In this project we review the method of using c-extremization and computing anomalies to obtain AdS/CFT theories. We start with a quick introduction to CFT's and AdS/CFT correspondence which gives us the tools to later understand the 2D N= (2,0) SCFT and its gravity duals in particular AdS_5xS^5 and AdS_7xS^4 compactified on Riemann surfaces.

Abstract Peer-to-Peer (P2P) networks have been applied in many applications for sharing resources such as storage space, media files or network bandwidth. Their main benefits include decentralization, self-organization, and scalability. Moreover, P2P technologies are evolving towards hybrid systems, where P2P networks are used in those parts of a larger system to leverage the decentralization most efficiently. The examples include cloud computing, where P2P networks are used in sharing computing resources, and Machine-to-Machine communication, where P2P networks are used for resource discovery. In super-peer overlays, the nodes are either regular nodes or super nodes that are located higher in the node hierarchy. This type of overlay explores the heterogeneity of peers in the overlay network to enable applications to run more efficiently. Leveraging the advantage of a super-peer overlay for service provision is an important issue. This thesis contributes to the research and development of super-peer-based coordination service provision from three aspects. Firstly, a super-peer-based coordinated service provision framework is proposed to coordinate different service groups and service peers in resource sharing, aiming to enable service groups to adapt to dynamic service demands. The proposed framework is evaluated using the following performance metrics: service response time, scalability, robustness, and communication traffic, in comparison to related work. Secondly, an efficient algorithm for rapidly constructing a robust super-peer overlay is proposed. The algorithm introduces a super-peer candidate based method for super-peer selection and a two-hop search method for finding client peers. Performance evaluation takes into account the convergence time of building a super-peer overlay, communication overhead, scalability, robustness. A comparison to related work is also conducted. Thirdly, the architecture of distributed resource discovery based on P2P overlay for Machine-to-Machine service provision is proposed. The architecture supports heterogeneous devices using different communication protocols in resource registration and discovery for achieving interoperability. As a part of the thesis, a functional real-world prototype is implemented and verified with a simple demonstration. Preliminary evaluation on the prototype indicates that caching can improve the response time of resource lookup dramatically. / Tiivistelmä Vertaisverkkoja on hyödynnetty resurssien kuten tallennustilan, mediasisältöjen ja tietoliikennekapasiteetin jakamisessa. Niiden etuja perinteisiin keskitettyihin järjestelmiin verrattuna ovat hajautettu arkkitehtuuri, itseorganisoituvuus ja skaalautuvuus. Vertaisverkkoja käytetään yhä useammin järjestelmän osien toteuttamisessa, joissa hajautettujen resurssien hyödyntämisellä saavutetaan suurimmat edut. Esimerkkeinä ovat pilvilaskenta, jossa vertaisverkkoa käytetään laskentaresurssien jakamiseen, sekä laitteidenvälinen kommunikaatio, jossa vertaisverkkoja käytetään resurssien löytämiseen. Hierarkkisissa vertaisverkoissa niihin kytkeytyneet laitteet jaotellaan laitteiden kapasiteetin mukaan tavallisiin noodeihin ja näiden yläpuolella hierarkiassa toimiviin ylinoodeihin. Ylinoodeihin perustuva vertaisverkon kuoriverkko hyödyntää yksittäisten verkon noodien eli laitteiden erilaisuutta, jotta verkko voisi toimia tehokkaammin. Tämän ominaisuuden hyödyntäminen on erityisen tärkeää palvelun tarjonnassa. Tässä työssä on tutkittu ylinoodeihin perustuvan vertaisverkon palvelun tarjontaa kolmesta näkökulmasta. Ensimmäiseksi, työssä ehdotetaan ylinoodien koordinoimaa palveluntarjonnan toimintamallia resurssien jakamisessa. Toimintamallissa palveluryhmät ja palvelunoodit adaptoituvat dynaamisesti palvelupyyntöjen tarpeisiin. Tämän ratkaisun suorituskykyä arvioidaan palvelun vasteajan, skaalautuvuuden, robustisuuden ja tietoliikennemäärän suhteen verrattuna aiempiin ratkaisuihin. Toiseksi, työssä esitellään tehokas algoritmi robustin ylinoodikuoriverkon nopeaan muodostamiseen. Algoritmi käyttää ylinoodiehdokasmenetelmää ja kahden hypyn hakumetodia asiakasnoodien etsimisessä. Suorituskyvyn arvioinnissa otetaan huomioon ylinoodikuoriverkon konvergoitumisaika, tietoliikenneviestinnän aiheuttama ylimääräinen kuormitus, sekä järjestelmän skaalautuvuus ja robustisuus. Esitetyn algoritmin tehokkuutta arvioidaan vertaamalla näitä suorituskykymittareita aiempiin ratkaisuihin. Kolmanneksi, työssä esitellään hajautettu resurssihakemiston arkkitehtuuri, joka perustuu laitteiden välisen kuoriverkon palveluntarjontaan. Arkkitehtuuri tukee erilaisten laitteiden ja niiden käyttämien protokollien resurssien rekisteröintiä ja löytämistä yhteensopivuuden saavuttamiseksi. Väitöskirjatyön osana on toteutettu toimiva prototyyppi, jonka toimivuus on todennettu demonstraation avulla. Prototyypillä tehdyt mittaukset antavat perustellun syyn olettaa, että esitetyn ratkaisun mukainen välimuistin käyttö voi merkittävästi lyhentää resurssien etsimisen vasteaikaa.

