检索结果-内蒙古大学图书馆

arXiv 2018年

作者： Zhao, Ye Li, Yinan Sentis, Luis Topcu, Ufuk Liu, Jun George W. Woodruff School Of Mechanical Engineering Georgia Tech United States Department Of Applied Mathematics University Of Waterloo Canada Department Of Aerospace Engineering And Engineering Mechanics UT Austin United States Institute For Computational Engineering And Sciences UT Austin United States

Contact-based decision and planning methods are becoming increasingly important to endow higher levels of autonomy for legged robots. Formal synthesis methods derived from symbolic systems have great potential for reasoning about high-level locomotion decisions and achieving complex maneuvering behaviors with correctness guarantees. This study takes a first step toward formally devising an architecture composed of task planning and control of whole-body dynamic locomotion behaviors in constrained and dynamically changing environments. At the high level, we formulate a two-player temporal logic game between the multi-limb locomotion planner and its dynamic environment to synthesize a winning strategy that delivers symbolic locomotion actions. These locomotion actions satisfy the desired high-level task specifications expressed in a fragment of temporal logic. Those actions are sent to a robust finite transition system that synthesizes a locomotion controller that fulfills state reachability constraints. This controller is further executed via a low-level motion planner that generates feasible locomotion trajectories. We construct a set of dynamic locomotion models for legged robots to serve as a template library for handling diverse environmental *** devise a replanning strategy that takes into consideration sudden environmental changes or large state disturbances to increase the robustness of the resulting locomotion behaviors. We formally prove the correctness of the layered locomotion framework guaranteeing a robust implementation by the motion planning layer. Simulations of reactive locomotion behaviors in diverse environments indicate that our framework has the potential to serve as a theoretical foundation for intelligent locomotion behaviors. Copyright © 2018, The Authors. All rights reserved.

关键词： Motion planning

来源：评论

学校读者我要写书评

暂无评论

Assessment of supervised longitudinal learning methods: Insights from predicting low birth weight and very low birth weight using prenatal ultrasound measurements

引用

Computers in Biology and Medicine 2024年 182卷 109084-109084页

作者： Zhang, Cancan Yu, Xiufan Zhang, Bo Division of General Medicine Beth Israel Deaconess Medical Center BostonMA United States Department of Applied and Computational Mathematics and Statistics University of Notre Dame Notre DameIN United States Department of Neurology and Biostatistics and Research Design Center Children's Hospital Harvard Medical School BostonMA02115 United States

Background: This study aimed to assess the efficacy of various supervised longitudinal learning approaches, comparing traditional statistical models and machine learning algorithms for prediction with longitudinal data. The primary objectives were to evaluate the predictive performance of different supervised longitudinal learning methods for low birth weight (LBW) and very low birth weight (VLBW) based on prenatal ultrasound measurements. Additionally, the study sought to extract interpretable risk features for disease prediction. Methods: The evaluation involved benchmarking the performance of longitudinal models against conventional machine learning methods. Classification accuracy for LBW and VLBW at birth, as well as prediction accuracy for birth weight using prenatal sonographic ultrasound measurements, were assessed. Results: Among the learning approaches we investigated in this study, the longitudinal machine learning approach, specifically, the mixed effect random forest (MERF), delivered the overall best performance in predicting birthweights and classifying LBW/VLBW disease status. Conclusion: The MERF combined the power of advanced machine learning algorithms to accommodate the inherent within-individual dependence in the observed data, delivering satisfactory performance in predicting the birthweight and classifying LBW/VLBW disease status. The study emphasized the importance of incorporating previous ultrasound measurements and considering correlations between repeated measurements for accurate prediction. The interpretable trees algorithm used for risk feature extraction proved reliable and applicable to other learning algorithms. These findings underscored the potential of longitudinal learning methods in improving birth weight prediction and highlighted the relevance of consistent risk features in line with established literature. © 2024 Elsevier Ltd

关键词： Self-supervised learning

来源：评论

学校读者我要写书评

暂无评论

The Small-World Effect for Interferometer Networks

arXiv

引用

arXiv 2023年

作者： Krawciw, Benjamin Carr, Lincoln D. Behn, Cecilia Diniz Department of Applied Mathematics and Statistics Colorado School of Mines GoldenCO United States Department of Physics Colorado School of Mines GoldenCO United States Quantum Engineering Program Colorado School of Mines GoldenCO United States

