697 research outputs found
The Understanding of Human Anatomy Elicited from Drawings of Some Bangladeshi Village Women and Children
There are a number of methods to obtain information about a person’s understanding of science (White & Gunston, 1992; Tunnicliffe & Reiss, 1999a). Drawings are considered one useful tool (Haney et al., 2004). Most techniques require respondents to talk or write their answers to questions. Osborne and Gilbert, 1980 used oral questions whilst written responses have been analysed, for example by Lewis, Leach and Wood-Robinson, 2000. Tunnicliffe and Reiss (1999b) elicited children’s spontaneous conversations about learners’ interpretations of brine shrimps
Structure of myelin P2 protein from equine spinal cord
Equine P2 protein has been isolated from horse spinal cord and its structure determined to 2.1 Å. Since equine myelin is a viable alternative to bovine tissue for large-scale preparations, characterization of the proteins from equine spinal cord myelin has been initiated. There is an unusually high amount of P2 protein in equine CNS myelin compared with other species. The structure was determined by molecular replacement and subsequently refined to an R value of 0.187 (<sub>free</sub> = 0.233). The structure contains a molecule of the detergent LDAO and HEPES buffer in the binding cavity and is otherwise analogous to other cellular retinol-binding proteins
Stochastic delocalization of finite populations
Heterogeneities in environmental conditions often induce corresponding
heterogeneities in the distribution of species. In the extreme case of a
localized patch of increased growth rates, reproducing populations can become
strongly concentrated at the patch despite the entropic tendency for population
to distribute evenly. Several deterministic mathematical models have been used
to characterize the conditions under which localized states can form, and how
they break down due to convective driving forces. Here, we study the
delocalization of a finite population in the presence of number fluctuations.
We find that any finite population delocalizes on sufficiently long time
scales. Depending on parameters, however, populations may remain localized for
a very long time. The typical waiting time to delocalization increases
exponentially with both population size and distance to the critical wind speed
of the deterministic approximation. We augment these simulation results by a
mathematical analysis that treats the reproduction and migration of individuals
as branching random walks subject to global constraints. For a particular
constraint, different from a fixed population size constraint, this model
yields a solvable first moment equation. We find that this solvable model
approximates very well the fixed population size model for large populations,
but starts to deviate as population sizes are small. The analytical approach
allows us to map out a phase diagram of the order parameter as a function of
the two driving parameters, inverse population size and wind speed. Our results
may be used to extend the analysis of delocalization transitions to different
settings, such as the viral quasi-species scenario
Allopatric and Sympatric Drivers of Speciation in Alviniconcha Hydrothermal Vent Snails
Despite significant advances in our understanding of speciation in the marine environment, the mechanisms underlying evolutionary diversification in deep-sea habitats remain poorly investigated. Here, we used multigene molecular clocks and population genetic inferences to examine processes that led to the emergence of the six extant lineages of Alviniconcha snails, a key taxon inhabiting deep-sea hydrothermal vents in the Indo-Pacific Ocean. We show that both allopatric divergence through historical vicariance and ecological isolation due to niche segregation contributed to speciation in this genus. The split between the two major Alviniconcha clades (separating A. boucheti and A. marisindica from A. kojimai, A. hessleri, and A. strummeri) probably resulted from tectonic processes leading to geographic separation, whereas the splits between co-occurring species might have been influenced by ecological factors, such as the availability of specific chemosynthetic symbionts. Phylogenetic origin of the sixth species, Alviniconcha adamantis, remains uncertain, although its sister position to other extant Alviniconcha lineages indicates a possible ancestral relationship. This study lays a foundation for future genomic studies aimed at deciphering the roles of local adaptation, reproductive biology, and host–symbiont compatibility in speciation of these vent-restricted snails
Evidence for a charge Kondo effect in Pb(1-x)Tl(x)Te from measurements of thermoelectric power
We report measurements of the thermoelectric power (TEP) for a series of
Pb(1-x)Tl(x)Te crystals with x = 0.0 to 1.3%. Although the TEP is very large
for x = 0.0, using a single band analysis based on older work for dilute
magnetic alloys we do find evidence for a Kondo contribution of 11 - 18 uV/K.
This analysis suggests that Tk is ~ 50 - 70 K, a factor 10 higher than
previously thought.Comment: 4 pages, 3 figure
Axial Seamount
Author Posting. © Oceanography Society, 2010. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 23, 1 (2010): 38-39.Axial Seamount is a hotspot volcano
superimposed on the Juan de Fuca Ridge
(JdFR) in the Northeast Pacific Ocean.
