Made available in DSpace on 2014-06-11T19:32:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-03-14Bitstream added on 2014-06-13T19:03:20Z : No. of bitstreams: 1 silva_tjb_dr_arafcl.pdf: 581647 bytes, checksum: f755830b590397031cd7b0dfe8705171 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Esta pesquisa, ancorada no quadro teórico da Teoria das Operações Predicativas e Enunciativas, objetiva a descrição do sistema de representação metalinguística, elaborado por Antoine Culioli, a partir do qual nos propomos a investigar os valores referenciais dos marcadores verbais ser e estar numa perspectiva semântico-enunciativa e por um viés operatório. Para tanto, consideramos a articulação entre linguagem e línguas naturais e que as línguas são representadas por sistemas dinâmicos e constitutivamente variáveis, o que lhes confere estabilidade e plasticidade. Nesse sentido, é que pretendemos analisar, com base nos conceitos de deformalidade e invariância, o funcionamento dessas unidades linguísticas que se manifestam nos enunciados por meio de operações e que se configuram em uma prática textual de produção e interpretação de significação. Assim, optando por um modelo de análise que se instaura na relação enunciador, enunciado e enunciação, pautamos nossas reflexões no modo de construção dos valores referenciais dos marcadores linguísticos, objeto da pesquisa, dada a singularidade do real valor significativo desses lexemas. Esse processo de construção que se manifesta na circunstância particular que a produz e na qual se inscreve o sujeito evidencia-se nos arranjos léxico-gramaticais, principalmente, quando os confrontamos com os cânones impostos pela tradição gramatical / This research is based on Enunciative and Predicative Operations Theory and aims to describe the metalinguistic representation system, elaborated by Antoine Culioli, from which we propose to investigate the reference values of the verbal markers “being”, within a semantic-enunciative perspective and by an operative bias. To this end, we consider the relationship between language and natural languages and the languages representation by dynamic systems and constitutively variable, which gives them stability and plasticity. The analysis is done from concepts on deformality and invariance, the functioning of these units language that are expressed in utterances through operations that take place in a textual practice of production and interpretation of meaning. Thus, by choosing an analysis model that establishes in the relationship enunciator, statement, and utterance, our reflections are based on the construction mode of reference values of the linguistic markers, object of this research, aiming at the uniqueness of the significant real value of these lexemes. This construction process that is manifested in the particular circumstance that produces it and which the subject is subscribed. The lexical grammatical arrangements are evidenced, mainly when they are confronted with the canons imposed by traditional grammar

Background Demands placed on individuals in occupational and social settings, as well as imbalances in personal traits and resources, can lead to chronic stress. The Trier Inventory for Chronic Stress (TICS) measures chronic stress while incorporating domain-specific aspects, and has been found to be a highly reliable and valid research tool. The aims of the present study were to confirm the German version TICS factorial structure in an English translation of the instrument (TICS-E) and to report its psychometric properties. Methods A random route sample of healthy participants (N = 483) aged 18–30 years completed the TICS-E. The robust maximum likelihood estimation with a mean-adjusted chi-square test statistic was applied due to the sample’s significant deviation from the multivariate normal distribution. Goodness of fit, absolute model fit, and relative model fit were assessed by means of the root mean square error of approximation (RMSEA), the Comparative Fit Index (CFI) and the Tucker Lewis Index (TLI). Results Reliability estimates (Cronbach’s α and adjusted split-half reliability) ranged from .84 to .92. Item-scale correlations ranged from .50 to .85. Measures of fit showed values of .052 for RMSEA (Cl = 0.50–.054) and .067 for SRMR for absolute model fit, and values of .846 (TLI) and .855 (CFI) for relative model-fit. Factor loadings ranged from .55 to .91. Conclusion The psychometric properties and factor structure of the TICS-E are comparable to the German version of the TICS. The instrument therefore meets quality standards for an adequate measurement of chronic stress.

