99 research outputs found

    Measurement of Anomalous Diffusion Using Recurrent Neural Networks

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    Anomalous diffusion occurs in many physical and biological phenomena, when the growth of the mean squared displacement (MSD) with time has an exponent different from one. We show that recurrent neural networks (RNN) can efficiently characterize anomalous diffusion by determining the exponent from a single short trajectory, outperforming the standard estimation based on the MSD when the available data points are limited, as is often the case in experiments. Furthermore, the RNN can handle more complex tasks where there are no standard approaches, such as determining the anomalous diffusion exponent from a trajectory sampled at irregular times, and estimating the switching time and anomalous diffusion exponents of an intermittent system that switches between different kinds of anomalous diffusion. We validate our method on experimental data obtained from sub-diffusive colloids trapped in speckle light fields and super-diffusive microswimmers.Comment: 6 pages, 4 figures. Supplemental material available as separate file in the Ancillary Files sectio

    Tunable graphene system with two decoupled monolayers

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    The use of two truly two-dimensional gapless semiconductors, monolayer and bilayer graphene, as current-carrying components in field-effect transistors (FET) gives access to new types of nanoelectronic devices. Here, we report on the development of graphene-based FETs containing two decoupled graphene monolayers manufactured from a single one folded during the exfoliation process. The transport characteristics of these newly-developed devices differ markedly from those manufactured from a single-crystal bilayer. By analyzing Shubnikov-de Haas oscillations, we demonstrate the possibility to independently control the carrier densities in both layers using top and bottom gates, despite there being only a nanometer scale separation between them

    Light-controlled Assembly of Active Colloidal Molecules

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    Thanks to a constant energy input, active matter can self-assemble into phases with complex architectures and functionalities such as living clusters that dynamically form, reshape and break-up, which are forbidden in equilibrium materials by the entropy maximization (or free energy minimization) principle. The challenge to control this active self-assembly has evoked widespread efforts typically hinging on engineering of the properties of individual motile constituents. Here, we provide a different route, where activity occurs as an emergent phenomenon only when individual building blocks bind together in a way that we control by laser light. Using experiments and simulations of two species of immotile microspheres, we exemplify this route by creating active molecules featuring a complex array of behaviors, becoming migrators, spinners and rotators. The possibility to control the dynamics of active self-assembly via light-controllable nonreciprocal interactions will inspire new approaches to understand living matter and to design active materials.Comment: 20 pages, 4 figures; New Version: corrected typos, added detailed sections about simulations, clarified phoretic interactions responsible for molecule formatio

    Transport of neutral optical excitations using electric fields

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    Mobile quantum impurities interacting with a fermionic bath form quasiparticles known as Fermi polarons. We demonstrate that a force applied to the bath particles can generate a drag force of similar magnitude acting on the impurities, realizing a novel, nonperturbative Coulomb drag effect. To prove this, we calculate the fully self-consistent, frequency-dependent transconductivity at zero temperature in the Baym-Kadanoff conserving approximation. We apply our theory to excitons and exciton polaritons interacting with a bath of charge carriers in a doped semiconductor embedded in a microcavity. In external electric and magnetic fields, the drag effect enables electrical control of excitons and may pave the way for the implementation of gauge fields for excitons and polaritons. Moreover, a reciprocal effect may facilitate optical manipulation of electron transport. Our findings establish transport measurements as a novel, powerful tool for probing the many-body physics of mobile quantum impurities.Comment: 18 + 11 pages, 4 figure

    Numerical investigation of turbulent-jet primary breakup using One-Dimensional Turbulence

