1731 research outputs found
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Le rôle dramatique de la vue et de l'ouïe dans la tragédie d'Euripide
No full textLe problème du rapport entre la vue et l'ouïe a passionnément animé le débat intellectuel en Grèce durant le cinquième siècle avant notre ère, dans des domaines aussi différents que la philosophie, l’historiographie, la rhétorique et la médecine. Dans un tel contexte, l'expérience du théâtre représente un cas fort intéressant. La tragédie attique consistait en effet en un spectacle chanté, dans lequel la musique et la danse jouaient un rôle important et qui sollicitait à la fois la vue et l'ouïe des spectateurs. Ce travail analyse donc la dialectique de la vue et de l’ouïe et la façon dont elle devient un instrument dramatique dans les mains du poète. L’analyse porte sur cinq tragédies d’Euripide : Alceste, Hippolyte, Héraclès, Hélène, et Les Bacchantes. Tout en articulant, cas par cas, les modalités de dramatisation aux questionnements contemporains sur la valeur épistémologique de la vue et de l’ouïe comme moyens d’acquisition du savoir, l’étude se focalise sur la manière dont les perceptions visuelles et auditives déterminent les divers degrés de conscience et de connaissance des événements qu’ont les différents personnages sur la scène ainsi que sur la manière dont le dramaturge se sert de ce double appel sensoriel et de cette coprésence d’effets visuels et acoustiques dans la construction de ses drames, à travers des jeux de surprise, de reprise, de renversement ou de décalage, pour caractériser ses personnages et pour orienter la réponse émotionnelle du public
On Efficient Algorithms for Stochastic Simulation of Biochemical Reaction Systems
No full textComputational techniques provide invaluable tools for developing a quantitative understanding the complexity of biological systems. The knowledge of the biological system under study is formalized in a precise form by a model. A simulation algorithm will realize the dynamic interactions encoded in the model. The simulation can uncover biological implications and derive further predictive experiments. Several successful approaches with different levels of detail have been introduced to deal with various biological pathways including regulatory networks, metabolic pathways and signaling pathways. The Stochastic simulation algorithm (SSA), in particular, is an exact method to realize the time evolution of a well-mixed biochemical reaction network. It takes the inherent randomness in biological reactions and the discrete nature of involved molecular species as the main source in sampling a reaction event. SSA is useful for reaction networks with low populations of molecular species, especially key species. The macroscopic response can be significantly affected when these species involved in the reactions both quantitatively and qualitatively. Even though the underlying assumptions of SSA are obviously simplified for real biological networks, it has been proved having the capability of reproducing the stochastic effects in biological behaviour.
Essentially, SSA uses a Monte Carlo simulation technique to realize temporal behaviour of biochemical network. A reaction is randomly selected to fire at a time according to its propensity by conducting a search procedure. The fired reaction leads the system to a new configuration. At this new configuration, reactions have to update their propensities to reflect the changes.
In this thesis we investigate new algorithms for improving performance of SSA. First, we study the application of tree-based search for improving the search of a reaction firing, and devise a solution to optimize the average search length. We prove that by a tree-based search the performance of SSA can be sensibly improved, moving the search from linear time complexity to logarithmic complexity. We combine this idea with others from the literature, and compare the performance of our algorithm with previous ones. Our experiments show that our algorithm is faster, especially on large models.
Second, we focus on reducing the cost of propensity updates. Although the computational cost for evaluating one reaction propensity is small, the cumulative cost for a large number of reactions contributes a significant portion to the simulation performance. Typical experiments show that the propensity updates contribute 65% to 85%, and in some special cases up to 99%, of the total simulation time even though a dependency graph was applied. Moreover, sometimes one models the kinetics using a complex propensity formula, further increasing the cost of propensity updates. We study and propose a new exact simulation algorithm, called RSSA named after Rejection-based SSA, to reduce the cost of propensity updates. The principle of RSSA is using an over-approximation of propensities to select a reaction firing. The exact propensity value is evaluated only as needed. Thus, the propensity updates are postponed and collapsed as much as possible. We show through experiments that the propensity updates by our algorithm is significantly reduced, and hence substantially improving the simulation time.
Third, we extend our study for reaction-diffusion processes. The simulation should explicitly account the diffusion of species in space. The compartment-based reaction-diffusion simulation is based on dividing the space into subvolumes so that the subvolumes are well-mixed. The diffusion of a species between subvolumes is modelled as an additional unimolecular reaction. We propose a new algorithm, called Rejection-based Reaction Diffusion (RRD), to efficiently simulate such reaction-diffusion systems. RRD combines the tree-based search and the idea of RSSA to select the next reaction firing in a subvolume. The highlight of RRD comparing with previous algorithms is the selection of both the subvolume and the reaction uses only the over-approximation of propensities. We prove the correctness and experimentally show performance improvement of RRD over other compartment-based approaches in literature.
