130 research outputs found
Invisible waveguides on metal plates for plasmonic analogues of electromagnetic wormholes
We introduce two types of toroidal metamaterials which are invisible to
surface plasmon polaritons (SPPs) propagating on a metal surface. The former is
a toroidal handlebody bridging remote holes on the metal surface: It works as a
kind of plasmonic counterpart of electromagnetic wormholes. The latter is a
toroidal ring lying on the metal surface: This bridges two disconnected metal
surfaces i.e. It connects a thin metal cylinder to a flat metal surface with a
hole. Full-wave numerical simulations demonstrate that an electromagnetic field
propagating inside these metamaterials does not disturb the propagation of SPPs
at the metal surface. A multilayered design of these devices is proposed, based
on effective medium theory for a set of reduced parameters: The former
plasmonic analogue of electromagnetic wormhole requires homogeneous isotropic
magnetic layers, while the latter merely requires dielectric layers.Comment: 17 figure
Acoustic cloaking and mirages with flying carpets
Carpets under consideration here, in the context of pressure acoustic waves
propagating in a compressible fluid, do not touch the ground: they levitate in
mid-air (or float in mid-water), which leads to approximate cloaking for an
object hidden underneath, or touching either sides of a square cylinder on, or
over, the ground. The tentlike carpets attached to the sides of a square
cylinder illustrate how the notion of a carpet on a wall naturally generalizes
to sides of other small compact objects. We then extend the concept of flying
carpets to circular cylinders. However, instead of reducing its scattering
cross-section like in acoustic cloaks, we rather mimic that of another
obstacle, say a square rigid cylinder. For instance, show that one can hide any
type of defects under such circular carpets, and yet they still scatter waves
just like a smaller cylinder on its own. Interestingly, all these carpets are
described by non-singular acoustic parameters. To exemplify this important
aspect, we propose a multi-layered carpet consisting of isotropic homogeneous
fluids with constant bulk modulus and varying density which works over a finite
range of wavelengths. We have discussed some applications, with the sonar boats
or radars cases as typical examples. For instance, we would like to render a
pipeline lying on the bottom of the sea or floating in mid-water undetectable
for a boat with a sonar at rest just above it on the surface of the sea.
Another possible application would be protecting parabolic antennas.Comment: 26 pages, 9 figures. Key words: Mathematical methods in physics;
Mathematical Physics, electromagnetic theory; Metamaterials;Anisotropic
optical materials; invisibility; cloa
Controlling surface plasmon polaritons in transformed coordinates
Transformational optics allow for a markedly enhanced control of the
electromagnetic wave trajectories within metamaterials with interesting
applications ranging from perfect lenses to invisibility cloaks, carpets,
concentrators and rotators. Here, we present a review of curved anisotropic
heterogeneous meta-surfaces designed using the tool of transformational
plasmonics, in order to achieve a similar control for surface plasmon
polaritons in cylindrical and conical carpets, as well as cylindrical cloaks,
concentrators and rotators of a non-convex cross-section. Finally, we provide
an asymptotic form of the geometric potential for surface plasmon polaritons on
such surfaces in the limit of small curvature.Comment: 14 pages, 9 figure
Specific Gaseous Conditions Significantly Improve Lactobacillus casei and Escherichia coli Survival to Freeze Drying and Rehydration
 Background and objective: Presence of oxygen during production and rehydration of freeze-dried starters and probiotics can decrease viability of the bacteria. Indeed, removal of water from cells during freeze-drying can promote dysfunction in anti-oxidative mechanisms, resulting in oxidative stress by accumulation of reactive oxygen species. The aim of this study was to show how atmospheric or less oxidative gaseous conditions affect bacterial survival to freeze-drying and rehydration of two strains, including Lactobacillus casei, a widely used bacteria in biotechnology, and Escherichia coli, a laboratory model bacteria.Material and methods: Lactobacillus casei ATCC 334 and Escherichia coli K12 were freeze dried for 24h in 5% sucrose (m v-1). Two gaseous conditions (an oxygen-free gas and atmospheric air) were used during various steps of the process, including bacterial cultivation, mixing of the bacteria with the protectant and rehydration. Oxygen-free gas condition was obtained with an oxygen-free gas, composed of nitrogen, hydrogen and carbon dioxide (N2H2CO2)and an anaerobic chamber.Results and conclusion: Gaseous conditions included significant effects on bacterial survival rates (P<0.001 for Lactobacillus casei and Escherichia coli). Interestingly, for both bacteria, the optimal combination was atmospheric air during mixing of the bacteria with the lyoprotectant (P<0.001 for Lactobacillus casei and Escherichia coli) and N2H2CO2 during rehydration (P<0.001 for Lactobacillus casei and P<0.05 for Escherichia coli). Management of gaseous conditions during a freeze-drying process and rehydration (atmospheric air during mixing of the bacteria with lyoprotectant and oxygen-free gas during rehydration) enhances survival of the bacteria by preserving them from oxidative stress.Conflict of interest: The authors declare no conflict of interest
