745 research outputs found
Decomposed Mutual Information Optimization for Generalized Context in Meta-Reinforcement Learning
Adapting to the changes in transition dynamics is essential in robotic
applications. By learning a conditional policy with a compact context,
context-aware meta-reinforcement learning provides a flexible way to adjust
behavior according to dynamics changes. However, in real-world applications,
the agent may encounter complex dynamics changes. Multiple confounders can
influence the transition dynamics, making it challenging to infer accurate
context for decision-making. This paper addresses such a challenge by
Decomposed Mutual INformation Optimization (DOMINO) for context learning, which
explicitly learns a disentangled context to maximize the mutual information
between the context and historical trajectories, while minimizing the state
transition prediction error. Our theoretical analysis shows that DOMINO can
overcome the underestimation of the mutual information caused by
multi-confounded challenges via learning disentangled context and reduce the
demand for the number of samples collected in various environments. Extensive
experiments show that the context learned by DOMINO benefits both model-based
and model-free reinforcement learning algorithms for dynamics generalization in
terms of sample efficiency and performance in unseen environments.Comment: NeurIPS 202
MUBen: Benchmarking the Uncertainty of Pre-Trained Models for Molecular Property Prediction
Large Transformer models pre-trained on massive unlabeled molecular data have
shown great success in predicting molecular properties. However, these models
can be prone to overfitting during fine-tuning, resulting in over-confident
predictions on test data that fall outside of the training distribution. To
address this issue, uncertainty quantification (UQ) methods can be used to
improve the models' calibration of predictions. Although many UQ approaches
exist, not all of them lead to improved performance. While some studies have
used UQ to improve molecular pre-trained models, the process of selecting
suitable backbone and UQ methods for reliable molecular uncertainty estimation
remains underexplored. To address this gap, we present MUBen, which evaluates
different combinations of backbone and UQ models to quantify their performance
for both property prediction and uncertainty estimation. By fine-tuning various
backbone molecular representation models using different molecular descriptors
as inputs with UQ methods from different categories, we critically assess the
influence of architectural decisions and training strategies. Our study offers
insights for selecting UQ and backbone models, which can facilitate research on
uncertainty-critical applications in fields such as materials science and drug
discovery
Meson Screening Mass in a Strongly Coupled Pion Superfluid
We calculate the meson screening mass in a pion superfluid in the framework
of Nambu--Jona-Lasinio model. The minimum of the attractive quark potential is
always located at the phase boundary of pion superfluid. Different from the
temperature and baryon density effect, the potential at finite isospin density
can not be efficiently suppressed and the matter is always in a strongly
coupled phase due to the Goldstone mode in the pion superfluid.Comment: 8 pages, 7 figures(Accepted by European Physical Journal C
Influence of Thermal Aging on Microstructure and Property of Gold Alloy Joint Soldered by Sn-based Solder
As an undisputed material of choice to guarantee reliability in a broad range of high performance and safety-critical applications in the electrical contacts and connectors, AuAgCu alloy was soldered with Ag-plated Cu wire using Sn-based solder. To clarify the embrittlement and strength reduction of the gold soldered joint, the microstructure and its influence on the macroand micro-mechanical properties of the soldered joint under various thermal aging conditions were studied. The result indicated that, taking the mechanical property consideration alone, Sn-based solder could be used to join AuAgCu alloy. Different from the embrittlement and strength reduction of the soldered joint of pure gold, although the brittle fracture features appeared in mechanical test of the soldered joints, the shear strength of soldered joint after thermal aging at 125 °C almost did not decrease in comparison with that before thermal aging. Nevertheless, too high temperature and long time still had bad influence on mechanical properties. Otherwise, thermal aging had a large effect on the IMCs layer, as aging temperature elevated and aging time increased, IMCs layer became thicker, more complex components and multiply-sublayers structure with different microhardness. The study provides a fundamental understanding for gold alloy soldering
Excellent performance of Pt-C/TiO2 for methanol oxidation:contribution of mesopores and partially coated carbon
Partial deposition of carbon onto mesoporous TiO2 (C/TiO2) were prepared as supporting substrate for Pt catalyst development. Carbon deposition is achieved by in-situ carbonization of furfuryl alcohol. The hybrid catalysts were characterized by XRD, Raman, SEM and TEM and exhibited outstanding catalytic activity and stability in methanol oxidation reaction. The heterogeneous carbon coated on mesoporous TiO2 fibers provided excellent electrical conductivity and strong interfacial interaction between TiO2 support and Pt metal nanoparticles. Methanol oxidation reaction results showed that the activity of Pt-C/TiO2 is 3.0 and 1.5 times higher than that of Pt-TiO2 and Pt-C, respectively. In addition, the Pt-C/TiO2 exhibited a 6.7 times enhanced stability compared with Pt-C after 2000 cycles. The synergistic effect of C/TiO2 is responsible for the enhanced activity of Pt-C/TiO2, and its excellent durability could be ascribed to the strong interfacial interaction between Pt nanoparticles and C/TiO2 support
Genetic analysis and QTL mapping of traits related to head shape in cabbage (Brassica oleracea var. capitata L.)
