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To overcome the limitations of single-phase plasma-sprayed coatings, where ceramic coatings exhibit high hardness but poor toughness while metallic coatings possess good ductility but insufficient hardness, AT40/Al metal–ceramic composite coatings were prepared by atmospheric plasma spraying. In this study, Al₂O₃–40%TiO₂ (AT40) ceramic was used as the hard phase and aluminum as the ductile phase. The effects of Al content (10%, 20%, and 30%) and key spraying parameters, including arc power (36–40 kW), spraying distance (85–130 mm), and gun traverse speed (400–1200 mm s⁻¹), on the microstructure and mechanical properties of the coatings were systematically investigated. The coatings were characterized using SEM, XRD, and EDS, and grey relational analysis was employed to evaluate the influence of process parameters. The results show that the introduction of an appropriate amount of Al significantly improves coating densification. When the Al content is 10%, the coating porosity decreases to 3.2%, compared with 8.5% for the pure AT40 coating. The optimal spraying parameters were determined to be 38 kW arc power, 100 mm spraying distance, and 400 mm s⁻¹ traverse speed, under which the coating exhibits a microhardness of 519.68 HV and a 45.3% improvement in impact resistance compared with the pure AT40 coating. Phase analysis indicates that partial transformation of α-Al₂O₃ to γ-Al₂O₃ occurs during spraying, while interfacial reactions between Al and TiO₂ lead to the formation of Al₂TiO₅, enhancing the interfacial bonding strength. The improved performance of the composite coating is attributed to the combined effects of structural densification, interfacial strengthening, and the synergistic interaction between ceramic and metallic phases. Full article

(This article belongs to the Section Ceramic Coatings and Engineering Technology)

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13 pages, 1994 KB

Open AccessArticle

Combustion Characteristics and Combustion Kinetics of Poplar Biomass Under Oxy-Fuel Conditions

by Yufeng Pei, Dandan Li, Xiuyan Zhang, Chang Yu, Jili Leng, Qing Wang, Da Cui and Shuang Wu

Energies 2026, 19(6), 1444; https://doi.org/10.3390/en19061444 (registering DOI) - 13 Mar 2026

Abstract

In this study, thermogravimetric analysis was employed to investigate the non-isothermal combustion behavior and kinetic characteristics of poplar biomass under air and oxy-fuel (O₂/CO₂) atmospheres. The effects of heating rate and oxygen concentration on combustion performance, gaseous emissions, and kinetic parameters were systematically analyzed. Results show that poplar biomass combustion consists of four distinct stages: moisture evaporation, devolatilization with volatile oxidation, char and fixed carbon oxidation, and final burnout. Increasing the heating rate intensifies the combustion process, shifting characteristic temperatures to higher values and significantly enhancing the comprehensive combustion index. Compared with air combustion, oxy-fuel conditions reduce ignition temperature and the temperature corresponding to the maximum combustion rate, leading to an earlier ignition and a more concentrated reaction interval. Higher oxygen concentrations further improve overall combustion performance and promote more complete carbon conversion. Gas emission analysis indicates that oxy-fuel combustion effectively suppresses NO₂ and SO₂ formation, demonstrating notable emission-reduction potential. Kinetic analysis using the Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa isoconversional methods shows that the activation energy varies with conversion degree and is generally higher under oxy-fuel atmospheres than in air. Overall, oxy-fuel combustion enhances biomass reactivity while achieving coordinated emission control through increased oxygen partial pressure and improved heat and mass transfer, supporting its practical application in biomass energy systems. Full article

(This article belongs to the Section I1: Fuel)

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17 pages, 2130 KB

Open AccessArticle

FogGate-YOLO: Traffic Object Detection in Foggy Environments Using Channel Selection Mechanisms

by Yuhe Yang, Suilian You, Jinpeng Yu and Bo Lu

Sensors 2026, 26(6), 1811; https://doi.org/10.3390/s26061811 (registering DOI) - 13 Mar 2026

