Transition Array Research Articles

EUV emission spectra in collisions of highly charged tantalum ions with nitrogen and oxygen molecules

We have performed ion beam collision experiments using multiply charged tantalum ions and observed EUV (extreme ultra-violet) emission spectra in collisions of ions with molecular targets, N2 and O2. Broad UTAs (un-resolved transition arrays) from multiply charged Ta ions were observed, and the mean wavelengths of the UTAs shifted and became shorter at higher charge statea of Ta ions. These UTAs may be attributed to the 4f–5d and 4f–5g transitions. Not only the UTA emission from incident ions, but also the sharp emission lines from multiply charged fragment atomic ions were observed. Production of temporary highly charged molecular ions, their kinetic energy and fragmentation processes have been investigated with coincident detection technique. However, the observation of emission from the fragments might be for the first time. The formation mechanisms of the multiply charged fragment atomic ions from target molecules are discussed.

Multiconfiguration Dirac-Hartree-Fock energy levels, oscillator strengths, transition probabilities, hyperfine constants and Landé g-factor of intermediate Rydberg series in neutral argon atom

We computed the energy levels, oscillator strengths $f_{ij}$ , the radiative transition rates $A_{ij}$ , the Lande g -factor, the magnetic dipole moment and the electric quadrupole hyperfine constants of the intermediate Rydberg series $n{\rm s}$ $[k]_{J}$ ( $ 4 \le n \le 6$ ), $n{\rm d}$ $ [k]_{J}$ ( $3 \le n \le 4$ ), $n{\rm p}$ $[k]_{J}$ ( $4 \le n \le 5$ ) relative to the ground state 3p6 1S0 for neutral argon atom spectra. The values are obtained in the framework of the multiconfiguration Dirac-Hartree-Fock (MCDHF) approach. In this approach, Breit interaction, leading quantum electrodynamics (QED) effects and self-energy correction are taken into account. Moreover, these spectroscopic parameters have been calculated for many levels belonging to the configuration 3p54s, 3p55s, 3p56s, 3p53d, 3p54d, 3p54p, 3p55p as well as for transitions between levels 3p54s-3p54p, 3p54p-3p53d, 3p54p-3p55s, 3p55s-3p55p and 3p55p-3p56s. The large majority of the lines from the 4p-5s and 4p-3d, 5s-5p and 5p-6s transition arrays have been observed and the calculations are consistent with the J -file-sum rule. The obtained theoretical values are compared with previous experimental and theoretical data available in the literature. An overall satisfactory agreement is noticed allowing assessing the reliability of our data.

Suppression of tungsten accumulation during ELMy H-mode by lower hybrid wave heating in the EAST tokamak

EAST tokamak has been equipped with upper tungsten divertor since 2014. The tungsten accumulation has been often observed in NBI-heated H-mode discharges suggesting deleterious tungsten confinement in the plasma core. It causes not only H-L back transition but also plasma disruption in several discharges. Suppression of the tungsten accumulation is therefore the most important issue in EAST to achieve a long pulse H-mode discharge. In order to study the tungsten behavior in the long pulse discharge, tungsten spectra have been measured at 20–140Å. The tungsten density, nw, is evaluated from the intensity of tungsten unresolved transition array (W-UTA) in a wavelength range of 45–70Å which is composed of several ionization stages of tungsten, e.g. W27+-W45+ at Te0∼2.5keV). It is found that the tungsten accumulation can be suppressed when the 4.6GHz LHW with PLHW∼0.8MW is superimposed on the NBI phase (PNBI= 1.9MW). During the superimposed phase the ELM frequency, fELM, increases from ∼30Hz to ∼60Hz and the tungsten density is halved compared to the NBI-heated discharge. The H-mode discharge can be thus steadily sustained for longer period. It is found that the nw is a large function of the ratio of LHW power to the total injection power, PLHW/(PLHW+PNBI), and the nw can be reduced, at least, in an order of magnitude smaller than that in NBI-heated discharges at PLHW/(PLHW+PNBI)≥0.8. The result strongly suggests a possible way toward the steady H-mode discharge.