Complex network theory has focused on properties of networks with real-valued edge weights. However, in signal transfer networks, such as those representing the transfer of light across an interferometer, complex-valued edge weights are needed to represent the manipulation of the signal in both magnitude and phase. These complex-valued edge weights introduce interference into the signal transfer, but it is unknown how such interference affects network properties such as small-worldness. To address this gap, we have introduced a small-world interferometer network model with complex-valued edge weights and generalized existing network measures to define the interferometric clustering coefficient, the apparent path length, and the interferometric small-world coefficient. Using high-performance computing resources, we generated a large set of small-world interferometers over a wide range of parameters in system size, nearest-neighbor count, and edge-weight phase and computed their interferometric network measures. We found that the interferometric small-world coefficient depends significantly on the amount of phase on complex-valued edge weights: for small edge-weight phases, constructive interference led to a higher interferometric small-world coefficient;while larger edge-weight phases induced destructive interference which led to a lower interferometric small-world coefficient. Thus, for the small-world interferometer model, interferometric measures are necessary to capture the effect of interference on signal transfer. This model is an example of the type of problem that necessitates interferometric measures, and applies to any wave-based network including quantum networks. Copyright © 2023, The Authors. All rights reserved.

关键词： Interferometers

来源：评论

学校读者我要写书评

暂无评论

Bose polaron as an instance of quantum Brownian motion

arXiv

引用

arXiv 2017年

作者： Lampo, Aniello Lim, Soon Hoe Garciá-March, Miguel Ángel Lewenstein, MacIej ICFO-Institut de Ciencies Fotoniques Barcelona Institute of Science and Technology Castelldefels08860 Spain Department of Mathematics Program in Applied Mathematics University of Arizona TucsonAZ85721-0089 United States ICREA-Institució Catalana de Recerca i Estudis Avancats Lluis Companys 23 BarcelonaE-08010 Spain

We study the dynamics of a quantum impurity immersed in a Bose-Einstein condensate as an open quantum system in the framework of the quantum Brownian motion model. We derive a generalized Langevin equation for the position of the impurity. The Langevin equation is an integro-differential equation that contains a memory kernel and is driven by a colored noise. These result from considering the environment as given by the degrees of freedom of the quantum gas, and thus depend on its parameters, e.g. interaction strength between the bosons, temperature, etc. We study the role of the memory on the dynamics of the impurity. When the impurity is untrapped, we find that it exhibits a super-diffusive behavior at long times. We find that back-flow in energy between the environment and the impurity occurs during evolution. When the particle is trapped, we calculate the variance of the position and momentum to determine how they compare with the Heisenberg limit. One important result of this paper is that we find position squeezing for the trapped impurity at long times. We determine the regime of validity of our model and the parameters in which these effects can be observed in realistic experiments. Copyright © 2017, The Authors. All rights reserved.

关键词： Degrees of freedom (mechanics)

来源：评论

学校读者我要写书评

暂无评论

Improved phase-field models of melting and dissolution in multi-component flows

arXiv

引用

arXiv 2020年

作者： Hester, Eric W. Couston, Louis-Alexandre Favier, Benjamin Burns, Keaton J. Vasil, Geoffrey M. University of Sydney School of Mathematics and Statistics SydneyNSW2006 Australia British Antarctic Survey CambridgeCB3 0ET United Kingdom Department of Applied Mathematics and Theoretical Physics University of Cambridge Cambridge United Kingdom Aix Marseille Univ CNRS Centrale Marseille IRPHE Marseille France Massachusetts Institute of Technology Department of Mathematics CambridgeMA02139 United States Center for Computational Astrophysics Flatiron Institute Simons Foundation New YorkNY10010 United States

We develop and analyse the first second-order phase-field model to combine melting and dissolution in multi-component flows. This provides a simple and accurate way to simulate challenging phase-change problems in existing codes. Phase-field models simplify computation by describing separate regions using a smoothed phase field. The phase field eliminates the need for complicated discretisations that track the moving phase boundary. However standard phase-field models are only first-order accurate. They often incur an error proportional to the thickness of the diffuse interface. We eliminate this dominant error by developing a general framework for asymptotic analysis of diffuse-interface methods in arbitrary geometries. With this framework we can consistently unify previous second-order phase-field models of melting and dissolution and the volume-penalty method for fluid-solid interaction. We finally validate second-order convergence of our model in two comprehensive benchmark problems using the open-source spectral code Dedalus. Copyright © 2020, The Authors. All rights reserved.

