24 documentos corresponden a la consulta.
Palabras contadas: electrons: 30
Rodriguez, J. - Skaf, M.S. - Laria, D.
J Chem Phys 2003;119(12):6044-6052
2003
Descripción: Solvation of excess electrons in supercritical ammonia along the T = 450 K isotherm was investigated. Equilibrium aspects of solvation were analyzed using combined path integral-molecular dynamics techniques. Observations showed transition from localized to quasifree states at approximately one fourth of the triple point density.
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Weissmann, M. - Cohan, N.V.
The Journal of Chemical Physics 1965;43(1):119-123
1965
Descripción: An SCF-MO-LCAO calculation for the four electrons involved in the straight hydrogen bond in ice is performed using a limited set of Slater-type orbitals. The energy of the four electrons plus the interaction between the "core potentials" is calculated as a function of the position of the proton along the line joining the oxygens. The energy of the hydrogen bond is obtained-8.2 kcal/mole-in good agreement with experiment. Electrostatic and delocalization contributions to the energy of the hydrogen bond are in excellent agreement with previous theoretical estimates. The potential energy for the motion of the proton results in a very asymmetric curve, with only one minimum. The dipole moment increases from 1.68 D for a free water molecule to 2.40 D thus confirming previous estimates.
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Aschenauer, E.C. - Stratmann, M. - Sassot, R.
Phys Rev D Part Fields Gravit Cosmol 2012;86(5)
2012
Descripción: We present a quantitative assessment of the impact a future electron-ion collider will have on determinations of helicity quark and gluon densities and their contributions to the proton spin. Our results are obtained by performing a series of global QCD analyses at next-to-leading order accuracy based on realistic sets of pseudo-data for the inclusive and semi-inclusive deep-inelastic scattering of longitudinally polarized electrons and protons at different, conceivable center-of-mass system energies. © 2012 American Physical Society.
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Aucar, I.A. - Gómez, S.S. - De Azúa, M.C.R. - Giribet, C.G.
J Chem Phys 2012;136(20)
2012
Temas: Born-Oppenheimer - Linear response - Molecular Hamiltonian - Molecular rotations - Nuclear magnetic shieldings - Perturbative expansion - Relativistic effects - Relativistic electron - Small components - Spectral parameters
Descripción: A theoretical study of the relation between the relativistic formulation of the nuclear magnetic shielding and spin-rotation tensors is presented. To this end a theoretical expression of the relativistic spin-rotation tensor is formulated, considering a molecular Hamiltonian of relativistic electrons and non-relativistic nuclei. Molecular rotation effects are introduced considering the terms of the Born-Oppenheimer decomposition, which couple the electrons and nuclei dynamics. The loss of the simple relation linking both spectral parameters in the non-relativistic formulation is further analyzed carrying out a perturbative expansion of relativistic effects by means of the linear response within the elimination of the small component approach. It is concluded that relativistic effects on the spin-rotation tensor are less important than those of the nuclear magnetic shielding tensor. © 2012 American Institute of Physics.
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Bochicchio, R.C. - Miranda-Quintana, R.A. - Rial, D.
J Chem Phys 2013;139(19)
2013
Temas: Chemical descriptors - Convexity properties - Density matrix - Many electron - Molecular systems - Number of electrons - Theoretical aspects - Physical chemistry - Physics - Quantum theory
Descripción: Grand-canonical like descriptions of many electron atomic and molecular open systems which are characterized by a non-integer number of electrons are presented. Their associated reduced density matrices (RDMs) are obtained by introducing the contracting mapping for this type of distributions. It is shown that there is loss of information when connecting RDMs of different order by partial contractions. The energy convexity property of these systems simplifies the description. Consequently, this formulation opens the possibility to a new look for chemical descriptors such as chemical potential and reactivity among others. Examples are presented to discuss the theoretical aspects of this work. © 2013 AIP Publishing LLC.
