The Influence of Stellar Wind Variability on Measurements of Interstellar O VI Along Sightlines to Early-Type Stars

A primary goal of the FUSE mission is to understand the origin of the O VI ion in the interstellar medium of the Galaxy and the Magellanic Clouds. Along sightlines to OB-type stars, these interstellar components are usually blended with O VI stellar wind profiles, which frequently vary in shape. In order to assess the effects of this time-dependent blending on measurements of the interstellar O VI lines, we have undertaken a mini-survey of repeated observations toward OB-type stars in the Galaxy and the Large Magellanic Cloud. These sparse time series, which consist of 2-3 observations separated by intervals ranging from a few days to several months, show that wind variability occurs commonly in O VI (about 60% of a sample of 50 stars), as indeed it does in other resonance lines. However, in the interstellar O VI $\lambda$1032 region, the O VI $\lambda$1038 wind varies only in $\sim$30% of the cases. By examining cases exhibiting large amplitude variations, we conclude that stellar-wind variability {\em generally} introduces negligible uncertainty for single interstellar O VI components along Galactic lines of sight, but can result in substantial errors in measurements of broader components or blends of components like those typically observed toward stars in the Large Magellanic Cloud. Due to possible contamination by discrete absorption components in the stellar O VI line, stars with terminal velocities greater than or equal to the doublet separation (1654 km/s) should be treated with care.Comment: Accepted for publication in the Astrophysical Journal Lette

Electromagnetic Moments of the Baryon Decuplet

We compute the leading contributions to the magnetic dipole and electric quadrupole moments of the baryon decuplet in chiral perturbation theory. The measured value for the magnetic moment of the $\Omega^-$ is used to determine the local counterterm for the magnetic moments. We compare the chiral perturbation theory predictions for the magnetic moments of the decuplet with those of the baryon octet and find reasonable agreement with the predictions of the large--$N_c$ limit of QCD. The leading contribution to the quadrupole moment of the $\Delta$ and other members of the decuplet comes from one--loop graphs. The pionic contribution is shown to be proportional to $I_z$ (and so will not contribute to the quadrupole moment of $I=0$ nuclei), while the contribution from kaons has both isovector and isoscalar components. The chiral logarithmic enhancement of both pion and kaon loops has a coefficient that vanishes in the $SU(6)$ limit. The third allowed moment, the magnetic octupole, is shown to be dominated by a local counterterm with corrections arising at two loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5

Dense, Parsec-Scale Clumps near the Great Annihilator

We report on Combined Array for Research in Millimeter-Wave Astronomy (CARMA) and James Clerk Maxwell Telescope (JCMT) observations toward the Einstein source 1E 1740.7-2942, a LMXB commonly known as the "Great Annihilator." The Great Annihilator is known to be near a small, bright molecular cloud on the sky in a region largely devoid of emission in 12-CO surveys of the Galactic Center. The region is of interest because it is interior to the dust lanes which may be the shock zones where atomic gas from HI nuclear disk is converted into molecular gas. We find that the region is populated with a number of dense (n ~ 10^5 cm^-3) regions of excited gas with small filling factors, and estimate that up to 1-3 x 10^5 solar masses of gas can be seen in our maps. The detection suggests that a significant amount of mass is transported from the shock zones to the GC star-forming regions in the form of small, dense bundles.Comment: 26 pages, 7 figures, accepted for publication by the Astrophysical Journal, abstract abridge

Chemical pretreatment of cells for enhanced MALDI-TOF-MS discrimination of clinical staphylococci including MRSA

