352 research outputs found
Influence of ink rheology and post processing in the structural performance of silicon nitride-based ceramics fabricated by robocasting
The fabrication of complex shaped Si3N4 parts by conventional methods is challenging due to its high hardness and mechanical strength. Additive manufacturing (AM) appeared as a competitive way to attain three-dimensional complexity at lower costs. However, most of AM technologies still present limitations in producing high dense ceramics, mainly due to several difficulties in developing proper feedstock. This work presents the fabrication of dense silicon nitride-based ceramics by using an extrusion based additive manufacturing technique (direct ink writing, also known as robocasting) and cold isostatic pressing (CIP) as a post processing step. Silicon-nitride aqueous based inks containing different amounts of solids loading (36, 38 and 39 vol%) and proper rheological characteristics for the printing process were studied. The use of CIP (200 MPa) is suggested to reduce or even eliminate defects and porosity and consequently, to improve mechanical performance of the final parts. Relative density, microhardness and flexural strength increased as solids loading in the inks increased and were further improved when CIP pressing was used. Parts produced by robocasting with an ink containing 39 vol% and cold isostatic pressed at 200 MPa exhibited an average relative density around 99%, 1475 HV2 microhardness value and 650 MPa flexural strength, values similar to those of silicon nitride ceramics fabricated by conventional processing.publishe
Homocysteine levels in pediatric renal transplant recipients.
Transplant Proc. 2003 May;35(3):1093-5.
Homocysteine levels in pediatric renal transplant recipients.
Mota C, Fonseca I, Santos MJ, Costa T, Faria MS, Henriques AC, Sarmento AM, Pereira E, Pereira M.
Department of Paediatric Nephrology, Maria Pia Children's Hospital, R. da Boavista, 827, 4050-111, Porto, Portugal. [email protected]
PMID: 12947872 [PubMed - indexed for MEDLIN
Arbuscular Mycorrhiza Extraradical Mycelium Promotes Si and Mn Subcellular Redistribution in Wheat Grown under Mn Toxicity
Abstract: Manganese (Mn) and aluminum (Al) toxicities are serious edaphic limitations to crop
production in acidic soils. Excess Mn can be countered using a stress-adapted soil microbiota that
establish symbiotic relationships with native plants. The arbuscular mycorrhizal fungi (AMF) associated with Lolium rigidum L. develop extraradical mycelia (ERM) that quickly colonize wheat and
lead to greater shoot growth by promoting stress-evading mechanisms that are not yet completely explained. In the present study, wheat growth was assessed after 3 weeks on disturbed and undisturbed
(intact ERM) acidic soil where the native non-mycotrophic Silene gallica L. or strongly mycotrophic
L. rigidum were previously developed. The physiological and biochemical mechanisms responsible for increased growth were analyzed by assessing wheat leaf chlorophyll content, photosystem
II quantum yield and performance index, enzymatic activity of ascorbate peroxidase (APX), catalase
(CAT), glutathione reductase (GR), guaiacol peroxidase (GPX), superoxide dismutase (SOD) and
contents and subcellular localization of Mn, Mg, Si and K. The soil from native plants had a beneficial
effect on shoot weight and chlorophyll levels. The highest benefits were obtained for wheat grown in
soil with intact ERM associated with L. rigidum. In this condition, where earlier mycorrhization was
favored, the Mn content decreased, alongside the content of Si, while the Mg/Mn ratio increased. Mn
was redirected to the apoplast, while Si was redirected to the symplast. The activity of APX, GPX and
SOD increased, probably due to increased metabolic growth (higher shoot weight and chlorophyll
content). Understanding the mechanisms induced by native AMF responsible for increasing wheat
performance can contribute to the establishment of sustainable approaches for crop production in
acidic soils with Mn toxicity. The use of native plant AMF developers can improve the sustainable
use of natural resources in the scope of greener agricultural practice
Fungal Communities of the Pine Wilt Disease Complex: Studying the Interaction of Ophiostomatales With Bursaphelenchus xylophilus
Original ResearchConsidered one of the most devastating plant–parasitic nematodes worldwide,
Bursaphelenchus xylophilus (commonly known as pinewood nematode, PWN) is the
causal agent of the pine wilt disease in the Eurasian coniferous forests. This migratory
parasitic nematode is carried by an insect vector (Monochamus spp.) into the host
