1,232 research outputs found
Learning Manipulation under Physics Constraints with Visual Perception
Understanding physical phenomena is a key competence that enables humans and animals to act and interact under uncertain perception in previously unseen environments containing novel objects and their configurations. In this work, we consider the problem of autonomous block stacking and explore solutions to learning manipulation under physics constraints with visual perception inherent to the task. Inspired by the intuitive physics in humans, we first present an end-to-end learning-based approach to predict stability directly from appearance, contrasting a more traditional model-based approach with explicit 3D representations and physical simulation. We study the model's behavior together with an accompanied human subject test. It is then integrated into a real-world robotic system to guide the placement of a single wood block into the scene without collapsing existing tower structure. To further automate the process of consecutive blocks stacking, we present an alternative approach where the model learns the physics constraint through the interaction with the environment, bypassing the dedicated physics learning as in the former part of this work. In particular, we are interested in the type of tasks that require the agent to reach a given goal state that may be different for every new trial. Thereby we propose a deep reinforcement learning framework that learns policies for stacking tasks which are parametrized by a target structure
To Fall Or Not To Fall: {A} Visual Approach to Physical Stability Prediction
Understanding physical phenomena is a key competence that enables humans and animals to act and interact under uncertain perception in previously unseen environments containing novel object and their configurations. Developmental psychology has shown that such skills are acquired by infants from observations at a very early stage. In this paper, we contrast a more traditional approach of taking a model-based route with explicit 3D representations and physical simulation by an end-to-end approach that directly predicts stability and related quantities from appearance. We ask the question if and to what extent and quality such a skill can directly be acquired in a data-driven way bypassing the need for an explicit simulation. We present a learning-based approach based on simulated data that predicts stability of towers comprised of wooden blocks under different conditions and quantities related to the potential fall of the towers. The evaluation is carried out on synthetic data and compared to human judgments on the same stimuli
Derivative-Coupling Models and the Nuclear-Matter Equation of State
The equation of state of saturated nuclear matter is derived using two
different derivative-coupling Lagrangians. We show that both descriptions are
equivalent and can be obtained from the sigma-omega model through an
appropriate rescaling of the coupling constants. We introduce generalized forms
of this rescaling to study the correlations amongst observables in infinite
nuclear matter, in particular, the compressibility and the effective nucleon
mass.Comment: 16 pages, 6 figures, 36 kbytes. To appear in Zeit. f. Phys. A
(Hadrons and Nuclei
Self-Consistent Relativistic Calculation of Nucleon Mean Free Path
We present a fully self-consistent and relativistic calculation of the
nucleon mean free path in nuclear matter and finite nuclei. Starting from the
Bonn potential, the Dirac-Brueckner-Hartree-Fock results for nuclear matter are
parametrized in terms of an effective - Lagrangian suitable for
the relativistic density-dependent Hartree-Fock (RDHF) approximation. The
nucleon mean free path in nuclear matter is derived from this effective
Lagrangian taking diagrams up to fourth-order into account. For the nucleon
mean free path in finite nuclei, we make use of the density determined by the
RDHF calculation in the local density approximation. Our microscopic results
are in good agreement with the empirical data and predictions by Dirac
phenomenology.Comment: 16 pages RevTex and 6 figures (paper, available upon request from
[email protected]) UI-NTH-931
Underexpression of Deleted in liver cancer 2 (DLC2) is associated with overexpression of RhoA and poor prognosis in hepatocellular carcinoma
<p>Abstract</p> <p>Background</p> <p>DLC2, a unique RhoGAP, has been recently identified as a tumor suppressor gene in hepatocellular carcinoma (HCC). However, the expression of DLC2 protein, and its relationship with RhoA in clinical hepatocellular carcinoma have not been studied. The aim of this study was to investigate the DLC2 protein expression and its correlation with expression of RhoA, as well as to evaluate the prognostic value of DLC2 for HCC patients.</p> <p>Methods</p> <p>Western blot and immunohistochemical staining were employed to detect DLC2 protein expression in 128 HCC specimens. The correlation between DLC2 protein expression and clinicopathologic outcome, and prognostic value of DLC2 for HCC patients were analyzed.</p> <p>Results</p> <p>HCC tissues revealed significantly lower level of DLC2 protein than pericarcinomatous liver tissues (PCLT). There was significant correlation between underexpression of DLC2 protein and cell differentiation. Meanwhile, underexpression of DLC2 protein was correlated with overexression of RhoA. Furthermore, HCC Patients with DLC2-negative expression showed a significantly poorer prognosis than those with DLC2-positve expression.</p> <p>Conclusion</p> <p>Our data strongly suggested that decreased DLC2 expression in HCC correlates with cell differentiation of HCC and overexpression of RhoA, underexpression of DLC2 is associated with poor prognosis in HCC patients.</p
