512 research outputs found
Avoiding indirect effects of COVID-19 on maternal and child health
The coronavirus 2019 (COVID-19) pandemic is challenging
the resilience of the most solid health systems in the
world. In many low-income and middle-income countries
(LMICs), the disease is rapidly spreading amid numerous
endemic health problems such as HIV, tuberculosis, malaria,
malnutrition, and frequent outbreaks of viral infections
with high associated mortality. All this occurs in a context
of weak health infrastructures that can barely cope with the
aforementioned existing health challenges
Integrated and dynamical oceanographic data management - IDOD
The goal of the IDOD project was to provide the federal government, the scientific community and other users with an up-to-date tool for collecting, managing and analysing marine scientific data.The resulting “marine information system” is hosted by the Belgian Marine Data Centre (BMDC), a team within the Management Unit of the Mathematical Mode's of the North Sec (MUMM). The BMDC committed itself to keep the IDOD information system alive and evolving. A remote user interface is available online at http:/ /www.mumm.ac.be/ datacentre.The project faced all the aspects of modern scientific data management. A major challenge was to establish a fruitful dialog with the data providers. This has been done through extensive discussions in the Users committee and during bilateral meetings. The topics that have then been clarified range from the principles (in order to write down a standard common “Rights and duties" agreement) to the very technical and scientific details, specific to each data set .A substantial effort has been put on the definition of guidelines for ensuring the data quality throughout their way from the field to the data centre. This has resulted, for instance, in the development of a “On-board registration of samples" computer programme, in a check list of meta-information to document the data or in the definition of a “common layout" for reporting data sets to the data centre.On the technical side, the variety and complexity of the data to be stored and made available for further use lead us to elaborate a complex and robust data base scheme, after an in-depth conceptual analysis. The database itself is implemented using the ORACLE technology.In parallel, a set of dedicated analysis and visualisation tools has been developed. They help the users and the data managers to tackle the data in their space and time dimensions and also allow cross-analysis between different parameters.The primary providers of data for the information system were the various teams participating in the (first) Programme for a sustainable development of the North Sea, financed by the Belgian Federal Office for scientific, technical and cultural affairs. These data are being complemented by data from other (earlier) scientific programmes and from governmental surveys.The project has been performed by MUMM, in partnership with the SURFACES laboratory (University of Liege) and the University Centre of Statistics (University of Leuven)
Billiards with polynomial mixing rates
While many dynamical systems of mechanical origin, in particular billiards,
are strongly chaotic -- enjoy exponential mixing, the rates of mixing in many
other models are slow (algebraic, or polynomial). The dynamics in the latter
are intermittent between regular and chaotic, which makes them particularly
interesting in physical studies. However, mathematical methods for the analysis
of systems with slow mixing rates were developed just recently and are still
difficult to apply to realistic models. Here we reduce those methods to a
practical scheme that allows us to obtain a nearly optimal bound on mixing
rates. We demonstrate how the method works by applying it to several classes of
chaotic billiards with slow mixing as well as discuss a few examples where the
method, in its present form, fails.Comment: 39pages, 11 figue
A maximum density rule for surfaces of quasicrystals
A rule due to Bravais of wide validity for crystals is that their surfaces
correspond to the densest planes of atoms in the bulk of the material.
Comparing a theoretical model of i-AlPdMn with experimental results, we find
that this correspondence breaks down and that surfaces parallel to the densest
planes in the bulk are not the most stable, i.e. they are not so-called bulk
terminations. The correspondence can be restored by recognizing that there is a
contribution to the surface not just from one geometrical plane but from a
layer of stacked atoms, possibly containing more than one plane. We find that
not only does the stability of high-symmetry surfaces match the density of the
corresponding layer-like bulk terminations but the exact spacings between
surface terraces and their degree of pittedness may be determined by a simple
analysis of the density of layers predicted by the bulk geometric model.Comment: 8 pages of ps-file, 3 Figs (jpg
Sistema Estadual de Pesquisa Agropecuária - SEPA: revitalização de um mecanismo de integração e parceria institucional.
