检索结果-南通市图书馆

Petroleum Science 2024年第3期21卷 1474-1487页

作者： Shu-Heng Du Yong-Min Shi State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing100190China School of engineering Science University of Chinese Academy of SciencesBeijing100049China School of Earth and Space sciences Peking UniversityBeijing100871China

In this study,a new image-based method for the extraction and characterization of pore-throat network for unconventional hydrocarbon storage and exploitation is proposed.“Pore-throat solidity”,which is analogous to particle solidity,and a new method for automatic identification of pores and throats in tight sandstone oil reservoirs are ***,the“pore-throat combination”and“pure pore”are defined and distinguished by drawing the cumulative probability curve of the pore-throat solidity and by selecting an appropriate cutoff *** the discrete grid set is recognized as a pore-throat combination,Legendre ellipse fitting and minimum Feret diameter are *** the pore and throat grid sets are identified as pure pores,the pore diameter can be directly *** the new method,the analytical results for the physical parameters and pore radius agree well with most prior *** results comparing the maximum ball and the new model could also prove the accuracy of the latter's in micro and nano *** new model provides a more practical theoretical basis and a new calculation method for the rapid and accurate evaluation of the complex processes of oil migration.

关键词： Hydrocarbon exploitation Pore Throat Porous media Identification

Design and evaluation of the traveling wave piezoelectric beam actuators

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2024年第7期40卷 152-163页

作者： Yuanshuai Ding Zengyao Lv Hangyu Li Yuyang Lin Yongmao Pei department of mechanics and engineering Science College of EngineeringPeking UniversityBeijing100871China department of Civil and Environmental engineering Northwestern UniversityEvanstonIL60208USA

Traveling wave piezoelectric beam actuators(TWPBAs)present an advantageous structural configuration for self-moving actuators and hold significant promise for operation in confined ***,current research on TWPBAs faces several limitations,including deficient design methods of excitation and structural parameters,inadequate evaluation metrics,and lack of a quantitative relationship between these parameters and evaluation *** study presents a systematic approach to determining TWPBAs'structure and excitation parameters,proposes criteria for determining the excitation parameters through an established analytical model,and introduces an effective evaluation method for TWPBAs'*** the analytical model and evaluation metrics,we reveal:(1)the coupling relationship between excitation parameters and structural parameters,(2)the influence of participating mode pairs on vibration response,(3)the quantitative relationship between the evaluation metrics and excitation parameters is also *** conclusions are substantiated by the results of finite element analysis,laser vibration measurements,and motion test ***,the practical application of TWPBAs in pipeline operations underscores their potential for use in endoscopy and precision instruments.

关键词： Piezoelectric actuator Exciter-Exciter method Wave propagation Vibration control

Theoretical and experimental investigation of the resonance responses and chaotic dynamics of a bistable laminated composite shell in the dynamic snap-through mode

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Applied Mathematics and mechanics(English Edition) 2024年第4期45卷 581-602页

作者： Meiqi WU Pengyu LV Hongyuan LI Jiale YAN Huiling DUAN Wei ZHANG State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering ScienceBIC-ESATCollege of EngineeringPeking UniversityBeijing 100871China Nanchang Innovation Institute of peking university Nanchang 330096China department of mechanics Guangxi UniversityNanning 530004China

The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic *** existence of the 1:1 resonance relationship between two order vibration modes of the system is *** resonance response of this class of bistable structures in the dynamic snap-through mode is investigated,and the four-dimensional(4D)nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales *** Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are *** discussion focuses on investigating the effects of key parameters,e.g.,excitation amplitude,damping coefficient,and detuning parameters,on the resonance *** numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the ***,the significant motions under particular excitation conditions are visualized by bifurcation diagrams,time histories,phase portraits,three-dimensional(3D)phase portraits,and Poincare ***,the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell,yielding results that are qualitatively consistent with the theoretical results.

关键词： bistable laminated composite shell dynamic snap-through mode Hopf bifurcation chaotic dynamics vibration experiment

Visualization of cristae and mtDNA interactions via STED nanoscopy using a low saturation power probe

在线全文

学校读者我要写书评

暂无评论

Light(Science & Applications) 2024年第9期13卷 1741-1756页

作者： Wei Ren Xichuan Ge Meiqi Li Jing Sun Shiyi Li Shu Gao Chunyan Shan Baoxiang Gao Peng Xi department of Biomedical engineering National Biomedical Imaging CenterCollege of Future TechnologyPeking UniversityBeijing 100871China Key Laboratory of Analytical Science and Technology of Hebei Province College of Chemistry and Material ScienceHebei UniversityBaoding 071002China School of Life sciences Peking UniversityBeijing 100871China National Center for Protein sciences Peking UniversityBeijing 100871China

