381 research outputs found
Multicellular rosettes drive fluid-solid transition in epithelial tissues
Models for confluent biological tissues often describe the network formed by
cells as a triple-junction network, similar to foams. However, higher order
vertices or multicellular rosettes are prevalent in developmental and {\it in
vitro} processes and have been recognized as crucial in many important aspects
of morphogenesis, disease, and physiology. In this work, we study the influence
of rosettes on the mechanics of a confluent tissue. We find that the existence
of rosettes in a tissue can greatly influence its rigidity. Using a generalized
vertex model and effective medium theory we find a fluid-to-solid transition
driven by rosette density and intracellular tensions. This transition exhibits
several hallmarks of a second-order phase transition such as a growing
correlation length and a universal critical scaling in the vicinity a critical
point. Further, we elucidate the nature of rigidity transitions in dense
biological tissues and other cellular structures using a generalized Maxwell
constraint counting approach. This answers a long-standing puzzle of the origin
of solidity in these systems.Comment: 11 pages, 5 figures + 8 pages, 7 figures in Appendix. To be appear in
PR
Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions
Graphene-based vertical heterostructures, particularly stacks incorporated
with other layered materials, are promising for nanoelectronics. The stacking
of two model Dirac materials, graphene and topological insulator, can
considerably enlarge the family of van der Waals heterostructures. Despite well
understanding of the two individual materials, the electron transport
properties of a combined vertical heterojunction are still unknown. Here we
show the experimental realization of a vertical heterojunction between Bi2Se3
nanoplate and monolayer graphene. At low temperatures, the electron transport
through the vertical heterojunction is dominated by the tunneling process,
which can be effectively tuned by gate voltage to alter the density of states
near the Fermi surface. In the presence of a magnetic field, quantum
oscillations are observed due to the quantized Landau levels in both graphene
and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an
exotic gate-tunable tunneling resistance under high magnetic field, which
displays resistance maxima when the underlying graphene becomes a quantum Hall
insulator
Absence of a transport signature of spin-orbit coupling in graphene with indium adatoms
Enhancement of the spin-orbit coupling in graphene may lead to various
topological phenomena and also find applications in spintronics. Adatom
absorption has been proposed as an effective way to achieve the goal. In
particular, great hope has been held for indium in strengthening the spin-orbit
coupling and realizing the quantum spin Hall effect. To search for evidence of
the spin-orbit coupling in graphene absorbed with indium adatoms, we carry out
extensive transport measurements, i.e., weak localization magnetoresistance,
quantum Hall effect and non-local spin Hall effect. No signature of the
spin-orbit coupling is found. Possible explanations are discussed.Comment: 5 pages, 4 figures, with supplementary material
Approximate Accuracy Approaches to Attribute Reduction for Information Systems
The key problem for attribute reduction to information systems is how to evaluate the importance of an attribute. The algorithms are challenged by the variety of data forms in information system. Based on rough sets theory we present a new approach to attribute reduction for incomplete information systems and fuzzy valued information systems. In order to evaluate the importance of an attribute effectively, a novel algorithm with rigorous theorem is proposed. Experiments show the effect of proposed algorithm
Cluster Analysis Based on Bipartite Network
Clustering data has a wide range of applications and has attracted considerable attention in data mining and artificial intelligence. However it is difficult to find a set of clusters that best fits natural partitions without any class information. In this paper, a method for detecting the optimal cluster number is proposed. The optimal cluster number can be obtained by the proposal, while partitioning the data into clusters by FCM (Fuzzy c-means) algorithm. It overcomes the drawback of FCM algorithm which needs to define the cluster number c in advance. The method works by converting the fuzzy cluster result into a weighted bipartite network and then the optimal cluster number can be detected by the improved bipartite modularity. The experimental results on artificial and real data sets show the validity of the proposed method
Hydrogen assisted growth of high quality epitaxial graphene on the C-face of 4H-SiC
We demonstrate hydrogen assisted growth of high quality epitaxial graphene on
the C-face of 4H-SiC. Compared with the conventional thermal decomposition
technique, the size of the growth domain by this method is substantially
increased and the thickness variation is reduced. Based on the morphology of
epitaxial graphene, the role of hydrogen is revealed. It is found that hydrogen
acts as a carbon etchant. It suppresses the defect formation and nucleation of
graphene. It also improves the kinetics of carbon atoms via hydrocarbon
species. These effects lead to increase of the domain size and the structure
quality. The consequent capping effect results in smooth surface morphology and
suppression of multilayer growth. Our method provides a viable route to fine
tune the growth kinetics of epitaxial graphene on SiC.Comment: 9 pages, 4 figure
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