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Analýza různých technologií odchovu telatHAMPLOVÁ, Michaela January 2019 (has links)
In cattle breeding, it is necessary to pay great attention to calves, especially to the quality of their housing. Calf rearing is one of the riskiest parts of the whole breed. This requires a thorough development of biological, nutritional, ethological and technological factors of breeding. The aim of this thesis was to compare two different ways of housing calves (individually vs. pairs) in roofed outdoor individual boxes with feedeng twice a day and evaluate their influence on the course of growth and health from birth to weaning. The experiment was carried out at the Číčov farm, which i sone of the centers of Alimex a.s. Nezvěstice, farming in the district of Plzeň - South. The actual monitoring of the calves took place from 1. 1. 2018 to 31. 7. 2018. Both groups of calves included in the experiment were fed the same amount of feed (native milk, milk replacer, TMR). Each group had the same number of pieces - 12 calves (heifers) of the Holstein cattle breed. At the end of the reporting period, calves that were raised together in pairs at average weight of 227.17 kg during the dairy period, while calves reared individually during the same period reached a final weight of 215 kg. The average daily increase in calves with a common rearing was 0.89 kg, in calves of the second group this value was lower, namely 0.83 kg. However, tthe difference between the mean final weights of both groups was not statistically significant (p > 0.05). All calves included tn the exxperiment were fed with appropriate quality colostrum (immunoglobulin content of 100 g/l or more) within 2 hours of delivery. Immunity of all experimental calves was sufficient, so the level of immunoglobulins did not fall below 50 g/l, with more than 85 % of calves having an immunoglobulin content above 55 g/l. In calves reared individually during the experiment, diarrhea was noted in three animals and respiratory disease in four animals. In rearing together, there was diarrhea in five calves. Respiratory disease occured in four calves. In both experimental groups of calves, it was observed that immediately after drinking, the animals were mutually sucking mules, but the calves housed together with a lower frequency also licked the polypropylene plates separating the VIB and nibbled empty buckets.
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Avaliação genética do sistema reprodutivo dos Pinguins-de-Magalhães (Spheniscus magellanicus) através de análises de paternidade / Genetic evaluation of the reproductive system of Magellanic Penguins trough paternity analysisMarasco, Anna Carolina Milo 14 April 2015 (has links)
Apesar de a monogamia social ser dominante entre as aves, análises genéticas revelaram relações de parentesco inesperadas, evidenciando diferentes estratégias de reprodução, como a paternidade extra-par e o parasitismo de ninho. Espécies de passeriformes estão entre as mais promíscuas, com altas taxas de paternidade extra-par, enquanto em aves marinhas esse comportamento demonstrou ser menos frequente. Pinguins (Família Spheniscidae) compõem um grupo de 18 espécies de aves marinhas pelágicas e que tem em comum a filopatria, fidelidade a um parceiro e intenso cuidado biparental. Portanto, espera-se que apresentem um comportamento estritamente monogâmico e taxas de paternidade extra-par insignificantes. Avaliamos pela primeira vez o sistema reprodutivo dos Pinguins-de-Magalhães através de uma abordagem genética, buscando investigar a existência e frequência de paternidade extra-par e parasitismo de ninho. O parentesco de 88 filhotes de 44 ninhos de uma colônia na Ilha Quiroga (Argentina) foi determinado com base em análises de 9 marcadores microssatélites. Encontramos baixas taxas de parasitismo de ninho (6%), mas altas taxas de paternidade extra-par (31% e 48% dos ninhos com pelo menos 1 filhote extra-par). Entre os dois anos coletados, encontramos uma pequena diferença na incidência de infidelidade (29% em 2010; 32% em 2011), mas não houve relação com as condições climáticas do período de reprodução da espécie. Além disso, apesar da alta taxa de filhotes extra-par, não encontramos diferença significativa na diversidade genética e nem viés da razão sexual secundária. Acreditamos que a alta taxa de paternidade extra-par encontrada possa ter relação com o comportamento reprodutivo em colônia, a densidade populacional, o sincronismo reprodutivo, ou que parte da paternidade que não correspondeu aos pais sociais seja resultado de troca de parceiros antes da definição final dos casais em cada estação reprodutiva. Nosso estudo pode ajudar a melhor entender e caracterizar o sistema reprodutivo dos Pinguins-de-Magalhães e indica que a espécie é socialmente, mas não geneticamente monogâmica. / Despite the social monogamy being dominant among birds, genetic analysis revealed unexpected kinship relations, showing different reproductive strategies, such as extra-pair paternity and brood parasitism. Passerine species are among the most promiscuous, with high extra-pair paternity rates, while in seabirds this behavior is typically rather less frequent. Penguins (Spheniscidae Family) are a group of 18 species of pelagic seabirds that have in common philopatric behavior, faithfulness to one partner and intense biparental care. Therefore, they are expected to have a strictly monogamous behavior and insignificant rates of extra-pair paternity. For the first time, we evaluated the reproductive system of Magellanic Penguins (Spheniscus magellanicus) through genetic analysis in order to investigate the existence and frequency of extra-pair paternity and brood parasitism. The kinship of 88 offspring of 44 nests from a colony on Quiroga Island (Argentina) was determined based on the analyses of 9 microsatellite markers. We found low rates of brood parasitism (6%), but high extra-pair paternity rates (31% and 48% of nests with at least one extra-pair offspring). Between the two years sampled, we found a small difference in the incidence of infidelity (29% in 2010; 32% in 2011), but no connection with the climatic conditions of each breeding season. In addition, despite the high rate of extra-pair offspring, we found no significant difference in the genetic diversity and no bias in the secondary sex ratio. We believe that the high rate of extra-pair paternity found in our study may be a result of their reproductive behavior of nesting in colonies, breeding synchrony, density, or that part of the mismatching paternity is due mate switching. Our study may help to better understand and characterize the reproductive system of Magellanic penguins and indicates that this species is socially but not sexually monogamous.
