CSEE Journal of Power and Energy Systems

Article	Citations
Composite braking control strategy of a novel electromechanical-hydraulic coupling driving electric vehicle	36
Grid voltage sensor-less protection scheme for one cycle-controlled single-phase photovoltaic inverter systems	35
Self-Sustaining of Critical Park Microgrids Integrating Mobile Emergency Generators Subjective to Major Outage	34
Voltage Support Capacity Improvement for Wind Farms with Reactive Power Substitution Control	33
Assessment and Enhancement of FRC of Power Systems Considering Thermal Power Dynamic Conditions	29
Integrated Optimization Planning of Multiple Energy Stations for Low Carbon Operation	28
Modeling and Stability Analysis of Meshed Smart Transformer-Fed Grid	25
Physical Mechanism Enabled Neural Network for Power System Dynamic Security Assessment	18
Effect of Frequency on Degradation in BOPP Films Under Repetitively Pulsed Voltage	18
Converters' loading balance and stability verification for doubly-fed induction generator	17
High Power Density EV Integrated Fast Battery Chargers Based on the General Torque Cancelation Law for Three-Phase Motors	17
System Strength Assessment Based on Multi-task Learning	17
Optimal Distributed Dispatch of Smart Multi-Agent Energy Hubs Based on Consensus Algorithm Considering Lossy Communication Network and Uncertainty	16
Electricity-Heat-Based Integrated Demand Response Considering Double Auction Energy Market with Multi-Energy Storage for Interconnected Areas	16
An incidence matrix based analytical method of N-1 contingency parallel analysis of main transformers in distribution networks	16
Transactive energy and flexibility provision in multi-microgrids using Stackelberg game	15
Data-driven transient stability assessment with sparse PMU sampling and online self-check function	15
Improving Operational Flexibility of Integrated Energy Systems Through Operating Conditions Optimization of CHP Units	14
Data-Driven Predictive Voltage Control for Distributed Energy Storage in Active Distribution Networks	14
The On-site Verification of Key Technologies for Kunbei-Liuzhou-Longmen Hybrid Multi-terminal Ultra HVDC Project	13
Transient Stability Analysis of Large-scale Power Systems: A Survey	13
Imbalance correction method based on ratio of loss function values for transient stability assessment	12
Optimal dispatch with flexible uncertainty set for multi-energy systems: An IGDT based two-stage decision framework	11
Robust Expansion Planning of Electric Vehicle Charging System and Distribution Networks	11
Impacts of COVID-19 Pandemic on Italian Electricity Demand and Markets	11

Frequency-Voltage Active Support Strategy for Hybrid Wind Farms Based on Grid-Following and Grid-Forming Hierarchical Subgroup Control	10
Robust N-k security-constrained optimal power flow incorporating preventive and corrective generation dispatch to improve power system reliability	10
Control Scheme of Spread Frequency Band for High Power Impedance Measuring Converter with Chirp Signal Injection	9
Planning Model for Energy Routers Considering Peer-to-Peer Energy Transactions Among Multiple Distribution Networks	9
An Edge Visual Incremental Perception Framework Based on Deep Semi-supervised Learning for Monitoring Power Transmission Lines	9
Large-Signal Stability Analysis of a Modular Multilevel Converter Based on Mixed Potential Theory	9
Unscented Particle Filter Algorithm Towards Data Quality Improvement in Sustainable Distribution Power Systems	9
Multi-timescale Energy Sharing with Grid-BESS Capacity Rental Considering Uncertainties	9
Modeling, Oscillation Analysis and Distributed Stabilization Control of Autonomous PV-based Microgrids	9
Improved Multi-Grained Cascade Forest Model for Transformer Fault Diagnosis	9
Improved Discontinuous SVM Based Fault-Tolerant Control of AC/DC Converter for All-DC Offshore Wind Power System	9
Power synchronization of smart transformers allowing universal operation in radial and meshed grids	8
An Efficient Method to Estimate Admittance of Black-boxed Inverter-based Resources for Varying Operating Points	8
Reinforcement Learning-Empowered Graph Convolutional Network Framework for Data Integrity Attack Detection in Cyber-Physical Systems	8
Optimal configuration of multitype energy storage for integrated energy system considering the system reserve value	8