Analysis of soft x-ray emission spectra of laser-produced dysprosium, erbium and thulium plasmas

Soft x-ray emission spectra of dysprosium, erbium and thulium ions created in laser-produced plasmas were recorded with a flat-field grazing-incidence spectrometer in the 2.5–8 nm spectral range. The ions were produced using an Nd:YAG laser of 7 ns pulse duration and the spectra were recorded at various power densities. The experimental spectra were interpreted with the aid of the Cowan suite of atomic structure codes and the flexible atomic code. At wavelengths above 5.5 nm the spectra are dominated by overlapping n = 4 − n = 4 unresolved transition arrays from adjacent ion stages. Below 6 nm, n = 4 − n = 5 transitions also give rise to a series of interesting overlapping spectral features.

Revised analysis of the fifth spectrum of rhenium (Re V)

The spectrum of rhenium was observed in the (500–2100) Å wavelength region. A 6.65 m normal incidence VUV spectrograph has been used to record the spectrum. The (5d3+5d26s)–5d26p transition array of four times ionized rhenium, Re V, has been investigated. The configurations 5d3, 5d26s and 5d26p had been previously studied, and all but one levels of these configurations (19, 15 and 45 levels, respectively) had been established. The previous analysis was based on 382 classified spectral lines. In the current analysis we have rejected 74 previously identified spectral lines and added 90 newly classified lines. New list of identified lines contains 398 entries. Comparing with the previous analysis, the current study is based on new spectrograms and significantly more accurate wavelength measurements. We have detected a large (up to 35 mÅ) systematic shift in wavelength measurements used in the previous analysis. In the current study, the standard deviations (by regions) of the undisturbed isolated lines from their Ritz positions are three to five times smaller and the largest deviation of strong isolated lines from their Ritz positions is about seven times smaller than in the previous work. We have confirmed identification of all but three previously found levels. One level has been rejected and two levels have been determined at new positions. One previously unidentified 5d26s level has been added. Based on the new wavelength measurements, we have corrected positions of all previously known 5d3, 5d26s and 5d26p energy levels (except for the ground level, rejected and newly determined levels) by up to 8.31cm−1. From all 80 theoretically possible levels of the configurations 5d3, 5d26s and 5d26p, only the level 5d26s (1S)2S1/2 is still not determined. The orthogonal operators technique was used to calculate the level structure and transition probabilities. The energy parameters have been determined by the least squares fit to the observed levels. Calculated transition probabilities, energy values, as well as LS-compositions obtained from the fitted parameters are presented.

Time integrated optical emission studies of the laser produced germanium plasma

We present new time integrated data on the optical emission spectra of laser produced germanium plasma using a Q-switched Nd:YAG laser (1064 nm), power density up to about 5 × 109 W cm−2 in conjunction with a set of five spectrometers covering a spectral range from 200 nm to 720 nm. Well resolved structure due to the 4p5s → 4p2 transition array of neutral germanium and a few multiplets of singly ionized germanium have been observed. Plasma temperature has been determined in the range (9000–11 000) K using four different techniques; two line ratio method, Boltzmann plot, Saha–Boltzmann plot and Marotta’s technique whereas electron density has been deduced from the Stark broadened line profiles in the range (0.5–5.0) × 1017 cm−3, depending on the laser pulse energy to produce the germanium plasma. Full width at half maximum (FWHM) of a number of neutral and singly ionized germanium lines have been extracted by the Lorentzian fit to the experimentally observed line profiles. In addition, we have compared the experimentally measured relative line strengths for the 4p5s 3P0,1,2 → 4p2 3P0,1,2 multiplet with that calculated in the LS-coupling scheme revealing that the intermediate coupling scheme is more appropriate for the level designations in germanium.

