Idealized Slab Plasma approach for the study of Warm Dense Matter

Recently, warm dense matter (WDM) has emerged as an interdisciplinary field that draws increasing interest in plasma physics, condensed matter physics, high pressure science, astrophysics, inertial confinement fusion, as well as materials science under extreme conditions. To allow the study of well-defined WDM states, we have introduced the concept of idealized-slab plasmas that can be realized in the laboratory via (i) the isochoric heating of a solid and (ii) the propagation of a shock wave in a solid. The application of this concept provides new means for probing the dynamic conductivity, equation of state, ionization and opacity. These approaches are presented here using results derived from first-principles (density-functional type) theory, Thomas-Fermi type theory, and numerical simulations.Comment: 37 pages, 21 figures, available, pdf file only. To appear in: Laser and Particle beams. To appear more or less in this form in Laser and Particle beam

Enhanced mass activity and stability of bimetallic Pd-Ni nanoparticles on boron-doped diamond for direct ethanol fuel cell applications

In this work, electrochemical deposition of Pd (palladium) and bimetallic Pd-Ni (nickel) nanoparticles on oxygen-terminated boron-doped diamond (BDD) substrate is described for use as electrocatalyst in direct ethanol fuel cell. A potentiostatic two-step electrochemical method involving the electrodeposition of Ni nanoparticles on BDD followed by mono-dispersed Pd nanoparticles was used for the fabrication of Pd-Ni/BDD electrode. The electrocatalytic activity of the bimetallic Pd-Ni nanoparticles was evaluated in an alkaline solution containing ethanol and compared to that of the Pd nanoparticles alone. The bimetallic Pd-Ni nanoparticles showed 2.4 times higher mass activity than the similar systems from literature as well as stability when operated in alkaline media. Higher electrochemical response towards the electrooxidation of ethanol observed for the bimetallic electrocatalysts was due to the synergistic effects of the electron interaction at the interface of the two metals. Chronopotentiometric measurements revealed that Pd is more stable when anchored to the Ni nanoparticles. The optimised loading of mono-dispersed Pd on a foreign Ni metal as nanoparticles plays a crucial role in achieving a high mass (3.63 x 106 mA/g) and specific (10.53 mA/cm2) electrocatalytic activity of Pd towards ethanol electrooxidation in alkaline media

Energy Levels and Transition Probabilities for Nitrogen-Like Fe xx

Energies of the 700 lowest levels in Fexx have been obtained using the multiconfiguration Dirac-Fock method. Configuration interaction method on the basis set of transformed radial orbitals with variable parameters taking into account relativistic corrections in the Breit-Pauli approximation was used to crosscheck our presented results. Transition probabilities, oscillator and line strengths are presented for electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transitions among these levels. The total radiative transition probabilities from each level are also provided. Results are compared with data compiled by NIST and with other theoretical work

Measurement of L-shell emission from mid-Z targets under non-LTE conditions using Transmission Grating Spectrometer and DANTE power diagnostics

Producción CientíficaIn this work, we present the measurement of L-band emission from buried Sc/V targets in experiments performed at the OMEGA laser facility. The goal of these experiments was to study non-local thermodynamic equilibrium plasmas and benchmark atomic physics codes. The L-band emission was measured simultaneously by the time resolved DANTE power diagnostic and the recently fielded time integrated Soreq-Transmission Grating Spectrometer (TGS) diagnostic. The TGS measurement was used to support the spectral reconstruction process needed for the unfolding of the DANTE data. The Soreq-TGS diagnostic allows for broadband spectral measurement in the 120 eV–2000 eV spectral band, covering L- and M-shell emission of mid- and high-Z elements, with spectral resolution λ/Δλ = 8–30 and accuracy better than 25%. The Soreq-TGS diagnostic is compatible with ten-inch-manipulator platforms and can be used for a wide variety of high energy density physics, laboratory astrophysics, and inertial confinement fusion experiments

Reaching Isochoric States of Matter by Ultrashort-Pulse Proton Heating

The aim of this LDRD is to develop two completely new methods for creating and probing warm dense states of matter (plasmas at several eV at solid density), which will enable the direct measurement of fundamental material properties such as the opacity and equation of state (EOS). There is in this warm dense regime an almost complete lack of quantitative experimental data--primarily because of the difficulty in creating uniform, single temperature/density plasmas on which to make measurements. In an ideal case one would volumetrically heat a target with a very short burst of energy--simultaneously making measurements prior to the subsequent hydrodynamic expansion of the target. However, no mechanism for such rapid, uniform heating of a material currently exists. We propose to develop a completely new technique that has the potential for creating large uniform plasmas in local thermodynamic equilibrium (LTE) at warm dense conditions. This technique is based on volumetric heating of solid density targets with a high energy, high-flux, short-pulse, laser-produced proton beam. We also propose to use this beam of protons to probe high-Z, solid density matter with both 2-dimensional spatial resolution and picosecond temporal resolution. The combination of these two techniques will enable us to make the very first quantitative measurements of the equation of state and opacity of an isochorically heated state of matter