L’étude précise des transitions ß de Fermi super-permises 0+ ? 0+ offre un outil précieux pour explorer les propriétés de l’interaction faible dans le cadre du Modèle Standard (SM). Collectivement, les forces (ft) mesurées pour ces transitions permettent de vérifier l’hypothèse CVC et contribuent au test le plus rigoureux de l’unitarité de la première ligne de la matrice de mélange des quarks CKM en fournissant l’évaluation la plus précise de l’élément dominant (Vud). Jusqu’à récemment, un apparent défaut d’unitarité a semé le doute sur la validité du SM minimal et a mobilisé un effort considérable afin d’élargir le champ d’étude à d’autres émetteurs de Fermi. Le 62Ga et 38Ca sont parmi des noyaux clés pour mener ces tests de précision au travers de la vérification de la fiabilité des corrections imposées aux valeurs ft expérimentales. La décroissance ß de 62Ga a été étudiée auprès du séparateur IGISOL à Jyväskylä, avec un dispositif composé de 3 Clovers EUROBALL pour la détection du rayonnement ?. La mise en évidence de raies ? de très faible intensité (<1‰), au travers de corrélations ß-? et ß-?-?, a permis de reconstruire partiellement le schéma de niveaux excités dans le 62Zn. Le rapport d’embranchement analogue déduit (B.R.A = 99.893(24) %) est utilisé pour extraire la valeur Ft(62Ga) universelle. Celle-ci s’avère en bon accord avec les 12 valeurs précises connues de la littérature. La compatibilité constatée entre la limite supérieure dressée ici sur le terme (d1IM) et la prédiction théorique confirme l’importance des corrections de brisure de symétrie d'isospin dans les émetteurs ß (A = 62). L’étude de la décroissance de 38Ca a été réalisée auprès de l’installation ISOLDE du CERN. L’utilisation de la fluoration des fragments de réaction, pour isoler chimiquement les isotopes d’intérêt, alliée au piégeage d’ions assisté par REXTRAP et l’analyse TOF, ont permis de s’affranchir totalement du contaminant contraignant 38mK. Pour la première fois, la durée de vie de 38Ca est mesurée avec un échantillon de haute pureté. Le résultat préliminaire établi T1/2(38Ca) = 445.8(10) ms améliore la précision par rapport à l’ancienne valeur d’un facteur proche de 10. / Precise measurements of Fermi superallowed 0+? 0+ ß decays provide a powerful tool to study the weak interaction properties in the framework of the Standard Model (SM). Collectively, the comparative half-lives (ƒt) of these transitions allow a sensitive probe of the CVC hypothesis and contribute to the most demanding test of the unitarity of the quarks-mixing CKM matrix top-row, by providing, so far, the most accurate determination of its dominant element (Vud). Until recently, an apparent departure from unity enhanced a doubt on the validity of the minimal SM and thus stimulated a considerable effort in order to extend the study to other Fermi emitters available. The 62Ga and 38Ca are among key nuclei to achieve these precision tests and verify the reliability of the corrections applied to the experimental ƒt-values. The 62Ga ß-decay was investigated at the IGISOL separator in Jyväskylä, with an experimental setup composed of 3 EUROBALL Clovers for ?-ray detection. Very weak intensity (<1‰) ?-rays were identified, via ß-? and ß-?-? correlations, and allowed a partial decay scheme reconstruction in 62Zn. The newly established analog branching-ratio (B.R.A = 99.893(24) %) was used to compute the universal Ft-value (62Ga). The latter turned out to be in good agreement with the 12 well-known cases. Compatibility between the upper limit set here on the term (d1IM) and the theoretical prediction suggests that the isospin-symmetry-breaking correction is indeed large for the heavy (A = 62) ß-emitters. The study of the 38a decay was performed at the CERN- ISOLDE facility. Injection of fluorine into the ion source, in order to chemically select the isotopes of interest, assisted by the REXTRAP Penning trap facility and a TOF analysis, enabled us to eliminate efficiently the troublesome 38mK. For the first time, the 38Ca half-life is measured with a highly purified radioactive sample. The preliminary result obtained, T1/2(38Ca) = 445.8(10) ms, improves the precision on the half-life as determined from previous measurements by a factor close to 10.

