1,088 research outputs found
Electrical and thermal properties of polyurethane/carbon nanotubes composites
The aim of this work was to study the effect of dispersing small amounts of CNT on the thermal diffusivity and electrical resistivity of PU/CNT composites. The PU nanocomposites were prepared with 0.5% and 1% weight of CNT. The composites were prepared by dispersion of the CNT in poly(propylene glycol) (PPG) followed by in situ polymerization, by mixing with 4,4′-Methylene di-p-phenyl diisocyanate (MDI). The PPG was characterized by an average molecular weight of 425 g/mol and a hydroxyl value 250 to 276 mg KOH/g. The MDI was characterized by a isocianate value (%NCO value) of 27.9-29.2.
It was observed that the thermal diffusivity slightly increased with the addition of the CNT, but the results obtained were within the typical range for polymers (in the order of 10-8 m2/s). The electrical resistivity measured for the composites showed a large decrease after the addition of 0.5% and 1% of CNT. The electrical resistivity decreased 3 and 7 decades (from 109 .m to 106 and 103 .m) for 0.5 and 1% CNT composites, respectively. Thus, the composite bearing 1% of CNT dispersed in the PU presented semiconductor behaviour
Propolis phenolic profile: a study in the Atlantic islands of Azores
Propolis it is a natural resinous substance that honeybees (Apis melifera, L.) collect from buds and
exudates of plants and transformed in the presence of bee enzymes. This substance plays an important
role in the hive as a construction and defence material due to its chemical and biological properties.[1]
Propolis composition is extremely complex and dependent on its vegetal source, geographical location
and climatic conditions. Typically this natural product includes resin (50%), beeswax (30%), essential
oils (10%), pollen (5%) and other organic compounds (5%).[2] Due to the abundance in phenolic
compounds (flavonoids, phenolic acids and their esters) and to its biological and pharmacological
properties this group of substances became the target of many research studies in propolis.
This work outlines an extensive qualitative and quantitative characterization of the phenolic
composition of Azorean islands propolis. For that, eleven samples of propolis, from S. Miguel and
Terceira island, were extracted and characterized according to the previous work.[3] The HPLC results
show a similar chromatographic profile for all samples, despite their origin, with 37 compounds identified
by ESI-MS/MSn analysis and confirmed by HPLC-DAD. Although the samples revealed a similar
phenolic composition, significant differences in the concentrations of the different compounds were
found, probably due to the differences in flora distribution around the beehive, and therefore resin
availability for bees
Methane and Nitrogen Abundances On Pluto and Eris
We present spectra of Eris from the MMT 6.5 meter telescope and Red Channel
Spectrograph (5700-9800 angstroms; 5 angstroms per pix) on Mt. Hopkins, AZ, and
of Pluto from the Steward Observatory 2.3 meter telescope and Boller and
Chivens spectrograph (7100-9400 angstroms; 2 angstroms per pix) on Kitt Peak,
AZ. In addition, we present laboratory transmission spectra of methane-nitrogen
and methane-argon ice mixtures. By anchoring our analysis in methane and
nitrogen solubilities in one another as expressed in the phase diagram of
Prokhvatilov and Yantsevich (1983), and comparing methane bands in our Eris and
Pluto spectra and methane bands in our laboratory spectra of methane and
nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are
about 10% and about 90%, and Pluto's bulk methane and nitrogen abundances are
about 3% and about 97%. Such abundances for Pluto are consistent with values
reported in the literature. It appears that the bulk volatile composition of
Eris is similar to the bulk volatile composition of Pluto. Both objects appear
to be dominated by nitrogen ice. Our analysis also suggests, unlike previous
work reported in the literature, that the methane and nitrogen stoichiometry is
constant with depth into the surface of Eris. Finally, we point out that our
Eris spectrum is also consistent with a laboratory ice mixture consisting of
40% methane and 60% argon. Although we cannot rule out an argon rich surface,
it seems more likely that nitrogen is the dominant species on Eris because the
nitrogen ice 2.15 micron band is seen in spectra of Pluto and Triton.Comment: The manuscript has 44 pages, 15 figures, and four tables. It will
appear in the Astrophysical Journa
Propolis phenolic profile: a study in the Atlantic islands of Azores
Propolis it is a natural resinous substance that honeybees (Apis melifera, L.) collect from buds and
exudates of plants and transformed in the presence of bee enzymes. This substance plays an important
role in the hive as a construction and defence material due to its chemical and biological properties.[1]
Propolis composition is extremely complex and dependent on its vegetal source, geographical location
and climatic conditions. Typically this natural product includes resin (50%), beeswax (30%), essential
oils (10%), pollen (5%) and other organic compounds (5%).[2] Due to the abundance in phenolic
compounds (flavonoids, phenolic acids and their esters) and to its biological and pharmacological
properties this group of substances became the target of many research studies in propolis.
This work outlines an extensive qualitative and quantitative characterization of the phenolic
composition of Azorean islands propolis. For that, eleven samples of propolis, from S. Miguel and
Terceira island, were extracted and characterized according to the previous work.[3] The HPLC results
show a similar chromatographic profile for all samples, despite their origin, with 37 compounds identified
by ESI-MS/MSn analysis and confirmed by HPLC-DAD. Although the samples revealed a similar
phenolic composition, significant differences in the concentrations of the different compounds were
found, probably due to the differences in flora distribution around the beehive, and therefore resin
availability for bees
A Ni hyperaccumulator and a congeneric non-accumulator reveal equally effective defenses against herbivory
The defense hypothesis is commonly used to explain the adaptive role ofmetal hyperaccumulation. We tested
this hypothesis using two Brassicaceae congeneric species: Alyssum pintodasilvae, a Ni hyperaccumulator, and
the non-accumulator Alyssum simplex both growing on serpentine soils in Portugal. Artificial diet disks
amended with powdered leaves from each plant species were used to compare the performance (mortality,
biomass change) and feeding behavior of Tribolium castaneum in no-choice and choice tests. The performance
of T. castaneum was not affected at several concentrations of A. pintodasilvae or A. simplex in no-choice tests.
