638 research outputs found
Learning to predict phases of manipulation tasks as hidden states
Phase transitions in manipulation tasks often occur
when contacts between objects are made or broken. A
switch of the phase can result in the robot’s actions suddenly
influencing different aspects of its environment. Therefore, the
boundaries between phases often correspond to constraints or
subgoals of the manipulation task.
In this paper, we investigate how the phases of manipulation
tasks can be learned from data. The task is modeled as an
autoregressive hidden Markov model, wherein the hidden phase
transitions depend on the observed states. The model is learned
from data using the expectation-maximization algorithm. We
demonstrate the proposed method on both a pushing task
and a pepper mill turning task. The proposed approach was
compared to a standard autoregressive hidden Markov model.
The experiments show that the learned models can accurately
predict the transitions in phases during the manipulation tasks
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
Policy search with high-dimensional context variables
Direct contextual policy search methods learn to improve policy
parameters and simultaneously generalize these parameters
to different context or task variables. However, learning
from high-dimensional context variables, such as camera images,
is still a prominent problem in many real-world tasks.
A naive application of unsupervised dimensionality reduction
methods to the context variables, such as principal component
analysis, is insufficient as task-relevant input may be ignored.
In this paper, we propose a contextual policy search method in
the model-based relative entropy stochastic search framework
with integrated dimensionality reduction. We learn a model of
the reward that is locally quadratic in both the policy parameters
and the context variables. Furthermore, we perform supervised
linear dimensionality reduction on the context variables
by nuclear norm regularization. The experimental results
show that the proposed method outperforms naive dimensionality
reduction via principal component analysis and
a state-of-the-art contextual policy search method
The Importance of Personal Possessions for the Development of a Sense of Home of Nursing Home Residents
Personal possessions of nursing home residents can contribute to their sense of home. This study investigated which of the personal belongings were considered most important, and if these items indeed contributed to a sense of home. A qualitative research was conducted with 27 nursing home residents. Photographs, paintings, and pieces of furniture are objects with sentimental value. The television set is valued for its practical function. Residents of larger rooms have more flexibility in bringing along personal items, including pieces of furniture. The results of this study can be used for the design of nursing homes or for making informed choices during the process of institutionalization
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&
Caregiver strain on informal caregivers when providing care for older patients undergoing major abdominal surgery:A longitudinal prospective cohort study
Background: Health-care systems nowadays rely on complementary patient care by informal caregivers. The need for, and burden on, informal caregivers will likely increase in the upcoming years. This study aimed to examine the burden on caregivers when providing care for elderly patients undergoing major abdominal surgery. Methods: A single-centre longitudinal cohort study was conducted between November 2015 and June 2018 in the Amphia hospital in Breda, the Netherlands. Patients aged 70+ undergoing elective surgery for colorectal carcinoma (CRC) or an abdominal aortic aneurysm (AAA) were included in this study. Informal caregiver burden was assessed and compared over time using the Caregiver Strain Index (CSI) at the outpatient clinic visit, at discharge, 2 weeks post-discharge and after 6 and 12 months. The effects of patient- and caregiver-related factors on the experienced caregiver strain were examined. Results: CSI scores of 248 caregivers were significantly increased at discharge (3.5 vs 2.6; p < 0.001) and 2 weeks post-discharge (3.3 vs 2.6; p < 0.001). After 12 months, scores dropped below baseline scores (1.8 vs 2.6; p = 0.012). The highest strain was observed 2 weeks post-discharge for AAA patients and at discharge for CRC patients. Older age, physical or cognitive impairment and burden of comorbidity were associated with an increased caregiver strain at baseline. Type of surgery was independently associated with the change in mean CSI scores over time; a bigger change in caregiver burden is observed after open surgery. Conclusion: In the early postoperative period, perceived caregiver strain was significantly increased. Psychological support for caregivers may be advisable, with timing of this support depending on diagnosis and patient-related factors. Trial registration: This manuscript was retrospectively registered on 05-04-2016 in the Netherlands Trial Register (NTR5932). http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=593
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
First-principles scattering matrices for spin-transport
Details are presented of an efficient formalism for calculating transmission
and reflection matrices from first principles in layered materials. Within the
framework of spin density functional theory and using tight-binding muffin-tin
orbitals, scattering matrices are determined by matching the wave-functions at
the boundaries between leads which support well-defined scattering states and
the scattering region. The calculation scales linearly with the number of
principal layers N in the scattering region and as the cube of the number of
atoms H in the lateral supercell. For metallic systems for which the required
Brillouin zone sampling decreases as H increases, the final scaling goes as
H^2*N. In practice, the efficient basis set allows scattering regions for which
H^{2}*N ~ 10^6 to be handled. The method is illustrated for Co/Cu multilayers
and single interfaces using large lateral supercells (up to 20x20) to model
interface disorder. Because the scattering states are explicitly found,
``channel decomposition'' of the interface scattering for clean and disordered
interfaces can be performed.Comment: 22 pages, 13 figure
Electrons in a ferromagnetic metal with a domain wall
We present theoretical description of conduction electrons interacting with a
domain wall in ferromagnetic metals. The description takes into account
interaction between electrons. Within the semiclassical approximation we
calculate the spin and charge distributions, particularly their modification by
the domain wall. In the same approximation we calculate local transport
characteristics, including relaxation times and charge and spin conductivities.
It is shown that these parameters are significantly modified near the wall and
this modification depends on electron-electron interaction.Comment: 10 pages with 4 figure
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