Skeleton-based violation action recognition method for safety supervision in the operation field of distribution network based on graph convolutional network	8
Market-based coordination of regional electric and natural gas systems: A peer-to-peer energy trading model	8
Confidence Estimation Transformer for Long-Term Renewable Energy Forecasting in Reinforcement Learning-based Power Grid Dispatching	8
Coordinated frequency control for isolated power systems with high penetration of DFIG-based wind power	8
Optimized operation of micro-energy grids considering the shared energy storage systems and balanced profit allocation	8
Optimal Time-of-use Pricing for Renewable Energy-powered Microgrids: A Multi-agent Evolutionary Game Theory-based Approach	8
Influence of repetitive impulse waveform on surface discharge characteristics and insulation life for polyimide film	8
Reliability Assessment for Integrated Power-gas Systems Considering Renewable Energy Uncertainty and Cascading Effects	8
Neural Network Based Fea sible Region Approximation Model for Optimal Operation of Integrated Electricity and Heating System	8
Synergistic Promotion of Electrical, Mechanical and Thermal Properties for Silicone Rubber-based Field Grading Material via Compound Modification	8
Event-based Two-stage Non-intrusive Load Monitoring Method Involving Multi-dimensional Features	7
DG Hosting Capacity Assessment Considering Dependence Among Wind Speed, Solar Radiation, and Load Demands	7
High Step-up SEPIC Converters Based on a Family of Coat Circuit	7
Pricing Binary Variables of System-Wide Constraints for Power System Optimization	7
A Delay-dependent Dynamic Wide Area Damping Controller for Renewable Energy Integrated Power System Resilient to Communication Failure	7
Model-Free Optimal Volt-VAR Control of Wind Farm Based on Data-Driven Lift-Dimension Linear Power Flow	7
Non-convexity Pricing and Allocating Costs in Stochastic Electricity Markets	7
Reference-input-based imaginary axis current estimation method for DQ control strategy of single-phase PWM converters	7
Hybrid bidirectional DC/DC converter: Mutual control and stability analysis	7
Research advances of bubbles dynamics in power transformer	6
Blockchain-Enabled Robust-Game Electricity Transaction Model for a Multi-Microgrid System Considering Wind Power Uncertainty	6
Overvoltage Calculation Method for Sending System Under DC Fault Disturbance Considering the Influence of Renewable Energy	6
Tube Model Predictive Control Based Cyber-Attack-Resilient Optimal Voltage Control Strategy in Wind Farms	6
Energy management of solid oxide fuel cell/lithium battery hybrid system	6
Physics insight of the inertia of power system and methods to provide inertial response	6
Integrated Planning of Charging Piles and Battery Swapping Stations Considering Spatiotemporal Distribution of Electric Vehicles	6
Influence of Parasitic Parameters on Dynamic Threshold Voltage Hysteresis of Silicon Carbide MOSFETs	6
Risk-averse two-stage distributionally robust economic dispatch model under uncertain renewable energy	6
Enhanced Transient Stability Strategy for Grid-Forming Converter Based on Current Limiting	6
Battery Storage Configuration of AC/DC Hybrid Distribution Networks	6
Complete Protection Strategy for Loss of Excitation in Large-Scale Synchronous Condensers Applied to UHVDC Transmission	6
Data-driven Based Uncertainty Set Modeling Method for Microgrid Robust Optimization with Correlated Wind Power	5
Direction Protection Based on Time-domain Travelling Wave for Flexible MTDC Grid	5
A currentless multiple switch open-circuit faults diagnosis strategy for modular multilevel converter with nearest level modulation in HVDC system	5
Thyristor-Inserted MMC Sub-Module Topology with DC Fault Blocking Capability	5

A novel dynamic additional frequency control strategy for VSC-MTDC system	5
An Improved DGA Feature Clustering-Based Method for Transformer Fault Diagnosis	5
A modular multilevel converter with wireless magnetic power decoupling approach for three-phase MV adjustable-speed drives	5
Extension of Distribution Transformer Life in the Presence of Smart Inverter-based Distributed Solar Photovoltaic Systems	5
Power System Reliability Assessment with Quantification of Demand Response Uncertainty Based on Advanced Sigmoid Cloud Model	5
Model Predictive Current Control for Low-Cost Shunt Active Power Filter	5
Time-domain protection for collector lines in large-scale wind farms based on random matrix theory	5
