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Perez, Alejandro, Salvatore Ribisi i Sami Viollet. "Modeling Quantum Particles Falling into a Black Hole: The Deep Interior Limit". Universe 9, nr 2 (31.01.2023): 75. http://dx.doi.org/10.3390/universe9020075.
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In this paper, we construct a solvable toy model of the quantum dynamics of the interior of a spherical black hole with falling spherical scalar field excitations. We first argue about how some aspects of the quantum gravity dynamics of realistic black holes emitting Hawking radiation can be modeled using Kantowski–Sachs solutions with a massless scalar field when one focuses on the deep interior region r≪M (including the singularity). Further, we show that in the r≪M regime, and in suitable variables, the KS model becomes exactly solvable at both the classical and quantum levels. The quantum dynamics inspired by loop quantum gravity is revisited. We propose a natural polymer quantization where the area a of the orbits of the rotation group is quantized. The polymer (or loop) dynamics is closely related to the Schroedinger dynamics away from the singularity with a form of continuum limit naturally emerging from the polymer treatment. The Dirac observable associated with the mass is quantized and shown to have an infinite degeneracy associated with the so-called ϵ-sectors. Suitable continuum superpositions of these are well-defined distributions in the fundamental Hilbert space and satisfy the continuum Schroedinger dynamics.
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Góamez-Jeria, J. S., J. Parra-Mouchet i D. Morales-Lagos. "Quantum-Chemical modeling of catecholamine storage including continuum solvent effects". International Journal of Quantum Chemistry 40, nr 3 (wrzesień 1991): 299–304. http://dx.doi.org/10.1002/qua.560400303.
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Zolochevsky, Alexander, Sophia Parkhomenko i Alexander Martynenko. "Quantum, molecular and continuum modeling in nonlinear mechanics of viruses". 44, nr 44 (13.04.2022): 5–34. http://dx.doi.org/10.26565/2313-6693-2022-44-01.
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Introdution. Viruses are a large group of pathogens that have been identified to infect animals, plants, bacteria and even other viruses. The 2019 novel coronavirus SARS-CoV-2 remains a constant threat to the human population. Viruses are biological objects with nanometric dimensions (typically from a few tens to several hundreds of nanometers). They are considered as the biomolecular substances composed of genetic materials (RNA or DNA), protecting capsid proteins and sometimes also of envelopes. Objective. The goal of the present review is to help predict the response and even destructuration of viruses taking into account the influence of different environmental factors, such as, mechanical loads, thermal changes, electromagnetic field, chemical changes and receptor binding on the host membrane. These environmental factors have significant impact on the virus. Materials and methods. The study of viruses and virus-like structures has been analyzed using models and methods of nonlinear mechanics. In this regard, quantum, molecular and continuum descriptions in virus mechanics have been considered. Application of single molecule manipulation techniques, such as, atomic force microcopy, optical tweezers and magnetic tweezers has been discussed for a determination of the mechanical properties of viruses. Particular attention has been given to continuum damage–healing mechanics of viruses, proteins and virus-like structures. Also, constitutive modeling of viruses at large strains is presented. Nonlinear elasticity, plastic deformation, creep behavior, environmentally induced swelling (or shrinkage) and piezoelectric response of viruses were taken into account. Integrating a constitutive framework into ABAQUS, ANSYS and in-house developed software has been discussed. Conclusion. Link between virus structure, environment, infectivity and virus mechanics may be useful to predict the response and destructuration of viruses taking into account the influence of different environmental factors. Computational analysis using such link may be helpful to give a clear understanding of how neutralizing antibodies and T cells interact with the 2019 novel coronavirus SARS-CoV-2.
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ROTKIN, SLAVA V., VAISHALI SHRIVASTAVA, KIRILL A. BULASHEVICH i N. R. ALURU. "ATOMISTIC CAPACITANCE OF A NANOTUBE ELECTROMECHANICAL DEVICE". International Journal of Nanoscience 01, nr 03n04 (czerwiec 2002): 337–46. http://dx.doi.org/10.1142/s0219581x02000279.
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An atomistic capacitance is derived for a single-wall carbon nanotube in a nano-electromechanical device. Multi-scale calculation is performed using a continuum model for the geometrical capacitance, and statistical and quantum mechanical approaches for the quantum capacitance of the nanotube. The geometrical part of the capacitance is studied in detail using full three-dimensional electrostatics. Results reported in this paper are useful for compact modeling of the electronic and electromechanical nanotube devices.
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SHAFEI, SHORESH, i MARK G. KUZYK. "THE EFFECT OF EXTREME CONFINEMENT ON THE NONLINEAR-OPTICAL RESPONSE OF QUANTUM WIRES". Journal of Nonlinear Optical Physics & Materials 20, nr 04 (grudzień 2011): 427–41. http://dx.doi.org/10.1142/s0218863511006224.
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This work focuses on understanding the nonlinear-optical response of a 1-D quantum wire embedded in 2-D space when quantum-size effects in the transverse direction are minimized using an extremely weighted delta function potential. Our aim is to establish the fundamental basis for understanding the effect of geometry on the nonlinear-optical response of quantum loops that are formed into a network of quantum wires. It is shown that in the limit of full confinement, the sum rules are obeyed when the transverse infinite-energy continuum states are included. While the continuum states associated with the transverse wavefunction do not contribute to the nonlinear optical response, they are essential to preserving the validity of the sum rules. This work is a building block for future studies of nonlinear-optical enhancement of quantum graphs (which include loops and bent wires) based on their geometry. These properties are important in quantum mechanical modeling of any response function of quantum-confined systems, including the nonlinear-optical response of any system in which there is confinement in at least one dimension, such as nanowires, which provide confinement in two dimensions.
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Norjmaa, Gantulga, Gregori Ujaque i Agustí Lledós. "Beyond Continuum Solvent Models in Computational Homogeneous Catalysis". Topics in Catalysis 65, nr 1-4 (16.11.2021): 118–40. http://dx.doi.org/10.1007/s11244-021-01520-2.
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AbstractIn homogeneous catalysis solvent is an inherent part of the catalytic system. As such, it must be considered in the computational modeling. The most common approach to include solvent effects in quantum mechanical calculations is by means of continuum solvent models. When they are properly used, average solvent effects are efficiently captured, mainly those related with solvent polarity. However, neglecting atomistic description of solvent molecules has its limitations, and continuum solvent models all alone cannot be applied to whatever situation. In many cases, inclusion of explicit solvent molecules in the quantum mechanical description of the system is mandatory. The purpose of this article is to highlight through selected examples what are the reasons that urge to go beyond the continuum models to the employment of micro-solvated (cluster-continuum) of fully explicit solvent models, in this way setting the limits of continuum solvent models in computational homogeneous catalysis. These examples showcase that inclusion of solvent molecules in the calculation not only can improve the description of already known mechanisms but can yield new mechanistic views of a reaction. With the aim of systematizing the use of explicit solvent models, after discussing the success and limitations of continuum solvent models, issues related with solvent coordination and solvent dynamics, solvent effects in reactions involving small, charged species, as well as reactions in protic solvents and the role of solvent as reagent itself are successively considered.
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Jirauschek, Christian, Alpar Matyas i Paolo Lugli. "Modeling bound-to-continuum terahertz quantum cascade lasers: The role of Coulomb interactions". Journal of Applied Physics 107, nr 1 (styczeń 2010): 013104. http://dx.doi.org/10.1063/1.3276160.
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Cédola, A. P., D. Kim, A. Tibaldi, M. Tang, A. Khalili, J. Wu, H. Liu i F. Cappelluti. "Physics-Based Modeling and Experimental Study of Si-Doped InAs/GaAs Quantum Dot Solar Cells". International Journal of Photoenergy 2018 (2018): 1–10. http://dx.doi.org/10.1155/2018/7215843.