AbstractTraits related to head shape, including Hvd (head vertical diameter), Htd (head transverse diameter), and Hsi (head shape index, the ratio of Hvd/Htd), are very important agronomic traits associated with both yield and quality in cabbage (Brassica oleracea var. capitata L.). However, reports of inheritance analysis and quantitative trait locus (QTL) mapping of these traits remain rare. In this study, a double haploid (DH) population with 130 lines constructed from a cross between 24-5 (inbred line, oblate head)×01-88 (inbred line, round head) was used to analyze inheritance and to detect QTLs related to Htd and Hsi using major gene plus polygene mixed inheritance analysis and inclusive composite interval mapping (ICIM). The results indicated that Htd was controlled by two independent major genes and polygenes with recessive-epistatic effects. Hsi was controlled by two linkage major genes and polygenes with cumulative effects. A genetic linkage map with 48 insertions or deletions (InDel) and 149 simple sequence repeat (SSR) markers was constructed based on the DH population, with a total length of 866.2cM and an average interval length of 4.40cM. Fourteen QTLs for Htd and Hsi were identified on six chromosomes based on two years of phenotypic data with ICIM. Ten of the QTLs explained greater than 10.0% of the phenotypic variance, and five QTLs could be repeatedly detected in two years. For Htd, two major QTLs, Htd 3.1 and Htd 8.1, explained 19.16–24.56% and 11.25–21.55% of the phenotypic variation in the two years, respectively. For Hsi, two major QTLs, Hsi 7.1 and Hsi 7.2, explained 22.30–24.93% and 14.85–16.79% of phenotypic variation in the two years, respectively. The results from QTL mapping and genetic analysis in both years were partially consistent and complemented each other. Our results provide a foundation for further research on genetic regulation, gene cloning and molecular marker-assisted selection (MAS) for head shape in cabbage
Towards Layer-Selective Quantum Spin Hall Channels in Weak Topological Insulator Bi4Br2I2
Weak topological insulators, constructed by stacking quantum spin Hall
insulators with weak interlayer coupling, offer promising quantum electronic
applications through topologically nontrivial edge channels. However, the
currently available weak topological insulators are stacks of the same quantum
spin Hall layer with translational symmetry in the out-of-plane direction,
leading to the absence of the channel degree of freedom for edge states. Here,
we study a candidate weak topological insulator, Bi4Br2I2, which is alternately
stacked by three different quantum spin Hall insulators, each with tunable
topologically non-trivial edge states. Our angle-resolved photoemission
spectroscopy and first-principles calculations show that an energy gap opens at
the crossing points of different Dirac cones correlated with different layers
due to the interlayer interaction. This is essential to achieve the tunability
of topological edge states as controlled by varying the chemical potential. Our
work offers a perspective for the construction of tunable quantized conductance
devices for future spintronic applications
Quark Potential in a Quark-Meson Plasma
We investigate quark potential by considering meson exchanges in the two
flavor Nambu--Jona-Lasinio model at finite temperature and density. There are
two kinds of oscillations in the chiral restoration phase, one is the Friedel
oscillation due to the sharp quark Fermi surface at high density, and the other
is the Yukawa oscillation driven by the complex meson poles at high
temperature. The quark-meson plasma is strongly coupled in the temperature
region with being the critical temperature of
chiral phase transition. The maximum coupling in this region is located at the
critical point.Comment: 8 pages and 8 figure
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