138 research outputs found
Verification and Synthesis of Robust Control Barrier Functions: Multilevel Polynomial Optimization and Semidefinite Relaxation
We study the problem of verification and synthesis of robust control barrier
functions (CBF) for control-affine polynomial systems with bounded additive
uncertainty and convex polynomial constraints on the control. We first
formulate robust CBF verification and synthesis as multilevel polynomial
optimization problems (POP), where verification optimizes -- in three levels --
the uncertainty, control, and state, while synthesis additionally optimizes the
parameter of a chosen parametric CBF candidate. We then show that, by invoking
the KKT conditions of the inner optimizations over uncertainty and control, the
verification problem can be simplified as a single-level POP and the synthesis
problem reduces to a min-max POP. This reduction leads to multilevel
semidefinite relaxations. For the verification problem, we apply Lasserre's
hierarchy of moment relaxations. For the synthesis problem, we draw connections
to existing relaxation techniques for robust min-max POP, which first use
sum-of-squares programming to find increasingly tight polynomial lower bounds
to the unknown value function of the verification POP, and then call Lasserre's
hierarchy again to maximize the lower bounds. Both semidefinite relaxations
guarantee asymptotic global convergence to optimality. We provide an in-depth
study of our framework on the controlled Van der Pol Oscillator, both with and
without additive uncertainty.Comment: Accepted to IEEE Conference on Decision and Control (CDC) 202
Graph Neural Networks for Natural Language Processing: A Survey
Deep learning has become the dominant approach in coping with various tasks
in Natural LanguageProcessing (NLP). Although text inputs are typically
represented as a sequence of tokens, there isa rich variety of NLP problems
that can be best expressed with a graph structure. As a result, thereis a surge
of interests in developing new deep learning techniques on graphs for a large
numberof NLP tasks. In this survey, we present a comprehensive overview onGraph
Neural Networks(GNNs) for Natural Language Processing. We propose a new
taxonomy of GNNs for NLP, whichsystematically organizes existing research of
GNNs for NLP along three axes: graph construction,graph representation
learning, and graph based encoder-decoder models. We further introducea large
number of NLP applications that are exploiting the power of GNNs and summarize
thecorresponding benchmark datasets, evaluation metrics, and open-source codes.
Finally, we discussvarious outstanding challenges for making the full use of
GNNs for NLP as well as future researchdirections. To the best of our
knowledge, this is the first comprehensive overview of Graph NeuralNetworks for
Natural Language Processing.Comment: 127 page
Thermal Hall effect in insulating quantum materials
The emerging ïŹeld of quantum materials involves an exciting new class of
materials in which charge, spin, orbital, and lattice degrees of freedom are inter-
twined, exhibiting a plethora of exotic physical properties. Quantum materials
include, but are not limited to, superconductors, topological quantum matter,
and systems with frustrated spins, which enable a wide range of potential
applications in biomedicine, energy transport and conversion, quantum sensing,
and quantum information processing.S.G. and X.C. acknowledge the support from National Science Foundation under grant No.
2144328.