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Arbó, D.G. - Ishikawa, K.L. - Persson, E. - Burgdörfer, J.
J. Phys. Conf. Ser. 2012;388(PART 3)
2012
Temas: Atom lasers - Dinger equation - Doubly differential - Intracycle interferences - Long-range potential - Momentum distributions - Numerical solution - Semiclassical model - Time dependent - Atoms
Descripción: We analyze the doubly-differential momentum distributions of electrons ejected at the interaction of strong IR laser pulses with atoms. With the help of a semiclassical model we clarify the interplay between intracycle and intercycle interferences. The model results are compared with numerical solutions of the time-dependent Schrödinger equation for atoms with long-range potentials. Similarities and differences will be discussed. © Published under licence by IOP Publishing Ltd.
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Bao, J. - Bragas, A.V. - Furdyna, J.K. - Merlin, R.
AIP Conf. Proc. 2005;772:1429-1430
2005
Descripción: A many-particle system may exhibit non-local behavior in that measurements performed on one of the particles can affect a second particle that is far apart. These so-called entangled states are essential for the implementation of quantum information protocols and gates for quantum computation. Here, we use ultrafast optical pulses and coherent techniques to create spin entangled states of non-interacting electrons bound to donors in a CdTe quantum well. © 2005 American Institute of Physics.
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Dasso, S. - Gratton, F.T. - Farrugia, C.J.
J. Geophys. Res. A. Space Phys. 2003;108(A4)
2003
Temas: Interplanetary coronal mass ejections - Ion-cyclotron instability - Kinetic instabilities - Magnetic clouds - Plasma waves - Thermal anisotropy
Descripción: Interplanetary coronal mass ejections (ICMEs) often possess a negative proton thermal anisotropy, Ap = T⊥,p/T ∥.p - 1 < 0 (T∥, T⊥: parallel and perpendicular temperatures, respectively) so that right-hand polarized electromagnetic ion cyclotron waves (EICWs) may be amplified by a kinetic instability [Famigia et ai, 1998a]. However, in view of the low proton beta of ICMEs, several physical parameters, besides Ap, need to be in the right range to excite this instability with significant growth rates. In this paper we present a parametric study of EICWs aimed at identifying those parameters which are most influential in fostering the emission of these waves in ICME scenarios. We analyze here the influence of: (1) thermal and suprathermal protons, (2) thermal alpha particles (αs), and (3) thermal electrons. We solve the dispersion relation of EICWs including protons, αs and electrons, all modeled with bi-Maxwellian distribution functions, and a minority population of suprathermal protons using a kappa function for the velocity component along the field. For physical regimes of ICMEs we find that the instability depends critically on the values of the following parameters: proton beta, proton thermal anisotropy, relative abundance of the suprathermal protons, α-to-proton relative abundance, α-to-proton temperature ratio, α particle thermal anisotropy, electron-to-proton temperature ratio, and thermal anisotropy of electrons. The effect of these parameters on the instability is either direct (when they increase the number of resonant particles) or indirect (when they decrease the phase speed of the wave so that more particles can resonate). Data surveys òn EICWs should take into account the whole set of parameters indicated here, since the expected level of wave excitation results from their combined action. The study may be useful in understanding the considerable level of magnetic fluctuations observed in interplanetary CMEs by the Wind spacecraft. Copyright 2003 by the American Geophysical Union.
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Bochicchio, R.C. - Torre, A. - Lain, L.
J Chem Phys 2005;122(8)
2005
Temas: Condensed matter - Cumulants - Molecular systems - Quantum fields - Computational methods - Correlation methods - Electrons - Functions - Mathematical models - Matrix algebra
Descripción: This paper describes a matrix formulation for the correlated hole theory within the framework of the domain-averaged model in many electron systems (atoms, molecules, condensed matter, etc.). General relationships between this quantity and one-particle reduced density matrices for any independent particle or correlated state functions are presented. This formulation turns out to be suitable for computational purposes due to the straightforward introduction of cumulants of two-particle reduced density matrices within the quantum field structure. Numerical calculations in selected simple molecular systems have been performed in order to determine preliminary correlated values for such a quantity.
