The dragonfly nearby galaxies survey. Iv. A giant stellar disk in ngc 2841

Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of the fact that deep HI observations typically probe to a lower mass surface density than visible wavelength data. This paper presents low surface brightness optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of $\sim$70 kpc (5 $R_{25}$ or 23 inner disk scale lengths). The structure in the stellar disk traces the morphology of HI emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than $\sim$20 kpc, the ratio of the stellar to gas mass surface density is a constant 3:1. Beyond $\sim$30 kpc, the low surface brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion and in-situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy.Comment: 11 pages, 5 figures, accepted for publication in Ap

Satellite Assessment of Bio-Optical Properties of Northern Gulf of Mexico Coastal Waters Following Hurricanes Katrina and Rita

The impacts of major tropical storms events on coastal waters include sediment resuspension, intense water column mixing, and increased delivery of terrestrial materials into coastal waters. We examined satellite imagery acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color sensor aboard the Aqua spacecraft following two major hurricane events: Hurricane Katrina, which made landfall on 29 August 2005, and Hurricane Rita, which made landfall on 24 September. MODIS Aqua true color imagery revealed high turbidity levels in shelf waters immediately following the storms indicative of intense resuspension. However, imagery following the landfall of Katrina showed relatively rapid return of shelf water mass properties to pre-storm conditions. Indeed, MODIS Aqua-derived estimates of diffuse attenuation at 490 nm (K_490) and chlorophyll (chlor_a) from mid-August prior to the landfall of Hurricane Katrina were comparable to those observed in mid-September following the storm. Regions of elevated K_490 and chlor_a were evident in offshore waters and appeared to be associated with cyclonic circulation (cold-core eddies) identified on the basis of sea surface height anomaly (SSHA). Imagery acquired shortly after Hurricane Rita made landfall showed increased water column turbidity extending over a large area of the shelf off Louisiana and Texas, consistent with intense resuspension and sediment disturbance. An interannual comparison of satellite-derived estimates of K_490 for late September and early October revealed relatively lower levels in 2005, compared to the mean for the prior three years, in the vicinity of the Mississippi River birdfoot delta. In contrast, levels above the previous three year mean were observed off Texas and Louisiana 7-10 d after the passage of Rita. The lower values of K_490 near the delta could be attributed to relatively low river discharge during the preceding months of the 2005 season. The elevated levels off Texas and Louisiana were speculated to be due to the presence of fine grain sediment or dissolved materials that remained in the water column following the storm, and may also have been associated with enhanced phytoplankton biomass stimulated by the intense vertical mixing and offshore delivery of shelf water and associated nutrients. This latter view was supported by observations of high chlor_a in association with regions of cyclonic circulation

Seasonal Variability in Air-Sea Fluxes of CO\u3csub\u3e2\u3c/sub\u3e in a River-Influenced Coastal Margin

Recent studies in the northern Gulf of Mexico and elsewhere have demonstrated that enhanced biological production in large river plumes may contribute to a net surface influx of atmospheric CO2. However, large rivers also deliver significant amounts of terrestrial carbon into continental margin waters; hence, the potential for large and variable signals in carbon flux exist in these regions. Here, we used a combination of satellite and ship-based observations to examine variability in surface pCO(2) and air-sea flux of carbon dioxide in relation to variations in river discharge and seasonal environmental conditions. Underway surface pCO(2) showed large seasonal differences based on observations acquired during cruises in August 2004, October 2005, and April 2006. Strong cross-shelf gradients in pCO(2) were observed during August 2004 and April 2006, influenced by river outflow. Uniformly high values observed during October 2005 likely reflected the disturbed nature of the system after two major storm events (hurricanes Katrina and Rita). Satellite-derived assessments of pCO(2) were used in conjunction with estimates of wind fields to produce regional maps of surface water pCO(2) and air-sea fluxes. The region was a net sink for atmospheric CO2 in August 2004 (-0.96 to -1.2 mmol C m(-2) d(-1)) and net source during October 2005 and April 2006 (1.0 to 5.4 mmol C m(-2) d(-1)). Uncertainties in flux estimates, particularly for low salinity waters in April 2006, highlighted the need for more extensive in situ observations. Our results illustrate the utility of satellite approaches for providing regional assessments of coastal carbon budgets

Natural Competence Is Common among Clinical Isolates of Veillonella parvula and Is Useful for Genetic Manipulation of This Key Member of the Oral Microbiome

