396 research outputs found
The Many Hats of Sonic Hedgehog Signaling in Nervous System Development and Disease.
Sonic hedgehog (Shh) signaling occurs concurrently with the many processes that constitute nervous system development. Although Shh is mostly known for its proliferative and morphogenic action through its effects on neural stem cells and progenitors, it also contributes to neuronal differentiation, axonal pathfinding and synapse formation and function. To participate in these diverse events, Shh signaling manifests differently depending on the maturational state of the responsive cell, on the other signaling pathways regulating neural cell function and the environmental cues that surround target cells. Shh signaling is particularly dynamic in the nervous system, ranging from canonical transcription-dependent, to non-canonical and localized to axonal growth cones. Here, we review the variety of Shh functions in the developing nervous system and their consequences for neurodevelopmental diseases and neural regeneration, with particular emphasis on the signaling mechanisms underlying Shh action
Cork suberin as a new source of chemicals: 2. crystallinity, thermal and rheological properties
Suberin samples, obtained by alkaline methanolysis
from cork (Quercus suber L.), were submitted to
various physical characterizations; DSC, TGA, optical
microscopy, density and rheological properties. A sub stantial proportion of these oligomers possessed a
microcrystalline character with a melting range
between 0 and 50°C. The amorphous part was liquid
at room temperature and did not display a detectable
glass transition upon cooling because of its wide
molecular weight distribution. The viscous behaviour
of suberin at room temperature was both plastic and
thixotropic because of the structuring role of the microcrystals.info:eu-repo/semantics/publishedVersio
Urethanes and polyurethanes from suberin 2: synthesis and characterization
Polyurethanes based on suberin from cork of Quercus suber L. and conventional isocyanate monomers were
prepared and fully characterized in terms of both structure (FTIR and 1
H NMR spectroscopy) and thermal properties
(differential scanning calorimetry and thermogravimetric analysis). Two fractions were systematically isolated, namely
(i) methylene-chloride soluble products, which corresponded to linear and branched macromolecules and (ii)
methylene-chloride insoluble products, representing the crosslinked material. The structures of these polymers were
regular and no appreciable side reactions were detected. DSC analyses provided information about the glass transition
temperature of both fractions and this parameter was correlated with the stiffness of the isocyanate used. The TGA
of these polyurethanes showed that they started to degrade at about 175°C and that the residue at 400°C was around
50%. The highest amounts of insoluble fractions, as well as the highest Tgs, were reached when an initial [NCO]/[OH]
of unity was used.info:eu-repo/semantics/publishedVersio
Fluctuating Dark Energy and the Luminosity Distance
The origin of dark energy driving the accelerated expansion of the universe
is still mysterious. We explore the possibility that dark energy fluctuates,
resulting in spatial correlations. Due to these fluctuations, the Hubble rate
itself becomes a fluctuating quantity. We discuss the effect this has on
measurements of type Ia supernovae, which are used to constrain the luminosity
distance. We show that the luminosity distance is affected by spatial
correlations in several ways. First, the luminosity distance becomes dressed by
the fluctuations, thereby differing from standard CDM. Second, angular
correlations become visible in the two-point correlation function of the
luminosity distance. To investigate the latter we construct the angular power
spectrum of luminosity distance fluctuations. We then perform a forecast for
two supernova surveys, the ongoing Dark Energy Survey (DES) and the upcoming
Legacy Survey of Space and Time (LSST), and compare this effect with
relativistic lensing effects from perturbed CDM. We find that the
signal can rise above the lensing effects and that LSST could test this effect
for a large part of the parameter space. As an example, a specific realisation
of such a scenario is that quantum fluctuations of some field in the early
universe imprint spatial correlations with a predictable form in the dark
energy density today. In this case, the Hubble rate fluctuates due to the
intrinsic quantum nature of the dark energy density field. We study whether the
signal of this specific model would be measurable, and conclude that testing
this model with LSST would be challenging. However, taking into account a speed
of sound of the dark energy fluid can make this model observable.Comment: 38 pages, 9 figure
Cork suberin as a new source of chemicals.: 1. isolation and chemical characterization of its composition
Extractive-free cork from Quercus suber L. was submitted to a solvolysis treatment with methanolic NaOH which yielded 37%
(o.d. cork) of suberin. This mixture of compounds was thoroughly characterized by FTIR, 1
H- and 13C-NMR, gas chromatogra phy coupled with mass spectrometric (GC–MS) analysis, vapour pressure osmometry (VPO), mass spectrography (MS) and gel
permeation chromatography (GPC). After derivatization, the main components of the volatile fraction, representing less than half
of the total, were found to be v-hydroxymonocarboxylates, a,v-dicarboxylates, simple alkanoates and 1-alkanols, all with chain
