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Artykuły w czasopismach na temat "Quantum-Continuum Modeling"
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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.
Rozprawy doktorskie na temat "Quantum-Continuum Modeling"
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Codony, David. "Mathematical and computational modeling of flexoelectricity at mesoscopic and atomistic scales". Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/671925.
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This PhD thesis focuses on the development of mathematical and computational models for flexoelectricity, a relatively new electromechanical coupling that is present in any dielectric at the micron and sub-micron scales. The work is framed in the context of both continuum and quantum mechanics, and explores the gap between these two disciplines.
On the one hand, the focus is put on the mathematical modeling of the flexoelectric effect by means of continuum (electro-)
mechanics, and the development of computational techniques required to numerically solve the associated boundary value
problems. The novel computational infrastructure developed in this work is able to predict the performance of engineered
devices for electromechanical transduction at sub-micron scales, where flexoelectricity is always present, without any
particular restrictions in geometry, material choice, boundary conditions or nonlinearity. The numerical examples within this
document show that flexoelectricity can be harnessed in multiple different ways towards the development of breakthrough
applications in nanotechnology.
On the other hand, the flexoelectric effect is also studied at an atomistic level by means of quantum mechanics. This work
proposes a novel methodology to quantify the flexoelectric properties of dielectric materials, by means of connecting ab-initio
atomistic simulations with the proposed models at a coarser, continuum scales. The developed approach sheds some light
on a controversial topic within the density functional theory community, where large disagreements among different
theoretical derivations are typically found. The ab-initio computations serve not only to assess the material parameters within
the continuum models, but also to validate their inherent assumptions regarding the relevant physics at the nanoscale.Aquesta tesi doctoral es centra en el desenvolupament de models matemàtics i computacionals per a la flexoelectricitat, un acoblament electromecànic relativament nou que es present en qualsevol material dielèctric a les escales microscòpica i nanoscòpica. El treball s'emmarca tant en el context de la mecànica del medi continu com de la mecànica quàntica, i explora l'espai entre aquestes dues disciplines. Per una banda, s'estudien els models matemàtics de l¿'efecte flexoelèctric mitjançant la mecànica del medi continu, i es desenvolupen tècniques computacionals necessàries per la resolució numèrica dels problemes de valor de contorn associats. La nova infraestructura computacional desenvolupada en aquest treball és capaç de predir el rendiment de dispositius funcionals per a la transducció electromecànica a la nanoescala, on la flexoelectricitat és sempre present, sense cap tipus de limitació en quant a geometria, propietats materials, condicions de contorn o no-linearitat. Els exemples numèrics en aquest document demostren que la flexoelectritat es pot aprofitar de diverses maneres per tal de desenvolupar aplicacions nanotecnològiques innovadores. Per altra banda, el efecte flexoelèctric es estudiat també a nivell atomístic mitjançant la mecànica quàntica. Aquest treball proposa una metodologia nova per quantificar les propietats flexoelèctriques de materials dielèctrics, connectant les simulacions atomístiques amb els models continus proposats. El mètode desenvolupat clarifica un tema controvertit en la comunitat de la teoria del funcional de la densitat (DFT), on els càlculs teòrics estan típicament en desacord entre ells. Les simulacions atomístiques no només serveixen per calcular els paràmetres flexoelèctrics dels materials considerats en models continus, sinó també per validar les hipòtesis en les quals es basen en relació amb les físiques rellevants a la nanoescala.
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Torsello, Mauro. "Structural and dynamic modeling of molecular systems at different length scales". Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424405.
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The continuous growth of computing power, both in terms of hardware and software resources, has made the computational (in-silico) approach to complex scientific problems a very profitable tool, which provides useful information to support, interpret or in some cases even reproduce the experimental datum from first principles. Methods have become cheaper and faster in the last two decades, thanks also to the development of more efficient algorithms, able to extract in full the computational power contained in novel hardware solutions (e.g. parallel computing and GPUs-based hardware), and to provide relatively easy-to-use software packages for diverse applications. Nowadays the computational approach is employed in several scientific areas, covering many different applied disciplines such as medicine, engineering, chemistry, physics, materials science and many others.
