4,043 research outputs found
Strongly Regular Graphs as Laplacian Extremal Graphs
The Laplacian spread of a graph is the difference between the largest
eigenvalue and the second-smallest eigenvalue of the Laplacian matrix of the
graph. We find that the class of strongly regular graphs attains the maximum of
largest eigenvalues, the minimum of second-smallest eigenvalues of Laplacian
matrices and hence the maximum of Laplacian spreads among all simple connected
graphs of fixed order, minimum degree, maximum degree, minimum size of common
neighbors of two adjacent vertices and minimum size of common neighbors of two
nonadjacent vertices. Some other extremal graphs are also provided.Comment: 11 pages, 4 figures, 1 tabl
Wideband mmWave Massive MIMO Channel Estimation and Localization
Spatial wideband effects are known to affect channel estimation and
localization performance in millimeter wave (mmWave) massive multiple-input
multiple-output (MIMO) systems. Based on perturbation analysis, we show that
the spatial wideband effect is in fact more pronounced than previously thought
and significantly degrades performance, even at moderate bandwidths, if it is
not properly considered in the algorithm design. We propose a novel channel
estimation method based on multidimensional ESPRIT per subcarrier, combined
with unsupervised learning for pairing across subcarriers, which shows
significant performance gain over existing schemes under wideband conditions
Advancements in Point Cloud Data Augmentation for Deep Learning: A Survey
Point cloud has a wide range of applications in areas such as autonomous
driving, mapping, navigation, scene reconstruction, and medical imaging. Due to
its great potentials in these applications, point cloud processing has gained
great attention in the field of computer vision. Among various point cloud
processing techniques, deep learning (DL) has become one of the mainstream and
effective methods for tasks such as detection, segmentation and classification.
To reduce overfitting during training DL models and improve model performance
especially when the amount and/or diversity of training data are limited,
augmentation is often crucial. Although various point cloud data augmentation
methods have been widely used in different point cloud processing tasks, there
are currently no published systematic surveys or reviews of these methods.
Therefore, this article surveys and discusses these methods and categorizes
them into a taxonomy framework. Through the comprehensive evaluation and
comparison of the augmentation methods, this article identifies their
potentials and limitations and suggests possible future research directions.
This work helps researchers gain a holistic understanding of the current status
of point cloud data augmentation and promotes its wider application and
development
Why a local moment induces an antiferromagnetic ordering: An RVB picture
Based on a Gutzwiller projected BCS wavefunction, it is shown that a local
S=1/2 moment is present around a vacancy site (zinc impurity) in a form of
staggered magnetic moments, which is a direct consequence of the short-ranged
resonating-valence-bond (RVB) pairing in the spin background.Comment: 4 pages, 3 figure
Bis[(diaminomethylidene)azanium] 5-(1-oxido-1H-1,2,3,4-tetrazol-5-yl)-1H-1,2,3,4-tetrazol-1-olate
The anion of the title salt, 2[C(NH2)3]+·C2N8O2
2−, lies on a center of inversion and its two five-membered rings are coplanar. The guanidinium cation forms N—H⋯O and N—H⋯N hydrogen bonds to the anion, generating an eight-membered ring. Other hydrogen bonds lead to the formation of a three-dimensional network
Simultaneously improving the mechanical and electrical properties of poly(vinyl alcohol) composites by high-quality graphitic nanoribbons
Although carbon nanotubes (CNTs) have shown great potential for enhancing the performance of polymer matrices, their reinforcement role still needs to be further improved. Here we implement a structural modification of multi-walled CNTs (MWCNTs) to fully utilize their fascinating mechanical and electrical properties via longitudinal splitting of MWCNTs into graphitic nanoribbons (GNRs). This nanofiller design strategy is advantageous for surface functionalization, strong interface adhesion as well as boosting the interfacial contact area without losing the intrinsic graphitic structure. The obtained GNRs have planar geometry, quasi-1D structure and high-quality crystallinity, which outperforms their tubular counterparts, delivering a superior load-bearing efficiency and conductive network for realizing a synchronous improvement of the mechanical and electrical properties of a PVA-based composite. Compared to PVA/CNTs, the tensile strength, Young’s modulus and electrical conductivity of the PVA/GNR composite at a filling concentration of 3.6 vol.% approach 119.1 MPa, 5.3 GPa and 2.4 × 10−4 S m−1, with increases of 17%, 32.5% and 5.9 folds, respectively. The correlated mechanics is further rationalized by finite element analysis, the generalized shear-lag theory and the fracture mechanisms
- …