396 research outputs found
The Impossibility of Approximate Agreement on a Larger Class of Graphs
Approximate agreement is a variant of consensus in which processes receive input values from a domain and must output values in that domain that are sufficiently close to one another. We study the problem when the input domain is the vertex set of a connected graph. In asynchronous systems where processes communicate using shared registers, there are wait-free approximate agreement algorithms when the graph is a path or a tree, but not when the graph is a cycle of length at least 4. For many graphs, it is unknown whether a wait-free solution for approximate agreement exists.
We introduce a set of impossibility conditions and prove that approximate agreement on graphs satisfying these conditions cannot be solved in a wait-free manner. In particular, the graphs of all triangulated d-dimensional spheres that are not cliques, satisfy these conditions. The vertices and edges of an octahedron is an example of such a graph. We also present a family of reductions from approximate agreement on one graph to another graph. This allows us to extend known impossibility results to even more graphs
Spin polarized nematic order, quantum valley Hall states, and field tunable topological transitions in twisted multilayer graphene systems
We theoretically study the correlated insulator states, quantum anomalous
Hall (QAH) states, and field-induced topological transitions between different
correlated states in twisted multilayer graphene systems. Taking twisted
bilayer-monolayer graphene and twisted double-bilayer graphene as examples, we
show that both systems stay in spin polarized, -broken insulator states
with zero Chern number at 1/2 filling of the flat bands under finite
displacement fields. In some cases these spin polarized, nematic insulator
states are in the quantum valley Hall phase by virtue of the nontrivial band
topology of the systems. The spin polarized insulator state is quasi-degenerate
with the valley polarized state when only the dominant intra-valley Coulomb
interactions are included. Such quasi-degeneracy can be split by atomic on-site
interactions such that the spin polarized, nematic state become the unique
ground state. Such a scenario applies to various twisted multilayer graphene
systems at 1/2 filling, thus can be considered as a universal mechanism.
Moreover, under vertical magnetic fields, the giant orbital Zeeman splittings
in twisited multilayer graphene systems compete with the atomic Hubbard
interactions, which can drive transitions from spin polarized zero-Chern-number
states to valley-polarized QAH states with small onset magnetic fields.Comment: 5+17 page
Ultra-wideband THz/IR Metamaterial Absorber based on Doped Silicon
Metamaterial-based absorbers have been extensively investigated in the
terahertz (THz) range with ever increasing performances. In this paper, we
propose an all-dielectric THz absorber based on doped silicon. The unit cell
consists of a silicon cross resonator with an internal cross-shaped air cavity.
Numerical results suggest that the proposed absorber can operate from THz to
mid-infrared, having an average power absorption of >95% between 0.6 and 10
THz. Experimental results using THz time-domain spectroscopy show a good
agreement with simulations. The underlying mechanisms for broadband absorptions
are attributed to the combined effects of multiple cavities modes formed by
silicon resonators and bulk absorption in the substrate, as confirmed by
simulated field patterns. This ultra-wideband absorption is polarization
insensitive and can operate across a wide range of the incident angle. The
proposed absorber can be readily integrated into silicon-based platforms and is
expected to be used in sensing, imaging, energy harvesting and wireless
communications systems.Comment: 6 pages, 5 figure
Open Knowledge Base Canonicalization with Multi-task Unlearning
The construction of large open knowledge bases (OKBs) is integral to many
applications in the field of mobile computing. Noun phrases and relational
phrases in OKBs often suffer from redundancy and ambiguity, which calls for the
investigation on OKB canonicalization. However, in order to meet the
requirements of some privacy protection regulations and to ensure the
timeliness of the data, the canonicalized OKB often needs to remove some
sensitive information or outdated data. The machine unlearning in OKB
canonicalization is an excellent solution to the above problem. Current
solutions address OKB canonicalization by devising advanced clustering
algorithms and using knowledge graph embedding (KGE) to further facilitate the
canonicalization process. Effective schemes are urgently needed to fully
synergise machine unlearning with clustering and KGE learning. To this end, we
put forward a multi-task unlearning framework, namely MulCanon, to tackle
machine unlearning problem in OKB canonicalization. Specifically, the noise
characteristics in the diffusion model are utilized to achieve the effect of
machine unlearning for data in OKB. MulCanon unifies the learning objectives of
diffusion model, KGE and clustering algorithms, and adopts a two-step
multi-task learning paradigm for training. A thorough experimental study on
popular OKB canonicalization datasets validates that MulCanon achieves advanced
machine unlearning effects
Tracing the Pace of COVID-19 research : topic modeling and evolution
COVID-19 has been spreading rapidly around the world. With the growing attention on the deadly pandemic, discussions and research on COVID-19 are rapidly increasing to exchange latest findings with the hope to accelerate the pace of finding a cure. As a branch of information technology, artificial intelligence (AI) has greatly expedited the development of human society. In this paper, we investigate and visualize the on-going advancements of early scientific research on COVID-19 from the perspective of AI. By adopting the Latent Dirichlet Allocation (LDA) model, this paper allocates the research articles into 50 key research topics pertinent to COVID-19 according to their abstracts. We present an overview of early studies of the COVID-19 crisis at different scales including referencing/citation behavior, topic variation and their inner interactions. We also identify innovative papers that are regarded as the cornerstones in the development of COVID-19 research. The results unveil the focus of scientific research, thereby giving deep insights into how the academic society contributes to combating the COVID-19 pandemic. © 2021 Elsevier Inc. **Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Jing Ren and Feng Xia" is provided in this record*
Stratified Rule-Aware Network for Abstract Visual Reasoning
Abstract reasoning refers to the ability to analyze information, discover
rules at an intangible level, and solve problems in innovative ways. Raven's
Progressive Matrices (RPM) test is typically used to examine the capability of
abstract reasoning. The subject is asked to identify the correct choice from
the answer set to fill the missing panel at the bottom right of RPM (e.g., a
33 matrix), following the underlying rules inside the matrix. Recent
studies, taking advantage of Convolutional Neural Networks (CNNs), have
achieved encouraging progress to accomplish the RPM test. However, they partly
ignore necessary inductive biases of RPM solver, such as order sensitivity
within each row/column and incremental rule induction. To address this problem,
in this paper we propose a Stratified Rule-Aware Network (SRAN) to generate the
rule embeddings for two input sequences. Our SRAN learns multiple granularity
rule embeddings at different levels, and incrementally integrates the
stratified embedding flows through a gated fusion module. With the help of
embeddings, a rule similarity metric is applied to guarantee that SRAN can not
only be trained using a tuplet loss but also infer the best answer efficiently.
We further point out the severe defects existing in the popular RAVEN dataset
for RPM test, which prevent from the fair evaluation of the abstract reasoning
ability. To fix the defects, we propose an answer set generation algorithm
called Attribute Bisection Tree (ABT), forming an improved dataset named
Impartial-RAVEN (I-RAVEN for short). Extensive experiments are conducted on
both PGM and I-RAVEN datasets, showing that our SRAN outperforms the
state-of-the-art models by a considerable margin.Comment: AAAI 2021 paper. Code: https://github.com/husheng12345/SRA
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