Is Purple a Red and Blue Chessboard? Brentano on Colour Mixtures

Can we maintain that purple seems composed of red and blue without giving up the impenetrability of the red and blue parts that compose it? Brentano thinks we can. Purple, according to him, is a chessboard of red and blue tiles which, although individually too small to be perceived, are together indistinctly perceived within the purple. After a presentation of Brentano’s solution, we raise two objections to it. First, Brentano’s solution commits him to unperceivable intentional objects (the chessboard’s tiles). Second, his chessboard account fails in the end to explain the phenomenal spatial continuity of compound colours. We then sketch an alternative account, which, while holding fast to the phenomenal compoundedness of the purple and to the impenetrability of component colours, avoids introducing inaccessible intentional objects and compromising on the continuity of the purple. According to our proposal, instead of being indistinctly perceived spatial parts of the purple, red and blue are distinctly perceived non- spatial parts of it

Submerged membrane bioreactor for waste water treatment: determination of the shear stresses produced by coarse bubbles

Submerged membrane bioreactor for waste water treatment: determination of the shear stresses produced by coarse bubble

Les compagnies aériennes, leurs menus et les religions qu'elles y reconnaissent

Partant de l’idée bien établie que la religion exerce une influence profonde sur les modes d’alimentation, trois chercheurs en théologie, en géographie et en sciences politiques ont unis leurs connaissances pour débusquer cette influence là où on ne l’attend pas, dans les menus proposés par les compagnies aériennes. Pour ce faire, ils ont identifié les menus religieux reconnus par l’IATA (hindou, halal, cacher et jaïn) ; visité les sites Internet de 34 compagnies aériennes pour savoir quelles compagnies proposent quels menus religieux ; identifié comment ces compagnies prétendent répondre aux prescriptions des différentes religions ; cherché à comprendre les logiques théologiques, géographiques et/ou politiques derrière les choix des compagnies aériennes ; évalué l’impact que les menus religieux proposés par les compagnies aériennes exercent sur la relation entre religion et alimentation

Rheological study of sludge of membranes bioreactors for water treatment: protocol, limitations and link with the filtration

The submerged membranes bio-reactors (sMBR) are more and more visible in the field of waste water treatment. The membrane fouling, that causes a drastic fall of the performances, can be limited by the application of a swarm of bubbles close to the membrane surfaces. This aeration as a major factor of the energetic expense of these processes, lets numerous studies to focus on the understanding of the mechanisms linking the bubbles swarm with fouling.. In this background, the rheological tools appeared to be useful to understand the behaviour of sludge under shear stress. In order to be sure to get significant results, we used three types of rheological measurements: i) the influence of shear rate on shear stress; ii) the influence of upward then downward stages of shear stress on viscosity; iii) the influence of the alternation of two stages of shear stress with implementation times identical to those of sMBR aeration. Besides a viscoplastic behaviour previously observed, a phenomenon of hysteresis appeared. The transparent upper plan used on the rheometer exhibited formations of aggregative structures “in roll”. Sludges of a sMBR using different sequencing of aeration are compared: the developed protocols enabled to differentiate those sludges, with characteristic results depending on mechanical applications. The aim of this work is, eventually, to propose some correlations between usual characteristics of the process and aeration operating parameters, in order to propose an aeration policy improving energetic performances

Searching for faint companions with VLTI/PIONIER. II. 92 main sequence stars from the Exozodi survey

The Exozodi survey aims to determine the occurrence rate of bright exozodiacal discs around nearby main sequence stars using infrared interferometry. Although the Exozodi survey targets have been carefully selected to avoid the presence of binary stars, the results of this survey can still be biased by the presence of unidentified stellar companions. Using the PIONIER data set collected within the Exozodi survey, we aim to search for the signature of point-like companions around the Exozodi target stars. We use both the closure phases and squared visibilities collected by PIONIER to search for companions within the ~100 mas interferometric field of view. The presence of a companion is assessed by computing the goodness of fit to the data for a series of binary models with various separations and contrasts. Five stellar companions are resolved for the first time around five A-type stars: HD 4150, HD 16555, HD 29388, HD 202730, and HD 224392 (although the companion to HD 16555 was independently resolved by speckle interferometry while we were carrying out the survey). In the most likely case of main sequence companions, their spectral types range from A5V to K4V. Three of these stars were already suspected to be binaries from Hipparcos astrometric measurements, although no information was available on the companions themselves so far. In addition to debiasing the statistics of the Exozodi survey, these results can also be used to revise the fraction of visual binaries among A-type stars, suggesting that an extra ~13% A-type stars are visual binaries in addition to the ones detected in previous direct imaging surveys. We estimate that about half the population of nearby A-type stars could be resolved as visual binaries using a combination of state-of-the-art interferometry and single-aperture imaging, and we suggest that a significant fraction of these binaries remains undetected to date.Comment: Accepted for publication in A&

Utilisation de dispositifs à transfert de charge pour la détection de muons cosmiques dans un contexte de tomographie

