Papers by Michael Aivazis
Addressing Multi-Scale Problems in Geophysics With Coupled Modeling Tools: Current Development Status of the Lithomop Deformation Modeling Code Within the Pyre Framework
Many fundamental problems in geophysics may be viewed as the interaction of phenomena that occur ... more Many fundamental problems in geophysics may be viewed as the interaction of phenomena that occur on different temporal and spatial scales. As an example, the occurrence of multiple earthquakes in a tectonically active region could be characterized in terms of at least three distinct scales: 1) The contribution to the regional stress field in the lithosphere from mantle convection (dynamic computations on large temporal and spatial scales). 2) Interseismic stress buildup and postseismic stress relaxation in the lithosphere (quasi-static computations on intermediate temporal and spatial scales). 3) Coseismic stress changes (dynamic computations on short time scales and small to intermediate spatial scales). In the past, the tendency has been to focus on one of the scales pertinent to the problem, and approximate the effects due to the other scales. With increasingly powerful computational abilities, however, it is now becoming more feasible to address the entire scope of these complex...
Group Theory in Physics, Jun 1, 1991
Let us consider the problem of counting all labeled trees of size n. By Cayley's theorem, the num... more Let us consider the problem of counting all labeled trees of size n. By Cayley's theorem, the number of such trees is n n−2 , but suppose we didn't know this. We could still efficiently count the labeled trees by means of the following result. If Γ is a (simple) graph, by an automorphism of Γ we mean a map f : Γ −→ Γ, or more precisely on the set of vertices, such that if x, y ∈ Γ then x and y are adjacent if and only if f (x) and f (y) are adjacent. For example, the following graph has two automorphisms: A − B − C − − D. The first automorphism is the identity map 1 Γ. The other one is the map that interchanges A and D and also B and C. Proposition 1 Let T 1 , • • • , T k be a complete set of nonisomorphic trees on n vertices. Let N i be the number of automorphisms of T i. Then there are
We have performed a QCD next-to-leading order (NLO) calculation for Deep Inelastic Scattering (DI... more We have performed a QCD next-to-leading order (NLO) calculation for Deep Inelastic Scattering (DIS) retaining the full parton and hadron mass dependencies. We find that the gluon initiated contributions to DIS processes, such as charm production, are comparable in magnitude (i.e., 30% to 100%) to the "leading-order" (LO) seaquark processes. The "slow-rescaling" prescription and the full NLO formalism are compared in a quantitative manner. The use of DIS distributions and the inclusion of the charm mass via slow-rescaling are not sufficient to mimic the correct NLO physics. These results imply that previous analyses of charm production data to extract the strange and charm content of the nucleon, as well as the precise determination of Standard Model parameters based on these analyses (such as the Weinberg angle), need to be reassessed.
Physical Review Letters, 1990
Gluon initiated contributions to DIS processes, such as charm production, can be comparable in ma... more Gluon initiated contributions to DIS processes, such as charm production, can be comparable in magnitude to the "leading-order" sea-quark processes. A proper next-to-leading order calculation in QCD confirms this and yields distinct dependencies of these two contributions on the kinematic variables and on the charm quark mass. These results imply that previous analyses of charm production data to extract the strange and charm content of the nucleon, as well as the precise determination of Standard Model parameters based on these analyses, need to be reassessed.
GeoFramework: A modeling framework for solid Earth geophysics
As data sets in geophysics become larger and of greater relevance to other earth science discipli... more As data sets in geophysics become larger and of greater relevance to other earth science disciplines, and as earth science becomes more interdisciplinary in general, modeling tools are being driven in new directions. There is now a greater need to link modeling codes to one another, link modeling codes to multiple datasets, and to make modeling software available to non modeling specialists. Coupled with rapid progress in computer hardware (including the computational speed afforded by massively parallel computers), progress in numerical algorithms, and the introduction of software frameworks, these lofty goals of merging software in geophysics are now possible. The GeoFramework project, a collaboration between computer scientists and geoscientists, is a response to these needs and opportunities. GeoFramework is based on and extends Pyre, a Python-based modeling framework, recently developed to link solid (Lagrangian) and fluid (Eulerian) models, as well as mesh generators, visualization packages, and databases, with one another for engineering applications. The utility and generality of Pyre as a general purpose framework in science is now being recognized. Besides its use in engineering and geophysics, it is also being used in particle physics and astronomy. Geology and geophysics impose their own unique requirements on software frameworks which are not generally available in existing frameworks and so there is a need for research in this area. One of the special requirements is the way Lagrangian and Eulerian codes will need to be linked in time and space within a plate tectonics context. GeoFramework has grown beyond its initial goal of linking a limited number of exiting codes together. The following codes are now being reengineered within the context of Pyre: Tecton, 3-D FE Visco-elastic code for lithospheric relaxation; CitComS, a code for spherical mantle convection; SpecFEM3D, a SEM code for global and regional seismic waves; eqsim, a FE code for dynamic earthquake rupture; SNAC, a developing 3-D coded based on the FLAC method for visco-elastoplastic deformation; SNARK, a 3-D FE-PIC method for viscoplastic deformation; and gPLATES an open source paleogeographic/plate tectonics modeling package. We will demonstrate how codes can be linked with themselves, such as a regional and global model of mantle convection and a visco-elastoplastic representation of the crust within viscous mantle flow. Finally, we will describe how http://GeoFramework.org has become a distribution site for a suite of modeling software in geophysics.
