150 research outputs found
Model Predictive Control for Autonomous Driving Based on Time Scaled Collision Cone
In this paper, we present a Model Predictive Control (MPC) framework based on
path velocity decomposition paradigm for autonomous driving. The optimization
underlying the MPC has a two layer structure wherein first, an appropriate path
is computed for the vehicle followed by the computation of optimal forward
velocity along it. The very nature of the proposed path velocity decomposition
allows for seamless compatibility between the two layers of the optimization. A
key feature of the proposed work is that it offloads most of the responsibility
of collision avoidance to velocity optimization layer for which computationally
efficient formulations can be derived. In particular, we extend our previously
developed concept of time scaled collision cone (TSCC) constraints and
formulate the forward velocity optimization layer as a convex quadratic
programming problem. We perform validation on autonomous driving scenarios
wherein proposed MPC repeatedly solves both the optimization layers in receding
horizon manner to compute lane change, overtaking and merging maneuvers among
multiple dynamic obstacles.Comment: 6 page
Large Rashba splittings in bulk and monolayer of BiAs
Two-dimensional materials with Rashba split bands near the Fermi level are
key to developing upcoming next-generation spintronics. They enable generating,
detecting, and manipulating spin currents without an external magnetic field.
Here, we propose BiAs as a novel layered semiconductor with large Rashba
splitting in bulk and monolayer forms. Using first-principles calculations, we
determined the lowest energy structure of BiAs and its basic electronic
properties. Bulk BiAs has a layered crystal structure with two atoms in a
rhombohedral primitive cell, similar to the parent Bi and As elemental phases.
It is a semiconductor with a narrow and indirect band gap. The spin-orbit
coupling leads to Rashba-Dresselhaus spin splitting and characteristic spin
texture around the L-point in the Brillouin zone of the hexagonal conventional
unit cell, with Rashba energy and Rashba coupling constant for valence
(conduction) band of = 137 meV (93 meV) and = 6.05 eV\AA~(4.6
eV{\AA}). In monolayer form (i.e., composed of a BiAs bilayer), BiAs has a much
larger and direct band gap at , with a circular spin texture
characteristic of a pure Rashba effect. The Rashba energy = 18 meV and
Rashba coupling constant = 1.67 eV{\AA} of monolayer BiAs are quite
large compared to other known 2D materials, and these values are shown to
increase under tensile biaxial strain.Comment: 15pages,9figure
Blind image quality evaluation using perception based features
This paper proposes a novel no-reference Perception-based Image Quality Evaluator (PIQUE) for real-world imagery. A majority of the existing methods for blind image quality assessment rely on opinion-based supervised learning for quality score prediction. Unlike these methods, we propose an opinion unaware methodology that attempts to quantify distortion without the need for any training data. Our method relies on extracting local features for predicting quality. Additionally, to mimic human behavior, we estimate quality only from perceptually significant spatial regions. Further, the choice of our features enables us to generate a fine-grained block level distortion map. Our algorithm is competitive with the state-of-the-art based on evaluation over several popular datasets including LIVE IQA, TID & CSIQ. Finally, our algorithm has low computational complexity despite working at the block-level
Predicting band gaps and band-edge positions of oxide perovskites using DFT and machine learning
Density functional theory within the local or semilocal density
approximations (DFT-LDA/GGA) has become a workhorse in electronic structure
theory of solids, being extremely fast and reliable for energetics and
structural properties, yet remaining highly inaccurate for predicting band gaps
of semiconductors and insulators. Accurate prediction of band gaps using
firstprinciples methods is time consuming, requiring hybrid functionals,
quasi-particle GW, or quantum Monte Carlo methods. Efficiently correcting
DFT-LDA/GGA band gaps and unveiling the main chemical and structural factors
involved in this correction is desirable for discovering novel materials in
high-throughput calculations. In this direction, we use DFT and machine
learning techniques to correct band gaps and band-edge positions of a
representative subset of ABO3 perovskite oxides. Relying on results of HSE06
hybrid functional calculations as target values of band gaps, we find a
systematic band gap correction of ~1.5 eV for this class of materials, where ~1
eV comes from downward shifting the valence band and ~0.5 eV from uplifting the
conduction band. The main chemical and structural factors determining the band
gap correction are determined through a feature selection procedure
The deep-acceptor nature of the chalcogen vacancies in 2D transition-metal dichalcogenides
Chalcogen vacancies in the semiconducting monolayer transition-metal
dichalcogenides (TMDs) have frequently been invoked to explain a wide range of
phenomena, including both unintentional p-type and n-type conductivity, as well
as sub-band gap defect levels measured via tunneling or optical spectroscopy.
