46 research outputs found
Magnetic fields of active galactic nuclei and quasars with polarized broad H-alpha lines
We present estimates of magnetic field in a number of AGNs from the
Spectropolarimetric atlas of Smith, Young & Robinson (2002) from the observed
degrees of linear polarization and the positional angles of spectral lines
(H-alpha) (broad line regions of AGNs) and nearby continuum. The observed
polarization is lower than the Milne value in a non-magnetized atmosphere. We
hypothesize that the polarized radiation escapes from optically thick
magnetized accretion discs and is weakened by the Faraday rotation effect. This
effect is able to explain both the value of the polarization and the position
angle. We estimate the required magnetic field in the broad line region by
using simple asymptotic analytical formulas for Milne's problem in magnetized
atmosphere, which take into account the last scattering of radiation before
escaping from the accretion disc. The polarization of a broad spectral line
escaping from disc is described by the same mechanism. The characteristic
features of polarization of a broad line is the minimum of the degree of
polarization in the center of the line and continuous rotation of the position
angle from one wing to another. These effects can be explained by existence of
clouds in the left (velocity is directed to an observer) and the right
(velocity is directed from an observer) parts of the orbit in a rotating
keplerian magnetized accretion disc. The base of explanation is existence of
azimuthal magnetic field in the orbit. The existence of normal component of
magnetic field makes the picture of polarization asymmetric. The existence of
clouds in left and right parts of the orbit with different emissions also give
the contribution in asymmetry effect. Assuming a power-law dependence of the
magnetic field inside the disc, we obtain the estimate of the magnetic field
strength at first stable orbit near the central SMBH for a number of AGNs.Comment: 15 pages, 4 figure
Matter in Strong Magnetic Fields
The properties of matter are significantly modified by strong magnetic
fields, Gauss (), as are typically
found on the surfaces of neutron stars. In such strong magnetic fields, the
Coulomb force on an electron acts as a small perturbation compared to the
magnetic force. The strong field condition can also be mimicked in laboratory
semiconductors. Because of the strong magnetic confinement of electrons
perpendicular to the field, atoms attain a much greater binding energy compared
to the zero-field case, and various other bound states become possible,
including molecular chains and three-dimensional condensed matter. This article
reviews the electronic structure of atoms, molecules and bulk matter, as well
as the thermodynamic properties of dense plasma, in strong magnetic fields,
. The focus is on the basic physical pictures and
approximate scaling relations, although various theoretical approaches and
numerical results are also discussed. For the neutron star surface composed of
light elements such as hydrogen or helium, the outermost layer constitutes a
nondegenerate, partially ionized Coulomb plasma if , and may be in
the form of a condensed liquid if the magnetic field is stronger (and
temperature K). For the iron surface, the outermost layer of the
neutron star can be in a gaseous or a condensed phase depending on the cohesive
property of the iron condensate.Comment: 45 pages with 9 figures. Many small additions/changes. Accepted for
publication in Rev. Mod. Phy
Preparation of Hydrogels Based on Modified Pectins by Tuning Their Properties for Anti-Glioma Therapy
The extracellular matrix (ECM) of the central nervous system (CNS), characterized by low stiffness and predominance of carbohydrates on protein components, mediates limited cell proliferation and migration. Pectins are polysaccharides derived from plants and could be very promising for a tunable hydrogel design that mimics the neural ECM. Aiming to regulate gel structure and viscoelastic properties, we elaborated 10 variants of pectin-based hydrogels via tuning the concentration of the polymer and the number of free carboxyl groups expressed in the degree of esterification (DE). Viscoelastic properties of hydrogels varied in the range of 3 to 900 Pa for G′ and were chosen as the first criteria for the selection of variants suitable for CNS remodeling. For extended reciprocal characterization, two pairs of hydrogels were taken to test pectins with opposite DEs close to 0% and 50%, respectively, but with a similar rheology exceeding 100 Pa (G′), which was achieved by adjusting the concentration of pectin. Hydrogel swelling properties and in vitro stability, together with structure characterization using SEM and FTIR spectroscopy, displayed some differences that may sense for biomedical application. Bioassays on C6 and U87MG glioblastoma cultures testified the potential prospects of the anti-glioma activity of hydrogels developed by decreasing cell proliferation and modulating migration but supporting the high viability of neural cells