Artículos de revistas: "Free Electron Model Calculations"

1

Meron, Mati y Brant M. Johnson. "Electron-loss calculations using the free-collision model". Physical Review A 41, n.º 3 (1 de febrero de 1990): 1365–74. http://dx.doi.org/10.1103/physreva.41.1365.

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2

Li, D. H., R. A. Moore y S. Wang. "Variational thermodynamic calculations for some liquid sd metals". Canadian Journal of Physics 64, n.º 1 (1 de enero de 1986): 75–83. http://dx.doi.org/10.1139/p86-011.

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A tractable and reliable expression for the one valence-electron eigenenergies, required in calculating the total energy of a disordered sd-type metal, is formulated in the context of the model-potential theory. With the aid of this expression, the variational calculation of the Helmholtz free energy using the hard-sphere model as a reference system, as employed in ab initio calculations of the thermodynamic properties for the nearly-free-electron-like (NFE) liquid metals, can now be extended with reasonable accuracy to those liquid sd metals in which the d-like valence-electron states below the Fermi level are not very localized. Also, the ab initio-type pseudopotential calculation of the interionic pair potentials, as carried out for the NFE-like metals in the literature, is made practical for these sd metals in their disordered states.

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3

Morrison, Michael A., Bidhan C. Saha y Thomas L. Gibson. "Electron-N2scattering calculations with a parameter-free model polarization potential". Physical Review A 36, n.º 8 (1 de octubre de 1987): 3682–98. http://dx.doi.org/10.1103/physreva.36.3682.

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4

Penn, David R. "Electron mean-free-path calculations using a model dielectric function". Physical Review B 35, n.º 2 (15 de enero de 1987): 482–86. http://dx.doi.org/10.1103/physrevb.35.482.

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5

Li, D. H., R. A. Moore y S. Wang. "Variational thermodynamic calculations for some liquid sd metals: II". Canadian Journal of Physics 64, n.º 7 (1 de julio de 1986): 852–56. http://dx.doi.org/10.1139/p86-147.

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A procedure employing a generalized, nonlocal, model-pseudopotential theory for the calculation of the total valence-electron energy in liquid metals was presented earlier and shown to be suitable for use in a variational calculation of the Helmholtz free energy, and hence also for other properties, of sd and the early 3d transition metals. In the first part of this paper we show that the same procedure also works well for the first four of the 4d transition metals. However, the accuracy of the calculations decreases with increasing number of d-like valence electrons. This is attributed to narrow valence d bands. Thus, in the second part of this paper we revise and generalize the earlier procedure to consider explicitly the localization of some of the d-like valence electrons on the ions. The validity of the revisions is shown by calculating a number of the properties of liquid metallic Cr, Mn, and Fe.

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6

Sigaud, G. M. "Free-collision model calculations for projectile electron loss by the H2molecule". Journal of Physics B: Atomic, Molecular and Optical Physics 44, n.º 22 (25 de octubre de 2011): 225201. http://dx.doi.org/10.1088/0953-4075/44/22/225201.

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7

Sigaud, G. M. "Free-collision model calculations for the electron detachment of anions by noble gases". Journal of Physics B: Atomic, Molecular and Optical Physics 41, n.º 1 (20 de diciembre de 2007): 015205. http://dx.doi.org/10.1088/0953-4075/41/1/015205.

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8

Perrot, F. y C. Dharma-Wardana. "Equation of state of dense Hydrogen and the plasma phase transition; A microscopic calculational model for complex fluids". International Astronomical Union Colloquium 147 (1994): 272–86. http://dx.doi.org/10.1017/s0252921100026403.

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AbstractWe discuss problems related to the electronic and ionic structure of fluid Hydrogen, for equation of state calculations in the domain where a ”plasma phase transition” (PPT) may occur. It is argued that the ionization of an electron bound to a particular nucleus proceeds through a progressive derealization involving ”hopping” electron states (i.e. cluster states). A description of the plasma containing pseudoatoms, pseudomolecules and free electrons is proposed. The PPT, if it exists, might be a mobility edge transition across a percolation threshold. It is shown how the effect of electron density, field-particle distributions and temperature on the binding energy of these pseudoatoms and pseudomolecules, can be included. Finally the abundances of these objects is determined by a minimization which allows the self-consistent optimization of ionic as well as electronic parameters contributing to the total free energy.

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9

Bose, S. K. y J. D. Poll. "On the formation of cavitylike small-polaronic states in solid deuterium". Canadian Journal of Physics 63, n.º 1 (1 de enero de 1985): 94–98. http://dx.doi.org/10.1139/p85-015.

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Certain infrared absorption features in tritiated as well as proton-irradiated samples of solid deuterium have been attributed to the formation of bubblelike electronic states localized in the lattice. These bubblelike states are shown to be energetically stable in the Wigner–Seitz model of the crystal and the gap between the ground-state energies in the bubble and the quasi-free states of the electron is calculated. An initial trapping of the electron by a vacancy is assumed in calculating the localized state energy. Calculations based on a continuum model of the solid yield the radius of such bubbles to close agreement with that obtained from the observed Stark shift of the vibrational levels of the neighbouring molecules due to the localized electrons. The model is used to interpret the radiation-induced absorption in proton-irradiated solid deuterium in the spectral region 4000–7500 cm−1.

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10

ARABSHAHI, HADI. "CALCULATION OF THE ELECTRON DRIFT MOBILITY IN Cr2+:ZnS AND Cr2+:ZnSe MATERIALS BY RODE ITERATION MODEL". International Journal of Modeling, Simulation, and Scientific Computing 01, n.º 04 (diciembre de 2010): 469–75. http://dx.doi.org/10.1142/s1793962310000262.

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The results of electron drift velocity in Cr2+:ZnS , and Cr2+:ZnSe are calculated for different temperatures, free-electron concentrations and compositions. The two-mode nature of the polar optic phonons is considered jointly with deformation potential acoustic, piezoelectric, alloy and ionized-impurity scattering. Band non-parabolocity, admixture of p functions, arbitrary degeneracy of the electron distribution, and the screening effects of free carriers on the scattering probabilities are incorporated. The Boltzmann equation is solved by an iterative technique using the currently established values of the material parameters. The iterative results are in fair agreement with other recent calculations obtained using the relaxation-time approximation and experimental methods.

