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1
Aït, Oukaci Kosseila. "Domaines magnétiques périodiques pour la propagation guidée d’ondes de spin." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0100.
Анотація:
L'International Technology Roadmap for Semiconductors a identifié les dispositifs à base d'ondes de spin comme une alternative à la technologie CMOS pour les dispositifs logiques. Cependant, les dispositifs standards souffrent de plusieurs inconvénients liés à la miniaturisation et n'offrent pas la possibilité d'aborder le domaine des dispositifs logiques entièrement reprogrammables. L'objectif de ma thèse est d'établir une nouvelle voie vers des dispositifs logiques évolutifs et reprogrammables. Cette voie repose sur la stabilisation de domaines magnétiques périodiques rectilignes dont l’orientation peut être configurée à souhait pour ouvrir ou fermer le canal de transmission de l’information. Ce canal sera formé dans un matériau à faible amortissement pour une propagation des ondes de spin sur des distances microniques. D’une part, des domaines magnétiques de type Weak Stripes ont été obtenus dans l’alliage Co₄₀Fe₄₀B₂₀. Nous avons montré que ces domaines sont facilement orientables, ce qui permettra de facilement ouvrir ou fermer le canal de transmission des ondes de spin. Un amortissement inférieur à 7.10⁻³ peut être obtenu. La microscopie magnétique nous a permis de déterminer l’angle de l’aimantation dans les bandes, sa distribution spatiale ainsi que sa variation sous champ magnétique. De plus, nous avons montré pour la première fois la configuration de surface de ces Weak Stripes, configuration en accord avec les simulations micromagnétiques. D’autre part, des domaines magnétiques de type Strong Stripes sont obtenus dans les multicouches [Co/Ni]n. Leurs propriétés sont proches de celles observées dans d’autres matériaux comme le Co épitaxié. Un coefficient d’amortissement inférieur à 8.8 ×10⁻³ est obtenu, parmi les plus petits pour des systèmes à aimantation perpendiculaire. Leurs propriétés magnétiques microscopiques montrent que l’orientation des bandes est plus difficile à obtenir à cause d’une transformation bandes/bulles non encore répertoriée dans la littératureThe International Technology Roadmap for Semiconductors has identified spin wave devices as an alternative to CMOS technology for logic devices. The interest of these emerging devices lies in the scalability needed to process the ever-increasing amount of data generated by our information and communication society while maintaining low power consumption. However, standard devices suffer from drawbacks related to miniaturization and do not offer the possibility to enter the field of fully reprogrammable logic devices. The objective of my thesis is to establish a new path towards scalable and reprogrammable logic devices. This path is based on the stabilization of rectilinear periodic magnetic domains whose orientation can be configured to open or close the transmission channel. This channel will be formed in a low-damping material for spin wave propagation over micron distances. On one hand, magnetic domains of the Weak Stripes type have been obtained in the Co₄₀Fe₄₀B₂₀ alloy. We have shown that these domains are easily orientable, which will allow to easily open or close the transmission channel of spin waves. We show that a damping lower than 7×10⁻³ can be obtained. Magnetic microscopy allowed us to determine the angle of magnetization in the stripes, its spatial distribution as well as its variation under magnetic field. In addition, we show for the first time the surface configuration of these Weak Stripes, a configuration in accordance with the micromagnetic simulations. On the other hand, Strong Stripes magnetic domains are obtained in the [Co/Ni]n multilayers. Their properties are close to those observed in other materials such as Co epitaxial films. A damping coefficient lower than 8.8 ×10⁻³ is obtained, among the smallest for perpendicular magnetization systems. The study of their microscopic magnetic properties shows that the orientation of straight domains is more difficult to obtain because of a stripe/bubble transformation which has not yet been documented in the literature
2
Khatun, Zohora. "On string and W-strings." Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297181.
3
Stiffler, Kory M. "A walk through superstring theory with an application to Yang-Mills theory: k-strings and D-branes as gauge/gravity dual objects." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/744.
Анотація:
Superstring theory is one current, promising attempt at unifying gravity with the other three known forces: the electromagnetic force, and the weak and strong nuclear forces. Though this is still a work in progress, much effort has been put forth toward this goal. A set of specific tools which are used are gauge/gravity dualities. This thesis consists of a specific implementation of gauge/gravity dualities to describe k-strings of strongly coupled gauge theories as objects dual to Dpbranes embedded in confining supergravity backgrounds from low energy superstring field theory.
Along with superstring theory, k-strings are also commonly investigated with lattice gauge theory and Hamiltonian methods. A k$string is a colorless combination of quark-anti-quark source pairs, between which a color flux tube develops. The two most notable terms of the k-string energy are, for large quark anti-quark separation L, the tension term, proportional to L, and the Coulombic 1/L correction, known as the Luscher term.
This thesis provides an overview of superstring theories and how gauge/gravity dualities emerge from them. It shows in detail how these dualities can be used for the specific problem of calculating the k-string energy in 2+1 and 3+1 space-time dimensions as the energy of Dp-branes in the dual gravitational theory. A detailed review of k-string tension calculations is given where good agreement is found with lattice gauge theory and Hamiltonian methods. In reviewing the k-string tension, we also touch on how different representations of k-strings can be described with Dp-branes through gauge/gravity dualities. The main result of this thesis is how the Luscher term is found to emerge from the energy calculation of Dp-branes. In 2+1 space-time dimensions, we have Luscher term data to compare with from lattice gauge theory, where we find good agreement.
4
Forini, Valentina. "Non trivial string backgrounds: Tachyons in String Field Theory and Plane-waves in DLCQ Strings." Doctoral thesis, Università degli studi di Trento, 2006. https://hdl.handle.net/11572/368486.
