Literatura académica sobre el tema "Atomic scale description"
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Artículos de revistas sobre el tema "Atomic scale description"
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Cruz, Eduardo y Klaus Schulten. "Atomic Scale Description of Ionic Behavior in Polymer Nanopores". Biophysical Journal 96, n.º 3 (febrero de 2009): 644a—645a. http://dx.doi.org/10.1016/j.bpj.2008.12.3835.
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Pignatelli, Isabella, Enrico Mugnaioli, Re´gine Mosser-Ruck, Odile Barres, Ute Kolb y Nicolas Michau. "A multi-technique, micrometer- to atomic-scale description of a synthetic analogue of chukanovite, Fe2(CO3)(OH)2". European Journal of Mineralogy 26, n.º 2 (11 de abril de 2014): 221–29. http://dx.doi.org/10.1127/0935-1221/2014/0026-2370.
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Fossati, Paul C. M., Michael J. D. Rushton y William E. Lee. "Atomic-scale description of interfaces in rutile/sodium silicate glass–crystal composites". Physical Chemistry Chemical Physics 20, n.º 26 (2018): 17624–36. http://dx.doi.org/10.1039/c8cp00675j.
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Zapolsky, H., G. Demange y Rafal Abdank-Kozubski. "From the Atomistic to the Mesoscopic Scale Modeling of Phase Transition in Solids". Diffusion Foundations 12 (septiembre de 2017): 111–26. http://dx.doi.org/10.4028/www.scientific.net/df.12.111.
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The phase-field method is a very powerful tool to model the phase transformation and microstructural evolution of solids at mesoscopic scale. However, several important phenomena, like defect formation, grain boundary motion, or reconstructive phase transitions require an atomic scale study. Recently an approach called the quasi-particle approach, based on the Atomic Density Function theory was developed to incorporate the atomic-level crystalline structures into standard continuum theory for pure and multicomponent systems. This review focuses on the description of different computational methods used to model microstructural evolution and self-assembly phenomena at mesoscopic and atomistic scales. Various application examples of these methods are also presented.
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Zhao, Zheng, Haoxiang Xu, Yi Gao y Daojian Cheng. "Universal description of heating-induced reshaping preference of core–shell bimetallic nanoparticles". Nanoscale 11, n.º 3 (2019): 1386–95. http://dx.doi.org/10.1039/c8nr08889f.
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To achieve universal description of the reshaping process of core–shell bimetallic nanoparticles, we combined the tight-binding Ising Hamiltonian model with molecular dynamic simulations to propose a general theoretical model at the atomic scale while considering the temperature, bond energy, atomic size, and surface energy effects.
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Lynch, Diane, Dow Hurst, Patti Reggio, Alan Grossfield y Mike Pitman. "Atomic Level Description of GPCR Activation Revealed by Microsecond Time Scale Molecular Dynamics". Biophysical Journal 96, n.º 3 (febrero de 2009): 365a. http://dx.doi.org/10.1016/j.bpj.2008.12.1965.
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Ruano Merchan, C., T. T. Dorini, F. Brix, L. Pasquier, M. Jullien, D. Pierre, S. Andrieu et al. "Two-dimensional square and hexagonal oxide quasicrystal approximants in SrTiO3 films grown on Pt(111)/Al2O3(0001)". Physical Chemistry Chemical Physics 24, n.º 12 (2022): 7253–63. http://dx.doi.org/10.1039/d1cp05296a.
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An all-thin-film approach allows the synthesis of novel two-dimensional quasicrystalline approximants and an atomic scale description is provided based on combined experimental and theoretical investigations.
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Turlo, V., O. Politano y F. Baras. "Microstructure evolution and self-propagating reactions in Ni-Al nanofoils: An atomic-scale description". Journal of Alloys and Compounds 708 (junio de 2017): 989–98. http://dx.doi.org/10.1016/j.jallcom.2017.03.051.
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Randrianandraina, Joharimanitra, Michael Badawi, Bruno Cardey, Manuel Grivet, Jean-Emmanuel Groetz, Christophe Ramseyer, Freddy Torrealba Anzola, Caroline Chambelland y Didier Ducret. "Adsorption of water in Na-LTA zeolites: an ab initio molecular dynamics investigation". Physical Chemistry Chemical Physics 23, n.º 34 (2021): 19032–42. http://dx.doi.org/10.1039/d1cp02624k.
