Made available in DSpace on 2017-07-21T19:26:02Z (GMT). No. of bitstreams: 1 Marlon Luiz Hneda.pdf: 6704011 bytes, checksum: b29186e60beebe411525b53a8023ea5d (MD5) Previous issue date: 2012-03-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work we report an experimental study about the effects of Fe doping, the variation of the current density and the application of low magnetic fields on the resistive transition and normal phase of the polycrystal ine and monocrystalline Ba2Cu2:985Fe0:015O7 samples. Three polycrystalline samples were produced, one without oxygenation and two that were oxygenated during 24 and 48 hours. Was produced, also, one well oxygenated monocrystalline sample. In the polycrystalline samples and in the single crystal sample were applied electrical currents of 5, 10 and 15 mA. The X-ray diffraction, with Rietveld refinement, shows a decrease in the lattice parameters when related with Y Ba2Cu3O7. Raman spectroscopy measurements of the polycrystalline samples reveal the displacement of bands at 150 and 500 cm1 when related with Ba2Cu3O7. The obtained results for the polycrystalline samples indicate that, in a general manner, the Fe addition and the oxygenation degree strongly affect the electronic transport properties in the normal state and in the resistive transition. Were not observed effects of the current intensity in the normal phase. In the resistive transition the current has moderate effects, similar to those produced by the application of low magnetic fields. Using the temperature derivative of the resistivity and the logarithmic derivative of the conductivity plotted as a function of the temperature, it is shown that the resistive transition is a two-step process, typical of disordered systems. In the normal phase Gaussian and critical fluctuations were observed. There were no effects of doping, oxynenation or electrical current on the paraconductivity. The paracoherent phase is strongly affected by the degree of oxygenation, but no effects were observed by the Fe doping. The effect of the electrical current was more intense in the poorly oxygenated sample. At temperatures close to the state of zero resistance it was observed, for the sample without oxygenation, a critical regime whose exponent is current dependent. For the samples oxygenated during 24 and 48 hours, the exponent was independent of the degree of oxygenation, doping with Fe, and the current intensity. The obtained values for the exponent suggest that the universality class for the coherence transition is that of the 3D-XY model where the non-trivial disorder is relevant. In the single crystal sample, were applied low magnetic fields between 0 and 500 Oe. The results showed that the Fe doping affects the electronic transport properties of both normal phase and resistive transition. There were no effects of the fields or the currents in the normal phase. The derivative of the resistiviry shows a structure of multiple peaks, suggesting the existence of a distribution of critical temperatures which can be connected with a multiple and subtle phase separation related to the presence of regions of the sample with different concentrations of Fe and/or O. In the study of the fluctuations for T TC it was observed the super-critical regime. The regime was not affected by the current intensity variation or magnetic field application. Resistivity measurements of greater accuracy, made by applying magnetic fields, also revealed the genuinely critical regime, that proved to be stable under the applied fields. / No presente trabalho é apresentado um estudo experimental dos efeitos da adição de Fe, da variação da intensidade de corrente e da aplicação de baixos campos magnéticos na transição resistiva e na fase normal do sistema Y Ba2Cu2:985Fe0:015O7 nas formas policristalina e monocristalina. Foram produzidas três amostras policristalinas, uma sem oxigenação e outras duas que foram oxigenadas durante 24 e 48 horas, e uma amostra monocristalina bem oxigenada. Tanto nas amostras policristalinas quanto na amostra monocristalina foram aplicadas correntes de 5, 10 e 15 mA. A difratometria de raios X, juntamente com refinamento Rietveld, mostram uma diminuição dos parâmetros de rede em relação ao Y Ba2Cu3O7. Medidas de espectroscopia Raman das amostras policristalinas revelam um deslocamento das bandas em 150 e 500 cm1 em relação ao Y Ba2Cu3O7. Os resultados obtidos para as amostras policristalinas indicam que, de maneira geral, a adição de Fe e o grau de oxigenação afetam fortemente as propriedades de transporte eletrônico no estado normal e na transição resistiva. Não foram observados efeitos da