Relevant bibliographies by topics / Diracův bod

Contents

  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers
  6. Reports

Academic literature on the topic 'Diracův bod'

Author: Grafiati
Published: 4 June 2021
Last updated: 17 February 2022

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Journal articles on the topic "Diracův bod"

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BÄKER, MARTIN. "THE PRINCIPLE OF INDIRECT ELIMINATION." International Journal of Modern Physics C 07, no. 04 (August 1996): 503–20. http://dx.doi.org/10.1142/s0129183196000442.

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The principle of indirect elimination states that an algorithm for solving discretized differential equations can be used to identify its own bad-converging modes. When the number of bad-converging modes of the algorithm is not too large, the modes thus identified can be used to strongly improve the convergence. The method presented here is applicable to any linear algorithm like relaxation or multigrid. An example from theoretical physics, the Dirac equation in the presence of almost-zero-modes arising from instantons, is studied. Using the principle, bad-converging modes are removed efficiently. It is sketched how the method can be used for a Conjugate Gradient algorithm. Applied locally, the principle is one of the main ingredients of the Iteratively Smoothing Unigrid algorithm.
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Massabó, M., R. Cianci, and O. Paladino. "An Analytical Solution of the Advection Dispersion Equation in a Bounded Domain and Its Application to Laboratory Experiments." Journal of Applied Mathematics 2011 (2011): 1–14. http://dx.doi.org/10.1155/2011/493014.

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We study a uniform flow in a parallel plate geometry to model contaminant transport through a saturated porous medium in a semi-infinite domain in order to simulate an experimental apparatus mainly constituted by a chamber filled with a glass beads bed. The general solution of the advection dispersion equation in a porous medium was obtained by utilizing the Jacobiθ3Function. The analytical solution here presented has been provided when the inlet (Dirac) and the boundary conditions (Dirichelet, Neumann, and mixed types) are fixed. The proposed solution was used to study experimental data acquired by using a noninvasive technique.
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Kauppinen, Jyrki K., and Eija K. Saario. "What is Wrong with MEM?" Applied Spectroscopy 47, no. 8 (August 1993): 1123–27. http://dx.doi.org/10.1366/0003702934067801.

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The maximum-entropy method (MEM) is a typical method, where the power spectral estimator is claimed to be proportional to the power of the transfer function of the autoregression (AR) model filter. The AR power spectral estimator is shown theoretically and with practical examples to be a very bad approximation of the true power spectrum. The estimator loses almost all the intensity (line strength) information of the power spectrum, and there can be very large distortions in the estimated power spectrum. The reason for the malfunction of the MEM is the approximation where the autocorrelation function of any random white noise is assumed to be the Dirac delta function. However, this is not true in practice.
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Barbero, Fernando, Marc Basquens, Valle Varo, and Eduardo J. S. Villaseñor. "Three Roads to the Geometric Constraint Formulation of Gravitational Theories with Boundaries." Symmetry 13, no. 8 (August 4, 2021): 1430. http://dx.doi.org/10.3390/sym13081430.

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The Hamiltonian description of mechanical or field models defined by singular Lagrangians plays a central role in physics. A number of methods are known for this purpose, the most popular of them being the one developed by Dirac. Here, we discuss other approaches to this problem that rely on the direct use of the equations of motion (and the tangency requirements characteristic of the Gotay, Nester and Hinds method), or are formulated in the tangent bundle of the configuration space. Owing to its interesting relation with general relativity we use a concrete example as a test bed: an extension of the Pontryagin and Husain–Kuchař actions to four dimensional manifolds with boundary.
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Xu, Xin Miao, and Yu Lu. "First-Principles Study of Energy Band Gap of Graphene-Like B-C-N by Strain." Advanced Materials Research 476-478 (February 2012): 1313–17. http://dx.doi.org/10.4028/www.scientific.net/amr.476-478.1313.

