Tesi sul tema "Space and time"
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1
Karacayir, Murat. "Space-time Codes". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612028/index.pdf.
Testo completoAbstract (sommario):
The phenomenon of fading constitutes a fundamental problem in wireless communications. Researchers have proposed many methods to improve the reliability of communication over wireless channels in the presence of fading. Many studies on this topic have focused on diversity techniques. Transmit diversity is a common diversity type in which multiple antennas are employed at the transmitter. Space-time coding is a technique based on transmit diversity introduced by Tarokh et alii in 1998.
In this thesis, various types of space-time codes are examined. Since they were originally introduced in the form of trellis codes, a major part is devoted to space-time trellis codes where the fundamental design criteria are established. Then, space-time block coding, which presents a different approach, is introduced and orthogonal spacetime block codes are analyzed in some detail. Lastly, rank codes from coding theory
are studied and their relation to space-time coding are investigated.
2
Dowker, Fay H. "Space-time wormholes". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359554.
Testo completo
3
Lamahewa, Tharaka Anuradha, e tharaka lamahewa@anu edu au. "Space-Time Coding and Space-Time Channel Modelling for Wireless Communications". The Australian National University. Research School of Information Sciences and Engineering, 2007. http://thesis.anu.edu.au./public/adt-ANU20070816.152647.
Testo completoAbstract (sommario):
In this thesis we investigate the effects of the physical
constraints such as antenna aperture size, antenna geometry and
non-isotropic scattering distribution parameters (angle of
arrival/departure and angular spread) on the performance of coherent
and non-coherent space-time coded wireless communication systems.
First, we derive analytical expressions for the exact pairwise error
probability (PEP) and PEP upper-bound of coherent and non-coherent
space-time coded systems operating over spatially correlated fading
channels using a moment-generating function-based approach. These
analytical expressions account for antenna spacing, antenna
geometries and scattering distribution models. Using these new PEP
expressions, the degree of the effect of antenna spacing, antenna
geometry and angular spread is quantified on the diversity advantage
(robustness) given by a space-time code. It is shown that the number
of antennas that can be employed in a fixed antenna aperture without
diminishing the diversity advantage of a space-time code is
determined by the size of the antenna aperture, antenna geometry and
the richness of the scattering environment.
¶
In realistic channel environments the performance of space-time
coded multiple-input multiple output (MIMO) systems is significantly
reduced due to non-ideal antenna placement and non-isotropic
scattering. In this thesis, by exploiting the spatial dimension of a
MIMO channel we introduce the novel use of linear spatial precoding
(or power-loading) based on fixed and known parameters of MIMO
channels to ameliorate the effects of non-ideal antenna placement on
the performance of coherent and non-coherent space-time codes. The
spatial precoder virtually arranges the antennas into an optimal
configuration so that the spatial correlation between all antenna
elements is minimum. With this design, the precoder is fixed for
fixed antenna placement and the transmitter does not require any
feedback of channel state information (partial or full) from the
receiver. We also derive precoding schemes to exploit non-isotropic
scattering distribution parameters of the scattering channel to
improve the performance of space-time codes applied on MIMO systems
in non-isotropic scattering environments. However, these schemes
require the receiver to estimate the non-isotropic parameters and
feed them back to the transmitter.
¶
The idea of precoding based on fixed parameters of MIMO channels is
extended to maximize the capacity of spatially constrained dense
antenna arrays. It is shown that the theoretical maximum capacity
available from a fixed region of space can be achieved by power
loading based on previously unutilized channel state information
contained in the antenna locations. We analyzed the correlation
between different modal orders generated at the transmitter region
due to spatially constrained antenna arrays in non-isotropic
scattering environments, and showed that adjacent modes contribute
to higher correlation at the transmitter region. Based on this
result, a power loading scheme is proposed which reduces the effects
of correlation between adjacent modes at the transmitter region by
nulling power onto adjacent transmit modes.
¶
Furthermore, in this thesis a general space-time channel model for
down-link transmission in a mobile multiple antenna communication
system is developed. The model incorporates deterministic
quantities such as physical antenna positions and the motion of the
mobile unit (velocity and the direction), and random quantities to
capture random scattering environment modeled using a bi-angular
power distribution and, in the simplest case, the covariance between
transmit and receive angles which captures statistical
interdependency. The Kronecker model is shown to be a special case
when the power distribution is separable and is shown to
overestimate MIMO system performance whenever there is more than one
scattering cluster. Expressions for space-time cross correlations
and space-frequency cross spectra are given for a number of
scattering distributions using Gaussian and Morgenstern's family of
multivariate distributions. These new expressions extend the
classical Jake's and Clarke's correlation models to general
non-isotropic scattering environments.
4
Lamahewa, Tharaka Anuradha. "Space-time coding and space-time channel modelling for wireless communications /". View thesis entry in Australian Digital Theses Program, 2006. http://thesis.anu.edu.au/public/adt-ANU20070816.152647/index.html.
Testo completo
5
Haron, Linariza. "Facility space-time management". Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326152.
Testo completo
6
Thompson, Philip R. Z. (Philip Reed Zane). "Space, time and acoustics". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/78997.
Testo completoAbstract (sommario):
Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1988.Includes bibliographical references (leaves 156-159).
This thesis describes the development of new concepts in acoustical analysis from their inception to implementation as a computer design tool. Research is focused on a computer program which aids the designer to visually conceive the interactions of acoustics within a geometrical~y defined environment by synthesizing the propagation of sound in a three dimensional space over time. Information is communicated through a unique use of images that are better suited for interfacing with the design process. The first part of this thesis describes the concepts behind the development of a graphic acoustical rendering program to a working level. This involves the development of a computer ray tracing prototype that is sufficiently powerful to explore the issues facing this new design and analysis methodology. The second part uses this program to evaluate existing performance spaces in order to establish qualitative criteria in a new visual format. Representational issues relating to the visual perception of acoustic spaces are also explored. In the third part, the program is integrated into the design process. I apply this acoustical tool to an actual design situation by remodeling a large performance hall in Medford, Massachusetts. Chevalier Auditorium is a real project, commissioned by the city of Medford, whose program requirements closely match my intentions in scope, scale and nature of a design for exploring this new acoustical analysis and design methodology. Finally, I summarize this program's effectiveness and discuss its potential in more sophisticated future design environments.
by Philip R.Z. Thompson.
M.Arch.
7
Sanders, Ralph Jarrett. "Space, time, and silence". Thesis, Virginia Polytechnic Institute and State University, 1990. http://hdl.handle.net/10919/56200.