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11

Journal, Baghdad Science. "Electronic Structure of Copper Antimony Using Compton Scattering Technique". Baghdad Science Journal 13, n.º 1 (30 de diciembre de 2018): 167–73. http://dx.doi.org/10.21123/bsj.13.1.167-173.

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In this paper we present the first ever measured experimental electron momentum density of Cu2Sb at an intermediate resolution (0.6 a.u.) using 59.54 keV 241Am Compton spectrometer. The measurements are compared with the theoretical Compton profiles using density function theory (DFT) within a linear combination of an atomic orbitals (LCAO) method. In DFT calculation, Perdew-Burke-Ernzerhof (PBE) scheme is employed to treat correlation whereas exchange is included by following the Becke scheme. It is seen that various approximations within LCAO-DFT show relatively better agreement with the experimental Compton data. Ionic model calculations for a number of configurations (Cu+x/2)2(Sb-x) (0.0≤x≤2.0) are also performed utilizing free atom profiles, the ionic model suggests transfer of 2.0 electrons per Cu atom from 4s state to 5p state of Sb.

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DAT, NGUYEN NHU. "PHONON-LIMITED MOBILITY IN A FREE-STANDING POLAR SEMICONDUCTOR QUANTUM WIRE". Modern Physics Letters B 09, n.º 26n27 (20 de noviembre de 1995): 1779–88. http://dx.doi.org/10.1142/s0217984995001807.

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A macroscopic continuum model is used to study the longitudinal optical phonons in a free-standing polar quantum wire with a rectangular cross section. The Fröhlich Hamiltonian describing the electron-phonon interaction is then obtained and used to calculate the electron mobility governed by confined LO phonons by means of the memory function approach, neglecting electron-electron interaction. Numerical calculations are given for a GaAs quantum wire, showing that the mobility is enhanced at least by one order of magnitude in comparison with the bulk-LO-phonon-limited one. It is shown that the contribution of intersubband scattering is important in wires of large width at high temperature.

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13

Abdulhadi Mirdan Ghaleb. "Investigation of electronic structure for β-Zr in the(s-d) subshell". Tikrit Journal of Pure Science 21, n.º 6 (8 de febrero de 2023): 126–31. http://dx.doi.org/10.25130/tjps.v21i6.1090.

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In this paper, a theoretical study of calculating Compton profiles(CPs) for β-Zr using the renormalized-free-atom model and free electron model for different configurations (4d3-x-5s1+x),where (x= 0.1 to 1 step 0.1) is presented .The theoretical results and previously experimental data show good agreement and the best electronic configuration found was (4d2.8-5s1.2 ). The cohesive energy of β-Zr is computed by using theoretical Compton profile data and compared with available data. The band structure and density of state of (β-Zr and -Zr) phases are determined from density functional theory (DFT) with use Quantum wise Atomistix Tool Kit (ATK),Virtual Nano Lab calculations within the framework of the local density approximation (LDA).

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14

Gu, X. F., T. Furuhara y W. Z. Zhang. "PTCLab: free and open-source software for calculating phase transformation crystallography". Journal of Applied Crystallography 49, n.º 3 (11 de mayo de 2016): 1099–106. http://dx.doi.org/10.1107/s1600576716006075.

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PTCLab(Phase Transformation Crystallography Lab) is free and open-source software to calculate the crystallographic features formed during a phase transformation, such as orientation relationship, interface orientation, interfacial structureetc. This program covers the crystallographic theories for both martensitic and diffusional transformation and allows users to represent the results in stereographic projection. The crystallographic models treated inPTCLabinclude the classical phenomenological theory of martensite crystallography (PTMC), the double shear version of PTMC, the invariant line model, O-lattice theory, the O-line model, the recently developed three-dimensional near coincidence site method, the edge-to-edge matching model and variant selection analysis. In addition, a number of basic crystallographic calculations for single or multiple crystal structures can be performed with the calculation pad. High-quality composite stereographic projection and electron diffraction patterns can be also obtained by the present application.PTCLabis written in Python, runnable cross platform, and is distributed at https://sourceforge.net/projects/tclab/.

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15

Mesyats, G. A., A. G. Reutova, K. A. Sharypov, V. G. Shpak, S. A. Shunailov y M. I. Yalandin. "On the observed energy of runaway electron beams in air". Laser and Particle Beams 29, n.º 4 (diciembre de 2011): 425–35. http://dx.doi.org/10.1017/s0263034611000541.

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AbstractExperiments with an air electrode gap have been performed where the current/charge of a picosecond beam of runaway electrons was measured over a wide range (up to four orders of magnitude) downstream of the absorbing foil filters. Measurements and calculations have made it possible to refer the beam current to the rise time of the accelerating voltage pulse to within picoseconds. It has been shown that, in contrast to a widespread belief, the runaway electron energies achieved are no greater than those corresponding to the mode of free acceleration of electrons in a nonstationary, highly nonuniform electric field induced by the cathode voltage. The experimental data agree with predictions of a numerical model that describes free acceleration of particles. It has been confirmed that the magnitude of the critical electric field that is necessary for electrons to go into the mode of continuous acceleration of electrons in atmospheric air corresponds to classical notions.

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16

Morrison, Michael A. y Bidhan C. Saha. "Investigation of parameter-free model polarization potentials for electron-molecule scattering calculations including the nuclear motion". Physical Review A 34, n.º 4 (1 de octubre de 1986): 2786–97. http://dx.doi.org/10.1103/physreva.34.2786.

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17

Djaoui, A., T. A. Hall, R. C. Albers, J. J. Rehr y J. Mustre. "Calculation of X-ray absorption structure above K-edge of laser shock-compressed aluminum". Laser and Particle Beams 8, n.º 1-2 (enero de 1990): 319–25. http://dx.doi.org/10.1017/s0263034600008065.

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Aluminum sandwich foils can be compressed to more than twice the normal density by the use of shock waves generated by laser beams. We present calculations of the K-edge absorption structure of two fold compressed aluminum, and compare the results with experimental data. The atomic potential is calculated using a spherical band-structure model with Fermi-Dirac statistics for the electrons. The structure above the K-edge is calculated according to the Müller-Shaich formula for the propagating photo-electron. The mean free path of the electron is taken into account through a complex exchange correlation potential. An appropriate Debye-Waller factor is used to represent the effect of the relatively high temperature encountered in these experiments.

