Thesis (diplomarbeit)--Bonn, 1988. / Includes bibliographical references.

Thesis (Ph.D.)--York University, 2005. Graduate Programme in Mathematics and Statistics. / Typescript. Includes bibliographical references (leaves 78-83). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNR11588

First published in the Bulletin of the American Mathematical Society in Vol.79, 1973, published by the American Mathematical Society

Η θεωρία των συμμετρικών χώρων αποτελεί μια σπουδαία κλάση των ομογενών χώρων, με εφαρμογές σε πολλούς κλάδους των μαθηματικών όπως στην αλγεβρική και την διαφορική γεωμετρία. Σε αυτήν την εργασία θα δώσουμμε τον ορισμό των συμμετρικών χώρων, τα βασικά τους χαρακτηριστικά και την ταξινόμησή τους. Θα περιγράψουμε τους χώρους αυτούς κυρίως αλγεβρικά, οπότε δεν θεωρείται απαραίτητο από τον αναγνώστη να γνωρίζει εκτενώς την θεωρία της διαφορικής γεωμετρίας για να κατανοήσει πλήρως την εργασία. / The theory of symmetric spaces is an important class of homogeneous spaces, with applications in many branches of mathematics such as algebraic and differential geometry. In this work we will define the symmetric spaces, their key features and sort them. We will describe these spaces mainly algebraic, so it is not considered necessary by the reader to know in detail the theory of differential geometry to understand the work.