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We report a first-principles investigation on BN dopped monolayer graphene sheet and examined the electronic band structure and band gaps in equilibrium state and under strain. The obtained results reveal that the doping of B-N pairs on the hexagonal sheet can open the gap at the Dirac-like point. With heavy doping and more B-N bonds the energy bad gap is found to be larger. Upon tensile deformation, the dopped BCN monolayer sheet represents a strong anisotropic stress-strain relation. Detailed strain-gap relation investigation reveals that the energy band gap presents desperate variation trends for strain applied along and direction. Versatile band-gap modulation schemes can then be obtained through direction-dependent strain engineering of the BCN nanosheet..
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Baratti, Roberto, Asterios Gavriilidis, Massimo Morbidelli, and Arvind Varma. "Optimization of a nonisothermal nonadiabatic fixed-bed reactor using dirac-type silver catalysts for ethylene epoxidation." Chemical Engineering Science 49, no. 12 (June 1994): 1925–36. http://dx.doi.org/10.1016/0009-2509(94)80077-4.

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Knudsen, G. M., K. D. Pettigrew, C. S. Patlak, and O. B. Paulson. "Blood-brain barrier permeability measurements by double-indicator method using intravenous injection." American Journal of Physiology-Heart and Circulatory Physiology 266, no. 3 (March 1, 1994): H987—H999. http://dx.doi.org/10.1152/ajpheart.1994.266.3.h987.

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The double-indicator technique with intracarotid bolus injection is useful for the estimation of transfer rates across the human blood-brain barrier. A method using intravenous tracer injection is developed whereby the input is measured at a peripheral artery and the output is measured at the jugular vein. To correct for differences in the brain input of test and reference substances, a five-parameter Dirac impulse response for passage through the cerebrovascular bed is computed from the input and output of the reference substance. This response is then combined with a capillary model of the brain. This is then convoluted with the arterial input curve of the test substance to yield a theoretical test output curve, which is compared with the actual test output curve. On the basis of these two curves and an appropriate mathematical model for the brain, estimates of blood-brain barrier permeability are obtained. In the present study, the techniques are compared in 13 patients in whom alternating intracarotid and intravenous bolus injections were given. For D-glucose, the two techniques yielded similar results. This was also the case for L-phenylalanine, provided that the erythrocyte compartment was taken into account. Data obtained after intravenous injection of leucine and water yielded similar results compared with previous intracarotid data.
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Seminara, Giovanni, Marco Colombini, and Gary Parker. "Nearly pure sorting waves and formation of bedload sheets." Journal of Fluid Mechanics 312 (April 10, 1996): 253–78. http://dx.doi.org/10.1017/s0022112096001991.

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Bedload sheets are coherent migrating patterns of bed material recently observed both in flume studies and in field streams with beds of coarse sand and fine gravel. This newly recognized feature is inherently associated with the heterogeneous character of the sediment and consists of sorting waves with distinct coarse fronts only one or two coarse grains high.The question of the formation of bedload sheets poses an interesting and peculiar stability problem for the grain size distribution. Sorting waves are essentially two-dimensional migrating perturbations associated with variations of this distribution. We show that their growth is strictly associated with grain sorting. In fact the latter gives rise to perturbations of bedload transport which drive small perturbations of bottom elevation the amplitude of which scales with grain size. The sorting wave also induces spatial variations of bottom roughness, and consequently alters the fluid motion, which conversely exerts a spatially varying stress on the bed. The feature of bedload sheets which allows them to be distinguished from dunes over beds with coarse sand or fine gravel is then the fact that sorting is the dominant effect controlling their growth, rather than being a relatively small perturbation of the mechanism which gives rise to dunes in the case of uniform sediment.The requirement that perturbations should not alter the sediment budget leads to an integral condition which gives rise to an integro-differential mathematical problem. With the help of recently developed bedload relationships suitable for mixtures, as well as appropriate modelling of turbulent channel flow over a bed with spatially periodic perturbations of bottom elevation and roughness we are able to derive a general dispersion relation which can be readily solved in terms of undisturbed size densities in the form of sums of Dirac distributions.Perturbations are found to be unstable within a range of wavenumbers depending on the relative roughness and Froude number. We show that when the effects of perturbations of bottom elevation are neglected the unstable region corresponds to the range of conditions where the bottom stress leads bottom roughness, a range distinct from that which characterizes the formation of dunes. This result is given a physical explanation which depends crucially on the deviation from equal mobility of different grain sizes in the surface layer. The effect of perturbations of bottom elevation is however not negligible when the bottom roughness is fairly large compared to depth. In the latter case perturbations of bottom elevation and of bottom roughness are equally important, and gravel sheets are not easily distinguished from small-amplitude dunes.Comparison with the field observations of Whiting et al. (1985, 1988) is satisfactory insofar as the bedload sheet mode is unstable under the conditions of the experiments, and the predicted wavelengths fall within the experimental range. The laboratory observations of Kuhnle & Southard (1988), on the other hand, appear to fall within a range of bottom roughness where the observed bedforms do not exhibit features unambiguously distinct from those of small-amplitude dunes.
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Dissertations / Theses on the topic "Diracův bod"

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Mareček, David. "Vliv elektronového svazku na grafenové polem řízené tranzistory." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-320004.

