Universal analytic properties of noise. Introducing the J-Matrix formalism

We propose a new method in the spectral analysis of noisy time-series data for damped oscillators. From the Jacobi three terms recursive relation for the denominators of the Pad\'e Approximations built on the well-known Z-transform of an infinite time-series, we build an Hilbert space operator, a J-Operator, where each bound state (inside the unit circle in the complex plane) is simply associated to one damped oscillator while the continuous spectrum of the J-Operator, which lies on the unit circle itself, is shown to represent the noise. Signal and noise are thus clearly separated in the complex plane. For a finite time series of length 2N, the J-operator is replaced by a finite order J-Matrix J_N, having N eigenvalues which are time reversal covariant. Different classes of input noise, such as blank (white and uniform), Gaussian and pink, are discussed in detail, the J-Matrix formalism allowing us to efficiently calculate hundreds of poles of the Z-transform. Evidence of a universal behaviour in the final statistical distribution of the associated poles and zeros of the Z-transform is shown. In particular the poles and zeros tend, when the length of the time series goes to infinity, to a uniform angular distribution on the unit circle. Therefore at finite order, the roots of unity in the complex plane appear to be noise attractors. We show that the Z-transform presents the exceptional feature of allowing lossless undersampling and how to make use of this property. A few basic examples are given to suggest the power of the proposed method.Comment: 14 pages, 8 figure

Density Power Spectrum of Compressible Hydrodynamic Turbulent Flows

Turbulent flows are ubiquitous in astrophysical environments, and understanding density structures and their statistics in turbulent media is of great importance in astrophysics. In this paper, we study the density power spectra, $P_{\rho}$, of transonic and supersonic turbulent flows through one and three-dimensional simulations of driven, isothermal hydrodynamic turbulence with root-mean-square Mach number in the range of 1 \la M_{\rm rms} \la 10. From one-dimensional experiments we find that the slope of the density power spectra becomes gradually shallower as the rms Mach number increases. It is because the density distribution transforms from the profile with {\it discontinuities} having $P_{\rho} \propto k^{-2}$ for $M_{\rm rms} \sim 1$ to the profile with {\it peaks} having $P_{\rho} \propto k^0$ for $M_{\rm rms} \gg 1$. We also find that the same trend is carried to three-dimension; that is, the density power spectrum flattens as the Mach number increases. But the density power spectrum of the flow with $M_{\rm rms} \sim 1$ has the Kolmogorov slope. The flattening is the consequence of the dominant density structures of {\it filaments} and {\it sheets}. Observations have claimed different slopes of density power spectra for electron density and cold H I gas in the interstellar medium. We argue that while the Kolmogorov spectrum for electron density reflects the {\it transonic} turbulence of $M_{\rm rms} \sim 1$ in the warm ionized medium, the shallower spectrum of cold H I gas reflects the {\it supersonic} turbulence of $M_{\rm rms} \sim$ a few in the cold neutral medium.Comment: To appear in ApJ Lett. Pdf file with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/kimryu.pd

Geothermal studies - Yellowstone National Park /test site 11/, Wyoming

Summary report of diamond drilling in thermal areas of Yellowstone National Park, and method for determining heat flow in thermal area

Environmental protection of titanium alloys in centrifugal compressors at 500°C in saline atmosphere

The use of the titanium alloy Ti-6246 (Ti–6Al–2Sn–4Zr–6Mo, wt-%) for gas turbine compressors allows an increase in working temperature and stress level. Under severe service conditions, the material experiences combined high temperature and high mechanical stress and, in saline atmospheres, stress corrosion cracking (SCC) can occur, leading to catastrophic mechanical failure. The present study was performed to evaluate the potential of several surface treatments to protect Ti-6246 alloy, after salt deposit, from hot salt SCC at temperatures ?500°C and 500 MPa static mechanical stress conditions. Shot peening, thermal oxidation and metal–ceramic coatings were investigated. Experimental results confirm the existence of brittle stress corrosion phenomena marked by a low residual elongation of test samples and the presence of oxides on the fracture surfaces. Both shot peening and metal–ceramic coatings increase the hot salt SCC resistance of the alloy. Times to rupture were improved by a factor of 3 for shot peening and by a factor of 10 for metal–ceramic coatings. Inversely, the time to rupture of preoxidised alloys has been halved compared with uncoated alloys. As well as these interesting quantitative results, structural studies of metal–ceramic coatings showed that they are mechanically and chemically compatible with the titanium alloy substructure and should work under severe thermomechanical stresses and aggressive atmospheres

La mesure de l’activité des banques en France.

