Atoms
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Latest open access articles published in Atoms at http://www.mdpi.com/journal/atoms<![CDATA[Atoms, Vol. 4, Pages 22: Atomic Structure Calculations and Study of Plasma Parameters of Al-Like Ions]]>
http://www.mdpi.com/2218-2004/4/3/22
In the present paper, the spectroscopic properties and plasma characteristics of Al-like ions are investigated in an extensive and detailed manner by adopting the GRASP2K package based on fully relativistic Multi-Configuration Dirac–Hartree–Fock (MCDHF) wave-functions in the active space approximation. We have presented energy levels for Al-like ions for Valence-Valence (VV) and Core-Valence (CV) correlations under the scheme of active space. We have also provided radiative data for E1 transitions for Al-like ions and studied the variation of the transition wavelength and transition probability for electric dipole (E1) Extreme Ultraviolet (EUV) transitions with nuclear charge. Our calculated energy levels and transition wavelengths match well with available theoretical and experimental results. The discrepancies of the GRASP2K code results with CIV3 and RMPBT (Relativistic Many Body Perturbation Theory) results are also discussed. The variations of the line intensity ratio, electron density, plasma frequency and plasma skin depth with plasma temperature and nuclear charge are discussed graphically in detail for optically thin plasma in Local Thermodynamic Equilibrium (LTE). We believe that our obtained results may be beneficial for comparisons and in fusion and astrophysical plasma research.Atoms2016-07-1143Article10.3390/atoms4030022222218-20042016-07-11doi: 10.3390/atoms4030022Arun GoyalIndu KhatriAvnindra SinghMan MohanRinku SharmaNarendra Singh<![CDATA[Atoms, Vol. 4, Pages 21: Analysis of Polarizability Measurements Made with Atom Interferometry]]>
http://www.mdpi.com/2218-2004/4/3/21
We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric ﬁeld gradient. The resulting polarizability values did not change, but the uncertainties were signiﬁcantly reduced. Then, we interpret several measurements of alkali metal atomic polarizabilities in terms of atomic oscillator strengths fik, Einstein coefﬁcients Aik, state lifetimes τk, transition dipole matrix elements Dik, line strengths Sik, and van der Waals C6 coefﬁcients. Finally, we combine atom interferometer measurements of polarizabilities with independent measurements of lifetimes and C6 values in order to quantify the residual contribution to polarizability due to all atomic transitions other than the principal ns-npJ transitions for alkali metal atoms.Atoms2016-07-0643Article10.3390/atoms4030021212218-20042016-07-06doi: 10.3390/atoms4030021Maxwell GregoireNathan BrooksRaisa TrubkoAlexander Cronin<![CDATA[Atoms, Vol. 4, Pages 20: Neutrons and Gamma-Ray Dose Calculations in Subcritical Reactor Facility Using MCNP]]>
http://www.mdpi.com/2218-2004/4/3/20
In nuclear experimental, training and teaching laboratories such as a subcritical reactor facility, huge measures of external radiation doses could be caused by neutron and gamma radiation. It becomes imperative to place the health and safety of staff and students in the reactor facility under proper scrutiny. The protection of these individuals against ionization radiation is facilitated by expected dose mapping and shielding calculations. A three-dimensional (3D) Monte Carlo model was developed to calculate the dose rate from neutrons and gamma, using the ANSI/ANS-6.1.1 and the ICRP-74 flux-to-dose conversion factors. Estimation for the dose was conducted across 39 areas located throughout the reactor hall of the facility and its training platform. It was found that the range of the dose rate magnitude is between 7.50 E−01 μSv/h and 1.96 E−04 μSv/h in normal operation mode. During reactor start-up/shut-down mode, it was observed that a large area of the facility can experience exposure to a significant radiation field. This field ranges from 2.99 E+03 μSv/h to 3.12 E+01 μSv/h. There exists no noticeable disparity between results using the ICRP-74 or ANSI/ANS-6.1.1 flux-to-dose rate conversion factors. It was found that the dose rate due to gamma rays is higher than that of neutrons.Atoms2016-06-3043Article10.3390/atoms4030020202218-20042016-06-30doi: 10.3390/atoms4030020Ned Xoubi<![CDATA[Atoms, Vol. 4, Pages 19: Prospects for Precise Measurements with Echo Atom Interferometry]]>
http://www.mdpi.com/2218-2004/4/3/19
Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration g and the determination of the atomic fine structure through measurements of the atomic recoil frequency ω q . Here we review the development of different configurations of echo interferometers that are best suited to achieve these goals. We describe experiments that utilize near-resonant excitation of laser-cooled rubidium atoms by a sequence of standing wave pulses to measure ω q with a statistical uncertainty of 37 parts per billion (ppb) on a time scale of ∼50 ms and g with a statistical precision of 75 ppb. Related coherent transient techniques that have achieved the most statistically precise measurements of atomic g-factor ratios are also outlined. We discuss the reduction of prominent systematic effects in these experiments using off-resonant excitation by low-cost, high-power lasers.Atoms2016-06-2743Article10.3390/atoms4030019192218-20042016-06-27doi: 10.3390/atoms4030019Brynle BarrettAdam CarewHermina BeicaAndrejs VorozcovsAlexander PouliotA. Kumarakrishnan<![CDATA[Atoms, Vol. 4, Pages 18: A Wigner Function Approach to Coherence in a Talbot-Lau Interferometer]]>
http://www.mdpi.com/2218-2004/4/2/18
Using a thermal gas, we model the signal of a trapped interferometer. This interferometer uses two short laser pulses, separated by time T, which act as a phase grating for the matter waves. Near time 2 T , there is an echo in the cloud’s density due to the Talbot-Lau effect. Our model uses the Wigner function approach and includes a weak residual harmonic trap. The analysis shows that the residual potential limits the interferometer’s visibility, shifts the echo time of the interferometer, and alters its time dependence. Loss of visibility can be mitigated by optimizing the initial trap frequency just before the interferometer cycle begins.Atoms2016-06-2242Article10.3390/atoms4020018182218-20042016-06-22doi: 10.3390/atoms4020018Eric ImhofJames StickneyMatthew Squires<![CDATA[Atoms, Vol. 4, Pages 17: Series of Broad Resonances in Atomic Three-Body Systems]]>
http://www.mdpi.com/2218-2004/4/2/17
We re-examine the series of resonances found earlier in atomic three-body systems by solving the Faddeev-Merkuriev integral equations. These resonances are rather broad and line up at each threshold with gradually increasing gaps. This lining up takes place in the same way for all thresholds and is irrespective of the spatial symmetry. We relate these resonances to the Gailitis mechanism, which is a consequence of the polarization potential.Atoms2016-06-2042Article10.3390/atoms4020017172218-20042016-06-20doi: 10.3390/atoms4020017Daniel DiazZoltan PappChi-Yu Hu<![CDATA[Atoms, Vol. 4, Pages 13: Multi-Configuration Dirac–Hartree–Fock (MCDHF) Calculations for B-Like Ions]]>
http://www.mdpi.com/2218-2004/4/2/13
Relativistic configuration interaction results are presented for several B-like ions (Ge XXVIII, Rb XXXIII, Sr XXXIV, Ru XL, Sn XLVI, and Ba LII) using the multi-configuration Dirac–Hartree–Fock (MCDHF) method. The calculations are carried out in the active space approximation with the inclusion of the Breit interaction, the finite nuclear size effect, and quantum electrodynamic corrections. Results for fine structure energy levels for 1s22s22p and 2s2p2 configurations relative to the ground state are reported. The transition wavelengths, transition probabilities, line strengths, and absorption oscillator strengths for 2s22p–2s2p2 electric dipole (E1) transitions are calculated. Both valence and core-valence correlation effects were accounted for through single-double multireference (SD-MR) expansions to increasing sets of active orbitals. Comparisons are made with the available data and good agreement is achieved. The values calculated using core–valence correlation are found to be very close to other theoretical and experimental values. The behavior of oscillator strengths as a function of nuclear charge is studied. We believe that our results can guide experimentalists in identifying the fine-structure levels in their future work.Atoms2016-05-0642Article10.3390/atoms4020013132218-20042016-05-06doi: 10.3390/atoms4020013Indu KhatriArun GoyalAvnindra SinghMan Mohan<![CDATA[Atoms, Vol. 4, Pages 16: The Faddeev-Merkuriev Differential Equations (MFE) and Multichannel 3-Body Scattering Systems]]>
http://www.mdpi.com/2218-2004/4/2/16
Numerical implementation of the modified Faddeev Equation (MFE) is presented in some detail. The Faddeev channel wave function displays unique properties of each and every open channel, respectively. In particular, near resonant energies, the structures of the resonances are beautifully displayed, from which, the life-time of the resonances can be determined by simply using the uncertainty principle. The phase shift matrix, or the K-matrix, provides unique information for each and every resonance. This information enables the identification of the physical formation mechanism of the Gailitis resonances. A few of these resonances, previously known as the mysterious shape resonances, have occurred in a number of different collision systems. The Gailitis resonances are actually produced by a quantized Stark-effect within the various collision systems. Since the Stark-effect is a universal phenomenon, the Gailitis resonances are expected to occur in much broader classes of collision systems. We will present the results of a precision calculation using the MFE method in sufficient detail for interested students who wish to explore the mysteries of nature with a powerful theoretical tool.Atoms2016-05-0342Communication10.3390/atoms4020016162218-20042016-05-03doi: 10.3390/atoms4020016Chi Hu<![CDATA[Atoms, Vol. 4, Pages 15: Novel Ion Trap Design for Strong Ion-Cavity Coupling]]>
