På bullriga arbetsplatser använder personal ofta hörselskydd med inbyggda högtalare för att lyssna på exempelvis musik i underhållningssyfte. Om användaren lyssnar på höga ljudnivåer under långa perioder kan bullerskador uppstå i dennes öron. Enligt lagstiftning måste nivån därför begränsas i förebyggande syfte. Bullernivån är ett genomsnitt av de ljudnivåer användaren exponerats för under en arbetsdag. Användaren måste vila öronen om gränsvärdet för bullernivån nås.Om man utnyttjar att det är ett genomsnitt kan användaren tillåtas lyssna på en hög ljudnivå under en begränsad tid för att sedan sänka den. Det går att bevara både säkerheten och lyssningsupplevelsen om en sänkning införs långsamt. Detta arbete beskriver hur en algoritm till en digital signalprocessor kan konstrueras för att reglera ljudnivån.Målsättningen var att algoritmen skulle skydda användarens hörsel utan att försämra lyssningsupplevelsen, och utan att förbruka mer energi än nödvändigt. I algoritmen ingick en prediktor som predikterar mängden buller användaren riskerar att utsättas för, om denne fortsätter lyssna på samma nivå.Långsamma sänkningar av ljudnivån kan då utföras i tid innan gränsvärdet nås. Det visade sig att algoritmen endast behövde ett fåtal samplingar per sekund för att skatta och reglera ljudnivån tillräckligt precist, vilket reducerade energiförbrukningen.Resultatet visar möjligheten att kombinera målen för säkerhet, lyssningsupplevelse och energieffektivitet i hörselskydd. Algoritmen implementerades inte på ett skarpt system.Den hade enbart tillgång till ljudsignalen användaren ämnade lyssna på i underhållningssyfte. / In noisy workplaces the staff are often using hearing protectors with built-in speakers for entertainment purposes. Prolonged exposure to loud sound levels can cause damage to the user’s ears. The legislation requires therefore a limiting mechanism for the speakers. The noise level is defined as the average of the sound levels the user has been exposed to during a working day. If the noise threshold is reached the user has to rest his ears. This definition can be exploited to allow the user to listen to a loud sound level for a limited time and then lowering it. If the sound level is lowered slowly, it is possible to preserve both safety and listening experience. This work describes how an algorithm can be designed for a digital signal processor with the purpose of controlling the sound level. The aim was to protect the user's hearing without spoiling the listening experience, and without consuming more power than necessary. The algorithm design included a predictor that predicts the amount of noise the user risk being subjected to, if he continues to listen at the same level. Slow reduction of the sound level can then be carried out in time before the noise threshold is reached. It turned out that the algorithm only needed a few samples per second to estimate and control the sound level sufficiently precisely, this reduced the power consumption. The results show that it is possible to combine the objectives for safety, listening experience and power consumption in hearing protectors. The algorithm was not implemented in a real system. The algorithm had only access to the audio signal which the user intended to listen to for entertainment purposes.

Les structures flexibles sont de plus en plus utilisées dans des domaines variés comme l'aérospatiale, l'automobile, etc. Les avantages du contrôle actif des vibrations sont son faible amortissement et sa sensibilité aux vibrations. Dans la réalité, en plus des exigences de réduction effective des vibrations, il faut également prendre en compte la quantité d'énergie nécessaire pour le contrôle, les entrées du contrôle pour éviter la saturation de commande, ainsi que la réduction des effets des bruits de mesure. D'autre part, comme les structures flexibles ont une infinité de modes de résonance et que seuls les premiers modes peuvent être utilisés dans la modélisation du système et dans la conception de contrôleur, les dynamiques négligées en hautes fréquences peuvent induire une instabilité dite "spill over". De plus, les incertitudes sur les paramètres modaux peuvent dégrader les performances de contrôle et même déstabiliser le système en boucle fermée. Dans ce contexte, on propose dans cette thèse une méthodologie quantitative de contrôle actif et robuste des vibrations des structures flexibles. Des stratégies de contrôle de la phase et du gain sont d'abord proposées pour assurer des spécifications dépendant de la fréquence sur la phase et le gain du contrôleur. Ces spécifications peuvent être réalisées par la conception du contrôleur par la méthode Hoo . Le contrôle H00 basé sur ces stratégies permet d'obtenir un compromis entre l'ensemble des objectifs de contrôle et d'offrir un contrôleur robuste qualitatif. En particulier, nous avons utilisé le contrôle LPV Hoo pour réduire l'énergie nécessaire au contrôle du système LPV. Le cadre généralisé du chaos polynomial (gPC) avec analyse par éléments finis, qui permet l'étude des effets des incertitudes de