L’explication des liens et différences entre valeur ajoutée des banques mesurée par la comptabilité nationale, et produit net bancaire, calculé selon les principes comptables des établissements de crédit, permet de construire une table de passage pour réconcilier ces indicateurs d’activité.Banques, établissements de crédit, intermédiation financière, produit net bancaire, valeur ajoutée, SIFIM, comptabilité bancaire, comptabilité nationale.

Long-range Ni/Mn structural order in epitaxial double perovskite La2NiMnO6 thin films

We report and compare the structural, magnetic, and optical properties of ordered La2NiMnO6 thin films and its disordered LaNi0.5Mn0.5O3 counterpart. An x-ray diffraction study reveals that the B-site Ni/Mn ordering induces additional XRD reflections as the crystal symmetry is transformed from a pseudocubic perovskite unit cell in the disordered phase to a monoclinic form with larger lattice parameters for the ordered phase. Polarized Raman spectroscopy studies reveal that the ordered samples are characterized by additional phonon excitations that are absent in the disordered phase. The appearance of these additional phonon excitations is interpreted as the clearest signature of Brillouin zone folding as a result of the long-range Ni/Mn ordering in La2NiMnO6. Both ordered and disordered materials display a single ferromagnetic-to-paramagnetic transition. The ordered films display also a saturation magnetization close to 4.8 mB/f.u. and a transition temperature (FM-TC) around 270 K, while the disordered ones have only a 3.7 mB/f.u. saturation magnetization and a FM-TC around 138 K. The differences in their magnetic behaviours are understood based on the distinct local electronic configurations of their Ni/Mn cations.Comment: 15 pages, 5 fig

Modeling planar degenerate wetting and anchoring in nematic liquid crystals

We propose a simple surface potential favoring the planar degenerate anchoring of nematic liquid crystals, i.e., the tendency of the molecules to align parallel to one another along any direction parallel to the surface. We show that, at lowest order in the tensorial Landau-de Gennes order-parameter, fourth-order terms must be included. We analyze the anchoring and wetting properties of this surface potential. In the nematic phase, we find the desired degenerate planar anchoring, with positive scalar order-parameter and some surface biaxiality. In the isotropic phase, we find, in agreement with experiments, that the wetting layer may exhibit a uniaxial ordering with negative scalar order-parameter. For large enough anchoring strength, this negative ordering transits towards the planar degenerate state

Phase formation, phonon behavior, and magnetic properties of novel ferromagnetic La3BAlMnO9 (B = Co or Ni) triple perovskites

In the quest for novel magnetoelectric materials, we have grown, stabilized and explored the properties of La3BAlMnO9 (B = Co or Mn) thin films. In this paper, we report the influence of the growth parameters that promote B/Al/Mn ordering in the pseudo-cubic unit cell and their likely influence on the magnetic and multiferroic properties. The temperature dependence of the magnetization shows that La3CoAlMnO9 is ferromagnetic up to 190 K while La3NiAlMnO9 shows a TC of 130 K. The behavior of these films are compared and contrasted with related La2BMnO6 double perovskites. It is observed that the insertion of AlO6 octahedra between CoO6 and MnO6 suppresses significantly the strength of the superexchange interaction, spin-phonon and spin-polar coupling.Comment: 13 pages, 3 fig

Field theoretic calculation of scalar turbulence

The cascade rate of passive scalar and Bachelor's constant in scalar turbulence are calculated using the flux formula. This calculation is done to first order in perturbation series. Batchelor's constant in three dimension is found to be approximately 1.25. In higher dimension, the constant increases as $d^{1/3}$.Comment: RevTex4, publ. in Int. J. Mod. Phy. B, v.15, p.3419, 200