290 research outputs found
Layer Construction of Three-Dimensional Z2 Monopole Charge Nodal Line Semimetals and prediction of the abundant candidate materials
The interplay between symmetry and topology led to the concept of
symmetry-protected topological states, including all non-interacting and weakly
interacting topological quantum states. Among them, recently proposed nodal
line semimetal states with space-time inversion () symmetry which
are classified by the Stiefel-Whitney characteristic class associated with real
vector bundles and can carry a nontrivial monopole charge have
attracted widespread attention. However, we know less about such 3D
nodal line semimetals and do not know how to construct them. In
this work, we first extend the layer construction previously used to construct
topological insulating states to topological semimetallic systems. We construct
3D nodal line semimetals by stacking of 2D
-symmetric Dirac semimetals via nonsymmorphic symmetries. Based
on our construction scheme, effective model and combined with first-principles
calculations, we predict two types of candidate electronic materials for
nodal line semimetals, namely 14 Si and Ge structures and 108
transition metal dichalcogenides (=Cr, Mo, W, =S, Se, Te). Our
theoretical construction scheme can be directly applied to metamaterials and
circuit systems. Our work not only greatly enriches the candidate materials and
deepens the understanding of nodal line semimetal states but
also significantly extends the application scope of layer construction
Selective Refinement Network for High Performance Face Detection
High performance face detection remains a very challenging problem,
especially when there exists many tiny faces. This paper presents a novel
single-shot face detector, named Selective Refinement Network (SRN), which
introduces novel two-step classification and regression operations selectively
into an anchor-based face detector to reduce false positives and improve
location accuracy simultaneously. In particular, the SRN consists of two
modules: the Selective Two-step Classification (STC) module and the Selective
Two-step Regression (STR) module. The STC aims to filter out most simple
negative anchors from low level detection layers to reduce the search space for
the subsequent classifier, while the STR is designed to coarsely adjust the
locations and sizes of anchors from high level detection layers to provide
better initialization for the subsequent regressor. Moreover, we design a
Receptive Field Enhancement (RFE) block to provide more diverse receptive
field, which helps to better capture faces in some extreme poses. As a
consequence, the proposed SRN detector achieves state-of-the-art performance on
all the widely used face detection benchmarks, including AFW, PASCAL face,
FDDB, and WIDER FACE datasets. Codes will be released to facilitate further
studies on the face detection problem.Comment: The first two authors have equal contributions. Corresponding author:
Shifeng Zhang ([email protected]
Design, Fabrication, and Properties of 2-2 Connectivity Cement/Polymer based Piezoelectric Composites with Varied Piezoelectric Phase Distribution
The laminated 2-2 connectivity cement/polymer based piezoelectric composites with variedpiezoelectric phase distribution were fabricated by employing Lead Zirconium Titanate ceramicas active phase, and mixture of cement powder, epoxy resin, and hardener as matrix phase with a mass proportion of 4:4:1. The dielectric, piezoelectric, and electromechanical coupling properties of the composites were studied. The composites with large total volume fraction ofpiezoelectric phase have large piezoelectric strain constant and relative permittivity, and thepiezoelectric and dielectric properties of the composites are independent of the dimensional variations of the piezoelectric ceramic layer. The composites with small total volume fraction of piezoelectric phase have large piezoelectric voltage constant, but also large dielectric loss. The composite with gradually increased dimension of piezoelectric ceramic layer has the smallest dielectric loss, and that with the gradually increased dimension of matrix layer has the largest piezoelectric voltage constant. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with varied surface vibration amplitude of thetransducer
Research on Embedded Sensors for Concrete Health Monitoring Based on Ultrasonic Testing
In this article, embedded ultrasonic sensors were prepared using 1–3-type piezoelectric composite and piezoelectric ceramic as the piezoelectric elements, respectively. The frequency bandwidth of the novel embedded ultrasonic sensors was investigated. To obtain the relationship between the receiving ultrasonic velocity and compressive strength, as well as their response signals to crack damage, the sensors were fabricated and embedded into the cement mortar before testing. The results demonstrated that the piezoelectric composite sensor had wider frequency bandwidth than the piezoelectric ceramic sensor. The compressive strength and ultrasonic velocity had a positive linear relationship, with a correlation coefficient of 0.9216. The head wave amplitude of the receiving ultrasonic signal was sensitive to the changing crack damage and gradually decayed with the increasing degree of cement damage. Thus, the novel embedded ultrasonic sensors are suitable for concrete health monitoring via ultrasonic non-destructive testing
