644 research outputs found
Nonlinear Interactions Between Gravitational Radiation and Modified Alfven Modes in Astrophysical Dusty Plasmas
We present an investigation of nonlinear interactions between Gravitational
Radiation and modified Alfv\'{e}n modes in astrophysical dusty plasmas.
Assuming that stationary charged dust grains form neutralizing background in an
electron-ion-dust plasma, we obtain the three wave coupling coefficients, and
calculate the growth rates for parametrically coupled gravitational radiation
and modified Alfv\'{e}n-Rao modes. The threshold value of the gravitational
wave amplitude associated with convective stabilization is particularly small
if the gravitational frequency is close to twice the modified Alfv\'en
wave-frequency. The implication of our results to astrophysical dusty plasmas
is discussed.Comment: A few typos corrected. Published in Phys. Rev.
Ferroplasmas: Magnetic Dust Dynamics in a Conducting Fluid
We consider a dusty plasma, in which the dust particles have a magnetic
dipole moment. A Hall-MHD type of model, generalized to account for the
intrinsic magnetization, is derived. The model is shown to be energy
conserving, and the energy density and flux is derived. The general dispersion
relation is then derived, and we show that kinetic Alfv\'en waves exhibit an
instability for a low temperature and high density plasma. We discuss the
implication of our results.Comment: 6 pages, 1 figur
The Mikheyev-Smirnov-Wolfenstein Effect as a Probe of the Solar Interior
We relate the MSW effect to the efective absorption of the electronic
collective motion energy by retaining the imaginary part of the index of
refraction associated with the charged-current scattering and show that the
small angle MSW solution to the solar neutrino anomaly can be used as a probe
of the physical conditions of the solar interior if it is correct. We find that
the constraint on the absorption imposed by the small angle MSW solution and
the theoretical estimate of the absorption by the Boltzmann kinetic theory are
consistent, which shows that a consistent theoretical picture can be developed
when plasma absorption processes are taken into account.Comment: 4 pages, no figure, REVTeX, to appear in Phys. Rev.
Scalar quantum kinetic theory for spin-1/2 particles: mean field theory
Starting from the Pauli Hamiltonian operator, we derive a scalar quantum
kinetic equations for spin-1/2 systems. Here the regular Wigner two-state
matrix is replaced by a scalar distribution function in extended phase space.
Apart from being a formulation of principal interest, such scalar quantum
kinetic equation makes the comparison to classical kinetic theory
straightforward, and lends itself naturally to currently available numerical
Vlasov and Boltzmann schemes. Moreover, while the quasi-distribution is a
Wigner function in regular phase space, it is given by a Q-function in spin
space. As such, nonlinear and dynamical quantum plasma problems are readily
handled. Moreover, the issue of gauge invariance is treated. Applications (e.g.
ultra-dense laser compressed targets and their diagnostics), possible
extensions, and future improvements of the presented quantum statistical model
are discussed.Comment: 21 pages, 2 figure
Gravitational wave detection using electromagnetic modes in a resonance cavity
We present a proposal for a gravitational wave detector, based on the
excitation of an electromagnetic mode in a resonance cavity. The mode is
excited due to the interaction between a large amplitude electromagnetic mode
and a quasi-monochromatic gravitational wave. The minimum metric perturbation
needed for detection is estimated to the order 7.10^(-23) using current data on
superconducting niobium cavities. Using this value together with different
standard models predicting the occurrence of merging neutron star or black hole
binaries, the corresponding detection rate is estimated to 1-20 events per
year, with a `table top' cavity of a few meters length.Comment: 8 pages, 1 figure, references adde
Very high frequency gravitational wave background in the universe
Astrophysical sources of high frequency gravitational radiation are
considered in association with a new interest to very sensitive HFGW receivers
required for the laboratory GW Hertz experiment. A special attention is paid to
the phenomenon of primordial black holes evaporation. They act like black body
to all kinds of radiation, including gravitons, and, therefore, emit an
equilibrium spectrum of gravitons during its evaporation. Limit on the density
of high frequency gravitons in the Universe is obtained, and possibilities of
their detection are briefly discussed.Comment: 14 page
The nature of the short wavelength excitations in vitreous silica: X-Rays Brillouin scattering study
The dynamical structure factor (S(Q,E)) of vitreous silica has been measured
by Inelastic X-ray Scattering varying the exchanged wavevector (Q) at fixed
exchanged energy (E) - an experimental procedure that, contrary to the usual
one at constant Q, provides spectra with much better identified inelastic
features. This allows the first direct evidence of Brillouin peaks in the
S(Q,E) of SiO_2 at energies above the Boson Peak (BP) energy, a finding that
excludes the possibility that the BP marks the transition from propagating to
localised dynamics in glasses.Comment: 4 pages, 3 Postscript figures. To appear in Physical Review Letter
Human NK Cells Differ More in Their KIR2DL1-Dependent Thresholds for HLA-Cw6-Mediated Inhibition than in Their Maximal Killing Capacity
In this study we have addressed the question of how activation and inhibition of human NK cells is regulated by the expression level of MHC class I protein on target cells. Using target cell transfectants sorted to stably express different levels of the MHC class I protein HLA-Cw6, we show that induction of degranulation and that of IFN-γ secretion are not correlated. In contrast, the inhibition of these two processes by MHC class-I occurs at the same level of class I MHC protein. Primary human NK cell clones were found to differ in the amount of target MHC class I protein required for their inhibition, rather than in their maximum killing capacity. Importantly, we show that KIR2DL1 expression determines the thresholds (in terms of MHC I protein levels) required for NK cell inhibition, while the expression of other receptors such as LIR1 is less important. Furthermore, using mathematical models to explore the dynamics of target cell killing, we found that the observed delay in target cell killing is exhibited by a model in which NK cells require some activation or priming, such that each cell can lyse a target cell only after being activated by a first encounter with the same or a different target cell, but not by models which lack this feature
- …