SEPA; Abordagem conceitual; Importância; Objetivo geral; Diretrizes; Organização e operacionalização; O papel da EMBRAPA em relação ao SNPA e aos SEPAs.bitstream/item/120249/1/Sistema-Estadual-de-Pesquisa-Agropecuaria-SEPA.pd
Topological entropy and secondary folding
A convenient measure of a map or flow's chaotic action is the topological
entropy. In many cases, the entropy has a homological origin: it is forced by
the topology of the space. For example, in simple toral maps, the topological
entropy is exactly equal to the growth induced by the map on the fundamental
group of the torus. However, in many situations the numerically-computed
topological entropy is greater than the bound implied by this action. We
associate this gap between the bound and the true entropy with 'secondary
folding': material lines undergo folding which is not homologically forced. We
examine this phenomenon both for physical rod-stirring devices and toral linked
twist maps, and show rigorously that for the latter secondary folds occur.Comment: 13 pages, 8 figures. pdfLaTeX with RevTeX4 macro
How metal films de-wet substrates - identifying the kinetic pathways and energetic driving forces
We study how single-crystal chromium films of uniform thickness on W(110)
substrates are converted to arrays of three-dimensional (3D) Cr islands during
annealing. We use low-energy electron microscopy (LEEM) to directly observe a
kinetic pathway that produces trenches that expose the wetting layer. Adjacent
film steps move simultaneously uphill and downhill relative to the staircase of
atomic steps on the substrate. This step motion thickens the film regions where
steps advance. Where film steps retract, the film thins, eventually exposing
the stable wetting layer. Since our analysis shows that thick Cr films have a
lattice constant close to bulk Cr, we propose that surface and interface stress
provide a possible driving force for the observed morphological instability.
Atomistic simulations and analytic elastic models show that surface and
interface stress can cause a dependence of film energy on thickness that leads
to an instability to simultaneous thinning and thickening. We observe that
de-wetting is also initiated at bunches of substrate steps in two other
systems, Ag/W(110) and Ag/Ru(0001). We additionally describe how Cr films are
converted into patterns of unidirectional stripes as the trenches that expose
the wetting layer lengthen along the W[001] direction. Finally, we observe how
3D Cr islands form directly during film growth at elevated temperature. The Cr
mesas (wedges) form as Cr film steps advance down the staircase of substrate
steps, another example of the critical role that substrate steps play in 3D
island formation
In vitro production of bovine embryos derived from individual donors in the Corral® dish
Background: Since the identity of the embryo is of outmost importance during commercial in vitro embryo production, bovine oocytes and embryos have to be cultured strictly per donor. Due to the rather low yield of oocytes collected after ovum pick-up (OPU) per individual cow, oocyte maturation and embryo culture take place in small groups, which is often associated with inferior embryo development. The objective of this study was to improve embryonic development in small donor groups by using the Corral (R) dish. This commercial dish is designed for human embryo production. It contains two central wells that are divided into quadrants by a semi-permeable wall. In human embryo culture, one embryo is placed per quadrant, allowing individual follow-up while embryos are exposed to a common medium. In our study, small groups of oocytes and subsequently embryos of different bovine donors were placed in the Corral (R) dish, each donor group in a separate quadrant.
Results: In two experiments, the Corral (R) dish was evaluated during in vitro maturation (IVM) and/or in vitro culture (IVC) by grouping oocytes and embryos of individual bovine donors per quadrant. At day 7, a significantly higher blastocyst rate was noted in the Corral (R) dish used during IVM and IVC than when only used during IVM (12.9% +/- 2.10 versus 22.8% +/- 2.67) (P < 0.05). However, no significant differences in blastocyst yield were observed anymore between treatment groups at day 8 post insemination.
Conclusions: In the present study, the Corral (R) dish was used for in vitro embryo production (IVP) in cattle; allowing to allocate oocytes and/or embryos per donor. As fresh embryo transfers on day 7 have higher pregnancy outcomes, the Corral (R) dish offers an added value for commercial OPU/IVP, since a higher blastocyst development at day 7 is obtained when the Corral (R) dish is used during IVM and IVC
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Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand
The synthesis, lanthanide complexation, and solvent ex- traction of actinide(III) and lanthanide(III) radiotracers from nitric acid solutions by a phenanthroline-derived quadridentate bis-triazine ligand are described. The ligand separates Am(III) and Cm(III) from the lanthanides with remarkably high efficiency, high selectivity, and fast extraction kinetics compared to its 2,2'-bipyridine counterpart. Structures of the 1:2 bis-complexes of the ligand with Eu(III) and Yb(III) were elucidated by X-ray crystallography and force field calculations, respec-tively. The Eu(III) bis-complex is the first 1:2 bis-complex of a quadridentate bis-triazine ligand to be characterized by crystallography. The faster rates of extraction were verified by kinetics measurements using the rotating membrane cell technique in several diluents. The improved kinetics of metal ion extraction are related to the higher surface activity of the ligand at the phase interface. The improvement in the ligand's properties on replacing the bipyridine unit with a phenanthroline unit far exceeds what was anticipated based on ligand design alone
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