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Financial literacy has been recognized as an essential skill for individuals to act in the complex economic context. However, the evidence indicates that financial literacy is a complex phenomenon that it can be determinant of other behavioral factors, besides presenting itself differently in different socioeconomic and demographic variables. Thus, the present research seeks to innovate and advance in this theme, aiming to develop a model capable of encompassing the direct and indirect relations of financial literacy with the behavioral factors: materialism, compulsive buying and propensity to debt. In addition to identifying the invariance of the proposed model according to the socioeconomic and demographic variables, when verifying if a single model is adequate to measure the financial literacy of different groups of individuals and to point out the differences of averages existing between them. For that, this research was carried out with 2,487 individuals, using confirmatory factorial analysis, structural equation modeling and multigroup analysis, with eight propositions and six research hypotheses that integrate the proposed model. The main results showed that the majority had a low level of financial literacy, and the model for their measurement was invariant only for the variables gender, schooling and own income, and confirming three research propositions. In addition, five research hypotheses were confirmed, showing that the impact of financial literacy on compulsory buying was the largest among the proposed direct relationships. The total effects that financial literacy has on behavioral factors, we can see that the greatest impact was on compulsive buying behavior, followed by the impact on the propensity to debt and, finally, on materialism. These results are important for the development of public policies and other actors interested in the theme, since financial literacy goes beyond the fact of impacting the financial health of those who have it, but it can also help in a broader way those who suffer of other psychosocial behaviors, such as compulsive buying behavior. Models of this theme become fundamental to understand the importance and possible impacts of adopting national financial literacy strategies, and it can help in the development of treatments. The results showed that the impact imagined when studying only the financial literacy in the propensity to debt of the individuals becomes even more expressive when other behavioral factors are involved in this relation. / A alfabetização financeira vem sendo reconhecida como uma habilidade essencial para os indivíduos atuarem no complexo contexto econômico que estão inseridos. No entanto, as evidências indicam que a alfabetização financeira é um fenômeno complexo e que pode ser determinante de outros fatores comportamentais, além de apresentar-se de maneira distinta em diferentes variáveis socioeconômicas e demográficas. Assim, o presente trabalho busca inovar e avançar neste tema, tendo como objetivo desenvolver um modelo capaz de abarcar as relações diretas e indiretas da alfabetização financeira com os fatores comportamentais: materialismo, compras compulsivas e propensão ao endividamento. Buscando ainda identificar a invariância do modelo proposto segundo as variáveis socioeconômicas e demográficas, ao verificar se um único modelo é adequado para mensurar a alfabetização financeira de diferentes grupos de indivíduos e nestes, apontar as diferenças de médias existentes entre eles. Para tal, realizou-se uma pesquisa com 2.487 indivíduos, utilizando análise fatorial confirmatória, modelagem de equações estruturais e análise multigrupo, com oito proposições e seis hipóteses de pesquisa que integram o modelo proposto. Os principais resultados demonstraram que a maioria dos pesquisados possui um baixo nível de alfabetização financeira e o modelo para mensuração da mesma apresentou-se invariante apenas para as variáveis gênero, escolaridade e renda própria, confirmando três proposições de pesquisa. Além disso, cinco hipóteses de pesquisa foram confirmadas, constatando-se que o impacto da alfabetização financeira nas compras compulsivas foi o maior entre as relações diretas propostas. Já no que tange aos efeitos totais que a alfabetização financeira possui nos fatores comportamentais, percebe-se que o maior impacto da mesma foi sobre o comportamento de compra compulsiva, seguido do impacto na propensão ao endividamento e, por fim, sobre o materialismo. Tais resultados tornam-se importantes para o desenvolvimento de políticas públicas e de outros agentes interessados no tema, uma vez que a alfabetização financeira vai além do fato de impactar na saúde financeira daqueles que a possuem, mas também pode auxiliar de uma forma mais ampla naqueles que sofrem de outros comportamentos psicossociais, como o comportamento de compras compulsivas. Modelos dessa natureza tornam-se fundamentais para que se entenda a importância e os possíveis impactos da adoção de estratégias nacionais de alfabetização financeira, podendo auxiliar na construção de tratamentos. Demonstrando que o impacto que se imaginava ao estudar apenas a alfabetização financeira na propensão ao endividamento dos indivíduos, se torna ainda mais expressivo quando outros fatores comportamentais estão envolvidos nesta relação.

