1,156 research outputs found
Efficient Trajectory Optimization for Robot Motion Planning
Motion planning for multi-jointed robots is challenging. Due to the inherent
complexity of the problem, most existing works decompose motion planning as
easier subproblems. However, because of the inconsistent performance metrics,
only sub-optimal solution can be found by decomposition based approaches. This
paper presents an optimal control based approach to address the path planning
and trajectory planning subproblems simultaneously. Unlike similar works which
either ignore robot dynamics or require long computation time, an efficient
numerical method for trajectory optimization is presented in this paper for
motion planning involving complicated robot dynamics. The efficiency and
effectiveness of the proposed approach is shown by numerical results.
Experimental results are used to show the feasibility of the presented planning
algorithm.Comment: submitted to ICARCV 2018. Video: https://youtu.be/EZmLXtO3C2
Quantum entanglement and entropy in particle creation
We investigate the basic theoretical issues in the quantum entanglement of
particle pairs created from the vacuum in a time-dependent background field or
spacetime. Similar to entropy generation from these processes which depends on
the choice of physical variables and how certain information is coarse-grained,
entanglement dynamics hinges on the choice of measurable quantities and how the
two parties are selected as well as the background dynamics of the field or
spacetime. We discuss the conditions of separability of quantum states in
particle creation processes and point out the differences in how the von
Neumann entropy is used as a measure of entropy generation versus for
entanglement dynamics. We show by an explicit construction that adoption of a
different set of physical variables yields a different entanglement entropy. As
an application of these theoretical considerations we show how the particle
number and the quantum phase enter the entanglement dynamics in cosmological
particle production.Comment: 14 pages, no figure; Typos corrected
A Learning Framework for Robust Bin Picking by Customized Grippers
Customized grippers have specifically designed fingers to increase the
contact area with the workpieces and improve the grasp robustness. However,
grasp planning for customized grippers is challenging due to the object
variations, surface contacts and structural constraints of the grippers. In
this paper, we propose a learning framework to plan robust grasps for
customized grippers in real-time. The learning framework contains a low-level
optimization-based planner to search for optimal grasps locally under object
shape variations, and a high-level learning-based explorer to learn the grasp
exploration based on previous grasp experience. The optimization-based planner
uses an iterative surface fitting (ISF) to simultaneously search for optimal
gripper transformation and finger displacement by minimizing the surface
fitting error. The high-level learning-based explorer trains a region-based
convolutional neural network (R-CNN) to propose good optimization regions,
which avoids ISF getting stuck in bad local optima and improves the collision
avoidance performance. The proposed learning framework with RCNN-ISF is able to
consider the structural constraints of the gripper, learn grasp exploration
strategy from previous experience, and plan optimal grasps in clutter
environment in real-time. The effectiveness of the algorithm is verified by
experiments.Comment: Submitted to 2019 IEEE/RSJ International Conference on Intelligent
Robots and Systems (IROS 2019). arXiv admin note: text overlap with
arXiv:1803.1129
CMB Constraints on the Holographic Dark Energy Model
We calculate the angular scale of the acoustic oscillation from the BOOMERANG
and WMAP data on the cosmic microwave background (CMB) to constrain the
holographic dark energy model recently proposed by Li. We find that only the
phantom-like holographic dark energy survives the cosmological tests. This is,
however, inconsistent with the positive energy condition implicitly assumed in
constructing Li's model. Therefore the model is marginally ruled out by the
present CMB data. As a supplementary check, we also calculate the suppression
of the matter density fluctuation due to the late time integrated Sach-Wolfe
effect by the holographic dark energy, the result is within the tolerance of
the cosmic variance. Some aspect about the saturation of the cosmic holographic
bound is also discussed.Comment: 13 pages, 4 figures;v2 point out the conflict between energy
condition and cmb constraint;v3 add references, redo ISW par
Refined Characterization of Lattice Chern Insulators by Bulk Entanglement Spectrum
We have studied extensively the band crossing patterns of the bulk
entanglement spectrum (BES) for various lattice Chern insulators. We find that
only partitions with dual symmetry can have either stable nodal-lines or
nodal-points in the BES when the system is in the topological phase of a
nonzero Chern number. By deforming the Hamiltonian to lift the accidental
symmetry, one can see that only nodal points are robust. They thus should bear
certain topological characteristics of the BES. By studying the band crossing
patterns in details we conclude that the topological characteristics of the BES
are inherited from the topological order of the underlying Chern insulators and
the former can have more refined topological structures. We then propose the
conjecture that the sum of the vorticities in the BES in a properly chosen
reduced Brillouin zone equals the Chern number of the underlying Chern
insulator. This relation is beyond the usual classification scheme of
topological insulators/superconductors.Comment: 19 pages, 32 figures; v3: revised with various improvements, version
to appear in PR
Entanglement Dynamics of Detectors in an Einstein Cylinder
We investigate how nontrivial topology affects the entanglement dynamics
between a detector and a quantum field and between two detectors mediated by a
quantum field. Nontrivial topology refers to both that of the base space and
that of the bundle. Using a derivative-coupling Unruh-DeWitt-like detector
model interacting with a quantum scalar field in an Einstein cylinder S1
(space) x R1 (time), we see the beating behaviors in the dynamics of the
detector-field entanglement and the detector-detector entanglement, which
distinguish from the results in the non-compact (1+1) dimensional Minkowski
space. The beat patterns of entanglement dynamics in a normal and a twisted
field with the same parameter values are different because of the difference in
the spectrum of the field modes. In terms of the kinetic momentum of the
detectors, we find that the contribution by the zero mode in a normal field to
entanglement dynamics has no qualitative difference from those by the nonzero
modes.Comment: 32 pages, 13 figures. Early-time analysis and comparison with
perturbative results added; Figs. 6-9, 11-12 update
Electronic and optical properties of graphene nanoribbons in external fields
A review work is done for electronic and optical properties of graphene
nanoribbons in magnetic, electric, composite, and modulated fields. Effects due
to the lateral confinement, curvature, stacking, non-uniform subsystems and
hybrid structures are taken into account. The special electronic properties,
induced by complex competitions between external fields and geometric
structures, include many one-dimensional parabolic subbands, standing waves,
peculiar edge-localized states, width- and field-dependent energy gaps,
magnetic-quantized quasi-Landau levels, curvature-induced oscillating Landau
subbands, crossings and anti-crossings of quasi-Landau levels, coexistence and
combination of energy spectra in layered structures, and various peak
structures in the density of states. There exist diverse absorption spectra and
different selection rules, covering edge-dependent selection rules,
magneto-optical selection rule, splitting of the Landau absorption peaks,
intragroup and intergroup Landau transitions, as well as coexistence of
monolayer-like and bilayer-like Landau absorption spectra. Detailed comparisons
are made between the theoretical calculations and experimental measurements.
