8,979 research outputs found
On the Origin of Pluto's Small Satellites by Resonant Transport
The orbits of Pluto's four small satellites (Styx, Nix, Kerberos, and Hydra)
are nearly circular and coplanar with the orbit of the large satellite Charon,
with orbital periods nearly in the ratios 3:1, 4:1, 5:1, and 6:1 with Charon's
orbital period. These properties suggest that the small satellites were created
during the same impact event that placed Charon in orbit and had been pushed to
their current positions by being locked in mean-motion resonances with Charon
as Charon's orbit was expanded by tidal interactions with Pluto. Using the
Pluto-Charon tidal evolution models developed by Cheng et al. (2014), we show
that stable capture and transport of a test particle in multiple resonances at
the same mean-motion commensurability is possible at the 5:1, 6:1, and 7:1
commensurabilities, if Pluto's zonal harmonic . However, the test
particle has significant orbital eccentricity at the end of the tidal evolution
of Pluto-Charon in almost all cases, and there are no stable captures and
transports at the 3:1 and 4:1 commensurabilities. Furthermore, a non-zero
hydrostatic value of destroys the conditions necessary for multiple
resonance migration. Simulations with finite but minimal masses of Nix and
Hydra also fail to yield any survivors. We conclude that the placing of the
small satellites at their current orbital positions by resonant transport is
extremely unlikely.Comment: 22 pages, including 7 figures; accepted for publication in Icaru
Complete Tidal Evolution of Pluto-Charon
Both Pluto and its satellite Charon have rotation rates synchronous with
their orbital mean motion. This is the theoretical end point of tidal evolution
where transfer of angular momentum has ceased. Here we follow Pluto's tidal
evolution from an initial state having the current total angular momentum of
the system but with Charon in an eccentric orbit with semimajor axis (where is the radius of Pluto), consistent with its impact origin.
Two tidal models are used, where the tidal dissipation function
1/frequency and constant, where details of the evolution are strongly
model dependent. The inclusion of the gravitational harmonic coefficient
of both bodies in the analysis allows smooth, self consistent
evolution to the dual synchronous state, whereas its omission frustrates
successful evolution in some cases. The zonal harmonic can also be
included, but does not cause a significant effect on the overall evolution. The
ratio of dissipation in Charon to that in Pluto controls the behavior of the
orbital eccentricity, where a judicious choice leads to a nearly constant
eccentricity until the final approach to dual synchronous rotation. The tidal
models are complete in the sense that every nuance of tidal evolution is
realized while conserving total angular momentum - including temporary capture
into spin-orbit resonances as Charon's spin decreases and damped librations
about the same.Comment: 36 pages, including 18 figures; accepted for publication in Icaru
Thirty-fold: Extreme gravitational lensing of a quiescent galaxy at
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at
located behind the massive galaxy cluster eMACSJ1341.92442 (). The
system was identified as a gravitationally lensed triple image in Hubble Space
Telescope images obtained as part of a snapshot survey of the most X-ray
luminous galaxy clusters at and spectroscopically confirmed in
ground-based follow-up observations with the ESO/X-Shooter spectrograph. From
the constraints provided by the triple image, we derive a first, crude model of
the mass distribution of the cluster lens, which predicts a gravitational
amplification of a factor of 30 for the primary image and a factor of
6 for the remaining two images of the source, making eMACSJ1341-QG-1 by
far the most strongly amplified quiescent galaxy discovered to date. Our
discovery underlines the power of SNAPshot observations of massive, X-ray
selected galaxy clusters for lensing-assisted studies of faint background
populations
Spin-dependent Quantum Interference in Single-Wall Carbon Nanotubes with Ferromagnetic Contacts
We report the experimental observation of spin-induced magnetoresistance in
single-wall carbon nanotubes contacted with high-transparency ferromagnetic
electrodes. In the linear regime the spin-induced magnetoresistance oscillates
with gate voltage in quantitative agreement with calculations based on a
Landauer-Buttiker model for independent electrons. Consistent with this
interpretation, we find evidence for bias-induced oscillation in the
spin-induced magnetoresistance signal on the scale of the level spacing in the
nanotube. At higher bias, the spin-induced magnetoresistance disappears because
of a sharp decrease in the effective spin-polarization injected from the
ferromagnetic electrodes.Comment: Replaced with published versio
Coherent States Formulation of Polymer Field Theory
We introduce a stable and efficient complex Langevin (CL) scheme to enable
the first numerical simulations of the coherent-states (CS) formulation of
polymer field theory. In contrast with Edwards' well known auxiliary-field (AF)
framework, the CS formulation does not contain an embedded non-linear,
non-local functional of the auxiliary fields, and the action of the field
theory has a fully explicit, finite-order and semi-local polynomial character.