intensidade de corrente na fase normal. Na transição resistiva a corrente tem efeitos moderados, semelhantes aos produzidos pela aplicação de baixos campos magnéticos. A partir da derivada da resistividade e da derivada logarítmica da condutividade em função da temperatura mostra-se que a transição resistiva das amostras policristalinas é um processo com duas etapas, geralmente observado em sistemas desordenados. Na fase normal foram identificadas flutuações Gaussianas e críticas. Não foram observados efeitos da dopagem, oxigenação ou corrente na paracondutividade. A fase paracoerente se mostrou fortemente afetada pelo grau de oxigenação, mas não foram observados efeitos da dopagem com Fe. O efeito da variação da corrente foi mais intenso na amostra pouco oxigenada. Em temperaturas próximas ao estado de resistência nula foi observado um regime crítico com expoente dependente de corrente para a amostra sem oxigenação. Para as amostras oxigenadas em 24 e 48 h, o expoente se mostrou independente do grau de oxigenação, da dopagem com Fe e da intensidade de corrente. Os valores obtidos para o expoente sugerem que a classe de universalidade da transição de coerência é a mesma de um modelo 3D-XY onde a desordem não trivial é relevante. Na amostra monocristalina foram aplicados campos magnéticos fracos, entre 0 e 500 Oe. A análise dos resultados revelou que a dopagem com Fe afeta as propriedades de transporte eletrônico tanto da fase normal quanto da transição resistiva. Não foram observados efeitos dos campos nem das correntes na fase normal. A derivada da resistividade mostra uma estrutura de múltiplos picos, que sugere a existência de uma distribuição de temperaturas críticas que pode estar ligada com uma múltipla e sutil separação de fases relacionada com a presença de regiões da amostra com diferentes concentrações de Fe e/ou O. No estudo das flutuações para T > TC foi identificado o regime super-crítico. O regime se mostrou estável frente às variações de corrente e de campo magnético. Medidas de resistividade de maior precisão experimental, feitas com a aplicação de campos magnéticos, mostraram também o regime genuinamente crítico, que se revelou estável frente a aplicação dos campos estudados.

A eletrodinâmica clássica estocástica pode ser entendida como sendo a teoria clássica de Maxwell, onde se inclui um novo elemento da realidade física: As flutuações eletromagnéticas de ponto zero. Sob esse enfoque, estudamos a interação de um \"ensemble\", de osciladores harmônicos carregados com a radiação térmica e de ponto zero (atérmica). Incluímos os efeitos de dissipação através da força de reação da radiação. Além disso estudamos também a excitação do oscilador por uma força determinística com dependência temporal arbitrária. Nossa análise estatística do sistema físico é baseada na solução exata da equação de Fokker-Planck adequada ao problema. Obtém-se a evolução temporal, no espaço de fase, para uma dada distribuição inicial que caracteriza um \"ensemble\" de osciladores forçados que apresentam estados excitados na forma de estados coerentes e estados coerentes comprimidos e pulsantes. A comparação direta com a formulação quântica do mesmo problema nos faz reconhecer que é possível obter da física clássica alguns resultados antes só obtidos pela teoria quântica. Identificamos na radiação de ponto zero o ingrediente que torna possível entender a estabilidade do estado fundamental e o princípio de incerteza. / Classical stochastic electrodynamics may be understood as classical electrodynamics theory, when a new element of physical reality is included: The zero point electrodynamics fluctuations. Under this approach, we study the interaction of a charged harmonic oscillator with the thermal radiation and zero point radiation. We include the effect of dissipation by the radiation reaction force. We also study the excitation of this oscillator by a deterministic force with arbitrary temporal dependence. Our statistical analysis of the physical system is based on the exact solution of the appropriate Fokker-Planck equation. We get the temporal evolution in phase space for a given initial distribution that characterizes one \"ensemble\" of forced oscillators that presents excited states in the coherent and squeezed states form. A direct comparison with the quantum formulation of the same problem make us recognize that it is possible to get some results from classical physics which were accomplished previously only by quantum theory. We identify in the zero point radiation the ingredient that makes it possible to understand the stability of the fundamental state and the uncertainty principle.