propriétés structurelles sur les fréquences naturelles et qui permet d'obtenir leurs informations probabilistes, est employé pour la quantification des incertitudes. Ensuite, en présence des incertitudes paramétriques et dynamiques, nous avons utilisé l'analyse 11/v et l'algorithme aléatoire en utilisant la méthode de Monte-Carlo pour assurer en même temps la stabilité en boucle fermée et les propriétés de robustesse de la performance à la fois dans le sens déterministe et le sens .probabiliste. La méthodologie de contrôle robuste quantitatif proposée est donc développée en employant des techniques diverses du contrôle automatique et du génie mécanique, et ainsi permet de réduire l'écart entre eux pour le contrôle robuste de la vibration pour des structures flexibles. Son efficacité est vérifiée par des simulations numériques et la validation expérimentale sur des poutres équipées de piézoélectriques non-colocalisés, LTI et LPV. / Flexible structures are increasingly used in various applications such as aerospace, automotive and so on. Since they are lightly damped and susceptible to vibrations, active vibration control is desirable. In practice, in addition to achieving effective vibration reduction, we have also to consider the required control energy to avoid the energy insufficiency, the control input to avoid control saturation and reduce the effects of measurement noises. On the other hand, as flexible structures have infinite number of resonant modes and only the first few can be employed in the system modeling and the controller design, there always exist neglected high-frequency dynamics, which can induce the spillover instability. Furthermore, the parametric uncertainties on modal parameters can degrade the control performances and even destabilize the closed-loop system. In this context, a quantitative robust control methodology for active vibration control of flexible structure is proposed in this thesis. Phase and gain control polices are first proposed to enforce frequency-dependent phase and gain requirements on the controller, which can be realized by the output feedback H1 control design. The phase and gain control polices based H1 control can make a trade-off among the complete set of control objectives and offer a qualitative robust controller. Especially, the LPV H1 control is used to reduce the required control energy for LPV systems. The generalized polynomial chaos (gPC) framework with finite element analysis is employed for uncertainty quantification. It allows us to investigate the effects of structural property uncertainties on natural frequencies and achieve their probabilistic information. Then, in the presence of parametric and dynamic uncertainties, µ / v analysis and the random algorithm using Monte Carlo Method are used to quantitatively ensure the closed-loop stability and performance robustness properties both in deterministic and probabilistic senses. The proposed quantitative robust control methodology is thus developed by employing various techniques from automatic control and mechanical engineering, thus reducing the gap between them for robust vibration control of flexible structures. Its effectiveness are verified by numerical simulations and experimental validation on LTI and LPV non-collocated piezoelectric cantilever beams.

The natural world provides sensory systems with noisy and ambiguous information, which is often transformed into a more stable categorical percept. This thesis aims to investigate the nature of the neural representations in the visual system that support this transformation. To do so, we will employ a behavioural task that requires participants to average several independent sources of perceptual information. This task allows for the dissociation of two theoretically orthogonal sources of decision uncertainty: the mean distance of the perceptual information from a category boundary and the variability of the evidence under consideration. Behaviourally, both decreasing the mean distance to bound of information and increasing information variability are associated with increased errors and prolonged response times. We will present a computational model that can account for the independent behavioural effects of these two sources of uncertainty by assuming that categorical decisions are made on the basis of a probabilistic transformation of perceptual evidence. BOLD measurements demonstrate that these effects of mean and variability are supported by a partially dissociable network of brain regions. Electroencephalography demonstrates the differential influence of mean and variance in the pre- and post-decision period. Furthermore, we show that there is adaptation at the level of the perceptual representation to the information variance. Not only does this show that the visual system must represent information at the summary level, in addition to individual feature-based representation, but it also suggests that the costs associated with this form of perceptual uncertainty can be largely mitigated by the adoption of a more suitable representational range.

