Coupled electric and magnetic dipole formulation for planar arrays of dipolar particles: metasurfaces with various electric and/or magnetic meta-atoms per unit cell

The optical properties of infinite planar array of scattering particles, metasurfaces and metagratings, are attracting special attention lately for their rich phenomenology, including both plasmonic and high-refractive-index dielectric meta-atoms with a variety of electric and magnetic resonant responses. Herein we derive a coupled electric and magnetic dipole (CEMD) analytical formulation to describe the reflection and transmission of such periodic arrays, including specular and diffractive orders, valid in the spectral regimes where only dipolar multipoles are needed. Electric and/or magnetic dipoles with all three orientations arising in turn from a single or various meta-atoms per unit cell are considered. The 2D lattice Green function is rewritten in terms of a 1D (chain) version that fully converges and can be easily calculated. Modes emerging as poles of such lattice Green function can be extracted. This formulation can be applied to investigate a wealth of plasmonic, all-dielectric, and hybrid metasurfaces/metagratings of interest throughout the electromagnetic spectrum.Comment: 8 pages, 4 figure

Measurements and calibration of the stripline BPM for the ELI-NP facility with the stretched wire method

A methodology has been developed to perform electrical characterization of the stripline BPMs for the future Gamma Beam System of ELI Nuclear Physics facility in Romania. Several prototype units are extensively benchmarked and the results are presented in this paper. The BPM sensitivity function is determined using a uniquely designed motorized test bench with a stretched wire to measure the BPM response map. Here, the BPM feedthroughs are connected to Libera Brilliance electronics and the wire is fed by continuous wave signal, while the two software-controlled motors provide horizontal and vertical motion of the BPM around the wire. The electrical offset is obtained using S-parameter measurements with a Network Analyzer (via the “Lambertson” method) and is referenced to the mechanical offse

Handling incomplete heterogeneous data using VAEs.

Variational autoencoders (VAEs), as well as other generative models, have been shown to be efficient and accurate for capturing the latent structure of vast amounts of complex high-dimensional data. However, existing VAEs can still not directly handle data that are heterogenous (mixed continuous and discrete) or incomplete (with missing data at random), which is indeed common in real-world applications. In this paper, we propose a general framework to design VAEs suitable for fitting incomplete heterogenous data. The proposed HI-VAE includes likelihood models for real-valued, positive real valued, interval, categorical, ordinal and count data, and allows accurate estimation (and potentially imputation) of missing data. Furthermore, HI-VAE presents competitive predictive performance in supervised tasks, outperforming supervised models when trained on incomplete data

HOMOGENEOUS RIEMANNIAN MANIFOLDS WITH NON-TRIVIAL NULLITY

We develop a general theory for irreducible homogeneous spaces M = G/H, in relation to the nullity distribution ν of their curvature tensor. We construct natural invariant (different and increasing) distributions associated with the nullity, that give a deep insight of such spaces. In particular, there must exist an order-two transvection, not in the nullity, with null Jacobi operator. This fact was very important for finding out the first homogeneous examples with non-trivial nullity, i.e., where the nullity distribution is not parallel. Moreover, we construct irreducible examples of conullity k = 3, the smallest possible, in any dimension. None of our examples admit a quotient of finite volume. We also proved that H is trivial and G is solvable if k = 3. Another of our main results is that the leaves, i.e., the integral manifolds, of the nullity are closed (we used a rather delicate argument). This implies that M is a Euclidean affine bundle over the quotient by the leaves of ν. Moreover, we prove that ν⊥ defines a metric connection on this bundle with transitive holonomy or, equivalently, ν⊥ is completely non-integrable (this is not in general true for an arbitrary autoparallel and at invariant distribution). We also found some general obstruction for the existence of non-trivial nullity: e.g., if G is reductive (in particular, if M is compact), or if G is two-step nilpotent

Earthquake damage on the vaulted nave of the Atlatlahucan Ex-Convent church in Morelos, Mexico

