Longitudinal and transverse noise in a moving Vortex Lattice

We have studied the longitudinal and the transverse velocity fluctuations of a moving vortex lattice (VL) driven by a transport current. They exhibit both the same broad spectrum and the same order of magnitude. These two components are insensitive to the velocity and to a small bulk perturbation. This means that no bulk averaging over the disorder and no VL crystallization are observed. This is consistently explained referring to a previously proposed noisy flow of surface current whose elementary fluctuator is measured isotropic.Comment: accepted for publication in Phys Rev

Stochastic excitation of non-radial modes I. High-angular-degree p modes

Turbulent motions in stellar convection zones generate acoustic energy, part of which is then supplied to normal modes of the star. Their amplitudes result from a balance between the efficiencies of excitation and damping processes in the convection zones. We develop a formalism that provides the excitation rates of non-radial global modes excited by turbulent convection. As a first application, we estimate the impact of non-radial effects on excitation rates and amplitudes of high-angular-degree modes which are observed on the Sun. A model of stochastic excitation by turbulent convection has been developed to compute the excitation rates, and it has been successfully applied to solar radial modes (Samadi & Goupil 2001, Belkacem et al. 2006b). We generalize this approach to the case of non-radial global modes. This enables us to estimate the energy supplied to high-($\ell$) acoustic modes. Qualitative arguments as well as numerical calculations are used to illustrate the results. We find that non-radial effects for $p$ modes are non-negligible: - for high-$n$ modes (i.e. typically $n > 3$) and for high values of $\ell$; the power supplied to the oscillations depends on the mode inertia. - for low-$n$ modes, independent of the value of $\ell$, the excitation is dominated by the non-diagonal components of the Reynolds stress term. We carried out a numerical investigation of high-$\ell$ $p$ modes and we find that the validity of the present formalism is limited to $\ell < 500$ due to the spatial separation of scale assumption. Thus, a model for very high-$\ell$ $p$-mode excitation rates calls for further theoretical developments, however the formalism is valid for solar $g$ modes, which will be investigated in a paper in preparation.Comment: 12 pages, accepted for publication in A&

Chikungunya Virus Infection-Associated Bone and Joint Disease

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that circulates predominantly in tropical and subtropical regions. Infection results in severe debilitating polyarthralgia during the acute phase of disease, and reports suggest that chronic arthralgia lasting months to years after the initial infection can occur. More severe and prolonged disease has been associated with pre-existing joint disease, though this has not been experimentally examined. In the research presented herein, two established mouse models (adult IRF 3/7 -/- -/- and wild-type C57BL/6J mice) were utilized to characterize CHIKV-associated bone and joint disease and evaluate its impact on the progression of pre-existing osteoarthritis (OA) utilizing histopathology, μCT, and serology. During acute stages of the disease, CHIKV infection resulted in synovitis, cartilage necrosis, and periosteal necrosis or periostitis. Additionally, IRF mice had severe ischemic bone marrow necrosis, and C57BL/6J mice developed periosteal new bone proliferation. During chronic stages of disease (90 DPI), there was ongoing and progressive synovitis, tendonitis, enthesitis, and cartilage damage, though periostitis and periosteal bone proliferation had resolved. Infection with CHIKV in mice with pre-existing OA had no significant impact on total synovitis scores or chondrocyte cell death, but caused a decrease in volume of osteophytes and subchondral bone, as compared to OA alone. Serology results in both the footpad and intra-articular C57BL/6J models indicated there were alterations in RANKL and OPG associated with CHIKV infection, demonstrating potential changes in bone dynamics. The current experiments demonstrated novel lesions of CHIKV-associated bone and joint disease that have important ramifications for the treatment and prevention of disease. Periosteal bone proliferation associated with CHIKV is a potentially painful but reversible process, whereas articular cartilage damage is progressive and represents a potential mechanism for chronic CHIKV-associated joint disease. Additionally, the alterations in bone associated with CHIKV infection and pre-existing OA, in conjunction with changes in the RANKL-OPG pathways, could have significance in clinical monitoring of OA and treatment choices in individuals with concurrent diseases. Future studies would help determine if RANKL and OPG levels could be useful for tracking disease progression in people and establish the long-term effects of CHIKV infection on OA progression

Electrodynamics of the vortex lattice in untwinned YBaCuO by complex impedance measurements

We report complex impedance measurements in an untwinned YBaCuO crystal. Our broad frequency range covers both the quasi static response and the resistive response of the vortex lattice. It allow us to characterize the irreversibility line without the need of any frequency dependent pinning parameters. We confirm the validity of the two modes model of vortex dynamic, and extract both the surface critical current and the flux flow resistivity around the first order transition $T_{m}$. This latter is identified by the abrupt loss of pinning and by an unexpected step of $\rho_{ff}(T)$ at $T_{m}$.Comment: accepted for publication in EPJ

Numerical constraints on the model of stochastic excitation of solar-type oscillations

Analyses of a 3D simulation of the upper layers of a solar convective envelope provide constraints on the physical quantities which enter the theoretical formulation of a stochastic excitation model of solar p modes, for instance the convective velocities and the turbulent kinetic energy spectrum. These constraints are then used to compute the acoustic excitation rate for solar p modes, P. The resulting values are found ~5 times larger than the values resulting from a computation in which convective velocities and entropy fluctuations are obtained with a 1D solar envelope model built with the time-dependent, nonlocal Gough (1977) extension of the mixing length formulation for convection (GMLT). This difference is mainly due to the assumed mean anisotropy properties of the velocity field in the excitation region. The 3D simulation suggests much larger horizontal velocities compared to vertical ones than in the 1D GMLT solar model. The values of P obtained with the 3D simulation constraints however are still too small compared with the values inferred from solar observations. Improvements in the description of the turbulent kinetic energy spectrum and its depth dependence yield further increased theoretical values of P which bring them closer to the observations. It is also found that the source of excitation arising from the advection of the turbulent fluctuations of entropy by the turbulent movements contributes ~ 65-75 % to the excitation and therefore remains dominant over the Reynolds stress contribution. The derived theoretical values of P obtained with the 3D simulation constraints remain smaller by a factor ~3 compared with the solar observations. This shows that the stochastic excitation model still needs to be improved.Comment: 11 pages, 9 figures, accepted for publication in A&

The influence of twin boundaries on the Flux Line Lattice structure in YBaCuO: a study by Small Angle Neutron Scattering

The influence of Twin Boundaries (TB) on the Flux Line Lattice(FLL) structure was investigated by Small Angle Neutron Scattering (SANS). YBaCuO single crystals possessing different TB densities were studied. The SANS experiments show that the TB strongly modify the structure of the FLL. The flux lines meander as soon as the magnetic field makes an angle with the TB direction. According to the value of this angle but also to the ratio of the flux lines density over the TB density, one observes that the FLL exhibits two different unit cells in the plane perpendicular to the magnetic field. One is the classical hexagonal and anisotropic cell while the other is affected by an additional deformation induced by the TB. We discuss a possible relation between this deformation and the increase of the critical current usually observed in heavily twinned samples.Comment: accepted for publication in Phys Rev