Interdisciplinary Research Center for Sustainable Energy Systems

Research output

Research output per year 1981 2019 2020 2021 2022 2023 2024 2025

• 105671 Citations
• 136 h-index
• 3134 Article
• 585 Conference contribution
• 261 Review article
• 173 Chapter
• 286 More
  • 96 Patent
  • 66 Conference article
  • 43 Comment/debate
  • 28 Paper
  • 26 Editorial
  • 21 Book
  • 4 Foreword/postscript
  • 1 Letter
  • 1 Short survey

Research output per year

Research output per year

Search results

• 2024

  DESALINATION SYSTEM OF SWEEPING GAS MEMBRANE DISTILLATION COMBINED WITH JET IMPINGEMENT CONDENSATION

  Abualkhair, M., Khalifa, A. & Alshehri, A., 2024, In: Proceedings of the Thermal and Fluids Engineering Summer Conference. p. 647-656 10 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Desalination System 100%
  • Sweeping Gas Membrane Distillation 100%
  • Condenser 83%
  • Thermal Energy 33%
  • Permeate Flux 33%

• Developing a Multipurpose Battery Swapping Station to Energize Mobile and Stationary Loads

  Gull, M. S., Rauf, H., Arshad, N. & Khalid, M., 2024, In: Energy Proceedings. 45

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Battery Swapping Station 100%
  • Electric Vehicle 100%
  • Battery (Electrochemical Energy Engineering) 75%
  • Peak Hour 50%
  • Degradation Process 25%

• Evaluation on the impact behavior of stir-casted Aluminum composites reinforced with SiC and Gr for lightweight applications

  Alam, M. A., Ya, H. H., Gerewal, L., Azeem, M., Masood, F., Yusuf, M., Ahmad, T., Khan, M. R. & Shozib, I. A., 2024, In: Journal of Physics: Conference Series. 2688, 1, 012004.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Aluminum Composite 100%
  • Silicon Carbide 100%
  • Aluminum 100%
  • Impact Strength 85%
  • Materials 42%

• Investigation of Thermoacoustic Instability for Swirling Flames in a Dual Annular Stratified Burner

  Mokheimer, E. M. A., Talal, Q., Shakeel, M. R. & Abubakar, Z., 2024, In: Energy Proceedings. 40

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Thermoacoustic Instability 100%
  • Equivalence Ratio 57%
  • Peak Amplitude 14%
  • Reynolds' Number 14%
  • Heat Release 14%

• MACHINE LEARNING STUDY OF THERMAL MANAGEMENT OF A BATTERY PACK IN A CONVERGED CHANNEL

  Saeed, A., Munteshari, O. & Alshehri, A., 2024, In: Proceedings of the Thermal and Fluids Engineering Summer Conference. p. 1279-1289 11 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Battery Pack 100%
  • Battery (Electrochemical Energy Engineering) 100%
  • Learning System 100%
  • Battery Thermal Management System 75%
  • Gaussians 75%

• Multi-objective optimization for an active air-cooling thermal management system

  Soultan, M. & Munteshari, O., 2024, In: Proceedings of the Thermal and Fluids Engineering Summer Conference. p. 1375-1384 10 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Cooling Air 100%
  • Multiobjective Optimization 100%
  • Battery Pack 100%
  • Control Parameter 66%
  • Genetic Algorithm 66%

• Optimizing Photovoltaic and Battery Integration for RO Desalination Using Differential Evolution Algorithm

  Qudah, A., Al-Merbati, A. S. & Mokheimer, E. M. A., 2024, In: Energy Proceedings. 43

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Desalination 100%
  • Photovoltaics 100%
  • Battery (Electrochemical Energy Engineering) 100%
  • Reverse Osmosis 100%
  • Seawater 25%

• Performance Analysis of a Counter-flow Cooling Tower Under Different Weather Conditions

  Hasan, A. M. A. & Mokheimer, E. M. A., 2024, In: Energy Proceedings. 41

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Counter-Flow Cooling Tower 100%

• PERFORMANCE IMPROVEMENT OF A THERMOELECTRIC WATER DISTILLER

  Afaneh, D. & Bahaidarah, H., 2024, In: Proceedings of the Thermal and Fluids Engineering Summer Conference. p. 607-611 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Performance Improvement 100%
  • Thermoelectrics 100%
  • Mathematical Model 11%
  • Operating Parameter 11%
  • Industrial Applications 11%

• Performance Investigation of a Single Effect Evaporator Desalination Unit: A Simulation Model