http://www.mdpi.com/2218-2004/4/2/15
We present a novel ion trap design which facilitates the integration of an optical fiber cavity into the trap structure. The optical fibers are confined inside hollow electrodes in such a way that tight shielding and free movement of the fibers are simultaneously achievable. The latter enables in situ optimization of the overlap between the trapped ions and the cavity field. Through numerical simulations, we systematically analyze the effects of the electrode geometry on the trapping characteristics such as trap depths, secular frequencies and the optical access angle. Additionally, we simulate the effects of the presence of the fibers and confirm the robustness of the trapping potential. Based on these simulations and other technical considerations, we devise a practical trap configuration that isviable to achieve strong coupling of a single ion.Atoms2016-04-2642Article10.3390/atoms4020015152218-20042016-04-26doi: 10.3390/atoms4020015Alejandro Márquez SecoHiroki TakahashiMatthias Keller<![CDATA[Atoms, Vol. 4, Pages 14: Atom Interferometry in the Presence of an External Test Mass]]>
http://www.mdpi.com/2218-2004/4/2/14
The influence of an external test mass on the phase of the signal of an atom interferometer is studied theoretically. Using traditional techniques in atom optics based on the density matrix equations in the Wigner representation, we are able to extract the various contributions to the phase of the signal associated with the classical motion of the atoms, the quantum correction to this motion resulting from atomic recoil that is produced when the atoms interact with Raman field pulses and quantum corrections to the atomic motion that occur in the time between the Raman field pulses. By increasing the effective wave vector associated with the Raman field pulses using modified field parameters, we can increase the sensitivity of the signal to the point where such quantum corrections can be measured. The expressions that are derived can be evaluated numerically to isolate the contribution to the signal from an external test mass. The regions of validity of the exact and approximate expressions are determined.Atoms2016-04-2142Article10.3390/atoms4020014142218-20042016-04-21doi: 10.3390/atoms4020014Boris DubetskyStephen LibbyPaul Berman<![CDATA[Atoms, Vol. 4, Pages 12: Obtaining Atomic Matrix Elements from Vector Tune-Out Wavelengths Using Atom Interferometry]]>
http://www.mdpi.com/2218-2004/4/2/12
Accurate values for atomic dipole matrix elements are useful in many areas of physics, and in particular for interpreting experiments such as atomic parity violation. Obtaining accurate matrix element values is a challenge for both experiment and theory. A new technique that can be applied to this problem is tune-out spectroscopy, which is the measurement of light wavelengths where the electric polarizability of an atom has a zero. Using atom interferometry methods, tune-out wavelengths can be measured very accurately. Their values depend on the ratios of various dipole matrix elements and are thus useful for constraining theory and broadening the application of experimental values. To date, tune-out wavelength measurements have focused on zeros of the scalar polarizability, but in general the vector polarizability also contributes. We show here that combined measurements of the vector and scalar polarizabilities can provide more detailed information about the matrix element ratios, and in particular can distinguish small contributions from the atomic core and the valence tail states. These small contributions are the leading error sources in current parity violation calculations for cesium.Atoms2016-03-3042Article10.3390/atoms4020012122218-20042016-03-30doi: 10.3390/atoms4020012Adam FallonCharles Sackett<![CDATA[Atoms, Vol. 4, Pages 11: Fundamental Features of Quantum Dynamics Studied in Matter-Wave Interferometry—Spin Weak Values and the Quantum Cheshire-Cat]]>
http://www.mdpi.com/2218-2004/4/1/11
The validity of quantum-mechanical predictions has been confirmed with a high degree of accuracy in a wide range of experiments. Although the statistics of the outcomes of a measuring apparatus have been studied intensively, little has been explored and is known regarding the accessibility of quantum dynamics. For these sorts of fundamental studies of quantum mechanics, interferometry using neutron matter-waves in particular, provides almost ideal experimental circumstances. In this device quantum interference between spatially separated beams occurs on a macroscopic scale. Recently, the full determination of weak-values of neutrons 1 2 - spin adds a new aspect to the study of quantum dynamics. Moreover, a new counter-intuitive phenomenon, called quantum Cheshire Cat, is observed in an interference experiment. In this article, we present an overview of these experiments.Atoms2016-03-1141Article10.3390/atoms4010011112218-20042016-03-11doi: 10.3390/atoms4010011Stephan SponarTobias DenkmayrHermann GeppertYuji Hasegawa<![CDATA[Atoms, Vol. 4, Pages 10: Relativistic Ionization of Hydrogen Atoms by Positron Impact]]>
http://www.mdpi.com/2218-2004/4/1/10
Relativistic triple differential cross-sections (TDCS) for ionization of hydrogen atoms by positron impact have been calculated in the symmetric coplanar geometry. We have used Dirac wave functions to describe free electron’s and positron’s sates. The relativistic formalism is examined by taking the non relativistic limit. Present results are compared with those for the corresponding electron-impact case. In the first Born approximation, we found that the TDCS for positron impact ionization exceeds that for electron impact for all energies in accordance with the result obtained by several other theories.Atoms2016-03-0441Article10.3390/atoms4010010102218-20042016-03-04doi: 10.3390/atoms4010010Amal ChahbouneBouzid ManautElmostafa HrourSouad Taj<![CDATA[Atoms, Vol. 4, Pages 9: Merkuriev Cut-off in e+ − H Multichannel Scattering Calculations]]>
http://www.mdpi.com/2218-2004/4/1/9
We present the results of positron-Hydrogen multichannel scattering calculations performed on the base of Faddeev-Merkuriev equations. We discuss an optimal choice of the Merkuriev’s Coulomb splitting parameters. Splitting the Coulomb potential in two-body configuration space is applicable for a limited energy range. Splitting the potential in three-body configuration space makes it possible to perform calculations in a broader range of energies and to optimize the numerical convergence. Scattering cross sections for zero total angular momentum for all processes between the positronium formation threshold and the third excitation threshold of the Hydrogen atom are reported.Atoms2016-03-0141Article10.3390/atoms401000992218-20042016-03-01doi: 10.3390/atoms4010009Vitaly GradusovVladimir RoudnevSergey Yakovlev<![CDATA[Atoms, Vol. 4, Pages 8: Second Order Stark-Effect Induced Gailitis Resonances in e + Ps and p + 7Li]]>
http://www.mdpi.com/2218-2004/4/1/8
We present a detailed comparison between the first order Stark-effect induced Gailitis resonance in e+ + H (n = 2) and the second order Stark-effect induced resonance in e + Ps (n = 1). Common characteristics as well as differences of these resonances will be identified. These results will be used to assess the presence of Gailitis resonances in the scattering of proton on the ground state of 7Li atom. During the lifetime of the Gailitis resonance, nuclear fusion is enhanced by the resonant entry of the proton into the nucleus of 7Li via a compound nuclear energy level of 8Be*.Atoms2016-02-2641Article10.3390/atoms401000882218-20042016-02-26doi: 10.3390/atoms4010008Chi HuZoltan Papp<![CDATA[Atoms, Vol. 4, Pages 7: Guest Editor’s Notes on the “Atoms” Special Issue on “Perspectives of Atomic Physics with Trapped Highly Charged Ions”]]>
http://www.mdpi.com/2218-2004/4/1/7
The study of highly charged ions (HCI) was pursued first at Uppsala (Sweden), by Edlén and Tyrén in the 1930s. Their work led to the recognition that the solar corona is populated by such ions, an insight which forced massive paradigm changes in solar physics. Plasmas aiming at controlled fusion in the laboratory, laser-produced plasmas, foil-excited swift ion beams, and electron beam ion traps have all pushed the envelope in the production of HCI. However, while there are competitive aspects in the race for higher ion charge states, the real interest lies in the very many physics topics that can be studied in these ions. Out of this rich field, the Special Issue concentrates on atomic physics studies that investigate highly charged ions produced, maintained, and/or manipulated in ion traps. There have been excellent achievements in the field in the past, and including fairly recent work, they have been described by their authors at conferences and in the appropriate journals. The present article attempts an overview over current lines of development, some of which are expanded upon in this Special Issue.Atoms2016-02-2441Editorial10.3390/atoms401000772218-20042016-02-24doi: 10.3390/atoms4010007Elmar Träbert<![CDATA[Atoms, Vol. 4, Pages 6: Two Photon Processes in an Atom Confined in Gaussian Potential]]>