tree (Pinus species), where it can feed on parenchymal cells and reproduce massively,
resulting in the tree wilting. In declining trees, PWN populations are strongly dependent
on fungal communities colonizing the host (predominantly ophiostomatoid fungi known
to cause sapwood blue-staining, the blue-stain fungi), which not only influence their
development and life cycle but also the number of individuals carried by the insect vector
into a new host. Our main aim is to understand if PWN-associated mycobiota plays a
key role in the development of PWD, in interaction with the PWN and the insect vector,
and to what extent it can be targeted to disrupt the disease cycle. For this purpose, we
characterized the fungal communities of Pinus pinaster trees infected and non-infected
with PWN in three collection sites in Continental Portugal with different PWD temporal
incidences. Our results showed that non-infected P. pinaster mycoflora is more diverse
(in terms of abundance and fungal richness) than PWN-infected pine trees in the most
recent PWD foci, as opposed to the fungal communities of long-term PWD history
sites. Then, due to their ecological importance for PWN survival, representatives of the
main ophiostomatoid fungi isolated (Ophiostoma, Leptographium, and Graphilbum) were
characterized for their adaptative response to temperature, competition in-between taxa,
and as food source for PWN. Under the conditions studied, Leptographium isolates
showed promising results for PWN control. They could outcompete the other species,
especially O. ips, and significantly reduce the development of PWN populations when
compared to Botrytis cinerea (routinely used for PWN lab culturing), suggesting this to
be a natural antagonist not only for the other blue-stain species but also for the PWNinfo:eu-repo/semantics/publishedVersio
Wheat Shoot Al, Fe, Mn and Zn Levels Are Influenced by Arbuscular Mycorrhiza Extraradical Mycelium Associated to Ornithopus compressus in Acidic Soils
In the present study, the levels of Al, Fe, Mn and Zn in wheat shoots were quantified
by inductively coupled plasma mass spectrometry (ICP-MS). Wheat was grown in an acidic soil
with toxic levels of Mn and with intact or disrupted extraradical mycelium (ERM) as the arbuscular
mycorrhizal fungi (AMF) inoculum source, resulting from the previous growth of O. compressus. In
the presence of an intact ERM, toxic Mn levels were reduced, and the concentrations of Al, Fe and
Zn decreased 2.3, 1.5 and 2.3-fold, respectively. Disruption of ERM, that leads to a later and slower
AM colonization, induced higher wheat shoot Mn and Zn levels (55% and 28%, respectively), but
not Al and Fe. Under Mn toxicity, the colonization of wheat by intact ERM of AMF associated with
O. compressus in an acidic soil appears to influence the uptake of Al, Fe and Zn, and positively
influence plant growth
Synergistic Activity of Cymbopogon citratus and Mentha piperita Essential Oils against the Pinewood Nematode
The pinewood nematode (PWN) Bursaphelenchus xylophilus is a major threat to pine forests.
Research on sustainable pest management strategies is now a priority. Essential oils (EOs) are
biodegradable, complex mixtures of volatiles that can show low toxicity to mammals and powerful
nematicidal activities depending on their chemical composition. In the present work, the EOs of four
plants were screened against the PWN, solely and in combination to identify possible synergistic
interactions. The combination of Cymbopogon citratus and Mentha piperita EOs (1:1) resulted in
higher activities than those of each tested solely, suggesting the occurrence of synergistic interactions
between the compounds of these EOs. Research on the combination of synergistic EOs may lead to
the development of plant based biopesticides with optimized activities against the PWN
Elastic Scattering and Total Reaction Cross Section for the 6He + 27Al System
The elastic scattering of the radioactive halo nucleus 6He on 27Al target was
measured at four energies close to the Coulomb barrier using the RIBRAS
(Radioactive Ion Beams in Brazil) facility. The Sao Paulo Potential(SPP) was
used and its diffuseness and imaginary strength were adjusted to fit the
elastic scattering angular distributions. Reaction cross-sections were
extracted from the optical model fits. The reduced reaction cross-sections of
6He on 27Al are similar to those for stable, weakly bound projectiles as
{6,7}Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al.Comment: 7 pages, 1 table, 3 figure
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