  Shboul, B., Zayed, M. E. & Ashraf, W. M., 2024, In: Energy Proceedings. 41

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Simulation Model 100%
  • Condenser 100%
  • Desalination Unit 100%
  • Evaporator 100%
  • Desalination 66%
• 2023

  AERODYNAMIC INTERFERENCE OF VERTICAL AXIS WIND TURBINES IN ARRAY CONFIGURATION

  Toor, Z., Bahaidarah, H. & Rehman, S., 2023, In: Proceedings of the Thermal and Fluids Engineering Summer Conference. 2023-March, p. 1385-1394 10 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Aerodynamic Interference 100%

• A PREDICTION OF HEAT TRANSFER ENHANCEMENT OF CONDENSATION FOR NEW FLUIDS ON PIN-FIN TUBE

  Obeidat, A. & Ali, H. M., 2023, In: International Heat Transfer Conference.

  Research output: Contribution to journal › Conference article › peer-review

  • Circumferential 100%
  • Heat Transfer Enhancement 100%
  • Surface Tension 100%
  • Attainment 50%
  • Design Process 50%

• A PREDICTION OF HEAT TRANSFER ENHANCEMENT OF CONDENSATION FOR NEW FLUIDS ON PIN-FIN TUBE

  Obeidat, A. & Ali, H. M., 2023, In: International Heat Transfer Conference.

  Research output: Contribution to journal › Conference article › peer-review

  • Fluid 100%
  • Heat Transfer 100%
  • Heat Transfer Enhancement for Application 100%
  • Surface Tension 100%
  • Refrigerant 100%

• Experimental and Numerical Analysis of a Thermoelectric Air Funnel Cooler System for Dry climatic Conditions

  Algarni, S. A. & Irshad, K., 2023, In: Proceedings - International Conference on Energy Research and Development, ICERD. 2023, November, p. 242-249 8 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Climatic Condition 100%
  • Thermoelectricity 100%
  • Cold Side 50%
  • Duct 33%
  • Heat Transfer Rate 16%

• Revolutionizing Solar Energy: Enhancing Panel Efficiency with Advanced Machine Learning Techniques and Data Filtering

  Hossain, M. K., Sarkar, D., Zaman, A., Arifuzzaman, M., Gazder, U., Tito, M. H. & Al-Duais, A. N., 2023, In: IET Conference Proceedings. 2023, 44, p. 374-377 4 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Solar Energy 100%
  • Filtration 100%
  • Air Pressure 100%
  • Machine Learning Technique 100%
  • Energy Production 50%
• 2022

  Electromagnetic Near-Field Distributions at the Interstitials of Plasmonic Nanoparticles through Finite-Difference Time-Domain Analysis

  Al-Jishi, A. & Hossain, M. K., 2022, In: International Conference on Metamaterials, Photonic Crystals and Plasmonics. p. 1227-1228 2 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Time Domain 100%
  • Plasmonics 100%
  • Field Distribution 100%
  • Domain Analysis 100%
  • Nanoparticles 100%

• Fabrication and Characterization of Multifunctional Copper Thin film by Direct Current Sputtering

  Al-Jishi, A. & Hossain, M. K., 2022, In: International Conference on Metamaterials, Photonic Crystals and Plasmonics. p. 1201-1202 2 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Characterization 100%
  • Copper 100%
  • Thin Films 100%
  • Hydrophobicity 50%
  • Glass 50%

• Fabrication of Copper-Doped Zinc Oxide Thin film in Nitrogen Environment for Solar Cell Applications

  Hossain, M. K. & Al-Rasheidi, M., 2022, In: International Conference on Metamaterials, Photonic Crystals and Plasmonics. p. 1212-1213 2 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Zinc Oxide 100%
  • Copper 100%
  • Solar Cell 100%
  • Thin Films 100%
  • Metal 50%

• Near-Field Surface-Enhanced Raman Scattering of a Well-Defined Gold Nanoaggregate

  Hossain, M. K., 2022, In: International Conference on Metamaterials, Photonic Crystals and Plasmonics. p. 871-872 2 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Raman Spectra 100%
  • Surface-Enhanced Raman Spectroscopy 100%
  • Time Domain Analysis 50%
  • Aggregates 50%
  • Correlation 50%
• 2021

  A comparison of numerical solvers for the delay eigenvalue problem of coupled oscillators