Abstract

To address the challenges posed by foggy conditions in object detection tasks, we propose FogGate-YOLO, an enhanced YOLOv8 framework designed for robust and efficient detection in foggy environments. Unlike traditional methods that rely on image dehazing or preprocessing enhancements, our approach directly strengthens the model’s feature representation by introducing two novel modules: GroupGatedConv and C2fGated. These modules collaboratively mitigate fog-induced degradation, improving feature extraction and enhancing performance without additional inference overhead. The GroupGatedConv module focuses on coarse-grained channel selection in the early to mid-stages of the backbone, suppressing noise while preserving essential structural features. The C2fGated module refines the aggregated features in both the backbone and neck after multi-branch fusion, enhancing fine-grained feature recalibration. Together, these two modules provide a hierarchical coarse to fine channel selection strategy that significantly improves the model’s discriminative power in foggy conditions. Full article

(This article belongs to the Topic Advances in Autonomous Vehicles, Automation, and Robotics)

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15 pages, 4148 KB

Open AccessArticle

Eco-Friendly Copper Oxide Nanoparticles Incorporated Polyvinylidene Difluoride Electrospun Nanofibers as Wearable Piezoelectric Nanogenerator

by Amrutha Bindhu, Sathiyanathan Ponnan, Shamim Reza Mohammad, Riya Karmakar, Hongdoo Kim, Arvind Mukundan and Anand Prabu Arun

Polymers 2026, 18(6), 699; https://doi.org/10.3390/polym18060699 (registering DOI) - 13 Mar 2026

Abstract

This study focuses on enhancing the performance of piezoelectric nanogenerators (PENGs) fabricated by electrospinning (ES) of polyvinylidene fluoride (PVDF) infused with varying concentrations (0, 1, 3, 5, and 7 wt.-%) of copper oxide (CuO) nanoparticles. Structural changes and the β-phase proportion in nanofibers (NFs) were examined using XRD and FTIR-ATR. Surface morphology and roughness were characterized using FE-SEM and AFM, respectively. The water-repellent characteristics of the NFs were assessed through WCA measurements. Electrical output (voltage and current) was evaluated under mechanical pressure using a customized setup that applied 1.0 kgf at 1.0 Hz. The pristine PVDF-based PENG generated an output of 1.7 V and 0.53 μA, while the composite NF with 5 wt.-% CuO (5PCu) delivered a significantly enhanced output of 13.7 V and 1.6 μA. The 5PCu device was further tested for detecting human activities, including tapping, wrist movements, walking, and jumping, thereby demonstrating its potential for self-powered wearable electronics. Full article

(This article belongs to the Special Issue Smart Polymers and Composites in Multifunctional Systems)

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16 pages, 8378 KB

Open AccessArticle

Optimization of Ornithopter Energy Efficiency Through Spring-Induced Harmonic Motion

by Jimin Kim and Ji-Chul Ryu

Biomimetics 2026, 11(3), 207; https://doi.org/10.3390/biomimetics11030207 (registering DOI) - 13 Mar 2026

Abstract

Ornithopters generate lift and thrust through periodic flapping-wing motion. While control-based optimization has been widely studied to improve the flight efficiency of ornithopters, passive mechanical tuning remains underexplored. This study investigates whether integrating a lightweight torsional spring can passively tune a flapping-wing system toward resonance to reduce input power and enhance aerodynamic performance. We evaluated springs of different stiffness on a 3D-printed, motor-driven flapping rig, recording input voltage and current as well as flapping frequency and thrust. Wing kinematics were analyzed using high-speed video, and free-oscillation tests identified a resonant period of ~0.14 s (~7.1 Hz). Experimental results show that an optimally tuned spring-assisted system achieves up to a threefold improvement in thrust efficiency and up to a twofold improvement in kinematic efficiency, compared to the no-spring baseline. Indoor flight tests using a commercial ornithopter (MetaFly) confirmed the improvement, showing a 12.8% increase in average endurance. The spring-assisted configuration also produced smoother stroke reversals, consistent with reduced energy losses. These results demonstrate that a low-complexity, lightweight torsional spring tuned near resonance can provide an effective passive means to enhance both energy efficiency and aerodynamic output in flapping-wing UAVs, serving as a practical, low-cost complement to control-based optimization methods. Full article

