High spectral resolution of GaAs/AlAs phononic cavities by subharmonic resonant pump-probe excitation

We present here precise measurement of the resonance frequency, lifetime and shape of confined acoustic modes in the tens of GHz regime in GaAs/AlAs superlattice planar and micropillar cavities at low temperature ($\sim 20\,\textrm{K}$). The subharmonic resonant pump-probe technique, where the repetition rate of the pump laser is tuned to a subharmonic of the cavity resonance to maximize the amplitude of the acoustic resonance, in combination with a Sagnac interferometer technique for high sensitivity ($\sim 10 \,\textrm{fm}$) to the surface displacement, has been used. The cavity fundamental mode at $\sim 20\,\textrm{GHz}$ and the higher order cavity harmonics up to $\sim 180\,\textrm{GHz}$ have been clearly resolved. Mechanical Q-values up to $2.7 \times 10^4$ have been measured in a planar superlattice, and direct spatial mapping of confined acoustic modes in a superlattice cavity micropillar has been demonstrated. The Q-frequency product obtained is $\sim 5 \times 10^{14}$ demonstrating the suitability of these superlattice cavities for optomechanical applications.Comment: 5 pages, 4 figure

L'enfant "riche": oublié des droits de l'enfant?

La Convention relative aux droits de l’enfant, adoptée en 1989 par l’Organisation des Nations Unies assure aux enfants des droits, notamment ceux d’être protégés contre toute forme de violence, d’être entendus et d’exprimer leur opinion sur toute question les concernant, et d’être traités dans la dignité sans discrimination de race, de sexe ou autre considération sociale. Les catégories d’enfants, situées aux extrêmes de l’échiquier social sont plus exposées au risque de voir leurs droits bafoués, comme cela a bien été démontré pour les enfants vivant dans une grande pauvreté. L’idée peut paraître saugrenue, mais des risques comparables existent-ils aussi pour les enfants les plus riches ? Répondre à cette question est l’objectif de ce travail

Fingerprinting stress: stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding-the case of the Monte Nero anticline in the Apennines, Italy

In this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold-and-thrust belt. First, we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion. Second, we use our new approach to present a high-resolution deformation and stress history that affected Meso-Cenozoic limestone strata in the Monte Nero Anticline during its late Miocene-Pliocene growth in the Umbria-Marche Arcuate Ridge (northern Apennines, Italy). In this area an extensive stylolite-joint/vein network developed during layer-parallel shortening (LPS), as well as during and after folding. Stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during LPS. The stress regime oscillated between strike slip and compressional during LPS before ultimately becoming strike slip again during late stage fold tightening. Our case study shows that high-resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses. Beyond regional implications, this study validates our approach as a new powerful toolbox to high-resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

Measuring the distortion of time with relativistic effects in large-scale structure

To test the theory of gravity one needs to test, on one hand, how space and time are distorted by matter and, on the other hand, how matter moves in a distorted space-time. Current observations provide tight constraints on the motion of matter, through the so-called redshift-space distortions, but they only provide a measurement of the sum of the spatial and temporal distortions, via gravitational lensing. In this Letter, we develop a method to measure the time distortion on its own. We show that the coming generation of galaxy surveys, like the Square Kilometer Array, will allow us to measure the distortion of time with an accuracy of 10-30\%. Such a measurement will be essential to test deviations from General Relativity in a fully model-independent way. In particular, it can be used to compare the spatial and temporal distortions of space-time, that are predicted to be the same in $\Lambda$CDM but generically differ in modified theories of gravity.Comment: 6 pages, 1 figure, 2 table

Magnetization dynamics: path-integral formalism for the stochastic Landau-Lifshitz-Gilbert equation

We construct a path-integral representation of the generating functional for the dissipative dynamics of a classical magnetic moment as described by the stochastic generalization of the Landau-Lifshitz-Gilbert equation proposed by Brown, with the possible addition of spin-torque terms. In the process of constructing this functional in the Cartesian coordinate system, we critically revisit this stochastic equation. We present it in a form that accommodates for any discretization scheme thanks to the inclusion of a drift term. The generalized equation ensures the conservation of the magnetization modulus and the approach to the Gibbs-Boltzmann equilibrium in the absence of non-potential and time-dependent forces. The drift term vanishes only if the mid-point Stratonovich prescription is used. We next reset the problem in the more natural spherical coordinate system. We show that the noise transforms non-trivially to spherical coordinates acquiring a non-vanishing mean value in this coordinate system, a fact that has been often overlooked in the literature. We next construct the generating functional formalism in this system of coordinates for any discretization prescription. The functional formalism in Cartesian or spherical coordinates should serve as a starting point to study different aspects of the out-of-equilibrium dynamics of magnets. Extensions to colored noise, micro-magnetism and disordered problems are straightforward.Comment: 47 pages + appendix, published versio

Criteria for the verification of feature models

Product Line (PL) based development is a promising approach to develop software intensive systems. Experience already report multiple benefits, such as reduced time to market, better reuse, and reduced development costs. PL modelling languages, in particular to create feature models (FMs), and PL configuration processes are now supported by market tools. Although there is a wealth of research works on the theme of FM verification, there is to our knowledge no comprehensive method, technique or tool. However, it is crucial that when verifying a FM, the right criteria are considered: any error in a FM will inevitably spread to the configured software and generate PL architecture stability issues, with a serious risk of undermining the expected benefits. Dealing with key issues such as selecting the 'right' set of verification criteria or defining a small core of criteria from which all other could be derived calls for a consistent definition of all the criteria. This paper presents an original literature survey of FM verification criteria in which all the criteria are (i) classified according to their purpose and (ii) formalized consistently using first order logic

Prosociality and the pandemic: adolescents from poorer backgrounds suffered more

Camille Terrier (University of Lausanne/LSE), Daniel L Chen (CNRS) and Matthias Sutter (Max Planck Institute) look at how COVID infections affected adolescents’ prosociality, an essential non-cognitive skill. The prosociality gap between students with high and low socio-economic status has doubled

Deriving Product Line Requirements: the RED-PL Guidance Approach

Product lines (PL) modeling have proven to be an effective approach to reuse in software development.Several variability approaches were developed to plan requirements reuse, but only little of them actuallyaddress the issue of deriving product requirements.This paper presents a method, RED-PL that intends to support requirements derivation. The originality ofthe proposed approach is that (i) it is user-oriented, (ii) it guides product requirements elicitation andderivation as a decision making activity, and (iii) it provides systematic and interactive guidance assistinganalysts in taking decisions about requirements. The RED-PL methodological process was validatedin an industrial setting by considering the requirement engineering phase of a product line of blood analyzers