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Efeito da deformação mecânica no transporte iônico em filmes poliméricos. / Effect of mechanical deformation on ionic transport in polimeric films.Sakamoto, Walter Katsumi 10 December 1990 (has links)
Recentemente um efeito piezoelétrico foi encontrado quando um filme polimérico, separando duas soluções de eletrólitos em diferentes concentrações, foi deformado. Este efeito foi atribuído à modulação da mobilidade dos íons no polímero. Foi observado que o efeito diminui com o aumento da concentração de eletrólitos. Para entender mais profundamente este último efeito, foram realizados estudos sobre o transporte de água e sal através do polímero, com e sem deformação, e os resultados podem ser resumidos como segue: a) O aumento da hidratação acarreta um aumento na porosidade e um decréscimo na cristalinidade do polímero. b) O aumento da concentração de sal, no interior do polímero acarreta um aumento na permeabilidade, sendo mais pronunciado na presença de deformação. Esses efeitos tornam mais difícil a modulação dos íons, diminuindo o sinal piezoelétrico observado. / Recently a piezoelectric effect was found when a polymeric film, separating two electrolyte solutions at different concentrations, was deformed. This effect was attributed to the modulation of the mobility of the íons in the polymer. It was observed that the effect decreases as the electrolyte concentrations increases. In order to understand more deeply this last effect a study on water and salt transport through the polymer with and without deformation was carried out, and the results may be summarized as follows: a) An increase in hydration of the polymer leads to an increase in porosity and a decrease in cristallinity. b) An increase in the concentration of the salt leads to an increase in permeability, which is more pronounced in the presence of deformation. The effects make more difficult the modulation of the íons, so lower piezoelectric signals are observed.
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Chromosome 1 abnormalities in human hepatocellular carcinoma.January 2002 (has links)
Lam Wai-Chun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves [64]-[73]). / Abstracts in English and Chinese. / Abstract (in English) --- p.i-ii / Abstract (in Chinese) --- p.iii -iv / Acknowledgements --- p.v / Table of contents --- p.vi -ix / List of Figures --- p.x / List of Tables --- p.x / Abbreviations --- p.xi -xii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Hepatocellular Carcinoma (HCC) --- p.1-2 / Chapter 1.2 --- Major risk factors of HCC / Chapter (1) --- Hepatitis B Virus (HBV) --- p.2-4 / Chapter (2) --- Hepatitis C Virus (HCV) --- p.5-6 / Chapter (3) --- Cirrhosis --- p.6 / Chapter (4) --- Dietary alfatoxin B1 (AFB1) --- p.6 -7 / Chapter (5) --- Alcoholic consumption --- p.7 / Chapter (6) --- Iron overload --- p.8 / Chapter 1.3 --- Genetic aberrations in HCC --- p.8-9 / Chapter (1) --- Chromosomal loss --- p.10-13 / Chapter (2) --- Chromosomal gains --- p.13-15 / Chapter 1.4 --- roposed study --- p.15 / Chapter (1) --- Hypomethylation of heterochromatin in chromosome 1q copy number gain. --- p.16 / Chapter (2) --- ositional mapping on 1q21 - q22 by interphase cytogenetics. --- p.16-17 / Chapter Chapter 2 --- Materials and Methods / Chapter 2.1 --- Materials / Chapter 2.1.1 --- Southern Blot Analysis for Satellite DNA Hypomethylation. --- p.18-19 / Chapter 2.1.2 --- ositional Mapping by Interphase Cytogenetics. --- p.19 -24 / Chapter 2.2 --- Methods / Chapter 2.2.1 --- Southern Blot Analysis for Satellite DNA Hypomethylation / Chapter (1) --- Extraction of high molecular weight DNA --- p.25 / Chapter (2) --- DNA digestion with methyl-sensitive restriction enzyme --- p.25 -26 / Chapter (3) --- Control for the complete DNA digestion. --- p.26 / Chapter (4) --- Southern Blotting. --- p.26 -27 / Chapter 2.2.2 --- ositional Mapping by Interphase Cytogenetics / Chapter (1) --- Yeast Artificial Chromosome (YAC) --- p.28 -29 / Chapter (i) --- YAC culturing --- p.29 -30 / Chapter (ii) --- YAC DNA extraction --- p.30 -31 / Chapter (iii) --- Inter-Alu-Polymerase Chain Reaction --- p.32 -33 / Chapter (2) --- -1 derived Bacterial Artificial Chromosome (PAC) --- p.34 / Chapter (i) --- AC culturing and DNA extraction --- p.34 -35 / Chapter (3) --- FISHrobe labeling by nick translation. --- p.35 / Chapter (4) --- FISHrobereparation --- p.36 / Chapter (5) --- Dot-blot analysis. --- p.36 -37 / Chapter (6) --- Verification of the YAC andACrobes by metaphase FISH --- p.37 / Chapter (7) --- Hybridization efficiency test --- p.38 / Chapter Chapter 3 --- Southern Blot Analysis for Satellite DNA Hypomethylation / Chapter 3.1 --- Introduction --- p.39 -40 / Chapter 3.2 --- Materials and Methods / Chapter (1) --- atients --- p.41 / Chapter (2) --- Mathyl-sensitive restriction enzyme digestion. --- p.42 / Chapter (3) --- Classical satellite 2 DNArobe labeling and hybridization. --- p.42 -43 / Chapter (4) --- Membrane washing and signal detection. --- p.43 / Chapter (5) --- Signal detection and reference ratio determination. --- p.43 -44 / Chapter (6) --- Comparative Genomic Hybridization (CGH) --- p.44 -45 / Chapter 