These conflicting interpretations of the deep versus shallow nature of the
chalcogen vacancies are due in part to shortcomings in prior first-principles
calculations of defects in the semiconducting two-dimensional (2D) TMDs that
have been used to explain experimental observations. Here we report results of
hybrid density functional calculations for the chalcogen vacancy in a series of
monolayer TMDs, correctly referencing the thermodynamic charge transition
levels to the fundamental band gap (as opposed to the optical band gap). We
find that the chalcogen vacancies are deep acceptors and cannot lead to n-type
or p-type conductivity. Both the (0/) and (1/2) transition levels
occur in the gap, leading to paramagnetic charge states S=1/2 and S=1,
respectively, in a collinear-spin representation. We discuss trends in terms of
the band alignments between the TMDs, which can serve as a guide to future
experimental studies of vacancy behavior
AUTOMATED SYSTEM AND METHOD OF RETAINING IMAGES BASED ON A USER'S FEEDBACK ON IMAGE QUALITY
An automated system and method for retaining images in a
smart phone are disclosed . The system may then determine
a no - reference quality score of the image using a PIQUE
module . The PIQUE module utilizes block level features of the image to determine the no - reference quality score . The system may present the image and the no - reference quality score to the user and accept a feedback towards quality of the image .The system may utilize a supervised learning model for continually learning a user ' s perception of quality of the image , the no -reference quality score determined by the PIQUE module , and the user feedback . Based on the learning , the supervised learning model may adapt the no - reference quality score and successively the image may either be retained or isolated for deletion , based on the
adapted quality score and a predefined threshold rang
Building an interpretable fuzzy rule base from data using Orthogonal Least Squares Application to a depollution problem
In many fields where human understanding plays a crucial role, such as
bioprocesses, the capacity of extracting knowledge from data is of critical
importance. Within this framework, fuzzy learning methods, if properly used,
can greatly help human experts. Amongst these methods, the aim of orthogonal
transformations, which have been proven to be mathematically robust, is to
build rules from a set of training data and to select the most important ones
by linear regression or rank revealing techniques. The OLS algorithm is a good
representative of those methods. However, it was originally designed so that it
only cared about numerical performance. Thus, we propose some modifications of
the original method to take interpretability into account. After recalling the
original algorithm, this paper presents the changes made to the original
method, then discusses some results obtained from benchmark problems. Finally,
the algorithm is applied to a real-world fault detection depollution problem.Comment: pre-print of final version published in Fuzzy Sets and System
A fuzzy feature fusion method for auto-segmentation of gliomas with multi-modality diffusion and perfusion magnetic resonance images in radiotherapy
The difusion and perfusion magnetic resonance (MR) images can provide functional information about
tumour and enable more sensitive detection of the tumour extent. We aimed to develop a fuzzy feature
fusion method for auto-segmentation of gliomas in radiotherapy planning using multi-parametric
functional MR images including apparent difusion coefcient (ADC), fractional anisotropy (FA) and
relative cerebral blood volume (rCBV). For each functional modality, one histogram-based fuzzy model
was created to transform image volume into a fuzzy feature space. Based on the fuzzy fusion result
of the three fuzzy feature spaces, regions with high possibility belonging to tumour were generated
automatically. The auto-segmentations of tumour in structural MR images were added in fnal autosegmented gross tumour volume (GTV). For evaluation, one radiation oncologist delineated GTVs for
nine patients with all modalities. Comparisons between manually delineated and auto-segmented GTVs
showed that, the mean volume diference was 8.69% (±5.62%); the mean Dice’s similarity coefcient
(DSC) was 0.88 (±0.02); the mean sensitivity and specifcity of auto-segmentation was 0.87 (±0.04)
and 0.98 (±0.01) respectively. High accuracy and efciency can be achieved with the new method,
which shows potential of utilizing functional multi-parametric MR images for target defnition in
precision radiation treatment planning for patients with gliomas
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