(This article belongs to the Section Locomotion and Bioinspired Robotics)

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Graphical abstract

25 pages, 13376 KB

Open AccessArticle

Effect of Freckle Defects on Hot Deformation Behavior and Dynamic Recrystallization Structure Inheritance of an Iron–Nickel-Based Superalloy

by Lianjie Zhang, Xiaojia Wang, Yuhan Wang, Lei Wang, Ran Duan, Shuo Huang, Guohua Xu and Yang Liu

Materials 2026, 19(6), 1113; https://doi.org/10.3390/ma19061113 (registering DOI) - 13 Mar 2026

Abstract

To study the influence of freckle defects on the hot deformation behavior and the inheritance of dynamic recrystallization (DRX) structure in GH4706 alloy, the microstructures of specimens with and without freckles and the evolution laws of hot-processing parameters were compared. Hot compression experiments were conducted on a thermal simulation testing machine at 950–1150 °C, strain rates of 0.001–1 s⁻¹, and 55% deformation. Freckle-containing specimens were tested under DRX critical conditions. The flow stresses of both specimens increase with strain rate or with decreasing temperature. The power dissipation coefficient (η) and instability value (ξ) follow complex laws. Electron back-scattering diffraction (EBSD) was used to analyze DRX microstructures and nucleation mechanisms. The DRX degree of freckle-containing specimens is lower, with a larger average grain size. The DRX mechanism initiates preferentially in freckle-containing specimens, and its volume fraction changes in a complex manner. Grain coarsening occurs in freckle-containing specimens at high temperatures and low strain rates. Freckle defects lead to significant differences in the DRX mechanism of GH4706 alloy. Freckle-containing specimens exhibit both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), whereas freckle-free specimens primarily display DDRX and second-phase particle-stimulated nucleation (PSN). The presence of MC carbides and Laves phases within freckle defects provides nucleation sites, further supporting a typical second-phase particle-stimulated nucleation mechanism. Full article

(This article belongs to the Special Issue Research on Performance Improvement of Advanced Alloys (2nd Edition))

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21 pages, 1986 KB

Open AccessArticle

Environmental Performance of Chlorella sp.-Based Phytoremediation Across Multiple Wastewater Scenarios: A Comparative Life Cycle Assessment

by Janet B. García-Martínez, Laura T. Ríos Niño, Lizeth N. Saavedra Gómez, Crisóstomo Barajas-Ferreira, Antonio Zuorro and Andrés F. Barajas-Solano

Environments 2026, 13(3), 155; https://doi.org/10.3390/environments13030155 (registering DOI) - 13 Mar 2026

Abstract

This study assesses the environmental performance of three wastewater treatment setups through an attributional, gate-to-gate life cycle assessment (functional unit: 1 m³ of treated wastewater): (Sc1) a traditional municipal wastewater treatment plant, (Sc2) an aquaculture recirculation system using microalgae, and (Sc3) a domestic system combining UASB pretreatment with microalgae polishing. Inventory data were analyzed in SimaPro with ReCiPe 2016 Midpoint (Hierarchist) across seven effect categories. Robustness was tested through sensitivity analyses (±20%) of power consumption and influent characteristics, as well as an additional scenario exploring the offset of methane-recovery electricity. The global warming impact remained consistent across scenarios, ranging from 60.5 to 65.1 kg CO₂-eq·m⁻³, indicating no significant difference within the operational parameters. In most categories, power consumption and influent-related burdens were the main contributors, while the impacts from flocculants and microalgae inoculum were minimal. Sc3 showed a lower freshwater eutrophication potential compared to Sc1 and Sc2 (0.028 vs. approximately 0.049 kg P-eq·m⁻³). Normalization highlighted human carcinogenic toxicity and aquatic ecotoxicity as key impact categories. The methane-offset scenario caused only slight changes at low CH₄ outputs, suggesting that energy recovery depends on context. Full article

