Fourier finite‐difference migration

Geophysics ◽  
1994 ◽  
Vol 59 (12) ◽  
pp. 1882-1893 ◽  
Author(s):  
Dietrich Ristow ◽  
Thomas Rühl
Keyword(s):  
Phase Shift ◽  
Finite Difference ◽  
Difference Operator ◽  
Shift Operator ◽  
Velocity Model ◽  
Downward Continuation ◽  
The Other ◽  
Finite Difference Schemes ◽  
Other Hand ◽  
Arbitrary Velocity

Many existing migration schemes cannot simultaneously handle the two most important problems of migration: imaging of steep dips and imaging in media with arbitrary velocity variations in all directions. For example, phase‐shift (ω, k) migration is accurate for nearly all dips but it is limited to very simple velocity functions. On the other hand, finite‐difference schemes based on one‐way wave equations consider arbitrary velocity functions but they attenuate steeply dipping events. We propose a new hybrid migration method, named “Fourier finite‐difference migration,” wherein the downward‐continuation operator is split into two downward‐continuation operators: one operator is a phase‐shift operator for a chosen constant background velocity, and the other operator is an optimized finite‐difference operator for the varying component of the velocity function. If there is no variation of velocity, then only a phase‐shift operator will be applied automatically. On the other hand, if there is a strong variation of velocity, then the phase‐shift component is suppressed and the optimized finite‐difference operator will be fully applied. The cascaded application of phase‐shift and finite‐difference operators shows a better maximum dip‐angle behavior than the split‐step Fourier migration operator. Depending on the macro velocity model, the Fourier finite‐difference migration even shows an improved performance compared to conventional finite‐difference migration with one downward‐continuation step. Finite‐difference migration with two downward‐continuation steps is required to reach the same migration performance, but this is achieved with about 20 percent higher computation costs. The new cascaded operator of the Fourier finite‐difference migration can be applied to arbitrary velocity functions and allows an accurate migration of steeply dipping reflectors in a complex macro velocity model. The dip limitation of the cascaded operator depends on the variation of the velocity field and, hence, is velocity‐adaptive.

scholarly journals Comparison of numerical methods to price zero coupon bonds in a two-factor CIR model

2021 ◽  
Vol 20 (1) ◽  
pp. 109-147
Author(s):  
S. Emslie ◽  
S. Mataramvura
Keyword(s):  
Numerical Methods ◽  
Finite Difference ◽  
Factor Model ◽  
The Other ◽  
Finite Difference Schemes ◽  
Bond Price ◽  
Cir Model ◽  
Alternating Direction Implicit ◽  
Alternating Direction ◽  
Runge Kutta

In this paper we price a zero coupon bond under a Cox–Ingersoll–Ross (CIR) two-factor model using various numerical schemes. To the best of our knowledge, a closed-form or explicit price functional is not trivial and has been less studied. The use and comparison of several numerical methods to determine the bond price is one contribution of this paper. Ordinary differential equations (ODEs) , finite difference schemes and simulation are the three classes of numerical methods considered. These are compared on the basis of computational efficiency and accuracy, with the second aim of this paper being to identify the most efficient numerical method. The numerical ODE methods used to solve the system of ODEs arising as a result of the affine structure of the CIR model are more accurate and efficient than the other classes of methods considered, with the Runge–Kutta ODE method being the most efficient. The Alternating Direction Implicit (ADI) method is the most efficient of the finite difference scheme methods considered, while the simulation methods are shown to be inefficient. Our choice of considering these methods instead of the other known and apparently new numerical methods (eg Fast Fourier Transform (FFT) method, Cosine (COS) method, etc.) is motivated by their popularity in handling interest rate instruments. Keywords: Cox–Ingersoll–Ross model; numerical methods; Runge–Kutta method; zero-coupon bonds; Alternating Direction Implicit method

scholarly journals Herramienta para el cálculo del factor de potencia y capacitores compensadores vectoriales en cargas inductivas

2019 ◽  
pp. 1-5
Author(s):  
Sergio Alejandro Villa-Aviña ◽  
Efrain Villalvazo-Laureano ◽  
Enrique Carlos Rosales-Busquets ◽  
Juan Miguel González-López
Keyword(s):  
Phase Shift ◽  
Power Factor ◽  
Single Phase ◽  
Compensation System ◽  
The Other ◽  
Current Phase ◽  
Electric Networks ◽  
Other Hand ◽  
Made In

In the present work, a power factor (PF) calculation tool for single-phase electric networks is shown. This tool is made in Matlab and Simulink; it contains several useful functions such as the condenser code to achieve the desired result, from the measured value to the unit. It is also possible to visualize the voltage and current phase shift when the system is in the compensation system and its decrease as the PF approaches the unit. On the other hand, it is worth noting the decrease in current by the increase of the PF or compensation. All benefits can be seen graphically for a better understanding of possible compensation solutions.

