154 research outputs found
Blow-Up Phenomena for Porous Medium Equation with Nonlinear Flux on the Boundary
We investigate the blow-up phenomena for nonnegative solutions of porous medium equation with Neumann boundary conditions. We find that the absorption and the nonlinear flux on the boundary have some competitions in the blow-up phenomena
Global exponential convergence of delayed inertial Cohen–Grossberg neural networks
In this paper, the exponential convergence of delayed inertial Cohen–Grossberg neural networks (CGNNs) is studied. Two methods are adopted to discuss the inertial CGNNs, one is expressed as two first-order differential equations by selecting a variable substitution, and the other does not change the order of the system based on the nonreduced-order method. By establishing appropriate Lyapunov function and using inequality techniques, sufficient conditions are obtained to ensure that the discussed model converges exponentially to a ball with the prespecified convergence rate. Finally, two simulation examples are proposed to illustrate the validity of the theorem results
DGRec: Graph Neural Network for Recommendation with Diversified Embedding Generation
Graph Neural Network (GNN) based recommender systems have been attracting
more and more attention in recent years due to their excellent performance in
accuracy. Representing user-item interactions as a bipartite graph, a GNN model
generates user and item representations by aggregating embeddings of their
neighbors. However, such an aggregation procedure often accumulates information
purely based on the graph structure, overlooking the redundancy of the
aggregated neighbors and resulting in poor diversity of the recommended list.
In this paper, we propose diversifying GNN-based recommender systems by
directly improving the embedding generation procedure. Particularly, we utilize
the following three modules: submodular neighbor selection to find a subset of
diverse neighbors to aggregate for each GNN node, layer attention to assign
attention weights for each layer, and loss reweighting to focus on the learning
of items belonging to long-tail categories. Blending the three modules into
GNN, we present DGRec(Diversified GNN-based Recommender System) for diversified
recommendation. Experiments on real-world datasets demonstrate that the
proposed method can achieve the best diversity while keeping the accuracy
comparable to state-of-the-art GNN-based recommender systems.Comment: 9 pages, WSDM 202
Uncovering the role of superplasticizer in developing nano-engineered ultra-high-performance concrete
The effect of superplasticizer (SP) on the performance of ultra-high-performance concrete (UHPC) and ultra-high-performance fiber-reinforced concrete (UHPFRC) has been systematically investigated aiming to optimize the use of SP. The slump flow, and V-funnel time were employed to evaluate the impact of SP on the workability, while compressive strength had been used for mechanical property. Moreover, the packing density, as well as the water film thickness had been calculated to uncover the mechanism. The obtained results indicated that the addition of SP improved the workability of specimens with an ultimate-low water-to-binder (W/B) ratio, while it benefited the strength development of UHPC with a lower W/B ratio. This novel phenomenon (SP enhances the mechanical properties of UHPC) is due to the fact that SP reduced the water film thickness and enhanced the packing structure, therefore resulting in an increased compressive strength. For UHPFRC, similar trends can be witnessed regarding the flowability. However, the alternation of the fresh behavior of UHPFRC, attributed to the inclusion of SP, had an obvious impact on the fiber distribution, which altered the strength development of UHPFRC. This study revealed the significant effect of SP on the performance, especially on the strength development, of UHPC and UHPFRC
Atomic Bose-Einstein condensate in a twisted-bilayer optical lattice
Observation of strong correlations and superconductivity in
twisted-bilayer-graphene have stimulated tremendous interest in fundamental and
applied physics. In this system, the superposition of two twisted honeycomb
lattices, generating a Moir pattern, is the key to the
observed flat electronic bands, slow electron velocity and large density of
states. Despite these observations, a full understanding of the emerging
superconductivity from the coupled insulating layers and the appearance of a
small magic angle remain a hot topic of research. Here, we demonstrate a
quantum simulation platform to study superfluids in twisted bilayer lattices
based on Bose-Einstein condensates loaded into spin-dependent optical lattices.
The lattices are made of two sets of laser beams that independently address
atoms in different spin states, which form the synthetic dimension of the two
layers. The twisted angle of the two lattices is controlled by the relative
angle of the laser beams. We show that atoms in each spin state only feel one
set of the lattice and the interlayer coupling can be controlled by microwave
coupling between the spin states. Our system allows for flexible control of
both the inter- and intralayer couplings. Furthermore we directly observe the
spatial Moir pattern and the momentum diffraction, which
confirm the presence of atomic superfluid in the bilayer lattices. Our system
constitutes a powerful platform to investigate the physics underlying the
superconductivity in twisted-bilayer-graphene and to explore other novel
quantum phenomena difficult to realize in materials.Comment: 6 pages, 5 figure
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