Time-modulated inerters as building blocks for nonreciprocal mechanical devices

In this work, we discuss the realization of mechanical devices with non-reciprocal attributes enabled by inertia-amplifying, time-modulated mechanisms. Our fundamental building-block features a mass, connected to a fixed ground through a spring and to a moving base through a mechanism-based inerter. Through analytical derivations and numerical simulations, we provide details on the nonlinear dynamics of such system. We demonstrate that providing a time modulation to the inerter's base produces two additions on the dynamics of the main spring-mass oscillator: i) an effective time-modulated mass term, and ii) a time varying force term; both quantities are functions of the modulating frequency. With specific choices of parameters, the modulation-induced force term -- that represents one of the main drawbacks in most experimental realizations of purely time-modulated systems -- vanishes and we are left with an effective time-varying mass. We then illustrate that this building block can be leveraged to realize non-reciprocal wave manipulation devices, and concentrate on a non-reciprocal beam-like waveguide. The simple design and the clean performance of our system makes it an attractive candidate for the realization of fully mechanical non-reciprocal devices

Acoustic properties of porous microlattices from effective medium to scattering dominated regimes

Microlattices are architected materials that allow for an unprecedented control of mechanical properties (e.g., stiffness, density, and Poisson's coefficient). In contrast to their quasi-static mechanical properties, the acoustic properties of microlattices remain largely unexplored. This paper analyzes the acoustic response of periodic millimeter-sized microlattices immersed in water using experiments and numerical simulations. Microlattices are fabricated using high-precision stereolithographic three-dimensional printing in a large variety of porosities and lattice topologies. This paper shows that the acoustic propagation undergoes a frequency dependent transition from a classic poroelastic behaviour that can be described by Biot's theory to a regime that is dominated by scattering effects. Biot's acoustic parameters are derived from direct simulations of the microstructure using coupled fluid and solid finite elements. The wave speeds predicted with Biot's theory agree well with the experimental measures. Within the scattering regime, the signals show a strong attenuation and dispersion, which is characterized by a cut-off frequency. The strong dispersion results in a frequency dependent group velocity. A simplified model of an elastic cylindrical scatterer allows predicting the signal attenuation and dispersion observed experimentally. The results in this paper pave the way for the creation of microlattice materials for the control of ultrasonic waves across a wide range of frequencies

La dramaturgie de la lumière strehlerienne

La lumière, Strehler a su en faire une composante fondamentale de ses spectacles jouant avec la transparence, la superposition de couches, l’ombre. Elle s’inscrit dans une époque théâtrale, comprise entre les années 1950 et 1990, et elle se développe d’une manière tout à fait personnelle, devenant une référence.  Héritier d’une culture avant-gardiste et européenne, l’imaginaire strehlerien se forge dans un environnement milanais sillonné, à partir des années 1920, par des artistes - scénographes et plasticiens - très attentifs aux problématiques d’espace et de lumière. Chez Strehler, la pratique des éclairages s’articule non seulement à la scénographie, mais aussi au jeu, dont elle devient partenaire, ou au rythme musical. Elle peut être considérée comme un outil dramaturgique au service de la mise en scène.La lumière, Strehler a su en faire une composante fondamentale de ses spectacles jouant avec la transparence, la superposition de couches, l’ombre. Elle s’inscrit dans une époque théâtrale, comprise entre les années 1950 et 1990, et elle se développe d’une manière tout à fait personnelle, devenant une référence.  Héritier d’une culture avant-gardiste et européenne, l’imaginaire strehlerien se forge dans un environnement milanais sillonné, à partir des années 1920, par des artistes - scénographes et plasticiens - très attentifs aux problématiques d’espace et de lumière. Chez Strehler, la pratique des éclairages s’articule non seulement à la scénographie, mais aussi au jeu, dont elle devient partenaire, ou au rythme musical. Elle peut être considérée comme un outil dramaturgique au service de la mise en scène

A dramaturgia da luz strehleriana

Luz, Strehler fez dela uma componente fundamental de seus espetáculos, atuando com transparência, sobreposição de camadas, sombra. Faz parte de uma era teatral, dos anos 1950 aos 1990, e se desenvolveu de uma forma muito pessoal, tornando-se um ponto de referência. Herdeiro de uma cultura avant-garde e europeia, o imaginário strehlerian foi forjado num ambiente milanês, atravessado, a partir dos anos 1920, por artistas - cenógrafos e artistas visuais - muito atentos aos problemas do espaço e da luz. Na prática de Strehler, a iluminação não se articula apenas com a cenografia, mas também com a interpretação, na qual ela se torna parceira, ou com o ritmo musical. Pode ser considerada como uma ferramenta dramatúrgica a serviço da mise-en-scène

