50 research outputs found
Interleukin-6 stimulates gene expression of extracellular matrix components in bovine mesangial cells in culture
Gravitating discs around black holes
Fluid discs and tori around black holes are discussed within different
approaches and with the emphasis on the role of disc gravity. First reviewed
are the prospects of investigating the gravitational field of a black
hole--disc system by analytical solutions of stationary, axially symmetric
Einstein's equations. Then, more detailed considerations are focused to middle
and outer parts of extended disc-like configurations where relativistic effects
are small and the Newtonian description is adequate.
Within general relativity, only a static case has been analysed in detail.
Results are often very inspiring, however, simplifying assumptions must be
imposed: ad hoc profiles of the disc density are commonly assumed and the
effects of frame-dragging and completely lacking. Astrophysical discs (e.g.
accretion discs in active galactic nuclei) typically extend far beyond the
relativistic domain and are fairly diluted. However, self-gravity is still
essential for their structure and evolution, as well as for their radiation
emission and the impact on the environment around. For example, a nuclear star
cluster in a galactic centre may bear various imprints of mutual star--disc
interactions, which can be recognised in observational properties, such as the
relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be
available from http://www.iop.org/EJ/journal/CQ
Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical disks
The most efficient energy sources known in the Universe are accretion disks.
Those around black holes convert 5 -- 40 per cent of rest-mass energy to
radiation. Like water circling a drain, inflowing mass must lose angular
momentum, presumably by vigorous turbulence in disks, which are essentially
inviscid. The origin of the turbulence is unclear. Hot disks of electrically
conducting plasma can become turbulent by way of the linear magnetorotational
instability. Cool disks, such as the planet-forming disks of protostars, may be
too poorly ionized for the magnetorotational instability to occur, hence
essentially unmagnetized and linearly stable. Nonlinear hydrodynamic
instability often occurs in linearly stable flows (for example, pipe flows) at
sufficiently large Reynolds numbers. Although planet-forming disks have extreme
Reynolds numbers, Keplerian rotation enhances their linear hydrodynamic
stability, so the question of whether they can be turbulent and thereby
transport angular momentum effectively is controversial. Here we report a
laboratory experiment, demonstrating that non-magnetic quasi-Keplerian flows at
Reynolds numbers up to millions are essentially steady. Scaled to accretion
disks, rates of angular momentum transport lie far below astrophysical
requirements. By ruling out purely hydrodynamic turbulence, our results
indirectly support the magnetorotational instability as the likely cause of
turbulence, even in cool disks.Comment: 12 pages and 4 figures. To be published in Nature on November 16,
2006, available at
http://www.nature.com/nature/journal/v444/n7117/abs/nature05323.htm
Consensus protocol for EEG and amplitude-integrated EEG assessment and monitoring in neonates
The aim of this work is to establish inclusive guidelines on electroencephalography (EEG) applicable to all neonatal intensive care units (NICUs). Guidelines on ideal EEG monitoring for neonates are available, but there are significant barriers to their implementation in many centres around the world. These include barriers due to limited resources regarding the availability of equipment and technical and interpretive round-the-clock personnel. On the other hand, despite its limitations, amplitude-integrated EEG (aEEG) (previously called Cerebral Function Monitor [CFM]) is a common alternative used in NICUs. The Italian Neonatal Seizure Collaborative Network (INNESCO), working with all national scientific societies interested in the field of neonatal clinical neurophysiology, performed a systematic literature review and promoted interdisciplinary discussions among experts (neonatologists, paediatric neurologists, neurophysiologists, technicians) between 2017 and 2020 with the aim of elaborating shared recommendations. A consensus statement on videoEEG (vEEG) and aEEG for the principal neonatal indications was established. The authors propose a flexible frame of recommendations based on the complementary use of vEEG and aEEG applicable to the various neonatal units with different levels of complexity according to local resources and specific patient features. Suggestions for promoting cooperation between neonatologists, paediatric neurologists, and neurophysiologists, organisational restructuring, and teleneurophysiology implementation are provided
Planetary Rings
Planetary rings are the only nearby astrophysical disks, and the only disks
that have been investigated by spacecraft. Although there are significant
differences between rings and other disks, chiefly the large planet/ring mass
ratio that greatly enhances the flatness of rings (aspect ratios as small as
1e-7), understanding of disks in general can be enhanced by understanding the
dynamical processes observed at close-range and in real-time in planetary
rings. We review the known ring systems of the four giant planets, as well as
the prospects for ring systems yet to be discovered. We then review planetary
rings by type. The main rings of Saturn comprise our system's only dense broad
disk and host many phenomena of general application to disks including spiral
waves, gap formation, self-gravity wakes, viscous overstability and normal
modes, impact clouds, and orbital evolution of embedded moons. Dense narrow
rings are the primary natural laboratory for understanding shepherding and
self-stability. Narrow dusty rings, likely generated by embedded source bodies,
are surprisingly found to sport azimuthally-confined arcs. Finally, every known
ring system includes a substantial component of diffuse dusty rings. Planetary
rings have shown themselves to be useful as detectors of planetary processes
around them, including the planetary magnetic field and interplanetary
impactors as well as the gravity of nearby perturbing moons. Experimental rings
science has made great progress in recent decades, especially numerical
simulations of self-gravity wakes and other processes but also laboratory
investigations of coefficient of restitution and spectroscopic ground truth.