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29 pages, 1884 KB

Open AccessReview

Nuclear Fuel Revival: Uranium Markets, SMRs, and Global Energy Security

by Brenda Huerta-Rosas and Eduardo Sánchez-Ramírez

Commodities 2026, 5(1), 7; https://doi.org/10.3390/commodities5010007 (registering DOI) - 13 Mar 2026

Abstract

This review examines the renewed strategic relevance of uranium within the evolving global energy system, emphasizing uranium market dynamics, emerging nuclear technologies, and geopolitical realignments. Moving beyond traditional perspectives that treat uranium primarily as a cyclical commodity or focus narrowly on reactor design, the article frames uranium as a critical strategic resource at the intersection of energy security, decarbonization, and industrial transformation. The analysis integrates market fundamentals with technological developments, particularly small modular reactors (SMRs) and advanced high-temperature reactor systems, and regional policy strategies to provide a holistic perspective largely absent from the existing literature. Quantitative evidence indicates a structurally tightening uranium market, with global reactor demand of approximately 67,500 tU per year and mine production historically meeting only 74–90% of annual requirements. Uranium prices have rebounded from below $20 lb⁻¹ U₃O₈ in 2016 to above $80 lb⁻¹ by late 2023, reflecting supply concentration, long development timelines for new mines, and renewed political commitments to nuclear energy. Demand projections suggest an increase of around 28% by 2030 and the potential for a doubling by mid-century under high-nuclear deployment scenarios. From a technological perspective, while SMRs and advanced reactors may increase uranium consumption per unit of electricity, they substantially expand nuclear energy deployment into new domains, including remote power systems, industrial heat applications, and large-scale low-carbon hydrogen production. Overall, the study highlights a qualitative shift in uranium’s role, positioning it as both a foundational component and a key enabler of integrated low-carbon energy systems spanning electricity, heat, and hydrogen production. Full article

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33 pages, 1672 KB

Open AccessReview

Organoid Models: Revolutionizing Disease Modeling and Personalized Therapeutics

by Zhifeng Xue, Runze Yang, Yaling Liu and Han Luo

Organoids 2026, 5(1), 9; https://doi.org/10.3390/organoids5010009 (registering DOI) - 13 Mar 2026

Abstract

As a three-dimensional in vitro model, organoid technology represents a revolutionary breakthrough in precision medicine. By harnessing the self-organizing capabilities of stem cells within biomimetic extracellular matrices, it enables the generation of miniature tissues that recapitulate key structural and functional characteristics of their source organs. Conventional two-dimensional cell cultures lack tissue architecture and microenvironmental cues, whereas animal models are hindered by interspecies differences and inadequate representation of human pathological heterogeneity. By effectively addressing these limitations, organoids have emerged as powerful platforms that are highly representative of human physiology and disease processes in oncology, genetic disorders, and infectious diseases. They demonstrate significant potential for use in drug screening, toxicity assessment, and the development of personalized treatment strategies. Although challenges such as limited vascularization, lack of standardized culture protocols, and ethical considerations remain, the integration of multidisciplinary approaches such as AI-assisted analysis, organ-on-a-chip systems, and 3D bioprinting, together with increasing policy support and industrial advancement, is accelerating the clinical translation of organoid technology. In this review, the construction strategies for and applications of organoid models are systematically summarized, and their value and limitations in disease modeling, precision medicine, and preclinical research are highlighted. Finally, future development pathways driven by multidisciplinary collaboration and standardization are outlined. Full article

(This article belongs to the Special Issue Advances in Organoid Technology: Bridging the Gap between Research and Therapy)

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24 pages, 8480 KB

Open AccessProtocol

Evaluating Microclimate Modification and Acute Cardiovascular Stress Responses to a Dense Urban Microforest: The Green Oasis (GRO) Protocol

by Rachel Keith, Sean Willis, Natalie Christian, Farzaneh Khayat, Jackie Gallagher, William Scott Gunter, Julia Kachanova, Andrew Mehring, Rachel Pigg, Doris Proctor, Allison E. Smith, Cameron K. Stopforth, Patrick Piuma, Ted Smith and Aruni Bhatnagar