Renewable energy penetration fostered using a reversible solid oxide cell installed in an office, school, and hotel	5
Edge Intelligence for Smart Grid: A Survey on Application Potentials	5
Demonstrating the Transient System Impact of Cyber-Physical Events Through Scalable Transmission and Distribution (T&D) Co-Simulation	4
Convexification of Hybrid AC-DC Optimal Power Flow with Line-Commutated Converters	4
Interface Finite Volume Method with Low Calculating Amount for Step Size Varying Electro-Quasistatic Field Problem	4
Delay-dependent wide-area damping controller synthesis approach using Jensen's inequality and evolution algorithm	4
P2P Energy Trading Considering Prosumer Preference and System Risk	4
Analysis of China's Electricity Price and Electricity Burden of Basic Industries Under the Carbon Peak Target Before 2030	4
Real-time Power Flow Control Strategy for Electric Railway FTSSs Integrated with PVs and ESSs	4
An adaptive and sustainable distribution system islanding strategy for post-restoration failures	4
Accurate Distinction of Weak and Strong AC Grids for Emerging Hierarchical-Infeed LCC-UHVDC Systems	4
High Efficient Design of a Reconfigurable Step-Up DC-DC Converter with Fault-Tolerant Capability	4
Comprehensive transient stability enhancement control of a VSG considering power angle stability and fault current limitation	4
Control and Stability of Large-scale Power System with Highly Distributed Renewable Energy Generation: Viewpoints from Six Aspects	4
Dispatchable Region for Active Distribution Networks Using Approximate Second-Order Cone Relaxation	4
Data-driven detection and identification of line parameters with PMU and unsynchronized SCADA measurements in distribution grids	4
Improving the Performance of DC Microgrids by Utilizing Adaptive Takagi-Sugeno Model Predictive Control	4
Correction of Time-varying PMU Phase Angle Deviation with Unknown Transmission Line Parameters	4
Design of Double-Loop Current Transformer Based on Magnetic Field Incomplete Cancellation	4
Optimal Secondary Control of Islanded AC Microgrids with Communication Time-delay Based on Multi-agent Deep Reinforcement Learning	4
Mixed-Integer Linear Programming Based Distribution Network Reconfiguration Model Considering Reliability Enhancement	4
Relationships of internal voltage dependence on power imbalance illustrating characteristics and roles in system dynamics of inertial-controlled DFIG-based wind turbines	4
Efficient calculation and component analysis of fault current in MMC-HVDC grid	3
Coordinated planning of fast charging station and distribution network based on an improved flow capture location model	3
Analytic Formulae for Estimating Motor Proportion of Load Model Under Small Disturbance	3
Risk-based Two-stage Optimal Scheduling of Energy Storage System with Second-life Battery Units	3
Incorporating optimal operation strategies into investment planning for wind/electrolyser system	3
A model and data hybrid driven approach for quantifying the meteorology-dependent demand flexibility of building thermal loads	3
A Hybrid Signal Processing Method Combining Mathematical Morphology and Walsh Theory for Power Quality Disturbance Detection and Classification	3
Single-stage Five-level Common Ground Transformerless Inverter with Extendable Structure for Centralized Photovoltaics	3
Mechanism analysis of additional damping control strategies for the high-frequency resonance of MMC connected to AC grid	3
Coordinated Suppression Method of Fault Current for DC Grid with Novel Dissipative Resistors Topology	3
A time-delay correction control strategy for HVDC frequency regulation service	3
Novel Control Method for the MMC Connected to Wind Farms	3
Data center power system stability — part II: System modeling and analysis	3
Robust forecasting-aided state estimation considering uncertainty in distribution system	3
A new incentive scheme to incentivize flexible customers for phase balancing	3
Online Monitoring Method for Junction Temperature of SiC MOSFETs based on Temperature Sensitive Electrical Parameter	3
A successive MISOCP algorithm for islanded distribution networks with soft open points	3
Resilient Smart Power Grid Synchronization Estimation Method for System Resilience with Partial Missing Measurements	3
Intelligent breakage assessment of composite insulator on overhead transmission line by ellipse detection based on IRHT	3
