Geomagnetic excursions, brief deviations in geomagnetic field behaviour from that expected during 'normal' secular variation, remain some of the most enigmatic features of geomagnetic field behaviour. This thesis presents high-resolution records of geomagnetic excursions recorded at the Blake-Bahama Outer Ridge in the Western North Atlantic. The highest resolution record yet of the Blake geomagnetic excursion (~125 ka) is measured in three cores from Ocean Drilling Program Site 1062 (ODP Leg 172). These cores have sufficiently high sedimentation rates (>10 cm ka^-1) to allow detailed reconstruction of the field behaviour at these sites during the excursions. Previous reconstructions of geomagnetic field behaviour during excursions from marine cores have been limited by low-resolution age models. This thesis discusses a new approach, whereby measurements of excess ²³⁰Th (²³⁰Th_xs) are used to constrain relative variations in sedimentation rate. Modifications are suggested to the methods previously used to calculate the concentration of ²³⁰Th_xs and a new MATLAB® program is developed and described that allows rapid and flexible calculation of ²³⁰Th_xs. Using this new approach, the duration (6.5±1.3 kyr) and age (129-122 ka) of the Blake excursion are accurately constrained. A palaeomagnetic study is also conducted on two ODP Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge to obtain a high-resolution record of the Laschamp geomagnetic excursion (~41 ka). The Blake excursion is found to be of 'long' duration (6.5±1.3 kyr) whilst the Laschamp excursion is relatively short (<400 years) showing that excursions do not have a characteristic duration, linked to the conductivity of the inner core, but instead occupy a continuous range of durations. The records of both the Blake excursion and the Laschamp excursion from the Blake-Bahama Ridge sites also show rapid transitions to excursional geomagnetic pole positions (less than 500 years), much faster than often quoted for full geomagnetic reversals. Based on current estimates for reversal durations, this would imply that excursions and reversals are controlled by different processes.

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In this thesis, a set of some prevailing rate-based models for bistable perception have been considered in order to find the implications of the novel results reported in Pastukhov & Braun (2011). These authors have quantified not only salient aspects of bistable perception (mean and dispersion of dominance distributions), but also some hidden hysteresis effects ignored up to now. Extensive computational simulations of different prevailing models rigorously demonstrate that the history-dependence of the perceptual process shown by Pastukhov & Braun (2011), effectively constrains the region of the parameter space able to replicate the empirical data. Concretely, that just small regions residing inside a bistable or two-attractor region of the whole parameter space are actually adequate to reproduce the experimental results, both for BR and KDE displays. Remarkably, the results remain valid across all the different classes of models considered, regardless the details of the neuronal implementation. The biological plausibility of the parameter region found for each of the models considered, is further stressed with respect to the widely known Levelt’s propositions. To that end, we make use of weighted sums across the parameter regions computed for each subject in the first part of this Thesis, an algorithm that constitutes an important improvement to the methodology proposed by Shpiro et al. (2007) to fit behavioral data by rate-based models. It is shown how different neuronal mechanisms clearly differ in their suitability to replicate Levelt’s propositions. For instance, models with a slow fatiguing process given by spike-frequency adaptation Wilson (2003); Shpiro et al. (2007), no matter if they are being described by linear Shpiro et al. (2007) or nonlinear Curtu et al. (2008)) functions of the activity, replicate quite well Levelt’s second law. Oppositely, a notable discrepancy between model and empirical results is