Regular Electric Field in Electromagnetic Coupled to a Scalar Field

In the framework of an electromagnetic field coupled nonminimally with a scalar field in flat spacetime, the existence of a non-singular electric field is proved for a point electric charge or electric monopole. In analogy with the Maxwell-dilaton system introduced by Gibbons and Wells, first, a Maxwell-anti-dilaton system is constructed where the radial electric field of a static electric monopole is coupled to an anti-dilaton. The field equations are solved analytically for the electric and dilaton fields and observe the nonsingular electric field. Also, the self-energy of the electric monopole is found to be finite. Furthermore, the formalism to a Maxwell-scalar field is generalized where a mechanism is introduced upon which the coupled regular-electric field and scalar field is obtained. The formalism shows that for a given regular electric field there are two supersymmetric coupling functions corresponding to a scalar and a phantom field.     

Plasma Photocathodes

Plasma wakefield accelerators offer accelerating and focusing electric fields three to four orders of magnitude larger than state-of-the-art radiofrequency cavity-based accelerators. Plasma photocathodes can release ultracold electron populations within such plasma waves and thus open a path toward tunable production of well-defined, compact electron beams with normalized emittance and brightness many orders of magnitude better than state-of-the-art. Such beams will have far-reaching impact for applications such as light sources, but also open up new vistas on high energy and high field physics. This paper reviews the innovation of plasma photocathodes, and reports on the experimental progress, challenges, and future prospects of the approach. Details of the proof-of-concept demonstration of a plasma photocathode in 90° geometry at SLAC FACET within the E-210: Trojan Horse program are described. Using this experience, alongside theoretical and simulation-supported advances, an outlook is given on future realizations of plasma photocathodes such as the upcoming E-310: Trojan Horse-II program at FACET-II with prospects toward excellent witness beam parameter quality, tunability, and stability. Future installations of plasma photocathodes also at compact, hybrid plasma wakefield accelerators, will then boost capacities and open up novel capabilities for experiments at the forefront of interaction of high brightness electron and photon beams.     

Flow field and thermal characteristics in a model of a tangentially fired furnace under different conditions of burner tripping

Tangentially fired furnaces are vortex-combustion units and are widely used in steam generators of industrial plants. The present study provides a numerical investigation of the problem of turbulent reacting flows in a model furnace of a tangentially fired boiler. The importance of this problem is mainly due to its relation to large boiler furnaces used in thermal power plants. In the present work, calculation of the flow field, temperature and species concentration-contour maps in a tangentially-fired model furnace are provided. The safety of these furnaces requires that the burner be tripped (its fuel is cut off) if the flame is extinguished. Therefore, the present work provides an investigation of the influence of number of tripped burners on the characteristics of the flow and thermal fields. The details of the flow, thermal and combustion fields are obtained from the solution of the conservation equations of mass, momentum and energy and transport equations for scalar variables in addition to the equations of the turbulence model. Available experimental measurements were used for validating the calculation procedure. The results show that the vortex created due to pressure gradient at the furnace center only influenced by tripping at least two burners. However, the temperature distributions are significantly distorted by tripping any of the burners. Regions of very high temperature close to the furnace walls appear as a result of tripping the fuel in one or two of the burners. Calculated heat flux along the furnace walls are presented.     

Comportements compares des sols et des roches

Résumé Les sols et les roches sont des corps dont le comportement rhéologique est régi par les liaisons de contact entre les éléments qui les constituent. On peut schématiser ces structures en disant que dans les sols, les contacts sont ponctuels entre les grains alors qu'ils ont lieu sur les surfaces que forment les fissures entre les blocs pour les massifs rocheux. Au cours des déformations qui précèdent la rupture, des glissements se produisent le long de surfaces irrégulières et les mouvements sont accompagnés d'une variation de volume, qui est positive pour les roches et les sables denses, et négative pour les sables lâches et la plupart des argiles. Les roches présentent un effet d'échelle: les caractéristiques mécaniques de la rupture sont des fonctions décroissantes de la dimension de la zone soumise aux contraintes et ceci est lié à l'hétérogénéité de la fissuration. Cet effet n'apparaît pas dans les sols, mais dans un champ de contraintes hétérogène, comme celui qui existe sous un poinçon, un phénomène analogue se produit pour les sables denses. On peut l'expliquer par l'hétérogénéité introduite dans le milieu par la création d'une ligne de glissement isolée.

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Summary Rheological behaviour of soils and rocks is determined by contact forces between constitutive elements. For soils, the contacts are punctual. For rocks they occur along the surfaces of cracks or joints. During the deformation before the failure, sliding movements occur along irregularly shaped surfaces with a volume change, which is positive for rocks and dense sands, negative for loose sands and most of clays. Size effect in rocks is due to cracks heterogeneity: mechanical characteristics at failure decrease with increasing size of specimens. This effect does not exist in soils, but in a heterogeneous stress field a similar phenomenon appears in dense sands. It is connected with the heterogeneity induced by the creation of an isolated slip line.