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18

Wang, Z. L. y Chen Zhang. "Absorption Potential for Dynamic Electron Diffraction - A Revisit". Microscopy and Microanalysis 4, S2 (julio de 1998): 340–41. http://dx.doi.org/10.1017/s1431927600021826.

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Quantitative analysis of structural information provided by transmission electron diffraction and imaging strongly relies on computer simulations. An important quantity in dynamic calculation is the “absorption” potential. The absorption here actually means that the electron is not absorbed by the specimen rather it is scattered out of the elastic state (or Bragg peaks) due to energy-loss and momentum transfer, resulting in a decrease in the intensity of the elastic wave. This is the effect of inelastic scattering (or diffuse scattering) on the Bragg reflected waves [1]. Almost all of the model calculations for the absorption potential have been based on the approximation o riginally introduced by Y o sh ioka, in which the Green's function is approximated by its form in free-space. Thus, the absorption potential is simplified into a non-local function that depends only on the nature of the inelastic scattering.

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19

Khera, Shabha, Narayan Lal Heda, Sonal Mathur y Babu Lal Ahuja. "Electronic Structure of Gadolinium and Dysprosium Using Compton Scattering Technique". Zeitschrift für Naturforschung A 61, n.º 5-6 (1 de junio de 2006): 299–305. http://dx.doi.org/10.1515/zna-2006-5-615.

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In this paper we present the first ever measured Compton profiles of polycrystalline gadolinium and dysprosium using 661.65 keV gamma-rays. The Compton data are compared with renormalized-freeatom (RFA) and free-electron model profiles. In both cases the RFA model (with e− - e− correlation) gives a better agreement with the experiment. The hybridization effects of s-, p-, d-, and f-electrons are discussed, using the first derivatives of the Compton profiles. We also report the cohesive energy of both samples, computed from the RFA calculations. - PACS numbers: 13.60.F, 71.15.Nc, 78.70. -g, 78.70.Ck

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20

Plottke, Chris y Igor Bray. "Calculation of the free-free transitions in the electron-hydrogen scattering S-wave model". Journal of Physics B: Atomic, Molecular and Optical Physics 33, n.º 2 (11 de enero de 2000): L71—L77. http://dx.doi.org/10.1088/0953-4075/33/2/103.

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21

Reynolds, Stephen P. "Model Images of Radio Halos Around Supernova Remnants". International Astronomical Union Colloquium 142 (1994): 845–56. http://dx.doi.org/10.1017/s0252921100078209.

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AbstractI present model calculations of profiles and two-dimensional images of the radio synchrotron emission of young supernova remnants, concentrating on observable effects of relativistic electrons diffusing upstream of the shock wave. If the preshock electron scattering mean free path is sufficiently long, observable synchrotron halos outside the bulk of the radio emission can potentially result; their absence can constrain the mean free path from above. If scattering is primarily due, as expected, to Alfvén waves with amplitude δB, the halo is expected to extend a distance of order rg c(δB/B)−2 /vs beyond the shock, where rg is the gyroradius of the electrons emitting at the observed frequency, B is the upstream magnetic field strength, vs is the shock velocity, and the amplitude δB refers to waves with wavelength comparable to rg , of order 1013 cm for typical supernova-remnant parameters. However, the detailed geometry of the halo varies with the assumptions about particle acceleration in the shock wave. I present an atlas of model profiles and images as a function of preshock diffusion length, of aspect angle between the magnetic field and the line of sight, and of other relevant parameters.Subject headings: radiation mechanisms: miscellaneous — shock waves — supernova remnants

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22

ZHANG, LI y JUN-JIE SHI. "POLAR VIBRATION SPECTRA OF INTERFACE AND SURFACE OPTICAL PHONONS AND THEIR FRÖHLICH ELECTRON-PHONON INTERACTIONS IN FREESTANDING SYMMETRICAL AND ASYMMETRICAL WURTZITEGaN/Ga1-xAlxNMULTI-LAYER HETEROSTRUCTURES". International Journal of Modern Physics B 20, n.º 05 (20 de febrero de 2006): 559–78. http://dx.doi.org/10.1142/s0217979206033425.

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Under the dielectric continuum model and Loudon's uniaxial crystal model, by adopting the transfer matrix method, the dispersion properties of the interface optical (IO) and surface optical (SO) phonon modes and their couplings with electrons in multi-layer coupling wurtzite quantum wells (QWs) are deduced and analyzed via the method of electrostatic potential expanding. Numerical calculations on a freestanding symmetrical wurtzite QW and an asymmetrical wurtzite QW have been performed. Results reveal that, in general, there are four branches of IO and two branches of SO phonon modes in the systems. The dispersions of these IO and SO phonon modes are obvious only when the free two-dimensional phonon wave number ktparallel to the heterostructure interfaces is small. The degenerating behavior for these phonon modes has been clearly observed for small kt. When ktis relatively large, with the increase in kt, the frequencies of the IO and SO phonon modes converge to some definite limiting frequencies in corresponding wurtzite single planar heterostructure. This feature have been analyzed in depth from the mathematical and physical viewpoints. The calculations of electron-phonon coupling function show that, the electrostatic potential distribution of the IO and SO mode in freestanding symmetrical wurtzite QW is either symmetrical or is antisymmetrical; but that in freestanding asymmetrical wurtzite QW is neither symmetrical nor is antisymmetric. The calculation also shows that the SO modes and the short wavelength phonon modes play a more important role in the electron-phonon interaction.

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23

Russ, John C. "Monte Carlo Modelling of Secondary Electron Yield from Rough Surfaces". Proceedings, annual meeting, Electron Microscopy Society of America 48, n.º 1 (12 de agosto de 1990): 422–23. http://dx.doi.org/10.1017/s0424820100180860.