3.3 --- Results / Chapter (1) --- Heterochromatin hypomethylation and 1q12 breakpoint. --- p.45 / Chapter (2) --- Heterochromatin hypomethylation in adjacent hepatitis Infected liver tissue. --- p.46 / Chapter 3.4 --- Discussion --- p.47-51 / Chapter Chapter4 --- ositional Mapping of 1q21 - q22 by Interphase Cytogenetics / Chapter 4.1 --- Introduction --- p.52-53 / Chapter 4.2 --- Materials and Methods / Chapter (1) --- atients --- p.53 / Chapter (2) --- YAC clones --- p.53 -54 / Chapter (3) --- AC clones --- p.55 / Chapter (4) --- Formalin-fixedaraffin-embedded tissue sections pretreatment. --- p.55 / Chapter (5) --- Hybridization --- p.56 / Chapter (6) --- Signal detection --- p.56 -57 / Chapter 4.3 --- Results / Chapter (1) --- Relative copy number gain on YAC examined. --- p.57 -59 / Chapter (2) --- AC findings --- p.60 / Chapter 4.4 --- Discussion --- p.60 -63 / References
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Rôle des états de Rydberg dans la dynamique de photoionisation et de formation de paires d’ions (NO+,O-) de la molécule NO2 : photoémission induite par rayonnement synchrotron et impulsions lasers femtosecondes / The role of Rydberg states in photoionization of NO2 and (NO+,O-) ion pair formation : photoemission induced by synchotron radiation and femtosecond pulsesMarggi Poullain, Sonia 14 January 2014 (has links)
L’étude comparée des réactions de formation de paires d’ions et de simple photoionisation de la molécule NO2 induites par rayonnement synchrotron (RS) d’une part et par impulsions laser femtosecondes (fs) d’autre part, démontre le rôle remarquable de l’excitation résonante d’états de Rydberg dans la dynamique électronique et nucléaire induite. Trois réactions principales, la photoionisation non dissociative (NO2+ (X 1Σ+g) + e), la photoionisation dissociative (NO+ (X 1Σ+) + O(3P) + e) et la formation de paires d'ions, (NO+ (X 1Σ+) + O- (2P)), ont été caractérisées en utilisant la méthode des corrélations vectorielles ou spectroscopie en coïncidence des impulsions du photoélectron et des photoions, auprès des sources RS (SOLEIL, DESIRS) et lasers fs (CEA, Saclay), respectivement. Le diagramme de corrélation des énergies cinétiques électron-ion, première observable issue de ces mesures, met en évidence un partage de l’énergie en excès entre noyaux et électrons qui dépend fortement du mode d’excitation photonique. Les déviations significatives observées par rapport aux profils d’ionisation de type Franck Condon sont attribuées à des couplages vibroniques entre états excités NO2*, tels que ceux induits par une intersection conique. Les chemins réactionnels identifiés confirment le rôle de l’excitation des séries de Rydberg [R*(6a1)-1] et [R*(4b2)-1] intervenant comme états intermédiaires dans l’excitation multiphotonique ou dans le continuum d’ionisation exploré. Une étude complémentaire par spectroscopie à haute résolution des états [R*(6a1)-1] a été mise en œuvre (UBC, Vancouver).Pour une réaction de photoionisation dissociative (PID), l’observable la plus complète est la distribution angulaire des photoélectrons dans le référentiel lié à la vitesse de recul de l’ion fragment (RFPAD) déduite de la mesure de la corrélation vectorielle (Vi, Ve, P). Afin d’accéder aux éléments de matrice dipolaire décrivant la photoionisation de l’état électronique considéré, le formalisme développé en collaboration avec R. R. Lucchese (Texas A&M) décrivant la photoémission dans le référentiel moléculaire pour la simple PID d'une molécule linéaire par excitation à un photon, a été étendu à l'étude des réactions de PID par excitation multiphotonique d'une molécule polyatomique, telle que la molécule NO2 de symétrie C2v. L’analyse multivariée de la RFPAD multiphotonique proposée constitue une stratégie fructueuse en vue d’extraire l’information optimale sur la dynamique complexe de photoionisation et de réaliser une comparaison détaillée entre les résultats expérimentaux et les calculs de photoionisation des états excités de la molécule. / The comparative study of ion pair formation and simple photoionization of the NO2 molecule induced by synchrotron radiation (SR) on the one hand and by femtosecond (fs) pulses on the other hand reveals the remarkable role of Rydberg states in the induced electronic and nuclear dynamics. Three main reactions, namely (NO2+ (X 1Σ+g) + e) non dissociative photoionization, (NO+ (X 1Σ+) + O(3P) + e) dissociative photoionization and (NO+ (X 1Σ+) + O- (2P)) ion pair formation have been characterized using the vector correlation method, or photoion and photoelectron coincidence momentum spectroscopy, at SR sources (SOLEIL DESIRS) and at fs laser platforms (CEA, Saclay), respectively. The electron-ion kinetic energy correlation diagram, which is the first observable obtained from these measurements, highlights the excess energy sharing among nuclei and electrons, which strongly depends on the photon excitation mode. The observed remarkable deviations from Franck Condon ionization profiles are attributed to vibronic couplings such as those induced at a conical intersection. The identified reaction pathways confirm the role of the [R*(6a1)-1] and [R*(4b2)-1] Rydberg series excitation as stepping