Akustische Signale dienen vielen Tierarten als Mittel zur Partnerfindung. Diese Tiere müssen ihre Entscheidung für den besten Paarungspartner durch die Integration der Parameter verfügbarer Signale treffen. Das Wahlverhalten weiblicher Grillen basiert auf der Attraktivität des zeitlichen Musters des männlichen Gesangs und auf dessen Intensität. Diese Eigenschaften korrelieren nicht zwangsweise positiv, daher wird sich kein Männchen in einer Aggregation von singenden Männchen als überragend abheben und somit wird dem Weibchen die Entscheidung erschwert. Die vorliegende Arbeit beschäftigt sich mit der Frage wie die relevanten Merkmale des männlichen Gesangs während der Entscheidungsfindung des Weibchens integriert werden. 6 Arten von Feldgrillen wurden in nicht-Wahl- und Wahlexperimenten hinsichtlich ihrer Antworten und Präferenzen für männliche Signale, welche sich in Pulsrate, Modulationstiefe, Intensität, Anordnung der Chirps während der Wiedergabe und der zeitlichen Verschiebung zweier Signale zueinander unterschieden, getestet. Des Weiteren wurde durch Transitivitätstests untersucht, ob dem Wahlverhalten weiblicher Grillen rationale oder vergleichende Entscheidungsmechanismen zugrunde liegen. Zusammenfassend zeigen die Ergebnisse, dass die Verarbeitungsmechanismen, welche der Entscheidungsfindung bei weiblichen Feldgrillen zugrunde liegen, in den untersuchten Arten ähnlich sind. Die Lokalisierung des Signals ist nicht unabhängig von der Erkennung. Neben einem generellen Verarbeitungsschema wurden zwischen den einzelnen untersuchten Arten charakteristische Unterschiede in der Mustererkennung, der Verarbeitung der Signalintensität und der Intensitätsgewichtung festgestellt. Jedoch wiesen nah verwandte Arten ähnlichere Präferenzen auf, als nicht nah verwandte Arten. Die Tests zur Transitivität der Präferenzen weisen auf vergleichende Entscheidungs-mechanismen hin und widersprechen einer rationalen Partnerwahl. / In many animals acoustic signals serve for mate attraction. They thus need to make a decision about which is the best mating partner in a choice situation by integrating the cues of the available signals. Choice behaviour in female crickets is based on the attractiveness of the temporal pattern of a male’s calling song and on its intensity. The parameters of a calling song are not necessarily positively correlated and no male will emerge as superior in an aggregation of singing males. The present thesis addresses the question on which cues decision making is based and how these relevant cues of a male’s song are integrated during the decision process of a female. To this aim no-choice and choice experiments with 6 species of field crickets were conducted. Experiments systematically varied pulse rate, modulation depth, intensity, chirp/trill arrangement and temporal shifts of synchronously presented signals. Furthermore, tests for transitivity of preferences examined if female choice behavior is based on rational or comparative decision making mechanisms. In summary, the results reveal that sensory processing underlying female decisions is similar in the 6 species studied here. Incoming signals are analyzed separately in bilaterally paired networks with parallel pathways for signal attractiveness and signal intensity. A gain-control mechanism fuses the outcome of both pathways and signal intensity is weighted by pattern attractiveness. Thus localization is not independent from signal recognition. Despite this general scheme remarkable characteristic differences between species were observed in pattern recognition, processing of signal intensity and weighting of signal intensity. Closely related species exhibited more similar preferences than unrelated species. Furthermore the tests for transitivity of preferences indicated that females use comparative decision making mechanism and contradicted rational mate choice.