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Transitions of an atom under the effect of a Gaussian potential and loose spherical confinement are studied. An accurate Bernstein-polynomial (B-polynomial) method has been applied for the calculation of the energy levels and radial matrix elements. The transition probability amplitudes, transparency frequencies, and resonance enhancement frequencies for transitions to various excited states have been evaluated. The effect of the shape of confining potential on these spectral properties is studied.Atoms2016-02-1741Article10.3390/atoms401000662218-20042016-02-17doi: 10.3390/atoms4010006Sonia LumbShalini LumbVinod Prasad<![CDATA[Atoms, Vol. 4, Pages 5: Acknowledgement to Reviewers of Atoms in 2015]]>
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The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2015. [...]Atoms2016-01-2241Editorial10.3390/atoms401000552218-20042016-01-22doi: 10.3390/atoms4010005 Atoms Editorial Office<![CDATA[Atoms, Vol. 4, Pages 4: Density Functional Theory (DFT) Study on the Ternary Interaction System of the Fluorinated Ethylene Carbonate, Li+ and Graphene Model]]>
http://www.mdpi.com/2218-2004/4/1/4
The ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ion (Li+) and a model of nano-structured graphene has been investigated by means of the density functional theory (DFT) method. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. The model of graphene consisting of 14 benzene rings was examined as a nano-structured graphene. The effects of fluorine substitution on the electronic state and binding energy were investigated from a theoretical point of view. It was found that both EC(F) and VC(F) bind to a hexagonal site corresponding to the central benzene ring of the model of the graphene surface. The binding energies of Li+EC(F) and Li+VC(F) to the model of graphene decreased with increasing number of fluorine atoms (n).Atoms2015-12-2941Article10.3390/atoms401000442218-20042015-12-29doi: 10.3390/atoms4010004Mami MutohShigeaki AbeTeruo KusakaMariko NakamuraYasuhiro YoshidaJunichiro IidaHiroto Tachikawa<![CDATA[Atoms, Vol. 4, Pages 3: Natural and Unnatural Parity Resonance States in the Positron-Hydrogen System with Screened Coulomb Interactions]]>
http://www.mdpi.com/2218-2004/4/1/3
In the present work, we report calculations of resonances in the positron-hydrogen system interacting with screened Coulomb potentials using the method of complex scaling together with employing correlated Hylleraas wave functions. Resonances with natural and unnatural parities are investigated. For the natural parity case, resonance parameters (energy and width) for D-wave resonance states with even parity lying below various positronium and hydrogen thresholds up to the H(N = 4) level are determined. For the unnatural parity case, results for P-even and D-odd resonance states with various screened Coulomb interaction strengths are located below different lower-lying Ps and H thresholds.Atoms2015-12-2641Article10.3390/atoms401000332218-20042015-12-26doi: 10.3390/atoms4010003Ye NingZong-Chao YanYew Ho<![CDATA[Atoms, Vol. 4, Pages 2: An Optomechanical Elevator: Transport of a Bloch Oscillating Bose–Einstein Condensate up and down an Optical Lattice by Cavity Sideband Amplification and Cooling]]>
http://www.mdpi.com/2218-2004/4/1/2
In this paper we give a new description, in terms of optomechanics, of previous work on the problem of an atomic Bose–Einstein condensate interacting with the optical lattice inside a laser-pumped optical cavity and subject to a bias force, such as gravity. An atomic wave packet in a tilted lattice undergoes Bloch oscillations; in a high-finesse optical cavity the backaction of the atoms on the light leads to a time-dependent modulation of the intracavity lattice depth at the Bloch frequency which can in turn transport the atoms up or down the lattice. In the optomechanical picture, the transport dynamics can be interpreted as a manifestation of dynamical backaction-induced sideband damping/amplification of the Bloch oscillator. Depending on the sign of the pump-cavity detuning, atoms are transported either with or against the bias force accompanied by an up- or down-conversion of the frequency of the pump laser light. We also evaluate the prospects for using the optomechanical Bloch oscillator to make continuous measurements of forces by reading out the Bloch frequency. In this context, we establish the significant result that the optical spring effect is absent and the Bloch frequency is not modified by the backaction.Atoms2015-12-2541Article10.3390/atoms401000222218-20042015-12-25doi: 10.3390/atoms4010002B. Prasanna VenkateshDuncan O’DellJonathan Goldwin<![CDATA[Atoms, Vol. 4, Pages 1: Cavity Optomechanics with Ultra Cold Atoms in Synthetic Abelian and Non-Abelian Gauge Field]]>
http://www.mdpi.com/2218-2004/4/1/1
In this article we present a pedagogical discussion of some of the optomechanical properties of a high finesse cavity loaded with ultracold atoms in laser induced synthetic gauge fields of different types. Essentially, the subject matter of this article is an amalgam of two sub-fields of atomic molecular and optical (AMO) physics namely, the cavity optomechanics with ultracold atoms and ultracold atoms in synthetic gauge field. After providing a brief introduction to either of these fields we shall show how and what properties of these trapped ultracold atoms can be studied by looking at the cavity (optomechanical or transmission) spectrum. In presence of abelian synthetic gauge field we discuss the cold-atom analogue of Shubnikov de Haas oscillation and its detection through cavity spectrum. Then, in the presence of a non-abelian synthetic gauge field (spin-orbit coupling), we see when the electromagnetic field inside the cavity is quantized, it provides a quantum optical lattice for the atoms, leading to the formation of different quantum magnetic phases. We also discuss how these phases can be explored by studying the cavity transmission spectrum.Atoms2015-12-2541Article10.3390/atoms401000112218-20042015-12-25doi: 10.3390/atoms4010001Bikash PadhiSankalpa Ghosh<![CDATA[Atoms, Vol. 3, Pages 495-508: Two-Photon Collective Atomic Recoil Lasing]]>
http://www.mdpi.com/2218-2004/3/4/495
We present a theoretical study of the interaction between light and a cold gasof three-level, ladder conﬁguration atoms close to two-photon resonance. In particular, weinvestigate the existence of collective atomic recoil lasing (CARL) instabilities in differentregimes of internal atomic excitation and compare to previous studies of the CARL instabilityinvolving two-level atoms. In the case of two-level atoms, the CARL instability is quenchedat high pump rates with signiﬁcant atomic excitation by saturation of the (one-photon)coherence, which produces the optical forces responsible for the instability and rapid heatingdue to high spontaneous emission rates. We show that in the two-photon CARL schemestudied here involving three-level atoms, CARL instabilities can survive at high pump rateswhen the atoms have signiﬁcant excitation, due to the contributions to the optical forces frommultiple coherences and the reduction of spontaneous emission due to transitions betweenthe populated states being dipole forbidden. This two-photon CARL scheme may form thebasis of methods to increase the effective nonlinear optical response of cold atomic gases.Atoms2015-11-2034Article10.3390/atoms30404954955082218-20042015-11-20doi: 10.3390/atoms3040495James McKelvieGordon Robb<![CDATA[Atoms, Vol. 3, Pages 474-494: Electron Impact Excitation and Dielectronic Recombination of Highly Charged Tungsten Ions]]>
http://www.mdpi.com/2218-2004/3/4/474
Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER.Atoms2015-11-2034Article10.3390/atoms30404744744942218-20042015-11-20doi: 10.3390/atoms3040474Zhongwen WuYanbiao FuXiaoyun MaMaijuan LiLuyou XieJun JiangChenzhong Dong<![CDATA[Atoms, Vol. 3, Pages 450-473: Cavity Quantum Electrodynamics of Continuously Monitored Bose-Condensed Atoms]]>
http://www.mdpi.com/2218-2004/3/3/450
We study cavity quantum electrodynamics of Bose-condensed atoms that are subjected to continuous monitoring of the light leaking out of the cavity. Due to a given detection record of each stochastic realization, individual runs spontaneously break the symmetry of the spatial profile of the atom cloud and this symmetry can be restored by considering ensemble averages over many realizations. We show that the cavity optomechanical excitations of the condensate can be engineered to target specific collective modes. This is achieved by exploiting the spatial structure and symmetries of the collective modes and light fields. The cavity fields can be utilized both for strong driving of the collective modes and for their measurement. In the weak excitation limit the condensate–cavity system may be employed as a sensitive phonon detector which operates by counting photons outside the cavity that have been selectively scattered by desired phonons.Atoms2015-09-2333Article10.3390/atoms30304504504732218-20042015-09-23doi: 10.3390/atoms3030450Mark LeeJanne Ruostekoski<![CDATA[Atoms, Vol. 3, Pages 433-449: A Realization of a Quasi-Random Walk for Atoms in Time-Dependent Optical Potentials]]>
http://www.mdpi.com/2218-2004/3/3/433
We consider the time dependent dynamics of an atom in a two-color pumped cavity, longitudinally through a side mirror and transversally via direct driving of the atomic dipole. The beating of the two driving frequencies leads to a time dependent effective optical potential that forces the atom into a non-trivial motion, strongly resembling a discrete random walk behavior between lattice sites. We provide both numerical and analytical analysis of such a quasi-random walk behavior.Atoms2015-09-2333Article10.3390/atoms30304334334492218-20042015-09-23doi: 10.3390/atoms3030433Torsten HinkelHelmut RitschClaudiu Genes<![CDATA[Atoms, Vol. 3, Pages 422-432: Quantum Entanglement and Shannon Information Entropy for the Doubly Excited Resonance State in Positronium Negative Ion]]>
