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   ISSN (Online) 2218-2004
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  • Atoms, Vol. 5, Pages 15: Shannon Information Entropy in Position Space for
           the Ground and Singly Excited States of Helium with Finite Confinements

    • Authors: Jen-Hao Ou, Yew Ho
      First page: 15
      Abstract: We provide benchmark values for Shannon information entropies in position space for the ground state and ls2s 1Se excited state of helium confined with finite confinement potentials by employing the highly correlated Hylleraas-type wave functions. For the excited state, a “tilt” (small oscillation) on the curve of Shannon entropy as a function of width size for the confinement potential is observed. Justified by the behavior of the electron density, the localization or delocalization of the helium wave functions confined with repulsive and attractive finite oscillator (FO) potentials are examined.
      PubDate: 2017-03-24
      DOI: 10.3390/atoms5020015
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 16: Multiconfiguration Dirac-Hartree-Fock
           Calculations with Spectroscopic Accuracy: Applications to Astrophysics

    • Authors: Per Jönsson, Gediminas Gaigalas, Pavel Rynkun, Laima Radžiūtė, Jörgen Ekman, Stefan Gustafsson, Henrik Hartman, Kai Wang, Michel Godefroid, Charlotte Froese Fischer, Ian Grant, Tomas Brage, Giulio Del Zanna
      First page: 16
      Abstract: Atomic data, such as wavelengths, spectroscopic labels, broadening parameters and transition rates, are necessary for many applications, especially in plasma diagnostics, and for interpreting the spectra of distant astrophysical objects. The experiment with its limited resources is unlikely to ever be able to provide a complete dataset on any atomic system. Instead, the bulk of the data must be calculated. Based on fundamental principles and well-justified approximations, theoretical atomic physics derives and implements algorithms and computational procedures that yield the desired data. We review progress and recent developments in fully-relativistic multiconfiguration Dirac–Hartree–Fock methods and show how large-scale calculations can give transition energies of spectroscopic accuracy, i.e., with an accuracy comparable to the one obtained from observations, as well as transition rates with estimated uncertainties of a few percent for a broad range of ions. Finally, we discuss further developments and challenges.
      PubDate: 2017-04-14
      DOI: 10.3390/atoms5020016
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 17: P-Wave Positron-Hydrogen Scattering,
           Annihilation, and Positronium Formation

    • Authors: Anand Bhatia
      First page: 17
      Abstract: In a previous paper (Bhatia A.K. 2016), a hybrid theory for the scattering of positrons from hydrogen atoms was applied to calculate S-wave phase shifts, annihilation, and positronium formation cross sections. This approach is now being applied to calculate P-wave positron-hydrogen scattering. The present results, obtained using short-range correlation functions along with long-range correlations in the Schrödinger equation at the same time, agree very well with the results obtained in an earlier calculation by Bhatia et al. (1974), using the Feshbach projection operator formalism. In these earlier calculations, the correction due to the long-range correlations was applied to the variational results. In spite of the fact that this ad hoc correction destroyed the variational bound, the final results have been considered accurate. Annihilation cross-sections, positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented.
      PubDate: 2017-04-18
      DOI: 10.3390/atoms5020017
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 18: Elementary Processes and Kinetic Modeling for
           Hydrogen and Helium Plasmas

    • Authors: Roberto Celiberto, Mario Capitelli, Gianpiero Colonna, Giuliano D’Ammando, Fabrizio Esposito, Ratko Janev, Vincenzo Laporta, Annarita Laricchiuta, Lucia Pietanza, Maria Rutigliano, Jogindra Wadehra
      First page: 18
      Abstract: We report cross-sections and rate coefficients for excited states colliding with electrons, heavy particles and walls useful for the description of H 2 /He plasma kinetics under different conditions. In particular, the role of the rotational states in resonant vibrational excitations of the H 2 molecule by electron impact and the calculation of the related cross-sections are illustrated. The theoretical determination of the cross-section for the rovibrational energy exchange and dissociation of H 2 molecule, induced by He atom impact, by using the quasi-classical trajectory method is discussed. Recombination probabilities of H atoms on tungsten and graphite, relevant for the determination of the nascent vibrational distribution, are also presented. An example of a state-to-state plasma kinetic model for the description of shock waves operating in H 2 and He-H 2 mixtures is presented, emphasizing also the role of electronically-excited states in affecting the electron energy distribution function of free electrons. Finally, the thermodynamic properties and the electrical conductivity of non-ideal, high-density hydrogen plasma are finally discussed, in particular focusing on the pressure ionization phenomenon in high-pressure high-temperature plasmas.
      PubDate: 2017-05-02
      DOI: 10.3390/atoms5020018
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 19: Radiative Rates and Electron Impact Excitation
           Rates for Transitions in He II