In particular in this thesis work, some of the main approaches of computational chemistry, namely quantum mechanics, classical molecular dynamics and hybrid methods, are applied to the study of biomolecules and macromolecules, in order to investigate different aspects like structure, dynamics, energetics and in particular flexibility. In addition to the aforementioned methods we also explore a fluido-dynamic approach to describe and simulate microfluidic systems, focusing the attention on the reactivity of the systems studied. All these approaches are size-dependent and because they have different computational costs, their application should be limited to a reasonable size of the studied system. The profound difference in terms of cost/accuracy are discussed, providing a link between the different methodologies scales, in order to exemplify how information gathered at smaller length scale can be considered as an accurate starting point to perform simulations at larger spatial scales, in what is nowadays know popularly as multiscale modeling. The connection between the high accuracy/high cost and low accuracy/low cost methods is commented upon, to illustrate how a multiscale modeling approach can allow, in specific cases, to augment at the same time the accuracy of the data calculated and the size of the system simulated.La continua crescita della potenza di calcolo, in termini di risorse hardware e software, ha reso l'approccio computazionale (in-silico) ai complessi problemi scientifici, uno strumento molto conveniente che permette di ottenere informazioni utili al fine di affiancare, interpretare ed, in alcuni casi, addirittura riprodurre i dati sperimentali a partire da principi primi. I metodi sono stati resi più veloci ed efficienti negli ultimi vent'anni, grazie anche allo sviluppo di algoritmi sempre più efficienti, in grado di sfruttare al meglio la potenza computazionale racchiusa nelle nuove soluzioni hardware (ad esempio architetture parallele basate sulle GPU), e di fornire pacchetti software di semplice utilizzo per molteplici applicazioni. Al giorno d'oggi l'approccio computazionale è impiegato in numerose aree scientifiche, che spaziano tra le più disparate discipline applicate come medicina, ingegneria, chimica, fisica, scienze dei materiali e molte altre. In particolare in questo lavoro di tesi, alcuni degli approcci della chimica computazionale quali meccanica quantistica, dinamica molecolare classica e metodi ibridi, sono applicati allo studio di biomolecole e macromolecole, al fine di investigare differenti aspetti come struttura, dinamica, energetica e in particolare la flessibilità. In aggiunta ai metodi su menzionati è stato anche esplorato un approccio fluido-dinamico al fine di descrivere e simulare sistemi microfluidici, focalizzando l'attenzione sulla reattività dei sistemi presi in esame. Tutti questi approcci sono dipendenti dall'estensione del sistema e, poiché hanno un differente costo computazionale, la loro applicazione dovrebbe essere limitata ad una ragionevole dimensione dei sistemi studiati. Le profonde differenze in termini di costo/accuratezza sono discusse, fornendo un collegamento tra le scale spaziali delle diverse metodologie, al fine di esplicare come le informazioni ottenute a scale spaziali inferiori possano essere considerate come punto di partenza accurato per effettuare simulazioni a scale spaziali maggiori, in un approccio che è oggi comunemente noto come modellazione multiscala. La connessione tra i metodi ad alta accuratezza/alto costo e quelli a bassa accuratezza/basso costo è commentata, illustrando così come un approccio multiscala possa permettere, in casi specifici, di incrementare al contempo l'accuratezza del dato calcolato e la dimensione del sistema simulato.
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Yewande, Emmanuel Oluwole. "Modelling and simulation of surface morphology driven by ion bombardment". Doctoral thesis, [S.l.] : [s.n.], 2006. http://webdoc.sub.gwdg.de/diss/2006/yewande.
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Shenoy, Bhamy Maithry. "Quantum-Continuum Modeling and Simulations of Semiconductor Nanostructures". Thesis, 2016. https://etd.iisc.ac.in/handle/2005/4380.
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This thesis proposes a multi-physics model to couple the electrical, mechanical, thermal and quantum mechanical interactions in semiconductor and their heterostructures. Governing differential equations and constitutive relations among the coupled fields are derived from the principles of irreversible thermodynamics. Variational principle is applied to solve the problem numerically using finite element method. Boundary and interface conditions are derived consistently.
In the first part of the thesis, semiconductor-solid interfaces are considered with the example
of III-N thin films. The contributions of individual physical fields in the coupled field interactions on electronic band structures are studied in detail. The effect of various boundary conditions, defused interfaces and doping are analysed using AlN/GaN heterostructures in the present framework.