Mitochondria are crucial organelles closely associated with cellular metabolism and *** DNA(mtDNA)encodes a variety of transcripts and proteins essential for cellular ***,the interaction between the inner membrane(IM)and mtDNA remains elusive due to the limitations in spatiotemporal resolution offered by conventional microscopy and the absence of suitable in vivo probes specifically targeting the ***,we have developed a novel fluorescence probe called HBmito Crimson,characterized by exceptional photostability,fluorogenicity within lipid membranes,and low saturation *** successfully achieved over 500 frames of lowpower stimulated emission depletion microscopy(STED)imaging to visualize the IM dynamics,with a spatial resolution of 40 *** utilizing dual-color imaging of the IM and mtDNA,it has been uncovered that mtDNA tends to habitat at mitochondrial tips or branch points,exhibiting an overall spatially uniform ***,the dynamics of mitochondria are intricately associated with the positioning of mtDNA,and fusion consistently occurs in close proximity to mtDNA to minimize pressure during cristae *** healthy cells,>66%of the mitochondria are Class III(i.e.,mitochondria>5μm or with>12 cristae),while it dropped to<18%in *** dynamics,orchestrated by cristae remodeling,foster the even distribution of ***,in conditions of apoptosis and ferroptosis where the cristae structure is compromised,mtDNA distribution becomes *** findings,achieved with unprecedented spatiotemporal resolution,reveal the intricate interplay between cristae and mtDNA and provide insights into the driving forces behind mtDNA distribution.

关键词： metabolism saturation utilizing

The Boundary Element Method for Ordinary State-Based Peridynamics

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Computer Modeling in engineering & sciences 2024年第6期139卷 2807-2834页

作者： Xue Liang Linjuan Wang State Key Laboratory for Turbulence and Complex Systems Department of Mechanics and Engineering ScienceCollege of EngineeringPeking UniversityBeijing100871China CAPT-HEDPS and IFSA Collaborative Innovation Center of MoECollege of EngineeringPeking UniversityBeijing100871China School of Astronautics Beihang UniversityBeijing100191China

The peridynamics(PD),as a promising nonlocal continuum mechanics theory,shines in solving discontinuous *** to now,various numerical methods,such as the peridynamic mesh-free particlemethod(PD-MPM),peridynamic finite element method(PD-FEM),and peridynamic boundary element method(PD-BEM),have been ***-BEM,in particular,outperforms other methods by eliminating spurious boundary softening,efficiently handling infinite problems,and ensuring high computational ***,the existing PD-BEM is constructed exclusively for bond-based peridynamics(BBPD)with fixed Poisson’s ratio,limiting its applicability to crack propagation problems and scenarios involving infinite or semi-infinite *** this paper,we address these limitations by introducing the boundary element method(BEM)for ordinary state-based peridynamics(OSPD-BEM).Additionally,we present a crack propagationmodel embeddedwithin the framework ofOSPD-BEM to simulate crack *** validate the effectiveness of OSPD-BEM,we conduct four numerical examples:deformation under uniaxial loading,crack initiation in a double-notched specimen,wedge-splitting test,and threepoint bending *** results demonstrate the accuracy and efficiency of OSPD-BEM,highlighting its capability to successfully eliminate spurious boundary softening phenomena under varying Poisson’s ***,OSPDBEMsignificantly reduces computational time and exhibits greater consistencywith experimental results compared to PD-MPM.

关键词： Ordinary state-based peridynamics boundary element method crack propagation fracture toughness

DDX21 is a new player in co-transcriptional RNA modification and functions

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science china(Life sciences) 2024年第10期67卷 2291-2293页

作者： Chengqi Yi State Key Laboratory of Protein and Plant Gene Research School of Life SciencesPeking UniversityBeijing 100871China peking-Tsinghua Center for Life sciences Peking UniversityBeijing 100871China department of Chemical Biology and Synthetic and Functional Biomolecules Center College of Chemistry and Molecular EngineeringPeking UniversityBeijing 100871China beijing Advanced Center of RNA Biology(BEACON) Peking UniversityBeijing 100871China

Ever since the first discovery of chemical modifications of RNA in 1951,researchers have been captivated by the diverse types of modifications,their associated enzymes and proteins(writers,erasers,or readers),and their downstream functional implications(Song and Yi,2017).Among the over 170 distinct types of RNA modifications identified thus far,N^(6)-methyladenosine(m6A)stands out as the most prevalent internal modification on mammalian messenger RNA(mRNA)(Song and Yi,2017).