states in multiphoton excitation or in the explored ionization continua. A complementary study of high resolution spectroscopy of [R*(6a1)-1] Rydberg series has been performed (UBC, Vancouver). For a dissociative photoionization (DPI) process, the most complete observable is the photoelectron angular distribution in the reference frame attached to the recoil ion fragment velocity (RFPAD) deduced from the measured (Vi, Ve, P) vector correlation. In order to get access to the dipole matrix elements describing photoionization of the considered excited electronic state, the formalism developed in collaboration with R. R. Lucchese (Texas A&M) describing molecular frame photoemission for a DPI of a linear molecule by one-photon excitation has been extended to the study of DPI processes induced by multiphoton excitation for a polyatomic molecule, such as the NO2 molecule of C2v symmetry. The proposed multivariate analysis of the multiphoton RFPAD constitutes a successful strategy to extract the optimal information on the complex photoionization dynamics and to perform a detailed comparison between experimental results and calculations of photoionization of the molecular excited states.
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Zhodnocování a zajišťování finančních prostředků na forexovém trhu / Evaluation and Security of Financial Means on the Forex MarketPlášil, Zdeněk January 2009 (has links)
The purpose of this thesis is analysis process of increasing financial resources on the foreign exchange market. This thesis is devided into two parts. Firts part gives basic information about foreign exchange market. Operative part contains analysis steps of entering into foreign exchange market and trading system aplied in real market.
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A Relativistic One Pion Exchange Model of Proton-Neutron Electron-Positron Pair ProductionPeterson, William A. 01 May 1973 (has links)
Proton-neutron electron-positron pair production cross sections are calculated in the framework of the pseudoscalar one-pion exchange model in a fully relativistic manner.
A computer program has been developed to evaluate invariants and Dirac traces for a given data point.
The sections for symmetric coplanar events for laboratory kinetic energies of 10 to 250 MeV were calculated for pair angles of 20° to 120°.
Frequency distributions were also calculated, at a laboratory energy of 200 MeV, using a random number generator to select data points. The frequency distributions are illustrated by curves.
It was noted that the inclusion of heavier bosons will not significantly improve the results at laboratory energies less than 200 MeV.
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A new synthetic strategy for low-dimensional compounds : Lone pair cations and alkaline earth spacersFredrickson, Rie Takagi January 2008 (has links)
<p>Complex transition metals oxyhalides containing a lone pair element, such as tellurium (IV), form an attractive research field because there is a high probability of finding new low-dimensionally arranged compounds and, particularly, a low-dimensionally arranged transition metals substructures, leading to interesting physical properties. Tellurium (IV) can drive the formation of many unusual structures because of its stereochemically active lone pair electrons, E. It commonly takes a coordination of three or four oxygen atoms to form either a TeO3E square pyramid or a TeO3+1E trigonal bipyramid. These lone pairs are very important players involved in lowering the dimensionality of crystal structures. Previous studies in transition metal tellurium (IV) oxohalide quarternary systems revealed a family of compounds, many of which exhibit interesting properties e.g. magnetic frustration. The unique point of this thesis is to employ alkaline earth elements (AE) to augment this ability of lone pair elements to lower the dimensionality of the transition metal arrangements. By this double usage of “chemical scissors” (a lone pair element used in conjunction with alkaline earth elements) we obtained new types of low-dimensionally arranged compounds.</p><p>This thesis is focused on the syntheses and characterization of a series of compounds in the pentanary (five components) system AE-TeIV-TM-O-X (AE=alkaline earth metal, TM=transition metal and X=halogen), in which nine new compounds were found. The crystal structures of each of these compounds were determined by the single crystal X-ray diffraction data.</p>
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Measurements of photon induced processes in CMS and forward proton detection at the LHCRouby, Xavier 26 September 2008 (has links)
High energy photon induced processes at the CERN Large Hadron Collider (LHC) constitutes a unique testing ground for physics within and beyond the Standard Model of Elementary Particles. Colliding protons can interact by the exchange of one or two high energy photons, leading to very clean final state topologies. Several issues related to the study of photon interactions at the LHC are addressed in this Thesis. The detection of
forward scattered protons, after the photon exchange, requires near-beam detectors.
