Li Tan

ORCID

Publication Activity (10 Years)

Years Active: 2001-2024
Publications (10 Years): 108

Top Venues

University of California, Riverside, USA (PHD)

Education History

University of California, Riverside, USA

PHD

Publications

Li Tan, Wei Ren, Xi-Ming Sun, Junlin Xiong
Motion Control of Two Mobile Robots Under Allowable Collisions. IEEE Robotics Autom. Lett. 9 (1) (2024)
Li Tan, Jiaqi Shi, Jing Gao, Haoyu Wang, Hongtao Zhang, Yu Zhang
Multi-UAV path planning based on IB-ABC with restricted planned arrival sequence. Robotica 41 (4) (2023)
Li Tan, Hongtao Zhang, Yuzhao Liu, Xinyue Lv, Haoyu Wang
Quality-based irregular area coverage algorithm in aerial sensor networks. Comput. Electr. Eng. 112 (2023)
Haodong Chen, Vera Yuk Ying Chung, Li Tan, Xiaoming Chen
Dense Voxel 3D Reconstruction Using a Monocular Event Camera. CoRR (2023)
Li Tan, Raymond A. de Callafon, Mai H. Nguyen, Ilkay Altintas
Ensemble Based Learning for Automated Safety Labeling of Prescribed Fires. ICCS (1) (2023)
Wei-Gang Cui, Junling Du, Mingyi Sun, Shimao Zhu, Shijie Zhao, Ziwen Peng, Li Tan, Yang Li
Dynamic multi-site graph convolutional network for autism spectrum disorder identification. Comput. Biol. Medicine 157 (2023)
Feiyang Jia, Li Tan, Ge Wang, Caiyan Jia, Zhineng Chen
A super-resolution network using channel attention retention for pathology images. PeerJ Comput. Sci. 9 (2023)
Li Tan, Ge Wang, Feiyang Jia, Xiaofeng Lian
Research status of deep learning methods for rumor detection. Multim. Tools Appl. 82 (2) (2023)
Hyun-Myung Woo, Xiaoning Qian, Li Tan, Shantenu Jha, Francis J. Alexander, Edward R. Dougherty, Byung-Jun Yoon
Optimal decision-making in high-throughput virtual screening pipelines. Patterns 4 (11) (2023)
Li Tan, Yangsheng Hu, Shuo Tan, Raymond A. de Callafon, Ilkay Altintas
Wildfire Perimeter Detection via Iterative Trimming Method. ICCS (1) (2023)
Linbo Wang, Li Tan, Xianyong Fang, Yanwen Guo, Shaohua Wan
Adaptively feature matching via joint transformational-spatial clustering. Multim. Syst. 29 (3) (2023)
Ziliang Shang, Li Tan, Hongtao Zhang, Xujie Jiang, Yuzhao Liu, Dongfang Li
Food23: A Chinese Food Safety Dataset for Fake News Detection. ICAAI (2023)
Li Tan, Hongtao Zhang, Jiaqi Shi, Yuzhao Liu, Tianli Yuan
A robust multiple Unmanned Aerial Vehicles 3D path planning strategy via improved particle swarm optimization. Comput. Electr. Eng. 111 (Part A) (2023)
Li Tan, Xinyue Lv, Ge Wang, Xiaofeng Lian
UAV image object recognition method based on small sample learning. Multim. Tools Appl. 82 (17) (2023)
Li Tan, Xujie Jiang, Zikang Liu, Hongtao Zhang, Ziliang Shang, Yuzhao Liu
Crowd counting in dense UAV images based on multiscale feature fusion. ICCEIC (2023)
Li Tan, Wei Ren, Xi-Ming Sun, Junlin Xiong
Motion Control of Two Mobile Robots under Allowable Collisions. CoRR (2023)
Ge Wang, Li Tan, Tianbao Song, Wei Wang, Ziliang Shang
Region-enhanced Deep Graph Convolutional Networks for Rumor Detection. CoRR (2022)
Ge Wang, Li Tan, Ziliang Shang, He Liu
Multimodal Dual Emotion with Fusion of Visual Sentiment for Rumor Detection. CoRR (2022)
Jiaqi Shi, Li Tan, Xiaofeng Lian, Tianying Xu, Hongtao Zhang, Yu Zhang