Interdependence between Collective Thermal Fluctuations and Elastic and Viscous Properties in Model Lipid Bilayers

Lipid membranes undergo an array of conformational and dynamic transitions, ranging from individual lipid motions to undulations of micron-sized patches of the membrane. However, the dynamics at intermediate length scales are largely unexplored due to experimental challenges in accessing the appropriate length and time scales. Over the past several years our group has used neutron spin echo spectroscopy (NSE) to provide unique insights into these elusive dynamics in model lipid bilayers, measuring collective bending and thickness fluctuations. These thermally induced collective membrane fluctuations are controlled by elastic and viscous properties of the membranes. It has long been known that the bending fluctuations are characterized by the bending modulus, κ, of the membranes and the motion is damped by the viscosity of solvent, η. By contrast, according to a recent theory proposed by Bingham, Smye and Olmsted, the collective thickness fluctuations are characterized by the bilayer area compressibility modulus, KA, which is damped by the membrane and solvent viscosities, μ and η, respectively. Therefore, by measuring these two collective membrane fluctuations the membrane's elastic and viscous parameters can be evaluated. Here we use this novel method to determine these characteristic parameters of lipid bilayers from neutron scattering data for a couple of simple saturated phosphatidylcholine bilayers. The estimated values are κ ∼ 10−19 J, KA ∼ 0.3 to 0.4 N/m, and μ ∼ 10 nPa s m, which are all consistent with literature values.

Optimal trajectories of brain state transitions

The complexity of neural dynamics stems in part from the complexity of the underlying anatomy. Yet how white matter structure constrains how the brain transitions from one cognitive state to another remains unknown. Here we address this question by drawing on recent advances in network control theory to model the underlying mechanisms of brain state transitions as elicited by the collective control of region sets. We find that previously identified attention and executive control systems are poised to affect a broad array of state transitions that cannot easily be classified by traditional engineering-based notions of control. This theoretical versatility comes with a vulnerability to injury. In patients with mild traumatic brain injury, we observe a loss of specificity in putative control processes, suggesting greater susceptibility to neurophysiological noise. These results offer fundamental insights into the mechanisms driving brain state transitions in healthy cognition and their alteration following injury.

Summation of the spectra of all partially resolved transition arrays in a supertransition array.

It is shown that the contributions of all partially resolved transition arrays (PRTAs) to the spectrum of a supertransition array (STA) may be summed by an efficient analytical method. The method is similar to the configurationally resolved super transition array method [G. Hazak and Y. Kurzweil, HighEnergy Density Phys. 8, 290 (2012)1574-181810.1016/j.hedp.2012.05.001] and avoids the Gaussianity assumption of the partially resolved super transition arrays method [B. G. Wilson, C. A. Iglesias, and M. H. Chen High Energy Density Phys. 14, 67 (2015)1574-181810.1016/j.hedp.2015.02.007], thus yielding an STA spectrum which is resolved down to the PRTA level.

The sixth spectrum of platinum (Pt VI)

The spectrum of platinum was observed in the (300–2100) Å wavelength region. The (5d5+5d46s)–5d46p transition array of five times ionized platinum, Pt VI, has been investigated and 1390 spectral lines have been classified in the region of (399–1564) Å. The analysis has led to the determination of the 5d5, 5d46s and 5d46p configurations. All 37 theoretically possible 5d5 levels, 46 of 63 possible 5d46s levels and 167 of 180 possible 5d46p levels have been established. The orthogonal operators technique was used to calculate the level structure and transition probabilities. The energy parameters have been determined by the least squares fit to the observed levels. Calculated transition probability and energy values, as well as LS-compositions obtained from the fitted parameters are presented. The uncertainties of the established energy levels and calculated (Ritz) wavenumbers are included.

Analysis of unresolved transition arrays in XUV spectral region from highly charged lead ions produced by subnanosecond laser pulse

Soft x-ray and extreme ultraviolet (XUV) spectra from lead (Pb, Z=82) laser-produced plasmas (LPPs) were measured in the 1.0–7.0nm wavelength region employing a 150-ps, 1064-nm Nd:YAG laser with focused power densities in the range from 3.1×1013W/cm2 to 1.4×1014W/cm2. The flexible atomic code (FAC) and the Cowan's suite of atomic structure codes were applied to compute and explain the radiation properties of the lead spectra observed. The most prominent structure in the spectra is a broad double peak, which is produced by Δn=0, n=4–4 and Δn=1, n=4–5 transition arrays emitted from highly charged lead ions. The emission characteristics of Δn=1, n=4–5 transitions were investigated by the use of the unresolved transition arrays (UTAs) model. Numerous new spectral features generated by Δn=1, n=4–5 transitions in ions from Pb21+ to Pb45+ are discerned with the aid of the results from present computations as well as consideration of previous theoretical predictions and experimental data.

