Algebraic symmetries of generic (m+1)(m+1) dimensional periodic Costas arrays

In this work we present two generators for the group of symmetries of the generic $(m+1)$ dimensional periodic Costas arrays over elementary abelian $(\mathbb{Z}_p)^m$ groups: one that is defined by multiplication on $m$ dimensions and the other by shear (addition) on $m$ dimensions. Through exhaustive search we observe that these two generators characterize the group of symmetries for the examples we were able to compute. Following the results, we conjecture that these generators characterize the group of symmetries of the generic $(m+1)$ dimensional periodic Costas arrays over elementary abelian $(\mathbb{Z}_p)^m$ groups

Multidimensional Costas Arrays and Their Periodicity

A novel higher-dimensional definition for Costas arrays is introduced. This definition works for arbitrary dimensions and avoids some limitations of previous definitions. Some non-existence results are presented for multidimensional Costas arrays preserving the Costas condition when the array is extended periodically throughout the whole space. In particular, it is shown that three-dimensional arrays with this property must have the least possible order; extending an analogous two-dimensional result by H. Taylor. Said result is conjectured to extend for Costas arrays of arbitrary dimensions

Artin's primitive root conjecture -a survey -

This is an expanded version of a write-up of a talk given in the fall of 2000 in Oberwolfach. A large part of it is intended to be understandable by non-number theorists with a mathematical background. The talk covered some of the history, results and ideas connected with Artin's celebrated primitive root conjecture dating from 1927. In the update several new results established after 2000 are also discussed.Comment: 87 pages, 512 references, to appear in Integer

Circuit Complexity and 2D Bosonisation

We consider the circuit complexity of free bosons, or equivalently free fermions, in 1+1 dimensions. Motivated by the results of [1] and [2, 3] who found different behavior in the complexity of free bosons and fermions, in any dimension, we consider the 1+1 dimensional case where, thanks to the bosonisation equivalence, we can consider the same state from both the bosonic and the fermionic perspectives. In this way the discrepancy can be attributed to a different choice of the set of gates allowed in the circuit. We study the effect in two classes of states: i) bosonic-coherent / fermionic-gaussian states; ii) states that are both bosonic- and fermionic-gaussian. We consider the complexity relative to the ground state. In the first class, the different results can be reconciled admitting a mode-dependent cost function in one of the descriptions. The differences in the second class are more important, in terms of the cutoff-dependence and the overall behavior of the complexity.Comment: Fix typos and add reference

Octonions and supergravity

This thesis makes manifest the roles of the normed division algebras R,C,H and O in various supergravity theories. Of particular importance are the octonions O, which frequently occur in connection with maximal supersymmetry, and hence also in the context of string and M-theory. Studying the symmetries of M-theory is perhaps the most straightforward route towards understanding its nature, and the division algebras provide useful tools for such study via their deep relationship with Lie groups. After reviews of supergravity and the definitions and properties of R,C,H and O, a division-algebraic formulation of pure super Yang-Mills theories is developed. In any spacetime dimension a Yang-Mills theory with Q real supercharge components is written over the division algebra with dimension Q/2. In particular then, maximal Q = 16 super Yang-Mills theories are written over the octonions, since O is eight-dimensional. In such maximally supersymmetric theories, the failure of the supersymmetry algebra to close off-shell (using the conventional auxiliary field formalism) is shown to correspond to the non-associativity of the octonions. Making contact with the idea of ‘gravity as the square of gauge theory’, these division-algebraic Yang-Mills multiplets are then tensored together in each spacetime dimension to produce a pyramid of supergravity theories, with the Type II theories at the apex in ten dimensions. The supergravities at the base of the pyramid have global symmetry groups that fill out the famous Freudenthal-Rosenfeld-Tits magic square. This magic square algebra is generalised to a ‘magic pyramid algebra’, which describes the global symmetries of each Yang-Mills-squared theory in the pyramid. Finally, a formulation of eleven-dimensional supergravity over the octonions is presented. Toroidally compactifying this version of the theory to four or three spacetime dimensions leads to an interpretation of the dilaton vectors (which organise the coupling of the seven or eight dilatons to the other bosonic fields) as the octavian integers – the octonionic analogue of the integers.Open Acces

