New continua for absorption spectroscopy from 40 to 2000 Å

The spectra of plasmas produced by focusing the output of a Q-switched ruby laser (output 1 J) on the rare-earth metals have been studied. From samarium (Z = 70), strong quasi-uniform continua are emitted in the wavelength range 40–2000 Å. Line emission from the target elements is absent over most of this wavelength region, particularly below about 600 Å. The use of these continua as simple, reliable background sources for absorption spectroscopy in the vacuum-ultraviolet and soft x-ray region down to 40 Å is demonstrated

Effects Of Perkinsus marinus Infection In The Eastern Oyster, Crassostrea virginica: II. Disease Development And Impact On Growth Rate At Different Salinities

In order to assess the impact of Perkinsus marinus infection on oyster growth and mortality, oysters were raised in floating rafts at six sites around Chesapeake Bay. The sites were comprised of two low salinity sites (8-10%0), two moderate salinity (12-15%0) sites and two high salinity sites (16-20%0). Oyster growth was monitored biweekly along with various water qualities including temperature and salinity. Condition index was measured monthly and disease diagnosis was perfonned bimonthly. Oyster growth was initially greatest at the high salinity sites but was subsequently retarded by Perkinsus infection at both the moderate and high salinity sites (where the parasite was more prevalent). Comparison of pre-infection and post-infection growth rates between sites showed that the reduction in growth rate was mitigated by lower salinity. Condition index was not related to salinity or site but was significantly reduced by P. marinus infection. Reduction in condition, however, was not associated with increased mortality. Mortality was also less related to salinity or temperature than it was to infection history (previous infection). Groups which incurred high infection prevalences and intensities exhibited low mortality during their first year, but suffered high mortality during the following year. The results are discussed in relation to management and aquacultural practices and their relation to genetics and selective breeding of disease resistant oysters

Table-top EUV continuum light source

Work in recent years on the development of a convenient "table-top" source of continuum radiation in the XUV and VUV from 4 to 200 nm is summarized. It was found that laser-produced plasmas on targets of high atomic number (62 leq Z leq 74) emitted apparently line-free continua over very substantial spectral regions in the XUV and VUV. The continua are very intense, reproducible, and relatively insensitive to ambient pressure. The effective absence of line emission can be explained on the basis of the electron configurations of the ionized species responsible for the emission. A high repetition rate modular version of the source is described. Applications and advantages of the light source are presented

Tracking ground state Ba+ ions in an expanding laser–plasma plume using time-resolved vacuum ultraviolet photoionization imaging

We report results from a study of the integrated column density and expansion dynamics of ground-state-selected Ba+ ions in a laser–plasma plume using a new experimental system—VPIF (vacuum-ultraviolet photoabsorption imaging facility). The ions are tracked by recording the attenuation of a pulsed and collimated vacuum ultraviolet beam, tuned to the 5p–6d inner-shell resonance of singly ionized barium, as the expanding plasma plume moves across it. The attenuated beam is allowed to fall on a CCD array where the spatial distribution of the absorption is recorded. Time-resolved ion velocity and integrated column density maps are readily extracted from the photoionization images

3p photoabsorption of free and bound Cr, Cr⁺, Mn, and Mn⁺

A dual-laser-plasma technique has been used to measure photoabsorption by atomic Cr and Mn and their ions at photon energies between 40 and 70 eV, where the dominant absorption mechanism is excitation of the 3p subshell. No dramatic differences are observed between the absorption spectra of Mn and Mn+, and these spectra are similar to those of Mn metal and MnCl2. The spectra of Cr and Cr+ are strikingly dissimilar, the mean excitation energy being about 5 eV greater in the ion. We attribute this to strong mixing of the localized 3d6 configuration with 3d5nd Rydberg configurations, an effect that is also responsible for the anomalous appearance of the Cr spectrum with respect to those of the other iron-period elements. The absorption spectra of Cr metal and CrCl2 take forms intermediate between those of Cr and Cr+. We give spectroscopic assignments to most of the sharp absorption features of Cr+ and determine the 3p ionization thresholds from quantum-defect analysis