http://www.mdpi.com/2218-2004/3/3/422
In the present work, we report an investigation on quantum entanglement in the doubly excited 2s2 1Se resonance state of the positronium negative ion by using highly correlated Hylleraas type wave functions, determined by calculation of the density of resonance states with the stabilization method. Once the resonance wave function is obtained, the spatial (electron-electron orbital) entanglement entropies (von Neumann and linear) can be quantified using the Schmidt decomposition method. Furthermore, Shannon entropy in position space, a measure for localization (or delocalization) for such a doubly excited state, is also calculated.Atoms2015-09-2133Article10.3390/atoms30304224224322218-20042015-09-21doi: 10.3390/atoms3030422Chien-Hao LinYew Ho<![CDATA[Atoms, Vol. 3, Pages 407-421: Extreme Ultraviolet Spectra of Few-Times Ionized Tungsten for Divertor Plasma Diagnostics]]>
http://www.mdpi.com/2218-2004/3/3/407
The extreme ultraviolet (EUV) emission from few-times ionized tungsten atoms has been experimentally studied at the Livermore electron beam ion trap facility. The ions were produced and confined during low-energy operations of the EBIT-I electron beam ion trap. By varying the electron-beam energy from around 30–300 eV, tungsten ions in charge states expected to be abundant in tokamak divertor plasmas were excited, and the resulting EUV emission was studied using a survey spectrometer covering 120–320 Å. It is found that the emission strongly depends on the excitation energy; below 150 eV, it is relatively simple, consisting of strong isolated lines from a few charge states, whereas at higher energies, it becomes very complex. For divertor plasmas with tungsten impurity ions, this emission should prove useful for diagnostics of tungsten flux rates and charge balance, as well as for radiative cooling of the divertor volume. Several lines in the 194–223 Å interval belonging to the spectra of five- and seven-times ionized tungsten (Tm-like W VI and Ho-like W VIII) were also measured using a high-resolution spectrometer.Atoms2015-09-0933Article10.3390/atoms30304074074212218-20042015-09-09doi: 10.3390/atoms3030407Joel ClementsonThomas LennartssonPeter Beiersdorfer<![CDATA[Atoms, Vol. 3, Pages 392-406: Probing and Manipulating Fermionic and Bosonic Quantum Gases with Quantum Light]]>
http://www.mdpi.com/2218-2004/3/3/392
We study the atom-light interaction in the fully quantum regime, with the focus on off-resonant light scattering into a cavity from ultracold atoms trapped in an optical lattice. The detection of photons allows the quantum nondemolition (QND) measurement of quantum correlations of the atomic ensemble, distinguishing between different quantum states. We analyse the entanglement between light and matter and show how it can be exploited for realising multimode macroscopic quantum superpositions, such as Schrödinger cat states, for both bosons and fermions. We provide examples utilising different measurement schemes and study their robustness to decoherence. Finally, we address the regime where the optical lattice potential is a quantum dynamical variable and is modified by the atomic state, leading to novel quantum phases and significantly altering the phase diagram of the atomic system.Atoms2015-09-0233Article10.3390/atoms30303923924062218-20042015-09-02doi: 10.3390/atoms3030392Thomas ElliottGabriel MazzucchiWojciech KozlowskiSantiago Caballero-Benitez Igor Mekhov<![CDATA[Atoms, Vol. 3, Pages 367-391: Experiments with Highly-Ionized Atoms in Unitary Penning Traps]]>
http://www.mdpi.com/2218-2004/3/3/367
Highly-ionized atoms with special properties have been proposed for interesting applications, including potential candidates for a new generation of optical atomic clocks at the one part in 1019 level of precision, quantum information processing and tests of fundamental theory. The proposed atomic systems are largely unexplored. Recent developments at NIST are described, including the isolation of highly-ionized atoms at low energy in unitary Penning traps and the use of these traps for the precise measurement of radiative decay lifetimes (demonstrated with a forbidden transition in Kr17+), as well as for studying electron capture processes.Atoms2015-08-1433Article10.3390/atoms30303673673912218-20042015-08-14doi: 10.3390/atoms3030367Shannon HoogerheideAung NaingJoan DreilingSamuel BrewerNicholas GuiseJoseph Tan<![CDATA[Atoms, Vol. 3, Pages 348-366: Cavity-Assisted Generation of Sustainable Macroscopic Entanglement of Ultracold Gases]]>
http://www.mdpi.com/2218-2004/3/3/348
Prospects for reaching persistent entanglement between two spatially-separated atomic Bose–Einstein condensates are outlined. The system setup comprises two condensates loaded in an optical lattice, which, in return, is confined within a high-Q optical resonator. The system is driven by an external laser that illuminates the atoms, such that photons can scatter into the cavity. In the superradiant phase, a cavity field is established, and we show that the emerging cavity-mediated interactions between the two condensates is capable of entangling them despite photon losses. This macroscopic atomic entanglement is sustained throughout the time-evolution apart from occasions of sudden deaths/births. Using an auxiliary photon mode and coupling it to a collective quadrature of the two condensates, we demonstrate that the auxiliary mode’s squeezing is proportional to the atomic entanglement, and as such, it can serve as a probe field of the macroscopic entanglement.Atoms2015-08-0433Article10.3390/atoms30303483483662218-20042015-08-04doi: 10.3390/atoms3030348Chaitanya JoshiJonas Larson<![CDATA[Atoms, Vol. 3, Pages 339-347: Influence of Virtual Photon Process on the Generation of Squeezed Light from Atoms in an Optical Cavity]]>
http://www.mdpi.com/2218-2004/3/3/339
We show that a collection of two-level atoms in an optical cavity beyond the rotating wave approximation and in the dispersive-adiabatic and non-dispersive adiabatic regime constitutes a nonlinear medium and is capable of generating squeezed state of light. It is found that squeezing produced in the non-dispersive adiabatic regime is significantly high compared to that produced in the dispersive-adiabatic limit. On the other hand, we also show that it could be possible to observe the Dicke superradiant quantum phase transition in the dispersive-adiabatic regime where the Ã2 term is negligible. Such a system can be an essential component of a larger quantum-communication system.Atoms2015-07-2433Article10.3390/atoms30303393393472218-20042015-07-24doi: 10.3390/atoms3030339Aranya Bhattacherjee<![CDATA[Atoms, Vol. 3, Pages 320-338: On the Classical Coupling between Gravity and Electromagnetism]]>
http://www.mdpi.com/2218-2004/3/3/320
Coupling between electromagnetism and gravity, manifested as the distorted Coulomb field of a charge distribution in a gravitational field, has never been observed. A physical system consisting of an electron in a charged shell provides a coupling that is orders of magnitude stronger than for any previously-considered system. A shell voltage of one megavolt is required to establish a gravitationally-induced electromagnetic force equal in magnitude to the force of gravity on an electron. The experimental feasibility of detecting these forces on an electron is discussed. The effect establishes a relation between Einstein’s energy-mass equivalence and the coupling between electromagnetism and gravity.Atoms2015-06-3033Article10.3390/atoms30303203203382218-20042015-06-30doi: 10.3390/atoms3030320Maria BeckerAdam CaprezHerman Batelaan<![CDATA[Atoms, Vol. 3, Pages 299-319: Detailed Analysis of Configuration Interaction and Calculation of Radiative Transition Rates in Seven Times Ionized Tungsten (W VIII)]]>
http://www.mdpi.com/2218-2004/3/3/299
A new set of oscillator strengths and transition probabilities for EUV spectral lines of seven times ionized tungsten (W VIII) is reported in the present paper. These results have been obtained using the pseudo-relativistic Hartree-Fock (HFR) method combined with a semi-empirical optimization of the radial parameters minimizing the discrepancies between computed energy levels and available experimental data. The final physical model considered in the calculations has been chosen further to a detailed investigation of the configuration interaction in this atomic system characterized by complex configurations of the type 4f145s25p5, 4f145s25p4nl, 4f145s5p6, 4f135s25p6, 4f135s25p5nl and 4f125s25p6nl (nl = 5d, 6s).Atoms2015-06-3033Article10.3390/atoms30302992993192218-20042015-06-30doi: 10.3390/atoms3030299Jérôme DeprincePascal Quinet<![CDATA[Atoms, Vol. 3, Pages 273-298: Spectra of W VIII and W IX in the EUV Region]]>
http://www.mdpi.com/2218-2004/3/3/273
The results obtained on the W VIII spectrum as well as on the isoelectronic spectra Lu V, Hf VI, Ta VII, and Re IX in the VUV wavelength region are summarized with emphasis on the main trends along the isoelectronic sequence. A total of 187 lines of W VIII in the region of 160–271 Å were accurately measured and identified, 98 levels were found, and transition probabilities calculated. The isoelectronic regularities support the data on W VIII. A list of spectral lines in the region of 170–199 Å, considered as belonging to W IX, is presented.Atoms2015-06-3033Article10.3390/atoms30302732732982218-20042015-06-30doi: 10.3390/atoms3030273Alexander RyabtsevEdward KononovRimma KildiyarovaWan-Ü Tchang-BrilletJean-Francois WyartNorbert ChampionChristophe Blaess<![CDATA[Atoms, Vol. 3, Pages 260-272: Tungsten Data for Current and Future Uses in Fusion and Plasma Science]]>