A compact real-time simulator with spatial-temporal parallel design for large-scale wind farms	3
Switching Behavior of Cascode GaN Under Influence of Gate Driver	3
A method to quantify the logical node importance for IEC 61850 based substation automation system	3
Interaction Quantification of MTDC Systems Connected with Weak AC Grids	3
Data-Driven Fault Detection of Multiple Open-Circuit Faults for MMC Systems Based on Long Short-Term Memory Networks	3
Enabling Inverter-based Resource Stability Control in Power Systems with High Renewable Penetration	3
Simplified Cluster Voltage Balancing Control Based on Zero-Sequence Voltage Injection for Star-Connected Cascaded H-Bridge STATCOM	3
Adaptive Emergency Control of Power Systems Based on Deep Belief Network	3
Energy planning of Beijing towards low-carbon, clean and efficient development in 2035	3
Optimal Operation Strategy for Rural Microgrid Considering Greenhouse Load Control	3
Power grid fault diagnosis based on a deep pyramid convolutional neural network	3
A Novel Harmonic State-space Modelling Method on the Modular Multilevel Matrix Converter and Coupling Analysis	3
Collaborative Fault Recovery and Network Reconstruction Method for Cyber-physical-systems Based on Double Layer Optimization	3
Joint Planning of Active Distribution Network and EV Charging Stations Considering Vehicle-to-Grid Functionality and Reactive Power Support	3
Extreme Scenarios Based Data-Adaptive Probability Uncertainty Set for Distributionally Robust Transmission Expansion Planning	3
Electricity Pricing with Continuous-time Commodity Model and Non-monotonic Load Curve	3
A novel protection scheme for MMC-MTDC transmission lines based on fault coefficient	3
Circulating Current Suppression and Current Sharing Strategy for Parallel IPT System Based on d-q Synchronous Rotating Frame	3
Communication Resources Allocation for Time Delay Reduction of Frequency Regulation Service in High Renewable Penetrated Power System	2
Constraint Learning-based Optimal Power Dispatch for Active Distribution Networks with Extremely Imbalanced Data	2
Operating-Point Identification from Dimensions of Alternating Signal Based on Incremental Iterative Mapping Mechanism for Analyzing Dynamics of AC Systems	2
Achieving an Accurate Random Process Model for PV Power Using Cheap Data: Leveraging the SDE and Public Weather Reports	2
A two-stage planning method of the energy router considering the optimal operation in distribution network	2
Surface Charge Accumulation Characteristics on DC GIL Three-post Insulators Considering the Influence of Temperature Gradient	2
Improved MPPT Control Strategy for PV Connected to Grid Using IncCond-PSO-MPC Approach	2
Detection Method for Cascading Failure of Power Systems Based on Epidemic Model	2
Planning of DC Electric Spring with Particle Swarm Optimization and Elitist Non-Dominated Sorting Genetic Algorithm	2
Novel Planning Approach for Fast-charging Station in Integrated System	2
Identification of the Worst-Case Static Voltage Stability Margin Interval of AC/DC Power System Considering Uncertainty of Renewables	2
Hybrid Physics and Data-driven Contingency Filtering for Security Operation of Micro Energy-water Nexus	2
Exploring the Potential of IoT-Blockchain Integration Technology for Energy Community Trading: Opportunities, Benefits, and Challenges	2
Energy savings estimation of a distribution system in presence of intelligent volt-VAr control based on IEEE Std. 1547-2018	2

Dynamic equivalent modeling for black-box microgrid under multi-operating-point by using LSTM	2
Distributed event-triggered control for frequency restoration in islanded microgrids with reduced trigger condition checking	2
A Two-Step Approach for Multi-Topology Identification and Parameter Estimation of Power Distribution Networks	2
Non-isolated Step-up DC-DC Converter Based on Switched Capacitor Cells	2
Adaptive Early Warning Method of Cascading Failures Caused by Coordinated Cyber-Attacks	2
Pressure-dependent thermal network for press-pack power module with prognostics of mechanical status	2
Adaptive Mitigation Control for Wideband Oscillations of Offshore Wind Farms With MMC-HVDC System	2
Forecasting of global solar insolation using ensemble Kalman filter based clearness index model	2
Cascaded Sliding-Mode Observer for High-Order Systems with Lower-Triangular Structure	2