Doctor of Philosophy / Department of Physics / Zenghu Chang / The first part of this thesis describes our novel design, test, and application of our X-ray streak camera to the pulse duration measurement of soft X-rays. We demonstrated a significant improvement in the resolution of the x-ray streak camera by reducing the electron beam size in the deflection plates. This was accomplished by adding a slit in front of the focusing lens and the deflection plates. The temporal resolution reached 280 fs when the slit width was 5 μm. The camera was operated in an accumulative mode and tested by using a 25 fs laser with 2 kHz repetition rate and 1-2% RMS pulse energy stability. We conclude that deflection aberrations, which limit the resolution of the camera, can be appreciably reduced by eliminating the wide-angle electrons. We also employed the same streak camera to demonstrate that it is capable of measuring the pulse duration of X-rays. We measured the pulse duration of X-rays emitted from Ni-like Ag and Cd grazing-incidence laser to be ~5ps. The measured value agrees with the prediction made by the model and the measurement made by changing the delay as a function of the pulse duration. The streak camera was also tested with various sources of X-ray such as high harmonics generation of soft x-rays from an argon atom using a high power Ti:sapphire laser source of KLS. The result of the measurement manifests its capability for serving as a detector in the study of ultrafast dynamics in the field of physics, chemistry, biology and medical sciences. The second part of this thesis describes our design of a spectrometer to study the effect of the Carrier envelope (CE) phase on polarization gated extreme-ultraviolet (XUV) super-continuum generation. Because the challenge of making single shot experiment possible is to generate a sufficient number of photons, our setup has been built to allow generation of high order harmonics at the maximum phase matched pressure. This is the first time to our knowledge that phase matching in the polarization gating process has been studied so far. We measured the maximum phase matching pressure to be ~ 55 Torr which is the pressure above which quadratic increase in intensity of the high harmonics spectrum ceases to appear. At this pressure the number of photons per laser shot was 104 which is sufficient for measuring the single shot XUV spectrum in the range 34 to 45 eV. The spectral profile was a super-continuum for some shots and discrete high harmonics for other shots. It is believed that the shot to shot variation of the spectra is due to the changes of the carrier envelope phase of the few-cycle laser pulses used for the polarization gating. An improved CE phase stabilization system in KLS further eliminated the statistical noise in our observation by allowing us to integrate data over several laser cycles for each CE phase value. The effect of CE phase on a polarization gated XUV spectrum was tested by changing the CE phase with two different methods. In the first method, the CE phase was changed by changing the thickness of fused silica plates on the beam path, and the result shows the shift in the spectral peak of the XUV when the gate width approached less than one optical cycle. As gate width was made less than half the optical cycle, the spectrum was observed with continuum harmonics separated by π radians. We believe that the presence of continuum and discrete harmonics spectra in the observation is due to single and double attosecond pulses generated in the polarization gating. In the second method the carrier-envelope phase of pulses from a grating-based chirped pulse amplification laser was varied smoothly to cover a 2π range by controlling the grating separation. The phase is measured simultaneously by an f-to-2f setup and by the variation of XUV spectra from polarization gated high harmonic generation. A very good similarity between the effect of single and double slits in Yong’s experiment and that of CE phase on the XUV spectrum in the polarization gating experiment has been found, giving better agreement with the theory. The effect of optical properties such as the Gouy phase shift on the polarization gated spectrum has also been studied in the course of investigating the best experimental optimizations to generate the most CE phase sensitive XUV spectrum with less statistical noise. This is the first time to our knowledge experimental study of the effect of the Gouy phase shift on a polarization gated XUV spectrum has been made.

