Re-examination of log-periodicity observed in the seismic precursors of the 1989 Loma Prieta earthquake

Based on several empirical evidence, a series of papers has advocated the concept that seismicity prior to a large earthquake can be understood in terms of the statistical physics of a critical phase transition. In this model, the cumulative Benioff strain (BS) increases as a power-law time-to-failure before the final event. This power law reflects a kind of scale invariance with respect to the distance to the critical point. A few years ago, on the basis of a fit of the cumulative BS released prior to the 1989 Loma Prieta earthquake, Sornette and Sammis [1995] proposed that this scale invariance could be partially broken into a discrete scale invariance (DSI). The observable consequence of DSI takes the form of log-periodic oscillations decorating the accelerating power law. They found that the quality of the fit and the predicted time of the event are significantly improved by the introduction of log-periodicity. Here, we present a battery of synthetic tests performed to quantify the statistical significance of this claim. We find that log-periodic oscillations with frequency and regularity similar to those of the Loma Prieta case are very likely to be generated by the interplay of the low pass filtering step due to the construction of cumulative functions together with the approximate power law acceleration. Thus, the single Loma Prieta case alone cannot support the initial claim and additional cases and further study are needed to increase the signal-to-noise ratio if any. The present study will be a useful methodological benchmark for future testing of additional events when the methodology and data to construct reliable Benioff strain function become available.Comment: LaTeX, JGR preprint with AGU++ v16.b and AGUTeX 5.0, use packages graphicx and psfrag, 23 eps figures, 17 pages. In press J. Geophys. Re

Compact frequency standard based on an intracavity sample of cold cesium atoms

We have demonstrated the possibility for a compact frequency standard based on a sample of cold cesium atoms. In a cylindrical microwave cavity, the atoms are cooled and interrogated during a free expansion and then detected. The operation of this experiment is different from conventional atomic fountains since all the steps are sequentially performed in the same position of space. In this paper we report the analysis of a Ramsey pattern observed to present a (47±5) Hz linewidth and a stability of (5±0.5)x10-13τ-1/2 for an integration time longer than 100 s. Some of the main limitations of the standard are analyzed. This present report demonstrates considerable improvement of our previous work [J. Opt. Soc. Am. B 25, 909 (2008)] where the atoms were in a free space and not inside a microwave cavity.FAPESPCNPqCAPESFAPESP-CNR

Compression-induced electrical percolation and enhanced mechanical properties of polydimethylsiloxane-based nanocomposites

YesIn this work, a compression-induced percolation threshold was found when the thickness of polydimethylsiloxane (PDMS) nanocomposite samples was reduced via a spatial confining forced network assembly (SCFNA) process from 1.0 mm to 0.1 mm. Such as for PDMS/2 wt% short carbon fiber/4 wt% carbon nanotube (CNT) composite, its conductivity was more than 8 times enhanced to 487 S/m from 59.5 S/m, and the mechanical properties of composites have been improved by more than 15% accordingly. Comparatively, when increased the concentration of CNT or Gr from 1 to 4 wt%, the electrical conductivity of PDMS nanocomposites at 1 mm thickness was barely changed as it generally reached saturation and became independent of filler loading. Compared with the traditional blending method, it indicates that the SCFNA process can further promote the maximum electrical conductivity of polymer nanocomposites when the filler concentration has little effect on the conductivity. Especially under the condition of relatively high filler concentration, the electrical conductivity enhancement effect becomes more significant that is contrary to the classical percolation theory. Moreover, the mechanical properties of the nanocomposites can be slightly improved by the mechanical compression, which makes it more suitable for flexible electronic devices' applications

Preliminary GPR Recommendations for Rescue Planning in Mining

The method of GPR location allows determining the location of the pit from the side wall in non-visual and non-mechanical, non-invasive contact condi- tions. Having determined the algorithm of the GPR data processing options, the location of the pit can be determined from the radio image. The GPR radio image of the pit model observed from the side wall was processed using the “Zond 12-e” GPR software, “Prizm 2.5” software, an algorithm developed by the Institute of Geophysics, the sector of applied and experimental geophysics in the GPR location and electrometry laboratory

Physical simulation of georadiolocation field in direct and inverse problems of electrodynamics

A method of physical simulation used in solving electrodynamics problems can be successfully used while solving the problems of georadiolocation for modeling electromagnetic fields of high frequency range with the help of super-high frequencies. The values of similarity coefficients of frequencies and geometric lengths in case of physical simulation under laboratory conditions have been found with regard to field conditions of georadiolocation studies with standard antennas of geo-radar «Zond-12e»

In Mining, the Location of Adits or Parts Thereof, by Radio Image and by Fixing their Inclination from the Day Surface by Georadar

The GPR method allows to determine the location of the adit or its parts from the day surface or other horizontal planes in non-visual and non-mechanical, non- invasive contact conditions. To solve these types of direct problems by the method of physical modeling, parallel GPR profiles were obtained from the horizontal surface of the modeling unit, radio images of inclined pipes of adit models were investigated

Phase space warping: A dynamical systems approach to diagnostics and prognostics

The concept of phase space warping is used to develop a general method for damage evolution tracking and failure prediction. After outlining the basic theory and describing its algorithmic implementation, a nonlinear vibrating beam experiment is described in which a crack propagates to complete fracture. Our method is shown to give real-time estimates of the current damage state, and remaining useful life is accurately predicted well in advance of actual failure. © 2005 Springer

Phase space warping: Nonlinear time-series analysis for slowly drifting systems

A new general dynamical systems approach to data analysis is presented that allows one to track slowly evolving variables responsible for non-stationarity in a fast subsystem. The method is based on the idea of phase space warping, which refers to the small distortions in the fast subsystem\u27s phase space that results from the slow drift, and uses short-time reference model prediction error as its primary measurement of this phenomenon. The basic theory is presented and the issues associated with its implementation in a practical algorithm are discussed. A vector-tracking version of the procedure, based on smooth orthogonal decomposition analysis, is applied to the study of a nonlinear vibrating beam experiment in which a crack propagates to complete fracture. Our method shows that the damage evolution is governed by a scalar process, and we are able to give real-time estimates of the current damage state and identify the governing damage evolution model. Using a final recursive estimation step based on this model, the time to failure is continuously and accurately predicted well in advance of actual failure. © 2006 The Royal Society