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Multiple Transient Memories in Experiments on Sheared Non-Brownian Suspensions

Physical Review Letters 2014年第6期113卷 068301-068301页

作者： Joseph D. Paulsen Nathan C. Keim Sidney R. Nagel Department of Physics University of Massachusetts Amherst Massachusetts 01003 USA Department of Polymer Science and Engineering University of Massachusetts Amherst Massachusetts 01003 USA James Franck Institute and Department of Physics The University of Chicago Chicago Illinois 60637 USA Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania Philadelphia Pennsylvania 19104 USA

A system with multiple transient memories can remember a set of inputs but subsequently forgets almost all of them, even as they are continually applied. If noise is added, the system can store all memories indefinitely. The phenomenon has recently been predicted for cyclically sheared non-Brownian suspensions. Here we present experiments on such suspensions, finding behavior consistent with multiple transient memories and showing how memories can be stabilized by noise.

关键词： Suspensions (fluids)

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Nanotribology of nanooxide materials in ionic liquids on silicon wafers

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AIP Conference Proceedings 2015年第1期1678卷

作者： Ahmad Termizi Hamidunsani Shahidan Radiman Masjuki Haji Hassan Irman Abdul Rahman 1School of Applied Physics Faculty of Science and Technology Universiti Kebangsaan Malaysia 43600 Bangi Selangor Malaysia 2Department of Mechanical Engineering Faculty of Engineering University of Malaya 50603 Kuala Lumpur Malaysia

Nanotribological properties have a significant impact on daily life. Ionic liquids (ILs) are becoming new favourable lubricants currently in researches. Addition of nanooxide materials in lubricants provide improvements to new technology. In this study, we determine nanotribological properties of BMIM+BF4− IL addition of different amount of ZnO nanomaterial on single crystals silicon wafer (Si110). The viscosity changes of IL samples against temperature increase were determined by rheological method. Nanotribological properties were determined by changes in friction coefficient and wear rate on silicon substrate surfaces using a reciprocating friction and wear monitor in 1 hour duration time. Aluminium cylinders acted as pins used to rub Si (110) substrate sample surfaces. Thus, on range between 0 mg to 3.5 mg of ZnO nanooxide material dispersed in 10ml BMIM+BF4− showed a good friction coefficient, wear and surface roughness reduction.

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Complexity in Surfaces of Densest Packings for Families of Polyhedra

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Physical Review X 2014年第1期4卷 011024-011024页

作者： Elizabeth R. Chen Daphne Klotsa Michael Engel Pablo F. Damasceno Sharon C. Glotzer School of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA Department of Chemical Engineering University of Michigan Ann Arbor Michigan 48109 USA Applied Physics Program University of Michigan Ann Arbor Michigan 48109 USA Department of Materials Science and Engineering University of Michigan Ann Arbor Michigan 48109 USA

Packings of hard polyhedra have been studied for centuries due to their mathematical aesthetic and more recently for their applications in fields such as nanoscience, granular and colloidal matter, and biology. In all these fields, particle shape is important for structure and properties, especially upon crowding. Here, we explore packing as a function of shape. By combining simulations and analytic calculations, we study three two-parameter families of hard polyhedra and report an extensive and systematic analysis of the densest known packings of more than 55 000 convex shapes. The three families have the symmetries of triangle groups (icosahedral, octahedral, tetrahedral) and interpolate between various symmetric solids (Platonic, Archimedean, Catalan). We find optimal (maximum) packing-density surfaces that reveal unexpected richness and complexity, containing as many as 132 different structures within a single family. Our results demonstrate the importance of thinking about shape not as a static property of an object, in the context of packings, but rather as but one point in a higher-dimensional shape space whose neighbors in that space may have identical or markedly different packings. Finally, we present and interpret our packing results in a consistent and generally applicable way by proposing a method to distinguish regions of packings and classify types of transitions between them.

关键词： Geometry

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Dynamics of magnetic particles near a surface: Model and experiments on field-induced disaggregation

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Physical Review E 2014年第4期89卷 042306-042306页

作者： A. van Reenen Y. Gao A. M. de Jong M. A. Hulsen J. M. J. den Toonder M. W. J. Prins Department of Applied Physics Eindhoven University of Technology Eindhoven The Netherlands Institute for Complex Molecular Systems (ICMS) Eindhoven The Netherlands Department of Mechanical Engineering Eindhoven University of Technology Eindhoven The Netherlands Philips Research Eindhoven The Netherlands

Magnetic particles are widely used in biological research and bioanalytical applications. As the corresponding tools are progressively being miniaturized and integrated, the understanding of particle dynamics and the control of particles down to the level of single particles become important. Here, we describe a numerical model to simulate the dynamic behavior of ensembles of magnetic particles, taking account of magnetic interparticle interactions, interactions with the liquid medium and solid surfaces, as well as thermal diffusive motion of the particles. The model is verified using experimental data of magnetic field-induced disaggregation of magnetic particle clusters near a physical surface, wherein the magnetic field properties, particle size, cluster size, and cluster geometry were varied. Furthermore, the model clarifies how the cluster configuration, cluster alignment, magnitude of the field gradient, and the field repetition rate play a role in the particle disaggregation process. The simulation model will be very useful for further in silico studies on magnetic particle dynamics in biotechnological tools.