Η ανάγκη για ασφαλή αποθήκευση και μετάδοση πληροφορίας είναι αναπόσπαστο κομμάτι της ανθρώπινης ιστορίας. Αυτή η ανάγκη αρχικά δημιουργήθηκε λόγω των διαφορών των ανθρώπων σε επίπεδο κοινωνικό, πολιτικό, στρατιωτικό ή ακόμη και θρησκευτικών πεποιθήσεων. Σήμερα, η ραγδαία ανάπτυξη των επικοινωνιακών συστημάτων προσφέρει, σε ένα μεγάλο ποσοστό ανθρώπων, πρόσβαση σε μία τεράστια ποσότητα πληροφορίας και μία ποικιλία από ηλεκτρονικά μέσα με σκοπό την ανταλλαγή προσωπικών δεδομένων. Για αυτό το λόγο, κάθε πληροφορία που μεταδίδεται χρειάζεται να μετατραπεί σε μία μη αναγνωρίσιμη μορφή έτσι ώστε να διασφαλιστεί η ασφάλεια της. Αυτή η επεξεργασία (κρυπτογράφηση) των δεδομένων είναι αναγκαίο να συμβεί σε πραγματικό χρόνο και για αυτό το λόγο έχουν αναπτυχθεί αρκετοί αλγόριθμοι κρυπτογράφησης. Σαν παράδειγμα υλοποίησης κρυπτογραφικών αλγόριθμων παρουσιάζονται στην παρούσα εργασία οι αλγόριθμοι DES και Triple DES (TDEA). Ο DES χρησιμοποιείται στον τομέα κρυπτογράφησης δεδομένων με μία σχετικά καλή απόδοση ασφάλειας. Η υλοποίηση του συνήθως διαχωρίζεται σε προσεγγίσεις λογισμικού (software) ή υλικού (hardware). Ο TDEA αποτελεί έναν αλγόριθμο, ο οποίος προέρχεται από τον DES και παρουσιάζει μεγαλύτερη ανθεκτικότητα από αυτόν σε κρυπταναλυτικές επιθέσεις. Στην παρούσα εργασία γίνεται θεωρητική ανάλυση των δύο αλγορίθμων με βάση το πρότυπο που τους περιγράφει καθώς και χρήση παραδειγμάτων πάνω σε αυτό. Στη συνέχεια οι αλγόριθμοι υλοποιούνται σε λογισμικό με τη χρήση της γλώσσας προγραμματισμού C++, αλλά και σε υλικό χρησιμοποιώντας τη γλώσσα VHDL. Πιο συγκεκριμένα στο 1ο κεφάλαιο γίνεται μία εισαγωγή στην κρυπτογραφία, η ιστορική αναδρομή της και παρουσιάζονται βασικοί ορισμοί και αλγόριθμοι κρυπτογράφησης. Στο 2ο κεφάλαιο μελεντώνται τα συμμετρικά κρυπτοσυστήματα και οι λειτουργίες τους, γίνεται αναφορά στους συμμετρικούς αλγορίθμους που χρησιμοποιούνται σήμερα, DES, TDEA, AES, Blowfish κ.α. Επίσης αναφέρονται τα βασικά σημεία των ασύμμετρων αλγορίθμων με σκοπό την σύγκριση τους με τα συμμετρικά. Βασικό κορμό της εργασίας αποτελεί το 3ο κεφάλαιο όπου μελετώνται αναλυτικά η λειτουργία, εφαρμογές και υλοποιήσεις των συμμετρικών αλγορίθμων DES και TDEA. Στο 4ο και 5ο κεφάλαιο αναλύεται η υλοποίηση των δύο αυτών αλγορίθμων τόσο σε επίπεδο λογισμικού όσο και σε επίπεδο υλικού και παρούσιάζεται η διαδικτυακή υλοποίηση τους. Στο 6ο και τελευταίο κεφάλαιο εξάγονται συμπεράσματα και γίνονται προτάσεις για μελλοντική εργασία. / Τhe need for secure storage or transfer of information has been an inseperable part of human history. This need was initially created by the difference in social, political, military or even religious persuasions among people. Nowadays, the rapid evolution of communication systems offers, to a very large percentage of population, access to a huge amount of information and a variety of means to use, in order to exchange personal data. Therefore, every single transmitted bit of information needs to be processed into an unrecognizable form in order to be secured. This encipherment of the data is necessary to take place in real time and for this procedure, a variety of encryption algorithms have been developed. DES (Data Encryption Standard) and Triple-DES algorithms are used as an example for the implementation of cryptographic algorithms. DES can be regarded as a data encryption standard technology which is widely used in the field of data encryption with a relatively good safety performance. Implementation of DES is usually divided into software and hardware approaches. The TDEA is an algorithm which is derived from DES and has greater resistance in cryptanalysis attacks. In this Master Thesis is presented a theoretical analysis of the two algorithms based on the standard and use of examples. Furthermore, the two algorithms are implemented in software using C++, but also in hardware using VHDL. More specifically, in the 1st chapter an introduction in cryptography , its historical eventuality and basic definitions are presented. The 2nd chapter describes the general characteristics of symmetric cryptosystems and their functions. A reference in symmetric algorithms that are used nowadays, is made, such as DES, TDEA, AES, Blowfish. Moreover, some of the basics of asymmetric algorithms are mentioned, in order to permorm a comparison analysis with symmetrics. The main part of this Master Thesis is the 3rd chapter, where the detailed function and applications of DES and TDEA are explained. In the next two chapters, the implementation of the two algorithms is presented, in both software and hardware. Furthermore, their implementation is extended so as to be used in a web application. In the 6th chapter concluding remarks are made and future work is suggested.

This thesis is about personal assistants, and how they experience their work. The aim of this study is twofold: First to examine the experiences of personal assistants and their work. Second, to examine the assistant’s experiences of feelings at work and how these feelings are managed from an emotionsociological perspective. The empirical base of the research builds upon interviews with personal assistants with a focus on the individual and subjective experiences of the work. The data shows that the assistants concentrate on the emotional aspects of their job. When asked to describe their work situation, the interviewees were preoccupied with the regulation of their own feelings in the relation to the employer. The analysis has an abductive approach, in which empirical sensitivity, interpretation and theory are combined. In terms of results, this study shows that the majority of assistants experience themselves as a friend to the client and they experience the job as meaningful. However, here lies the duplicity of the situation because being a friend to the client, who is also the supervisor, can lead to problems when setting the boundaries for intimacy. The study also shows relatively stable structures in relation to the dimensions of power and subordination, where the assistants’ experience themselves as subordinates and the client as superior. At the same time that the assistants finds purpose in their job there are also challenges connected to being subordinate in a face-to-face situation. It is important to the assistants to have control over feelings and outward expressions. Feelings of subordination seem to be linked to the status and power the assistants have in society at large. Thus, how vulnerable they are in the subordinate position depends on age, gender and education. Another effect described by the assistants is a kind of emotional dissonance, where their own feelings are in conflict with how they wish to act in the social interaction with the clients. In the final chapter the concepts of asymmetric and symmetric interaction are used to understand different types of feelings the assistants’ experience. The asymmetric interaction can trigger feelings of irritation, frustration and anger which are energy draining. Symmetric interaction often seems to lead to feelings of contentment, joy and purpose, which are uplifting and energy renewing. As a concluding remark emotional labour seems to be a significant part of the assistants work. By using an emotionsociological perspective it has been possible to gain knowledge about different aspects of the personal assistants’ emotional labour.