Testo completoAbstract (sommario):
This thesis is a meditation upon silence, upon its ontological relationship to architecture. As such, it relies more upon insight and contemplation than analysis. It seeks to explore this realm through the making of a trappist monastery, to ask fundamental questions about the nature of human dwelling in the most complete sense, to stir the memory and perhaps to move the heart toward that silence which is beyond thought, which precedes and bounds and yet pervades all human experience.Master of Architecture
8
Pak, Anne On-Yi 1977. "Euclidean space codes as space-time block codes". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86722.
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9
Kamela, Martin J. "Space-time duality, superduality, and effective actions on anti-de-Sitter space-time". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ64585.pdf.
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10
Liesenjohann, Thilo. "Foraging in space and time". Phd thesis, Universität Potsdam, 2010. http://opus.kobv.de/ubp/volltexte/2010/4856/.
Testo completoAbstract (sommario):
All animals are adapted to the environmental conditions of the habitat they chose to live in. It was the aim of this PhD-project, to show which behavioral strategies are expressed as mechanisms to cope with the constraints, which contribute to the natural selection pressure acting on individuals. For this purpose, small mammals were exposed to different levels and types of predation risk while actively foraging. Individuals were either exposed to different predator types (airborne or ground) or combinations of both, or to indirect predators (nest predators). Risk was assumed to be distributed homogeneously, so changing the habitat or temporal adaptations where not regarded as potential options. Results show that wild-caught voles have strategic answers to this homogeneously distributed risk, which is perceived by tactile, olfactory or acoustic cues. Thus, they do not have to know an absolut quality (e.g., in terms of food provisioning and risk levels of all possible habitats), but they can adapt their behavior to the actual circumstances. Deriving risk uniform levels from cues and adjusting activity levels to the perceived risk is an option to deal with predators of the same size or with unforeseeable attack rates. Experiments showed that as long as there are no safe places or times, it is best to reduce activity and behave as inconspicuous as possible as long as the costs of missed opportunities do not exceed the benefits of a higher survival probability. Test showed that these costs apparently grow faster for males than for females, especially in times of inactivity. This is supported by strong predatory pressure on the most active groups of rodents (young males, sexually active or dispersers) leading to extremely female-biased operative sex ratios in natural populations.
Other groups of animals, those with parental duties such as nest guarding, for example, have to deal with the actual risk in their habitat as well. Strategies to indirect predation pressure were tested by using bank vole mothers, confronted with a nest predator that posed no actual threat to themselves but to their young (Sorex araneus). They reduced travelling and concentrated their effort in the presence of shrews, independent of the different nutritional provisioning of food by varying resource levels due to the different seasons. Additionally, they exhibited nest-guarding strategies by not foraging in the vicinity of the nest site in order to reduce conspicuous scent marks. The repetition of the experiment in summer and autumn showed that changing environmental constraints can have a severe impact on results of outdoor studies. In our case, changing resource levels changed the type of interaction between the two species.
The experiments show that it is important to analyze decision making and optimality models on an individual level, and, when that is not possible (maybe because of the constraints of field work), groups of animals should be classified by using the least common denominator that can be identified (such as sex, age, origin or kinship). This will control for the effects of the sex or stage of life history or the individual´s reproductive and nutritional status on decision making and will narrow the wide behavioral variability associated with the complex term of optimality.Das Verhalten von Tieren ist das Ergebnis eines kontinuierlichen Anpassungsprozesses im Laufe der Evolution einer Art und damit der Veränderung der Umgebung in der es lebt und der Interaktion mit anderen Arten. Dies wird besonders deutlich im Verhalten von potentiellen Beutetieren, ihre Strategien beinhalten meist ein möglichst unauffälliges Verhalten im Zusammenspiel mit reduzierter Bewegung und möglichst guter Tarnung. Dementgegen stehen essentielle Bedürfnisse, wie zum Beispiel die Nahrungssuche, die Verteidigung von Ressourcen (zum Beispiel Territorien, Futterstellen) und die Suche nach Paarungspartnern. Beutetiere leben also in einem Spannungsfeld indem sie Ihr Verhalten optimieren müssen. Hierbei stehen die Ernährung, erfolgreiche Verpaarung und andere Chancen auf der einen Seite, die Vermeidung von Begegnungen mit Prädatoren auf der anderen. Vor allem Kleinsäuger sind häufig als Beutetiere mit einer Vielzahl von Prädatoren aus der Luft und auf dem Boden konfrontiert. Sie müssen für die verschiedenen Bedrohungen adaptive Verhaltensanpassungen bereit haben und in der Lage sein, auf die optischen, olfaktorischen oder akustischen Signale, die die Gefahr durch Prädatoren anzeigen, mit plastischen Verhaltensmustern zu reagieren. Die vorliegende Dissertation beschäftigt sich mit bisher als Konstanten behandelten Faktoren und untersucht anhand von Verhaltensexperimenten mit wilden Wühlmäusen (Microtus arvalis) folgende Fragestellungen: - Wie verhalten sich Tiere, die einer homogenen Risikoverteilung ausgesetzt sind, zum Beispiel weil ihr Prädator genauso gross ist wie sie, im gleichen Habitat lebt und es keinen sicheren Ort gibt? - Mit welchen Anpassungen reagieren Tiere, wenn sie gleichzeitig verschiedenen Prädatoren ausgesetzt sind? - Wie unterscheiden sich die Nahrungssuchstrategien von Männchen und Weibchen? - Wie verhalten sich laktierende Weibchen, die einer permanenten, indirekten Gefahr, z.B. durch einen Nestprädator ausgesetzt sind? Die Ergebnisse der verschiedenen Versuche in künstlichen Arenen und Aussengehegen zeigen, dass die Mäuse in der Lage sind, adaptive Verhaltensanpassung an homogenes Risiko und verschiedene Prädationstypen abzurufen. So sind sie in der Lage, Luft- von Bodenprädatoren zu unterscheiden und jeweils das Verhalten zu zeigen, dass die größtmögliche Sicherheit mit sich bringt. Die simultane Kombination von verschiedenen Prädatoren bewirkt hierbei additive Effekte. Gibt es keine Auswahl zwischen Habitaten, sondern nur unterschiedliche homogene Risikolevel, reagieren sie auf steigendes Risiko immer mit verminderter Aktivität und konzentrieren ihre Nahrungssuche auf weniger Futterstellen, beuten diese dafür jedoch länger aus. Die Wertigkeit von Futterstellen und alternativen Optionen verändert sich also mit dem Risikolevel. Ähnliches zeigt sich auch in den unterschiedlichen Futtersuchstrategien von Männchen und Weibchen. Die untersuchte Art ist polygyn und multivoltin, dementsprechend verbinden die Männchen mit ihrer Nahrungssuche Aktivitäten wie die Suche nach Paarungspartnern und unterscheiden sich die Aktivitätsmuster zwischen Männchen und Weibchen. Zusätzlich zeigen die Ergebnisse, das laktierende Weibchen in der Lage sind, das Risiko für sich und für Ihre Jungen abzuschätzen, wenn sie mit einem Nestprädator (Sorex araneus) konfrontiert werden. Für die Interaktion zwischen diesen beiden Arten ist jedoch die Saison (und damit die Ressourcenlage), in der sie sich begegnen, von entscheidender Bedeutung. Wühlmäuse reagieren mit entsprechenden Verhaltensanpassungen zum Schutz des Nestes um die Überlebenschancen ihrer letzten Würfe im Herbst zu erhöhen. Die vorliegende Arbeit konnte grundsätzliche Probleme der antiprädatorischen Verhaltensanpassung von Beutetieren klären und wichtige Faktoren der Entscheidungsfindung unter Prädationsdruck analysieren. Sie zeigt, dass Tiere das Risiko in ihrer Umgebung nicht unbedingt über direkt Signale wahrnehmen, sondern ihre Verhaltensstrategien einem empfundenen Gesamtrisikolevel anpassen. Dies ermöglicht ihnen, adaptive Strategien zu verfolgen, auch wenn sie keine Auswahl an sicheren Habitaten haben. Sie zeigt auch die unterschiedliche Wahrnehmung von Risiken durch Männchen und Weibchen, die durch die unterschiedlichen mit der Aktivität zusätzlich wahrgenommenen Chancen verknüpft zu sein scheint. Zusätzlich wurde der Einfluss des reproduktiven Status (z.B. laktierend), sowie der Ressourcenlage (z. B. je nach Saison) nachgewiesen.
