1,112 research outputs found
Impaired Cerebral Perfusion in Multiple Sclerosis: Relevance of Endothelial Factors.
Magnetic resonance imaging techniques measuring in vivo brain perfusion and integrity of the blood-brain barrier have developed rapidly in the past decade, resulting in a wide range of available methods. This review first discusses their principles, possible pitfalls, and potential for quantification and outlines clinical application in neurological disorders. Then, we focus on the endothelial cells of the blood-brain barrier, pointing out their contribution in regulating vascular tone by production of vasoactive substances. Finally, the role of these substances in brain hypoperfusion in multiple sclerosis is discussed
Dynamic response studies on aggregation and breakage dynamics of colloidal dispersions in stirred tanks
Aggregation and breakage of aggregates of fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tanks using small-angle static light scattering. It was found that the steady-state values of the root-mean-square radius of gyration are fully reversible upon changes of stirring speed as well as solid volume fraction. Steady-state values of the root-mean-square radius of gyration were decreasing with decreasing solid volume fraction as well as with increasing stirring speed. Moreover, it was found that the steady-state structure and shape of the aggregates is not influenced by the applied stirring speed
Statistics and Universality in Simplified Models of Planetary Formation
In this paper, we modify Laskar's simplified model of planetary evolution and
accretion [J. Laskar, Phys. Rev. Lett, vol 84, p 3240 (2000)] to account for
the full conservation of the total angular momentum of the system, and extend
it to incorporate an accretion probability that depends on the mass and
relative velocity of the colliding particles. We present statistical results
for the mass and eccentricity of the planets formed, in terms of their
semi-major axes, for a large number of realisations of different versions of
the model. In particular, we find that by combining the mass-dependent
accretion probability and the velocity-selection mechanism, the planets formed
display a systematic occurrence at specific locations. By introducing properly
scaled variables, our results are universal with respect to the total angular
momentum of the system, the mass of the planetesimal disc, and the mass of the
central star.Comment: 13 pages, 21 figures, some in colour. Accepted in MNRA
Ranges of Atmospheric Mass and Composition of Super Earth Exoplanets
Terrestrial-like exoplanets may obtain atmospheres from three primary
sources: Capture of nebular gases, degassing during accretion, and degassing
from subsequent tectonic activity. Here we model degassing during accretion to
estimate the range of atmospheric mass and composition on exoplanets ranging
from 1 to 30 Earth masses. We use bulk compositions drawn from primitive and
differentiated meteorite compositions. Degassing alone can create a wide range
of masses of planetary atmospheres, ranging from less than a percent of the
planet's total mass up to ~6 mass% of hydrogen, ~20 mass% of water, and/or ~5
mass% of carbon compounds. Hydrogen-rich atmospheres can be outgassed as a
result of oxidizing metallic iron with water, and excess water and carbon can
produce atmospheres through simple degassing. As a byproduct of our atmospheric
outgassing models we find that modest initial water contents (10 mass% of the
planet and above) create planets with deep surface liquid water oceans soon
after accretion is complete.Comment: ApJ, in press. 32 pages, 6 figure
Nitric oxide modulates the angiogenic phenotype of middle-T transformed endothelial cells.
The role of nitric oxide (NO) in the induction of angiogenesis was evaluated in a murine heart endothelioma cell line (H.end.FB) carrying the mT oncogene. Two clonal derivatives of H.end.FB, H80 and H73, exhibiting different NO synthase (NOS) activities were selected and used in the study. The relationship among NOS activity and tumor cell behaviour (growth, and angiogenic capacity) and the molecular control of gene expression were investigated. H.end.FB and H80 on one side and H73 on the other side exhibited the highest and lowest NOS activity, respectively. Cell growth was inversely correlated to the amount of NO produced by the cell lines. Conversely, in the avascular rabbit cornea assay, H.end.FB and H80 cells were strongly angiogenic, while H73 were poorly angiogenic, indicating that the ability of the cells to induce neovascularization was associated with the extent of NO produced. Consistently, systemic administration to rabbits of the NOS inhibitor N(w)-nitro-L-arginine methyl ester (L-NAME) significantly reduced the angiogenicity of H.end.FB cells. RT-PCR evidenced that H.end.FB expressed mRNA for TGF-beta1 and all VEGF isoforms, VEGF165 being predominantly expressed. NOS inhibition reduced the basal expression of VEGF isoforms, while it markedly potentiated TGF-beta1 expression. These results indicate that the endogenous production of NO in tumor cells can serve as an autocrine/paracrine signalling mechanism of progression, by controlling angiogenic factor/modulator expressio
The GSC-II-based survey of ancient cool white dwarfs I. The sample of spectroscopically confirmed WDs
The GSC-II white dwarf survey was designed to identify faint and high proper
motion objects, which we used to define a new and independent sample of cool
white dwarfs. With this survey we aim to derive new constraints on the halo
white dwarf space density. Also, these data can provide information on the age
of thick disk and halo through the analysis of the luminosity function. On the
basis of astrometric and photometric parameters, we selected candidates with mu
> 0.28 as/yr and R_F > 16 in an area of 1150 square degrees. Then, we separated
white dwarfs from late type dwarfs and subdwarfs by means of the reduced proper
motion diagram. Finally, spectroscopic follow-up observations were carried out
to confirm the white dwarf nature of the selected candidates. We found 41 white
dwarfs of which 24 are new discoveries. Here we present the full sample and for
each object provide positions, absolute proper motions, photometry, and
spectroscopy.Comment: 14 pages, 7 figures, submitted to A&
On Secular Resonances of Small Bodies in the Planetary Systems
We investigate the secular resonances for massless small bodies and
Earth-like planets in several planetary systems. We further compare the results
with those of Solar System. For example, in the GJ 876 planetary system, we
show that the secular resonances and (respectively, resulting
from the inner and outer giant planets) can excite the eccentricities of the
Earth-like planets with orbits 0.21 AU 0.50 AU and eject them out of
the system in a short timescale. However, in a dynamical sense, the potential
zones for the existence of Earth-like planets are in the area 0.50 AU 1.00 AU, and there exist all stable orbits last up to yr with low
eccentricities. For other systems, e.g., 47 UMa, we also show that the
Habitable Zones for Earth-like planets are related to both secular resonances
and mean motion resonances in the systems.Comment: 8 pages, 3 figures, accepted to IAU236. Proceeding of IAU 236: Near
Earth Objects, Our Celestial Neighbors: Opportunity and Risk, in pres
- …