Developments of edgeless sensor prototypes have been realised as possible solutions for such an application. A proper design of these detectors has required developing a dedicated simulator (Hector) for the transport of charged particles particles in beamlines. Finally, the analyses of
detection in the CMS experiment of the photon-induced exclusive production of lepton pairs are presented. In view of application early from the LHC start-up, in particular for the absolute luminosity measurement – the fundamental parameter
of the LHC.
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Utilisation de l'optique fibrée pour la manipulation et la génération d'états quantiques: pile ou face quantique et paires de photons/ Fiber optics for the manipulation and the generation of quantum states of light: quantum coin tossing and photon pairs.Nguyen, Anh Tuan A.T. 07 November 2008 (has links)
La physique quantique fut introduite au début du 20e siècle. Elle
apporte une nouvelle description du monde qui nous entoure et en
particulier de ce qu'on appelle le monde de l'infiniment
petit. Cette nouvelle théorie permet une description adéquate
notamment de l'effet photoélectrique, des niveaux énergétiques des
atomes, des réactions nucléaires, ... Elle apporte également une
réponse à de nombreuses problématiques telles que la catastrophe
ultraviolette. Néanmoins aussi séduisante que soit cette théorie,
les prédictions pour le moins contre-intuitives qu'elle apporte,
amène rapidement la controverse. Par exemple, en 1935, A.
Einstein, B. Podolski et N. Rosen en arrivent à mettre en doute la
physique quantique à cause d'une particularité que l'on y
rencontre, à savoir l'enchevêtrement. Il s'en
suit le célèbre débat avec N. Bohr et l'école de Copenhagen. Parmi
les autres aspects propres au monde quantique on peut encore citer
la superposition des états, le postulat de la mesure, le principe
d'incertitude d'Heisenberg, la dualité onde-corpuscule, le
théorème de non clonage, ... Toutes ces spécificités font de la
physique quantique un monde passionnant dans lequel, à l'instar du
pays des merveilles d'Alice, l'intuition est souvent dépassée.
Cette thèse est le fruit de quatre années de travail au cours
desquelles nous avons tenté d'observer et d'étudier certains des
effets intrigants que nous propose la physique quantique. Plus
précisément nous avons utilisé des états particuliers de la
lumière afin d'explorer une partie de ce qu'on appelle
l'optique quantique.
Dans un premier temps nous nous sommes intéressés aux possibilités
offertes par l'utilisation d'états cohérents de la lumière. En
utilisant ces états particuliers nous nous sommes penchés sur
l'étude ainsi que sur la réalisation expérimentale d'une tâche qui
se révèle impossible classiquement sans hypothèse computationelle.
Cette tâche consiste à réaliser un pile ou face entre deux joueurs
éloignés l'un de l'autre, par exemple deux joueurs communiquant
par téléphone. En effet, classiquement, un des deux joueurs pourra
toujours tricher de manière à avoir 100% de chance de gagner le
pile ou face.
Au contraire, si on utilise les ressources offertes par la
communication quantique, il est possible de construire des
protocoles ne permettant plus à aucun des deux joueurs de tricher
parfaitement et ce, sans aucune hypothèse supplémentaire. Même si
aucun protocole quantique ne peut empêcher totalement toute
tricherie, leur démonstration constitue une preuve de principe
quant aux possibilités offertes par la physique quantique dans la
réalisation de tâches classiquement impossibles.
Lors de notre étude du problème, nous avons développé un protocole
de pile ou face quantique et étudié ses performances. Nous avons
montré que les tentatives de tricherie des deux joueurs avaient
une probabilité de succès limitée à 99,7%<100% (biais inférieur
à 0,497). L'originalité de cette étude se situe dans le fait que
les imperfections expérimentales (efficacité des détecteurs,
pertes de transmission, visibilité réduite, ...) furent prises en
compte, ce qui à notre connaissance n'avait jamais été réalisé. En
outre nous avons réalisé une implémentation en optique fibrée de
notre protocole et démontré la réalisation d'un pile ou face
unique au cours duquel aucun des deux joueurs ne pouvait
influencer parfaitement le résultat, ce qui à notre connaissance
n'avait également jamais été démontré. L'emploi d'états cohérents
de la lumière fortement atténués nous a donc permis de concevoir
un protocole de pile ou face quantique et de réaliser une
démonstration expérimentale en optique fibrée, d'une tâche
impossible à réaliser classiquement.
Après avoir travaillé avec des états cohérents fortement atténués,
nous nous sommes intéressés à un autre état quantique de la
lumière, à savoir les paires de photons. Ces états constituent non
seulement une ressource essentielle pour sonder les effets
quantiques de la lumière mais également une ressource
incontournable pour l'information et la communication quantique.
Nous nous sommes donc attelés à la réalisation d'une source
produisant ces paires de photons.
Les premières sources de paires
de photons furent basées sur l'utilisation de cristaux dans
lesquels il existe une interaction non linéaire entre la lumière
et le matériau du cristal. Malheureusement le désavantage majeur
de ces sources est la difficulté à collecter les paires de photons
générées. Nous avons donc étudié la possibilité de générer des
paires de photons directement dans une fibre optique, la
collection des paires y étant réalisée de facto.