Finally, we focus on performing a statistical analysis of the targeted event by stochastic simulation. A direct application of SSA is generating trajectories and then counting the number of the successful ones. Rare events, which occur only with a very small probability, however, make this approach infeasible since a prohibitively large number of trajectories would need to be generated before the estimation becomes reasonably accurate. We propose a new method, called splitting SSA (sSSA), to improve the accuracy and efficiency of stochastic simulation while applying to this problem. Essentially, sSSA is a kind of biased simulation in which it encourages the evolution of the system making the target event more likely, yet in such a way that allows one to recover an unbiased estimated probability. We compare both performance and accuracy for sSSA and SSA by experimenting in some concrete scenarios. Experimental results prevail that sSSA is more efficient than the naive SSA approach
Integration of Head-Centric Optic Flow and Head Rotation signals account for the perception of surface tilt by the active observer
No full textAn observer who approaches a planar surface that rotates about the vertical axis (e.g. a flag hinging on a pole) generates the same Optic Flow (OF) that is produced by a planar surface that rotates about an horizontal axis viewed by a static observer. In spite of this ambiguity, perceived surface orientation by the active observer is usually veridical. This result is consistent with an interpretation of the OF that takes into account egomotion signals (1). Here, we suggest an alternative interpretation based on a computational model that ignores linear egomotion signals (2, 3). An implication of our model is that perceived orientation should flip by 90 degrees whenever the OF undergoes a translational motion in a direction orthogonal to the surface axis of rotation. OF translational motion is always present when an observer moves towards or away from a stimulus display, due to the natural rotations and translations of the head.
Main conclusion:
In the present experiments, we tested our alternative explanation by asking observers to judge surface orientation in three conditions: 1) when a random-dot planar surface is rotated about a stationary axis, 2) when the axis of rotation was tethered to a coordinate system centered on the observer’s head, so as to eliminate the translational components of the OF, and 3) when a translational component was added to the OF produced in 2). The results are consistent with the predictions of our model. Perceived surface orientation (i) was veridical in 1), (ii) was ambiguous in 2), and (iii) underwent a 90 degrees flip with respect to veridical in 3). A similar pattern of results was found when the same OFs, generated by the observer’s movements, were replayed to a static observer.
Next steps:
This is inconsistent with the idea that extra-retinal information resulting from head movements is used to extract a veridical interpretation of optic flow
Essays on Farm Household Decision-Making: Evidence from Vietnam
No full textThis thesis contains three studies which provide theoretical analysis and empirical evidence on the decision-making of farm households under shocks and imperfect markets in Vietnam. The first study attempts to investigate the effects of the 2007-08 global food crisis on the investment, saving and consumption decisions of household producers by using the panel data of the Vietnam Household Living Standard Survey (VHLSS), covering 2006 and 2008. The results show that the high food prices had a positive effect on only fixed asset investments in the period of the crisis. When the price shocks are incorporated in the financial conditions, the findings reveal that the effects of household incomes, loans obtained and land sizes matter.
The second study uses the Vietnam Access to Resources Household Survey (VARHS) of 2010 to assess the determinants of chemical fertiliser adoption for rice cultivation, and effects on productivity and household welfare. The analysis implements both nonparametric (propensity score matching) and parametric (instrumental variables) approaches. The findings show determinants affecting decision of adoption differ from those affecting decision of adoption intensity. The results show unsurprisingly positive impact on outcomes, but focus on advantage of using parametric approach to estimate these impacts.
The third study employs a sub-sample from the 2008 VHLSS that is restricted to rural areas and to children from 10 to 14 years old to explore the relationship between farmland and the employment of children on their family’s farm. The hypothesis is tested in three models (the Tobit, Heckit and double-hurdle models), in which the dependent variables are examined for two stages of decision-making, including the probability of participation and the extent of participation. Empirical evidence supports the hypothesis that child labour increases in land-rich households and decreases in land-poor households
Effect of process parameters on the dimensional and geometrical precision of PM steel parts
No full textThe standard powder metallurgy process is composed by three main step, the powder production, the compaction and the sintering, and the possible secondary operation that allow to improve the mechanical properties and/or the dimensional and geometrical precision. The present work aims at investigating the influence of processing variables on the dimensional and geometrical precision of parts produced by Powder Metallurg
Protein structural dynamics and thermodynamics from advanced simulation techniques
No full textIn this work we apply simulation techniques, namely Monte Carlo simulations and a path integral based
method called Dominant Reaction Pathways
(DRP) approach, in order to study aspects of dynamics and thermodynamics in three different families of peculiar proteins. These proteins are, for reasons such as the presence of an intermediate state in the folding path or topological constraints or large size, different from ideal systems, as may be considered small globular proteins that fold in a two state manner.
The first treated topic is represented by the colicin immunity proteins IM9 and IM7, very similar in structure but with an apparently different folding mechanism. Our simulations suggest that the two proteins should fold with a similar folding mechanism via a populated on-pathway intermediate state.
Then, two classes of pheromones that live in temperate and arctic water respectively are investigated. The two types of pheromones, despite the high structural similarity, show a different thermodynamic behavior, that could be explained, according to our results, by considering the role played by the location of CYS-CYS bonds along the chain.