However, the consumption of plant-amended disks was significantly lower than that of control disks,
irrespectively of the species fed. Accordingly, when insects were given an alternative food choice, disks of
both plant species were significantly less consumed than control disks. Moreover, insects did not discriminate
between disks in the combination “A. pintodasilvae + A. simplex”. Contrary to our expectations, these results
suggest that both plant species have equally effective defenses against herbivory. While Ni is believed to be
part of the deterrence mechanism in the hyperaccumulator A. pintodasilvae, it seems likely that organic compounds,
possibly glucosinolates, play an important role in the defense of A. simplex or in both species.This study was fully supported by the Centre for Functional Ecology, University of Coimbra
Serum markers of B-cell activation in pregnancy during late gestation, delivery, and the postpartum period
B cells are vital for the normal evolution of pregnancy due to their humoral and possible regulatory activities. Our group and others have documented that circulating B-cell subsets undergo changes from normal late pregnancy to the postpartum period. However, the underlying mechanisms are poorly understood. Therefore, this study examined the degree of B-cell activation in normal pregnancy by analyzing the levels of serum markers in healthy pregnant women during the third trimester of pregnancy, the day of delivery, and the postpartum period.
METHOD OF STUDY:
A prospective study including pregnant and non-pregnant women attending routine care was undertaken at a hospital clinic. Sociodemographic and clinical data were collected, along with peripheral blood samples. The serum levels of soluble CD23 (sCD23), B-cell-activating factor (BAFF), kappa (κ) and lambda (λ) free light chains (FLC), IgA, IgG, and IgM were quantified.
RESULTS:
Our study included 43 third trimester pregnant and 35 non-pregnant women. In the pregnant women, the median levels of sCD23, BAFF, IgG, and κ FLC were significantly higher during the postpartum period than during the third trimester of pregnancy. Compared to the non-pregnant women, the third trimester pregnant women had higher median BAFF levels and lower sCD23, IgA, IgG, and FLC levels.
CONCLUSION:
Changes in serum markers of B-cell kinetics that occur during pregnancy often persist into the postpartum period and affect the secretion of immunoglobulins from different classes. Further studies are needed to clarify the biological significance of our observations.info:eu-repo/semantics/publishedVersio
Informação adicional sobre um surto de sarna causado por Allopsoroptoides galli (Acari: Psoroptoididae) em uma granja de poedeiras no Estado de São Paulo
This paper reports additional information about a mange outbreak by the mite Allopsoroptoides galli in a commercial egg-laying hen facility in the state of São Paulo, Brazil. About half of the 76,000 multi-age birds of the flock were affected. Experimental infestations carried out on naive hens resulted in clinical signs similar to those diagnosed in naturally infested hens, such as generalized scaly dermatitis, presence of mucus-like material and yellowish crusts on the skin and around the calami, feather loss and strong unpleasant odor. About 30% drop of egg production was estimated. The possible source of infestation were wild birds identified on the ground and roofs of the sheds348760762Este artigo acrescenta informações adicionais sobre um surto de sarna causado por Allopsoroptoides galli em uma instalação comercial de galinhas de postura no estado de São Paulo, Brasil. Approximadamente metade das 76.000 aves, com várias idades, mantidas em uma granja, foram infestadas. Um total de 12 galinhas sem prévio contato com os ácaros e infestadas experimentalmente apresentaram sinais clínicos semelhantes aos diagnosticados em galinhas naturalmente infestadas, tais como dermatite escamosa generalizada, presença de material mucoso, crostas amareladas na pele e em torno dos câlamos, perda de penas e forte odor desagradável. A perda na produçãode ovos foi estimada em 30%. As possíveis fontes de infestação foram aves silvestres observadas no chão próximo aos galpões e telhadossem informaçã
Inhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission
CONTEXT: In July 2010 the ESA spacecraft Rosetta will fly-by the main belt
asteroid 21 Lutetia. Several observations of this asteroid have been so far
performed, but its surface composition and nature are still a matter of debate.
For long time Lutetia was supposed to have a metallic nature due to its high
IRAS albedo. Later on it has been suggested to have a surface composition
similar to primitive carbonaceous chondrite meteorites, while further
observations proposed a possible genetic link with more evolved enstatite
chondrite meteorites. AIMS: In order to give an important contribution in
solving the conundrum of the nature of Lutetia, in November 2008 we performed
visible spectroscopic observations of this asteroid at the Telescopio Nazionale
Galileo (TNG, La Palma, Spain). METHODS: Thirteen visible spectra have been
acquired at different rotational phases. RESULTS: We confirm the presence of a
narrow spectral feature at about 0.47-0.48 micron already found by Lazzarin et
al. (2009) on the spectra of Lutetia. We also find a spectral feature at about
0.6 micron, detected by Lazzarin et al. (2004) on one of their Lutetia's
spectra. More importantly, our spectra exhibit different spectral slopes
between 0.6 and 0.75 micron and, in particular, we found that up to 20% of the
Lutetia surface could have flatter spectra. CONCLUSIONS: We detected a
variation of the spectral slopes at different rotational phases that could be
interpreted as possibly due to differences in the chemical/mineralogical
composition, as well as to inhomogeneities of the structure of the Lutetia's
surface (e.g., the presence of craters or albedo spots) in the southern
hemisphere.Comment: 3 pages, 2 figures. Accepted for publication in Astronomy and
Astrophysics. Updated on 25 March 2010
- …