Rise and fall of the 4d¹⁰→4d⁹4f resonance in the Xe isoelectronic sequence

The extreme ultraviolet photoabsorption spectrum of a laser-produced lanthanum plasma has been recorded and found to contain a number of discrete features in the 130-eV region. These have been analyzed as 4d10→4d9nf,np transitions in La3+. We show that the 4f transition, which is expected to be the strongest, is not in evidence. The reason is that this resonance, after the collapse of the 4f wave function, has a large autoionization width. We conclude that the 4f orbital in Ba2+ is only partially collapsed, which settles a long-standing discussion of this point

Dramatic changes in the 3s autoionization process at the beginning of the Ar I sequence

The 3s→np resonances were observed to change dramatically in appearance with increasing ionization along the Ar I sequence, and within the 3s→np channel of Ca2+. By applying the Dyson equation method to positive ions for the first time, newly investigated double-electron processes were shown to play a crucial role in the interpretation of the resonance structure. The changes within the resonances result from their position relative to the Cooper minima in the 3s and 3p photoabsorption

First observation of a photon-induced triply excited state in atomic lithium

Using a dual laser plasma technique we have measured for the first time the photoabsorption spectrum of atomic lithium at energies corresponding to the simultaneous excitation of both 1s electrons. We have observed the main triply excited 1s22s(2S)→2s2p(2P) transition with Fano parameters E0=142.32±0.05 eV Γ=0.20±0.04 eV, and q=-2.2±0.6. Our experiment represents the first step in photoionization studies of this fundamental atomic system in which the motion of the three electrons in the field of the nucleus is so highly correlated

Selective Histone Deacetylase 6 Inhibitors Restore Cone Photoreceptor Vision or Outer Segment Morphology in Zebrafish and Mouse Models of Retinal Blindness.

Blindness arising from retinal or macular degeneration results in significant social, health and economic burden. While approved treatments exist for neovascular ('wet') age-related macular degeneration, new therapeutic targets/interventions are needed for the more prevalent atrophic ('dry') form of age-related macular degeneration. Similarly, in inherited retinal diseases, most patients have no access to an effective treatment. Although macular and retinal degenerations are genetically and clinically distinct, common pathological hallmarks can include photoreceptor degeneration, retinal pigment epithelium atrophy, oxidative stress, hypoxia and defective autophagy. Here, we evaluated the potential of selective histone deacetylase 6 inhibitors to preserve retinal morphology or restore vision in zebrafish atp6v0e1 -/- and mouse rd10 models. Histone deacetylase 6 inhibitor, tubastatin A-treated atp6v0e1 -/- zebrafish show marked improvement in photoreceptor outer segment area (44.7%, p = 0.027) and significant improvement in vision (8-fold, p ≤ 0.0001). Tubastatin A-treated rd10/rd10 retinal explants show a significantly (p = 0.016) increased number of outer-segment labeled cone photoreceptors. In vitro, ATP6V0E1 regulated HIF-1α activity, but significant regulation of HIF-1α by histone deacetylase 6 inhibition in the retina was not detected. Proteomic profiling identified ubiquitin-proteasome, phototransduction, metabolism and phagosome as pathways, whose altered expression correlated with histone deacetylase 6 inhibitor mediated restoration of vision

Absolute photoionization cross sections and resonance structure of doubly ionized silicon in the region of the 2p-1 threshold: experiment and theory

We present the absolute photoionization cross section of doubly ionized silicon as a function of photon energy. These were obtained by merging a Si2+ ion beam generated in an electron cyclotron resonance source with monochromatized synchrotron radiation from an undulator. The photoion yield measurements were carried out in the photon energy range between 95 eV and 170 eV, i.e., the region corresponding to the excitation followed by the ionization (threshold ∼133.8eV) of an inner-subshell 2p electron. Resonance structure due to 2p excitation in the 2p63s3p3P metastable state was also observed with its contribution to the total cross section not exceeding 3%. Calculation of the 2p photoionization continuum cross section as a function of photon energy was carried out using the relativistic random-phase approximation (RRPA) and agreed very well with the corresponding measurements. The resonance structure in the 3s cross section below the 2p threshold was found to be in good agreement with the multiconfiguration atomic structure calculations of Sayyad et al. [J. Phys. B 28, 1715 (1995)], while the corresponding RRPA-RMQDT (relativistic multi-channel quantum-defect theory) calculations proved less successful