Erratum: Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter [Phys. Rev. Lett. 120, 025002 (2018)].

This corrects the article DOI: 10.1103/PhysRevLett.120.025002.

Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter.

This Letter presents a novel approach to study electron transport in warm dense matter. It also includes the first x-ray Thomson scattering (XRTS) measurement from low-density CH foams compressed by a strong laser-driven shock at the OMEGA laser facility. The XRTS measurement is combined with velocity interferometry (VISAR) and optical pyrometry (SOP) providing a robust measurement of thermodynamic conditions in the shock. Evidence of significant preheat contributing to elevated temperatures reaching 17.5-35 eV in shocked CH foam is measured by XRTS. These measurements are complemented by abnormally high shock velocities observed by VISAR and early emission seen by SOP. These results are compared to radiation hydrodynamics simulations that include first-principles treatment of nonlocal electron transport in warm dense matter with excellent agreement. Additional simulations confirm that the x-ray contribution to this preheat is negligible.

Free Energy Based Equation of State for Pentaerythritol Tetranitrate.

An equation of state for the energetic molecular crystal pentaerythritol tetranitrate (PETN) has been developed from a parametrized model for its Helmholtz free energy. The ion motion contribution to the free energy is represented by a sum of Debye models for the vibrational modes of mainly lattice phonon and intramolecular character. The dependence of the frequencies of the normal modes on density is captured using the quasi-harmonic approximation whereby the Debye temperatures for both populations of modes depend explicitly on specific volume. The dependence of the Debye temperatures on specific volume was parametrized to normal-mode frequencies computed from solid state dispersion-corrected density functional theory. The model provides a good description of the thermophysical properties of PETN. The equation of state has been applied to the calculation of thermodynamic states along the principal Hugoniot of single crystal PETN.

Equation of state measurements of warm dense carbon using laser-driven shock and release technique.

We present a new approach to equation of state experiments that utilizes a laser-driven shock and release technique combined with spatially resolved x-ray Thomson scattering, radiography, velocity interferometry, and optical pyrometry to obtain independent measurements of pressure, density, and temperature for carbon at warm dense matter conditions. The uniqueness of this approach relies on using a laser to create very high initial pressures to enable a very deep release when the shock moves into a low-density pressure standard. This results in material at near normal solid density and temperatures around 10 eV. The spatially resolved Thomson scattering measurements facilitate a temperature determination of the released material by isolating the scattering signal from a specific region in the target. Our results are consistent with quantum molecular dynamics calculations for carbon at these conditions and are compared to several equation of state models.

Monte Carlo N-Particle forward modeling for density reconstruction of double shell capsule radiographs.

In the Double Shell Inertial Confinement Fusion concept, characterizing the shape asymmetry of imploding metal shells is vital for understanding energy-efficient compression and radiative losses of the thermonuclear fuel. The Monte Carlo N-Particle MCNP® code forward models radiography of Double Shell capsule implosions using the Advanced Radiographic Capability at the National Ignition Facility. A procedure is developed for using MCNP to reconstruct density profiles from the radiograph image intensity. For a given Double Shell imploding target geometry, MCNP radiographs predict image contrast, which can help guide experimental design. In future work, the calculated MCNP synthetic radiographs will be compared with experimental radiographs to determine the radial and azimuthal density profiles of the Double Shell capsules.

Squalene in petroleum asphaltenes.

Squalene, 2,6,10,15,19,23-hexamethyl-2,6,10,14,18,22-tetracosahexaene, a new biological marker, has been detected in various petroleum asphaltenes and their pyrolysis products. Since squalene is the most common triterpenoid in nature and the biological precursor of the important tetra- and pentacyclic triterpane markers, its detection in asphaltene suggests new ways for marker correlations.

Direct-drive double-shell implosion: A platform for burning-plasma physics studies.

