Dissipative lateral walls are sufficient to trigger convection in vibrated granular gases

Buoyancy-driven (thermal) convection in dilute granular media, fluidized by a vibrating base, is known to appear without the need of lateral boundaries in a restricted region of parameters (inelasticity, gravity, intensity of energy injection). We have recently discovered a second buoyancy-driven convection effect which occurs at any value of the parameters, provided that the impact of particles with the lateral walls is inelastic (Pontuale et al., Phys. Rev. Lett. 117, 098006 (2016)). It is understood that this novel convection effect is strictly correlated to the existence of perpendicular energy fluxes: a vertical one, induced by both bulk and wall inelasticity, and a horizontal one, induced only by dissipation at the walls. Here we first review those previous results, and then present new experimental and numerical data concerning the variations of box geometry, intensity of energy injection, number of particles and width of the box.Comment: 4 pages, 4 figures, conference Powders and Grains 201

Brownian ratchet in a thermal bath driven by Coulomb friction

The rectification of unbiased fluctuations, also known as the ratchet effect, is normally obtained under statistical non-equilibrium conditions. Here we propose a new ratchet mechanism where a thermal bath solicits the random rotation of an asymmetric wheel, which is also subject to Coulomb friction due to solid-on-solid contacts. Numerical simulations and analytical calculations demonstrate a net drift induced by friction. If the thermal bath is replaced by a granular gas, the well known granular ratchet effect also intervenes, becoming dominant at high collision rates. For our chosen wheel shape the granular effect acts in the opposite direction with respect to the friction-induced torque, resulting in the inversion of the ratchet direction as the collision rate increases. We have realized a new granular ratchet experiment where both these ratchet effects are observed, as well as the predicted inversion at their crossover. Our discovery paves the way to the realization of micro and sub-micrometer Brownian motors in an equilibrium fluid, based purely upon nano-friction.Comment: main paper: 4 pages and 4 figures; supplemental material joined at the end of the paper; a movie of the experiment can be viewed http://www.youtube.com/watch?v=aHrdY4BC71k ; all the material has been submitted for publication [new version with substantial changes in the order of the presentation of the results; differences with previous works have been put in evidence

Ga+ Ion Irradiation-Induced Tuning of Artificial Pinning Sites to Control Domain Wall Motion

Domain-wall-based devices are considered one of the candidates for the next generation of storage memories and nanomagnetic logic devices due to their unique properties, such as nonvolatility, scalability, and low power consumption. Field or current-driven domain walls require a regular and controlled motion along the track in which they are stored in order to maintain the information integrity during operation. However, their dynamics can vary along the track due to film inhomogeneities, roughness of the edges, and thermal fluctuations. Consequently, the final position of the domain walls may be difficult to predict, making difficult the development of memory and logic applications. In this paper, we demonstrate how Ga+ ion irradiation can be used to locally modify the material properties of the Ta/ CoFeB/MgO thin film, creating regions in which the domain wall can be trapped, namely motion barriers. The aim is to push the domain wall to overcome thin-film inhomogeneities effects, while stopping its motion at artificially defined positions corresponding to the irradiated regions. Increasing the driving force strength, the domain wall can escape, allowing the shifting between consecutive irradiated regions. In this way, the correct positioning of the domain walls after the motion is ensured. The study shows that the driving force strength, namely current density or magnetic field amplitude, needed to overcome the irradiated regions depends on the ion dose. These results show a reliable approach for domain wall manipulation, enabling a precise control of the domain wall position along a track with synchronous motion

The Rizzoli Multiple Osteochondromas Classification revised: describing the phenotype to improve clinical practice

Multiple osteochondromas (MO) is a rare disorder, characterized by benign osteocartilaginous tumors (osteochondromas), arising from the perichondrium of bones. The osteochondromas increase during growth, frequently causing deformities and limitations. Our study aims to analyze the data captured by the Registry of Multiple Osteochondromas, to refine Istituto Ortopedico Rizzoli (IOR) Classification, providing a representative picture of the phenotypic manifestations throughout the lifespan. We conducted a single-institution cross-sectional study. Patients were categorized according to IOR Classification, which identifies three patients' classes on the presence/absence of deformities and/or limitations. The present dataset was compared with our previously published data, to refine the classification. Nine hundred sixty-eight patients were included: 243 children (<10 years), 136 adolescents (10–15 years), and 589 adults. Of the entire population, half patients presented at least one deformity, and one quarter reported at least one limitation. Compared with our previous study, the amount of children was more than doubled and the percentage of mild/moderate cases was notably increased, giving a better disease overview throughout the lifespan and suggesting a different cut-off for dividing Class II in subclasses. We confirmed that MO is characterized by phenotypic heterogeneity, suggesting that an early classification of the disease may offer a useful tool to follow disease pattern and evolution, to support clinical practice, and to propose timely interventions