found when such negative feedback is described as a long-term depression affecting the synapses between the competing neurons representing the two alternative interpretations Laing & Chow (2002); Shpiro et al. (2007). The present work finishes with a study about the capability of the mentioned models to reproduce the resonance effects happening when varying external frequencies, as shown by Kim et al. (2006). Importantly, a resonance respect to the noise dispersion (i.e., a true stochastic resonance ) is clearly demonstrated here for the first time. Previous estimations of noise dispersion (20 − 30% of the input) and its locus (adaptation variables) are questioned, by demonstrating that increased sensitivity to even weak signals of the order of less than 10% can be obtained with the models considered, with the noise variable simply entering as part of the net input feeding the neuron. / En este trabajo, son considerados una serie de modelos para frecuencia neuronal ampliamente aceptados en percepción bi-estable, con el objetivo de evaluar las implicaciones de los resultados recientemente reportados en Pastukhov & Braun (2011). Estos autores han cuantificado no solamente aspectos más conocidos sobre el fenómeno (media y dispersión de las distribuciones de dominancia), sino también efectos de historia que habían sido ignorados hasta el presente. Por medio de simulaciones computacionales, se demuestra rigurosamente que la dependencia de la historia del proceso perceptual encontrada por Pastukhov & Braun (2011) efectivamente restringe la región válida de parámetros que es adecuada para reproducir los datos empíricos. Concretamente, que solamente pequeñas regiones del espacio de parámetros disponible, y que se encuentran dentro de una región dinámica bi-estable caracterizada por dos atractores, son realmente adecuadas, tanto para rivalidad binocular (BR) como para estímulos de estructura por movimiento (KDE). Resulta importante destacar que los resultados permanecen válidos de un modelo a otro, independientemente de los detalles de implementación neuronal. La plausibilidad biológica de la región de parámetros encontrada para cada modelo es entonces considerada, en el contexto de las ampliamente conocidas proposiciones de Levelt. Con tal objetivo, hacemos uso de un algoritmo de suma pesada para extraer valores medios de la regiones de parámetros correspondientes a cada sujeto. Este algoritmo constituye una importante mejora a la metodología propuesta por Shpiro et al. (2007) para ajustar modelos de frecuencia neuronal a datos comportamentales de percepción bi-estable. Es entonces mostrado como cada mecanismo neuronal considerado es clara- mente diferente en su capacidad para reproducir las proposiciones de Levelt. Por ejemplo, modelos conteniendo procesos lentos de retroalimentación negativa da- dos por adaptación de frecuencia de disparo Wilson (2003); Shpiro et al. (2007), sin importar si están descritos por funciones lineales Shpiro et al. (2007) or no lineales Curtu et al. (2008)) de la actividad, consiguen reproducir de modo razonable la segunda proposición de Levelt. Por el contrario, una notable discrepancia entre modelo y resultados empíricos es encontrada cuando tales procesos están dados por la presencia de depresión sináptica de larga duración. El presente trabajo culmina con un estudio sobre la capacidad de los mencionados modelos para reproducir los efectos de resonancia que ocurren al variar la frecuencia externa de modulación Kim et al. (2006). Es de destacar que en nuestro caso, un efecto de resonancia es encontrado respecto a la dispersión del ruido, lo cual indica la presencia de una verdadera resonancia del tipo estocástico. Este efecto es claramente demostrado para estos modelos, por primera vez, en el presente trabajo. Previas estimaciones de la dispersión del ruido (20 − 30 % de la señal de entrada) y su localización (variables de adaptación) son analizadas. Se demuestra que un incremento de la sensibilidad a incluso muy pequeñas señales de menos del 10% puede ser encontrada en estos modelos, con sólo incluir la variable de ruido como parte de la corriente neta que alimenta la neurona.

Mon laboratoire d’accueil a participé à l’identification du gène R-spondin1, dont les mutations sont responsables d’anomalies cutanées telles que l’hyperkératose palmo-plantaire, les prédispositions aux cancers spinocellulaires et certains types d’inversions de sexe. La génération du modèle murin a permis de montrer que RSPO1, un activateur de la voie de signalisation Wnt/ßcatenin, est nécessaire à la différenciation ovarienne. R-spondin1 et Sox9 sont connus comme étant des facteurs clé de la détermination du sexe femelle et mâle respectivement. J’ai tout d’abord participé à l’étude de leur fonction dans les pathologies d’inversions de sexe afin de déterminer le rôle de chacune de ces voies dans ces processus. L’étude de 2 modèles murins, d’invalidation conditionnelle du gène Sox9, ainsi que de double invalidation des gènes Sox9 et R-spondin1, a permis de montrer que la détermination du sexe est une balance entre la voie de signalisation mâle activée par les Sox et la voie de signalisation femelle activée par R-spondin1. Dans la 2ème partie de ma thèse j’ai évalué le rôle de R-spondin1 dans la physiologie de l’ovaire post-natal en étudiant un modèle murin de gain-de-fonction de R-spondin1 dans l’ovaire, puisque celui-ci est normalement faiblement exprimé au stade adulte. Cette partie de l ‘étude a démontré que le maintien de l'expression de R-spondin1 empêche les cellules nourricières de l’ovaire, les cellules de la granulosa, de se différencier, empêche l'atrésie folliculaire et favorise l’apparition de kystes sanguins après ovulation. / Our lab has contributed to the identification of the R-spondin1 (Rspo1) gene. Disruption of this gene leads to different defects such as palmoplantar hyperkeratosis, predisposition to squamous cell carcinoma and sex reversals. Establishment of the mouse model led to the result that RSPO1, which activates the WNT/ßcatenin signaling pathway, is necessary for ovarian differentiation. Rspo1 and Sox9 are known to be key factors in female and male sex determination, respectively. I first participated to the study of their role in sex reversals, in order to determine the role of each pathway in these processes. The study of 2 different mouse models (conditional knockout of Sox9 and R-spondin1/Sox9 double knockout), led us to the conclusion that sex determination is a balance between the male pathway activated by Sox genes and the female pathway activated by R-spondin1. I then evaluated the role of R-spondin1 in the adult ovary using a mouse model over expressing R-spondin1 in the ovary, as it is usually downregulated in the adult. I was able to observe that maintenance of R-spondin1 expression in the adult keeps the granulosa cell lineage from differentiating properly, prevents atresia in the ovary and may contribute to the formation of blood filled cysts following ovulation. In conclusion, our study shows that sex determination and adult ovary homeostasis need to be highly regulated. Deregulation of key genes such as R-spondin1 can lead to different pathologies, such as sex reversal and tumor formation.

Det är genom den finansiella redovisningen som företag redogör för sina prestationer. Företag eftersträvar att redovisa höga vinster i syfte att värna om relationen till intressenter, vilken är relaterad till finansiell information. Earnings management utgör ett verktyg för att styra redovisad information i önskad riktning. Det bidrar till snedvridning och minskad trovärdighet för den finansiella rapporteringen.Dåvarande ordförande för U.S. Security and Exchange Commission, Arthur Levitt, uttrycker att earnings management är problematiskt, det försämrar kvaliteten på redovisat resultat och finansiella rapporter. Earnings management innebär ett utnyttjande av bedömningsutrymmen i syfte att manipulera den finansiella informationen. En redovisningspost som skapar tillfälle för företeelsen är avsättningar, vilka baseras på bedömningar. Avsättningar kan övervärderas för att skapa utrymme för framtida återföring, med avsikt att öka redovisat resultat. Av tidigare forskning framgår att återföring av avsättningar används mer frekvent när företag redovisar ett negativt resultat. Det har även konstaterats att företag återför avsättningar för att nå upp till förväntningar eller för att undvika att rapportera nedgång i vinster.Syftet med studien är att, inom ramen för earnings management, studera effekter av när företag på Nasdaq OMX Stockholm Large Cap återför avsättningar. Detta med fokus på företagens resultat samt måluppfyllelse. I studien är relationen mellan redovisat resultat och återföring av avsättningar central. Det undersöks huruvida avsättningar återförs, antingen för att undvika att redovisa ett förlustresultat eller för att nå upp till vinstmål. Det ska mynna ut i en slutsats om huruvida earnings management förekommer. Tidigare forskare har uttryckt ett behov av denna sortens studie, då det finns få empiriska studier där återföring av avsättningar granskas med koppling till earnings management.Studien har en deduktiv ansats och en kvantitativ metod har tillämpats för att besvara forskningsfrågorna. Datamaterialet utgörs av 222 stycken årsredovisningar under tidsperioden 2010-2015. Relevant finansiell information har hämtats ur dem för att testas och vidare analyseras. Datamaterialet har testats genom statistiska sambandstest och dess resultat analyseras med hjälp av tidigare