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The very wide range of applications of LTA zeolites, including the storage of tritiated water, implies that a detailed and accurate atomic-scale description of the adsorption processes taking place in their structure is crucial.
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Caballero, Francisca G., Jonathan D. Poplawsky, Hung Wei Yen, Rosalia Rementeria, Lucia Morales-Rivas, Jer Ren Yang y Carlos García-Mateo. "Complex Nano-Scale Structures for Unprecedented Properties in Steels". Materials Science Forum 879 (noviembre de 2016): 2401–6. http://dx.doi.org/10.4028/www.scientific.net/msf.879.2401.
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Processing bulk nanoscrystalline materials for structural applications still poses a significant challenge, particularly in achieving an industrially viable process. In this context, recent work has proved that complex nanoscale steel structures can be formed by solid reaction at low temperatures. These nanocrystalline bainitic steels present the highest strength ever recorded, unprecedented ductility, fatigue on par with commercial bearing steels and exceptional rolling-sliding wear performances. A description of the characteristics and significance of these remarkable structures in the context of the atomic mechanism of transformation is provided.
Tesis sobre el tema "Atomic scale description"
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Ellezam, Laura. "Dopage (Co/Fe) de nanoparticules de RuO2 : synthèse, modélisation et caractérisation structurale". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS304.
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Ce travail concerne l’analyse complète des nanoparticules (NPs) de RuO2 dopées au Co ou au Fe. Le défi ici réside dans la taille des systèmes, comprise entre 1 et 2,5nm. Les synthèses sont réalisées par trois voies différentes de chimie douce en solvant aqueux : la voie sol-gel, hydrothermale, et co-précipitation. Le Fe se substitue facilement au Ru, le Co plus difficilement. À l’issue de l’étude de ces méthodes de synthèse, des NPs dopées au Co et au Fe ont été synthétisées. Afin de les caractériser et de comprendre l’influence, notamment structurale, des dopants, les calculs DFT et la caractérisation par l’étude de la fonction de distribution de paires atomiques (PDF) ont été couplés. La construction de modèle bulk puis des modèles de NPs ont été construits et optimisés. Les études de localisation des dopants montrent qu’ils se concentrent préférentiellement en surface, éloignés par des atomes de Ru dans le cas d’un nombre très faible d’atome. En augmentant le nombre d’atomes dopants, une étude préliminaire suggère un regroupement de surface des atomes dopants. À partir de ces modèles, des PDFs sont calculées et comparées aux PDFs expérimentales des NPs synthétisées. Ainsi il est possible d’attribuer en détail les PDFs expérimentales et de décrire l’arrangement local des NPs dopées ainsi que de valider les modèles DFT. Il a donc été mis en place un protocole de caractérisation permettant de décrire l’arrangement locale et de démontrer le dopage, dans des NPs de moins de 5 nm en utilisant la DFT et l’analyse PDF, avec confirmation par des analyses STEM-HAADF-EELSThe aim of this work is the full analysis of RuO2 nanoparticles (NPs) doped with Co or Fe. This is a big challenge because of the size of these systems (1.0 - 2.5 nm). Synthesis were conducted by three different aqueous pathways at low temperature: via sol-gel, hydrothermal and by co-precipitation methods. Fe atoms replaces easily Ru, whereas it is more difficult for Co. Several parameters had to be changed to obtain a successful doping. In order to characterize the local structure of Co or Fe-doped RuO2 nanoparticles, and understand the structural modifications, a coupling between modelling with DFT calculation and analysis by Pair Distribution Function (PDF) was set up. First a bulk model and after a NP model was built and optimized by DFT. It was seen that numerous doping atoms tend to be localized at the surface of the NPs whereas it is more thermodynamically stable to have a good dispersion when the number of doping atom is smaller. From these DFT model, PDF curves were calculated and compared with experimental PDF curves. These comparisons allow to identify the rutile structure, describe the local structure, and to validate DFT models. It also allows the attribution of distances in the structure and shows the need to consider specifically the surface modifications. This PDF/DFT conclusions were validated by high level STEM-HAADF-EELS analysis
Capítulos de libros sobre el tema "Atomic scale description"
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Ostermeyer, Georg-Peter y Andreas Krumm. "Abstract Methods on Mesoscopic Scales of Friction". En Springer Tracts in Mechanical Engineering, 127–42. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-60124-9_6.