BACKGROUND: Limited success has been reported for matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) differentiation of staphylococci, including methicillin resistant Staphylococcus aureus (MRSA) strains. Chemical pretreatment of cells prior to MALDI-TOF-MS analysis has not been systematically investigated for enhanced discrimination of S.aureus strains. OBJECTIVES: To evaluate various chemical pretreatment of cells for MALDI-TOF-MS discrimination of clinical staphylococcal isolates, with a focus on differentiation of MRSA from methicillin sensitive S. aureus (MSSA) strains and from other staphylococcal species. METHOD: MALDI-TOF-MS of a well-characterised S. aureus strain(s) was optimised with respect to matrix chemical(s), matrix solvent and target plating method. Various chemical pretreatments (solvents, reductants, detergents) and pretreatment application methods were then evaluated for enhancement of spectral richness. The three most promising pretreatments were applied to MALDI-TOF-MS discrimination of three set of clinical isolates comprising non-S.aureus staphylococci (77 isolates ), MSSA (36) and MRSA (43), with analysis by total or set specific resolved peaks. RESULTS: The optimized MALDI-TOF-MS protocol involved α-cyano-4-hydroxycinnamic acid (CHCA) as matrix chemical (in 1:2 acetonitrile:H2O and 2% trifluoroacetic acid), with application as an overlay onto smeared cells (on-probe). On-probe application of chemical pretreatment was most effective at enhancing MALDI-TOF-MS spectral richness. Use of reductants and detergents as pretreatments were ineffective. The three most effective solvents/acid pretreatments - ethanol:formate, ethanol:acetate and formate:isopropanol - each generated reproducible and distinct spectra over the 2,000 -10,000 m/z range. For the combined sets of clinical isolates (114), all three of these pretreatments increased the total number of resolved peaks in comparison with no pretreatment controls. The ethanol:formate pretreatment gave 100% clustering of non-S. aureus staphylococci, based on total resolved peaks. The formate:isopropanol pretreatment generated the largest increase in number of MRSA set specific peaks (from 18 to 32; 78% increase) and clustered the majority (77%) of the MRSA strains together, although compete discrimination of the MSSA and MRSA was not achieved. CONCLUSION: MALDI-TOF-MS discrimination of clinical isolates of staphylococci is enhanced through chemical pretreatment of cells. Three chemical pretreatments, not previously applied to staphylococci, are highlighted for enhancing spectral richness and offering new opportunities for improved discrimination of staphylococci, including MRSA and MSSA strains

Chemical pretreatment of cells for enhanced MALDI-TOF-MS discrimination of clinical staphylococci including MRSA

BACKGROUND: Limited success has been reported for matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) differentiation of staphylococci, including methicillin resistant Staphylococcus aureus (MRSA) strains. Chemical pretreatment of cells prior to MALDI-TOF-MS analysis has not been systematically investigated for enhanced discrimination of S.aureus strains. OBJECTIVES: To evaluate various chemical pretreatment of cells for MALDI-TOF-MS discrimination of clinical staphylococcal isolates, with a focus on differentiation of MRSA from methicillin sensitive S. aureus (MSSA) strains and from other staphylococcal species. METHOD: MALDI-TOF-MS of a well-characterised S. aureus strain(s) was optimised with respect to matrix chemical(s), matrix solvent and target plating method. Various chemical pretreatments (solvents, reductants, detergents) and pretreatment application methods were then evaluated for enhancement of spectral richness. The three most promising pretreatments were applied to MALDI-TOF-MS discrimination of three set of clinical isolates comprising non-S.aureus staphylococci (77 isolates ), MSSA (36) and MRSA (43), with analysis by total or set specific resolved peaks. RESULTS: The optimized MALDI-TOF-MS protocol involved α-cyano-4-hydroxycinnamic acid (CHCA) as matrix chemical (in 1:2 acetonitrile:H2O and 2% trifluoroacetic acid), with application as an overlay onto smeared cells (on-probe). On-probe application of chemical pretreatment was most effective at enhancing MALDI-TOF-MS spectral richness. Use of reductants and detergents as pretreatments were ineffective. The three most effective solvents/acid pretreatments - ethanol:formate, ethanol:acetate and formate:isopropanol - each generated reproducible and distinct spectra over the 2,000 -10,000 m/z range. For the combined sets of clinical isolates (114), all three of these pretreatments increased the total number of resolved peaks in comparison with no pretreatment controls. The ethanol:formate pretreatment gave 100% clustering of non-S. aureus staphylococci, based on total resolved peaks. The formate:isopropanol pretreatment generated the largest increase in number of MRSA set specific peaks (from 18 to 32; 78% increase) and clustered the majority (77%) of the MRSA strains together, although compete discrimination of the MSSA and MRSA was not achieved. CONCLUSION: MALDI-TOF-MS discrimination of clinical isolates of staphylococci is enhanced through chemical pretreatment of cells. Three chemical pretreatments, not previously applied to staphylococci, are highlighted for enhancing spectral richness and offering new opportunities for improved discrimination of staphylococci, including MRSA and MSSA strains