Facile electrochemical synthesis of Pd nanoparticles with enhanced electrocatalytic properties from surfactant-free electrolyte

Synthesis of low-dimensional metallic nanoparticles with a clean surface, high dispersibility, and enhanced atomic surface distribution is extremely important, as these factors strongly influence the electrocatalytic properties of the nanoparticles. In this study, the early stage electrochemical nucleation and growth of palladium nanoparticles (Pd NPs) under potentiostatic control has been investigated on a Au(111) textured substrate. The size distribution and structural characterization of the ex situ as-deposited Pd NPs by means of high-resolution field emission gun-scanning electron microscopy (FEG-SEM) at different stages combined with electrochemical measurements revealed that the cluster of nuclei grew independently through the reduction of metal ions. The electrodeposited Pd NPs were very pure, as confirmed by X-ray photoelectron spectroscopy (XPS), owing to the surfactant-free green electrodeposition process, and they exhibited a highly dispersed average particle size of 2–5 nm. The average nanoparticle size becomes smaller with higher overpotentials for the same deposition time. The synthesized Pd NPs demonstrated the largest specific surface area (four times that of commercial Pd−C) and electrocatalytic activity in ferrocyanide/ferricyanide redox and ethanol electrooxidation processes (35 times that of commercial Pd−C). This work represents an important step in achieving the fundamental understanding of nucleation and growth of nanoparticles correlating the electrocatalytic performances

Radiation Science Using Z-Pinch X-Rays

Present-day Z-pinch experiments generate 200 TW peak power, 5–10 ns duration x-ray bursts that provide new possibilities to advance radiation science. The experiments support both the underlying atomic and plasma physics, as well as inertial confinement fusion and astrophysics applications. A typical configuration consists of a sample located 1–10 cm away from the pinch, where it is heated to 10–100 eV temperatures by the pinch radiation. The spectrally-resolved sample-plasma absorption is measured by aiming x-ray spectrographs through the sample at the pinch. The pinch plasma thus both heats the sample and serves as a backlighter. Opacitymeasurements with this source are promising because of the large sample size, the relatively long radiation duration, and the possibility to measureopacities at temperatures above 100 eV. Initial opacity experiments are under way with CH-tamped NaBr foil samples. The Na serves as a thermometer and absorption spectra are recorded to determine the opacity of Br with a partially-filled M-shell. The large sample size and brightness of the Z pinch as a backlighter are also exploited in a novel method measuring re-emission from radiation-heated gold plasmas. The method uses a CH-tamped layered foil with Al+MgF2 facing the radiationsource. A gold backing layer that covers a portion of the foil absorbs radiation from the source and provides re-emission that further heats the Al+MgF2. The Al and Mg heating is measured using space-resolved Kα absorption spectroscopy and the difference between the two regions enables a determination of the gold re-emission. Measurements are also performed at lower densities where photoionization is expected to dominate over collisions. Absorption spectra have been obtained for both Ne-like Fe and He-like Ne, confirming production of the relevant charge states needed to benchmark atomic kinetics models. Refinement of the methods described here is in progress to address multiple issues for radiation science

TRH: Pathophysiologic and clinical implications

Thyrotropin releasing hormone is thought to be a tonic stimulator of the pituitary TSH secretion regulating the setpoint of the thyrotrophs to the suppressive effect of thyroid hormones. The peptide stimulates the release of normal and elevated prolactin. ACTH and GH may increase in response to exogenous TRH in pituitary ACTH and GH hypersecretion syndromes and in some extrapituitary diseases. The pathophysiological implications of extrahypothalamic TRH in humans are essentially unknown. The TSH response to TRH is nowadays widely used as a diganostic amplifier in thyroid diseases being suppressed in borderline and overt hyperthyroid states and increased in primary thyroid failure. In hypothyroid states of hypothalamic origin, TSH increases in response to exogenous TRH often with a delayed and/or exaggerated time course. But in patients with pituitary tumors and suprasellar extension TSH may also respond to TRH despite secondary hypothyroidism. This TSH increase may indicate a suprasellar cause for the secondary hypothyroidism, probably due to portal vessel occlusion. The TSH released in these cases is shown to be biologically inactive

X-ray Astronomy in the Laboratory with a Miniature Compact Object Produced by Laser-Driven Implosion

Laboratory spectroscopy of non-thermal equilibrium plasmas photoionized by intense radiation is a key to understanding compact objects, such as black holes, based on astronomical observations. This paper describes an experiment to study photoionizing plasmas in laboratory under well-defined and genuine conditions. Photoionized plasma is here generated using a 0.5-keV Planckian x-ray source created by means of a laser-driven implosion. The measured x-ray spectrum from the photoionized silicon plasma resembles those observed from the binary stars Cygnus X-3 and Vela X-1 with the Chandra x-ray satellite. This demonstrates that an extreme radiation field was produced in the laboratory, however, the theoretical interpretation of the laboratory spectrum significantly contradicts the generally accepted explanations in x-ray astronomy. This model experiment offers a novel test bed for validation and verification of computational codes used in x-ray astronomy.Comment: 5 pages, 4 figures are included. This is the original submitted version of the manuscript to be published in Nature Physic