Double-shell ignition designs have been studied with the indirect-drive inertial confinement fusion (ICF) scheme in both simulations and experiments in which the inner-shell kinetic energy was limited to ∼10-15 kJ, even driven by megajoule-class lasers such as the National Ignition Facility. Since direct-drive ICF can couple more energy to the imploding shells, we have performed a detailed study on direct-drive double-shell (D^{3}S) implosions with state-of-the-art physics models implemented in radiation-hydrodynamic codes (lilac and draco), including nonlocal thermal transport, cross-beam energy transfer (CBET), and first-principles-based material properties. To mitigate classical unstable interfaces, we have proposed the use of a tungsten-beryllium-mixed inner shell with gradient-density layers that can be made by magnetron sputtering. In our D^{3}S designs, a 70-µm-thick beryllium outer shell is driven symmetrically by a high-adiabat (α≥10), 1.9-MJ laser pulse to a peak velocity of ∼240 km/s. Upon spherical impact, the outer shell transfers ∼30-40 kJ of kinetic energy to the inner shell filled with deuterium-tritium gas or liquid, giving neutron-yield energies of ∼6 MJ in one-dimensional simulations. Two-dimensional high-mode draco simulations indicated that such high-adiabat D^{3}S implosions are not susceptible to laser imprint, but the long-wavelength perturbations from the laser port configuration along with CBET can be detrimental to the target performance. Nevertheless, neutron yields of ∼0.3-1.0-MJ energies can still be obtained from our high-mode draco simulations. The robust α-particle bootstrap is readily reached, which could provide a viable platform for burning-plasma physics studies. Once CBET mitigation and/or more laser energy becomes available, we anticipate that break-even or moderate energy gain might be feasible with the proposed D^{3}S scheme.

Association between radiographic severity of rheumatoid arthritis and shared epitope alleles: differing mechanisms of susceptibility and protection.

OBJECTIVE: To investigate the association of a recently described classification of Human leukocyte antigen (HLA)-DRB1 shared epitope alleles with rheumatoid factors (RF) and anti-cyclic citrullinated peptide (CCP) production and radiological severity in rheumatoid arthritis (RA). METHODS: Patients with RA (n = 962) were studied. Genotyping of DRB1 alleles and assays for RF and anti-CCP were performed. Radiological severity was measured using the modified Larsen score. RESULTS: In accordance with previous reports, we found carriage of S2 alleles (K-R-A-A at positions 71-74) to be associated with more severe disease with a gene-dose effect (p = 0.0059), and also associated with the presence of anti-CCP and RF (p<0.001). Carriage of S1 alleles (D-E-R-A-A at positions 70-74) was associated with less severe disease (p = 0.01), however there was no association between S1 and either anti-CCP or RF, suggesting that the basis for this possible protective effect was not related to autoantibody-producing B cells. CONCLUSIONS: These data suggest that multiple biological mechanisms underlie the DRB1 association with rheumatoid arthritis severity.

Short pulse laser train for laser plasma interaction experiments.

A multiframe, high-time resolution pump-probe diagnostic consisting of a consecutive train of ultrashort laser pulses (approximately ps) has been developed for use with a chirped pulse amplification (CPA) system. A system of high quality windows is used to create a series of 1054 nm picosecond-laser pulses which are injected into the CPA system before the pulse stretcher and amplifiers. By adding or removing windows in the pulse train forming optics, the number of pulses can be varied. By varying the distance and thickness of the respective optical elements, the time in between the pulses, i.e., the time in between frames, can be set. In our example application, the CPA pulse train is converted to 527 nm using a KDP crystal and focused into a preformed plasma and the reflected laser light due to stimulated Raman scattering is measured. Each pulse samples different plasma conditions as the plasma evolves in time, producing more data on each laser shot than with a single short pulse probe. This novel technique could potentially be implemented to obtain multiple high-time resolution measurements of the dynamics of physical processes over hundreds of picoseconds or even nanoseconds with picosecond resolution on a single shot.

Experimental investigation of stimulated Raman and Brillouin scattering instabilities driven by two successive collinear picosecond laser pulses.

Backward stimulated Raman and Brillouin scattering (SRS and SBS) are experimentally investigated by using two successive 1-µm, 1.5-ps FWHM laser pulses. The collinear pulses, separated by 3 or 6 ps and of moderate laser intensities (∼2×10^{16}Wcm^{-2}), are fired into a preionized He plasma of density ∼2.5-6×10^{19}cm^{-3}. The electron plasma waves and ion acoustic waves, respectively driven by SRS and SBS, are analyzed through space- and time-resolved Thomson scattering. Depending on the laser and plasma parameters, we observe the effect of the first pulse on the time-resolved SRS and SBS signals of the second pulse. The measurements are found to qualitatively agree with the results of a large-scale particle-in-cell simulation.

Publisher's Note: Experimental investigation of stimulated Raman and Brillouin scattering instabilities driven by two successive collinear picosecond laser pulses [Phys. Rev. E 93, 043209 (2016)].

This corrects the article DOI: 10.1103/PhysRevE.93.043209.