Анотація:
One of the most interesting problems in string theory is to understand how the background space-time on which the string propagates arises in a self-consistent way. For open strings, there are two main approaches to this problem, boundary string field theory (BSFT) and cubic string field theory (CSFT). In the first part of this Thesis we deal with the construction of the spacetime tachyon effective action in BSFT. Renormalization fixed points are solutions of classical equations of motion and should be viewed as solutions of classical string field theory. We have constructed the Witten-Shatashvili (WS) space-time action S and shown that some solitonic solutions are lower dimensional D-branes for which the finite value of S provides a quite accurate prediction of the D-brane tension. We have derived the explicit relation between the CSFT and WS action as a field redefinition which is nonsingular on-shell only when the normalization factor in the WS action coincides with the tension of the D25-brane, in agreement with the conjectures involving tachyon condensation. We have also found a time-dependent solution of CSFT whose evolution is driven by a diffusion equation that makes the equations of motion local with respect to the time variable. The analysis here proposed has attracted a good deal of attention for its potential cosmological applications. The profile can be expressed in terms of a series in powers of exponentials of the time coordinate, and gives evidence of a well-defined but wildly oscillatory behavior. The tachyon rolls well past the minimum of the potential, then turns around and begins to oscillate with ever increasing amplitude. Furthermore, we have derived an analytic series solution of the elliptic equations providing the 4-tachyon off-shell amplitude. From such a solution we computed the exact coefficient of the quartic effective action relevant for time-dependent solutions and we derived the exact coefficient of the quartic tachyon coupling. We studied the rolling tachyon solution expressed as a series of exponentials of the time coordinate both using level-truncation computations and the exact 4-tachyon amplitude. The results for the level-truncated coefficients converge to those derived using the exact string amplitude and confirm the wild oscillatory behavior.
In the second part of the Thesis we consider the extension of the gauge/gravity correspondence to systems with reduced and hence more realistic supersymmetry, which is one of the main steps towards a non-perturbative description of confining, QCD-like, gauge theories in terms of gravitational backgrounds. If string theory on AdS5xS5 is integrable, the theory on simple orbifolds of that space would also be expected to be integrable. We have computed the planar finite size corrections to the spectrum of the dilatation operator acting on states of a certain limit of conformal N = 2 quiver gauge field theory which is a ZM-orbifold of N = 4 SYM theory. We matched the result to the string dual, IIB superstrings on a pp-wave background with a periodically identified null coordinate. Up to two loops, we have shown that the computations done by using an effective Hamiltonian technique and a twisted Bethe Ansatz agree with each other and also agree with a computation of the analogous quantity in string theory. Our results are consistent with integrability of the N = 2 theory.
5
Forini, Valentina. "Non trivial string backgrounds: Tachyons in String Field Theory and Plane-waves in DLCQ Strings." Doctoral thesis, University of Trento, 2006. http://eprints-phd.biblio.unitn.it/1059/1/ForiniDocTh.pdf.
Анотація:
One of the most interesting problems in string theory is to understand how the background space-time on which the string propagates arises in a self-consistent way. For open strings, there are two main approaches to this problem, boundary string field theory (BSFT) and cubic string field theory (CSFT). In the first part of this Thesis we deal with the construction of the spacetime tachyon effective action in BSFT. Renormalization fixed points are solutions of classical equations of motion and should be viewed as solutions of classical string field theory. We have constructed the Witten-Shatashvili (WS) space-time action S and shown that some solitonic solutions are lower dimensional D-branes for which the finite value of S provides a quite accurate prediction of the D-brane tension. We have derived the explicit relation between the CSFT and WS action as a field redefinition which is nonsingular on-shell only when the normalization factor in the WS action coincides with the tension of the D25-brane, in agreement with the conjectures involving tachyon condensation. We have also found a time-dependent solution of CSFT whose evolution is driven by a diffusion equation that makes the equations of motion local with respect to the time variable. The analysis here proposed has attracted a good deal of attention for its potential cosmological applications. The profile can be expressed in terms of a series in powers of exponentials of the time coordinate, and gives evidence of a well-defined but wildly oscillatory behavior. The tachyon rolls well past the minimum of the potential, then turns around and begins to oscillate with ever increasing amplitude. Furthermore, we have derived an analytic series solution of the elliptic equations providing the 4-tachyon off-shell amplitude. From such a solution we computed the exact coefficient of the quartic effective action relevant for time-dependent solutions and we derived the exact coefficient of the quartic tachyon coupling. We studied the rolling tachyon solution expressed as a series of exponentials of the time coordinate both using level-truncation computations and the exact 4-tachyon amplitude. The results for the level-truncated coefficients converge to those derived using the exact string amplitude and confirm the wild oscillatory behavior.
In the second part of the Thesis we consider the extension of the gauge/gravity correspondence to systems with reduced and hence more realistic supersymmetry, which is one of the main steps towards a non-perturbative description of confining, QCD-like, gauge theories in terms of gravitational backgrounds. If string theory on AdS5xS5 is integrable, the theory on simple orbifolds of that space would also be expected to be integrable. We have computed the planar finite size corrections to the spectrum of the dilatation operator acting on states of a certain limit of conformal N = 2 quiver gauge field theory which is a ZM-orbifold of N = 4 SYM theory. We matched the result to the string dual, IIB superstrings on a pp-wave background with a periodically identified null coordinate. Up to two loops, we have shown that the computations done by using an effective Hamiltonian technique and a twisted Bethe Ansatz agree with each other and also agree with a computation of the analogous quantity in string theory. Our results are consistent with integrability of the N = 2 theory.
6
Sandoval, Leonidas. "String scattering amplitudes." Thesis, King's College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261874.
7
Wulff, Linus. "Strings, boundary fermions and coincident D-branes." Doctoral thesis, Stockholm : Department of Physics, Stockholm University, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-6576.
8
Morris, Willie J. "Strings /." View online, 2010. http://repository.eiu.edu/theses/docs/32211131524721.pdf.
9
Grieser, Diane R. "string specialists' and non-string specialists' content knowledge and pedagogical knowledge of string-specific techniques in the intermediate strings class." Thesis, Boston University, 2014. https://hdl.handle.net/2144/11004.
