A seismic passive imaging step beyond SPAC and ReMi

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. KS63-KS72 ◽  
Author(s):  
Francesco Mulargia ◽  
Silvia Castellaro
Keyword(s):  
Passive Imaging ◽  
Small Aperture ◽  
Simple Geometry ◽  
Recording Station ◽  
Refraction Microtremor ◽  
A New Technique ◽  
Statistical Mode ◽  
The One ◽  
Aperture Arrays ◽  
The Waves

The basic property of passive imaging is that, given any two points, one of them can be taken as the source of the waves and the other as the recording station. This property can be derived from the statistical self-alignment of the rays along the vector joining the two points, and applies also to nondiffuse wavefields like seismic tremor. It provides a statistical basis for the use of the stationary phase integral, allowing passive interferometry under the mild constraint of mechanical homogeneity at a local scale. Combined with the tremor’s large spectral bandwidth, it allows one to recover the local Green’s function from spatial correlation. Furthermore, combining this property also with the azimuthal isotropy of either the wavefield or the array, and using the statistical mode as the estimator, provides a new technique to measure the local velocity dispersion in the subsoil. This technique exploits the potential of spatial autocorrelation (SPAC) and refraction microtremor (ReMi), allowing one (1) to use sparse small-aperture arrays with simple geometry, (2) to dispense with the fitting of Bessel functions, and (3) to measure, in a few minutes, the local (phase and group) wave velocity as a function of frequency of potentially all the wave-propagation modes — body and surface — and not just of the one prevailing at each frequency.

Detection and source parameterization of small-energy fireball events in Western Alps with ground-based infrasonic arrays

2021 ◽  
Author(s):  
Giacomo Belli ◽  
Emanuele Pace ◽  
Emanuele Marchetti
Keyword(s):  
Western Alps ◽  
Apparent Velocity ◽  
Array Analysis ◽  
Small Energy ◽  
Small Aperture ◽  
Energy Estimation ◽  
Trajectory Reconstruction ◽  
Tnt Equivalent ◽  
Back Azimuth ◽  
Aperture Arrays

Summary We present infrasound signals generated by four fireball events occurred in Western Alps between 2016 and 2019 and that were recorded by small aperture arrays at source-to receiver distances < 300 km. Signals consist in a series of short-lived infrasonic arrivals that are closely spaced in time. Each arrival is identified as a cluster of detections with constant wave parameters (back-azimuth and apparent velocity), that change however from cluster to cluster. These arrivals are likely generated by multiple infrasonic sources (fragmentations or hypersonic flow) along the entry trajectory. We developed a method, based on 2D ray-tracing and on the independent optically determined time of the event, to locate the source position of the multiple arrivals from a single infrasonic array data and to reconstruct the 3D trajectory of a meteoroid in the Earth's atmosphere. The trajectories derived from infrasound array analysis are in excellent agreement with trajectories reconstructed from eyewitnesses reports for the four fireballs. Results suggest that the trajectory reconstruction is possible for meteoroid entries located up to ∼300 km from the array, with an accuracy that depends on the source-to-receiver distance and on the signal-to-noise level. We also estimate the energy of the four fireballs using three different empirical laws, based both on period and amplitude of recorded infrasonic signals, and discuss their applicability for the energy estimation of small energy fireball events ($\le 1{\rm{kt\,\,TNT\,\,equivalent}}$).

Polarization and coherence of 5 to 30 Hz seismic wave fields at a hard-rock site and their relevance to velocity heterogeneities in the crust

1990 ◽  
Vol 80 (2) ◽  
pp. 430-449 ◽  
Author(s):  
William Menke ◽  
Arthur L. Lerner-Lam ◽  
Bruce Dubendorff ◽  
Javier Pacheco
Keyword(s):  
Hard Rock ◽  
Scale Effects ◽  
Spatial Coherence ◽  
Compressional Wave ◽  
P Wave ◽  
Transverse Motion ◽  
S Wave ◽  
Chemical Explosions ◽  
Aperture Arrays ◽  
The Waves

Abstract Except for its very onset, the P wave of earthquakes and chemical explosions observed at two narrow-aperture arrays on hard-rock sites in the Adirondack Mountains have a nearly random polarization. The amount of energy on the vertical, radial, and transverse components is about equal over the frequency range 5 to 30 Hz, for the entire seismogram. The spatial coherence of the seismograms is approximately exp(−cfΔx), where c is in the range 0.4 to 0.7 km−1Hz−1, f is frequency and Δx is the distance between array elements. Vertical, radial, and transverse components were quite coherent over the aperture of the array, indicating that the transverse motion of the compressional wave is a property of relatively large (106 m3) volumes of rock, and not just an anomaly caused by a malfunctioning instrument, poor instrument-rock coupling, or out-crop-scale effects. The spatial coherence is approximately independent of component, epicentral azimuth and range, and whether P- or S-wave coda is being considered, at least for propagation distances between 5 and 170 km. These results imply a strongly and three-dimensionally heterogeneous crust, with near-receiver scattering in the uppermost crust controlling the coherence properties of the waves.