In the context of a polymer solution model, we demonstrate that the new CS-CL
dynamical scheme for sampling fluctuations in the space of coherent states
yields results in good agreement with now-standard AF simulations. The
formalism is potentially applicable to a broad range of polymer architectures
and may facilitate systematic generation of trial actions for use in
coarse-graining and numerical renormalization-group studies.Comment: 14pages 8 figure
Parametrical optimization of laser surface alloyed NiTi shape memory alloy with Co and Nb by the Taguchi method
Different high-purity metal powders were successfully alloyed on to a nickel titanium (NiTi) shape memory alloy (SMA) with a 3 kW carbon dioxide (CO2) laser system. In order to produce an alloyed layer with complete penetration and acceptable composition profile, the Taguchi approach was used as a statistical technique for optimizing selected laser processing parameters. A systematic study of laser power, scanning velocity, and pre-paste powder thickness was conducted. The signal-to-noise ratios (S/N) for each control factor were calculated in order to assess the deviation from the average response. Analysis of variance (ANOVA) was carried out to understand the significance of process variables affecting the process effects. The Taguchi method was able to determine the laser process parameters for the laser surface alloying technique with high statistical accuracy and yield a laser surface alloying technique capable of achieving a desirable dilution ratio. Energy dispersive spectrometry consistently showed that the per cent by weight of Ni was reduced by 45 per cent as compared with untreated NiTi SMA when the Taguchi-determined laser processing parameters were employed, thus verifying the laser's processing parameters as optimum
Inherent Mach-Zehnder interference with "which-way" detection for single particle scattering in one dimension
We study the coherent transport of single photon in a one-dimensional
coupled-resonator-array, "non-locally" coupled to a two-level system. Since its
inherent structure is a Mach-Zehnder interferometer, we explain the destructive
interference phenomenon of the transmission spectrums according to the effect
of which-way detection. The quantum realization of the present model is a
nano-electromechanical resonator arrays with two nearest resonators coupled to
a single spin via their attached magnetic tips. Its classical simulation is a
waveguide of coupled defected cavity array with double couplings to a side
defected cavity.Comment: 5 papges, 4 figure
High-Q nested resonator in an actively stabilized optomechanical cavity
Experiments involving micro- and nanomechanical resonators need to be
carefully designed to reduce mechanical environmental noise. A small scale
on-chip approach is to add an additional resonator to the system as a
mechanical low-pass filter. Unfortunately, the inherent low frequency of the
low-pass filter causes the system to be easily excited mechanically. Fixating
the additional resonator ensures that the resonator itself can not be excited
by the environment. This, however, negates the purpose of the low-pass filter.
We solve this apparent paradox by applying active feedback to the resonator,
thereby minimizing the motion with respect the front mirror of an
optomechanical cavity. Not only does this method actively stabilize the cavity
length, but it also retains the on-chip vibration isolation.Comment: Minor adjustments mad
LIGHT AND ELECTRON MICROSCOPIC RADIOAUTOGRAPHY OF HEPATIC CELL NUCLEOLI IN MICE TREATED WITH ACTINOMYCIN D
Nucleolar partition induced by actinomycin D was used to demonstrate some aspects of nucleolar RNA synthesis and release in mouse hepatic cells, with light and electron microscopic radioautography. The effect of the drug on RNA synthesis and nucleolar morphology was studied when actinomycin D treatment preceded labeling with tritiated orotic acid. Nucleolar partition, consisting of a segegration into granular and fibrillar parts was visible if a dosage of 25 µg of actinomycin D was used, but nucleolar RNA was still synthesized. After a dosage of 400 µg of actinomycin D, nucleolar RNA synthesis was completely stopped If labeling with tritiated orotic acid preceded treatment with 400 µg of actinomycin D, labeled nucleolar RNA was present 15 min after actinomycin D treatment while high resolution radioautography showed an association of silver grains with the granular component. At 30 min after actinomicyn D treatment all labeling was lost. Since labeling was associated with the granular component the progressive loss of label as a result of actinomycin D treatment indicated a release of nucleolar granules. The correlation between this release and the loss of 28S RNA from actinomycin D treated nucleoli as described in the literature is discussed
RNA SYNTHESIS IN RAT AND MOUSE HEPATIC CELLS AS STUDIED WITH LIGHT AND ELECTRON MICROSCOPE RADIOAUTOGRAPHY
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