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This diploma thesis deals with electrical conductivity of a graphene sample, preparation of a graphene field-effect transistor and his irradiation by electron beam. In the theoretical part of the thesis, we describe electronic properties of graphene, preparation of graphene by CVD and its transfer to Si substrate with SiO_2 layer. Experimental part of this thesis is focused on the preparation of a graphene field-effect transistor for use in UHV conditions. Futher describes electron beam scanning over the transistor and creation of current maps of tranzistor. In the last part, the thesis deals with influence of electron beam on transport properties of graphene layer and doping of graphene layer by electron beam.
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Piastek, Jakub. "Příprava grafenových vrstev pokrytých Ga atomy a charakterizace jejich elektrických vlastností." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231957.

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This master's thesis deals with the study of electric properties of graphene layers covered by Ga atoms in UHV conditions. The substrates were prepared by using laser litography and the graphene layer was prepared by using chemical vapor deposition (CVD). Dependence of Dirac point location on gallium atoms deposition time and influence of electrical properties of graphene on hydrogen atoms deposition time were studied. Experimental results and their evaluation are discussed.
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Iqbal, Yasir. "Liquides de spin dans les modèles antiferromagnétiques quantiques sur réseaux bi-dimensionnels frustrés." Phd thesis, Université Paul Sabatier - Toulouse III, 2012. http://tel.archives-ouvertes.fr/tel-00752096.

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La recherche de phases magnétiques exotiques de la matière qui fondent même à T=0 uniquement sous l'action des fluctuations quantiques a été long et ardu, à la fois théoriquement et expérimentalement. La percée est venue récemment avec la découverte de l'Herbertsmithite, un composé formant un réseau kagome parfait avec des moments magnétiques de spin-1/2. Des expériences pionnières, mêlant des mesures de NMR, µSR et de diffusion de neutrons, ont montré une absence totale de gel ou d'ordre des moments magnétiques de spin, fournissant ainsi une forte signature d'une phase paramgnétique quantique. Théoriquement, l'Herbertsmithite est extrêmement bien modélisé par le modèle de Heisenberg quantique antiferromagnétique pour des spins-1/2 sur le réseau kagome, problème qui n'a pas été résolu jusqu'à présent. Plusieurs méthodes approximatives numériques et analytiques ont donné différents états fondamentaux, allant des liquides de spins Z2 gappés et un liquide de spins exotique algébrique U(1) de Dirac aux liquides de spins chiraux et les cristaux à liaisons de valence. Dans cette thèse, le problème est traité dans le cadre d'une approche particule-esclave fermionique, à savoir le formalisme des fermions de Schwinger SU(2). Il est conclu qu'un liquide de spins sans gap algébrique de Dirac a l'énergie variationnelle la plus basse et peut en fait constituer un vrai état fondamental physique de liquide de spins. Une implémentation sophistiquée de méthodes numériques de pointes comme le Monte-Carlo variationnel, le Monte-Carlo fonctions de Green et l'application de pas Lanczos dans un schéma variationnel ont été utilisés. Il est montré que contrairement à la croyance habituelle, le liquide de spins de Dirac U(1) projeté en "2+1" dimensions est remarquablement robuste par rapport à une large classe de perturbations, incluant les liquides de spins topologiques Z2 et les cristaux à liaisons de valence. De plus, l'application de deux pas Lanczos sur la fonction d'onde du liquide de spins de Dirac U(1) montre que son énergie est compétitive avec celles proposées pour les liquides de spins topologiques Z2. Ce résultat, combiné avec les indications expérimentales qui pointent vers un liquide de spins sans gap pour l'Herbertsmithite, appuie l'affirmation que le vrai état fondamental de ce modèle est en fait un liquide de spins algébrique de Dirac.
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Liu, Bin. "Two body dirac equations and nucleon nucleon scattering phase shift analysis." 2001. http://etd.utk.edu/2001/LiuBin.pdf.

