Slater Model Research Articles

Energy and Z dependence of low velocity Nq+ ion induced M X-ray relative intensities for some heavy elements

The intensity ratios, IMk/IMn (exp)(k = ξ, γ, m1; n = total, αβ), for some heavy elements, 70Yb, 79Au, 81Tl, 82Pb and 83Bi induced by 1000 keV−1750 keV Nq+ (q = 4, 5) ions have been measured in order to investigate their dependence on the projectile energy and atomic number of the respective target elements. The measured intensity ratios have been compared with two sets of values calculated using the Mj (j = 1–5) sub-shell ionization cross sections based on the ECPSSR-UA model, the X-ray emission rates based on the Dirac-Hartree Slater (DHS) model, two sets of the fluorescence and Coster-Kronig yields based on the DHS model and those evaluated by McGuire employing non-relativistic Hartree-Slater model. Significant differences have been observed between the present measured IMk/IMαβ (exp) (k = ξ, γ, m1) intensity ratios and those calculated using independent particle approximation (IPA) models based single atomic vacancy state physical parameters.

L-shell x-ray fluorescence relative intensities for elements with 62 ≤ Z ≤ 83 at 18 keV and 23 keV by synchrotron radiation

The relative intensities of L-subshell x-ray fluorescence (XRF) for elements with atomic numbers 62 ≤ Z ≤ 83 were measured at two excitation energies, 18 keV and 23 keV, using a synchrotron radiation source at a beamline of the Synchrotron Light Center for Experimental Science and Applications in the Middle East (SESAME), Jordan. The experimentally measured results of the relative intensities were compared with the calculated results using the subshell fluorescence yield and the Coster–Kronig transition probabilities recommended by Campbell and the values based on the Dirac–Hartree–Slater model by Puri. The experimental and theoretical results are in agreement. In this work, L XRF relative intensities for the elements Sm, Gd, Tb, Er, Ta, W, Re, Hg, Pb and Bi at energies of 18 keV and 23 keV were measured.

Evaluation of copper spall response using Mie-Grüneisen equation-of-state parameters determined from molecular dynamics

In this study, the formation and application of an across-scale modeling approach is presented to study the influence of shock loading conditions on copper spallation performance. Molecular dynamics simulations coupled with multi-scale shock technology are conducted to determine characteristic parameters of the Mie-Grüneisen equation of state involved in the Slater and Dugdale-MacDonald models. Afterwards, the resultant parameters are embedded into the finite element method to explore the dependence of spall strength, strain rate, and damage evolution rate. It is found that an increase in loading velocity promotes the spallation occur in advance. Combined with free surface velocity and spall plane pressure, it is also discovered that the material experiences an entire spallation prior to ''pullback signal''. As expected, the spall strength determined as the maximum stress is higher than that estimated from the free surface velocity. Besides, there is a temperature-rise effect caused by void-induced thermal dissipation during the spallation. Moreover, the position of spall plane is strongly dependent upon flyer thickness, thereby exhibiting a strain rate effect on spallation behavior. A comparison between numerical results and published experimental data highlights the adequacy of such a hybrid method to capture the copper spall response.

Theoretical study of the enhancement of saturable absorption of Kr under x-ray free-electron laser

The generation of hollow atoms will reduce the probability of light absorption and provide a high-quality diffraction image in the experiment. In this paper, we calculated the ionization rate of the Kr atom under x-ray free-electron laser (XFEL) using Hartree–Fock–Slater model and simulated the ionization model of Kr atom using Monte–Carlo method to determine the response of the hollow atom of Kr atom to the XFEL photon energy. Calculating the correlation between the total photoionization cross-section of the ground state of Kr atom and the photon energy, we determined three particular photon energies of 1.75 keV, 1.90 keV, and 14.30 keV. The dynamics simulation under the experimental condition’s 17.50 keV photon energy was achieved by implementing the Monte–Carlo method and calibrating the photon flux modeling parameters. Consequently, our calculated data are more consistent with experimental phenomena than previous theoretical studies. The saturable absorption of Kr at 1.75 keV, 1.90 keV, 14.30 keV, and 17.50 keV energies was further investigated by using the optimized photon flux model theory. We compared the statistics on main ionization paths under those four specific photon energies and calculated the population changes of various Kr hollow atoms with different configurations. The results demonstrate that the population of hollow atoms produced at the critical ionization photon energy is high. Furthermore, the change of population with respect to position is smooth, which shows a significant difference between the generation mode of ions with low and high photon energies. The result is important for the study of medium- and high-Z element hollow atoms, which has substantial implications for the study of hollow atoms with medium and high charge states, as well as for the scaling of photon energy of free electron lasers.

