A higher-than-predicted measurement of iron opacity at solar interior temperatures.

Nearly a century ago it was recognized that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models. A particular problem arose when refined photosphere spectral analysis led to reductions of 30-50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9-2.3 million kelvin and electron densities of (0.7-4.0) × 10(22) per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30-400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

Systematic Study of L-Shell Opacity at Stellar Interior Temperatures.

The first systematic study of opacity dependence on atomic number at stellar interior temperatures is used to evaluate discrepancies between measured and modeled iron opacity [J. E. Bailey et al., Nature (London) 517, 56 (2015)NATUAS0028-083610.1038/nature14048]. High-temperature (>180 eV) chromium and nickel opacities are measured with ±6%-10% uncertainty, using the same methods employed in the previous iron experiments. The 10%-20% experiment reproducibility demonstrates experiment reliability. The overall model-data disagreements are smaller than for iron. However, the systematic study reveals shortcomings in models for density effects, excited states, and open L-shell configurations. The 30%-45% underestimate in the modeled quasicontinuum opacity at short wavelengths was observed only from iron and only at temperature above 180 eV. Thus, either opacity theories are missing physics that has nonmonotonic dependence on the number of bound electrons or there is an experimental flaw unique to the iron measurement at temperatures above 180 eV.

Benchmark Experiment for Photoionized Plasma Emission from Accretion-Powered X-Ray Sources.

The interpretation of x-ray spectra emerging from x-ray binaries and active galactic nuclei accreted plasmas relies on complex physical models for radiation generation and transport in photoionized plasmas. These models have not been sufficiently experimentally validated. We have developed a highly reproducible benchmark experiment to study spectrum formation from a photoionized silicon plasma in a regime comparable to astrophysical plasmas. Ionization predictions are higher than inferred from measured absorption spectra. Self-emission measured at adjustable column densities tests radiation transport effects, demonstrating that the resonant Auger destruction assumption used to interpret black hole accretion spectra is inaccurate.

Development and integration of photonic Doppler velocimetry as a diagnostic for radiation driven experiments on the Z-machine.

Plasma density measurements are key to a wide variety of high-energy-density (HED) and laboratory astrophysics experiments. We present a creative application of photonic Doppler velocimetry (PDV) from which time- and spatially resolved electron density measurements can be made. PDV has been implemented for the first time in close proximity, ∼6 cm, to the high-intensity radiation flux produced by a z-pinch dynamic hohlraum on the Z-machine. Multiple PDV probes were incorporated into the photoionized gas cell platform. Two probes, spaced 4 mm apart, were used to assess plasma density and uniformity in the central region of the gas cell during the formation of the plasma. Electron density time histories with subnanosecond resolution were extracted from PDV measurements taken from the gas cells fielded with neon at 15 Torr. As well, a null shot with no gas fill in the cell was fielded. A major achievement was the low noise high-quality measurements made in the harsh environment produced by the mega-joules of x-ray energy emitted at the collapse of the z-pinch implosion. To evaluate time dependent radiation induced effects in the fiber optic system, two PDV noise probes were included on either side of the gas cell. The success of this alternative use of PDV demonstrates that it is a reliable, precise, and affordable new electron density diagnostic for radiation driven experiments and more generally HED experiments.

Background measurement methods for opacity experiments conducted at the Z facility.

Laboratory experiments typically test opacity models by measuring spectrally resolved transmission of a sample using bright backlight radiation. A potential problem is that any unaccounted background signal contaminating the spectrum will artificially reduce the inferred opacity. Methods developed to measure background signals in opacity experiments at the Sandia Z facility are discussed. Preliminary measurements indicate that backgrounds are 9%-11% of the backlight signal at wavelengths less than 10 Å. Background is thus a relatively modest correction for all Z opacity data published to date. Future work will determine how important background is at longer wavelengths.

Observation of ionization trends in a laboratory photoionized plasma experiment at Z.

