, that is <a style='text-decoration: none; border-bottom: 3px double;' href="http://www.serverlogic3.com/lm/rtl3.asp?si=22&k=heart%20rate" onmouseover="window.status='heart rate'; return true;" onmouseout="window.status='; return true;">heart rate</a>, JT interval, systolic and diastolic <a style='text-decoration: none; border-bottom: 3px double;' href="http://www.serverlogic3.com/lm/rtl3.asp?si=22&k=blood%20pressure" onmouseover="window.status='blood pressure'; return true;" onmouseout="window.status='; return true;">blood pressure</a> have been studied. Interpolation of discrete data from the physical load obtained by provocative incremental bicycle ergometry stress test was made by cubic spline. For those approximated parameters fractal dimensions (capacity, information, correlation) were counted. The differences for various groups of persons (sportsmen, healthy persons, patients with ischemic heart disease) were investigated. Fractal dimensions integrates all features of reaction to load and recovery. The study revealed that distributions of fractal dimensions significantly differs between... [to full text]

Šiame darbe nagrinėjami fraktalų – iteruoųjų funkcijų sistemų (IFS) atraktorių – sintezės algoritmai. Pagrindinis dėmesys skiriamas pabėgimo laiko (PL)-algoritmui. PL-algoritmas yra pakankamai universalus. Pagrindinės šio algoritmo panaudojimo sričitys – netiesinių dinaminių sistemų, veikiančių kompleksinėje plokštumoje, analizė, kompleksinių daugianarių šaknų pritraukimo baseinų vizualizavimas ir kt. Geometrinių fraktalų (IFS atraktorių) sintezei šis algoritmas iki šiol nebuvo naudojamas, nors tokia galimybė, kaip teorinis rezultatas, yra žinoma. Pagrindinė to priežastis – IFS sudarančių afiniųjų transformacijų veikimo zonų atskyrimo kriterijaus nebuvimas. Tokio kriterijaus paieškai ir realizacijai darbe skiriamas didžiausias dėmesys. Rezultatas – nauja adaptyvi IFS sudarančių afiniųjų transformacijų veikimo zonų atskyrimo procedūra. Lygegrečiai spendžiama tolygaus spalvinio sintezuojamo (PL-algoritmo pagalba) fraktalinio vaizdo užpildymo problema. Pasiūlytas originalus sprendimas – problemiškai oriantuota iteracij�� skaičiaus (sintezės metu) korekcija. Darbe pristatomi ir preliminarūs su fraktalinių vaizdų (IFS atraktorių) sinteze susijusių eksperimentų rezultatai. / The contribution of this work is a new version of the escape time algoritm adapted for synthesizing fractal images, indentified with atractors of iterated functions systems (IFS). The proposesd synthesis algorithm is based on the use of shift dynamics, associated with one or another IFS. The strategy for the seperation of extended domains of the inverse affine transformations, specified by IFS, is developed. In the field of computerized real word image models (digital images) the fractal approach is of outmost importance, because it facilitates perception and understanding of the information content of an image. To say more, it provides us with a powerful means to catch sight of a fundamental real word image property generally known as self-similarity. Due to this property, the research and development of algorithms („fractal techniques“) to extract imortant fractal parameters from appropriate digital data has received significant attention in recent years. In this work, the basic concepts and ideas that are needed to describe, state and solve the problem of synthesizing fractal images, identified with attractors of IFS, are introduced and explored. A new original approach (idea), leading to practical implementation of the shift dynamical system, associated with a particular IFS, is proposed (part 3). Some experimental results are given (Part 4).

Šiame darbe buvo analizuojama Niutono fraktalų Žulija aibės. Dažniausiai Žulija ir užpildytų Žulija aibių vaizdai gaunami, panaudojant "pabėgimo laiko" algoritmą. Norėdami šį algoritmą naudoti kompleksinio daugianario šaknų vizualizacijai, turime nurodyti iteracijų skaiči��, algoritmo tikslumą, žingsnį bei kompleksiniu Niutono metodu rasti daugianario šaknis. Taikant Niutono metodą, buvo susidurta su pradinių taškų parinkimo problema. Tyrimo metu patvirtinta, kad pakanka Niutono iteracinę funkciją taikyti taškams z, kurių modulis 2. Darbe buvo pasiūlytas šaknų lokalizacijos srities nustatymo būdas. Naudojant PL-algoritmą, pasirinktu žingsniu pereiname visus taškus, kurie patenka į šią sritį. Taip gauname Niutono-Rafsono fraktalus ir lygiagrečiai analizuojame Žulija aibes bei užpildytas Žulija aibes. / Julia sets and filled Julia sets of Newton‘s fractals are analyzed in this work. The Escape Time Algorithm provides us with a means for "seeing" the filled Julia sets of Newton‘s fractals, but roots, (zeros) of the polynomial under investigation should be known. The Newton‘s method for finding roots of an algebraic equation is well known. Here in the paper the complex Newton method for finding roots of a complex polynomial is presented. The main difficulties, associated with implementation of this method in practice, are discussed, namely: construction of the set of initial points (first approximations of the roots), finding the basin of attraction for a particular root and so forth. Some experimental results are presented.