Made available in DSpace on 2015-05-14T12:14:07Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 735779 bytes, checksum: 2ffa25e5b45beedc0c8f4f31d5f79b06 (MD5) Previous issue date: 2013-06-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this thesis, we review some basic concepts related to Lorentz symmetry violation and Horava-Lifshitz-like theories. We present our contribution to the calculation of the effective potential in two frameworks that exhibit Lorentz invariance violation. First, we calculate the effective potential for some HL-like theories. We obtained results for the pure scalar model, for the scalar QED with critical exponent z = 2 and z generic, and for the Yukawa model also with z = 2 and with arbitrary values of z. For the latter model, we show that the effective potential vanishes for even z and has nontrivial values for odd z. The second framework is the Kostelecký-Berger model that implements the Lorentz symmetry breaking in supersymmetry. We develop the theory of superfields for three and four-dimensional space-time based on this model and show how this development leads to a theory of superfields with ether-like Lorentz violation. We also obtained the one loop contributions to the effective action and effective potential in this theory. / Nesta tese, revisamos alguns conceitos básicos relacionados à violação da simetria de Lorentz e a teorias do tipo Horava-Lifshitz. Apresentamos nossa contribuição ao cálculo do potencial efetivo em duas formulações que exibem violação da invariância de Lorentz. Primeiro, calculamos o potencial efetivo para algumas teorias do tipo HL. Obtivemos resultados para o modelo escalar puro, para a QED escalar com expoente crítico z = 2 e z genérico, e para o modelo de Yukawa também com z = 2 e com valores arbitrários de z. Para este último modelo, demonstramos que o potencial efetivo se anula para z par e possui valores não triviais para z ímpar. A segunda formulação é o modelo de Kostelecký-Berger que implementa a quebra da simetria de Lorentz em supersimetria. Desenvolvemos a teoria de supercampos para três e quatro dimensões do espaço-tempo com base neste modelo e mostramos como este desenvolvimento leva a uma teoria de supercampos com violação de Lorentz do tipo-éter. Obtemos também as contribuições de um loop para a ação efetiva e para potencial efetivo nesta teoria.

The study of conformal symmetry is motivated through an example in statistical mechanics and then rigorously developed in quantum field theories in general spatial dimensions. In particular, primary fields are introduced as the fundamental objects of such theories and then studied in the formalism of radial quantization. The implications of conformal invariance on the functional form of correlation functions are studied in detail. Conformal blocks are defined and various approaches to their analytical and numerical calculation are presented with a special emphasis on the one-dimensional case. Building on these preliminaries, a modern formulation of the conformal bootstrap program and its various extensions are discussed. Examples are given in which bounds on the scaling dimensions in a one-dimensional theory are derived numerically. Using these results I motivate the technique of using the extremal functional bootstrap which I then develop in more detail. Many technical details are discussed and examples shown. After a brief discussion of conformal field theories with a boundary I apply numerical methods to find constraints on the spectrum of the 3D Ising model. Another application is presented in which I study the 4-point function on the boundary of a particular theory in Anti-de-Sitter space in order to approximate the mass spectrum of the theory. / O estudo da simetria conforme é motivado através de um exemplo em mecânica estatística e em seguida rigorosamente desenvolvido em teorias de campos quânticos em dimensões espaciais gerais. Em particular, os campos primários são introduzidos como os objetos fundamentais de tais teorias e então estudados através do formalismo de quantização radial. As implicações da invariância conforme na forma funcional das funções de correlação são estudadas em detalhe. Blocos conformes são definidos e várias abordagens para seu cálculo analítico e numérico são apresentadas com uma ênfase especial no caso unidimensional. Com base nessas preliminares, uma formulação moderna do programa de bootstrap conforme e suas várias extensões são discutidas. Exemplos são dados em que limites nas dimensões de escala em uma teoria unidimensional são derivados numericamente. Usando esses resultados, motivei a técnica de usar o bootstrap funcional extremo, que depois desenvolvo em mais detalhes. Diversos detalhes técnicos são discutidos e exemplos são apresentados. Após uma breve discussão das teorias de campo conformes com fronteiras, eu aplico métodos numéricos para encontrar restrições no espectro do modelo de Ising em 3D. Outra aplicação é apresentada em que eu estudo a função de 4 pontos na fronteira de uma teoria particular no espaço Anti-de-Sitter, a fim de aproximar o espectro de massa da teoria.

