Distortions of perception of the Müller-Lyer, Delboeuf, Oppel-Kundt and Zöllner type have been studied in psychophysical experiments conducted under computer control with a program of our own design arranging the stimuli, presenting them on the monitor, introducing alterations according to the subject’s command, recording responses, and handling the results. Our illusory figures designed by heteroluminant colours yielded the effects of perceived distortion qualitatively and quantitatively similar to the effects evoked by the white and black figures. Variations of luminance of colours of the figures and backgrounds within a relatively wide interval of its values did not evoke a noticeable change in strength of the perceived distortions, but if the luminance of the stimulus colour approached the magnitude which was determined as isoluminant with the background colour, the strength of the distortions changed significantly; it increased for the Brentano figure and decreased for the Delboeuf, Oppel-Kundt and Zöllner figures. The curves obtained for different subjects with different colour combinations were similar in shape, though horizontal parts and peaks of the curve were not at the same level. For isoluminant figures, the experimental curves demonstrating the strength variations of the perceived distortions in dependence of spatial parameters of the stimuli were similar in shape with the curves for heteroluminant figures, but lay above (Brentano) or below (Delboeuf... [to full text]

A 3D arrangement graph G is the abstract graph induced by an arrangement of planes in general position where the intersection of any two planes forms a line of intersection and an intersection of three planes creates a point. The properties of three classes of arrangement graphs — four, five and six planes — are investigated. For graphs induced from six planes, specialized methods were developed to ensure all possible graphs were discovered. The main results are: the number of 3D arrangement graphs induced by four, five and six planes are one, one and 43 respectively; the three classes are Hamiltonian; and the 3D arrangement graphs created from four and five planes are planar but none of the graphs created from six planes are planar. / x, 89 leaves : ill. (some col.) ; 29 cm

In intraplate seismic zones (e.g. the New Madrid Seismic Zone, NMSZ, in the southcentral United States), the source of stress that drives earthquake is very complex. Data from the NMSZ indicate 3 earthquake of magnitude M~7, occurring at an approximate interval of 500 years during the last 2000 years. One hypothesis that satisfies these conditions proposes that short-lived bursts of earthquakes may result from perturbations in the local or regional stress field. This causes relaxation of a lower crustal weak zone which drive repeated earthquakes. The number of earthquakes is dependent on the geometry and rheology of the weak zone. Using finite element techniques which employ contact surfaces to model discrete faulting events and a maximum shear stress criteria evaluated at each node. We investigate the relevant parameter space, as it affects the concentration of stress at the base of the seismogenic fault and the number of earthquakes generated over a given time interval. Parameters that can be varied include earthquake stress drop, background tectonic stress, and maximum shear stress at failure. Results show that solutions are non-unique. With the addition of existing observational evidence, however, we can place bounds on the range of parameters which satisfy above observations.

No description available.

No description available.

In this study, novel Ray Based finite difference method for Time Domain electromagnetics(RBTD) has been developed. Instead of solving Maxwell&rsquo / s hyperbolic partial differential equations directly, Geometrical Optics tools (wavefronts, rays) and Taylor series have been utilized. Discontinuities of electromagnetic fields lie on wavefronts and propagate along rays. They are transported in the computational domain by transport equations which are ordinary differential equations. Then time dependent field solutions at a point are constructed by using Taylor series expansion in time whose coefficients are these transported distincontinuties. RBTD utilizes grid structure conforming to wave fronts and rays and treats all electromagnetic problems, regardless of their dimensions, as one dimensional problem along the rays. Hence CFL stability condition is implemented always at one dimensional eqaulity case on the ray. Accuracy of RBTD depends on the accuracy of grid generation and numerical solution of transport equations. Simulations for isotropic medium (homogeneous/inhomogeneous) have been conducted. Basic electromagnetic phenomena such as propagation, reflection and refraction have been implemented. Simulation results prove that RBTD eliminates numerical dispersion inherent to FDTD and is promising to be a novel method for computational electromagnetics.

