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Search Results: 1 - 10 of 881 matches for " Bill Poirier "
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Using ScalIT for Performing Accurate Rovibrational Spectroscopy Calculations for Triatomic Molecules: A Practical Guide  [PDF]
Corey Petty, Bill Poirier
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.517263
Abstract: This paper presents a practical guide for use of the ScalIT software package to perform highly accurate bound rovibrational spectroscopy calculations for triatomic molecules. At its core, ScalIT serves as a massively scalable iterative sparse matrix solver, while assisting modules serve to create rovibrational Hamiltonian matrices, and analyze computed energy levels (eigenvalues) and wavefunctions (eigenvectors). Some of the methods incorporated into the package include: phase space optimized discrete variable representation, preconditioned inexact spectral transform, and optimal separable basis preconditioning. ScalIT has previously been implemented successfully for a wide range of chemical applications, allowing even the most state-of-the-art calculations to be computed with relative ease, across a large number of computational cores, in a short amount of time.
Reconciling Semiclassical and Bohmian Mechanics: V. Wavepacket Dynamics
Bill Poirier
Physics , 2008, DOI: 10.1063/1.2850207
Abstract: In previous articles [J. Chem. Phys. 121 4501 (2004), J. Chem. Phys. 124 034115 (2006), J. Chem. Phys. 124 034116 (2006), J. Phys. Chem. A 111 10400 (2007)] a bipolar counter-propagating wave decomposition, Psi = Psi+ + Psi-, was presented for stationary states Psi of the one-dimensional Schrodinger equation, such that the components Psi+- approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. In this paper, the method is generalized for time-dependent wavepacket dynamics applications, and applied to several benchmark problems, including multisurface systems with nonadiabatic coupling.
Flux Continuity and Probability Conservation in Complexified Bohmian Mechanics
Bill Poirier
Physics , 2008, DOI: 10.1103/PhysRevA.77.022114
Abstract: Recent years have seen increased interest in complexified Bohmian mechanical trajectory calculations for quantum systems, both as a pedagogical and computational tool. In the latter context, it is essential that trajectories satisfy probability conservation, to ensure they are always guided to where they are most needed. In this paper, probability conservation for complexified Bohmian trajectories is considered. The analysis relies on time-reversal symmetry considerations, leading to a generalized expression for the conjugation of wavefunctions of complexified variables. This in turn enables meaningful discussion of complexified flux continuity, which turns out not to be satisfied in general, though a related property is found to be true. The main conclusion, though, is that even under a weak interpretation, probability is not conserved along complex Bohmian trajectories.
Development and Numerical Analysis of "Black-box" Counterpropagating Wave Algorithm for Exact Quantum Scattering Calculations
Bill Poirier
Physics , 2008,
Abstract: In a recent series of papers [J. Chem. Phys. 121 4501 (2004), J. Chem. Phys. 124 034115 (2006), J. Chem. Phys. 124 034116 (2006)] a bipolar counter-propagating wave decomposition, Psi = Psi+ + Psi-, was presented for stationary bound states Psi of the one-dimensional Shrodinger equation, such that the components Psi+- approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. In this paper, the earlier results are used to construct a universal ``black-box'' algorithm, numerically robust, stable and efficient, for computing accurate scattering quantities of any quantum dynamical system in one degree of freedom.
Reconciling Semiclassical and Bohmian Mechanics: I. Stationary states
Bill Poirier
Physics , 2008, DOI: 10.1063/1.1775766
Abstract: The semiclassical method is characterized by finite forces and smooth, well-behaved trajectories, but also by multivalued representational functions that are ill-behaved at turning points. In contrast, quantum trajectory methods--based on Bohmian mechanics (quantum hydrodynamics)--are characterized by infinite forces and erratic trajectories near nodes, but also well-behaved, single-valued representational functions. In this paper, we unify these two approaches into a single method that captures the best features of both, and in addition, satisfies the correspondence principle. Stationary eigenstates in one degree of freedom are the primary focus, but more general applications are also anticipated.
Reconciling Semiclassical and Bohmian Mechanics: IV. Multisurface Dynamics
Bill Poirier,Gerard Parlant
Physics , 2008, DOI: 10.1063/1.2969102
Abstract: In previous articles [J. Chem. Phys. 121 4501 (2004), J. Chem. Phys. 124 034115 (2006), J. Chem. Phys. 124 034116 (2006)] a bipolar counter-propagating wave decomposition, Psi = Psi+ + Psi-, was presented for stationary states Psi of the one-dimensional Schrodinger equation, such that the components Psi+- approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. In this paper, the method is generalized for multisurface scattering applications, and applied to several benchmark problems. A natural connection is established between intersurface transitions and (+/-) transitions.