La première solution que nous avons envisagée consiste à utiliser
la non-linéarité du troisième ordre de la silice composant les
fibres optiques. Plus précisément le phénomène utilisé est appelé
l'instabilité de modulation. Ce phénomène permet de détruire deux
photons de pompe afin de générer une paire de photons vérifiant
les conservations de l'énergie et de l'impulsion. En outre nous
avons choisi d'utiliser une fibre optique microstructurée. Ces
fibres permettent en effet un plus grand confinement de la lumière
que les fibres standards. Il en résulte une interaction non
linéaire plus importante, permettant ainsi de générer des paires
de photons de manière plus efficace. La fibre utilisée est en
outre biréfringente, ce qui permet d'avoir accès à deux types
particuliers d'instabilité de modulation: l'instabilité scalaire
et l'instabilité vectorielle.
Dans un premier temps, nous avons observé le processus
d'instabilité de modulation dans un régime classique. Les
paramètres particuliers de notre fibre microstructurée - forte
dispersion anormale et biréfringence modérée
- nous ont permis d'observer un régime
d'instabilité dans lequel l'instabilité de modulation vectorielle
se produit à des fréquences proches de la fréquence de pompe
($Omegasim 1$THz). Il en résulte que les bandes de gain liées à
l'instabilité de modulation vectorielle sont très proches des
bandes de gain liées à l'instabilité de modulation scalaire. Nous
avons observé que dans ce régime particulier, les densités
d'énergie générées par instabilité de modulation vectorielle sont
supérieures à celles générées par instabilité de modulation
scalaire. A notre connaissance, il s'agit de la première
observation expérimentale permettant de mettre en évidence un gain
vectoriel supérieur au gain scalaire.
La génération de paires de photons grâce à ce processus nécessite
de diminuer la puissance de pompe envoyée dans la fibre.
Malheureusement nous avons mesuré que dans ce régime de faible
puissance (régime quantique), la qualité des paires de photons
générées était fortement dégradée par la présence de photons
parasites générés par diffusion Raman spontanée. Nous avons estimé
que lorsque la puissance de pompe est abaissée suffisamment pour
générer en moyenne 0,1~photons dans la bande de gain d'instabilité
de modulation vectorielle ($sim$1543 nm), environ 75% des
photons détectés auront été générés par diffusion Raman spontanée.
Afin de mettre en oeuvre des expériences d'optique quantique
utilisant des paires de photons, des solutions doivent donc être
appliquées à notre source afin de réduire le nombre de photons
générés par diffusion Raman spontanée. Parmi ces solutions nous
pouvons citer la discrimination en polarisation des photons
générés ainsi que le refroidissement de la fibre grâce à de
l'azote liquide. Ces solutions permettraient de réduire le nombre
de photons Raman anti-Stokes d'un facteur 18 et le nombre de
photons Raman Stokes d'un facteur 4. Malheureusement la tenue de
la fibre microstructurée à de très basses températures reste
incertaine et l'implémentation de ces solutions rendrait la source
difficilement utilisable.
Notre première tentative pour générer des paires de photons dans
une fibre optique nous a montré que les paires de photons générées
grâce à un processus d'interaction non linéaire du troisième ordre
étaient polluées par des photons générés par diffusion Raman
spontanée. Une source de paires de photons efficace ne pouvait
donc pas être obtenue sans l'aide de solutions technologiques
assez lourdes à mettre en oeuvre.
Nous avons donc investigué une deuxième solution afin de réaliser
une source produisant des paires de photons dans une fibre
optique. Puisque les non-linéarités du troisième ordre semblent
être peu adaptées pour la génération de paires de photons, nous
sommes revenus à une non-linéarité du second ordre. Dans ces
processus c'est un photon de pompe qui est détruit afin de générer
une paire de photons, tout en respectant les conservations de
l'énergie et de l'impulsion. Malheureusement les fibres optiques
ne permettent pas l'apparition de non-linéarités du second ordre
et ce, à cause de la centrosymétrie macroscopique du verre de
silice qui compose ces fibres.
Afin d'induire une non-linéarité du second ordre dans une fibre
optique nous avons travaillé en collaboration avec l'équipe du
Prof. P. G. Kazansky de l'université de Southampton. En utilisant
les techniques de poling thermique et d'effacement par
illumination UV, ils réalisèrent une fibre optique twin-hole
périodiquement polée dans laquelle les non-linéarités du second
ordre furent possibles.
Grâce à cette fibre nous avons réalisé une source de paires de
photons combinant les avantages des effets non linéaires du second
ordre, i.e. la puissance de pompe nécessaire est moindre
que dans le cas d'une non-linéarité du troisième ordre, la
diffusion Raman spontanée n'influence aucunement les paires de
photons générées, et les avantages de la fibre optique,
i.e. la collection des paires de photons y est réalisée
de facto, le mode spatial transverse des paires de photons
est bien défini. La mesure du pic de coïncidences de notre source
fournit un rapport entre le sommet du pic et le niveau des
coïncidences accidentelles de 7,5. Une efficacité conversion
$P_s/P_p=1,2,10^{-11}$ fut obtenue en utilisant 43~mW de
puissance de pompe. En outre les paires de photons générées
possèdent une longueur d'onde de 1556~nm se trouvant ainsi dans la
bande C des télécommunications optiques (1530-1565~nm). Elles sont
donc bien adaptées à une éventuelle application en communication
quantique, dans les réseaux de fibres optiques actuellement
utilisés pour les télécommunications optiques. Enfin nous avons
utilisé ces paires de photons afin de réaliser l'expérience de
Hong-Ou-Mandel permettant de mettre en évidence un effet propre à
la physique quantique, à savoir le photon bunching. Une visibilité
nette de 40% fut obtenue pour le Mandel dip dans une
configuration où la visibilité maximale vaut 50%. En outre cette
expérience nous a permis de développer une expertise dans la
réalisation d'interféromètres fibrés, stabilisés et contrôlés en
température.