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AbstractIn recent years, research has increasingly focused on the complex processes involved in friction contacts. Especially in tribological high-loaded contacts, characterized by the presence of contact modifying wear particles, macroscopic friction shows a surprisingly high dynamic complexity on many temporal and local scales. There are dominant effects on mesoscopic scales such as the geometric self-organization structures of the wear dust in the contact, which can significantly change the local contact surfaces. For the description and simulation of these phenomena, abstract methods have shown their effectiveness. One class of methods are cellular automata, both volume- and particle-based. The latter are in particular the Movable Cellular Automata developed by Sergey Psakhie. The scales of these discrete methods are freely selectable in wide ranges between the macro world and the atomic scale. Nevertheless, they provide reliable information on mesoscopic balances in the boundary layer and thus also on the macroscopic behavior of the tribocontact. The success of these methods is shown by the example of an automotive brake. The question of the relative insensitivity of the scales of these mesoscopic methods is examined in detail.
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Dyall, Kenneth G. y Knut Faegri. "One-Electron Atoms". En Introduction to Relativistic Quantum Chemistry. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195140866.003.0012.
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The development of quantum chemistry, that is, the solution of the Schrödinger equation for molecules, is almost exclusively founded on the expansion of the molecular electronic wave function as a linear combination of atom-centered functions, or atomic orbitals—the LCAO approximation. These orbitals are usually built up out of some set of basis functions. The properties of the atomic functions at large and small distances from the nucleus determines to a large extent what characteristics the basis functions must have, and for this purpose it is sufficient to examine the properties of the hydrogenic solutions to the Schrödinger equation. If we are to do the same for relativistic quantum chemistry, we should first examine the properties of the atomic solutions to determine what kind of basis functions would be appropriate. However, the atomic solutions of the Dirac equation provide more than merely a guide to the choice of basis functions. The atoms in a molecule retain their atomic identities to a very large extent, and the modifications caused by the molecular field are quite small for most properties. In order to arrive at a satisfactory description of the relativistic effects in molecules, we must first of all be able to treat these effects at the atomic level. The insight gained into the effects of relativity on atomic structure is therefore a necessary and useful starting point for relativistic quantum chemistry. As in the nonrelativistic case, most of the salient features of the atomic systems are exposed in the treatment of the simplest of these, the hydrogen-like one-electron atoms. In Hartree atomic units the time-independent Dirac equation yields the coupled equations where we have shifted the energy by −mc2 (with m = 1), as discussed in section 4.6. We will use this shifted energy scale for the rest of the book unless otherwise explicitly indicated. V is here a scalar, central potential.
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Pink, David A., M. Shajahan G. Razul, T. Gordon, B. Quinn y A. J. MacDonald. "Computer Simulation Techniques for Modelling Statics and Dynamics of Nanoscale Structures". En Edible Nanostructures, 230–99. The Royal Society of Chemistry, 2014. http://dx.doi.org/10.1039/bk9781849738958-00230.
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This chapter describes computer simulation techniques that are used to model the statics and dynamics of nanoscale structures and their self-organized assemblies via their physical interactions. We describe some models which cannot be enabled without employing computer simulation but do not explicitly address models such as self-consistent field approaches or DLVO theory. The chapter is divided into four sections: introduction and background, atomic scale molecular dynamics, coarse-grained modelling and stochastic processes, and fluid flow. It is introduced via brief descriptions of protein folding and crystalline microscale structures in edible oils. A brief background to important aspects of statistical mechanics is followed by a description of atomic scale molecular dynamics. The spatial scale is then expanded and coarse-graining of atomic interactions is described. This leads into nanoscale systems and stochastic processes, and we describe the various applications of Monte Carlo techniques. The fourth section deals with fluid flow and we describe dissipative particle dynamics and, to a lesser extent, lattice-Boltzmann theory. In all sections we give steps to follow (recipes) in using these techniques. In addition, we give one or two examples of modelling and how computer simulation was used. Although our choices of methods and examples reflect our principal interests, we are not pushing for the use of one technique rather than another. We describe techniques which either continue to play fundamental roles in computer simulation of soft matter and fluids or are newer developments which have shown increased use in the last decade.
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Netzer, Falko P. y Claudine Noguera. "Methods of study". En Oxide Thin Films and Nanostructures, 39–83. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198834618.003.0003.