Simulated performance of the optical Thomson scattering diagnostic designed for the National Ignition Facility.

An optical Thomson scattering diagnostic has been designed for the National Ignition Facility to characterize under-dense plasmas. We report on the design of the system and the expected performance for different target configurations. The diagnostic is designed to spatially and temporally resolve the Thomson scattered light from laser driven targets. The diagnostic will collect scattered light from a 50 × 50 × 200 µm volume. The optical design allows operation with different probe laser wavelengths. A deep-UV probe beam (λ0 = 210 nm) will be used to Thomson scatter from electron plasma densities of ∼5 × 1020 cm-3 while a 3ω probe will be used for plasma densities of ∼1 × 1019 cm-3. The diagnostic package contains two spectrometers: the first to resolve Thomson scattering from ion acoustic wave fluctuations and the second to resolve scattering from electron plasma wave fluctuations. Expected signal levels relative to background will be presented for typical target configurations (hohlraums and a planar foil).

Human cathepsin E produced in E. coli.

A cDNA for procathepsin E was generated from human gastric adenocarcinoma (AGS) cells, amplified by PCR and inserted into the T7 dependent vector pET 22b for expression in E. coli. Purification of the resultant product was accomplished simply, without the need to resort to column chromatography. The recombinant protein displayed comparable properties to those of its naturally occurring counterpart. The yield of homogeneous active enzyme obtained was approximately 3 mg per 40 g of cells. This is sufficient to permit crystallisation and structural analysis to begin and a mutagenesis programme to examine structure/activity relationships now to be undertaken.

Investigation of the covalent modification of the catalytic triad of human cytomegalovirus protease by pseudo-reversible beta-lactam inhibitors and a peptide chloromethylketone.

An investigation into the interaction between human cytomegalovirus (HCMV) protease and several beta-lactams, with characterization of the resulting acylenzymes using mass spectrometry, is reported. The time dependence of the inhibitors is highlighted by making comparisons of values obtained for inhibition and acylation. Analysis of inactivated HCMV protease revealed a beta-lactam: protease stoichiometry of 1. Subsequent enzymatic digestion with trypsin, peptide mapping using liquid chromatography coupled with electrospray ionization mass spectrometry and sequencing by nanoelectrospray tandem mass spectrometry (NanoES-MS/MS) allowed the identification of the site of covalent modification and confirmed Ser 132 as the active site hydroxyl nucleophile. Further, treatment of the protease with a peptide chloromethylketone and sequence analysis using NanoES-MS/MS of the alkylated enzyme confirmed His 63 as the active site imidazole nucleophile.

An efficient process for production of N-acetylneuraminic acid using N-acetylneuraminic acid aldolase.

N-acetyl-D-neuraminic acid (Neu5Ac) aldolase (EC 4.1.3.3) has bee reported for synthesis of Neu5Ac,1-5 but there are no reports of processes which do not have significant drawbacks for large-scale operation. Here, Neu5Ac aldolase from an overexpressing recombinant strain of Escherichia coli has been used to develop an immobilized enzyme process for production of Neu5Ac. The enzyme was immobilized onto Eupergit-C and could be reused many times in the reaction. Base-catalyzed epimerization of N-acetyl-D-glucosamine (GlcNAc) yielded GlcNAc/N-acetyl-D-mannosamine (ManNAc) mixtures (c 4:1) which could be used directly in the aldolase reaction; however, inhibition of the enzyme by GlcNAc limited the concentration of ManNAc which could be used in the reaction by this approach. This necessitated the addition of a large molar excess of pyruvate (five- to seven-fold) to drive the equilibrium over to Neu5Ac; nevertheless, a method has been developed to remove the excess pyruvate effectively by complexation with bisulfite, thus allowing Neu5Ac to be recovered by absorption onto an anion-exchange resin. In a second approach, a method has been developed to enrich GlcNAc/ManNAc mixtures for ManNAc. ManNAc can be used at high concentrations in the reaction, thus obviating the need to use a large molar excess of pyruvate. Neu5Ac can be isolated from such reaction mixtures by a simple crystallization. This work shows the importance of integrated process solutions for the effective scale-up of biotransformation reactions.

Enzymatic production of optically pure (2'R-cis)-2'-deoxy-3'-thiacytidine (3TC, lamivudine): a potent anti-HIV agent.

