146 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
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
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
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
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
Spectrometric method to detect exoplanets as another test to verify the invariance of the velocity of light
Hypothetical influences of variability of light velocity due to the
parameters of the source of radiation, for the results of spectral measurements
of stars to search for exoplanets are considered. Accounting accelerations of
stars relative to the barycenter of the star - a planet (the planets) was
carried out. The dependence of the velocity of light from the barycentric
radial velocity and barycentric radial acceleration component of the star
should lead to a substantial increase (up to degree of magnitude) semi-major
axes of orbits detected candidate to extrasolar planets. Consequently, the
correct comparison of the results of spectral method with results of other
well-known modern methods of detecting extrasolar planets can regard the
results obtained in this paper as a reliable test for testing the invariance of
the velocity of light.Comment: 11 pages, 5 figure
Ferro-electric phase transition in a polar liquid and the nature of \lambda-transition in supercooled water
We develop a series of approximations to calculate free energy of a polar
liquid. We show that long range nature of dipole interactions between the
molecules leads to para-electric state instability at low temperatures and to a
second-order phase transition. We establish the transition temperature, T_{c},
both within mean field and ring diagrams approximation and show that the
ferro-electric transition may play an important role explaining a number of
peculiar properties of supercooled water, such as weak singularity of
dielectric constant as well as to a large extent anomalous density behavior.
Finally we discuss the role of fluctuations, shorter range forces and establish
connections with phenomenological models of polar liquids.Comment: 5 pages, 1 eps figure, density anomaly at T=4C analysis adde
Effect of transition layers on the electromagnetic properties of composites containing conducting fibres
The approach to calculating the effective dielectric and magnetic response in
bounded composite materials is developed. The method is essentially based on
the renormalisation of the dielectric matrix parameters to account for the
surface polarisation and the displacement currents at the interfaces. This
makes it possible the use of the effective medium theory developed for
unbounded materials, where the spatially-dependent local dielectric constant
and magnetic permeability are introduced. A detailed mathematical analysis is
given for a dielectric layer having conducting fibres with in-plane positions.
The surface effects are most essential at microwave frequencies in
correspondence to the resonance excitation of fibres. In thin layers (having a
thickness of the transition layer), the effective dielectric constant has a
dispersion region at much higher frequencies compared to those for unbounded
materials, exhibiting a strong dependence on the layer thickness. For the
geometry considered, the effective magnetic permeability differs slightly from
unity and corresponds to the renormalised matrix parameter. The magnetic effect
is due entirely to the existence of the surface displacement currents.Comment: PDF, 33 pages, 10 figure
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