http://www.mdpi.com/2218-2004/3/2/260
We give a brief overview of our recent experimental and theoretical work involving highly charged tungsten ions in high-temperature magnetically confined plasmas. Our work includes X-ray and extreme ultraviolet spectroscopy, state-of-the-art structure calculations, the generation of dielectronic recombination rate coefficients, collisional-radiative spectral modeling and assessments of the atomic data need for X-ray diagnostics monitoring of the parameters of the core plasma of future tokamaks, such as ITER. We give examples of our recent results in these areas.Atoms2015-06-1532Article10.3390/atoms30202602602722218-20042015-06-15doi: 10.3390/atoms3020260Peter BeiersdorferJoel ClementsonUlyana Safronova<![CDATA[Atoms, Vol. 3, Pages 195-259: MCDHF Calculations and Beam-Foil EUV Spectra of Boron-Like Sodium Ions (Na VII)]]>
http://www.mdpi.com/2218-2004/3/2/195
Atomic data, such as wavelengths and line identifications, are necessary for many applications, especially in plasma diagnostics and for interpreting the spectra of distant astrophysical objects. The number of valence shell electrons increases the complexity of the computational problem. We have selected a five-electron ion, Na6+ (with the boron-like spectrum Na VII), for looking into the interplay of measurement and calculation. We summarize the available experimental work, perform our own extensive relativistic configuration interaction (RCI) computations based on multi-configuration Dirac–Hartree–Fock (MCDHF) wave functions, and compare the results to what is known of the level structure. We then discuss problems with databases that have begun to combine observations and computations.Atoms2015-06-0932Article10.3390/atoms30201951952592218-20042015-06-09doi: 10.3390/atoms3020195Per JönssonJörgen EkmanElmar Träbert<![CDATA[Atoms, Vol. 3, Pages 182-194: Photon-Induced Spin-Orbit Coupling in Ultracold Atoms inside Optical Cavity]]>
http://www.mdpi.com/2218-2004/3/2/182
We consider an atom inside a ring cavity, where a plane-wave cavity field together with an external coherent laser beam induces a two-photon Raman transition between two hyperfine ground states of the atom. This cavity-assisted Raman transition induces effective coupling between atom’s internal degrees of freedom and its center-of-mass motion. In the meantime, atomic dynamics exerts a back-action to cavity photons. We investigate the properties of this system by adopting a mean-field and a full quantum approach, and show that the interplay between the atomic dynamics and the cavity field gives rise to intriguing nonlinear phenomena.Atoms2015-05-2632Article10.3390/atoms30201821821942218-20042015-05-26doi: 10.3390/atoms3020182Lin DongChuanzhou ZhuHan Pu<![CDATA[Atoms, Vol. 3, Pages 162-181: Tungsten Ions in Plasmas: Statistical Theory of Radiative-Collisional Processes]]>
http://www.mdpi.com/2218-2004/3/2/162
The statistical model for calculations of the collisional-radiative processes in plasmas with tungsten impurity was developed. The electron structure of tungsten multielectron ions is considered in terms of both the Thomas-Fermi model and the Brandt-Lundquist model of collective oscillations of atomic electron density. The excitation or ionization of atomic electrons by plasma electron impacts are represented as photo-processes under the action of flux of equivalent photons introduced by E. Fermi. The total electron impact single ionization cross-sections of ions Wk+ with respective rates have been calculated and compared with the available experimental and modeling data (e.g., CADW). Plasma radiative losses on tungsten impurity were also calculated in a wide range of electron temperatures 1 eV–20 keV. The numerical code TFATOM was developed for calculations of radiative-collisional processes involving tungsten ions. The needed computational resources for TFATOM code are orders of magnitudes less than for the other conventional numerical codes. The transition from corona to Boltzmann limit was investigated in detail. The results of statistical approach have been tested by comparison with the vast experimental and conventional code data for a set of ions Wk+. It is shown that the universal statistical model accuracy for the ionization cross-sections and radiation losses is within the data scattering of significantly more complex quantum numerical codes, using different approximations for the calculation of atomic structure and the electronic cross-sections.Atoms2015-05-2532Article10.3390/atoms30201621621812218-20042015-05-25doi: 10.3390/atoms3020162Alexander DemuraMikhail KadomtsevValery LisitsaVladimir Shurygin<![CDATA[Atoms, Vol. 3, Pages 120-161: Fusion-Related Ionization and Recombination Data for Tungsten Ions in Low to Moderately High Charge States]]>
http://www.mdpi.com/2218-2004/3/2/120
Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten atoms in all charge states, a project has been initiated in which electron-impact and photon-induced ionization as well as photorecombination of Wq+ ions are studied. Cross sections and rate coefficients were determined for charge states q ranging from q = 1 to q = 5 for photoionization, for q = 1 up to q = 19 for electron-impact ionization and for q = 18 to q = 21 for electron-ion recombination. An overview, together with a critical assessment of the methods and results is provided.Atoms2015-05-2032Article10.3390/atoms30201201201612218-20042015-05-20doi: 10.3390/atoms3020120Alfred Müller<![CDATA[Atoms, Vol. 3, Pages 86-119: Radiative Recombination and Photoionization Data for Tungsten Ions. Electron Structure of Ions in Plasmas]]>
http://www.mdpi.com/2218-2004/3/2/86
Theoretical studies of tungsten ions in plasmas are presented. New calculations of the radiative recombination and photoionization cross-sections, as well as radiative recombination and radiated power loss rate coefficients have been performed for 54 tungsten ions for the range W6+–W71+. The data are of importance for fusion investigations at the reactor ITER, as well as devices ASDEX Upgrade and EBIT. Calculations are fully relativistic. Electron wave functions are found by the Dirac–Fock method with proper consideration of the electron exchange. All significant multipoles of the radiative field are taken into account. The radiative recombination rates and the radiated power loss rates are determined provided the continuum electron velocity is described by the relativistic Maxwell–Jüttner distribution. The impact of the core electron polarization on the radiative recombination cross-section is estimated for the Ne-like iron ion and for highly-charged tungsten ions within an analytical approximation using the Dirac–Fock electron wave functions. The effect is shown to enhance the radiative recombination cross-sections by ≲20%. The enhancement depends on the photon energy, the principal quantum number of polarized shells and the ion charge. The influence of plasma temperature and density on the electron structure of ions in local thermodynamic equilibrium plasmas is investigated. Results for the iron and uranium ions in dense plasmas are in good agreement with previous calculations. New calculations were performed for the tungsten ion in dense plasmas on the basis of the average-atom model, as well as for the impurity tungsten ion in fusion plasmas using the non-linear self-consistent field screening model. The temperature and density dependence of the ion charge, level energies and populations are considered.Atoms2015-05-1832Article10.3390/atoms3020086861192218-20042015-05-18doi: 10.3390/atoms3020086Malvina TrzhaskovskayaVladimir Nikulin<![CDATA[Atoms, Vol. 3, Pages 76-85: Collisional-Radiative Modeling of Tungsten at Temperatures of 1200–2400 eV]]>
http://www.mdpi.com/2218-2004/3/2/76
We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.Atoms2015-04-3032Article10.3390/atoms302007676852218-20042015-04-30doi: 10.3390/atoms3020076James ColganChristopher FontesHonglin ZhangJoseph Abdallah<![CDATA[Atoms, Vol. 3, Pages 53-75: Fully Relativistic Electron Impact Excitation Cross-Section and Polarization for Tungsten Ions]]>
http://www.mdpi.com/2218-2004/3/2/53
Electron impact excitation of highly charged tungsten ions in the framework of a fully relativistic distorted wave approach is considered in this paper. Calculations of electron impact excitation cross-sections for the M- and L-shell transitions in the tungsten ions Wn+ (n = 44–66) and polarization of the decay of photons from the excited tungsten ions are briefly reviewed and discussed. New calculations in the wide range of incident electron energies are presented for M-shell transitions in the K-like through Ne-like tungsten ions.Atoms2015-04-2832Article10.3390/atoms302005353752218-20042015-04-28doi: 10.3390/atoms3020053 Priti DiptiLalita SharmaRajesh Srivastava<![CDATA[Atoms, Vol. 3, Pages 2-52: Ab-Initio Calculations of Level Energies, Oscillator Strengths and Radiative Rates for E1 Transitions in Beryllium-Like Iron]]>
http://www.mdpi.com/2218-2004/3/1/2
In the present work, energy levels, oscillator strengths, radiative rates and wavelengths of Be-like iron (Fe\(^{22+}\)) from ab-initio calculations using the multiconfiguration Dirac-Hartree-Fock method are presented. These quantities have been calculated for a set of configurations in the general form \(1s^2\,nl\,n'l'\) where \(n=2,3\) and \(\,n'=2,3,4,5\) and \(l=s,p,d\) and \(\,l'=s, p, d, f, g\). In addition, excitations of up to four electrons, including core-electron excitations, have been considered to improve the quality of the wave functions. This study comprises an extensive set of E1 transition rates between states with different \(J\). The present results are compared with the available experimental and theoretical data.Atoms2015-01-2031Article10.3390/atoms30100022522218-20042015-01-20doi: 10.3390/atoms3010002Ahmed El-MaarefStefan SchippersAlfred Müller<![CDATA[Atoms, Vol. 3, Pages 1: Acknowledgement to Reviewers of Atoms in 2014]]>
