No description available.

In the aerospace industry, burr removal is a very important part of the manufacturing process. Stacks of material on sections of an aircraft are assembled and drilled by hand. Due to extensive burr formation the sheets must be destacked so that burrs can be removed and then the stacks are reassembled and fastened together. If burrs are minimized in the drilling process, this would reduce the necessity for the sheets to be destacked and deburred. One approach to minimizing burrs is to lower the thrust force in drilling through suitable modification of the drill geometry such as the use of a step drill. Although prior researchers have analyzed different drill geometries such as step drills and their effect on hole exit burr formation in the drilling process through experimentation, no work has been reported on modeling and analysis of step drilling forces and their relationship to burr formation as a function of the step drill geometry parameters. Consequently, this thesis focuses on the modeling of the thrust force and torque for step drills and analyzes their relationship with burr size as a function of the step drill geometry parameters. In the first step, a mechanistic model for thrust and torque in drilling is implemented for a standard twist drill. This mechanistic model is then adapted to predict the thrust and torque for a step drill. Subsequently, experiments are performed to validate the mechanistic model and to evaluate burr formation with standard and step drills. The influence of thrust and torque on hole exit burr formation is analyzed for different step drill geometries and experimental feeds and speeds. The results show that the predicted thrust and torque values for both drill geometries are in good agreement with measured values, although the torque model consistently underpredicts. For standard drill geometry in the calibration tests, the average error in the thrust prediction is 7.09% and the average error in the torque prediction is -18.05%. In validation tests, the average error for predicted thrust is 2.29% and the average error for predicted torque is -18.46%. For the step drill model the average error in thrust is 0.72% while the average error in torque is -8.72%. In addition, a reduction in the predicted thrust force for a step drill relative to the standard twist drill is found to correlate well with a reduction in the measured burr size. However, further reduction in the thrust force by varying the step angle and diameter ratio do not correlate well with the measured burr size. Likely reasons for these results are presented in this thesis.

Im vorliegenden Artikel werden Moeglichkeiten zum Einsatz von STEP als Basis einer systemneutralen und rein anwendungsbezogenen Produktdatenmodellierung vorgestellt. Dabei wird auf einen CA-systemneutralen Ansatz der Betriebsdatenhaltung reflektiert, fuer welchen als praedestinierte Systeme objektorientierte Datenbanken zum Einsatz kommen sollen. Auf dem Wege der produktstruktur- basierten Modellierung von Daten kann der Anwender produktspezifische Anforderungen beruecksichtigen. Ausserdem kann die Auswahl der einzusetzenden CA-Systeme nach rein funktional-wirtschaftlichen Kriterien erfolgen.

Project (D. Min.)--Iliff School of Theology, 2006. / Includes abstract. Includes bibliographical references (leaves 107-109).

Obesity is a problem of vast social concern in the United States. One factor that has been linked to reduction in body fat and the health problems associated with obesity is increasing physical activity. Although in-person behavioral interventions have been shown effective at increasing physical activity, attention is now being placed on disseminating these interventions through the use of technology. Several internet-based interventions have been developed and are readily available. The purpose of this study was to evaluate "Fitbit," a web-based behavioral intervention for increasing physical activity and losing weight. Additionally, this study examined if the addition of contact from a behavioral coach through videoconference and email enhanced the effectiveness of this program. Through a multiple-baseline design across seven participants this research project evaluated the effectiveness of the "Fitbit" program with and without a behavioral coach. Step counts were recorded by a Fitbit sensor as a measure of physical activity. The Fitbit program alone increased physical activity for some of the participants, and the addition of the behavioral coach resulted in further increases in mean step counts.