Darbe pateikiamas naujas lokaliojo koliažo principu grįstas fraktalinių interpoliacinių funkcijų generavimo algoritmas (procedūra) su pilna kompiuterine realizacija. Siūlomas įrankis orientuotas į realaus pasaulio objektų (sistem��), pasižyminčių "atsikartojimu savyje" (fraktališkumu), modeliavimą. Atlikti preliminarūs eksperimentai patvirtina metodo perspektyvumą. / In the paper, a new method (tool) for the generation of fractal interpolation functions is presented. The proposed interpolation tool is oriented to process data arrays having links with real-world objects. The interpolation process itself explores self-similiarities found within data arrays under processing, as well as exciting properties of the local collage theorem. Some preliminary experimental results are presented.

The objective of this study was to examine the link between radiographic measures of bone quality and total knee implant migration as measured by radiostereometric analysis (RSA). Two uncemented total knee arthroplasty studies (n=65) with RSA and bone mineral density (BMD) exams up to two years post surgery, and one study with cemented total knees with one year RSA data (n=18) were examined. Radiograph image texture analysis was used to characterize the bone microarchitecture, and a feasibility study was conducted to determine if a given x-ray machine could be used to obtain bone mineral density at the same time as the RSA exams. Random ForestTM ensemble classification tree statistical models classified patients into groups based on implant migration with a range of cut-points. Models based on bone texture parameters measured from the two year radiographs had a sensitivity of 87.5% and specificity of 80% when classifying patients who had more than 0.3mm maximum total point motion (MTPM) at two years using the one year exam as reference. Other cut-points were examined, with models generally having a lower specificity if the acceptable migration was smaller, and lower sensitivity if higher migrations were tolerable. In a predictive model, post-operative bone texture could be used to create a model with a sensitivity of 75% and a specificity of 80% when predicting those subjects with cemented implants who went on to more than 0.4mm total migration by one year. Bone mineral density of the proximal tibia, as determined by clinical scanners, was not found to increase the accuracy of implant migration group classification. An empirical fit to central regions of a purposed-built cross-wedge calibration phantom returned residuals of less than ±1.5% for the bone-equivalent thicknesses. The coefficient of variation of the region greyscale values in three images spread over three days is under 4%, showing the stability of the system to hold a calibration between phantom exams and patient scans. Scatter and dynamic range issues will need to be considered for an accurate calibration across the full range of areal bone mineral densities in the distal femur and proximal tibia.

Ce mémoire traite de la compression des images fixes par fractales, fondée sur la théorie des systèmes de fonctions itérées (IFS). Après quelques rappels sur les principales méthodes de codage entropique et de compression réversible et irréversible des images nous introduisons les notions nécessaires à la compréhension de la théorie des IFS. Nous détaillons ensuite les principaux algorithmes de compression des images naturelles selon l'approche fractale. Ces derniers consistent à approximer chacun des éléments d'une partition à l'aide d'une transformation locale contractante appliquée sur une autre partie de l'image. Ceci nous conduit à présenter les modèles de partitionnement utilisés pour coder les similarités locales des images. La partie suivante constitue la contribution majeure du travail. Nous présentons un algorithme de codage par fractales fondé sur la triangulation de Delaunay. La souplesse de ce modèle nous permet d'utiliser diverses triangulations adaptées au contenu de l'image à compresser. Nous proposons ensuite différentes solutions ayant pour but d'améliorer le schéma de codage-decodage. La premiere vise à réduire la complexité de la phase de codage en diminuant le nombre de comparaisons inter-blocs, par un algorithme de quantification vectorielle de l'espace de recherche. La seconde vise à réduire le nombre de blocs traités tout en améliorant les résultats visuels, pour des taux de compression élevés. Ceci est fait en introduisant des quadrilatères dans la triangulation de l'image. Nous concluons le mémoire en commentant différents résultats de décompression obtenus à partir des partitionnements étudiés, puis comparons ces résultats à ceux obtenus à partir de méthodes hybrides liant le codage par fractales à une décomposition multirésolution de l'image ou à la transformée en cosinus discrète.

