Benzimidazolium Surfactants for Modification of Clays for Use with Styrenic Polymers

Nanocomposites of polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays

Differences between Neural Activity in Prefrontal Cortex and Striatum during Learning of Novel Abstract Categories

Learning to classify diverse experiences into meaningful groups, like categories, is fundamental to normal cognition. To understand its neural basis, we simultaneously recorded from multiple electrodes in lateral prefrontal cortex and dorsal striatum, two interconnected brain structures critical for learning. Each day, monkeys learned to associate novel abstract, dot-based categories with a right versus left saccade. Early on, when they could acquire specific stimulus-response associations, striatum activity was an earlier predictor of the corresponding saccade. However, as the number of exemplars increased and monkeys had to learn to classify them, PFC activity began to predict the saccade associated with each category before the striatum. While monkeys were categorizing novel exemplars at a high rate, PFC activity was a strong predictor of their corresponding saccade early in the trial before the striatal neurons. These results suggest that striatum plays a greater role in stimulus-response association and PFC in abstraction of categories.Simons FoundationHardy, RichardHardy, LindaNational Institute of Mental Health (U.S.) (5RC1MH088316-02

Σχεδιασμός 6-όροφου εμπορικού κέντρου με κτίρια από μεταλλικό σκελετό

164 σ.Αντικείμενο της παρούσας διπλωματικής εργασίας είναι η διαδικασία σχεδιασμού και διαστασιολόγησης ενός μεγάλου έργου σε δύο μοντέλα (με και χωρίς συνδέσμους δυσκαμψίας) με χαλύβδινο φέροντα οργανισμό χωρίς σύμμικτη με σύμμικτες πλάκες από οπλισμένο σκυρόδεμα, με χρήση ενός εμπορικά διατιθέμενου προγράμματος. Το κτίριο που επιλέχθηκε προς μελέτη είναι ένα εξαώροφο κτίριο μεγάλων ανοιγμάτων για εμπορική χρήση με υπόγειο χώρο στάθμευσης και ένα κεντρικό άνοιγμα-στοά. Οι διαστάσεις του κτιρίου είναι είναι 52 m x 30 m. Η ανάλυση και η διαστασιολόγηση του κτιρίου πραγματοποιήθηκε με βάση τους Ευρωκώδικες. Πιο συγκεκριμένα χρησιμοποιήθηκαν οι ακόλουθοι κανονισμοί: - Ευρωκώδικας 0: Βάσεις σχεδιασμού - Ευρωκώδικας 1: Γενικές δράσεις (Μέρος 1-1) Φορτία χιονιού (Μέρος 1-3) Δράσεις ανέμου (Μέρος 1-4) - Ευρωκώδικας 3: Σχεδιασμός μεταλλικών κατασκευών (Μέρος 1-1) Σχεδιασμός κόμβων (Μέρος 1-8) - Ευρωκώδικας 4: Σχεδιασμός σύμμικτων κατασκευών από χάλυβα και σκυρόδεμα (Μέρος 1-1) - Ευρωκώδικας 8: Αντισεισμικός σχεδιασμός (Μέρος 1-1) Η επίλυση του κτιρίου έγινε με το πρόγραμμα ανάλυσης και διαστασιολόγησης SAP2000version15. Στο πρώτο κεφάλαιο παρουσιάζεται το κτίριο, περιγράφεται η αρχιτεκτονική και η κατασκευή του έργου και παρατίθενται στοιχεία σχετικά με την ανέγερσή του. Στο τέλος του κεφαλαίου περιγράφεται το πρόγραμμα ανάλυσης και διαστασιολόγησης SAP2000. Στο δεύτερο κεφάλαιο γίνεται εκτενής αναφορά στον προσδιορισμό των φορτίων που καταπονούν την κατασκευή, ενώ παρατίθενται και αντίστοιχα αποσπάσματα των κανονισμών βάσει των οποίων προέκυψαν τα επιβαλλόμενα φορτία. Στο τρίτο κεφάλαιο παρουσιάζονται οι σεισμικές δράσεις όπως περιγράφονται από τον Ευρωκώδικα 8 και τα Εθνικά Προσαρτήματα, καθώς και ορισμένα στοιχεία για την ιδιομορφική ανάλυση του κτιρίου. Στο τέταρτο κεφάλαιο περιγράφονται οι συνδυασμοί των δράσεων στην οριακή κατάσταση αστοχίας και λειτουργικότητας όπως απαιτείται από τις διατάξεις του Ευρωκώδικα 1 και Ευρωκώδικα 8. Στο πέμπτο κεφάλαιο διατυπώνονται οι απαιτούμενοι έλεγχοι σύμφωνα με τους Ευρωκώδικες 3 και 4, παρουσιάζονται τα αποτελέσματα των αναλύσεων όπως προέκυψαν από το SAP2000, και η ακολουθεί η διαστασιολόγηση του έργου, η οποία πραγματοποιήθηκε με τη βοήθεια υπολογιστικών φύλλων EXCEL, αντίστοιχα για τα δύο εναλλακτικά μοντέλα του κτιρίου (με και χωρίς συνδέσμους δυσκαμψίας). Στο έκτο κεφάλαιο παρουσιάζεται η διαδικασία σχεδιασμού ορισμένων συνδέσεων και κόμβων του κτιρίου,ξανά με τη βοήθεια υπολογιστικών φύλλων EXCEL, σύμφωνα με τις διατάξεις του Ευρωκώδικα 3 για τα δυο εναλλακτικά μοντέλα της παρούσας εργασίας. Τέλος, στο έβδομο κεφάλαιο, παρουσιάζονται τα αποτελέσματα της σύγκρισης των δύο εναλλακτικών μοντέλων του κτιρίου και γίνεται μία συνολική αποτίμηση της εν λόγω εργασίας.This dissertation deals with the design process of a large steel-framed structure using two alternative structural models (one with and one without braced frames) with composite slabs from steel sheets and reinforced concrete, by using a commercially available software. The building that is being studied, is a six-storey structure of large openings, with an underground parking place and a central gap in the middle and is intended to be used as a shopping center. The dimensions of the building are 52 m x 30 m. The analysis and design process were carried out according to the regulations of the Eurocodes. More specifically, the following regulations were used: - Eurocode 0: Basis of structural design - Eurocode 1: Actions on structures (Part 1-1) Snow loads (Part 1-3) Wind actions (Part 1-4) - Eurocode 3: Design of steel structures-General rules an rules for buildings (Part 1-1) Design of joints (Part 1-8) - Eurocode 4: Design of composite steel and concrete structures (Part 1-1) - Eurocode 8: Design of structures for earthquake resistance (Part 1-1) The structural design took place by using the statics and analysis software SAP2000version15. In the first chapter, the building is being introduced, its architecture and some basic structural elements are being described and some information about the building erection is being listed. In the end of the chapter, the SAP2000 analysis program is being introduced. In the second chapter, there is an extensive reference of the determination of the loads which are straining the construction and the relevant extracts of the regulations are being given. In the third chapter, the seismic actions that take place are being described, as determined by the Eurocode 8 and the National Annexes. In addition there is some information about the modal analysis of the building. In the fourth chapter, the load combinations in the ultimate limit state and functionality are being described, as required by the provisions of Eurocode 1 and Eurocode 8. Ιn the fifth chapter, the required tests according to Eurocode 3 and 4 are taking place and the analysis results as taken from the SAP2000 processing are being presented. Then follows the structural design of the project, conducted with the help of EXCEL spreadsheets, respectively for the two alternative structural models (with and without braced frames). In the sixth chapter, the design process of some characteristic joints of the two alternative structural models is being presented, also conducted with the help of EXCEL spreadsheets. Finally, in chapter seven, there is a presentation of the results of the comparison between the two alternative building models and an overall assessment of this work is taking place.Πάτσης ευάγγελο