Revised and extended analysis of the eighth spectrum of platinum (Pt VIII)

The spectrum of platinum was observed in the 300–2100 Å wavelength region. Grazing and normal incidence VUV spectrographs have been used to record the spectrum. The (5d3+5d26s)−5d26p transition array of seven times ionized platinum, Pt VIII, has been investigated. The configurations 5d3 and 5d26p had been previously studied, and all levels of these configurations (19 and 45 levels, respectively) had been established. The previous analysis was based on 178 classified spectral lines. In the current analysis we have confirmed identification of all previously found levels and all but 10 previously assigned spectral lines, although we have detected a large (up to 35 mÅ) systematic shift in wavelength measurements used in the previous analysis. Based on new wavelength measurements, we have corrected the 5d3 and 5d26p energy level values (by up to 55 cm−1) and established for the first time 14 out of 16 theoretically possible 5d26s levels in Pt VIII. The total list of identified lines (including 180 new lines) contains 349 entries. The orthogonal operators technique was used to calculate the level structure and transition probabilities. The energy parameters have been determined by the least squares fit to the observed levels. Calculated transition probability and energy values, as well as LS-compositions obtained from the fitted parameters are presented.

The seventh spectrum of platinum (Pt VII): Analysis of the [formula omitted]–[formula omitted] transition array

The spectrum of platinum was observed in the (300–2100) Å wavelength region. The (5d4+5d36s)–5d36p transition array of six times ionized platinum, Pt VII, has been investigated and 759 spectral lines have been classified in the region of (337–1273) Å. The analysis has led to the determination of the 5d4, 5d36s and 5d36p configurations. All 34 theoretically possible 5d4 levels, 35 of 38 possible 5d36s levels and 108 of 110 possible 5d36p levels have been established. The orthogonal operators technique was used to calculate the level structure and transition probabilities. The energy parameters have been determined by the least squares fit to the observed levels. Calculated transition probability and energy values, as well as LS-compositions obtained from the fitted parameters are presented.

Origin of the satellites Lα6 and Lα7 in the elements 40Zr to 50Sn

The origin of the satellites Lα6 and Lα7 have been explained in the elements from 40Zr to 50Sn. The energies and the intensities of the various transitions corresponding to the L3Mx - MxM4,5 (where x = 1-5) transition array, which may give rise to these satellites, have been calculated theoretically. The transition energies have been calculated using the available Hartree-Fock-Slater data for K-LM and L-MM Auger transition energies. The intensities of the various transitions have been estimated by considering cross sections L1-L3MX for Coster- Kronig transitions as well as for M-shell shake-off process occurring simultaneous to a L3 hole creation. The total cross sections for initial two-hole states have been then distributed statistically amongst various allowed transitions from the initial states L3Mx to the final states MxM4,5. Each transition has been assumed to give rise to a Gaussian line and then the theoretical satellite spectrum has been computed by summing up these Gaussian lines. The calculated energies have been found to be comparable with the measured energies of the satellites Lα6 and Lα7. Consequently, the transitions which give rise to these satellites have been identified. The satellite Lag has been assigned the transition 3D2L3M3 - 3F3M3M5 and the satellite Lα7 the transition 3PqL3M3 - 3P1M3M5 in all the elements from 40Zr to 50Sn.

Up-down asymmetry measurement of tungsten distribution in large helical device using two extreme ultraviolet (EUV) spectrometers.

Two space-resolved extreme ultraviolet spectrometers working in wavelength ranges of 10-130 Å and 30-500 Å have been utilized to observe the full vertical profile of tungsten line emissions by simultaneously measuring upper- and lower-half plasmas of LHD, respectively. The radial profile of local emissivity is reconstructed from the measured vertical profile in the overlapped wavelength range of 30-130 Å and the up-down asymmetry is examined against the local emissivity profiles of WXXVIII in the unresolved transition array spectrum. The result shows a nearly symmetric profile, suggesting a good availability in the present diagnostic method for the impurity asymmetry study.

Spatial diagnostics of the laser-produced tin plasma in air

We present here new experimental studies on the laser-produced tin plasma generated by focusing the beam of a Q-switched Nd:YAG laser (532 nm) on the sample in air at atmospheric pressure. The optical emission spectra were recorded with a set of five spectrometers covering the spectral range from 200–720 nm. The electron temperature has been calculated to be about (10 600 ± 600) K using three methods; the two-line ratio, Boltzmann plot and the Saha–Boltzmann plot method, whereas the electron number density of about (9.0 ± 0.8) × 1016 cm−3 has been calculated using the Stark broadened line profiles of tin lines and the hydrogen Hα-line. Furthermore, the branching fractions have been deduced for 15 spectral lines of the 5p5d → 5p2 transition array in tin, whereas the absolute values of the transition probabilities have been calculated by combining the experimental branching fractions with the lifetimes of the excited levels. Our measured values are compared with those reported in the literature and NIST data base, showing good agreement.

Characteristics of extreme ultraviolet emission from high-Z plasmas

We demonstrate the extreme ultraviolet (EUV) and soft x-ray sources in the 2 to 7 nm spectral region related to the beyond EUV (BEUV) question at 6.x nm and the water window source based on laser-produced high-Z plasmas. Resonance emission from multiply charged ions merges to produce intense unresolved transition arrays (UTAs), extending below the carbon K edge (4.37 nm). An outline of a microscope design for single-shot live cell imaging is proposed based on high-Z plasma UTA source, coupled to multilayer mirror optics.

Estrogen- and progesterone-mediated structural neuroplasticity in women: evidence from neuroimaging

There is substantial evidence that the ovarian sex hormones, estrogen and progesterone, which vary considerably over the course of the human female lifetime, contribute to changes in brain structure and function. This structured, quantitative literature reviews aims to summarize neuroimaging literature addressing physiological variation in brain macro- and microstructure across an array of hormonal transitions including the menstrual cycle, use of hormonal contraceptives, pregnancy, and menopause. Twenty-five studies reporting structural neuroimaging of women, addressing variation across hormonal states, were identified from a structured search of PUBMED and were systematically reviewed. Although the studies are heterogenous with regard to methodology, overall the results point to overlapping areas of hormone related effects on brain structure particularly affecting the structures of the limbic system. These findings are in keeping with functional data that point to a role for estrogen and progesterone in mediating emotional processing.

Controlling Membrane Dynamics by Tuning the Hydrophobic Mismatch and Lipid Compostion

Lipid membranes undergo an array of conformational and dynamic transitions, ranging from individual lipid motions to undulations of micron-sized patches of the membrane. However, the dynamics at intermediate length scales are largely unexplored due to experimental challenges in accessing the appropriate length and time scales. Here we use neutron spin echo spectroscopy (NSE) to provide unique insights into these elusive dynamics and measure both bending and collective thickness fluctuations in model lipid bilayers. We build on our previous direct measurements of thickness fluctuations in single component lipid vesicles and extend the use of NSE to study more complex two component systems. We show that hydrophobic mismatch between lipids with different acyl chain lengths tunes the thickness fluctuation amplitude and relaxation time in a way not achievable in single component systems. In the mixed lipid systems, the fluctuation amplitude is enhanced in the fluid phase and reaches approximately 20% of the bilayer thickness, presumably due to an increase in the bilayer compressibility. Meanwhile the fluctuation relaxation time is comparable to the result for single component bilayers in the fluid phase but slows upon gelation of the longer-tailed lipid. Interestingly, our results suggest a decoupling of the fluctuation amplitude with the relaxation time, implying the potential for independent control over the fluctuation space and time domains and providing new insights into the role of lipid diversity in controlling the rich dynamics of biomembranes.

Eighth spectrum of palladium: Pd VIII

The spectrum of seven-times ionized palladium (Pd VIII) has been studied in the 170–310 Å region for the first time. Spectra were obtained on a 3 m 3600 lines/mm grazing incidence spectrograph with a triggered vacuum spark as a source of excitation. 178 lines of 4d3–4d25p transitions were identified with the use of parametric calculation based on the orthogonal operator technique. All 19 and 45 energy levels respectively in the 4d3 ground configuration and in the 4d25p excited configuration were determined. Using Cowan code calculations 183 lines of the 4d3–(4d24f + 4p54d4) transition array were classified, 51 levels of the mixed 4d24f + 4p54d4 configurations were located.