Анотація:
Thesis (D.M.A.)--Boston UniversityThis study examines the pedagogical content knowledge of music teachers who teach in or out of their field of expertise. The primary goal of this study was to observe string specialists' and non-string specialists' content knowledge, pedagogical knowledge, and the instructional strategies used to teach vibrato, shifting, and spiccato bowing technique in an intermediate string class. The study provided an in-depth understanding of string specialists' and non-string specialists' (a) content knowledge of vibrato, shifting, and spiccato bowing; (b) content and pedagogical knowledge to teach vibrato, shifting, and spiccato bowing technique; and (c) how pedagogical content knowledge is used to teach vibrato, shifting, and spiccato bowing technique. A multiple case study design was used to examine how pedagogical content knowledge was used by string specialists and non-string specialists to teach string-specific technique. A purposeful sample of 6 cases was selected for the study. String specialists and non-string specialists were purposefully chosen to understand how pedagogical knowledge is used to teach string-specific technique. In order to perform a cross-case analysis, similar cases (e.g., location, level, program size) were chosen. Data were collected through observations of rehearsals and interviews with string specialists and non-string specialists. Each participant was observed teaching three rehearsals, and three interviews were conducted with each participant. Through the coding process, emergent themes were explored to provide detailed insight into the pedagogical and content knowledge of string specialists and non-string specialists. Interview transcripts were coded using WEFT QDA 1.01 software (Fenton, 2006). The findings suggest that non-string specialists in this study have a limited understanding of the fundamental general principles for vibrato, shifting, and spiccato bowing technique. The non-string specialists' content knowledge of vibrato, shifting, and spiccato bowing had more misconceptions, more misunderstandings, and a less organized understanding of the content when compared to string specialists. Additionally, non-string specialists with limited content knowledge chose less challenging instructional strategies than string specialists. This research will help to inform the string profession regarding the importance of string-specific content knowledge and pedagogical strategies, and assist non-string specialists who teach string classes in better understanding the knowledge and approaches they might presently be lacking.
10
Harnish, Robert George. "The statistical properties of random surfaces." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257940.
11
Mitchell, D. G. "Strings in cosmology." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47184.
12
Vicedo, Benoît. "Finite-g strings." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612467.
13
Wentworth, Hillary B. "Something like strings." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-1/rp/wentworthh/hillarywentworth.pdf.
14
Görlich, Lars. "N = 1 and non-supersymmetric open string theories in six and four space-time dimensions." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2003. http://dx.doi.org/10.18452/14978.
Анотація:
Die vorliegende Arbeit beinhaltet ein einführendes Kapitel über Orbifold-Konstruktionen in dem neben rudimentären Grundlagen bereits speziellere Themen wie Diskrete Torsion und asymmetrische Orbifold-Gruppen behandelt werden. Als Beispiele für Orbifolde werden Kompaktifizierungen auf Tori sowie das asymmetrische T^4/Z(3)^L x Z(3)^R Orbifold behandelt. Danach wird eine allgemein gehaltene Einführung in Orientifolde gegeben, einschließlich des offenen String Sektors samt Chan-Paton Freiheitsgraden. Die darauf folgenden Kapitel 4-7 behandeln von mir durchgeführte Forschungsarbeiten. Kapitel 4 beschäftigt sich mit der Quantisierung des offenen Strings mit linearen Randbedingungen, wie sie bei Strings in elektro-magnetischen Feldern auftreten. Weiterhin wird die Quantisierung der Null- und Impuls-Moden des offenen Strings in Torus-Kompaktifizierungen durchgeführt. Außerdem wird für den Fall allgemeiner konstanter Hintergrund Neveu-Schwarz U(1)-Hintergrundfelder der Kommutator der Stringkoordinaten berechnet. Dieser stützt bisherige Resultate zur Nicht-Kommutativität von offenen Stringtheorien in Neveu-Schwarz Hintergründen. Kapitel 5 gibt, zusammen mit einigen neuen Erkenntnissen, Resultate von [1] über asymmetrische Orientifolde, insbesondere deren D-Branen Inhalt wieder. Kapitel 6 faßt die Veröffentlichung [2] zusammen, in der untersucht wurde, inwieweit sich phänomenolgisch interessante Modelle in Orientifolden von Torus-Kompaktifizierungen finden lassen. Insbesondere tragen die D9-Branen magnetische Flüsse, womit chirale Fermionen im Spektrum auftreten. Die Rechnungen werden größtenteils im gleichwertigen, T-dualen Bild ausgeführt. In diesem ist die Anzahl der chiralen Fermionen durch die topologische Schnittzahl der D-Branen gegeben. Existieren auf Torus-Kompaktifizierungen entweder nur nicht-chirale oder nicht-supersymmetrische Modelle, so lassen sich auf gewissen Orbifolden beide Eigenschaften miteinander vereinbaren. Kapitel 7 behandelt das "sigma Omega"-Orientifold auf einem T^6/Z(4) Orbifold. Als besonders interessantes Beispiel wird ein supersymmetrisches U(4) x U(2)^3_L x U(2)^3_R Modell vorgestellt, daß durch Einschalten geeigneter Hintergrundfelder in der effektiven Niederenergie-Wirkung auf ein Modell gebrochen wird, daß dem MSSM (minimalem supersymmetrischen Standard Modell) sehr ähnlich ist. Dieses Kapitel basiert auf unserer Publikation [3]. Ferner ist der Arbeit ein Anhang beigefügt, der einige der verwendeten Formeln sowie Beweise zu zwei Sätzen enthält, die im Text verwendet wurden.This thesis contains an introductory chapter on orbifolds. Besides rudimentary basics we discuss more advanced topics like discrete torsion and asymmetric orbifold groups. As examples we investigate torus compactifications and an asymmetric T^4/Z(3)^L x Z(3)^R orbifold. The following chapter explains the foundations of orientifolds, including open strings with Chan-Paton degrees of freedom. Chapters 4-7 present own research. In chapter 4 we quantize open strings with linear boundary conditions, as they show up in electro-magnetic fields. We quantize the zero- and momentum-modes for toroidal compactifications, too. As an application we calculate the commutator of the coordinate fields in the case of general constant Neveu-Schwarz U(1)-field strengths. Thereby we confirm previous results on non-commutativity of open string theories in Neveu-Schwarz backgrounds. Chapter 5 reviews the results of a former publication [1] on asymmetric orientifolds, supplemented by some recent insights in connection with the preceeding chapter. Chapter 6 is a summary of [2]. In this publication we investigated to what extend one can build phenomenologically interesting models from toroidal orientifolds. By turning on magnetic fluxes on D9-branes we induce chiral fermions. Most calculations are performed in an (equivalent) T-dual picture. Here the number of chiral fermions is given by the topological intersection number of D-branes. In orientifolds of toroidal compactifications one obtains either non-chiral or non-supersymmetric orientifold solutions. However both properties can be reconciled in orientifolds that are obtained from specific supersymmetric orbifold compactifications. In chapter 7 we present the "sigma Omega"-Orientifold on a T^6/Z(4) orbifold. As a very attractive example we investigate a supersymmetric U(4) x U(2)^3_L x U(2)^3_R model that is broken to an MSSM-like model by switching on suitable background fields in the low energy effective action. This chapter is based on our publication [3]. The thesis is supplemented by an appendix with formulas applied in the text, as well as proofs to two theorems that were used as well.