forskning och studiens teoretiska referensram. Den teoretiska referensramen utgörs av positiv redovisningsteori, systemorienterade teorier och designad redovisning.Studien resulterar i ett enhetligt svar på forskningsfrågorna. Svaren indikerar på att earnings management genom återföring av avsättningar inte förekommer på Nasdaq OMX Stockholm Large Cap. Resultatet skiljer sig från tidigare forskning. / The financial statements are meant to convey the performance of a company. Companies strive to report high profits in order to safeguard their relationships with stakeholders, which are related to the financial information. Earnings management represents a tool for controlling reported information in a desired direction. It contributes to distortion and reduced credibility of the financial reporting.Former chairman of the U.S. Security and Exchange Commission, Arthur Levitt, states that earnings management is problematic, it’s causing an erosion in the quality of reported earnings and the financial reports. Earnings management involves the use of discretion in order to manipulate the financial information. Provisions, which are based on estimates, create an opportunity for the phenomenon. Provisions can be overstated to provide reserves for future reversals, with the intention to increase reported earnings. Prior research shows that reversals are used more frequently when companies report a loss. It has also been stated that companies use reversals to meet forecasts or to avoid reporting a decline in profits.The purpose of this study is to examine, in the context of earnings management, effects of reversal of provisions on Nasdaq OMX Stockholm Large Cap. This while focusing on reported earnings and earnings targets. Central for this study is the relationship between reported earnings and reversals. It is examined whether provisions are reversed in order to avoid to report a loss or with the aim to reach an earnings target. This will appear in a conclusion whether earnings management occurs or not. Prior researchers have expressed a need for this kind of study, as there are few empirical studies in which reversal of provisions, in the context of earnings management, is examined.The study has a deductive approach and a quantitative method has been applied in order to answer the research questions. The data material consists of 222 annual reports during the period 2010-2015. Relevant financial information has been collected from the annual reports in order to be investigated and analyzed. The data has been tested through statistical correlation tests and the results are analyzed using prior research and the theoretical framework. The theoretical framework consists of positive accounting theory, systems-oriented theories and designed accounting. The study results in a uniform answer. The answers indicate that earnings management through reversal of provisions does not occur on the Nasdaq OMX Stockholm Large Cap. This result is not consistent with prior research.This thesis is written in Swedish.

This thesis studies the strain response of mastic asphalt to arbitrary tension, arbitrary compression, alternating tension/compression, loading, zigzag loading and sinusoidal loading. In order to model the strain response to different loading histories, the scissors model is employed. Matlab modules are developed that are able to predict strain response not only for creep loading but also for other types of non constant stress loading such as zigzag loading and sinusoidal loading. In addition, another phenomological model, i.e. the viscoelastoplastic continuum damage model, is summarized and discussed in detail with respect to its applicability for the available data set.

This dissertation is comprised of two papers. The first paper (Chapter 1) provides the theoretical foundation for the estimation of systematic downside risk. Using a new approach, I derive a measure of downside systematic risk, downside beta, that is free of the endogeneity problem and thus straightforward to calculate. Since there is no consensus in the literature regarding the appropriate method for the estimation of downside beta, I review the alternative specifications proposed in the past. I explicitly show that the derived formula here is more efficient in capturing downside risk on both theoretical grounds and in terms of empirical results. Using this efficient specification of systematic downside risk, I show that downside beta has increased explanatory power towards the cross-section of equity returns as compared to unconditional beta. In particular, downside beta predicts larger and more significant future premia, insignificant intercepts in portfolio cross-section tests and cannot be subsumed by additional risk factors proposed in the past literature. I attribute this superior performance to the ability of downside risk to capture distress risk and to the fact that it does not penalize (reward) good (bad) events in good states. In the second paper (Chapter 2) that is co-authored with my advisor, Gregory Kadlec, we exploit the notion of downside risk to explain a long-withstanding market anomaly; the long-term stock return reversals. We show that downside betas of past losers are significantly greater than downside betas of past winners, and the inclusion of downside beta in Fama-Macbeth regressions subsumes the reversal effect. / Ph. D.

