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Search Results: 1 - 10 of 1784 matches for " Roald Hoffmann "
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Review of “Stereochemistry Workbook, 191 Problems and Solutions” by K.-H. Hellwich and C. D. Siebert
Roald Hoffmann
Beilstein Journal of Organic Chemistry , 2009, DOI: 10.3762/bjoc.5.38
Abstract:
Thoughts on Aesthetics and Visualization (essay)
Roald Hoffmann
Hyle : International Journal for Philosophy of Chemistry , 2003,
Abstract: essay of Thoughts on Aesthetics and Visualization
The Exact Form of the Green's Function of the Hückel (Tight Binding) Model
Ramis Movassagh,Yuta Tsuji,Roald Hoffmann
Physics , 2014,
Abstract: The applications of the H\"uckel (tight binding) model are ubiquitous in quantum chemistry and solid state physics. The matrix representation is isomorphic to an unoriented vertex adjacency matrix of a bipartite graph, which is also the Laplacian matrix plus twice the identity. In this paper, we analytically calculate the determinant and, when it exists, the inverse of this matrix in connection with the Green's function, $\mathbf{G}$, of the $N\times N$ H\"uckel matrix for linear chains and cyclic systems. For an open linear chain we prove that $\mathbf{G}$ is a real symmetric matrix whose entries are $G\left(r,s\right)=\left(-1\right)^{\frac{r+s-1}{2}}$ when $ $$r$ is even and $s
Ockham's Razor and Chemistry
Roald Hoffmann,Vladimir I. Minkin,Barry K. Carpenter
Hyle : International Journal for Philosophy of Chemistry , 1997,
Abstract: We begin by presenting William of Ockham's various formulations of his principle of parsimony, Ockham's Razor. We then define a reaction mechanism and tell a personal story of how Ockham's Razor entered the study of one such mechanism. A small history of methodologies related to Ockham's Razor, least action and least motion, follows. This is all done in the context of the chemical (and scientific) community's almost unthinking acceptance of the principle as heuristically valuable. Which is not matched, to put it mildly, by current philosophical attitudes toward Ockham's Razor. What ensues is a dialogue, pro and con. We first present a context for questioning, within chemistry, the fundamental assumption that underlies Ockham's Razor, namely that the world is simple. Then we argue that in more than one pragmatic way the Razor proves useful, without at all assuming a simple world. Ockham's Razor is an instruction in an operating manual, not a world view. Continuing the argument, we look at the multiplicity and continuity of concerted reaction mechanisms, and at principal component and Bayesian analysis (two ways in which Ockham's Razor is embedded into modern statistics). The dangers to the chemical imagination from a rigid adherence to an Ockham's Razor perspective, and the benefits of the use of this venerable and practical principle are given, we hope, their due.
Naturressursene og verdenspolitikken p Svalbard 1596-2011
Roald Berg
Nordlit : Tidsskrift i litteratur og kultur , 2012,
Abstract: The history of Spitsbergen/Svalbard has been characterized by a combination of masculine heroism and continuous struggle for the natural resources at the islands. In the beginning, from the 16th century, it was an international struggle for the harvesting of the whale and walrus; its value was so great that international conflicts led to the development of such doctrines as mare clausum and mare liberum ininternational law. The competition for the utilization of the coal resources led the Americans near annexation during the first decade of the 20th century before Norway received sovereignty over the islands after the first world war and the services of the Norwegian merchant fleet during that war. After the cold war the oil deposits in the Barents Sea might trigger another period of resource struggle at the islands and the oceans around them.
Naturressursene og verdenspolitikken p Svalbard 1596-2011
Roald Berg
Nordlit : Tidsskrift i litteratur og kultur , 2012,
Abstract: The history of Spitsbergen/Svalbard has been characterized by a combination of masculine heroism and continuous struggle for the natural resources at the islands. In the beginning, from the 16th century, it was an international struggle for the harvesting of the whale and walrus; its value was so great that international conflicts led to the development of such doctrines as mare clausum and mare liberum ininternational law. The competition for the utilization of the coal resources led the Americans near annexation during the first decade of the 20th century before Norway received sovereignty over the islands after the first world war and the services of the Norwegian merchant fleet during that war. After the cold war the oil deposits in the Barents Sea might trigger another period of resource struggle at the islands and the oceans around them.
A Soliton Model of the Electron with an internal Nonlinearity cancelling the de Broglie-Bohm Quantum Potential
Roald Ekholdt
Physics , 2009,
Abstract: The paper proposes an envelope soliton model of the electron that propagates as a protuberance on a fictitious waveguide, which acts as trajectory. The model is based on de Broglie's original electron wave-particle relativistic theory, and on the observation that the Klein-Gordon equation governs the propagation mode of a common microwave waveguide - with the Schroedinger equation as a low group velocity approximation. This analogy opened for practical physical models, including solitons. In the linear case a conceived corpuscle zigzags within the fictitious waveguide - a zigzagging that resembles Penrose's picture of Dirac's electron theory. The soliton envelope is defined by a special nonlinear version of the Schroedinger equation. The nonlinearity cancels the de Broglie/Bohm Quantum Potential of the envelope. The wavefunction is confined by the envelope, and thus the concept of the collapse of the wavefunction is eliminated. Since the electron model is based directly on the Special theory of relativity it also illustrates that theory. The corpuscle, incorporating spin and charge, which moves at the speed of light, needs further study relating it to the photon. A model of the photon based on the mutual coupling of two modes of an optical fiber at the Planck scale, is suggested. One of these modes is thought to carry two orthogonal polarized electromagnetic external fields, while the other, internal, mode carries a corpuscle that moves helically and thus represents the spin. A single electron is considered to have one polarization only, without any superposition possibility; hence, the concept of collapse in a polarization measurement is eliminated.
The gravitation energy for a cylindrically and spherically symmetrical system
Roald Sosnovskiy
Physics , 2005,
Abstract: It has been shown that t00 component of the energy-momentum pseudotensor in the case of cylindrically symmetrical static gravitational field cannot be interpreted as energy density of the gravitation field. An approach has been suggested allows one to express the energy density of the cylindrically or spherically symmetrical static gravitation field in terms of the metric tensor components. The approach based on the consideration of the process of isothermal compression of a cylinder consisted of incoherent matter.
A spatial envelope soliton model of the electron - propagating within a fictitious waveguide
Roald Ekholdt
Physics , 2008,
Abstract: The paper proposes an envelope soliton model of the electron. The soliton propagates within a waveguide which size varies with the potential. The soliton is the solution of the Schroedinger equation with the addition of a nonlinear term that is the negative of Bohm's Quantum potential. This potential is interpreted as representing the dispersion of the linear equation. The model is based on de Broglie's original wave-particle concept, which is based on the Special theory of relativity. The model thus illustrates that theory.
The modification of Einstein`s gravitational field equation following from the energy conservation law
Roald Sosnovskiy
Physics , 2008,
Abstract: The cause of an infringement in GR of a gravitational field energy conservation law is investigated . The equation of a gravitational field not contradicting to the energy conservation law is suggested. This equation satisfy to the Einstein,s requirement of equivalence of all energy kinds as sources of a gravitational field. This equation is solved in paper for cosmic objects. It is showed, that results for some objects - for black holes and gravitating strings-essentialy differ from such for Einstein,s equation, have the symple meaning and do not contradictions.
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