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Thesis (Ph. D.)--University of Tennessee, Knoxville, 2001.
Title from title page screen. Document formatted into manuscript-like pagination: xi, 252 leaves : ill. Vita. Includes bibliographical references (leaves 194-198).
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Books on the topic "Diracův bod"

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T, Ivancevic Tijana, ed. Quantum leap: From Dirac and Feynman, across the universe, to human body and mind. Singapore: World Scientific, 2008.

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Succi, Sauro. QLB for Quantum Many-Body and Quantum Field Theory. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199592357.003.0033.

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Chapter 32 expounded the basic theory of quantum LB for the case of relativistic and non-relativistic wavefunctions, namely single-particle quantum mechanics. This chapter goes on to cover extensions of the quantum LB formalism to the overly challenging arena of quantum many-body problems and quantum field theory, along with an appraisal of prospective quantum computing implementations. Solving the single particle Schrodinger, or Dirac, equation in three dimensions is a computationally demanding task. This task, however, pales in front of the ordeal of solving the Schrodinger equation for the quantum many-body problem, namely a collection of many quantum particles, typically nuclei and electrons in a given atom or molecule.
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Eriksson, Olle, Anders Bergman, Lars Bergqvist, and Johan Hellsvik. Density Functional Theory. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198788669.003.0001.

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Density functional theory (DFT) has established itself as a very capable platform for modelling from first principles electronic, optical, mechanical and structural properties of materials. Starting out from the Dirac equation for the many-body system of electrons and nuclei, an effective theory has been developed allowing for materials specific and parameter free simulations of non-magnetic and magnetic solid matter. In this Chapter an introduction will be given to DFT, the Hohenberg-Kohn theorems, the Kohn-Sham equation, and the formalism for how to deal with non-collinear magnetism.
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Swendsen, Robert H. An Introduction to Statistical Mechanics and Thermodynamics. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198853237.001.0001.

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This is a textbook on statistical mechanics and thermodynamics. It begins with the molecular nature of matter and the fact that we want to describe systems containing many (1020) particles. The first part of the book derives the entropy of the classical ideal gas using only classical statistical mechanics and Boltzmann’s analysis of multiple systems. The properties of this entropy are then expressed as postulates of thermodynamics in the second part of the book. From these postulates, the structure of thermodynamics is developed. Special features are systematic methods for deriving thermodynamic identities using Jacobians, the use of Legendre transforms as a basis for thermodynamic potentials, the introduction of Massieu functions to investigate negative temperatures, and an analysis of the consequences of the Nernst postulate. The third part of the book introduces the canonical and grand canonical ensembles, which are shown to facilitate calculations for many models. An explanation of irreversible phenomena that is consistent with time-reversal invariance in a closed system is presented. The fourth part of the book is devoted to quantum statistical mechanics, including black-body radiation, the harmonic solid, Bose–Einstein and Fermi–Dirac statistics, and an introduction to band theory, including metals, insulators, and semiconductors. The final chapter gives a brief introduction to the theory of phase transitions. Throughout the book, there is a strong emphasis on computational methods to make abstract concepts more concrete.
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Book chapters on the topic "Diracův bod"

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Moshinsky, M. "The One Body Dirac Oscillator." In Symmetries in Science VI, 503–14. Boston, MA: Springer US, 1993. http://dx.doi.org/10.1007/978-1-4899-1219-0_42.

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Marcos, S., R. Niembro, M. López-Quelle, L. N. Savushkin, and P. Bernardos. "The Pseudospin Symmetry in Finite Nuclei: Dirac Phenomenology." In The Nuclear Many-Body Problem 2001, 131–36. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0460-2_18.

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Claro, F., and P. Robles. "Graphene-Like Massless Dirac Fermions in Harper Systems." In Many-body Approaches at Different Scales, 35–41. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-72374-7_4.

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Mendl, Ch B., S. Palpacelli, A. Kamenev, and S. Succi. "Quantum Lattice Boltzmann Study of Random-Mass Dirac Fermions in One Dimension." In Many-body Approaches at Different Scales, 321–30. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-72374-7_26.

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Moshinsky, M., G. Loyola, and C. Villegast. "Relativistic invariance of a many body system with a Dirac oscillator interaction." In Group Theoretical Methods in Physics, 339–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 1991. http://dx.doi.org/10.1007/3-540-54040-7_127.