Le sujet de cette thèse est la question du nombre minimal d’orbites de Reeb distinctes sur une variété de contact qui est le bord d’une variété symplectique compacte. L’homologie symplectique S1-équivariante positive est un des outils principaux de cette thèse; elle est construite à partir d’orbites périodiques de champs de vecteurs hamiltoniens sur une variété symplectique dont le bord est la variété de contact considérée.Nous analysons la relation entre les différentes variantes d’homologie symplectique d’une variété symplectique exacte compacte (domaine de Liouville) et les orbites de Reeb de son bord. Nous démontrons certaines propriétés de ces homologies. Pour un domaine de Liouville plongé dans un autre, nous construisons un morphisme entre leurs homologies.Nous étudions ensuite l’invariance de ces homologies par rapport au choix de la forme de contact sur le bord. Nous utilisons l’homologie symplectique S1-équivariante positive pour donner une nouvelle preuve d’un théorème de Ekeland et Lasry sur le nombre minimal d’orbites de Reeb distinctes sur certaines hypersurfaces dans R2n. Nous indiquons comment étendre au cas de certaines hypersurfaces dans certains fibrés en droites complexes négatifs.Nous donnons une caractérisation et une nouvelle fa ç on de calculer l’indice de Conley-Zehnder généralisé, défini par Robbin et Salamon pour tout chemin de matrices symplectiques. Ceci nous a mené à développer de nouvelles formes normales de matrices symplectiques. / This thesis deals with the question of the minimal number of distinct periodic Reeb orbits on a contact manifold which is the boundary of a compact symplectic manifold.The positive S1-equivariant symplectic homology is one of the main tools considered in this thesis. It is built from periodic orbits of Hamiltonian vector fields in a symplectic manifold whose boundary is the given contact manifold.Our first result describes the relation between the symplectic homologies of an exact compact symplectic manifold with contact type boundary (also called Liouville domain), and the periodic Reeb orbits on the boundary. We then prove some properties of these homologies. For a Liouville domain embedded into another one, we construct a morphism between their homologies. We study the invariance of the homologies with respect to the choice of the contact form on the boundary.We use the positive S1-equivariant symplectic homology to give a new proof of a Theorem by Ekeland and Lasry about the minimal number of distinct periodic Reeb orbits on some hypersurfaces in R2n. We indicate how it extends to some hypersurfaces in some negative line bundles. We also give a characterisation and a new way to compute the generalized Conley-Zehnder index defined by Robbin and Salamon for any path of symplectic matrices. A tool for this is a new analysis of normal forms for symplectic matrices.

Des modèles de Gravité Quantique (QG) prédisent une violation de l'invariance de Lorentz (LIV), se manifestant par une dispersion de la lumière dans le vide. Si un tel effet existe, des photons d'énergies différentes émis en même temps par une source distante sont détectés sur Terre à des moments différents. Les émissions transitoires à (très) hautes énergies provenant de sources astrophysiques lointaines, comme les sursauts gamma (GRBs) et les blazars sont utilisées pour contraindre cet effet LIV. Cet ouvrage présente les études menées avec deux télescopes gamma majeurs : H.E.S.S. -- pour lequel une étude de la qualité des données étalonnées a été réalisée -- et Fermi-LAT. Les énergies et les temps d'arrivée de photons individuels ont été utilisés pour contraindre le paramètre de dispersion dans le vide ainsi que l'échelle d'énergie E_QG à laquelle des effets LIV peuvent apparaitre. La méthode de maximum de vraisemblance est décrite, avec une étude détaillée des systématiques. Une modification dans le cas de fond non négligeable est appliquée aux données de l'éruption d'un blazar observé par H.E.S.S. : les limites obtenues sur E_QG sont moins contraignantes que les meilleures limites précédentes, mais elles se trouvent à un redshift non couvert à ce jour. Quatre GRBs observés par Fermi-LAT ont aussi été analysés, en déterminant la courbe de lumière de deux manières : ajustements gaussiens et estimation par densité de noyaux. Les meilleures limites sur E_QG pour le cas linéaire/subluminal sont obtenus avec GRB090510 : E_QG,1 > 7,6 E_Planck. Des limites plus robustes, tenant compte des effets intrinsèques à la source, ont également été produites. / Some Quantum Gravity (QG) theories allow for a violation of Lorentz invariance (LIV), manifesting as a dependence on the velocity of light in vacuum on its energy. If such a dependence exists, then photons of different energies emitted together by a distant source will arrive at the Earth at different times. (Very) high energy transient emissions from distant astrophysical sources such as Gamma-ray Bursts (GRBs) and blazars can be used to search for and constrain LIV. This work presents the studies obtained with two leading Gamma-ray telescopes: H.E.S.S. -- for which a study of the quality of the calibrated data was performed -- and Fermi-LAT. The energies and arrival times of individual photons were used to constrain the vacuum dispersion parameter and the energy scale EQG at which QG effects causing LIV may arise. The maximum likelihood method is described, with detailed studies of the systematics. A modification for a non-negligible background is provided and applied to the data of an AGN flare observed by H.E.S.S.: the obtained limits on the QG energy scale are less constraining than the previous best limits obtained with blazars; yet, the new limits lie a redshift range not covered this far. Four bright and quasi background-free GRBs observed by the Fermi-LAT were also analysed, with two different template light curve determinations -- Gaussian fits and Kernel Density Estimates. The best limits on the E_QG scale for the linear/subluminal case are from the shortest burst, GRB090510: E_QG,1 > 7.6 E_Planck. More robust limits, considering the intrinsic effects possibly occurring at the source, were also derived.