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This paper presents an experimental and theoretical study on the impact of doping and recombination mechanisms on quantum dot solar cells based on the InAs/GaAs system. Numerical simulations are built on a hybrid approach that includes the quantum features of the charge transfer processes between the nanostructured material and the bulk host material in a classical transport model of the macroscopic continuum. This allows gaining a detailed understanding of the several physical mechanisms affecting the photovoltaic conversion efficiency and provides a quantitatively accurate picture of real devices at a reasonable computational cost. Experimental results demonstrate that QD doping provides a remarkable increase of the solar cell open-circuit voltage, which is explained by the numerical simulations as the result of reduced recombination loss through quantum dots and defects.
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Szefer, G., i D. Jasińska. "Modeling of strains and stresses of material nanostructures". Bulletin of the Polish Academy of Sciences: Technical Sciences 57, nr 1 (1.03.2009): 41–46. http://dx.doi.org/10.2478/v10175-010-0103-6.
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Modeling of strains and stresses of material nanostructuresStress and deformation analysis of materials and devices at the nanoscale level are topics of intense research in materials science and mechanics. In these investigations two approaches are observed. First, natural for the atomistic scale description is based on quantum and molecular mechanics. Second, characteristic for the macroscale continuum model description, is modified by constitutive laws taking atomic interactions into account. In the present paper both approaches are presented. For a discrete system of material points (atoms, molecules, clusters), measures of strain and stress, important from the mechanical viewpoint, are given. Numerical examples of crack propagation and deformation of graphite sheets (graphens) illustrate the behavior of the discrete systems.
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Zhang, Yang, Trithep Devakul i Liang Fu. "Spin-textured Chern bands in AB-stacked transition metal dichalcogenide bilayers". Proceedings of the National Academy of Sciences 118, nr 36 (2.09.2021): e2112673118. http://dx.doi.org/10.1073/pnas.2112673118.
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While transition-metal dichalcogenide (TMD)–based moiré materials have been shown to host various correlated electronic phenomena, topological states have not been experimentally observed until now [T. Li et al., Quantum anomalous Hall effect from intertwined moiré bands. arXiv [Preprint] (2021). https://arxiv.org/abs/2107.01796 (Accessed 5 July 2021)]. In this work, using first-principle calculations and continuum modeling, we reveal the displacement field–induced topological moiré bands in AB-stacked TMD heterobilayer MoTe2/WSe2. Valley-contrasting Chern bands with nontrivial spin texture are formed from interlayer hybridization between MoTe2 and WSe2 bands of nominally opposite spins. Our study establishes a recipe for creating topological bands in AB-stacked TMD bilayers in general, which provides a highly tunable platform for realizing quantum-spin Hall and interaction-induced quantum anomalous Hall effects.
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Husain, Mudassir M., i Maneesh Kumar. "First-Principles Modeling of the Smallest Molecular Single Electron Transistor". Journal of Atomic, Molecular, Condensate and Nano Physics 2, nr 1 (30.07.2015): 33–39. http://dx.doi.org/10.26713/jamcnp.v2i1.270.
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Using first-principles method the charging energy has been calculated; of the smallest single electron transistor (SET) consisting of only two carbon atoms while operating in coulumb blockade regime. The ethyne (C2H2) molecule is acting like a quantum dot (with discrete energy levels) and is weakly coupled to the gold electrodes (continuum). The quantum effects are significant and the conduction of current takes place through incoherent method via electron tunneling. The electronic levels of the molecule determine the electron transport properties. The molecule may be in several charged states from +2 to -2. It has been observed that the HOMO-LUMO gap is strongly reduced in solid state environment with metallic electrodes, as compared to the vacuum. This reduction is attributed to the image charges generated in the source and drain electrodes. This results in strong localization of charges in the molecule, a phenomenon addressed earlier. The charging energy has been calculated in vacuum and in SET environment. The interaction between molecule and the electrodes is treated self-consistently through Poisson equation. The charge stability diagram of the smallest molecular SET has been obtained.
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Gevorkyan, Ashot S., Alexander V. Bogdanov i Vladimir V. Mareev. "Hidden Dynamical Symmetry and Quantum Thermodynamics from the First Principles: Quantized Small Environment". Symmetry 13, nr 8 (23.08.2021): 1546. http://dx.doi.org/10.3390/sym13081546.
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Evolution of a self-consistent joint system (JS), i.e., a quantum system (QS) + thermal bath (TB), is considered within the framework of the Langevin–Schrödinger (L-Sch) type equation. As a tested QS, we considered two linearly coupled quantum oscillators that interact with TB. The influence of TB on QS is described by the white noise type autocorrelation function. Using the reference differential equation, the original L-Sch equation is reduced to an autonomous form on a random space–time continuum, which reflects the fact of the existence of a hidden symmetry of JS. It is proven that, as a result of JS relaxation, a two-dimensional quantized small environment is formed, which is an integral part of QS. The possibility of constructing quantum thermodynamics from the first principles of non-Hermitian quantum mechanics without using any additional axioms has been proven. A numerical algorithm has been developed for modeling various properties and parameters of the QS and its environment.
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Choi, YongMan, David S. Mebane, Jeng-Han Wang i Meilin Liu. "Continuum and Quantum-Chemical Modeling of Oxygen Reduction on the Cathode in a Solid Oxide Fuel Cell". Topics in Catalysis 46, nr 3-4 (28.11.2007): 386–401. http://dx.doi.org/10.1007/s11244-007-9011-x.
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Saputra, Andrian, Karna Wijaya, Ria Armunanto, Lisa Tania i Iqmal Tahir. "Determination of Effective Functional Monomer and Solvent for R(+)-Cathinone Imprinted Polymer Using Density Functional Theory and Molecular Dynamics Simulation Approaches". Indonesian Journal of Chemistry 17, nr 3 (30.11.2017): 516. http://dx.doi.org/10.22146/ijc.24311.
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Determination of effective functional monomer and solvent for R(+)-cathinone imprinted polymer through modeling has been done using density functional theory (DFT) and molecular dynamics (MD) simulation approaches. The selection criteria of the best monomer and solvent are based on the classical potential energy (ΔEMM) from molecular dynamics simulation and confirmed further by quantum potential energy (ΔEDFT) from DFT calculation. The DFT calculation was performed in B3LYP exchange-correlation functional within the 6-31G(d) basis set of function including Polarizable Continuum Model (PCM) solvation effect. From this research, it is obtained that N,N’-methylene bis acrylamide and chloroform are respectively the best candidates for effective functional monomer and solvent, for the synthesis of R(+)-cathinone imprinted polymer.
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Shenderovich, Ilya G., i Gleb S. Denisov. "Modeling of Solute-Solvent Interactions Using an External Electric Field—From Tautomeric Equilibrium in Nonpolar Solvents to the Dissociation of Alkali Metal Halides". Molecules 26, nr 5 (26.02.2021): 1283. http://dx.doi.org/10.3390/molecules26051283.
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An implicit account of the solvent effect can be carried out using traditional static quantum chemistry calculations by applying an external electric field to the studied molecular system. This approach allows one to distinguish between the effects of the macroscopic reaction field of the solvent and specific solute–solvent interactions. In this study, we report on the dependence of the simulation results on the use of the polarizable continuum approximation and on the importance of the solvent effect in nonpolar solvents. The latter was demonstrated using experimental data on tautomeric equilibria between the pyridone and hydroxypyridine forms of 2,6-di-tert-butyl-4-hydroxy-pyridine in cyclohexane and chloroform.
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Zheng, Fang, i Chang-Guo Zhan. "Computational Modeling of Solvent Effects on Protein-Ligand Interactions Using Fully Polarizable Continuum Model and Rational Drug Design". Communications in Computational Physics 13, nr 1 (styczeń 2013): 31–60. http://dx.doi.org/10.4208/cicp.130911.121011s.