In the second part, we study three-dimensional Si quantum dots/ nanocrystals embedded in SiO2 matrix. The purpose of this analysis is to introduce atomic continuum framework in the present scheme. The matrix embedded structure is first created using atomistic simulations based on molecular dynamics theory. The scheme is to create simulated annealing so that realistic Si/SiO2 interface is formed. The interface properties namely width, stoichiometry, point defects and their statistics are studied with respect to nanocrystal size. Residual strain due to thermal annealing is computed. The local properties are then applied in the proposed continuum framework via interpolation functions to calculate the electronic band structure of the nanocrystals. The electronic energy bandgap variation with quantum dot diameter is estimated and compared with
reported literature. The corrections applied via local strain is observed to improve the accuracy of computation. In the final part of the thesis, we apply the multi-physics model to study semiconductor- fluid interfaces. Semiconductor nanostructures in microfluidic environment are emerging as frontiers in next generation of bioengineering and biomedical fields. The complexity
and multi-disciplinary nature of the problem poses a highly challenging task in understanding and designing new designs. In this direction, our model aims at addressing coupled electrical, mechanical and quantum mechanical effects on fluid ow in microfluidic channels consisting of semiconductor nanostructures. To illustrate this, we analyse the effect of nanowire array on electric field and ow in microfluidic channels. A systematic study on the effect of geometry, orientations and inter-nanowire spacing on the physical fields are studied. Nanowire arrays of Si, Si/SiO2 and ZnO in microfluidic channel is considered as examples. Further, their implications on particle trajectories are discussed in the context of trapping and lysing of biological cells. Additionally, we study the effect of electrolytic fluid on the electronic band structure of ZnO nanowires by varying the diameter, tip pointedness and applied electric field.
To summarize, the thesis proposes a fully coupled quantum-continuum multi-physics modelling framework and provide computational examples having potential applications in nanostructure-based devices. The contribution made in this thesis would be useful in advancing the current understanding of nano-scale phenomena involving electro-thermal mechanical interactions, quantum effect, nanostructure heterojunctions, semiconductor- fluid interfaces and several others, and towards developing better tools in designing new nano-electronic devices from concepts to operation.
Książki na temat "Quantum-Continuum Modeling"
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Bellman Continuum Workshop (3rd 1988 Sophia-Antipolis, France). Modeling and control of systems in engineering, quantum mechanics, economics, and biosciences: Proceedings of the Bellman Continuum Workshop 1988, June 13-14, Sophia Antipolis, France. Redaktor Blaquière Austin. Berlin: Springer-Verlag, 1989.
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Modeling and Control of Systems in Engineering, Quantum Mechanics, Economics and Biosciences: Proceedings of the Bellmann Continuum Workshop 1988, June 13-14, Sophia Antipolis, France. Springer-Verlag Berlin and Heidelberg GmbH & Co. KG, 1989.
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Asuncion L. Magsino, Maria. "A Biosemiotic Modeling of the Body-“Self” Synechism". W Mind and Matter - Challenges and Opportunities in Cognitive Semiotics and Aesthetics [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.100037.
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As a counterargument to the Cartesian split that has impacted both speculative and practical fields of knowledge and culture, we propose Peirce’s doctrine of synechism to show the continuity in the semiotic activity that moves from the body as an Interpretant to the emergence of another Interpretant called the “self.” Biosemiotics, a nascent field of interdisciplinary research that tackles inquiries about signs, communication, and information involving living organisms is used as the framework in the discussion. The main question of whether a non-material “self” can emerge from a material body is tackled in many stages. First, the biosemiotic continuum is established in the natural biological processes that takes place in the body. These processes can be taken as an autonomous semiotic system generating the “language” of the body or the Primary Modeling System (PMS). Second, synechism is also observed in the relationship between the mind and the body and this is evident in any physician’s clinical practice. The patient creates a Secondary Modeling System (SMS) of how she perceives what the body communicates to her regarding its state or condition. Finally, the question about whether the emergence of “self” is synechistic as well is tackled. There is one organ from which emerges an Interpretant that is capable of generating a dialog between a Subject, that is the “self,” with its Object, and that is the brain. It is the primordial seat of specifically human activities like thought and language. The recent theory on quantum consciousness supports the doctrine synechism between the body as Interpretant to the “self” as Interpretant. This synechism is crucial for the creation of Secondary Models of “reality” that will, in turn, determine the creation of Tertiary Models more familiarly called culture.
