Micro-Macro Modelling of an Array of Spheres Interacting Through Lubrication Forces

We consider here a discrete system of spheres interacting through a lubrication force. This force is dissipative, and singular near contact: it behaves like the reciprocal of interparticle distance. We propose a macroscopic constitutive equation which is built as the natural continuous counterpart of this microscopic lubrication model. This model, which is of the newtonian type, relies on an elongational viscosity, which is proportional to the reciprocal of the local fluid fraction. We then establish the convergence in a weak sense of solutions to the discrete problem towards the solution to the partial differential equation which we identified as the macroscopic constitutive equation

De la planification au marché

Au moment de l’Indépendance, l’Inde souhaite s’orienter vers un système de soins public accessible à tous. Soixante ans plus tard, le secteur privé est devenu l’entrée privilégiée du système de soins pour le patient indien. À travers une approche sensible aux discontinuités territoriales, nous mettons en perspective les mécanismes politiques, économiques et sociaux à l’œuvre dans la privatisation des soins en Inde depuis 1947. La privatisation des soins hospitaliers n’a pas tant été le fait d’une réorientation des politiques de santé à l’échelle nationale, que le résultat d’une transformation endogène du secteur hospitalier. On s’interroge en conclusion sur la capacité de l’État indien à assurer sa nouvelle mission de régulation du secteur hospitalier privé.At the time of Independence, India wished to provide universal public health care. Sixty years later, the private sector has become the main access to hospital care for Indian patients. Keeping in mind the territorial discontinuities that divide the country, this article examines the political, economic and social mechanisms leading to the privatization of Indian hospital care. We argue that this privatization has less to do with liberal health sector reform policies than with long-term endogenous changes in Indian hospital care. We also question the capacity of the Indian state to enforce new regulation schemes on private hospital care

Pre-electoral Coalitions, Party System and Electoral Geography: A Decade of General Elections in India (1999–2009)

Between 1999 and 2009, since no single party was in a position to lead a majority in the Lok Sabha, pre-electoral coalitions have become the only option for parties to exercise executive power at the Centre. Looking at the trajectory of two pre-electoral coalitions over ten years, namely the BJP-led National Democratic Alliance and the Congress-led United Progressive Alliance, the paper attempts to contribute to the nascent research on pre-electoral coalitions. Much has been written on the importance of disproportionate electoral systems or the ideological distance between parties in the formation of governing coalitions. This paper explores the importance of different geographical bases of support in the composition and sustainability of Indian pre-electoral coalitions, election after election, and proposes preliminary elements for a dynamic theory of pre-electoral coalition formation

Laboratory measurements of electrostatic solitary structures generated by electron beam injection

Electrostatic solitary structures are generated by injection of a suprathermal electron beam parallel to the magnetic field in a laboratory plasma. Electric microprobes with tips smaller than the Debye length ($\lambda_{De}$) enabled the measurement of positive potential pulses with half-widths 4 to 25$\lambda_{De}$ and velocities 1 to 3 times the background electron thermal speed. Nonlinear wave packets of similar velocities and scales are also observed, indicating that the two descend from the same mode which is consistent with the electrostatic whistler mode and result from an instability likely to be driven by field-aligned currents.Comment: 5 pages, 4 figures http://link.aps.org/doi/10.1103/PhysRevLett.105.11500