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AbstractThis is a brief review of the computational modeling of protein-ligand interactions using a recently developed fully polarizable continuum model (FPCM) and rational drug design. Computational modeling has become a powerful tool in understanding detailed protein-ligand interactions at molecular level and in rational drug design. To study the binding of a protein with multiple molecular species of a ligand, one must accurately determine both the relative free energies of all of the molecular species in solution and the corresponding microscopic binding free energies for all of the molecular species binding with the protein. In this paper, we aim to provide a brief overview of the recent development in computational modeling of the solvent effects on the detailed protein-ligand interactions involving multiple molecular species of a ligand related to rational drug design. In particular, we first briefly discuss the main challenges in computational modeling of the detailed protein-ligand interactions involving the multiple molecular species and then focus on the FPCM model and its applications. The FPCM method allows accurate determination of the solvent effects in the first-principles quantum mechanism (QM) calculations on molecules in solution. The combined use of the FPCM-based QM calculations and other computational modeling and simulations enables us to accurately account for a protein binding with multiple molecular species of a ligand in solution. Based on the computational modeling of the detailed protein-ligand interactions, possible new drugs may be designed rationally as either small-molecule ligands of the protein or engineered proteins that bind/metabolize the ligand. The computational drug design has successfully led to discovery and development of promising drugs.
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Filonenko, О. V., E. M. Demianenko i V. V. Lobanov. "Quantum chemical modeling of orthophosphoric acid adsorption sites on hydrated anatase surface". Surface 12(27) (30.12.2020): 20–35. http://dx.doi.org/10.15407/surface.2020.12.020.
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Quantum chemical modeling of orthophosphoric acid adsorption sites on the hydrated surface of anatase was performed by the method of density functional theory (exchange-correlation functional PBE0, basis set 6-31 G(d,p)). The influence of the aqueous medium was taken into account within the framework of the continual solvent model. The work uses a cluster approach. The anatase surface is simulated by a neutral Ti(OH)4(H2O)2 cluster. The results of analysis of the geometry and energy characteristics of all the calculated complexes show that the highest interaction energy is inherent to the intermolecular complex of orthophosphoric acid and hydrated surface of anatase, where the oxygen atom of the phosphoryl group (О=Р≡) forms a hydrogen bond with a hydrogen atom of the coordinated water molecule of Ti(OH)4(H2O)2 cluster and two hydrogen atoms of the hydroxyl groups of the orthophosphoric acid molecule form two hydrogen bonds with two oxygen atoms of the titanol groups. The formation energy effect of this complex is -134.0 kJ/mol. The formation energy effect of the complex with separated charges by the proton transfer from the molecule H3PO4 to the Ti(OH)4(H2O)2 cluster with the formation of dihydrogen phosphate anion and the protonated form of the titanol group (º) is -131.1 kJ/mol, so indicating less thermodynamic probability of such intermolecular interaction. The smallest thermodynamic probability (-123.9 kJ/mol) of complexation between orthophosphoric acid and hydrated anatase surface where a water molecule moves from the coordination sphere of the titanium atom. The calculation results indicate a possible adsorption of the H3PO4 molecule in an aqueous solution on the hydrated anatase surface. Taking into account the effect of the solvent within the polarization continuum insignificantly changes the adsorption energy, which is -44.5 kJ/mol; for vacuum conditions this value is -49.0 kJ/mol.
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Farrokhabadi, Amin, Naeimeh Abadian, Faramarz Kanjouri i Mohamadreza Abadyan. "Casimir force-induced instability in freestanding nanotweezers and nanoactuators made of cylindrical nanowires". International Journal of Modern Physics B 28, nr 19 (12.06.2014): 1450129. http://dx.doi.org/10.1142/s021797921450129x.
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The quantum vacuum fluctuation i.e., Casimir attraction can induce mechanical instability in ultra-small devices. Previous researchers have focused on investigating the instability in structures with planar or rectangular cross-section. However, to the best knowledge of the authors, no attention has been paid for modeling this phenomenon in the structures made of nanowires with cylindrical geometry. In this regard, present work is dedicated to simulate the Casimir force-induced instability of freestanding nanoactuator and nanotweezers made of conductive nanowires with circular cross-section. To compute the quantum vacuum fluctuations, two approaches i.e., the proximity force approximation (for small separations) and scattering theory approximation (for large separations), are considered. The Euler-beam model is employed, in conjunction with the size-dependent modified couple stress continuum theory, to derive governing equations of the nanostructures. The governing nonlinear equations are solved via three different approaches, i.e., using lumped parameter model, modified variation iteration method (MVIM) and numerical solution. The deflection of the nanowire from zero to the final stable position is simulated as the Casimir force is increased from zero to its critical value. The detachment length and minimum gap, which prevent the instability, are computed for both nanosystems.
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Kawczak, Piotr, Leszek Bober i Tomasz Bączek. "Evaluation of Chemotherapeutic Activity of the Selected Bases’ Analogues of Nucleic Acids Supported by ab initio Various Quantum Chemical Calculations". Current Computer-Aided Drug Design 16, nr 2 (25.03.2020): 93–103. http://dx.doi.org/10.2174/1573409915666190206212024.
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Background: Pharmacological and physicochemical classification of bases’ selected analogues of nucleic acids is proposed in the study. Objective: Structural parameters received by the PCM (Polarizable Continuum Model) with several types of calculation methods for the structures in vacuo and in the aquatic environment together with the huge set of extra molecular descriptors obtained by the professional software and literature values of biological activity were used to search the relationships. Methods: Principal Component Analysis (PCA) together with Factor Analysis (FA) and Multiple Linear Regressions (MLR) as the types of the chemometric approach based on semi-empirical ab initio molecular modeling studies were performed. Results: The equations with statistically significant descriptors were proposed to demonstrate both the common and differentiating characteristics of the bases' analogues of nucleic acids based on the quantum chemical calculations and biological activity data. Conclusion: The obtained QSAR models can be used for predicting and explaining the activity of studied molecules.
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Cheng, Tao, Andres Jaramillo-Botero, Qi An, Daniil V. Ilyin, Saber Naserifar i William A. Goddard. "First principles-based multiscale atomistic methods for input into first principles nonequilibrium transport across interfaces". Proceedings of the National Academy of Sciences 116, nr 37 (3.08.2018): 18193–201. http://dx.doi.org/10.1073/pnas.1800035115.
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This issue of PNAS features “nonequilibrium transport and mixing across interfaces,” with several papers describing the nonequilibrium coupling of transport at interfaces, including mesoscopic and macroscopic dynamics in fluids, plasma, and other materials over scales from microscale to celestial. Most such descriptions describe the materials in terms of the density and equations of state rather than specific atomic structures and chemical processes. It is at interfacial boundaries where such atomistic information is most relevant. However, there is not yet a practical way to couple these phenomena with the atomistic description of chemistry. The starting point for including such information is the quantum mechanics (QM). However, practical QM calculations are limited to a hundred atoms for dozens of picoseconds, far from the scales required to inform the continuum level with the proper atomistic description. To bridge this enormous gap, we need to develop practical methods to extend the scale of the atomistic simulation by several orders of magnitude while retaining the level of QM accuracy in describing the chemical process. These developments would enable continuum modeling of turbulent transport at interfaces to incorporate the relevant chemistry. In this perspective, we will focus on recent progress in accomplishing these extensions in first principles-based atomistic simulations and the strategies being pursued to increase the accuracy of very large scales while dramatically decreasing the computational effort.
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Madeo, Angela, Alessandro Della Corte, Ivan Giorgio i Daria Scerrato. "Modeling and designing micro- and nano-structured metamaterials: Towards the application of exotic behaviors". Mathematics and Mechanics of Solids 22, nr 4 (4.12.2015): 873–84. http://dx.doi.org/10.1177/1081286515616036.