11
Silvester, Anna-Marie. "Space-time continuous phase modulation". Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/14721.
Testo completoAbstract (sommario):
The combination of Space-Time (ST) coding and Continuous-Phase Modulation (CPM) produces a low power, energy efficient communication scheme suitable for wireless transmission. Space-time coding increases the reliability of transmission, and continuous-phase modulation (CPM) has the
potential to provide considerable energy savings. CPM is a modulation technique that involves the transmission of a signal with continuous-phase and a constant envelope, where the continuous-phase property produces a very bandwidth efficient signal, and the constant-envelope property enables non
linear (and thus energy efficient) signal amplification. The ST-CPM code is of special interest for wireless sensors because in the wireless sensor network environment energy consumption is highly constrained. The combination of ST codes and CPM is non-trivial and thus ST-CPM codes based upon
block-based orthogonal and diagonal signal matrices are presented. These codes are forms the basis of a distributed ST-CPM code. The distributed ST codes are designed to operate in wireless networks containing a large set of nodes, of which only a small a priori unknown subset will be active at any
time. The devised distributed ST-CPM scheme combines the ST-CPM code with a diagonal signaling matrix, (commonly assigned to all relay nodes) with signature vectors(uniquely assigned to nodes). The energy consumption of the proposed distributed ST-CPM scheme is compared with that of a distributed ST linear modulation (LM) scheme. The distributed ST-CPM scheme is shown to
outperform the distributed ST-LM scheme for all but short-range transmission. Finally, a serially concatenated code for ST-CPM is proposed. The concatenated code consists of the diagonal signalling matrix as the inner code, and a class of double parity check (DPC) codes as the outer code. The
resulting concatenated codes that are formed from the ST-CPM code and a DPC code are shown to provide performance close to capacity, and to provide performance superior to that provided by the more common combination of CPM, or ST-CPM schemes with convolutional codes.
12
South-Dickinson, Ian James. "Globally consistent space-time reconstruction". Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43207.
Testo completoAbstract (sommario):
We present a novel algorithm for space-time reconstruction of deforming meshes. Based on partial meshes at every frame, and sparse optical flow information between frames, we reconstruct a globally consistent, crossparameterized, and hole filled sequence of meshes. Our method is based on pair-wise merging of frame sequences while correcting for changes in topology, filling in missing geometry, and repairing inconsistencies. We also introduce a robust method for filling in missing geometry in each frame of the sequence using geometry from another frame. Using this method we can propagate geometry over the full frame sequence, correcting errors and filling in holes even in regions of the object that are not observed in the input meshes for extended periods of time. Unlike other approaches, our method does not require template geometry, nor is it limited to narrow classes of objects or purely isometric deformations.
13
Yang, Ho. "Partially adaptive space-time processing". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13028.
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Seliktar, Yaron. "Space-time adaptive monopulse processing". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/13075.
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15
Holm, Jens Christian. "Spinors in discrete space-time". Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/27901.
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16
Ramlochand, John. "Japanese cinema : time space nation". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102159.
Testo completoAbstract (sommario):
This work utilizes a spatial theory approach to meditate on postwar Japanese society and cinema. It is not a history of Japanese postwar cinema, or a survey of notable directors and genres. Rather, the focus is specifically on film and its relation to the deeper tropes of Japanese society; in particular, on how the sense of nation is affirmed and/or challenged within a postwar period of remarkable change. Understanding such a structure greatly aids in analyzing the forms and meanings within the films. The question of National Cinema, then, is approached by exploring how the interaction of spatial-temporal elements affect both the social construction and filmic practices of the nation.The first part of the dissertation features an extended analysis of Japanese society using a variety of historical, philosophical and theoretical sources, both Japanese and foreign. They provide a theoretical base and a social history that ground the critical readings of the selected films; all of which are well-known and widely available. Part two is a close textual analysis of five 1950s productions---from a range of films and genres---that are contrasted with three films from the late 1980s/early 1990s. The final chapter examines notions about National Cinema in light of the preceding film analysis.
17
Mason, Lionel J. "Twistors in curved space time". Thesis, University of Oxford, 1985. http://ora.ox.ac.uk/objects/uuid:29de7cd1-84c9-4374-8f7d-9a402dd9e0ed.