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    Primary breakup to form droplets at liquid surfaces is an important fundamental process to study as it determines the initial properties of the dispersed phase, which affect mixing rates, secondary breakup, droplet collisions, and flow separation within the dispersed flow region. Primary breakup can be regarded as one of the least developed model components for simulating and predicting liquid jet breakup. However, it is of paramount importance in many technical applications, e.g. fuel injection in engines and spray painting. This paper presents a numerical investigation of primary breakup of a turbulent liquid jet in still air at standard conditions using the one-dimensional turbulence (ODT) modeling framework. ODT is a stochastic model that simulates turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. An important feature of ODT is the resolution of all relevant scales, both temporal and spatial. The restriction to one spatial dimension in ODT permits affordable high resolution of interfacial and single-phase property gradients, which is key to capturing the local behavior of the breakup process and allows simulations at high Reynolds and Weber numbers that are currently not accessible to direct numerical simulations (DNS). This paper summarizes our extensions of the ODT model to simulate geometrically simple jet breakup problems, including representations of Rayleigh wave breakup, turbulent breakup, and shear-driven breakup. Each jet breakup simulation consists of a short temporal channel section to initialize a turbulent velocity profile at the nozzle exit followed by an adjacent jet section. The simulations are carried out for jet exit Reynolds number of 11,500, 23,000, 46,000 and 92,000 while the Weber number is varied within the range 102–107. We present results on breakup statistics including spatial locations of droplet release, droplet sizes and liquid core length. The results on primary breakup are compared to experimental results and models

    Enhanced fluctuations of the tunneling density of states near bottoms of Landau bands measured by a local spectrometer

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    We have found that the local density of states fluctuations (LDOSF) in a disordered metal, detected using an impurity in the barrier as a spectrometer, undergo enhanced (with respect to SdH and dHvA effects) oscillations in strong magnetic fields, omega _c\tau > 1. We attribute this to the dominant role of the states near bottoms of Landau bands which give the major contribution to the LDOSF and are most strongly affected by disorder. We also demonstrate that in intermediate fields the LDOSF increase with B in accordance with the results obtained in the diffusion approximation.Comment: 4 pages, 4 figure

    Technical feasibility of lined mining tunnels in closed coal mines as underground reservoirs of compressed air energy storage systems

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    [EN] In this paper, four mining levels in a closed coal mine in the Asturian Central Coal Basin (NW Spain) have been selected as a case study to investigate the technical feasibility of underground compressed air energy storage systems. First, in order to determine the suitable level and type of concrete lining, a numerical model has been established to analyze the geomechanical performance considering air pressures of 6, 10, 20 and 25 MPa and three different embodiments of concrete lining. Then, another numerical model is used to study the coupled thermo-mechanical performance at level 3, considering 100 operation cycles between 6 and 10 MPa air pressure using a circular concrete lining with a 20 mm thick sealing layer. The results obtained indicate that the deformations are lower at levels 1 and 3, where the shales are located at the top of the coal seam. Deformations and tensile stresses are significantly reduced when a circular concrete lining is used. As the thermal analysis shows, temperature fluctuations are restricted to sealing layer and concrete lining and do not reach the rock mass itself. Therefore, negligible deformations are produced by the effect of temperature compared to the effect of air pressure. Maximum tensile stress and total displacements during the operation occur at the top of the mining drift and reach 9.5 MPa and 3.6 mm, respectively. A technical feasibility can be achieved using a circular concrete lining with a suitable reinforcement system.S

    Consistent Atomic Geometries and Electronic Structure of Five Phases of Potassium Niobate from Density-Functional Theory

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    We perform a comprehensive theoretical study of the structural and electronic properties of potassium niobate (KNbO3) in the cubic, tetragonal, orthorhombic, monoclinic, and rhombohedral phase, based on density-functional theory. The influence of different parametrizations of the exchange-correlation functional on the investigated properties is analyzed in detail, and the results are compared to available experimental data. We argue that the PBEsol and AM05 generalized gradient approximations as well as the RTPSS meta-generalized gradient approximation yield consistently accurate structural data for both the external and internal degrees of freedom and are overall superior to the local-density approximation or other conventional generalized gradient approximations for the structural characterization of KNbO3. Band-structure calculations using a HSE-type hybrid functional further indicate significant near degeneracies of band-edge states in all phases which are expected to be relevant for the optical response of the material
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