Diese Dissertation betrachtet verschiedene Schritte einer sozialwissenschaftlichen Erhebung zur Integration Geflüchteter in Deutschland. Anhand von vier Zeitschriftenartikeln wird eine neuartige Strategie, um eine Zufallsstichprobe von Geflüchteten in Deutschland zu ziehen, besprochen, die Folgen fehlender muttersprachlicher Übersetzungen von Fragebögen analysiert, latente Konstrukte auf Vergleichbarkeit getestet und Fragen ökonomischer Integration in sich verändernden Migrationsregimen diskutiert. Der erste Artikel befasst sich mit einer sequentiellen Ziehungsstrategie für Zufallsstichproben. Diese ermöglicht eine zeitnahe Erhebung von Zuwanderern in Zeiten hoher Immigration, da Registerdaten Migranten nur mit zeitlicher Verzögerung umfassend abdecken. Im zweiten Artikel wird gezeigt, dass fehlende muttersprachliche Übersetzungen von Umfragen die Item-Nonresponse erhöhen. Auch die Bereitstellung von Audio-Aufnahmen kann diesem Effekt nicht entgegenwirken. Im dritten Artikel wird die Vergleichbarkeit latenter Konstrukte in multikulturellen und multisprachlichen Erhebungen am Beispiel von Vorstellungen zu demokratischen Systemen untersucht. Messinvarianztests deuten darauf hin, dass Vorstellungen von Demokratie über verschiedene Herkunftsländer und Sprachen nicht vergleichbar sind. Der letzte Artikel beschäftigt sich mit der ökonomischen Integration Geflüchteter und argumentiert, dass diese auf institutioneller Ebene betrachtet werden muss. Fixed-Effects- Regressionsanalysen kombiniert mit einem exakten Matching führen zu der Schlussfolgerung, dass sichere Aufenthaltstitel und die Teilnahme an Integrationskursen bei Geflüchteten in Deutschland zu einer erhöhten Anstrengung führt Zugang zum Arbeitsmarkt zu bekommen. / This dissertation looks at the different steps in the process of conducting a survey on refugees living in Germany and discusses key focal points of integration research. In four different articles, I discuss the novel sampling strategy used in a survey of refugees, analyze the effects of missing questionnaire languages, test latent constructs for measurement invariance, and discuss the analysis of economic integration in a changing migration regime. In the first article, I propose a sequential sampling strategy to sample refugees in times of high immigration. In the second article, I show that the lack of questionnaires in a respondent’s mother tongue increases item nonresponse. Providing additional audio recordings of the questions does not diminish this effect. In the third article, I use conceptions of democracy as a case study to show that latent constructs in multi-cultural and multi-linguistic surveys face specific challenges and limitations in their comparability. By employing tests for measurement invariance, my results show that conceptions of democracy are likely not comparable across countries of origin or across languages. The fourth and last article looks at the economic integration of refugees. In it, I propose that integration trajectories have to be observed within the specific institutional settings in which they take place. Fixed-effects regression analyses combined with a coarsened exact matching lead to the conclusion that a secure residence permit and participation in integration classes lead to increasing investments in future labor market access of refugees in Germany.