Experimental validation of theoretically predicted cut-off of L1–L3M4,5 transitions at Z = 50 through measurements of fluorescence and Coster–Kronig yields for Sn and Sb

In the present work, we have deduced the fluorescence (ω 1, ω 2, ω 3) and Coster–Kronig (CK)(f 12, f 13, f 23) yields for Sn (Z = 50) and Sb (Z = 51) from the L i (i = 1–3) sub-shell x-ray intensities measured using the energy tunable synchrotron radiation employing the selective photoionization method. For both the elements, yields have been obtained using two sets of theoretical photoionization cross sections based on the non-relativistic Hartree–Fock–Slater (HFS) model and the self-consistent Dirac–Hartree–Fock (DHF) model. In case of Sb, we have obtained a third set of measured yields also by using the experimental photoionization cross sections evaluated from independent measurements of the mass-attenuation coefficients. The experimental yields for Sb are reported for the first time by us. We have compared the present deduced fluorescence and CK yields with the Dirac–Hartree–Slater model based values, the semi-empirical values tabulated by Krause and the earlier reported values. In case of Sn, using the DHF and the HFS model based photoionization cross sections, two sets of present measured L1 sub-shell fluorescence yields (ω 1) are found to be 0.039 ± 0.007 and 0.036 ± 0.003, and the CK yields (f 13) are found to be 0.428 ± 0.107 and 0.405 ± 0.028, respectively. In case of Sb, using three sets of the photoionization cross sections (DHF, HFS and recent experimental values), the ω 1 values are measured to be 0.042 ± 0.007, 0.040 ± 0.004 and 0.047 ± 0.005, and the CK yields are measured to be 0.343 ± 0.085, 0.297 ± 0.021 and 0.247 ± 0.022, respectively. The comparison of these present measured yields with the theoretical values provided a reliable experimental evidence indicating cut-off of the intense L1–L3M4,5 CK transitions at Z = 50.

Application of quantum-statistical methods to studies of thermodynamic and radiative processes in hot dense plasmas

Calculations of thermodynamic and radiative characteristics of hot dense plasmas within different quantum-statistical approaches, such as the use of the Hartree–Fock–Slater model and the ion model, are presented. Calculated equations of state of different substances are used to investigate findings from absolute and relative measurements of the compressibility of solid aluminum samples in strong shock waves. It is shown that our calculated Hugoniot adiabat of aluminum is in a good agreement with experimental data and other theoretical results from first principles. We also present a review of the most important applications of the quantum-statistical approach to the study of radiative properties of hot dense plasmas. It includes the optimization problem of hohlraum wall materials for laser inertial fusion, calculations of the radiative efficiency of complex materials for optically thin plasma in X-pinch, modeling of radiative and gas-dynamic processes in plasma for experiments, where both intense laser and heavy ion beams are used, and temperature diagnostics for X- and Z-pinch plasmas.

STRUCTURAL EQUATION MODELLING OF THE EFFECTS OF MANAGEMENT ATTITUDE AND PERCEPTION, INDUSTRY CHARACTERISTICS, AND EXPORT MARKETING STRATEGY ON EXPORT PERFORMANCE IN THE WOOD INDUSTRY IN GHANA

ABSTRACT Improved globalization has driven a developing number of firms to look past their customary domestic markets and spotlight on high-development export markets not exclusively to grow yet in addition to guarantee their exceptional survival. Therefore, the job of exporting in firms' movement has turned out to be progressively critical and examination into export performance goes back to the imaginative work of Tookey (1964). Notwithstanding, despite these exploration endeavors, there is an absence of combination and assertion in the conceptualization and operationalization of the develop (Sousa, 2004). The study examined whether there is an inter-relationship between the factors that are perceived to influence export performance in the wood industry in Ghana. The theoretical model underpinning the study is the Aaby and Slater (1989) model. A quantitative approach was employed. A structured questionnaire was administered to wood exporting firms identified by the help of forestry commission. A structural equation modeling was conducted to examine whether there is an inter-relationship between the factors that are perceived to influence export performance in the wood industry in Ghana. The results reveal that all three predictor variables examined, i.e. Industry Characteristics, Export Marketing Strategy and Management Perception and attitude are all key determinants of export performance at various levels Keywords Management, export, strategy, Ghana

Structural and optical properties of CsI thin films: Influence of film thickness and humidity

Structural and optical studies have been performed on the thermally-evaporated “as-deposited’’ and “humid air aged’’ CsI thin films. The structural analysis for both “as-deposited’’ and “humid air aged’’ films shows a well-oriented peaks position of (110) and (220) lattice planes with a compressive stress in the films. The crystal quality has been investigated through the structural parameters. The increase in peak intensity as well as sharpness with film thickness implies the improvement of crystallinity. The optical absorbance of CsI films has been analyzed in the wavelength range of 190 nm–900 nm in order to estimate the band gap energy of the films. Slater's model has also been used to explain the degradation of band gap energy with the increase in crystallite size.