Metal-Free Optical Pressure Sensor with High Sensitivity and Extensive Range	2
Design of Robust Var Reserve Contract for Enhancing Reactive Power Ancillary Service Market Efficiency	2
Very Short-Term Forecasting of Distributed PV Power Using GSTANN	2
Robust load frequency control for isolated microgrid based on double-loop compensation	2
Zero-Phase CARIMA Filtering and Application in Wind-Storage System Sizing and Power Dispatch Optimization	2
Data-Driven Approach for Analyzing and Correlating Energy Market Products: Case Studies of Denmark and Croatia	2
Specific Position and Influence of Moisture in Newly-Installed Composite Insulators	2
A residue based open-loop modal analysis method for detecting LFMR of PMSG-WFs penetrated power systems	2
Optical Sensor with Wide Range and High Sensitivity for Internal Magnetic Field Detection of Transformer	2
Grid Forming H∞ Control for HVDC Diode Rectifier-connected Wind Power Plants	2
CVaR-based reserve optimization for isolated multi-energy complementary generation system in mixed time scale	2
Microgrid Energy Management: Classification, Review and Challenges	2
Stochastic Flexibility Evaluation for Virtual Power Plants by Aggregating Distributed Energy Resources	2
Stability Improvement Method for Multi-Converter Distribution Systems Based on Impedance Sensitivity	2
Discharge characteristics of bubbles at the interface between AlN ceramic and FC-72 liquid	2
Energy Management of Price-Maker Community Energy Storage by Stochastic Dynamic Programming	2
Composite Converter Combined APFC with Switched-capacitor Converter	2
Transient Stability Analysis and Design of VSGs with Different DC-Link Voltage Controllers	2
Stochastic and distributed optimal energy management of active distribution network with integrated office buildings	2
Insulation Properties and Degradation Mechanism for XLPE Subjected to Different Aging Periods	2
Graph computing and its application in power grid analysis	2
Understanding of DC partial discharge: Recent progress, challenges, and outlooks	2
Filler Size Effect on Tuning Electrical, Mechanical, and Thermal Properties of Field Grading Composites	2
Simulation Analysis of DC Fault Interruption Characteristics of Superconducting Electric Aircraft Propulsion	2
Cooperative Electricity-Hydrogen Trading Model for Optimizing Low-Carbon Travel Using Nash Bargaining Theory	2
Microgrid Energy Management with Energy Storage Systems: A Review	2
Development of Mixed Insulation Oil as Alternative Liquid Dielectric: A Review	2
Multi-stage Defender-Attacker-Defender Model for Distribution System Resilience Enhancement in Ice Storms with Line Hardening, Mobile Device and Repair Crew Dispatching	2
Data-driven Static Equivalence with Physics-informed Koopman Operators	2
Real-time Energy Management of Low-carbon Ship Microgrid Based on Data-driven Stochastic Model Predictive Control	1
Partial Solution Operator Discretization-Based Methods for Efficiently Computing Least-Damped Eigenvalues of Large Time Delayed Power Systems	1
Multi-Time Interval Forecasting-Aided State Estimation Incorporating Phasor Measurements for Power Systems with Renewable Energy Sources	1
Economy Analysis of Flexible LCC-HVDC Systems with Controllable Capacitors	1
A finite element method for the transient electric field by using indirect Laplace transform with high accuracy	1
Assessment Method of Offshore Wind Resource Based on Multi-dimensional Indexes System	1
New-Type Power System Stabilizers (NPSS) for Damping Wideband Oscillations in Converter-Dominated Power Systems	1
Mode-varying Cell Equalizer Based on Interleaved Parallel Multiple Transformers	1
Stochastic Economic Dispatch Based Optimal Market Clearing Strategy Considering Flexible Ramping Products Under Wind Power Uncertainties	1
A cyber-physical test case for distribution grid operation and control	1
Interface Finite Element Method with Lower Calculation Amount for Step Size-varying Electro-quasistatic Field Problem	1
Characteristics of Bi-2223 HTS tapes under short-circuit current impacts in hybrid energy transmission pipeline	1
Design Considerations on Voltage and Current Transfer Ratio of High-Frequency Transformers	1
Optimal Dispatch and Pricing of Industrial Parks Considering CHP Mode Switching and Demand Response	1
Hybrid AC/DC Collection and HVDC Transmission Topology for Large-scale Offshore Wind Farms	1