Low Pressure Die Casting (LPDC) process is one the most common casting process to produce structural automotive components, such as alloy wheels and suspension components. It has been identified that cavity filling and solidification process are two most critical aspects to produce premium quality casting components.During the solidification process of casting alloy, it is a well known phenomenon that metal experiences volumetric shrinkage due to its density difference between liquid and solid phase. When this volumetric shrinkage is not properly compensated, then a casting defect commonly known as solidification shrinkage occurs. The solidification shrinkage has very detrimental effects on structural integrity required for premium quality casting such as aluminium alloy wheels.Literature and practical experiences of foundry men show that it is critical to achieve unidirectional solidification pattern by avoiding an isolated hot spot in order to minimise the solidification shrinkage. However, it is found that the geometry of industrial casting applications is often constrained by other design factors that would not naturally avoid these isolated hot spots. The subject of this research, aluminium alloy wheels, is not excluded from this constraint.In aluminium alloy wheels, an isolated hot spot is commonly observed in an area known as rim and spoke junction due to its geometry constraints. Consequently, the solidification shrinkage is commonly experienced, which is undesirable due to its detrimental effects for the structural integrity of alloy wheels. In order to minimise the solidification shrinkage, forced cooling method is applied to avoid an isolated hot spot. The control of this forced cooling is achieved by cooling media, flow rate of cooling media and duration cooling circuit. Foundry experiments in industrial environment were conducted producing aluminium alloy wheels using commercially treated A356 (Al-Si) alloy, where different durations of cooling circuit were used to understand the sensitivity of solidification shrinkage formation to the duration of cooling circuit. This was followed by metallurgical structure analysis and numerical modelling to suggest the sensitivity of cooling circuit duration in controlling solidification shrinkage.The major finding conclusion of this research is that control of the shrinkage formation is not very sensitive to the duration cooling circuit. It is suggested that as casting solidifies initially from the mould wall, it retracts away from the cast-mould interface due to thermal contraction. Consequently, air gap is formed between casting and mould interface, creating an effective thermal resistance layer. Thereafter, heat transfer across the cast-mould interface is not sensitive to the change in the cooling channel which is a distance to the cast-mould interface.Some limitations of numerical modelling and metallurgical analysis were also identified during this research and recommendations were made to improve the accuracy of local hot spot prediction in production of aluminium alloy wheels. More specifically, numerical modelling of the effect of grain refinement and use of non homogeneous material property (particularly fraction of solid) for rapidly chilled area. Fraction of eutectic rather than secondary dendrites arm spacing is a proper microstructure parameter that can be used to locate the hot spot.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Σκοπός της διπλωματικής εργασίας είναι η εκτίμηση και η αναγνώριση των γεωμετρικών χαρακτηριστικών των ερυθρών αιμοσφαιρίων με ψηφιακή επεξεργασία της σκεδασμένης ακτινοβολίας. Αποτελείται από 8 κεφάλαια και ένα παράρτημα Α. Σε αυτά περιλαμβάνεται η μελέτη και η εφαρμογή μεθόδων επίλυσης του προβλήματος αναγνώρισης γεωμετρικών χαρακτηριστικών των ανθρώπινων ερυθρών αιμοσφαιρίων από ψηφιοποιημένες εικόνες Ηλεκτρομαγνητικής Ακτινοβολίας ενός He-Ne Laser 632. 8 nm. Oι αλγόριθμοι εκπαίδευσης των νευρωνικών δικτύων ακτινικής συνιστώσας που εφαρμόσθηκαν υλοποιήθηκαν με τη βοήθεια του MATLAB R2009a. Οι κώδικες προγραμματίστηκαν από τον Κύριο Aποστολόπουλο Γεώργιο και τα αποτελέσματα τους αξιολογήθηκαν σε συνεργασία με τον καθηγητή κ. Δερματά. Επίσης, αρκετά στοιχεία και έννοιες πάρθηκαν για καθαρά μόνο εκπαιδευτικό σκοπό από την Διδακτορική Διατριβή Του κ. Αποστολόπουλου Γεωργίου και τον ευχαριστώ πάρα πολύ για την πολύτιμη βοήθεια του. Στο πρώτο κεφάλαιο γίνεται μια εισαγωγή στις ιδιότητες και τα χαρακτηριστικά του ανθρώπινου ερυθρού αιμοσφαιρίου δίνοντας έμφαση στα γεωμετρικά χαρακτηριστικά των υγιών απαραμόρφωτων ερυθροκυττάρων. Τέλος, γίνεται μία αναφορά στις ανωμαλίες των ερυθροκυττάρων και στους μέχρι τώρα υπάρχοντες τρόπους ανίχνευσης τους. Στο δεύτερο κεφάλαιο γίνεται μια αναφορά και μια επεξήγηση κάποιων θεωρητικών εννοιών όσον αφορά την θεωρία του Ηλεκτρομαγνητισμού, ξεκινώντας από την αρχή της ιστορίας του Ηλεκτρισμού, με αναφορά στο ηλεκτρικό φορτίο, την αρχή όλων. Γίνεται μια αναλυτική παρουσίαση των εξισώσεων Maxwell και τέλος γίνεται η επεξήγηση της ηλεκτρομαγνητικής Ακτινοβολίας και του