A multi- unmanned aerial vehicle dynamic task assignment method based on bionic algorithms. Comput. Electr. Eng. 99 (2022)
Li Tan, Qiongqiong Wang, Haonan Zheng, Yi Si
Piecewise fitting of distorted image edge contour. EBIMCS (2022)
Li Tan, Raymond A. de Callafon, Ilkay Altintas
Characterizing Wildfire Perimeter Polygons from QUIC-Fire. ICCS (1) (2022)
Austin Clyde, Stephanie Galanie, Daniel W. Kneller, Heng Ma, Yadu N. Babuji, Ben Blaiszik, Alexander Brace, Thomas S. Brettin, Kyle Chard, Ryan Chard, Leighton Coates, Ian T. Foster, Darin Hauner, Vilmos Kertesz, Neeraj Kumar, Hyungro Lee, Zhuozhao Li, André Merzky, Jurgen G. Schmidt, Li Tan, Mikhail Titov, Anda Trifan, Matteo Turilli, Hubertus Van Dam, Srinivas C. Chennubhotla, Shantenu Jha, Andrey Kovalevsky, Arvind Ramanathan, Martha S. Head, Rick Stevens
High-Throughput Virtual Screening and Validation of a SARS-CoV-2 Main Protease Noncovalent Inhibitor. J. Chem. Inf. Model. 62 (1) (2022)
Xinyi Wei, Xiaohui Liu, Yawen Fan, Li Tan, Qing Liu
A Unified Test for the AR Error Structure of an Autoregressive Model. Axioms 11 (12) (2022)
Jiaqi Shi, Li Tan, Hongtao Zhang, Xiaofeng Lian, Tianying Xu
Adaptive multi-UAV path planning method based on improved gray wolf algorithm. Comput. Electr. Eng. 104 (Part) (2022)
Li Tan, Ge Wang, Feiyang Jia, Xiaofeng Lian
Research Status of Deep Learning Methods for Rumor Detection. CoRR (2022)
Wei Jin, Li Tan
Two-geodesic-transitive graphs which are locally self-complementary. Discret. Math. 345 (8) (2022)
Wei Jin, Li Tan
On diameter two Cayley graphs. Appl. Math. Comput. 434 (2022)
Li Tan, Qiongqiong Wang, Haonan Zheng, Yi Si
Subpixel edge contour extraction based on Zernike orthogonal moments. ICIIP (2022)
Li Tan, Raymond A. de Callafon, Jessica Block, Daniel Crawl, Tolga Çaglar, Ilkay Altintas
Estimation of wildfire wind conditions via perimeter and surface area optimization. J. Comput. Sci. 61 (2022)
Yaoshen Cui, Haifan Yin, Li Tan, Marco Di Renzo
A 3D Positioning-based Channel Estimation Method for RIS-aided mmWave Communications. CoRR (2022)
Zipeng Wang, Li Tan, Haifan Yin, Kai Wang, Xilong Pei, David Gesbert
A Received Power Model for Reconfigurable Intelligent Surface and Measurement-based Validations. CoRR (2021)
Li Tan, Xinyue Lv, Xiaofeng Lian, Ge Wang
YOLOv4_Drone: UAV image target detection based on an improved YOLOv4 algorithm. Comput. Electr. Eng. 93 (2021)
Li Tan, Chenggui Yuan
A note on strong convergence of implicit scheme for SDEs under local one-sided Lipschitz conditions. Int. J. Comput. Math. 98 (2) (2021)
Li Tan, Zhou Ting, Huang Zheng
The effect of organizational justice on knowledge workers' job crafting - - A chain mediation model of psychological ownership and organizational trust. ICEME (2021)
Xilong Pei, Haifan Yin, Li Tan, Lin Cao, Zhanpeng Li, Kai Wang, Kun Zhang, Emil Björnson
RIS-Aided Wireless Communications: Prototyping, Adaptive Beamforming, and Indoor/Outdoor Field Trials. IEEE Trans. Commun. 69 (12) (2021)
Li Tan, Haoyu Wang, Xiaofeng Lian, Jiaqi Shi, Minji Wang
Improved LEACH-M Protocol for Processing Outlier Nodes in Aerial Sensor Networks. IEICE Trans. Commun. (5) (2021)