Evolution frequently plays out over ecological timescales. Local adaptation under the joint action of evolutionary and ecological processes frequently leads to novel outcomes, as is evidenced by the theoretical work on adaptation at species' borders. However, to date this body of work does not have a theory for the effect of stochastic processes on local adaptation. The primary goal of this thesis is to show that demographic and genetic fluctuations can significantly impact upon local adaptation. In addition, the effect of polygenic evolution is also analysed. Specifically, three types of models are considered. First a deterministic mainland-island, subject to hard directional selection, maladaptive gene flow and density regulation is solved for two different trait architectures: an explicit multilocus trait and a quantitative trait. The maladaptive and adaptive steady states can be bistable. This depends on the underlying architecture of the trait, as well as locus number and ploidy. Sourcesink structure can emerge, accompanied by a novel, upper critical threshold above which maladaptation occurs. The most favourable condition for local adaptation occurs for few loci and low migration. Second, a stochastic version of the mainland-island model is analysed as a diffusion process. This is the central premise of the thesis and is explored by examining properties of the stationary distributions of both trait architectures, and the first-passage properties of the single locus case. It is found that across a range of migration rates that depend on locus number and migrant polymorphism, local adaptation may be reversed or escape from maladaptation becomes possible at varying transition rates. The diffusion model is compared to a similar discrete model. The continuous model is in good qualitative agreement with the discrete model. Third, the stochastic model is generalised to the infinite island model, which evolves deterministically. Under deterministic dynamics a range of equilibria are possible, depending on whether habitat size varies or is fixed. Multilocus dynamics restrict the conditions for polymorphism. Stochastic dynamics can have potentially detrimental consequences for the persistence of the island population when drift is strong. The relevance of the stochastic model to border populations is discussed. Although the diffusion process imposes severe constraints on the permissible parameter ranges, it is still able to provide a good qualitative understanding of the impact demographic and genetic fluctuations have on local adaptation.

<p>Gustina populacija i sezonske fluktuacije u<br />brojnosti voluharica i mi&scaron;eva (Rodentia:<br />Muridae) predstavljaju najvažniji faktor u<br />diverzitetu, distribuciji i abundanci<br />ektoparazitskih vrsta. Epidemiolo&scaron;ki modeli<br />ukazuju da bi povećanje gustine populacija<br />glodara dovelo i do povećanja gustine<br />populacija ektoparazita zbog postojanja većeg<br />izbora preferentnih habitata (jedinke domaćina).<br />Voluharice i mi&scaron;evi predstavljaju grupu glodara<br />koja ima izuzetan vektorski potencijal za veliki<br />broj vrsta iksodidnih krpelja (Acari: Ixodidae),<br />naročito triksenih i diksenih vrsta. Ako se<br />gustina populacija potencijalnih domaćina<br />(voluharica i mi&scaron;eva) posmatra kao stani&scaron;te za<br />iksodidne krpelje, tada se i meĎu njima mogu<br />uočiti razlike koje u kvalitativnom ili<br />kvantitativnom smislu podržavaju različite<br />gustine populacija krpelja. Većina vrsta glodara<br />zbog svojih &scaron;irokih areala, sezonskih migracija i<br />fluktuacija brojnosti predstavlja jednu vrstu<br />specifičnog &bdquo;epidemiolo&scaron;kog mosta&ldquo; koji je<br />odgovoran za održavanje visokih gustina<br />populacija krpelja u okviru odreĎenih stani&scaron;ta,<br />ali, &scaron;to je jo&scaron; značajnije, i prostorno preno&scaron;enje<br />pojedinih vrsta iksodidnih krpelja van okvira<br />datog habitata. Na osnovu dokazanog<br />vektorskog potencijala glodara, utvrĎen je i cilj<br />istraživanja koji podrazumeva tačno<br />odreĎivanje sezonske fluktuacije i prostorne<br />disperzije voluharica i mi&scaron;eva na odabranim<br />lokalitetima, utvrĎivanje dinamike populacija<br />prikupljenih krpelja iz prirode i brojnosti krpelja<br />prisutnih na domaćinu, vektorsku i<br />ektoparazitsku povezanost glodara i krpelja u<br />odnosu na tip