Tribological behavior of shape-specific microplate-enriched synovial fluids on a linear two-axis tribometer

Nano- and micro-particles are being increasingly used to tune interfacial frictional properties in diverse applications, from friction modifiers in industrial lubrication to enhanced biological fluids in human osteoarthritic joints. Here, we assessed the tribological properties of a simulated synovial fluid enriched with non-spherical, poly lactic-co-glycolic acid (PLGA) microparticles (μPL) that have been previously demonstrated for the pharmacological management of osteoarthritis (OA). Three different μPL configurations were fabricated presenting a 20 μm 20 μm square base and a thickness of 5 μm (thin, 5H μPL), 10 μm (10H μPL), and 20 μm (cubical, 20H μPL). After extensive morphological and physicochemical characterizations, the apparent Young’s modulus of the μPL was quantified under compressive loading returning an average value of 6 kPa, independently of the particle morphology. Then, using a linear two-axis tribometer, the static (μs) and dynamic (μd) friction coefficients of the μPL-enriched simulated synovial fluid were determined in terms of particle configuration and concentration, varying from 0 (fluid only) to 6105 μPL/mL. The particle morphology had a modest influence on friction, possibly because the μPL were fully squeezed between two mating surfaces by a 5.8 N normal load realizing boundary-like lubrication conditions. Differently, friction was observed to depend on the dimensionless parameter , defined as the ratio between the total volume of the μPL enriching the simulated synovial fluid and the volume of the fluid itself. Both coefficients of friction were documented to grow with reaching a plateau of μs 0.4 and μd 0.15, already at  210-3. Future investigations will have to systematically analyze the effect of sliding velocity, normal load, and rigidity of the mating surfaces to elucidate in full the tribological behavior of μPL in the context of osteoarthritis

Modeling Swash Zone Hydrodynamics Using Discontinuous Galerkin Finite-Element Method

A 2D numerical model for the solution of the Nonlinear Shallow Water Equations (NSWEs) using the Discontinuous Galerkin Finite Element Method (DGFEM) is presented. A new adaptation of the thin film approach is developed for the wetting/drying treatment. The model is applied to a number of test cases that can be characterized as swash flows, or as cases that are particularly useful for swash flow modelling. The DGFEM model shows robustness and provides accurate predictions of water depth, velocities, and shoreline movement. For the case of bore collapse on a plane beach the model performs well against a state-of-the-art finite volume swash code. The new wetting/drying algorithm is tested against a previous algorithm within the same framework for simulating a solitary wave propagating on a beach with bottom friction, showing a noticeable improvement in the shoreline prediction. The model is also tested against a more subtle test case, including generation of subharmonic edge waves, in order to test the effectiveness of DGFEM in reproducing second order effects. The model simulates the excitation and development of the sub-harmonic edge waves when compared to the analytical solutions in the literature. Overall, it is shown here for the first time that the DGFEM technique can be used to simulate accurately a wide range of swash zone flows and therefore swash zone processes

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum

The status of GEO 600

The GEO 600 laser interferometer with 600m armlength is part of a worldwide network of gravitational wave detectors. GEO 600 is unique in having advanced multiple pendulum suspensions with a monolithic last stage and in employing a signal recycled optical design. This paper describes the recent commissioning of the interferometer and its operation in signal recycled mode