Engineering topics
Bishop, Alan
Publications and source records attributed to Bishop, Alan.
IN HONOR of NITANT KENKRE
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Thermalization in the one-dimensional Salerno model lattice
The Salerno model constitutes an intriguing interpolation between the integrable Ablowitz-Ladik (AL) model and the more standard (nonintegrable) discrete nonlinear Schrödinger (DNLS) one. The competition of local on-site nonlinearity and nonlinear dispersion governs the thermalization of this model. Here, we investigate the statistical mechanics of the Salerno one-dimensional lattice model in the nonintegrable case and illustrate the thermalization in the Gibbs regime. As the parameter interpolating between the two limits (from DNLS toward AL) is varied, the region in the space of initial energy and norm densities leading to thermalization expands. The thermalization in the non-Gibbs regime heavily depends on the finite system size; we explore this feature via direct numerical computations for different parametric regimes.
A Lattice Litany for Transition Metal Oxides
In this tribute to K Alex Müeller, I describe how his early insights have influenced future decades of research on perovskite ferroelectrics and more broadly transition metal oxides (TMOs) and related quantum materials. I use his influence on my own research journey to discuss impacts in three areas: structural phase transitions, precursor structure, and quantum paraelectricity. I emphasize materials functionality in ground, metastable, and excited states arising from competitions among lattice, charge, and spin degrees of freedom, which results in highly tunable landscapes and complex networks of multiscale configurations controlling macroscopic functions. I discuss competitions between short- and long-range forces as particularly important in TMOs (and related materials classes) because of their localized and directional metal orbitals and the polarizable oxygen ions. I emphasize crucial consequences of elasticity and metal–oxygen charge transfer
Multiscale Patterning from Competing Interactions and Length Scales
We live in an era of complexity marked by impressive new tools powering the scientific method to accelerate discovery, prediction, and control of increasingly complex systems. In common with many disciplines and societal challenges and opportunities, materials and condensed matter sciences are beneficiaries. The volume and fidelity of experimental, computational, and visualization data available, and tools to rapidly interpret them, are remarkable. Conceptual frameworks, including multiscale, multiphysics modeling of this complexity, are fueled by the data and, in turn, guide directions for future experimental and computational strategies. In this spirit, we discuss the importance of competing interactions, length scales, and constraints as pervasive sources of spatio-temporal complexity. We use representative examples drawn from materials and condensed matter, including the important role of elasticity in some technologically important quantum materials.
Double-Period Breathers in a Driven-Damped Lattice
Spatially localized and temporally oscillating solutions, known as discrete breathers, have been experimentally and theoretically discovered in many physical systems. Here, we consider a lattice of coupled damped and driven Helmholtz-Duffing oscillators in which we found a spatial coexistence of oscillating solutions with different frequencies. Specifically, we demonstrate that stable period-doubled solutions coexist with solutions oscillating at the frequency of the driving force. Such solutions represent period-doubled breathers resulting from a stability overlap between subharmonic and harmonic solutions and exist up to a certain strength of the lattice coupling. Our findings suggest that this phenomenon can occur in any driven lattice where the nonlinearity admits bistability (or multi-stability) of subharmonic and harmonic solutions.
Scientific Excellence for Mission Impact: The Importance of Collaborations [Slides]
Abstract not provided.
2ND PHYSICS INFORMED MACHINE LEARNING CONFERENCE
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Charge to the Engineering Capability Review
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Lewis-Kuhn Lab Overview 11-3-16
This presentation describes the mission of LANL, its projects, funding portfolio, and collaborations.
Bishop All Hands 11-3-16
This presentation describes the mission of LANL, its projects, funding portfolio, and collaborations.
Provost Abdallah Meet and Greet
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Los Alamos National Laboratory: Overview for Carl Schramm
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Scientific Excellence for Mission Impact [Slides]
Our strategy as a multi-program, national security laboratory is to develop and apply the best science, technology, and engineering solutions to the toughest national security missions: Multidisciplinary science, technology, and engineering challenges. Problems demanding unique experimental and computational facilities. Highly complex security issues requiring fundamental breakthroughs.
Phonon localization drives polar nanoregions in a relaxor ferroelectric
Relaxor ferroelectrics1, which are utilized as actuators and sensors2-4, exemplify a class of poorly understood materials where interplay between disorder and phase instability results in inhomogeneous nanoregions. There is no definitive explanation for the onset of relaxor behavior (Burns temperature5, Td) or the origin of polar nanoregions (PNRs). Here we show a vibrational mode that localizes on cooling to Td, remains localized as PNRs form, and then delocalizes as PNRs grow using neutron scattering on relaxor (Pb(Mg1/3Nb2/3)O3)0.69-(PbTiO3)0.31 (PMN-31%PT). Although initially appearing like intrinsic local modes (ILMs)6-10, these modes differ below Td as they form a resonance with the ferroelectric phonon. At the resonance, nanoregions of standing ferroelectric phonons develop with a coherence length matching the PNRs. The size, shape, distribution, and temporal fluctuations of PNRs, and our observations, are explained by ferroelectric phonons trapped by disordered resonance modes via Anderson localization11-13. Our results show the size and shape of PNRs are not dictated by complex structural details, as always assumed, but by a phonon resonance wavevector. This simplification could guide the design of next generation relaxors.
Welcome to Los Alamos National Laboratory August 15, 2013
Abstract Not Provided