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Mitnik, D.M. - Badnell, N.R.
Astron. Astrophys. 2004;425(3):1153-1159
2004
Temas: Atomic data - Atomic processes - Plasmas - Approximation theory - Database systems - Electrons - Ionization - Mathematical models - Nitrogen - Potential energy
Descripción: Dielectronic recombination data for nitrogen-like ions forming oxygen-like ions has been calculated as part of the assembly of a level-resolved dielectronic recombination database necessary for the modelling of dynamic finite-density plasmas (Badnell et al. 2003). Dielectronic recombination rate coefficients for a selection of ions from O+ to Xe47+ are presented and the results discussed.
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Alcoba, D.R. - Lain, L. - Torre, A. - Bochicchio, R.C.
J Chem Phys 2005;123(14)
2005
Temas: Atomic domains - Density matrix - Electron system - Spatial decomposition - Atoms - Chemical bonds - Eigenvalues and eigenfunctions - Electrons - Matrix algebra - Molecules
Descripción: This work describes a simple spatial decomposition of the first-order reduced density matrix corresponding to an N -electron system into first-order density matrices, each of them associated to an atomic domain defined in the theory of atoms in molecules. A study of the representability of the density matrices arisen from this decomposition is reported and analyzed. An appropriate treatment of the eigenvectors of the matrices defined over atomic domains or over unions of these domains allows one to describe satisfactorily molecular properties and chemical bondings within a determined molecule and among its fragments. Numerical determinations, performed in selected molecules, confirm the reliability of our proposal. © 2005 American Institute of Physics.
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Badnell, N.R. - O'Mullane, M.G. - Summers, H.P. - Altun, Z. - Bautista, M.A. - Colgan, J. - Gorczyca, T.W. - Mitnik, D.M. - Pindzola, M.S. - Zatsarinny, O.
Astron. Astrophys. 2003;406(3):1151-1165
2003
Temas: Atomic data - Atomic processes - Plasmas - Astrophysics - Database systems - Electrons - Ground state - Plasmas - Dielectronic recombination data - Dynamic finite-density plasmas
Descripción: A programme is outlined for the assembly of a comprehensive dielectronic recombination database within the generalized collisional-radiative (GCR) framework. It is valid for modelling ions of elements in dynamic finite-density plasmas such as occur in transient astrophysical plasmas such as solar flares and in the divertors and high transport regions of magnetic fusion devices. The resolution and precision of the data are tuned to spectral analysis and so are sufficient for prediction of the dielectronic recombination contributions to individual spectral line emissivities. The fundamental data are structured according to the format prescriptions of the Atomic Data and Analysis Structure (ADAS) and the production of relevant GCR derived data for application is described and implemented following ADAS. The requirements on the dielectronic recombination database are reviewed and the new data are placed in context and evaluated with respect to older and more approximate treatments. Illustrative results validate the new high-resolution zero-density dielectronic recombination data in comparison with measurements made in heavy-ion storage rings utilizing an electron cooler. We also exemplify the role of the dielectronic data on GCR coefficient behaviour for some representative light and medium weight elements.
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Kelly, H. - Márquez, A. - Pirrera, M.
