Convection in rotating annuli: Ginzburg-Landau equations with tunable coefficients

The coefficients of the complex Ginzburg-Landau equations that describe weakly nonlinear convection in a large rotating annulus are calculated for a range of Prandtl numbers $\sigma$. For fluids with $\sigma \approx 0.15$, we show that the rotation rate can tune the coefficients of the corresponding amplitude equations from regimes where coherent patterns prevail to regimes of spatio-temporal chaos.Comment: 4 pages (latex,multicol,epsf) including 3 figure

Contact Changes of Sheared Systems: Scaling, Correlations, and Mechanisms

We probe the onset and effect of contact changes in 2D soft harmonic particle packings which are sheared quasistatically under controlled strain. First, we show that in the majority of cases, the first contact changes correspond to the creation or breaking of contacts on a single particle, with contact breaking overwhelmingly likely for low pressures and/or small systems, and contact making and breaking equally likely for large pressures and in the thermodynamic limit. The statistics of the corresponding strains are near-Poissonian. The mean characteristic strains exhibit scaling with the number of particles N and pressure P, and reveal the existence of finite size effects akin to those seen for linear response quantities. Second, we show that linear response accurately predicts the strains of the first contact changes, which allows us to study the scaling of the characteristic strains of making and breaking contacts separately. Both of these show finite size scaling, and we formulate scaling arguments that are consistent with the observed behavior. Third, we probe the effect of the first contact change on the shear modulus G, and show in detail how the variation of G remains smooth and bounded in the large system size limit: even though contact changes occur then at vanishingly small strains, their cumulative effect, even at a fixed value of the strain, are limited, so that effectively, linear response remains well-defined. Fourth, we explore multiple contact changes under shear, and find strong and surprising correlations between alternating making and breaking events. Fifth, we show that by making a link with extremal statistics, our data is consistent with a very slow crossover to self averaging with system size, so that the thermodynamic limit is reached much more slowly than expected based on finite size scaling of elastic quantities or contact breaking strains

Stresses in Smooth Flows of Dense Granular Media

The form of the stress tensor is investigated in smooth, dense granular flows which are generated in split-bottom shear geometries. We find that, within a fluctuation fluidized spatial region, the form of the stress tensor is directly dictated by the flow field: The stress and strain-rate tensors are co-linear. The effective friction, defined as the ratio between shear and normal stresses acting on a shearing plane, is found not to be constant but to vary throughout the flowing zone. This variation can not be explained by inertial effects, but appears to be set by the local geometry of the flow field. This is in agreement with a recent prediction, but in contrast with most models for slow grain flows, and points to there being a subtle mechanism that selects the flow profiles.Comment: 5 pages, 4 figure

Parent and Family Outcomes of PEERS: A Social Skills Intervention for Adolescents with Autism Spectrum Disorder

Raising a child with an Autism Spectrum Disorder (ASD) is associated with increased family chaos and parent distress. Successful long-term treatment outcomes are dependent on healthy systemic functioning, but the family impact of treatment is rarely evaluated. The Program for the Education and Enrichment of Relational Skills (PEERS) is a social skills intervention designed for adolescents with high-functioning ASD. This study assessed the impact of PEERS on family chaos, parenting stress, and parenting self-efficacy via a randomized, controlled trial. Results suggested beneficial effects for the experimental group in the domain of family chaos compared to the waitlist control, while parents in the PEERS experimental group also demonstrated increased parenting self-efficacy. These findings highlight adjunctive family system benefits of PEERS intervention and suggest the need for overall better understanding of parent and family outcomes of ASD interventions

Contact Changes near Jamming

We probe the onset and effect of contact changes in soft harmonic particle packings which are sheared quasistatically. We find that the first contact changes are the creation or breaking of contacts on a single particle. We characterize the critical strain, statistics of breaking versus making a contact, and ratio of shear modulus before and after such events, and explain their finite size scaling relations. For large systems at finite pressure, the critical strain vanishes but the ratio of shear modulus before and after a contact change approaches one: linear response remains relevant in large systems. For finite systems close to jamming the critical strain also vanishes, but here linear response already breaks down after a single contact change.Comment: 5 pages, 4 figure

Shocks near Jamming

Non-linear sound is an extreme phenomenon typically observed in solids after violent explosions. But granular media are different. Right when they jam, these fragile and disordered solids exhibit a vanishing rigidity and sound speed, so that even tiny mechanical perturbations form supersonic shocks. Here, we perform simulations in which two-dimensional jammed granular packings are dynamically compressed, and demonstrate that the elementary excitations are strongly non-linear shocks, rather than ordinary phonons. We capture the full dependence of the shock speed on pressure and impact intensity by a surprisingly simple analytical model.Comment: Revised version. Accepted for publication in Phys. Rev. Let

Anticipatory Smiling: Linking Early Affective Communication and Social Outcome

In anticipatory smiles, infants appear to communicate pre-existing positive affect by smiling at an object and then turning the smile toward an adult. We report two studies in which the precursors, development, and consequences of anticipatory smiling were investigated. Study 1 revealed a positive correlation between infant smiling at 6 months and the level of anticipatory smiling at 8 and 10 months during joint attention episodes, as well as a positive correlation between anticipatory smiling and parent-rated social expressivity scores at 30 months. Study 2 confirmed a developmental increase in the number of infants using anticipatory smiles between 9 and 12 months that had been initially documented in the Study 1 sample [Venezia, M., Messinger, D. S., Thorp, D., & Mundy, P. (2004). The development of anticipatory smiling. Infancy, 6(3), 397–406]. Additionally, anticipatory smiling at 9 months positively predicted parent-rated social competence scores at 30 months. Findings are discussed with regard to the importance of anticipatory smiling in early socioemotional development

Critical jamming of frictional grains in the generalized isostaticity picture

While frictionless spheres at jamming are isostatic, frictional spheres at jamming are not. As a result, frictional spheres near jamming do not necessarily exhibit an excess of soft modes. However, a generalized form of isostaticity can be introduced if fully mobilized contacts at the Coulomb friction threshold are considered as slipping contacts. We show here that, in this framework, the vibrational density of states (DOS) of frictional discs exhibits a plateau when the generalized isostaticity line is approached. The crossover frequency to elastic behavior scales linearly with the distance from this line. Moreover, we show that the frictionless limit, which appears singular when fully mobilized contacts are treated elastically, becomes smooth when fully mobilized contacts are allowed to slip.Comment: 4 pages, 4 figures, submitted to PR