138 research outputs found

    Molecular Dynamics Simulation of Iron — A Review

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    Limits on Fundamental Limits to Computation

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    An indispensable part of our lives, computing has also become essential to industries and governments. Steady improvements in computer hardware have been supported by periodic doubling of transistor densities in integrated circuits over the last fifty years. Such Moore scaling now requires increasingly heroic efforts, stimulating research in alternative hardware and stirring controversy. To help evaluate emerging technologies and enrich our understanding of integrated-circuit scaling, we review fundamental limits to computation: in manufacturing, energy, physical space, design and verification effort, and algorithms. To outline what is achievable in principle and in practice, we recall how some limits were circumvented, compare loose and tight limits. We also point out that engineering difficulties encountered by emerging technologies may indicate yet-unknown limits.Comment: 15 pages, 4 figures, 1 tabl

    On‐Demand Reconfiguration of Nanomaterials: When Electronics Meets Ionics

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    Rapid advances in the semiconductor industry, driven largely by device scaling, are now approaching fundamental physical limits and face severe power, performance, and cost constraints. Multifunctional materials and devices may lead to a paradigm shift toward new, intelligent, and efficient computing systems, and are being extensively studied. Herein examines how, by controlling the internal ion distribution in a solid‐state film, a material’s chemical composition and physical properties can be reversibly reconfigured using an applied electric field, at room temperature and after device fabrication. Reconfigurability is observed in a wide range of materials, including commonly used dielectric films, and has led to the development of new device concepts such as resistive random‐access memory. Physical reconfigurability further allows memory and logic operations to be merged in the same device for efficient in‐memory computing and neuromorphic computing systems. By directly changing the chemical composition of the material, coupled electrical, optical, and magnetic effects can also be obtained. A survey of recent fundamental material and device studies that reveal the dynamic ionic processes is included, along with discussions on systematic modeling efforts, device and material challenges, and future research directions.By controlling the internal ion distribution in a solid‐state film, the material’s chemical composition and physical (i.e., electrical, optical, and magnetic) properties can be reversibly reconfigured, in situ, using an applied electric field. The reconfigurability is achieved in a wide range of materials, and can lead to the development of new memory, logic, and multifunctional devices and systems.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141225/1/adma201702770.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141225/2/adma201702770_am.pd

    Roadmap on Machine learning in electronic structure

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    AbstractIn recent years, we have been witnessing a paradigm shift in computational materials science. In fact, traditional methods, mostly developed in the second half of the XXth century, are being complemented, extended, and sometimes even completely replaced by faster, simpler, and often more accurate approaches. The new approaches, that we collectively label by machine learning, have their origins in the fields of informatics and artificial intelligence, but are making rapid inroads in all other branches of science. With this in mind, this Roadmap article, consisting of multiple contributions from experts across the field, discusses the use of machine learning in materials science, and share perspectives on current and future challenges in problems as diverse as the prediction of materials properties, the construction of force-fields, the development of exchange correlation functionals for density-functional theory, the solution of the many-body problem, and more. In spite of the already numerous and exciting success stories, we are just at the beginning of a long path that will reshape materials science for the many challenges of the XXIth century

    Anomalous relaxation in colloidal systems

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    The Mpemba effect refers to a phenomenon where a sample of hot water may cool and begin to freeze more quickly than a cool or warm water sample prepared under identical conditions. Although the effect has been known since the time of Aristotle, it is named after the Tanzanian teenager Erasto Mpemba, who discovered the effect in the 1960s. Although Mpemba and Osborne showed the effect in laboratory experiments, it has always been mysterious, its underlying mechanism a topic of hot debate. In this thesis, we experimentally show the Mpemba effect in a colloidal system with a micron-sized silica bead diffusing in a bath. The bead is subjected to an external double-well potential created by a feedback-based optical tweezer. When a system is quenched from an initially hot equilibrium state to a cold equilibrium state, the evolution of the system between the initial and the final state is a strongly nonequilibrium process. As a nonequilibrium state cannot, in general, be characterized by a single temperature, we adopt the notion of a “distance” measure as a proxy for temperature. We show Mpemba effects in an asymmetric double-well potential. Our experimental results agree quantitatively with predictions based on the Fokker-Planck equation. Using understanding gained from the Mpemba effect, we design an experiment to investigate the opposite effect and present the first experimental evidence for this inverse Mpemba effect. Contrary to the cooling effect, the inverse effect is related to a phenomenon where a system that is initially cold heats up faster than an initially warm system. By understanding the underlying mechanism of these anomalous effects, we demonstrate strong Mpemba and inverse Mpemba effects, where a system can cool or heat exponentially faster to the bath temperature than under typical conditions. Finally, we ask whether asymmetry in the potential is necessary and show experimentally that an anomalous cooling effect can be observed in a symmetric potential, leading to a higher-order Mpemba effect

