2,547 research outputs found
Population Dynamics of Long-tailed Ducks Breeding on the Yukon-Kuskokwim Delta, Alaska
Population estimates for long-tailed ducks in North America have declined by nearly 50% over the past 30 years. Life history and population dynamics of this species are difficult to ascertain, because the birds nest at low densities across a broad range of habitat types. Between 1991 and 2004, we collected information on productivity and survival of long-tailed ducks at three locations on the Yukon-Kuskokwim Delta. Clutch size averaged 7.1 eggs, and nesting success averaged 30%. Duckling survival to 30 days old averaged 10% but was highly variable among years, ranging from 0% to 25%. Apparent annual survival of adult females based on mark-recapture of nesting females was estimated at 74%. We combined these estimates of survival and productivity into a matrix-based population model, which predicted an annual population decline of 19%. Elasticities indicated that population growth rate (?) was most sensitive to changes in adult female survival. Further, the relatively high sensitivity of ? to duckling survival suggests that low duckling survival may be a bottleneck to productivity in some years. These data represent the first attempt to synthesize a population model for this species. Although our analyses were hampered by the small sample sizes inherent in studying a dispersed nesting species, our model provides a basis for management actions and can be enhanced as additional data become available.Les estimations de populations dâhareldes kakawis en AmĂ©rique du Nord ont chutĂ© de prĂšs de 50 pour cent ces 30 derniĂšres annĂ©es. Le cycle biologique et la dynamique des populations de cette espĂšce sont difficiles Ă Ă©tablir car ces oiseaux nichent moyennant de faibles densitĂ©s dans une vaste gamme dâhabitats. De 1991 Ă 2004, nous avons recueilli des donnĂ©es sur la productivitĂ© et la survie des hareldes kakawis Ă trois emplacements du delta Yukon-Kuskokwim. Les couvĂ©es atteignaient 7,1 oeufs en moyenne, tandis que le succĂšs de reproduction sâĂ©tablissait gĂ©nĂ©ralement Ă 30 pour cent. En moyenne, 10 pour cent des jeunes canards survivaient jusquâĂ lâĂąge de 30 jours, mais ce taux variait beaucoup dâune annĂ©e Ă lâautre, allant de 0 pour cent Ă 25 pour cent. Annuellement, dâaprĂšs la mĂ©thode par marquage et recapture des femelles nidificatrices, la survie apparente des femelles adultes Ă©tait Ă©valuĂ©e Ă 74 pour cent. Nous avons combinĂ© ces estimations de survie et de productivitĂ© dans un modĂšle de population matriciel, ce qui a permis de prĂ©dire un dĂ©clin de population annuel de 19 pour cent. Selon les Ă©lasticitĂ©s, le taux de croissance de la population (?) Ă©tait plus sensible aux changements dans le cas de la survie des femelles adultes. Par ailleurs, la sensibilitĂ© relativement Ă©levĂ©e du ? par rapport Ă la survie des jeunes canards laisse croire que le faible taux de survie des jeunes canards pourrait prĂ©senter une embĂ»che en matiĂšre de productivitĂ© dâici quelques annĂ©es. Ces donnĂ©es reprĂ©sentent la premiĂšre tentative de synthĂšse dâun modĂšle de population pour cette espĂšce. Bien que nos analyses aient Ă©tĂ© gĂȘnĂ©es par la petite taille des Ă©chantillons inhĂ©rente Ă lâĂ©tude dâespĂšces de nidification dispersĂ©es, notre modĂšle fournit un fondement permettant dâaboutir Ă des mesures de gestion en plus de prĂ©senter la possibilitĂ© dâĂȘtre amĂ©liorĂ© au fur et Ă mesure que des donnĂ©es supplĂ©mentaires sont disponibles
Color confinement and dual superconductivity of the vacuum. III
It is demonstrated that monopole condensation in the confined phase of SU(2)
and SU(3) gauge theories is independent of the specific Abelian projection used
to define the monopoles. Hence the dual excitations which condense in the
vacuum to produce confinement must have magnetic U(1) charge in all the Abelian
projections. Some physical implications of this result are discussed.Comment: 6 pages, 5 postscript figure
Dual superconductivity in the SU(2) pure gauge vacuum: a lattice study
We investigate the dual superconductivity hypothesis in pure SU(2) lattice
gauge theory. We focus on the dual Meissner effect by analyzing the
distribution of the color fields due to a static quark-antiquark pair. We find
evidence of the dual Meissner effect both in the maximally Abelian gauge and
without gauge fixing. We measure the London penetration length. Our results
suggest that the London penetration length is a physical gauge-invariant
quantity. We put out a simple relation between the penetration length and the
square root of the string tension. We find that our extimation is quite close
to the extrapolated continuum limit available in the literature. A remarkable
