The direct observation of small oscillating structures with the help of a scanning electron beam is a new approach to study the vibrational dynamics of cantilevers and microelectromechanical systems. ...In the scanning electron microscope, the conventional signal of secondary electrons (SE, dc part) is separated from the signal response of the SE detector, which is correlated to the respective excitation frequency for vibration by means of a lock-in amplifier. The dynamic response is separated either into images of amplitude and phase shift or into real and imaginary parts. Spatial resolution is limited to the diameter of the electron beam. The sensitivity limit to vibrational motion is estimated to be sub-nanometer for high integration times. Due to complex imaging mechanisms, a theoretical model was developed for the interpretation of the obtained measurements, relating cantilever shapes to interaction processes consisting of incident electron beam, electron-lever interaction, emitted electrons and detector response. Conclusions drawn from this new model are compared with numerical results based on the Euler-Bernoulli equation.
We use a dynamic scanning electron microscope (DySEM) to analyze the movement of oscillating micromechanical structures. A dynamic secondary electron (SE) signal is recorded and correlated to the ...oscillatory excitation of scanning force microscope (SFM) cantilever by means of lock-in amplifiers. We show, how the relative phase of the oscillations modulate the resulting real part and phase pictures of the DySEM mapping. This can be used to obtain information about the underlying oscillatory dynamics. We apply the theory to the case of a cantilever in oscillation, driven at different flexural and torsional resonance modes. This is an extension of a recent work (Schröter et al 2012 Nanotechnology 23 435501), where we reported on a general methodology to distinguish nonlinear features caused by the imaging process from those caused by cantilever motion.
The dynamics of external contributions to the geomagnetic field is investigated by applying time-frequency methods to magnetic observatory data. Fractal models and multiscale analysis enable ...obtaining maximum quantitative information related to the short-term dynamics of the geomagnetic field activity. The stochastic properties of the horizontal component of the transient external field are determined by searching for scaling laws in the power spectra. The spectrum fits a power law with a scaling exponent
β
, a typical characteristic of self-affine time-series. Local variations in the power-law exponent are investigated by applying wavelet analysis to the same time-series. These analyses highlight the self-affine properties of geomagnetic perturbations and their persistence. Moreover, they show that the main phases of sudden storm disturbances are uniquely characterized by a scaling exponent varying between 1 and 3, possibly related to the energy contained in the external field. These new findings suggest the existence of a long-range dependence, the scaling exponent being an efficient indicator of geomagnetic activity and singularity detection. These results show that by using magnetogram regularity to reflect the magnetosphere activity, a theoretical analysis of the external geomagnetic field based on local power-law exponents is possible.
An increasing number of regional inversions of gravity and magnetic field data have recently been computed, some based on satellite and ground data, some on satellite data only. In each case it is ...important to quantify the errors resulting from the confined data region or the satellite parameters. In this study we investigate the error distribution of regional inversions for scalar gravity and vector geomagnetic data from satellite data only. We include the effects of satellite altitude, size of the data region, signal-to-noise ratio and spherical harmonic degree of an a priori global field model. We evaluate our results on the basis of a regional inversion of the Earth's magnetic field.
'Hirschsprung's Disease and Allied Disorders'is the third edition of a comprehensive study of the neuronal disorders of the lower gastrointestinal tract in children. Important new studies and ...progress in research on bowel motility and motility disorders are covered in detail as well as new aspects concerning the embryology, functional anatomy of the enteric nervous system. In particular new insights have been received from the studies in the genetics of Hirschsprung's disease. Special emphasis is laid on new surgical techniques, especially on the laparoscopic approach in combination with Soave's or Duhamel's technique.
SUMMARY
In the eighties, the analysis of satellite altimetry data leads to the major discovery of gravity lineations in the oceans, with wavelengths between 200 and 1400 km. While the existence of ...the 200 km scale undulations is widely accepted, undulations at scales larger than 400 km are still a matter of debate. In this paper, we revisit the topic of the large‐scale geoid undulations over the oceans in the light of the satellite gravity data provided by the GRACE mission, considerably more precise than the altimetry data at wavelengths larger than 400 km.