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The experimental and theoretical characterization of oxide nanostructures is addressed. The experimental techniques are classified according to their information content, revealing atomic geometry, chemical composition, electronic structure as well as magnetic, vibrational and chemical properties. Due to the nanometer scale dimensions of oxide nanosystems, many experimental techniques are derived fom the field of surface science and involve ultrahigh vacuum technology. The quantum-theoretical simulations for the description of oxide materials are presented by progressing from simple to increasingly sophisticated methods; the latter become necessary to accurately treat electron correlation effects, which are significant in many oxide materials, in particular at low dimension. Electronic structure methods, total energy methods and atomic structure simulation methods are introduced and discussed.
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Batterman, Robert W. "Hydrodynamics". En A Middle Way, 49–66. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780197568613.003.0003.
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This chapter begins the argument that the best way to understand the relations of relative autonomy between theories at different scales is through a mesoscale hydrodynamic description of many-body systems. It focuses on the evolution of conserved quantities of those systems in near, but out of equilibrium states. A relatively simple example is presented of a system of spins where the magnetization is the conserved quantity of interest. The chapter introduces the concepts of order parameters, of local quantities, and explains why we should be focused on the gradients of densities that inhabit the mesoscale between the scale of the continuum and that of the atomic. It introduces the importance of correlation functions and linear response.
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Janin, Joël. "Challenges in structural molecular biology: genomics in three dimensions". En Structure and Dynamics of Biomolecules: Neutron and Synchrotron Radiation for Condensed Matter Studies, 3–13. Oxford University PressOxford, 2000. http://dx.doi.org/10.1093/oso/9780198504535.003.0001.
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Abstract Challenges are the daily bread of science. Research is all about creating new knowledge, new ways of understanding and mastering the world around us. Structural molecular biology is even more so, as a relatively new and fast moving field of investigation. Its specific aim is to give a description of biological macromolecules and their assemblies at the atomic level, and to relate their structure to the many elaborate functions they perform in cells and organisms. The founding example, arguably still the best example of a structure that explains a function, is the DNA double helix discovered by Jim Watson and Francis Crick in 1953 (Watson and Crick 1953). Their discovery entirely changed biology, and the consequences are still far from exhausted. A few years after the double helix, Max Perutz and John Kendrew found the haemoglobin structure (Perutz et al. 1959) and established X-ray crystallography as the major tool for determining macromolecular structures at the atomic level. At the end of this century, crystallography has been joined by electron microscopy and high resolution nuclear magnetic resonance (NMR). The three techniques have different capacities and limitations, they complement each other and, together, they strive to meet new challenges. One of these is to tackle larger and larger objects and to make structural biology progress upwards from the angstrom (A) scale of the atom to the micrometre (pm) scale of cells, where optical microscopy can take over. In specific cases, X-ray crystallography almost reaches there, as it has succeeded in solving the atomic structure of viruses nearly 1000 A, or 0.1 pm, in diameter. Still, viruses are best studied by the very powerful combination of crystallography and electron microscopy pioneered by Aaron Klug (1983) and now extended to macromolecular assemblies such as the ribosome or the cell membrane. In general, large structures are being approached by crystallography in parallel with other techniques, among which near-field microscopies may become important contributors in coming years.
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Lindsay, S. M. "Microscopy and manipulation tools". En Introduction to Nanoscience, 135–77. Oxford University PressOxford, 2009. http://dx.doi.org/10.1093/oso/9780199544202.003.0004.
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Abstract This chapter describes the important imaging and manipulation tools without which Nanoscience would be impossible. We begin with a description of the scanning tunneling microscope (STM; Section 4.1) because this was the first instrument that made the manipulation of single atoms feasible. Atomic scale imaging had been possible (using electron microscopes) for some time before the STM was invented, but the ease of operation and construction of STMs popularized Nanoscience and Nanotechnology. The STM has largely been superseded by its close relation, the atomic force microscope (AFM), because the AFM is capable of imaging insulating surfaces and therefore has a more general set of applications (Section 4.2). The AFM also enabled the measurement of the mechanical properties of individual molecules, and this application to single molecule force measurements is also reviewed here (Section 4.2.6). Despite these enormous advances in scanning probe microscopy, the electron microscope still offers the most accurate measurement of many nanoscale structures and we review some aspects of electron microscopy in Section 4.3. At around the same time that the AFM was becoming popular, the optics community began to develop techniques and dyes for fluorescent imaging of single molecules (Section 4.4). These methods broke the classical limits on optical resolution, allowing particles to be located with nanometer accuracy in optical images. The new optical methods also enabled new approaches to measuring motion at a single molecule level. The discovery that small particles could be manipulated with a light beam also occurred in this time frame (the mid-1980s), leading to the development of devices that manipulate single molecules attached to small particles (Section 4.5). Methods for the direct imaging of nanostructures and the measurement of their mechanical properties and their fluctuations have undergone a dramatic revolution in the past 20 years.