We report experimental and modeling results for the charge state distribution of laboratory photoionized neon plasmas in the first systematic study over nearly an order of magnitude range of ionization parameter ξ∝F/N_{e}. The range of ξ is achieved by flexibility in the experimental platform to adjust either the x-ray drive flux F at the sample or the electron number density N_{e} or both. Experimental measurements of photoionized plasma conditions over such a range of parameters enable a stringent test of atomic kinetics models used within codes that are applied to photoionized plasmas in the laboratory and astrophysics. From experimental transmission data, ion areal densities are extracted by spectroscopic analysis that is independent of atomic kinetics modeling. The measurements reveal the net result of the competition between photon-driven ionization and electron-driven recombination atomic processes as a function of ξ as it affects the charge state distribution. Results from radiation-hydrodynamics modeling calculations with detailed inline atomic kinetics modeling are compared with the experimental results. There is good agreement in the mean charge and overall qualitative similarities in the trends observed with ξ but significant quantitative differences in the fractional populations of individual ions.

X-ray heating and electron temperature of laboratory photoionized plasmas.

We discuss the experimental and modeling results for the x-ray heating and temperature of laboratory photoionized plasmas. A method is used to extract the electron temperature based on the analysis of transmission spectroscopy data that is independent of atomic kinetics modeling. The results emphasized the critical role of x-ray heating and radiation cooling in determining the energy balance of the plasma. They also demonstrated the dramatic impact of photoexcitation on excited-state populations, line emissivity, and radiation cooling. Modeling calculations performed with astrophysical codes significantly overestimated the measured temperature.

Toward a science of metabolic engineering.

Application of recombinant DNA methods to restructure metabolic networks can improve production of metabolite and protein products by altering pathway distributions and rates. Recruitment of heterologous proteins enables extension of existing pathways to obtain new chemical products, alter posttranslational protein processing, and degrade recalcitrant wastes. Although some of the experimental and mathematical tools required for rational metabolic engineering are available, complex cellular responses to genetic perturbations can complicate predictive design.

Characterization of bacterial growth by means of flow microfluorometry.

By means of flow microfluorometry, the protein and nucleic acid contents of individual bacterial cells may be measured at the rate of several thousand cells per second. Accumulation of such information over a few minutes yields the composition distribution of the microbial population. These distributions have been determined at different times during batch growth of Bactillus subtilis, and the results indicate that the variance of cell composition decreases as the population passes through the exponential into the stationary phase. The relative abundance of endospores and vegetative cells as well as the protein distributions of these subpopulations may be readily determined from flow microfluorometry data. Experimental access to such details of microbial population dynamics should foster improved understanding of cell growth, spore germination, and spore formation kinetics.

A comparison of the effects of a subtype selective and non-selective benzodiazepine receptor agonist in two CO(2) models of experimental human anxiety.

Studies in human volunteers that can demonstrate proof of concept are attractive in that possible mechanisms and potential new drug treatments can be examined. We have been developing models of anxiety disorders using the inhalation of 7.5% CO(2) for 20 min to model generalised anxiety disorder, as well as using the previously reported 35% CO(2) as a model for panic anxiety. In a double-blind, placebo-controlled, three-way crossover study in 12 healthy volunteer subjects, we compared a full agonist at the benzodiazepine receptor that binds to four alpha-subtypes of the receptor (alpha-1,-2,-3,-5) (alprazolam 1 mg), with zolpidem (5 mg), an agonist selective for the alpha-1 subtype of the gamma amino butyric acid-receptor subtype A (GABA-A) receptor, which is a widely used hypnotic drug. Compared with placebo, both drugs significantly attenuated peak CO(2)-induced changes in subjective feelings after the inhalation of 7.5% CO(2) for 20 min. However, there were fewer significant differences after a single vital capacity inhalation of 35% CO(2), where zolpidem was less efficacious than alprazolam at reducing CO(2)-induced symptoms. In conclusion, our results show that zolpidem shows some anxiolytic efficacy in the 7.5% CO(2) model, similar to alprazolam, and this is the first report of such an effect of zolpidem in a model of anxiety. These and other studies of benzodiazepines in clinical and volunteer studies suggest a definite role of the GABA-A receptor in CO(2)-induced anxiety, and it would be of interest to examine other GABA-A receptor subtype selective drugs, which are now in early phase clinical studies and are showing selective efficacy in pharmacodynamic studies.

