1,169 research outputs found
Specificity of Salt Marsh Diazotrophs for Vegetation Zones and Plant Hosts: Results from a North American marsh
Salt marshes located on the east coast of temperate North America are highly productive, typically nitrogen-limited, and support diverse assemblages of free-living nitrogen fixing (diazotrophic) bacteria. This article reviews and analyzes data from North Inlet estuary (SC, USA), addressing diazotroph assemblage structure and the influence of plant host and environmental conditions on the assemblage. The North Inlet estuary is a salt marsh ecosystem in which anthropogenic influences are minimal and the distributions of diazotrophs are governed by the natural biota and dynamics of the system. Denaturing gradient gel electrophoresis fingerprinting and phylogenetic analyses of recovered sequences demonstrated that the distributions of some diazotrophs reflect plant host specificity and that diazotroph assemblages distributed across marsh gradients are also heavily influenced by edaphic conditions. Broadly distributed diazotrophs that are capable of maintaining populations under all environmental conditions spanning such gradients are also present in these assemblages. Statistical analyses indicate that the structures of diazotroph assemblages in different vegetation zones are significantly (p < 0.01) different. New data presented here demonstrate the heterogeneity of salt marsh rhizosphere microenvironments, and corroborate previous findings from different plant hosts growing at several locations within this estuary. The data from these collected works support the hypothesis that the biogeography of microorganisms is non-random and these biogeographic patterns are predictable
A Forced-Choice Rating Scale for College Instructors
The purpose of this study was to construct a forced-choice rating scale for evaluating students\u27 opinions of college instructors. The scale constructed consists of 20 tetrads, or groups of 4 statements descriptive of instructors. These statements were chosen so that a pair of favorable items, both appearing to be equally favorable, and a pair of unfavorable items, both appearing to be equally unfavorable, make up each tetrad. From each tetrad the rater must choose the item most characteristic and the item least characteristic of the ratee. The reason for choosing items in this manner can be seen in Sisson\u27s statement of the basic assumptions underlying the forced-choice method, which was used in rating Army officers
Dynamic Stability and Control Characteristics of a Delta-wing Vertically Rising Airplane Model in Take-offs, Landings and Hovering Flight
Additional Studies of the Stability and Controllability of an Unswept-wing Vertically Rising Airplane Model in Hovering Flight Including Studies of Various Tethered Landing Techniques
Effects of Low Tide Rainfall on Intertidal Zone Material Cycling
Sediment transport by rainfall-runoff processes is well documented for terrestrial landscapes but few studies have focused on rainfall-runoff effects in intertidal areas. Here we present geochemical analyses performed on sediment samples collected during low tide irrigation experiments, and tidal channel turbidity measurements taken during natural rainfall over North Inlet Marsh, South Carolina. Order of magnitude approximations indicate that a single 10 minute storm may entrain 8-15% of the local annual average sediment accumulation. This rainfall-entrained material is enriched in organic nitrogen and marine algal matter, and therefore of high nutritional quality
Dynamic Stability and Control Characteristics of a Vertically Rising Airplane Model in Hovering Flight
The Quintuple Quasar: Radio and Optical Observations
We present results from high-resolution radio and optical observations of PMN
J0134-0931, a gravitational lens with a unique radio morphology and an
extremely red optical counterpart. Our data support the theory of Keeton & Winn
(2003): five of the six observed radio components are multiple images of a
single quasar, produced by a pair of lens galaxies. Multi-frequency VLBA maps
show that the sixth and faintest component has a different radio spectrum than
the others, confirming that it represents a second component of the background
source rather than a sixth image. The lens models predict that there should be
additional faint images of this second source component, and we find evidence
for one of the predicted images. The previously-observed large angular sizes of
two of the five bright components are not intrinsic (which would have excluded
the possibility that they are lensed images), but are instead due to scatter
broadening. Both the extended radio emission observed at low frequencies, and
the intrinsic image shapes observed at high frequencies, can be explained by
the lens models. The pair of lens galaxies is marginally detected in HST
images. The differential extinction of the quasar images suggests that the
extreme red color of the quasar is at least partly due to dust in the lens
galaxies.Comment: ApJ, in press. 22 pp, 10 fig
Late-Onset Erythropoietic Porphyria Caused by a Chromosome 18q Deletion in Erythroid Cells
The erythropoietic porphyrias, erythropoietic protoporphyria and congenital erythropoietic porphyria, result from germline mutations in the ferrochelatase gene and uroporphyrinogen III synthase gene, respectively. Both conditions normally present in childhood but rare cases with onset past the age of 40 y have been reported. Here we show that late-onset erythropoietic protoporphyria can be caused by deletion of the ferrochelatase gene in hematopoietic cells with clonal expansion as part of the myelodysplastic process. This is the first direct demonstration of porphyria produced by an acquired molecular defect restricted to one tissue. Some other cases of late-onset erythropoietic porphyria may be explained by a similar mechanism
Impacts of colonial waterbirds on vegetation and potential restoration of island habitats
Colonial waterbirds have impacted forested island ecosystems throughout their breeding range, changing vegetation, and soil characteristics and bird communities. Our objectives were to (1) determine effects of three levels of colonial waterbird exclusion on overall vegetation diversity and growth, and survival of a candidate restoration species (black elderberry; Sambucus nigra canadensis); (2) investigate effects of different planting techniques on survival and growth of black elderberry; and (3) determine effects of waterbird colonization on soil chemistry. In 2012, we investigated effects of three levels of waterbird exclusion (none control plots [CON]; partial, which excluded waterbirds larger than gulls [PEX]; and full which excluded all waterbirds [FEX]) on bird use, existing vegetation growth and diversity, and survival of planted black elderberry on three islands in Door County, WI, Lake Michigan. In 2013, we evaluated survival of black elderberry established with four planting treatments within three waterbird exclusion treatments on two islands in 2013.We also compared soil chemistry characteristics between islands with and without nesting waterbirds for 2 years. Overall plant growth was greater in exclosures, but elderberry survival was similar among treatments. Soil replacement and weed suppression planting treatments did not affect survival, but generally increased overall elderberry biomass. Soil from nesting islands was more acidic and had greater nutrient concentrations than reference islands. Exclusion or removal of colonial nesting waterbirds from islands may improve overall vegetation growth, but successful restoration of woody vegetation may require significant soil manipulation and planting
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