1,252 research outputs found
Change of the thermoelectric power of p-Gasb under a weak magnetic field and the scattering mechanism
No full textTurbulent drag reduction by hydrophobic surfaces with shear-dependent slip length
No full textThe stabilisation of a parabolic equilibrium profile in a three-dimensional (3D) turbulent channel flow for an incompressible fluid is addressed with the objective of achieving drag reduction. The formulation of this problem stems from Balogh’s work [1] where Lyapunov stability analysis was used to devise prototype feedback laws and prove global stability of the solutions. This treatment only considers the controller as a mathematical artefact, but it can actually be linked to physical control strategies modelling hydrophobic surfaces and porous media. In the former, only linear slip velocity boundary conditions (BC) were considered [8]. However, experiments [2] have suggested that the slip length may be shear-dependent. Motivated by these, the effect on drag reduction of a shear-dependent slip length surface is examined in the present study using Direct Numerical Simulations (DNS) at Re τ0 = u τ0 δ/ν ≃ 180. δ is the channel half height, u τ0 the wall-shear velocity for regular no-slip walls channel and ν the kinematic viscosity. The theoretical analysis in [5], is extended to this new model. The proposed formulation shows that the skin-friction coefficient can be reduced by tuning the parameters in the shear-dependent slip length model. The results, which verified by DNS simulations, show that by taking a slip length value based on a constant slip model [8] and combining it within a shear-dependent model, up to 50% drag reduction can be obtained. The effect of control is further assessed by formulating the Fukagata identity [4] with general boundaries; the weighted Reynolds shear-stress for each quadrant shows an enhanced reduction in the sweep/ejection events compared to the constant slip model
Paraconductivity along c-axis direction in a plane of a thin film of YBaCuO
No full textThin films of YBaCuO have been grown using a PrBa2Cu3O7-x template with the c-axis aligned in the plane of the films. Conductivity and hence paraconductivity have been measured along the c-axis direction on this plane. Thermal fluctuation studies have been attempted along this direction, and the dimensionality effect was studied for this configuration. As a main characteristic a dimensionality equal to zero is emerged from the data. This dimensionality is consistent with the phenomena of fluctuation along the c-axis. © 1997 Plenum Publishing Corporation
Two thermomagnetic effects and the electronic thermal conductivity in p-GaSb
No full textTwo thermomagnetic effects are studied in a single crystal ρvariant-GaSb. The influence of a weak magnetic field, up to 20 kG, upon the thermoelectric effect and the thermal conductivity of the semiconductor for different temperatures is investigated. From the measurement of the change of the above transport properties in a magnetic field conclusions concerning their field and temperature dependence, the r (exponent in scattering law) and the electron component of the thermal conductivity and its dependence on temperature have been derived. © 1983
Electrical resistivity of a-Fe2O3 and comparison to TEP at the first order Morin transition
No full textThe electrical resistivity of hematite is measured in the region of the first order Morin transition and the above trasport property is compared to the thermoelectric power (TEP) in the same region. Some similarities can be found in the detailed behaviour, of the electrical resistivity which can be distinguished generally as a step-like change, at the temperature of the transition, and the behaviour of the thermoelectric power at the same temperature. The above behaviour of the two transport effects is compared to that observed in other materials at a first order transition. © 1984
Hydrodynamical turbulence by fractal fourier decimation
No full textWe present a systematic numerical investigation of high-resolution 3D isotropic and homogeneous turbulence resolved on a decimated set of Fourier modes. Fractal decimation acts to decrease the effective dimensionality of the flow by allowing triadic interactions only in a set of Fourier modes N(k) proportional to k^DF for large k. While keeping the symmetries of the original 3D Navier-Stokes equations unchanged, a dramatic change in small-scale statistics is detected at decreasing the fractal dimension DF . Already at fractal dimension DF = 2.8, a global self-similar behaviour is observed in the inertial range of scales, the consequence of such transition are the restoration of the scaling symmetry and vorticity distribution that becomes close to Gaussian. We relate the results to the different roles of local vs non-local interactions in the energy transfer range
Fault current limiter model device: characterisation and simulation
No full textA simulation of the performance of superconducting fault current limiters is presented. Testing methods of the superconducting material are proposed in order to collect all the required material data. Thermal recovery is also included in order to simulate the performance of the device and its response under an actual electro-thermal environment
Specific heat of antiferromagnetic spin fluctuations in cuprate superconductors
No full textIt has been shown that the temperature dependence of the specific heat of the antiferromagnetic spin fluctuations in cuprate superconductors has the form C = αT2. The present thermodynamical calculations are the additional test confirming d-pairing in the cuprate superconductors
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