Jiaqi Shi, Li Tan, Xiaofeng Lian, Xinyue Lv, Tianying Xu
Multi-UAV Task Allocation Method Based on Improved Bat Algorithm. ICAIS (1) (2021)
Li Tan, Raymond A. de Callafon, Jessica Block, Daniel Crawl, Ilkay Altintas
Improving Wildfire Simulations by Estimation of Wildfire Wind Conditions from Fire Perimeter Measurements. ICCS (5) (2021)
Zipeng Wang, Li Tan, Haifan Yin, Kai Wang, Xilong Pei, David Gesbert
A Received Power Model for Reconfigurable Intelligent Surface and Measurement-based Validations. SPAWC (2021)
Hyungro Lee, André Merzky, Li Tan, Mikhail Titov, Matteo Turilli, Dario Alfè, Agastya Bhati, Alex Brace, Austin Clyde, Peter V. Coveney, Heng Ma, Arvind Ramanathan, Rick Stevens, Anda Trifan, Hubertus Van Dam, Shunzhou Wan, Sean Wilkinson, Shantenu Jha
Scalable HPC & AI infrastructure for COVID-19 therapeutics. PASC (2021)
Francis J. Alexander, James Ang, Jenna A. Bilbrey, Jan Balewski, Tiernan Casey, Ryan Chard, Jong Choi, Sutanay Choudhury, Bert J. Debusschere, Anthony M. DeGennaro, Nikoli Dryden, J. Austin Ellis, Ian T. Foster, Cristina Garcia-Cardona, Sayan Ghosh, Peter Harrington, Yunzhi Huang, Shantenu Jha, Travis Johnston, Ai Kagawa, Ramakrishnan Kannan, Neeraj Kumar, Zhengchun Liu, Naoya Maruyama, Satoshi Matsuoka, Erin McCarthy, Jamaludin Mohd-Yusof, Peter Nugent, Yosuke Oyama, Thomas Proffen, David Pugmire, Sivasankaran Rajamanickam, Vinay Ramakrishniah, Malachi Schram, Sudip K. Seal, Ganesh Sivaraman, Christine Sweeney, Li Tan, Rajeev Thakur, Brian Van Essen, Logan T. Ward, Paul M. Welch, Michael Wolf, Sotiris S. Xantheas, Kevin G. Yager, Shinjae Yoo, Byung-Jun Yoon
Co-design Center for Exascale Machine Learning Technologies (ExaLearn). Int. J. High Perform. Comput. Appl. 35 (6) (2021)
Jiaqi Shi, Li Tan, Xiaofeng Lian, Tianying Xu, Hongtao Zhang
UAV Task Allocation Method Using Swarm Intelligence Optimization Algorithm. CWSN (2021)
Li Tan, Jie Xu, Hui Huang, Bowen Deng
Data-driven Anomaly Detection and Forewarning Based on Grey Prediction Model. EBIMCS (2021)
Li Tan, Qiongqiong Wang, Haonan Zheng, Fei Ke
Two-dimensional Steel Cutting Based on Recursive Algorithm. EBIMCS (2021)
Hyun-Myung Woo, Xiaoning Qian, Li Tan, Shantenu Jha, Francis J. Alexander, Edward R. Dougherty, Byung-Jun Yoon
Optimal Decision Making in High-Throughput Virtual Screening Pipelines. CoRR (2021)
Jing Gao, Xuan Sun, Li Tan, Zihao Ma
Rumor Detection Based on Generalized Text Feature. EITCE (2021)
Agastya P. Bhati, Shunzhou Wan, Dario Alfè, Austin R. Clyde, Mathis Bode, Li Tan, Mikhail Titov, André Merzky, Matteo Turilli, Shantenu Jha, Roger R. Highfield, Walter Rocchia, Nicola Scafuri, Sauro Succi, Dieter Kranzlmüller, Gerald Mathias, David Wifling, Yann Donon, Alberto Di Meglio, Sofia Vallecorsa, Heng Ma, Anda Trifan, Arvind Ramanathan, Tom Brettin, Alexander Partin, Fangfang Xia, Xiaotan Duan, Rick Stevens, Peter V. Coveney
Pandemic Drugs at Pandemic Speed: Accelerating COVID-19 Drug Discovery with Hybrid Machine Learning- and Physics-based Simulations on High Performance Computers. CoRR (2021)