Cette thèse est la R&D de l’électronique de front-end destinée à la camera de deuxième génération du télescope de grande taille LST de projet CTA, étant basée sur les détecteurs de type SiPM. Cette étude rassemble des équipes du LAPP, de l’université de Padoue, de l’INFN et du MPI de Munich. La première partie de cette thèse porte sur les tests de caractérisations d’une matrice de 16 SiPMs fabriquée par Hamamatsu. Les résultats de ces tests ont souligné les avantages qui pourraient être apportés par l’utilisation de tels détecteurs. Un cahier des charges pour l’électronique a été défini à l’issue de ces tests. Notamment, une nécessité de corriger la dispersion en gain entre les 16 pixels qui a été trouvée d’environ 10%. La seconde partie est la conception d’un circuit intégré (ASIC) qui pourrait lire les signaux des pixels -SiPM avec la moindre perturbation possible de fonctionnement du détecteur. Cet ASIC inclut des fonctions de contrôle (slow control) qui permettent l’ajustement de gain des pixels, l’amélioration de l’uniformité de gain et la possibilité de supprimer les canaux bruyants ou encore même le contournement du processus de contrôle de gain. Ces fonctionnalités peuvent unifier le gain de 16 canaux. Les sorties des 16 canaux seront sommées pour en faire deux signaux seulement à la sortie de l’ASIC. Ces deux signaux, un sur le haut gain et l’autre sur le bas gain seront fournis au système d’acquisition qui suivra l’ASIC. Une fonction de déclenchement génèrera un signal de trigger qui sera ainsi transmis au système d’acquisition. Cet ASIC a été réalisée avec la technologie AMS 0.35um BiCMOS. Les simulations ont montré une gamme dynamique linéairement couverte jusqu’à 2000 photoélectrons et la possibilité de mesurer le photoélectron unique grâce au bon rapport signal sur bruit électronique. Les tests au laboratoire confirment une grande partie de ces résultats. / This thesis is the R&D on front-end electronics for a second generation camera based on the SiPM detectors for the Large Size Telescope (LST) of the CTA project. It is a part of the SiPM collaboration involving the LAPP, the University of Padua, the INFN and the MPI in Munich. The first part of the thesis is the characterization of an array of 16 SiPMs from Hamamatsu. The study proves the advantages of using such detectors in the LST. It defines the specifications of the readout electronics that are the aim of this work. Especially that it should ameliorate the gain dispersion of the 16 pixels that was found of about 10%. The second part is the design of the readout ASIC. The scheme tends to measure the SiPMs’ signals with minimum disturbance of the detector. It integrates slow control facilities that adjust the detector’s gain, minimize the dispersion in gain and provide the possibility of deleting noisy channels or even completely jumping over the control process. These facilities could perfectly get rid of the gain dispersion. Outputs of the 16 pixels will be summed on both high gain and low gain so that only two signals are delivered to the acquisition system that follows. A trigger function will also generate a trigger signal to the acquisition system. The choice was made to realize this ASIC according to the rules of the AMS 0.35um BiCMOS technology. Simulation shows a linearly-covered dynamic range up to 2000 photoelectrons with good signal to noise ratio that allows the measurement of the single photoelectron. Laboratory tests confirm a great part of these results.

Normalization is important for a large range of phenomena in biological neural systems such as light adaptation in the retina, context dependent decision making and probabilistic inference. In a normalizing circuit the activity of one neuron/-group of neurons is divisively rescaled in relation to the activity of other neurons/­­groups. This creates neural responses invariant to certain stimulus dimensions and dynamically adapts the range over which a neural system can respond discriminatively on stimuli. This thesis examines whether a biologically realistic normalizing circuit can be implemented by a spiking neural network model based on the columnar structure found in cortex. This was done by constructing and evaluating a highly structured spiking neural network model, modelling layer 2/3 of a cortical hypercolumn using a group of neurons as the basic computational unit. The results show that the structure of this hypercolumn module does not per se create a normalizing network. For most model versions the modulatory effect is better described as subtractive inhibition. However three mechanisms that shift the modulatory effect towards normalization were found: An increase in membrane variance for increased modulatory inputs; variability in neuron excitability and connections; and short-term depression on the driving synapses. Moreover it is shown that by combining those mechanisms it is possible to create a spiking neural network that implements approximate normalization over at least ten times increase in input magnitude. These results point towards possible normalizing mechanisms in a cortical hypercolumn; however more studies are needed to