A compact multi-plane broadband (0.5-17 keV) spectrometer using a single acid phthalate crystal.

Acid phthalate crystals such as KAP crystals are a method of choice to record x-ray spectra in the soft x-ray regime (E ∼ 1 keV) using the large (001) 2d = 26.63 Šspacing. Reflection from many other planes is possible, and knowledge of the 2d spacing, reflectivity, and resolution for these reflections is necessary to evaluate whether they hinder or help the measurements. Burkhalter et al. [J. Appl. Phys., 52, 4379 (1981)] showed that the (013) reflection has efficiency comparable to the 2nd order reflection (002), and it can overlap the main first order reflection when the crystal bending axis ( b -axis) is contained in the dispersion plane, thus contaminating the main (001) measurement in a convex crystal geometry. We present a novel spectrograph concept that makes these asymmetric reflections helpful by setting the crystal b -axis perpendicular to the dispersion plane. In such a case, asymmetric reflections do not overlap with the main (001) reflection and each reflection can be used as an independent spectrograph. Here we demonstrate an achieved spectral range of 0.8-13 keV with a prototype setup. The detector measurements were reproduced with a 3D ray-tracing code.

A randomized trial to determine the change in alanine aminotransferase during 10 days of paracetamol (acetaminophen) administration in subjects who consume moderate amounts of alcohol.

BACKGROUND: Previous studies have suggested that therapeutic doses of paracetamol (acetaminophen) are safe in alcoholic patients when administered for up to 3 days. However, 14 days of therapeutic doses of paracetamol has been associated with an increase in serum transaminases. AIM: To determine the effect of 10 days of the maximal therapeutic dose of paracetamol on serum alanine aminotransferase (ALT) activity in subjects who consume 1 to 3 alcoholic beverages per day. METHODS: This was a randomized, double blind, placebo-controlled trial. Subjects took 4 g of paracetamol (or placebo) daily for 10 days. Serum aspartate aminotransferase (AST), ALT, bilirubin and INR were measured at baseline, day 4 and day 11. Symptoms potentially related to liver injury were also recorded. RESULTS: Paracetamol and placebo groups had no change from baseline values at day 4, but the paracetamol group had an increase in mean ALT at day 11 of 8.7 IU/L. No subject developed symptoms of liver injury or met predefined criteria for hepatotoxicity or liver failure. CONCLUSION: Therapeutic dosing of paracetamol administered for 10 days appears to elevate serum ALT in moderate drinkers, but does not produce clinically evident liver injury.

D-Cycloserine and performance under different states of anxiety in healthy volunteers.

RATIONALE: There is interest in the development of augmentation therapy in the treatment of anxiety disorders. Recent publications have shown that D-cycloserine can benefit exposure therapy in a group of acrophobic (height phobic) subjects and in patients with social anxiety disorder. These studies were based on the animal data suggesting that drugs acting to enhance glutamate function may be developed to accelerate the behavioural treatment of anxiety disorders. Perhaps by enhancing glutamate/N-methyl-D-aspartate receptor function, learning is thus enhanced. This study examines the effects of D-cycloserine 50 mg on a task that involves learning. We manipulated anxiety levels to model the effects of high anxiety. OBJECTIVES: To evaluate performance and learning, we used the Manikin task. Two groups of 24 healthy volunteers participated in a double-blind, placebo-controlled study. One group received the inhalation of CO(2) 7.5% to model high anxiety, and the second group received air to represent lower anxiety. Subjects received D-cycloserine 50 mg or placebo, and the Manikin task was performed during the gas inhalation. RESULTS: There were significant differences in the group inhaling air, but not CO(2), with the D-cycloserine group showing an increase in correct responses. This difference was apparent at several time blocks during the 20-min task. These findings were supported by subjective measures in that participants who received D-cycloserine reported that the task was easier. CONCLUSIONS: We have shown that at lower anxiety levels, D-cycloserine 50 mg improved the performance of this challenging visuospatial cognitive task. This increase in performance was not seen when anxiety was higher, and D-cycloserine did not appear to increase subjective anxiety. These data lend support to the use of D-cycloserine and related glutamate enhancers as cognitive modulators and suggest that the actions of D-cycloserine are not simply related to increased arousal or anxiety.