Testo completoAbstract (sommario):
This thesis is concerned with an investigation of twistorial structures present in curved Lorentzian space-times. Chapter 1 introduces the basic definitions and some theorems that will be used later in the text. Chapter 2 investigates generalised connections that arise in twister theory. First the Cartan con-formal connection is studied, and some of the geometry underlying it is shown to be that used by Fefferman and Graham C133. Also a condition that a space-time is conformal to vacuum is given. Secondly the theory of the Chern connection associated to a C.R. manifold is developed in such a way as to make the calculation of the connection associated to a twistor C.R. manifold straight forward. A new proof of the Chern theorem of existence and uniqueness is given. The Chern connection of a twistor C.R. manifold is then calculated, and discussed. In particular S-dimensionai C.R. manifolds arising as twistor C.R. manifolds are characterised. Canonical structures peculiar to the twister case are discussed. Applications of C.R. manifold theory to algebraically special space-times are suggested. Chapter three analyses how various twistorial structures behave in linearised general relativity. First, deformations of the space of complex null geodesies corresponding to variations of the conformal structure of space-time are shown to be generated by hami1tonians. Those that correspond to variations in the metric satisfying the field equations are given, along with hamiltonians corresponding to different fields and field equations. Beneralisations to nonlinear equations are discussed. These ideas are applied to hypersurface twisters in linearised theory, using fiat hypersurfaces and Cech cohoeology. Expressions are obtained for the deformation of the complex structure of the spaces and their evolution. The results are generalised to non flat hypersurfaces using Dolbeault cohomolcgy. It is shown that certain canonically defined forms on the spin bundle are preferred Dolbeault representatives for derivatives of the twister cohomology classes corresponding to the linearised field. In chapter four I generalise the results of chapter three to curved space using the Chern connection. In particular twistorial formulations of the constraint equations are given, and a formula for the evolution that satisfies the the vacuum evolution equations is given in terms of an "infinity" twistor and a "time" twister. This is then discussed. In chapter five I make some comments on the interpretation of a three form on the spin bundle discovered by B.A.J. Sparling as the gravitational hami1tonian. I then use this to show that one can give an interpretation of Penrose's quasi-local angular momentum twistor in terms of the canonical formalism.
18
Dang, Xiaoyu. "Space-Time Shaped Offset QPSK". International Foundation for Telemetering, 2008. http://hdl.handle.net/10150/606190.
Testo completoAbstract (sommario):
ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, CaliforniaThis paper describes the use of orthogonal space-time block codes to overcome the performance and complexity difficulties associated with the use of Shaped Offset QPSK (SOQPSK) modulation, a ternary continuous phase modulation (CPM), in multiple-input multiple-output telemetry systems. The orthogonal space-time block code is applied to SOQPSK waveforms in the same way it would be applied to symbols. The procedure allows the receiver to orthogonalize the link. The main benefits of this orthogonalization are the easy realization of the transmit diversity for the offset-featured SQOSPK, and the removal of the noise correlation at the input to the space-time decoder and the elimination of I/Q interference when space time orthogonalization is applied to the symbol level.
19
Asbell, Jonathan Clark. "Thresholds in Space and Time". Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/100920.
Testo completoAbstract (sommario):
In architecture there is perhaps no better opportunity to capture movement and change than in the design of thresholds. They can be a simple strip of metal beneath a doorway, barely noticed as you pass over it, or a grand atrium that you stop and marvel at on your way into the office. They can manifest as a change of materials or finishes, or of some parameter such as ceiling height. They might even be immaterial altogether, like the boundary between light and shadow.
Thresholds transcend the physical to effect a psychological experience. They can be spatial or temporal or some combination of the two, but whatever form they take, all thresholds can be said to be mediators of our movement from one spatial status to another. Inside to outside, public to private, here to there. Too often our buildings relegate these changes to doors or openings that have little connection to the buildings they are a part of, and so our awareness of passage from space to space is diminished. This thesis explores ways to enrich the architecture of the threshold so that it doesn't merely recede to the bounds of our perception.Master of Architecture
The term "threshold" often brings to mind a strip of material at the base of a doorway, but architecture considers thresholds more broadly as moments of movement or change. This thesis examines such moments in an original building design, proposing several threshold types and exploring their impact on occupants.
20
Boué, Stéphanie. "Transcripts in space and time". Université Louis Pasteur (Strasbourg) (1971-2008), 2006. https://publication-theses.unistra.fr/public/theses_doctorat/2006/BOUE_Stephanie_2006.pdf.
Testo completoAbstract (sommario):
Les biologistes moléculaires cherchent à comprendre comment fonctionnent les organismes au niveau moléculaire. Le but ultime de ces recherches est d’offrir la possibilité de manipuler sans risque des cellules et/ou des organismes afin de combattre des maladies génétiques, d’éradiquer les maladies contagieuses ou par exemple d’améliorer les qualités nutritives de l’alimentation. Actuellement, la manière la plus précise et pratique de comprendre le fonctionnement d’un organisme est d’étudier son transcriptome et ses variations dans l’espace et le temps. Suivant cette logique, le but de ma thèse de doctorat a été double: (1) estimer l’importance de l’épissage alternatif qui engendre une diversité des transcripts (2) étudier les transcriptomes de deux organismes modèles : Mus musculus et Drosophila melanogaster, respectivement dans l’espace et le temps. Durant ces années de recherche, j’ai rassemblé des découvertes intéressantes concernant l’expression des gènes et sa régulation. D’abord, l’épissage alternatif s’est avéré être un méchanisme important non seulement en terme de fréquence (des transcripts alternatifs sont générés pour une vaste majorité des gènes, et ce dans de multiples espèces), mais aussi en terme d’évolution (l’épissage alternatif semble permettre à un gène d’évoluer sans conséquences trop négatives pour l’organisme). Par ailleurs nous avons prouvé que le niveau d’expression de transcripts n’est pas en soi synonyme de fonction: il y a en effet une quantité non négligeable d’expression neutre, qui doit être prise en compte lors de l’assignation d’une fonction à un gène, uniquement basée sur la similarité de son profil d’expression par rapport à celui d’un gène de fonction connue. Enfin, nous avons étudié des séries de puces à ADN appliquées à l’embryogenèse de la mouche dans le temps, en utilisant une technique non conventionnelle pour ce type d’approche. Nous avons réparti les gènes en différentes classes selon leurs profils d’expression. Nous avons pu prouver que ces classes de gènes ont des critères biologiques en commun, ce qui laisse supposer que les gènes inconnus ou mal caractérisés qui tombent dans ces classes sont d’interessants points de départ pour de futures recherches. Des découvertes inestimables ont été et seront encore faites en biologie moléculaire grâce à l’étude des transcriptomes dans des organismes variés, analysés dans différentes conditions. Cependant, il est devenu clair qu’à cause de la présence de nombreuses étapes de régulation après la transcription, dont l’épissage alternatif, seule l’analyse des protéomes permettra d’obtenir une vision complète de la biologie de la cellule.
21
Mangitli, Irem. "Infinity in time and space". College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1458.
Testo completoAbstract (sommario):
Thesis (M.F.A.) -- University of Maryland, College Park, 2004.Thesis research directed by: Dept. of Art. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
22
Boué, Stéphanie Stévenin James Bork Peer. "Transcripts in space and time". Strasbourg : Université Louis Pasteur, 2006. http://eprints-scd-ulp.u-strasbg.fr:8080/499/01/Boue_PhD_Transcripts_Space_Time_2006.pdf.
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Ghosh, Sourav. "Thermodynamics of Margulis Space Time". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112137/document.
