scholarly journals Front propagation and arrival times in networks with application to neurodegenerative diseases

2022 ◽  
Author(s):  
Prama Setia Putra ◽  
Hadrien Oliveri ◽  
Travis B Thompson ◽  
Alain Goriely
Keyword(s):  
Neurodegenerative Diseases ◽  
Arrival Time ◽  
Initial Conditions ◽  
Front Propagation ◽  
Small Concentration ◽  
Single Node ◽  
Arrival Times ◽  
Toxic Protein ◽  
Time Estimates ◽  
Analytical Complexity

Many physical, epidemiological, or physiological dynamical processes on networks support front-like propagation, where an initial localized perturbation grows and systematically invades all nodes in the network. A key question is then to extract estimates for the dynamics. In particular, if a single node is seeded at a small concentration, when will other nodes reach the same initial concentration? Here, motivated by the study of toxic protein propagation in neurodegenerative diseases, we present and compare three different estimates for the arrival time in order of increasing analytical complexity: the linear arrival time, obtained by linearizing the underlying system; the Lambert time, obtained by considering the interaction of two nodes; and the nonlinear arrival time, obtained by asymptotic techniques. We use the classic Fisher-Kolmogorov-Petrovsky-Piskunov equation as a paradigm for the dynamics and show that each method provides different insight and time estimates. Further, we show that the nonlinear asymptotic method also gives an approximate solution valid in the entire domain and the correct ordering of arrival regions over large regions of parameters and initial conditions.

Seismological measurements and measurement error

1968 ◽  
Vol 58 (4) ◽  
pp. 1261-1271 ◽  
Author(s):  
Helen W. Freedman
Keyword(s):  
Probability Distribution ◽  
Related Problem ◽  
Arrival Time ◽  
Focal Depth ◽  
Degree Of Contamination ◽  
Origin Time ◽  
Arrival Times ◽  
Time Estimates ◽  
Error Variable ◽  
Hypocentral Location

Abstract A seismological measurement, such as arrival time or, less directly origin time, is an example of a measurement variable which can be considered as the sum of a parameter—the quantity being measured—and an error variable. Optimal methods for the estimation of this parameter vary with the probability distribution of the error variable. In particular, estimation in the presence of bias or of gross errors is discussed, together with the related problem of precision versus accuracy of the estimate. Errors in estimates of arrival times, origin times and hypocentral location contribute to variation in travel-time estimates; these are analyzed separately. Each of these, with the exception of focal depth, has a distribution which can be fitted to a mixture of a normal distribution and some contamination. The degree of contamination varies; methods for truncation are suggested. The presence of possible, often undetectable, bias in locations and travel times may make confidence statements about these parameters unreliable.

scholarly journals Detection of specific areas and densities for ultrasound tomography

2019 ◽  
pp. 121-127
Author(s):  
Victoria Erofeeva ◽  
Vasilisa Galyamina ◽  
Kseniya Gonta ◽  
Anna Leonova ◽  
Oleg Granichin ◽  
...  
Keyword(s):  
Image Reconstruction ◽  
Ultrasound Imaging ◽  
Arrival Time ◽  
Detection Accuracy ◽  
Problem Solution ◽  
Ultrasound Tomography ◽  
Arrival Times ◽  
Whole Process ◽  
Imaging Reconstruction ◽  
Tomography Data

In this paper we consider the problem of ultrasound tomography. Recently, an increased interest in ultrasound tomography has been caused by non-invasiveness of the method and increased detection accuracy (as compared to radiation tomography), and also ultrasound tomography does not put at risk human health. We study possibilities of detection of specific areas and determining their density using ultrasound tomography data. The process of image reconstruction based on ultrasound data is computationally complex and time consuming. It contains the following parts: calculation of the time-of-flight (TOF) of a signal, detection of specific areas, calculation of density of specific areas. The calculation of the arrival time of a signal is a very important part, because the errors in the calculation of quantities strongly influence the total problem solution. We offer ultrasound imaging reconstruction technology that can be easily parallelized. The whole process is described: from extracting the arrival times of signals raw data feeding from physical receivers to obtaining the desired results.

Arrival Time Estimates of Earth-Directed CME-Driven Shocks

Solar Physics ◽  
2022 ◽  
Vol 297 (1) ◽  
Author(s):  
K. Suresh ◽  
N. Gopalswamy ◽  
A. Shanmugaraju
Keyword(s):  
Arrival Time ◽  
Time Estimates

scholarly journals On optimal periodic dividend and capital injection strategies for spectrally negative Lévy models

2018 ◽  
Vol 55 (4) ◽  
pp. 1272-1286 ◽  
Author(s):  
Kei Noba ◽  
José-Luis Pérez ◽  
Kazutoshi Yamazaki ◽  
Kouji Yano
Keyword(s):  
Arrival Time ◽  
Arrival Times ◽  
Classical Sense ◽  
Capital Injection ◽  
Dividend Payments ◽  
Poisson Arrival ◽  
Optimal Dividend ◽  
Injection Strategies

Abstract De Finetti’s optimal dividend problem has recently been extended to the case when dividend payments can be made only at Poisson arrival times. In this paper we consider the version with bail-outs where the surplus must be nonnegative uniformly in time. For a general spectrally negative Lévy model, we show the optimality of a Parisian-classical reflection strategy that pays the excess above a given barrier at each Poisson arrival time and also reflects from below at 0 in the classical sense.