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Avec 9 figures     

Complete Asymptotic Expansions of Solutions of the System of Elastostatics in the Presence of an Inclusion of Small Diameter and Detection of an Inclusion

We consider the system of elastostatics for an elastic medium consisting of an imperfection of small diameter, embedded in a homogeneous reference medium. The Lamé constants of the imperfection are different from those of the background medium. We establish a complete asymptotic formula for the displacement vector in terms of the reference Lamé constants, the location of the imperfection and its geometry. Our derivation is rigorous, and based on layer potential techniques. The asymptotic expansions in this paper are valid for an elastic imperfection with Lipschitz boundaries. In the course of derivation of the asymptotic formula, we introduce the concept of (generalized) elastic moment tensors (Pólya–Szegö tensor) and prove that the first order elastic moment tensor is symmetric and positive (negative)-definite. We also obtain estimation of its eigenvalue. We then apply these asymptotic formulas for the purpose of identifying with high precision the order of magnitude of the diameter of the elastic inclusion, its location, and its elastic moment tensors.     

An experimental investigation of heat transfer to pulsating pipe air flow with different amplitudes

Heat transfer characteristics to both laminar and turbulent pulsating pipe flows under different conditions of Reynolds number, pulsation frequency, pulsator location and tube diameter were experimentally investigated. The tube wall of uniform heat flux condition was considered for both cases. Reynolds number varied from 750 to 12,320 while the frequency of pulsation ranged from 1 to 10 Hz. With locating the pulsator upstream of the inlet of the test section tube, results showed an increase in heat transfer rate due to pulsation by as much as 30% with flow Reynolds number of 1,643 and pulsation frequency of 1 Hz, depending on the upstream location of the pulsator valve. Closer the valve to the tested section inlet, the better improvement in the heat transfer coefficient is achieved. Upon comparing the heat transfer results of the upstream and the downstream pulsation, at Reynolds number of 1,366 and 1,643, low values of the relative mean Nusselt number were obtained with the upstream pulsation. Comparing the heat transfer results of the two studied test sections tubes for Reynolds number range from 8,000 to 12,000 and pulsation frequency range from 1.0 to 10 Hz showed that more improvement in heat transfer rate was observed with a larger tube diameter. For Reynolds number ranging from 8,000 to 12,000 and pulsation frequency of 10 Hz, an improvement in the relative mean Nusselt number of about 50% was obtained at Reynolds number of 8,000 for the large test section diameter of 50 mm. While, for the small test section diameter of 15 mm, at same conditions of Reynolds number and frequency, a reduction in the relative mean Nusselt number of up to 10% was obtained.     

Recovery of small electromagnetic inhomogeneities from partial boundary measurementsIdentification de petites inhomogénéités diélectriques à partir de mesures partielles

We consider for the inverse problem of identifying locations and certain properties of the shapes of small dielectric inhomogeneities in a homogeneous background medium from boundary measurements on part of the boundary or dynamic boundary measurements for a finite time interval. Using as weights particular background solutions we develop asymptotic methods based on appropriate averaging of the data. To cite this article: H. Ammari, A.G. Ramm, C. R. Mecanique 330 (2002) 199–205.     

A chitosan–polypyrrole magnetic nanocomposite as μ-sorbent for isolation of naproxen

An extracting medium based on chitosan–polypyrrole (CS–PPy) magnetic nanocomposite was synthesized by chemical polymerization of pyrrole at the presence of chitosan magnetic nanoparticles (CS-MNPs) for micro-solid phase extraction. In this work, magnetic nanoparticles, the modified CS-MNPs and different types of CS–PPy magnetic nanocomposites were synthesized. Extraction efficiency of the CS–PPy magnetic nanocomposite was compared with the CS-MNPs and Fe₃O₄ nanoparticles for the determination of naproxen in aqueous samples, via quantification by spectrofluorimetry. The scanning electron microscopy images obtained from all the prepared nanocomposites revealed that the CS–PPy magnetic nanocomposite possess more porous structure. Among different synthesized magnetic nanocomposites, CS–PPy magnetic nanocomposite showed a prominent efficiency. Influencing parameters on the morphology of CS–PPy magnetic nanocomposite such as weight ratio of components was also assayed. In addition, effects of different parameters influencing the extraction efficiency of naproxen including desorption solvent, desorption time, amount of sorbent, ionic strength, sample pH and extraction time were investigated and optimized. Under the optimum condition, a linear calibration curve in the range of 0.04–10 μg mL⁻¹ (R² = 0.9996) was obtained. The limits of detection (3S_b) and limits of quantification (10S_b) of the method were 0.015 and 0.04 μg mL⁻¹ (n = 3), respectively. The relative standard deviation for water sample spiked with 0.1 μg mL⁻¹ of naproxen was 3% (n = 5) and the absolute recovery was 92%. The applicability of method was extended to the determination of naproxen in tap water, human urine and plasma samples. The relative recovery percentages for these samples were in the range of 56–99%.