关键词： Constrained optimization

来源：评论

学校读者我要写书评

暂无评论

Relaxation Dynamics of Semiflexible Polymers

引用

Physical Review Letters 2004年第9期92卷 098101-098101页

作者： Y. Bohbot-Raviv W. Z. Zhao M. Feingold C. H. Wiggins R. Granek Department of Materials and Interfaces Weizmann Institute of Science Rehovot 76100 Israel Department of Physics and The Ilse Katz Center for Nanotechnology Ben-Gurion University Beer Sheva 84105 Israel Department of Applied Physics and Applied Mathematics and Center for Computational Biology and Bioinformatics Columbia University 500 West 120th Street New York New York 10027 USA The Kavli Institute for Theoretical Physics University of California Santa Barbara California 93106 USA Department of Biotechnology Engineering and The Institute for Applied Biosciences Ben-Gurion University Beer Sheva 84105 Israel

We study the relaxation dynamics of a semiflexible chain by introducing a time-dependent tension. The chain has one of its ends attached to a large bead, and the other end is fixed. We focus on the initial relaxation of the chain that is initially strongly stretched. Using a tension that is self-consistently determined, we obtain the evolution of the end-to-end distance with no free parameters. Our results are in good agreement with single molecule experiments on double stranded DNA.

关键词： Polymers

来源：评论

学校读者我要写书评

暂无评论

Phase-field simulations of the effect of temperature and interface for zirconium δ-hydrides

arXiv

引用

arXiv 2023年

作者： Chen, Zi-Hang Sheng, Jie Liu, Yu Shi, Xiao-Ming Huang, Houbing Xu, Ke Wang, Yue-Chao Wu, Shuai Sun, Bo Liu, Hai-Feng Song, Hai-Feng School of Materials Science and Engineering Beijing Institute of Technology Beijing100081 China Advanced Research Institute of Multidisciplinary Science Beijing Institute of Technology Beijing100081 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China Department of Physics University of Science and Technology Beijing Beijing100083 China

Hydride precipitation in zirconium cladding materials can damage their integrity and durability. Service temperature and material defects have a significant effect on the dynamic growth of hydrides. In this study, we have developed a phase field model based on the assumption of elastic behaviour within a specific temperature range (613-653K). This model allows us to study the influence of temperature and interfacial effects on the morphology, stress, and average growth rate of zirconium hydride. The results suggest that changes in temperature and interfacial energy influence the aspect ratio and average growth rate of the hydride morphology. The ultimate determinant of hydride orientation is the loss of interfacial coherence, primarily induced by interfacial dislocation defects and quantifiable by the mismatch degree q. An escalation in interfacial coherence loss leads to a transition of hydride growth from horizontal to vertical, accompanied by the onset of redirection behaviour. Interestingly, redirection occurs at a critical mismatch level, denoted qc, and remains unaffected by variations in temperature and interfacial energy. However, this redirection leads to an increase in the maximum stress, which may influence the direction of hydride crack propagation. This research highlights the importance of interfacial coherence and provides valuable insights into the morphology and growth kinetics of hydrides in zirconium alloys. Copyright © 2023, The Authors. All rights reserved.

关键词： Hydrides

来源：评论

学校读者我要写书评

暂无评论

Modeling heterogeneous materials via two-point correlation functions. II. Algorithmic details and applications

引用

Physical Review E 2008年第3期77卷 031135-031135页

作者： Y. Jiao F. H. Stillinger S. Torquato Department of Chemistry Princeton University Princeton New Jersey 08544 USA Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Princeton Center for Theoretical Physics Princeton University Princeton New Jersey 08544 USA and School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08540 USA

