2,614 research outputs found
"Wet-to-Dry" Conformational Transition of Polymer Layers Grafted to Nanoparticles in Nanocomposite
The present communication reports the first direct measurement of the
conformation of a polymer corona grafted around silica nano-particles dispersed
inside a nanocomposite, a matrix of the same polymer. This measurement
constitutes an experimental breakthrough based on a refined combination of
chemical synthesis, which permits to match the contribution of the neutron
silica signal inside the composite, and the use of complementary scattering
methods SANS and SAXS to extract the grafted polymer layer form factor from the
inter-particles silica structure factor. The modelization of the signal of the
grafted polymer on nanoparticles inside the matrix and the direct comparison
with the form factor of the same particles in solution show a clear-cut change
of the polymer conformation from bulk to the nanocomposite: a transition from a
stretched and swollen form in solution to a Gaussian conformation in the matrix
followed with a compression of a factor two of the grafted corona. In the
probed range, increasing the interactions between the grafted particles (by
increasing the particle volume fraction) or between the grafted and the free
matrix chains (decreasing the grafted-free chain length ratio) does not
influence the amplitude of the grafted brush compression. This is the first
direct observation of the wet-to-dry conformational transition theoretically
expected to minimize the free energy of swelling of grafted chains in
interaction with free matrix chains, illustrating the competition between the
mixing entropy of grafted and free chains, and the elastic deformation of the
grafted chains. In addition to the experimental validation of the theoretical
prediction, this result constitutes a new insight for the nderstanding of the
general problem of dispersion of nanoparticles inside a polymer matrix for the
design of new nanocomposites materials
Dinoflagellates Amyloodinium and Ichthyodinium (Dinophyceae), parasites of marine fishes in the South Atlantic Ocean
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Diseases of Aquatic Organisms 131 (2018): 29-37, doi:10.3354/dao03274.The morphology and molecular phylogeny of the parasitic dinoflagellates
Ichthyodinium chabelardi and Amyloodinium ocellatum was investigated off Brazil
(South Atlantic Ocean). This is the first record of Ichthyodinium and the first molecular
data of both parasites from the southern hemisphere. Ichthyodinium chabelardi infected
the yolk of eggs of feral populations of Argentine anchovy (Engraulis anchoita;
Engraulidae) and Brazilian sardinella (Sardinella brasiliensis; Clupeidae) in different
seasons. The SSU rRNA and ITS gene sequences were identical and confirmed
Ichthyodinium as a host generalist. The new sequences clustered with the type species I.
chabelardi from the North Atlantic and environmental sequences from the Pacific
Ocean. A second species from the western Pacific remains undescribed. Amyloodinium
ocellatum was isolated from the gills of a cultured cobia fish (Rachycentron canadum)
after causing mortality. The SSU rRNA gene sequence of the Brazilian isolate was
almost identical to those from the northern hemisphere. This suggests a single species
with a widespread distribution, although it is uncertain whether the species has a natural
pantropical distribution or is the result of artificial distribution due to the humaninduced
fish transport.F.G. was supported by the Brazilian Conselho Nacional de
Desenvolvimento Científico e Tecnológico [grant number BJT 370646/2013–14]
Brain Amino Acids and Biogenic Amines Under Various Atmospheric Mixtures Semiannual Report, 1 Mar. 1965 - 30 Apr. 1966
Effects of exposure to different gaseous atmospheric mixtures on free amino acids and biogenic amines in rat brain
Trends in Europe in higher education
Published ArticleThis article deals with the developments in the higher education sector in Europe. It addresses the specific European context in which the changes take place. It also touches upon the important trends that can be noted over the last years. A number of them have a fundamental effect on the development of the European higher education systems towards a more unified system, allowing for a significant increase of mobility among staff and students, and rationalising the educational systems
A kleptoplastidic dinoflagellate and the tipping point between transient and fully integrated plastid endosymbiosis
Plastid endosymbiosis has been a major force in the evolution of eukaryotic cellular complexity, but how endosymbionts are integrated is still poorly understood at a mechanistic level. Dinoflagellates, an ecologically important protist lineage, represent a unique model to study this process because dinoflagellate plastids have repeatedly been reduced, lost, and replaced by new plastids, leading to a spectrum of ages and integration levels. Here we describe deep-transcriptomic analyses of the Antarctic Ross Sea dinoflagellate (RSD), which harbors long-term but temporary kleptoplasts stolen from haptophyte prey, and is closely related to dinoflagellates with fully integrated plastids derived from different haptophytes. In some members of this lineage, called the Kareniaceae, their tertiary haptophyte plastids have crossed a tipping point to stable integration, but RSD has not, and may therefore reveal the order of events leading up to endosymbiotic integration. We show that RSD has retained its ancestral secondary plastid and has partitioned functions between this plastid and the kleptoplast. It has also obtained genes for kleptoplast-targeted proteins via horizontal gene transfer (HGT) that are not derived from the kleptoplast lineage. Importantly, many of these HGTs are also found in the related species with fully integrated plastids, which provides direct evidence that genetic integration preceded organelle fixation. Finally, we find that expression of kleptoplast-targeted genes is unaffected by environmental parameters, unlike prey-encoded homologs, suggesting that kleptoplast-targeted HGTs have adapted to posttranscriptional regulation mechanisms of the host