The State of Morelos, in Mexico, has an architectural heritage conformed by 4614 religious and civil buildings, many of which were severely affected by the earthquake that occurred on September 19, 2017, which also caused damages to the built heritage in the states of Puebla, Tlaxcala, Mexico and Mexico City. A total of about 2800 heritage buildings suffered different damages degrees, reaching in many cases the collapse of elements such as vaults, domes, bell towers as well as their cloisters. The Ex-Convent of San Mateo in Atlatlahucan, Morelos, suffered damages on its main nave, in the pinnacles on the longitudinal side walls as well as in the clock box located on the front façade. In the present work, an analysis is made of the damages observed in the building, as well as a preliminary analytical diagnosis of the behavior of the main nave in order to propose future reinforcement actions for the building

Stability of relative equilibria with singular momentum values in simple mechanical systems

A method for testing $G_\mu$-stability of relative equilibria in Hamiltonian systems of the form "kinetic + potential energy" is presented. This method extends the Reduced Energy-Momentum Method of Simo et al. to the case of non-free group actions and singular momentum values. A normal form for the symplectic matrix at a relative equilibrium is also obtained.Comment: Partially rewritten. Some mistakes fixed. Exposition improve

Pâturage: une alternative pour la cultures d’orge à faible rendement

An experiment was performed to evaluate the nutritive value of vitreous-grain barley grazed by sheep (instantaneous stocking rate of 66 sheep/ha). Available biomass (2353 kg dry matter (DM)/ha, on average) was determined at the beginning of the experimental period, which lasted for three consecutive weeks, and barley heads, leaves and stems were separated for quantification. Important amounts of Wimmera ryegrass (Lolium rigidum) were also found. Diet selection, intake and digestibility were estimated using the nalkanes technique. Rumen fermentation characteristics and in situ degradation parameters were obtained from rumen cannulated animals. Transit kinetics of barley heads, leaves and stems was also assessed. The proportion of barley heads in the diet consumed was high (0.53 on average) and varied along the grazing period (0.30 in the first, 0.64 in the second and 0.65 in the third week). Wimmera ryegrass was highly selected during the first week of the experimental period (0.7) and much lesser afterwards (0.35). Estimated total DM intake was low (428, 376 and 657 g/day for weeks 1, 2 and 3, respectively), and chan ged with the botanical composition of the paddock and biomass availability. Average DM digestibility of the diet consumed was also low (56%) and decreased as the grazing period advanced (67%, 55% and 47% for weeks 1, 2 and 3, respectively). Rumen pH was, on average, 6.6, whereas ammonia concentration reached a value of 93 mg/l. Proportions of acetic (0.65), propionic (0.15) and butyric (0.15) acids were representative of a rumen environment driven by fibre fermentation. Effective DM degradability of barley heads, leaves and stems was, on average, 81%, 66% and 55%, respectively.Un essai a été mené pour évaluer la valeur nutritive de l’orge en stade de grain vitreux pâturé par les ovins (taux de charge animale instantanée de 66 brebis/ha). La biomasse disponible (2353 kilogrammes de matière sèche (MS)/ha, en moyenne) a été déterminée au début de la période expérimentale, qui a duré trois semaines consécutives, et les épis, les feuilles et les tiges de l’orge ont été séparés pour leur quantification. Des quantités importantes d’ivraie raide (Lolium rigidum) ont été également rencontrées. Le choix alimentaire, les quantités ingérées et la digestibilité du régime ont été estimés en utilisant la technique des nalcanes. Les caractéristiques de fermentation ruminale et les paramètres de dégradation in situ ont été obtenues en utilisant des animaux canulés dans le rumen. La cinétique de passage des épis, des feuilles et des tiges d’orge a été également évaluée. La proportion des épis d’orge dans le régime consommé était élevée (0,53 en moyenne) et variait le long de la période de pâturage (0,30, 0,64 et 0,65 pendant la première, la deuxième et la troisième semaine respectivement). L’ivraie raide a été fortement choisie pendant la première semaine de la période expérimentale (0,7) et beaucoup moins après (0,35). Les quantités ingérées estimées de MS étaient faibles (428, 376 et 657 g/j pendant la 1ère, 2ème et 3ème semaine, respectivement), et changeaient avec la composition botanique et la disponibilité de la biomasse. La digestibilité moyenne de MS du régime consommé était également faible (56%) et diminuait avec la progression de la période du pâturage (67%, 55% et 47% durant la 1ère, 2ème et 3ème semaine, respectivement). Le pH ruminal était, en moyenne, de 6,6, tandis que la concentration en ammoniaque atteignait une valeur 93 de mg/l. Les proportions d’acide acétique (0,65), propionique (0,15) et butyrique (0,15) étaient représentatives d’un milieu ruminal propice d’une fermentation cellulolytique. La dégradabilité effective de la MS des épis, des feuilles et des tiges d‘orge était, en moyenne, 81%, 66% et 55%, respectivement

