80 research outputs found
Fast Simulation of Vehicles with Non-deformable Tracks
This paper presents a novel technique that allows for both computationally
fast and sufficiently plausible simulation of vehicles with non-deformable
tracks. The method is based on an effect we have called Contact Surface Motion.
A comparison with several other methods for simulation of tracked vehicle
dynamics is presented with the aim to evaluate methods that are available
off-the-shelf or with minimum effort in general-purpose robotics simulators.
The proposed method is implemented as a plugin for the open-source
physics-based simulator Gazebo using the Open Dynamics Engine.Comment: Submitted to IROS 201
Evaluation of the importance of spin-orbit couplings in the nonadiabatic quantum dynamics with quantum fidelity and with its efficient "on-the-fly" ab initio semiclassical approximation
We propose to measure the importance of spin-orbit couplings (SOCs) in the
nonadiabatic molecular quantum dynamics rigorously with quantum fidelity. To
make the criterion practical, quantum fidelity is estimated efficiently with
the multiple-surface dephasing representation (MSDR). The MSDR is a
semiclassical method that includes nuclear quantum effects through interference
of mixed quantum-classical trajectories without the need for the Hessian of
potential energy surfaces. Two variants of the MSDR are studied, in which the
nuclei are propagated either with the fewest-switches surface hopping or with
the locally mean field dynamics. The fidelity criterion and MSDR are first
tested on one-dimensional model systems amenable to numerically exact quantum
dynamics. Then, the MSDR is combined with "on-the-fly" computed electronic
structure to measure the importance of SOCs and nonadiabatic couplings (NACs)
in the photoisomerization dynamics of CH2NH2+ considering 20 electronic states
and in the collision of F + H2 considering six electronic states.Comment: 9 pages, 3 figures, submitted to J. Chem. Phy
Three applications of path integrals: equilibrium and kinetic isotope effects, and the temperature dependence of the rate constant of the [1,5] sigmatropic hydrogen shift in (Z)-1,3-pentadiene
Recent experiments have confirmed the importance of nuclear quantum effects even in large biomolecules at physiological temperature. Here we describe how the path integral formalism can be used to describe rigorously the nuclear quantum effects on equilibrium and kinetic properties of molecules. Specifically, we explain how path integrals can be employed to evaluate the equilibrium (EIE) and kinetic (KIE) isotope effects, and the temperature dependence of the rate constant. The methodology is applied to the [1,5] sigmatropic hydrogen shift in pentadiene. Both the KIE and the temperature dependence of the rate constant confirm the importance of tunneling and other nuclear quantum effects as well as of the anharmonicity of the potential energy surface. Moreover, previous results on the KIE were improved by using a combination of a high level electronic structure calculation within the harmonic approximation with a path integral anharmonicity correction using a lower level metho
Self-Supervised Depth Correction of Lidar Measurements from Map Consistency Loss
Depth perception is considered an invaluable source of information in the
context of 3D mapping and various robotics applications. However, point cloud
maps acquired using consumer-level light detection and ranging sensors (lidars)
still suffer from bias related to local surface properties such as measuring
beam-to-surface incidence angle, distance, texture, reflectance, or
illumination conditions. This fact has recently motivated researchers to
exploit traditional filters, as well as the deep learning paradigm, in order to
suppress the aforementioned depth sensors error while preserving geometric and
map consistency details. Despite the effort, depth correction of lidar
measurements is still an open challenge mainly due to the lack of clean 3D data
that could be used as ground truth. In this paper, we introduce two novel point
cloud map consistency losses, which facilitate self-supervised learning on real
data of lidar depth correction models. Specifically, the models exploit
multiple point cloud measurements of the same scene from different view-points
in order to learn to reduce the bias based on the constructed map consistency
signal. Complementary to the removal of the bias from the measurements, we
demonstrate that the depth correction models help to reduce localization drift.