La source de paires de photons que nous avons réalisée constitue
une démonstration de principe quant à la faisabilité d'une telle
source. A l'époque de ce travail, la fibre dont nous disposions
était l'une des premières fibres twin-hole périodiquement polées.
Aujourd'hui de nombreux paramètres de la fibre ont été améliorés
et permettent la réalisation d'une source de paires de photons
tout à fait compétitive avec les autres sources existantes. Ainsi
l'équipe du Prof. Kazansky est capable de réaliser des fibres
périodiquement polées de 20 cm de long possédant une efficacité de
conversion normalisée de seconde harmonique de
$eta_{SH}=8;10^{-2}$\%/W. Si l'on suppose toujours une puissance
de pompe de 43 mW, cela mène à une efficacité de conversion de
$1,0;10^{-9}$ pour le processus de fluorescence paramétrique,
soit une amélioration de deux ordres de grandeurs par rapport à
notre démonstration. La réalisation d'une source de paires de
photons dans une fibre optique périodiquement polée qui serait non
seulement utilisable dans des expériences de physique fondamentale
mais également dans des applications en communication quantique,
est donc tout à fait envisageable dans un futur proche.
Pour résumer, nous avons, au cours de cette thèse, réalisé, dans
un premier temps, la tâche classiquement impossible qui consiste à
jouer à pile ou face à distance. Ensuite dans l'optique de générer
des paires de photons, nous avons étudié le processus
d'instabilité de modulation dans une fibre microstructurée. Nous
avons ainsi observé un régime particulier dans lequel
l'instabilité de modulation vectorielle possède un gain supérieur
à celui de l'instabilité de modulation scalaire. Enfin toujours en
quête d'une source de paires de photons, nous avons réalisé une
source produisant des paires de photons par fluorescence
paramétrique dégénérée au sein d'une fibre optique twin-hole
périodiquement polée. Les trois principaux sujets abordés au cours
de cette thèse ont donc en commun l'utilisation de l'optique
fibrée pour la manipulation ou la génération d'états quantiques de
la lumière. Il en a résulté l'obtention de trois résultats
originaux qui nous ont ainsi permis d'explorer une partie du monde
intrigant et fascinant de l'optique quantique.
/
Quantum physics was introduced early in the 20th century. It
brings a whole new description of our world, mostly at the
microscopic level. Since then, this new theory has allowed one to
explain and describe lots of physical features like the
photoelectric effect, the energy levels of atoms, nuclear
reactions, ... It also brought an answer to lots of remaining
unanswered questions like the so-called ultraviolet catastrophe.
Though, as attractive as this new theory was at that time, some of
its counter-intuitive predictions quickly gave rise to
controversy. For instance, in 1935, due to one quantum physics
feature called entanglement, A. Einstein, B. Podolski and N. Rosen
asked the question: "Can quantum-mechanical description of
physical reality be considered complete?". This led to
the famous debate with N. Bohr and his Copenhagen interpretation.
Amongst other particular features of quantum physics one can cite:
the superposition principle, the wave function collapse, the
Heisenberg uncertainty principle, the wave-particle duality, the
no-cloning theorem, ... As in Alice in wonderland, all those
features actually make quantum physics a fascinating world where
intuition is most of the time useless.
In this thesis we tried to observe and study some of the
intriguing features of quantum physics. More precisely we tried to
use specific light states to explore part of what is called
quantum optics.
First we studied the use of coherent states of light to perform
tasks you can not perform using classical physics. For instance in
1984, Ch. Bennett and G. Brassard proposed the first quantum
cryptography protocol which has an absolute security
while classical protocol security still relies on some
computational assumptions (the assumption is that today
computers computational power is not sufficient to threaten the
security of classical protocols. Though this means that classical
protocols are not intrinsically secure). Since then quantum
physics has been proven useful to perform lots of classically
impossible tasks like bit commitment, quantum computation, random
number generation, ... In this work we were interested in the
problem of coin tossing by telephone introduced by M. Blum
in 1981. In this problem two untrustful and distant
players try to perform a coin flip. Classically one can show that,
if no computational assumptions are made, one of the players can
always force the outcome of the coin flip.
On the opposite if one uses quantum communication resources, a
protocol in which none of the players can cheat perfectly can be
built, i.e. none of the players have 100\% chance of
winning the protocol even by using the best possible cheating
strategy. Moreover this is possible without any other assumption
than the validity of the laws of physics. Though a quantum
protocol for coin tossing can not completely prevent from cheating, the demonstration of such a protocol would
be a proof of principle of the potential of quantum communication
to implement classically impossible tasks.