Face à la menace du terrorisme nucléaire, plusieurs pays se sont procurés des détecteurs de matériaux radioactifs pour protéger leurs frontières. Ces systèmes détectent habituellement des émissions de rayons gammas, beta ou alpha qui proviennent d’uranium, radium, césium ou autre matériel radioactif. Cependant, la source radioactive peut être dissimulée par une épaisseur de plomb et d’autres matériels absorbants ces rayonnements. Avec une quantité suffisante de blindage, un individu désirant faire de la contrebande de matériel nucléaire peut traverser les frontières sans alerter les autorités. Pour faire face à ce risque, plusieurs laboratoires à travers le monde travaillent sur une technologie de tomographie par muons qui pourrait être utilisée pour identifier des sources nucléaires blindées. Celle-ci se base sur l’analyse de la déviation d’un muon cosmique traversant un cargo d’intérêt. Cette déviation étant fonction du nombre Z des atomes traversés (le nombre de protons dans le noyau), il est en principe possible de déterminer le contenu du cargo. Pour calculer cette déviation angulaire, il faut d’abord mesurer la position des muons sur quatre plans horizontaux (deux pré-cargo, deux après). Cette tâche est traditionnellement dévolue à des détecteurs comme des chambres à fils ou des scintillateurs mais pourrait aussi être remplie par des détecteurs CCDs (Chargle-Coupled Devices ou dispositifs à transfert de charge). Cet ouvrage se penche spécifiquement sur l’utilisation de CCDs pour la tomographie par muons. Ce mémoire a pour but de déterminer la faisabilité d’utiliser un détecteur de muons à base de CCDs commerciales. Pour répondre à cette question, des simulations numériques ont été réalisées en utilisant le logiciel Geant4. Ces travaux nous permettent d’obtenir le dépôt d’énergie théorique de muons de diverses énergies cinétiques dans une plaque de silicium représentant une puce de CCD. Ces résultats sont ensuite comparés à la théorie préalablement exposée pour vérifier leur validité. L’énergie des muons varie de 50 MeV à 1 TeV et les épaisseurs étudiées sont de 300 et 775 μm. Les résultats indiquent qu’un muon de 4 GeV (énergie la plus probable pour des muons d’origines cosmiques) devrait déposer environ 106 et 281 keV en moyenne pour des épaisseurs de 300 et 775 μm, ce qui se traduit par 28 000 et 76 000 paires électron-trou comme signal pour les deux épaisseurs étudiées. Tous les résultats obtenus concordent avec la théorie connue des dépôts d’énergie dans les semi-conducteurs minces.----------AbstractFaced with the threat of nuclear terrorism, many countries have purchased radioactive material detectors to protect their borders. These systems usually detect gamma, beta or alpha ray emissions coming from uranium, radium, cesium or other radioactive material. However,the radioactive source can be concealed by thick lead shielding and radiation absorbing material. With enough shielding, an individual wishing to smuggle illicit nuclear material could cross borders without alerting the authorities. To address this risk, several laboratories worldwide are working on muon tomography technology. This technique aims to detect shielded nuclear material by measuring the deflection of a cosmic muon after crossing the cargo of interest. Since this deviation is a function of the Z number of atoms (the number of protons inside the nucleus), it is possible to determine the contents of the cargo. To calculate the angular deviation, we must first measure the position of the muon on four succeding horizontal planes (two pre-cargo, two after). This task is traditionally assigned to wire chambers or scintillators detectors but could also be fulfilled by CCD detectors (Chargle-Coupled Devices). This work specifically addresses the use of CCDs for muon tomography. This thesis’ objective is to determine the feasibility of using a commercial CCD based muon detector. To answer this question, numerical simulations have been performed using the software Geant4. This work allows us to obtain the theoretical energy deposition of muons of various kinetic energies into a silicon wafer representing a CCD chip. These results are then compared to numerical values derived from the theory presented in the literature to verify their validity. The muons’ energy is varied from 50 MeV to 1 TeV and silicium thicknesses of 300 and 775 μm are studied. The results obtained indicate that a muon of 4 GeV (most probable cosmic muon energy) should deposit 106 and 281 keV for an average thickness of 300 and 775 μm respectively, which translates to 28 000 and 76 000 electron-hole pairs as signal for the two thicknesses. All the results obtained through Geant4 are consistent with the known theory of energy deposits in thin semiconductor materials. A practical experimentation was also considered, using an astronomical camera DMK51 AU02.AS to capture a series of images hidden from light with the camera turned towards the sky. The pixels presenting a high intensity are considered to be the consequence of the passage of a muon. The expected rate of detection according to the size of the detector was 0.372 muons per minute but the results were 0.1578 muons per minute for data taken inside Polytechnique and 0.1615 for images taken outside

Development of an Analytical Model to Determine the Heat Fluxes to a Structural Element Due to a Travelling Fire

peer reviewedThe term “travelling fire” is used to label fires which burn locally and move across the floor over a period of time in large compartments. Through experimental and numerical campaigns and while observing the tragic travelling fire events, it became clear that such fires imply a transient heating of the surrounding structure. The necessity to better characterize the thermal impact generated on the structure by a travelling fire motivated the development of an analytical model allowing to capture, in a simple manner, the multidimensional transient heating of a structure considering the effect of the ventilation. This paper first presents the basic assumptions of a new analytical model which is based on the virtual solid flame concept; a comparison of the steel temperatures measured during a travelling fire test in a steel-framed building with the ones obtained analytically is then presented. The limitations inherent to the analyticity of the model are also discussed. This paper suggests that the developed analytical model can allow for both an acceptable representation of the travelling fire in terms of fire spread and steel temperatures while not being computationally demanding, making it potentially desirable for pre-design