Reconciling Semiclassical and Bohmian Mechanics: II. Scattering states for discontinuous potentials
Corey Trahan,Bill Poirier
Physics , 2008, DOI: 10.1063/1.2145883
Abstract: In a previous paper [J. Chem. Phys. 121 4501 (2004)] a unique bipolar decomposition, Psi = Psi1 + Psi2 was presented for stationary bound states Psi of the one-dimensional Schroedinger equation, such that the components Psi1 and Psi2 approach their semiclassical WKB analogs in the large action limit. Moreover, by applying the Madelung-Bohm ansatz to the components rather than to Psi itself, the resultant bipolar Bohmian mechanical formulation satisfies the correspondence principle. As a result, the bipolar quantum trajectories are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. In this paper, the previous decomposition scheme is modified in order to achieve the same desirable properties for stationary scattering states. Discontinuous potential systems are considered (hard wall, step, square barrier/well), for which the bipolar quantum potential is found to be zero everywhere, except at the discontinuities. This approach leads to an exact numerical method for computing stationary scattering states of any desired boundary conditions, and reflection and transmission probabilities. The continuous potential case will be considered in a future publication.
Reconciling Semiclassical and Bohmian Mechanics: III. Scattering states for continuous potentials
Corey Trahan,Bill Poirier
Physics , 2008, DOI: 10.1063/1.2145923
Abstract: In a previous paper [J. Chem. Phys. 121 4501 (2004)] a unique bipolar decomposition, Psi = Psi1 + Psi2 was presented for stationary bound states Psi of the one-dimensional Schroedinger equation, such that the components Psi1 and Psi2 approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories, as defined in the usual Bohmian mechanical formulation, are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. A modification for discontinuous potential stationary stattering states was presented in a second paper [J. Chem. Phys. 124 034115 (2006)], whose generalization for continuous potentials is given here. The result is an exact quantum scattering methodology using classical trajectories. For additional convenience in handling the tunneling case, a constant velocity trajectory version is also developed.
Not All “BAD” Cholesterol Carriers Are Necessarily Bad and Not All “GOOD” Cholesterol Carriers Are as Good as Can Be: Plasma Delipidation, a Non-Pharmacological Treatment for Atherosclerosis  [PDF]
Bill Cham
International Journal of Clinical Medicine (IJCM) , 2015, DOI: 10.4236/ijcm.2015.69092
Abstract: More than four decades ago it was established that an elevated low-density lipoprotein-cholesterol level was a risk for developing coronary artery disease. For the last two decades, statins have been the cornerstone of reducing low-density lipoprotein-cholesterol, but despite significant clinical efficacy in the majority of patients, a large number of patients suffer from side effects and cannot tolerate the required statin dose to reach their recommended low-density lipoprotein-cholesterol goals. Preliminary clinical studies indicate that monoclonal antibodies to PCSK9 appear to be highly efficacious in lowering low-density lipoprotein-cholesterol with a favourable adverse event profile. However, further longer-term clinical studies are required to determine their safety. From the early-proposed concept for high-density lipoprotein-mediated cholesterol efflux for the treatment of coronary artery disease, the concentration of the cholesterol content in high-density lipoprotein particles has been considered a surrogate measurement for the efficacy of the reverse cholesterol transport process. However, unlike the beneficial effects of the statins and monoclonal antibodies to PCSK9 in reducing low-density lipoprotein-cholesterol, no significant advances have been made to increase the levels of high-density lipoprotein-cholesterol. Here it is shown that by a non-pharmacological plasma delipidation means, the atherogenic low-density lipoproteins can be converted to anti-atherogenic particles and that the high-density lipoproteins are converted to particles with extreme high affinity to cause rapid regression of atherosclerosis.
Retour sur la notion d’expérience prolétarienne : Claude Lefort à Socialisme ou Barbarie
Nicolas Poirier
Variations : Revue Internationale de Théorie Critique , 2012,
Abstract: L’une des principales contributions de Claude Lefort au travail de réflexion critique développé par le groupe et la revue Socialisme ou Barbarie au cours des années 1950 a été de mettre en valeur l’idée d’expérience prolétarienne, qui est ce processus dynamique par lequel la classe ouvrière se constitue comme sujet historique, porteur d’un projet d’émancipation sociale dans le cadre d’une praxis conservant son autonomie par rapport à la théorie.La notion d’expérience prolétarienne doit se com...
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