The Impact of Extended Heat Exposure on Rapid Sulphoaluminate Cement Concrete Up To 120°C
This study examined the stability of rapid sulphoaluminate cement concrete (R-SACC) when exposed to heat for extended periods of time. The physicochemical processes present in R-SACC as a function of temperature were determined through various tests. The general behavior of rapid sulphoaluminate cement (R-SAC) at a range of temperatures is summarized. The results show that observing color change could be a simple way to identify deterioration of R-SACC, along with the rebound hammer. The matrix formation of ettringite was broken and the mass of the hydrated product decreased with heat exposure; the major mineral composition of the paste consisted of CaSO4, CaCO3 and β-C2S; and the interface between aggregate and paste in the R-SACC become loosely structured with cracks. Between 50°C and 120°C, the rapid sulphoaluminate cement (R-SAC) paste first expanded and then shrank, and the shrinkage rate of R-SAC was much greater than that of R-SACC
Relational Learning for Joint Head and Human Detection
Head and human detection have been rapidly improved with the development of
deep convolutional neural networks. However, these two tasks are often studied
separately without considering their inherent correlation, leading to that 1)
head detection is often trapped in more false positives, and 2) the performance
of human detector frequently drops dramatically in crowd scenes. To handle
these two issues, we present a novel joint head and human detection network,
namely JointDet, which effectively detects head and human body simultaneously.
Moreover, we design a head-body relationship discriminating module to perform
relational learning between heads and human bodies, and leverage this learned
relationship to regain the suppressed human detections and reduce head false
positives. To verify the effectiveness of the proposed method, we annotate head
bounding boxes of the CityPersons and Caltech-USA datasets, and conduct
extensive experiments on the CrowdHuman, CityPersons and Caltech-USA datasets.
As a consequence, the proposed JointDet detector achieves state-of-the-art
performance on these three benchmarks. To facilitate further studies on the
head and human detection problem, all new annotations, source codes and trained
models will be public
3D carbon allotropes: Topological quantum materials with obstructed atomic insulating phases, multiple bulk-boundary correspondences, and real topology
The study of topological phases with unconventional bulk-boundary
correspondences and nontrivial real Chern number has garnered significant
attention in the topological states of matter. Using the first-principle
calculations and theoretical analysis, we perform a high-throughput material
screening of the 3D obstructed atomic insulators (OAIs) and 3D real Chern
insulators (RCIs) based on the Samara Carbon Allotrope Database (SACADA).
Results show that 422 out of 703 3D carbon allotropes are 3D OAIs with multiple
bulk-boundary correspondences, including 2D obstructed surface states (OSSs)
and 1D hinge states, which are in one dimension and two dimensions lower than
the 3D bulk, respectively. The 2D OSSs in these OAIs can be modified when
subjected to appropriate boundaries, which benefits the investigation of
surface engineering and the development of efficient topological catalysts.
These 422 OAIs, which have 2D and 1D boundary states, are excellent platforms
for multi-dimensional topological boundaries research. Remarkably, 138 of 422
OAIs are also 3D RCIs, which show a nontrivial real topology in the protection
of spacetime inversion symmetry. Our work not only provides a comprehensive
list of 3D carbon-based OAIs and RCIs, but also guides their application in
various aspects based on multiple bulk-boundary correspondences and real
topological phases
Dynamics of Associative Polymers with High Density of Reversible Bonds
We design and synthesize unentangled associative polymers carrying
unprecedented high fractions of stickers, up to eight per Kuhn segment, that
can form strong pairwise hydrogen bonding of without microphase
separation. The reversible bonds significantly slow down the polymer dynamics
but nearly do not change the shape of linear viscoelastic spectra. Moreover,
the structural relaxation time of associative polymers increases exponentially
with the fraction of stickers and exhibits a universal yet non-Arrhenius
dependence on the distance from polymer glass transition temperature. These
results cannot be understood within the framework of the classic sticky-Rouse
model but are rationalized by a renormalized Rouse model, which highlights an
unexpected influence of reversible bonds on the structural relaxation rather
than the shape of viscoelastic spectra for associative polymers with high
concentrations of stickers.Comment: 4 figure
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