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The lack of suitable computational methods has significantly restricted the creativity of engineers in designing the materials to be used in technological applications. When one wants exact analytical solutions for a given physical system, then usually drastic and restrictive simplifying assumptions are needed. In particular, homogeneity of physical and geometrical properties at lower length-scale is the standard assumption in continuum mechanics. On the other hand, it is well-known since the pioneering work of Gabrio Piola, and then re-established in the works by Mindlin, Toupin, Green, Adkins and Germain, that it is possible to synthetically describe microscopic inhomogeneity by means of field theories incorporating additional kinematical fields. The characteristic length-scale affecting macro-behavior can even be of the order of nanometers, in which case the intuition due to Richard Feynman about the importance of quantum effects at macro-scale could open the path to technological advancements. In the present paper we review some of the literature in the field and try to indicate some research perspectives that seem to us potentially ground-breaking. In particular, following the suggestion of Professor dell’Isola, we briefly describe his concept of pantographic lattices and sheets whose importance in nano-technology could be relevant.
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Li, Guanchen, Michael R. von Spakovsky, Fengyu Shen i Kathy Lu. "Multiscale Transient and Steady-State Study of the Influence of Microstructure Degradation and Chromium Oxide Poisoning on Solid Oxide Fuel Cell Cathode Performance". Journal of Non-Equilibrium Thermodynamics 43, nr 1 (26.01.2018): 21–42. http://dx.doi.org/10.1515/jnet-2017-0013.
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AbstractOxygen reduction in a solid oxide fuel cell cathode involves a nonequilibrium process of coupled mass and heat diffusion and electrochemical and chemical reactions. These phenomena occur at multiple temporal and spatial scales, making the modeling, especially in the transient regime, very difficult. Nonetheless, multiscale models are needed to improve the understanding of oxygen reduction and guide cathode design. Of particular importance for long-term operation are microstructure degradation and chromium oxide poisoning both of which degrade cathode performance. Existing methods are phenomenological or empirical in nature and their application limited to the continuum realm with quantum effects not captured. In contrast, steepest-entropy-ascent quantum thermodynamics can be used to model nonequilibrium processes (even those far-from equilibrium) at all scales. The nonequilibrium relaxation is characterized by entropy generation, which can unify coupled phenomena into one framework to model transient and steady behavior. The results reveal the effects on performance of the different timescales of the varied phenomena involved and their coupling. Results are included here for the effects of chromium oxide concentrations on cathode output as is a parametric study of the effects of interconnect-three-phase-boundary length, oxygen mean free path, and adsorption site effectiveness. A qualitative comparison with experimental results is made.
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Zamiri, Marziyeh, Farhana Anwar, Brianna A. Klein, Amin Rasoulof, Noel M. Dawson, Ted Schuler-Sandy, Christoph F. Deneke, Sukarno O. Ferreira, Francesca Cavallo i Sanjay Krishna. "Antimonide-based membranes synthesis integration and strain engineering". Proceedings of the National Academy of Sciences 114, nr 1 (16.12.2016): E1—E8. http://dx.doi.org/10.1073/pnas.1615645114.
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Antimonide compounds are fabricated in membrane form to enable materials combinations that cannot be obtained by direct growth and to support strain fields that are not possible in the bulk. InAs/(InAs,Ga)Sb type II superlattices (T2SLs) with different in-plane geometries are transferred from a GaSb substrate to a variety of hosts, including Si, polydimethylsiloxane, and metal-coated substrates. Electron microscopy shows structural integrity of transferred membranes with thickness of 100 nm to 2.5 μm and lateral sizes from 24×24μm2 to 1×1 cm2. Electron microscopy reveals the excellent quality of the membrane interface with the new host. The crystalline structure of the T2SL is not altered by the fabrication process, and a minimal elastic relaxation occurs during the release step, as demonstrated by X-ray diffraction and mechanical modeling. A method to locally strain-engineer antimonide-based membranes is theoretically illustrated. Continuum elasticity theory shows that up to ∼3.5% compressive strain can be induced in an InSb quantum well through external bending. Photoluminescence spectroscopy and characterization of an IR photodetector based on InAs/GaSb bonded to Si demonstrate the functionality of transferred membranes in the IR range.
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Ibrahim, Khaled Z., i François Bodin. "Efficient SIMDization and Data Management of the Lattice QCD Computation on the Cell Broadband Engine". Scientific Programming 17, nr 1-2 (2009): 153–72. http://dx.doi.org/10.1155/2009/634756.
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Lattice Quantum Chromodynamic (QCD) models subatomic interactions based on a four-dimensional discretized space–time continuum. The Lattice QCD computation is one of the grand challenges in physics especially when modeling a lattice with small spacing. In this work, we study the implementation of the main kernel routine of Lattice QCD that dominates the execution time on the Cell Broadband Engine. We tackle the problem of efficient SIMD execution and the problem of limited bandwidth for data transfers with the off-chip memory. For efficient SIMD execution, we present runtime data fusion technique that groups data processed similarly at runtime. We also introduce analysis needed to reduce the pressure on the scarce memory bandwidth that limits the performance of this computation. We studied two implementations for the main kernel routine that exhibit different patterns of accessing the memory and thus allowing different sets of optimizations. We show the attributes that make one implementation more favorable in terms of performance. For lattice size that is significantly larger than the local store, our implementation achieves 31.2 GFlops for single precision computations and 16.6 GFlops for double precision computations on the PowerXCell 8i, an order of magnitude better than the performance achieved on most general-purpose processors.
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Johnson, H. T., B. Liu i Y. Y. Huang. "Electron Transport in Deformed Carbon Nanotubes". Journal of Engineering Materials and Technology 126, nr 3 (29.06.2004): 222–29. http://dx.doi.org/10.1115/1.1743426.
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Carbon nanotubes are a material system of increasing technological importance with superb mechanical and electrical properties. It is well known that depending on details of atomic structure, nanotubes may be electrically conducting, semiconducting, or insulating, so deformation is believed to have strong effects on nanotube electrical properties. In this paper, a combination of continuum, empirical atomistic, and quantum atomistic modeling methods are used to demonstrate the effect of homogeneous deformation—tension, compression, and torsion—on the electrical conductance and current versus voltage (I(V)) characteristics of a variety of single wall carbon nanotubes. The modeling methods are used in a coupled and efficient multiscale formulation that allows for computationally inexpensive analysis of a wide range of deformed nanotube configurations. Several important observations on the connection between mechanical and electrical behavior are made based on the transport calculations. First, based on the I(V) characteristics, electron transport in the nanotubes is evidently fairly insensitive to homogeneous deformation, though in some cases there is a moderate strain effect at either relatively low or high applied voltages. In particular, the conductance, or dI/dV behavior, shows interesting features for nanotubes deformed in torsion over small ranges of applied bias. Second, based on a survey of a range of nanotube geometries, the primary determining feature of the I(V) characteristics is simply the number of conduction electrons available per unit length of nanotube. In other words, when the current is normalized by the number of free electrons on the tube cross section per unit length, which itself is affected by extensional (but not torsional) strain, the I(V) curves of all single walled carbon nanotubes are nearly co-linear.
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Grujicic, M., JS Snipes, S. Ramaswami, R. Galgalikar, C.-F. Yen i BA Cheeseman. "Computational analysis of the intermetallic formation during the dissimilar metal aluminum-to-steel friction stir welding process". Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 233, nr 6 (2.05.2017): 1080–100. http://dx.doi.org/10.1177/1464420716673670.