Testo completoAbstract (sommario):
Dans ma thèse, je décris les feuilles stables et instables pour le flot géodésique sur l’espace des géodésiques non-errant de type espace d’un espace-temps de Margulis et je démontre des propriétés de contraction des feuilles sous le flot. Je montre aussi que la monodromie d’un espace-temps de Margulis est une représentation Anosov dans un groupe de Lie non semisimple. En outre, je montre que les applications limites et reparamétrisation varient analytiquement. Enfin, à l’aide de la propriété métrique Anosov, nous définissons la métrique de pression sur l’espace modulaire des espaces-temps de Margulis sans pointes et je démontre qu’elle est définie positive sur les sections d’entropie constanteIn my thesis I describe the stable and unstable leaves for the geodesic flow on the space of non-wandering spacelike geodesics of a Margulis Space Time and prove contraction properties of the leaves under the flow. I also show that monodromy of Margulis Space Times are “Anosov representations in non semi-simple Lie groups”. Moreover, I show that the limit maps and reparametrizations vary analytically. Finally using the metric Ansosov property we define the Pressure metric on the Moduli Space of Margulis Space Times without “cusps” and show that it is positive definite on the constant entropy sections
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Rivera, Monica Alexandra. "Slowing Down Time, studies on spatial time". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/33992.
Testo completoAbstract (sommario):
The experience of time is not fixed by a rigid mathematical measure, instead, it flows at vaying rates.
There are certain occasions in which we would like to extend time with all our force, up to the limit of our stretched arms and further. Conversely there are moments which we'd like to last no more that the sparkle of a flash, but as we all have noticed, those are the longest in our life.
How does the space that we inhabit influence on our perception of time? May we identify especial elements that contribute in one or other sense to accelerate or slowdown the time?
It's said that time and space is an inseparable unity, as two aspects of the same thing. If this is so, then it also must be true that by shaping space in one way or another, we might influence the experience of time through it. Wouldn't it be delightful to believe that we may be magicians of time through manipulation of architecture?Master of Architecture
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Acharya, Om Nath, e Sabin Upadhyaya. "Space Time Coding For Wireless Communication". Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-19424.
Testo completoAbstract (sommario):
As the demand of high data rate is increasing, a lot of research is being conducted in the field of wireless communication. A well-known channel coding technique called Space-Time Coding has been implemented in the wireless Communication systems using multiple antennas to ensure the high speed communication as well as reliability by exploiting limited spectrum and maintaining the power. In this thesis, Space-Time Coding is discussed along with other related topics with special focus on Alamouti Space-Time Block Code. The Alamouti Codes show good performance in terms of bit error rate over Rayleigh fading channel. The performance of Altamonte’s code and MIMO capacity is evaluated by using MATLAB simulation.
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Healy, Eithne. "Allegories of space : allegories of time". Thesis, University of East London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.532879.
Testo completoAbstract (sommario):
Taking identity as a point of departure, I examine specific cultural and philosophical concerns relating to ideas of alienation, and consider the impact of buildings and space - and their more universal implications - on the formation of historical, psychological and social perceptions of (the) `self. My research has introduced me to new writers, theorists and practitioners including Anthony Vidler's meditations on the spatial and emotional anxieties that architecture evokes. - Artists and filmmakers I refer to include, Anslem Kiefer, Werner Herzog, Peter Doig and Stan Douglas. In forming the 'modern' perception of the world, Nicholas Temple considers Friedrich Hölderlin's understanding of topography as the decisive link to a 'mythical past and a transient present'. ' I reflect on Hölderlin's perspective of the world through the notion of 'divine absence' and Heidegger's interpretation of that understanding on the nature of being. Documentation of my practice consists of colour image video stills and text from 2003-2008. CONCLUSION I consider some of the core ideas explored and developed during the doctorate programme and suggest future projects. Temple, N. (2007) Disclosing Horizons: Architecture, perspective and redemptive space. Oxon: Routledge, p. 5.
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Carlbaum, Oskar, e Michael Novén. "Real-Time Magnetohydrodynamic Space Weather Visualization". Thesis, Linköpings universitet, Medie- och Informationsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-141686.
Testo completoAbstract (sommario):
This work describes the design and implementation of space weather related phenomena within the interactive astro-visualization software OpenSpace. Data sets from the Community Coordinated Modelling Center (CCMC) at the National Aeronautics and Space Administration (NASA) were used to implement time-varying high-resolution solar imagery from space observatory spacecraft and time-varying field lines from the different models produced at the CCMC. The obtained results were used to take an audience on an interactive journey through the solar system, at the worlds first ever live planetarium show about space weather.
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Scott, Susan M. "New approaches to space-time singularities /". Title page, contents and abstract only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phs429.pdf.
Testo completo
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Huang, Li-Ke. "Space-time DS-CDMA communication systems". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397681.
Testo completo
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Youngman, Ben. "Space-time modelling of extreme values". Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555232.
Testo completoAbstract (sommario):
The motivation for the work in this thesis is the study of models for extreme values that have clear practical benefit. Specific emphasis is placed on the modelling of extremes of environmental phenomena, which often exhibit spatial or temporal dependence, or both, or are forced by external factors. The peaks-over-threshold approach to modelling extremes combats temporal dependence, providing a way in which likelihood-based methods may he used reliably. The method is widely used and has sound asymptotic foundations. However its performance in practical situations is less well understand. The essence of the method is to identify clusters of extremes and estimate the required extremal properties based only on the cluster peaks. A simulation study is used here to assess the performance of the method. This study shows that while not robust to some of its arbitrary choices, such as cluster identification procedure, if clusters are identified using Ferro and Segers' (2003) automatic procedure then the peaks-over-threshold method typically gives accurate estimates of extremal properties. It is often common for extreme values to be affected by external factors. For example environmental extremes may be expected to behave differently at different times of the year. Incorporating beliefs about external factors was recognised early on in the development of extremal models as an important consideration, and a simple way in which this can be achieved is by allowing parameters of extremal distributions to depend on covariates. The work here considers whether choosing logical covariate forms for variation in parameters leads to improved estimation of extremal properties. It is found that a degree of improved accuracy in estimates can be achieved upon choice of a suitable model. but that the uncertainty in estimates, which is important to report, is poorly quantified.
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Santiago-GermaÌn, Wenceslao. "Space-time structure and hidden dimensions". Thesis, University of Newcastle Upon Tyne, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289215.
Testo completo
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Wilson, Daniel. "Local time-space calculus with applications". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/local-timespace-calculus-with-applications(f04e32e3-4c9b-4348-a7f3-803dee125e43).html.
Testo completo
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Fitriani. "Multiscale Dynamic Time and Space Warping". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45279.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2008.Includes bibliographical references (p. 149-151).