No description available.

High quality image /video has become an integral part in our day-to-day life ranging from many areas of science, engineering and medical diagnosis. All these imaging applications call for high resolution, properly focused and crisp images. However, in real situations obtaining such a high quality image is expensive, and in some cases it is not practical. In imaging systems such as digital camera, blur and noise degrade the image quality. The recorded images look blurred, noisy and unable to resolve the finer details of the scene, which are clearly notable under zoomed conditions. The post processing techniques based on computational methods extract the hidden information and thereby improve the quality of the captured images. The study in this thesis focuses on deconvolution and eventually blind de-convolution problem of a single frame captured at low light imaging conditions arising from digital photography/surveillance imaging applications. Our intention is to restore a sharp image from its blurred and noisy observation, when the blur is completely known/unknown and such inverse problems are ill-posed/twice ill-posed. This thesis consists of two major parts. The first part addresses deconvolution/blind deconvolution problem using Bayesian approach with fuzzy logic based gradient potential as a prior functional. In comparison with analog cameras, artifacts are visible in digital cameras when the images are enlarged and there is a demand to enhance the resolution. The increased resolution can be in spatial, temporal or even in both the dimensions. Super resolution reconstruction methods reconstruct images/video containing spectral information beyond that is available in the captured low resolution images. The second part of the thesis addresses resolution enhancement of observed monochromatic/color images using multiple frames of the same scene. This reconstruction problem is formulated in Bayesian domain with an aspiration of reducing blur, noise, aliasing and increasing the spatial resolution. The image is modeled as Markov random field and a fuzzy logic filter based gradient potential is used to differentiate between edge and noisy pixels. Suitable priors are adaptively applied to obtain artifact free/reduced images. In this work, all our approaches are experimentally validated using standard test images. The Matlab based programming tools are used for carrying out the validation. The performance of the approaches are qualitatively compared with results of recently proposed methods. Our results turn out to be visually pleasing and quantitatively competitive.

The thesis entitled Comparison of revenue and expenditure of the state budget for the self-employed and employees for the entire active and retirement period of life of individuals under conditions of 2015 deals with how, whether and under what conditions the self-employed are less taxed than their colleagues working in full-time employment with a comparable income. The model example points out the income threshold at which individual is better off being self-employed, and when it is more advantageous from the viewpoint of the state to be an independent contractor, not an employee. The models include the self-employed, who are misclassified as well as factors such as different amount of sick leave, lower pensions, lower unemployment benefits caused by lower deductions for social insurance, and other factors that are not immediately obvious but markedly influence the total amount of income and expenses to the state of the individual when working as self-employed or an employee.