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The extent of inter-material mixing and the formation of intermetallic compounds play a critical role in the structural integrity and mechanical properties of the joints in the case of dissimilar metal friction stir welding. In general, there is a critical volume fraction of the intermetallic compounds in the mix zone of the friction stir welding-joint at which the mechanical properties of the joint are maximized. That is, insufficient inter-material mixing and the accompanying sub-critical volume fraction of the intermetallic compounds results in insufficient inter-material bonding and inferior joint strength. Conversely, super-critical volume fraction of the intermetallic compounds typically gives rise to the joint embrittlement. To address the problem of the effect of the friction stir welding process parameters on the extent of intermetallic compound formation, a multi-physics computational framework has been developed and applied to the case of dissimilar metal friction stir welding involving commercially pure (CP) aluminum and AISI 1005 low-carbon steel. The multi-physics framework comprises the following main modules: (a) finite-element-based friction stir welding-process modeling; (b) quantum-mechanics, atomistic and CALPHAD-type continuum material thermodynamics analyses of the intermetallic compound-nucleation process; (c) a continuum-type analysis of multi-component diffusion-controlled growth of the intermetallic compounds; and (d) Kolmogorov–Johnson–Mehl–Avrami type analysis of the evolution of the intermetallic compound volume fraction within the friction stir welding joint as a function of the friction stir welding process parameters. The results obtained revealed that: (i) the extent and the spatial distribution of the intermetallic compounds is a sensitive function of the friction stir welding-process parameters; and (ii) among the six potential Al-Fe intermetallic compounds, FeAl and Fe3Al are associated with the largest volume fractions and, hence, play a key role in both attaining the required joint strength and in the potential loss of the joint fracture toughness.
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Qian,, Dong, Gregory J. Wagner, and, Wing Kam Liu, Min-Feng Yu i Rodney S. Ruoff. "Mechanics of carbon nanotubes". Applied Mechanics Reviews 55, nr 6 (16.10.2002): 495–533. http://dx.doi.org/10.1115/1.1490129.
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Soon after the discovery of carbon nanotubes, it was realized that the theoretically predicted mechanical properties of these interesting structures–including high strength, high stiffness, low density and structural perfection–could make them ideal for a wealth of technological applications. The experimental verification, and in some cases refutation, of these predictions, along with a number of computer simulation methods applied to their modeling, has led over the past decade to an improved but by no means complete understanding of the mechanics of carbon nanotubes. We review the theoretical predictions and discuss the experimental techniques that are most often used for the challenging tasks of visualizing and manipulating these tiny structures. We also outline the computational approaches that have been taken, including ab initio quantum mechanical simulations, classical molecular dynamics, and continuum models. The development of multiscale and multiphysics models and simulation tools naturally arises as a result of the link between basic scientific research and engineering application; while this issue is still under intensive study, we present here some of the approaches to this topic. Our concentration throughout is on the exploration of mechanical properties such as Young’s modulus, bending stiffness, buckling criteria, and tensile and compressive strengths. Finally, we discuss several examples of exciting applications that take advantage of these properties, including nanoropes, filled nanotubes, nanoelectromechanical systems, nanosensors, and nanotube-reinforced polymers. This review article cites 349 references.
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Improta, R., A. di Matteo i V. Barone. "Effective modeling of intrinsic and environmental effects on the structure and electron plaramagnetic resonance parameters of nitroxides by an integrated quantum mechanical/molecular mechanics/polarizable continuum model approach". Theoretical Chemistry Accounts: Theory, Computation, and Modeling (Theoretica Chimica Acta) 104, nr 3-4 (21.07.2000): 273–79. http://dx.doi.org/10.1007/s002140000122.
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Cunha, Renato D., Livia J. Ferreira, Ednilsom Orestes, Mauricio D. Coutinho-Neto, James M. de Almeida, Rogério M. Carvalho, Cleiton D. Maciel, Carles Curutchet i Paula Homem-de-Mello. "Naphthenic Acids Aggregation: The Role of Salinity". Computation 10, nr 10 (22.09.2022): 170. http://dx.doi.org/10.3390/computation10100170.
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Naphthenic Acids (NA) are important oil extraction subproducts. These chemical species are one of the leading causes of marine pollution and duct corrosion. For this reason, understanding the behavior of NAs in different saline conditions is one of the challenges in the oil industry. In this work, we simulated several naphthenic acid species and their mixtures, employing density functional theory calculations with the MST-IEFPCM continuum solvation model, to obtain the octanol–water partition coefficients, together with microsecond classical molecular dynamics. The latter consisted of pure water, low-salinity, and high-salinity environment simulations, to assess the stability of NAs aggregates and their sizes. The quantum calculations have shown that the longer chain acids are more hydrophobic, and the classical simulations corroborated: that the longer the chain, the higher the order of the aggregate. In addition, we observed that larger aggregates are stable at higher salinities for all the studied NAs. This can be one factor in the observed low-salinity-enhanced oil recovery, which is a complex phenomenon. The simulations also show that stabilizing the aggregates induced by the salinity involves a direct interplay of Na+ cations with the carboxylic groups of the NAs inside the aggregates. In some cases, the ion/NA organization forms a membrane-like circular structural arrangement, especially for longer chain NAs.
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Ramasubramaniam, A., i V. B. Shenoy. "Growth and Ordering of Si-Ge Quantum Dots on Strain Patterned Substrates". Journal of Engineering Materials and Technology 127, nr 4 (30.01.2005): 434–43. http://dx.doi.org/10.1115/1.1924559.
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Manipulating the strain distribution along the surface of a substrate has been shown experimentally to promote spatial ordering of self-assembled nanostructures in heteroepitaxial film growth without having to resort to expensive nanolithographic techniques. We present here numerical studies of three-dimensional modeling of self-assembly in Si-Ge systems with the aim of understanding the effect of spatially varying mismatch strain-fields on the growth and ordering of quantum dots. We use a continuum model based on the underlying physics of crystallographic surface steps in our calculations. Using appropriate parameters from atomistic studies, the (100) orientation is found to be unstable under compressive strain; the surface energy now develops a new minimum at an orientation that may be interpreted as the (105) facet observed in SiGe∕Si systems. This form of surface energy allows for the nucleationless growth of quantum dots which start off via a surface instability as shallow stepped mounds whose sidewalls evolve continuously toward their low-energy orientations. The interaction of the surface instability with one- and two-dimensional strain modulations is considered in detail as a function of the growth rate. One-dimensional strain modulations lead to the formation of rows of dots in regions of low mismatch—there is some ordering within these rows owing to elastic interactions between dots but this is found to depend strongly upon the kinetics of the growth process. Two-dimensional strain modulations are found to provide excellent ordering within the island array, the growth kinetics being less influential in this case. For purposes of comparison, we also consider self-assembly of dots for an isotropic surface energy. While the results do not differ significantly from those for the anisotropic surface energy with the two-dimensional strain variation, the one-dimensional strain variation produces profoundly different behavior. The surface instability is seen to start off initially as stripes in regions of low mismatch. However, since stripes are less effective at relaxing the mismatch strain they eventually break up into islands. The spacing of these islands is determined by the wavelength of the fastest growing mode of the Asaro-Tiller-Grinfeld instability. However, the fact that such a growth mode is not observed experimentally indicates the importance of accounting for surface energy anisotropy in growth models.
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Maranganti, R., i P. Sharma. "Revisiting quantum notions of stress". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, nr 2119 (15.02.2010): 2097–116. http://dx.doi.org/10.1098/rspa.2009.0636.
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An important aspect of multi-scale modelling of materials is to link continuum concepts, such as fields, to the underlying discrete microscopic behaviour in a seamless manner. With the growing importance of atomistic calculations to understand material behaviour, reconciling continuum and discrete concepts is necessary to interpret molecular and quantum-mechanical simulations. In this work, we provide a quantum-mechanical framework to a distinctly continuum quantity: mechanical stress. While the concept of the global macroscopic stress tensor in quantum mechanics has been well established, there still exist open issues when it comes to a spatially varying local quantum stress tensor. We attempt to shed some light on this topic by establishing a general quantum-mechanical operator-based approach to continuity equations and from those, introduce a local quantum-mechanical stress tensor. Further, we elucidate the analogies that exist between the (classical) molecular-dynamics-based stress definition and the quantum stress. Our derivations appear to suggest that the local quantum-mechanical stress may not be an observable in quantum mechanics and therefore traces the non-uniqueness of the atomistic stress tensor to the gauge arbitrariness of the quantum-mechanical state function. Lastly, the virial stress theorem (of empirical molecular dynamics) is re-derived in a transparent manner that elucidates the analogy between quantum-mechanical global stresses.
