Boron Abundances in Diffuse Interstellar Clouds

We present a comprehensive survey of B abundances in diffuse interstellar clouds from HST/STIS observations along 56 Galactic sight lines. Our sample is the result of a complete search of archival STIS data for the B II resonance line at 1362 angstroms, with each detection confirmed by the presence of absorption from other dominant ions at the same velocity. The data probe a range of astrophysical environments including both high-density regions of massive star formation as well as low-density paths through the Galactic halo, allowing us to clearly define the trend of B depletion onto interstellar grains as a function of gas density. Many extended sight lines exhibit complex absorption profiles that trace both local gas and gas associated with either the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher B/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of the Sun, which may suggest that B production in the current epoch is dominated by a secondary process. The average gas-phase B abundance in the warm diffuse ISM is consistent with the abundances determined for a variety of Galactic disk stars, but is depleted by 60 percent relative to the solar system value. Our survey also reveals sight lines with enhanced B abundances that potentially trace recent production of B-11 either by cosmic-ray or neutrino-induced spallation. Such sight lines will be key to discerning the relative importance of the two production routes for B-11 synthesis.Comment: To be published in the proceedings of the IAU Symposium 268, Light Elements in the Universe, C. Charbonnel, M. Tosi, F. Primas & C. Chiappini, ed

The Interstellar N/O Abundance Ratio: Evidence for Local Infall?

Sensitive measurements of the interstellar gas-phase oxygen abundance have revealed a slight oxygen deficiency ($\sim$ 15%) toward stars within 500 pc of the Sun as compared to more distant sightlines. Recent $FUSE$ observations of the interstellar gas-phase nitrogen abundance indicate larger variations, but no trends with distance were reported due to the significant measurement uncertainties for many sightlines. By considering only the highest quality ($\geq$ 5 $\sigma$) N/O abundance measurements, we find an intriguing trend in the interstellar N/O ratio with distance. Toward the seven stars within $\sim$ 500 pc of the Sun, the weighted mean N/O ratio is 0.217 $\pm$ 0.011, while for the six stars further away the weighted mean value (N/O = 0.142 $\pm$ 0.008) is curiously consistent with the current Solar value (N/O = 0.138$^{+0.20}_{-0.18}$). It is difficult to imagine a scenario invoking environmental (e.g., dust depletion, ionization, etc.) variations alone that explains this abundance anomaly. Is the enhanced nitrogen abundance localized to the Solar neighborhood or evidence of a more widespread phenomenon? If it is localized, then recent infall of low metallicity gas in the Solar neighborhood may be the best explanation. Otherwise, the N/O variations may be best explained by large-scale differences in the interstellar mixing processes for AGB stars and Type II supernovae.Comment: accepted for publication in the Astrophysical Journal Letter

Vergleich von Antibeschlagmethoden in der Endoskopie: Was wirklich hilft

Zusammenfassung: Hintergrund und Fragestellung: Endoskopische Verfahren, wie die fiberoptische Intubation, haben sich als Standard in der Anästhesie etabliert. Obwohl allgemein bekannt ist, dass zur sicheren Anwendung von Endoskopen eine Antibeschlagmethode unerlässlich ist, fehlen Studien zum Vergleich der Wirksamkeit verschiedener Antibeschlagmethoden. Ziel dieser Studie war es, die Wirksamkeit von 7Antibeschlagmethoden im Einsatz mit einem flexiblen und einem starren Endoskop zu untersuchen. Material und Methoden: Die Wirksamkeit von je 2Antibeschlaglösungen und -tüchern, einem induktiven Endoskopvorwärmer, sowie kontinuierlichem Sauerstofffluss über den Arbeitskanal der Optik wurde in einem Atemwegsmodell mithilfe eines flexiblen und eines starren Endoskops getestet sowie verblindet beurteilt. Ergebnisse: Insgesamt wurden 300Testbilder aufgezeichnet und analysiert. Sowohl in der Gruppe mit dem flexiblen als auch in der Gruppe mit dem starren Endoskop erzielten je eine Antibeschlaglösung und ein -tuch die besten Ergebnisse. Flexible Endoskopie: Anti-Fog (Versagerquote: 3%), Lina Clear (4%). Starre Endoskopie: Ultrastop (5%), Lina Clear (3,5%). Der Endoskopvorwärmer mit 2-maliger Anwendung zeigte in beiden Gruppen sehr gute Ergebnisse (6% und 10%). Keinen positiven Effekt gegen das Beschlagen eines Endoskops ergab die Verwendung des Sauerstoffflusses (93,5%). Schlussfolgerungen: Die Studie konnte aufzeigen, dass es Unterschiede in der Effektivität von Antibeschlagtüchern und -lösungen gibt. Der klinische Einsatz ist aber auch von weiteren Faktoren wie Endoskoptyp und Häufigkeit der Verwendung, Kosten- und Hygieneaspekten abhängig. Der induktive Endoskopvorwärmer kann trotz hoher Anschaffungskosten eine Alternative darstellen. Jedoch fehlen bislang klare Sicherheitshinweise zur mehrfachen Anwendung durch den Hersteller. Der kontinuierliche Sauerstofffluss über den Arbeitskanal einer flexiblen Optik kann nicht als Antibeschlagmethode empfohlen werde

