1,377 research outputs found
The world wide spread of space technology
Space technological capabilities and developments in US, USSR, Western Europe, Japan, China, and developing nation
Anthropogenic nutrients and harmful algae in coastal waters
© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Environmental Management 146 (2014): 206-216, doi:10.1016/j.jenvman.2014.07.002.Harmful algal blooms (HABs) are thought to be increasing in coastal waters worldwide. Anthropogenic nutrient enrichment has been proposed as a principal causative factor of this increase through elevated inorganic and/or organic nutrient concentrations and modified nutrient ratios. We assess: 1) the level of understanding of the link between the amount, form and ratio of anthropogenic nutrients and HABs; 2) the evidence for a link between anthropogenically generated HABs and negative impacts on human health; and 3) the economic implications of anthropogenic nutrient/HAB interactions. We demonstrate that an anthropogenic nutrient-HAB link is far from universal, and where it has been demonstrated, it is most frequently associated with high biomass rather than low biomass (biotoxin producing) HABs. While organic nutrients have been shown to support the growth of a range of HAB species, insufficient evidence exists to clearly establish if these nutrients specifically promote the growth of harmful species in preference to benign ones, or if/how they influence toxicity of harmful species. We conclude that the role of anthropogenic nutrients in promoting HABs is site-specific, with hydrodynamic processes often determining whether blooms occur. We also find a lack of evidence of widespread significant adverse health impacts from anthropogenic nutrient-generated HABs, although this may be partly due to a lack of human/animal health and HAB monitoring. Detailed economic evaluation and cost/benefit analysis of the impact of anthropogenically generated HABs, or nutrient reduction schemes to alleviate them, is also frequently lacking.The work described here is based in part on a project âHarmful Algae, Nuisance Blooms and Anthropogenic Nutrient Enrichmentâ funded by the UK Department for Environment, Food and Rural Affairs (contract ME2208). In addition KD was supported by the FP7 project Asimuth and funding from the NERC Shelf Seas Biogeochemistry and PURE Associates programmes. PJH was supported by University Grants Council of Hong Kong AoE project (AoE/P-04/0401). PH and LEF were funded by the US National Science Foundation (NSF) Award 1009106; LEF was funded in part by the European Regional Development Fund and European Social Fund (University of Exeter, Truro, Cornwall, UK). GM was supported by a NERC PhD studentship
Anomalous Dynamics of Translocation
We study the dynamics of the passage of a polymer through a membrane pore
(translocation), focusing on the scaling properties with the number of monomers
. The natural coordinate for translocation is the number of monomers on one
side of the hole at a given time. Commonly used models which assume Brownian
dynamics for this variable predict a mean (unforced) passage time that
scales as , even in the presence of an entropic barrier. However, the time
it takes for a free polymer to diffuse a distance of the order of its radius by
Rouse dynamics scales with an exponent larger than 2, and this should provide a
lower bound to the translocation time. To resolve this discrepancy, we perform
numerical simulations with Rouse dynamics for both phantom (in space dimensions
and 2), and self-avoiding (in ) chains. The results indicate that
for large , translocation times scale in the same manner as diffusion times,
but with a larger prefactor that depends on the size of the hole. Such scaling
implies anomalous dynamics for the translocation process. In particular, the
fluctuations in the monomer number at the hole are predicted to be
non-diffusive at short times, while the average pulling velocity of the polymer
in the presence of a chemical potential difference is predicted to depend on
.Comment: 9 pages, 9 figures. Submitted to Physical Review
Determination of the Axial-Vector Weak Coupling Constant with Ultracold Neutrons
A precise measurement of the neutron decay -asymmetry has been
carried out using polarized ultracold neutrons (UCN) from the pulsed spallation
UCN source at the Los Alamos Neutron Science Center (LANSCE). Combining data
obtained in 2008 and 2009, we report , from which we determine the ratio of the
axial-vector to vector weak coupling of the nucleon .Comment: 5 pages, 2 figure
Anomalous Dynamics of Forced Translocation
We consider the passage of long polymers of length N through a hole in a
membrane. If the process is slow, it is in principle possible to focus on the
dynamics of the number of monomers s on one side of the membrane, assuming that
the two segments are in equilibrium. The dynamics of s(t) in such a limit would
be diffusive, with a mean translocation time scaling as N^2 in the absence of a