Tailoring accidental double bound states in the continuum in all-dielectric metasurfaces

Bound states in the continuum (BICs) have been thoroughly investigated due to their formally divergent Q-factor, especially those emerging in all-dielectric, nanostructured metasurfaces from symmetry protection at the $\Gamma$ point (in-plane wavevector $k_{||}=0$). Less attention has been paid to accidental BICs that may appear at any other $k_{||}\not =0$ in the band structure of supported modes, being in turn difficult to predict. Here we make use of a coupled electric/magnetic dipole model to determine analytical conditions for the emergence of accidental BICs, valid for any planar array of meta-atoms that can be described by dipolar resonances, which is the case of many nanostructures in the optical domain. This is explored for all-dielectric nanospheres through explicit analytical conditions that allow us in turn to predict accidental BIC positions in the parameter space $(\omega,\bf{k_{||}}$). Finally, such conditions are exploited to determine not only single, but also double (for both linear polarizations) accidental BICs occurring at the same position in the dispersion relation $\omega-\bf{k_{||}}$ for realistic semiconductor nanodisk meta-atoms. This might pave the way to a variety of BIC-enhanced light-matter interaction phenomena at the nanoscale such as lasing or non-linear conversion, that benefit from emerging at wavevectors away from the $\Gamma$ point (off-normal incidence) overlapping for both linear polarizations.Comment: 18 pages, 7 figure

Modified dipole-dipole interaction and dissipation in an atomic ensemble near surfaces

We study how the radiative properties of a dense ensemble of atoms can be modified when they are placed near or between metallic or dielectric surfaces. If the average separation between the atoms is comparable or smaller than the wavelength of the scattered photons, the coupling to the radiation field induces long-range coherent interactions based on the interatomic exchange of virtual photons. Moreover, the incoherent scattering of photons back to the electromagnetic field is known to be a many-body process, characterized by the appearance of superradiant and subradiant emission modes. By changing the radiation field properties, in this case by considering a layered medium where the atoms are near metallic or dielectric surfaces, these scattering properties can be dramatically modified. We perform a detailed study of these effects, with focus on experimentally relevant parameter regimes. We finish with a specific application in the context of quantum information storage,where the presence of a nearby surface is shown to increase the storage time of an atomic excitation that is transported across a one-dimensional chain

Fe-doping and strain effects on structural and magnetotransport properties in La2/3Ca1/3Mn1−yFeyO3 thin films

ABSTRACT: The influence of 57Fe-doping and strain effects on the structural and magnetotransport properties of undoped and lightly doped 57Fe (1 and 3% at Mn site) La2/3Ca1/3MnO3 thin films and bulk powder samples have been studied. Thin films were grown on (100)-SrTiO3 STO and 100 -LaAlO3 (LAO) single crystal substrates, via high O2 pressure (500 mTorr) using dc magnetron sputtering. Conversion electron Mössbauer (CEM) spectra measured at room temperature in the paramagnetic regime of the Fe-doped samples do not show significant differences in the isomeric shift for the case of the La2/3Ca1/3MnO3 films doped with 1 and 3% iron. The isomeric shift values correspond to the presence of Fe in the 3+ state with octahedral coordination, thus indicating that Fe is incorporated into the structure by substituting Mn. The absence of further states in the spectra indicates that Fe is not involved in forming other additional impurity phases. The x-ray θ-2θ scan showed that all thin films on LAO and STO have single phase and c-axis strong orientation along the growth direction and the Fe doping gives rise to a relaxation of the epitaxial strain. Finally, we have observed that the saturation magnetization, Curie temperature, metal-insulator transition, and magnetoresistance vary nonmonotonically with increased Fe concentration. This behavior can be understood in terms of competing influences from the strain relaxation, which enhances the tendency to order ferromagnetically, and the reduced double exchange, which is detrimental to the ferromagnetic order