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Nitzan, Abraham. "Introduction To Liquids". En Chemical Dynamics in Condensed Phases. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198529798.003.0010.
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The statistical mechanics of atomic motion in gases and solids have convenient starting points. For gases it is the ideal gas limit where intermolecular interactions are disregarded. In solids, the equilibrium structure is pre-determined, the dynamics at normal temperature is characterized by small amplitude motions about this structure and the starting point for the description of such motions is the harmonic approximation that makes it possible to describe the system in terms of noninteracting normal modes (phonons). Liquids are considerably more difficult to describe on the atomic/molecular level: their densities are of the same order as those of the corresponding solids, however, they lack symmetry and rigidity and, with time, their particles execute large-scale motions. Expansion about a noninteracting particle picture is therefore not an option for liquids. On the other hand, with the exclusion of low molecular mass liquids such as hydrogen and helium, and of liquid metals where some properties are dominated by the conduction electrons, classical mechanics usually provides a reasonable approximation for liquids at and above room temperature. For such systems concepts from probability theory (see Section 1.1.1) will be seen to be quite useful. This chapter introduces the reader to basic concepts in the theory of classical liquids. It should be emphasized that the theory itself is general and can be applied to classical solids and gases as well, as exemplified by the derivation of the virial expansion is Section 5.6 below. We shall limit ourselves only to concepts and methods needed for the rest of our discussion of dynamical processes in such environments.
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"Scattering in Three Dimensions". En Quantum Mechanics Classical Results, Modern Systems, and Visualized Examples, editado por Richard W. Robinett, 596–635. Oxford University PressOxford, 2006. http://dx.doi.org/10.1093/oso/9780198530978.003.0019.
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Abstract While much of our knowledge of the microscopic world has been gleaned from bound state problems (e.g. the spectroscopy of atoms, molecules, nuclei, etc.), scattering experiments have also provided a wealth of information on the nature of the constituents of matter and their interactions on atomic scales and below.É Because much of the formalism of scattering is similar in the classical and quantum formulations, we begin by discussing some generalities shared by the two descriptions.
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Batterman, Robert W. "Introduction". En A Middle Way, xiv—25. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780197568613.003.0001.
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This chapter introduces a conception of the relative autonomy of upper-scale, continuum theories from lower-scale more fundamental molecular and atomic theories. It contrasts a notion of foundational philosophical problems with an understanding of autonomy and fundamentality. It lays out the key ingredients required to argue for a middle-out, mesoscale approach to many-body systems, including hydrodynamic descriptions, representative volume elements, and fluctuation and dissipation.
Actas de conferencias sobre el tema "Atomic scale description"
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Martel, Sylvain M., Lorenzo Cervera Olague, Juan Bautista Coves Ferrando, Stefen Riebel, Torsten Koker, Jeremy Suurkivi, Timothy Fofonoff, Mark Sherwood, Robert Dyer y Ian W. Hunter. "General description of the wireless miniature NanoWalker robot designed for atomic-scale operations". En Intelligent Systems and Advanced Manufacturing, editado por Bradley J. Nelson y Jean-Marc Breguet. SPIE, 2001. http://dx.doi.org/10.1117/12.444130.
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Glasgow, S., P. Meystre y N. Wilkens. "Doppleron-catalyzed Bragg resonances in atom optics". En OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.tuaaa4.
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Effective atomic beam splitters providing large scattering angles are central to atom optics and atom interferometry. Their most common optical realization relies on first-order Bragg scattering, which generates a splitting of the atomic wave function in momentum space. For typical atomic beam velocities of the order of 100 m/s, 2ħk produces very small scattering angles. Higher-order Bragg scattering is of questionable practicality, because of the need for atom–field interaction times that scale exponentially with the scattering order. Attempts at solving this problem include the introduction of multiple laser beams, the use of three-level transition schemes, and the application of velocity-tuned, or Doppleron, resonances. We present a novel scheme that uses a Doppleron resonance as a catalyst to speed up a high-order Bragg resonance by orders of magnitude. This effect occurs when the atom–field frequency detuning is such that the Bragg resonance and the Doppleron resonance become degenerate. Alternatively, in the band-theoretical description of the near-resonant Kapitza–Dirac effect, the Doppleron resonance is required to occur either at the center or at the boundary of the first Brillouin zone.