Complexity lies halfway between stochasticity and determinism, suggesting that brain activity is neither fully random nor fully predictable but lives by the rules of nonlinear high- and low-complexity dynamics. One important aspect of brain function is noise-like activity (NLA), defined as background, electrical potential fluctuations in the nervous system distinct from spiking rhythms in the foreground. The objective of this thesis was to investigate the neurodynamical complexity of NLA recorded at the cellular and local network scales in in vitro preparations of mouse and human hippocampal tissue, under healthy and epileptiform conditions. In particular, it was found that neuronal NLA arises out of the physiological contributions of gap junctions and chemical synaptic channels and is characterized by a spectrum of complexity, ranging from high- to low-complexity, that was measured using methods from nonlinear dynamical systems theory. Importantly, the complexity of background, neuronal NLA was shown to depend on the degree of cellular interconnectivity to the surrounding local network. In addition, the complexity and multifractality of NLA was further studied at the cellular and local network scales in epileptiform transitions to seizure-like events, identifying emergent low-complexity and reduced multifractality (bordering on monofractal-type dynamics) in the pathological ictal state. Finally, dual intracellular recordings of hippocampal epileptiform activity were analyzed to measure NLA synchronicity, showing evidence for increased same- and cross-frequency correlations and increased phase synchronization in the pathological ictal state. Convergence towards increased phase synchrony manifested in lower frequency regions including theta (4-10 Hz) and beta (12-30 Hz), but also in higher frequency bands (gamma, 30-80 Hz). In summary, there is evidence to suggest that background NLA captures important neurodynamical information pertinent to the classification and identification of brain state transitions in healthy and epileptiform hippocampal dynamics, using sophisticated neuroengineering analyses of these physiological signals.

La présente recherche est une approche transdisciplinaire et pluridisciplinaire qui a pour objet principal, la réévaluation et la redéfinition du concept du mythe littéraire, en abordant la vision des sciences biologiques, plus précisément la génétique dont les instruments et concepts servent de notre point de vue à la reconfiguration des structures déjà classiques de l'imaginaire. Nous avons comme objectif de proposer une définition du mythe qui rend compte de son évolution dans les cultures, non pas une définition statique, immobile ; mais une définition qui suppose l'idée de l'évolution. Le biologiste anglais, Richard Dawkins, écrit en 1976 Le Gène égoïste, dans lequel il explique que «toute vie évolue en fonction des chances de survie des entités répliquées». Selon lui, le gène est la principale unité de sélection dans l'évolution. Dawkins invente aussi le concept de « mème » comme étant l'unité de l'évolution culturelle par analogie avec le gène. Donc, il estime qu'il y a un rapport très fort entre la génétique et la culture humaine, autrement dit, entre le monde physique, le cerveau humain et l'imaginaire. Claude Lévi-Strauss dans, Roger Caillois, Gilbert Durand et Richard Dawkins voyaient une liaison forte entre l'imaginaire et la biologie. Mais, leurs recherches n'aboutissent pas à présenter un modèle concret. Ce que nous essayerons de présenter dans notre recherche, est un nouveau parcours vers ce but avec le nouvel outil de la génétique. Nous étudions quelque domaine crucial de l'imaginaire tel que l'origine ou le Big Bang de l'imaginaire, la frontière dans l'imaginaire et le réel, le tableau des gènes littéraires et les codes des gènes littéraires. C'est une sorte de redécouverte de l'imaginaire basé sur le gène et mythe littéraire. Pour prouver notre point de vue, nous appliquons la méthode du repérage des gènes littéraires sur un récit. Cette recherche transdisciplinaire veut mettre en évidence que le mythe, comme il est défini par les mythologues, les ethnographes, les anthropologues etc., n'est pas seulement un phénomène culturel, religieux, historique, ou déterminé par les représentations littéraires, mais il est en fait, déterminé par les structures génétiques qui préparent l'homme à la propension et la compétence de raconter des « histoires »/ des « récits ». / This research is an interdisciplinary and multidisciplinary approach has the main purpose, reassessment and redefining the concept of literary myth, addressing the vision of Biological Sciences, specifically the genetic tools and concepts which serve as our point of view reconfiguration of the structures already classics of the imagination. We aim to offer a definition of myth that reflects its evolution in the cultures, not a static definition, motionless, but a definition that implies the idea of evolution. The British biologist Richard Dawkins wrote The Selfish Gene in 1976, in which he explains that "all life evolves according to the survival of replicated entities. He said the gene is the main unit of selection in evolution. Dawkins also invented the concept of "meme" as the unit of cultural evolution by analogy with the gene. So he sees a strong relationship between genetics and human culture, between the physical world, the human brain and “imaginaire”. Claude Levi-Strauss, Roger Caillois, Gilbert Durand and Richard Dawkins saw a strong link between “imaginaire” and biology. But their researches fail to present a concrete model. What we try to the present research, is a new route to this goal with the new tool of genetics. We study some crucial area of the imaginaire as the origin or the Big Bang of imaginaire; and the borders into imaginaire and the real; and the table of literary genes and codes of literary genes. It is a kind of rediscovery of imaginaire, based on the literary gene and myth. To prove our point of view, we apply this method of identification of the genes on a literary text. This interdisciplinary research will highlight the myth, as defined by the mythologies, ethnographers, anthropologists etc., is not only a cultural phenomenon, religious, historical, or determined by literary representations; but it is in fact, determined by the genetic structures that prepare the human propensity and ability to tell "histoires" / "récits".