In our work, we have developed a quantum coin tossing protocol and
studied its performances. We have shown that the success cheating
probability of the players is bounded by 99,7%<100%, which is
better than what is achieved in any classical protocol. One of the
originalities of our work is that, for the first time to our
knowledge, experimental imperfections (detectors efficiency,
losses, limited interference visibility, ...) have been taken into
account in the theoretical analysis. Moreover, using coherent
states of light, we have demonstrated a fiber optic experimental
implementation of our protocol and performed a single coin flip
where none of the two players could perfectly influence the
outcome. This is to our knowledge the first experimental
demonstration of single quantum coin tossing.
After coherent states of light, we wanted to work with a more
complex quantum state: photon pairs. Not only those states are
useful for fundamental physics tests but they also are an
important resource for quantum communication. For those reasons
our first objective was to build a source that would generate
those photon pairs.
First photon pairs sources were based on bulk nonlinear crystals.
Unfortunately the main drawback of those sources is the low
collection efficiency of the generated photon pairs. That's why we
investigated the possibility of generating the photon pairs
directly in a waveguiding structure where they would be readily
collected.
The first solution that we envisaged was to use the natural third
order nonlinearity of silica fibers. More precisely the phenomenon
we wanted to used is called modulation instability. In this
process, two pump photons are destroyed and a photon pair is
created with energy and momentum conservations. Moreover we
decided to use this process in a photonic crystal fiber. The high
confinement of light in this kind of fiber allows a higher
nonlinearity and thus a more efficient generation of photon pairs.
Finally the fiber we used was birefringent which enables both
vectorial and scalar modulation instability to occur.
As a first experiment, we decided to observe modulation
instability in a classical regime where a lot of photons are
created. The specific parameters of our photonic crystal fiber -
high anomalous dispersion and moderate birefringence - allowed us
to observe a regime where the vectorial instability gain band has
a similar detuning from the pump as the scalar instability gain
band. In this regime we also observed an enhancement of the
vectorial gain above the scalar gain which has been confirmed
theoretically. To our knowledge this was the first experimental
observation of this particular regime of instability.
To generate photon pairs with this instability process we need to
lower down the pump power. Unfortunately we measured that, when
pump power was sufficiently lowered to generate ~0,1 photon
pairs per pump pulse sent in the fiber, about 75% of generated
photons were created by spontaneous Raman scattering and not
modulation instability. In order to build an efficient photon pair
source, some technological solutions have to be found to reduce
the number of photons generated by spontaneous Raman scattering.
Amongst those solutions, one can cite polarization discrimination
of the generated photons and cooling of the fiber with liquid
nitrogen. Using those solutions one could hope to reduce
anti-Stokes Raman photon and Stokes Raman photon by respectively a
factor 18 and 4. Unfortunately the main concern is how the
photonic crystal fiber will react to very low temperatures. So
even if technological solutions exist to build a photon pair
source based on modulation instability in photonic crystal fiber,
those seem to be really hard to implement. Moreover such a photon
pair source would be very inconvenient to use in any quantum
applications.
So our first attempt to build a fiber photon pair source showed
that photon pairs generated by a third order nonlinearity were
polluted by photons generated by spontaneous Raman scattering.
Such an efficient source couldn't be realized without heavy
technological solutions.
We have thus investigated another solution to generate photon
pairs in an optical fiber. As third order nonlinearities don't
seem to be suitable, we decided to go back to a second order
nonlinearity. In this process one photon from the pump is
destroyed to create a photon pair with energy and momentum
conservations. Unfortunately the macroscopic centro-symetry of
silica glass prevents those second order nonlinearities to occur
in optical fibers.
In order to enable second order nonlinearities in silica optical
fiber, we worked with the team of Prof. P. G. Kazansky from the
Optoelectronics Research Center of the university of Southampton.
By using thermal poling and UV erasure technics, they were able to
induce a second order nonlinearity in a twin-hole optical fiber.
Thanks to 8 cm of periodically poled twin-hole fiber, were able to
build a fiber photon pair source combining advantages of a second
order nonlinearity (less pump power needed than for a third order
nonlinearity, no influence of Raman photons) and of the fiber
waveguiding structure (photon pairs readily collected, transverse
spatial mode of the photon pairs well defined). A coincidence
measurement was performed resulting in a coincidence peak with a
7,5 ratio between the peak and the accidental coincidences level.
A conversion efficiency $P_s/P_p=1,2,10^{-11}$ was obtained using
43 mW of pump power. Moreover photon pairs were generated around
1556~nm in the optical communications C-band, which makes them
suitable for quantum communication applications using installed
fiber optic networks. Finally using the generated photon pairs we
performed the Hong-Ou-Mandel experiment highlighting the bosonic
nature of photons. We obtained a Mandel dip with a net visibility
of 40% in a configuration where the maximum visibility is 50%.
The photon pair source that we realized is a proof of principle of
the high potential of poled fibers in quantum applications. Indeed
today, Prof. P. G. Kazansky's team is able to make a 20 cm poled
fiber with a nonlinearity $eta_{SH}=8;10^{-2}$\%/W. If we still
suppose 43~mW of pump power, this leads to a $1,0;10^{-9}$
conversion efficiency for parametric fluorescence, improving our
result by two orders of magnitude. The realization of an efficient
photon pair source based on parametric fluorescence in
periodically poled twin-hole fiber suitable for quantum
applications is thus absolutely possible in a very near future.
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