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Ji, Pengfei, Mengzhe He, Yiming Rong, Yuwen Zhang y Yong Tang. "Multiscale Investigation of Thickness Dependent Melting Thresholds of Nickel Film Under Femtosecond Laser Heating". En ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-86947.
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A multiscale modeling that integrates electronic scale ab initio quantum mechanical calculation, atomic scale molecular dynamics simulation, and continuum scale two-temperature model description of the femtosecond laser processing of nickel film at different thicknesses is carried out in this paper. The electron thermophysical parameters (heat capacity, thermal conductivity, and electron-phonon coupling factor) are calculated from first principles modeling, which are further substituted into molecular dynamics and two-temperature model coupled energy equations of electrons and phonons. The melting thresholds for nickel films of different thicknesses are determined from multiscale simulation. Excellent agreement between results from simulation and experiment is achieved, which demonstrates the validity of modeled multiscale framework and its promising potential to predict more complicate cases of femtosecond laser material processing. When it comes to process nickel film via femtosecond laser, the quantitatively calculated maximum thermal diffusion length provides helpful information on choosing the film thickness.
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Qian, Dong y Qingjin Zheng. "Coarse-Grained Modeling and Simulation of Nanoscale Systems Based on Discrete Hyper-Elastic Model". En ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-68088.
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The subject of developing equivalent continuum models from the atomistic models has attracted significant attention in recent years. An outstanding issue in extending the continuum model to smaller scales is the size effect. Such a size effect is intimately related to the discrete nature of the atomic structure and nonlocal interaction among the atoms. In many of the existing continuum approaches, discrete variables are introduced in the constitutive model to account for these non-continuum effects. In this paper, we present a discrete hyperelasticity model as an alternative. Our approach, however, is fundamentally different from the conventional approach in that it treats the concept of deformation mapping in the discrete sense. The resulting deformation measure is referred to as spatial secant and the corresponding material model is called the spatial secant model. We then formulate the potential energy density functional and derive stress-like measure based on the spatial secant. After a brief description on the formulation and its comparison with the classical hyper-elastic model, we show the application of this model to both low-dimensional carbon nanostructures and general three-dimensional nanostructures. The concept of geometric-exact mapping is discussed through the examples. Comparisons with full-scale molecular mechanics simulations are made to illustrate the robustness of this approach.
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Kogut, L. y K. Komvopoulos. "Adhesion Analysis for MEMS Based on Electrical Contact Resistance Measurements". En STLE/ASME 2003 International Joint Tribology Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/2003-trib-0271.
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Because adhesion forces are especially important at the submicron scale, they play a dominant role in several fields of nanotechnology, such as biology, atomic force microscope (AFM) imaging, magnetic disk drives, and microelectromechanical systems (MEMS). The profound importance of adhesion forces in MEMS has been the principal theme of several studies. A common approach for measuring the surface energy is based on balancing the elastic energy stored in microcantilever beams partially adhered to substrates with the work of adhesion, assumed equal to the surface energy multiplied by the apparent area of the attached beam length. However, because the apparent contact area is significantly larger than the real contact area and the elastic energy stored in the deformed asperity microcontacts is neglected, this traditional method may greatly underestimate the interfacial adhesion energy. Consequently, the objective of this study was to develop a method for determining indirectly adhesion forces and adhesion energies form relatively simple in situ electrical contact resistance (ECR) measurements. The method presented herein is based on a theoretical treatment of the ECR encountered during contact of isotropic, conductive, rough surfaces, using multi-scale fractal description of the equivalent surface topography, constitutive contact relations for elastic-perfectly plastic asperity microcontacts, and size-dependent constriction resistance of microcontacts. Results are presented for the adhesion force and adhesion energy in terms of ECR for different surface topographies.
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Khan, M. M., G. Zatzman y M. R. Islam. "The Formulation of a Comprehensive Mass and Energy Balance Equation". En ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-69171.