    • Authors: Kanti Aggarwal, Akinori Igarashi, Francis Keenan, Shinobu Nakazaki
      First page: 19
      Abstract: We report calculations of energy levels, radiative rates, collision strengths and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of He II. The general-purpose relativistic atomic structure package (grasp) and Dirac atomic R-matrix code (darc) are adopted for the calculations. Radiative rates, oscillator strengths and line strengths are reported for all electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions among the 25 levels. Furthermore, collision strengths and effective collision strengths are listed for all 300 transitions among the above 25 levels over a wide energy (temperature) range up to 9 Ryd (10 5.4 K). Comparisons are made with earlier available results, and the accuracy of the data is assessed.
      PubDate: 2017-05-02
      DOI: 10.3390/atoms5020019
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 20: Configuration Interaction Effects in Unresolved
           5p65dN+1−5p55dN+2+5p65dN5f1 Transition Arrays in Ions Z = 79–92

    • Authors: Luning Liu, Deirdre Kilbane, Padraig Dunne, Xinbing Wang, Gerry O’Sullivan
      First page: 20
      Abstract: Configuration interaction (CI) effects can greatly influence the way in which extreme ultraviolet (EUV) and soft X-ray (SXR) spectra of heavier ions are dominated by emission from unresolved transition arrays (UTAs), the most intense of which originate from Δn = 0, 4p64dN+1−4p54dN+2+4p64dN4f1 transitions. Changing the principle quantum number n, from 4 to 5, changes the origin of the UTA from Δn = 0, 4p64dN+1−4p54dN+2+4p64dN4f1 to Δn = 0, 5p65dN+1−5p55dN+2+5p65dN5f1 transitions. This causes unexpected and significant changes in the impact of configuration interaction from that observed in the heavily studied n = 4 – n = 4 arrays. In this study, the properties of n = 5 – n = 5 arrays have been investigated theoretically with the aid of Hartree-Fock with configuration interaction (HFCI) calculations. In addition to predicting the wavelengths and spectral details of the anticipated features, the calculations show that the effects of configuration interaction are quite different for the two different families of Δn = 0 transitions, a conclusion which is reinforced by comparison with experimental results.
      PubDate: 2017-05-21
      DOI: 10.3390/atoms5020020
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 21: Inter-Series Interactions on the Atomic
           Photoionization Spectra Studied by the Phase-Shifted Multichannel-Quantum
           Defect Theory

    • Authors: Chun-Woo Lee
      First page: 21
      Abstract: Development in mathematical formulations of parameterizing the resonance structures using the phase-shifted multichannel quantum defect theory (MQDT) and their use in analyzing the effect of inter-series interactions on the autoionizing Rydberg spectra is reviewed. Reformulation of the short-range scattering matrix into the form analogous to S = SBSR in scattering theory are the crucial step in this development. Formulation adopts different directions and goals depending on whether autoionizing series converge to the same limit (degenerate) or to different limits (nondegenerate) because of the different nature of the perturbation. For the nondegenerate case, finding the simplest form of profile index functions of the autoionizing spectra with the minimal number of parameters is the main goal and some results are reviewed. For the degenerate case where perturbation acts uniformly throughout the entire series, isolation of the overlapped autoionizing series into the unperturbed autoionizing series is the key objective in research and some results in that direction are reviewed.
      PubDate: 2017-05-20
      DOI: 10.3390/atoms5020021
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 22: Detailed Opacity Calculations for Astrophysical

    • Authors: Jean-Christophe Pain, Franck Gilleron, Maxime Comet
      First page: 22
      Abstract: Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments involving hot dense plasmas produced by ultra-high-intensity laser irradiation. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. The focus is on iron, due to its crucial role in understanding asteroseismic observations of β Cephei-type and Slowly Pulsating B stars, as well as of the Sun. For instance, in β Cephei-type stars, the iron-group opacity peak excites acoustic modes through the “kappa-mechanism”. Particular attention is paid to the higher-than-predicted iron opacity measured at the Sandia Z-machine at solar interior conditions. We discuss some theoretical aspects such as density effects, photo-ionization, autoionization or the “filling-the-gap” effect of highly excited states.
      PubDate: 2017-05-30
      DOI: 10.3390/atoms5020022
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 23: The Third Spectrum of Indium: In III