assess whether any of those could in fact be a viable explanation for normalization in the biological nervous system. / Normalisering är viktigt för en lång rad fenomen i biologiska nervsystem såsom näthinnans ljusanpassning, kontextberoende beslutsfattande och probabilistisk inferens. I en normaliserande krets skalas aktiviteten hos en nervcell/grupp av nervceller om i relation till aktiviteten hos andra nervceller/grupper. Detta ger neurala svar som är invarianta i förhållande till vissa dimensioner hos stimuli, och anpassar dynamiskt för vilka inputmagnituder ett system kan särskilja mellan stimuli. Den här uppsatsen undersöker huruvida en biologiskt realistisk normal­iserande krets kan implementeras av ett spikande neuronnätverk konstruerat med utgångspunkt från kolumnstrukturen i kortex. Detta gjordes genom att konstruera och utvärdera ett hårt strukturerat rekurrent spikande neuronnätverk, som modellerar lager 2/3 av en kortikal hyperkolumn med en grupp av neuroner som grundläggande beräkningsenhet. Resultaten visar att strukturen i hyperkolumn­modulen inte i sig skapar ett normaliserande nätverk. För de flesta nätverks­versioner implementerar nätverket en modulerande effekt som bättre beskrivs som subtraktiv inhibition. Dock hittades tre mekanismer som skapar ett mer normaliserande nätverk: Ökad membranvarians för större modulerande inputs; variabilitet i excitabilitet och inkommande kopplingar; och korttidsdepression på drivande synapser. Det visas också att genom att kombinera dessa mekanismer är det möjligt att skapa ett spikande neuronnät som approximerar normalisering över ett en åtminstone tio gångers ökning av storleken på input. Detta pekar på möjliga normaliserande mekanismer i en kortikal hyperkolumn, men ytterligare studier är nödvändiga för att avgöra om en eller flera av dessa kan vara en förklaring till hur normalisering är implementerat i biologiska nervsystem.

[pt] Objetivando suprimir as instabilidades dinâmicas de ganho em um amplificador à fibra dopada com Érbio (EDFA), uma nova configuração de laser em anel é apresentada e demonstrada. Neste trabalho, analizamos os efeitos da variação do nível de atenuação no laço de re-alimentação sobre a resposta transitória do EDFA. Particularmente, observamos as excursões de ganho experimentadas pelo canal sobrevivente quando sete dentre oito canais da rede são adicionados ou removidos, à exemplo do que ocorre em sistemas WDM reais. Sob esta análise, avaliamos o desempenho do sistema em suprimir as instabilidades dinâmicas de ganho do EDFA. / [en] A new ring laser configuration to eliminate the gain dynamic instabilities of an erbium doped fiber amplifier (EDFA) is proposed and demonstrated. We examine the effect of the attenuation level in the optical feedback path over thetransient response of the EDFA. In particular, we look at the transient gain excursions experienced by surviving channel when seven of eight channels are added or dropped, like in real WDM systems. Using this analysis as a guide, we highlight the robustness of the approach and evaluate its performance to EDFA gain stabilization.

Existing neurocomputational and empirical data link deficient neuromodulation of the fronto-parietal and hippocampal-striatal circuitries with aging-related increase in processing noise and declines in various cognitive functions. Specifically, the theory of aging neuronal gain control postulates that aging-related suboptimal neuromodulation may attenuate neuronal gain control, which yields computational consequences on reducing the signal-to-noise-ratio of synaptic signal transmission and hampering information processing within and between cortical networks. Intervention methods such as cognitive training and non-invasive brain stimulation, e.g., transcranial direct current stimulation (tDCS), have been considered as means to buffer cognitive functions or delay cognitive decline in old age. However, to date the reported effect sizes of immediate training gains and maintenance effects of a variety of cognitive trainings are small to moderate at best; moreover, training-related transfer effects to non-trained but closely related (i.e., near-transfer) or other (i.e., far-transfer) cognitive functions are inconsistent or lacking. Similarly, although applying different tDCS protocols to reduce aging-related cognitive impairments by inducing temporary changes in cortical excitability seem somewhat promising, evidence of effects on short- and long-term plasticity is still equivocal. In this article, we will review and critically discuss existing findings of cognitive training- and stimulation-related behavioral and neural plasticity effects in the context of cognitive aging, focusing specifically on working memory and episodic memory functions, which are subserved by the fronto-parietal and hippocampal-striatal networks, respectively. Furthermore, in line with the theory of aging neuronal gain control we will highlight that developing age-specific brain stimulation protocols and the concurrent applications of tDCS during cognitive training may potentially facilitate short- and long-term cognitive and brain plasticity in old age.