Streszczenia konferencji na temat "Quantum-Continuum Modeling"
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Friedman, Lawrence H. "Stochastic continuum modeling self-assembled epitaxial quantum dot formation". W NanoScience + Engineering, redaktorzy Geoffrey B. Smith i Akhlesh Lakhtakia. SPIE, 2008. http://dx.doi.org/10.1117/12.795615.
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Oates, William S. "Correlations Between Quantum Mechanics and Continuum Mechanics for Ferroelectric Material Simulations". W ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/smasis2013-3184.
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Higher order effects in ferroelectric materials are investigated by integrating electron density calculations using quantum mechanics into a homogenized, nonlinear continuum modeling framework. Electrostatic stresses based on the Hellmann-Feynman theorem are used to identify connections with the higher order quadrupole density. These higher order relations are integrated into a nonlinear mechanics free energy function to simulate electromechanical coupling. A specific example is investigated by conducting density functional theory (DFT) calculations on barium titanate and fitting the results to a thermodynamic potential function. Through the use of nonlinear geometric effects, electromechanical coupling is obtained without the use of electrostrictive or piezoelectric coupling coefficients.
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Ji, Pengfei, Mengzhe He, Yiming Rong, Yuwen Zhang i Yong Tang. "Multiscale Investigation of Thickness Dependent Melting Thresholds of Nickel Film Under Femtosecond Laser Heating". W 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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Li, Guanchen, i Michael R. von Spakovsky. "Study of the Transient Behavior and Microstructure Degradation of a SOFC Cathode Using an Oxygen Reduction Model Based on Steepest-Entropy-Ascent Quantum Thermodynamics". W ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53726.
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Oxygen reduction in a solid oxide fuel cell (SOFC) cathode involves a non-equilibrium process of coupled mass and heat diffusion and electrochemical and chemical reactions. These phenomena occur at multiple temporal and spatial scales, from the mesoscopic to the atomistic level, making the modeling, especially in the transient regime, very difficult. Nonetheless, multi-scale models are needed to improve an understanding of oxygen reduction and guide fuel cell cathode design. Existing methods are typically phenomenological or empirical in nature so their application is limited to the continuum realm and quantum effects are not captured. Steepest-entropy-ascent quantum thermodynamics (SEAQT) can be used to model non-equilibrium processes (even those far-from equilibrium) from the atomistic to the macroscopic level. The non-equilibrium relaxation is characterized by the entropy generation, and the study of coupled heat and mass diffusion as well as electrochemical and chemical activity are unified into a single framework. This framework is used here to study the transient and steady state behavior of oxygen reduction in an SOFC cathode system. The result reveals the effects on performance of the different timescales of the varied phenomena involved and their coupling. In addition, the influence of cathode microstructure changes on performance is captured.
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Liu, Wing Kam, i Ashfaq Adnan. "Multiscale Modeling and Simulation for Nanodiamond-Based Therapeutic Delivery". W ASME 2010 First Global Congress on NanoEngineering for Medicine and Biology. ASMEDC, 2010. http://dx.doi.org/10.1115/nemb2010-13273.
