检索结果-南通市图书馆

Local-contrastive-learning machine with both generalization and adversarial robustness: A statistical physics analysis

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 109-123页

作者： Mingshan Xie Yuchen Wang Haiping Huang PMI lab School of Physics Sun Yat-sen University Guangdong Provincial Key lab.ratory of Magnetoelectric Physics and Devices Sun Yat-sen University

Distinct from human cognitive processing, deep neural networks trained by backpropagation can be easily fooled by adversarial examples. To design a semantically meaningful representation learning, we discard backpropagation, and instead, propose a local contrastive learning, where the representations for the inputs bearing the same lab.l shrink(akin to boson) in hidden layers,while those of different lab.ls repel(akin to fermion). This layer-wise learning is local in nature, being biologically plausible.A statistical mechanics analysis shows that the target fermion-pair-distance is a key parameter. Moreover, the application of this local contrastive learning to MNIST benchmark dataset demonstrates that the adversarial vulnerability of standard perceptron can be greatly mitigated by tuning the target distance, i.e., controlling the geometric separation of prototype manifolds.

关键词： machine learning statistical mechanics adversarial robustness neural networks

The intrinsic depth of horizontal convection

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Oceanology and Limnology 2010年第3期28卷 643-648页

作者：陈琛王伟吴德星 Physical Oceanography lab. Ocean University of China

The mainstream depth of a return flow can be viewed as an intrinsic depth of horizontal convection. By using a theoretical tube model combined with the application of the Maximum Entropy Production Principle (MaxEPP) in thermodynamics, the following statements can be made. Under fixed external forcing, the system chooses a particular depth as the mainstream depth of its return flow, the depth of which not only satisfies the maximum circulation rate and the maximum heat transport, but also satisfies the maximum entropy production rate. A comparison between this intrinsic depth and the container height leads to the definition of a relative partial and full-penetration pattern of the circulation. Moreover, this intrinsic depth is found to vary with the external forcing; the regulation of this variation is related to the Modified Rayleigh number.

关键词： tube model maximum velocity maximum entropy production rate

XFEM modeling of hydraulic fracture in porous rocks with natural fractures

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2017年第8期60卷 45-59页

作者： Tao Wang ZhanLi Liu QingLei Zeng Yue Gao Zhuo Zhuang Applied Mechanics lab. School of Aerospace Engineering Tsinghua University

Hydraulic fracture （HF） in porous rocks is a complex multi-physics coupling process which involves fluid flow, diffusion and solid deformation. In this paper, the extended finite element method （XFEM） coupling with Biot theory is developed to study the HF in permeable rocks with natural fractures （NFs）. In the recent XFEM based computational HF models, the fluid flow in fractures and interstitials of the porous media are mostly solved separately, which brings difficulties in dealing with complex fracture morphology. In our new model the fluid flow is solved in a unified framework by considering the fractures as a kind of special porous media and introducing Poiseuille-type flow inside them instead of Darcy-type flow. The most advantage is that it is very convenient to deal with fluid flow inside the complex frac^xre network, which is important in shale gas extraction. The weak formulation for the new coupled model is derived based on virtual work principle, which includes the XFEM formulation for multiple fractures and fractures intersection in porous media and finite element formulation for the unified fluid flow. Then the plane strain Kristianovic-Geertsma-de Klerk （KGD） model and the fluid flow inside the fracture network are simulated to validate the accuracy and applicability of this method. The numerical results show that large injection rate, low rock permeability and isotropic in-situ stresses tend to lead to a more uniform and productive fracture network.

关键词： hydraulic fracture XFEM porous media fluid flow multi-physics coupling

Simulation of Ultrasonic Propagation Based on Raying　Model in Typical Structure

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2003年第z1期19卷 125-128页

作者： Tie GANG Weizhi ZHANG Liwei GUO State Key lab. of AWPT Harbin Institute of Technology Harbin 150001 China State Key Lab. of AWPT Harbin Institute of Technology Harbin 150001 China State Key Lab. of AWPT Harbin Institute of Technology Harbin 150001 China

The convenient and useful raying mode was selected to develop the analysis module of ultrasonic parameters, and the simulation of ultrasonic propagation in typical plane structure was carried out. Using this model, the ultrasonic propagation in the water immersion testing was analyzed. For the complex plate structure, the intelligent analysis and simulation module was developed.

关键词： Ultrasonic testing, Ray modeling, Computer simulation

Magnetic transitions and butterfly-shaped hysteresis of Sm-Fe-Al-based perovskite-type orthoferrite

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Rare Earths 2015年第9期33卷 965-971页

作者： M.A.Ahmed N.G.Imam M.K.Abdelmaksoud Y.A.Saeid Materials Science lab. Physics Department Faculty of Science Cairo University Materials Science lab. Experimental Physics Department Nuclear Research Center Atomic Energy Authority

A1 doped SmFeO3 （SmFel_xmlxO3; 0.0〈x〈0.15; step 0.05） were prepared by double sintering ceramic technique. The obtained samples were crystallized in single phase structure except the sample with x=0.15. The unit cell volume was found to decrease with increasing AI substitution in orthoferrite. The effective magnetic moment （μeff） and the Curie constant （C） were calculated from the reciprocal of the molar magnetic susceptibility （Z-1） versus absolute temperature plot and found to attain maximum value for the parent sample. The magnetic behavior showed two different magnetic transitions, viz, N6el temperature （TN） and spin reorientation （TsR） transitions. The M-H hysteresis loop of the parent sample took butterfly-shape as a result of different contributions anisotropies. From the magnetic properties measurements, it was obviously found that B-site cation dilution resulted in a drastic decrease in the magnetization. Surprisingly large value of the coercive field was obtained for the undoped sample;Hc=6198.80e. Based on the mentioned results, one can recommend the use of such orthoferrite in magnetic recording media and as pining layer in spin valve for spin- tronic applications.

