An HI absorbing circumnuclear disk in Cygnus A

We present Very Long Baseline Array (VLBA) HI absorption observations of the core region of the powerful radio galaxy Cygnus A. These data show both broad (FWHM = 231 +/- 21 km s(-1)) and narrow (FWHM < 30 km s(-1)) velocity width absorption components. The broad velocity absorption shows high opacity on the counter-jet, low opacity against the core and no absorption on the jet side. We argue that these results are most naturally explained by a circumnuclear Hi absorbing disk orientated roughly perpendicular to the jet axis. We estimate that the Hi absorbing gas lies at a radius of similar to 80 pc has a scale height of about 20 pc, density n > 10(4) cm(-3) and total column density in the range 10(23)-10(24) cm(-2). Models in which the Hi absorption is primarily from an atomic or a molecular gas phase can both fit our data. Modelling taking into account the effective beam shows that the broad Hi absorbing gas component does not cover the radio core in Cygnus A and therefore does not contribute to the gas column that blocks our view of the hidden quasar nucleus. If however Cygnus A were observed from a different direction, disk gas on similar to 100 pc radius scales would contribute significantly to the nuclear column density, implying that in some radio galaxies gas on these scales may contribute to the obscuration of the central engine. We argue that the circumnuclear torus in Cygnus A contains too little mass to power the AGN over > 10(7) yr but that material in the outer Hi absorbing gas disk can provide a reservoir to fuel the AGN and replenish torus clouds. The second narrow Hi absorption component is significantly redshifted (by 186 km s(-1))with respect to the systemic velocity and probably traces infalling gas which will ultimately fuel the source. This component could arise either within a tidal tail structure associated with a recent (minor) merger or be associated with an observed infalling giant molecular cloud

Extrasolar Planets in the Classroom

The field of extrasolar planets is still, in comparison with other astrophysical topics, in its infancy. There have been about 300 or so extrasolar planets detected and their detection has been accomplished by various different techniques. Here we present a simple laboratory experiment to show how planets are detected using the transit technique. Following the simple analysis procedure describe we are able to determine the planetary radius to be 1.27 +/- 0.20 R_{J} which, within errors agrees with the establish value of 1.32 +/- 0.25 R_{J}.Comment: 7 pages, 2 figures, published in Physics Educatio

Role of type 1 and type 3 fimbriae in Klebsiella pneumoniae biofilm formation

<p>Abstract</p> <p>Background</p> <p><it>Klebsiella pneumoniae </it>is an important gram-negative opportunistic pathogen causing primarily urinary tract infections, respiratory infections, and bacteraemia. The ability of bacteria to form biofilms on medical devices, e.g. catheters, has a major role in development of many nosocomial infections. Most clinical <it>K. pneumoniae </it>isolates express two types of fimbrial adhesins, type 1 fimbriae and type 3 fimbriae. In this study, we characterized the role of type 1 and type 3 fimbriae in <it>K. pneumoniae </it>biofilm formation.</p> <p>Results</p> <p>Isogenic fimbriae mutants of the clinical <it>K. pneumoniae </it>isolate C3091 were constructed, and their ability to form biofilm was investigated in a flow cell system by confocal scanning laser microscopy. The wild type strain was found to form characteristic biofilm and development of <it>K. pneumoniae </it>biofilm occurred primarily by clonal growth, not by recruitment of planktonic cells. Type 1 fimbriae did not influence biofilm formation and the expression of type 1 fimbriae was found to be down-regulated in biofilm forming cells. In contrast, expression of type 3 fimbriae was found to strongly promote biofilm formation.</p> <p>Conclusion</p> <p>By use of well defined isogenic mutants we found that type 3 fimbriae, but not type 1 fimbriae, strongly promote biofilm formation in <it>K. pneumoniae </it>C3091. As the vast majority of clinical <it>K. pneumoniae </it>isolates express type 3 fimbriae, this fimbrial adhesin may play a significant role in development of catheter associated <it>K. pneumoniae </it>infections.</p

Homozygous disruption of P450 side-chain cleavage (CYP11A1) is associated with prematurity, complete 46,XY sex reversal, and severe adrenal failure