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Scerri, Eric R. "The Changing Views of a Philosopher of Chemistry on the Question of Reduction." In Essays in the Philosophy of Chemistry. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780190494599.003.0012.

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The question of the reduction of chemistry to quantum mechanics has been inextricably linked with the development of the philosophy of chemistry since the field began to develop in the early 1990s. In the present chapter I would like to describe how my own views on the subject have developed over a period of roughly 30 years. A good place to begin might be the frequently cited reductionist dictum that was penned in 1929 by Paul Dirac, one of the founders of quantum mechanics. . . . The underlying laws necessary for the mathematical theory of a larger part of physics and the whole of chemistry are thus completely known, and the difficulty is only that exact applications of these laws lead to equations, which are too complicated to be soluble. (Dirac 1929) . . . These days most chemists would probably comment that Dirac had things backward. It is clear that nothing like “the whole of chemistry” has been mathematically understood. At the same time most would argue that the approximate solutions that are afforded by modern computers are so good as to overcome the fact that one cannot obtain exact or analytical solutions to the Schrödinger equation for many-electron systems. Be that as it may, Dirac’s famous quotation, coming from one of the creators of quantum mechanics, has convinced many people that chemistry has been more or less completely reduced to quantum mechanics. Another quotation of this sort (and one using more metaphorical language) comes from Walter Heitler who together with Fritz London was the first to give a quantum mechanical description of the chemical bond. . . . Let us assume for the moment that the two atomic systems ↑↑↑↑ . . . and ↓↓↓↓ . . . are always attracted in a homopolar manner. We can, then, eat Chemistry with a spoon. (Heitler 1927) . . . Philosophers of science eventually caught up with this climate of reductionism and chose to illustrate their views with the relationship with chemistry and quantum mechanics.
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Wijesundera, Wasantha, Ian Grant, and Patrick Norrington. "Electron scattering from atomic targets: application of Dirac R-matrix theory." In Many-Body Atomic Physics, 325–48. Cambridge University Press, 1998. http://dx.doi.org/10.1017/cbo9780511470790.016.

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Dyall, Kenneth G., and Knut Faegri. "Introduction." In Introduction to Relativistic Quantum Chemistry. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195140866.003.0005.

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The quote above from Paul Adrian Maurice Dirac (1929) has been somewhat of an article of faith for modern quantum chemistry. Intensive efforts on the development of theory, algorithms, and techniques have made computational quantum chemistry a very successful representative of the “third way” in modern science—computer modeling has come into its own alongside experiment and theory. Fifty years ago this was a branch of science where predictions were at best qualitative, founded on rather approximate models. Many of these models were quite sophisticated, and much of the insight gained is still valid and valuable, but the developments in both methods and computer hardware up to the present have very much transformed this field. Today standard quantum chemical methods are capable of predicting results with chemical accuracy: reaction energies may be determined within a few kilojoules per mole, and spectral data within a few reciprocal centimeters. At least, this sort of reliability can be expected for “normal” areas of application. Dirac’s main contribution to science was a merging of the two great developments of 20th century physics—quantum mechanics and the (special) theory of relativity. Most of the successful development in quantum chemistry has been based on nonrelativistic quantum mechanics. This may be justified by considering that special relativity is needed primarily to describe objects moving at velocities approaching the speed of light, and that this is mostly not the case for chemical systems. After all, most chemical reactions and phenomena occur at energies below the relativistic domain. Or could relativistic effects nevertheless be important? Even without the recent advances in computational chemistry, it became clear fairly early that nonrelativistic theory was unable to explain certain trends in observed properties. A few examples will suffice to illustrate the anomalies. Experimental determination of the metal–carbon bond length in the group 12 dimethyl compounds showed an increase in bond length from Zn to Cd, but a decrease in bond length from Cd to Hg (Rao et al. 1960). The expected trend was an increase from Zn to Cd and again from Cd to Hg.
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Swendsen, Robert H. "Ideal Quantum Gases." In An Introduction to Statistical Mechanics and Thermodynamics, 350–68. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198853237.003.0027.