Aymen Al Saadi, Dario Alfè, Yadu N. Babuji, Agastya Bhati, Ben Blaiszik, Alexander Brace, Thomas S. Brettin, Kyle Chard, Ryan Chard, Austin Clyde, Peter V. Coveney, Ian T. Foster, Tom Gibbs, Shantenu Jha, Kristopher Keipert, Dieter Kranzlmüller, Thorsten Kurth, Hyungro Lee, Zhuozhao Li, Heng Ma, Gerald Mathias, André Merzky, Alexander Partin, Arvind Ramanathan, Ashka Shah, Abraham C. Stern, Rick Stevens, Li Tan, Mikhail Titov, Anda Trifan, Aristeidis Tsaris, Matteo Turilli, Huub J. J. Van Dam, Shunzhou Wan, David Wifling, Junqi Yin
IMPECCABLE: Integrated Modeling PipelinE for COVID Cure by Assessing Better LEads. ICPP (2021)
Xilong Pei, Haifan Yin, Li Tan, Lin Cao, Zhanpeng Li, Kai Wang, Kun Zhang, Emil Björnson
RIS-Aided Wireless Communications: Prototyping, Adaptive Beamforming, and Indoor/Outdoor Field Trials. CoRR (2021)
Shuaibin Gao, Junhao Hu, Li Tan, Chenggui Yuan
Strong convergence rate of the truncated Euler-Maruyama method for stochastic differential delay equations with Poisson jumps. CoRR (2020)
Li Tan, Wenbin Yao, Xiaoyong Li
Expanding Training Set for Graph-Based Semi-supervised Classification. DEXA (2) (2020)
Li Tan, Xiaojiang Tang, Anbar Hussain, Haoyu Wang
A Weighted Voronoi Diagram-Based Self-Deployment Algorithm for Heterogeneous Directional Mobile Sensor Networks in Three-Dimensional Space. IEICE Trans. Commun. (5) (2020)
Hyungro Lee, André Merzky, Li Tan, Mikhail Titov, Matteo Turilli, Dario Alfè, Agastya Bhati, Alex Brace, Austin Clyde, Peter V. Coveney, Heng Ma, Arvind Ramanathan, Rick Stevens, Anda Trifan, Hubertus Van Dam, Shunzhou Wan, Sean Wilkinson, Shantenu Jha
Scalable HPC and AI Infrastructure for COVID-19 Therapeutics. CoRR (2020)
Aymen Al Saadi, Dario Alfè, Yadu N. Babuji, Agastya Bhati, Ben Blaiszik, Thomas S. Brettin, Kyle Chard, Ryan Chard, Peter V. Coveney, Anda Trifan, Alex Brace, Austin Clyde, Ian T. Foster, Tom Gibbs, Shantenu Jha, Kristopher Keipert, Thorsten Kurth, Dieter Kranzlmüller, Hyungro Lee, Zhuozhao Li, Heng Ma, André Merzky, Gerald Mathias, Alexander Partin, Junqi Yin, Arvind Ramanathan, Ashka Shah, Abraham C. Stern, Rick Stevens, Li Tan, Mikhail Titov, Aristeidis Tsaris, Matteo Turilli, Huub J. J. Van Dam, Shunzhou Wan, David Wifling
IMPECCABLE: Integrated Modeling PipelinE for COVID Cure by Assessing Better LEads. CoRR (2020)
Yanyan Song, Li Tan, Lina Zhou, Xinyue Lv, Zihao Ma
Video Action Recognition Based on Hybrid Convolutional Network. ICAIS (2) (2020)
Abhishek Subramanian, Li Tan, Raymond A. de Callafon, Daniel Crawl, Ilkay Altintas
Recursive Updates of Wildfire Perimeters Using Barrier Points and Ensemble Kalman Filtering. ICCS (6) (2020)
Li Tan, Yanyan Song, Zihao Ma, Xinyue Lv, Xu Dong
Deep Learning Video Action Recognition Method Based on Key Frame Algorithm. ICAIS (1) (2020)
Li Tan, Zhongcai Li, Gang Su, Desheng Wang
Asymptotically Linear Analysis and Gate Probability Allocation Schemes in Probabilistic Circuits. IEEE Trans. Very Large Scale Integr. Syst. 28 (2) (2020)
Yi Xu, Shanglin Yang, Wei Sun, Li Tan, Hui Zhou
Virtual Garment Using Joint Landmark Prediction and Part Segmentation. VR (2019)
Li Tan, Minji Wang, Haoyu Wang, Li Liu
Improved LEACH-M Protocol for Aerial Sensor Networks. CITS (2019)