http://www.mdpi.com/2218-2004/3/1/1
The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...]Atoms2015-01-0931Editorial10.3390/atoms3010001112218-20042015-01-09doi: 10.3390/atoms3010001 Atoms Editorial Office<![CDATA[Atoms, Vol. 2, Pages 382-390: Estimating Relative Uncertainty of Radiative Transition Rates]]>
http://www.mdpi.com/2218-2004/2/4/382
We consider a method to estimate relative uncertainties of radiative transition rates in an atomic spectrum. Few of these many transitions have had their rates determined by more than two reference-quality sources. One could estimate uncertainties for each transition, but analyses with only one degree of freedom are generally fraught with difficulties. We pursue a way to empirically combine the limited uncertainty information in each of the many transitions. We “pool” a dimensionless measure of relative dispersion, the “Coefficient of Variation of the mean,” \(C_{V}^{n} \equiv s/(\bar{x}\sqrt{n})\). Here, for each transition rate, “s” is the standard deviation, and “\(\bar{x}\)” is the mean of “n” independent data sources. \(C_{V}^{n}\) is bounded by zero and one whenever the determined quantity is intrinsically positive.) We scatter-plot the \(C_{V}^{n} \)as a function of the “line strength” (here a more useful radiative transition rate than transition probability). We find a curve through comparable \(C_{V}^{n} \)as that envelops a specified percentage of the \(C_{V}^{n} \)s (e.g. 95%). We take this curve to represent the expanded relative uncertainty of the mean. The method is most advantageous when the number of determined transition rates is large while the number of independent determinations per transition is small. The transition rate data of Na III serves as an example.Atoms2014-11-2524Article10.3390/atoms20403823823902218-20042014-11-25doi: 10.3390/atoms2040382Daniel Kelleher<![CDATA[Atoms, Vol. 2, Pages 378-381: Special Issue on Spectral Line Shapes in Plasmas]]>
http://www.mdpi.com/2218-2004/2/3/378
Line-shape analysis is one of the most important tools for diagnostics of both laboratory and space plasmas. Its reliable implementation requires sufficiently accurate calculations, which imply the use of analytic methods and computer codes of varying complexity, and, necessarily, varying limits of applicability and accuracy. However, studies comparing different computational and analytic methods are almost non-existent. The Spectral Line Shapes in Plasma (SLSP) code comparison workshop series [1] was established to fill this gap. Numerous computational cases considered in the two workshops organized to date (in April 2012 and August 2013 in Vienna, Austria) not only serve the purpose of code comparison, but also have applications in research of magnetic fusion, astrophysical, laser-produced plasmas, and so on. Therefore, although the first workshop was briefly reviewed elsewhere [2], and will likely be followed by a review of the second one, it was unanimously decided by the participants that a volume devoted to results of the workshops was desired. It is the main purpose of this special issue.Atoms2014-08-0723Editorial10.3390/atoms20303783783812218-20042014-08-07doi: 10.3390/atoms2030378Evgeny StambulchikAnnette CalistiHyun-Kyung ChungManuel González<![CDATA[Atoms, Vol. 2, Pages 357-377: On the Application of Stark Broadening Data Determined with a Semiclassical Perturbation Approach]]>
http://www.mdpi.com/2218-2004/2/3/357
The significance of Stark broadening data for problems in astrophysics, physics, as well as for technological plasmas is discussed and applications of Stark broadening parameters calculated using a semiclassical perturbation method are analyzed.Atoms2014-08-0723Article10.3390/atoms20303573573772218-20042014-08-07doi: 10.3390/atoms2030357Milan DimitrijevićSylvie Sahal-Bréchot<![CDATA[Atoms, Vol. 2, Pages 334-356: Spectral-Kinetic Coupling and Effect of Microfield Rotation on Stark Broadening in Plasmas]]>
http://www.mdpi.com/2218-2004/2/3/334
The study deals with two conceptual problems in the theory of Stark broadening by plasmas. One problem is the assumption of the density matrix diagonality in the calculation of spectral line profiles. This assumption is closely related to the definition of zero wave functions basis within which the density matrix is assumed to be diagonal, and obviously violated under the basis change. A consistent use of density matrix in the theoretical scheme inevitably leads to interdependence of atomic kinetics, describing the population of atomic states with the Stark profiles of spectral lines, i.e., to spectral-kinetic coupling. The other problem is connected with the study of the influence of microfield fluctuations on Stark profiles. Here the main results of the perturbative approach to ion dynamics, called the theory of thermal corrections (TTC), are presented, within which the main contribution to effects of ion dynamics is due to microfield fluctuations caused by rotations. In the present study the qualitative behavior of the Stark profiles in the line center within predictions of TTC is confirmed, using non-perturbative computer simulations.Atoms2014-07-3023Article10.3390/atoms20303343343562218-20042014-07-30doi: 10.3390/atoms2030334Alexander DemuraEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 319-333: Line-Shape Code Comparison through Modeling and Fitting of Experimental Spectra of the C ii 723-nm Line Emitted by the Ablation Cloud of a Carbon Pellet]]>
http://www.mdpi.com/2218-2004/2/3/319
Various codes of line-shape modeling are compared to each other through the profile of the C ii 723-nm line for typical plasma conditions encountered in the ablation clouds of carbon pellets, injected in magnetic fusion devices. Calculations were performed for a single electron density of 1017 cm−3 and two plasma temperatures (T = 2 and 4 eV). Ion and electron temperatures were assumed to be equal (Te = Ti = T). The magnetic field, B, was set equal to either to zero or 4 T. Comparisons between the line-shape modeling codes and two experimental spectra of the C ii 723-nm line, measured perpendicularly to the B-field in the Large Helical Device (LHD) using linear polarizers, are also discussed.Atoms2014-07-1423Article10.3390/atoms20303193193332218-20042014-07-14doi: 10.3390/atoms2030319Mohammed KoubitiMotoshi GotoSandrine FerriStephanie HansenEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 299-318: Ion Dynamics Effect on Stark-Broadened Line Shapes: A Cross-Comparison of Various Models]]>
http://www.mdpi.com/2218-2004/2/3/299
Modeling the Stark broadening of spectral lines in plasmas is a complex problem. The problem has a long history, since it plays a crucial role in the interpretation of the observed spectral lines in laboratories and astrophysical plasmas. One difficulty is the characterization of the emitter’s environment. Although several models have been proposed over the years, there have been no systematic studies of the results, until now. Here, calculations from stochastic models and numerical simulations are compared for the Atoms 2014, 2 300 Lyman-α and -β lines in neutral hydrogen. Also discussed are results from the Helium-α and -β lines of Ar XVII.Atoms2014-07-0423Article10.3390/atoms20302992993182218-20042014-07-04doi: 10.3390/atoms2030299Sandrine FerriAnnette CalistiCaroline MosséJoël RosatoBernard TalinSpiros AlexiouMarco GigososManuel GonzálezDiego González-HerreroNatividad LaraThomas GomezCarlos IglesiasSonja LorenzenRoberto ManciniEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 277-298: Spectral Line Shapes of He I Line 3889 Å]]>
http://www.mdpi.com/2218-2004/2/2/277
Spectral line shapes of neutral helium 3889 Å(23S–33P) transition line are calculated by using several theoretical methods. The electronic contribution to the line broadening is calculated from quantum statistical many-particle theory by using thermodynamic Green's function, including dynamic screening of the electron-atom interaction. The ionic contribution is taken into account in a quasistatic approximation, where a static microfield distribution function is presented. Strong electron collisions are consistently considered with an effective two-particle T-matrix approach, where Convergent Close Coupling method gives scattering amplitudes including Debye screening for neutral helium. Then the static profiles converted to dynamic profiles by using the Frequency Fluctuation Model. Furthermore, Molecular Dynamics simulations for interacting and independent particles are used where the dynamic sequence of microfield is taken into account. Plasma parameters are diagnosed and good agreements are shown by comparing our theoretical results with the recent experimental result of Jovićević et al. (J. Phys. B: At. Mol. Opt. Phys. 2005, 38, 1249). Additionally, comparison with various experimental data in a wide range of electron density ne ≈ (1022− 1024)m−3 and temperature T ≈ (2−6) × 104 K are presented.Atoms2014-06-2322Article10.3390/atoms20202772772982218-20042014-06-23doi: 10.3390/atoms2020277Banaz OmarManuel GonzálezMarco GigososTlekkabul RamazanovMadina JelbuldinaKarlygash DzhumagulovaMark ZammitDmitry FursaIgor Bray<![CDATA[Atoms, Vol. 2, Pages 259-276: Influence of Microfield Directionality on Line Shapes]]>
http://www.mdpi.com/2218-2004/2/2/259