关键词： modification player stands

Constrained re-calibration of two-equation Reynolds-averaged Navier–Stokes models

在线全文

学校读者我要写书评

暂无评论

Theoretical & Applied mechanics Letters 2024年第2期14卷 82-89页

作者： Yuanwei Bin Xiaohan Hu Jiaqi Li Samuel J.Grauer Xiang I.A.Yang department of Mechanical engineering Pennsylvania State UniversityUniversity ParkPA 16802USA State Key Laboratory for Turbulence and Complex Systems Peking UniversityBeijing 100871China College of engineering Peking UniversityBeijing 100871China

Machine-learned augmentations to turbulence models can be advantageous for flows within the training dataset but can often cause harm *** lack of generalizability arises because the constants(as well as the functions)in a Reynolds-averaged Navier–Stokes(RANS)model are coupled,and un-constrained re-calibration of these constants(and functions)can disrupt the calibrations of the baseline model,the preservation of which is critical to the model's *** safeguard the behaviors of the baseline model beyond the training dataset,machine learning must be constrained such that basic calibrations like the law of the wall are kept *** letter aims to identify such constraints in two-equation RANS models so that future machine learning work can be performed without violating these *** demonstrate that the identified constraints are not ***,they help preserve the generalizability of the baseline model.

关键词： Machine learning Turbulence modeling Reynolds-averaged Navier-Stokes

Polyelectrolyte Complexes and Coacervates Formed by De novo-Designed Peptides and Oligonucleotide

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Polymer Science 2024年第9期42卷 1333-1340,I0007页

作者： Tian-Hao Ren De-Hai Liang beijing National Laboratory for Molecular sciences Department of Polymer Science and Engineering and the Key Laboratory of Polymer Chemistry and Physics of the Ministry of EducationCollege of Chemistry and Molecular EngineeringPeking UniversityBeijing100871China

The liquid-liquid phase separation of biopolymers in living cells contains multiple interactions and occurs in a dynamic *** the regulation mechanism is still a *** this work,we designed a series of peptides(XXLY)_(6)SSSGSS and studied their complexation and coacervation behavior with single-stranded ***“X”and“Y”are varied to combine known amounts of charged and non-charged amino acids,together with the introduction of secondary structures and pH *** show that the electrostatic interaction,which is described as charge density,controls both the strength of complexation and the degree of chain relaxation,and thus determines the growth and size of the *** hydrophobic interaction is prominent when the charges are ***,the secondary structures of peptides exhibit profound effect on the morphology of the phases,such as solid phase to liquid phase *** study gains insight into the phase separation under physiological *** is also helpful to create coacervates with desirable structures and functions.

关键词： Polyelectrolyte complex Coacervate Peptides Secondary structure Electrostatic interaction

Formation adaptation in obstacle-cluttered environments via MPC-based trajectory planning

在线全文

学校读者我要写书评

暂无评论

Science china(Information sciences) 2024年第7期67卷 321-323页

作者： Yuda CHEN Zhongkui LI department of mechanics and engineering Science College of Engineering Peking University

Formation is a typical collective behavior in multiagent systems utilized in areas such as inspection, surveillance, and transportation. Commonly-used approaches to achieve formation include virtual structure [1], con...

关键词：

Grasp Detection with Hierarchical Multi-Scale Feature Fusion and Inverted Shuffle Residual

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Tsinghua Science and Technology 2024年第1期29卷 244-256页

作者： Wenjie Geng Zhiqiang Cao Peiyu Guan Fengshui Jing Min Tan Junzhi Yu State Key Laboratory of Multimodal Artificial Intelligence Systems Institute of AutomationChinese Academy of SciencesBeijing 100190China School of Artificial Intelligence University of Chinese Academy of SciencesBeijing 100049China department of Advanced Manufacturing and Robotics College of EngineeringPeking UniversityBeijing 100871China

Grasp detection plays a critical role for robot *** pixel-wise grasp detection networks with encoder-decoder structure receive much attention due to good accuracy and ***,they usually transmit the high-level feature in the encoder to the decoder,and low-level features are *** is noted that low-level features contain abundant detail information,and how to fully exploit low-level features remains ***,the channel information in high-level feature is also not well ***,the performance of grasp detection is *** solve these problems,we propose a grasp detection network with hierarchical multi-scale feature fusion and inverted shuffle *** low-level and high-level features in the encoder are firstly fused by the designed skip connections with attention module,and the fused information is then propagated to corresponding layers of the decoder for in-depth feature *** a hierarchical fusion guarantees the quality of grasp ***,an inverted shuffle residual module is created,where the high-level feature from encoder is split in channel and the resultant split features are processed in their respective *** such differentiation processing,more high-dimensional channel information is kept,which enhances the representation ability of the ***,an information enhancement module is added before the encoder to reinforce input *** proposed method attains 98.9%and 97.8%in image-wise and object-wise accuracy on the Cornell grasping dataset,respectively,and the experimental results verify the effectiveness of the method.

关键词： grasp detection hierarchical multi-scale feature fusion skip connections with attention inverted shuffle residual