Auxetic two-dimensional lattice with Poisson's Ratio arbitrarily close to -1

In this paper we propose a new lattice structure having macroscopic Poisson's ratio arbitrarily close to the stability limit -1. We tested experimentally the effective Poisson's ratio of the micro-structured medium; the uniaxial test has been performed on a thermoplastic lattice produced with a 3d printing technology. A theoretical analysis of the effective properties has been performed and the expression of the macroscopic constitutive properties is given in full analytical form as a function of the constitutive properties of the elements of the lattice and on the geometry of the microstructure. The analysis has been performed on three micro-geometry leading to an isotropic behaviour for the cases of three-fold and six-fold symmetry and to a cubic behaviour for the case of four-fold symmetry.Comment: 26 pages, 12 figures (26 subfigures

Measuring non-linear functionals of quantum harmonic oscillator states

Using only linear interactions and a local parity measurement we show how entanglement can be detected between two harmonic oscillators. The scheme generalizes to measure both linear and non-linear functionals of an arbitrary oscillator state. This leads to many applications including purity tests, eigenvalue estimation, entropy and distance measures - all without the need for non-linear interactions or complete state reconstruction. Remarkably, experimental realization of the proposed scheme is already within the reach of current technology with linear optics.Comment: 5 pages, 2 figures. Minor corrections and some new references adde

Global Dynamics of Subsurface Solar Active Regions

We present three-dimensional numerical simulations of a magnetic loop evolving in either a convectively stable or unstable rotating shell. The magnetic loop is introduced in the shell in such a way that it is buoyant only in a certain portion in longitude, thus creating an \Omega-loop. Due to the action of magnetic buoyancy, the loop rises and develops asymmetries between its leading and following legs, creating emerging bipolar regions whose characteristics are similar to the ones of observed spots at the solar surface. In particular, we self-consistently reproduce the creation of tongues around the spot polarities, which can be strongly affected by convection. We moreover emphasize the presence of ring-shaped magnetic structures around our simulated emerging regions, which we call "magnetic necklace" and which were seen in a number of observations without being reported as of today. We show that those necklaces are markers of vorticity generation at the periphery and below the rising magnetic loop. We also find that the asymmetry between the two legs of the loop is crucially dependent on the initial magnetic field strength. The tilt angle of the emerging regions is also studied in the stable and unstable cases and seems to be affected both by the convective motions and the presence of a differential rotation in the convective cases.Comment: 23 pages (ApJ 2-column format), 19 figures, accepted for publication in Ap

Polar cap magnetic field reversals during solar grand minima: could pores play a role?

We study the magnetic flux carried by pores located outside active regions with sunspots and investigate their possible contribution to the reversal of the global magnetic field of the Sun. We find that they contain a total flux of comparable amplitude to the total magnetic flux contained in polar caps. The pores located at distances of 40--100~Mm from the closest active region have systematically the correct sign to contribute to the polar cap reversal. These pores can predominantly be found in bipolar magnetic regions. We propose that during grand minima of solar activity, such a systematic polarity trend, akin to a weak magnetic (Babcock-Leighton-like) source term could still be operating but was missed by the contemporary observers due to the limited resolving power of their telescopes.Comment: 11 pages, 9 figures, accepted for publication in Astronomy&Astrophysic

Impingement of Water Droplets on an Ellipsoid with Fineness Ratio 5 in Axisymmetric Flow

The presence of radomes and instruments that are sensitive to water films or ice formations in the nose section of all-weather aircraft and missiles necessitates a knowledge of the droplet impingement characteristics of bodies of revolution. Because it is possible to approximate many of these bodies with an ellipsoid of revolution, droplet trajectories about an ellipsoid of revolution with a fineness ratio of 5 were computed for incompressible axisymmetric air flow. From the computed droplet trajectories, the following impingement characteristics of the ellipsoid surface were obtained and are presented in terms of dimensionless parameters: (1) total rate of water impingement, (2) extent of droplet impingement zone, (3) distribution of impinging water, and (4) local rate of water impingement

Characterizing the propagation of gravity waves in 3D nonlinear simulations of solar-like stars

The revolution of helio- and asteroseismology provides access to the detailed properties of stellar interiors by studying the star's oscillation modes. Among them, gravity (g) modes are formed by constructive interferences between progressive internal gravity waves (IGWs), propagating in stellar radiative zones. Our new 3D nonlinear simulations of the interior of a solar-like star allows us to study the excitation, propagation, and dissipation of these waves. The aim of this article is to clarify our understanding of the behavior of IGWs in a 3D radiative zone and to provide a clear overview of their properties. We use a method of frequency filtering that reveals the path of {individual} gravity waves of different frequencies in the radiative zone. We are able to identify the region of propagation of different waves in 2D and 3D, to compare them to the linear raytracing theory and to distinguish between propagative and standing waves (g modes). We also show that the energy carried by waves is distributed in different planes in the sphere, depending on their azimuthal wave number. We are able to isolate individual IGWs from a complex spectrum and to study their propagation in space and time. In particular, we highlight in this paper the necessity of studying the propagation of waves in 3D spherical geometry, since the distribution of their energy is not equipartitioned in the sphere.Comment: 14 pages, 12 figues, accepted by Astronomy & Astrophysic

Effects of burying and removing dead leaves from the ground on the development of scab epidemics in an apple organic orchard.

Ascospores produced on scabbed leaves in the leaf litter constitute the primary inoculum causing scab infections in apple orchards during the year. The trial, carried out in a commercial organic orchard, permitted to evaluate the effects of the removal of dead leaves located on the inter-row supplemented by the ploughing in of the leaves left on the row, on the development of scab epidemics. From the first recorded contamination to harvest time, lesions on leaves and fruits were counted to determine reduction in disease incidence and severity, compared with the untreated plots. Disease severity as a function of the distance from the untreated plot was also observed, to evaluate the spore dispersal gradient within the orchard. The results show that the ploughing in and the removal of the litter reduced disease incidence by 62% on leaves, and by almost 82% on fruits to harvest. Moreover, measurements of the dispersal gradient show that the spores do not disperse, or little, beyond 20m of the untreated zone