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Nanotechnologies are considered to be the driver of the Information-Age engineering. Recent discoveries in practically all aspects of engineering developments indicate that properties at nano-levels are starkly different from properties at bulk levels. These discoveries signal great potentials for nanotechnologies that can revolutionize all technologies, ranging from medicine to energy. However, the same discoveries also point to the fact that conventional laws and theories that have enjoyed long-standing confidence of the scientific community do not apply to nanotechnologies. In absence of such laws that describe nano-scale phenomena, it is difficult if not impossible to predict long-term impacts of nanotechnologies. This paper presents a comprehensive formulation of mass and energy balance equations. This formulation gives rise to a unique set of equations that apply to both nano- and bulk scale natural phenomena. The formulation is based on momentum balance, which is preserved at all scales, ranging from cosmic to nano- and even the inter-atomic level. Although Newton posited gravitation as a universally acting force, we now know that electromagnetic forces predominate in matter at the nano or inter-atomic level. Electromagnetic forces, like frictional forces, however, can exist and persist without ever having been externally applied. Reasoning thus “by exhaustion”, Newton’s Three Laws of Motion plus the principle of universal gravitation are actually special cases of “something else”. That “something else” is far more general, viz., the universal preservation of mass-energy balance and conservation of momentum. The connecting element of this universal balance is that motion is the mode of existence of all matter. This renders time a characteristic of matter itself within the overall context of mass-energy-momentum conservation. In other words, time ceases to be mainly or only a derivative of some spatial displacement of matter. In this way, it becomes possible at last to treat time, consistently, as a true fourth dimension — and no longer as merely the independent variable. This description is consistent with Einstein’s revolutionary relativity theory, but does not rely on Maxwell’s equations as the starting point. The resulting equation is shown to be continuous in time, thereby allowing transition from mass to energy. As a result a single governing equation emerges. This equation is solved for a number of cases and is shown to be successful in discerning between various natural and artificial sources of mass and energy. With this equation, the difference between chemical and organic fertilizers, microwave and wood stove heating, and sunlight and fluorescent light can be made with unprecedented clarity. By applying this equation, a complete pathway analysis of nanomaterials is made and it is shown that engineering at nano-scale will have long-term impacts. This analysis would not be possible with conventional techniques. Finally, analysis results are shown for a number of energy- and material-related prospects.
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Park, Pilyeon, Mirna Urquidi-Macdonald y Digby D. Macdonald. "Application of the PDM (Point Defect Model) to the Oxidation of Zircaloy Fuel Cladding in Water-Cooled Nuclear Reactors". En 12th International Conference on Nuclear Engineering. ASMEDC, 2004. http://dx.doi.org/10.1115/icone12-49098.
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The PDM [Point Defect Model, D. D. Macdonald, Pure Appl. Chem., 71, 951 (1999)] describes the corrosion of passive metals in aqueous media in terms of the generation and annihilation of point defects at the passive film interfaces. In the current work, we have modified the PDM to provide a comprehensive, atomic scale description of the growth of bilayer passive films on zirconium to simulate the corrosion of Zircaloy fuel cladding in BWRs and PWRs under high burn-up conditions. Two models have been formulated; one comprising a hydride inner (barrier) layer and an oxide outer layer and other comprising an oxide inner layer and an oxide outer layer for PWR and BWR cladding, respectively. Since there are currently no experimental data for the kinetics of defect generation and annihilation at the passive film interfaces for Zircaloys under PWR/BWR conditions, of the type that are required for this analysis, this paper focuses only on exploring and predicting trends in the corrosion behavior of Zircaloy by using prototypical values for various electrochemical parameters. We derive equations for predicting the barrier layer thickness as a function of the applied voltage, pH, porosity, and temperature for both BWR and PWR primary water chemistry conditions.
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Moinereau, Dominique, Ste´phane Chapuliot, Ste´phane Marie y Philippe Gilles. "NESC VII: A European Project for Application of WPS in RPV Assessment Including Biaxial Loading". En ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/pvp2010-25399.