consequence of our study is that an effective Abelian theory can account for
the long range properties of the SU(2) confining vacuum.Comment: 38 pages, uuencoded compressed (using GNU's gzip) tar file containing
1 LaTeX2e file (to be processed 3 times) + 16 encapsulated Postscript
figures. A full Postscript version of this paper is available at
http://www.ba.infn.it/disk$gruppo_4/cosmai/www/papers/195-95.P
Chromosome conformation maps in fission yeast reveal cell cycle dependent sub nuclear structure
Successful progression through the cell cycle requires spatial and temporal regulation of gene transcript levels and the number, positions and condensation levels of chromosomes. Here we present a high resolution survey of genome interactions in Schizosaccharomyces pombe using synchronized cells to investigate cell cycle dependent changes in genome organization and transcription. Cell cycle dependent interactions were captured between and within S. pombe chromosomes. Known features of genome organization (e.g. the clustering of telomeres and retrotransposon long terminal repeats (LTRs)) were observed throughout the cell cycle. There were clear correlations between transcript levels and chromosomal interactions between genes, consistent with a role for interactions in transcriptional regulation at specific stages of the cell cycle. In silico reconstructions of the chromosome organization within the S. pombe nuclei were made by polymer modeling. These models suggest that groups of genes with high and low, or differentially regulated transcript levels have preferred positions within the S. pombe nucleus. We conclude that the S. pombe nucleus is spatially divided into functional sub-nuclear domains that correlate with gene activity. The observation that chromosomal interactions are maintained even when chromosomes are fully condensed in M phase implicates genome organization in epigenetic inheritance and bookmarking
Graphene oxide functional nanohybrids with magnetic nanoparticles for improved vectorization of doxorubicin to neuroblastoma cells
With the aim to obtain a site-specific doxorubicin (DOX) delivery in neuroblastoma SH-SY5Y cells, we designed an hybrid nanocarrier combining graphene oxide (GO) and magnetic iron oxide nanoparticles (MNPs), acting as core elements, and a curcuminâhuman serum albumin conjugate as functional coating. The nanohybrid, synthesized by redox reaction between the MNPs@GO system and albumin bioconjugate, consisted of MNPs@GO nanosheets homogeneously coated by the bioconjugate as verified by SEM investigations. Drug release experiments showed a pH-responsive behavior with higher release amounts in acidic (45% at pH 5.0) vs. neutral (28% at pH 7.4) environments. Cell internalization studies proved the presence of nanohybrid inside SH-SY5Y cytoplasm. The improved efficacy obtained in viability assays is given by the synergy of functional coating and MNPs constituting the nanohybrids: while curcumin moieties were able to keep low DOX cytotoxicity levels (at concentrations of 0.44â0.88 ”M), the presence of MNPs allowed remote actuation on the nanohybrid by a magnetic field, increasing the dose delivered at the target site
Economics of education research: a review and future prospects
In this paper we offer an appraisal of the economics of education research area, charting its history as a field and discussing the ways in which economists have contributed both to education research and to education policy-making. In particular, we highlight the theoretical and methodological contributions that economists have made to the field of education during the last 50 years. Despite the success of the economics of education as a field of inquiry, we argue that some of the contributions made by economists could be limited if the economics of education is seen as quite distinct from the other disciplines working in the field of education. In these areas of common interest, economists need to work side by side with the other major disciplines in the field of education if their contribution to the field is to be maximised, particularly in terms of applying improved methodology. We conclude that the study of education acquisition and its economic and social impact in the economics of education research area is very likely to remain a fertile research ground. Acknowledgement
New approaches to the restoration of shallow marginal peatlands