Li Tan, Marc Charest, Nathan DeBardeleben, Qiang Guan, Ben Bergen
Soft Error Resilience and Failure Recovery for Continuum Dynamics Applications. CoRR (2019)
Yangsheng Hu, Li Tan, Raymond A. de Callafon
Persistent Excitation Condition for MIMO Volterra System Identification with Gaussian Distributed Input Signals. CDC (2019)
Yi Xu, Shanglin Yang, Wei Sun, Li Tan, Kefeng Li, Hui Zhou
3D Virtual Garment Modeling from RGB Images. CoRR (2019)
Li Tan, Minji Wang, Haoyu Wang, Li Liu
ME-CCHP: Copy Cluster Head Routing Protocol Based on Maximum Energy. ICCT (2019)
Li Tan, Nathan DeBardeleben
Failure Analysis and Quantification for Contemporary and Future Supercomputers. CoRR (2019)
Yi Xu, Shanglin Yang, Wei Sun, Li Tan, Kefeng Li, Hui Zhou
3D Virtual Garment Modeling from RGB Images. ISMAR (2019)
Li Tan, Wenfeng Luo, Meng Yang
Weakly-Supervised Semantic Segmentation with Mean Teacher Learning. IScIDE (1) (2019)
Li Tan, Chaoyu Yang, Minghua Yang, Xiaojiang Tang
Path self-deployment algorithm of three-dimensional space in directional sensor networks. Int. J. High Perform. Comput. Netw. 14 (3) (2019)
Xiaojiang Tang, Li Tan, Anbar Hussain, Minji Wang
Three-dimensional Voronoi Diagram-based Self-deployment Algorithm in IoT Sensor Networks. Ann. des Télécommunications 74 (7-8) (2019)
Li Tan, Xiaojiang Tang, Minghua Yang, Haoyu Wang
A Weighted Voronoi Diagram Based Self-deployment Algorithm for Heterogeneous Mobile Sensor Network in Three-Dimensional Space. CWSN (2019)
Jianqiang Hao, Jianzhi Sun, Yi Chen, Qiang Cai, Li Tan
Optimal Reliable Point-in-Polygon Test and Differential Coding Boolean Operations on Polygons. Symmetry 10 (10) (2018)
Li Tan, Nathan DeBardeleben, Qiang Guan, Sean Blanchard, Michael Lang
Using virtualization to quantify power conservation via near-threshold voltage reduction for inherently resilient applications. Parallel Comput. 73 (2018)
Li Tan, Chenggui Yuan
Strong convergence of a tamed theta scheme for NSDDEs with one-sided Lipschitz drift. Appl. Math. Comput. 338 (2018)
Vinith Vijavarajan, Jingzhao Dai, Li Tan, Jean Jiang
Channel Sparsity-Aware Diagonal Structure Volterra Filters for Nonlinear Acoustic Echo Cancellation. EIT (2018)
Lu Feng, Gang Su, Niyonsaba Alexandre, Li Tan
Inter-cell Interference Coordination in LTE Self Organizing Network. IntelliSys (2) (2018)
Jean Jiang, Roger Brewer, Ryan Jakubowski, Li Tan
Development of a Piano Frequency Detecting System Using the Goertzel Algorithm. EIT (2018)
Jingzhao Dai, Vinith Vijayarajan, Xuan Peng, Li Tan, Jean Jiang
Speech Recognition Using Sparse Discrete Wavelet Decomposition Feature Extraction. EIT (2018)
Li Tan, Xu Dong, Yuxi Ma, Chongchong Yu
A Multiple Object Tracking Algorithm Based on YOLO Detection. CISP-BMEI (2018)
Xinnian Guo, Yang Li, Jean Jiang, Chen Dong, Sidan Du, Li Tan
Sparse Modeling of Nonlinear Secondary Path for Nonlinear Active Noise Control. IEEE Trans. Instrum. Meas. 67 (3) (2018)
Liandeng Li, Teng Yu, Wenlai Zhao, Haohuan Fu, Chenyu Wang, Li Tan, Guangwen Yang, John Thomson
for heterogeneous many-core supercomputers. SC (2018)
Li Tan
Almost sure convergence rate of θ-EM scheme for neutral SDDEs. J. Comput. Appl. Math. 342 (2018)