The Kilauea 2018 eruption: Insight from surface deformation and topography change observations
Group Theory in Physics
Group Theory in Physics, 1991
Bulletin of the Seismological Society of America, 2014
Great earthquakes rarely occur within active accretionary prisms, despite the intense long-term d... more Great earthquakes rarely occur within active accretionary prisms, despite the intense long-term deformation associated with the formation of these geologic structures. This paucity of earthquakes is often attributed to partitioning of deformation across multiple structures as well as aseismic deformation within and at the base of the prism (Davis et al., 1983). We use teleseismic data and satellite optical and radar imaging of the 2013 M w 7.7 earthquake that occurred on the southeastern edge of the Makran plate boundary zone to study this unexpected earthquake. We first compute a multiple point-source solution from W-phase waveforms to estimate fault geometry and rupture duration and timing. We then derive the distribution of subsurface fault slip from geodetic coseismic offsets. We sample for the slip posterior probability density function using a Bayesian approach, including a full description of the data covariance and accounting for errors in the elastic structure of the crust. The rupture nucleated on a subvertical segment, branching out of the Chaman fault system, and grew into a major earthquake along a 50°north-dipping thrust fault with significant along-strike curvature. Fault slip propagated at an average speed of 3:0 km=s for about 180 km and is concentrated in the top 10 km with no displacement on the underlying décollement. This earthquake does not exhibit significant slip deficit near the surface, nor is there significant segmentation of the rupture. We propose that complex interaction between the subduction accommodating the Arabia-Eurasia convergence to the south and the Ornach Nal fault plate boundary between India and Eurasia resulted in the significant strain gradient observed prior to this earthquake. Convergence in this region is accommodated both along the subduction megathrust and as internal deformation of the accretionary wedge.
Key questions that scientists and engineers typically want to address can be formulated in terms ... more Key questions that scientists and engineers typically want to address can be formulated in terms of predictive science. Questions such as: "How well does my computational model represent reality?", "What are the most important parameters in the problem?", and "What is the best next experiment to perform?" are fundamental in solving scientific problems. mystic is a framework for massively-parallel optimization and rigorous sensitivity analysis that enables these motivating questions to be addressed quantitatively as global optimization problems. Often realistic physics, engineering, and materials models may have hundreds of input parameters, hundreds of constraints, and may require execution times of seconds or longer. In more extreme cases, realistic models may be multi-scale, and require the use of high-performance computing clusters for their evaluation. Predictive calculations, formulated as a global optimization over a potential surface in design pa...
CITIZEN EMPOWERED SEISMOLOGY/Special Section edited by R. Bossu and P.S. Earle Community Seismic Network
Subject classification: Seismology/Ground motion, Instruments and techniques, Seismic risk, Compu... more Subject classification: Seismology/Ground motion, Instruments and techniques, Seismic risk, Computational geophysics/Algorithms and implementation, Data dissemination/Seismological data. The article describes the design of the Community Seismic Network, which is a dense open seismic network based on low cost sensors. The inputs are from sensors hosted by volunteers from the community by direct connection to their personal computers, or through sensors built into mobile devices. The server is cloud-based for robustness and to dynamically handle the load of impulsive earthquake events. The main product of the network is a map of peak acceleration, delivered within seconds of the ground shaking. The lateral variations in the level of shaking will be valuable to first responders, and the waveform information from a dense network will allow detailed mapping of the rupture process. Sensors in buildings may be useful for monitoring the state-of-health of the structure after major shaking.
Experimental Inelastic Neutron Scattering
This book is distributed as an Acrobat pdf document, and we recommend keeping it in this form. Ma... more This book is distributed as an Acrobat pdf document, and we recommend keeping it in this form. Many details of the software documentation are far too extensive to include inside this document directly, and are provided on web sites. Especially in Chapter 7, the software module
The article describes the design of the Community Seismic Network, which is a dense open seismic ... more The article describes the design of the Community Seismic Network, which is a dense open seismic network based on low cost sensors. The inputs are from sensors hosted by volunteers from the community by direct connection to their personal computers, or through sensors built into mobile devices. The server is cloud-based for robustness and to dynamically handle the load of impulsive earthquake events. The main product of the network is a map of peak acceleration, delivered within seconds of the ground shaking. The lateral variations in the level of shaking will be valuable to first responders, and the waveform information from a dense network will allow detailed mapping of the rupture process. Sensors in buildings may be useful for monitoring the state-of-health of the structure after major shaking.