lengths ranging from C16 to C24. A second fraction, with an average molecular weight about three times higher, was detected by
VPO, MS and GPC. The presence of this important fraction in cork suberin had not been recognized in earlier studies. Both
fractions constitute interesting precursors for the elaboration of new materials.info:eu-repo/semantics/publishedVersio
Effectiveness of a pomegranate peel extract (PGE) in reducing Listeria monocytogenes in vitro and on fresh-cut pear, apple and melon
Pomegranate peel extract (PGE) is a new promising natural alternative control substance with large spectrum of activity against wide range of pathogenic microorganisms. In the present study, PGE was firstly investigated as natural antimicrobial against Listeria monocytogenes both in vitro and on fresh-cut fruits. The in vitro results showed quick and strong bactericidal and bacteriostatic activity against five different strains which were almost completely inhibited by the extract. Furthermore, it significantly decreased growth rate and maximum growth of all tested strains. In vivo trials, confirmed a strong antibacterial activity of the extract that significantly reduced the bacterial load on fresh-cut apple, melon and pear and maintained the population at low levels throughout the storage period (7 days). PGE at 12 g/l reduced L. monocytogenes by 1.24, 1.89, and 0.91 log units soon after treatment and by 3.81, 1.53, and 2.99 log units, after 7 days of storage on apple, pear and melon, respectively. This high antibacterial activity could be mainly related to the high content of polyphenols (ellagitannins) in the extract. Overall, results of this study suggest a potential industrial application of PGE to reduce the growth of the pathogenic microorganisms in fresh-cut fruit and ensure a microbial safety in case of contamination.info:eu-repo/semantics/acceptedVersio
Optical Properties of Wide Band Gap Indium Sulphide Thin Films Obtained by Physical Vapor Deposition
Thin films of indium sulphide containing oxygen have been synthesized following a dry physical process. The constituents are deposited by thermal evaporation on glass substrates and then annealed under argon flow. Polycrystalline β-In2S3 containing oxygen thin films are obtained as soon as the temperature of annealing is between 623 and 723 K. In this paper, these β-In2S3 thin films have optically been studied. The optical band gap is direct. Its value is not dependent on the temperature of annealing. It is about 2.8 eV, which is higher than that of β-In2S3 single crystal. This high value is related to the presence of oxygen in the films. The extinction coefficient k and the refractive index n of the films have also been found independent of the annealing temperature. These optical properties make the films studied good candidates to be substituted to CdS in Cu(In,Ga)Se2 based solar cells
The organosolv fractionation of cork components
Extractive-free cork from Quercus suber L. was submitted to organosolv fractionation and the effects
of different process variables, such as ethanol/water ratio, temperature, time and the presence of acidic
or alkaline catalysts, were studied. The variation of the relative proportions of extracted components, as
a function of the processing conditions, could thus be established. Whereas the addition of 0.1 M acetic
acid only increased the yield of extracted materials from about 15 to 23%, the use of sodium hydroxide,
at the same concentration, produced a jump to 76%. In the case of the alkaline organosolv fractiona tion, an increase in process temperature, time and catalyst concentration led to an increase in the
extraction yield, although in some cases this increase did not follow a sustained trend, as in the case of
reaction time. Increasing the ethanol/water ratio led to a higher selectivity in favour of suberin
extraction. Residual cork from different organosolv processes was characterised by FTIR and 13C
solid-state NMR. The latter technique provided some valuable information about both process
selectivity and cork morphology, particularly with respect to the positioning of suberin macromolecules
in the cell wall.info:eu-repo/semantics/publishedVersio
Cork suberin as an additive in offset lithographic printing inks
Suberin oligomers, isolated from cork (Quercus suber L.), were used as additives in ‘Waterless’ and vegetable-oil ink formulations, in the range of 2–10% w/w. The rheological behaviour of the suberin oligomers as well as of the inks,
with and without suberin, were investigated as a function of temperature. It was shown that the addition of suberin
induces a decrease of viscosity of both inks. The tack of pristine inks, suberin oligomers and their mixtures were
determined at different temperatures: the variation of this parameter as a function of time provided information
about the drying kinetics of these formulations. The tack of the ‘Waterless’ ink was found to increase with the
introduction of suberin, whereas that of vegetable-oil based counterparts decreased. All the trends observed were
interpreted in terms of the differences in composition between the two types of inks. Preliminary printing tests were
carried out with the various suberin-containing inks.info:eu-repo/semantics/publishedVersio
Analysis of the oxypropylation process of a lignocellulosic material, almond shell, using the response surface methodology (RSM)
info:eu-repo/semantics/publishedVersio
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