Scaling characteristics of ULF geomagnetic fields at the Guam seismoactive area and their dynamics in relation to the earthquake

International audienceThe long-term evolution of scaling (fractal) characteristics of the ULF geomagnetic fields in the seismoactive region of the Guam Island is studied in relation to the strong (Ms = 8.0) nearby earthquake of 8 August 1993. The selected period covers 10 months before and 10 months after the earthquake. The FFT procedure, Burlaga-Klein approach and Higuchi method, have been applied to calculate the scaling exponents and fractal dimensions of the ULF time series. It is found that the spectrum of ULF emissions exhibits, on average, a power law behaviour S(f ) ? f -b , which is a fingerprint of the typical fractal (self-affine) time series. The spectrum slope b fluctuates quasi-periodically during the course of time in a range of b = 2.5?0.7, which corresponds to the fractional Brownian motion with both persistent and antipersistent behaviour. An tendency is also found for the spectrum slope to decrease gradually when approaching the earthquake date. Such a tendency manifests itself at all local times, showing a gradual evolution of the structure of the ULF noise to a typical flicker noise structure in proximity to the large earthquake event. We suggest considering such a peculiarity as an earthquake precursory signature. One more effect related to the earthquake is revealed: the longest quasi-period, which is 27 days, disappeared from the variations of the ULF emission spectrum slope during the earthquake, and it reappeared three months after the event. Physical interpretation of the peculiarities revealed has been done on the basis of the SOC (self-organized criticality) concept

Optical characteristics of single wavelength-tunable InAs/InGaAsP/InP(100) quantum dots emitting at 1.55 um

We have studied the emission properties of individual InAs quantum dots (QDs) grown in an InGaAsP matrix on InP(100) by metal-organic vapor-phase epitaxy. Low-temperature microphotoluminescence spectroscopy shows emission from single QDs around 1550 nm with characteristic exciton-biexciton behavior, and a biexciton antibinding energy of more than 2 meV. Temperature-dependent measurements reveal negligible optical-phonon induced broadening of the exciton line up to 50 K, and emission from the exciton state clearly persists above 70 K. Furthermore, we find no measurable polarized fine structure splitting of the exciton state within the experimental precision. These results are encouraging for the development of a controllable photon source for fiber-based quantum information and cryptography systems.Comment: 3 pages, 4 figures, submitted AP

Charged exciton emission at 1.3 μ\mum from single InAs quantum dots grown by metalorganic chemical vapor deposition

We have studied the emission properties of self-organized InAs quantum dots (QDs) grown in an InGaAs quantum well by metalorganic chemical vapor deposition. Low-temperature photoluminescence spectroscopy shows emission from single QDs around 1300 nm; we clearly observe the formation of neutral and charged exciton and biexciton states, and we obtain a biexciton binding energy of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV, indicating strong confinement.Comment: 3 pages, 3 figures, submitted AP

Fine structure and magneto-optics of exciton, trion, and charged biexciton states in single InAs quantum dots emitting at 1.3 um

We present a detailed investigation into the optical characteristics of individual InAs quantum dots (QDs) grown by metalorganic chemical vapor deposition, with low temperature emission in the telecoms window around 1300 nm. Using micro-photoluminescence (PL) spectroscopy we have identified neutral, positively charged, and negatively charged exciton and biexciton states. Temperature-dependent measurements reveal dot-charging effects due to differences in carrier diffusivity. We observe a pronounced linearly polarized splitting of the neutral exciton and biexciton lines (~250 ueV) resulting from asymmetry in the QD structure. This asymmetry also causes a mixing of the excited trion states which is manifested in the fine structure and polarization of the charged biexciton emission; from this data we obtain values for the ratio between the anisotropic and isotropic electron-hole exchange energies of (Delta1)/(Delta0)= 0.2--0.5. Magneto-PL spectroscopy has been used to investigate the diamagnetic response and Zeeman splitting of the various exciton complexes. We find a significant variation in g-factor between the exciton, the positive biexciton, and the negative biexciton; this is also attributed to anisotropy effects and the difference in lateral extent of the electron and hole wavefunctions.Comment: 7 pages, 6 figures, submitted to Phys. Rev.

Multifractal PDF analysis for intermittent systems

The formula for probability density functions (PDFs) has been extended to include PDF for energy dissipation rates in addition to other PDFs such as for velocity fluctuations, velocity derivatives, fluid particle accelerations, energy transfer rates, etc, and it is shown that the formula actually explains various PDFs extracted from direct numerical simulations and experiments performed in a wind tunnel. It is also shown that the formula with appropriate zooming increment corresponding to experimental situation gives a new route to obtain the scaling exponents of velocity structure function, including intermittency exponent, out of PDFs of velocity fluctuations.Comment: 10 pages, 5 figure

Analysis of Velocity Derivatives in Turbulence based on Generalized Statistics

A theoretical formula for the probability density function (PDF) of velocity derivatives in a fully developed turbulent flow is derived with the multifractal aspect based on the generalized measures of entropy, i.e., the extensive Renyi entropy or the non-extensive Tsallis entropy, and is used, successfully, to analyze the PDF's observed in the direct numerical simulation (DNS) conducted by Gotoh et al.. The minimum length scale r_d/eta in the longitudinal (transverse) inertial range of the DNS is estimated to be r_d^L/eta = 1.716 (r_d^T/eta = 2.180) in the unit of the Kolmogorov scale eta.Comment: 6 pages, 1 figur

Experimental Lagrangian Acceleration Probability Density Function Measurement

We report experimental results on the acceleration component probability distribution function at $R_\lambda = 690$ to probabilities of less than $10^{-7}$. This is an improvement of more than an order of magnitude over past measurements and allows us to conclude that the fourth moment converges and the flatness is approximately 55. We compare our probability distribution to those predicted by several models inspired by non-extensive statistical mechanics. We also look at acceleration component probability distributions conditioned on a velocity component for conditioning velocities as high as 3 times the standard deviation and find them to be highly non-Gaussian.Comment: submitted for the special issue of Physica D: "Anomalous Distributions" 11 pages, 6 figures revised version: light modifications of the figures and the tex

Fabrication of aligned carbon nanotube-filled rubber composite

ArticleScripta Materialia. 54(1):31-35 (2006)journal articl