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The Reactor Pressure Vessel (RPV) is an essential component liable to limit the lifetime duration of PWR plants. The assessment of defects in RPV subjected to PTS transients made at a European level do not necessarily take into account the beneficial effect of load history (warm pre-stress WPS) on the resistance of RPV material regarding the risk of brittle failure. A 4-year European Research & Development program — SMILE — was successfully conducted between 2002 and 2005 as part of the 5th Framework of the European Atomic Energy Community (EURATOM). The objective of the SMILE project (‘Structural Margin Improvements in aged-embrittled RPV with Load history Effects’) was to provide sufficient evidence in order to demonstrate, to model and to validate the beneficial WPS effect in a RPV integrity assessment. Numerous experimental, analytical and numerical results have been obtained which confirm the beneficial effect of warm pre-stress on RPV steels, with an effective significant increase of the material resistance regarding the risk of brittle failure. In addition to SMILE, a new project dealing with WPS — NESC VII — has been launched in 2008 (linking with the European Network of Excellence NULIFE) with the participation of numerous international organizations (R&D, Utilities and Manufacturers). Based on experimental, analytical and numerical tasks, the project is focused on topics generally not covered by past experience on WPS: biaxiality of loading on large-scale specimens, effect of irradiation, applicability to intergranular fracture, modeling (including analytical and numerical models) … Among these tasks, some new novel WPS experiments are being conducted on large scale cruciform bend bar specimens in order to study the influence of biaxial loading on WPS effect, using a fully representative RPV steel (18MND5 steel similar to A533B steel). After a synthesis of main WPS results available from previous projects on representative RPV steels, a description of the NESC VII project is presented in this paper together with the corresponding organization, including the present status of the project.
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Rajan, K. K., G. Vijayakumar, S. Chandramouli, K. Madhusoodhanan, P. Kalyanasundaram y G. Vaidyanathan. "Experimental Evaluation of Wire Type Leak Detector Layout for Prototype Fast Breeder Reactor (PFBR)". En 17th International Conference on Nuclear Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/icone17-75822.
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Wire type leak detectors working on conductivity principle are used for detecting sodium leak in the secondary sodium circuits of FBRs. It is required to assess the performance of these detectors and confirm that they are meeting the requirements. A test facility by name LEENA was constructed at Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam to test the wire type leak detector lay out by simulating sodium leaks of different rates. This test facility consists of a sodium dump tank, a test vessel, interconnecting pipelines with valves, micro filter and test section with leak simulators. There are three different test sections in the test set up of length 1000 mm each. These test sections simulate piping of Prototype Fast Breeder Reactor (PFBR) secondary circuit and the leak detector layout in full scale. All test sections are provided with leak simulator. A leak simulator consists of a hole of size one mm drilled in the test section and closed with a tapered pin. The pin position is adjusted by a screw mechanism and there by the annular gap of flow area is varied for getting different leak rates. Test facility was commissioned and 20 experiments were attempted at 350°C to 550°C. Out of 20 experiments 11 experiments were successfully completed and 9 experiments were terminated in between due to the choke in the simulator hole. From the experimental data it is found that sodium leak rate of 200 g/h and above can be detected within 6 hours. A relationship between leak rate and detection time was established from the experimental results and found that sodium leak rate of 100g/h is likely to be detected in 11.4 hours. This paper deals with the details of wire type leak detector layout for the secondary sodium circuit of PFBR, performance requirement of leak detection system as per codes, description of test facility, experimental procedure and test results. Paper also reviews the experiment conducted in CEA, Cadrache and compares with results of present experimental study.
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Gurol, Sam y Bob Baldi. "Overview of the General Atomics Urban Maglev Technology Development Program". En ASME/IEEE 2004 Joint Rail Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/rtd2004-66031.
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General Atomics is developing Urban Maglev technology sponsored by the Federal Transit Administration and funded under the Transportation Equity Act for the 21st Century (TEA-21). The system is levitated, propelled, and guided by electromagnetic forces. Levitation is achieved by using simple, passive permanent magnets arranged in a “Halbach” array configuration. Propulsion, and guidance are achieved by a linear synchronous motor mounted on the track. The uniqueness of the approach is its simplicity, ruggedness, and performance, including 10% grade, 18.3 m (60 ft.) turn radius, one-inch levitation gap, and quiet operation. Use of elevated guideways, coupled with the quiet operation of the system, eliminates the need to tunnel underground for noise-abatement, and can result in significantly lower system costs. We have built full-scale hardware to demonstrate the levitation, propulsion, guidance, and location detection systems. We are currently building a 120 m (400 ft.) test track with a full-scale chassis and power system at General Atomics in San Diego, CA. The chassis and power systems have already been built and are under-going initial testing. The track will be completed for dynamic testing in 2004. This paper reports on the overall program progress to date and description of the planned testing.