Paleontology in France: 200 years in the footsteps of Cuvier and Lamarck

International audienceDue to its richness in fossil localities and Fossil-Lagerstätten, France played a major role in the 18th and 19th centuries in establishing paleontology and biostratigraphy as scientific disciplines. The French naturalist and zoologist Cuvier (1769-1832) established the fields of comparative anatomy and paleontology, and proposed the concept of 'catastrophism' in geology. The naturalist Lamarck (1744-1829) is considered the founder of invertebrate paleontology and biostratigraphy and an early pioneer in the studies of evolution, developing the idea of 'transformism' and creating the word 'fossil', while his successor Blainville (1777-1850) was the first to use the word 'paleontology'. Based on this rich heritage, numerous French scientists strengthened paleontology as an important discipline during the 19th and 20th centuries. Paleontology was present at the universities of most major French cities, as documented by the rich collections in over 50 natural history museums and university collections. The most significant paleontological collection is that housed in the Muséum National d'Histoire Naturelle (MNHN) at Paris that currently hosts the largest research unit in paleontology of France with over 100 scientists, curators and technicians. The second largest collection (and the largest in terms of invertebrate fossils) is housed at the University of Lyon1, where the most important university paleontology research team is present. About 250 professional paleontologists are currently working in research units that are mostly affiliated to the Centre National de Recherche Scientifique (CNRS), in public or private museums, or in the numerous natural parcs. A significant generation change took place in the early 2000s, with the retirement of the paleontologists recruited in the 1960s and 1970s, that were often specialized in alpha-taxonomy and stratigraphy, and the arrival of a young generation of scientists that attempts to answer more 'modern' questions, such as global (climate) change, biodiversity, or evolution. This new generation of paleontologists faces modified funding schemes with project-based supporting structures in a more and more competitive environment. In the present paper we attempt to summarize the current situation of paleontology as a discipline in the very complex academic and scientific context of France. After a short overview on the history of French paleontology in the last centuries, a synopsis on institutions and funding agencies is presented briefly. The major research departments and their research themes are then described, together with the most important collections, the paleontological associations, journals, and databases, etc. Paleontological training possibilities and job opportunities, in particular in academia, are next documented, concluding with a summary of the prospects of the discipline

Simultaneous gas and spray PIV measurements in an optical engine

International audienceEngine internal aerodynamic reveals complex flow involving multi-scale turbulence, flow structure compression, two-phase interactions and are responsible for the mixing process and the engine performance and efficiency. Recent efforts have been made to describe in details in-cylinder flows either with temporal (HR-PIV) or spatial (Tomo-PIV) resolution. However, for gasoline direct injection engine (GDI), the dynamic coupling between gas and spray droplets should also be undertaken for a correct evaluation of in-cylinder aerodynamics. Simultaneous measurements of instantaneous gas and droplets velocities during intake and compression strokes are proposed by means of two-phase PIV based on fluorescence [1, 2]. The technique is adapted to the constraints of optical engine and associated to specific algorithms development for the liquid phase. The engine test bench consists in a mono-cylinder GDI engine (AVL) which operates up to 3000 rpm in optical configuration with a displacement volume of 450 cm 3 and a compression ratio of 8.5. The optical accesses to the combustion chamber is enabled by a quartz-glass liner. The injection system is composed of a solenoid multi-hole injector Bosch fed up by a pressurized volume to ensure a stable injection pressure up to 100 bar. An injector power control module (EFS IPOD) is used to drive the injector and control injection timings in the engine cycle. The two-phase PIV technique is based on the use of two different dyes dissolved in the seeding particle and gasoline, producing fluorescent emissions on separated spectral bands for each phase [1, 2]. The phase separation is enabled by a detection system consisting of a dichroic window distributing the collection signal on two synchronized PIV cameras (Hamamatsu 12 bits 2018×2048 pixels) equipped with Nikkor lenses (50mm f/#2) and adapted pass-band filters. Angular controls are mounted at the base of the dichroic sheet and both cameras in order to adjust with precision the common camera field of view. A refined adjustment based on a polynomial approach of 5 th degree is then numerically performed from calibration grid images to ensure a perfect images overlap and to correct image distortion induced by the glass liner. Dyes excitation is performed with two lasers at different wavelengths (532 nm for the gas and 355 nm for the spray) in order to independently adjust the PIV acquisition delays to the high velocity shift between phases in the early stage of injection. The use of two wavelength also improve the spectral separation of fluorescence signal and then the phase discrimination. An original synchronisation of the laser and camera with the engine cycle is ensured by means of a programmable time board to get rid of engine speed fluctuations and guarantee a fixed working frequency for the lasers while limiting injection and fouling to the acquisition triggering. Velocities of the gas and the liquid phases can thus be acquired simultaneously for engine conditions where the two phases are present, typically early after the start of injection [2, 3]. Prior to the correlation step, a pre-processing of the fluorescence images is performed to enhance the correlation level. A masking technique, with adaptation of the masking surface at each angular position is also used. The PIV post-processing is then adapted to the present configuration with two different algorithms for each phase. The velocity fields of the gaseous phase are obtained by a multi-pass subpixel shift correlation algorithm based on the correlation of the seeding patterns [4]. Interrogation window size of 32×32 pixels (1.85×1.85 mm 2) with an overlap of 50% has been used with a vectors filtering based on a minimum value of the Signal to Noise Rate (SNR) and on a median filter which are adapted to each experimental condition. This enables to reject most of non-valid vectors. Gas phase velocity calculation for internal engine flow is validated in our configuration by means of simultaneous Mie-based PIV and fluorescence based PIV. Comparison of mean and instantaneous velocities show less than 5 % differences. The density of the liquid phase is heterogeneous with a very dense part near the injector nozzle and a dispersed part after the breaking of the liquid sheet. In the spray dispersed part, velocities are processed with a particle approach, whereas in the dense part of the spray, a specific algorithm based on pattern correlation is developed. Preferential direction and topology of the spray are taken into account through the window shape and size