The age of self-sustained ring systems is a matter of debate; formation
scenarios are most plausible in the context of the early solar system, while
signs of youthfulness indicate at least that rings have never been static
phenomena.Comment: 82 pages, 34 figures. Final revision of general review to be
published in "Planets, Stars and Stellar Systems", P. Kalas and L. French
(eds.), Springer (http://refworks.springer.com/sss
MIKiS: The Multi-instrument Kinematic Survey of Galactic Globular Clusters. I. Velocity Dispersion Profiles and Rotation Signals of 11 Globular Clusters
We present the first results of the Multi-Instrument Kinematic Survey of
Galactic Globular Clusters, a project aimed at exploring the internal
kinematics of a representative sample of Galactic globular clusters from the
radial velocity of individual stars, covering the entire radial extension of
each system. This is achieved by exploiting the formidable combination of
multi-object and integral field unit spectroscopic facilities of the ESO Very
Large Telescope. As a first step, here we discuss the results obtained for 11
clusters from high and medium resolution spectra acquired through a combination
of FLAMES and KMOS observations. We provide the first kinematical
characterization of NGC 1261 and NGC 6496. In all the surveyed systems, the
velocity dispersion profile declines at increasing radii, in agreement with the
expectation from the King model that best fits the density/luminosity profile.
In the majority of the surveyed systems we find evidence of rotation within a
few half-mass radii from the center. These results are in general overall
agreement with the predictions of recent theoretical studies, suggesting that
the detected signals could be the relic of significant internal rotation set at
the epoch of the cluster's formation.Comment: 39 pages, 12 figures, ApJ, in pres
Endothelium-derived endothelin-1
One year after the revelation by Dr. Furchgott in 1980 that the endothelium was obligatory for acetylcholine to relax isolated arteries, it was clearly shown that the endothelium could also promote contraction. In 1988, Dr. Yanagisawa’s group identified endothelin-1 (ET-1) as the first endothelium-derived contracting factor. The circulating levels of this short (21-amino acid) peptide were quickly determined in humans, and it was reported that, in most cardiovascular diseases, circulating levels of ET-1 were increased, and ET-1 was then tagged as “a bad guy.” The discovery of two receptor subtypes in 1990, ET(A) and ET(B), permitted optimization of the first dual ET-1 receptor antagonist in 1993 by Dr. Clozel’s team, who entered clinical development with bosentan, which was offered to patients with pulmonary arterial hypertension in 2001. The revelation of Dr. Furchgott opened a Pandora’s box with ET-1 as one of the actors. In this brief review, we will discuss the physiological and pathophysiological role of endothelium-derived ET-1 focusing on the regulation of the vascular tone, and as much as possible in humans. The coronary bed will be used as a running example in this review because it is the most susceptible to endothelial dysfunction, but references to the cerebral and renal circulation will also be made. Many of the cardiovascular complications associated with aging and cardiovascular risk factors are initially attributable, at least in part, to endothelial dysfunction, particularly dysregulation of the vascular function associated with an imbalance in the close interdependence of nitric oxide and ET-1