In the framework of the Spectral Line Shapes in Plasmas Code Comparison Workshop (SLSP), large discrepancies appeared between the different approaches to account for ion motion effects in spectral line shape calculations. For a better understanding of these effects, in the second edition of the SLSP in August, 2013, two cases were dedicated to the study of the ionic field directionality on line shapes. In this paper, the effects of the direction and magnitude fluctuations are separately analyzed. The effects of two variants of electric field models, (i) a pure rotating field with constant magnitude and (ii) a time-dependent magnitude field in a given direction, together with the effects of the time-dependent ionic field on shapes of the He II Lyman-α and -β lines for different densities and temperatures, are discussed.Atoms2014-06-1922Article10.3390/atoms20202592592762218-20042014-06-19doi: 10.3390/atoms2020259Annette CalistiAlexander DemuraMarco GigososDiego González-HerreroCarlos IglesiasValery LisitsaEvgeny Stambulchik<![CDATA[Atoms, Vol. 2, Pages 253-258: Ideal Coulomb Plasma Approximation in Line Shape Models: Problematic Issues]]>
http://www.mdpi.com/2218-2004/2/2/253
In weakly coupled plasmas, it is common to describe the microfield using a Debye model. We examine here an “artificial” ideal one-component plasma with an infinite Debye length, which has been used for the test of line shape codes. We show that the infinite Debye length assumption can lead to a misinterpretation of numerical simulations results, in particular regarding the convergence of calculations. Our discussion is done within an analytical collision operator model developed for hydrogen line shapes in near-impact regimes. When properly employed, this model can serve as a reference for testing the convergence of simulations.Atoms2014-06-1922Article10.3390/atoms20202532532582218-20042014-06-19doi: 10.3390/atoms2020253Joel RosatoHubert CapesRoland Stamm<![CDATA[Atoms, Vol. 2, Pages 225-252: Widths and Shifts of Isolated Lines of Neutral and Ionized Atoms Perturbed by Collisions With Electrons and Ions: An Outline of the Semiclassical Perturbation (SCP) Method and of the Approximations Used for the Calculations]]>
http://www.mdpi.com/2218-2004/2/2/225
“Stark broadening” theory and calculations have been extensively developed for about 50 years. The theory can now be considered as mature for many applications, especially for accurate spectroscopic diagnostics and modeling, in astrophysics, laboratory plasma physics and technological plasmas, as well. This requires the knowledge of numerous collisional line profiles. In order to meet these needs, the “SCP” (semiclassical perturbation) method and numerical code were created and developed. The SCP code is now extensively used for the needs of spectroscopic diagnostics and modeling, and the results of the published calculations are displayed in the STARK-B database. The aim of the present paper is to introduce the main approximations leading to the impact of semiclassical perturbation method and to give formulae entering the numerical SCP code, in order to understand the validity conditions of the method and of the results; and also to understand some regularities and systematic trends. This would also allow one to compare the method and its results to those of other methods and codes. 1Atoms2014-06-1022Article10.3390/atoms20202252252522218-20042014-06-10doi: 10.3390/atoms2020225Sylvie Sahal-BréchotMilan DimitrijevićNabil Nessib<![CDATA[Atoms, Vol. 2, Pages 215-224: Validation and Implementation of Uncertainty Estimates of Calculated Transition Rates]]>
http://www.mdpi.com/2218-2004/2/2/215
Uncertainties of calculated transition rates in LS-allowed electric dipole transitions in boron-like O IV and carbon-like Fe XXI are estimated using an approach in which differences in line strengths calculated in length and velocity gauges are utilized. Estimated uncertainties are compared and validated against several high-quality theoretical data sets in O IV, and implemented in large scale calculations in Fe XXI.Atoms2014-05-1522Review10.3390/atoms20202152152242218-20042014-05-15doi: 10.3390/atoms2020215Jörgen EkmanMichel GodefroidHenrik Hartman<![CDATA[Atoms, Vol. 2, Pages 207-214: Electron-Impact Widths and Shifts of B III 2p-2s Lines]]>
http://www.mdpi.com/2218-2004/2/2/207
In this paper, we present results for the relativistic quantum mechanical calculations of electron-impact line widths and shifts of 2p-2s transitions in doubly ionized boron (B III) ions. We use the Dirac R-matrix methods to solve (N + 1)-electron colliding systems for the scattering matrices that are required. The line widths are calculated for an electron density 1:81 × 1018 cm-3 and electron temperature 10:6 eV. The obtained results agree well with all the semiempirical calculations and most of the semiclassical calculations, and are closer to the experimental results published by Glenzer and Kunze (Glenzer, S.; Kunze, H.-J. Stark broadening of resonance transitions in B III. Phys. Rev. A 1996, 53, 2225–2229). Our line widths are almost twice as large as the earlier quantum mechanical calculations for the set of particular plasma conditions.Atoms2014-05-1522Article10.3390/atoms20202072072142218-20042014-05-15doi: 10.3390/atoms2020207Bin DuanMuhammad BariZeqing WuJun Yan<![CDATA[Atoms, Vol. 2, Pages 195-206: Hydrogen Spectral Line Shape Formation in the SOL of Fusion Reactor Plasmas]]>
http://www.mdpi.com/2218-2004/2/2/195
The problems related to the spectral line-shape formation in the scrape of layer (SOL) in fusion reactor plasma for typical observation chords are considered. The SOL plasma is characterized by the relatively low electron density (1012–1013 cm−3) and high temperature (from 10 eV up to 1 keV). The main effects responsible for the line-shape formation in the SOL are Doppler and Zeeman effects. The main problem is a correct modeling of the neutral atom velocity distribution function (VDF). The VDF is determined by a number of atomic processes, namely: molecular dissociation, ionization and charge exchange of neutral atoms on plasma ions, electron excitation accompanied by the charge exchange from atomic excited states, and atom reflection from the wall. All the processes take place step by step during atom motion from the wall to the plasma core. In practice, the largest contribution to the neutral atom radiation emission comes from a thin layer near the wall with typical size 10–20 cm, which is small as compared with the minor radius of modern devices including international test experimental reactor ITER (radius 2 m). The important problem is a strongly non-uniform distribution of plasma parameters (electron and ion densities and temperatures). The distributions vary for different observation chords and ITER operation regimes. In the present report, most attention is paid to the problem of the VDF calculations. The most correct method for solving the problem is an application of the Monte Carlo method for atom motion near the wall. However, the method is sometimes too complicated to be combined with other numerical codes for plasma modeling for various regimes of fusion reactor operation. Thus, it is important to develop simpler methods for neutral atom VDF in space coordinates and velocities. The efficiency of such methods has to be tested via a comparison with the Monte Carlo codes for particular plasma conditions. Here a new simplified method for description of neutral atoms penetration into plasma is suggested. The method is based on the ballistic motion of neutrals along the line-of-sight (LoS) in the forward–back approximation. As a result, two-dimensional distribution functions, dependent on the LoS coordinate and the velocity projection on the LoS, and responsible for the Doppler broadening of the line shape, are calculated. A comparison of the method with Monte Carlo calculations allows the evaluation of the accuracy of the ballistic model. The Balmer spectral line shapes are calculated for specific LoS typical for ITER diagnostics.Atoms2014-05-1522Review10.3390/atoms20201951952062218-20042014-05-15doi: 10.3390/atoms2020195Valery LisitsaMikhail KadomtsevVladislav KotovVladislav NeverovVladimir Shurygin<![CDATA[Atoms, Vol. 2, Pages 178-194: Review of Langmuir-Wave-Caused Dips and Charge-Exchange-Caused Dips in Spectral Lines from Plasmas and their Applications]]>
http://www.mdpi.com/2218-2004/2/2/178
We review studies of two kinds of dips in spectral line profiles emitted by plasmas—dips that have been predicted theoretically and observed experimentally: Langmuir-wave-caused dips (L-dips) and charge-exchange-caused dips (X-dips). There is a principal difference with respect to positions of L-dips and X-dips relative to the unperturbed wavelength of a spectral line: positions of L-dips scale with the electron density Ne roughly as Ne1/2, while positions of X-dips are almost independent of Ne (the dependence is much weaker than for L-dips). L-dips and X-dips phenomena are important, both fundamentally and practically. The fundamental importance is due to a rich physics behind each of these phenomena. L-dips are a multi-frequency resonance phenomenon caused by a single-frequency (monochromatic) electric field. X-dips are due to charge exchange at anticrossings of terms of a diatomic quasi-molecule, whose nuclei have different charges. As for important practical applications, they are as follows: observations of L-dips constitute a very accurate method to measure the electron density in plasmas—a method that does not require knowledge of the electron temperature. L-dips also allow measuring the amplitude of the electric field of Langmuir waves—the only spectroscopic method available for this purpose. Observations of X-dips provide an opportunity to determine rate coefficient of charge exchange between multi-charged ions. This is an important reference data, virtually inaccessible by other experimental methods. The rate coefficients of charge exchange are important for magnetic fusion in Tokamaks, for population inversion in the soft x-ray and VUV ranges, for ion storage devices, as well as for astrophysics (e.g., for the solar plasma and for determining the physical state of planetary nebulae).Atoms2014-05-1322Review10.3390/atoms20201781781942218-20042014-05-13doi: 10.3390/atoms2020178Elisabeth DalimierEugene OksOldrich Renner<![CDATA[Atoms, Vol. 2, Pages 157-177: The Second Workshop on Lineshape Code Comparison: Isolated Lines]]>
