Embedding approach to modeling electromagnetic fields in a complex two-dimensional environment

An approach is presented to combine the response of a two-dimensionally inhomogeneous dielectric object in a homogeneous environment with that of an empty inhomogeneous environment. This allows an efficient computation of the scattering behavior of the dielectric cylinder with the aid of the CGFFT method and a dedicated extrapolation procedure. Since a circular observation contour is adopted, an angular spectral representation can be employed for the embedding. Implementation details are discussed for the case of a closed 434 MHz microwave scanner, and the accuracy and efficiency of all steps in the numerical procedure are investigated. Guidelines are proposed for choosing computational parameters such as truncation limits and tolerances. We show that the embedding approach does not increase the CPU time with respect to the forward problem solution in a homogeneous environment, if only the fields on the observation contour are computed, and that it leads to a relatively small increase when the fields on the mesh are computed as well

Numerical Computation of approximate Generalized Polarization Tensors

In this paper we describe a method to compute Generalized Polarization Tensors. These tensors are the coefficients appearing in the multipolar expansion of the steady state voltage perturbation caused by an inhomogeneity of constant conductivity. As an alternative to the integral equation approach, we propose an approximate semi-algebraic method which is easy to implement. This method has been integrated in a Myriapole, a matlab routine with a graphical interface which makes such computations available to non-numerical analysts

On certain constructions for latin squares with no latin subsquares of order two

AbstractA latin square is said to be an N2-latin square (see[1] and [2]) if it contains no latin subsquare of order 2. The existence of N2-latin squares of all orders except 2k has been proved in [2]. Trivially, there are no such squares of orders 2 and 4. M. McLeish [3] has shown that there exist N2-latin squares of all orders 2k for k ⩾ 6. The present paper introduces a construction for N2-latin squares of all even orders n with n ≠ 0 (mod 3) and n ≠ 3 (mod 5). The problem is thus solved for the orders 24 and 25.For 24, the only remaining case, Eric Regener of the Faculty of Music, Université de Montréal, has constructed the following example of an N2-latin square and kindly granted us the permission to reproduce it here: 81234567823156784314678254682135758273461657182437458213687634512 The existence problem of N2-latin squares is thus completely solved

On a combinatorial problem of antennas in radio astronomy

International audienc

Investigation of gamma-ray sensitivity of neutron detectors based on thin converter films

Currently, many detector technologies for thermal neutron detection are in development in order to lower the demand for the rare 3He gas. Gas detectors with solid thin film neutron converters readout by gas proportional counter method have been proposed as an appropriate choice for applications where large area coverage is necessary. In this paper, we investigate the probability for gamma-rays to generate a false count in a neutron measurement. Simulated results are compared to measurement with a 10B thin film prototype and a 3He detector. It is demonstrated that equal gamma-ray rejection to that of 3He tubes is achieved with the new technology. The arguments and results presented here are also applicable to gas detectors with converters other than solid 10B layers, such as 6Li layers and 10BF3 gas.Comment: Submitted to Journal of Instrumentatio

Emergent spatial structures in flocking models: a dynamical system insight

We show that hydrodynamic theories of polar active matter generically possess inhomogeneous traveling solutions. We introduce a unifying dynamical-system framework to establish the shape of these intrinsically nonlinear patterns, and show that they correspond to those hitherto observed in experiments and numerical simulations: periodic density waves, and solitonic bands, or polar-liquid droplets both cruising in isotropic phases. We elucidate their respective multiplicity and mutual relations, as well as their existence domain

Propagation of surge waves in channels with large-scale bank roughness

In open channels, a sudden rise in water elevation generates a positive surge. Positive surges are commonly observed in man-made channels (Bazin 1865, Treske 1994) and a natural occurrence is the tidal bore in macro-tidal estuaries (Tricker 1965, Chanson 2011a). The positive surge may propagate upstream or downstream (Fig. D1). It is a rapidly-varied flow and the flow properties immediately upstream and downstream of the front must satisfy the continuity and momentum principles (Rouse 1938, Liggett 1994). The authors investigated positive surge waves in a long channel with a range of sidewall configuration. Their configuration corresponded to a downstream surge configuration (Fig. D1, right). The contribution is a welcome addition to the literature on rapidly-varied unsteady open channel flows. In this discussion, it is shown that the effects of boundary friction were previously documented, and a recent investigation provided some insight into the energy dissipation induced by large-scale sidewall roughness

Femtosecond laser irradiation of dielectric materials containing randomly-arranged nanoparticles

International audienceWe investigate femtosecond laser irradiation of dielectric materials containing randomly-arranged nanoparticles. For this, numerical modeling is performed based on three different methods: Mie theory, static solution of linear Maxwell's equations and a solution of nonlinear Maxwell's equations together with kinetic equations for free electron excitation/relaxation processes. First two approaches are used to define the static intensity distribution and to analyze the electromagnetic interaction between the nanoparticles. The third method allows us to investigate the complex dynamics of the laser-matter interaction. Multiphoton absorption is shown to be responsible for electron plasma generation in the regions of strong intensity enhancements in the vicinity of nanoparticles. The irradiation of the dielectric material leads to the elongation of nanoplasmas by the near-field enhancement perpendicular to the laser polarization and to their strong interaction resulting in periodic arrangement. Numerical results shed light on such effects as femtosecond laser-induced nanograting formation