Proceedings of JAC 2010. Journées Automates Cellulaires

The second Symposium on Cellular Automata “Journ´ees Automates Cellulaires” (JAC 2010) took place in Turku, Finland, on December 15-17, 2010. The first two conference days were held in the Educarium building of the University of Turku, while the talks of the third day were given onboard passenger ferry boats in the beautiful Turku archipelago, along the route Turku–Mariehamn–Turku. The conference was organized by FUNDIM, the Fundamentals of Computing and Discrete Mathematics research center at the mathematics department of the University of Turku. The program of the conference included 17 submitted papers that were selected by the international program committee, based on three peer reviews of each paper. These papers form the core of these proceedings. I want to thank the members of the program committee and the external referees for the excellent work that have done in choosing the papers to be presented in the conference. In addition to the submitted papers, the program of JAC 2010 included four distinguished invited speakers: Michel Coornaert (Universit´e de Strasbourg, France), Bruno Durand (Universit´e de Provence, Marseille, France), Dora Giammarresi (Universit` a di Roma Tor Vergata, Italy) and Martin Kutrib (Universit¨at Gie_en, Germany). I sincerely thank the invited speakers for accepting our invitation to come and give a plenary talk in the conference. The invited talk by Bruno Durand was eventually given by his co-author Alexander Shen, and I thank him for accepting to make the presentation with a short notice. Abstracts or extended abstracts of the invited presentations appear in the first part of this volume. The program also included several informal presentations describing very recent developments and ongoing research projects. I wish to thank all the speakers for their contribution to the success of the symposium. I also would like to thank the sponsors and our collaborators: the Finnish Academy of Science and Letters, the French National Research Agency project EMC (ANR-09-BLAN-0164), Turku Centre for Computer Science, the University of Turku, and Centro Hotel. Finally, I sincerely thank the members of the local organizing committee for making the conference possible. These proceedings are published both in an electronic format and in print. The electronic proceedings are available on the electronic repository HAL, managed by several French research agencies. The printed version is published in the general publications series of TUCS, Turku Centre for Computer Science. We thank both HAL and TUCS for accepting to publish the proceedings.Siirretty Doriast

Characterisation of optical metamaterials: effective parameters and beyond

Die vorliegende Arbeit beschäftigt sich mit der Charakterisierung von Metamaterialien. Für eine umfassendere Einführung in die Thematik sei auf Kapitel 1 verwiesen. Als künstliche Medien mit Perioden kleiner als die relevante Wellenlänge werden diese zumeist als effektiv homogene Materialien beschrieben. Diese Art der Beschreibung und deren kritische Untersuchung und Bewertung stehen im Mittelpunkt der Kapitel 2-4. Im Kapitel 2 werden die Grundlagen für die Beschreibung künstlicher Strukturen mittels homogener Maxwell Gleichungen und insbesondere der entsprechenden Materialgleichungen gelegt. In diesem Kapitel wird vor allem die Beschreibung künstlich magnetischer Materialien auf der Basis einer komplexen, räumlichen dispersiven Materialantwort abgeleitet. Die erzielten Materialgleichungen für Medien mit schwacher räumlicher Dispersion werden dann in Kapitel 3 zur Bestimmung der effektiven Eigenschaften zugrunde gelegt. Die Bestimmung erfolgt durch den sogenannten S-parameter retrieval, d.h. der Inversion der Fresnelgleichung für Reflexion und Transmission an einer optischen Schicht. Diese Methode wird ausführlich auch vom Standpunkt allgemein periodischer Medien her betrachtet, wodurch sich grundsätzliche Zusammenhänge und insbesondere Limitierungen ableiten lassen. In Kapitel 4 werden die zuvor bereitgestellten Methoden der Charakterisierung auf Metamaterialien mit zunehmender Symmetrie angewandt. Es wird gezeigt, dass eine Reduktion der optischen Antwort auf einzelne effektive Materialparameter selten möglich ist. In Konsequenz der vorherigen Resultate und mit Hinblick auf ein Design optischer Funktionalität anstatt des Designs etwaiger Materialien wird in Kapitel 5 eine Beschreibung der optischen Antwort auf Basis von Jones-Matrizen vorgeschlagen. Es wird ein Zusammenhang zwischen Symmetrie und allgemeiner Form der Jones-Matrix hergeleitet. Dieser Ansatz erlaubt sowohl die Beschreibung als auch das Design der polarisationsabhängigen Response von Metamaterialien

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method