731 research outputs found
Learning robot in-hand manipulation with tactile features
Dexterous manipulation enables repositioning of
objects and tools within a robot’s hand. When applying dexterous
manipulation to unknown objects, exact object models
are not available. Instead of relying on models, compliance and
tactile feedback can be exploited to adapt to unknown objects.
However, compliant hands and tactile sensors add complexity
and are themselves difficult to model. Hence, we propose acquiring
in-hand manipulation skills through reinforcement learning,
which does not require analytic dynamics or kinematics models.
In this paper, we show that this approach successfully acquires
a tactile manipulation skill using a passively compliant hand.
Additionally, we show that the learned tactile skill generalizes
to novel objects
Sensitivity of PDR Calculations to Microphysical Details
Our understanding of physical processes in Photodissociation regions or
Photon Dominated Regions (PDRs) largely depends on the ability of spectral
synthesis codes to reproduce the observed infrared emission-line spectrum. In
this paper, we explore the sensitivity of a single PDR model to microphysical
details. Our calculations use the Cloudy spectral synthesis code, recently
modified to include a wealth of PDR physical processes. We show how the
chemical/thermal structure of a PDR, along with the calculated spectrum,
changes when the treatment of physical processes such as grain physics and
atomic/molecular rates are varied. We find a significant variation in the
intensities of PDR emission lines, depending on different treatments of the
grain physics. We also show how different combinations of the cosmic-ray
ionization rate, inclusion of grain-atom/ion charge transfer, and the grain
size distribution can lead to very similar results for the chemical structure.
Additionally, our results show the utility of Cloudy for the spectral modeling
of molecular environments.Comment: 36 pages, 17 figures, accepted for publication in Ap
An asteroseismic study of the Beta Cephei star Theta Ophiuchi: photometric results
We have carried out a three-site photometric campaign for the Beta Cephei
star Theta Ophiuchi from April to August 2003. 245 hours of differential
photoelectric uvy photometry were obtained during 77 clear nights. The
frequency analysis of our measurements resulted in the detection of seven
pulsation modes within a narrow frequency interval between 7.116 and 7.973 c/d.
No combination or harmonic frequencies were found. We performed a mode
identification of the individual pulsations from our colour photometry that
shows the presence of one radial mode, one rotationally split l=1 triplet and
possibly three components of a rotationally split l=2 quintuplet. We discuss
the implications of our findings and point out the similarity of the pulsation
spectrum of Theta Ophiuchi to that of another Beta Cephei star, V836 Cen.Comment: 8 pages, 6 figure
Herschel spectral-mapping of the Helix Nebula (NGC 7293): Extended CO photodissociation and OH+ emission
The Helix Nebula (NGC 7293) is the closest planetary nebulae. Therefore, it
is an ideal template for photochemical studies at small spatial scales in
planetary nebulae. We aim to study the spatial distribution of the atomic and
the molecular gas, and the structure of the photodissociation region along the
western rims of the Helix Nebula as seen in the submillimeter range with
Herschel. We use 5 SPIRE FTS pointing observations to make atomic and molecular
spectral maps. We analyze the molecular gas by modeling the CO rotational lines
using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model.
For the first time, we have detected extended OH+ emission in a planetary
nebula. The spectra towards the Helix Nebula also show CO emission lines (from
J= 4 to 8), [NII] at 1461 GHz from ionized gas, and [CI] (2-1), which together
with the OH+ lines, trace extended CO photodissociation regions along the rims.
The estimated OH+ column density is (1-10)x1e12 cm-2. The CH+ (1-0) line was
not detected at the sensitivity of our observations. Non-LTE models of the CO
excitation were used to constrain the average gas density (n(H2)=(1-5)x1e5
cm-3) and the gas temperature (Tk= 20-40 K). The SPIRE spectral-maps suggest
that CO arises from dense and shielded clumps in the western rims of the Helix
Nebula whereas OH+ and [CI] lines trace the diffuse gas and the UV and X-ray
illuminated clumps surface where molecules reform after CO photodissociation.
[NII] traces a more diffuse ionized gas component in the interclump medium.Comment: Accepted for publication in Astronomy and Astrophysic
E6,7,8 Magnetized Extra Dimensional Models
We study 10D super Yang-Mills theory with the gauge groups , and
. We consider the torus/orbifold compacfitication with magnetic fluxes and
Wilson lines. They lead to 4D interesting models with three families of quarks
and leptons, whose profiles in extra dimensions are quasi-localized because of
magnetic fluxes.Comment: 17 pages, 1 figur
Domain Wall Resistance based on Landauer's Formula
The scattering of the electron by a domain wall in a nano-wire is calculated
perturbatively to the lowest order. The resistance is calculated by use of
Landauer's formula. The result is shown to agree with the result of the linear
response theory if the equilibrium is assumed in the four-terminal case
Herschel imaging of the dust in the Helix Nebula (NGC 7293)
In our series of papers presenting the Herschel imaging of evolved planetary
nebulae, we present images of the dust distribution in the Helix nebula (NGC
7293). Images at 70, 160, 250, 350, and 500 micron were obtained with the PACS
and SPIRE instruments on board the Herschel satellite. The broadband maps show
the dust distribution over the main Helix nebula to be clumpy and predominantly
present in the barrel wall. We determined the spectral energy distribution of
the main nebula in a consistent way using Herschel, IRAS, and Planck flux
values. The emissivity index of 0.99 +/- 0.09, in combination with the carbon
rich molecular chemistry of the nebula, indicates that the dust consists mainly
of amorphous carbon. The dust excess emission from the central star disk is
detected at 70 micron and the flux measurement agree with previous measurement.