Effect of ARS1 mutations on chromosome stability in Saccharomyces cerevisiae.

We have used a set of deletion mutations in the ARS1 element of Saccharomyces cerevisiae to measure their effect on chromosome stability. This work establishes the previously proposed existence of three domains in ARS1. Domain C, which we have previously inferred, but not proved, to be a part of ARS1, is now established. In addition, we show that increasingly large deletions of the domain have increasingly large effects, which was not realized before. Furthermore, we have provided the first positive evidence for the central importance of a 14-base-pair core sequence containing the ARS consensus element by showing that it has the ability to act as a replicator on a plasmid containing no other ARS1 flanking sequence. The method of analyzing plasmid stability used in our study employs a novel and sensitive flow cytometry assay for beta-galactosidase. We discuss ways in which flow cytometry, based on this assay, could be generalized beyond its particular application in this work to studying other aspects of the cell biology of yeast and higher cells. The actual flow cytometry method will be described in detail elsewhere.

DNA polymerase I is required for premeiotic DNA replication and sporulation but not for X-ray repair in Saccharomyces cerevisiae.

We have used a set of seven temperature-sensitive mutants in the DNA polymerase I gene of Saccharomyces cerevisiae to investigate the role of DNA polymerase I in various aspects of DNA synthesis in vivo. Previously, we showed that DNA polymerase I is required for mitotic DNA replication. Here we extend our studies to several stages of meiosis and repair of X-ray-induced damage. We find that sporulation is blocked in all of the DNA polymerase temperature-sensitive mutants and that premeiotic DNA replication does not occur. Commitment to meiotic recombination is only 2% of wild-type levels. Thus, DNA polymerase I is essential for these steps. However, repair of X-ray-induced single-strand breaks is not defective in the DNA polymerase temperature-sensitive mutants, and DNA polymerase I is therefore not essential for repair of such lesions. These results suggest that DNA polymerase II or III or both, the two other nuclear yeast DNA polymerases for which roles have not yet been established, carry out repair in the absence of DNA polymerase I, but that DNA polymerase II and III cannot compensate for loss of DNA polymerase I in meiotic replication and recombination. These results do not, however, rule out essential roles for DNA polymerase II or III or both in addition to that for DNA polymerase I.

Deletion mutations affecting autonomously replicating sequence ARS1 of Saccharomyces cerevisiae.

DNAs that contain specific yeast chromosomal sequences called ARSs transform Saccharomyces cerevisiae at high frequency and can replicate extrachromosomally as plasmids when introduced into S. cerevisiae by transformation. To determine the boundaries of the minimal sequences required for autonomous replication in S. cerevisiae, we have carried out in vitro mutagenesis of the first chromosomal ARS described, ARS1. Rather than identifying a distinct and continuous segment that mediates the ARS+ phenotype, we find three different functional domains within ARS1. We define domain A as the 11-base-pair (bp) sequence that is also found at most other ARS regions. It is necessary but not sufficient for high-frequency transformation. Domain B, which cannot mediate high-frequency transformation, or replicate by itself, is required for efficient, stable replication of plasmids containing domain A. Domain B, as we define it, is continuous with domain A in ARS1, but insertions of 4 bp between the two do not affect replication. The extent of domain B has an upper limit of 109 bp and a lower limit of 46 bp in size. There is no obvious sequence homology between domain B of ARS1 and any other ARS sequence. Finally, domain C is defined on the basis of our deletions as at least 200 bp flanking domain A on the opposite side from domain B and is also required for the stability of domain A in S. cerevisiae. The effect of deletions of domain C can be observed only in the absence of domain B, at least by the assays used in the current study, and the significance of this finding is discussed.