Ηλεκτρομαγνητικού Φάσματος καθώς επίσης και της απορρόφησης του φωτός από τα ερυθρά αιμοσφαίρια. Στο τρίτο κεφάλαιο παρουσιάζεται διεξοδικά το φαινόμενο της σκέδασης και της ανάκλασης, αφού η σκέδαση είναι προϊόν πολλαπλής ανάκλασης, γίνεται η συσχέτιση της απορρόφησης της σκέδασης της Ηλεκτρομαγνητικής ακτινοβολίας από τα ερυθρά αιμοσφαίρια. Γίνεται η επεξήγηση του «ευθέως προβλήματος της σκέδασης» και τέλος γίνεται μια απλή αναφορά στις εφαρμογές της σκέδασης στους διάφορους τομείς της επιστήμης και της ανθρώπινης ζωής. Στο τέταρτο κεφάλαιο αναλύεται διεξοδικά το «αντίστροφο πρόβλημα της σκέδασης ηλεκτρομαγνητικής ακτινοβολίας» δηλαδή, το γεγονός του να γνωρίζουμε το σκεδαζόμενο πεδίο και το προσπίπτον κύμα και το να προσπαθούμε να βρούμε το σχήμα και το μέγεθος του σκεδαστή. Στη συγκεκριμένη έρευνα προσπαθούμε με τη βοήθεια μιας πειραματικής συσκευής να αναγνωρίσουμε τα ανθρώπινα αιμοσφαίρια και να εκτιμήσουμε με την βοήθεια των νευρωνικών δικτύων ακτινικής συνιστώσας τα γεωμετρικά χαρακτηριστικά των ερυθροκυττάρων μέσω των ψηφιοποιημένων εικόνων σκέδασης. Στο πέμπτο κεφάλαιο περιγράφονται αναλυτικά και γίνεται μια εκτενής αναφορά στα Τεχνητά Νευρωνικά Δίκτυα, ξεκινώντας από την αρχή της ιστορίας τους. Γίνεται μια εισαγωγή σε θεωρητικές έννοιες, οι οποίες θα μας βοηθήσουν στην διάρκεια της ερευνάς μας, να μπορέσουμε να κατανοήσουμε επαρκέστερα είτε τη λειτουργία των Τεχνητών Νευρωνικών Δικτύων (Artificial Intelligence) και Των Νευρωνικών Δικτύων Ακτινικής Συνιστώσας (RBF-NN) είτε την μεθοδολογία και την επιστημονική αξία της εκπαίδευσης των προηγουμένων. Στο έκτο κεφάλαιο γίνεται μια αναφορά στις έννοιες, της ψηφιακής επεξεργασίας εικόνας, της Συμπίεσης των εικόνων,της κανονικοποίησης των εικόνων, της Διαδικασίας ανάκτησης πληροφορίας, στις μεθόδους εξαγωγής χαρακτηριστικών από ψηφιοποιημένες εικόνες, όπου στην συγκεκριμένη εργασία χρησιμοποιήθηκαν ο Διακριτός μετασχηματισμός συνημιτόνου (DCT), Ο Διακριτός μετασχηματισμός Κυματιδίου (DWT), Ο Γωνιακός Ακτινικός Μετασχηματισμός (ART), Τα φίλτρα Gabor και τέλος οι Ροπές Zernike. Στο έβδομο κεφάλαιο εισχωρούμε πλέον στην βαθύτερη και ουσιαστικότερη πλευρά της ερευνάς μας. Είμαστε πλέον έτοιμοι,από πλευράς θεωρητικών εννοιών. Κάνουμε εκτενή αναφορά στο «Αντίστροφο πρόβλημα της σκέδασης» στην συγκεκριμένη περίπτωση, δηλαδή στην Διαδικασία Ανάκτησης (με την χρήση δισδιάστατων Μετασχηματισμών, οι οποίοι περιγράφονται αναλυτικότατα), αναγνώρισης και Ταξινόμησης (με την μέθοδο των Νευρωνικών δικτύων ακτινικής Συνιστώσας) της Πληροφορίας μας (την αναγνώριση των ερυθρών αιμοσφαιρίων και την εκτίμηση των γεωμετρικών χαρακτηριστικών τους). Στο Όγδοο κεφάλαιο εμφανίζονται τα αποτελέσματα της πειραματικής διαδικασίας μέσω διαγραμμάτων και σχολίων - συμπερασμάτων. Παρατίθενται οι γραφικές παραστάσεις του Μέσου Απόλυτου Σφάλματος (Mean Regression Error) και του ποσοστού επιτυχίας Αναγνώρισης (Mean Identification Error). Στο Παράρτημα Α παρουσιάζονται τα πειραματικά αποτελέσματα σε μορφή πινάκων Excel, δηλαδή παρατίθενται οι πίνακες του μέσου Απόλυτου Σφάλματος (Regression Error)συναρτήσει του αριθμού των Νευρώνων(Number of Neurons) και το Μέσο Ποσοστό Επιτυχίας Αναγνώρισης (Mean Identification Error) συναρτήσει του αριθμού των Νευρώνων αλλά και συναρτήσει του Λευκό Gaussian θορύβου SNR(dB). / The aim of this particular scientific project is the estimation and the recognition of the geometrical characteristics of healthy, undistorted Red blood Human Cells using scattering images of visible light. This means that we use scattering images throughout scattering phenomena in the visible spectrum of electromagnetic radiation. This project includes and focuses on the study and the use of several important methods such as, Image Feature Extraction, Image Feature Normalization, Estimation and Identification of the geometrical Features of RBCs, throughout Neural Networks. We make an important and a sufficient reference on the theories, that we are going to use on this survey such as the theory of Electromagnetic Radiation, the theory of Artificial Intelligence, the theory of Scattering Images, the theory of Compressing Images throughout Transforms and at last but not least the theory of the Forward scattering Problem. On This project we use, 5 well-known Transforms for the Image Feature Extraction, such as, Discrete Cosine Transform (DCT), Discrete wavelet Transform (DWT), Angular Radial Transform (ART), Zernike Transform and Gabor’s Filters. The each proposed method is evaluated in both, Regression and Identification Tasks when Three Important geometrical properties of The Human RBC are estimated using Database of 1575 simulated images generated with the boundary element Method. The experimental set up consists of a light beam at 632.8 nm and moving RBCs in a thin glass and additive noise distortion is simulated using White Gaussian Noise from 10 to 60 dB SNR. We give our whole attention on the diagrams which show us, The Mean Regression Error of the three geometrical properties versus The Number of Neurons, and the Mean Identification Error versus the Noise Distortion.