15
Vanchurin, Vitaly. "Evolution of cosmic strings /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2005.
Анотація:
Thesis (Ph.D.)--Tufts University, 2005.Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics and Astronomy. Includes bibliographical references (leaf 99). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
16
Earnshaw, Michael Andrew. "Cosmic strings and baryogenesis." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321324.
17
James, Margaret Elizabeth Rose. "Electroweak strings and sphalerons." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320060.
18
Hindmarsh, Mark Bernard. "Cosmic strings and beads." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38034.
19
Riveros, Jaeger Cristian. "Repairing strings and trees." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:012d384f-d1d0-471b-ae6e-bbf337892680.
Анотація:
What do you do if a computational object fails a specification? An obvious approach is to repair it, namely, to modify the object minimally to get something that satisfies the constraints. In this thesis we study foundational problems of repairing regular specifications over strings and trees. Given two regular specifications R and T we aim to understand how difficult it is to transform an object satisfying R into an object satisfying T. The setting is motivated by considering R to be a restriction -- a constraint that the input object is guaranteed to satisfy -- while T is a target -- a constraint that we want to enforce. We first study which pairs of restriction and target specifications can be repaired with a ``small'' numbers of changes. We formalize this as the bounded repair problem -- to determine whether one can repair each object satisfying R into T with a uniform number of edits. We provide effective characterizations of the bounded repair problem for regular specifications over strings and trees. These characterizations are based on a good understanding of the cyclic behaviour of finite automata. By exploiting these characterizations, we give optimal algorithms to decide whether two specifications are bounded repairable or not. We also consider the impact of limitations on the editing process -- what happens when we require the repair to be done sequentially over serialized objects. We study the bounded repair problem over strings and trees restricted to this streaming setting and show that this variant can be characterized in terms of finite games. Furthermore, we use this characterization to decide whether one can repair a pair of specifications in a streaming fashion with bounded cost and how to obtain a streaming repair strategy in this case. The previous notion asks for a uniform bound on the number of edits, but having this property is a strong requirement. To overcome this limitation, we study how to calculate the maximum number of edits per character needed to repair any object in R into T. We formalize this as the asymptotic cost -- the limit of the number of edits divided by the length of the input in the worst case. Our contribution is an algorithm to compute the asymptotic cost for any pair of regular specifications over strings. We also consider the streaming variant of this cost and we show how to compute it by reducing this problem to mean-payoff games.
20
Clifford, Raphael. "Indexed strings for large scale genomic analysis." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268368.
21
Hollowood, Timothy James. "Twisted strings, vertex operators and algebras." Thesis, Durham University, 1988. http://etheses.dur.ac.uk/6424/.
Анотація:
This work is principally concerned with the operator approach to the orbifold compactification of the bosonic string. Of particular importance to operator formalism is the con formal structure and the operator product expansion. These are introduced and discussed in detail. The Frenkel-Kac-Segal mechanism is then examined and is shown to be a consequence of the duality of dimension one operators of an analytic bosonic string compactified on a certain torus. Possible generalizations to higher dimension operators are discussed, this includes the cross-bracket algebra which plays a central role in the vertex operator representation of Griess's algebra, and hence the Fischer-Griess Monster Group. The mechanism of compactification is then extended to orbifolds. The exposition includes a detailed account of the twisted sectors, especially of the zero-modes and the twisted operator cocycles. The conformal structure, vertex operators and correlation functions for twisted strings are then introduced. This leads to a discussion of the vertex operators which represent the emission of untwisted states. It is shown how these operators generate Kac-Moody algebras in the twisted sectors. The vertex operators which insert twisted states are then constructed, and their role as intertwining operators is explained. Of particular importance in this discussion is the role of the operator cocycles, which are seen to be crucial for the correct working of the twisted string emission vertices. The previously established formalism is then applied in detail to the reflection twist. This includes an explicit representation of the twisted operator cocycles by elements of an appropriate Clifford algebra and the elucidation of the operator algebra of the twisted emission vertices, for the ground and first excited states in the twisted sector. This motivates the 'enhancement mechanism', a generalization of the Frenkel-Kac-Segal mechanism, involving twisted string emission vertices, in dimensions 8, 16 and 24. associated with rank 8 Lie algebras, rank 16 Lie algebras and the cross-bracket algebra for the Leech lattice, respectively. Some of the relevant characters of the 'enhanced" modules are determined, and the connection of the cross-bracket algebra to the phenomenon of 'Monstrous Moonshine' and the Monster Group is explained. Algebra enhancement is then discussed from the greatly simplified shifted picture and extensions to higher order twists are considered. Finally, a comparison of this work with other recent research is given. In particular, the connection with the path integral formalism and the extension to general asymmetric orbifolds is discussed. The possibility of reformulating the moonshine module in a 'covaxiant' twenty-six dimensional setting is also considered.
22
Pankiewicz, Ari. "Strings in plane wave backgrounds." Doctoral thesis, [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968799981.
23
Jünemann, Klaus. "Symmetrien des N=2 Strings." [S.l. : s.n.], 1999. http://deposit.ddb.de/cgi-bin/dokserv?idn=956853765.
24
Hecht, Michael. "Effective actions and topological strings." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-135759.
25
Orloff, Jean. "Hot fundamental strings and cosmology." Doctoral thesis, Universite Libre de Bruxelles, 1991. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/213025.
26
Siemens, Xavier. "Gravitational waves and cosmic strings /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2002.
Анотація:
Thesis (Ph.D.)--Tufts University, 2002.Adviser: Alexander Vilenkin. Submitted to the Dept. of Physics. Includes bibliographical references (leaves 95-98). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
27
Ilyenko, Kostyantyn. "Twistor description of null strings." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301181.
28
Skliros, Dimitri P. "Vertex operators for cosmic strings." Thesis, University of Sussex, 2011. http://sro.sussex.ac.uk/id/eprint/48134/.
