639 research outputs found
Nonlinear Terms of MHD Equations for Homogeneous Magnetized Shear Flow
We have derived the full set of MHD equations for incompressible shear flow
of a magnetized fluid and considered their solution in the wave-vector space.
The linearized equations give the famous amplification of slow magnetosonic
waves and describe the magnetorotational instability. The nonlinear terms in
our analysis are responsible for the creation of turbulence and self-sustained
spectral density of the MHD (Alfven and pseudo-Alfven) waves. Perspectives for
numerical simulations of weak turbulence and calculation of the effective
viscosity of accretion disks are shortly discussed in k-space.Comment: 13 pages, no figures; AIP Conference Proceedings 1356, Proceedings of
the School and Workshop on Space Plasma Physics (1--12 September 2010, Kiten,
Bulgaria), American Institute of Physics, Melville, NY, 201
ANTIGENIC UNITY BETWEEN PHYTOHEMAGGLUTININ OF PHASEOLUS VULGARIS AND SOME BACTERIA AND VIRA
No abstract
Reconstruction of a Broadband Spectrum of Alfvenic Fluctuations
Alfvenic fluctuations in the solar wind exhibit a high degree of velocities and magnetic field correlations consistent with Alfven waves propagating away and toward the Sun. Two remarkable properties of these fluctuations are the tendencies to have either positive or negative magnetic helicity (-1 less than or equal to sigma(sub m) less than or equal to +1) associated with either left- or right- topological handedness of the fluctuations and to have a constant magnetic field magnitude. This paper provides, for the first time, a theoretical framework for reconstructing both the magnetic and velocity field fluctuations with a divergence-free magnetic field, with any specified power spectral index and normalized magnetic- and cross-helicity spectrum field fluctuations for any plasma species. The spectrum is constructed in the Fourier domain by imposing two conditions-a divergence-free magnetic field and the preservation of the sense of magnetic helicity in both spaces-as well as using Parseval's theorem for the conservation of energy between configuration and Fourier spaces. Applications to the one-dimensional spatial Alfvenic propagation are presented. The theoretical construction is in agreement with typical time series and power spectra properties observed in the solar wind. The theoretical ideas presented in this spectral reconstruction provide a foundation for more realistic simulations of plasma waves, solar wind turbulence, and the propagation of energetic particles in such fluctuating fields
Amplification of Slow Magnetosonic Waves by Shear Flow: Heating and Friction Mechanisms of Accretion Disks
Propagation of three dimensional magnetosonic waves is considered for a
homogeneous shear flow of an incompressible fluid. The analytical solutions for
all magnetohydrodynamic variables are presented by confluent Heun functions.
The problem is reduced to finding a solution of an effective Schroedinger
equation. The amplification of slow magnetosonic waves is analyzed in great
details. A simple formula for the amplification coefficient is derived. The
velocity shear primarily affects the incompressible limit of slow magnetosonic
waves. The amplification is very strong for slow magnetosonic waves in the
long-wavelength limit. It is demonstrated that the amplification of those waves
leads to amplification of turbulence. The phenomenology of Shakura-Sunyaev for
the friction in accretion disks is derived in the framework of the Kolmogorov
turbulence. The presented findings may be the key to explaining the anomalous
plasma heating responsible for the luminosity of quasars. It is suggested that
wave amplification is the keystone of the self-sustained turbulence in
accretion disks.Comment: 26pages, 11 figures, In Space Plasma Physics, Proceedings of the
School and Workshop on Space Plasma Physics, 31 August--7 September 2008,
Sozopol, Bulgaria, Editor: I. Zhelyazkov, American Institute of Physics, AIP
Conference Proceedings (2009). 5 new references are given in version 2.
Analytical expression for long wavelength amplificatio
On the origin of solar wind. Alfven waves induced jump of coronal temperature
Absorbtion of Alfven waves is considered to be the main mechanism of heating
in the solar corona. It is concluded that the sharp increase of the plasma
temperature by two orders of magnitude is related to a self-induced opacity
with respect to Alfven waves. The maximal frequency for propagation of Alfven
waves is determined by the strongly temperature dependent kinematic viscosity.
In such a way the temperature jump is due to absorption of high frequency
Alfven waves in a narrow layer above the solar surface. It is calculated that
the power per unit area dissipated in this layer due to damping of Alfven waves
blows up the plasma and gives birth to the solar wind. A model short
wave-length (WKB) evaluation takes into account the 1/f^2 frequency dependance
of the transversal magnetic field and velocity spectral densities. Such
spectral densities agree with old magnetometric data taken by Voyager 1 and
recent theoretical calculations in the framework of Langevin-Burgers MHD. The
present theory predicts existence of intensive high frequency MHD Alfven waves
in the cold layer beneath the corona. It is briefly discussed how this
statement can be checked experimentally. It is demonstrated that the magnitude
of the Alfven waves generating random noise and the solar wind velocity can be
expressed only in terms of satellite experimental data. It is advocated that
investigation of properties of the solar surface as a random driver by optical
methods is an important task for future solar physics. Jets of accretion disks
are speculated as a special case of the wind from magnetized turbulent plasma.Comment: 4 pages, no figures, minor corrections, final version for EPJ
A Simultaneous Quantum Secure Direct Communication Scheme between the Central Party and Other M Parties
We propose a simultaneous quantum secure direct communication scheme between
one party and other three parties via four-particle GHZ states and swapping
quantum entanglement. In the scheme, three spatially separated senders, Alice,
Bob and Charlie, transmit their secret messages to a remote receiver Diana by
performing a series local operations on their respective particles according to
the quadripartite stipulation. From Alice, Bob, Charlie and Diana's Bell
measurement results, Diana can infer the secret messages. If a perfect quantum
channel is used, the secret messages are faithfully transmitted from Alice, Bob
and Charlie to Diana via initially shared pairs of four-particle GHZ states
without revealing any information to a potential eavesdropper. As there is no
transmission of the qubits carrying the secret message in the public channel,
it is completely secure for the direct secret communication. This scheme can be
considered as a network of communication parties where each party wants to
communicate secretly with a central party or server.Comment: 4 pages, no figur
Deterministic secure direct communication using GHZ states and swapping quantum entanglement
We present a deterministic secure direct communication scheme via
entanglement swapping, where a set of ordered maximally entangled
three-particle states (GHZ states), initially shared by three spatially
separated parties, Alice, Bob and Charlie, functions as a quantum information
channel. After ensuring the safety of the quantum channel, Alice and Bob apply
a series local operations on their respective particles according to the
tripartite stipulation and the secret message they both want to send to
Charlie. By three Alice, Bob and Charlie's Bell measurement results, Charlie is
able to infer the secret messages directly. The secret messages are faithfully
transmitted from Alice and Bob to Charlie via initially shared pairs of GHZ
states without revealing any information to a potential eavesdropper. Since
there is not a transmission of the qubits carrying the secret message between
any two of them in the public channel, it is completely secure for direct
secret communication if perfect quantum channel is used.Comment: 9 pages, no figur
- …