This dissertation investigates various design metrologies on designing freeform surfaces for LED illumination applications. The major goal of this dissertation is to study designing freeform optical surfaces to redistribute the radiance (which can be simplified as intensity distribution for point source) of LED sources for various applications. Nowadays many applications, such as road lighting systems, automotive headlights, projection displays and medical illuminators, require an accurate control of the intensity distribution. Freeform optical lens is commonly used in illumination system because there are more freedoms in controlling the ray direction. Design methods for systems with rotational and translational symmetry were well discussed in the 1930's. However, designing freeform optical lenses or reflectors required to illuminate targets without such symmetries have been proved to be much more challenging. For the simplest case when the source is an ideal point source, the determination of the freeform surface in a rigorous manner usually leads to the tedious Monge-Ampère second order nonlinear partial different equation, which cannot be solved with standard numerical integration techniques. Instead of solving the differential equation, ray mapping is an easier and more efficient method in controlling one or more freeform surfaces for prescribed irradiance patterns. In this dissertation, we investigate the ray mapping metrologies in different coordinate systems to meet the integrability condition for generating smooth and continuous freeform surfaces. To improve the illumination efficiency and uniformity, we propose a composite ray mapping method for designing the total internal reflective (TIR) freeform lens for non-rotational illumination. Another method called "double pole" ray mapping method is also proposed to improve system performance. The ray mapping designs developed for the point source do not work well for extended sources, we have investigated different design methodologies including optimization method, deconvolution method and feedback modification method to design freeform optical surfaces for extended sources.