Gold charge state distributions in highly ionized, low-density beam plasmas.

We present a systematic study of Au charge state distributions (CSDs) from low density, nonlocal thermodynamic equilibrium plasmas created in the Livermore electron beam ion traps (EBIT-I and EBIT-II). X-ray emission from Ni-like to Kr-like Au ions has been recorded from monoenergetic electron beam plasmas having E(beam)=2.66, 2.92, 3.53, and 4.54 keV, and the CSDs of the beam plasmas have been inferred by fitting the collisionally excited line transitions and radiative recombination emission features with synthetic spectra. We have modeled the beam plasmas using a collisional-radiative code with various treatments of the atomic structure for the complex M- and N-shell ions and find that only models with extensive doubly excited states can properly account for the dielectronic recombination (DR) channels that control the CSDs. This finding would be unremarkable for plasmas with thermal electron distributions, where many such states are sampled, and the importance of DR is well established. But in an EBIT source, the beam is resonant with only a subset of such states having spectator electrons in orbitals with high principal quantum number n (8≤n≤20). The inclusion of such states in the model was also necessary to obtain agreement with observed stabilizing transitions in the x-ray spectra.

Energy-dependent excitation cross section measurements of the diagnostic lines of Fe XVII.

By implementing a large-area, gain-stabilized microcalorimeter array on an electron beam ion trap, the electron-impact excitation cross sections for the dominant x-ray lines in the Fe XVII spectrum have been measured as a function of electron energy establishing a benchmark for atomic calculations. The results show that the calculations consistently predict the cross section of the resonance line to be significantly larger than measured. The lower cross section accounts for several problems found when modeling solar and astrophysical Fe XVII spectra.

State-selective quantum interference observed in the recombination of highly charged Hg 75+...78+ mercury ions in an electron beam ion trap.

We present experimental data on the state-selective quantum interference between different pathways of photorecombination, namely, radiative and dielectronic recombination, in the KLL resonances of highly charged mercury ions. The interference, observed for well resolved electronic states in the Heidelberg electron beam ion trap, manifests itself in the asymmetry of line shapes, characterized by "Fano factors," which have been determined with unprecedented precision, as well as their excitation energies, for several strong dielectronic resonances.

Observation of a multiply ionized plasma with index of refraction greater than one.

We present clear experimental evidence showing that the contribution of bound electrons can dominate the index of refraction of laser-created plasmas at soft x-ray wavelengths. We report anomalous fringe shifts in soft x-ray laser interferograms of Al laser-created plasmas. The comparison of measured and simulated interferograms shows that this results from the dominant contribution of low charge ions to the index of refraction. This usually neglected bound electron contribution can affect the propagation of soft x-ray radiation in plasmas and the interferometric diagnostics of plasmas for many elements.

X-ray-line diagnostic of magnetic field strength for high-temperature plasmas.

An x-ray line diagnostic for use in magnetic field measurements in high-temperature plasmas has been identified. The intensity of the otherwise strictly forbidden 1s(2)2s(2)2p(1/2)2p(4)(3/2)3s(1/2) 3P0-->1s(2)2s(2)2p(6) 1S0 transition in neonlike ions is shown to depend on the magnetic field strength. The field dependence is illustrated between one and 3 T in the Ar8+ spectrum. The line is well resolved, bright, and close to reference lines, making it an experimentally simple to use diagnostic.

Beyond fast mapping: young children's extensions of novel words and novel facts.

L. Markson and P. Bloom (1997) concluded that there was evidence against a dedicated system for word learning on the basis of their finding that children remembered a novel word and a novel fact equally well. However, a word-learning system involves more than recognition memory; it must also provide a means to guide the extension of words to additional exemplars, and words and facts may differ with regard to extendibility. Two studies are reported in which 2-4-year-old children learned novel words and novel facts for unfamiliar objects and then were asked to extend the words and facts to additional exemplars of the training objects. In both studies, children extended the novel word to significantly more category members than they extended the novel fact. The results show that by 2 years of age, children honor the necessary extendibility of novel count nouns but are uncertain about the extendibility of arbitrary facts.