Braz. J. Phys. 2004;34(4 B):1513-1517
2004
Descripción: Measurements on the ion flux transmission in a magnetically filtered d-c vacuum arc are presented. The device includes a metallic plasma-generating chamber with water-cooled electrodes coupled to a substrate chamber through a quarter-torus magnetic filter. It is employed a Copper cathode (6 cm in diameter) with a Copper annular anode. The filter consists in a steel cylinder 500 mm length and 100 mm inner diameter with 90° of bending angle and corrugated lateral walls, surrounded by a magnetic field generating coil. The arc is operated at a current level of 100 A, and the intensity of the filtering magnetic field was in the range 0-200 G (measured at the knee of the filter). This magnetic field is enough high so as to magnetize the electrons but not the ions. The discharge is ignited by bringing (and later removing) a tungsten striker into contact with the cathode. The arc voltage drop, the floating potentials of the filter and the plasma, and the ion current collected by probes located at different positions as functions of the magnetic field intensity are reported and compared with measurements presented in the literature with other similar devices.
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Kelly, H. - Marquez, A. - Pirrera, M.
AIP Conf. Proc. 2006;875:254-257
2006
Descripción: Three-dimensional measurements of the ion flux along the filter of a magnetically filtered d-c vacuum arc are presented. The device includes a metallic plasma-generating chamber with cooper electrodes coupled to a substrate chamber through a quarter-torus magnetic filter. The filtering magnetic field was high enough to magnetize the electrons but not the ions. The ion current distribution was studied using a multi-element Cu probes, placed at three different positions along the filter. The ion saturation current of each probe was measured by biasing the probe at -70V with respect the grounded anode. Preliminary results of the three dimensional ion flux distribution and the floating potential of the plasma as functions of the bias filter voltage and magnetic field intensity are reported. © 2006 American Institute of Physics.
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Cantero, E.D. - Montanari, C.C. - Behar, M. - Fadanelli, R.C. - Lantschner, G.H. - Miraglia, J.E. - Arista, N.R.
J. Phys. Conf. Ser. 2012;388(PART 13)
2012
Temas: Condensed matter physics - Zinc - Friedel sum rule - Inner shell - Measurements of - Stopping power - Transport cross-section - Valence electron - Heavy ions
Descripción: We present stopping power measurements of Zn for C and O ions and compare them with a theoretical description given by the Transport Cross Section - Extended Friedel Sum Rule (TCS-EFSR) for the valence electrons, and two different models for the inner-shells: the Shellwise Local Plasma Approximation (SLPA) and the CasP approach. The SLPA, which successfully applies to projectiles from H to B, is slightly high for C ions and clearly overestimates the data for O ions. On the other hand, total stopping results using the CasP description for the inner-shells show good agreement with the data for C and O ions, and also with the SRIM predictions. © Published under licence by IOP Publishing Ltd.
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Grondona, D. - Kelly, H. - Minotti, F.O.
J Appl Phys 2006;99(4)
2006
Temas: Argon - Hydrodynamics - Ions - Mathematical models - Titanium - Electron energy equation - Metallic ions - Vacuum arc - Vacuum
Descripción: A stationary, one-dimensional fluid model is presented to describe the interelectrode region of a nonfiltered vacuum arc operated with a background gas. The model includes the electron energy equation and the main elastic and inelastic atomic processes among metallic ions, electrons, and gas particles. To validate the model predictions an experimental study of the plasma-neutral gas structure, using a titanium (Ti) cathode and argon (Ar) as the background gas, is presented. The measured electron temperature and the experimental dependence on the pressure of neutral Ti and Ar spectroscopic emission lines are well reproduced, using a simple atomic model to interpret the plasma radiation emission. © 2006 American Institute of Physics.
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Alcoba, D.R. - Torre, A. - Lain, L. - Massaccesi, G.E. - Oña, O.B.