Run Wen, Li Tan
结合HS算法与ESN算法的光伏发电短期出力预测 (Short-term Power Forecasting for Photovoltaic Generation Based on HS-ESN). 计算机科学 44 (6) (2017)
Li Tan, Yucheng Chen, Minghua Yang, Jipeng Hu, Jingjing Lian
Connecting priority algorithm for node deployment in directional sensor networks. Int. J. Grid Util. Comput. 8 (1) (2017)
Nicholas Chimitt, William Misch, Li Tan, Alain Togbé, Jean Jiang
Comparative study of simple feature extraction for single-channel EEG based classification. EIT (2017)
Jean Jiang, Dillon Seniff, David Callahan, Li Tan, Yoonill Lee
Development of a radiation detecting rover system. UEMCON (2017)
Gang Su, Ya Xu, Li Tan, Lu Feng
A novel dynamic clustering strategy on energy efficiency for dense network deployment. ICNC-FSKD (2017)
Jean Jiang, Alex McCoy, Eric Lee, Li Tan
Development of a motion controlled robotic arm. UEMCON (2017)
Li Tan, Jifeng Sun
Reference-free compression of next-generation sequencing data in FASTQ format. CIBCB (2017)
Li Tan, Vinith Vijayarajan, Nicholas M. Chimitt, Jean Jiang, Alain Togbé
Channel sparsity-aware recursive least squares algorithms for nonlinear system modeling and active noise control. UEMCON (2017)
Li Tan, Chaoyu Yang, Minghua Yang, Xiaojiang Tang
Path Self-Deployment Algorithm of Three-Dimensional Space in Directional Sensor Networks. CSE/EUC (1) (2017)
Li Tan, Nathan DeBardeleben, Qiang Guan, Sean Blanchard, Michael Lang
RSVP: Soft Error Resilient Power Savings at Near-Threshold Voltage Using Register Vulnerability. DSN Workshops (2017)
Jianqiang Hao, Yunzhan Gong, Yawen Wang, Li Tan, Jianzhi Sun
-Mix-Neighborhood Subdigraphs to Compute Canonical Labelings of Digraphs. Entropy 19 (2) (2017)
Li Tan, Chaoyu Yang, Xiaojiang Tang, Yaoyao Jiao
A Target Tracking Algorithm Based on Path Virtual Force. CSE/EUC (1) (2017)
Wei Jin, Li Tan
Finite two-distance-transitive graphs of valency 6. Ars Math. Contemp. 11 (1) (2016)
Jieyang Chen, Li Tan, Panruo Wu, Dingwen Tao, Hongbo Li, Xin Liang, Sihuan Li, Rong Ge, Laxmi N. Bhuyan, Zizhong Chen
GreenLA: green linear algebra software for GPU-accelerated heterogeneous computing. SC (2016)
Li Tan, Hongfei Hou, Qin Zhang
An Extensible Software Platform for Cloud-Based Decision Support and Automation in Precision Agriculture. IRI (2016)
Yiannis Ampatzidis, Li Tan, Ronald Haley, Matthew D. Whiting
Cloud-based harvest management information system for hand-harvested specialty crops. Comput. Electron. Agric. 122 (2016)
Li Tan, Zhongcai Li, Chao Xu, Desheng Wang
Partly random multiple weighting matrices selection for orthogonal random beamforming. J. Commun. Networks 18 (6) (2016)
Qiang Guan, Nathan DeBardeleben, Panruo Wu, Stephan J. Eidenbenz, Sean Blanchard, Laura Monroe, Elisabeth Baseman, Li Tan
Design, Use and Evaluation of P-FSEFI: A Parallel Soft Error Fault Injection Framework for Emulating Soft Errors in Parallel Applications. SimuTools (2016)
Chen Dong, Li Tan, Xinnian Guo, Sidan Du
Efficient adaptive bilinear filters for nonlinear active noise control. ICSPCS (2016)

Li Tan.css-eqlu8i{font-size:small;padding-left:4px;}

Publication Activity (10 Years)

Top Topics

Top Venues

Li Tan