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Monte-Carlo programs are well recognized for their ability to model electron beam interactions with samples, and to incorporate boundary conditions such as compositional or surface variations which are difficult to handle analytically. This success has been especially powerful for modelling X-ray emission and the backscattering of high energy electrons. Secondary electron emission has proven to be somewhat more difficult, since the diffusion of the generated secondaries to the surface is strongly geometry dependent, and requires analytical calculations as well as material parameters. Modelling of secondary electron yield within a Monte-Carlo framework has been done using multiple scattering programs, but is not readily adapted to the moderately complex geometries associated with samples such as microelectronic devices, etc.This paper reports results using a different approach in which simplifying assumptions are made to permit direct and easy estimation of the secondary electron signal from samples of arbitrary complexity. The single-scattering program which performs the basic Monte-Carlo simulation (and is also used for backscattered electron and EBIC simulation) allows multiple regions to be defined within the sample, each with boundaries formed by a polygon of any number of sides. Each region may be given any elemental composition in atomic percent. In addition to the regions comprising the primary structure of the sample, a series of thin regions are defined along the surface(s) in which the total energy loss of the primary electrons is summed. This energy loss is assumed to be proportional to the generated secondary electron signal which would be emitted from the sample. The only adjustable variable is the thickness of the region, which plays the same role as the mean free path of the secondary electrons in an analytical calculation. This is treated as an empirical factor, similar in many respects to the λ and ε parameters in the Joy model.

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24

Murata, Shigeo, Maged El-Kemary y M. Tachiya. "Two-Dimensional Free Energy Surfaces for Electron Transfer Reactions in Solution". International Journal of Photoenergy 2008 (2008): 1–8. http://dx.doi.org/10.1155/2008/150682.

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Change in intermolecular distance between electron donor (D) and acceptor (A) can induce intermolecular electron transfer (ET) even in nonpolar solvent, where solvent orientational polarization is absent. This was shown by making simple calculations of the energies of the initial and final states of ET. In the case of polar solvent, the free energies are functions of both D-A distance and solvent orientational polarization. On the basis of 2-dimensional free energy surfaces, the relation of Marcus ET and exciplex formation is discussed. The transient effect in fluorescence quenching was measured for several D-A pairs in a nonpolar solvent. The results were analyzed by assuming a distance dependence of the ET rate that is consistent with the above model.

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25

KISAND, V., M. KIRM, S. VIELHAUER y G. ZIMMERER. "AN ANALYSIS OF ELECTRON–HOLE RECOMBINATION IN SOLID KRYPTON USING TIME-RESOLVED VUV-LUMINESCENCE SECTROSCOPY". Surface Review and Letters 09, n.º 02 (abril de 2002): 783–88. http://dx.doi.org/10.1142/s0218625x02002956.

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For the first time, the free exciton (FE) VUV-luminescence decay curves were systematically investigated in solid Kr using photoexcitation in the energy region above band gap energy. Delayed electron–hole recombination and "prompt" (in terms of the time resolution of the experimental setup) creation of secondary excitons were separated using the time-resolved experimental technique. A detailed model for the dynamics of electron–hole recombination into the FE state was developed. The delayed component of the free exciton decay curve was reproduced with model calculations, including thermalization of the carriers via scattering on acoustic phonons, and the recombination cross-section, which depends on the actual carrier temperatures. A satisfactory agreement between experiment and theory was found.

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Amarsi, A. M., P. S. Barklem, M. Asplund, R. Collet y O. Zatsarinny. "Inelastic O+H collisions and the O I 777 nm solar centre-to-limb variation". Astronomy & Astrophysics 616 (agosto de 2018): A89. http://dx.doi.org/10.1051/0004-6361/201832770.

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The O I 777 nm triplet is a key diagnostic of oxygen abundances in the atmospheres of FGK-type stars; however, it is sensitive to departures from local thermodynamic equilibrium (LTE). The accuracy of non-LTE line formation calculations has hitherto been limited by errors in the inelastic O+H collisional rate coefficients; several recent studies have used the Drawin recipe, albeit with a correction factor SH that is calibrated to the solar centre-to-limb variation of the triplet. We present a new model oxygen atom that incorporates inelastic O+H collisional rate coefficients using an asymptotic two-electron model based on linear combinations of atomic orbitals, combined with a free electron model based on the impulse approximation. Using a 3D hydrodynamic STAGGER model solar atmosphere and 3D non-LTE line formation calculations, we demonstrate that this physically motivated approach is able to reproduce the solar centre-to-limb variation of the triplet to 0.02 dex, without any calibration of the inelastic collisional rate coefficients or other free parameters. We infer log ϵO = 8.69 ± 0.03 from the triplet alone, strengthening the case for a low solar oxygen abundance.

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Brunelle, Patrick, Christian Schöneich y Arvi Rauk. "One-electron oxidation of methionine peptides — Stability of the three-electron S—N(amide) bond". Canadian Journal of Chemistry 84, n.º 6 (1 de junio de 2006): 893–904. http://dx.doi.org/10.1139/v06-079.

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The possibility of sulfur–nitrogen (S—N) three-electron bond formation in a one-electron oxidized methionine peptide model was investigated computationally following the detection of such species in pulse radiolysis experiments (C. Schöneich, D. Pogocki, G.L. Hug, and K. Bobrowski. J. Am. Chem. Soc. 125, 13700 (2003)). Geometry optimiza tions were carried out at the B3LYP/6-31G(d) level of theory. Relative free energies in aqueous solution at pH 7 were predicted for all intermediates with enthalpy evaluations at the CCSD(T)/6-31+G(d′) level and free energies of solvation predicted using a continuum model (CPCM). Both the initial oxidation product and the intermediate formed at higher pH were identified as cyclic S—N bonded species in which the intramolecular three-electron interaction is between the S atom and the π orbital of the amide group. TD-B3LYP calculations of the UV spectra support the assignments. A mechanism for the conversion to the most stable α-C-centered radical is proposed. The mechanism involves a novel deprotonation–reprotonation via an intermediate backbone-delocalized radical anion.Key words: methionine oxidation, three-electron bonding, S—N bonding, B3LYP.

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TORNOW, W., N. G. CZAKON, C. R. HOWELL, A. HUTCHESON, J. H. KELLEY, V. N. LITVINENKO, S. MIKHAILOV, I. V. PINAYEV, G. J. WEISEL y H. WITAŁA. "ANALYZING POWER FOR THE PHOTODISINTEGRATION OF THE DEUTERON BETWEEN Eγ = 2.4 AND 4.0 MEV". Modern Physics Letters A 18, n.º 02n06 (28 de febrero de 2003): 282–85. http://dx.doi.org/10.1142/s021773230301034x.

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The photon analyzing power for the photodisintegration of the deuteron was measured for seven gamma-ray energies between 2.39 and 4.05 MeV using the linearly polarized gamma-ray beam of the High-Intensity Gamma-ray Source at the Duke Free-Electron Laser Laboratory. The data provide a stringent test of theoretical calculations for the inverse reaction, the neutron-proton radiative capture reaction at energies important for Big-Bang nucleosynthesis. Our data are in excellent agreement with potential model and effective field theory calculations.

