Flow rate--pressure drop relation for deformable shallow microfluidic channels

Laminar flow in devices fabricated from soft materials causes deformation of the passage geometry, which affects the flow rate--pressure drop relation. For a given pressure drop, in channels with narrow rectangular cross-section, the flow rate varies as the cube of the channel height, so deformation can produce significant quantitative effects, including nonlinear dependence on the pressure drop [{Gervais, T., El-Ali, J., G\"unther, A. \& Jensen, K.\ F.}\ 2006 Flow-induced deformation of shallow microfluidic channels.\ \textit{Lab Chip} \textbf{6}, 500--507]. Gervais et. al. proposed a successful model of the deformation-induced change in the flow rate by heuristically coupling a Hookean elastic response with the lubrication approximation for Stokes flow. However, their model contains a fitting parameter that must be found for each channel shape by performing an experiment. We present a perturbation approach for the flow rate--pressure drop relation in a shallow deformable microchannel using the theory of isotropic quasi-static plate bending and the Stokes equations under a lubrication approximation (specifically, the ratio of the channel's height to its width and of the channel's height to its length are both assumed small). Our result contains no free parameters and confirms Gervais et. al.'s observation that the flow rate is a quartic polynomial of the pressure drop. The derived flow rate--pressure drop relation compares favorably with experimental measurements.Comment: 20 pages, 6 figures; v2 minor revisions, accepted for publication in the Journal of Fluid Mechanic

Essai de domestication de lentinus squarrosulus mont. a partir d’une souche du Gabon

Dans le cadre d’un vaste programme de valorisation des ressources biologiques initié par les autorités gabonaises en vue de garantir la sécurité alimentaire des populations locales, une souche sauvage de Lentinus squarrosulus récoltée au nord du Gabon, a été mise en culture en utilisant essentiellement des matériaux locaux. Au cours de ce processus, cinq principales étapes ont été mise en œuvre; il s’agit notamment de la production du blanc de semis et du substrat de culture, du lardage du substrat, de l’incubation et de la  fructification du champignon. La production du blanc regroupe les étapes qui ont obligatoirement été exécutées dans un laboratoire parfaitement équipé en vue de garantir des conditions d’asepsie rigoureuses, tandis que la production du substrat de culture, l’inoculation et l’incubation ont parfaitement été réalisées à l’échelle villageoise en utilisant du matériel de fabrication traditionnelle; notamment une unité de pasteurisation constituée d’un fût en aluminium de 250 litres muni d’étagères et d’une chambre contenant de l’eau, ainsi qu’une armoire traditionnelle d’inoculation. Par ce processus, quatre-vingt sacs de 1kg ont été inoculés dont quatorze ont montré un très bon envahissement mycélien et une fructification satisfaisante; ce qui donne un rendement en terme de sac d’environ 17 %. Cependant, cinquante-six sacs n’ont pas été bien envahis par le mycélium et n’ont donc pas donné de champignon, de plus dix sacs ont été contaminés. Mots clés : domestication, souche sauvage, Lentinus squarrosulus, matériaux locaux, Gabon English title: Domestication test of lentinus squarrosulus mont. from a Gabon strain As part of a vast program to develop biological resources initiated by the Gabonese authorities with a view to guaranteeing food security for local populations, a wild strain of Lentinus squarrosulus harvested in northern Gabon was cultivated using mainly local materials. During this process, five main steps were implemented; these include the production of seedling white and growing medium, larding of the substrate, incubation and fruiting of the fungus. The production of the blank includes the steps which must have been carried out in a perfectly equipped laboratory in order to guarantee rigorous aseptic conditions, while the production of the culture substrate, inoculation and incubation have been perfectly carried out at village scale using traditional manufacturing  equipment; including a pasteurization unit consisting of a 250-liter aluminum drum with shelves and a chamber containing water, as well as a traditional inoculation cabinet. By this method, eighty bags (1kg) were inoculated, fourteen of which showed very good mycelial invasion and satisfactory fruiting; which gives a yield of around 17%. However, fifty-six bags were not well invaded by the mycelium and therefore did not give a fungus, and ten bags were contaminated. Keywords: domestication, wild strain, Lentinus squarrosulus, local materials, Gabo