Dynamic Time and Space Warping (DTSW) is a technique used in video matching applications to find the optimal alignment between two videos. Because DTSW requires O(N4) time and space complexity, it is only suitable for short and coarse resolution videos. In this thesis, we introduce Multiscale DTSW: a modification of DTSW that has linear time and space complexity (O(N)) with good accuracy. The first step in Multiscale DTSW is to apply the DTSW algorithm to coarse resolution input videos. In the next step, Multiscale DTSW projects the solution from coarse resolution to finer resolution. A solution for finer resolution can be found effectively by refining the projected solution. Multiscale DTSW then repeatedly projects a solution from the current resolution to finer resolution and refines it until the desired resolution is reached. I have explored the linear time and space complexity (O(N)) of Multiscale DTSW both theoretically and empirically. I also have shown that Multiscale DTSW achieves almost the same accuracy as DTSW. Because of its efficiency in computational cost, Multiscale DTSW is suitable for video detection and video classification applications. We have developed a Multiscale-DTSW-based video classification framework that achieves the same accuracy as a DTSW-based video classification framework with greater than 50 percent reduction in the execution time. We have also developed a video detection application that is based on Dynamic Space Warping (DSW) and Multiscale DTSW methods and is able to detect a query video inside a target video in a short time.
by Fitriani.
S.M.
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Feldgoise, Jeffrey. "Thermal design through space and time". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/65983.
Testo completoAbstract (sommario):
Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1997.Includes bibliographical references (p. 89-90).
One of the primary roles of architecture is to control the environment at the service of a building's inhabitants. Thermal qualities are a significant factor in the overall experience one has inside and outside a building. However, thermal issues are not often considered within the context of the architectural design process, resulting in buildings that are not responsive to thermal concerns. Heat has the potential to influence the form of architectural space. The methods by which architects can use thermal energy as a formative element in design is open to further exploration. In this thesis, I explore new methods for architects to describe thermal intentions and visualize thermal qualities of design proposals. Beyond the economic issue of energy conservation, the thermal qualities of building spaces affect the quality of human inhabitation. The capability to describe and visualize heat would allow architects to adjust the building's thermal characteristics to modify a person's experience of the place. With a more complete understanding of thermal qualities of their building proposals, architects would be able to design for the complete gamut of thermal sensations that humans can experience. What is needed is a working vocabulary that describes the range of thermal conditions possible in buildings. In this work, I describe a vocabulary for a building's thermal qualities using four sets of measurable, opposing terms: open versus protected, bright versus dim, warm versus cool, and active versus still. Next, I then articulate the thermal qualities of a co-housing project to create a thermal experience that enhances the community aspects of co-housing. Using a variety of visualization techniques, I verify that the design proposal is achieving the intended thermal goals. Using the knowledge gained from this and future thermal design exercises, we can begin to reflect on the general relationships between thermal phenomena and physical building forms, learning about the thermal qualities of architecture.
Jeffrey Feldgoise.
M.Arch.
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Dodis, Yevgeniy 1976. "Space-time tradoffs for graph properties". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/47497.
Testo completo
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Brodsky, Micah Z. (Micah Zev). "Synthetic morphogenesis : space, time, and deformation". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92963.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 127-133).
Synthetic biology has presented engineers with a fascinating opportunity: can we understand the principles of our origins { animal embryonic development - by re-engineering it in the laboratory? I investigate, from an engineer's perspective, some of problems that arise in developing geometric form in a deformable substrate. More abstractly, I attack the problem of establishing spatial patterns, when rearranging and deforming parts of the system is inherent to the process. Deformable, foam-like cellular surfaces are developed as a model for embryonic epithelia (polarized cellular sheets), one of the principal tissue types in early animal development. I explore ways in which simple agent programs running within the individual cells can collectively craft large-scale structures. The mechanical properties of the substrate prove crucial to the patterning process. In such a distributed, heterogeneous substrate, little can be assumed about the progress of time. In one branch of my work, I develop patterning techniques where convergence is transparently and locally detectable, drawing insights from clockless digital circuits and casting the problem as distributed constraint propagation. In another branch of work, I avoid the problem of timing by making all patterns self- correcting. In self-correcting patterning, I attempt to understand "canalization" - how development is naturally robust to perturbations. I formulate a model for regional patterning, inspired by regeneration experiments in developmental biology, and using mathematical principles from classical models of magnetic domains and phase separation. The problem again becomes a form of distributed constraint propagation, now using soft constraints. I explore some of the resulting phenomena and then apply the mechanism to crafting surface geometries, where self-correction makes the process robust to both damage and self-deformation. I conclude with a look at how this naturally leads to an example of partial redundancy { multiple systems that partly but not completely overlap in function - yielding confusing responses to the effects of virtual knock-out experiments, reminiscent of the confusing behavior of knock-out experiments in biology.
by Micah Z. Brodsky.
Ph. D.
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Hunn, Craig Andrew. "Chronobiogeography : synthesising time, space and phylogeny". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619995.
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Kandler, Anne, e James Steele. "Innovation diffusion in time and space". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188644.
Testo completoAbstract (sommario):
In this paper we consider the spread of modern technological innovations. We contrast social learning and threshold heterogeneity models of innovation diffusion, and show how the typical temporal evolution of the distribution of adopters may be consistent with either explanation. Noting the likelihood that each model contains some useful independent explanatory power, we introduce a combined model. We also consider a spatially-structured population in which the spread of an innovation by social influence is modelled as a reaction-diffusion system, and show that the typical spatiotemporal evolution of the distribution is also consistent with a heterogeneity explanation. Additional contextual information is required to estimate the relative importance of social learning and of economic inequalities in observed adoption lags.
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Jensen, Michael A., e Michael D. Rice. "SPACE-TIME CODING FOR WIRELESS COMMUNICATIONS". International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/605605.
Testo completoAbstract (sommario):
International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, CaliforniaSignal fading and intersymbol interference created by multipath propagation have traditionally limited the throughput on wireless communications systems. However, recent research has demonstrated that by using multiple antennas on both transmit and receive ends of the link, the multipath channel can actually be exploited to achieve increased communication throughput over single-antenna systems. This paper provides an introductory description of such multi-antenna communications systems, focusing on basic explanations of how they achieve capacity gains. Computed and measured capacity results are used to demonstrate the potential of these systems.
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Elmabrouk, T. "Visualizing light cones in space-time". Thesis, Coventry University, 2013. http://curve.coventry.ac.uk/open/items/2d7e9956-f278-475c-b230-5a7a9dd08647/1.
