67,871 research outputs found
Circularizing Planet Nine through dynamical friction with an extended, cold planetesimal belt
Unexpected clustering in the orbital elements of minor bodies beyond the
Kuiper belt has led to speculations that our solar system actually hosts nine
planets, the eight established plus a hypothetical "Planet Nine". Several
recent studies have shown that a planet with a mass of about 10 Earth masses on
a distant eccentric orbit with perihelion far beyond the Kuiper belt could
create and maintain this clustering. The evolutionary path resulting in an
orbit such as the one suggested for Planet Nine is nevertheless not easily
explained. Here we investigate whether a planet scattered away from the
giant-planet region could be lifted to an orbit similar to the one suggested
for Planet Nine through dynamical friction with a cold, distant planetesimal
belt. Recent simulations of planetesimal formation via the streaming
instability suggest that planetesimals can readily form beyond 100au. We
explore this circularisation by dynamical friction with a set of numerical
simulations. We find that a planet that is scattered from the region close to
Neptune onto an eccentric orbit has a 20-30% chance of obtaining an orbit
similar to that of Planet Nine after 4.6Gyr. Our simulations also result in
strong or partial clustering of the planetesimals; however, whether or not this
clustering is observable depends on the location of the inner edge of the
planetesimal belt. If the inner edge is located at 200au the degree of
clustering amongst observable objects is significant.Comment: Accepted to MNRA
Working with Nonassociative Geometry and Field Theory
We review aspects of our formalism for differential geometry on
noncommutative and nonassociative spaces which arise from cochain twist
deformation quantization of manifolds. We work in the simplest setting of
trivial vector bundles and flush out the details of our approach providing
explicit expressions for all bimodule operations, and for connections and
curvature. As applications, we describe the constructions of physically viable
action functionals for Yang-Mills theory and Einstein-Cartan gravity on
noncommutative and nonassociative spaces, as first steps towards more elaborate
models relevant to non-geometric flux deformations of geometry in closed string
theory.Comment: 20 pages; v2: Reference added; Contribution to the proceedings of the
Corfu Summer Institute on Elementary Particle Physics and Gravity, September
1-26, 2015, Corfu, Greece; Final version published in Proceedings of Scienc
Double (implicit and explicit) dependence of the electromagnetic field of an accelerated charge on time: Mathematical and physical analysis of the problem
We considered the electromagnetic field of a charge moving with a constant
acceleration along an axis. We found that this field obtained from the
Li\'enard-Wiechert potentials does not satisfy Maxwell equations if one
considers exclusively a retarded interaction (i.e. pure implicit dependence
this field on time). We show that if and only if one takes into account both
retarded interaction and direct interaction (so called "action-at-a-distance")
the field produced by an accelerated charge satisfies Maxwell equations.Comment: ReVTeX file, no figures, 12p
Monodromy in the CMB: Gravity Waves and String Inflation
We present a simple mechanism for obtaining large-field inflation, and hence
a gravitational wave signature, from string theory compactified on twisted
tori. For Nil manifolds, we obtain a leading inflationary potential
proportional to phi^(2/3) in terms of the canonically normalized field phi,
yielding predictions for the tilt of the power spectrum and the
tensor-to-scalar ratio, and with 60
e-foldings of inflation; we note also the possibility of a variant with a
candidate inflaton potential proportional to phi^(2/5). The basic mechanism
involved in extending the field range -- monodromy in D-branes as they move in
circles on the manifold -- arises in a more general class of compactifications,
though our methods for controlling the corrections to the slow-roll parameters
require additional symmetries.Comment: 43 pages, latex. 4 figure
The effects of forcing and dissipation on phase transitions in thin granular layers
Recent experimental and computational studies of vibrated thin layers of
identical spheres have shown transitions to ordered phases similar to those
seen in equilibrium systems. Motivated by these results, we carry out
simulations of hard inelastic spheres forced by homogenous white noise. We find
a transition to an ordered state of the same symmetry as that seen in the
experiments, but the clear phase separation observed in the vibrated system is
absent. Simulations of purely elastic spheres also show no evidence for phase
separation. We show that the energy injection in the vibrated system is
dramatically different in the different phases, and suggest that this creates
an effective surface tension not present in the equilibrium or randomly forced
systems. We do find, however, that inelasticity suppresses the onset of the
ordered phase with random forcing, as is observed in the vibrating system, and
that the amount of the suppression is proportional to the degree of
inelasticity. The suppression depends on the details of the energy injection
mechanism, but is completely eliminated when inelastic collisions are replaced
by uniform system-wide energy dissipation.Comment: 10 pages, 5 figure
CARETS: A prototype regional environmental information system. Volume 7: Land use information and air quality planning
The author has identified the following significant results. The pilot air quality system provided data for updating information on the sources of point and area emissions of SO2 and particulate matter affecting the Norfolk-Portsmouth area of Virginia for 1971-72 winter and the annual 1972 period. During the 1971-72 winter, estimated SO2 amounts over an area with a SW-NE axis in the central section of Norfolk exceeded both primary and secondary levels
Isolation, identification and continuous culture of coronary endothelial cells from guinea pig hearts
Optical response of high- cuprates: possible role of scattering rate saturation and in-plane anisotropy
We present a generalized Drude analysis of the in-plane optical conductivity
(,) in cuprates taking into account the effects of
in-plane anisotropy. A simple ansatz for the scattering rate
(,), that includes anisotropy, a quadratic frequency
dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce
recent normal state data on an optimally doped cuprate over a wide frequency
range. We highlight the potential importance of including anisotropy in the
full expression for (,) and challenge previous
determinations of () in which anisotropy was neglected and
() was indicated to be strictly linear in frequency over a wide
frequency range. Possible implications of our findings for understanding
thermodynamic properties and self-energy effects in high- cuprates will
also be discussed.Comment: 8 pages, 7 figures. To be published in Physical Review
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