habitata, meteorolo&scaron;ke parametre<br />(sezonu), uzrasnu klasu i pol glodara. TakoĎe će<br />se razmatrati i četiri postavljene radne hipoteze<br />koje se tiču odnosa glodari &ndash; krpelji: (1) broj<br />različitih stadijuma krpelja na individuama<br />domaćina se povećava sa povećanjem starosne<br />grupe (mase tela) domaćina, (2) broj različitih<br />stadijuma krpelja na individuama domaćina se<br />smanjuje sa povećanjem gustine populacije<br />domaćina, (3) veći broj različitih stadijuma<br />krpelja na individuama domaćina se konstatuje<br />na ženkama, nego na mužjacima i (4) najveći<br />broj parazitirajućih stadijuma krpelja se nalazi<br />na glavi domaćina. Tokom četvorogodi&scaron;njeg<br />ispitivanja (od 2008. do 2011. godine) sezonske<br />dinamike glodara na lokalitetima Apatin,<br />Bogojevo, Labudnjača (Kamari&scaron;te) i Čelarevo<br />ukupno je izlovljeno 2.736 jedinki, od kojih je<br />najbrojnija vrsta A. terrestris, zatim slede: A.<br />agrarius, A. flavicollis, A. sylvaticus i C.<br />glareolus. Ukupan broj konstatovanih krpelja<br />iznosio je 257. Krpelji su pripadali sledećim<br />vrstama i razvojnim stadijumima: I. ricinus<br />(larve i nimfe), I. trianguliceps (larve), D.<br />marginatus (larve i nimfe), H. concinna (larve i<br />nimfe) i R. sanguineus (larve i nimfe). U okviru<br />proučavanih ekosistema, glodari imaju značajnu<br />ulogu u održavanju krpeljskih populacija<br />različitih vrsta, omogućavajući i olak&scaron;avajući<br />transstadijalni kontinuitet u ciklusu razvića.<br />Dalje, na osnovu bioekolo&scaron;kih karakteristika, a<br />naročito arela kretanja za vreme perioda<br />intenzivne ishrane i parenja, sve ispitivane vrste<br />glodara predstavljaju i veoma dobre vektore<br />determinisanih vrsta iksodidnih krpelja izmeĎu<br />različitih tipova stani&scaron;ta, obezbeĎujući im<br />prostornu i vremensku disperziju, &scaron;to je od<br />velikog ekolo&scaron;kog, medicinskog i veterinarskog<br />značaja.</p> / <p>The population density and seasonal fluctuations<br />of voles and mice (Rodentia: Muridae) are the<br />most important factors in the diversity,<br />distribution and abundance of ectoparasites.<br />Epidemiological models indicate that an increase<br />in the rodent population density could stimulate<br />an increase in population density of ectoparasites<br />due to the greater variety of preferred habitat<br />(individual hosts). Voles and mice are a group of<br />rodents that have exceptional vector potential for<br />a large number of ixodid ticks species (Acari:<br />Ixodidae), especially tree-host and two-host<br />species. If the densities of the potential host<br />population (voles and mice) are observed as the<br />habitats for ixodid ticks, the qualitative and<br />quantitative differences among them are<br />noticeable, so as different species diversity and<br />population densities of ixodid ticks. Because of<br />the wide ranges of activity, seasonal migrations<br />and population size fluctuations, most rodent<br />species represent a specific type of an<br />&quot;epidemiological bridge&quot; which is responsible<br />for the maintenance of high population density<br />of ticks within certain habitats, but more<br />importantly, the spatial transfer of certain ixodid<br />tick species beyond the boundaries of the certain<br />habitat. Based on the proven vector potential of<br />rodents, the aims of the research were to<br />determine: the seasonal fluctuations and spatial<br />dispersion of voles and mice at selected<br />localities, the dynamics of tick populations<br />collected from nature and obtained from the<br />hosts, vector and ectoparasitic relation between<br />rodents and ticks concerning the type of habitat,<br />meteorological parameters (season), age classes<br />and gender. The four hypotheses will be<br />reviewed: (1) the number of different stages of<br />ticks on the hosts increases with the age group<br />(body mass) of the host, (2) the number of<br />different stages of ticks on the hosts decreases<br />with increasing host population density, (3) a<br />larger number of ticks obtained from the hosts<br />are found on the females than on the males, and<br />(4) the highest number of ticks could be found<br />on the host&rsquo;s head. The four year study (2008 to<br />2011) of seasonal dynamics of voles and mice<br />was conducted at four localities: Apatin,<br />Bogojevo, Labudnjača (Kamari&scaron;te) and<br />Čelarevo. The total of 2.736 rodent specimens<br />were caught. The most numerous species was A.