Due to its robust magma supply, it rises
~ 800 m above the rest of JdFR and has
a large elongate summit caldera with
two rift zones that parallel and overlap
with adjacent segments of the spreading
center
Resuspension by fish facilitates the transport and redistribution of coastal sediments
Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 57 (2012): 945-958, doi:10.4319/lo.2012.57.4.0945.Oxygen availability restricts groundfish to the oxygenated, shallow margins of Saanich Inlet, an intermittently anoxic fjord in British Columbia, Canada. New and previously reported 210Pb measurements in sediment cores compared with flux data from sediment traps indicate major focusing of sediments from the oxygenated margins to the anoxic basin seafloor. We present environmental and experimental evidence that groundfish activity in the margins is the major contributor to this focusing. Fine particles resuspended by groundfish are advected offshore by weak bottom currents, eventually settling in the anoxic basin. Transmittance and sediment trap data from the water column show that this transport process maintains an intermediate nepheloid layer (INL) in the center of the Inlet. This INL is located above the redox interface and is unrelated to water density shifts in the water column. We propose that this INL is shaped by the distribution of groundfish (as resuspension sources) along the slope and hence by oxygen availability to these fish. We support this conclusion with a conceptual model of the resuspension and offshore transport of sediment. This fish-induced transport mechanism for sediments is likely to enhance organic matter decomposition in oxygenated sediments and its sequestration in anoxic seafloors.The VENUS Project and University of Victoria
supported the ship and submersible time for field experiments,
and the U.S. Geological Survey and Coastal and Marine
Geological Program generously supported J.C. The project was
supported by Discovery Grants from the Natural Sciences and
Engineering Research Council of Canada to V.T. and P.S. and a
Yohay Ben-Nun fellowship and Moshe Shilo Center for Marine
Biogeochemistry Fund award to T.K
Structural Basis for the Recognition of Cellular mRNA Export Factor REF by Herpes Viral Proteins HSV-1 ICP27 and HVS ORF57
The herpesvirus proteins HSV-1 ICP27 and HVS ORF57 promote viral mRNA export by utilizing the cellular mRNA export machinery. This function is triggered by binding to proteins of the transcription-export (TREX) complex, in particular to REF/Aly which directs viral mRNA to the TAP/NFX1 pathway and, subsequently, to the nuclear pore for export to the cytoplasm. Here we have determined the structure of the REF-ICP27 interaction interface at atomic-resolution and provided a detailed comparison of the binding interfaces between ICP27, ORF57 and REF using solution-state NMR. Despite the absence of any obvious sequence similarity, both viral proteins bind on the same site of the folded RRM domain of REF, via short but specific recognition sites. The regions of ICP27 and ORF57 involved in binding by REF have been mapped as residues 104–112 and 103–120, respectively. We have identified the pattern of residues critical for REF/Aly recognition, common to both ICP27 and ORF57. The importance of the key amino acid residues within these binding sites was confirmed by site-directed mutagenesis. The functional significance of the ORF57-REF/Aly interaction was also probed using an ex vivo cytoplasmic viral mRNA accumulation assay and this revealed that mutants that reduce the protein-protein interaction dramatically decrease the ability of ORF57 to mediate the nuclear export of intronless viral mRNA. Together these data precisely map amino acid residues responsible for the direct interactions between viral adaptors and cellular REF/Aly and provide the first molecular details of how herpes viruses access the cellular mRNA export pathway
Phenotypic variation and fitness in a metapopulation of tubeworms (Ridgeia piscesae Jones) at hydrothermal vents
We examine the nature of variation in a hot vent tubeworm, Ridgeia piscesae, to determine how phenotypes are maintained and how reproductive potential is dictated by habitat. This foundation species at northeast Pacific hydrothermal sites occupies a wide habitat range in a highly heterogeneous environment. Where fluids supply high levels of dissolved sulphide for symbionts, the worm grows rapidly in a ‘‘short-fat’’ phenotype characterized by lush gill plumes; when plumes are healthy, sperm package capture is higher. This form can mature within months and has a high fecundity with continuous gamete output and a lifespan of about three years in unstable conditions. Other phenotypes occupy low fluid flux habitats that are more stable and individuals grow very slowly; however, they have low reproductive readiness that is hampered further by small, predator cropped branchiae, thus reducing fertilization and metabolite uptake. Although only the largest worms were measured, only 17% of low flux worms were reproductively competent compared to 91% of high flux worms. A model of reproductive readiness illustrates that tube diameter is a good predictor of reproductive output and that few low flux worms reached critical reproductive size. We postulate that most of the propagules for the vent fields originate from the larger tubeworms that live in small, unstable habitat patches. The large expanses of worms in more stable low flux habitat sustain a small, but long-term, reproductive output. Phenotypic variation is an adaptation that fosters both morphological and physiological responses to differences in chemical milieu and predator pressure. This foundation species forms a metapopulation with variable growth characteristics in a heterogeneous environment where a strategy of phenotypic variation bestows an advantage over specialization
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