6,747 research outputs found
Daños por impacto en frutos : parámetros y métodos experimentales.
El estudio del impacto en frutos se realiza sobre la base de modelos mecánicos del impacto en sólidos; la naturaleza viscoelástica de los productos biológicos exige la utilización de modelos viscoelásticos, tanto en el caso del impacto como de las cargas estáticas. La respuesta de los frutos a la aplicación de cargas estáticas puede investigarse con métodos bien conocidos, aunque aun no tipificados de forma general; la respuesta a cargas dinámicas (impactos) requiere de métodos de ensayo y análisis específicos que han de ser investigados. El resultado de la aplicación de los impactos en frutos como la pera y la manzana es la aparición de magulladuras, cuya naturaleza y desarrollo exige mayores estudios
Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946
The characteristics of ionized and HI gas in the peculiar star/cluster
complex in NGC 6946, obtained with the 6-m telescope (BTA) SAO RAS, the Gemini
North telescope, and the Westerbork Synthesis Radio Telescope (WSRT), are
presented. The complex is unusual as hosting a super star cluster, the most
massive known in an apparently non-interacting giant galaxy. It contains a
number of smaller clusters and is bordered by a sharp C-shaped rim. We found
that the complex is additionally unusual in having peculiar gas kinematics. The
velocity field of the ionized gas reveals a deep oval minimum, ~300 pc in size,
centered 7" east of the supercluster. The Vr of the ionized gas in the dip
center is 100 km/s lower than in its surroundings, and emission lines within
the dip appear to be shock excited. This dip is near the center of an HI hole
and a semi-ring of HII regions. The HI (and less certainly, HII) velocity
fields reveal expansion, with the velocity reaching ~30 km/s at a distance
about 300 pc from the center of expansion, which is near the deep minimum
position. The super star cluster is at the western rim of the minimum. The
sharp western rim of the whole complex is plausibly a manifestation of a
regular dust arc along the complex edge. Different hypotheses about the complex
and the Vr depression origins are discussed, including a HVC/dark mini-halo
impact, a BCD galaxy merging, and a gas outflow due to release of energy from
the supercluster stars.Comment: MN RAS, accepte
Vitamin d3 enriches ceramide content in exosomes released by embryonic hippocampal cells
The release of exosomes can lead to cell\u2013cell communication. Nutrients such as vitamin D3 and sphingolipids have important roles in many cellular functions, including proliferation, dif-ferentiation, senescence, and cancer. However, the specific composition of sphingolipids in exo-somes and their changes induced by vitamin D3 treatment have not been elucidated. Here, we ini-tially observed neutral sphingomyelinase and vitamin D receptors in exosomes released from HN9.10 embryonic hippocampal cells. Using ultrafast liquid chromatography tandem mass spec-trometry, we showed that exosomes are rich in sphingomyelin species compared to whole cells. To interrogate the possible functions of vitamin D3, we established the optimal conditions of cell treatment and we analyzed exosome composition. Vitamin D3 was identified as responsible for the vitamin D receptor loss, for the increase in neutral sphingomyelinase content and sphingomyelin changes. As a consequence, the generation of ceramide upon vitamin D3 treatment was evident. Incubation of the cells with neutral sphingomyelinase, or the same concentration of ceramide pro-duced in exosomes was necessary and sufficient to stimulate embryonic hippocampal cell differen-tiation, as vitamin D3. This is the first time that exosome ceramide is interrogated for mediate the effect of vitamin D3 in inducing cell differentiation
The introduction of modern physics: overcoming a deformed vision of science
In this paper, we try to show initially that modern physics is usually introduced in high school curricula without reference to the difficulties of classical physics, simply juxtaposing the two paradigms or even mixing them up. As a result, serious misconceptions arise. We then present another way of introducing modern physics, based on a contructivist view of science learning, and give some results obtained with the new materials
Flavonoids patterns of French honeys with different floral origin
The flavonoid profiles of 12 different unifloral French honey samples were analysed by HPLC to evaluate if these substances could be used as markers of the floral origin of honey. In this analysis, the characteristic flavonoids from propolis and/or beeswax (chrysin, galangin, tectochrysin, pinocembrin and pinobanksin) were separated from those originating mainly from nectar and/or pollen (polyhydroxylated flavonoid aglycones), which would be related to their floral origin. All the analysed samples contained a common flavonoid profile consisting of polyhydroxylated flavonoid aglycones including 8-methoxykaempferol, kaempferol, quercetin, isorhamnetin, luteolin and apigenin, suggesting that flavonoid analysis does not generally prove differences between French monofloral honey samples. However, some individual honey samples showed potential floral markers. Thus, heather honey was characterized by the presence of myricetin, calluna honey by ellagic acid and citrus honey by the flavanone hesperetin. In other samples, the relative amount of 1 individual flavonoid could be related to the floral origin. Thus, sunflower honeys contained an important relative amount of quercetin, and in alder honey only 8-methoxykaempferol was detected. This preliminary study shows that flavonoid and phenolic compound analyses could be a very valuable complementary biochemical technique in the objective determination of the floral origin of some specific monofloral honey samples, but further studies with a larger number of samples is necessary to confirm the observed differences
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