185 research outputs found
HAGNN: Hybrid Aggregation for Heterogeneous Graph Neural Networks
Heterogeneous graph neural networks (GNNs) have been successful in handling
heterogeneous graphs. In existing heterogeneous GNNs, meta-path plays an
essential role. However, recent work pointed out that simple homogeneous graph
model without meta-path can also achieve comparable results, which calls into
question the necessity of meta-path. In this paper, we first present the
intrinsic difference about meta-path-based and meta-path-free models, i.e., how
to select neighbors for node aggregation. Then, we propose a novel framework to
utilize the rich type semantic information in heterogeneous graphs
comprehensively, namely HAGNN (Hybrid Aggregation for Heterogeneous GNNs). The
core of HAGNN is to leverage the meta-path neighbors and the directly connected
neighbors simultaneously for node aggregations. HAGNN divides the overall
aggregation process into two phases: meta-path-based intra-type aggregation and
meta-path-free inter-type aggregation. During the intra-type aggregation phase,
we propose a new data structure called fused meta-path graph and perform
structural semantic aware aggregation on it. Finally, we combine the embeddings
generated by each phase. Compared with existing heterogeneous GNN models, HAGNN
can take full advantage of the heterogeneity in heterogeneous graphs. Extensive
experimental results on node classification, node clustering, and link
prediction tasks show that HAGNN outperforms the existing modes, demonstrating
the effectiveness of HAGNN
Simple and Efficient Partial Graph Adversarial Attack: A New Perspective
As the study of graph neural networks becomes more intensive and
comprehensive, their robustness and security have received great research
interest. The existing global attack methods treat all nodes in the graph as
their attack targets. Although existing methods have achieved excellent
results, there is still considerable space for improvement. The key problem is
that the current approaches rigidly follow the definition of global attacks.
They ignore an important issue, i.e., different nodes have different robustness
and are not equally resilient to attacks. From a global attacker's view, we
should arrange the attack budget wisely, rather than wasting them on highly
robust nodes. To this end, we propose a totally new method named partial graph
attack (PGA), which selects the vulnerable nodes as attack targets. First, to
select the vulnerable items, we propose a hierarchical target selection policy,
which allows attackers to only focus on easy-to-attack nodes. Then, we propose
a cost-effective anchor-picking policy to pick the most promising anchors for
adding or removing edges, and a more aggressive iterative greedy-based attack
method to perform more efficient attacks. Extensive experimental results
demonstrate that PGA can achieve significant improvements in both attack effect
and attack efficiency compared to other existing graph global attack methods
DIFER: Differentiable Automated Feature Engineering
Feature engineering, a crucial step of machine learning, aims to extract
useful features from raw data to improve data quality. In recent years, great
efforts have been devoted to Automated Feature Engineering (AutoFE) to replace
expensive human labor. However, existing methods are computationally demanding
due to treating AutoFE as a coarse-grained black-box optimization problem over
a discrete space. In this work, we propose an efficient gradient-based method
called DIFER to perform differentiable automated feature engineering in a
continuous vector space. DIFER selects potential features based on evolutionary
algorithm and leverages an encoder-predictor-decoder controller to optimize
existing features. We map features into the continuous vector space via the
encoder, optimize the embedding along the gradient direction induced by the
predicted score, and recover better features from the optimized embedding by
the decoder. Extensive experiments on classification and regression datasets
demonstrate that DIFER can significantly improve the performance of various
machine learning algorithms and outperform current state-of-the-art AutoFE
methods in terms of both efficiency and performance.Comment: 8 pages, 5 figure
Zeolite-cage-lock strategy for in situ synthesis of highly nitrogen-doped porous carbon for selective separation of carbon dioxide gas
Porous carbon structures doped with 18.14% nitrogen and prepared by a carbonizing organic template in ZSM-39 zeolitic cages show high CO2 adsorption capacity.</p
Polar phase transitions in heteroepitaxial stabilized La0.5Y0.5AlO3 thin films
PAPER
Polar phase transitions in heteroepitaxial stabilized La0.5Y0.5AlO3 thin films
Shenghua Liu1, Chunfeng Zhang1, Mengya Zhu1, Qian He2, Jak Chakhalian3, Xiaoran Liu3,4, Albina Borisevich2, Xiaoyong Wang1 and Min Xiao1,4
Published 1 September 2017 • © 2017 IOP Publishing Ltd
Journal of Physics: Condensed Matter, Volume 29, Number 40
Article PDF
Figures
References
PDF
18 Total downloads
Turn on MathJax
Get permission to re-use this article
Share this article
Article information
Abstract
We report on the fabrication of epitaxial La0.5Y0.5AlO3 ultrathin films on (001) LaAlO3 substrates. Structural characterizations by scanning transmission electron microscopy and x-ray diffraction confirm the high quality of the film with a − b + c − AlO6 octahedral tilt pattern. Unlike either of the nonpolar parent compound, LaAlO3 and YAlO3, second harmonic generation measurements on the thin films suggest a nonpolar–polar phase transition at T c near 500 K, and a polar–polar phase transition at T a near 160 K. By fitting the angular dependence of the second harmonic intensities, we further propose that the two polar structures can be assigned to the Pmc2 1 and Pmn2 1 space group, while the high temperature nonpolar structure belongs to the Pbnm space group
Unique allosteric effect driven rapid adsorption of carbon dioxide on a new ionogel [P4444][2-Op]@MCM-41 with excellent cyclic stability and loading-dependent capacity
Allosteric effect-driven rapid stepwise CO2 adsorption of pyridine-containing anion functionalized ionic liquid [P4444][2-Op] confined into mesoporous silica MCM-41.</p
Efficient Thermal Conductance in Organometallic Perovskite CH3NH3PbI3 Films
Perovskite-based optoelectronic devices have shown great promise for solar
conversion and other optoelectronic applications, but their long-term
performance instability is regarded as a major obstacle to their widespread
deployment. Previous works have shown that the ultralow thermal conductivity
and inefficient heat spreading might put an intrinsic limit on the lifetime of
perovskite devices. Here, we report the observation of a remarkably efficient
thermal conductance, with conductivity of 11.2 +/- 0.8 W m^-1 K^-1 at room
temperature, in densely-packed perovskite CH3NH3PbI3 films, via noncontact
time-domain thermal reflectance measurements. The temperature-dependent
experiments suggest the important roles of organic cations and structural phase
transitions, which are further confirmed by temperature-dependent Raman
spectra. The thermal conductivity at room temperature observed here is over one
order of magnitude larger than that in the early report, suggesting that
perovskite device performance will not be limited by thermal stability
Laboratory Study on Properties of Diatomite and Basalt Fiber Compound Modified Asphalt Mastic
In order to improve the performance of asphalt mastic, some researchers have added diatomite or basalt fiber as a modifier to the asphalt mastic, and the results show that some properties of the asphalt mastic were improved. For the simultaneous addition of diatomite and basalt fiber, two kinds of modifier, compound modified asphalt mastic had not been reported; in this paper, thirteen groups of diatomite and basalt fiber (DBFCMAM) compound modified asphalt mastic with different content were prepared to study the performance. Softening point, cone penetration, viscosity, and DSR tests were conducted, for the high temperature performance evaluation of DBFCMAM, whereas force ductility and BBR tests were used in the low temperature performance study of the DBFCMAM. The results demonstrated that the high temperature performance of DBFCMAM was increased; moreover, the low temperature performance of DBFCMAM improved by diatomite and basalt fiber according to the results of the force ductility test; however, the conclusion of the BBR test data was inconsistent with the force ductility test. In summary, the high temperature and low temperature properties of DBFCMAM had been improved
- …