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Ruffing, Andreas. "Discretized representations of harmonic variables by bilateral Jacobi operators". Discrete Dynamics in Nature and Society 4, nr 4 (2000): 297–308. http://dx.doi.org/10.1155/s1026022600000285.
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Starting from a discrete Heisenberg algebra we solve several representation problems for a discretized quantum oscillator in a weighted sequence space. The Schrödinger operator for a discrete harmonic oscillator is derived. The representation problem for aq-oscillator algebra is studied in detail. The main result of the article is the fact that the energy representation for the discretized momentum operator can be interpreted as follows: It allows to calculate quantum properties of a large number of non-interacting harmonic oscillators at the same time. The results can be directly related to current research on squeezed laser states in quantum optics. They reveal and confirm the observation that discrete versions of continuum Schrodinger operators allow more structural freedom than their continuum analogs do.
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WEI, GUO-WEI. "MULTISCALE, MULTIPHYSICS AND MULTIDOMAIN MODELS I: BASIC THEORY". Journal of Theoretical and Computational Chemistry 12, nr 08 (grudzień 2013): 1341006. http://dx.doi.org/10.1142/s021963361341006x.
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This work extends our earlier two-domain formulation of a differential geometry based multiscale paradigm into a multidomain theory, which endows us the ability to simultaneously accommodate multiphysical descriptions of aqueous chemical, physical and biological systems, such as fuel cells, solar cells, nanofluidics, ion channels, viruses, RNA polymerases, molecular motors, and large macromolecular complexes. The essential idea is to make use of the differential geometry theory of surfaces as a natural means to geometrically separate the macroscopic domain of solvent from the microscopic domain of solute, and dynamically couple continuum and discrete descriptions. Our main strategy is to construct energy functionals to put on an equal footing of multiphysics, including polar (i.e. electrostatic) solvation, non-polar solvation, chemical potential, quantum mechanics, fluid mechanics, molecular mechanics, coarse grained dynamics, and elastic dynamics. The variational principle is applied to the energy functionals to derive desirable governing equations, such as multidomain Laplace–Beltrami (LB) equations for macromolecular morphologies, multidomain Poisson–Boltzmann (PB) equation or Poisson equation for electrostatic potential, generalized Nernst–Planck (NP) equations for the dynamics of charged solvent species, generalized Navier–Stokes (NS) equation for fluid dynamics, generalized Newton's equations for molecular dynamics (MD) or coarse-grained dynamics and equation of motion for elastic dynamics. Unlike the classical PB equation, our PB equation is an integral-differential equation due to solvent–solute interactions. To illustrate the proposed formalism, we have explicitly constructed three models, a multidomain solvation model, a multidomain charge transport model and a multidomain chemo-electro-fluid-MD-elastic model. Each solute domain is equipped with distinct surface tension, pressure, dielectric function, and charge density distribution. In addition to long-range Coulombic interactions, various non-electrostatic solvent–solute interactions are considered in the present modeling. We demonstrate the consistency between the non-equilibrium charge transport model and the equilibrium solvation model by showing the systematical reduction of the former to the latter at equilibrium. This paper also offers a brief review of the field.
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Alkire, Richard C. "Historical Perspectives on Electroplating during the Past 100 Years". ECS Meeting Abstracts MA2022-02, nr 24 (9.10.2022): 1000. http://dx.doi.org/10.1149/ma2022-02241000mtgabs.
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The development of electrodeposition practice and the underlying science and engineering methods that emerged during the past century will be traced. Beginning in the late 19th century, many large-scale electrolytic technologies became feasible owing to the invention of the electric generator. These included electrowinning, electrorefining, and electrodeposition, among others. Their early development and commercial use took place before the recognition of many fundamental scientific and engineering principles. As a result, these industries came to be characterized by slow evolutionary change based on past experience and intuitive insight. In 1913, a symposium on electrodeposition was arguably the first to apply systematic academic effort to the art of the plater, and thus promote cooperation between science and technology. The success of these activities led, in 1922, to formation of the Electrodeposition Division. For several subsequent decades, the growth of electrodeposition technology took place while electrochemists developed experimental tools (e.g. polarography), data (e.g., thermodynamic) and theories (e.g. non-ideal electrolytic solutions). By the 1950s there were an enormous number of electrodeposition applications, but the sense was emerging that progress based on empirical experimentation was rapidly coming to a close, and that further significant advances could be made only when the fundamentals of the plating processes are more completely understood. During the 1960s, the invention of new materials revolutionized the electrodeposition industries. In addition, the digital computer came into use for obtaining the current distribution in simple geometries. In addition, refined experimental research methods were developed, iincluding the potentiostatic power supply, rotating disk, “model” experimental systems, and various electroanalytical and surface-science techniques, In the 1970s, the field of electrodeposition technology saw significant new demands arising from changed availability of energy, feedstock, and capital as well as increased attention to waste treatment. These events shattered the empirical traditions of the past, and triggered new interest in ‘modern’ electrodeposition science and engineering built o a foundation of thermodynamics, kinetics, transport phenomena, and current distribution aspects. In the 1980s, the magnetic thin-film storage head, energized the entire microelectronics field of electrodeposition technology. Also, studies with single crystal electrodes and with surface scanning microscopies provided spectacular new capabilities for investigations at time scales, molecular specificity, and spatial resolution that were orders of magnitude superior to those of only a decade earlier. By the 1990s, important advances were made in understanding phenomena associated with defects, additives, solvent effects, nanoscale phenomena, surface films, mechanisms of lattice formation, among others. In addition, mathematical modeling of electrodeposition systems moved down-scale to include both continuum and non-continuum phenomena. During the 2000s, the shift from aluminum to electrodeposited copper for on-chip interconnections represented one of the most important change in materials since the beginning of the semiconductor industry. In the 2010s, the mathematical tools used to explore electrochemical systems expanded beyond the traditional continuum methods to include kinetic Monte Carlo, molecular dynamics, and quantum chemistry. In conclusion, throughout the history of electrodeposition science and technology, several high-level trends may be recognized: Advances often came from outside the electrodeposition field. It is important to read the literature widely, and with enough informed judgment to recognize analogies between seemingly different situations; Many electrodeposition systems have been improved over the course of many years. The literature contains a gold mine of applications worth further study. It is important to recognize when new science or engineering materials and methods can provide fresh insights to improving old, but very important, applications; Over the past century, there have been periods when significant gaps existed between scientific understanding of electrochemical phenomena, and our ability to incorporate it into engineering practice. It is important to identify problems worth solving and to release impedements to introduction of new ideas. Today, the ability to use numerical simulations to achieve precise quantitative understanding at new levels of magnitude, sophistication, and completeness offers a significant challenge. It is therefore important to develop re-usable electrochemical engineering methods, and to align tight integration of discovery science, application design, research prototyping and manufacturing collaboration.
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Farrelly, Terry. "A review of Quantum Cellular Automata". Quantum 4 (30.11.2020): 368. http://dx.doi.org/10.22331/q-2020-11-30-368.
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Discretizing spacetime is often a natural step towards modelling physical systems. For quantum systems, if we also demand a strict bound on the speed of information propagation, we get quantum cellular automata (QCAs). These originally arose as an alternative paradigm for quantum computation, though more recently they have found application in understanding topological phases of matter and have} been proposed as models of periodically driven (Floquet) quantum systems, where QCA methods were used to classify their phases. QCAs have also been used as a natural discretization of quantum field theory, and some interesting examples of QCAs have been introduced that become interacting quantum field theories in the continuum limit. This review discusses all of these applications, as well as some other interesting results on the structure of quantum cellular automata, including the tensor-network unitary approach, the index theory and higher dimensional classifications of QCAs.
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Corral Bustamante, R. Leticia, Evelyn M. Rodríguez Corral, José Nino Hernández Magdaleno i Gilberto Irigoyen Chávez. "Energy Transfer and Fluid Flow around a Massive Astrophysical Object". Defect and Diffusion Forum 348 (styczeń 2014): 189–215. http://dx.doi.org/10.4028/www.scientific.net/ddf.348.189.