Stacking Fault Contrast in an Ordered L12 Lattice

1968 ◽  
Vol 26 ◽  
pp. 260-261
Author(s):  
J. M. Oblak ◽  
B. H. Kear
Keyword(s):  
Phase Shift ◽  
Nearest Neighbor ◽  
Antiphase Boundary ◽  
Stacking Fault ◽  
The Other ◽  
Diffraction Vector ◽  
Physical Difference ◽  
Close Packed Plane ◽  
Other Hand ◽  
Fundamental Reflection

Stacking fault contrast arises from the phase shift α = 2π ḡ · experienced by the diffracted wave at the fault. In an ordered L12 lattice, the displacement <111> is not necessarily equivalent to a displacement of the type <112>. 1 and 2 differ by a displacement <110> which can introduce a phase shift of π when ḡ is a superlattice diffraction vector. The physical difference can be seen by examining the formation of an intrinsic fault. When the fault is produced by removal of a close packed plane, <111>, no nearest neighbor violations of order result; on the other hand,nearest neighbor order is disrupted by shear of the <112> type.Similarly, there are two types of extrinsic faults. Values of α are listed in Table I for [111] and [112] with ḡ of the form 100, 200, and 300. As expected, the two representations are equivalent when ḡ is a fundamental reflection. For g = 100, 010 the values of α for 1 and 2 differ by π because of the antiphase boundary associated with the latter displacement.

scholarly journals Solusi numerik model matematika SHEIR pada penyebaran penyakit campak dengan vaksinasi Dan kekebalan kelompok

SAINTIFIK ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 15-20
Author(s):  
Darmawati Darmawati
Keyword(s):  
Mathematical Model ◽  
Finite Difference ◽  
Finite Difference Method ◽  
Difference Method ◽  
Herd Immunity ◽  
The Other ◽  
Transmission Dynamics ◽  
Other Hand ◽  
Nonstandard Finite Difference

In this paper, mathematical model of measles transmission dynamics considering vaccination and herd immunity is discussed. The solution of the model is investigated using euler, atangana, dan nonstandard finite difference method. After comparing the solutions of the model, we observe that the solutions obtained by using euler and atangana method diverge for certain step. On the other hand, the solutions obtained by using nonstandard finite difference always converge.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

Can the Academic Self-Concept be Positive and Realistic?

2005 ◽  
Vol 19 (3) ◽  
pp. 129-132 ◽  
Author(s):  
Reimer Kornmann
Keyword(s):  
Academic Performance ◽  
Opposite Effect ◽  
Self Esteem ◽  
Point Of View ◽  
The Other ◽  
Self Concept ◽  
High Ability ◽  
Self Image ◽  
Other Hand

Summary: My comment is basically restricted to the situation in which less-able students find themselves and refers only to literature in German. From this point of view I am basically able to confirm Marsh's results. It must, however, be said that with less-able pupils the opposite effect can be found: Levels of self-esteem in these pupils are raised, at least temporarily, by separate instruction, academic performance however drops; combined instruction, on the other hand, leads to improved academic performance, while levels of self-esteem drop. Apparently, the positive self-image of less-able pupils who receive separate instruction does not bring about the potential enhancement of academic performance one might expect from high-ability pupils receiving separate instruction. To resolve the dilemma, it is proposed that individual progress in learning be accentuated, and that comparisons with others be dispensed with. This fosters a self-image that can in equal measure be realistic and optimistic.

Stories and the Self

2020 ◽  
Vol 32 (2) ◽  
pp. 47-58 ◽  
Author(s):  
Stefan Krause ◽  
Markus Appel
Keyword(s):  
Meta Analysis ◽  
The Self ◽  
The Other ◽  
Lower Degree ◽  
Contrast Effects ◽  
Self Perception ◽  
Self Perceptions ◽  
Other Hand ◽  
The One ◽  
Implicit And Explicit

Abstract. Two experiments examined the influence of stories on recipients’ self-perceptions. Extending prior theory and research, our focus was on assimilation effects (i.e., changes in self-perception in line with a protagonist’s traits) as well as on contrast effects (i.e., changes in self-perception in contrast to a protagonist’s traits). In Experiment 1 ( N = 113), implicit and explicit conscientiousness were assessed after participants read a story about either a diligent or a negligent student. Moderation analyses showed that highly transported participants and participants with lower counterarguing scores assimilate the depicted traits of a story protagonist, as indicated by explicit, self-reported conscientiousness ratings. Participants, who were more critical toward a story (i.e., higher counterarguing) and with a lower degree of transportation, showed contrast effects. In Experiment 2 ( N = 103), we manipulated transportation and counterarguing, but we could not identify an effect on participants’ self-ascribed level of conscientiousness. A mini meta-analysis across both experiments revealed significant positive overall associations between transportation and counterarguing on the one hand and story-consistent self-reported conscientiousness on the other hand.

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