Disruption of the P450 side-chain cleavage cytochrome (P450scc) enzyme due to deleterious mutations of the CYP11A1 gene is thought to be incompatible with fetal survival because of impaired progesterone production by the fetoplacental unit. We present a 46, XY patient with a homozygous disruption of CYP11A1.The child was born prematurely with complete sex reversal and severe adrenal insufficiency. Laboratory data showed diminished or absent steroidogenesis in all pathways. Molecular genetic analysis of the CYP11A1 gene revealed a homozygous single nucleotide deletion leading to a premature termination at codon position 288. This mutation will delete highly conserved regions of the P450scc enzyme and thus is predicted to lead to a nonfunctional protein. Both healthy parents were heterozygous for this mutation.Our report demonstrates that severe disruption of P450scc can be compatible with survival in rare instances. Furthermore, defects in this enzyme are inherited in an autosomal-recessive fashion, and heterozygote carriers can be healthy and fertile. The possibility of P450scc-independent pathways of steroid synthesis in addition to the current concept of luteoplacental shift of progesterone synthesis in humans has to be questioned

An atomic circumnuclear disk in Cygnus A

ABSTRACT We present Very Long Baseline Array (VLBA) H i absorption observations of the core region of the powerful radio galaxy Cygnus A. These data show both broad (FWHM = 244 ± 22km s −1 ) and narrow (FWHM &lt; 30km s −1 ) velocity components. Modeling of the broad velocity absorption shows high opacity on the counter-jet, low opacity against the core and no absorption on the jet side; we argue this is most naturally explained by a circumnuclear H i disk orientated roughly perpendicular to the jet axis. We estimate that the H i absorbing gas lies at a radius of ∼ 80 pc and has a scale height of about 20 pc. We estimate this gas has a minimum density n &gt; 10 4 cm −3 and a total column density in the range 10 23 − 10 24 cm −2 ; we cannot however determine whether it is primarily an atomic or molecular phase. We find that this gas component does not cover the radio core in Cygnus A and therefore does not contribute to the total gas column that blocks our view of the hidden quasar nucleus. If however we were observing Cygnus A from a different direction it could add significantly. This implies that in some radio galaxies gas on ∼ 100 pc scales may contribute to the obscuration of the central engine. We argue that the circumnuclear torus in Cygnus A contains too little mass to power the AGN over &gt; 10 7 yr but that material in the outer H i absorbing gas disk can provide a reservoir to fuel the AGN and replenish torus clouds. The second narrow H i absorption component is significantly redshifted (by 180km s −1 ) with respect to the systemic velocity and probably traces infalling gas which will ultimately fuel the source. This component could arise either within a tidal tail structure associated with a recent (minor) merger or be associated with an observed infalling giant molecular cloud

Sub-chronic inhalation of high concentrations of manganese sulfate induces lower airway pathology in rhesus monkeys

BACKGROUND: Neurotoxicity and pulmonary dysfunction are well-recognized problems associated with prolonged human exposure to high concentrations of airborne manganese. Surprisingly, histological characterization of pulmonary responses induced by manganese remains incomplete. The primary objective of this study was to characterize histologic changes in the monkey respiratory tract following manganese inhalation. METHODS: Subchronic (6 hr/day, 5 days/week) inhalation exposure of young male rhesus monkeys to manganese sulfate was performed. One cohort of monkeys (n = 4–6 animals/exposure concentration) was exposed to air or manganese sulfate at 0.06, 0.3, or 1.5 mg Mn/m(3 )for 65 exposure days. Another eight monkeys were exposed to manganese sulfate at 1.5 mg Mn/m(3 )for 65 exposure days and held for 45 or 90 days before evaluation. A second cohort (n = 4 monkeys per time point) was exposed to manganese sulfate at 1.5 mg Mn/m(3 )and evaluated after 15 or 33 exposure days. Evaluations included measurement of lung manganese concentrations and evaluation of respiratory histologic changes. Tissue manganese concentrations were compared for the exposure and control groups by tests for homogeneity of variance, analysis of variance, followed by Dunnett's multiple comparison. Histopathological findings were evaluated using a Pearson's Chi-Square test. RESULTS: Animals exposed to manganese sulfate at ≥0.3 mg Mn/m(3 )for 65 days had increased lung manganese concentrations. Exposure to manganese sulfate at 1.5 mg Mn/m(3 )for ≥15 exposure days resulted in increased lung manganese concentrations, mild subacute bronchiolitis, alveolar duct inflammation, and proliferation of bronchus-associated lymphoid tissue. Bronchiolitis and alveolar duct inflammatory changes were absent 45 days post-exposure, suggesting that these lesions are reversible upon cessation of subchronic high-dose manganese exposure. CONCLUSION: High-dose subchronic manganese sulfate inhalation is associated with increased lung manganese concentrations and small airway inflammatory changes in the absence of observable clinical signs. Subchronic exposure to manganese sulfate at exposure concentrations (≤0.3 mg Mn/m(3)) similar to the current 8-hr occupational threshold limit value established for inhaled manganese was not associated with pulmonary pathology