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In this work it is presented the modeling and simulation of energy transfer and fluid flow of a stationary spherical arrangement of particles surrounding a gravitational body such as an astrophysical object that carries the curvature of space-time continuum in general relativity, taking into account the thermodynamics of the second law. This model also predicts the drag of space and time around an astrophysical object as it rotates, with results close to the experimental data reported by other authors. To model the energy transfer of the mass and the fluid flow in the space-time, it is used a 4-dimensional system. In order to make measurements of entropy in the arrow of time (past-present), tensors in General Relativity were used to calculate this thermodynamic quantity and with this, the big bang ́s low entropy condition in phase space of coarse graining (Hawking ́s box), according to Weyl curvature hypothesis (WCH) of Roger Penrose. Contribution of this paper is presented by tensors which carry information that has to do with something as non-distortion effect in fluid flow around the astrophysical object and the low entropy condition that is believed to exist in the past, in the big bang;what leads us to search for a new physical-mathematical science to continue. At this point, the Einstein field equations are out of context, which leads us to conclude that it is necessary a mathematical science that allows us to make calculations to rescue lost information due to collapse of matter to a black hole. This math should allow us to clear up physical phenomena (like origin of the universe) and their relationship, with the objective of unifying theories that lead to a physical science without uncertainties, as at the present time. In this regard, we propose a metric in hyperbolic coodinates to build a physical wormhole shaped object where gravitational bodies can be housed that allow us to link the past entropy with the present entropy according to the second law of thermodynamics, as a kind of mathematical space or alternative model to compensate in some way, the link between WCH and the phase space volume of the Hawking's box, and the link between WCH and the quantum-mechanical state-vector reduction, , proposed by Penrose which still have not been determined by any author. Nomenclature
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Aisenberg, James, Itamar Sela, Tsampikos Kottos, Doron Cohen i Alex Elgart. "Quantum decay into a non-flat continuum". Journal of Physics A: Mathematical and Theoretical 43, nr 9 (9.02.2010): 095301. http://dx.doi.org/10.1088/1751-8113/43/9/095301.
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Nemaura, Tafireyi. "Classical and Quantum Structures of the Wave: Modelling the Controlled, Optimised, Continuum-System". Journal of Applied Mathematics and Physics 10, nr 03 (2022): 611–22. http://dx.doi.org/10.4236/jamp.2022.103044.
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Ramsey, J. J., E. Pan i P. W. Chung. "Modelling of strain fields in quantum wires with continuum methods and molecular statics". Journal of Physics: Condensed Matter 20, nr 48 (28.10.2008): 485215. http://dx.doi.org/10.1088/0953-8984/20/48/485215.
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Truong, Thanh N. "Quantum modelling of reactions in solution: An overview of the dielectric continuum methodology". International Reviews in Physical Chemistry 17, nr 4 (październik 1998): 525–46. http://dx.doi.org/10.1080/014423598230045.
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Keil, Frerich J. "Molecular Modelling for Reactor Design". Annual Review of Chemical and Biomolecular Engineering 9, nr 1 (7.06.2018): 201–27. http://dx.doi.org/10.1146/annurev-chembioeng-060817-084141.
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Chemical reactor modelling based on insights and data on a molecular level has become reality over the last few years. Multiscale models describing elementary reaction steps and full microkinetic schemes, pore structures, multicomponent adsorption and diffusion inside pores, and entire reactors have been presented. Quantum mechanical (QM) approaches, molecular simulations (Monte Carlo and molecular dynamics), and continuum equations have been employed for this purpose. Some recent developments in these approaches are presented, in particular time-dependent QM methods, calculation of van der Waals forces, new approaches for force field generation, automatic setup of reaction schemes, and pore modelling. Multiscale simulations are discussed. Applications of these approaches to heterogeneous catalysis are demonstrated for examples that have found growing interest over the last few years, such as metal-support interactions, influence of pore geometry on reactions, noncovalent bonding, reaction dynamics, dynamic changes in catalyst nanoparticle structure, electrocatalysis, solvent effects in catalysis, and multiscale modelling.
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Buehler, Markus J. "Atomistic and continuum modeling of mechanical properties of collagen: Elasticity, fracture, and self-assembly". Journal of Materials Research 21, nr 8 (1.08.2006): 1947–61. http://dx.doi.org/10.1557/jmr.2006.0236.
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We report studies of the mechanical properties of tropocollagen molecules under different types of mechanical loading including tension, compression, shear, and bending. Our modeling yields predictions of the fracture strength of single tropocollagen molecules and polypeptides, and also allows for quantification of the interactions between tropocollagen molecules. Atomistic modeling predicts a persistence length of tropocollagen molecules ξ ≈ 23.4 nm, close to experimental measurements. Our studies suggest that to describe large-strain or hyperelastic properties, it is critical to include a correct description of the bond behavior and breaking processes at large bond stretch, information that stems from the quantum chemical details of bonding. We use full atomistic calculations to derive parameters for a mesoscopic bead-spring model of tropocollagen molecules. We demonstrate that the mesoscopic model enables one to study the finite temperature, long-time scale behavior of tropocollagen fibers, illustrating the dynamics of solvated tropocollagen molecules for different molecular lengths.
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Dinc, Fatih, İlke Ercan i Agata M. Brańczyk. "Exact Markovian and non-Markovian time dynamics in waveguide QED: collective interactions, bound states in continuum, superradiance and subradiance". Quantum 3 (9.12.2019): 213. http://dx.doi.org/10.22331/q-2019-12-09-213.
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We develop a formalism for modelling exact time dynamics in waveguide quantum electrodynamics (QED) using the real-space approach. The formalism does not assume any specific configuration of emitters and allows the study of Markovian dynamics fully analytically and non-Markovian dynamics semi-analytically with a simple numerical integration step. We use the formalism to study subradiance, superradiance and bound states in continuum. We discuss new phenomena such as subdivision of collective decay rates into symmetric and anti-symmetric subsets and non-Markovian superradiance effects that can lead to collective decay stronger than Dicke superradiance. We also discuss possible applications such as pulse-shaping and coherent absorption. We thus broaden the range of applicability of real-space approaches beyond steady-state photon transport.
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CANCÈS, E., C. LE BRIS, B. MENNUCCI i J. TOMASI. "INTEGRAL EQUATION METHODS FOR MOLECULAR SCALE CALCULATIONS IN THE LIQUID PHASE". Mathematical Models and Methods in Applied Sciences 09, nr 01 (luty 1999): 35–44. http://dx.doi.org/10.1142/s021820259900004x.
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We report here a series of works1–5 devoted to the modelling of the liquid phase for quantum chemistry calculations. The question under consideration is the computation of the electrostatic interaction between charge densities in the presence of a continuum dielectric medium. It consists of solving an elliptic problem of the form - div (∊(x) ∇ V)=ρ where the field ∊(x) exhibits a discontinuity on a closed surface. We show how an enhanced use of integral equations methods has recently led to significant progress in this field: reduction of the computational cost in the standard cases, extension of existing methods to sophisticated cases out of reach so far, development of new possibilities. This work has a wide range of applications in chemistry and biology.
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Mazzanti, Andrea, Matthew Parry, Alexander N. Poddubny, Giuseppe Della Valle, Dragomir N. Neshev i Andrey A. Sukhorukov. "Enhanced generation of angle correlated photon-pairs in nonlinear metasurfaces". New Journal of Physics 24, nr 3 (1.03.2022): 035006. http://dx.doi.org/10.1088/1367-2630/ac599e.