ArticleGlobally, the historic and recent exploitation of peatlands through management practices such as agricultural reclamation, peat harvesting or forestry, have caused extensive damage to these ecosystems. Their value is now increasingly recognised, and restoration and rehabilitation programmes are underway to improve some of the ecosystem services provided by peatlands: blocking drainage ditches in deep peat has been shown to improve the storage of water, decrease carbon losses in the long-term, and improve biodiversity. However, whilst the restoration process has benefitted from experience and technical advice gained from restoration of deep peatlands, shallow peatlands have received less attention in the literature, despite being extensive in both uplands and lowlands. Using the experience gained from the restoration of the shallow peatlands of Exmoor National Park (UK), and two test catchments in particular, this paper provides technical guidance which can be applied to the restoration of other shallow peatlands worldwide. Experience showed that integrating knowledge of the historical environment at the planning stage of restoration was essential, as it enabled the effective mitigation of any threat to archaeological features and sites. The use of bales, commonly employed in other upland ecosystems, was found to be problematic. Instead, âleaky damsâ or wood and peat combination dams were used, which are both more efficient at reducing and diverting the flow, and longer lasting than bale dams. Finally, an average restoration cost (ÂŁ306 ha-1) for Exmoor, below the median national value across the whole of the UK, demonstrates the cost-effectiveness of these techniques. However, local differences in peat depth and ditch characteristics (i.e. length, depth and width) between sites affect both the feasibility and the cost of restoration. Overall, the restoration of shallow peatlands is shown to be technically viable; this paper provides a template for such process over analogous landscapes.South West WaterUniversity of ExeterTechnology Strategy BoardNERCKnowledge Transfer Partnership programm
Linear and nonlinear rheology of wormlike micelles
Several surfactant molecules self-assemble in solution to form long,
cylindrical, flexible wormlike micelles. These micelles can be entangled with
each other leading to viscoelastic phases. The rheological properties of such
phases are very interesting and have been the subject of a large number of
experimental and theoretical studies in recent years. We shall report on our
recent work on the macrorheology, microrheology and nonlinear flow behaviour of
dilute aqueous solutions of a surfactant CTAT (Cetyltrimethylammonium
Tosilate). This system forms elongated micelles and exhibits strong
viscoelasticity at low concentrations ( 0.9 wt%) without the addition of
electrolytes. Microrheology measurements of have been done using
diffusing wave spectroscopy which will be compared with the conventional
frequency sweep measurements done using a cone and plate rheometer. The second
part of the paper deals with the nonlinear rheology where the measured shear
stress is a nonmonotonic function of the shear rate . In
stress-controlled experiments, the shear stress shows a plateau for
larger than some critical strain rate, similar to the earlier
reports on CPyCl/NaSal system. Cates et al have proposed that the plateau is a
signature of mechanical instability in the form of shear bands. We have carried
out extensive experiments under controlled strain rate conditions, to study the
time-dependence of shear stress. The measured time series of shear stress has
been analysed in terms of correlation integrals and Lyapunov exponents to show
unambiguously that the behaviour is typical of low dimensional dynamical
systems.Comment: 15 pages, 10 eps figure
The Role of Spokesperson in Ambiguous and Complex Crises: The CDC and Anthrax
This study evaluates the role of spokespersons in complex organizations facing ambiguous crises. Specifically, the Centers for Disease Control and Preventionâs (CDC) response to the anthrax crisis in 2001 is offered as a case study. A content analysis of the print media coverage of the anthrax crisis reveals that many claiming affiliation with the CDC spoke on behalf of the organization, resulting in what appeared to be a fragmented CDC message. The study concludes that the CDCâs failure to provide a central spokesperson contributed to the ambiguity of the situation
Black Holes, Mergers, and the Entropy Budget of the Universe
Vast amounts of entropy are produced in black hole formation, and the amount
of entropy stored in supermassive black holes at the centers of galaxies is now
much greater than the entropy free in the rest of the universe. Either mergers
involved in forming supermassive black holes are rare,or the holes must be very
efficient at capturing nearly all the entropy generated in the process.
We argue that this information can be used to constrain supermassive black
hole production, and may eventually provide a check on numerical results for
mergers involving black holes
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