  Abdelrahman, A. S., Al-Qahtani, H. & Alharbi, F. H., 3 Feb 2021, In: Journal of Physics: Conference Series. 1730, 1, 012114.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Chebyshev 100%
  • Eigenvalue Problem 100%
  • Interpolation 100%
  • Harmonic Oscillator 100%
  • Delay-Differential Equation 50%
  1 Scopus citations

• Experimental investigation of convective heat transfer using ethylene glycol-based nano-fluid

  Shoaib Rafiq, M., Muhammad Ali, H. & Sultan, A., 10 Feb 2021, In: E3S Web of Conferences. 239, 00022.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Experimental Investigation 100%
  • Fluid 100%
  • Heat Convection 100%
  • Heat Transfer 50%
  • Convective Heat Transfer Coefficient 40%
  1 Scopus citations
• 2020

  An investigation of thermal stability and heat capacity of imidazolium based ionic liquids at elevated temperature

  Bakthavatchalam, B., Habib, K., Saidur, R., Irshad, K. & Hussein, O. A., 12 Jun 2020, In: IOP Conference Series: Materials Science and Engineering. 863, 1, 012026.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Thermal Stability 100%
  • Reaction Temperature 100%
  • Heat Capacity 100%
  • Ionic Liquid 100%
  • Specific Heat 100%
  7 Scopus citations

• Techno-economic study on grid-connected PV system for major cities in Saudi Arabia

  Ali, A., Hussain, M., Al-Sulaiman, F. A., Tahir, S., Irshad, K., Zahir, M. H. & Malik, M. Z., 9 Jun 2020, In: E3S Web of Conferences. 173, 02005.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Net Present 100%
  • Economics 100%
  • Environmental Performance 100%
  • Cost 100%
  • Residential Building 50%
  5 Scopus citations
• 2019

  A Multi Tone Modeling for Seismic Data Compression

  Liu, B., Mohandes, M., Nuha, H., Deriche, M., Iqbal, N., Fekri, F. & McClellan, J. H., 10 Aug 2019, In: SEG Technical Program Expanded Abstracts. p. 263-267 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Seismic Data 100%
  • Data Compression 100%
  • Model 100%
  • Modeling 100%
  • Component Model 100%
  2 Scopus citations

• Compression of Seismic Signals via Recurrent Neural Networks: Lossy and Lossless Algorithms

  Payani, A., Fekri, F., AlRegib, G., Mohandes, M. & Deriche, M., 10 Aug 2019, In: SEG Technical Program Expanded Abstracts. p. 4082-4086 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Algorithm 100%
  • Compression 100%
  • Sample 75%
  • Show 50%
  • Data Set 50%
  4 Scopus citations

• Seismic Data Compression Using Deep Neural Network Predictors

  Nuha, H., Balghonaim, A., Mohandes, M., Liu, B. & Fekri, F., 10 Aug 2019, In: SEG Technical Program Expanded Abstracts. p. 258-262 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Deep Neural Network 100%
  • Neural Network Predictor 100%
  • Prediction 40%
  • Dataset 20%
  • Collected Data 20%
  5 Scopus citations
• 2018

  Seismic data compression using auto-associative neural network and restricted Boltzmann machine

  Nuha, H., Mohandes, M. & Liu, B., 27 Aug 2018, In: SEG Technical Program Expanded Abstracts. p. 186-190 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Data Compression 100%
  • Boltzmann Machine 100%
  • Neural Network 100%
  • Boltzmann Equation 100%
  • Geophone 100%
  3 Scopus citations

• Seismic model estimation using particle swarm optimization

  Liu, B., Mohandes, M. & Nuha, H., 27 Aug 2018, In: SEG Technical Program Expanded Abstracts. p. 4216-4220 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Models 100%
  • Estimation 100%
  • Particle Swarm Optimization 100%
  • Model 100%
  • Optimization 100%
  2 Scopus citations

• What causes the variability in the properties of energetic storm particle (ESP) events?