J.Z. acknowledges the support from National Science Foundation through the Center
for Dynamics and Control of Materials: an NSF MRSEC unnder Cooperative Agreement
No. DMR-1720595.Center for Dynamics and Control of Material
Comment on âQuantitative biochronology of the PermianâTriassic boundary in South China based on conodont unitary associationsâ by Brosse et al. (2016)
Recently, Brosse et al. (2016) have proposed the use of conodont Unitary Associations Zones (UAZs) to substantially modify the biostratigraphy of the PermianâTriassic transition and to redefine the PermianâTriassic boundary (PTB). However, in our opinion, the UAZ analysis presented by Brosse et al. (2016) is based on unreliable taxonomic data sets with unjustified taxonomic re-assessments. No evidence shows that the UAZ approach improves the biozone biostratigraphy currently used to date the PTB
The involvement of the phenylpropanoid and jasmonate pathways in methyl jasmonate-induced soft rot resistance in kiwifruit (Actinidia chinensis)
Botryosphaeria dothidea is a major postharvest causal agent of soft rot in kiwifruit. Methyl jasmonate (MeJA) is an important plant hormone that participates as a plant defense against pathogens from a signal molecule. However, the impact and regulatory mechanism of MeJA on the attenuation of kiwifruit fungal decay remains unknown. This work investigated the effects of exogenous MeJA on the enzyme activity, metabolite content and gene expression of the phenylpropanoid and jasmonate pathways in kiwifruit. The results revealed that MeJA inhibited the expansion of B. dothidea lesion diameter in kiwifruit (Actinidia chinensis cv. âHongyangâ), enhanced the activity of enzymes (phenylalanine ammonia lyase, cinnamate 4-hydroxylase, 4-coumarate: coenzyme A ligase, cinnamyl alcohol dehydrogenase, peroxidase and polyphenol oxidase), and upregulated the expression of related genes (AcPAL, AcC4H, Ac4CL, and AcCAD). The accumulation of metabolites (total phenolics, flavonoids, chlorogenic acid, caffeic acid and lignin) with inhibitory effects on pathogens was promoted. Moreover, MeJA enhanced the expression of AcLOX, AcAOS, AcAOC, AcOPR3, AcJAR1, AcCOI1 and AcMYC2 and reduced the expression of AcJAZ. These results suggest that MeJA could display a better performance in enhancing the resistance of disease in kiwifruit by regulating the phenylpropanoid pathway and jasmonate pathway
Molecular and morphological evidence support a new species of Rosaceae Prunus subg. Cerasus from Wuyishan National Park, southeast China
Prunus tongmuensis, a new species of cherry blossom, is described and illustrated from Wuyishan National Park, southeast China. This species is characterized by its tubular to nearly bottle-shaped receptacles and dark purple drupes. It can be distinguished from other wild cherry trees by its flowers and leaves, reddish brown young leaves, presence of 1â2 glands at the base of leaves, petioles densely covered with yellowish brown villi, longer pedicels (0.6â2.5 cm), villous pistil, and dark purple drupes. In the present study, we conducted a comprehensive morphological study based on specimens of the new species and its morphologically close species, field observations, and examination of pollen morphology. In addition, our phylogenetic analysis based on the complete plastid genome sequences further confirms the status of the new species and indicates that it is closely related to Prunus clarofolia, however, it notably differs in leaf shape, size, petiole villus color, gland location, timing of flower and leaf openings, and reflexed or spread sepals, as well as drupe color
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Optimized degradation and inhibition of α-glucosidase activity by Gracilaria lemaneiformis polysaccharide and its production in vitro
Gracilaria lemaneiformis polysaccharide (GLP) exhibits good physiological activities, and it is more beneficial as it is degraded. After its degradation by hydrogen peroxide combined with vitamin C (H2O2-Vc) and optimized by BoxâBehnken Design (BBD), a new product of GLP-HV will be generated. While using GLP as control, two products of GLP-H (H2O2-treated) and GLP-V (Vc-treated) were also produced. These products chemical characteristics (total sugar content, molecular weight, monosaccharide composition, UV spectrum, morphological structure, and hypolipidemic activity in vitro) were assessed. The results showed that the optimal conditions for H2O2-Vc degradation were as follows: H2O2-Vc concentration was 18.7 mM, reaction time was 0.5 h, and reaction temperature was 56 °C. The total sugar content of GLP and its degradation products (GLP-HV, GLP-H and GLP-V) were more than 97%, and their monosaccharides are mainly glucose and galactose. The SEM analysis demonstrated that H2O2-Vc made the structure loose and broken. Moreover, GLP, GLP-HV, GLP-H, and GLP-V had significantly inhibition effect on α-glucosidase, and their IC50 value were 3.957, 0.265, 1.651, and 1.923 mg/mL, respectively. GLP-HV had the best inhibition effect on α-glucosidase in a dose-dependent manner, which was the mixed type of competitive and non-competitive. It had a certain quenching effect on fluorescence of α-glucosidase, which may be dynamic quenching
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