Testo completoAbstract (sommario):
Although introductory courses in special relativity give an introduction to the causal structure of Minkowski space, it is common for causal structure in general space- times to be regarded as an advanced topic, and omitted from introductory courses in general relativity, although the related topic of gravitational lensing is often included. Here a numerical approach to visualizing the light cones in exterior Schwarzschild space taking advantage of the symmetries of Schwarzschild space and the conformal invariance of null geodesics is formulated, and used to make some of these ideas more accessible. By means of the Matlab software developed, a user is able to produce figures showing how light cones develop in Schwarzschild space, starting from an arbitrary point and developing for any length of time. The user can then interact with the figure, changing their point of view, or zooming in or out, to investigate them. This approach is then generalised, using the symbolic manipulation facility of Matlab, to allow the user to specify a metric as well as an initial point and time of development. Finally, the software is demonstrated with a selection of metrics.
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Alfowzan, Mohammed Fowzan, e Mohammed Fowzan Alfowzan. "Solutions to Space-Time Inverse Problems". Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621791.
Testo completoAbstract (sommario):
Two inverse problems are investigated in this dissertation, taking into account both the spatial and temporal aspects. The first problem addresses the under determined image reconstruction problem for dynamic SPECT. The quality of the reconstructed image is often limited due to having fewer observations than the number of voxels. The proposed algorithms make use of the generalized α-divergence function to improve the estimation performance. The first algorithm is based on an alternating minimization framework to minimize a regularized α-divergence objective function. We demonstrate that selecting an adaptive α policy depending on the time evolution of the voxels gives better performance than a fixed α assignment. The second algorithm is based on Newton's method. A regularized approach has been taken to avoid stability issues. Newton's method is generally computationally demanding due to the complexity associated with inverting the Hessian matrix. A fast Newton-based method is proposed using majorization-minimization techniques that diagonalize the Hessian matrix. In dynamically evolving systems, the prediction matrix plays an important role in the estimation process. An estimation technique is proposed to estimate the prediction matrix using the α-divergence function. The simulation results show that our algorithms provide better performance than the techniques based on the Kullback-Leibler distance. The second problem is the recovery of data transmitted over free-space optical communication channels using orbital angular momentum (OAM). In the presence of atmospheric turbulence, crosstalk occurs among OAM optical modes resulting in an error floor at a relatively high bit error rate. The modulation format considered for the underlying problem is Q-ary pulse position modulation (PPM). We propose and evaluate three joint detection strategies to overcome the OAM crosstalk problem: i) maximum likelihood sequence estimation (MLSE). ii) Q-PPM factor graph detection. iii) branch-and-bound detection. We compare the complexity and the bit-error-rate performance of these strategies in realistic scenarios.
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Tomasevic, Marija. "Quantum Aspects of Space and Time". Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672688.
Testo completoAbstract (sommario):
In this thesis, we explore different ways in which spacetime exhibits peculiar properties when subjected to the rules of quantum mechanics. These rules are naturally implemented at the level of semiclassical physics, where the dynamical nature of the spacetime metric is neglected. In particular, we explore how quantum effects modify some of the fundamental statements of General Relativity, ranging from different possible solutions, such as traversable wormholes and time machines, to some of the more foundational conjectures, with an emphasis to the one of cosmic censorship.
Chapter One takes a deeper look into the connection between geometry and entropy. We revisit the original reasoning leading to their entwinement, and we clarify the different notions of entropy that play a role in it. We emphasize the recurring theme and the pattern in such a relationship: how the union between area and entropy makes sense when put together on the same footing, hinting towards a deeper meaning in a complete theory of quantum gravity. This seemingly simple unification is then shown to lead to incredible results, ranging from improved conjectures about quantum gravity, to illuminating one of the most critical problems of modern theoretical physics - the black hole information paradox. In particular, we mainly focus on one example of semiclassical statements, the (quantum) Penrose inequality, and we show in detail the difficulties one has to overcome for a meaningful conjecture to hold. Furthermore, we revise the basic arguments underlying the recent progress regarding the black hole interior and lay out the possible paths to the interpretation of these striking results.
Chapter Two explores different solutions that classical General Relativity forbade, but quantum physics advanced. A number of no-go theorems get circumvented, and configurations previously thought of as impossible become available, and even natural. This is especially clear for solutions such as traversable wormholes and their inherent use in studies of entanglement structures. Indeed, such connections will be relevant in gauge/gravity duality for a fuller understanding of the holographic dictionary. But we can also see the way in which other no-go theorems become easier to infer. In essence, the creation of closed causal curves was understood as a problem of quantum gravity due to the incredibly high energies one seems to need for their demise. However, we show how simple, low-energy arguments are enough to shatter the fiction of time machines.
The final Chapter Three perhaps comes closer to the study of quantum gravity than the previous ones. We undertake the problem of naked singularities in gravity, and we see how including quantum effects solidifies some foundational statements while completely fragmenting other ones. In a nutshell, the strong cosmic censorship conjecture is shown to be on much firmer ground than previously thought. Quantum physics is used to destabilize the relevant Cauchy horizon once and for all. However, including quantum effects necessarily means we must abandon our na¨ıve understanding of the weak cosmic censorship and embark on a much stranger path towards a meaningful statement about naked singularities. In doing so, we discuss the purpose of cosmic censorship and its interpretation in the realm of quantum gravity.
We finish the dissertation with a summary and a further discussion on the nature of naked sin- gularities, providing a framework in which these questions can be meaningfully posed. After a brief overview of recent developments in this research line, we discuss the possible ways in which we can tackle such a perplexing problem. Namely, the role of critical phenomena in gravitational collapse is emphasized, and a proposal for a future study is outlined.Como es propio de toda teoría clásica, la Relatividad General no puede aspirar a ser más que una teoría efectiva, cuyo campo de estudio se reduce al de fenómenos emergentes de estructuras más elementales. Sin embargo, se trata de una teoría dificil de tratar al poseer propiedades no compartidas por el resto de teorías clásicas: una descripción holográfica. A pesar de no haber proporcionado todas las respuestas que buscábamos acerca de la naturaleza del espacio y del tiempo, la holografía ha jugado un papel fundamental; en especial mostrándonos una conexión entre nociones tan dispares como la información cuántica y la geometría, similar a la conexión que Gibbons y Hawking [1] dieron a conocer entre el área y la entropía. Esta tesis tiene como objetivo el estudio de casos en los que esta relación se vuelve manifiesta, usando el régimen semiclásico de gravedad. El primer capítulo profundiza en la conexión entre área y entropía y algunas de las consecuencias que esta implica: la formulación semiclásica de la Desigualdad de Penrose y las posibles intepretaciones relativas al interior de los agujeros negros. El segundo capítulo se adentra en el estudio de escenarios prohibidos por la Relatividad General pero que resultan accesibles, y naturales, al considerar efectos cuánticos. Se centra en los agujeros de gusano y su relación con el entrelazamiento cuántico (a través de la dualidad “gauge/gravity”), así como en la imposibilidad de transformarse en máquinas del tiempo. El capítulo tercero es el que más avanza hacia el régimen cuántico de la gravedad, explorando el problema de las singularidades desnudas y la Hipótesis de la Censura Cósmica. Se muestra cómo la versión fuerte sale reforzada tras un análisis semiclásico, mientras que la versión débil requiere de nuevas reinterpretaciones para su adaptación a la nueva realidad cuántica. Finalmente se ofrece un resumen junto con una discusión adicional sobre la naturaleza de las singularidades desnudas, con un pequeño repaso sobre los avances en este campo y las posibles rutas que tomar, haciendo hincapié en el papel del colapso crítico gravitatorio y proponiendo una línea de investigación más allá de esta tesis. Bibliografía: [1] G. W. Gibbons and S. W. Hawking, “Action integrals and partition functions in quantum gravity,” Phys. Rev. D 15 (May, 1977) 2752–2756. https://link.aps.org/doi/10.1103/PhysRevD.15.2752.