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Myrvang, Margaretha, Carsten Baumann y Ingrid Mann. "Modelling the influence of meteoric smoke particles on artificial heating in the D-region". Annales Geophysicae 39, n.º 6 (17 de diciembre de 2021): 1055–68. http://dx.doi.org/10.5194/angeo-39-1055-2021.

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Abstract. We investigate if the presence of meteoric smoke particles (MSPs) influences the electron temperature during artificial heating in the D-region. By transferring the energy of powerful high-frequency radio waves into thermal energy of electrons, artificial heating increases the electron temperature. Artificial heating depends on the height variation of electron density. The presence of MSPs can influence the electron density through charging of MSPs by electrons, which can reduce the number of free electrons and even result in height regions with strongly reduced electron density, so-called electron bite-outs. We simulate the influence of the artificial heating by calculating the intensity of the upward-propagating radio wave. The electron temperature at each height is derived from the balance of radio wave absorption and cooling through elastic and inelastic collisions with neutral species. The influence of MSPs is investigated by including results from a one-dimensional height-dependent ionospheric model that includes electrons, positively and negatively charged ions, neutral MSPs, singly positively and singly negatively charged MSPs, and photochemistry such as photoionization and photodetachment. We apply typical ionospheric conditions and find that MSPs can influence both the magnitude and the height profile of the heated electron temperature above 80 km; however, this depends on ionospheric conditions. During night, the presence of MSPs leads to more efficient heating and thus a higher electron temperature above altitudes of 80 km. We found differences of up to 1000 K in electron temperature for calculations with and without MSPs. When MSPs are present, the heated electron temperature decreases more slowly. The presence of MSPs does not much affect the heating below 80 km for night conditions. For day conditions, the difference between the heated electron temperature with MSPs and without MSPs is less than 25 K. We also investigate model runs using MSP number density profiles for autumn, summer and winter. The night-time electron temperature is expected to be 280 K hotter in autumn than during winter conditions, while the sunlit D-region is 8 K cooler for autumn MSP conditions than for the summer case, depending on altitude. Finally, an investigation of the electron attachment efficiency to MSPs shows a significant impact on the amount of chargeable dust and consequently on the electron temperature.

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Melnyk, I. V., S. B. Tuhai, V. O. Kyryk y I. S. Shved. "Modeling of Electrode Systems of Gas-discharge Guns with Focusing of an Electronic Beam in a Magnetic Field of a Short Lens". Èlektronnoe modelirovanie 43, n.º 6 (6 de diciembre de 2021): 76–94. http://dx.doi.org/10.15407/emodel.43.06.076.

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In the article, based on the analysis of the basic provisions of the theory of high - voltage glow discharge (HVGD), a method of modeling electrode systems of gas discharge guns with focusing of the electron beam in the field of a short magnetic lens is proposed. To calculate the electric field in the electrode system the finite-difference Poisson equation has been used, which, to simplify its using in the software, is written in the form of an arithmetic-logical expression. Analysis of the guiding of the electron beam in the free drift region was performed with using a system of equations of discrete mathematics based on the Rutherford scattering model. A numerical algorithm for calculating the focus position of the electron beam and its focal diameter is also proposed. To estimate the position of the plasma boundary, a simulation method based on the conversion of the anode plasma volume from a one-dimensional system to the actual spatial geometry of the electrodes was used. In this case, the calculation of the height of the anode plasma in a real electrode system is reduced to the analytical solution of the cubic equation. The calculation of the magnetic field of a short lens was performed using the Yavor model. To implement the proposed methods of modeling HVGD guns, it is proposed to use arithmetic and logical expressions and methods of matrix programming. The obtained results of calculations on the distribution of the electric field in the electrode system, the boundary trajectories of the electron beam in the field of magnetic lense, as well as the distribution of the current density in the focal plane of the hollow electron beam with the ring focus are presented.

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31

Abdul Amir, Haider F., Abu Hassan Husin, Saafie Salleh y Fuei Pien Chee. "A Model for Neutron Radiation Damage in Metal Oxide Semiconductor (MOS) Structures". Key Engineering Materials 706 (agosto de 2016): 51–54. http://dx.doi.org/10.4028/www.scientific.net/kem.706.51.

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Neutron bombardment on semiconductor material causes defects, one such primary physical effect is the formation of displacement defects within the crystal lattice structure, and such defects effectively decrease the mean free path and thus shorten the recombination time. Ionizing radiation causes creation of electron-hole pair in the gate oxide and in parasitic insulating layers of the MOS devices. Calculations show increase of the dark current in depletion region caused by a single neutron. Determination of energy and angular distribution of primary knock on atoms, with 14 MeV neutron irradiation in silicon are presented.

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32

Gatti, Carlo. "Looking at local classical and quantum forces in stable crystals using multipole-model refined electron densities and orbital-free DFT approximations". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, n.º 5 (29 de septiembre de 2020): 724–26. http://dx.doi.org/10.1107/s2052520620012895.

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Two distinct approaches, that of energy and that of force, are adopted in quantum mechanics to get insights on chemical processes. In the second one, the net forces acting on the electrons and nuclei in a system (Ehrnefest and Hellmann–Feynman forces, respectively) are determined and a local version of the approach, in terms of force density fields rather than forces, has also been proposed for electrons. This is the path followed by Tsirelson & Stash (2020) in this issue of Acta Crystallographica Section B, to study for the first time the spatial distribution of the electronic forces of different nature acting in stable crystals. Interestingly, by relying on approximations taken from orbital-free DFT, all components of the inner-crystal force can be easily retrieved from multipole-model refined experimental electron densities and their derivatives. No less important is that these calculations are becoming easily doable for any X-ray density crystallographer thanks to a new version of the computer program WinXPRO, purposely developed in the study which is discussed in this commentary.

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33

Shcherbakov, A. V., D. A. Gaponova, A. V. Gudenko, A. P. Sliva, R. V. Rodyakina, A. L. Goncharov, S. A. Ovechnikov y V. K. Dragunov. "Modeling of heat and mass transfer and electrons scattering in electron beam welding and additive manufacturing". Journal of Physics: Conference Series 2275, n.º 1 (1 de junio de 2022): 012011. http://dx.doi.org/10.1088/1742-6596/2275/1/012011.

