Determination of airplane model structure from flight data by using modified stepwise regression

The linear and stepwise regressions are briefly introduced, then the problem of determining airplane model structure is addressed. The MSR was constructed to force a linear model for the aerodynamic coefficient first, then add significant nonlinear terms and delete nonsignificant terms from the model. In addition to the statistical criteria in the stepwise regression, the prediction sum of squares (PRESS) criterion and the analysis of residuals were examined for the selection of an adequate model. The procedure is used in examples with simulated and real flight data. It is shown that the MSR performs better than the ordinary stepwise regression and that the technique can also be applied to the large amplitude maneuvers

Evidence for electron-phonon interaction in Fe1−x_{1-x}Mx_{x}Sb2_{2} (M=Co, Cr) single crystals

We have measured polarized Raman scattering spectra of the Fe$_{1-x}$Co$_{x}$Sb$_{2}$ and Fe$_{1-x}$Cr$_{x}$Sb$_{2}$ (0$\leq x\leq$0.5) single crystals in the temperature range between 15 K and 300 K. The highest energy $B_{1g}$ symmetry mode shows significant line asymmetry due to phonon mode coupling width electronic background. The coupling constant achieves the highest value at about 40 K and after that it remains temperature independent. Origin of additional mode broadening is pure anharmonic. Below 40 K the coupling is drastically reduced, in agreement with transport properties measurements. Alloying of FeSb$_2$ with Co and Cr produces the B$_{1g}$ mode narrowing, i.e. weakening of the electron-phonon interaction. In the case of A$_{g}$ symmetry modes we have found a significant mode mixing

Evolution of Magnetic and Superconducting Fluctuations with Doping of High-Tc Superconductors

Electronic Raman scattering from high- and low-energy excitations was studied as a function of temperature, extent of hole doping, and energy of the incident photons in Bi_2Sr_2CaCu_2O_{8 \pm \delta} superconductors. For underdoped superconductors, short range antiferromagnetic (AF) correlations were found to persist with hole doping, and doped single holes were found to be incoherent in the AF environment. Above the superconducting (SC) transition temperature T_c, the system exhibits a sharp Raman resonance of B_{1g} symmetry and energy of 75 meV and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi particles. The occupancy of the coherent state increases with cooling until phase ordering at T_c produces a global SC state.Comment: 6 pages, 4 color figures, PDF forma

Generation of periodic surface structures on silica fibre surfaces using 405 nm CW diode lasers

Periodic surface structures have been observed on the end surfaces of synthetic silica fibres when they are exposed to long-term irradiation with light from a 405 nm CW diode laser. The surface structures are generated when the laser power is at a level which is three magnitudes of order lower than that of the damage threshold. They exhibit multiple bends, break-ups and bifurcations, unlike interference patterns but rather like the effect caused by short-pulsed laser irradiation on wide band-gap insulators. The detailed investigation undertaken in this work has concluded that the key parameters that contribute to the generation of the surface structures are power density, surface roughness, polarisation direction and the presence of ultraviolet defect centres

Dynamics of two coupled vortices in a spin valve nanopillar excited by spin transfer torque

We investigate the dynamics of two coupled vortices driven by spin transfer. We are able to independently control with current and perpendicular field, and to detect, the respective chiralities and polarities of the two vortices. For current densities above $J=5.7*10^7 A/cm^2$, a highly coherent signal (linewidth down to 46 kHz) can be observed, with a strong dependence on the relative polarities of the vortices. It demonstrates the interest of using coupled dynamics in order to increase the coherence of the microwave signal. Emissions exhibit a linear frequency evolution with perpendicular field, with coherence conserved even at zero magnetic field

The relativistic solar particle event of 2005 January 20: origin of delayed particle acceleration

The highest energies of solar energetic nucleons detected in space or through gamma-ray emission in the solar atmosphere are in the GeV range. Where and how the particles are accelerated is still controversial. We search for observational information on the location and nature of the acceleration region(s) by comparing the timing of relativistic protons detected on Earth and radiative signatures in the solar atmosphere during the particularly well-observed 2005 Jan. 20 event. This investigation focuses on the post-impulsive flare phase, where a second peak was observed in the relativistic proton time profile by neutron monitors. This time profile is compared in detail with UV imaging and radio spectrography over a broad frequency band from the low corona to interplanetary space. It is shown that the late relativistic proton release to interplanetary space was accompanied by a distinct new episode of energy release and electron acceleration in the corona traced by the radio emission and by brightenings of UV kernels. These signatures are interpreted in terms of magnetic restructuring in the corona after the coronal mass ejection passage. We attribute the delayed relativistic proton acceleration to magnetic reconnection and possibly to turbulence in large-scale coronal loops. While Type II radio emission was observed in the high corona, no evidence of a temporal relationship with the relativistic proton acceleration was found

High power 405 nm diode laser fiber-coupled single-mode system with high long-term stability

Fiber-coupled 405 nm diode laser systems are rarely used with fiber output powers higher than 50 mW. A quick degradation of fiber-coupled high power modules with wavelengths in the lower range of the visible spectrum is known for several years. Meanwhile, the typical power of single-mode diode lasers around 400 nm is in the order of 100 to 300 mW, leading to single-mode fiber core power densities in the 1 MW/cm² range. This is three magnitudes of order below the known threshold for optical damage. Our profound investigations on the influence of 405 nm laser light irradiation of single-mode fibers found the growth of periodic surface structures in the form of ripples responsible for the power loss. The ripples are found on the proximal and distal fiber end surfaces, negatively impacting power transmission and beam quality, respectively. Important parameters in the generation of the surface structures are power density, surface roughness and polarization direction. A fiber-coupled high-power 405 nm diode laser system with a high long-term stability will be introduced and described

Quantum theory of large amplitude collective motion and the Born-Oppenheimer method

We study the quantum foundations of a theory of large amplitude collective motion for a Hamiltonian expressed in terms of canonical variables. In previous work the separation into slow and fast (collective and non-collective) variables was carried out without the explicit intervention of the Born Oppenheimer approach. The addition of the Born Oppenheimer assumption not only provides support for the results found previously in leading approximation, but also facilitates an extension of the theory to include an approximate description of the fast variables and their interaction with the slow ones. Among other corrections, one encounters the Berry vector and scalar potential. The formalism is illustrated with the aid of some simple examples, where the potentials in question are actually evaluated and where the accuracy of the Born Oppenheimer approximation is tested. Variational formulations of both Hamiltonian and Lagrangian type are described for the equations of motion for the slow variables.Comment: 29 pages, 1 postscript figure, preprint no UPR-0085NT. Latex + epsf styl