<br />terrestris, followed by: A. agrarius, A .<br />flavicollis, A. sylvaticus and C. glareolus. The<br />total number of identified ticks was 257,<br />belonging to the following species and<br />developmental stages: I. ricinus (larvae and<br />nymphs), I. trianguliceps (larvae), D.<br />marginatus (larvae and nymphs), H. concinna<br />(larvae and nymphs) and R. sanguineus (larvae<br />and nymphs). Within the studied ecosystems,<br />rodents play a significant role in maintaining<br />different species of tick populations, enabling<br />and facilitating transstadial continuity in the life<br />cycles. Furthermore, based on bio-ecological<br />characteristics, especially areal activity during<br />the period of intensive feeding and mating, all<br />observed rodent species were very good vectors<br />of certain ixodid tick species among different<br />types of habitats, providing them spatial and<br />temporal dispersion, which is of great<br />ecological, medical and veterinary importance.</p>

This research examines moraine and lacustrine records of glacier fluctuations, in combination with palynological records of vegetation change, from the previously unstudied northwestern Ahklun Mountains in southwestern Alaska. Morain mapping reveals that ice-cap outlet glaciers in the study area extended ca. 60 km from the center of the Ahklun Mountians ice dome during the early Wisconsin (sensu lato), and ca. 40 km during the late Wisconsin. Correlations with well-studied moraines in the southern Ahklun Mountains indicate an asymmetry of glaciation over the range, with ice-cap outlet glaciers more extensive to the south. This asymmetry was more striking during the early Wisconsin (s.l.) than during the late Wisconsin. Alpine glaciers have repeatedly advanced from cirques within the study area. Because these alpine glaciers were confluent or sub-confluent with outlet glaciers during the late Wisconsin maximum, the alpine-glacier moraine record is relatively young. Lacustrine sedimentology from Little Swift Lake records significant retreat of alpine glaciers ca 12.8 ka (coeval with the onsent of the North Atlantic Younger Dryas). Moraines upvalley of the lake suggests a minor glacier (or rock glacier) advance occurred ca 5.5 ka. Lacustrine records of vegetation from Little Swift Lake extend back to ca. 13.4 ka. Most vegetation changes resulted from the post-glacial spread of trees and shrubs, including Betula, alnus, and Picea, to their modern ranges. However, pollen assemblages and other paleoclimate proxies suggest some major changes in late-glacial and Holocene climate. Major vegetation change, most notably the dramatic expansion of Poaceae, occurred ca. 100 yr after the 12.8-ka glacier retreat and persisted for more than 2 ka. The inferred reversal to dry (and possibly cool) climate was followed by a period of exceptionally productive mesic conditions during the early Holocene, ca. 11 to 9 ka. The pattern of latest-Quaternary climate changes documented in this study may be evidence that, as previous workers have concluded regarding the Pleistocene glaciations, the late-glacial and early Holocene climate of the Ahklun Mountains region was strongly modulated by changes in the proximity and temperature of the Bering Sea.

Abstract not available

L'hétérogénéité des espaces urbains et l'interaction avec les bâtiments sont à l'origine de processus complexes à prendre en compte dans les études de pollution atmosphérique et de climat urbain à petite échelle. Afin d'estimer l'impact des bâtiments sur l'écoulement et la dispersion de polluants, une étude détaillée dans un milieu urbain idéalisé a été effectuée avec le modèle numérique tridimensionnel Mercure_Saturne, en modélisant à la fois les concentrations moyennes et leurs fluctuations. Pour prendre en compte le rayonnement atmosphérique en milieu bâti et les effets thermiques des bâtiments, nous avons implémenté un modèle radiatif tridimensionnel adapté à la géométrie complexe. Ce modèle, adapté d'un schéma utilisé pour le rayonnement thermique, résout l'équation des transferts radiatifs en milieu semi-transparent, en utilisant la méthode des ordonnées discrètes. Le nouveau schéma a été validé en milieu transparent sur des cas idéalisés et comparé à un cas complet.