Parallel Isosurface Calculation and Rendering of Large Data Sets in IRIS Explorer
The foremost challenge in visualization is the ability to best convey large amounts of informatio... more The foremost challenge in visualization is the ability to best convey large amounts of information given limited resources. In this paper we study a framework that offers diverse high level visualization tools to scientists whose primary computer interface is a desktop workstation networked to multi-processor compute engine. As a case study we discuss an implementation for isosurface computation and display encapsulated as a module in NAG's IRIS Explorer. 1 Introduction As part of the Center for Simulation of Dynamic Response of Materials [CSDR], a DOE ASCI/ASAP Center of Excellence at Caltech, we are confronted with the task of creating valuable visualizations for time sequenced data sets that reach sizes of over a terabyte. It has been the experience at center that visualization systems such as NAG's Iris Explorer are extremely valuable for data sets around and below the size of a hundred megabytes. (For example a finite element or finite difference grid of dimensions 25...
Making Remote Tools Available for Visualization of Large Data Sets: Parallel Isosurface Calculation and Rendering of Large Data Sets in IRIS Explorer
A sail and a method for constructing a sail or any pliable lifting surface where the lift for or ... more A sail and a method for constructing a sail or any pliable lifting surface where the lift for or the motive power therefor is wind.
The economic feasibility of exploiting the resources of unconventional oil and gas increases when... more The economic feasibility of exploiting the resources of unconventional oil and gas increases when it is possible to analyze a priori with reasonable accuracy, the effects of different schemes of hydraulic fracturing, of different fracturing fluids, of different proppant additions and of different well patterns, and compare these results in terms of the expected production. The basic ingredients for these analyses are a reliable numerical technique and an adequate geomechanical characterization of the formations to be fractured. A simulation technique adopted for modeling the hydraulic fracturing process, based on the Discontinuous Galerkin Method [1] [2] [3] [4], is discussed in this paper. This technique is being implemented to simulate the hydraulic fracturing of shale reservoirs using very large models that can be efficiently processed resorting to parallel computing. It is important to remark that the resulting models incorporate the proper fracture mechanical concepts required ...
s of the Satellite Meeting on Powder Diffraction of the XV Congress of the IUCr, Toulouse, France... more s of the Satellite Meeting on Powder Diffraction of the XV Congress of the IUCr, Toulouse, France, (1990). 39. Th. Proffen and S. J. L. Billinge, “PDFFIT, a program for full profile structural refinement of the atomic pair distribution function”, J. Appl. Crystallogr. 32, 572 (1999). 40. A. A. Coelho, TOPAS V2.0: General profile and structure analysis (2000). 41. G.S. Pawley “Unit Cell Refinement from Powder Diffraction Scans,” J. Appl. Cryst. 14, 357-361 (1981). 42. A. Le Bail, H. Duroy, J. L. Fourquet, “Ab initio Structure Determination of LiSbWO6 by X-ray Powder Diffraction” Mater. Res. Bull. 23, 447-452 (1988). 43. D. Dragoi, E. Üstündag, B. Clausen and M.A.M. Bourke, “Investigation of thermal residual stresses in tungstenfiber/bulk metallic glass matrix composites,” Scripta Mater. 45, 245-252 (2001). 44. B. Clausen, S.Y. Lee, E. Üstündag, C.C. Aydiner, R.D. Conner and M.A.M. Bourke, “Compressive yielding of tungsten fiber reinforced bulk metallic glass composites,” Scripta Mate...
ASCI Alliance Center for Simulation of Dynamic Response in Materials FY 2000 Annual Report
Introduction: This annual report describes research accomplishments for FY 00 of the Center for S... more Introduction: This annual report describes research accomplishments for FY 00 of the Center for Simulation of Dynamic Response of Materials. The Center is constructing a virtual shock physics facility in which the full three dimensional response of a variety of target materials can be computed for a wide range of compressive, tensional, and shear loadings, including those produced by detonation of energetic materials. The goals are to facilitate computation of a variety of experiments in which strong shock and detonation waves are made to impinge on targets consisting of various combinations of materials, compute the subsequent dynamic response of the target materials, and validate these computations against experimental data.
Group Theory in Physics: Problems and Solutions
This solutions booklet is a supplement to the text book 'Group Theory in Physics' by Wu-K... more This solutions booklet is a supplement to the text book 'Group Theory in Physics' by Wu-Ki Tung. It will be useful to lecturers and students taking the subject as detailed solutions are given.
Plan for the ARCS Software Project
A plan is presented here for the ARCS software project, with descriptions of the mission, scope, ... more A plan is presented here for the ARCS software project, with descriptions of the mission, scope, capabilities, architecture, implementation, schedule, and resources. The scope of this project is consistent with the scientific missions of ARCS and inelastic chopper spectrometers with similar characteristics. The software architecture is based on the data flow paradigm, where analysis is performed with reusable computational components that are connected to each other with data streams. The software architecture could serve other instruments too, and the difference in scope of such an effort is explained. For ARCS, however, the software project will provide a complete solution to the data analysis and visualization needs, with an interface for theory and simulation.
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Papers by Michael Aivazis