256 research outputs found
Multimodal Hierarchical Dirichlet Process-based Active Perception
In this paper, we propose an active perception method for recognizing object
categories based on the multimodal hierarchical Dirichlet process (MHDP). The
MHDP enables a robot to form object categories using multimodal information,
e.g., visual, auditory, and haptic information, which can be observed by
performing actions on an object. However, performing many actions on a target
object requires a long time. In a real-time scenario, i.e., when the time is
limited, the robot has to determine the set of actions that is most effective
for recognizing a target object. We propose an MHDP-based active perception
method that uses the information gain (IG) maximization criterion and lazy
greedy algorithm. We show that the IG maximization criterion is optimal in the
sense that the criterion is equivalent to a minimization of the expected
Kullback--Leibler divergence between a final recognition state and the
recognition state after the next set of actions. However, a straightforward
calculation of IG is practically impossible. Therefore, we derive an efficient
Monte Carlo approximation method for IG by making use of a property of the
MHDP. We also show that the IG has submodular and non-decreasing properties as
a set function because of the structure of the graphical model of the MHDP.
Therefore, the IG maximization problem is reduced to a submodular maximization
problem. This means that greedy and lazy greedy algorithms are effective and
have a theoretical justification for their performance. We conducted an
experiment using an upper-torso humanoid robot and a second one using synthetic
data. The experimental results show that the method enables the robot to select
a set of actions that allow it to recognize target objects quickly and
accurately. The results support our theoretical outcomes.Comment: submitte
Crystal Growth of BiSrCaCuO Whiskers from Pulverized Amorphous Precursors
High-transition temperature superconducting whiskers of
BiSrCaCuO were successfully grown from
pulverized amorphous precursors. The obtained whiskers revealed a typical
composition and diffraction patterns of a superconducting Bi-2212 phase. The
whiskers from tiny precursors exhibit a spiral feature, suggesting a
contribution from the growth mechanism of both vapor-liquid-solid and
compressive stress models. The proposed method provides longer whiskers against
the growth period, compared with that from conventional root-growth method
Data-driven Exploration of New Pressure-induced Superconductivity in PbBiTe with Two Transition Temperatures
Candidates compounds for new thermoelectric and superconducting materials,
which have narrow band gap and flat bands near band edges, were exhaustively
searched by the high-throughput first-principles calculation from an inorganic
materials database named AtomWork. We focused on PbBiTe which has the
similar electronic band structure and the same crystal structure with those of
a pressure-induced superconductor SnBi2Se4 explored by the same data-driven
approach. The PbBiTe was successfully synthesized as single crystals
using a melt and slow cooling method. The core level X-ray photoelectron
spectroscopy analysis revealed Pb2+, Bi3+ and Te2- valence states in
PbBiTe. The thermoelectric properties of the PbBiTe sample were
measured at ambient pressure and the electrical resistivity was also evaluated
under high pressure using a diamond anvil cell with boron-doped diamond
electrodes. The resistivity decreased with increase of the pressure, and two
pressure-induced superconducting transitions were discovered at 3.4 K under
13.3 GPa and at 8.4 K under 21.7 GPa. The data-driven approach shows promising
power to accelerate the discovery of new thermoelectric and superconducting
materials
Effect of Dy substitution in the giant magnetocaloric properties of HoB
Recently, a massive magnetocaloric effect near the liquefaction temperature
of hydrogen has been reported in the ferromagnetic material HoB. Here we
investigate the effects of Dy substitution in the magnetocaloric properties of
HoDyB alloys ( = 0, 0.3, 0.5, 0.7, 1.0). We
find that the Curie temperature () gradually increases upon
Dy substitution, while the magnitude of the magnetic entropy change || at = decreases from 0.35 to 0.15
J cm K for a field change of 5 T. Due to the presence of two
magnetic transitions in these alloys, despite the change in the peak magnitude
of ||, the refrigerant capacity () and
refrigerant cooling power () remains almost constant in all
doping range, which as large as 5.5 J cm and 7.0 J cm for a field
change of 5 T. These results imply that this series of alloys could be an
exciting candidate for magnetic refrigeration in the temperature range between
10-50 K.Comment: 19 pages, 5 figures, 2 table
Manipulation of Non-classical Atomic Spin States
We report successful manipulation of non-classical atomic spin states. We
generate squeezed spin states by a spin quantum nondemolition measurement, and
apply an off-resonant circularly-polarized light pulse to the atoms. By
changing the pulse duration, we have clearly observed a rotation of anisotropic
quantum noise distribution in good contrast with the case of manipulation of a
coherent spin state where the quantum noise distribution is always isotropic.
This is an important step for quantum state tomography, quantum swapping, and
precision spectroscopic measurement
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