The MAGIC simulation of surface water acidification at, and first year results from, the Bear Brook Watershed Manipulation, Maine, USA.

The catchments of East and West Bear Brooks, Maine, USA, have been hydrologically and chemically monitored for 3.5 years. Stream chemistries and hydrographs are similar. These clear water streams are low in ANC (0-70 microeq litre(-1)), with variations caused by changing concentrations of base cations, SO4, NO3 and Cl. The latter range between 90-120, 0-40 and 65-75 microeq litre(-1), respectively. The West Bear catchment is being treated with six applications per year of dry (NH4)2SO4 at 1800 eq ha(-1) year(-1). After one year of treatment, the response of the stream chemistry and the response modelled by MAGIC are similar. Retentions of NH4 and SO4 are nearly 100% and greater than 80%, respectively. The additional flux of SO4 is compensated principally by an increased Ca concentration. Episodes of high discharge in the treated catchment are now characterized by lower ANC and pH, and higher Al than prior to the manipulation. Concentrations of NO3 have increased about 10 microeq litre(-1) during the dormant season, presumably due to additional nitrification of N from NH4. Discharge-chemistry relationships indicate that changes in stream chemistry, except for NO3, are dominated by ion exchange reactions in the upper part of the soil profile.

Reinvestigating the early resonantly photopumped x-ray laser schemes.

Although H and He-like resonantly photopumped laser schemes were among the earliest methods proposed for producing x-ray lasers, demonstrating these schemes in the laboratory has proved to be elusive. Nevertheless the resonantly photopumped schemes remain interesting both because of their potential to improve the efficiency of lasers that otherwise operate through other process such as recombination and because of their potential for yielding entirely new and relatively efficient lasers. We present an expanded list of candidate lasers that operate by utilizing Ly-alpha or He-alpha radiation from a pump ion to photopump an electron from the ground state of a H or He-like lasant ion to the n = 3 or 4 state, with subsequent lasing between the n = 4 ? n = 3 or n = 3 ? n = 2 states of the H or He-like ion. The example of the potassium-pumped chlorine scheme, which exhibits both 4 ? 3 and 3 ? 2 laser lines, has been modeled extensively, and the results of the calculation are presented.

Identification of proteolytic cleavage sites in the conversion of profilaggrin to filaggrin in mammalian epidermis.

Profilaggrin consists of multiple filaggrin domains joined by linker segments which are removed during proteolytic conversion to filaggrin. Analysis of tryptic peptides of filaggrin defined a 26-residue linker segment when aligned on the amino acid sequence of one repeat unit of mouse profilaggrin deduced from a cDNA sequence (Rothnagel, J. A., Mehrel, T., Idler, W. W., Roop, D. R., and Steinert, P. M. (1987) J. Biol. Chem. 262, 15643-15648). Two types of linker segments were distinguished by their different susceptibility to thermolysin and by the presence of a Phe-Tyr-Pro-Val sequence in only one type. These data led to a model of profilaggrin in which the two types of linker segments alternate along the length of profilaggrin. This model provides a structural basis for the two stages of proteolytic processing seen in vivo. In the first stage intermediates accumulate which have several filaggrin domains still joined by linker segments lacking Phe-Tyr-Pro-Val. In the second stage, the other linker segments are cleaved and mature filaggrin domains are released. Proteolytic activity with specificity consistent with first stage cleavage was partially purified from rat epidermis. Chymostatin inhibited both the in vitro enzymatic activity and the processing of profilaggrin in a cultured rat keratinocyte cell line. The products formed in vitro were 3-5 kDa larger than intermediates produced in vivo, suggesting that the linker segments are cleaved at one end only. This implies the existence of a third protease which completes the removal of the linker segments.

Characterization of an epidermal phosphatase specific for filaggrin phosphorylated by casein kinase II.