Int. J. Environ. Res. Public Health 2026, 23(3), 365; https://doi.org/10.3390/ijerph23030365 (registering DOI) - 13 Mar 2026

Abstract

The Green Oasis (GRO) Project is a targeted urban greening intervention designed to evaluate the environmental and health impacts of compact, high-density plantings in dense built environments. Initiated in downtown Louisville, the project transformed Founders Square, a 0.64-acre sparsely planted park, into a microforest (“Trager Microforest”), a multilayered planting of 119 trees and more than 200 shrubs. The impact of this intervention is being assessed through a randomized crossover study in which participants walk in the microforest and a nearby impervious parking lot. Physiological outcomes include heart rate, heart rate variability, arterial stiffness, and stress biomarkers measured in saliva, urine, and sweat. Environmental conditions are continuously monitored by fixed and mobile weather stations, air pollution sensors, and biodiversity surveys. Baseline assessments were conducted in 2023 and 2024, with post-planting evaluations now underway (2025–). Power calculations indicate adequate sensitivity (n ≈ 40–50) to detect changes in cardiovascular stress responses in participants. Complementary ecological measurements include soil microbiome composition, greenhouse gas fluxes, and avian diversity. This study addresses critical gaps in understanding how small-scale, high-density greening interventions affect cardiovascular resilience, stress physiology, and microclimatic regulation. By integrating environmental, biological, and human health data, GRO establishes a comprehensive framework for evaluating the efficacy of urban microforests as nature-based solutions. The results are expected to inform urban planning, public health strategies, and climate adaptation policies, demonstrating how compact greening interventions can simultaneously mitigate heat, reduce pollution, enhance biodiversity, and promote human wellbeing in dense urban cores. Full article

(This article belongs to the Section Environmental Health)

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12 pages, 427 KB

Open AccessArticle

Monitoring Physical Activity in Students with Intellectual Disabilities: The Contribution of Physical Education, Gender and Disability Level

by Yannis Ntovolis, Lida Skoufa, Christina Evangelinou and Vassilis Barkoukis

Sensors 2026, 26(6), 1808; https://doi.org/10.3390/s26061808 (registering DOI) - 13 Mar 2026

Abstract

Individuals with intellectual disabilities (IDs) consistently demonstrate lower levels of objectively measured physical activity (PA) compared to the general population, yet limited evidence exists regarding how activity accumulated during physical education (PE) contributes to overall daily movement within structured school contexts. Within the school setting, PE represents one of the primary structured opportunities for engaging students with IDs in PA. Although objective physical activity monitoring approaches are recommended for school-based PA assessment, limited evidence exists on the contribution of PE to total school-day activity in students with intellectual disabilities, a gap addressed in the present study. In this context, the present study objectively recorded PA levels of students with IDs both during PE lessons and across five school days, in order to examine the contribution of PE to overall PA. Potential differences in PA according to gender and severity of the ID were also examined. Twenty students aged 15–25 years with mild and moderate IDs participated in the study. PA was assessed using the YAMAX Power Walker EX-510 pedometer, which automatically recorded step counts. The results indicated that only six participants reached step-count reference values. Students with mild IDs accumulated significantly more steps than those with moderate IDs, while male students were more physically active than female students, both during PE lessons and across the school day. PE lessons contributed approximately 4% to the total PA accumulated across the five monitored school days. These findings highlight the limited contribution of PE to overall PA and underscore the importance of promoting greater movement opportunities within adapted PE lessons. Full article

(This article belongs to the Special Issue Wearable Devices for Physical Activity and Healthcare Monitoring)

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36 pages, 11335 KB

Open AccessArticle

An Intelligent Hybrid PIDF Enhanced by a Fuzzy Fractional-Order Controller for Robust Load Frequency Regulation in a Two-Area Interconnected Power System

by Saleh Almutairi, Fatih Anayi, Michael Packianather, Mohammad Almutairi and Mokhtar Shouran

Energies 2026, 19(6), 1442; https://doi.org/10.3390/en19061442 (registering DOI) - 12 Mar 2026