    • Authors: Swapnil, Tauheed Ahmad
      First page: 23
      Abstract: The present investigation reports on the extended study of the third spectrum of indium (In III). This spectrum was previously analyzed in many articles, but, nevertheless, this study represents a significant extension of the previous analyses. The main new contribution is connected to the observation of transitions involving core-excited configurations. Previous data are critically evaluated and in some cases are corrected. The spectra were recorded on 3-m as well as on 10.7-m normal incidence spectrographs using a triggered spark source. Theoretical calculations were made with Cowan’s code. The analysis results in the identifications of 70 spectral lines and determination of 24 new energy levels. In addition, the manuscript represents a compilation of all presently available data on In III.
      PubDate: 2017-06-13
      DOI: 10.3390/atoms5020023
      Issue No: Vol. 5, No. 2 (2017)
  • Atoms, Vol. 5, Pages 1: Acknowledgement to Reviewers of Atoms in 2016

    • Authors: Atoms Editorial Office
      First page: 1
      Abstract: The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...]
      PubDate: 2017-01-10
      DOI: 10.3390/atoms5010001
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 2: An Investigation on the He−(1s2s2 2S)
           Resonance in Debye Plasmas

    • Authors: Arijit Ghoshal, Yew Ho
      First page: 2
      Abstract: The effect of Debye plasma on the 1 s 2 s 2 2 S resonance states in the scattering of electron from helium atom has been investigated within the framework of the stabilization method. The interactions among the charged particles in Debye plasma have been modelled by Debye–Huckel potential. The 1 s 2 s excited state of the helium atom has been treated as consisting of a H e + ionic core plus an electron moving around. The interaction between the core and the electron has then been modelled by a model potential. It has been found that the background plasma environment significantly affects the resonance states. To the best of our knowledge, such an investigation of 1 s 2 s 2 2 S resonance states of the electron–helium system embedded in Debye plasma environment is the first reported in the literature.
      PubDate: 2017-01-11
      DOI: 10.3390/atoms5010002
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 3: Combining Multiconfiguration and Perturbation
           Methods: Perturbative Estimates of Core–Core Electron Correlation
           Contributions to Excitation Energies in Mg-Like Iron

    • Authors: Stefan Gustafsson, Per Jönsson, Charlotte Froese Fischer, Ian Grant
      First page: 3
      Abstract: Large configuration interaction (CI) calculations can be performed if part of the interaction is treated perturbatively. To evaluate the combined CI and perturbative method, we compute excitation energies for the 3 l 3 l ′ , 3 l 4 l ′ and 3 s 5 l states in Mg-like iron. Starting from a CI calculation including valence and core–valence correlation effects, it is found that the perturbative inclusion of core–core electron correlation halves the mean relative differences between calculated and observed excitation energies. The effect of the core–core electron correlation is largest for the more excited states. The final relative differences between calculated and observed excitation energies is 0.023%, which is small enough for the calculated energies to be of direct use in line identifications in astrophysical and laboratory spectra.
      PubDate: 2017-01-12
      DOI: 10.3390/atoms5010003
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 4: High-Precision Measurements of the Bound
           Electron’s Magnetic Moment

    • Authors: Sven Sturm, Manuel Vogel, Florian Köhler-Langes, Wolfgang Quint, Klaus Blaum, Günter Werth
      First page: 4
      Abstract: Highly charged ions represent environments that allow to study precisely one or more bound electrons subjected to unsurpassed electromagnetic fields. Under such conditions, the magnetic moment (g-factor) of a bound electron changes significantly, to a large extent due to contributions from quantum electrodynamics. We present three Penning-trap experiments, which allow to measure magnetic moments with ppb precision and better, serving as stringent tests of corresponding calculations, and also yielding access to fundamental quantities like the fine structure constant α and the atomic mass of the electron. Additionally, the bound electrons can be used as sensitive probes for properties of the ionic nuclei. We summarize the measurements performed so far, discuss their significance, and give a detailed account of the experimental setups, procedures and the foreseen measurements.
      PubDate: 2017-01-21
      DOI: 10.3390/atoms5010004
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 5: Hyperfine Structure and Isotope Shifts in Dy II

    • Authors: Dylan Del Papa, Richard Holt, S. Rosner
      First page: 5
      Abstract: Using fast-ion-beam laser-fluorescence spectroscopy (FIBLAS), we have measured the hyperfine structure (hfs) of 14 levels and an additional four transitions in Dy II and the isotope shifts (IS) of 12 transitions in the wavelength range of 422–460 nm. These are the first precision measurements of this kind in Dy II. Along with hfs and IS, new undocumented transitions were discovered within 3 GHz of the targeted transitions. These atomic data are essential for astrophysical studies of chemical abundances, allowing correction for saturation and the effects of blended lines. Lanthanide abundances are important in diffusion modeling of stellar interiors, and in the mechanisms and history of nucleosynthesis in the universe. Hfs and IS also play an important role in the classification of energy levels, and provide a benchmark for theoretical atomic structure calculations.
      PubDate: 2017-01-20
      DOI: 10.3390/atoms5010005
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 6: JJ2LSJ Transformation and Unique Labeling for
           Energy Levels