Additionally, we release a data set that contains point cloud data captured in
an indoor corridor environment with precise localization and ground truth
mapping information.Comment: Accepted to RA-L 2023: https://www.ieee-ras.org/publications/ra-
Data-driven Policy Transfer with Imprecise Perception Simulation
The paper presents a complete pipeline for learning continuous motion control
policies for a mobile robot when only a non-differentiable physics simulator of
robot-terrain interactions is available. The multi-modal state estimation of
the robot is also complex and difficult to simulate, so we simultaneously learn
a generative model which refines simulator outputs. We propose a coarse-to-fine
learning paradigm, where the coarse motion planning is alternated with
imitation learning and policy transfer to the real robot. The policy is jointly
optimized with the generative model. We evaluate the method on a real-world
platform in a batch of experiments.Comment: Submitted to IROS 2018 with RAL optio
MonoForce: Self-supervised learning of physics-aware grey-box model for predicting the robot-terrain interaction
We introduce an explainable, physics-aware, and end-to-end differentiable
model which predicts the outcome of robot-terrain interaction from camera
images. The proposed MonoForce model consists of a black-box module, which
predicts robot-terrain interaction forces from the onboard camera, followed by
a white-box module, which transforms these forces through the laws of classical
mechanics into the predicted trajectories. As the white-box model is
implemented as a differentiable ODE solver, it enables measuring the physical
consistency between predicted forces and ground-truth trajectories of the
robot. Consequently, it creates a self-supervised loss similar to MonoDepth. To
facilitate the reproducibility of the paper, we provide the source code. See
the project github for codes and supplementary materials such as videos and
data sequences
Measuring nonadiabaticity of molecular quantum dynamics with quantum fidelity and with its efficient semiclassical approximation
We propose to measure nonadiabaticity of molecular quantum dynamics
rigorously with the quantum fidelity between the Born-Oppenheimer and fully
nonadiabatic dynamics. It is shown that this measure of nonadiabaticity applies
in situations where other criteria, such as the energy gap criterion or the
extent of population transfer, fail. We further propose to estimate this
quantum fidelity efficiently with a generalization of the dephasing
representation to multiple surfaces. Two variants of the multiple-surface
dephasing representation (MSDR) are introduced, in which the nuclei are
propagated either with the fewest-switches surface hopping (FSSH) or with the
locally mean field dynamics (LMFD). The LMFD can be interpreted as the
Ehrenfest dynamics of an ensemble of nuclear trajectories, and has been used
previously in the nonadiabatic semiclassical initial value representation. In
addition to propagating an ensemble of classical trajectories, the MSDR
requires evaluating nonadiabatic couplings and solving the Schr\"{o}dinger (or
more generally, the quantum Liouville-von Neumann) equation for a single
discrete degree of freedom. The MSDR can be also used to measure the importance
of other terms present in the molecular Hamiltonian, such as diabatic
couplings, spin-orbit couplings, or couplings to external fields, and to
evaluate the accuracy of quantum dynamics with an approximate nonadiabatic
Hamiltonian. The method is tested on three model problems introduced by Tully,
on a two-surface model of dissociation of NaI, and a three-surface model
including spin-orbit interactions. An example is presented that demonstrates
the importance of often-neglected second-order nonadiabatic couplings.Comment: 14 pages, 4 figures, submitted to J. Chem. Phy
Path integral evaluation of equilibrium isotope effects
A general and rigorous methodology to compute the quantum equilibrium isotope
effect is described. Unlike standard approaches, ours does not assume
separability of rotational and vibrational motions and does not make the
harmonic approximation for vibrations or rigid rotor approximation for the
rotations. In particular, zero point energy and anharmonicity effects are
described correctly quantum mechanically. The approach is based on the
thermodynamic integration with respect to the mass of isotopes and on the
Feynman path integral representation of the partition function. An efficient
estimator for the derivative of free energy is used whose statistical error is
independent of the number of imaginary time slices in the path integral,
speeding up calculations by a factor of 60 at 500 K. We describe the
implementation of the methodology in the molecular dynamics package Amber 10.
The method is tested on three [1,5] sigmatropic hydrogen shift reactions.
Because of the computational expense, we use ab initio potentials to evaluate
the equilibrium isotope effects within the harmonic approximation, and then the
path integral method together with semiempirical potentials to evaluate the
anharmonicity corrections. Our calculations show that the anharmonicity effects
amount up to 30% of the symmetry reduced reaction free energy. The numerical
results are compared with recent experiments of Doering and coworkers,
confirming the accuracy of the most recent measurement on
2,4,6,7,9-pentamethyl-5-(5,5-H)methylene-11,11a-dihydro-12H-naphthacene
as well as concerns about compromised accuracy, due to side reactions, of
another measurement on
2-methyl-10-(10,10-H)methylenebicyclo[4.4.0]dec-1-ene.Comment: 14 pages, 8 figures, 6 table
Teachers in concordance for pseudo-labeling of 3D sequential data
Automatic pseudo-labeling is a powerful tool to tap into large amounts of
sequential unlabeled data. It is specially appealing in safety-critical
applications of autonomous driving, where performance requirements are extreme,
datasets are large, and manual labeling is very challenging. We propose to
leverage sequences of point clouds to boost the pseudolabeling technique in a
teacher-student setup via training multiple teachers, each with access to
different temporal information. This set of teachers, dubbed Concordance,
provides higher quality pseudo-labels for student training than standard
methods. The output of multiple teachers is combined via a novel pseudo label
confidence-guided criterion. Our experimental evaluation focuses on the 3D
point cloud domain and urban driving scenarios. We show the performance of our
method applied to 3D semantic segmentation and 3D object detection on three
benchmark datasets. Our approach, which uses only 20% manual labels,
outperforms some fully supervised methods. A notable performance boost is
achieved for classes rarely appearing in training data.Comment: This work has been submitted to the IEEE for publicatio
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