Finally, the conformational changes occurring in serpin proteins are studied. The serpins are very flexible, with a large size, more than 350 residues, and slow dynamics, from hours to weeks, completely beyond the possibilities of the simulation techniques to date. In this thesis we present the first all-atom simulations, obtained with the DRP approach, of the mechanism related to serpins and a complete characterization of the serpin dynamics is performed. Moreover, important implications for what concerns medical research field, in particular
in drug design, are drown from this detailed analysis
Le rappresentazioni di significato nel servizio sociale nella giustizia penale in contesti orientati dal neoliberismo
No full textLa ricerca analizza una vicenda in cui si ipotizza in atto un fenomeno di erosione delle politiche del welfare state nel settore penale al fine di comprendere come reagiscono gli assistenti sociali e come definiscono la propria posizione professionale
Genetically encoded division machinery for cell free synthetic biology
No full textThe de novo construction of cellular life requires, in part, the assembly of components that confer the ability to
replicate. Herein we describe efforts to reconstitute parts of the Escherichia coli cell division machinery inside of water-in-oil emulsion compartments and synthetic phospholipid vesicles. The system was built with DNA and purified transcription and translation machinery housed in a
compartment. A particular emphasis was placed on FtsZ, a protein that oligomerizes into a ring at the midcell and splits the cell into two. FtsZ does not contain a membrane interaction domain. In vivo, FtsZ interactions with the membrane are mediated by FtsA and ZipA. Therefore, the influence of FtsA on the behavior of FtsZ also was investigated. Fluorescently tagged constructs were used to facilitate evaluation by microscopy. The data showed that FtsZ readily assembles into rings in the presence of FtsA, thereby suggesting that the Fts system can be exploited for building a genetically encoded, self-replicating, cell-like
system. We also explored additional methods of dividing compartments, such as the use of aqueous two and three phase systems
Linguistically Motivated Reordering Modeling for Phrase-Based Statistical Machine Translation
No full textWord reordering is one of the most difficult aspects of Statistical Machine Translation (SMT), and an important factor of its quality and efficiency.
While short and medium-range reordering is reasonably handled by the phrase-based approach (PSMT), long-range reordering still represents a challenge for state-of-the-art PSMT systems. As a major cause of this problem, we point out the inadequacy of existing reordering constraints and models to cope with the reordering phenomena occurring between distant languages.
On one hand, the reordering constraints used to control translation complexity appear to be too coarse-grained. On the other hand, the reordering models used to score different reordering decisions during translation are not discriminative enough to effectively guide the search over very large sets of hypotheses.
In this thesis we propose several techniques to improve the definition of the reordering search space in PSMT by exploiting prior linguistic knowledge, so that long-range reordering may be adequately handled without sacrificing efficiency.
In particular, we focus on Arabic-English and German-English: two language pairs characterized by uneven distributions of reordering phenomena, with long-range movements concentrating on few patterns.
All our techniques aim at improving the definition of the reordering search space by exploiting prior linguistic knowledge, but they do this with different means: namely, chunk-based reordering rules and word reordering lattices, modified distortion matrices and early reordering pruning.
Through extensive experiments, we show that our techniques can significantly advance the state of the art in PSMT for these challenging language pairs.
When compared with a popoular tree-based SMT approach, our best PSMT systems achieve comparable or higher reordering accuracies while being considerably faster
Growth by radio frequency sputtering and characterisation of rare earth doped wide bandgap oxides
No full textThe thesis reports the results of an experimental research on rare earth ion-doping effects on the structural, chemical, optical and near-infra-red photoluminescence properties of wide band gap oxide films. The aim of the work was to develop materials with good photoluminescence properties, which can be applied to increase the photovoltaic conversion efficiency of crystalline Si-based solar cells, through the increase of the most efficient and useful fraction of the solar spectrum which hits the cells, thanks to a photon frequency down-shifting process.
Neodymium trivalent ion (Nd3+) was used as dopant of TiO2 and ZnO thin films. The films, with different Nd concentrations were grown onto quartz by RF plasma co-sputtering and annealed at different temperatures (400°-800°C). Different film architectures were investigated for their photoluminescence properties. Structural changes such as phase transformation from anatase to rutile, internal strain building and lattice distortion due to Nd3+ incorporation in titania, correlated with optical changes, were evidenced. Exciting titania and zinc oxide matrices with optimal Nd concentrations, with ultra-violet (UV) light energies equal to or above their gap values resulted in an efficient frequency down-shifting from UV to near-infra-red emission. The joint study of the vibrational, chemical and structural properties of the doped films allows the understanding of the excitation energy transfer process between the matrix to the ion, where self-trapped excitons can be involved. To conclude this study, the doped films were tested as down-shifter layers onto a Si-solar cell where they gave promising results. They were also tested for their photoactivity with methylene blue, showing their inhibitor effect on the photo-degradation of this organic dye molecule.
Keywords: Co-Sputtering, rare earth doping, Neodymium, Titanium dioxide, Zinc oxide thin films, Photoluminescenc