Recent developments in two-phases fluorescence PIV: Application to the dynamic of high pressure gasoline sprays

International audienceThe purpose of the present work is to develop and to demonstrate the ability of the two-phase PIV by fluorescence technique for the study of two-phase flows dynamics. In particular, the dynamic of a high-pressure spray and its interaction with surrounding air is investigated in this study. For the single-phase flows, the PIV is a well-established technique to measure the velocity of the continuous phase but not easily applicable on two-phase flows without adaptation and new developments. Ten years ago, fluorescence PIV were developed to investigate dynamic of spray injection [1][2]. For phase discrimination, each phase is labelled by two different dyes allowing the acquisition of two separate pairs of images which are then analysed separately and provide the instantaneous velocity fields of the two phases. In the present paper, an extension of our previous work is proposed [2] by associating two PIV lasers at 532 nm and 355 nm in order to make separation of fluorescence signals of the two phases more efficient and then to access to velocity measurements in the denser part of the spray. This arrangement permits also an optimisation of the two PIV delays in order to account for the high velocity difference between the phases in high pressure injections. For the imaging system, the two fluorescence signals are collected simultaneously on two 12 bits Hamamatsu cameras (C9300-4M pixels). Two selected passband filters are placed in front of the cameras, for the discrimination of the fluorescence in each phase. To ensure a perfect overlap of the velocity measurements, image deformation technique based on 5 th order polynomial functions are applied on particle images to correct any differences of magnifications, orientation and optical deformation of images. In the first part of the paper, the selection of a couple of fluorescent dyes adapted to our experimental conditions is addressed. In the second part, a novel PIV measurement based on pattern correlation is proposed to measure the velocity of the liquid phase in the dense part of the liquid jet near the injector nozzle. In the final part, our fluorescence PIV technique is validated on two high pressure gasoline injectors placed in a closed pressurized chamber (single and multi-holes injectors up to 100). bar). The major criteria of dyes selection are: maximum of absorption spectrum close to the laser wavelengths; fluorescence signal in a spectral range close to maximum quantum efficiency of the PIV cameras; high fluorescence efficiency, especially for the dye labelling the seeding particles; distinct fluorescence emission to permit the optical filtering of the two phases; the solubility of the dyes in the liquid phase and the seeding particles. Considering all these criteria and numerous tests, our dye selection has been stopped on Stilbene 420 for the seeding particles and Pyrromethene 597 for the liquid phase. Figure 1 presents instantaneous images in the case of single hole injector without any processing of the fluorescence signal of each dye. These images show that there is no signal from the seeding particles of the gas remaining on the spray image (Figure 1-A). The gas image (Figure 1-B) shows that the spray signal is correctly filtered in spite of the high intensity of droplets Mie scattering and fluorescence. This is confirmed in Figure 1-C by the superimposition of both phases at the location of the red rectangle plotted in Figure 1-B. Indeed, the spray droplets (in red) are clearly distinguished from the seeding particles of the gas (in black)

Biogenic Iron Preserves Structures during Fossilization: A Hypothesis

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Solutan echinoderms from the Lower Ordovician of the Montagne Noire (France): new data and palaeobiogeographic implications

Solutans are relatively common members of echinoderm assemblages in the Saint-Chinian Formation (upper Tremadocian) of the Montagne Noire (France). The revision of all available material confirms that most specimens can be assigned to Minervaecystis vidali, which is here reconstructed for the first time. The occurrence of Plasiacystis mobilis is evidenced based on a single, well-preserved dististele. The interpretation of the small-sized individual as a putative dendrocystitid is rejected: it corresponds to a juvenile specimen of M. vidali. Early Ordovician solutans from the Montagne Noire partly fill the gap between Laurentian midâlate Cambrian syringocrinids and Avalonian-Gondwanan EarlyâMiddle Ordovician taxa