  Dayeh, M. A., Desai, M. I., Ebert, R. W., Elliott, H., Farahat, A., Kozarev, K. & Li, G., 24 Oct 2018, In: Journal of Physics: Conference Series. 1100, 1, 012008.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Cause 100%
  • Event 100%
  • Energetics 100%
  • Particles 100%
  • Storms 100%
  11 Scopus citations
• 2017

  A numerical investigation of hydrogen production in an integrated membrane reformer-combustor

  Sanusi, Y. S. & Mokheimer, E. M. A., 2017, In: Energy Procedia. 142, p. 1077-1082 6 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Carbon Monoxide 100%
  • Hydrogen Production 100%
  • Hydrogen 100%
  • Combustion 100%
  • Oxygen 50%
  2 Scopus citations

• Assessing the accuracy of globe thermometer method in predicting outdoor mean radiant temperature under Malaysia tropical microclimate

  Khrit, N. G., Alghoul, M. A., Sopian, K., Lahimer, A. A. & Elayeb, O. K., 20 Nov 2017, In: E3S Web of Conferences. 23, 01006.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Microclimate 100%
  • Thermometer 100%
  12 Scopus citations

• Boosting Gas Turbine Combined Cycles in Hot Regions Using Inlet Air Cooling including Solar Energy

  Abdel Rahman, A. A. & Mokheimer, E. M. A., 2017, In: Energy Procedia. 142, p. 1509-1515 7 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Solar Energy 100%
  • Gas Turbine Combined Cycle 100%
  • Inlet Air 100%
  • Absorption Chiller 100%
  • Gas Turbine 60%
  15 Scopus citations

• Concise Approach for Determining the Optimal Annual Capacity Shortage Percentage using Techno-Economic Feasibility Parameters of PV Power System

  Alghoul, M. A., Ali, A., Kannanaikal, F. V., Amin, N. & Sopian, K., 20 Nov 2017, In: E3S Web of Conferences. 23, 07003.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Economic Feasibility 100%
  • Annual Capacity 100%
  • Power Engineering 100%
  • Input Data 42%
  • Reference Value 28%
  1 Scopus citations

• Effect of Different Solar Radiation Data Sources on the Variation of Techno-Economic Feasibility of PV Power System

  Alghoul, M. A., Ali, A., Kannanaikal, F. V., Amin, N., Aljaafar, A. A., Kadhim, M. & Sopian, K., 20 Nov 2017, In: E3S Web of Conferences. 23, 01007.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Economic Feasibility 100%
  • Radiation Data 100%
  • Power Engineering 100%
  • Solar Radiation 100%
  • Data Source 100%
  1 Scopus citations

• Investigating the Effect of Titanium Dioxide (TiO2) Pollution on the Performance of the Mono-crystalline Solar Module

  Ahmed Darwish, Z., Sopian, K., Kazem, H. A., Alghoul, M. A. & Alawadhi, H., 20 Nov 2017, In: E3S Web of Conferences. 23, 01005.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Titanium Dioxide (Tio2) 100%
  • Density 100%
  • Performance 100%
  • Pollution 100%
  • Module 100%
  1 Scopus citations

• Multi-step Ahead Wind Forecasting Using Nonlinear Autoregressive Neural Networks

  Ahmed, A. & Khalid, M., 2017, In: Energy Procedia. 134, p. 192-204 13 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Prediction 100%
  • Speed Data 50%
  • Simulation Result 50%
  • Benchmark 50%
  • Major Factor 50%
  52 Scopus citations

• Numerical Modeling of Oxy-Fuel Combustion in a Model Gas Turbine Combustor: Effect of Combustion Chemistry and Radiation Model

  Raghib Shakeel, M., Sanusi, Y. S. & Mokheimer, E. M. A., 2017, In: Energy Procedia. 142, p. 1647-1652 6 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Gas Turbine Combustors 100%
  • Oxyfuel Combustion 100%
  • Models 100%
  • Radiation 100%
  • Combustion 100%
  10 Scopus citations

• Optimum Design Parameters of Box Window DSF Office at Different Glazing Types under Sub Interval of Intermediate Sky Conditions (20-40 klux)

  Elayeb, O. K., Alghoul, M. A., Sopian, K. & Khrita, N. G., 20 Nov 2017, In: E3S Web of Conferences. 23, 05003.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Subinterval 100%
  • Design Parameter 100%
  • Optimum Design 100%
  • Windows 100%
  • Daylighting 75%
  4 Scopus citations

• Stability of Propane-air and oxyfuel diffusion flames in a swirl-stabilized combustor; An experimental study

  Abubakar, Z., Sanusi, S. Y. & Mokheimer, E. M. A., 2017, In: Energy Procedia. 142, p. 1552-1557 6 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Transition Point 100%
  8 Scopus citations

• Surface Engineering towards Self-Cleaning Applications: Laser Textured Silicon Surface

  Yilbas, B. S., Keles, O. & Toprakli, A. Y., 2017, In: Procedia Engineering. 184, p. 716-724 9 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Silicon Surface 100%
  • Engineering 100%
  • Surface 100%
  • Laser Application 100%
  • Surface Engineering 100%
  26 Scopus citations