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As a preliminary to discussing the properties of Bose–Einstein and Fermi–Dirac gases, this chapter presents the basic quantum equations that underlie both. The process of building N-body states from single-particle states is described, along with notation necessary to simplify the problem. The average number of particles in a given energy state and chemical potential is derived for fermions and bosons. Although all atoms are either bosons or fermions, and therefore indistinguishable, there are nevertheless real systems that are composed of distinguishable particles. Although all atoms are either bosons or fermions, and therefore indistinguishable, there are nevertheless real systems that are composed of distinguishable particles.
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Kenyon, Ian R. "Review of basic quantum physics." In Quantum 20/20, 1–20. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198808350.003.0001.

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Basic experimental evidence is sketched: the black body radiation spectrum, the photoeffect, Compton scattering and electron diffraction; the Bohr model of the atom. Quantum mechanics is reviewed using the Copenhagen interpretation: eigenstates, observables, hermitian operators and expectation values are explained. Wave-particle duality, Schrödinger’s equation, and expressions for particle density and current are described. The uncertainty principle, the collapse of the wavefunction, Schrödinger’s cat and the no-cloning theorem are discussed. Dirac delta functions and the usage of wavepackets are explained. An introduction to state vectors in Hilbert space and the bra-ket notation is given. Abstracts of special relativity and Lorentz invariants follow. Minimal electromagnetic coupling and the gauge transformations are explained.
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Conference papers on the topic "Diracův bod"

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Desplanques, B. "A relativistic quantum mechanics approach inspired by the Dirac’s point form." In FEW-BODY PROBLEMS IN PHYSICS: The 19th European Conference on Few-Body Problems in Physics. AIP, 2005. http://dx.doi.org/10.1063/1.1932970.

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Crater, Horace W., James Schiermeyer, Joshua Whitney, and Cheuk-Yin Wong. "Applications of Two Body Dirac Equations to Hadron and Positronium Spectroscopy." In Proceedings of CST-MISC Joint Symposium on Particle Physics — from Spacetime Dynamics to Phenomenology —. Journal of the Physical Society of Japan, 2015. http://dx.doi.org/10.7566/jpscp.7.010002.

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Ito, Hitoshi. "Two-body Dirac equation and its wave function at the origin." In The seventh international conference on hadron spectroscopy. AIP, 1998. http://dx.doi.org/10.1063/1.56040.

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Crater, Horace W., and Peter Van Alstine. "Relativistic extensions of heavy quark static potentials through two body Dirac equations." In AIP Conference Proceedings Volume 132. AIP, 1985. http://dx.doi.org/10.1063/1.35369.

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Huang, Wei-Xi, Cheong Bong Chang, and Hyung Jin Sung. "An Improved Penalty Immersed Boundary Method for Fluid-Flexible Body Interaction." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-20006.

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An improved penalty immersed boundary (pIB) method has been proposed for simulation of fluid-flexible body interaction problems. In the proposed method, the fluid motion is defined on the Eulerian domain, while the solid motion is described by the Lagrangian variables. To account for the interaction, the flexible body is assumed to be composed of two parts: massive material points and massless material points, which are assumed to be linked closely by a stiff spring with damping. The massive material points are subjected to the elastic force of solid deformation but do not interact with the fluid directly, while the massless material points interact with the fluid by moving with the local fluid velocity. The flow solver and the solid solver are coupled in this framework and are developed separately by different methods. The fractional step method is adopted to solve the incompressible fluid motion on a staggered Cartesian grid, while the finite element method is developed to simulate the solid motion using an unstructured triangular mesh. The interaction force is just the restoring force of the stiff spring with damping, and is spread from the Lagrangian coordinates to the Eulerian grids by a smoothed approximation of the Dirac delta function. In the numerical simulations, three-dimensional simulations of fluid-flexible body interaction are carried out, including deformation of a spherical capsule in a linear shear flow. A comparison between the numerical results and the theoretical solutions is presented.
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Melot, Vincent, Jean Franc¸ois Sigrist, Christian Lane, Bruno Auvity, and Hassan Peerhossaini. "Fluid Forces on a Moving Body at Low Amplitude in Fluid at Rest: Part 1 — A Review of Literature." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93018.