Transverse dam-break waves

2014 ◽  
Vol 758 ◽  
Author(s):  
S. Karimpour Ghannadi ◽  
Vincent H. Chu
Keyword(s):  
Froude Number ◽  
Flow Rate ◽  
Main Flow ◽  
Dam Break ◽  
The Other ◽  
Water Diversion ◽  
The Family ◽  
The One ◽  
Limiting Case ◽  
The Waves

AbstractNumerical simulations of the transverse dam-break waves (TDWs) produced by the sudden removal of a gate on the side of a waterway are conducted based on the shallow-water equations to find solutions to a family of water-diversion problems. The Froude numbers in the main flow identify the members of the family. The depth and discharge profiles are analysed in terms of Ritter’s similarity variable. For subcritical main flow, the waves are comprised of a supercritical flow expansion followed by a subcritical outflow. For supercritical main flow, on the other hand, the waves are analogous to the Prandtl–Meyer expansion in gas dynamics. The diversion flow rate of two-dimensional TDWs on a flat bed is 55 % greater than the one-dimensional flow rate of Ritter in the limiting case of zero main flow, and approaches the rate of Ritter in the other limit when the value of the Froude number in the main flow approaches infinity. The diversion flow rate over a weir is generally higher than the rate over a flat bed depending on the Froude number of the main flow. These numerical simulation results are consistent with laboratory observations.

scholarly journals One-Time Cortical Lamina: A New Technique for Horizontal Ridge Augmentation. A Case Series

2021 ◽  
Vol 8 (6) ◽  
pp. 22-30
Author(s):  
Vincenzo Foti ◽  
Davide Savio ◽  
Roberto Rossi
Keyword(s):  
Fibrin Sealant ◽  
Case Series ◽  
X Rays ◽  
Marginal Bone Loss ◽  
Ridge Augmentation ◽  
Keratinized Tissue ◽  
A New Technique ◽  
The One ◽  
Hard Consistency

The aim of this case series is to introduce the One-Time Cortical Lamina Technique, a simplification of the F.I.R.S.T. (Fibrinogen-Induced Regeneration Sealing Technique) in cases where only horizontal augmentation is needed. The indications for this technique are ASA2 and ASA1 anxious patients. Pre-requisites for this surgical technique are: a good amount of keratinized tissue, sufficient alveolar ridge width for placement of implants, thickness of vestibular bone at CBCT planning less than 1 mm with risk of threads exposure. Five patients with horizontal deficiencies were selected to test the efficacy of this approach. The defects were augmented using a porcine cortical bone lamina in combination with collagenated porcine bone mixed with fibrin sealant. The cortical lamina was placed only buccal to the implants and stabilized with fibrin sealant, without pins or screws. Upon completion of the implant surgery, healing abutments were connected to the implants and the soft tissue sutured around them. The healing was uneventful in all cases. Six months after surgery impressions for final restorations were taken and screwed crowns delivered. The new volume had hard consistency and the follow-up CBCT measured an average of 4.17 mm of horizontal bone augmentation. One to three years of follow up demonstrated the maintenance of vestibular volume, hard consistency and clinical stability. Intraoral X-rays showed no marginal bone loss. An advantage of this technique could be the one stage surgery that creates a stable environment for regeneration from day one.

scholarly journals WAVE RECORDING ON THE IJSSELMEER

2011 ◽  
Vol 1 (7) ◽  
pp. 3
Author(s):  
P. W. Roest
Keyword(s):  
Average Period ◽  
Recording Time ◽  
Ice Drift ◽  
Recording Station ◽  
Long Time ◽  
Wave Heights ◽  
Wave Research ◽  
The Difference ◽  
Hydraulics Laboratory ◽  
The Waves

The dimensions of the dikes in the Ijsselmeer are mainly determined by wave-attack. The dimensions of the waves as a result of the design gale are calculated with the diagram of the Hydraulics Laboratory at Delft (ref« 1). This diagram is based on data of Sverdrup for deep water and principally on laboratory studies for shallow water. For a long time there has been a need of wave recordings on the lake in order to verify the calculated wave heights. A problem is the impossibility of maintaining a permanent recording station on the lake due to ice-drift in wintertime. Otherwise the Ijsselmeer lends itself admirably to wave-research, because there are vast regions with only small variations in waterdepth. Another advantage is that frequently more or less stationary conditions will occur under the influence of winds of constant force and direction. When Dr. Dorrestein of the Royal Dutch Meteorological Institute introduced his new floating waverecorder, it was possible to take observations in every place of the lake. Soon it appeared that this recorder has many advantages. The equipment consists of an accelerometer mounted on a little raft of one meter each way, that follows the movement of the water surface. The signal of the accelerometer is transmitted by an electric cable to the ship, where it is double integrated and then recorded (ref. 3). During the last winter several observations have been carried out with an instrument of this type* As a result of initial troubles with the electronic equipment the number of observations during gale-conditions has been limited. The usual duration of each recording is about 15 minutes. The average period of the waves lies between three and a half and five seconds, so each diagram consists of 180 to 250 waves. Wave height is measured as the difference in height between a trough and the next crest. The average period is determined by dividing the total recording time by half the number of zerocrossings.

