228 research outputs found
On the conical refraction of hydromagnetic waves in plasma with anisotropic thermal pressure
A phenomenon analogous to the conical refraction widely known in the
crystalooptics and crystaloacoustics is discovered for the
magnetohydrodynamical waves in the collisionless plasma with anisotropic
thermal pressure. Angle of the conical refraction is calculated for the medium
under study which is predicted to be . Possible
experimental corroborating of the discovered phenomenon is discussed.Comment: 6 pages, REVTeX, Accepted in Physics of Plasma
Differential rotation and angular momentum
Differential rotation not only occurs in astrophysical plasmas like accretion disks, it is also measured in laboratory plasmas as manifested in the toroidal rotation of tokamak plasmas. A re-examination of the Lagrangian of the system shows that the inclusion of the angular momentumâs radial variation in the derivation of the equations of motion produces a force term that couples the angular velocity gradient with the angular momentum. This force term is a property of the angular velocity field, so that the results are valid wherever differential rotation is present
High-resolution ellipsometric study of an n-alkane film, dotriacontane, adsorbed on a SiO2 surface
doi:10.1063/1.1429645Using high-resolution ellipsometry and stray light intensity measurements, we have investigated during successive heating-cooling cycles the optical thickness and surface roughness of thin dotriacontane (n-C32H66) films adsorbed from a heptane (n-C7H16) solution onto SiO2-coated Si(100) single-crystal substrates. Our results suggest a model of a solid dotriacontane film that has a phase closest to the SiO2 surface in which the long-axis of the molecules is oriented parallel to the interface. Above this "parallel film" phase, a solid monolayer adsorbs in which the molecules are oriented perpendicular to the interface. At still higher coverages and at temperatures below the bulk melting point at Tb = 341 K, solid bulk particles coexist on top of the "perpendicular film." For higher temperatures in the range TbTs, a uniformly thick fluid film wets to the parallel film phase. This structure of the alkane/SiO2 interfacial region differs qualitatively from that which occurs in the surface freezing effect at the bulk alkane fluid/vapor interface. In that case, there is again a perpendicular film phase adjacent to the air interface but no parallel film phase intervenes between it and the bulk alkane fluid. Similarities and differences between our model of the alkane/SiO2 interface and one proposed recently will be discussed. Our ellipsometric measurements also show evidence of a crystalline-to-plastic transition in the perpendicular film phase similar to that occurring in the solid bulk particles present at higher coverages. In addition, we have performed high-resolution ellipsometry and stray-light measurements on dotriacontane films deposited from solution onto highly oriented pyrolytic graphite substrates. After film deposition, these substrates proved to be less stable in air than SiO2.This work was supported by the Chilean government under CONICYT Grant No. 018/AT/005NSF and FONDECYT Grant No. 1980586 and by the U.S. National Science Foundation under Grant Nos. INT-9605227, DMR-9802476, and DMR-0109057
Compressed multiple pattern matching
Peer reviewe
High-Energy Emission From Millisecond Pulsars
The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is
investigated in a model for acceleration and pair cascades on open field lines
above the polar caps. Although these pulsars have low surface magnetic fields,
their short periods allow them to have large magnetospheric potential drops,
but the majority do not produce sufficient pairs to completely screen the
accelerating electric field. The accelerating particles maintain high Lorentz
factors and undergo cyclotron resonant absorption of radio emission, that
produces and maintains a large pitch angle, resulting in a strong synchrotron
component. The resulting spectra consist of several distinct components:
curvature radiation from primary electrons dominating from 1 - 100 GeV,
synchrotron radiation from primary and secondary electrons dominating up to
about 100 MeV, and much weaker inverse-Compton radiation from primary electrons
at 0.1 - 1 TeV. We find that the relative size of these components depends on
pulsar period, period derivative, and neutron star mass and radius with the
level of the synchrotron component also depending sensitively on the radio
emission properties. This model is successful in describing the observed X-ray
and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking
around 100 MeV and extending up to a turnover around several GeV. The predicted
curvature radiation components from a number of millisecond pulsars, as well as
the collective emission from the millisecond pulsars in globular clusters,
should be detectable with AGILE and GLAST. We also discuss a hidden population
of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the
pair death line, some of which may be detectable by telescopes sensitive above
1 GeV.Comment: 34 pages, 6 figures, accepted for publication in Astrophysical
Journa
Frequency range and explicit expressions for negative permittivity and permeability for an isotropic medium formed by a lattice of perfectly conducting particles
An analytical model is presented for a rectangular lattice of isotropic
scatterers with electric and magnetic resonances. Each isotropic scatterer is
formed by putting appropriately 6 -shaped perfectly conducting
particles on the faces of a cubic unit cell. A self-consistent dispersion
equation is derived and then used to calculate correctly the effective
permittivity and permeability in the frequency band where the lattice can be
homogenized. The frequency range in which both the effective permittivity and
permeability are negative corresponds to the mini-band of backward waves within
the resonant band of the individual isotropic scatterer.Comment: 25 pages, 6 figure
Transverse quasilinear relaxation in inhomogeneous magnetic field
Transverse quasilinear relaxation of the cyclotron-Cherenkov instability in
the inhomogeneous magnetic field of pulsar magnetospheres is considered. We
find quasilinear states in which the kinetic cyclotron-Cherenkov instability of
a beam propagating through strongly magnetized pair plasma is saturated by the
force arising in the inhomogeneous field due to the conservation of the
adiabatic invariant. The resulting wave intensities generally have nonpower law
frequency dependence, but in a broad frequency range can be well approximated
by the power law with the spectral index -2. The emergent spectra and fluxes
are consistent with the one observed from pulsars.Comment: 14 Pages, 4 Figure
Mesoscopic effective material parameters for thin layers modeled as single and double grids of interacting loaded wires
As an example of thin composite layers we consider single and double grids of
periodically arranged interacting wires loaded with a certain distributed
reactive impedance. Currents induced to the wires by a normally incident plane
wave are rigorously calculated and the corresponding dipole moment densities
are determined. Using this data and the averaged fields we assign mesoscopic
material parameters for the proposed grid structures. These parameters depend
on the number of grids, and measure the averaged induced polarizations. It is
demonstrated that properly loaded double grids possess polarization response
that over some frequency range can be described by assigning negative values
for the mesoscopic parameters. Discussion is conducted on the physical
meaningfulness to assign such material parameters for thin composite slabs. The
results predicted by the proposed method for the double-grid structures are
compared with the results obtained using the commonly adopted S-parameter
retrieval procedure.Comment: 36 pages, 23 figure
Nonlinear theory of mirror instability near threshold
An asymptotic model based on a reductive perturbative expansion of the drift
kinetic and the Maxwell equations is used to demonstrate that, near the
instability threshold, the nonlinear dynamics of mirror modes in a magnetized
plasma with anisotropic ion temperatures involves a subcritical
bifurcation,leading to the formation of small-scale structures with amplitudes
comparable with the ambient magnetic field
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