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Al-Ghadhban, Samir Naser. "Multi-layered Space Frequency Time Codes". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29498.
Testo completoAbstract (sommario):
This dissertation focuses on three major advances on multiple-input multiple-output (MIMO) systems. The first studies and compares decoding algorithms for multi-layered space time coded (MLSTC) systems. These are single user systems that combine spatial multiplexing and transmit diversity. Each layer consists of a space time code. The detection algorithms are based on multi-user detection theory. We consider joint, interference nulling and cancellation, and spatial sequence estimation algorithms. As part of joint detection algorithms, the sphere decoder is studied and its complexity is evaluated over MIMO channels. The second part contributes to the field of space frequency time (SFT) coding for MIMO-OFDM systems. It proposes a full spatial and frequency diversity codes at much lower number of trellis states. The third part proposes and compares uplink scheduling algorithms for multiuser systems with spatial multiplexing. Several scheduling criteria are examined and compared.
The capacity and error rate study of MLSTBC reveals the performance of the detection algorithms and their advantage over other open loop MIMO schemes. The results show that the nulling and cancellation operations limit the diversity of the system to the first detected layer in serial algorithms. For parallel algorithms, the diversity of the system is dominated by the performance after parallel nulling. Theoretically, parallel cancellation should provide full receive diversity per layer but error propagations as a result of cancellation prevent the system from reaching this goal. However, parallel cancellation provides some gains but it doesn't increase the diversity. On the other hand, joint detection provides full receive diversity per layer. It could be practically implemented with sphere decoding which has a cubic complexity at high SNR.
The results of the SFT coding show the superiority of the IQ-SFT codes over other codes at the same number of sates. The IQ-SFT codes achieve full spatial and frequency diversity at much lower number of trellis states compared to conventional codes. For V-BLAST scheduling, we propose V-BLAST capacity maximizing scheduler and we show that scheduling based on optimal MIMO capacity doesn't work well for V-BLAST. The results also show that maximum minimum singularvalue (MaxMinSV) scheduling performs very close to the V-BLAST capacity maximizing scheduler since it takes into account both the channel power and the orthogonality of the channel.Ph. D.
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Thomas, Zachary Micah. "Bayesian Hierarchical Space-Time Clustering Methods". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1435324379.
Testo completo
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Nelson, N. Thomas. "Space-Time Coding with Offset Modulations". Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2155.pdf.
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Díaz, Avalos Carlos. "Space-time analysis of forest fires /". Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/6375.
Testo completo
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Vee, Erik. "Time-space tradeoffs for nonuniform computation /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/6915.
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Tanaksaranond, G. "Visualisation of traffic in space-time". Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1418541/.
Testo completoAbstract (sommario):
Road traffic congestion is the most persistent and debilitating problem in nearly all cities. Understanding congestion in space-time can greatly facilitate understanding of the beginning and evolution of congestion. Visualisation can be a tool to solve traffic congestion by getting insight into traffic data. This thesis focuses on developing visualisation techniques that can reveal space-time characteristics of traffic congestion, inclusive of how traffic congestion starts, disperses, and dissipates over the road network. Three main techniques are developed in this thesis, which include: wall map, isosurface, and constraint isosurface. The 3D wall map visualises the change of traffic and highlights congestion on each link. The 3D isosurface reveals sizes and shapes, and also the development of congestion. The constrained isosurface gives similar information to the isosurface, but locations of congestion are more localized. The three methods show how the origins and dispersion of congestion occurred. They also show different details of traffic data. A Graphic User Interface (GUI) was developed to allow users to interact with the traffic data and also to manipulate the visualisation to effectively support the identification of congested areas and relevant spatio-temporal information. The user-centred design approach was employed from the beginning of the GUI design process to ensure the ease of use. The massive amounts of traffic data are organised by data warehousing and by online analytical processing (OLAP) techniques, which improve multidimensional query response time. The system is implemented for link travel time data from Automatic Number Plate Recognition (ANPR). The combination of visualisation techniques with GUI and effective data management can help traffic managers to better understand how traffic congestion changes on the road network, and to uncover the solutions to congestion.
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Nahmias, J. "Real time sub-pixel space-time stereo on the GPU". Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1389423/.
Testo completoAbstract (sommario):
Recent advances in virtual reality, 3d computer generated graphics and computer vision are making the goal of producing a compelling interactive 3d face to face communication system more tractable. The problem with producing such a system is reconstructing the 3d geometry of the users in real-time. There are many ways of tackling this problem however many of them require prior knowledge (i.e model fitting methods). These add unnecessary constraints and limit the usability of the system to reconstructing known entities. Other high quality methods using laser triangulation require too many samples and therefore cannot handle dynamic and deformable shapes such as the human face. A more suited approach is to use stereo based algorithm that function using two of more views and augmenting their capabilities using structured light. The work presented in this thesis will examine and evaluate various stereo vision algorithms and hybrids with the goal of producing accurate 3d representations of human faces in real time. Various dynamic programming algorithms will be presented and hybrid variations. These will be extended into the space-time domain and the impact of using different structured light patterns with various algorithms and cost functions will be examined. Most real-time correspondence algorithms are limited to producing pixel value disparities; these can be augmented into producing sub-pixel disparities by smoothing functions. Applying such smoothing functions tends to remove detail. Another approach is to use non-linear optimization on a spatial-temporal warp function. These algorithms tend to be very computationally expensive and therefore not feasible for real time applications. With recent development of GPUs (Graphics Processing Units) driven by the consumer demand for complex real time 3d graphics, these cards are capable of processing large amounts of data in parallel. This makes them very amenable to solving large linear algebra problems. . The result being a tuneable stereo reconstruction framework that has been reformulated into streaming problems in order to be processed on the GPU to produce real time sub-pixel depth maps of human faces that can be triangulated to produce accurate 3d models.
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Lin, Chengjiang. "Time and Space Efficient Wavelet Transform for Real-Time Applications". The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1392314817.
Testo completo