Although equipotent in terms of antiviral activity, the two enantiomers of 2'-deoxy-3'-thiacytidine (BCH 189) differ markedly in their cytotoxicity. (2'R-cis)-2'-deoxy-3'-thiacytidine (3TC) is substantially less toxic than its optical antipode, and is undergoing development for the therapy of HIV infection. Cytidine deaminase from Escherichia coli is shown here to deaminate 2'-deoxy-3'-thiacytidine enantioselectively to leave 3TC essentially optically pure. This reaction has been used to develop a process for production of 3TC in multikilogram amounts. The production of cytidine deaminase was enhanced by strain improvement, fermentation development, and finally by cloning and overexpression of the gene. The enzyme was immobilized on Eupergit-C, which allowed it to be reused many times. The biotransformation conditions were optimized so that the best use could be made of the catalyst. A robust scaleable product isolation process was developed to yield the crystalline product. Overall, yields through the resolution process of 76% were obtained. All aspects of this process are capable of substantial further scaleup with only minor modifications.

Temperature measurements of shocked silica aerogel foam.

We present recent results of equation-of-state (EOS) measurements of shocked silica (SiO_{2}) aerogel foam at the OMEGA laser facility. Silica aerogel is an important low-density pressure standard used in many high energy density experiments, including the novel technique of shock and release. Due to its many applications, it has been a heavily studied material and has a well-known Hugoniot curve. This work then complements the velocity and pressure measurements with additional temperature data providing the full EOS information within the warm dense matter regime for the temperature interval of 1-15 eV and shock velocities between 10 and 40 km/s corresponding to shock pressures of 0.3-2 Mbar. The experimental results were compared with hydrodynamic simulations and EOS models. We found that the measured temperature was systematically lower than suggested by theoretical calculations. Simulations provide a possible explanation that the emission measured by optical pyrometry comes from a radiative precursor rather than from the shock front, which could have important implications for such measurements.

Demonstration of x-ray fluorescence imaging of a high-energy-density plasma.

Experiments at the Trident Laser Facility have successfully demonstrated the use of x-ray fluorescence imaging (XRFI) to diagnose shocked carbonized resorcinol formaldehyde (CRF) foams doped with Ti. One laser beam created a shock wave in the doped foam. A second laser beam produced a flux of vanadium He-α x-rays, which in turn induced Ti K-shell fluorescence within the foam. Spectrally resolved 1D imaging of the x-ray fluorescence provided shock location and compression measurements. Additionally, experiments using a collimator demonstrated that one can probe specific regions within a target. These results show that XRFI is a capable alternative to path-integrated measurements for diagnosing hydrodynamic experiments at high energy density.

Imaging x-ray Thomson scattering spectrometer design and demonstration (invited).

In many laboratory astrophysics experiments, intense laser irradiation creates novel material conditions with large, one-dimensional gradients in the temperature, density, and ionization state. X-ray Thomson scattering is a powerful technique for measuring these plasma parameters. However, the scattered signal has previously been measured with little or no spatial resolution, which limits the ability to diagnose inhomogeneous plasmas. We report on the development of a new imaging x-ray Thomson spectrometer (IXTS) for the Omega laser facility. The diffraction of x-rays from a toroidally curved crystal creates high-resolution images that are spatially resolved along a one-dimensional profile while spectrally dispersing the radiation. This focusing geometry allows for high brightness while localizing noise sources and improving the linearity of the dispersion. Preliminary results are presented from a scattering experiment that used the IXTS to measure the temperature profile of a shocked carbon foam.

Phase-contrast imaging using ultrafast x-rays in laser-shocked materials.

High-energy x-rays, >10 keV, can be efficiently produced from ultrafast laser target interactions with many applications to dense target materials in inertial confinement fusion and high-energy density physics. These same x-rays can also be applied to measurements of low-density materials inside high-density Hohlraum environments. In the experiments presented, high-energy x-ray images of laser-shocked polystyrene are produced through phase contrast imaging. The plastic targets are nominally transparent to traditional x-ray absorption but show detailed features in regions of high density gradients due to refractive effects often called phase contrast imaging. The 200 TW Trident laser is used both to produce the x-ray source and to shock the polystyrene target. X-rays at 17 keV produced from 2 ps, 100 J laser interactions with a 12 µm molybdenum wire are used to produce a small source size, required for optimizing refractive effects. Shocks are driven in the 1 mm thick polystyrene target using 2 ns, 250 J, 532 nm laser drive with phase plates. X-ray images of shocks compare well to one-dimensional hydro calculations.