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Abstract The mathematical formulation of electron beam melting and liquid metal transfer model in wire-based additive manufacturing with temperature dependencies of thermophysical properties is described. A description of the model algorithmic implementation based on the use of numerical methods for solving the Navier-Stokes equations system and the Volume of Fluid (VOF) method for tracking the free surface of a liquid on the cubic mesh cells is given. An iterative method for calculating the pressure field that ensures the fulfillment of the incompressibility condition for a viscous fluid is described. The paper also paid attention to the description of methodology for calculating the forces acting on the free surface of the melt, including surface tension forces and metal vapor pressure forces. One of the key elements of the proposed model is method for volumetric distribution of electron losses calculating, considering their scattering during the interaction of an electron beam with a curved melt surface. Electron beam focusing influence on the distribution of energy losses and the dynamics of penetration channel formation has been studied. An algorithm for visualizing the free surface of the melt based on the use of the Gaussian function, is described.

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34

Gavriljuk, Valentin G., Bela D. Shanina, Vladyslav N. Shyvanyuk y Sergey M. Teus. "Hydrogen embrittlement of austenitic steels: electron approach". Corrosion Reviews 31, n.º 2 (1 de agosto de 2013): 33–50. http://dx.doi.org/10.1515/corrrev-2013-0024.

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AbstractA review of available hypotheses for hydrogen embrittlement (HE) in its relation to austenitic steels is presented. It is shown that the hydrogen-enhanced localized plasticity theory adequately describes the features of HE. Nevertheless, being developed within the frame of continuum mechanics, it overestimates the hydrogen-induced shielding of the elastic interaction between dislocations and does not take into account the hydrogen-induced change in the electron structure of austenitic steels. Ab initio calculations and experimental studies of the electron structure show that the hydrogen in austenitic steels increases the concentration of free electrons, nf, and the interpretation of available experimental data shows that when designing steel, alloying the steel with elements that decrease nf improves hydrogen resistance. Experimental tests are carried out, and their results are discussed. Based on the hydrogen-increased concentration of thermodynamic equilibrium vacancies in the interstitial solid solutions, a new model for hydrogen-induced shear localization is proposed.

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35

TARENTO, R. J., P. JOYES y J. VAN DE WALLE. "SIMPLE APPROACHES TO FULLERENES AND BUCKONIONS ELECTRONIC STRUCTURE: GUTZWILLER AND SHELL-MODEL CALCULATIONS". Surface Review and Letters 03, n.º 01 (febrero de 1996): 849–51. http://dx.doi.org/10.1142/s0218625x96001522.

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The electronic structure of fullerenes and buckonions have been investigated using quantum-mechanical methods: the Gutzwiller and shell-model techniques. In the first part, fullerenes have been modeled with the Hubbard Hamiltonian and the electronic correlation has been examined within the Gutzwiller framework. It has been derived various characteristic energies of fullerenes ( C 60 and C 240) in the free state (first and second ionization energies, electron affinity, and singlet and triplet energies). The second part deals with buckonions. Fullerenes and buckonions have been modeled with the spherical shell-model approach. The calculation has led to the electronic structure of fullerenes and of buckonions. So if we compare the energy levels of the buckonions with those of the fullerenes which build the buckonions, only the buckonions energy levels coming from the outer shell are changed by the coupling between shells.

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36

Taubmann, Gerhard. "Calculation of the Hückel parameter β [beta] from the free-electron model". Journal of Chemical Education 69, n.º 2 (febrero de 1992): 96. http://dx.doi.org/10.1021/ed069p96.

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37

Ghezali, Sara y Amina Mahdad-Benzerdjeb. "Adsorption of 2,4,6-trichlorophenol on kaolinite: DFT calculations". Aceh International Journal of Science and Technology 6, n.º 3 (31 de diciembre de 2017): 141–52. http://dx.doi.org/10.13170/aijst.6.3.6987.

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The aim of this work is to explore the adsorption process of an organic pollutant the 2,4,6-trichlorophenol on the clay mineral (kaolinite) surface in order to identify the sites of adsorption as well as conformations corresponding to the lowest energies. Ab-initio calculations have been used to investigate the adsorption process using a representative cluster model. According to the results obtained on the various studied models, the orientation of TCP on the surfaces clay affect the parameters such as : HOMO-LUMO energy gap, the enthalpy change (ΔH), the thermal Gibbs free energy (ΔG) and entropy contribution (ΔS). The results point out a preferential adsorption of TCP on the octahedral surface and the NBO analysis indicates that the electron donor-acceptor complex was the dominant adsorption mechanism.

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38

Sovago, Ioana, Anna A. Hoser y Anders Ø. Madsen. "A combined model of electron density and lattice dynamics refined against elastic diffraction data. Thermodynamic properties of crystalline L-alanine". Acta Crystallographica Section A Foundations and Advances 76, n.º 1 (1 de enero de 2020): 32–44. http://dx.doi.org/10.1107/s205327331901355x.

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Thermodynamic stability is an essential property of crystalline materials, and its accurate calculation requires a reliable description of the thermal motion – phonons – in the crystal. Such information can be obtained from periodic density functional theory (DFT) calculations, but these are costly and in some cases insufficiently accurate for molecular crystals. This deficiency is addressed here by refining a lattice-dynamics model, derived from DFT calculations, against accurate high-resolution X-ray diffraction data. For the first time, a normal-mode refinement is combined with the refinement of aspherical atomic form factors, allowing a comprehensive description and physically meaningful deconvolution of thermal motion and static charge density in the crystal. The small and well diffracting L-alanine system was used. Different lattice-dynamics models, with or without phonon dispersion, and derived from different levels of theory, were tested, and models using spherical and aspherical form factors were compared. The refinements indicate that the vibrational information content in the 23 K data is too small to study lattice dynamics, whereas the 123 K data appear to hold information on the acoustic and lowest-frequency optical phonons. These normal-mode models show slightly larger refinement residuals than their counterparts using atomic displacement parameters, and these features are not removed by considering phonon dispersion in the model. The models refined against the 123 K data, regardless of their sophistication, give calculated heat capacities for L-alanine within less than 1 cal mol−1 K−1 of the calorimetric measurements, in the temperature range 10–300 K. The findings show that the normal-mode refinement method can be combined with an elaborate description of the electron density. It appears to be a promising technique for free-energy determination for crystalline materials at the expense of performing a single-crystal elastic X-ray diffraction determination combined with periodic DFT calculations.