    • Authors: Gediminas Gaigalas, Charlotte Fischer, Pavel Rynkun, Per Jönsson
      First page: 6
      Abstract: The JJ2LSJ program, which is important not only for the GRASP2K package but for the atom theory in general, is presented. The program performs the transformation of atomic state functions(ASFs) from a jj-coupled CSF basis into an LSJ-coupled CSF basis. In addition, the program implements a procedure that assigns a unique label to all energy levels. Examples of how to use the JJ2LSJ program are given. Several cases are presented where there is a unique labeling problem.
      PubDate: 2017-01-27
      DOI: 10.3390/atoms5010006
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 7: Core Effects on Transition Energies for 3dk
           Configurations in Tungsten Ions

    • Authors: Charlotte Fischer, Gediminas Gaigalas, Per Jönsson
      First page: 7
      Abstract: Allenergylevelsofthe3dk,k=1,2,...,8,9,configurationsfortungstenions,computedusing the GRASP2K fully relativistic code based on the variational multiconfiguration Dirac–Hartree–Fock method, are reported. Included in the calculations are valence correlation where all 3s,3p,3d orbitals are considered to be valence orbitals, as well as core–valence and core–core effects from the 2s,2p subshells. Results are compared with other recent theory and with levels obtained from the wavelengths of lines observed in the experimental spectra. It is shown that the core correlation effects considerably reduce the disagreement with levels linked directly to observed wavelengths, but may differ significantly from the NIST levels, where an unknown shift of the levels could not be determined from experimental wavelengths. For low values of k, levels were in good agreement with relativistic many-body perturbation levels, but for 2 < k < 8, the present results were in better agreement with observation.
      PubDate: 2017-02-08
      DOI: 10.3390/atoms5010007
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 8: Calculation of Rates of 4p–4d Transitions in
           Ar II

    • Authors: Alan Hibbert
      First page: 8
      Abstract: Recent experimental work by Belmonte et al. (2014) has given rates for some 4p–4d transitions that are significantly at variance with the previous experimental work of Rudko and Tang (1967) recommended in the NIST tabulations. To date, there are no theoretical rates with which to compare. In this work, we provide such theoretical data. We have undertaken a substantial and systematic configuration interaction calculation, with an extrapolation process applied to ab initio mixing coefficients, which gives energy differences in agreement with experiment. The length and velocity forms give values that are within 10%–15% of each other. Our results are in sufficiently close agreement with those of Belmonte et al. that we can confidently recommend that their results are much more accurate than the early results of Rudko and Tang, and should be adopted in place of the latter.
      PubDate: 2017-02-21
      DOI: 10.3390/atoms5010008
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 9: The Cu II Spectrum

    • Authors: Alexander Kramida, Gillian Nave, Joseph Reader
      First page: 9
      Abstract: New wavelength measurements in the vacuum ultraviolet (VUV), ultraviolet and visible spectral regions have been combined with available literature data to refine and extend the description of the spectrum of singly ionized copper (Cu II). In the VUV region, we measured 401 lines using a concave grating spectrograph and photographic plates. In the UV and visible regions, we measured 276 lines using a Fourier-transform spectrometer. These new measurements were combined with previously unpublished data from the thesis of Ross, with accurate VUV grating measurements of Kaufman and Ward, and with less accurate older measurements of Shenstone to construct a comprehensive list of ≈2440 observed lines, from which we derived a revised set of 379 optimized energy levels, complemented with 89 additional levels obtained using series formulas. Among the 379 experimental levels, 29 are new. Intensities of all lines observed in different experiments have been reduced to the same uniform scale by using newly calculated transition probabilities (A-values). We combined our calculations with published measured and calculated A-values to provide a set of 555 critically evaluated transition probabilities with estimated uncertainties, 162 of which are less than 20%.
      PubDate: 2017-02-24
      DOI: 10.3390/atoms5010009
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 10: The Role of the Hyperfine Structure for the
           Determination of Improved Level Energies of Ta II, Pr II and La II