Numerical simulation of bone screw induced pretension: The cases of under-tapping and conical profile

Even though screw induced pretension impacts the holding strength of bone screws, its implementation into the numerical simulation of the pullout phenomenon remains a problem with no apparent solution. The present study aims at developing a new methodology to simulate screw induced pretension for the cases of: a) cylindrical screws inserted with under-tapping and b) conical screws. For this purpose pullout was studied experimentally using synthetic bone and then simulated numerically. Synthetic bone failure was simulated using a bilinear cohesive zone material model. Pretension generation was simulated by allowing the screw to expand inside a hole with smaller dimensions or different shape than the screw itself. The finite element models developed here were validated against experimental results and then utilized to investigate the impact of under-tapping and conical angle. The results indicated that pretension can indeed increase a screw's pullout force but only up to a certain degree. Under-tapping increased cylindrical screws' pullout force up to 12%, 15% and 17% for synthetic bones of density equal to 0.08 g/cc, 0.16 g/cc and 0.28 g/cc respectively. Inserting a conical screw into a cylindrical hole increased pullout force up to 11%. In any case an optimum level of screw induced pretension exists

Delay-induced destabilization of entrainment of nerve impulses on ephaptically coupled nerve fibers

We study the effect of delay on the synchronization of two nerve impulses traveling along two ephaptically coupled, unmyelinated nerve fibers. The system is modeled as a pair of delay-coupled Fitzhugh-Nagumo equations. A multiple-scale perturbation approach is used for the analysis of these equations in the limit of weak coupling. In the absence of delay, two pulses with identical speeds are shown to be entrained precisely. However, as the delay is increased beyond a critical value, we show that this precise entrainment becomes unstable. We make quantitative estimates for the actual values of delay at which this can occur in the case of squid giant axons and compare them with the relevant time-scales involved