Giant Quantum Reflection of Neon Atoms from a Ridged Silicon Surface

The specular reflectivity of slow, metastable neon atoms from a silicon surface was found to increase markedly when the flat surface was replaced by a grating structure with parallel narrow ridges. For a surface with ridges that have a sufficiently narrow top, the reflectivity was found to increase more than two orders of magnitude at the incident angle of 10 mRad from the surface. The slope of the reflectivity vs the incident angle near zero was found to be nearly an order of magnitude smaller than that of a flat surface. A grating with 6.5% efficiency for the first-order diffraction was fabricated by using the ridged surface structure.Comment: 5 pages, 4 figures. To be published in J. Phys. Soc. Jp

Resolved diffraction patterns from a reflection grating for atoms

We have studied atomic diffraction at normal incidence from an evanescent standing wave with a high resolution using velocity selective Raman transitions. We have observed up to 3 resolved orders of diffraction, which are well accounted for by a scalar diffraction theory. In our experiment the transverse coherence length of the source is greater than the period of the diffraction grating.Comment: 8 pages, 4 figure

Using atomic interference to probe atom-surface interaction

We show that atomic interference in the reflection from two suitably polarized evanescent waves is sensitive to retardation effects in the atom-surface interaction for specific experimental parameters. We study the limit of short and long atomic de Broglie wavelength. The former case is analyzed in the semiclassical approximation (Landau-Zener model). The latter represents a quantum regime and is analyzed by solving numerically the associated coupled Schroedinger equations. We consider a specific experimental scheme and show the results for rubidium (short wavelength) and the much lighter meta-stable helium atom (long wavelength). The merits of each case are then discussed.Comment: 11 pages, including 6 figures, submitted to Phys. Rev. A, RevTeX sourc

Modeling and Optimization of Lactic Acid Synthesis by the Alkaline Degradation of Fructose in a Batch Reactor

The present work deals with the determination of the optimal operating conditions of lactic acid synthesis by the alkaline degradation of fructose. It is a complex transformation for which detailed knowledge is not available. It is carried out in a batch or semi-batch reactor. The ‘‘Tendency Modeling’’ approach, which consists of the development of an approximate stoichiometric and kinetic model, has been used. An experimental planning method has been utilized as the database for model development. The application of the experimental planning methodology allows comparison between the experimental and model response. The model is then used in an optimization procedure to compute the optimal process. The optimal control problem is converted into a nonlinear programming problem solved using the sequencial quadratic programming procedure coupled with the golden search method. The strategy developed allows simultaneously optimizing the different variables, which may be constrained. The validity of the methodology is illustrated by the determination of the optimal operating conditions of lactic acid production

Optical binding of particles with or without the presence of a flat dielectric surface

Optical fields can induce forces between microscopic objects, thus giving rise to new structures of matter. We study theoretically these optical forces between two spheres, either isolated in water, or in presence of a flat dielectric surface. We observe different behavior in the binding force between particles at large and at small distances (in comparison with the wavelength) from each other. This is due to the great contribution of evanescent waves at short distances. We analyze how the optical binding depends of the size of the particles, the material composing them, the wavelength and, above all, on the polarization of the incident beam. We also show that depending on the polarization, the force between small particles at small distances changes its sign. Finally, the presence of a substrate surface is analyzed showing that it only slightly changes the magnitudes of the forces, but not their qualitative nature, except when one employs total internal reflection, case in which the particles are induced to move together along the surface.Comment: 8 pages, 9 figures, and 1 tabl

A {\mu}-TPC detector for the characterization of low energy neutron fields

The AMANDE facility produces monoenergetic neutron fields from 2 keV to 20 MeV for metrological purposes. To be considered as a reference facility, fluence and energy distributions of neutron fields have to be determined by primary measurement standards. For this purpose, a micro Time Projection Chamber is being developed to be dedicated to measure neutron fields with energy ranging from 8 keV up to 1 MeV. In this work we present simulations showing that such a detector, which allows the measurement of the ionization energy and the 3D reconstruction of the recoil nucleus, provides the determination of neutron energy and fluence of these neutron fields

Photothermal Heterodyne Imaging of Individual Metallic Nanoparticles: Theory versus Experiments

We present the theoretical and detailed experimental characterizations of Photothermal Heterodyne Imaging. An analytical expression of the photothermal heterodyne signal is derived using the theory of light scattering from a fluctuating medium. The amplitudes of the signals detected in the backward and forward configurations are compared and their frequency dependences are studied. The application of the Photothermal Heterodyne detection technique to the absorption spectroscopy of individual gold nanoparticles is discussed and the detection of small individual silver nanoparticles is demonstrated