Анотація:
Superstring theory posits that as complicated as nature may seem to the naive observer, the variety of observed phenomena may be explained by postulating that at the fundamental scale, matter is composed of lines of energy, namely strings. These oscillating lines would be elementary and would hence have no substructure. They are expected to be incredibly tiny, their line-like structure would become noticeable at scales close to the string scale (which may lie anywhere from the TeV scale all the way up to the Planck scale) and would appear to be point-like to the macroscopic observer. Internal consistency then also requires the presence of higher dimensional objects, namely D-branes, all of which conspire and combine in such a way so as to give rise to the observable Universe. Advances in cosmology suggest the early universe was much hotter and denser than is the Universe at present, that the Universe has expanded and continues to expand (exponentially in fact) at present. This in turn has led a number of theorists to point out the remarkable possibility that some of these strings or D-branes were also stretched with the expansion. The resulting macroscopic strings, the so-called cosmic strings, would potentially stretch across the entire Universe. Cosmic strings make their presence manifest by oscillating, scattering off other structures, by decaying, producing gravitational waves and so on, and this in turn hints at the available handles that may be used to observe them. Before we can hope to observe cosmic strings however, the first step is then clearly to understand these properties which determine their evolution. A number of approximate (classical) descriptions of cosmic strings have been constructed to date, but approximations break down, especially when potentially interesting things happen (e.g. close to cusps, i.e. points on the string that reach the speed of light) and can obscure the physics. Thankfully, one can go beyond these approximations: all properties of cosmic strings can be concisely and accurately contained or encoded in a single object, the so-called fundamental cosmic string vertex operator. In the present thesis I construct precisely this, covariant vertex operators for general cosmic strings and this is the first such construction. Cosmic strings, being macroscopic, are likely to exhibit classical behaviour in which case they would most accurately be described by a string theory analogue of the well known harmonic oscillator coherent states. By minimally extending the standard definition of coherent states, so as to include the string theory requirements, I go on to construct both open and closed covariant coherent state vertex operators. The naive construction of the latter requires the existence of a lightlike compactification of spacetime. When the lightlike winding states in the underlying Hilbert space are projected out, the resulting vertex operators have a classical interpretation and can consistently propagate in noncompact spacetime. Using the DDF map I identify explicitly the corresponding general lightcone gauge classical solutions around which the exact macroscopic quantum states are fluctuating. We go on to show that both the covariant gauge coherent vertex operators, the corresponding lightcone gauge coherent states and the classical solutions all share the same mass and angular momenta, which leads us to conjecture that the covariant and lightcone gauge states are different manifestations of the same state and share identical interactions. Apart from the coherent state vertices I also present a complete set of covariant mass eigenstate vertex operators and these may also be relevant in cosmic string evolution. Finally, I also present the first amplitude computation with the coherent states, the graviton emission amplitude (including the effects of gravitational backreaction) for a simple class of cosmic string loops. As a byproduct of the above, I find that the fundamental building blocks of arbitrarily massive covariant string states are given by elementary Schur polynomials (equivalently complete Bell polynomials). This construction enables one to address the aforementioned questions concerning the properties of cosmic strings, their cosmological signatures, and may lead to the first observations of such objects in the sky. This in turn would be a remarkable way of verifying Superstring theory as the framework underlying the structure of our Universe.
29
HANSSON, PER. "Braided Body, Strings That Move." Thesis, Högskolan i Borås, Institutionen Textilhögskolan, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-18104.
Анотація:
The perception of the expression of traditional handcrafts needs to be challenged. Therefore his bachelor degree work aims to develop new expressions in contemporary men`s wear through experimentations with tubular braiding. This works aims to utilize and express a progressive approach of the technique in terms of materials and method with the desire to create a contemporary expression when a handcraft method is utilized in fashion Starting to explore the handcraft technique braiding the tubular braiding technique was found. While the technique itself is similar in expression and properties to flat braiding the tubular braiding opens up for other possibilities for garment construction. Using the tubular braid as a starting point, the aim is to explore new ways of constructing contemporary menswear garments with the technique itself as well to construct new materials and find to a new expressions. The work also deals with the gap between the technique flat braiding, tubular braiding, construction and materials with different properties altering the initial expression of the technique. By experimenting with unconventional materials and scale for such an handcraft technique as braiding the expression and the traditional view of braiding and its construction and use will be altered and questioned - discovering that the tubular braid has possibilities to construct or sculpt garments on the body in a seamless manner. Hopefully machine-engineers of the future can invent new and progressive braiding processes to create fabrics for commercial application in fashion and also understand the potential of the tubular braiding method formed by the examples here.Program: Modedesignutbildningen
30
Wu, Jiun-Huei Proty. "Cosmological perturbations from cosmic strings." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624542.
31
Kapitaniak, Marcin. "Nonlinear dynamics of drill-strings." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=227960.
Анотація:
This thesis has been motivated by the need to construct reliable, experimentally callibrated models of the drill-string assembly, that capture important phenomena associated with the drilling process, such as torsional oscillations, stick-slip and whirling. This can be achieved using a continuous finite element model, as well as low-dimensional torsional pendulum models in limited cases. The importance of this work lies in the fact, that the experimental rig utilizes real industrial drillbits and rock samples, which after careful identification of TOB speed curves, allows to use an equivalent friction model to accommodate for both frictional and cutting components of the bit-rock interactions. As a first step, a preliminary calibration of the FE model for a straight configuration of the drill-string is carried out, that allows to utilize the low-dimensional model to replicate behaviour of the system. In both of these cases, the agreement between experiments and modelling is achieved. Based on these preliminary studies, it is possible to verify the model in a prebuckled drill-string configuration, for which case a qualitative as well as quantitative agreement with the experiment is obtained. This allows to identify regions where the most dangerous phenomenon of stick-slip is present in parameter space of WOB and top angular speed. Next, the analysis is focused on the whirling phenomenon and calibration of the reduced order rotor model to replicate the motion of the BHA in the bore-hole. A qualitative agreement with the experiments is obtained. An interesting phenomenon of co-existing forward and backward periodic whirling solutions are observed both experimentally and numerically. The influence of the initial conditions and the friction between the BHA and the borehole are investigated, what revealed that there is a threshold value of friction coefficient for which the whirling direction changes from forward to backward.
32
Setterqvist, Eric. "Taut Strings and Real Interpolation." Doctoral thesis, Linköpings universitet, Matematik och tillämpad matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-132421.
