7,784 research outputs found
Normal Modes of Black Hole Accretion Disks
This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigenfrequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and examine the role of viscosity, as it appears to render some of the modes unstable to rapid growth
On the common origin of the AB Dor moving group and the Pleiades cluster
AB Dor is the nearest identified moving group. As with other such groups, the
age is important for understanding of several key questions. It is important,
for example, in establishing the origin of the group and also in comparative
studies of the properties of planetary systems, eventually surrounding some of
the AB Dor group members, with those existing in other groups. For AB Dor two
rather different estimates for its age have been proposed: a first one, of the
order of 50 Myr, by Zuckerman and coworkers from a comparison with
Tucana/Horologium moving group and a second one of about 100-125 Myr by Luhman
and coworkers from color-magnitude diagrams (CMD). Using this last value and
the closeness in velocity space of AB Dor and the Pleiades galactic cluster,
Luhman and coworkers suggested coevality for these systems. Because strictly
speaking such a closeness does not still guarantee coevality, here we address
this problem by computing and comparing the full 3D orbits of AB Dor, Pleiades,
alpha Persei and IC 2602. The latter two open clusters have estimated ages of
about 85-90 Myr and 50 Myr. The resulting age 119 20 Myr is consistent
with AB Dor and Pleiades being coeval. Our solution and the scenario of open
cluster formation proposed by Kroupa and collaborators suggest that the AB Dor
moving group may be identified with the expanding subpopulation (Group I)
present in this scenario. We also discuss other related aspects as iron and
lithium abundances, eventual stellar mass segregation during the formation of
the systems and possible fraction of debris discs in AB Dor group.Comment: 11 pages, 5 figures and 2 table
Hyperthermia-Triggered Doxorubicin Release from Polymer-Coated Magnetic Nanorods
In this paper, it is proposed that polymer-coated magnetic nanorods (MNRs) can be
used with the advantage of a double objective: first, to serve as magnetic hyperthermia agents,
and second, to be used as magnetic vehicles for the antitumor drug doxorubicin (DOX). Two di erent
synthetic methodologies (hydrothermal and co-precipitation) were used to obtain MNRs of maghemite
and magnetite. They were coated with poly(ethyleneimine) and poly(sodium 4-styrenesulfonate),
and loaded with DOX, using the Layer-by-Layer technique. Evidence of the polymer coating and
the drug loading was justified by ATR-FTIR and electrophoretic mobility measurements, and the
composition of the coated nanorods was obtained by a thermogravimetric analysis. The nanorods
were tested as magnetic hyperthermia agents, and it was found that they provided sufficiently large
heating rates to be used as adjuvant therapy against solid tumors. DOX loading and release were
determined by UV-visible spectroscopy, and it was found that up to 50% of the loaded drug was
released in about 5 h, although the rate of release could be regulated by simultaneous application of
hyperthermia, which acts as a sort of external release-trigger. Shape control offers another physical
property of the particles as candidates to interact with tumor cells, and particles that are not too
elongated can easily find their way through the cell membrane.This research work is supported by Junta de AndalucĂa (PE2012-FQM694); Feder Funds UE; and MINECO
RamĂłn y Cajal programme (RYC-2014-16901)
Trigonometry of 'complex Hermitian' type homogeneous symmetric spaces
This paper contains a thorough study of the trigonometry of the homogeneous
symmetric spaces in the Cayley-Klein-Dickson family of spaces of 'complex
Hermitian' type and rank-one. The complex Hermitian elliptic CP^N and
hyperbolic CH^N spaces, their analogues with indefinite Hermitian metric and
some non-compact symmetric spaces associated to SL(N+1,R) are the generic
members in this family. The method encapsulates trigonometry for this whole
family of spaces into a single "basic trigonometric group equation", and has
'universality' and '(self)-duality' as its distinctive traits. All previously
known results on the trigonometry of CP^N and CH^N follow as particular cases
of our general equations. The physical Quantum Space of States of any quantum
system belongs, as the complex Hermitian space member, to this parametrised
family; hence its trigonometry appears as a rather particular case of the
equations we obtain.Comment: 46 pages, LaTe
'Stable' QPOs and Black Hole Properties from Diskoseismology
We compare our calculations of the frequencies of the fundamental g, c, and
p--modes of relativistic thin accretion disks with recent observations of high
frequency QPOs in X-ray binaries with black hole candidates. These classes of
modes encompass all adiabatic perturbations of such disks. The frequencies of
these modes depend mainly on only the mass and angular momentum of the black
hole; their weak dependence on disk luminosity is also explicitly indicated.