Association between inflammatory mediators and response to inhaled nitric oxide in a model of endotoxin-induced lung injury
INTRODUCTION: Inhaled nitric oxide (INO) allows selective pulmonary vasodilation in acute respiratory distress syndrome and improves PaO2 by redistribution of pulmonary blood flow towards better ventilated parenchyma. One-third of patients are nonresponders to INO, however, and it is difficult to predict who will respond. The aim of the present study was to identify, within a panel of inflammatory mediators released during endotoxin-induced lung injury, specific mediators that are associated with a PaO2 response to INO. METHODS: After animal ethics committee approval, pigs were anesthetized and exposed to 2 hours of endotoxin infusion. Levels of cytokines, prostanoid, leucotriene and endothelin-1 (ET-1) were sampled prior to endotoxin exposure and hourly thereafter. All animals were exposed to 40 ppm INO: 28 animals were exposed at either 4 hours or 6 hours and a subgroup of nine animals was exposed both at 4 hours and 6 hours after onset of endotoxin infusion. RESULTS: Based on the response to INO, the animals were retrospectively placed into a responder group (increase in PaO2 > or = 20%) or a nonresponder group. All mediators increased with endotoxin infusion although no significant differences were seen between responders and nonresponders. There was a mean difference in ET-1, however, with lower levels in the nonresponder group than in the responder group, 0.1 pg/ml versus 3.0 pg/ml. Moreover, five animals in the group exposed twice to INO switched from responder to nonresponder and had decreased ET-1 levels (3.0 (2.5 to 7.5) pg/ml versus 0.1 (0.1 to 2.1) pg/ml, P < 0.05). The pulmonary artery pressure and ET-1 level were higher in future responders to INO. CONCLUSIONS: ET-1 may therefore be involved in mediating the response to INO
Facteurs influençant l'apparition précoce d'une pneumoconiose chez le mineur de charbon
National audienceL'incidence de la pneumonoconiose a diminue continuellement parmi les mineurs des houilleres pendant les 30 dernieres annees. Actuellement la plupart des cas sont diagnostiques chez les retraites en moyenne vers l'age de 56 ans. Dans ce contexte l'apparition precoce d'une pneumoconiose est un important probleme de sante au travail
Low frequency acoustic stop bands in cubic arrays of thick spherical shells with holes
We analyse the propagation of pressure waves within a fluid filled with a three-dimensional array of rigid coated spheres (shells). We first draw band diagrams for corresponding Floquet-Bloch waves. We then dig a channel terminated by a cavity within each rigid shell and observe the appearance of a low frequency stop band. The underlying mechanism is that each holey shell now acts as a Helmholtz resonator supporting a low frequency localized mode: Upon resonance, pressure waves propagate with fast oscillations in the thin water channel drilled in each shell and are localized in each fluid filled inner cavity. The array of fluid filled shells is approximated by a simple mechanical model of springs and masses allowing for asymptotic estimates of the low frequency stop band. We finally propose a realistic design of periodic macrocell with a large defect surrounded by 26 resonators connected by thin straight rigid wires, which supports a localized mode in the low frequency stop band
Low frequency acoustic stop bands in cubic arrays of thick spherical shells with holes
We analyse the propagation of pressure waves within a fluid filled with a three-dimensional array of rigid coated spheres (shells). We first draw band diagrams for corresponding Floquet-Bloch waves. We then dig a channel terminated by a cavity within each rigid shell and observe the appearance of a low frequency stop band. The underlying mechanism is that each holey shell now acts as a Helmholtz resonator supporting a low frequency localized mode: Upon resonance, pressure waves propagate with fast oscillations in the thin water channel drilled in each shell and are localized in each fluid filled inner cavity. The array of fluid filled shells is approximated by a simple mechanical model of springs and masses allowing for asymptotic estimates of the low frequency stop band. We finally propose a realistic design of periodic macrocell with a large defect surrounded by 26 resonators connected by thin straight rigid wires, which supports a localized mode in the low frequency stop band
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