During cellular remodeling that accompanies cornification of epidermal cells, the highly phosphorylated protein, profilaggrin, is dephosphorylated and proteolytically cleaved to filaggrin, the keratin matrix protein. Using rat filaggrin phosphorylated by bovine casein kinase II (CK II) as a substrate, we have partially purified a phosphatase from rat epidermis which dephosphorylates rat profilaggrin in vitro. Anion exchange, hydroxylapatite, and gel filtration chromatography yielded a 100-fold purification of phosphatase from a low-salt extract. Further purification led to loss of activity; therefore, only the partially purified phosphatase was characterized. Two forms of the phosphatase, with molecular weights of approximately 170 and 40 kDa, were resolved during gel filtration. The 170-kDa form could be converted to the 40-kDa form in the presence of dithiothreitol. Both forms had pH optima of 6.6, and were strongly inhibited by NaCl (50% inhibition at 35-40 mM). Neither form hydrolyzed para-nitrophenylphosphate or dephosphorylated casein or the synthetic peptide arg3-glu3-thr-glu3, which were phosphorylated by casein kinase II. The two forms were similarly inhibited by known inorganic phosphatase inhibitors, with 22%-36% inhibition by 0.1 mM Na+/K+ tartrate, 55%-60% inhibition by 0.1 mM NaF, and 75% inhibition by 0.1 mM Na pyrophosphate. Para-chloromercuribenzoate also inhibited the activity, suggesting that reduced thiols may be important in catalysis. One mM calcium chloride altered the activity in a complex manner depending on the pH, suggesting a possible role for calcium in regulating enzyme activity.

Creation and repair of diaphragmatic hernia in the fetal lamb: techniques and survival.

Diaphragmatic hernias were created in 54 fetal lambs at 72 to 82 days gestation via a left thoracotomy. The diaphragmatic hernia was repaired in 30 lambs at 106 to 123 days gestation, and 14 of these lambs subsequently aborted. The majority of those surviving to term were delivered for survival. Four lambs with an unrepaired diaphragmatic hernia were intensively resuscitated at delivery and their diaphragmatic hernias repaired; survival in these lambs ranged from 20 minutes to 89 hours. Nine lambs with repaired diaphragmatic hernia were resuscitated following delivery; survival times ranged from one hour, 45 minutes to 123 days, with three lambs surviving to be sacrificed at 43, 62, and 123 days. Three of the lambs that died before sacrifice, died of causes unrelated to their lung function. These results show that in-utero repair of the diaphragmatic hernia in the fetal lamb results in improved survival. We feel, however, that direct application of these results in humans would be premature.

Identification of filaggrin in cultured mouse keratinocytes and its regulation by calcium.

Filaggrin is a histidine-rich cationic protein present in cells of the stratum corneum in vivo and derived from a precursor in keratohyalin granules. Biochemical and immunologic methods were used to determine the presence of filaggrin in keratinocytes cultured in vitro and induced to differentiate by increasing the extracellular calcium concentration from 0.07 to 1.2 mM. Indirect immunofluorescence using antibody to rat filaggrin was negative in cells cultured in low-calcium medium but positive in cells switched to high-calcium medium. Large immunofluorescent granules were identified in a perinuclear distribution starting at 6 hours after the shift in calcium concentration, coinciding with the time of appearance of phase-dense cytoplasmic granules. Radiolabeled histidine was preferentially incorporated into proteins of 95, 37, and 27 K. The 37 and 27 K bands were not adsorbed by DE52 cellulose and therefore are cationic. A 27 K cationic, histidine-labeled protein was readily extracted from frozen pellets of cells cultured in high-calcium medium. It comigrates with purified mouse filaggrin (27 K) and reacts with antibody to rat filaggrin on immunoautoradiography. Only trace amounts of this protein could be detected in cells cultured in low-calcium medium. Our observation of filaggrin-immunoreactive granules confirms the previous ultrastructural identification of keratohyalin granules after the shift to high-calcium medium. The results suggest that filaggrin synthesis is stimulated in keratinocytes induced to differentiate by the shift to high extracellular calcium concentration.