Step and Flash Imprint Lithography (S-FIL) is a high resolution, next-generation lithography technique that uses an ambient temperature and low pressure process to replicate high resolution images in a UV-curable liquid material. Application of the S-FIL process in conjunction with multi-level imprint templates and new imprint materials enables one S-FIL step to reproduce the same structures that require two photolithography steps, thereby greatly reducing the number of patterning steps required for the copper, dual damascene process used to fabricate interconnect wirings in modern integrated circuits. Two approaches were explored for the implementation of S-FIL in the dual damascene process: sacrificial imprint materials and imprintable dielectric materials. Sacrificial imprint materials function as a pattern recording medium during S-FIL and a three-dimensional etch mask during the dielectric substrate etch, enabling the simultaneous patterning of both the via and metal structures in the dielectric substrate. Development of sacrificial imprint materials and the associated imprint and etch processes are described. Application of S-FIL and the sacrificial imprint material in a commercial copper dual damascene process successfully produced functional copper interconnect structures, demonstrating the feasibility of integrating multi-level S-FIL in the copper dual damascene process. Imprintable dielectric materials are designed to combine the multi-level patterning capability of S-FIL with novel dielectric precursor materials, enabling the simultaneous deposition and patterning of the interlayer dielectric material. Several candidate imprintable dielectric materials were evaluated: sol-gel, polyhedral oligomeric silsesquioxane (POSS) epoxide, POSS acrylate, POSS azide, and POSS thiol. POSS thiol shows the most promise as functional imprintable dielectric material, although additional work in the POSS thiol formulation and viscous dispense process are needed to produce functional interconnect structures. Integration of S-FIL with imprintable dielectric materials would enable further streamlining of the dual damascene fabrication process. The fabrication of electronic devices on flexible substrates represents an opportunity for the development of macroelectronics such as flexible displays and large area devices. Traditional optical lithography encounters alignment and overlay limitations when applied on flexible substrates. A thermally activated, dual-tone photoresist system and its associated etch process were developed to enable the simultaneous patterning of two device layers on a flexible substrate. / text

Το θέμα της παρούσας διπλωματικής είναι η μελέτη των βηματικών τάσεων σε ένα σύστημα γείωσης, με το ισοδύναμο ανθρώπινο κύκλωμα, μέσω της εξομοίωσής του με το λογισμικό EMTP-ATP, έχοντας συμπεριλάβει στους υπολογισμούς και το φαινόμενο του ιονισμού. Αρχικά, στα δύο πρώτα κεφάλαιο δίνονται ορισμοί και βασικές έννοιες για τις γειώσεις, τις μεθόδους γείωσης που υπάρχουν καθώς και για την επίδραση του ηλεκτρικού ρεύματος στον ανθρώπινο οργανισμό και την ηλεκτροπληξία. Έπειτα, στο τρίτο κεφάλαιο περιγράφεται αναλυτικά το φαινόμενο του ιονισμού και η προσέγγιση του μέσα από τα αντίστοιχα μοντέλα που έχουν αναπτυχθεί και των κριτηρίων υπολογισμού ακτίνας του ηλεκτροδίου του αγωγού γείωσης σε σχέση με το πεδίο ιονισμού του εδάφους E0. Στο τέταρτο κεφάλαιο γίνεται εκτενής ανάλυση των μοντέλων των συστημάτων γείωσης που έχουν αναπτυχθεί, παραθέτοντας και αυτά που χρησιμοποιούνταν κατά το παρελθόν, αλλά και τα επικρατέστερα σύγχρονα. Τέλος , επιλέγοντας το μοντέλο της εξομοίωσης, χρησιμοποιώντας το λογισμικό EMTP-ATP, γίνεται σύγκριση των αποτελεσμάτων των βηματικών τάσεων με θεωρητικές επιτρεπτές βηματικές τάσεις και παρατίθενται τα συμπεράσματα και οι επιπτώσεις που έχουν τα αποτελέσματα στον άνθρωπο. Ακολουθεί μια σύντομη περιγραφή των κεφαλαίων Στο Κεφάλαιο 1 αναφέρεται η έννοια και ο ρόλος της γείωσης, καθώς και σε διάφορα είδη γειωτών και υπολογισμό των παραμέτρων τους. Στο Κεφάλαιο 2 δίνονται οι ορισμοί των βηματικών τάσεων και τάσεων επαφής και αναλύονται οι διάφορες επιπτώσεις του ηλεκτρικού ρεύματος στον ανθρώπινο οργανισμό. Στο Κεφάλαιο 3 παρουσιάζεται το φαινόμενο του ιονισμού του εδάφους, οι μηχανισμοί διάσπασης του και τα διάφορα μοντέλα που προτείνονται για την περιγραφή του. Στο Κεφάλαιο 4 παρατίθεται μια ανασκόπηση των διάφορων μοντέλων εξομοίωσης ενός συστήματος γείωσης. Στο Κεφάλαιο 5 γίνεται αρχικά η επιλογή του μοντέλου προσομοίωσης, παρουσιάζονται τα αποτελέσματα και συγκρινόμενα με θεωρητικές και πρακτικές τιμές στο τέλος παρουσιάζονται και τα συμπεράσματα. / The subject of the present diploma thesis is the study of step voltages in a grounding system, with the aid of a human equivalent circuit, by means of simulation using the EMTP-ATP software, considering in the calculations the phenomenon of soil ionization. In the two first chapters basic terms and concepts are defined regarding grounding systems, available grounding methods and the effects of electrical current and electrocution on the human body. In the third chapter the ionization phenomenon is analytically described and its approach through the corresponding models, which have been developed and the criteria for the calculation of the radius of the grounding conductor in accordance to the soil ionization field Eo. In chapter four there is an extended analysis of grounding systems models which have been developed, quoting those which have been used in the past but also the most dominate modern models. Finally, choosing a simulation model by utilizing EMTP-ATP software, there is a comparison of the results regarding step voltages and considering the allowable theoretical step voltage thresholds and introducing the conclusions and the effects on the human body. A brief description of the thesis chapters: Chapter 1: The concept and the role of grounding are presented, also including the different grounding systems and their parameter calculations. Chapter 2: The definitions of step voltages and contact voltages are presented while the effects of electric current on the human body are analyzed. Chapter 3: The soil ionization phenomenon is presented, including soil rupture mechanisms and the various models which are proposed to describe the phenomenon. Chapter 4: A review of the various simulation models of grounding systems is presented. Chapter 5: Initially a simulation model choice is described. The calculated results are presented and are compared with theoretical and experimental values. Finally conclusions are presented.