The Herschel Virgo cluster survey: V. Star-forming dwarf galaxies - dust in metal-poor environments
We present the dust properties of a small sample of Virgo cluster dwarf
galaxies drawn from the science demonstration phase data set of the Herschel
Virgo Cluster Survey. These galaxies have low metallicities (7.8 < 12 +
log(O/H) < 8.3) and star-formation rates < 10^{-1} M_{sun}/yr. We measure the
spectral energy distribution (SED) from 100 to 500 um and derive dust
temperatures and dust masses. The SEDs are fitted by a cool component of
temperature T < 20 K, implying dust masses around 10^{5} M_{sun} and
dust-to-gas ratios D within the range 10^{-3}-10^{-2}. The completion of the
full survey will yield a larger set of galaxies, which will provide more
stringent constraints on the dust content of star-forming dwarf galaxies.Comment: Letter accepted for publication in A&A (Herschel special issue
Infrared nanoscopy of Dirac plasmons at the graphene-SiO2 interface
We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac
fermions in graphene. This is achieved by confining mid-IR radiation at the
apex of a nanoscale tip: an approach yielding two orders of magnitude increase
in the value of in-plane component of incident wavevector q compared to free
space propagation. At these high wavevectors, the Dirac plasmon is found to
dramatically enhance the near-field interaction with mid-IR surface phonons of
SiO2 substrate. Our data augmented by detailed modeling establish graphene as a
new medium supporting plasmonic effects that can be controlled by gate voltage.Comment: 12 pages, 4 figure
The Herschel Reference Survey: Dust in Early-Type Galaxies and Across the Hubble Sequence
We present Herschel observations of 62 Early-Type Galaxies (ETGs), including
39 galaxies morphologically classified as S0+S0a and 23 galaxies classified as
ellipticals using SPIRE at 250, 350 and 500 microns (and PACS 100 and 160
microns for 19 sources) as part of the volume-limited Herschel Reference
Survey. We detect dust emission in 24% of the ellipticals and 62% of the S0s.
The mean temperature of the dust is 23.9+/-0.8 K, warmer than that found for
late-type galaxies in the Virgo Cluster. Including the non-detections, the mean
dust mass is log(Mdust) = 5.9+/-0.1 and 5.2+/-0.1 Msun for the S0s and
elliptical galaxies respectively. The mean dust-to-stellar mass is
log(Mdust/Mstar) = -4.4+/-0.1 (S0s) and -5.8+/-0.1 (ellipticals). Virtually all
the galaxies lie close to the red sequence yet the large number of detections
of cool dust, the gas-to-dust ratios and the ratios of far-infrared to radio
emission all suggest that many ETGs contain a cool interstellar medium similar
to that in late-type galaxies. The mean dust-to-stellar mass ratio for S0s is
approximatly a factor of ten less than for early-type spirals and the sizes of
the dust sources in the S0s are also much smaller. We show that the difference
cannot be explained by either the different bulge-to-disk ratios or
environmental effects such as ram-pressure stripping. The wide range in the
dust-to-stellar mass ratio for ETGs and the lack of a correlation between dust
mass and optical luminosity suggest that much of the dust in the ETGs detected
by Herschel has been acquired as the result of gravitational interactions;
these interactions are unlikely to have had a major effect on the stellar
masses of the ETGs. The Herschel observations tentatively suggest that in the
most massive ETGs, the mass of the interstellar medium is unconnected to the
evolution of the stellar populations.Comment: 28 Pages, 12 Figures. Submitted to ApJ December 2011; accepted
January 201
The Herschel Exploitation of Local Galaxy Andromeda (HELGA). I: Global far-infrared and sub-mm morphology
We have obtained Herschel images at five wavelengths from 100 to 500 micron
of a ~5.5x2.5 degree area centred on the local galaxy M31 (Andromeda), our
nearest neighbour spiral galaxy, as part of the Herschel guaranteed time
project "HELGA". The main goals of HELGA are to study the characteristics of
the extended dust emission, focusing on larger scales than studied in previous
observations of Andromeda at an increased spatial resolution, and the obscured
star formation. In this paper we present data reduction and Herschel maps, and
provide a description of the far-infrared morphology, comparing it with
features seen at other wavelengths. We use high--resolution maps of the atomic
hydrogen, fully covering our fields, to identify dust emission features that
can be associated to M31 with confidence, distinguishing them from emission
coming from the foreground Galactic cirrus. Thanks to the very large extension
of our maps we detect, for the first time at far-infrared wavelengths, three
arc-like structures extending out to ~21, ~26 and ~31 kpc respectively, in the
south-western part of M31. The presence of these features, hosting ~2.2e6 Msol
of dust, is safely confirmed by their detection in HI maps. Overall, we
estimate a total dust mass of ~5.8e7 Msol, about 78% of which is contained in
the two main ring-like structures at 10 and 15 kpc, at an average temperature
of 16.5 K. We find that the gas-to-dust ratio declines exponentially as a
function of the galacto-centric distance, in agreement with the known
metallicity gradient, with values ranging from 66 in the nucleus to ~275 in the
outermost region. [Abridged]Comment: 15 Pages, 9 Figures. Accepted for publication in Astronomy and
Astrophysics. A high resolution version of the paper can be found at
http://wazn.ugent.be/jfritz/HelgaI_final.pd
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