The predicted results, the parabolic subbands, edge-localized states, gap
opening and modulation, and spatial distribution of Landau subbands, have been
verified by various experimental measurements
SERoCS: Safe and Efficient Robot Collaborative Systems for Next Generation Intelligent Industrial Co-Robots
Human-robot collaborations have been recognized as an essential component for
future factories. It remains challenging to properly design the behavior of
those co-robots. Those robots operate in dynamic uncertain environment with
limited computation capacity. The design objective is to maximize their task
efficiency while guaranteeing safety. This paper discusses a set of design
principles of a safe and efficient robot collaboration system (SERoCS) for the
next generation co-robots, which consists of robust cognition algorithms for
environment monitoring, efficient task planning algorithms for reference
generations, and safe motion planning and control algorithms for safe
human-robot interactions. The proposed SERoCS will address the design
challenges and significantly expand the skill sets of the co-robots to allow
them to work safely and efficiently with their human counterparts. The
development of SERoCS will create a significant advancement toward adoption of
co-robots in various industries. The experiments validate the effectiveness of
SERoCS.Comment: 19 page
Real-Time Robust Finger Gaits Planning under Object Shape and Dynamics Uncertainties
Dexterous manipulation has broad applications in assembly lines, warehouses
and agriculture. To perform large-scale manipulation tasks for various objects,
a multi-fingered robotic hand sometimes has to sequentially adjust its grasping
gestures, i.e. the finger gaits, to address the workspace limits and guarantee
the object stability. However, realizing finger gaits planning in dexterous
manipulation is challenging due to the complicated grasp quality metrics,
uncertainties on object shapes and dynamics (mass and moment of inertia), and
unexpected slippage under uncertain contact dynamics. In this paper, a
dual-stage optimization based planner is proposed to handle these challenges.
In the first stage, a velocity-level finger gaits planner is introduced by
combining object grasp quality with hand manipulability. The proposed finger
gaits planner is computationally efficient and realizes finger gaiting without
3D model of the object. In the second stage, a robust manipulation controller
using robust control and force optimization is proposed to address object
dynamics uncertainties and external disturbances. The dual-stage planner is
able to guarantee stability under unexpected slippage caused by uncertain
contact dynamics. Moreover, it does not require velocity measurement or
expensive 3D/6D tactile sensors. The proposed dual-stage optimization based
planner is verified by simulations on Mujoco.Comment: Accepted by IEEE/RSJ International Conference on Intelligent Robots
and Systems (IROS) 201
Landau quantization in buckled monolayer GaAs
Magneto-electronic properties of buckled monolayer GaAs is studied by the
developed generalized tight-binding model, considering the buckled structure,
multi-orbital chemical bondings, spin-orbit coupling, electric field, and
magnetic field simultaneously. Three group of spin-polarized Landau levels
(LLs) near the Fermi level are induced by the magnetic quantization, whose
initial energies, LL degeneracy, energy spacings, magnetic-field-dependence,
and spin polarization are investigated. The Landau state probabilities
describing the oscillation patterns, localization centers, and node
regularities of the dominated/minor orbitals are analyzed, and their
energy-dependent variations are discussed. The given density of states directly
reflects the main features of the LL energy spectra in the structure, height,
number, and frequency of the spin-polarized LL peaks. The electric field causes
the monotonous/nonmonotonous LL energy dispersions, LL crossing, gap
modulation, phase transition and spin splitting enhancement. The complex gap
modulations and phase transitions based on the competition between magnetic and
electric fields are explored in detail by the phase diagram. The
field-controlled gap modulations and phase transitions are helpful in designing
the top-gated and phase-change electronic devices. These predicted
magneto-electronic properties could be verified by scanning tunneling
spectroscopy measurements
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