Revising Sentence Outline for a Committee Report

Proposed Sentence Outline Sentence Outline of Final Report
TITLE: Modelling the Unmeasurable Mesoscale in Materials and Geophysics TITLE: Toward a Better Understanding of the Materials that Make Our Earth Interesting.
Executive Summary Executive Summary
Not written until final draft finished. A complete copy of the report is avaiable.
Introduction Introduction
Materials and geophysics are the central to our way of life and its continuation.

The crucial link between well understood microscopic phenomena and the observed or desired macroscopic behavior is a set of structures and processes occurring at an scale intermediate between the the micro and macro length and time scales: the mesoscale.

Engineering, modifying or understanding the mesoscale is essential to developing new materials, finding new energy/material resources or protecting our environment.

The mesoscale is intrinsically unmeasurable: hence it must be modeled.

Table (and associated discussion) showing micro-, meso- and micro-scales in length and time demonstrates both the inadequacy of present computer simulations and the need for teraflop modeling.

The central concept is that large-scale simulation at microscale should lead to an effective model at meso scale; simulation of meso scale should lead to macroscopic behavior. That stimulation at one scale develops the effective model and its parameter at the next scale is called multiscale simulation.

That infrequent events dominate important behavior (diffusion in materials, stick-slide in faults) necessitates exceptionally long-time simulation; for example, not from 10-14 seconds to 10-10 but to 10-6, further emphasizing the need for teraflop computing.

The local nature of the interactions permits parallelization which in turn demands visualization tools for code debugging and on-line monitor of running code.

Understanding the earth -- geosciences -- and the materials derived from it -- matrials sciences -- is central to our civilization and its continuation. This understanding must extend to all size and time scales: microscale, mesoscale and macroscale.

The table serves to show the magnitude of length and time associated with these three scales in the materials sciences and geosciences.

Linking information across the extremes in this table is a critical step, but making that step is hampered by problems in providing adequate descriptions at the mesoscale. Computer simulations of behavior in the mesoscale offer opportunities to create such descriptions, but these simulations make enormously greater demands on computational hardware and software.

A simple example for materials sets the scale of computational needs.

There are four additional points that overlay the whole discussion.

Measurements. While there are excellent measurement tools for probing the microscale and macroscale, the tools for monitoring the mesoscale are limited so that simulation is essential for timely progress.

Multiscale simulation. The central concept is that a large-scale simulation at the microscale should lead to an effective model at the mesoscale; simulation at the mesoscale should lead to macroscopic behavior.

Infrequent events. That infrequent events dominate important behavior (diffusion in materials, faulting in geosciences) necessitates exceptionally long-time simulation.

Driven systems. A major intellectual step must be to move beyond simulation of static systems to finite-temperature non-equilibrium ones.

Materials Materials
The mesoscale or microstructure of materials consists of small single-crystal grains threaded with extended displacements of the lattice structure -- called dislocations -- and seeded with point-like defects -- vacancies and impurities.

Important properties are determined by microstructure but none of these mechanisms has been verified experimentally or by realistic modeling.

Detailed understanding of the principles controlling microstructure is essential to tailoring the microstructure by processing to achieve specific objectives.

The current 10-15 years required to take a new material from synthesis to product must be reduced to five years; simulation is the only approach.

Magnetics: Understanding the detailed magnetic response of individual magnetic grains and the complex mechanical and magnetic interactions between grains is necessary to create new magnets and to develop empirical models to predict bulk properties.

Innovative materials. Mesoscale simulations would speed the development of constitutive relations needed to predict macroscale behavior for materials such as fracture-resistant cast steels; toughened yet creep resistant high-temperature ceramics and ceramic composities; hard, corrosion resistant coatings.

Environmental affects: Long-time molecular dynamics could study dominant mesoscale effects on film growth and oxidation.

The mesoscale or microstructure of materials consists of aggregates of small single-crystal grains joined together at interfaces -- grain boundaries -- threaded with extended displacements of the lattice structure -- such as dislocations -- and seeded with point-like defects -- such as vacancies and impurities.

The preeminent questions are: how can we tailor the mesoscale:

By tailoring the mesoscale, we mean not only understanding the element of the mesoscale (e.g, grains, extended defects, and local defects) but also processing material to achieve the microstructure necessary for the desired macroscopic properties.

The prime benefit of all examples is time: using simulation to understand the micro-meso-macro connections, the current 10-15 years required to take a new material from synthesis to product could be reduced to five years.

Control of microstructure -- mesoscale elements such as grain size, dislocations, defects -- is the primary goal of the engineering development of materials processing.