Cascade Mi (i = 1–5) subshell X‐ray emission at incident photon energies across the Lj (j = 1–3) subshell absorption edges of 66Dy

The total M shell and the Mk (k = ξ, αβ, γ, m) X‐ray production cross sections for 66Dy have been measured at incident photon energies across its Lj (j = 1–3) subshell absorption edge energies, ranging 7.8–9.2 keV. This study aims to investigate the evolution of the probability for cascade decay of Lj subshell vacancies as the tunable incident energy ionizes progressively different 66Dy Lj subshells. The experimental X‐ray production cross sections have been compared with theoretical ones calculated using the nonrelativistic Hartree–Fock–Slater (HFS) model‐based photoionization cross sections; three sets of the X‐ray emission rates, fluorescence and Coster–Kronig yield based on the nonrelativistic Hartree–Slater (NRHS) model, Dirac–Hartree–Slater (DHS) model and Dirac–Fock (DF) model; the Lj (j = 1–3) subshell to the Mi (i = 1–5) subshell vacancy transfer probabilities evaluated in the present work. Presently measured total M shell and the Mαβ X‐ray production cross sections are found to be significantly lower than the theoretical ones evaluated using physical parameters based on the relativistic Dirac–Fock/Dirac–Hartree–Slater model calculations, whereas a much better agreement is observed with respect to the NRHS model‐based calculations; however, the measured X‐ray production cross sections are still systematically lower than the NRHS values.

M sub-shell X-ray fluorescence cross-section measurements for six elements in the range Z = 78–92 at tuned synchrotron photon energies 5, 7 and 9 keV.

M sub-shell X-ray fluorescence cross-sections of elements Pt, Au, Hg, Pb, Th and U have been measured with linearly polarized photon beams from Indus-II synchrotron source at Raja Ramanna Centre for Advanced Technology (RRCAT), India at tuned 5, 7 and 9 keV energies less than the L3 edge energy of elements. Measurements at present energies and elements are not available in literature. Therefore, measured cross-sections for Mξ, Mδ, Mα, Mβ, Mγ, Mm1 and Mm2 group of X-rays were compared with calculated theoretical values based upon Non Relativistic Hartree–Slater (NRHS) and relativistic Dirac-Fork (DF) and Dirac–Hartree–Slater (DHS) models. The measured cross-sections along with our earlier quoted measurements at 8 and 10 keV by Kaur et al. [Nucl. Instrum. Meth. B, 2014; 320: 37] are found in good agreement with DF and DHS values around 20% deviations and are highly deviated from NRHS values. Most of the spots of observed high deviations in measured and theoretical cross-sections are found to coincide with the presence of crisscrosses/sharp variations in contributing physical parameters photo-ionization cross-sections σMi’s and Coster–Kronig yields fij’s with Zs.

Spectra for the reemission of attosecond and shorter electromagnetic pulses by multielectron atoms

Based on the analytical solution of the Schrodinger equation, we have considered the reemission of attosecond and shorter electromagnetic pulses by multielectron atoms in the sudden perturbation approximation. We have developed a technique of calculating the spectra for the reemission of attosecond and shorter electromagnetic pulses by neutral multielectron atoms with nuclear charges from 1 to 92. The results are presented in the form of analytical formulas dependent on several coefficients and screening parameters tabulated for all of the atoms whose electron densities are described by the well-known Dirac–Hartree–Fock–Slater model. As examples we have calculated the spectra for the reemission by lithium, carbon, calcium, and iron atoms for two types of incident pulse: Gaussian and “sombrero.”

Radiative properties of matter based on quantum statistical method

We present the preliminary results of our code OPAQS (opacity calculation using quantum statistical model) that is based on the self consistent Hartree–Fock–Slater model for the average atom. The code is capable of performing robust calculations of average charge state, frequency-dependent and mean opacities. The accuracy of the atomic model is verified by comparing the calculations of average charge state with various published results. The monochromatic opacities for iron computed at different sets of temperatures and densities are compared with LEDCOP. The Rosseland and Planck opacities for iron and aluminum are validated with some state-of-the-art codes. The results are in good agreement with the published data.