Abstract

Maintaining frequency regulation in interconnected power systems becomes increasingly difficult in the presence of nonlinear operating conditions. To address this issue, this study develops a hybrid load frequency control scheme in which a fuzzy fractional-order FOPI–FOPD controller is incorporated within a PIDF framework for a two-area LFC system. The controller parameters are optimized using the Dwarf Mongoose Optimization Algorithm (DMOA) and the Catch Fish Optimization Algorithm (CFOA), while the Integral of Time-Weighted Absolute Error (ITAE) is adopted as the performance criterion. The proposed strategy is examined under both linear and nonlinear scenarios, including the effects of Governor Dead Band (GDB) and Generation Rate Constraints (GRC). In the linear case, the DMOA-based design achieves an ITAE of 0.02939 with a tie-line settling time of 13.5478 s, whereas the CFOA-based design produces a bounded and convergent response with an ITAE of 0.03937 and a settling time of 14.4947 s. When GDB nonlinearity is introduced, the DMOA-tuned controller exhibits performance deterioration, yielding an ITAE of 0.1098 and a settling time of 19.0416 s, while the CFOA-tuned design shows more favorable time-domain performance with a lower ITAE of 0.05845 and a bounded settling time of 16.3595 s. These findings indicate that the CFOA-optimized PIDF–Fuzzy FOPI–FOPD controller provides an effective LFC solution under the examined nonlinear operating conditions. Full article

(This article belongs to the Special Issue Challenges and Innovations in Stability and Control of Power Systems)

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24 pages, 5318 KB

Open AccessArticle

Assessment of Potential Wind Sites for Power Integration in Ethiopia: A Case Study of Arerti, Sela Dingay, Debre Berhan, Mega, and Gode

by Solomon Feleke, Mulat Azene, Degarege Anteneh, Wenfa Kang, Yun Yu, Mahshid Javidsharifi, Solomon Mamo, Josep M. Guerrero, Juan C. Vasquez and Yajuan Guan

Energies 2026, 19(6), 1440; https://doi.org/10.3390/en19061440 - 12 Mar 2026

Abstract

With hydropower supplying nearly 94% of Ethiopia’s electricity, the national power grid is extremely vulnerable to recurrent droughts and erratic rainfall. To mitigate this risk, this study examines the wind power potential across five specific locations: Arerti, Sela Dingay, Debre Berhan, Mega, and Gode. By combining on-site mast measurements with datasets from NASA and the Global Wind Atlas, we evaluated wind characteristics at industry-standard hub heights of 80 m and 100 m. The analysis focused on wind power density (WPD), Weibull stability parameters (k and c), and directional consistency. The results indicate that Gode and Mega are the premier choices for commercial development, showing average speeds above 8.5 m/s and power densities exceeding 500 W/m2 at the 100 m level. Gode stands out as the most reliable site, with a Weibull shape factor (k) of 2.8 and a scale factor (c) of 9.1 m/s. We modeled a standard 3 MW turbine while factoring in a 20% loss for real-world conditions; this yielded net annual energy productions of 9461 MWh (36% CF) for Gode, 9040 MWh (34.4% CF) for Mega, and 8619 MWh (32.8% CF) for Arerti. While Sela Dingay and Debre Berhan have lower initial yields, their feasibility improves significantly when using towers taller than 80 m. Wind rose data reveals that Gode and Arerti have highly unidirectional flows, which simplifies turbine micro-siting. Notably, Arerti provides a unique economic advantage due to its location right next to existing 132/230 kV transmission infrastructure and industrial load centers. Overall, these findings provide a definitive technical roadmap for Ethiopia to diversify its energy portfolio and meet its Climate-Resilient Green Economy (CRGE) objectives. Full article

(This article belongs to the Special Issue Modeling, Control and Optimization of Wind Power Systems)