In the first part of this series of two papers, we proposed a theoretical formalism that enables one to model and categorize heterogeneous materials (media) via two-point correlation functions S2 and introduced an efficient heterogeneous-medium (re)construction algorithm called the “lattice-point” algorithm. Here we discuss the algorithmic details of the lattice-point procedure and an algorithm modification using surface optimization to further speed up the (re)construction process. The importance of the error tolerance, which indicates to what accuracy the media are (re)constructed, is also emphasized and discussed. We apply the algorithm to generate three-dimensional digitized realizations of a Fontainebleau sandstone and a boron-carbide/aluminum composite from the two-dimensional tomographic images of their slices through the materials. To ascertain whether the information contained in S2 is sufficient to capture the salient structural features, we compute the two-point cluster functions of the media, which are superior signatures of the microstructure because they incorporate topological connectedness information. We also study the reconstruction of a binary laser-speckle pattern in two dimensions, in which the algorithm fails to reproduce the pattern accurately. We conclude that in general reconstructions using S2 only work well for heterogeneous materials with single-scale structures. However, two-point information via S2 is not sufficient to accurately model multiscale random media. Moreover, we construct realizations of hypothetical materials with desired structural characteristics obtained by manipulating their two-point correlation functions.

关键词： RECONSTRUCTING RANDOM-MEDIA TOPOLOGY OPTIMIZATION MICROSTRUCTURES COMPOSITES DESIGN TRANSPORT

来源：评论

学校读者我要写书评

暂无评论

Controlling catalytic activity of gold cluster on MgO thin film for water splitting

引用

Physical Review Materials 2017年第4期1卷 045404-045404页

作者： Zijing Ding Lei Yan Zi Li Wei Ma Gang Lu Sheng Meng Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China Department of Physics and Astronomy California State University Northridge Northridge California 91330 USA Institute of Applied Physics and Computational Mathematics Beijing 100088 China Ningxia Key Laboratory of Photovoltaic Materials Ningxia University Yinchuan 750021 China

We propose that supported gold clusters on MgO thin film can potentially serve as an efficient photocatalyst for water splitting. The catalytic activity of the gold cluster is enhanced by excess electrons occupying its quantum well states (QWSs) and can be controlled by varying the oxide thickness, introducing defects/doping in the substrate, and modulating the plasmonic response of the Au cluster. We find that the bonding between the water molecule and certain QWSs can significantly reduce the water splitting energy barrier in its ground state. More importantly, the water splitting is nearly spontaneous when the QWS is photoexcited. First-principles real-time electron dynamics simulations reveal that the excited QWS in the supported gold cluster has a long lifetime on the scale of picoseconds. Generation of activated hydrogen atoms is predicted to occur spontaneously following photoexcitation, and the yield of H2 gas is maintained by enriching hydrogen concentration without poisoning the catalyst. These results illustrate promising routes for promoting photocatalysis via engineering the energy levels of supported metal clusters.

关键词： Electronic structure Plasmons Nanoclusters First-principles calculations

来源：评论

学校读者我要写书评

暂无评论

Growing heterogeneous tumors in silico

引用

Physical Review E 2009年第5期80卷 051910-051910页

作者： Jana Gevertz S. Torquato Program in Applied and Computational Mathematics Princeton University Princeton New Jersey 08544 USA Department of Chemistry Princeton University Princeton New Jersey 08544 USA Princeton Center for Theoretical Science Princeton University Princeton New Jersey 08544 USA Princeton Institute for the Science and Technology of Materials Princeton University Princeton New Jersey 08544 USA School of Natural Sciences Institute for Advanced Study Princeton New Jersey 08540 USA

An in silico tool that can be utilized in the clinic to predict neoplastic progression and propose individualized treatment strategies is the holy grail of computational tumor modeling. Building such a tool requires the development and successful integration of a number of biophysical and mathematical models. In this paper, we work toward this long-term goal by formulating a cellular automaton model of tumor growth that accounts for several different inter-tumor processes and host-tumor interactions. In particular, the algorithm couples the remodeling of the microvasculature with the evolution of the tumor mass and considers the impact that organ-imposed physical confinement and environmental heterogeneity have on tumor size and shape. Furthermore, the algorithm is able to account for cell-level heterogeneity, allowing us to explore the likelihood that different advantageous and deleterious mutations survive in the tumor cell population. This computational tool we have built has a number of applications in its current form in both predicting tumor growth and predicting response to treatment. Moreover, the latent power of our algorithm is that it also suggests other tumor-related processes that need to be accounted for and calls for the conduction of new experiments to validate the model’s predictions.

关键词： Tumors

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：