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The study of a interaction fluid-structure problem requires the calculation of fluid forces acting on moving boundaries. Since the first studies carried out by Stokes, a lot of work has been performed to derive various expressions of fluid forces, in particular for the case of simple geometry, such as infinite planes, spheres or circular cylinders. These bodies are subjected to elementary motions, namely harmonic motions or Dirac acceleration motions, (i.e. constant speed velocity motions). The present paper exposes a review of fluid forces exerted on accelerated rigid body in an incompressible viscous fluid initially at rest. The principal objective of this paper is to carry out a synthesis of the current literature and to develop a general analytical formulation of the fluid forces in order to deal with more general rigid body motions. The analytical formulation is exposed in the present paper for fluid forces acting on any moving body. This approach is limited to low displacements of the solid body, i.e. the non linear convective term of NS equation is not taken into account. The non-dimensional numbers is pointed out and detailed. The different solutions given in the literature are especially discussed with the influence of the viscosity compared to the irrotational model.
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Mazidi, A., S. A. Fazelzadeh, and P. Marzocca. "Effects of Rolling Angular Velocity on the Flutter of Wing-Store Under Follower Force." In ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30378.

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Abstract:
The flutter analysis of a swept aircraft wing-store configuration subjected to follower force and undergoing a roll maneuver is presented. Concentrated mass, follower force, and roll angular velocity terms are combined in the governing equations which are obtained using the Hamilton’s principle. The wing is modeled from a classical beam theory and incorporates bending-torsion flexibility. Heaviside and Dirac delta functions are used to consider the location and properties of the external mass and the follower force. Also, Peter’s unsteady aerodynamic pressure loadings are considered and modified to take the wing sweep angle effect into account. The Galerkin method is applied to convert the partial differential equations into a set of ordinary differential equations. Numerical simulations are validated with available published results. In addition, simulation results are presented to show the effects of the roll angular velocity, sweep angle, follower force, and engine mass and location, on the wing flutter. Results are indicative of the significant effect of the rigid body roll angular velocity and the follower force on the wing-engine dynamic stability. Furthermore, distances between the engine center of gravity and the wing elastic axis contribute considerable effects in the wing-engine flutter speed and frequency.
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8

Zhang, Cheng, and Wei Zhao. "Large Eddy Simulation of a Swirl-Stabilized Flame." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-65100.

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Swirl is used in a wide range of combustions systems such as engines, furnaces, gasifiers, and boilers, to enhance mixing, stabilize flames, and reduce pollutant emissions. Numerical modeling of swirling flows remains a challenging task, since there may exist complex recirculating flow patterns and flow instabilities associated with vortex breakdown, precessing vortex core, and jet precession. In swirling flames, the situation becomes more complex because the unsteady heat release can add other modes of instability. The origins and nature of these instabilities are still not well understood despite many experimental and numerical studies have been conducted in the area. The Sydney swirl burner flame series provide an excellent platform for validating numerical methods for turbulence-chemistry interactions and have been target flames for the TNF workshop series. The burner has well-defined boundary conditions and comprehensive experimental data sets have been documented for different fuel compositions and flow conditions. Compared with the piloted and bluff-body stabilized flames, swirl-stabilized flames pose an additional challenge to numerical modeling because of the complex flow patterns and inherent flow instabilities. In this study, a large eddy simulation (LES)-based multi-environment turbulent combustion model is used to model the Sydney swirl burner flame SMH1. The multi-environment filtered density function model (MEFDF) depicts the filtered density function (FDF) as a weighted summation of a small number of multi-dimensional Dirac delta functions in composition space. It is derived from the transport FDF equation using the direct quadrature method of moments (DQMOM). The MEFDF method with multiple reactive scalars retains the unique property of the joint FDF model of treating the chemical source term exactly. A 19-species mechanism reduced from GRI-Mech 2.11 is employed for chemical kinetics. The in situ adaptive tabulation algorithm (ISAT) is used to speed-up the evaluation of the chemical source term. The predicted radial profiles of the axial velocity, azimuthal velocity, mixture fraction, temperature, and species mass fractions of CO2, CO, and NO are in reasonable agreement with the experimental data. It has been found that, compared with the experimental data, the profiles of the temperature and species mass fractions shifted slightly outward in the radial direction at downstream locations and NO mass fraction is slightly over-predicted at most locations. Further work will be needed to find out possible reasons for these discrepancies.
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Reports on the topic "Diracův bod"

1

Crater, H., R. Becker, C. Wong, and P. Van Alstine. A detailed study of nonperturbative solutions of two-body Dirac equations. Office of Scientific and Technical Information (OSTI), December 1992. http://dx.doi.org/10.2172/6832686.

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