Анотація:
The taut string problem concerns finding the function with the shortest graph length, i.e. the taut string, in a certain set of continuous piecewise linear functions. It has appeared in a broad range of applications including statistics, image processing and economics. As it turns out, the taut string has besides minimal graph length also minimal energy and minimal total variation among the functions in Ω. The theory of real interpolation is based on Peetre’s K-functional. In terms of the K-functional, we introduce invariant K-minimal sets and show a close connection between taut strings and invariant K-minimal sets. This insight leads to new problems of interpolation theory, gives possibility to generalize the notion of taut strings and provides new applications. The thesis consists of four papers. In paper I, connections between invariant K-minimal sets and various forms of taut strings are investigated. It is shown that the set Ω′ of the derivatives of the functions in can be interpreted as an invariant K-minimal set for the Banach couple (ℓ1, ℓ∞) on Rn. In particular, the derivative of the taut string has minimal K-functional in Ω′. A characterization of all bounded, closed and convex sets in Rn that are invariant K-minimal for (ℓ1, ℓ∞) is established. Paper II presents examples of invariant K-minimal sets in Rn for (ℓ1, ℓ∞). A convergent algorithm for computing the element with minimal K-functional in such sets is given. In the infinite-dimensional setting, a sufficient condition for a set to be invariant K-minimal with respect to the Banach couple L1 ([0,1]m) ,L∞ ([0,1]m) is established. With this condition at hand, different examples of invariant K-minimal sets for this couple are constructed. Paper III considers an application of taut strings to buffered real-time communication systems. The optimal buffer management strategy, with respect to minimization of a class of convex distortion functions, is characterized in terms of a taut string. Further, an algorithm for computing the optimal buffer management strategy is provided. In paper IV, infinite-dimensional taut strings are investigated in connection with the Wiener process. It is shown that the average energy per unit of time of the taut string in the long run converges, if it is constrained to stay within the distance r > 0 from the trajectory of a Wiener process, to a constant C2/r2 where C ∈ (0,∞). While the exact value of C is unknown, the numerical estimate C ≈ 0.63 is obtained through simulations on a super computer. These simulations are based on a certain algorithm for constructing finite-dimensional taut strings.
33
Lize, Matheus Loss. "Scattering amplitudes using twistor strings." São Paulo, 2017. http://hdl.handle.net/11449/154417.
Анотація:
Orientador: Nathan Jacob BerkovitsBanca: Andrey Yuryevich Mikhaylov
Banca: Diego Trancanelli
Resumo: Neste trabalho revisamos as amplitudes de MHV no contexto da teoria de super-Yang-Mills. Nós estudamos as simetrias das amplitudes de MHV no espaço de twistors como uma motivação para introduzir a teoria de cordas com twistors . A teoria de cordas com twistors feita por Nathan Berkovits [3] é revisada e uma fórmula geral é dada para calcular amplitudes de espalhamento com n gluons. No final, a partir desta fórmula deduzimos a amplitude de MHV
Abstract In this work we review the maximal helicity violating (MHV) scattering amplitude in the context of super-Yang-Mills theory. We study the symmetries of the MHV amplitude in the twistor space as a motivation to introduce the twistor string theory. The twistor string action introduced by Nathan Berkovits [3] is reviewed and also a general formula is given for the scattering amplitude with n gluons. In the end, the MHV amplitude is derived from this formula
Mestre
34
Sjödin, Robert. "Cosmic strings in general relativity." Thesis, University of Southampton, 2001. https://eprints.soton.ac.uk/50619/.
Анотація:
In this thesis we examine the properties of Cosmic Strings in the theory of General Relativity. We begin by considering static Cosmic Strings in flat space-time. We derive the field equations for the Cosmic String and show that the solution depends upon a single scaling parameter a which is constructed from the physical constants. Using this result we construct 1-parameter families of solutions which depend on an auxiliary parameter e and which describe the thin-string limit of a Cosmic String. By interpreting these solutions as elements of the simplified Colombeau algebra we may interpret the relativistic energy density Too of the thin string as an element of the Colombeau algebra with delta-function mass-per-unit-length. Furthermore, for a critically coupled Cosmic String the energymomentum tensor in the thin-string limit may be given a distributional interpretation. We also solve the string equations numerically for various values of a. This is done by compactifying the space-time to include infinity as part of the numerical grid and then using a relaxation method to suppress exponentially growing un-physical solutions. In curved space-time we derive the equations for the scalar and vector fields which are now coupled to the geometric variables through Einstein's equations. We again examine the thin-string limit in the Colombeau algebra by considering a 1-parameter family of solutions. W'e derive an expression for the deficit angle in terms of the distributional energy-momentum tensor of the thin string. We use this result to investigate the gravitational lensing properties of the string and relate this to the deficit angle. In the special case of a cone we find the scattering angle is equal to the deficit angle. We also solve the coupled equations numerically using techniques similar to those used in flat space-time. The second part of the thesis involves the dynamics of Cosmic Strings. Einstein's equations then lead to wave equations for both the matter and metric variables. However, the space-time is not asymptotically flat and this leads to problems in applying the appropriate boundary conditions. By using a Geroch transformation it is possible to reformulate the equations in terms of geometrical variables defined on an asymptotically flat (2+l)-dimensional space-time. Three exact vacuum solutions describing gravitational radiation due to Weber-Wheeler, Xanthopoulos and Piran et al. are used to excite the string which is found to oscillate with frequencies which are proportional to the masses of the scalar and vector fields of the string. This is in agreement with the exact results obtained using the linearised equations of the thin dynamic string. The behaviour of the dynamic string is studied by solving the equations numerically using an implicit fully characteristic scheme. The use of the Geroch transformation allows us to compactify the space-time and include null infinity as part of the numerical grid. This enables us to use the correct boundary conditions at infinity and hence suppress un-physical divergent solutions. The code is tested by comparing the results with exact solutions, by checking that it agrees with the static code and by undertaking a time dependent convergence test. The code is found to be accurate, stable and exhibit clear second order convergence.
35
Klotz, Anthony. "Spontaneous Knotting of Agitated Strings." VCU Scholars Compass, 2009. http://scholarscompass.vcu.edu/etd/1823.
36
Duplessis, Francis. "Structure formation from cosmic strings." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119586.