Cette thèse porte sur l’étude de la synthèse et des données thermodynamiques des clathrates intermétalliques du système Na-Si, qui sont des matériaux pertinents pour les applications thermoélectriques et qui sont les précurseurs pour de nouvelles formes de Si prometteuses pour des applications photovoltaïques et photoniques. Dans ce travail la formation de clathrates Na-Si a été étudiée in situ et ex situ sous haute pression et haute température. Un nombre de nouvelles formes de silicium a été observé en chauffant des clathrates sous vide. Sous pression inférieure à 3 GPa les clathrates ne se forment pas par l’interaction des éléments. A la place, le siliciure Na4Si4 se forme et reste stable jusqu’à la fusion. Au-dessus de 3 GPa, Na4Si4 formé au début du chauffage, réagit avec l’excès de Si et donne Na30Si136 (structure II) et ensuite, si Na30Si136 réagit avec l’excès de Si pour former Na8Si46 (structure I) au dessous de 7 GPa et le clathrate NaSi6 au-dessus de 7 GPa. Des expériences ont été réalisées en utilisant des cellules standard Paris-Edimbourg (enclumes opposées) jusqu'à 6 GPa et la presse multi-enclumes pour les pressions au-dessus de 6 GPa. La forte sensibilité des produits de cristallisation à la concentration en sodium a été observée. Un schéma de transformations de clathrate pour les pressions entre 0 à 10 GPa et températures entre 300 et 1500 K a été proposé. Le diagramme de phase (concentration – température sous 4 GPa) qui représente les transformations observées et les domaines de stabilité a également été proposé et suggère l’existence de trois équilibres eutectiques : entre Si et structure I, entre structures I et II, et entre structure II et Na4Si4. Pour comprendre la thermodynamique et les interactions dans le système Na-Si, on a également effectué la modélisation du diagramme de phase à pression ambiante, ce que nous a permis de trouver les caractéristiques thermodynamiques de fusion et les équations des liquidus observés. Pour prendre en compte l’impact de la pression sur la thermodynamique, les équations d’état p-V-T de Si à structure diamant, structure I et la forme haute pression de structure II ont été utilisés. / The objective of this thesis is to study the synthesis and thermodynamics of intermetallic clathrates of the Na-Si system, which are the important materials for thermoelectric applications and are the promising precursors for new forms of Si for the photovoltaic and photonic applications. In this work the formation of the Na-Si clathrates have been studied in situ and ex situ at high pressure and high temperature. A number of new forms of silicon have been observed while heating the clathrates under vacuum. Under pressures below 3 GPa the clathrates does not form by the interaction of elements. Instead, the silicide Na4Si4 forms and remains stable up to melting. Above 3 GPa, Na4Si4 formed in the beginning of the heating, react with the excess of Si and gives Na30Si136 (structure II) and after that, if Na30Si136 react with the excess of Si, to form Na8Si46 (structure I) below 7 GPa and the clathrate NaSi6 above 7 GPa. The experiments have been performed by using the standard Paris-Edinburg cell (opposite anvils) up to 6 GPa and multianvil press for pressures above 6 GPa. The strong sensibility of the crystallization product to the concentration of sodium has been observed. The diagram of transformations in clathrates for pressures between 0 and 10 GPa and temperatures between 300 and 1500 K has been proposed. The phase diagram (concentration – temparature at 4 GPa) that represents the observed transformations and stability domains has been also proposed and suggests the existence of three eutetic equilibria: between Si and structure I, between structures I and II, and between structure II and Na4Si4. To understand the thermodynamics and interactions in the system Na-Si, the modelisation of phase diagram at ambient pressure has also been performed that allowed us to establish the thermodynamic characteristics of melting and the equations of observed liquidi. To take into account the impact of pressure on the thermodynamics, the p-V-T equations of state of diamond Si, structure I and high-pressure form of structure II have been used.