force, and proportional to N when a force is applied. We demonstrate that the
assumption of equilibrium must break down for sufficiently long polymers (more
easily when forced), and provide lower bounds for the translocation time by
comparison to unimpeded motion of the polymer. These lower bounds exceed the
time scales calculated on the basis of equilibrium, and point to anomalous
(sub-diffusive) character of translocation dynamics. This is explicitly
verified by numerical simulations of the unforced translocation of a
self-avoiding polymer. Forced translocation times are shown to strongly depend
on the method by which the force is applied. In particular, pulling the polymer
by the end leads to much longer times than when a chemical potential difference
is applied across the membrane. The bounds in these cases grow as N^2 and
N^{1+\nu}, respectively, where \nu is the exponent that relates the scaling of
the radius of gyration to N. Our simulations demonstrate that the actual
translocation times scale in the same manner as the bounds, although influenced
by strong finite size effects which persist even for the longest polymers that
we considered (N=512).Comment: 13 pages, RevTeX4, 16 eps figure
Implications of teacher life-work histories for conceptualisations of âcareâ: narratives from rural Zimbabwe
Schools are increasingly seen as key sites for support to HIV-affected and other vulnerable children, and teachers are assigned the critical role of identifying and providing psychosocial support. Drawing on the life-work history narratives of twelve teachers in Zimbabwe, this paper explores the psychosocial processes underpinning teachersâ conceptualisations of these caring roles. The influence of prolonged adversity, formative relationships, and broader patterns of social and institutional change in teacher identity formation processes speak to the complex and embodied nature of understandings of âcareâ. In such extreme settings teachers prioritise the material and disciplinary aspects of âcareâ that they see as essential for supporting children to overcome hardship. This focus not only means that emotional support as envisaged in international policy is commonly overlooked, but also exposes a wider ideological clash about childrearing. This tension together with an overall ambivalence surrounding teacher identities puts further strain on teacher-student relationships. We propose the current trainings on providing emotional support are insufficient and that more active focus needs to be directed at support to teachers in relation with their students
Atomistic modelling of large-scale metal film growth fronts
We present simulations of metallization morphologies under ionized sputter
deposition conditions, obtained by a new theoretical approach. By means of
molecular dynamics simulations using a carefully designed interaction
potential, we analyze the surface adsorption, reflection, and etching reactions
taking place during Al physical vapor deposition, and calculate their relative
probability. These probabilities are then employed in a feature-scale
cellular-automaton simulator, which produces calculated film morphologies in
excellent agreement with scanning-electron-microscopy data on ionized sputter
deposition.Comment: RevTeX 4 pages, 2 figure
Uncoupling growth from phosphorus uptake in Lemna: Implications for use of duckweed in wastewater remediation and P recovery in temperate climates
Phosphorus (P) is an essential nutrient for crop growth and the second most limiting after N. Current supplies rely on Pârich rocks that are unevenly distributed globally and exploited unsustainably, leading to concerns about future availability and therefore food security. Duckweeds (Lemnaceae) are aquatic macrophytes used in wastewater remediation with the potential for nutrient recycling as feed or fertilizer. The use of duckweeds in this way is confined to tropical regions as it has previously been assumed that growth in the colder seasons of the temperate regions would be insufficient. In this study, the combined effects of cool temperatures and short photoperiods on growth and P uptake and accumulation in Lemna were investigated under controlled laboratory conditions. Growth and P accumulation in Lemna can be uncoupled, with significant P removal from the medium and accumulation within the plants occurring even at 8°C and 6âhr photoperiods. Direct measurement of radiolabeled phosphate uptake confirmed that while transport is strongly temperature dependent, uptake can still be measured at 5°C. Prior phosphate starvation of the duckweed and use of nitrate as the nitrogen (N) source also greatly increased the rate of P removal and inâcell accumulation. These results form the basis for further examination of the feasibility of duckweedâbased systems for wastewater treatment and P recapture in temperate climates, particularly in small, rural treatment works
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