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Abstract We reveal that strongly enhanced generation of photon pairs with narrow frequency spectra and sharp angular correlations can be realised through spontaneous parametric down-conversion in metasurfaces. This is facilitated by creating meta-gratings through nano-structuring of nonlinear films of sub-wavelength thickness to support the extended bound state in the continuum resonances, associated with ultra-high Q-factors, at the biphoton wavelengths across a wide range of emission angles. Such spectral features of photons can be beneficial for various applications, including quantum imaging. Our modelling demonstrates a pronounced enhancement, compared to unpatterned films, of the total photon-pair generation rate normalized to the pump power reaching 1.75 kHz mW−1, which is robust with respect to the angular bandwidth of the pump, supporting the feasibility of future experimental realisations.
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Quan, Chaoyu, Benjamin Stamm i Yvon Maday. "A domain decomposition method for the polarizable continuum model based on the solvent excluded surface". Mathematical Models and Methods in Applied Sciences 28, nr 07 (19.06.2018): 1233–66. http://dx.doi.org/10.1142/s0218202518500331.
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In this paper, an efficient solver for the polarizable continuum model in quantum chemistry is developed which takes the solvent excluded surface (the smooth molecular surface) as the solute–solvent boundary. This model requires to solve a generalized Poisson (GP) equation defined in [Formula: see text] with a space-dependent dielectric permittivity function. First, the original GP-equation is transformed into a system of two coupled equations defined in a bounded domain. Then, this domain is decomposed into overlapping balls and the Schwarz domain decomposition method is used. This method involves a direct Laplace solver and an efficient GP-solver to solve the local sub-equations in balls. For each solver, the spherical harmonics are used as basis functions in the angular direction of the spherical coordinate system. A series of numerical experiments are presented to test the performance of this method.
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Xu, Xiaopeng, Xi-Wei Lin, Youxin Gao i Soren Smidstrup. "(Invited) 3DIC Hierarchical Thermal and Mechanical Analysis with Continuum and Atomistic Modeling". ECS Meeting Abstracts MA2022-02, nr 17 (9.10.2022): 845. http://dx.doi.org/10.1149/ma2022-0217845mtgabs.
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3D IC heterogeneous integration technologies employ numerous materials with widely varying thermal and mechanical properties and distinct deformation behaviors. During 3D integration processes, the constituent materials undergo various thermal cycles. Because of thermal expansion coefficient mismatch, the materials are essentially subject to mechanical loadings for these thermal ramps. The resulting chip, package, and board interactions lead to 3D stack warpage, silicon mobility variation, and material damage. Under operation conditions, heat can be trapped between insulation layers and leads to nonuniform temperature rises. Elevated local temperatures can change carrier mobility, relax mechanical stress, and affect material deformation behaviors. Consequently, these local temperature rises can affect device performance, structure integrity, and material reliability. To accurately assess these thermal and mechanical effects, extract design rules, optimize designs, and develop performance and reliability mitigation methodologies, it is of paramount importance to characterize material deformation and interface de-bonding behaviors, map chip temperature distributions, and analyze stress hotspot evolutions during integration process and under operation conditions while developing 3D IC integration technologies [1]. In this study, a multiscale hierarchical modeling approach is assembled to analyze thermal, mechanical, and material deformation and interface de-bonding behaviors under 3D integration process and operation conditions for a newly designed 3D IC package with a 2nm SOC die copper-bonded on an RDL interposer [2]. The 3DIC structures are constructed directly using GDSII design and ITF technology data [3]. Each structural layer is divided into small smear tiles. Each tile is represented by anisotropic thermal and mechanical properties that depend on local feature patterns in the tile. Under given operation conditions, power grids are generated and used as heat sources for thermal analysis. For multiscale hierarchical modeling, the global thermal and mechanical analyses that call for coarse grain resolution are first performed. The subsequent local analyses that provide fine grain resolution in areas of interests utilize boundary conditions that are extracted from the global analyses. The material deformation and interface de-bonding behaviors are simulated using molecular dynamics [4]. Several 3D integration design options are explored. The 3D configuration effects on chip temperature distributions during operations, stack warpages, silicon mobility variations, and chip package interaction induced stress hotspots are examined. The elevated temperature impacts on material deformation and de-bonding process are also investigated. References: “Heterogenous Integration Roadmap”, 2022, https://eps.ieee.org/hir “Heterogeneous Integration Enabled by the State-of-the-Art 3DIC and CMOS Technologies: Design, Cost, and Modeling”, X. Lin et al., International Electron Devices Meeting, IEDM Technical Dig., 2021 “Sentaurus Interconnect User Guide”, 2022, https://www.synopsys.com/silicon/tcad “Quantum ATK: An integrated platform of electronic and atomic-scale modelling tools”, S. Smidstrup et al., J. Phys.: Condens. Matter 32, 015901, 2020
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Dinç, Fatih, i İlke Ercan. "Quantum mechanical treatment of two-level atoms coupled to continuum with an ultraviolet cutoff". Journal of Physics A: Mathematical and Theoretical 51, nr 35 (20.07.2018): 355301. http://dx.doi.org/10.1088/1751-8121/aad165.
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Greaves, G. Neville. "Poisson's ratio over two centuries: challenging hypotheses". Notes and Records: the Royal Society Journal of the History of Science 67, nr 1 (5.09.2012): 37–58. http://dx.doi.org/10.1098/rsnr.2012.0021.
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This article explores Poisson's ratio, starting with the controversy concerning its magnitude and uniqueness in the context of the molecular and continuum hypotheses competing in the development of elasticity theory in the nineteenth century, moving on to its place in the development of materials science and engineering in the twentieth century, and concluding with its recent re-emergence as a universal metric for the mechanical performance of materials on any length scale. During these episodes France lost its scientific pre-eminence as paradigms switched from mathematical to observational, and accurate experiments became the prerequisite for scientific advance. The emergence of the engineering of metals followed, and subsequently the invention of composites—both somewhat separated from the discovery of quantum mechanics and crystallography, and illustrating the bifurcation of technology and science. Nowadays disciplines are reconnecting in the face of new scientific demands. During the past two centuries, though, the shape versus volume concept embedded in Poisson's ratio has remained invariant, but its application has exploded from its origins in describing the elastic response of solids and liquids, into areas such as materials with negative Poisson's ratio, brittleness, glass formation, and a re-evaluation of traditional materials. Moreover, the two contentious hypotheses have been reconciled in their complementarity within the hierarchical structure of materials and through computational modelling.
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Coccia, Emanuele, i Eleonora Luppi. "Time-dependent ab initio approaches for high-harmonic generation spectroscopy". Journal of Physics: Condensed Matter 34, nr 7 (23.11.2021): 073001. http://dx.doi.org/10.1088/1361-648x/ac3608.
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Abstract High-harmonic generation (HHG) is a nonlinear physical process used for the production of ultrashort pulses in XUV region, which are then used for investigating ultrafast phenomena in time-resolved spectroscopies. Moreover, HHG signal itself encodes information on electronic structure and dynamics of the target, possibly coupled to the nuclear degrees of freedom. Investigating HHG signal leads to HHG spectroscopy, which is applied to atoms, molecules, solids and recently also to liquids. Analysing the number of generated harmonics, their intensity and shape gives a detailed insight of, e.g., ionisation and recombination channels occurring in the strong-field dynamics. A number of valuable theoretical models has been developed over the years to explain and interpret HHG features, with the three-step model being the most known one. Originally, these models neglect the complexity of the propagating electronic wavefunction, by only using an approximated formulation of ground and continuum states. Many effects unravelled by HHG spectroscopy are instead due to electron correlation effects, quantum interference, and Rydberg-state contributions, which are all properly captured by an ab initio electronic-structure approach. In this review we have collected recent advances in modelling HHG by means of ab initio time-dependent approaches relying on the propagation of the time-dependent Schrödinger equation (or derived equations) in presence of a very intense electromagnetic field. We limit ourselves to gas-phase atomic and molecular targets, and to solids. We focus on the various levels of theory employed for describing the electronic structure of the target, coupled with strong-field dynamics and ionisation approaches, and on the basis used to represent electronic states. Selected applications and perspectives for future developments are also given.