Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the low-frequency range using a pick-up coil wound around the sample. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance was observed. The asymmetry is attributed to the formation of a hard magnetic crystalline phase at the ribbon surface. The experimental results are interpreted in terms of the surface impedance tensor. It is assumed that the ribbon consists of an inner amorphous region and surface crystalline layers. The coupling between the crystalline and amorphous phases is described through an effective bias field. A qualitative agreement between the calculated dependences and experimental data is demonstrated. The results obtained may be useful for development of weak magnetic-field sensors.Comment: 19 pages, 6 figure

The thermopower as a fingerprint of the Kondo breakdown quantum critical point

We propose that the thermoelectric power distinguishes two competing scenarios for quantum phase transitions in heavy fermions : the spin-density-wave (SDW) theory and breakdown of the Kondo effect. In the Kondo breakdown scenario, the Seebeck coefficient turns out to collapse from the temperature scale $E^{*}$, associated with quantum fluctuations of the Fermi surface reconfiguration. This feature differs radically from the physics of the SDW theory, where no reconstruction of the Fermi surface occurs, and can be considered as the hallmark of the Kondo breakdown theory. We test these ideas, upon experimental results for YbRh$_2$Si$_2$

Higgs-mediated flavor-changing neutral currents in the general framework with two Higgs doublets -- an RGE analysis

We consider the standard model with two Higgs doublets with the most general Yukawa coupling terms (``type III''). In the model, the neutral-Higgs-mediated flavor-changing neutral currents (FCNC's) are allowed, but must be reasonably suppressed at low energies of probes. It has been known that the existing hierarchies of quark masses render this suppression at low energies rather natural. On the other hand, the model has been regarded by many as unnatural because of the absence of any symmetry that would ensure persistence of this suppression as the energy of probes increases. The opinion has been based on the expectation that the mentioned FCNC's would increase by large factors at increasing energies. We performed a numerical analysis of the flow of these FCN coupling parameters as governed by the one-loop renormalization group equations (RGE's), in a simplified case when Yukawa couplings of the first quark generation are neglected. The analysis shows a remarkable persistence of the mentioned FCNC suppression and thus indicates that the model is not unnatural in the RGE sense. Further, we point out two mistakes in the Yukawa RGE's of Machacek and Vaughn at one-loop level.Comment: LaTeX (REVTeX), 30 pages, 14 eps-figures, slight modifications performed to adjust to the published versio

Hypersonic turbulent wall boundary layer computations

The Baldwin-Lomax algebraic turbulence model was modified for hypersonic flow conditions. Two coefficients in the outer layer eddy viscosity model were determined as functions of Mach number and temperature ratio. By matching the solutions from the Baldwin-Lomax model to those from the Cebeci-Smith model for a flat plate at hypersonic speed, the new values of the coefficient were obtained. The results show that the values of C sub cp and C sub kleb are functions of both Mach number and wall temperature ratio. The C sub cp and C sub kleb variations with Mach number and wall temperature were used for the calculations of both a 4 deg wedge flow at Mach 18 and an axisymmetric Mach 20 nozzle flow. The Navier-Stokes equations with thin layer approximation were solved for the above hypersonic flow conditions and the results were compared with existing experimental data. The agreement between the numerical solutions and the existing experimental data were good. The modified Baldwin-Lomax model thus is useful in the computations of hypersonic flows