723 research outputs found
Electronic structure of the compound from ab initio local interactions
We used fully correlated ab initio calculations to determine the effective
parameters of Hubbard and t - J models for the thermoelectric misfit compound
. As for the family the Fermi level orbitals
are the orbitals of the cobalt atoms ; the being always lower
in energy by more than 240\,meV. The electron correlation is found very large
as well as the parameters fluctuations as a function of the
structural modulation. The main consequences are a partial electrons
localization and a fluctuation of the in-plane magnetic exchange from AFM to
FM. The behavior of the Seebeck coefficient as a function of temperature is
discussed in view of the ab initio results, as well as the 496\,K phase
transition
3D Pose Estimation and 3D Model Retrieval for Objects in the Wild
We propose a scalable, efficient and accurate approach to retrieve 3D models
for objects in the wild. Our contribution is twofold. We first present a 3D
pose estimation approach for object categories which significantly outperforms
the state-of-the-art on Pascal3D+. Second, we use the estimated pose as a prior
to retrieve 3D models which accurately represent the geometry of objects in RGB
images. For this purpose, we render depth images from 3D models under our
predicted pose and match learned image descriptors of RGB images against those
of rendered depth images using a CNN-based multi-view metric learning approach.
In this way, we are the first to report quantitative results for 3D model
retrieval on Pascal3D+, where our method chooses the same models as human
annotators for 50% of the validation images on average. In addition, we show
that our method, which was trained purely on Pascal3D+, retrieves rich and
accurate 3D models from ShapeNet given RGB images of objects in the wild.Comment: Accepted to Conference on Computer Vision and Pattern Recognition
(CVPR) 201
The crucial importance of the -- hybridization in transition metal oxides
We studied the influence of the trigonal distortion of the regular octahedron
along the (111) direction, found in the layers. Under such a
distortion the orbitals split into one and two degenerated
orbitals. We focused on the relative order of these orbitals.
Using quantum chemical calculations of embedded clusters at different levels of
theory, we analyzed the influence of the different effects not taken into
account in the crystalline field theory; that is metal-ligand hybridization,
long-range crystalline field, screening effects and orbital relaxation. We
found that none of them are responsible for the relative order of the
orbitals. In fact, the trigonal distortion allows a mixing of the and
orbitals of the metallic atom. This hybridization is at the origin of the
-- relative order and of the incorrect prediction of the
crystalline field theory
An ab initio study of magneto-electric coupling of
The present paper proposes the direct calculation of the microscopic
contributions to the magneto-electric coupling, using ab initio methods. The
electrostrictive and the Dzyaloshinskii-Moriya contributions were evaluated
individually. For this purpose a specific method was designed, combining DFT
calculations and embedded fragments, explicitely correlated, quantum chemical
calculations. This method allowed us to calculate the evolution of the magnetic
couplings as a function of an applied electric field. We found that in the Dzyaloshinskii-Moriya contribution to the magneto-electric effect
is three orders of magnitude weaker than the electrostrictive contribution.
Strictive effects are thus dominant in the magnetic exchange evolution under an
applied electric field, and by extension on the magneto-electric effect. These
effects remain however quite small and the modifications of the magnetic
excitations under an applied electric field will be difficult to observe
experimentally. Another important conclusion is that the amplitude of the
magneto-electric effect is very small. Indeed, it can be shown that the linear
magneto-electric tensor is null due to the inter-layer symmetry operations.Comment: J. Phys. Cond. Matter 201
: a complete model for the chain sub-system
A second neighbor model for the chain subsystem of the
has been extracted from ab-initio calculations. This
model does not use periodic approximation but describes the entire chain
through the use of the four-dimensional crystallographic description. Second
neighbors interactions are found to be of same order than the first neighbors
ones. The computed values of the second neighbors magnetic interaction are
coherent with experimental estimations of the intra-dimer magnetic
interactions, even if slightly smaller. The reasons of this underestimation are
detailed. The computed model allowed us to understand the origin of the chain
dimerisation and predicts correctly the relative occurrence of dimers and free
spins. The orbitals respectively supporting the magnetic electrons and the
holes have been found to be essentially supported by the copper 3d orbitals
(spins) and the surrounding oxygen orbitals (holes), thus giving a strong
footing to the existence of Zhang-Rice singlets
GP2C: Geometric Projection Parameter Consensus for Joint 3D Pose and Focal Length Estimation in the Wild
We present a joint 3D pose and focal length estimation approach for object
categories in the wild. In contrast to previous methods that predict 3D poses
independently of the focal length or assume a constant focal length, we
explicitly estimate and integrate the focal length into the 3D pose estimation.
For this purpose, we combine deep learning techniques and geometric algorithms
in a two-stage approach: First, we estimate an initial focal length and
establish 2D-3D correspondences from a single RGB image using a deep network.
Second, we recover 3D poses and refine the focal length by minimizing the
reprojection error of the predicted correspondences. In this way, we exploit
the geometric prior given by the focal length for 3D pose estimation. This
results in two advantages: First, we achieve significantly improved 3D
translation and 3D pose accuracy compared to existing methods. Second, our
approach finds a geometric consensus between the individual projection
parameters, which is required for precise 2D-3D alignment. We evaluate our
proposed approach on three challenging real-world datasets (Pix3D, Comp, and
Stanford) with different object categories and significantly outperform the
state-of-the-art by up to 20% absolute in multiple different metrics.Comment: Accepted to International Conference on Computer Vision (ICCV) 201
Location Field Descriptors: Single Image 3D Model Retrieval in the Wild
We present Location Field Descriptors, a novel approach for single image 3D
model retrieval in the wild. In contrast to previous methods that directly map
3D models and RGB images to an embedding space, we establish a common low-level
representation in the form of location fields from which we compute pose
invariant 3D shape descriptors. Location fields encode correspondences between
2D pixels and 3D surface coordinates and, thus, explicitly capture 3D shape and
3D pose information without appearance variations which are irrelevant for the
task. This early fusion of 3D models and RGB images results in three main
advantages: First, the bottleneck location field prediction acts as a
regularizer during training. Second, major parts of the system benefit from
training on a virtually infinite amount of synthetic data. Finally, the
predicted location fields are visually interpretable and unblackbox the system.
We evaluate our proposed approach on three challenging real-world datasets
(Pix3D, Comp, and Stanford) with different object categories and significantly
outperform the state-of-the-art by up to 20% absolute in multiple 3D retrieval
metrics.Comment: Accepted to International Conference on 3D Vision (3DV) 2019 (Oral
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