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39

Frémont, François. "Transverse Momentum Transfer Distributions Following Single Ionization in 3.6 MeV/amu Au53+ + He Collisions: A 4-Body Classical Treatment". Atoms 6, n.º 4 (3 de diciembre de 2018): 68. http://dx.doi.org/10.3390/atoms6040068.

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A four-body classical model based on the resolution of Hamilton equations of motion was used here to determine and analyze ionization doubly-differential cross sections following 3.6 MeV/amu Au53+ + He collisions. Our calculation was not able to reproduce the binary peaks experimentally observed in the transverse momentum distributions for electron emission energies larger than 10 eV. Surprisingly, by introducing a large number of free or quasi-free electrons that followed the projectile at the same velocity, the agreement between the experiment and our calculation was improved, since our model reproduced, at least qualitatively, the experimental binary peaks. The origin of the presence of such electrons is discussed.

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40

Perrot, F. "New approximation for calculating free-free absorption in hot dense plasmas". Laser and Particle Beams 14, n.º 4 (diciembre de 1996): 731–48. http://dx.doi.org/10.1017/s0263034600010430.

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We propose a model for calculating free-free absorption (inverse bremsstrahlung) in hot dense plasmas. This model writes the total Gaunt factor as the product of a static factor and a dynamic factor. The treatment of the static part is based on a relation between the absorption cross section and the elastic scattering cross section, which is exact for very low frequencies and becomes asymptotically correct when the Born approximation is valid. Generalizing this relation provides an expression of the absorption cross section Q(k, k′), which depends on the initial and final wave vectors k and k′, as an integral of a unique function S*(k). The calculation of nondiagonal matrix elements (k ≠ k′) is thus avoided. The analytic summation of the high angular momenta in the partial wave expansion of the cross section makes possible to apply the model in the limit of weak electron screening. The collective effects are accounted for in a dynamic Gaunt factor and in an index of refraction different from unity. Numerical results for the Gaunt factor in cesium are presented and discussed. An application to the mean opacities of carbon is also shown.

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41

Heard, GL y BF Yates. "Theoretical Evaluation of Alternative Pathways in the Stevens Rearrangement". Australian Journal of Chemistry 48, n.º 8 (1995): 1413. http://dx.doi.org/10.1071/ch9951413.

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Ab initio and semi-empirical molecular orbital theory has been used to explore the ion-pair and lithium-catalysed pathways in the Stevens rearrangement of an alkylammonium ylide to an amine. These pathways represent alternatives to the concerted and free radical mechanisms which we have previously studied. Solvation effects have been included via a polarizable continuum model. Finally, the calculations have been extended to a set of experimentally observable compounds. For the nine systems studied here, the stepwise free radical pathway is predicted in every case to be the favourable mechanism for the Stevens rearrangement. Single-point MP2/6-31G(d) calculations on fully optimized PM3 geometries are shown to provide a useful method of including electron correlation at low computational cost.

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42

KRISTOFFEL, NIKOLAI, PAVEL RUBIN y TEET ÖRD. "MULTIBAND MODEL OF CUPRATE SUPERCONDUCTIVITY". International Journal of Modern Physics B 22, n.º 30 (10 de diciembre de 2008): 5299–327. http://dx.doi.org/10.1142/s0217979208049443.

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A minimal model for the description of cuprate superconductor characteristics on doping scale (hole and electron) is developed. The leading interband pairing channel couples an itinerant band and defect states created by doping. Bare gaps between them are supposed and become closed by extended doping. Band overlap conditions determine special points in the phase diagram. Nodal and antinodal momentum regions are distinguished. Illustrative calculations have been made using a mean-field pair-transfer multiband Hamiltonian and corresponding free-energy expansions. The results are self-consistent and demonstrate that the elaborated approach is able to reproduce characteristic features of cuprate superconductors as, e.g., the doping dependence of Tc, superconducting gaps and pseudogaps, supercarrier density and effective mass, coherence length and penetration depth, critical magnetic fields and some other properties. Interband pairing scheme is suggested to be an essential aspect of cuprate superconductivity.

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43

Scheins, S., B. Dittrich, M. Messerschmidt, C. Paulmann y P. Luger. "Atomic volumes and charges in a system with a strong hydrogen bond: L-tryptophan formic acid". Acta Crystallographica Section B Structural Science 60, n.º 2 (18 de marzo de 2004): 184–90. http://dx.doi.org/10.1107/s0108768104001739.

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A high-resolution X-ray diffraction data set was collected within 48 h at 100 K with synchrotron radiation and area detection. A full topological analysis was applied to the resulting electron-density model. This analysis was followed by a Bader partitioning making use of the zero-flux surfaces of the electron-density gradient vector field. The atomic and bonding properties obtained were compared with the results of previous experimental studies, and with theoretical calculations for the title complex and free tryptophan as reported in the literature. The agreement between experiment and theory is similar to the agreement between different theoretical calculations. There is no charge transfer via the strong hydrogen bond; however, its strength is indicated by the very small atomic volume of the H atom involved.

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44

Ageeva, Aleksandra A., Alexander I. Kruppa, Ilya M. Magin, Simon V. Babenko, Tatyana V. Leshina y Nikolay E. Polyakov. "New Aspects of the Antioxidant Activity of Glycyrrhizin Revealed by the CIDNP Technique". Antioxidants 11, n.º 8 (17 de agosto de 2022): 1591. http://dx.doi.org/10.3390/antiox11081591.

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Electron transfer plays a crucial role in ROS generation in living systems. Molecular oxygen acts as the terminal electron acceptor in the respiratory chains of aerobic organisms. Two main mechanisms of antioxidant defense by exogenous antioxidants are usually considered. The first is the inhibition of ROS generation, and the second is the trapping of free radicals. In the present study, we have elucidated both these mechanisms of antioxidant activity of glycyrrhizin (GL), the main active component of licorice root, using the chemically induced dynamic nuclear polarization (CIDNP) technique. First, it was shown that GL is capable of capturing a solvated electron, thereby preventing its capture by molecular oxygen. Second, we studied the effect of glycyrrhizin on the behavior of free radicals generated by UV irradiation of xenobiotic, NSAID—naproxen in solution. The structure of the glycyrrhizin paramagnetic intermediates formed after the capture of a solvated electron was established from a photo-CIDNP study of the model system—the dianion of 5-sulfosalicylic acid and DFT calculations.

