R Aquarii: The Large-Scale Optical Nebula and the Mira Variable Position

The R Aquarii symbiotic star system is surrounded by a large-scale optical nebula. We present observations of the nebular [O III] structure and discuss its morphological significance in context with previously observed small-scale radio-continuum features, which may be related. We suggest that a precessing accretion disk may explain the global features of both the large-scale optical emission and the small-scale radio emission. Moreover, we have determined an accurate position of the system\u27s Mira, which suggests that a recent theoretical model, yielding an egg-shaped central H II region for symbiotic systems with certain physical parameters, may apply to R Aquarii. The optical position of the 387d period Mira variable is consistent with our previous findings in the radio, that SiO maser emission is far removed from the Mira photosphere

Comparisons of SiO Maser and Long-Period Variable Positions in the Aquarii and Omicron Ceti Binary Systems

We have determined that the absolute position of the centroid of SiO maser-emitting spots toward both R A~r ~nd o Cet are coincident with the position of the long-period variables (LPVs) in these binary systems to within the errors of measurement. The SiO positions were determined with the Hat Creek interferometer while the LPV positions were determined with the 8 inch (20 em) transit circle of the US Naval Observatory: These results contradict an earlier report of a circumbinary SiO maser far removed from the LPV in the R Aqr binary system, and we suggest statistical reasons for the discrepancy. We present high-resolution spectra of both sources and discuss possible models

CsgD regulatory network in a bacterial trait-altering biofilm formation

In response to the limited nutrients and stressful conditions of their habitats, many microorganisms including Salmonella form a biofilm by secreting a polymeric matrix to interweave individual cells and to build structural communities on an abiotic or living surface. The biofilm formation in Salmonella is tightly regulated by a regulatory network that involves multiple transcriptional regulators. As a master transcriptional regulator in biofilm formation, curli subunit gene D (csgD) functions by activating the biosynthesis of the extracellular polymeric matrix composed of exopolysaccharide cellulose, curli and biofilm-associated proteins (Baps), assisting bacterial cells in transitioning from the planktonic stage to the multicellular state. The expression of CsgD itself is affected by cell growth stage and environmental stimuli through the action of other transcriptional factors, bis-(3′–5′)-cyclic dimeric guanosine monophosphate (c-di-GMP), regulatory small RNAs (sRNAs) and other elements. The formation of biofilm confers new physiological characteristics on the bacteria within, especially resistance against unfavorable environmental conditions. Herein, we summarize the CsgD regulatory network of Salmonella biofilm formation and the new traits acquired by Salmonella when within biofilm

Ethnic minorities in Dutch newspapers 1990-5: Patterns of criminalization and problematization

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