    Rugged free-energy landscapes in disordered spin systems

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    This thesis is an attempt to provide a new outlook on complex systems, as well as some physical answers for certain models, taking a computational approach. We have focused on disordered systems, addressing two traditional problems in three spatial dimensions: the Edwards-Anderson spin glass and the Diluted Antiferromagnet in a Field (the physical realisation of the random-field Ising model). These systems have been studied by means of large-scale Monte Carlo simulations, exploiting a variety of platforms, which include the Janus special-purpose supercomputer. Two main themes are explored throughout: a) the relationship between the (experimentally unreachable) equilibrium phase and the non-equilibrium evolution and b) the computation and efficient treatment of rugged free-energy landscapes. We perform a thorough study of the low-temperature phase of the D=3 Edwards-Anderson spin glass, where we establish a time-length dictionary and a finite-time scaling formalism to link, in a quantitative way, the experimental non-equilibrium regime and the finite-size equilibrium phase. At the experimentally relevant scales, the replica symmetry breaking theory emerges as the appropriate theoretical picture. We also introduce Tethered Monte Carlo, a general strategy for the study of systems with rugged free-energy landscapes. This formalism provides a general method to guide the exploration of the configuration space by constraining one or more reaction coordinates. From these tethered simulations, the Helmholtz potential associated to the reaction coordinates is reconstructed, yielding all the information about the system. We use this method to provide a comprehensive picture of the critical behaviour in the Diluted Antiferromagnet in a Field.Comment: PhD Thesis. Defended at the Universidad Complutense de Madrid on October 21, 201

    V Jornadas de InvestigaciĂłn de la Facultad de Ciencia y TecnologĂ­a. 2016

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    171 p.I. Abstracts. Ahozko komunikazioak / Comunicaciones orales: 1. Biozientziak: Alderdi Molekularrak / Biociencias: Aspectos moleculares. 2. Biozientziak: Ingurune Alderdiak / Biociencias: Aspectos Ambientales. 3. Fisika eta Ingenieritza Elektronika / FĂ­sica e IngenierĂ­a ElectrĂłnica. 4. GeologĂ­a / GeologĂ­a. 5. Matematika / MatemĂĄticas. 6. Kimika / QuĂ­mica. 7. Ingenieritza Kimikoa eta Kimika / IngenierĂ­a QuĂ­mica y QuĂ­mica. II. Abstracts. Idatzizko Komunikazioak (Posterrak) / Comunicaciones escritas (PĂłsters): 1. Biozientziak / Biociencias. 2. Fisika eta Ingenieritza Elektronika / FĂ­sica e IngenierĂ­a ElectrĂłnica. 3. Geologia / Geologia. 4. Matematika / MatemĂĄticas. 5. Kimika / QuĂ­mica. 6. Ingenieritza Kimikoa / IngenierĂ­a QuĂ­mica

    RNA-induced conformational switching and clustering of G3BP drive stress granule assembly by condensation

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    Stressed cells shut down translation, release mRNA molecules from polysomes, and form stress granules (SGs) via a network of interactions that involve G3BP. Here we focus on the mechanistic underpinnings of SG assembly. We show that, under non-stress conditions, G3BP adopts a compact auto-inhibited state stabilized by electrostatic intramolecular interactions between the intrinsically disordered acidic tracts and the positively charged arginine-rich region. Upon release from polysomes, unfolded mRNAs outcompete G3BP auto-inhibitory interactions, engendering a conformational transition that facilitates clustering of G3BP through protein-RNA interactions. Subsequent physical crosslinking of G3BP clusters drives RNA molecules into networked RNA/protein condensates. We show that G3BP condensates impede RNA entanglement and recruit additional client proteins that promote SG maturation or induce a liquid-to-solid transition that may underlie disease. We propose that condensation coupled to conformational rearrangements and heterotypic multivalent interactions may be a general principle underlying RNP granule assembly
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