Joint microseismic event location and anisotropic velocity inversion with the cross double-difference method using downhole microseismic data

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. KS63-KS73
Author(s):  
Yangyang Ma ◽  
Congcong Yuan ◽  
Jie Zhang
Keyword(s):  
Arrival Time ◽  
Velocity Model ◽  
P Wave ◽  
Double Difference ◽  
S Wave ◽  
Arrival Times ◽  
Monitoring Well ◽  
The Cross ◽  
Microseismic Event ◽  
Wave Arrival

We have applied the cross double-difference (CDD) method to simultaneously determine the microseismic event locations and five Thomsen parameters in vertically layered transversely isotropic media using data from a single vertical monitoring well. Different from the double-difference (DD) method, the CDD method uses the cross-traveltime difference between the S-wave arrival time of one event and the P-wave arrival time of another event. The CDD method can improve the accuracy of the absolute locations and maintain the accuracy of the relative locations because it contains more absolute information than the DD method. We calculate the arrival times of the qP, qSV, and SH waves with a horizontal slowness shooting algorithm. The sensitivities of the arrival times with respect to the five Thomsen parameters are derived using the slowness components. The derivations are analytical, without any weak anisotropic approximation. The input data include the cross-differential traveltimes and absolute arrival times, providing better constraints on the anisotropic parameters and event locations. The synthetic example indicates that the method can produce better event locations and anisotropic velocity model. We apply this method to the field data set acquired from a single vertical monitoring well during a hydraulic fracturing process. We further validate the anisotropic velocity model and microseismic event locations by comparing the modeled and observed waveforms. The observed S-wave splitting also supports the inverted anisotropic results.

scholarly journals The Astrometric Possibilities of Very-Long-Baseline Interferometry

1986 ◽  
Vol 109 ◽  
pp. 143-155
Author(s):  
D. S. Robertson
Keyword(s):  
Plane Wave ◽  
Arrival Time ◽  
Very Long Baseline Interferometry ◽  
Radio Sources ◽  
Arrival Times ◽  
Long Baseline ◽  
The Difference ◽  
Different Sources

In the application of Very-Long-Baseline Interferometry (VLBI) to astrometric problems the fundamental observable is the difference in the arrival times of a wavefront at two widely separated receiving stations. Since the radio sources being observed are sufficiently distant that the arriving wavefront can be considered to be a plane wave, the differential arrival time is a measure of the component of the baseline in the direction of the source. Equivalently, if the baseline is known, the differential arrival time is sufficient to determine a circle on the sky containing the source. It is easy to show that a minimum of ten observations distributed among three different sources is sufficient to determine all of the source coordinates and the baseline coordinates simultaneously (Robertson, 1975).

scholarly journals Periodic Changes in Intensity and Arrival Time of Pulses from the Vela Pulsar: Evidence for Free Precession?

1996 ◽  
Vol 160 ◽  
pp. 101-102
Author(s):  
A.A. Deshpande ◽  
P.M. McCulloch
Keyword(s):  
Arrival Time ◽  
Time Of Arrival ◽  
Free Precession ◽  
Dual Frequency ◽  
Arrival Times ◽  
Routine Monitoring ◽  
Vela Pulsar ◽  
Observed Behaviour ◽  
Pulse Arrival ◽  
Periodic Changes

We present dual-frequency measurements on the Vela pulsar with a view to study the slow variations in the pulsed flux and the apparent differences in the pulse arrival times. We examine the data for correlated variations between the pulse intensities and arrival times at the two frequencies and discuss two main possibilities in order to explain the observed behaviour.The data presented here consists of a) Pulse intensities, S635& S950, at S635& S950MHz respectively and b) the ‘residual’ differences in the time of arrival of the pulse at the lower frequency, ΔTOA, with respect to that at the higher frequency. These data, over a span of ~1300 days (during 1988-92), were obtained as a part of the routine monitoring of the Vela pulsar from Mt. Pleasant Observatory of University of Tasmania, Hobart (see McCullochet al. 1990).

scholarly journals QUENCH FRONT PROPAGATION IN THE ANNULAR CHANNEL

2016 ◽  
Vol 4 ◽  
pp. 97
Author(s):  
Jan Stepanek ◽  
Vaclav Blaha ◽  
Vaclav Dostal
Keyword(s):  
Stainless Steel ◽  
Test Section ◽  
Initial Conditions ◽  
Front Propagation ◽  
Glass Tube ◽  
Annular Channel ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Outer Diameter ◽  
Inner Diameter

Understanding the quench front propagation during bottom core reflooding is crucial for the effective cooling during the LOCA accident. The results presented in this paper were obtained on an experimental loop with an annular test section. The test section consists of a vertical electrically heated stainless steel tube with outer diameter 9 mm and length of 1.7 m. The heated tube is placed inside a glass tube with the inner diameter 14.5 mm. Water mass flux during the reflooding is in the range from 100 kg.m<sup>−2</sup>.s<sup>−1</sup> up to 140 kg.m<sup>−2</sup>.s<sup>−1</sup> and the initial wall temperature of the stainless steel tube is in the range from 250 °C up to 800 °C. The presented results show the influence of the initial conditions on the quench front propagation and the complexity of the phenomenon.

scholarly journals Shear wave arrival time estimates correlate with local speckle pattern

2015 ◽  
Vol 62 (12) ◽  
pp. 2054-2067 ◽  
Author(s):  
Stephen A. Mcaleavey ◽  
Laurentius O. Osapoetra ◽  
Jonathan Langdon
Keyword(s):  
Shear Wave ◽  
Arrival Time ◽  
Speckle Pattern ◽  
Time Estimates ◽  
Wave Arrival
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