• The Effect of Solar Reflective Cover on Soak Air Temperature and Thermal Comfort of Car Parked under the Sun

  Lahimer, A. A., Alghoul, M. A., Sopian, K. & Khrit, N. G., 20 Nov 2017, In: E3S Web of Conferences. 23, 08003.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Air Temperature 100%
  • Thermal Comfort 100%
  • Railroad Cars 100%
  • Temperature 40%
  • Ambient Temperature 20%
  6 Scopus citations
• 2016

  Disributed principal component analysis for data compression of sequential seismic sensor arrays

  Liu, B., Nuha, H., Mohandes, M., Deriche, M. & Fekri, F., 2016, In: SEG Technical Program Expanded Abstracts. 35, p. 250-254 5 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Sensor Array 100%
  • Component Analysis 100%
  • Principal Components 100%
  • Sensor 50%
  • Compression Scheme 25%
  11 Scopus citations
• 2015

  An Exploratory of Residents' Views Towards Applying Renewable Energy Systems in Saudi Dwellings

  Alrashed, F. & Asif, M., 2015, In: Energy Procedia. 75, p. 1341-1347 7 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Renewable Energy System 100%
  • Fossil Fuel 66%
  • Residential Sector 66%
  • Energy Engineering 66%
  • Solar Photovoltaic 66%
  26 Scopus citations

• Climatic Classifications of Saudi Arabia for Building Energy Modelling

  Alrashed, F. & Asif, M., 2015, In: Energy Procedia. 75, p. 1425-1430 6 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Energy Modelling 100%
  • Buildings 100%
  • Energy Performance 25%
  • Matrix Method 25%
  • Great Deal 25%
  41 Scopus citations

• LabVIEW based PV panel online characteristics and parameters estimation

  Ahmed, C. B., Kassas, M. & Ahmed, S. E., 2015, In: Procedia Computer Science. 52, 1, p. 876-882 7 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Photovoltaic Panel 100%
  • Virtual Instrument 100%
  • Parameter Estimation 100%
  • Engineering 100%
  • Characteristics 100%
  3 Scopus citations

• Modeling and simulation of residential HVAC systems energy consumption

  Kassas, M., 2015, In: Procedia Computer Science. 52, 1, p. 754-763 10 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Energy Engineering 100%
  • Energy Systems 100%
  • Outdoor Temperature 60%
  • Air Conditioning System 40%
  • Models 40%
  29 Scopus citations

• Performance Comparative Analysis of Three Different CSP Technologies Integrated with Gas Turbine Cogeneration Systems in Saudi Arabia

  Mokheimer, E. M. A., Dabwan, Y. N. & Habib, M. A., 2015, In: Energy Procedia. 75, p. 527-532 6 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Gas Turbine 100%
  • Comparative Analysis 100%
  • Cogeneration System 100%
  • Performance 100%
  • Concentrating Solar Power Technology 100%
  4 Scopus citations
• 2014

  Saudi building industry's views on sustainability in buildings: Questionnaire survey

  Alrashed, F. & Asif, M., 2014, In: Energy Procedia. 62, p. 382-390 9 p.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Sustainable Development 100%
  • Sustainable Building 100%
  • Buildings 100%
  • Building Industry 100%
  • Energy Performance 33%
  31 Scopus citations

• Silver nanoparticles on Zinc Oxide thin film: An insight in fabrication and characterization

  Hossain, M. K., Drmosh, Q. A., Yamani, Z. H. & Tabet, N., 2014, In: IOP Conference Series: Materials Science and Engineering. 64, 1, 012018.

  Research output: Contribution to journal › Conference article › peer-review

  Open Access

  • Characterization 100%
  • Silver Nanoparticles 100%
  • Zinc Oxide 100%
  • Thin Films 100%
  • Nanoparticle 62%
  6 Scopus citations
• 2005

  HVOF coating and laser treatment: Three-point bending tests

  Yilbas, B. S., Arif, A. F. M. & Gondal, M. A., 15 May 2005, In: Journal of Materials Processing Technology. 164-165, p. 954-957 4 p.

  Research output: Contribution to journal › Conference article › peer-review

  • Base Material 100%
  • Three-Point Bending Test 100%
  • Integration 100%
  • High Velocity Oxygen Fuel Coating 100%
  • Coating 100%
  29 Scopus citations