http://www.mdpi.com/2218-2004/2/2/157
In this work, we briefly summarize the theoretical aspects of isolated line broadening. We present and discuss test run comparisons from different participating lineshape codes for the 2s-2p transition for LiI, B III and NV.Atoms2014-05-1222Article10.3390/atoms20201571571772218-20042014-05-12doi: 10.3390/atoms2020157Spiros AlexiouMilan DimitrijevićSylvie Sahal-BrechotEvgeny StambulchikBin DuanDiego González-HerreroMarco Gigosos<![CDATA[Atoms, Vol. 2, Pages 123-156: AtomPy: An Open Atomic Data Curation Environment for Astrophysical Applications]]>
http://www.mdpi.com/2218-2004/2/2/123
We present a cloud-computing environment, referred to as AtomPy, based on Google-Drive Sheets and Pandas (Python Data Analysis Library) DataFrames to promote community-driven curation of atomic data for astrophysical applications, a stage beyond database development. The atomic model for each ionic species is contained in a multi-sheet workbook, tabulating representative sets of energy levels, A-values and electron impact effective collision strengths from different sources. The relevant issues that AtomPy intends to address are: (i) data quality by allowing open access to both data producers and users; (ii) comparisons of different datasets to facilitate accuracy assessments; (iii) downloading to local data structures (i.e., Pandas DataFrames) for further manipulation and analysis by prospective users; and (iv) data preservation by avoiding the discard of outdated sets. Data processing workﬂows are implemented by means of IPython Notebooks, and collaborative software developments are encouraged and managed within the GitHub social network. The facilities of AtomPy are illustrated with the critical assessment of the transition probabilities for ions in the hydrogen and helium isoelectronic sequences with atomic number Z ≤ 10.Atoms2014-05-0222Article10.3390/atoms20201231231562218-20042014-05-02doi: 10.3390/atoms2020123Claudio MendozaJosiah BoswellDavid AjokuManuel Bautista<![CDATA[Atoms, Vol. 2, Pages 86-122: Assessing Uncertainties of Theoretical Atomic Transition Probabilities with Monte Carlo Random Trials]]>
http://www.mdpi.com/2218-2004/2/2/86
This paper suggests a method of evaluation of uncertainties in calculated transition probabilities by randomly varying parameters of an atomic code and comparing the results. A control code has been written to randomly vary the input parameters with a normal statistical distribution around initial values with a certain standard deviation. For this particular implementation, Cowan’s suite of atomic codes (R.D. Cowan, The Theory of Atomic Structure and Spectra, Berkeley, CA: University of California Press, 1981) was used to calculate radiative rates of magnetic-dipole and electric-quadrupole transitions within the ground configuration of titanium-like iron, Fe V. The Slater parameters used in the calculations were adjusted to fit experimental energy levels with Cowan’s least-squares fitting program, RCE. The standard deviations of the fitted parameters were used as input of the control code providing the distribution widths of random trials for these parameters. Propagation of errors through the matrix diagonalization and summation of basis state expansions leads to significant variations in the resulting transition rates. These variations vastly differ in their magnitude for different transitions, depending on their sensitivity to errors in parameters. With this method, the rate uncertainty can be individually assessed for each calculated transition.Atoms2014-04-1422Article10.3390/atoms2020086861222218-20042014-04-14doi: 10.3390/atoms2020086Alexander Kramida<![CDATA[Atoms, Vol. 2, Pages 15-85: Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View]]>
http://www.mdpi.com/2218-2004/2/1/15
The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.Atoms2014-03-1921Article10.3390/atoms201001515852218-20042014-03-19doi: 10.3390/atoms2010015Elmar Träbert<![CDATA[Atoms, Vol. 2, Pages 1-14: Evaluation and Comparison of the Configuration Interaction Calculations for Complex Atoms]]>
http://www.mdpi.com/2218-2004/2/1/1
Configuration interaction (CI) methods are the method of choice for the determination of wave functions for complex atomic systems from which a variety of atomic properties may be computed. When applied to highly ionized atoms, where few, if any, energy levels from observed wavelengths are available, the question arises as to how a calculation may be evaluated. Many different codes are available for such calculations. Agreement between the results from different codes in itself is not a check on accuracy, but may be due to a similarity in the computational procedures. This paper reviews basic theory, which, when applied in a systematic manner, can be the basis for the evaluation of accuracy. Results will be illustrated in the study of 4s24p5 (odd) and 4s24p44d (even) levels in W39+ and the transitions between them.Atoms2014-03-1921Article10.3390/atoms20100011142218-20042014-03-19doi: 10.3390/atoms2010001Charlotte Fischer<![CDATA[Atoms, Vol. 1, Pages 14-16: Notes on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities]]>
http://www.mdpi.com/2218-2004/1/3/14
Atomic structure and transition probabilities are fundamental physical data required in many fields of science and technology. Atomic physics codes are freely available to other community users to generate atomic data for their interest, but the quality of these data is rarely verified. This special issue addresses estimation of uncertainties in atomic structure and transition probability calculations, and discusses methods and strategies to assess and ensure the quality of theoretical atomic data.Atoms2013-08-0813Editorial10.3390/atoms103001414162218-20042013-08-08doi: 10.3390/atoms1030014Hyun-Kyung ChungPer JönssonAlexander Kramida<![CDATA[Atoms, Vol. 1, Pages 13: Special Issue on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities]]>
http://www.mdpi.com/2218-2004/1/2/13
There exist several codes in the atomic physics community to generate atomic structure and transition probabilities freely and readily distributed to researchers outside atomic physics community, in plasma, astrophysical or nuclear physics communities. Users take these atomic physics codes to generate the necessary atomic data or modify the codes for their own applications. However, there has been very little effort to validate and verify the data sets generated by non-expert users. [...]Atoms2013-06-2112Editorial10.3390/atoms102001313132218-20042013-06-21doi: 10.3390/atoms1020013Per JönssonHyun-Kyung Chung<![CDATA[Atoms, Vol. 1, Pages 2-12: Emission of β+ Particles Via Internal Pair Production in the 0+ – 0+ Transition of 90Zr: Historical Background and Current Applications in Nuclear Medicine Imaging]]>
http://www.mdpi.com/2218-2004/1/1/2
90Y is traditionally considered as a pure β– emitter. However, the decay of this radionuclide has a minor branch to the 0+ first excited state of 90Zr at 1.76 MeV, that is followed by a β+/β– emission. This internal pair production has been largely studied in the past because it is generated by a rare electric monopole transition (E0) between the states 0+/0+ of 90Zr. The positronic emission has been recently exploited for nuclear medicine applications, i.e. positron emission tomography (PET) acquisitions of 90Y-labelled radiopharmaceuticals, widely used as therapeutic agents in internal radiation therapy. To date, this topic is gaining increasing interest in the radiation dosimetry community, as the possibility of detecting β+ emissions from 90Y by PET scanners may pave the way for an accurate patient-specific dosimetry. This could lead to an explosion in scientific production in this field. In the present paper the historical background behind the study of the internal pair production of the 0+/0+ transition of 90Zr is presented along with most up to date measured branch ratio values. An overview of most recent studies that exploit β+ particles emitted from 90Y for PET acquisitions is also provided.Atoms2013-03-0811Review10.3390/atoms10100022122218-20042013-03-08doi: 10.3390/atoms1010002Marco D'Arienzo<![CDATA[Atoms, Vol. 1, Pages 1: Welcome to Atoms: A New Open Access Journal]]>
http://www.mdpi.com/2218-2004/1/1/1
There is no doubt that it is an exciting time to be studying quantum properties of atoms, molecules, and nuclei. Increasingly deep connections between long-established fields: “atomic physics”, “molecular physics”, “chemical physics”, “nuclear physics”, “scattering theory”, “nuclear magnetic resonance”, “quantum optics”, etc., are blurring old research labels. Atoms is a new open access journal with a broad scope that will aim to capture some of these exciting changes and developments, with a quantum flavor. The Editorial Board's collective expertise spans the fields involved and reflects the international communities active in these areas. [...]Atoms2012-12-1711Editorial10.3390/atoms1010001112218-20042012-12-17doi: 10.3390/atoms1010001James Babb