Materials by Design:

Three-Dimensional (3D) Nano-Architected Meta-Materials. Part I

Julia R. Greer

Departments of Materials Science, Mechanics, and Medical Engineering

California Institute of Technology, Pasadena, CA

http://www.jrgreer.caltech.edu

Creation of extremely strong and simultaneously ultra lightweight materials can be achieved by incorporating architecture into material design. In our research, we design and fabricate three-dimensional (3D) nano-architected materials that can exhibit superior and often tunable thermal, photonic, electrochemical, and ­mechanical pro­­­per­­ties at ex­tre­me­ly low mass densities (lighter than aerogels), which renders them useful, and often enabling, in many scientific pursuits and tech­no­lo­gi­cal applications. Dominant properties of such meta-materials are driven by their multi-scale nature: from characteristic material microstructure (atoms) to individual constituents (nanometers) to structural components (microns) to overall architectures (millimeters and above). 

To harness the beneficial properties of 3D nano-architected meta-materials, it is critical to assess their properties at each relevant scale while capturing over­all structural complexity. Our research is focused on fabrication and synthesis of such architected materials using 3D lithography, nanofabrication, and additive manufacturing (AM) techniques, as well as on investigating their mechanical, biochemical, electrochemical, electromechanical, and thermal properties as a function of architecture, constituent materials, and microstructural detail. We strive to uncover the synergy between the internal atomic-level microstructure and the nano-sized external dimensionality, where competing material- and structure-induced size effects drive overall response and govern these properties.

In Part I of the Seidman Lectures, I will focus on the mechanics of 3D nano-architected materials, which include compression, tension, and fracture experiments and simulations, as well as quasi-static vs. dynamic loading for a broad range of materials. I will describe an example where unusual mechanical properties of these nano-architected materials enable creating stimulus-responsive reconfigurable materials through electrochemistry.

Some relevant publications:

1. D. Yee, M. Lifson, J.R. Greer, Additive manufacturing of 3D architected multifunctional metal oxides, Adv. Mater. (2019) in press, DOI: 10.1002/adma.201901345.
2. X. Zhang et al, Lightweight, flaw-tolerant, and ultrastrong nanoarchitected carbon. PNAS, 116(14) (2019) 6665-72.
3. X. Xia et al., Electrochemically reconfigurable architected materials, Nature, 573 (2019) 205-13.
4. A.J. Mateos et al., Discrete‐continuum duality of architected materials: Failure, flaws, and fracture, Adv. Funct Mater., 29 (2019) article 1806772.
5. L.A. Shaw et al., Computationally efficient design of directionally compliant metamaterials, Nature Commun., 10 (2019) article 291.
6. A. Vyatskikh et al., Additive manufacturing of 3D nano-architected metals, Nature Commun., 9 (2018) article 593.
7. V. Chernow et al., Polymer nanolattices as mechanically tunable 3-dimensional photonic crystals, Appl. Phys. Lett., 107 (2015) article 101905.
8. L.R. Meza, S. Das, J.R. Greer, Strong, lightweight and recoverable three-dimensional ceramic nanolattices, Science,  345 (2014) 1322-6.

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SCHOOL OF MECHANICAL ENGINEERING SEMINAR
Wednesday, November 20, 2019 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Co-evolving rationalizable strategies in multi-objective games

Erella Eisenstadt-Matalon
PhD student of Ami Moshaiov

The vast majority of game-theoretic studies are on Single Objective Games (SOG), also known as single payoff games. The area of Multi-Objective Games (MOGs), which are also termed as multi payoff, multi criteria or vector payoff games, has received lesser attention. Yet, in many practical problems, in economics and engineering, the players must cope with multiple objectives or payoffs.
The considered MOGs are static, non-cooperative, two-persons, zero-sum games with pure strategies, in which each player has self-conflicting objectives and none of the players has a-priori objective preferences. Yet, each player knows all the available strategies of the opponent and all the payoff vectors that result from all possible interactions between the player's strategies and those of the opponent. Here, common knowledge of rationality is assumed. Namely, it is assumed that each player is rational, and that each player knows it, and so on.
The common approach to deal with MOGs is to assume that the objective preferences of the players are known a-priori. In such a case a utility function is employed which transforms the MOG into a surrogate SOG (usually by a weighted-sum approach). However, players may have doubts when trying to a-priori make a rational decision on their objective preferences. Moreover, existing solution techniques, such as by equilibrium or by a MiniMax approach, suffer from not considering the performance trade-offs. In contrast, here it is assumed that in general, decision-makers should take into account performance trade-offs when making a decision. In view of this assertion and of the state-of-the-art, a novel solution concept to MOGs is suggested, which is based on the idea of rationalizability.
The proposed mutual-rationalizability solution concept for solving MOGs involves two-stages. In the first stage, a Set of Rationalizable Strategies (SRS) and their associated payoff vectors are sought for each of the players. This is done using Pareto-based best replies of the opponent, under the assumptions of common knowledge of rationality and undecided objective preferences by the players. The proposed approach results with trade-off information at the end of the first stage. In the second stage, Multi-Criteria Decision Analysis (MCDA) techniques are used to select a strategy out of the obtained SRSs based on the trade-off information that is revealed in the first stage. To realize the proposed two-stage solution approach, a multi-objective co-evolutionary algorithm is devised, which co-evolve the players’ strategies and finds approximated SRS for each of them.
To demonstrate the proposed approach, a novel MOG version of the Traveling Salesperson Problem (TSP) is suggested. It amalgamates two known versions of the TSP including the competing TSP and the selective TSP. The demonstration shows the capabilities of the proposed search algorithm and the significance of the proposed solution approach.

You are invited to attend a lecture
Evidence of absorption dominating over scattering in light attenuation by nanodiamonds
By:
Sergei Koniakhin

Researcher, Université Clermont Auvergne, Institut Pascal, Photon-N2, France
Senior Researcher, Zhores Alferov St. Petersburg Academic University, Russia

Abstract
We show an experimental evidence of the domination of absorption over scattering in absorbance spectra of detonation nanodiamonds. We perform the absorbance measurements on the UV-Vis spectrophotometer equipped with integrating sphere and compare them with conventional absorbance spectra. Additionally, we measure the scattering light intensity at the cuvette side wall (scattering at 90 degrees angle). The obtained experimental data were interpreted using the simulations of photon random walk in turbid media and Kubelka-Munk approach. The scattering cross sections and indicatrices were obtained by Mie theory.
 We discover that despite being very close to -4 power law (like Rayleigh scattering) the light extinction by the primary 4 nm diamond crystallites is due to absorption only and scattering can be neglected. That is the reason why previously absorption and scattering contributions were confused. The scattering is governed only by the agglomerates of 100 nm and larger in size remaining in the hydrosols and their fraction can be effectively controlled by centrifugation. Only Mie theory reproduces correctly the close to -2 scattering by the agglomerates accounting for the weird interplay between their size, fractal dimension, and dielectric properties. Finally, using the obtained absorbance spectra we estimate the fraction of non diamond phase in nanodiamonds and their agglomerates.

On Tuesday, Nov 12, 2019, 15:00
Room 011, Kitot building