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It has been demonstrated from recent research that nanodiamond(ND)-enabled drug delivery as cancer therapeutics represents an important component of optimized device functionality. The goal of the current research is to develop a multiscale modeling technique to understand the fundamental mechanism of a ND-based cancer therapeutic drug delivery system. The major components of the proposed device include nanodiamonds (ND), parylene buffer layer and doxorubicin (DOX) drugs, where DOX loaded self-assembled nanodiamonds are packed inside parylene capsule. The efficient functioning of the device is characterized by its ability to precisely detect targets (cancer cells) and then to release drugs at a controlled manner. The fundamental science issues concerning the development of the ND-based device includes (a) a precise identification of the equilibrium structure, surface electrostatics and self assembled morphology of nanodiamonds, (b) understanding of the drug/biomarker adsorption and desorption process to and from NDs, (c) rate of drug release through the parylene buffers, and finally, (d) device performance under physiological condition. In this study, we aim to systematically address these issues using a multscale computational framework. Specifically, the structure and electrostatics of the functionalized NDs are predicted by quantum scale calculation (Density Functional Tight Binding). The DFTB) study on smaller NDs suggests a facet dependent charge distributions on ND surfaces. Using the charges for smaller NDs (∼ valid for 1–3.3 nm dia ND), we then determined surface charges for larger (4–10 nm) truncated octahedral nanodiamonds (TOND). We found that the [100] face and the [111] face contain positively and negatively charged atoms, respectively. Employing this surface electrostatics of nanodiamonds, atomistic-scale simulations are performed to simulate the self-assembly process of the NDs and drug molecules in a solution as well as to evaluate nanoscale diffusion coefficient of DOX molecules. In order to quantify the nature of the aggregate morphology, a fractal analysis has been performed. The mass fractal dimensions for a variety of aggregate size have been obtained from molecular simulations assuming ‘diffusion-limited aggregation (DLA)’ process. Then, by considering the experimentally observed aggregate dimensions, by using DLA based fractal analysis and by utilizing Lagvankar-Gemmell Model for aggregate density, a continuum model for larger aggregates will be developed to characterize aggregate strengths and break-up mechanism, which in turn will help us to understand how aggregate size can be reduced. In this talk, an outline for this continuum model will be discussed. In addition, we have been performing molecular simulations on DOX-ND where multiple drug molecules are allowed to interact with a cluster of self-assembled nanodiamonds in pH controlled solution. The purpose of this study is to find the effect of solution pH on the loading and release of drug to and from nanodiamonds. Our initial results show that a higher pH is necessary to ensure drug release from nanodiamonds. Once we completely understand the essential physics of pH controlled drug loading and release, we plan to develop multiscale models of tumor nodules to represent them as a collection of individual tumor cells. Each cell will be then modeled as a deformable body comprised of three homogenous materials: cortex membrane, cytosol and nucleus. The cortex membrane and the cytosol will serve as a weak permeable medium where the absorption coefficients of the doxorubicin remain constant and obey Fick’s law. In this study, it will be assumed that drug release from the microdevice to its outer periphery will be governed by Fickian Diffusion. It will also be assumed that the complex flow of drug through the interstitial fluid of the body will be dictated by Darcy’s law. It will be assumed that the solute drug transport in these regions will be due to a combination of convection, diffusion, elimination in the intra- and extra-cellular space, receptive cell internalization and degradation. Results from this study will provide fundamental insight on the definitive targeting of infected cells and high resolution controlling of drug molecules.
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Queiroz, Nayhara B. D. F., i M. S. Amaral. "EFEITOS DE MICRO-HIDRATAÇÃO EM PROPRIEDADES CONFORMACIONAIS E ESPECTROSCÓPICAS DO ANTIBIÓTICO MARBOFLOXACINO". W VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol2020177.
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Marbofloxacin (MRB) is a fluoroquinolone used as a veterinary antibiotic. Some analytical methods of optical absorption are used for their determination in pharmaceutical formulations. Thus, we decided to study the electronic absorption spectrum of MRB in the UV-Vis region. For this, we use the TD-DFT, COSMO methods - based on the solvation continuum model - and micro-hydration. The interactions of MRB in both water and vacuum were simulated using computational modeling techniques. Ab initio quantum calculations were used to optimize the geometry of the isolated molecule and in the optical transition energy calculations. The solute-solvent simulation was performed with the Molecular Dynamics technique in the NpT ensemble using a temperature of 300 K in the Amber computer package. The system balance was monitored by Root Mean Square Deviation. The analyzes of the absorption spectra were carried out using the micro-hydration method. This method involved the use of different numbers, from 2 to 8, of the water molecules of the first solvation layer to calculate transition energies. The transition energies were calculated using the TD-DFT method at the theory level B3LYP / 6-311G using together the Conductor-like Screening Model solvation model that assesses the effect of the solvent implicit in the system. For all micro-hydration systems, energy absorption decreases as the wavelength increases. Observing the values it is noticed that there was a deviation in the absorption spectrum 325.4 nm (in the isolated molecule) to 274.1 (with the addition of water). These values are within the experimental ones where we have the bands with maximum absorption at 268 nm and 335 nm.