A model has been developed to predict the yield stress of the aluminum alloy AA6111 after multi-step heat treatments which involve combinations of ambient temperature ageing and high temperature artificial ageing. The model framework follows the internal state variable framework where the two principal state variables are i) the volume fraction of clusters which form at ambient temperature and ii) the volume fraction of metastable phases which form during high temperature ageing. The evolution of the these state variables has modeled using a set of coupled differential equations. The mechanical response (the yield stress) is then formulated in terms of the state variables through an appropriate flow stress addition law. To test the model predictions a series of experiments were conducted which examined two scenarios for multi-step heat treatments. In general, good agreement was observed between the model predictions and the experimental results. However, for the case where a short thermal excursion at 250oC was applied immediately after the solution treatment, the results were not satisfactory. This can be understood in terms of the importance of the temperature dependence for the nucleation density of metastable precipitates.

This thesis presents the design of a step-up DC-DC converter with on-chip coupled inductors. Circuit theory of DC-DC converters in general is presented, after which a mathematical model of a step up converter is developed. A circuit implementation optimized from results of the mathematical model follows. For a completely integrated step-up converter, the inductor size is reduced by increasing the frequency of operation and using a circuit topology that employs coupled inductors. Spiral inductors are also studied to achieve maximum quality factor and inductance. A fast PWM control system is used to regulate the high-frequency converter. The fabrication was done in standard TSMC 0.18-$\mu$m digital CMOS process for four circuits, including one with a conventional topology and the others with a coupled inductor topology with varying inductor geometries. Measurement results from a fabricated prototype have been presented, demonstrating the functionality of the four circuits with coupled inductors on the fabricated chip and the improvement of the coupled solution over the conventional design. It is demonstrated that the circuits with coupled inductors have a significant improvement in performance based on conversion ratio and efficiency. Finally, the design process is evaluated and recommendations are made for future work. Furthermore, a new self-oscillating and robust control system is proposed that enables simpler and more efficient regulation for high-frequency converters such as one developed for this thesis.

No description available.