J Chem Phys 2013;139(8)
2013
Temas: Change of basis - Configuration interactions - Expectation values - Natural orbitals - Quantitative evaluation - Rapid convergence - Slater determinants - Unitary transformations - Electrospinning - Magnetic moments
Descripción: This work extends the concept of seniority number, which has been widely used for classifying N-electron Slater determinants, to wave functions of N electrons and spin S, as well as to N-electron spin-adapted Hilbert spaces. We propose a spin-free formulation of the seniority number operator and perform a study on the behavior of the expectation values of this operator under transformations of the molecular basis sets. This study leads to propose a quantitative evaluation for the convergence of the expansions of the wave functions in terms of Slater determinants. The non-invariant character of the seniority number operator expectation value of a wave function with respect to a unitary transformation of the molecular orbital basis set, allows us to search for a change of basis which minimizes that expectation value. The results found in the description of wave functions of selected atoms and molecules show that the expansions expressed in these bases exhibit a more rapid convergence than those formulated in the canonical molecular orbital bases and even in the natural orbital ones. © 2013 AIP Publishing LLC.
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Zaccari, D. - Melo, J.I. - Ruiz De Azúa, M.C. - Giribet, C.G.
J Chem Phys 2009;130(8)
2009
Temas: Alternative approaches - Component methods - Geometric approximations - Heavy atoms - Linear response approximations - Nuclear magnetic shielding - Numerical calculations - Numerical values - Propagator matrixes - Relativistic corrections
Descripción: An alternative approach for the calculation of the electron-positron (e-p) contribution to magnetic properties based on two-component Breit-Pauli spinors is presented. In it, the elimination of the small component scheme is applied to the inverse propagator matrix of e-p pairs. The effect of the positronic manifold is expressed as an operator acting on Breit-Pauli spinors. The operator form thus obtained sums up the relativistic correction as a geometric series and as a result a totally different behavior in the vicinity of a nucleus is obtained as compared to the one of the linear response approximation. This feature has deep influence in numerical values of the e-p contribution to the nuclear magnetic shielding of heavy atoms. Numerical calculations carried out for Kr, Xe, and I show that with this approach, the e-p contributions to this property are in good agreement with those of four-component methods. © 2009 American Institute of Physics.
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Ruiz, J.A. - Fernández, R.O. - Nikel, P.I. - Méndez, B.S. - Pettinari, M.J.
FEMS Microbiol. Lett. 2006;258(1):55-60
2006
Temas: arcA - O2 consumption - PHB - ROS - Toluidine blue - poly(3 hydroxybutyric acid) - tolonium chloride - aerobic metabolism - article - controlled study
Descripción: arcA codes for a central regulator in Escherichia coli that responds to redox conditions of growth. Mutations in this gene, originally named dye, confer sensitivity to toluidine blue and other redox dyes. However, the molecular basis for the dye-sensitive phenotype has not been elucidated. In this work, we show that toluidine blue redirects electrons to O2 and causes an increase in the generation of reactive O2 species (ROS). We also demonstrate that synthesis of poly (3-hydroxybutyrate) suppresses the Dye phenotype in E. coli recombinants, as the capacity to synthesize the polymer reduces sensitivity to toluidine blue, O2 consumption and ROS production levels. © 2006 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.
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Minotti, F. - Giuliani, L. - Grondona, D. - Della Torre, H. - Kelly, H.
J Appl Phys 2013;113(11)
2013
Temas: Collision term - Collisionality - Different-magnetic fields - Electron mass - Electron momentum equations - Filtered arc - Microinstabilities - Boundary layers - Carrier concentration - Electron density measurement
Descripción: A model is developed to describe the electrostatic boundary layer in a positively biased magnetic filter in filtered arcs with low collisionality. The set of equations used includes the electron momentum equation, with an anomalous collision term due to micro-instabilities leading to Bohm diffusion, electron mass conservation, and Poisson equation. Analytical solutions are obtained, valid for the regimes of interest, leading to an explicit expression to determine the electron density current to the filter wall as a function of the potential of the filter and the ratio of electron density at the plasma to that at the filter wall. Using a set of planar and cylindrical probes it is verified experimentally that the mentioned ratio of electron densities remains reasonably constant for different magnetic field values and probe bias, which allows to obtain a closed expression for the current. Comparisons are made with the experimentally determined current collected at different sections of a positively biased straight filter. © 2013 American Institute of Physics.
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