关键词： SmFeO3 magnetization FESEM crystal structure spintronics spin reorientation butterfly-shaped hysteresis anisotropy rare earths

Effect of surface morphology on the electron mobility of epitaxial graphene grown on 0° and 8° Si-terminated 4H-SiC substrates

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2012年第9期21卷 466-469页

作者：李佳王丽冯志红蔚翠刘庆彬敦少博蔡树军 Science and Technology on ASIC lab. Hebei Semiconductor Research Institute Information Center of Science and Technology Science and Technology on ASIC lab. Hebei Semiconductor Research Institute

Graphene with different surface morphologies were fabricated on 8°-off-axis and on-axis 4H-SiC（0001） substrates by high-temperature thermal decompositions. Graphene grown on Si-terminated 8°-off-axis 4H-SiC（0001） shows lower Hall mobility than the counterpart of on-axis SiC substrates. The terrace width is not responsible for the different electron mobility of graphene grown on different substrates, as the terrace width is much larger than the mean free path of the electrons. The electron mobility of graphene remains unchanged with an increasing terrace width on Si- terminated on-axis SiC. Interface scattering and short-range scattering are the main factors affecting the mobility of epitaxial graphene. After the optimization of the growth process, the Hall mobility of the graphene reaches 1770 cm^2/V.s at a carrier density of 9.8.×10^12 cm^-2. Wafer-size graphene was successfully achieved with an excellent double-layer thickness uniformity of 89.7% on a 3-inch SiC substrate.

关键词： graphene morphology Hall mobility 3-inch SiC substrate

RE-SEGNN:recurrent semantic evidence-aware graph neural network for temporal knowledge graph forecasting

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2025年

作者： Wenyu CAI Mengfan LI Xuanhua SHI Yuanxin FAN Quntao ZHU Hai JIN National Engineering Research Center for Big Data Technology and System Services Computing Technology and System Lab Cluster and Grid Computing Lab School of Computer Science and TechnologyHuazhong University of Science and Technology

Temporal knowledge graph(TKG) reasoning, has seen widespread use for modeling real-world events, particularly in extrapolation settings. Nevertheless, most previous studies are embedded models, which require both entity and relation embedding to make predictions, ignoring the semantic correlations among different entities and relations within the same timestamp. This can lead to random and nonsensical predictions when unseen entities or relations occur. Furthermore, many existing models exhibit limitations in handling highly correlated historical facts with extensive temporal depth. They often either overlook such facts or overly accentuate the relationships between recurring past occurrences and their current counterparts. Due to the dynamic nature of TKG, effectively capturing the evolving semantics between different timestamps can be *** address these shortcomings, we propose the recurrent semantic evidenceaware graph neural network(RE-SEGNN), a novel graph neural network that can learn the semantics of entities and relations simultaneously. For the former challenge, our model can predict a possible answer to missing quadruples based on semantics when facing unseen entities or relations. For the latter problem, based on an obvious established force, both the recency and frequency of semantic history tend to confer a higher reference value for the current. We use the Hawkes process to compute the semantic trend, which allows the semantics of recent facts to gain more attention than those of distant facts. Experimental results show that RE-SEGNN outperforms all SOTA models in entity prediction on 6 widely used datasets, and 5 datasets in relation prediction. Furthermore, the case study shows how our model can deal with unseen entities and relations.

关键词：

Plasma-Sprayed Coating of an Apatite-Type Lanthanum Silicate Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs)

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Plasma Science and Technology 2013年第7期15卷 673-676页

作者：陈军黄建军李信军刘英齐冰江石寿王喜省 SZU-ASIPP Joint lab. for Applied Plasma Shenzhen University

Apatite-type lanthanum silicate was successfully synthesized via a solid state re- action protocol at 1400~C in a vacuum for 4 hours. The powder was synthesized faster and at a lower reaction temperature than by conventional solid state reaction methods. The resulting powder was used in the fabrication of a coating deposited by atmospheric plasma spray （APS） technology. The microstructure of the coating was analyzed by X-ray diffraction and scanning electron microscopy. Heat treatment was found to fully crystallize the coating, increasing its den-sity. The ionic conductivity of the apatite coating was 0.39 （0.054） mS/cm at 850 （700） ℃, and its activation energy was 0.67 eV.

关键词： lanthanum silicate solid oxide fuel cell atmospheric plasma spraying ionicconductivity activation energy

ELECTRO-ELASTIC FUNDAMENTAL SOLUTIONS OF ANISOTROPIC PIEZOELECTRIC MATERIALS WITH AN ELLIPTICAL HOLE

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 1997年第1期13卷 54-62页

作者：刘金喜王彪杜善义 Composite Materials lab. Harbin Institute of TechnologyHarbin 150001China

By using Stroh' complex formalism and Cauchy's integral method, the electro-elastic fundamental solutions of an infinite anisotropic piezoelectric solid containing an elliptic hole or a crack subjected to a Line force and a line charge are presented in closed form. Particular attention is paid to analyzing the characteristics of the stress and electric displacement intensity factors. When a line force-charge acts on the crack surface, the real form expression of intensity factors is obtained. It is shown through a special example that the present work is correct.

关键词： piezoelectric material fundamental solution elliptic hole intensity factor