Magnets. Crafted microstructure is crucial for the ubiquitous high quality permanent magnets found in familiar devices, for example, motors, transformers, generators, sensors, and computer hard drives.

Innovative materials. Mesoscale simulations would speed the development of constitutive relations needed to predict macroscale behavior for materials such as fracture-resistant cast steels; toughened yet creep-resistant high-temperature ceramics and ceramic composities; hard, corrosion-resistant coatings.

Environmental effects. Long-time molecular dynamics could study dominant mesoscale effects on oxidation -- a major cause of aging, especially at high temperature or high stress.

Damaged materials. DOE interest in modeling damaged materials ranges from high-energy neutron irradiation of bulk materials to the fusion plasma interaction at the interior tokamk surface.

Methods Methods
Central to any modeling is high-speed numerical integration of the equations of motion for atoms interacting with each other -- that is, molecular dynamics simulations.

For increasing number of atoms, first-principles methods must give way to well-calibrated effective potentials: tight-binding and classical potentials.

At the mesoscale, molecular dynamics must track the response of the microstructure to internal strains, interactions between defects and dislocations, and external mechanical and thermal forces.

Systematic mesoscale calculations -- only possible when such calculations are routine -- would build up the data base to establish. validated phenomenological models with realistic parameters.

Central to any modeling is high-speed numerical integration of the equations of motion for atoms interacting with each other -- that is, molecular dynamics simulations.

For increasing number of atoms, first-principles methods must give way to well-calibrated and physically motivated effective potentials.

At the mesoscale, molecular dynamics must track the response of the microstructure to internal strains, interactions between defects and dislocations, and external mechanical and thermal forces.

Geosciences Geosciences
While geophysics shares many opportunities and problems with materials, it is distinguished by two aspects: (1) additional computational requirements; vastly larger range of length/time scales and significantly greater data storage. (2) nature of computation more dependent on the problem.

For this second reason, organization is by problem: exploration/extraction of resources; environmental geosciences; earthquake and crustal dynamics

The obvious value of ``inverting'' seismic and electromagnetic data to image energy and mineral resources poses several significant scientific challenges: (1) multi-terabyte data sets, (2) realistic models that include shear wave, fluid-filled porous media, discontinuities on all length scales, and (3) effectively using joint seismic and electromagnetic data sets.

The actual and potential environmental impact of organic, inorganic and radioactive waste necessitates predictive computer models that account for physical/chemical events over enormous length/time scales in complex subsurface environments.

To provide a basis for risk assessment of earthquake involve modeling nonlinear behavior over long time scales at four length scales: (i) rock friction and fracture, (ii) microcracks, (iii) single faults and (iv) fault systems.

Geoscience shares many of the opportunities and problems of materials. At the same time,geoscience is distinguished by two aspects: i. additional computational requirements; ii. nature of computation more dependent on the problem.

Energy and mineral resources. The obvious value of "inverting" seismic and electromagnetic data to image energy and mineral resources poses several significant scientific challenges: (1) multi-terabyte data sets; (2) realistic seismic and electromagnetic models that include shear wave, fluid-filled porous media, anisotropy and discontinuities on all length scales; and (3) effectively using joint seismic and electromagnetic data sets.

Seismic imaging. A typical offshore seismic survey yields ten terabyte data which must be ``inverted'' to image the overall structure, its strata, the rock formations and porosity.

Combined seismic and electromagnetic imaging. Electromagnetic wave propagation more directly samples the ionic conductivity of fluids in rocks, which depend on the porosity.

Environmental geosciences. The actual and potential environmental impact of organic, inorganic and radioactive waste necessitates predictive computer models that account for physical/chemical events over enormous length/time scales in complex subsurface environments.

Earthquake and crustal dynamics. To provide a basis for risk assessment of earthquakes involves modeling nonlinear behavior over long time scales at four length scales: (i) rock friction and fracture, (ii) microcracks and fluid flow, (iii) single faults and (iv) fault systems.

Volcanic processes. The distinct modeling challenge of volcano flows arise from nonlinearity, multicomponents and extreme property range.

Computational Issues Computational Issues
Scalable sparse matrix operations. Locality of interactions in many models -- for example, tight-binding potentials -- calls for advances in handling parallel sparse matrix-matrix operations.

Visualization. As the codes involve increasingly large data bases run on remote machines, visualization must provide tools for code performance/debugging and data visualization that run in real time and can be shared between distributed collaborators.

Remote steering. Scientists at geographically different locations need the ability to interactively steer a simulation in time and/or space.

Integrated development environment. Any given user should be able to simply construct an interface for a particular application without having to know anything about the particular programming paradigm or how to construct a visual environment.

Unchanged.