关键词： Magnetic fields

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Effects of size polydispersity on electron mobility in a two-dimensional quantum-dot superlattice

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Physical Review B 2014年第14期90卷 144202-144202页

作者： Shicheng Xu Dickson Thian Shengkai Wang Yanming Wang Fritz B. Prinz Department of Mechanical Engineering Stanford University Stanford California 94305 USA Department of Applied Physics Stanford University Stanford California 94305 USA Department of Material Science and Engineering Stanford University Stanford California 94305 USA

We found that the transitions between delocalized electronic states in quantum-dot superlattices with smaller size dispersion can account for higher electron mobility. In particular, we solved for the quantum states of a two-dimensional quantum-dot (QD) superlattice using a one-electron approximation. Electron transport properties were studied by considering hopping transitions among coupled delocalized electronic states. Molecular dynamics simulations were employed to introduce disorders in superlattice configurations as a function of QD size and size dispersion for calculation of electron mobility. The interparticle spacing, size, and temperature dependence of the electron mobility can be well explained within the framework of our analysis.

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Approaching Truly Freestanding Graphene: The Structure of Hydrogen-Intercalated Graphene on 6H−SiC(0001)

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Physical Review Letters 2015年第10期114卷 106804-106804页

作者： J. Sforzini L. Nemec T. Denig B. Stadtmüller T.-L. Lee C. Kumpf S. Soubatch U. Starke P. Rinke V. Blum F. C. Bocquet F. S. Tautz Peter Grünberg Institut (PGI-3) Forschungszentrum Jülich 52425 Jülich Germany Jülich Aachen Research Alliance (JARA) Fundamentals of Future Information Technology 52425 Jülich Germany Fritz-Haber-Institut der Max-Planck-Gesellschaft 14195 Berlin Germany Max Planck Institute for Solid State Research Heisenbergstraße 70569 Stuttgart Germany Diamond Light Source Ltd Didcot OX110DE Oxfordshire United Kingdom COMP/Department of Applied Physics Aalto University P.O. Box 11100 Aalto FI-00076 Finland Department of Mechanical Engineering and Material Science Duke University Durham North Carolina 27708 USA

We measure the adsorption height of hydrogen-intercalated quasifreestanding monolayer graphene on the (0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density functional calculation for the full (63×63)−R30° unit cell, based on a van der Waals corrected exchange correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments, a very low buckling of the graphene layer, a very homogeneous electron density at the interface, and the lowest known adsorption energy per atom for graphene on any substrate. A structural comparison to other graphenes suggests that hydrogen-intercalated graphene on 6H−SiC(0001) approaches ideal graphene.

关键词： Graphene

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On wave-driven "Shingle" beach dynamics in a table-top hele-shaw cell 34

On wave-driven "Shingle" beach dynamics in a table-top hele-...

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34th International Conference on Coastal engineering, ICCE 2014

作者： Bokhove, O. Van Der Horn, A.J. Van Der Meer, D. Thornton, A.R. Zweers, W. School of Mathematics University of Leeds LeedsLS2 9JT United Kingdom Department of Physics University of Twente Enschede7500 AE Netherlands Department of Applied Mathematics/Mechanical Engineering University of Twente Enschede7500 AE Netherlands FabLab. Saxion College Enschede7513 AB Netherlands

ISBN: (纸本)9780989661126

The primary evolution of beaches by wave action takes place during storms. Beach evolution by non-linear breaking waves is 3D, multi-scale, and involves particle-wave interactions. We will show how a novel, three-phase extension to the classic "Hele-Shaw" laboratory experiment is designed to create beach morphologies with breaking waves in a quasi-2D setting. Idealized beaches emerge in tens of minutes due to several types of breaking waves, with about 1s periods. The thin Hele-Shaw cell simplifies the inherent complexity of three-phase dynamics by reducing the turbulence. Given the interest in the Hele-Shaw table-top demonstrations at ICCE2014, we will also discuss how different versions of the Hele-Shaw cell have been constructed. Construction can be inexpensive thus yielding an accessible and flexible coastal engineering demonstration as well as research tool. Beach evolution is sufficiently fast and can start very far from equilibrium, allowing an unusually large dynamical range to be investigated.

关键词： Beaches

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Acoustic streaming and its modeling in a traveling-wave thermoacoustic heat engine 7

Acoustic streaming and its modeling in a traveling-wave ther...