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31 pages, 751 KB

Open AccessSystematic Review

The Impact of Mini-Grids on Rural Energy-Access Indicators in Developing Countries: A Systematic Review

by Ibanga Effiong, Gabrial Anandarajah and Olivier Dessens

Energies 2026, 19(6), 1441; https://doi.org/10.3390/en19061441 - 12 Mar 2026

Abstract

Mini-grids are increasingly deployed to expand rural electrification in developing countries, yet evidence on service-quality performance remains uneven. This systematic review synthesises empirical evidence from 22 peer-reviewed studies (2005–2025) on rural mini-grid performance across six energy-access indicators: electrification rate, availability of supply, hours of supply, affordability, reliability, and consistency (power quality). Using PRISMA-guided database searches in Scopus and Web of Science, 138 records were identified; following de-duplication and screening, 22 studies met the inclusion criteria. The evidence base is concentrated in Africa and Asia, and most studies adopt mixed-methods approaches combining household- and/or enterprise-level evidence with system or operational data. Across indicators, electrification outcomes are frequently positive but reported using heterogeneous metrics, often relying on connection counts rather than population-referenced rates (10/22 studies report electrification outcomes). Service availability and hours of supply vary widely, ranging from evening-only provision (~5 h/day) to near-continuous service (24 h/day), with several studies documenting demand–capacity mismatch and load shedding (9/22 quantify availability; 12/22 quantify hours). Affordability is most frequently reported (16/22 studies), spanning substantial household cost reductions in some settings to high tariffs that constrain uptake in remote contexts. Reliability is seldom quantified using extractable outage/downtime metrics (4/22 studies). No study reports standardised voltage/frequency power-quality measures; only proxy evidence relates to consistency, leaving power quality as a major evidence gap. Mini-grids can deliver meaningful improvements in rural electricity access, but the literature remains constrained by inconsistent indicator definitions, limited standardised reliability/power-quality measurement, and short monitoring horizons. Future research and regulation should prioritise harmonised service-quality metrics and longer-term, field-based performance evaluation. Full article

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13 pages, 2167 KB

Open AccessArticle

Low-Cost Portable Near-Infrared Spectroscopy for Predicting Soil Properties in Paddy Fields of Southeastern China

by Minwei Li, Yechen Jin, Hancheng Guo, Dietian Yu, Jianping Qian, Qiangyi Yu, Zhou Shi and Songchao Chen

Sensors 2026, 26(6), 1805; https://doi.org/10.3390/s26061805 - 12 Mar 2026

Abstract

Timely and accurate soil property information is critical for sustainable agriculture and precision nutrient management. Conventional laboratory methods are accurate but costly and labor-intensive, restricting their feasibility for high-density soil mapping. Low-cost, portable near-infrared (NIR) spectroscopy presents a promising alternative for rapid, on-site, and non-destructive soil analysis. This study aimed to evaluate the potential of a low-cost, portable NIR sensor (NeoSpectra) for the quantitative prediction of key soil properties in paddy fields from Southeastern China. The target properties were soil organic matter (SOM), total nitrogen (TN), pH, and particle size fractions (clay, silt, and sand). A total of 995 soil samples were collected from representative paddy fields in the region and spectra measurements were conducted in the laboratory on air-dried samples. We developed and compared the performance of multiple machine learning algorithms, including partial least squares regression (PLSR), Cubist, random forest (RF) and memory-based learning (MBL), to build robust calibration models. The predictive models showed substantial performance for SOM and TN, indicating high accuracy (R² > 0.75, LCCC > 0.85, RPD > 2) for quantitative prediction. Predictions for pH, silt, sand, and clay were less accurate (R² of 0.48–0.53, LCCC of 0.67–0.71, RPD of 1.39–1.49), suggesting the sensor’s utility is limited to indicating general trends for these properties. Among the tested algorithms, MBL consistently provided the most accurate and robust predictions across the majority of soil properties. Our findings demonstrate that the low-cost portable NIR sensor, when coupled with appropriate machine learning algorithms, is a powerful and viable tool for the rapid and reliable estimation of critical paddy soil fertility properties (SOM and TN). This technology has significant potential to support field-level soil health monitoring, precision fertilization strategies, and sustainable land management in the agricultural systems of Southeastern China. Full article

(This article belongs to the Special Issue Soil Sensing and Mapping in Precision Agriculture: 2nd Edition)

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