scholarly journals Dynamical behavior of a stochastic predator-prey model with general functional response and nonlinear jump-diffusion

2021 ◽  
Vol 0 (0) ◽  
pp. 0
Author(s):  
Xinhong Zhang ◽  
Qing Yang
Keyword(s):  
Functional Response ◽  
Dynamical Behavior ◽  
Uniform Boundedness ◽  
Jump Diffusion ◽  
Necessary Condition ◽  
Predator Prey ◽  
Predator Prey Model ◽  
Prey Model ◽  
A New Technique ◽  
The One

<p style='text-indent:20px;'>In this paper, we consider a stochastic predator-prey model with general functional response, which is perturbed by nonlinear Lévy jumps. Firstly, We show that this model has a unique global positive solution with uniform boundedness of <inline-formula><tex-math id="M1">\begin{document}$ \theta\in(0,1] $\end{document}</tex-math></inline-formula>-th moment. Secondly, we obtain the threshold for extinction and exponential ergodicity of the one-dimensional Logistic system with nonlinear perturbations. Then based on the results of Logistic system, we introduce a new technique to study the ergodic stationary distribution for the stochastic predator-prey model with general functional response and nonlinear jump-diffusion, and derive the sufficient and almost necessary condition for extinction and ergodicity.</p>

scholarly journals The Missing Label Problem: Addressing False Assumptions Improves Ligand-Based Virtual Screening

2019 ◽  
Author(s):  
Lewis Martin ◽  
Michael Bowen
Keyword(s):  
Virtual Screening ◽  
Binding Sites ◽  
Design Theory ◽  
Mapping Function ◽  
True Negative ◽  
Binding Interactions ◽  
Multiple Binding Sites ◽  
A New Technique ◽  
The One ◽  
Machine Readable

<div>Ligand-based virtual screening (LBVS) uses machine readable representations of chemicals to learn a mapping function that can predict binding interactions with protein labels. Because it is highly scalable it is increasingly used in drug development in academic and pharmaceutical contexts. We have identified assumptions commonly used in LBVS that are false, which collectively can be described as the missing label problem. Firstly, many of the binding interactions in the bioactivity databases typically used to train LBVS models have never been tested before, but the absence of a label is interpreted by most models as a true negative. Secondly, many proteins have multiple binding sites with unrelated shapes but the associated ligands are grouped together under the one protein label. These assumptions frustrate the ability of the model to learn a correct mapping function. Here we use statistical techniques to predict values for the missing labels and binding sites and show how this improves the ability of LBVS models to rank ligands correctly. In the process we introduce a new technique for removing bias during model evaluation based on data blocking from experimental design theory. All data and code for analysis and generating figures is publicly available on github (https://github.com/ljmartin/Missing_label_problem).<br></div>

Inhomogeneous thermal conduction equations

1978 ◽  
Vol 56 (7) ◽  
pp. 928-935
Author(s):  
C. S. Lai
Keyword(s):  
Differential Equations ◽  
Thermal Conduction ◽  
Series Solution ◽  
Nonlinear Differential Equations ◽  
Three Dimensional ◽  
Incompressible Fluids ◽  
Self Similar Solution ◽  
Self Similar ◽  
A New Technique ◽  
The One

The method of self-similar solution of partial differential equations is applied to the one-, two-, and three-dimensional inhomogeneous thermal conduction equations with the thermometric conductivities χ ~ rmWn. Analytical solutions are obtained for the case that the total amount of heat is conserved. For the case that the temperature is maintained constant at r = 0, a new technique of the series solution about the point of intercept is proposed to solve the resultant nonlinear differential equations. The solutions obtained are useful in studying the thermal conduction characteristics of some incompressible fluids.

The Continuity of the English Revolution (The Prothero Lecture)

1991 ◽  
Vol 1 ◽  
pp. 121-135
Author(s):  
Lord Dacre
Keyword(s):  
Glorious Revolution ◽  
English Revolution ◽  
Oliver Cromwell ◽  
The One ◽  
The Glorious Revolution ◽  
The Waves

In our history, the twenty years from 1640 to 1660 are, at first sight, years of desperate, even meaningless change. It is difficult to keep pace with those crowded events or to see any continuity in them. At the time, men struggled from day to day and then sank under the tide. Even Oliver Cromwell, the one man who managed, with great agility, but spluttering all the time, to ride the waves, constantly lamented his inability to control them. When all was over, men looked back on the whole experience with disgust. It was a period of ‘blood and confusion’ from which no one had gained anything except the salutary but costly lesson of disillusion. How different from the Glorious Revolution of 1688: that straightforward aristocratic revolt against a king who had so considerately simplified the issues, and ensured a quick neat result, by seeking to convert the nation, like himself, to Catholicism!

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