A mathematical model of caspase function in apoptosis.

Caspases (cysteine-containing aspartate-specific proteases) are at the core of the cell's suicide machinery. These enzymes, once activated, dismantle the cell by selectively cleaving key proteins after aspartate residues. The events culminating in caspase activation are the subject of intense study because of their role in cancer, and neurodegenerative and autoimmune disorders. Here we present a mechanistic mathematical model, formulated on the basis of newly emerging information, describing key elements of receptor-mediated and stress-induced caspase activation. We have used mass-conservation principles in conjunction with kinetic rate laws to formulate ordinary differential equations that describe the temporal evolution of caspase activation. Qualitative strategies for the prevention of caspase activation are simulated and compared with experimental data. We show that model predictions are consistent with available information. Thus, the model could aid in better understanding caspase activation and identifying therapeutic approaches promoting or retarding apoptotic cell death.

Transgenic tobacco expressing Vitreoscilla hemoglobin exhibits enhanced growth and altered metabolite production.

The gene for Vitreoscilla hemoglobin (VHb) has been introduced and expressed in Nicotiana tabaccum (tobacco). Transgenic tobacco plants expressing VHb exhibited enhanced growth, on average 80-100% more dry weight after 35 days of growth compared to wild-type controls. Furthermore, germination time is reduced from 6-8 days for wild-type tobacco to 3-4 days and the growth phase from germination to flowering was 3-5 days shorter for the VHb-expressing transgenes. Transgenic plants contained, on average, 30-40% more chlorophyll and 34% more nicotine than controls. VHb expression also resulted in an altered distribution of secondary metabolites: In the trangenic tobacco plants anabasine content was decreased 80% relative to control plants.

Controlled proliferation by multigene metabolic engineering enhances the productivity of Chinese hamster ovary cells.

The eukaryotic cell cycle is regulated by a complex network of many proteins. Effective reprogramming of this complex regulatory apparatus to achieve bioprocess goals, such as cessation of proliferation at high cell density to allow an extended period of high production, can require coordinated manipulation of multiple genes. Previous efforts to establish inducible cell-cycle arrest of Chinese hamster ovary (CHO) cells by regulated expression of the cyclin-dependent kinase inhibitor (CDI) p21 failed. By tetracycline-regulated coexpression of p21 and the differentiation factor CCAAT/enhancer-binding protein alpha (which both stabilizes and induces p21), we have achieved effective cell-cycle arrest. Production of a model heterologous protein (secreted alkaline phosphatase; SEAP) has been increased 10-15 times, on a per cell basis, relative to an isogenic control cell line. Because activation of apoptosis response is a possible complication in a proliferation-arrested culture, the survival gene bcl-xL was coexpressed with another CDI, p27, found to enable CHO cell-cycle arrest predominantly in G1 phase. CHO cells stably transfected with a tricistronic construct containing the genes for these proteins and for SEAP showed 30-fold higher SEAP expression than controls.

Engineered glycoforms of an antineuroblastoma IgG1 with optimized antibody-dependent cellular cytotoxic activity.

The glycosylation pattern of chCE7, an antineuroblastoma chimeric IgG1, was engineered in Chinese hamster ovary cells with tetracycline-regulated expression of beta(1,4)-N-acetylglucosaminyltransferase III (GnTIII), a glycosyltransferase catalyzing formation of bisected oligosaccharides that have been implicated in antibody-dependent cellular cytotoxicity (ADCC). Measurement of the ADCC activity of chCE7 produced at different tetracycline levels showed an optimal range of GnTIII expression for maximal chCE7 in vitro ADCC activity, and this activity correlated with the level of constant region-associated, bisected complex oligosaccharides determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The new optimized variants of chCE7 exhibit substantial ADCC activity and, hence, may be useful for treatment of neuroblastoma. The strategy presented here should be applicable to optimize the ADCC activity of other therapeutic IgGs.