Анотація:
The search for cosmic strings has been of renewed interest with the advent of precision cosmology. In this thesis we discuss the possibility of observing cosmic strings through their signature in the large scale structure. We review the standard picture of structure formation caused by primordial fluctuations in the matter density and introduce the notion of cosmic strings while presenting how they would act as early seeds for structure formation. We also discuss previous work that studied structures formed from cosmic string loops and the recent result that these could allow for observational effects by giving rise to significant star formation at early times. Finally we give a quantitative description of the nonlinear matter density fluctuations that can form from ascaling network of cosmic string wakes. Specifically, we compute the distribution of dark matter halos. These halos would possess strong correlations in position space that should have survived until today. We also discuss the challenges involved in their detection due to their small size and the complex dynamics of their formation.L'intérêt pour la recherche de cordes cosmiques c'est récemment renouvelé avec l'arrivée de nouvelles technologies permettant d'étudier la cosmologie avec grande précision. Dans cette thèse, nous discutons de la possibilité d'observer ces cordes cosmiques par leur effet sur les structures à grande échelle de l'univers. Nous présentons le savoir standard associé à la formation de structure causée par des fluctuations primordiales dans la densité de matière. Par la suite, nous expliquons la notion de cordes cosmiques et leur effet catalyseur sur la croissance de structure. Nous discutons également des travaux antérieurs qui ont été effectués sur les structures former par les cordes cosmiques bouclées. Ces travaux démontrent que ces structures peuvent potentiellement générer des étoiles très tôt dans l'histoire de l'univers, cela causerait des effets observables. Finalement, nous donnons une description quantitative des fluctuations de densité non-linéaire causée dans le sillage de longues cordes cosmiques. Spécifiquement, nous calculons la distribution des halos de matière noire. Ces halos posséderaient de fortes corrélations spatial qui devrait avoir survécues jusqu'à aujourd'hui. Nous discutons aussi des obstacles, dûs à leurs petites masses et aux dynamiques complexes de leur formation, auxquels nous devrons surmonter en essayant de détecter les signaux de ces halos.
37
Prudenziati, Andrea. "Topics in Open Topological Strings." Doctoral thesis, SISSA, 2010. http://hdl.handle.net/20.500.11767/4136.
Анотація:
This thesis is based on some selected topics in open topological string theory which I have worked on during my Ph.D. It comprises an introductory part where I have focused on the points most needed for the later chapters, trading completeness for conciseness and clarity. Then, following [12], we discuss tadpole cancellation for topological strings where we mainly show how its implementation is needed for ensuring the same "odd" moduli decoupling encountered in the closed theory. Next we move to analyse how the open and closed effective field theories for the B model interact writing the complete Lagrangian. We first check it deriving some already known tree level amplitudes in term of target space quantities, and then we extend the recipe to new results; later we implement open closed duality from a target field theory perspective. This last subject is also analysed from a worldsheet point of view extending the analysis of [13]. Some ideas for future research are briefly reported.
38
Vazquez-Cruz, Alfredo. "Gravitational properties of quantum bosonic strings." Thesis, University of Sussex, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361405.
39
Playle, Samuel Rhys. "Gauge theory effective actions from open strings." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8847.
Анотація:
In an introductory chapter, a summary of the construction of string theories is given, for both the bosonic string and the RNS superstring. Relevant mathematical technology is introduced, including super-Riemann surfaces. Conformal field theory is discussed and BRST quantization of the string is explained. (Super) Schottky groups for the construction of higher-genus Riemann surfaces are introduced. As an example of the use of Schottky groups and super-Riemann surfaces, the one-loop gluon two point function is calculated from string theory. The incorporation of background gauge fields into string theory via nontrivial monodromies (twists) is discussed. The two loop Prym period matrix determinant is computed in the Schottky parametrization. The string theory model with N parallel separated D3-branes is introduced, and the formulae for the the vacuum amplitude are written down. A manifestly symmetric parametrization of two loop Schottky space is introduced. The relationship between worldsheet moduli and Feynman graph Schwinger times is given. The 0 ! 0 limit of the amplitude is written down explicitly. The lagrangian for the corresponding gauge theory is found, making use of a generalization of Gervais-Neveu gauge which accounts for scalar VEVs. Propagators in the given gauge field background are written down. All of the 1PI two-loop Feynman diagrams are written down, including diagrams with vertices with an odd number of scalars. Illustrative example Feynman graphs are computed explicitly in position space. These results are compared with the preceding string theory results and exact agreement is obtained for the 1PI diagrams. An example application is given: the computation of the function of scalar QED at two loops with the same methods, leading to the same result as found in the literature.
40
McBride, Michael A. (Michael Anthony). "The Warp and Weft of Fabric: A Composition for Strings." Thesis, University of North Texas, 1999. https://digital.library.unt.edu/ark:/67531/metadc278386/.
Анотація:
The six-movement work is scored for two violins, a viola, and a violoncello. A new approach toward the decision making of the compositional process is revealed which structures the parameters of the composition along an arbitrary frame of reference. This reference is selected prior to composition and influences every aspect of the work. The reference chosen is an existing musical work used in quotation and for stylistic modeling, paraphrase, and variation. Consonance, dissonance, and thematic development are defined in terms of this source.
41
Hedlund, Anna Maria. "Stripped Says to Stand Strong : Christina Aguilera's Voice and Feminist Narratology." Thesis, Halmstad University, School of Humanities (HUM), 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-125.
Анотація:
Throughout history women have been subject to oppression by patriarchal society.
However, there have always been those who have tried to rise against it. This study will shed light upon one example: a female artist who personally defies the patriarchal norms at the same time as her music encourages others to do the same. The musician in question is Christina Aguilera, and the album studied is Stripped.
What this study shows is that Stripped can be read as a feminist statement. The lyrics deal with two main themes: patriarchal society’s objectification and oppression of women, and the struggles of love and relationships. What these two themes have in common is that they both encourage women to stand their ground and believe in themselves.
However, the lyrics on the album also suggest that Aguilera is aware of the fact that her message will not suit everyone. She knows that she works within an industry whose goal is to make money out of its artists, and therefore she has to keep repeating like a mantra to herself and to others that she, and her music, is not just a product of this industry. The message her music brings actually matters.
To come to this conclusion I have examined Aguilera’s lyrics in terms of what messages they bring and who their narratees might be, all in accordance with feminist narratology. Secondary sources from the fields of popular music studies, media studies and gender studies as well as interviews with and about Aguilera and biographies have been consulted.
42
Losi, Manuel. "Spiky strings and the AdS/CFT correspondence." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/240629.