First, we develop a dedicated method of directional Poisson wavelet analysis on the sphere with significance testing, in order to detect and characterize directional structures in geophysical data on the sphere at different spatial scales. This method is particularly well suited for potential field analysis. We validate it on a series of synthetic tests, and then apply it to analyze recent gravity models, as well as a bathymetry data set independent from gravity. Our analysis confirms the existence of gravity undulations at large scale in the oceans, with characteristic scales between 600 and 2000 km. Their direction correlates well with present‐day plate motion over the Pacific ocean, where they are particularly clear, and associated with a conjugate direction at 1500 km scale. A major finding is that the 2000 km scale geoid undulations dominate and had never been so clearly observed previously. This is due to the great precision of GRACE data at those wavelengths. Given the large scale of these undulations, they are most likely related to mantle processes. Taking into account observations and models from other geophysical information, as seismological tomography, convection and geochemical models and electrical conductivity in the mantle, we conceive that all these inputs indicate a directional fabric of the mantle flows at depth, reflecting how the history of subduction influences the organization of lower mantle upwellings.
We explore the concept of maximum possible earthquake magnitude, M, in a region represented by an earthquake catalog from the viewpoint of statistical testing. For this aim, we assume that earthquake ...magnitudes are independent events that follow a doubly truncated Gutenberg‐Richter distribution and focus on the upper truncation M. In earlier work, it has been shown that the value of M cannot be well constrained from earthquake catalogs alone. However, for two hypothesized values M and M′, alternative statistical tests may address the question: Which value is more consistent with the data? In other words, is it possible to reject a magnitude within reasonable errors, i.e., the error of the first and the error of the second kind? The results for realistic settings indicate that either the error of the first kind or the error of the second kind is intolerably large. We conclude that it is essentially impossible to infer M in terms of alternative testing with sufficient confidence from an earthquake catalog alone, even in regions like Japan with excellent data availability. These findings are also valid for frequency‐magnitude distributions with different tail behavior, e.g., exponential tapering. Finally, we emphasize that different data may only be useful to provide additional constraints for M, if they do not correlate with the earthquake catalog, i.e., if they have not been recorded in the same observational period. In particular, long‐term geological assessments might be suitable to reduce the errors, while GPS measurements provide overall the same information as the catalogs.
Key Points
Mmax is poorly constrained by data
Mmax is not testable on the basis of earthquake catalogs
Longterm geological data can reduce uncertainties of Mmax
In this paper, we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry. We computed ...a refined gravity field in the south central Pacific based on the GRACE satellite GGM02S global gravity field and the KMS02 altimetric grid, and a magnetic anomaly field based on CHAMP data. The magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the Tuamotu region, which we interpret as evidence for crustal thickening. We interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution. We also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources. According to the gravity signature of the different chains as revealed by our analysis, various processes are at the origin of the volcanism in French Polynesia. As evidence, we show a large‐scale anomaly over the Society Islands that we interpret as the gravity signature of a deeply anchored mantle plume. The gravity signature of the Cook‐Austral chain indicates a complex origin which may involve deep processes. Finally, we discuss the particular location of the Marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field, or else related to the presence of the nearby Tuamotu plateau.
Aftershocks rates seem to follow a power law decay, but the question of the aftershock frequency immediately after an earthquake remains open. We estimate an average aftershock decay rate within one ...day in southern California by stacking in time different sequences triggered by main shocks ranging in magnitude from 2.5 to 4.5. Then we estimate the time delay before the onset of the power law aftershock decay rate. For the last 20 years, we observe that this time delay suddenly increase after large earthquakes, and slowly decreases at a constant rate during periods of low seismicity. In a band‐limited power law model such variations can be explained by different patterns of stress distribution at different stages of the seismic cycle. We conclude that, on regional length scales, the brittle upper crust exhibits a collective behavior reflecting to some extent the proximity of a threshold of fracturing.
In the present paper, we consider and summarize applications of the continuous wavelet transform to 2C and 3C polarization analysis and filtering, modeling the dispersed and attenuated wave ...propagation in the time–frequency domain, and estimation of the phase and group velocity and the attenuation from a seismogram. Along with a mathematical overview of each of the presented methods, we show that all these algorithms are logically combined into one software package “Geophysical Wavelet Library” developed by the authors. The novelty of this package is that we incorporate the continuous wavelet transform into the library, where the kernel is the time–frequency polarization and dispersion analysis. This library has a wide range of potential applications in the field of signal analysis and may be particularly suitable in geophysical problems that we illustrate by analyzing synthetic, geomagnetic and real seismic data.
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