L'évolution d'une quinzaine de glaciers de la Cordillère Orientale de Bolivie (16-17°S ; 68°W), depuis leur phase d'extension maximale du Petit Age Glaciaire (PAG) jusqu'à la fin du 20ème siècle, a pu être reconstruite sur la base des dix principales moraines observées sur les marges proglaciaires et de six couples de photographies aériennes. L'ensemble des moraines, dont la correspondance géomorphologique a pu être établie d'un glacier à l'autre, a été daté par lichenométrie (Rhizocarpon geographicum s.l.) en utilisant une nouvelle méthode de traitement statistique des données basée sur la théorie des valeurs extrêmes. Le maximum d'extension des glaciers est daté de la deuxième moitié du 17ème siècle. Les glaciers ont gardé, jusque durant la première moitié du 18ème siècle, une position quasiment équivalente à ce maximum. A partir des années 1730-40 s'amorce une phase de retrait continue des glaciers. Les moraines les plus importantes attestent de périodes de stagnation des fronts ou de réavancées n'ayant cependant jamais été d'ampleur suffisante pour remanier les dépôts morainiques précédemment mis en place. La fin du 19ème et le début du 20ème siècle sont marqués par une accélération du recul des glaciers. Durant le 20ème siècle, la décrue reste rapide. Sur l'ensemble de la période d'étude, les glaciers enregistrent une perte moyenne de près de 60% de leur surface maximale, ce qui correspond à une remontée d'environ 135 m de l'altitude de leur ligne d'équilibre. Les datations du maximum du PAG et des stades morainiques ultérieurs, aussi bien que l'évolution des glaciers boliviens depuis la fin du 19ème siècle sont concordants avec les données disponibles dans d'autres massifs des Andes intertropicales, notamment au Pérou et en Equateur. On émet l'hypothèse d'un synchronisme de l'évolution des glaciers à l'échelle régionale en réponse à un forçage climatique commun. L'interprétation paléoclimatique des données obtenues permet de supposer que l'extension maximale des glaciers boliviens correspond à une période pendant laquelle les précipitations étaient supérieures de 20 à 30% à leur niveau actuel et les températures inférieures de 0,4 à 0,6°C. En outre, on note la concomitance entre les périodes de moindre activité solaire et celles d'avancée des glaciers. Le retrait, à partir de la première moitié du 18ème siècle, serait en grande partie dû à une baisse des précipitations. Ces hypothèses sont en accord avec les indications issues d'autres « proxies » du climat, encore peu nombreux dans cette région des Andes, que sont par exemple les carottes de glace extraites de la calotte glaciaire de Quelccaya au sud du Pérou. L'occurrence de nombreux et intenses phénomènes El Niño à la fin du 19ème et au début du 20ème siècle, mise en évidence par plusieurs indicateurs, pourrait être responsable de l'accélération du retrait des glaciers à cette période et aurait sans doute précipité la fin du PAG à l'échelle des tropiques andins. Contrairement aux périodes précédentes pendant lesquelles l'évolution des glaciers semble avoir été principalement contrôlée par les précipitations, leur retrait durant le 20ème siècle apparaît comme résultant d'une hausse combinée des températures et de l'humidité.

Les fluctuations des cours de la bourse ont des propriétés étonnantes. La volatilité (l'amplitude de ces fluctuations) est environ un ordre de grandeur plus grand que les prédictions de la théorie des marches efficients, et est corrèlee sur des échelles de temps très longs. Les agents sur réagissent aux informations. On montre que ces propriétés apparaissent lorsque les agents agissent en fonction de leur expérience et du passe du marché. On étudie aussi la microstructure des marchés, qui régulent les échanges aux temps courts. On explique pourquoi le prix est diffusif bien que les ordres marchés (les chocs subis par les prix) soient très corrélés. On évalue la fourchette des prix par des arguments de symétrie.

Dans les composés antiferromagnétiques Heisenberg à géométrie kagomé, la frustration des interactions est à l'origine d'un état liquide de spins à T=0. Un état RVB, originalement proposé par Anderson dans les réseaux triangulaires puis dans les cuprates, décrit probablement ce fondamental, dont l'état singulet est dégénéré exponentiellement dans un faible gap singulet-triplet. Peu de composés expérimentaux se rapprochent aujourd'hui du système idéal et l'existence de perturbations ou d'anisotropie lève souvent la dégénérescence du fondamental lorsque T->0. Une étude par RMN, MuSR et SQUID, a été réalisée dans les composés à géométrie de bicouches kagomé de spin 3/2, Ba2Sn2ZnGa10-7pCr7pO22 et SrCr9pGa12-9pO19, considérés comme les archétypes d'un hamiltonien de spins purement Heisenberg sur un réseau kagomé. Outre l'absence caractéristique de transition jusqu'à une température Tg~2 K bien plus basse que la température de Curie-Weiss thetaCW~250 K, des propriétés physiques semblables dans ces deux systèmes sont mesurées malgré des défauts radicalement différent. Les propriétés intrinsèques de cette géométrie en sont déduites, à savoir: - une décroissance de la susceptibilité en dessous de 45 K (RMN) interprétée par de très faibles longueurs de corrélations magnétiques, au moins pour T>10 K, malgré les fortes interactions antiferromagnétiques (thetaCW~250 K). Ce maximum de la susceptibilité reste compatible avec l'existence d'un gap de spin; - l'existence de fluctuations quantiques pour T>30 mK, beaucoup plus bas que Tg (MuSR); - la corrélation entre l'apparition de ces fluctuations et celle d'un état de type verre de spin à Tg. Un modèle phénoménologique décrivant la relaxation des muons est présenté, pour la première fois dans ces systèmes, et suggère la stabilisation d'un état de type RVB en dessous de Tg.