    • Authors: Laurentius Windholz
      First page: 10
      Abstract: For the determination of improved energy levels of ionic spectra of elements with large values of nuclear magnetic dipole moment (and eventually large values of nuclear quadrupole moments), it is necessary to determine the center of gravity of spectral lines from resolved hyperfine structure patterns appearing in highly resolved spectra. This is demonstrated on spectral lines of Ta II, Pr II and La II. Blend situations (different transitions with accidentally nearly the same wave number difference between the combining levels) must also be considered.
      PubDate: 2017-02-28
      DOI: 10.3390/atoms5010010
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 11: Resonance Transitions in the Spectra of the
           Ag6+–Ag8+ Ions

    • Authors: Alexander Ryabtsev, Edward Kononov
      First page: 11
      Abstract: The spectrum of silver, excited in a vacuum spark, was recorded in the region 150–350 Å on a 3-m grazing incidence spectrograph. The resonance 4dk–(4dk−15p + 4dk−14f + 4p54dk+1) was studied in the Ag6+–Ag8+ spectra (Ag VII–Ag IX) with k = 5–3, respectively. Several hundred lines were identified with the aid of the Cowan code and orthogonal operator technique calculations. The energy levels were found and the transition probabilities were calculated.
      PubDate: 2017-03-04
      DOI: 10.3390/atoms5010011
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 12: Spectral Analysis of Moderately Charged Rare-Gas

    • Authors: Jorge Reyna Almandos, Mónica Raineri
      First page: 12
      Abstract: This article presents a review concerning the spectral analysis of several ions of neon, argon, krypton and xenon, with impact on laser studies and astrophysics that were mainly carried out in our collaborative groups between Argentina and Brazil during many years. The spectra were recorded from the vacuum ultraviolet to infrared regions using pulsed discharges. Semi-empirical approaches with relativistic Hartree–Fock and Dirac-Fock calculations were also included in these investigations. The spectral analysis produced new classified lines and energy levels. Lifetimes and oscillator strengths were also calculated.
      PubDate: 2017-03-07
      DOI: 10.3390/atoms5010012
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 13: Direct Observation of the M1 Transition between
           the Ground Term Fine Structure Levels of W VIII

    • Authors: Momoe Mita, Hiroyuki Sakaue, Daiji Kato, Izumi Murakami, Nobuyuki Nakamura
      First page: 13
      Abstract: We present a direct observation of the M1 transition between the fine structure splitting in the 4 f 13 5 s 2 5 p 6 2 F ground term of W VIII. The spectroscopic data of few-times ionized tungsten ions are important for the future ITER diagnostics, but there is a serious lack of data. The present study is part of an ongoing effort to solve this problem. Emission from the tungsten ions produced and trapped in a compact electron beam ion trap is observed with a Czerny–Turner visible spectrometer. Spectra in the EUV range are also observed at the same time to help identify the previously-unreported visible lines. The observed wavelength 574.47 ± 0.03 nm (air), which corresponds to the fine structure splitting of 17,402.5 ± 0.9 cm − 1 , shows reasonable agreement with the previously reported value 17,410 ± 5 cm − 1 obtained indirectly through the analysis of EUV spectra [Ryabtsev et al., Atoms 3 (2015) 273].
      PubDate: 2017-03-08
      DOI: 10.3390/atoms5010013
      Issue No: Vol. 5, No. 1 (2017)
  • Atoms, Vol. 5, Pages 14: Electroweak Decay Studies of Highly Charged
           Radioactive Ions with TITAN at TRIUMF

    • Authors: Kyle Leach, Iris Dillmann, Renee Klawitter, Erich Leistenschneider, Annika Lennarz, Thomas Brunner, Dieter Frekers, Corina Andreoiu, Anna Kwiatkowski, Jens Dilling
      First page: 14
      Abstract: Several modes of electroweak radioactive decay require an interaction between the nucleus and bound electrons within the constituent atom. Thus, the probabilities of the respective decays are not only influenced by the structure of the initial and final states in the nucleus, but can also depend strongly on the atomic charge. Conditions suitable for the partial or complete ionization of these rare isotopes occur naturally in hot, dense astrophysical environments, but can also be artificially generated in the laboratory to selectively block certain radioactive decay modes. Direct experimental studies on such scenarios are extremely difficult due to the laboratory conditions required to generate and store radioactive ions at high charge states. A new electron-beam ion trap (EBIT) decay setup with the TITAN experiment at TRIUMF has successfully demonstrated such techniques for performing spectroscopy on the radioactive decay of highly charged ions.
      PubDate: 2017-03-21
      DOI: 10.3390/atoms5010014
      Issue No: Vol. 5, No. 1 (2017)
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