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Dielectrophoretic levitation of droplets and bubbles
Uncharged droplets and bubbles can be levitated dielectrophoretically in liquids using strong, nonuniform electric fields. The general equations of motion for a droplet or bubble in an axisymmetric, divergence-free electrostatic field allow determination of the conditions necessary and sufficient for stable levitation. The design of dielectrophoretic (DEP) levitation electrode structures is simplified by a Taylor-series expansion of cusped axisymmetric electrostatic fields. Extensive experimental measurements on bubbles in insulating liquids verify the simple dielectrophoretic model. Other have extended dielectrophoretic levitation to very small particles in aqueous media. Applications of DEP levitation to the study of gas bubbles, liquid droplets, and solid particles are discussed. Some of these applications are of special interest in the reduced gravitational field of a spacecraft
End-point of the rp process and periodic gravitational wave emission
The general end-point of the rp process in rapidly accreting neutron stars is
believed to be a surface distribution of matter whose nuclear composition may
depend on position. Its evolution during compression beyond the neutron-drip
threshold density is determined by the presence of nuclear formation enthalpy
minima at the proton closed shells. At threshold, a sequence of weak
interactions with capture or emission of neutron pairs rapidly transform nuclei
to the most accessible proton closed shell. Therefore, angular asymmetries in
nuclear composition present in accreted matter at neutron drip are preserved
during further compression to higher densities provided transition rates
between closed shells are negligible. Although it has been confirmed that this
condition is satisfied for predicted internal temperatures and for the
formation enthalpy distribution used in this work, it would not be so if the
true enthalpy differences between maxima and minima in the distribution were a
factor of two smaller. For this reason, it does not appear possible to assert
with any confidence that position-dependent surface composition can lead to
significant angle-dependence of the equation of state and to potentially
observable gravitational radiation. The effect of non-radial internal
temperature gradients on angle-dependency of the equation of state is also not
quantifiable.Comment: This version corrects a major error in estimating the effect of
composition asymmetry on the equation of state. Its conclusions are less
definite than those of the previous version. 9 pages RevTex; 1 figure. To be
published in Phys. Rev.
Pulsar emission: Langmuir modes in a relativistic multi-component plasma
Ions, protons and possibly a small flux of electrons and positrons are
accelerated outward from the polar cap of a normal or millisecond pulsar whose
rotational spin is antiparallel with its magnetic moment. The Langmuir modes of
this relativistic plasma have several properties of significance for the origin
of coherent radio emission. The characteristics of the mode are determined by
the sequence of singularities in the dielectric tensor at real angular
frequencies, which in turn is fixed by the electron-positron momentum
distribution. We find that under a certain condition on its momentum
distribution, an electron-positron flux two orders of magnitude smaller than
the Goldreich-Julian flux stabilizes the plasma and extinguishes the mode. But
more generally, both the growth rate and wavenumber of the multi-component
Langmuir mode can be as much as an order of magnitude larger than those of the
two-component ion-proton mode. It appears to be a further effective source for
the plasma turbulence whose decay is probably responsible for the observed
emission.Comment: 6 pages, 1 figur
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