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45

Sazykina, T. G. y A. I. Kryshev. "Model for calculating energy absorption in environmental objects from incorporated sources of monoenergetic electrons". "Radiation and Risk" Bulletin of the National Radiation and Epidemiological Registry 30, n.º 2 (2021): 113–22. http://dx.doi.org/10.21870/0131-3878-2021-30-2-113-122.

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Model is suggested to calculating energy absorption in organisms of various geometry from in-corporated sources of monoenergetic electrons. The effectiveness of the approach was demon-strated for spheres, ellipsoids, and cylinders by comparison of analytical values with large inter-national testing data. Model equations are free of any fitting parameters; computer approximating procedures are not employed. The method allows to make correct express-calculations of inter-nal absorbed doses in various biological objects from beta emitting radionuclides; the calcula-tions are performed without Monte Carlo codes. The model may be used in the internal radiation dosimetry for non-human biota, and in environmental radiation protection.

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46

Korzhavyi, Pavel A. y Jing Zhang. "Free Energy of Metals from Quasi-Harmonic Models of Thermal Disorder". Metals 11, n.º 2 (21 de enero de 2021): 195. http://dx.doi.org/10.3390/met11020195.

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A simple modeling method to extend first-principles electronic structure calculations to finite temperatures is presented. The method is applicable to crystalline solids exhibiting complex thermal disorder and employs quasi-harmonic models to represent the vibrational and magnetic free energy contributions. The main outcome is the Helmholtz free energy, calculated as a function of volume and temperature, from which the other related thermophysical properties (such as temperature-dependent lattice and elastic constants) can be derived. Our test calculations for Fe, Ni, Ti, and W metals in the paramagnetic state at temperatures of up to 1600 K show that the predictive capability of the quasi-harmonic modeling approach is mainly limited by the electron density functional approximation used and, in the second place, by the neglect of higher-order anharmonic effects. The developed methodology is equally applicable to disordered alloys and ordered compounds and can therefore be useful in modeling realistically complex materials.

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47

Arutyunyan, Rafael, Yuri Obukhov y Petr Vabishchevich. "NUMERICAL SIMULATION OF CHARGED FULLERENE SPECTRUM". Mathematical Modelling and Analysis 24, n.º 2 (18 de marzo de 2019): 263–75. http://dx.doi.org/10.3846/mma.2019.017.

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The mathematical model of the electron spectrum of a charged fullerene is constructed on the basis of the potential of a charged sphere and the spherically symmetric potential of an uncharged fullerene. The electron spectrum is defined as the solution of the spectral problem for the one-dimensional Schr\"odinger equation. For the numerical solution of the spectral problem, piecewise-linear finite elements are used. The computational algorithm was tested on the analytical solution of the problem of the spectrum of the hydrogen atom. For solution of matrix spectral problems, a free library for solving spectral problems of SLEPc is used. The results of calculations of the electron spectrum of a charged fullerene C60 are presented.

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48

Zarychta, Bartosz, Jacek Zaleski, Janusz Kyzioł, Zdzisław Daszkiewicz y Christian Jelsch. "Charge-density analysis of 1-nitroindoline: refinement quality using free R factors and restraints". Acta Crystallographica Section B Structural Science 67, n.º 3 (14 de mayo de 2011): 250–62. http://dx.doi.org/10.1107/s0108768111013140.

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Nitramines and related N-nitro compounds have attracted significant attention owing to their use in rocket fuel and as explosives. The charge density of 1-nitroindoline was determined experimentally and from theoretical calculations. Electron-density refinements were performed using the multipolar atom formalism. In order to design the ideal restraint strategy for the charge-density parameters, R-free analyses were performed involving a series of comprehensive refinements. Different weights were applied to the charge-density restraints, namely the similarity between chemically equivalent atoms and local symmetry. Additionally, isotropic thermal motion and an anisotropic model calculated by rigid-body analysis were tested on H atoms. The restraint weights which resulted in the lowest values of the averaged R-free factors and the anisotropic H-atom model were considered to yield the best charge density and were used in the final refinement. The derived experimental charge density along with intra- and intermolecular interactions was analysed and compared with theoretical calculations, notably with respect to the symmetry of multipole parameters. A comparison of different refinements suggests that the appropriate weighting scheme applied to charge-density restraints can reduce the observed artefacts. The topological bond orders of the molecule were calculated.

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49

Nishida, Michio y Masashi Matsumotob. "Thermochemical Nonequilibrium in Rapidly Expanding Flows of High-Temperature Air". Zeitschrift für Naturforschung A 52, n.º 4 (1 de abril de 1997): 358–68. http://dx.doi.org/10.1515/zna-1997-0411.

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Abstract • This paper describes a computational study of the thermal and chemical nonequilibrium occuring in a rapidly expanding flow of high-temperature air transported as a free jet from an orifice into low-density stationary air. Translational, rotational, vibrational and electron temperatures are treated separately, and in particular the vibrational temperatures are individually treated; a multi-vibrational temperature model is adopted. The governing equations are axisymmetric Navier-Stokes equations coupled with species vibrational energy, electron energy and species mass conservation equations. These equations are numerically solved, using the second order upwind TVD scheme of the Harten-Yee type. The calculations were carried out for two different orifice temperatures and also two different orifice diameters to investigate the effects of such parameters on the structure of a nonequilibrium free jet.

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50

Frémont, François. "Doubly and Triply Differential Cross Sections for Single Ionization of He by Fast Au53+ Using a Multi-Body Quasiclassical Model". Atoms 8, n.º 2 (6 de mayo de 2020): 19. http://dx.doi.org/10.3390/atoms8020019.

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A multi-body multi-center quasiclassical model was used to determine doubly- and triply-differential cross sections following single ionization in 3.6 MeV/amu Au53+ + He collisions. The present model improved recent calculations, in which free electrons were added in the collision to reproduce, at least qualitatively, the experimental binary peak. In the present calculations, the electrons, that were assumed to originate from the collisions of Au53+ with surfaces before colliding with the He target, were now considered to be in the field of the projectile, with nearly the same velocity. The agreement between the calculations and the experiment was improved, for both the doubly- and the triply-differential cross sections and was better than previous calculations based on quantum mechanics.

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