Impact of Frequency Anti-windup Limiter on Synchronization Stability of Grid Feeding Converter	1
Inertial PLL of grid-connected converter for fast frequency support	1
Interval Economic Dispatch for Commercial Campus Integrated Energy System with Demand Response Considering Multiple Uncertainties	1
Conjugate Vectors Method Applied to Asymmetrical Fault Analysis of Power Electronized Power Systems	1
Networked Protection Scheme with Feeding Section as a Unit for High-speed Railway Traction Power Supply System	1
Optimal Power Flow Based on Branch Flow Model for Bipolar DC Distribution Networks	1
Advanced System-Level Model Reduction Method for Multi-Converter DC Power Systems	1
Multifunctional bidirectional charging system for EVs and the grid with improved power quality using sparse proportionate-NLMF based method	1
Distributionally Robust Optimal Dispatch of Offshore Wind Farm Cluster Connected by VSC-MTDC Considering Wind Speed Correlation	1
Integrated Model for Resilience Evaluation of Power-Gas Systems Under Windstorms	1
Optimal Allocation Strategy for Electric EPSVs and Hydrogen Fuel Cell EPSVs Balancing Resilience and Economics	1
Intelligent Predetermination of Generator Tripping Scheme: Knowledge Fusion-based Deep Reinforcement Learning Framework	1
CFD analysis of an 800 kV HVDC transformer with the rapeseed oil as cooling fluid	1
Day-ahead complementary operation for wind-hydro-thermal system considering the multi-dimensional uncertainty	1
A Survey on Model Predictive Control of DFIGs in Wind Energy Conversion Systems	1
Reweighted L0 norm variable step size continuous mixed p-norm control scheme for mitigating power quality problems of grid coupled solar PV system	1
Optimal Over-Frequency Droop Control for DFIG-Based Wind Farms Under Unreliable Communication	1
Community-detection-based approach to distribution network partition	1
The impact of electric field treatment on nonlinear conductivity of tetra-needle-shaped ZnO whisker/carbon fiber/liquid silicone rubber composites	1
Detection in Optical Remote Sensing Images of Transmission Tower Based on Oriented Object Detection	1
Impact of Dead-Time on Resonance in Doubly Fed Induction Generator Under Weak Grid	1
Texas electric power crisis 2021 warns of a new mode of blackout	1
New Hybrid Model of Power Transformer Fault Classification using C-Set & MFCM — MCSVM	1
Research on a Multiport Parallel Type Hybrid Circuit Breaker for HVDC Grids: Modeling and Design	1
Open-loop Phase Synchronization Method of Positive and Negative Sequences for Three-phase Asymmetric Grid	1
Multifactor-Influenced Reliability-Constrained Reserve Expansion of Integrated Electricity-Gas Systems Considering Failure Propagation	1
Transient Characteristics and Accommodative Current Limiting Strategy for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids	1
Credibility Copula-Based Robust Multistage Plan for Industrial Parks Under Exogenous and Endogenous Uncertainties	1
Data center power system stability — part I: Power supply impedance modeling	1
A high impedance fault detection method based on novel attention mechanism and object detection	1
Modified Dynamic Model and Small-signal Stability Analysis for LCC- HVDC Systems	1
Connections between induction generator effect and open-loop modal proximity to cause sub-synchronous oscillations in a series-compensated power system	1
Self-correction sensor for measuring medium DC voltage based on resistance voltage divider	1
Capacity Allocation of Renewable Energy Sources Considering Complementarity	1
Stochastic accelerated alternating direction method of multipliers for hedging communication noise in combined heat and power dispatch	1
Many-objective Optimization Method Based on Dimension Reduction for Operation of Large-scale Cooling Energy Systems	1
Demand Response Management with Latency Difference in Distributed Wireless Network	1
Resilient Power Systems Operation with Offshore Wind Farms and Cloud Data Centers	1
Review of Networked Microgrid Protection: Architectures, Challenges, Solutions, and Future Trends	1
Electrical Tracking, Erosion and Fire Retardancy Performance of Silicone Rubber Insulation Containing Aluminum Trihydrate, Graphene and Glass Fiber Additives	1
Improved Control Strategy of Current-Source Converter for HVDC System	1
Distributionally Robust Chance-Constrained Optimization for Soft Open Points Operation in Active Distribution Networks	1