Rubidium in the Interstellar Medium

We present observations of interstellar rubidium toward o Per, zeta Per, AE Aur, HD 147889, chi Oph, zeta Oph, and 20 Aql. Theory suggests that stable 85Rb and long-lived 87Rb are produced predominantly by high-mass stars, through a combination of the weak s- and r-processes. The 85Rb/87Rb ratio was determined from measurements of the Rb I line at 7800 angstroms and was compared to the solar system meteoritic ratio of 2.59. Within 1-sigma uncertainties all directions except HD 147889 have Rb isotope ratios consistent with the solar system value. The ratio toward HD 147889 is much lower than the meteoritic value and similar to that toward rho Oph A (Federman et al. 2004); both lines of sight probe the Rho Ophiuchus Molecular Cloud. The earlier result was attributed to a deficit of r-processed 85Rb. Our larger sample suggests instead that 87Rb is enhanced in these two lines of sight. When the total elemental abundance of Rb is compared to the K elemental abundance, the interstellar Rb/K ratio is significantly lower than the meteoritic ratio for all the sight lines in this study. Available interstellar samples for other s- and r- process elements are used to help interpret these results.Comment: 24 pages, 3 figures. Accepted for publication in Ap

Silica containing composite anion exchange membranes by sol–gel synthesis: a short review

This short review summarizes the literature on composite anion exchange membranes (AEM) containing an organo-silica network formed by sol-gel chemistry. The article covers AEM for diffusion dialysis (DD), for electrochemical energy technologies including fuel cells and redox flow batteries, and for electrodialysis. By applying a vast variety of organically modified silica compounds (ORMOSIL), many composite AEM reported in the last 15 years are based on poly (vinylalcohol) (PVA) or poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) used as polymer matrix. The most stringent requirements are high permselectivity and water flux for DD membranes, while high ionic conductivity is essential for electrochemical applications. Furthermore, the alkaline stability of AEM for fuel cell applications remains a challenging problem that is not yet solved. Possible future topics of investigation on composite AEM containing an organo-silica network are also discussed

Slow, Steady-State Transport with "Loading" and Bulk Reactions: the Mixed Ionic Conductor La2_2CuO4+δ_{4+\delta}

We consider slow, steady transport for the normal state of the superconductor La$_2$CuO$_{4+\delta}$ in a one-dimensional geometry, with surface fluxes sufficiently general to permit oxygen to be driven into the sample (``loaded'') either by electrochemical means or by high oxygen partial pressure. We include the bulk reaction O$\to$O$^{2-}+2h$, where neutral atoms ($a$) go into ions ($i$) and holes ($h$). For slow, steady transport, the transport equations simplify because the bulk reaction rate density $r$ and the bulk loading rates $\partial_t n$ then are uniform in space and time. All three fluxes $j$ must be specified at each surface, which for a uniform current density $J$ corresponds to five independent fluxes. These fluxes generate two types of static modes at each surface and a bulk response with a voltage profile that varies quadratically in space, characterized by $J$ and the total oxygen flux $j_O$ (neutral plus ion) at each surface. One type of surface mode is associated with electrical screening; the other type is associated both with diffusion and drift, and with chemical reaction (the {\it diffusion-reaction mode}). The diffusion-reaction mode is accompanied by changes in the chemical potentials $\mu$, and by reactions and fluxes, but it neither carries current (J=0) nor loads the system chemically ($j_O=0$). Generation of the diffusion-reaction mode may explain the phenomenon of ``turbulence in the voltage'' often observed near the electrodes of other mixed ionic electronic conductors (MIECs).Comment: 11 pages, 1 figur

Crosslinked SPEEK membranes: Mechanical, thermal, and hydrothermal properties

The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK)membranes annealed at 180 degrees C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications

Oscillator Strengths for B-X, C-X, and E-X Transitions in Carbon Monoxide

Band oscillator strengths for electronic transitions in CO were obtained at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Our focus was on transitions that are observed in interstellar spectra with the Far Ultraviolet Spectroscopic Explorer; these transitions are also important in studies of selective isotope photodissociation where fractionation among isotopomers can occur. Absorption from the ground state (X ^1Sigma^+ v'' = 0) to A ^1Pi (v'= 5), B ^1Sigma^+ (v' = 0, 1), C ^1Sigma^+ (v' = 0, 1), and E ^1Pi (v' = 0) was measured. Fits to the A - X (5, 0) band, whose oscillator strength is well known, yielded the necessary column density and excitation temperature. These parameters were used in a least-squares fit of the observed profiles for the transitions of interest to extract their band oscillator strengths. Our oscillator strengths are in excellent agreement with results from recent experiments using a variety of techniques. This agreement provides the basis for a self-consistent set of f-values at far ultraviolet wavelengths for studies of interstellar (and stellar) CO.Comment: 22 pages, 3 figures, ApJS (in press