Phylogeny and synonymy of Gyrodinium heterostriatum comb. nov. (Dinophyceae), a common unarmored dinoflagellate in the world oceans
© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gómez, F., Artigas, L.F., Gast, R.J. Phylogeny and synonymy of Gyrodinium heterostriatum comb. nov. (Dinophyceae), a common unarmored dinoflagellate in the world oceans. Acta Protozoologica, 59 (2), (2020): 77-87, doi: 10.4467/16890027AP.20.007.12675.The North Sea and the English Channel are regions with a long tradition of plankton studies, where the colony-forming haptophyte Phaeocystis globosa dominates the spring phytoplankton blooms. Among its predators, we investigated an abundant unarmored dinoflagellate (~3000 cells per liter) in the North Sea in May 2019. It has been reported in the literature as Gymnodinium heterostriatum or G. striatissimum, and often identified as Gyrodinium spirale. Phylogenetic analyses using the small-, large subunit- and Internal Transcriber Spacers of the ribosomal RNA (SSU-, LSU-, ITS rRNA) gene sequences indicate that our isolates clustered within the Gyrodinium clade. The new sequences formed a sister group with sequences of the freshwater taxon Gyrodinium helveticum, being one of the infrequent marine-freshwater transitions in the microbial world. This isolate is the first characterized member of a clade of numerous environmental sequences widely distributed from cold to tropical seas. This common and abundant taxon has received several names due to its morphological plasticity (changes of size and shape, often deformed after engulfing prey) and the difficulty in discerning surface striation. We conclude that the priority is for the species name Gymnodinium heterostriatum Kofoid & Swezy 1921, a new name that was proposed for Gymnodinium spirale var. obtusum sensu Dogiel 1906. The species Gyrodinium striatissimum (Hulburt 1957) Gert Hansen & Moestrup 2000 and Gymnodinium lucidum D. Ballantine in Parke & Dixon 1964 (=G. hyalinum M. Lebour 1925) are posterior synonyms. We propose Gyrodinium heterostriatum comb. nov. for Gymnodinium heterostriatum.F.G. was partly supported by the convention #2101893310 between CNRS INSU and the French Ministry of Ecology (MTES) for the implementation of the Monitoring Program of the European Marine Strategy Framework directive (MSFD) for pelagic habitats and the descriptor ‘biodiversity’. Samples were collected within the framework of JERICO-NEXT (www.jerico-ri.eu), a European (H2020) project to establish a joint international network of coastal observatories, during a 4-day collaborative monitoring
campaign of the Southern North Sea. Part of the infrastructure and data were provided by VLIZ (Flanders Marine Institute) and
funded by Research Foundation-Flanders (FWO) as part of the Belgian contribution to the LifeWatch project
Gel transitions in colloidal suspensions
The idealized mode coupling theory (MCT) is applied to colloidal systems
interacting via short-range attractive interactions of Yukawa form. At low
temperatures MCT predicts a slowing down of the local dynamics and ergodicity
breaking transitions. The nonergodicity transitions share many features with
the colloidal gel transition, and are proposed to be the source of gelation in
colloidal systems. Previous calculations of the phase diagram are complemented
with additional data for shorter ranges of the attractive interaction, showing
that the path of the nonergodicity transition line is then unimpeded by the
gas-liquid critical curve at low temperatures. Particular attention is given to
the critical nonergodicity parameters, motivated by recent experimental
measurements. An asymptotic model is developed, valid for dilute systems of
spheres interacting via strong short-range attractions, and is shown to capture
all aspects of the low temperature MCT nonergodicity transitions.Comment: 12 pages, LaTeX, 5 eps figures, uses ioplppt.sty, to appear in J.
Phys.: Condens. Matte
Single-case experimental designs: Reflections on conduct and analysis
In this editorial discussion we reflect on the issues addressed by, and arising from, the papers in this Special Issue on Single Case Experimental Design (SCED) study methodology. We identify areas of consensus and disagreement regarding the conduct and analysis of SCED studies. Despite the long history of application of SCEDs in studies of interventions in clinical and educational settings, the field is still developing. There is an emerging consensus on methodological quality criteria for many aspects of SCEDs, but disagreement on what are the most appropriate methods of SCED data analysis. Our aim is to stimulate this ongoing debate and highlight issues requiring further attention from applied researchers and methodologists. In addition we offer tentative criteria to support decision making in relation to selection of analytical techniques in SCED studies. Finally, we stress that large-scale interdisciplinary collaborations, such as the current Special Issue, are necessary if SCEDs are going to play a significant role in the development of the evidence base for clinical practice
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