Is Centaurus A special? A neutral hydrogen perspective

Due to the proximity, the neutral hydrogen belonging to Centaurus A can be observed at high resolution with good sensitivity. This allows to study the morphology and kinematics in detail in order to understand the evolution of this radio-loud source (e.g. merger history, AGN activity). At the same time, it is important to compare the results to other sources of the same class (i.e. early-type galaxies in general and radio galaxies in particular) to see how Centaurus A fits into the global picture of early-type/radio galaxy evolution. The amount of HI, the morphology of a warped disk with HI clouds surrounding the disk and the regular kinematics of the inner part of the HI disk are not unusual for early-type galaxies. The growing evidence that mergers are not necessarily responsible for AGN activity fits with the observational result that the recent merger event in Centaurus A is not connected to the current phase of activity. Based on these results, we conclude that Centaurus A has typical neutral hydrogen properties for an early-type and radio galaxy and it can therefore - from an HI perspective - be seen as a typical example of its class.Comment: submitted to PASA; 7 pages, 4 figure

Structural and functional studies of Escherichia coli Aggregative Adherence Fimbriae (AAF/V) reveal a deficiency in extracellular matrix binding

Enteroaggregative Escherichia coli (EAEC) is an emerging cause of acute and persistent diarrhea worldwide. The pathogenesis of different EAEC stains is complicated, however, the early essential step begins with attachment of EAEC to intestinal mucosa via aggregative adherence fimbriae (AAFs). Currently, five different variants have been identified, which all share a degree of similarity in the gene organization of their operons and sequences. Here, we report the solution structure of Agg5A from the AAF/V variant. While preserving the major structural features shared by all AAF members, only Agg5A possesses an inserted helix at the beginning of the donor strand, which together with altered surface electrostatics, renders the protein unable to interact with fibronectin. Hence, here we characterize the first AAF variant with a binding mode that varies from previously described AAF

The EXPLORE Project I: A Deep Search for Transiting Extrasolar Planets

(Abridged) We discuss the design considerations of the EXPLORE (EXtra-solar PLanet Occultation REsearch) project, a series of transiting planet searches using 4-m-class telescopes to continuously monitor a single field of stars in the Galactic Plane in each ~2 week observing campaign. We discuss the general factors which determine the efficiency and the number of planets found by a transit search, including time sampling strategy and field selection. The primary goal is to select the most promising planet candidates for radial velocity follow-up observations. We show that with very high photometric precision light curves that have frequent time sampling and at least two detected transits, it is possible to uniquely solve for the main parameters of the eclipsing system (including planet radius) based on several important assumptions about the central star. Together with a measured spectral type for the star, this unique solution for orbital parameters provides a powerful method for ruling out most contaminants to transiting planet candidates. For the EXPLORE project, radial velocity follow-up observations for companion mass determination of the best candidates are done on 8-m-class telescopes within two or three months of the photometric campaigns. This same-season follow-up is made possible by the use of efficient pipelines to produce high quality light curves within weeks of the observations. We conclude by presenting early results from our first search, EXPLORE I, in which we reached <1% rms photometric precision (measured over a full night) on ~37,000 stars to I <= 18.2.Comment: accepted by ApJ. Main points unchanged but more thorough discussion of some issues. 36 pages, including 14 figure