Анотація:
In this dissertation, we explore some aspects of semiclassical type IIB string theory on AdS3 x S1 and on pure AdS3 in the limit of large angular momentum S. We first focus on the integrability technique known as finite-gap formalism for strings in AdS3 x S1, leading to the definition of a hyperelliptic Riemann surface, the spectral curve, which encodes, albeit in a rather implicit fashion, the semiclassical spectrum of a very large family of string solutions. Then, we show that, in the large angular momentum limit, the spectral curve separates into two distinct surfaces, allowing the derivation of an explicit expression for the spectrum, which is correspondingly characterised by two separate branches. The latter may be interpreted in terms of two kinds of spikes appearing on the strings: 'large' spikes, yielding an infinite contribution to the energy and angular momentum of the string, and 'small' spikes, representing finite excitations over the background of the 'large' spikes. According to the AdS/CFT correspondence, strings moving in AdS3 x S1 should be dual to single trace operators in the sl(2) sector of N = 4 super Yang-Mills theory. The corresponding one-loop spectrum in perturbation theory may also be computed through integrability methods and, in the large conformal spin limit S → ∞ (equivalent to the AdS3 angular momentum in string theory) is also expressed in terms of a spectral curve and characterised in terms of the so-called holes. We show that, with the appropriate identifications and with the usual extrapolation from weak to strong 't Hooft coupling described by the cusp anomalous dimension, the large-S spectra of gauge theory and of string theory coincide. Furthermore, we explain how 'small' and 'large' holes may be identified with 'small' and 'large' spikes. Finally, we discuss several explicit spiky string solutions in AdS3 which, at the leading semiclassical order, display the previously studied finite-gap spectrum. We compute the spectral curves of these strings in the large S limit, finding that they correspond to specific regions of the moduli space of the finite-gap curves. We also explain how 'large' spikes may be used in order to extract a discrete system of degrees of freedom from string theory, which can then be matched with the degrees of freedom of the dual gauge theory operators, and how 'small' spikes are in fact very similar to the Giant Magnons living in R x S2.
43
Yang, Benjamin H. (Benjamin Hoh). "A Study of the Relationship Between Motive and Structure in Brahms's op. 51 String Quartets." Thesis, University of North Texas, 1989. https://digital.library.unt.edu/ark:/67531/metadc332309/.
Анотація:
In 1873, Brahms completed the two op. 51 quartets. These were not the first string quartets Brahms composed, hut they were the first that Brahms allowed to be published. He found the string quartet difficult; as he confided to his friend Alwin Cranz, he sketched out twenty string quartets before producing a pair he thought worthy of publishing. Questions arise: what aspect of the string quartet gave Brahms so much trouble, and what in the op. 51 quartets gave him the inclination to publish them for the first time in his career?
The op. 51 quartets are essential to understanding the evolution of Brahms's compositional technique. Brahms had difficulty limiting his massive harmony and polyphony to four solo strings. This difficulty was compounded by his insistence on deriving even the accompaniment from the opening main motivic material.
This study investigates the manner in which Brahms distributes the main motivic material to all four voices in these quartets, while at the same time highlighting each voice effectively in the dialogue.
44
Goodband, Michael James. "Perturbations about topological defects." Thesis, University of Sussex, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336276.
45
Niemeyer, Bernd. "N=2 strings und selbstduale Feldtheorien." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962822698.
46
Körs, Boris. "Open strings in magnetic background fields." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=962714895.
47
Hendy, Shaun. "Cosmic strings in black hole spacetimes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0007/NQ29046.pdf.
48
Oliveira, Luiz Eduardo Soares. "Automatic recognition of handwritten numerical strings." Mémoire, Montréal : École de technologie supérieure, 2003. http://wwwlib.umi.com/cr/etsmtl/fullcit?pNQ85289.
Анотація:
Thèse (Ph.D.)--École de technologie supérieure, Montréal, 2003."Thesis presented to the École de technologie supérieure in partial fulfillment of the thesis requirement for the degree of philosophiae doctor in engineering". La numérotation de cet ouvrage est erronée. Bibliogr.: f. [149]-163. Également disponible en version électronique.
49
Bougourzi, M. Abdelhamid. "Heterotic strings compactified on asymmetric orbifolds." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61979.
50
Mistry, Bina. "Braneworld black holes and black strings." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2242/.
Анотація:
This thesis involves the study of strong and weak gravity phenomenology within the braneworld paradigm. We begin with a general overview of the hypothesised concept of extra spatial dimensions and explain why they are so interesting. Turning next to the topic of classical four-dimensional black holes, we discuss their formation via gravitational collapse and indicate some of the strong observational evidence of their existence. We then merge the two independent theories of extra dimensions and black holes together to form braneworld black holes. Focusing our attention on two distinct braneworld scenarios, we examine the effects produced from either strong or weak gravity. The prospect of obtaining experimental verification of the existence of additional spacelike dimensions in the upcoming ground-based accelerators, makes the theoretical research of braneworld gravity within this thesis even more enticing. We start with a non-perturbative approach to look for exact, spherically symmetric star or black hole solutions on a Randall-Sundrum brane from the perspective of the five-dimensional spacetime. By fixing the background, we explore the permissible braneworld trajectories within it that correspond to a braneworld observer, the solutions of the brane Tolmann-Oppenheimer-Volkoff equations. A variety of static gravitating matter sources on the brane are obtained in a range of different backgrounds. Our final aim is a consistent brane embedding in a Schwarzschild- Anti de Sitter spacetime as these solutions are potential candidates for brane stars or black holes. The weak and dominant energy conditions determine the physically sensible solutions which have the interpretation of braneworld stars. We then study time-dependent trajectories as a possible description of time-dependent braneworld black holes. This work is then generalised by relaxing the simplifying assumption of Z(_2)-symmetry, previously imposed around the brane. Non-Z(_2) symmetric spacetimes are applicable in processes which concern only one side of the brane, for example black hole recoil or the emission of Hawking radiation. We determine that a subset of the allowed brane trajectories in an asymmetric background are exactly the same as the Z(_2)-symmetric case. Next, we explore perturbative gravity in the Hofava-Witten model of heterotic M-theory. The study of scalar and gravitational fluctuations determines that the radion mode is coupled to the bulk scalar field, indicating only one single degree of freedom. Our analysis also determines the instability of a black string. We then compute the complete mass spectrum of the graviton mode. Using the five-dimensional gravitational physics, we determine what the gravitational interaction an observer on the braneworld would perceive. This analysis involves the computation of the Newtonian potential between two test masses on the visible brane, together with the four-dimensional tensor structure of the massless graviton propagator. Finally, as an application to the earlier work, we comment on work which is in progress: the study of possible brane black hole solutions in low energy heterotic M-theory.