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Buehler, Markus J. "Defining Nascent Bone by the Molecular Nanomechanics of Mineralized Collagen Fibrils". W ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-12137.
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Here we focus on recent advances in understanding the deformation and fracture behavior of collagen, Nature’s most abundant protein material and the basis for many biological composites including bone, dentin or cornea. We show that it is due to the basis of the collagen structure that leads to its high strength and ability to sustain large deformation, as relevant to its physiological role in tissues such as bone and muscle. Experiment has shown that collagen isolated from different sources of tissues universally displays a design that consists of tropocollagen molecules with lengths of approximately 300 nanometers. Using a combination of theoretical analyses and multi-scale modeling, we have discovered that the characteristic structure and characteristic dimensions of the collagen nanostructure is the key to the ability to take advantage of the nanoscale properties of individual tropocollagen molecules at larger scales, leading to a tough material at the micro- and mesoscale. This is achieved by arranging tropocollagen molecules into a staggered assembly at a specific optimal molecular length scale. During bone formation, nanoscale mineral particles precipitate at highly specific locations in the collagen structure. These mineralized collagen fibrils are highly conserved, nanostructural primary building blocks of bone. By direct molecular simulation of the bone’s nanostructure, we show that it is due to the characteristic nanostructure of mineralized collagen fibrils that leads to its high strength and ability to sustain large deformation, as relevant to its physiological role, creating a strong and tough material. We present a thorough analysis of the molecular mechanisms of protein and mineral phases in deformation, and report discovery of a new fibrillar toughening mechanism that has major implications on the fracture mechanics of bone. Our studies of collagen and bone illustrate how hierarchical multi-scale modeling linking quantum chemistry with continuum fracture mechanics approaches can be used to develop predictive models of hierarchical protein materials. We conclude with a discussion of the significance of hierarchical multi-scale structures for the material properties and illustrate how these structures enable one to overcome some of the limitations of conventional materials design, combining disparate material properties such as strength and robustness.
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Medlar, Michael P., i Edward C. Hensel. "Validation of a Physics Based Three Phonon Scattering Algorithm Implemented in the Statistical Phonon Transport Model". W ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23307.
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Abstract Three phonon scattering is the primary mechanism by which phonon transport is impeded in insulating and semiconducting bulk materials. Accurate computational modeling of this scattering mechanism is required for high fidelity simulations of thermal transport across the ballistic (quantum mechanics) to Fourier (continuum mechanics) range of behavior. Traditional Monte Carlo simulations of phonon transport use a scaling factor such that each scattering event is considered representative of a large number of phonons, often on the order of 104 physical phonons per simulated event. The ability to account for every phonon scattering event is desirable to enhance model fidelity. A physics-based model using time dependent perturbation theory (Fermi’s Golden Rule) is implemented to compute three phonon scattering rates for each permissible phonon interaction subject to selection rules. The strength of the interaction is based on use of a Gruneisen-like parameter. Both Type I and Type II scattering rates are computed for the allowable interactions that conserve energy and momentum (up to the addition of a reciprocal lattice vector) on a given discretization of momentum space. All of the phonons in the computational domain are represented and phonon populations are updated in momentum space and real space based on the computed number of phonons involved in given scattering events. The computational algorithm is tested in an adiabatic single cell of silicon of dimension 100 × 100 × 100 nm at a nominal temperature of 500 Kelvin containing approximately 108 fully anisotropic phonons. The results indicate that phonon populations return to equilibrium if artificially displaced from that condition. Two approaches are introduced to model the relaxation time of phonon states: the single mode relaxation time (SMRT) which is consistent with the underlying assumptions for previously reported theoretical estimates, and the multi model relaxation time (MMRT) which is more consistent with in-situ conditions. The trends meet physical expectations and are comparable to other literature results. In addition, an estimate of error associated with the relaxation times is presented using the statistical nature of the model. The three phonon scattering model presented provides a high fidelity representation of this physical process that improves the computational prediction of anisotropic phonon transport in the statistical phonon transport model.