Substitutional impurity in single-layer graphene: The Koster–Slater and Anderson models

The Koster–Slater and Anderson models are used to consider substitutional impurities in free-standing single-layer graphene. The density of states of graphene is described using a model (the M model). For the nitrogen and boron impurities, the occupation numbers and the parameter η which defines the fraction of delocalized electrons of the impurity are determined. In this case, experimental data are used for both determination of the model parameters and comparison with the results of theoretical estimations. The general features of the Koster–Slater and Anderson models and the differences between the two models are discussed. Specifically, it is shown that the band contributions to the occupation numbers of a nitrogen atom in both models are comparable, whereas the local contributions are substantially different: the local contributions are decisive in the Koster–Slater model and negligible in the Anderson model. The asymptotic behavior of the wave functions of a defect is considered in the Koster–Slater model, and the electron states of impurity dimers are considered in the Anderson model.

Microscopic study on magnetocaloric and electrocaloric effects near the critical point

Adiabatic temperature changes of magnetocaloric/electrocaloric effects are analytically investigated. The analytical studies are based on the microscopic statistical models such as Husimi–Temperley model and Slater model. As a result, we show the characteristic scales of the adiabatic processes correspond to microscopic parameters, namely exchange couplings and Slater energy. The scaled parameter dependence become stronger near the critical point. Furthermore, using a general Hamiltonian method, we clarify the adiabatic temperature changes depend on the relative ratio of characteristic scales. The present study may propose a useful aspect for applications.

Pressure–Temperature Dependence of Thermodynamic Properties of $$\hbox {ScAlO}_{3}$$ Perovskite from First Principles

First-principles calculations have been performed to obtain the thermodynamic properties of $$\hbox {ScAlO}_{3}$$ perovskite in a wide range of pressure (0 GPa to 30 GPa) and temperature (0 K to 1400 K). Calculations have been performed by using the pseudo-potential method within the generalized gradient approximation. Both pressure- and temperature-dependent thermodynamic properties including the bulk modulus, thermal expansion, thermal expansion coefficient, and the heat capacity at constant volume and constant pressure were calculated using three different approaches based on the quasi-harmonic Debye model: the Slater, Dugdale–MacDonald (DM), and Vaschenko–Zubarev (VZ) approaches. Also, empirical energy corrections are applied to the results of models to correct the systematic errors introduced by the functional. It is found that the VZ model provides more accurate estimates in comparison with the DM and Slater models, especially after an empirical energy correction. The results obtained from the VZ analysis on the corrected static energy show that this method can be used to determine the thermodynamic properties of $$\hbox {ScAlO}_{3}$$ compounds with reasonable accuracy.

Thermodynamic Properties of Copper in a Wide Range of Pressure and Temperature Within the Quasi-Harmonic Approximation

A first-principles calculations have been performed based on density functional theory to study the thermal properties of copper. Calculations have been performed using the pseudo-potential method within the generalized gradient approximation (GGA) and local density approximation. Thermodynamic properties including the bulk modulus, thermal expansion coefficient, and heat capacities at constant volume and constant pressure were calculated as a function of pressure and temperature using three different models based on the quasi-harmonic approximation: the Debye–Slater model, the Debye–Gruneisen model, and the full quasi-harmonic model (that requires the phonon density of states at each calculated volume). Also, empirical energy corrections are applied to the results of the three models. The electronic contributions to the specific heat are calculated and discussed, and it was found that they become important at high temperatures. The calculated values are in good agreement with experimental results. It is found that the full quasi-harmonic model with the GGA approximation provides more accurate estimates in comparison with the other models.

Effect of 3d transition elements substitution for Ni in Ni2Mn1+xSn1-x on the phase stability and magnetic properties: A first principle investigation

In hope of understanding the origin of the 3d-transition elements doping effect on the phase stability and magnetic properties of the ferromagnetic shape memory Heusler alloy Ni–Mn–Sn, the Ni–Z–Mn–Sn system with Z=Ni, Cu, Co, Fe, Mn and Cr is investigated using first-principles calculations. The calculated results show that the energetically favorable magnetic order of the L21 structure is antiferromagnetic for Z=Ni and Cu, and ferromagnetic for the Z=Co, Fe, Mn and Cr. However, for L10 structure, the antiferromagnetic state has an energetical preference for each alloy. Accordingly, a magnetic transition accompanies with the martensite phase transformation and a large change in the magnetic moment can be observed in the alloys with the L21 under the ferromagnetic state, which is mainly dependent on the coupling behaviors of the doped atoms. The weak ferromagnetic coupling between the Ni/Cu and Mn, the strong ferromagnetic coupling between Co/Fe and Mn and the antiferromagnetic coupling between Mn/Cr and Mn play an important role on the magnetic order of L21 structures. Furthermore, the Bethe–Slater model is employed to gain a further understanding and regulation of the coupling behaviors of different doping elements, which is very sensitive to the interatomic distance. These calculated results may help in gaining an insight into the doping behavior of these transition metals and provide some theoretical aid to the material design.