We present the temperature and dust column density maps. The total dust mass
across the Helix nebula (without its halo) is determined to be 0.0035 solar
mass at a distance of 216 pc. The temperature map shows dust temperatures
between 22 and 42 K, which is similar to the kinetic temperature of the
molecular gas, strengthening the fact that the dust and gas co-exist in high
density clumps. Archived images are used to compare the location of the dust
emission in the far infrared (Herschel) with the ionized (GALEX, Hbeta) and
molecular hydrogen component. The different emission components are consistent
with the Helix consisting of a thick walled barrel-like structure inclined to
the line of sight. The radiation field decreases rapidly through the barrel
wall.Comment: 8 pages, 9 figures, revised version A&A in pres
Herschel Planetary Nebula Survey (HerPlaNS) - First Detection of OH+ in Planetary Nebulae
We report the first detections of OH emission in planetary nebulae (PNe).
As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the
PACS and SPIRE instruments aboard the Herschel Space Observatory, we performed
a line survey in these PNe over the entire spectral range between 51 and
672m to look for new detections. OH rotational emission lines at
152.99, 290.20, 308.48, and 329.77m were detected in the spectra of three
planetary nebulae: NGC 6445, NGC 6720, and NGC 6781. Excitation temperatures
and column densities derived from these lines are in the range of 27 to 47 K
and 210 to 4 10 cm, respectively. In PNe,
the OH+ rotational line emission appears to be produced in the
photodissociation region (PDR) in these objects. The emission of OH+ is
observed only in PNe with hot central stars (T > 100000 K), suggesting
that high-energy photons may play a role in the OH+ formation and its line
excitation in these objects, as it seems to be the case for ultraluminous
galaxies.Comment: 9 pages, 7 figures; accepted for publication in A&
Herschel/PACS observations of the 69 band of crystalline olivine around evolved stars
We present 48 Herschel/PACS spectra of evolved stars in the wavelength range
of 67-72 m. This wavelength range covers the 69 m band of crystalline
olivine (). The width and
wavelength position of this band are sensitive to the temperature and
composition of the crystalline olivine. Our sample covers a wide range of
objects: from high mass-loss rate AGB stars (OH/IR stars,
M/yr), through post-AGB stars with and without circumbinary disks, to
planetary nebulae and even a few massive evolved stars. The goal of this study
is to exploit the spectral properties of the 69 m band to determine the
composition and temperature of the crystalline olivine. Since the objects cover
a range of evolutionary phases, we study the physical and chemical properties
in this range of physical environments. We fit the 69 m band and use its
width and position to probe the composition and temperature of the crystalline
olivine. For 27 sources in the sample, we detected the 69 m band of
crystalline olivine (). The
69 m band shows that all the sources produce pure forsterite grains
containing no iron in their lattice structure. The temperature of the
crystalline olivine as indicated by the 69 m band, shows that on average
the temperature of the crystalline olivine is highest in the group of OH/IR
stars and the post-AGB stars with confirmed Keplerian disks. The temperature is
lower for the other post-AGB stars and lowest for the planetary nebulae. A
couple of the detected 69 m bands are broader than those of pure
magnesium-rich crystalline olivine, which we show can be due to a temperature
gradient in the circumstellar environment of these stars. continued...Comment: Accepted for publication in A&
Effect of a Domain Wall on the Conductance Quantization in a Ferromagnetic Nanowire
The effect of the domain wall (DW) on the conductance in a ballistic
ferromagnetic nanowire (FMNW) is revisited by exploiting a specific
perturbation theory which is effective for a thin DW; the thinness is often the
case in currently interested conductance measurements on FMNWs. Including the
Hund coupling between carrier spins and local spins in a DW, the conductance of
a FMNW in the presence of a very thin DW is calculated within the
Landauer-B\"{u}ttiker formalism. It is revealed that the conductance plateaus
are modified significantly, and the switching of the quantization unit from
to ``about '' is produced in a FMNW by the introduction of a
thin DW. This accounts well for recent observations in a FMNW.Comment: 5 pages, 2 figures, Corrected typos and added reference
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