The six Veillonella species found in the human oral cavity are among the most abundant members of the oral flora, occurring in both supra- and subgingival dental plaque as well as on the oral mucosa. Epidemiological data have also implicated these species in the development of the most common oral diseases. Despite their ubiquity, abundance, and ecological significance, surprisingly little is known about Veillonella biology, largely due to the difficulties associated with their genetic manipulation. In an effort to improve genetic analyses of Veillonella species, we isolated a collection of veillonellae from clinical plaque samples and screened for natural competence using a newly developed transformation protocol. Numerous strains of V. parvula were found to exhibit a natural competence ability that was highly influenced by growth medium composition. By exploiting this ability, we were able to utilize cloning-independent allelic exchange mutagenesis to identify the likely source of DNA uptake machinery within a locus homologous to type II secretion systems (T2SS). Interestingly, V. parvula natural competence was found to exhibit a clear hierarchy of preference for different sources of DNA (plasmid < PCR product < genomic DNA), which is unlike most naturally competent species. Genomic comparisons with other members of the Veillonellaceae family suggest that natural competence is likely to be widely distributed within this group. To the best of our knowledge, this study is the first demonstration of natural competence and targeted allelic exchange mutagenesis within the entire Veillonellaceae family and demonstrates a simple and rapid method to study Veillonella genetics

Human Xq28 Inversion Polymorphism: From Sex Linkage to Genomics - A Genetic Mother Lode

An inversion polymorphism of the filamin and emerin genes at the tip of the long arm of the human X-chromosome serves as the basis of an investigative laboratory in which students learn something new about their own genomes. Long, nearly identical inverted repeats flanking the filamin and emerin genes illustrate how repetitive elements can lead to alterations in genome structure (inversions) through nonallelic homologous recombination. The near identity of the inverted repeats is an example of concerted evolution through gene conversion. While the laboratory in its entirety is designed for college level genetics courses, portions of the laboratory are appropriate for courses at other levels. Because the polymorphism is on the X-chromosome, the laboratory can be used in introductory biology courses to enhance understanding of sex-linkage and to test for Hardy-Weinberg equilibrium in females. More advanced topics, such as chromosome interference, the molecular model for recombination, and inversion heterozygosity suppression of recombination can be explored in upper-level genetics and evolution courses. DNA isolation, restriction digests, ligation, long PCR, and iPCR provide experience with techniques in molecular biology. This investigative laboratory weaves together topics stretching from molecular genetics to cytogenetics and sex-linkage, population genetics and evolutionary genetics

Confined granular packings: structure, stress, and forces

The structure and stresses of static granular packs in cylindrical containers are studied using large-scale discrete element molecular dynamics simulations in three dimensions. We generate packings by both pouring and sedimentation and examine how the final state depends on the method of construction. The vertical stress becomes depth-independent for deep piles and we compare these stress depth-profiles to the classical Janssen theory. The majority of the tangential forces for particle-wall contacts are found to be close to the Coulomb failure criterion, in agreement with the theory of Janssen, while particle-particle contacts in the bulk are far from the Coulomb criterion. In addition, we show that a linear hydrostatic-like region at the top of the packings unexplained by the Janssen theory arises because most of the particle-wall tangential forces in this region are far from the Coulomb yield criterion. The distributions of particle-particle and particle-wall contact forces $P(f)$ exhibit exponential-like decay at large forces in agreement with previous studies.Comment: 11 pages, 11 figures, submitted to PRE (v2) added new references, fixed typo

BioVEC: A program for Biomolecule Visualization with Ellipsoidal Coarse-graining

Biomolecule Visualization with Ellipsoidal Coarse-graining (BioVEC) is a tool for visualizing molecular dynamics simulation data while allowing coarse-grained residues to be rendered as ellipsoids. BioVEC reads in configuration files, which may be output from molecular dynamics simulations that include orientation output in either quaternion or ANISOU format, and can render frames of the trajectory in several common image formats for subsequent concatenation into a movie file. The BioVEC program is written in C++, uses the OpenGL API for rendering, and is open source. It is lightweight, allows for user-defined settings for and texture, and runs on either Windows or Linux platforms

A rare case of an aldosterone secreting metastatic adrenocortical carcinoma and papillary thyroid carcinoma in a 31-year-old male

We report a rare synchronous presentation of adrenocortical carcinoma (ACC) and papillary thyroid carcinoma (PTC). A 31-year-old male first presented with a large left adrenal mass that was identified during the workup for refractory hypertension due to hyperaldosteronism. The mass was removed surgically with pathology showing ACC. The patient was then treated with adjuvant radiation therapy and mitotane chemotherapy. Four months post ACC resection, metastatic ACC to the right upper lung and PTC in the left lobe of the thyroid were found in surveillance imaging. He subsequently developed pulmonary, contralateral adrenal and brain metastases from his ACC. Li Fraumeni syndrome and Multiple Endocrine Neoplasia Type I (MEN I) were considered, but testing of both P53 and menin genes showed no mutation. We also performed a review of the literature and found three similar cases, however gene mutation analysis was not performed.