Stream ciphers are counted as an important part of symmetric encryption method. Their basic idea comes from One-Time-Pad cipher using XOR operator on the plain text and the key to generate the cipher. The present work brings a new idea in symmetric encryption method, which inherits stream key generation idea from synchronous stream cipher and uses division instead of xoring. The Usage of division to combine the plain text with stream key gives numerous abilities to this method that the most important one is using random factors to produce the ciphers.

Abstract Internal rotation in symmetric top molecules offers an excellent opportunity to investigate large amplitude motion in a relatively simple intramolecular environment. Due to specific symmetry characteristics of a symmetric top molecular frame, the internal rotation degree of freedom is in the zeroth order approximation separable from the small amplitude vibrations and the overall rotation, thus enabling to characterize the vibrational-torsional-rotational energy structure with a relatively simple Hamiltonian. Lessons from symmetric internal rotor studies may be applied to more complex systems, such as asymmetric internal rotors and macromolecules. This thesis deals with internal rotation in CH3SiH3, CH3SiD3, CH3CF3 which have become a prototype of symmetric internal rotors. The thesis presents high resolution vibration-torsion-rotation spectra and detailed analysis of these molecules. Particular attention is focused on torsion-mediated interactions, such as Coriolis-type interactions and Fermi-type interactions, coupling the internal rotation and the small amplitude vibrational motion. The studies show that the expansion of the data to the small amplitude vibrations and inclusion of the torsion-mediated interactions play a crucial role in order to obtain an appropriate characterization of the vibrational-torsional-rotational energy level structure and physically meaningful molecular parameters.

Abstract This thesis deals with the rotation-vibration theory and high resolution infrared spectroscopy of semirigid C3 molecules. Semirigid molecules form a class of molecules which are strongly bound with one well defined structure, and without low frequency internal motions. The theory, as well as the experimental studies of semirigid molecules are of special importance in the field of rotation-vibration spectroscopy. They provide a good starting point for interpreting and analyzing the spectra of practically all types of molecules. In this work, the theory is reviewed fromthe standpoint of one particular molecule, 13CH3I, which is a prolate symmetric top with C3 symmetry. The origin and the properties of the rotation-vibration Hamiltonian are discussed in detail. Molecular symmetry plays an important role in these studies. The expansion of the Hamiltonian for nuclear motion in powers of the vibrational operators converges rapidly as numerical examples thoughout the treatment indicate. The molecule is thus a good subject for the perturbation calculations, also reviewed here in detail. 13CH3I can be considered as a model example of semirigid molecules. From the spectroscopic point of view, this thesis is a study of the six fundamental bands of 13CH3I. The rotational analysis of the vibrational ground state is first given. Special attention is paid to obtaining the axial rotational constants which are problematic for symmetric top molecules. The relatively high energy level density of 13CH3I leads to several resonances. The fundamental bands, especially the higher ones, must therefore be treated as parts of band systems. Care is paid to properly take into account the effects of the near-lying vibrational levels on the constants of the fundamentals. Certain ambiguities in the rotation-vibration Hamiltonian of 13CH3I are also discussed.

M.Sc. / In this dissertation, a symmetry analysis of a third order non-linear partial differential equation which describes the filtration of a non-Newtonian liquid in porous media is performed. A review of the derivation of the partial differential equation is given which is based on the Darcy Law. The partial differential equation contains a parameter n and a function f. We derive the Lie Point Symmetries of the partial differential equation for all cases of n and f. These symmetries are used to find the invariant solutions of the partial differential equation. We find that there is only one conservation law for the partial differential equation with f and n arbitrary and we prove that there is no potential symmetry corresponding to this conservation law for any case of n and f.