Cette thèse de doctorat traite de la mise en œuvre du procédé de soulèvement épitaxial (ou ELO pour epitaxial lift-off) à partir d'un substrat d'InP permettant le détachement des couches actives et le recyclage du substrat afin de rendre économiquement compétitive la fabrication de cellules solaires multi-jonctions pour le photovoltaïque concentré. Ce procédé, qui consiste à sous-graver sélectivement une couche sacrificielle comprise entre le substrat et les couches actives, est bien connu et maîtrisé sur un substrat de GaAs avec l'utilisation d'une couche sacrificielle d'AlAs d'épaisseur voisine de 5 nm, ce qui n'est pas possible sur un substrat d'InP en raison du fort désaccord de maille cristalline existant entre l'AlAs et l'InP. Pour l'adapter à un substrat d'InP, le développement d'une couche sacrificielle spécifique basée sur un super-réseau AlAs/InAlAs a été réalisé, ce qui permet de contourner les problématiques liées au désaccord de maille et à la croissance de matériaux contraints. Après optimisation des conditions de croissance de ce super-réseau, les épaisseurs atteintes et donc les vitesses de sous-gravure obtenues en utilisant ce type de couche sacrificielle ont satisfait aux exigences du procédé ELO. Ensuite, le report et le soulèvement de structures actives de cellules solaires InGaAs en couches minces cristallines ont été développés. Les cellules solaires ainsi fabriquées ont montré des performances semblables à celles réalisées par épitaxie standard sur un substrat d'InP, voire meilleures sous concentration en raison d'effets de confinement optique. Finalement, le recyclage du substrat d'InP réalisé avec un procédé utilisant seulement deux étapes de nettoyage par voies chimiques humides, a permis de produire des surfaces d'InP de qualité suffisante pour réaliser une reprise d'épitaxie satisfaisante. / This PhD thesis deals with the implementation of the epitaxial lift-off (ELO) process from an InP substrate allowing the detachment of active layers and the substrate recycling. The final target is to realize multi-junction solar cells in an economically competitive way for concentrated photovoltaic. The ELO process consists in the under-etching of a sacrificial layer inserted between the substrate and the active layers. It is well known and mastered on a GaAs substrate with the use of a sacrificial layer of AlAs with a thickness of about 5 nm. Such a layer is not usable on an InP substrate due to the high lattice mismatch between AlAs and InP. In order to adapt the ELO process to an InP substrate, this work aimed to develop a specific sacrificial layer based on an AlAs/InAlAs superlattice. Thus, it is possible to circumvent problems related to the lattice mismatch and to the strained layer growth. After optimization of growth conditions of this superlattice, using this type of sacrificial layer, we achieve a sufficient thickness and therefore a sufficient under-etching rate in order to meet the requirements of the ELO process. Then, the transfer and lift-off of thin crystalline film based InGaAs solar cells have been developed. This kind of solar cells showed performances similar to those obtained with a standard epitaxial growth on an InP substrate, or even better under concentration due to optical confinement effects. Finally, the recycling of the InP substrate carried out by a process using only two wet chemical cleaning steps made it possible to produce InP surfaces of sufficient quality to achieve a promising second epitaxial growth.

Dans cette thèse, on a d’abord considéré une équation d'onde. On a premièrement montré que l’équation est bien-posée presque sûre par la méthode de décomposition de fréquence de Bourgain sous l’hypothèse de régularité que s > 2(p−3)/(p-1). Ensuite, nous avons réduit de cette exigence de régulation à (p-3)/(p−1) en appelant une estimation probabiliste a priori. Nous considérons également l’approximation des solutions obtenues ci-dessus par des solutions lisses et la stabilité de cette procédure d’approximation. Et nous avons conclu que l’équation est partout mal-posée dans le régime de super-critique. Nous avons considéré ensuite l’équation du faisceau quintique sur le tore 3D. Et nous avons montré que cette équation est presque sûr bien-posée globalement dans certain régimes de super-critique. Enfin, nous avons prouvé que la mesure de l’image de la mesure gaussienne sous l’application de flot de l’équation BBM généralisé satisfait une inégalité de type log-Sobolev avec une petit peu de perte de l’intégrabilité. / In this thesis, we consider a wave equation. We first showed that the equation is almost sure global well-posed via Bourgain’s high-low frequency decomposition under the regularity assumption s > 2(p−3)/(p−1). Then we lowered down this regularity requirement to be (p−3)/(p−1) by invoking a probabilistic a priori estimate. We also consider approximation of the above achieved solutions by smooth solutions and the stability of this approximating procedure. And we concluded that this equation is everywhere ill-posed in the super-critical regime. Next, we considered the quintic beam equation on 3D torus. And we showed that this equation is almost sure global well-posed in certain super-critical regime. Lastly, we proved that the image measure of the Gaussian measure under the generalized BBM flow map satisfies a log-Sobolev type inequality with a little bit loss of integrability.