Enhancing allocentric spatial recall in pre-schoolers through navigational training programme

Unlike for other abilities, children do not receive systematic spatial orientation training at school, even though navigational training during adulthood improves spatial skills. We investigated whether navigational training programme (NTP) improved spatial orientation skills in pre-schoolers. We administered 12-week NTP to seventeen 4- to 5-year-old children (training group, TG). The TG children and 17 age-matched children (control group, CG) who underwent standard didactics were tested twice before (T0) and after (T1) the NTP using tasks that tap into landmark, route and survey representations. We determined that the TG participants significantly improved their performances in the most demanding navigational task, which is the task that taps into survey representation. This improvement was significantly higher than that observed in the CG, suggesting that NTP fostered the acquisition of survey representation. Such representation is typically achieved by age seven. This finding suggests that NTP improves performance on higher-level navigational tasks in pre-schooler

Engineered metabarrier as shield from seismic surface waves

Resonant metamaterials have been proposed to reflect or redirect elastic waves at different length scales, ranging from thermal vibrations to seismic excitation. However, for seismic excitation, where energy is mostly carried by surface waves, energy reflection and redirection might lead to harming surrounding regions. Here, we propose a seismic metabarrier able to convert seismic Rayleigh waves into shear bulk waves that propagate away from the soil surface. The metabarrier is realized by burying sub-wavelength resonant structures under the soil surface. Each resonant structure consists of a cylindrical mass suspended by elastomeric springs within a concrete case and can be tuned to the resonance frequency of interest. The design allows controlling seismic waves with wavelengths from 10-to-100 m with meter-sized resonant structures. We develop an analytical model based on effective medium theory able to capture the mode conversion mechanism. The model is used to guide the design of metabarriers for varying soil conditions and validated using finite-element simulations. We investigate the shielding performance of a metabarrier in a scaled experimental model and demonstrate that surface ground motion can be reduced up to 50% in frequency regions below 10 Hz, relevant for the protection of buildings and civil infrastructures

Documentary heritage: fungal deterioration in Compact Discs

AbstractIn recent years, there has been an exponential growth in the use of digital media for data storage and the creation of museums, libraries and digital archives. In particular, Compact Discs Recordable (CD-R) have become one of the most used tools for archiving documents related to cultural heritage. Many authors have investigated only the CD longevity, but very few studies have focused on their biological deterioration. The aim of this work was to examine the CD-R biodeterioration following two ways: (1) search badly preserved CD-R, showing clear degradation spots and verify that it is fungal deterioration; (2) fungal inoculation tests on blank CD-R to verify their bioreceptivity. The analysis of a badly preserved CD-R showed clear degradation spots, highlighting, after cultural and molecular analysis, the presence on the surface of three different fungi: Chaetomium globosum, Trichoderma atroviride e Coniochaeta sp. For the in vitro inoculation tests we used conidia suspensions of Cladosporium cladosporioides and Penicillium chrysogenum, and we observed the growth for 6 months. At the end of experiment, both fungi colonized the CD-R surface with hyphae and mycelia clearly visible, causing also loss of material and fractal structure presence. For the CD-R use as cultural heritage archiving, the correct storage is an essential phase and, in light of the results obtained, it will be necessary not only to consider the environmental factors (temperature, relative humidity) but also the biological deterioration caused by airborne fungi. Therefore, effort needs to be taken to regularly monitor temperature and relative humidity and it is essential to periodically conduct cleaning of optical media

O país do futuro, visto da Argentina

Se trata de una discusión a la luz de las trayectorias históricas de ambos países, de aspecto de la cultura política brasileña, y de las percepciones argentinas sobre Brasil, su presente y su futuro.Como o Brasil é percebido por seu vizinho mais próximo? Que imagens projeta? Qual é a percepção sobre seu futuro? A partir da análise das trajetórias históricas, expressões da cultura política de ambos os países e alguns textos significativos, o artigo identifica traços fundamentais do Brasil – a continuidade do Estado, a persistência da desigualdade, a suposta cordialidade de seu povo – que ajudam a entender a imagem do Brasil que prevalece na Argentina, o que, por sua vez, permite definir melhor a ideia que os próprios argentinos têm de seu país.Fil: Palermo, Vicente Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin