Dielectronic satellite emission from a solid-density Mg plasma: Relationship to models of ionization potential depression.

We report on experiments where solid-density Mg plasmas are created by heating with the focused output of the Linac Coherent Light Source x-ray free-electron laser. We study the K-shell emission from the helium- and lithium-like ions using Bragg crystal spectroscopy. Observation of the dielectronic satellites in lithium-like ions confirms that the M-shell electrons appear bound for these high charge states. An analysis of the intensity of these satellites indicates that when modeled with an atomic-kinetics code, the ionization potential depression model employed needs to produce depressions for these ions which lie between those predicted by the well known Stewart-Pyatt and Ecker-Kroll models. These results are largely consistent with recent density functional theory calculations.

Numerical investigation of nonequilibrium electron effects on the collisional ionization rate in the collisional-radiative model.

The interplay of kinetic electron physics and atomic processes in ultrashort laser-plasma interactions provides a comprehensive understanding of the impact of the electron energy distribution on plasma properties. Notably, nonequilibrium electrons play a vital role in collisional ionization, influencing ionization degrees and spectra. This paper introduces a computational model that integrates the physics of kinetic electrons and atomic processes, utilizing a Boltzmann equation for nonequilibrium electrons and a collisional-radiative model for atomic state populations. The model is used to investigate the influence of nonequilibrium electrons on collisional ionization rates and its effect on the population distribution, as observed in a widely known experiment [Young et al., Nature (London) 466, 56 (2010)0028-083610.1038/nature09177]. The study reveals a significant nonequilibrium electron presence during XFEL-matter interactions, profoundly affecting collisional ionization rates in the gas plasma, thereby necessitating careful consideration of the Collisional-Radiative model applied to such systems.

Recommended electron-impact excitation and ionization cross sections for Be I.

Analytic fits to the recommended electron-impact excitation and ionization cross sections for Be I are presented. The lowest 19 terms of configurations 2snl (n ≤ 4) and 2p 2 terms below the first ionization limit are considered. The fits are based on the accurate calculations with the convergent close coupling (CCC) method as well as the B-spline R-matrix (BSR) approach. The fitted cross sections provide rate coefficients that are believed to approximate the original data within 10% with very few exceptions. The oscillator strengths for the dipole-allowed transitions between all the considered states are calculated with the relativistic multi-configuration Dirac-Hartree-Fock (MCDHF) approach and compared with the CCC and BSR results. This comparison shows a very good agreement except for a handful of cases with likely strong cancellations.

Diagnosis of warm dense conditions in foil targets heated by intense femtosecond laser pulses using Kα imaging spectroscopy.

Warm dense conditions in titanium foils irradiated with intense femtosecond laser pulses are diagnosed using an x-ray imaging spectroscopy technique. The line shapes of radially resolved titanium Kα spectra are measured with a toroidally bent GaAs crystal and an x-ray charge-coupled device. Measured spectra are compared with the K-shell emissions modeled using an atomic kinetics - spectroscopy simulation code. Kα line shapes are strongly affected by warm (5-40 eV) bulk electron temperatures and imply multiple temperature distributions in the targets. The spatial distribution of temperature is dependent on the target thickness, and a thin target shows an advantage to generate uniform warm dense conditions in a large area.

Clocking Femtosecond Collisional Dynamics via Resonant X-Ray Spectroscopy.

Electron-ion collisional dynamics is of fundamental importance in determining plasma transport properties, nonequilibrium plasma evolution, and electron damage in diffraction imaging applications using bright x-ray free-electron lasers (FELs). Here we describe the first experimental measurements of ultrafast electron impact collisional ionization dynamics using resonant core-hole spectroscopy in a solid-density magnesium plasma, created and diagnosed with the Linac Coherent Light Source x-ray FEL. By resonantly pumping the 1s→2p transition in highly charged ions within an optically thin plasma, we have measured how off-resonance charge states are populated via collisional processes on femtosecond time scales. We present a collisional cross section model that matches our results and demonstrates how the cross sections are enhanced by dense-plasma effects including continuum lowering. Nonlocal thermodynamic equilibrium collisional radiative simulations show excellent agreement with the experimental results and provide new insight on collisional ionization and three-body-recombination processes in the dense-plasma regime.

Observation of Reverse Saturable Absorption of an X-ray Laser.

A nonlinear absorber in which the excited state absorption is larger than the ground state can undergo a process called reverse saturable absorption. It is a well-known phenomenon in laser physics in the optical regime, but is more difficult to generate in the x-ray regime, where fast nonradiative core electron transitions typically dominate the population kinetics during light matter interactions. Here, we report the first observation of decreasing x-ray transmission in a solid target pumped by intense x-ray free electron laser pulses. The measurement has been made below the K-absorption edge of aluminum, and the x-ray intensity ranges are 10^{16} -10^{17} W/cm^{2}. It has been confirmed by collisional radiative population kinetic calculations, underscoring the fast spectral modulation of the x-ray pulses and charge states relevant to the absorption and transmission of x-ray photons. The processes shown through detailed simulations are consistent with reverse saturable absorption, which would be the first observation of this phenomena in the x-ray regime. These light matter interactions provide a unique opportunity to investigate optical transport properties in the extreme state of matters, as well as affording the potential to regulate ultrafast x-ray free-electron laser pulses.

Measurements of the K-Shell Opacity of a Solid-Density Magnesium Plasma Heated by an X-Ray Free-Electron Laser.

We present measurements of the spectrally resolved x rays emitted from solid-density magnesium targets of varying sub-µm thicknesses isochorically heated by an x-ray laser. The data exhibit a largely thickness-independent source function, allowing the extraction of a measure of the opacity to K-shell x rays within well-defined regimes of electron density and temperature, extremely close to local thermodynamic equilibrium conditions. The deduced opacities at the peak of the Kα transitions of the ions are consistent with those predicted by detailed atomic-kinetics calculations.

Review of the 9th NLTE code comparison workshop.

We review the 9th NLTE code comparison workshop, which was held in the Jussieu campus, Paris, from November 30th to December 4th, 2015. This time, the workshop was mainly focused on a systematic investigation of iron NLTE steady-state kinetics and emissivity, over a broad range of temperature and density. Through these comparisons, topics such as modeling of the dielectronic processes, density effects or the effect of an external radiation field were addressed. The K-shell spectroscopy of iron plasmas was also addressed, notably through the interpretation of tokamak and laser experimental spectra.

Development of a krypton-doped gas symmetry capsule platform for x-ray spectroscopy of implosion cores on the NIF.

The electron temperature at stagnation of an ICF implosion can be measured from the emission spectrum of high-energy x-rays that pass through the cold material surrounding the hot stagnating core. Here we describe a platform developed on the National Ignition Facility where trace levels of a mid-Z dopant (krypton) are added to the fuel gas of a symcap (symmetry surrogate) implosion to allow for the use of x-ray spectroscopy of the krypton line emission.

Measurements of continuum lowering in solid-density plasmas created from elements and compounds.

The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations.

Free-electron X-ray laser measurements of collisional-damped plasmons in isochorically heated warm dense matter.

We present the first highly resolved measurements of the plasmon spectrum in an ultrafast heated solid. Multi-keV x-ray photons from the Linac Coherent Light Source have been focused to one micrometer diameter focal spots producing solid density aluminum plasmas with a known electron density of n_{e}=1.8×10^{23} cm^{-3}. Detailed balance is observed through the intensity ratio of up- and down-shifted plasmons in x-ray forward scattering spectra measuring the electron temperature. The plasmon damping is treated by electron-ion collision models beyond the Born approximation to determine the electrical conductivity of warm dense aluminum.

Investigation of femtosecond collisional ionization rates in a solid-density aluminium plasma.

The rate at which atoms and ions within a plasma are further ionized by collisions with the free electrons is a fundamental parameter that dictates the dynamics of plasma systems at intermediate and high densities. While collision rates are well known experimentally in a few dilute systems, similar measurements for nonideal plasmas at densities approaching or exceeding those of solids remain elusive. Here we describe a spectroscopic method to study collision rates in solid-density aluminium plasmas created and diagnosed using the Linac Coherent light Source free-electron X-ray laser, tuned to specific interaction pathways around the absorption edges of ionic charge states. We estimate the rate of collisional ionization in solid-density aluminium plasmas at temperatures ~30 eV to be several times higher than that predicted by standard semiempirical models.

Saturable absorption of an x-ray free-electron-laser heated solid-density aluminum plasma.

High-intensity x-ray pulses from an x-ray free-electron laser are used to heat and probe a solid-density aluminum sample. The photon-energy-dependent transmission of the heating beam is studied through the use of a photodiode. Saturable absorption is observed, with the resulting transmission differing significantly from the cold case, in good agreement with atomic-kinetics simulations.

A proteomic analysis using an animal model for hyperlipidemia-related erectile dysfunction.

To investigate the pathogenesis of hyperlipidemia-related erectile dysfunction and the effects of DA-8159, a new phosphodiesterase-5 inhibitor, on protein expression, we performed a proteomic analysis of differentially expressed proteins in the corpus cavernosum of hyperlipidemic rats by two-dimensional electrophoresis-mass spectrometry. Rats were fed high-cholesterol diet and treated with 5 mg·kg(-1)·day(-1) DA-8159 concurrently. After 5 months apparent hyperlipidemia and significantly decreased maximal intra-cavernous pressure were observed in the control group with the alteration of 8 proteins, which were restored by DA-8159 treatment. The proteins whose levels decreased >2-fold and attenuated by DA-8159 were determined alcohol dehydrogenase, aldolase A, annexin 1, and tropomyosin-rat, whereas proteins increased>2-fold and recovered by DA-8159 were found to be aldehyde dehydrogenase complex, guanine deaminase, creatine kinase-B, and phosphoglycerate mutase type B subunit.

Alterations in white matter microstructures and cognitive dysfunctions in benign childhood epilepsy with centrotemporal spikes.

BACKGROUND AND PURPOSE: Although benign childhood epilepsy with centrotemporal spikes (BECTS) is known to have good prognosis, patients often manifest neuropsychological impairments. This study aimed to investigate cognitive dysfunctions and their relationship with white matter microstructural changes in BECTS patients. METHODS: Nineteen BECTS and 25 normal subjects aged 7-16 years were included. Neuropsychological performances were assessed by the Wechsler Intelligence Scale for Children III, executive function tests, verbal and visuospatial memory tests, the verbal fluency and Boston naming tests. Diffusion tensor imaging (DTI) was performed to measure the fractional anisotropy (FA), axial (AD), radial (RD), and mean diffusivities (MD). The voxel-wise tract-based spatial statistics and region of interest methods were used for DTI, and their correlations with cognitive variables were analyzed. RESULTS: Patients with BECTS had lower intelligence quotient (IQ) scores compared with those of the control group. Higher AD and MD values were found in the left superior longitudinal fasciculus, the retrolenticular part of the internal capsule, posterior thalamic radiation, sagittal stratum and the body of the corpus callosum in BECTS patients compared with controls. Lower performances in verbal IQ, freedom from distractibility and processing speed were correlated with higher AD in the left superior fronto-occipital fasciculus, and lower verbal IQ scores were correlated with decreased FA values in the splenium of the corpus callosum in these patients. CONCLUSIONS: White matter microstructural changes predominantly in the left hemisphere might contribute to their cognitive abnormalities especially verbal IQ in BECTS patients.

Endoscopic management of pediatric sinonasal schwannoma: case report.

OBJECTIVES: To describe an extremely rare pediatric sinonasal schwannoma, and to reviewmanagement strategies and relevant literature. METHODS: Case report of pediatric sinonasal schwannoma, that was imaged with computed tomography and magnetic resonance imaging and managed endoscopically. Immunohistochemical analysis was performed to determine pathology. RESULTS: A 12-year-old girl presented with a 2-month history of progressive left exophthalmos. Imaging studies showed a large heterogeneous tumour arising from the ethmoid sinus and extending to the base of the skull and to the orbital cavity. The lesion was removed with an endonasal radical excision. The final pathological diagnosis was schwannoma. There was no tumour recurrence or any major complication during the 2-year follow up. CONCLUSION: Schwannoma should be considered in the differential diagnosis for pediatric patients with intranasal masses. Depending on the location and extent of the tumour, endonasal endoscopic excision could be a suitable management strategy.

Observations of the effect of ionization-potential depression in hot dense plasma.

The newly commissioned Orion laser system has been used to study dense plasmas created by a combination of short pulse laser heating and compression by laser driven shocks. Thus the plasma density was systematically varied between 1 and 10 g/cc by using aluminum samples buried in plastic foils or diamond sheets. The aluminum was heated to electron temperatures between 500 and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. The K-shell spectra show the effect of the ionization potential depression as a function of density. The data are compared to simulated spectra which account for the change in the ionization potential by the commonly used Stewart and Pyatt prescription and an alternative due to Ecker and Kröll suggested by recent x-ray free-electron laser experiments. The experimental data are in closer agreement with simulations using the model of Stewart and Pyatt.

Clinical and histopathological study of Charcot-Marie-Tooth neuropathy with a novel S90W mutation in BSCL2.

The objective of the study was to investigate the disease-causing mutation in an autosomal dominant Charcot-Marie-Tooth disease type 2 family and examine the clinical and histopathological evaluation. We enrolled a family of Korean origin with axonal Charcot-Marie-Tooth disease neuropathy (FC305; 13 males, six females) and applied genome-wide linkage analysis. Whole exome sequencing was performed for two patients. In addition, sural nerve biopsies were obtained from two patients. Through whole exome sequencing, we identified an average of 20,336 coding variants from two patients. We also found evidence of linkage mapped to chromosome 11p11-11q13.3 (LOD score of 3.6). Among these variants in the linkage region, we detected a novel p.S90W mutation in the Berardinelli-Seip congenital lipodystrophy 2 (BSCL2) gene, after filtering 31 Korean control exomes. Our p.S90W patients had frequent sensory disturbances, pyramidal tract signs, and predominant right thenar muscle atrophy in comparison with reported p.S90L patients. The phenotypic spectra were wide and demonstrated intrafamilial variability. Two patients with different clinical features underwent sural nerve biopsies; the myelinated fiber densities were increased slightly in both patients, which differed from two previous case reports of BSCL2 mutations (p.S90L and p.N88S). This report expands the variability of the clinical spectrum associated with the BSCL2 gene and describes the first family with the p.S90W mutation.

Direct measurements of the ionization potential depression in a dense plasma.

We have used the Linac Coherent Light Source to generate solid-density aluminum plasmas at temperatures of up to 180 eV. By varying the photon energy of the x rays that both create and probe the plasma, and observing the K-α fluorescence, we can directly measure the position of the K edge of the highly charged ions within the system. The results are found to disagree with the predictions of the extensively used Stewart-Pyatt model, but are consistent with the earlier model of Ecker and Kröll, which predicts significantly greater depression of the ionization potential.