Development of YAG:Dy Thermographic Phosphor Coatings for Turbine Engine Applications

The selection and development of thermographic phosphor coatings were pursued to meet the objective of demonstrating luminescence-decay-based temperature measurements up to 1300C on the surface of a vane in an operating demonstrator turbine engine. To meet this objective, YAG:Dy was selected based on the desirable luminescence performance observed for YAG:Dy powder: (1) excellent temperature sensitivity and intensity at operating turbine engine temperatures, (2) an emission peak at the relatively short wavelength of 456 nm, where the interference from background blackbody radiation is fairly low, and (3) its nearly single exponential decay which makes for a simple, reliable temperature calibration. However, implementation of YAG:Dy for surface temperature measurements required application of YAG:Dy as a coating onto the surface of a superalloy component with a preexisting yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC). An inherent dilemma in producing a YAG:Dy coating is that coating processing is constrained to be performed at temperatures below (less than 1200C) what is considered safe for the superalloy component, much lower than temperatures used to produce the high quality crystalline powder. Therefore, YAG:Dy coatings tend to exhibit lower luminescence performance compared to well prepared YAG:Dy powder, and the luminescence performance of the coating will depend on the method of coating deposition. In this presentation, the luminescence performance of YAG:Dy coatings prepared by the different methods of (1) application of a binder-based YAG:Dy-containing paint, (2) solution precursor plasma spray (SPPS), and (3) electron-beam physical vapor deposition (EB-PVD) and the effect of post-deposition heat treatments will be discussed

Velocity correlations in granular materials

A system of inelastic hard disks in a thin pipe capped by hot walls is studied with the aim of investigating velocity correlations between particles. Two effects lead to such correlations: inelastic collisions help to build localized correlations, while momentum conservation and diffusion produce long ranged correlations. In the quasi-elastic limit, the velocity correlation is weak, but it is still important since it is of the same order as the deviation from uniformity. For system with stronger inelasticity, the pipe contains a clump of particles in highly correlated motion. A theory with empirical parameters is developed. This theory is composed of equations similar to the usual hydrodynamic laws of conservation of particles, energy, and momentum. Numerical results show that the theory describes the dynamics satisfactorily in the quasi-elastic limit, however only qualitatively for stronger inelasticity.Comment: 12 pages (REVTeX), 15 figures (Postscript). submitted to Phys. Rev.

Inherent Rheology of a Granular Fluid in Uniform Shear Flow

In contrast to normal fluids, a granular fluid under shear supports a steady state with uniform temperature and density since the collisional cooling can compensate locally for viscous heating. It is shown that the hydrodynamic description of this steady state is inherently non-Newtonian. As a consequence, the Newtonian shear viscosity cannot be determined from experiments or simulation of uniform shear flow. For a given degree of inelasticity, the complete nonlinear dependence of the shear viscosity on the shear rate requires the analysis of the unsteady hydrodynamic behavior. The relationship to the Chapman-Enskog method to derive hydrodynamics is clarified using an approximate Grad's solution of the Boltzmann kinetic equationComment: 10 pages, 4 figures; substantially enlarged version; to be published in PR

Imaging the essential role of spin-fluctuations in high-Tc superconductivity

We have used scanning tunneling spectroscopy to investigate short-length electronic correlations in three-layer Bi2Sr2Ca2Cu3O(10+d) (Bi-2223). We show that the superconducting gap and the energy Omega_dip, defined as the difference between the dip minimum and the gap, are both modulated in space following the lattice superstructure, and are locally anti-correlated. Based on fits of our data to a microscopic strong-coupling model we show that Omega_dip is an accurate measure of the collective mode energy in Bi-2223. We conclude that the collective mode responsible for the dip is a local excitation with a doping dependent energy, and is most likely the (pi,pi) spin resonance.Comment: 4 pages, 4 figure