This dissertation consists of two essays. In the first essay, I examine the source of momentum in stock returns. The reversal of momentum returns has been interpreted as evidence that momentum results from delayed overreaction to information. I examine momentum and reversals conditional on firms’ share issuance (net of repurchases) during the momentum holding period and show that (1) among losers, the momentum returns are statistically significant, but the reversals are non-existent, for both issuers and non-issuers; (2) among winners, momentum and reversals are restricted to issuers, but are non-existent among non-issuers. After further conditioning on firm size, I find that winner reversals are restricted to small, equity issuing firms. After excluding these small issuers from the sample, the remaining firms have strong momentum profits with no accompanying reversals. The evidence suggests that the return reversals are a manifestation of the poor performance of equity issuing firms. Further, while investor overreaction potentially contributes to the momentum among winners, a large fraction of firms do not earn any significant abnormal returns following initial price continuation, suggesting that underreaction, and not delayed overreaction to information, is the dominant source of momentum in stock returns. In the second essay, I examine alternative explanations of reversals in stock returns. George and Hwang (2007) find that long-term reversals in stock returns are driven by investors’ incentive to defer payment of taxes on locked-in capital gains rather than by overreaction to information. I show that return reversals are instead attributable to the negative relationship between firms’ composite share issuance and future stock returns documented in Daniel and Titman (2006). The ability of locked-in capital gains measures to forecast stock returns is largely subsumed by the composite share issuance measure. My results do not support the hypothesis that capital gains taxes drive long-term return reversals. / Ph. D.

Absolute numerousness judgement (ANJ) is numerical competence in which the concrete number is discriminated. ANJ hasn't been tested in pigeons (Columba livia) yet. Therefore six individuals were tested in discrimination of number "three" from ratio 2 vs. 3: two pigeons on "touch screen" and all six by opening small bowls that were closed by discriminated stimulus. Pigeons didn't reach required level of 70 % (they answered with success approx. 30 - 65 %) in any testing environment. Mixed presentation was created such as control of size, possition and shape of discrimination stimulus. It was also studied wheather pigeons used alternative strategies. Success in ANJ was compared with previous discrimination tasks (Kocourková, 2016) in both environment (discrimination of reduced black and white stimulus on the cap and discrimination of round-shaped black and white areas in the Skinner box). If was found out that pigeons weren't able to learn in the same condition discrimination 2 vs. 3 stimulus during the same number of trials which they needed in the previous discrimination task. During answering to the stimulus they didn't use any alternative strategies with one exception. The effect of social hierarchy in the group on the performance of pigeons wasn't found out. Keywords: Columba livia, numerical...

When viewing ambiguous figures, individuals can exert selective attentional control over their perceptual reversibility behaviour (e.g., Strüber & Stadler, 1999). In the current study, we replicated this finding but we also found that ambiguous figures containing faces are processed quite differently from those containing objects. Furthermore, inverting an ambiguous figure containing faces (i.e., Rubin’s vase-face) resulted in an “inversion effect”. These findings highlight the importance of considering how we attend to faces in addition to how we perceive and process faces. Describing the perceptual reversal patterns of individuals in the general population allowed us to draw comparisons to behaviours exhibited by individuals with Asperger Syndrome (AS). The group data suggested that these individuals were less affected by figure type or stimulus inversion. Examination of individual scores, moreover, revealed that the majority of participants with AS showed an atypical reversal pattern, particularly with ambiguous figures containing faces, and an atypical inversion effect. Together, our results show that ambiguous figures can be a very valuable tool for examining face processing mechanisms in the general population and other distinct groups of individuals, particularly those diagnosed with AS. / October 2008