La propagation des rayons Ɣ de très haute énergie (E > 100GeV) dans l'univers est affectée par les propriétés du milieu extragalactique. Ces photons à l'échelle du TeV, issus des processus d'accélération de particules dans les noyaux actifs de galaxies, peuvent en effet interagir avec des photons du fond optique et infrarouge qui baignent l'univers et produire des paires d'électrons et de positrons. Ce processus réduit la transparence de l'univers aux rayons Ɣ de très haute énergie mais permet en revanche de sonder les propriétés du milieu extragalactique de façon unique. Dans cette thèse, les données prises par le réseau de télescopes à imagerie Tcherenkov atmosphérique H.E.S.S. sont analysées et utilisées afin de caractériser la transparence de l'univers aux rayons Ɣ de très haute énergie. Une mesure indépendante de la distribution spectrale en énergie du fond cosmologique optique et infrarouge est réalisée à travers l'ajustement des modulations observées dans les spectres en énergie obtenus avec H.E.S.S. pour un échantillon de noyaux actifs de galaxies brillants dans une gamme en redshift 0.03 < z < 0.28. Les résultats obtenus sont compatibles avec les limites inférieures dérivées par comptages de galaxies et ne suggèrent pas d'anomalie de la transparence de l'univers aux rayons Ɣ vis à vis des modèles actuels du fond de lumière extragalactique. Des processus de second ordre affectant la propagation des rayons Ɣ de très haute énergie sont également explorés. Des limites sur une brisure de la symétrie de Lorentz à l'échelle de Planck sont obtenues à partir de l'analyse spectrale du noyau actif Mrk 501 observé dans un état de flux exceptionnel par H.E.S.S. en 2014, à grand angle zénithal. Enfin, des contraintes sur le champ magnétique extragalactique sont dérivées en considérant l'émission Ɣ secondaire attendue à partir de simulations des cascades électromagnétiques initiées lors du processus d'absorption pour le noyau actif distant PG 1553+113 vu par H.E.S.S. et le télescope spatial Fermi. Cette thèse a également été l'occasion d'une participation aux développements de certains aspects de la calibration et de l'analyse des données de H.E.S.S. / The propagation of very high energy Ɣ rays in the universe depends on the properties of the extragalactic medium. Such TeV-scale photons travelling cosmological distances are -emitted through particle acceleration mechanisms in active galaxy nuclei- can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. This effect reduces the transparency of the universe to very high energy Ɣ rays but it also provides a unique opportunity to probe the properties of the extragalactic medium. In this thesis, data taken with the H.E.S.S. array of Cherenkov telescopes are analyzed and used to characterize the transparency of the universe to very high energy Ɣ rays. A independent measurement of the spectral energy distribution of the EBL with H.E.S.S. is presented. It is obtained by extracting the EBL absorption signal from the fit of spectral modulations in the high-quality spectra of a sample of bright blazars in the redshift range 0.03 < z < 0.28. The intensity of the EBL obtained in different spectral bands is presented together with the associated Ɣ-ray horizon. The obtained results are consistent with lower limits derived from galaxy counts and do not suggest an anomaly of the transparency of the universe to Ɣ rays with respect to current models of the extragalactic background light. Second-order processes affecting the propagation of very high energy Ɣ rays in the universe are also considered. Limits on Lorentz invariance violation at Planck scale are obtained from the spectral analysis of the active galaxy nucleus Mrk 501 observed during a high-flux state by H.E.S.S. in 2014, at large zenith angle. Finally, constraints on the extragalactic magnetic field properties are derived by considering the secondary Ɣ-ray emission expected from the simulation of electromagnetic cascades initiated by the absorption process for the distant active galaxy nucleus PG 1553+113 seen by H.E.S.S. and the Fermi Ɣ-ray space telescope. In this thesis some developments related to the calibration and analysis of H.E.S.S. data are also presented.

We extend Følner’s amenability criterion to the realm of general topological groups. Building on this, we show that a topological group G is amenable if and only if its left-translation action can be approximated in a uniform manner by amenable actions on the set G. As applications we obtain a topological version of Whyte’s geometric solution to the von Neumann problem and give an affirmative answer to a question posed by Rosendal.