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AIAA AVIATION 2014 -7th AIAA Theoretical Fluid Mechanics Conference 2014

作者： Scalo, Carlo Lele, Sanjiva K. Hesselink, Lambertus Center for Turbulence Research Stanford CA 94305 United States Dept. of Aeronautics and Astronautics Department of Mechanical Engineering Stanford CA 94305 United States Dept. of Electrical Eng. and Applied Physics Dept. of Aeronautics and Astronautics Stanford CA 94305 United States

ISBN: (数字)9781624102936

ISBN: (纸本)9781624102936

We have investigated acoustic nonlinearities at the limit cycle in the numerical simulations by Scalo et al., (2013)13 of a three-dimensional traveling-wave thermoacoustic heat-engine. The setup is composed of a long variable-area resonator with the hot and ambient heat-exchangers (HHX, AHX) and the regenerator (REG) located at one end enclosed in a coaxial annular tube. Heat-transfer in the heat-exchangers is modeled via source terms which drive the local gas temperature towards the imposed temperature. Turning on the sources terms generates a finite-amplitude perturbation that is amplified until a limit cycle is reached. Simulations have been carried out for HHX temperatures in the range 460K - 500K and an AHX temperature of 300K. Acoustic nonlinearities are detectable from the early stages of operation in the form of streaming. Complex system-wide streaming flow patterns rapidly develop and control the operation of the device in the nonlinear stages. A solution decomposition based on sharp-spectral filtering is adopted to extract the wave-induced Reynolds stresses and energy fluxes at the limit cycle. The key processes involved are traveling-wave streaming in the feedback inertance, periodic vortex roll-up around the edges of the annular tube and near-wall acoustic shear-stresses in the variable-area sections of the resonator. The first drives the mean advection of hot fluid away from the HX/REG (Gedeon streaming), causing heat leakage. The latter is contained by introducing an AHX2 (creating a thermal buffer tube, or TBT) resulting in the saturation of acoustic energy growth in the system. A simplified numerical model is adopted to directly simulate acoustic streaming as an axially symmetric incompressible flow driven by the acoustic wave-induced stresses. Key features such as the intensity of Gedeon streaming are correctly predicted. The evaluation of the nonlinear energy fluxes reveals that the efficiency of the device deteriorates with the drive ratio and tha

关键词： Heat exchangers

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Laser induced breakdown spectroscopy for in situ heavy metal analysis of ocean sediments

Laser induced breakdown spectroscopy for in situ heavy metal...

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OCEANS

作者： Anna P. M. Michel Frederick Sonnichsen Alexandra Padilla Matthew Gschwend Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA Department of Mechanical Engineering University of Puerto Rico Mayagez Mayagez P.R.

Highly contaminated sediments exist in harbors and coastal environments due to shipping, poor management of waste, and anthropogenic inputs. Contaminated sediment is detrimental to fisheries, shell fishing, benthic communities, and human health. Measurement of heavy metals in sediments is of interest for identifying areas with elevated levels that should be targeted for remediation and for monitoring levels during and after remediation efforts. Developing in situ sensors capable of measuring heavy metals in sediments would enable rapid analysis and large spatial observations. Here we investigate the use of Laser induced-breakdown spectroscopy (LIBS), a type of atomic emission spectroscopy that can be used for elemental analysis of samples, for heavy metal analysis of sediments. We present our laboratory-based investigation that to date has demonstrated the ability of LIBS to measure cadmium, nickel, zinc, lead, and copper and to measure zinc underwater.

关键词： Sediments Sea measurements Metals Spectroscopy Measurement by laser beam Pollution measurement Optical pulses

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Dense periodic packings of tori

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Physical Review E 2014年第2期89卷 022133-022133页

作者： Ruggero Gabbrielli Yang Jiao Salvatore Torquato Interdisciplinary Laboratory for Computational Science Department of Physics University of Trento 38123 Trento Italy. Materials Science and Engineering Program School for Engineering of Matter Transport and Energy Arizona State University Tempe Arizona 85281 USA. Department of Chemistry Department of Physics Program in Applied and Computational Mathematics Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA.

Dense packings of nonoverlapping bodies in three-dimensional Euclidean space R3 are useful models of the structure of a variety of many-particle systems that arise in the physical and biological sciences. Here we investigate the packing behavior of congruent ring tori in R3, which are multiply connected nonconvex bodies of genus 1, as well as horn and spindle tori. Specifically, we analytically construct a family of dense periodic packings of unlinked tori guided by the organizing principles originally devised for simply connected solid bodies [Torquato and Jiao, Phys. Rev. E 86, 011102 (2012)]. We find that the horn tori as well as certain spindle and ring tori can achieve a packing density not only higher than that of spheres (i.e., π/18=0.7404...) but also higher than the densest known ellipsoid packings (i.e., 0.7707...). In addition, we study dense packings of clusters of pair-linked ring tori (i.e., Hopf links), which can possess much higher densities than corresponding packings consisting of unlinked tori.

关键词： Condensed matter physics

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