Identifying the recently discovered relatively stable QPO pairs with the
fundamental g and c modes provides a determination of the mass and angular
momentum of the black hole. For GRO J1655-40, M=5.9\pm 1.0 M_\sun,
, in agreement with spectroscopic mass
determinations. For GRS 1915+105, M=42.4\pm 7.0 M_\sun, or (less favored) M=18.2\pm 3.1 M_\sun, . We briefly address the issues of the amplitude, frequency width,
and energy dependence of these QPOs.Comment: 10 pages, 1 figure. Accepted for publication in Astrophysical Journal
Letter
ROBUST REGULATION FOR SYSTEMS WITH POLYNOMIAL NONLINEARITY APPLIED TO RAPID THERMAL PROCESSES
Abstract. A problem of output robust control for a system with power nonlinearity is considered. The considered problem can be rewritten as a stabilization problem for a system with polynomial nonlinearity by introducing the error term. The problem of temperature regulation is considered as application; the rapid thermal processes in vapor deposition processing are studied. Modern industrial equipment uses complex sensors and control systems; these devices are not available for laboratory setups. The limited amount of available sensors and other technical restrictions for laboratory setups make it an actual problem to design simple low-order output control laws. The problem is solved by the consecutive compensator approach. The paper deals with a new type of restriction which is a combination of linear and power restrictions. It is shown that the polynomial nonlinearity satisfies this restriction. Asymptotical stability of the closed-loop system is proved by the Lyapunov functions approach for the considered nonlinear function; this contribution extends previously known results. Numerical simulation of the vapor deposition processing illustrates that the proposed approach results in zero-mean tracking error with standard deviation less than 1K
The Sound of Topology in the AdS/CFT Correspondence
Using the gauge/gravity correspondence, we study the properties of 2-point
correlation functions of finite-temperature strongly coupled gauge field
theories, defined on a curved space of general spatial topology with a dual
black hole description. We derive approximate asymptotic expressions for the
correlation functions and their poles, supported by exact numerical
calculations, and study their dependence on the dimension of spacetime and the
spatial topology. The asymptotic structure of the correlation functions depends
on the relation between the spatial curvature and the temperature, and is
noticeable when they are of the same order. In the case of a hyperbolic
topology, a specific temperature is identified for which exact analytical
solutions exist for all types of perturbations. The asymptotic structure of the
correlation functions poles is found to behave in a non-smooth manner when
approaching this temperature.Comment: 65 pages, LaTeX, 21 figures, 1 table; fixed a small error in
subsection 3.
Spin-orbit splitting of image states
We quantify the effect of the spin-orbit interaction on the Rydberg-like
series of image state electrons at the (111) and (001) surface of Ir, Pt and
Au. Using relativistic multiple-scattering methods we find Rashba-like
dispersions with Delta E(K)=gamma K with values of gamma for n=1 states in the
range 38-88 meV Angstrom. Extending the phase-accumulation model to include
spin-orbit scattering we find that the splittings vary like 1/(n+a)^3 where a
is the quantum defect and that they are related to the probability of spin-flip
scattering at the surface. The splittings should be observable experimentally
being larger in magnitude than some exchange-splittings that have been resolved
by inverse photoemission, and are comparable to linewidths from inelastic
lifetimes.Comment: 10 pages, 4 figure
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