X-ray relative intensities at incident photon energies across the [formula omitted] ([formula omitted]) absorption edges of elements with [formula omitted

The intensity ratios, ILk/ILα1 (k=l,η,α2,β1,β2,15,β3,β4,β5,7,β6,β9,10,γ1,5,γ6,8,γ2,3,γ4) and ILj/ILα (j=β,γ), have been evaluated at incident photon energies across the Li (i=1–3) absorption edge energies of all the elements with 35≤Z≤92. Use is made of what are currently considered to be more reliable theoretical data sets of different physical parameters, namely, the Li (i=1–3) sub-shell photoionization cross sections based on the relativistic Hartree–Fock–Slater (RHFS) model, the X-ray emission rates based on the Dirac–Fock model, and the fluorescence and Coster–Kronig yields based on the Dirac–Hartree–Slater model. In addition, the Lα1 X-ray production cross sections for different elements at various incident photon energies have been tabulated so as to facilitate the evaluation of production cross sections for different resolved L X-ray components from the tabulated intensity ratios. Further, to assist evaluation of the prominent (Li−Sj) (Sj=Mj, Nj and i=1–3, j=1–7) resonant Raman scattered (RRS) peak energies for an element at a given incident photon energy (below the Li sub-shell absorption edge), the neutral-atom electron binding energies based on the relaxed orbital RHFS calculations are also listed so as to enable identification of the RRS peaks, which can overlap with the fluorescent X-ray lines.

Spectral induced polarization measurements for predicting the hydraulic conductivity in sandy aquifers

Abstract. Field and laboratory spectral induced polarization (SIP) measurements are integrated to characterize the hydrogeological conditions at the Schillerslage test site in Germany. The phase images are capable of monitoring thin peat layers within the sandy aquifers. However, the field results show limitations of decreasing resolution with depth. In comparison with the field inversion results, the SIP laboratory measurements show a certain shift in SIP response due to different compaction and sorting of the samples. The SIP data are analyzed to derive an empirical relationship for predicting the hydraulic conductivity (K). In particular, two significant but weak correlations between individual real resistivities (ρ') and relaxation times (τ), based on a Debye decomposition (DD) model, with measured K are found for the upper groundwater aquifer. The maximum relaxation time (τmax) and logarithmically weighted average relaxation time (τlw) show a better relation with K values than the median value τ50. A combined power law relation between individual ρ' and τ with K is developed with an expression of A · (ρ')B · (τlw)C, where A, B and C are determined using a least-squares fit between the measured and predicted K. The suggested approach with the calculated coefficients of the first aquifer is applied for the second. Results show good correlation with the measured K indicating that the derived relationship is superior to single phase angle models as Börner or Slater models.

Temperature effect on structural and optoelectronic properties of Bi2S3 nanocrystalline thin films deposited by spray pyrolysis method

Bismuth sulfide (Bi2S3) nanocrystalline thin films exhibit a low band gap, a high absorbance coefficient and good dispersity. In this study, the structural, optical and electrical properties of Bi2S3 nanocrystalline thin films prepared from bismuth chloride (BiCl3) and thiourea (CS(NH2)2) solutions and deposited by a spray pyrolysis method, are investigated as a function of the substrate temperature (TS). TS has been increased from 140 to 280°C by step of 40°C. Characterizations of the films have been carried out using X-ray diffraction (XRD), scanning electron microscopy, ultra-violet–visible–near infrared (UV–vis–NIR) spectroscopy and electrical resistivity measurements. These studies reveal that Bi2S3 films consist of nanocrystalline grains. Average grain size was calculated using Debye–Scherrer formula. As TS increases, the grain size of Bi2S3 crystallites increases from 40 to 60nm. In addition, a blue shift of 0.20eV in the optical band gap energy Eg, which is in agreement with Slater's model, and a decrease in electrical resistivity from 2.61 to 1.05Ωcm was observed.