Journal Articles

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12504/113

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Revisiting the exoplanet radius valley with host stars from SWEET-Cat
(Astronomy&Astrophysics, 2026-01-13) Kamulali, Juma; V. Adibekyan; B. Nsamba; S. G. Sousa; T. L. Campante; A. Weiss; B. Kabugho; N. Moedas; N. C. Santos; O. Trust
Context. The radius valley, a deficit in the number of planets with radii around 2 R⊕, was observed among exoplanets that have sizes of ≲5 R and orbital periods of <100 days by NASA’s Kepler mission. This feature separates two distinct populations: super-Earths (rocky planets with radii ≲1.9 R⊕) and sub-Neptunes (planets with substantial volatile envelopes and radii ≳2 R⊕). The valley has been proposed to stem from either planet formation conditions or evolutionary atmospheric loss processes. Disentangling these mechanisms has led to numerous studies of population-level trends, although the resulting interpretations remain sensitive to sample selection and the robustness of host-star parameters. Aims. Our aim is to re-examine the existence and depth of the radius valley, and how its location varies with orbital period, incident flux, stellar mass, and stellar age. Methods. We derived robust fundamental stellar parameters of 1221 main-sequence stars (hosting 1405 confirmed planets) from the SWEET-Cat database using a grid-based machine-learning tool (MAISTEP), which incorporates effective temperatures and metallic-ities from spectroscopy, as well as Gaia-based luminosities. Our analysis covers stars with effective temperatures between 4400 and 7500 K (FGK spectral types) and estimated radii between 0.62 and 2.75 R⊕. We attained a median uncertainty of 2% in both stellar radius and stellar mass. Combining the updated stellar radii with planet-to-star radius ratios from the NASA Exoplanet Archive, we recomputed the planetary radii, achieving a median uncertainty of 5%. Results. Our findings confirm a partially filled planet radius valley near 2 R⊕. The valley depends on the orbital period, incident flux, and stellar mass, with slopes of −0.12−0.01+0.02, 0.10−0.03+0.02, 0.19−0.07+0.09, respectively. We also find a stronger mass-dependent trend in average sizes of sub-Neptunes than super-Earths of slopes 0.17−0.04+0.04 and 0.11−0.05+0.05, respectively. With stellar age, the super-Earth/sub-Neptune number ratio increases from 0.51−0.08+0.11 (<3 Gyr) to 0.64−0.11+0.11 (≥3 Gyr). In addition, the valley becomes shallower and shifts to larger radii, indicating age-dependent evolution in planet sizes. A four-dimensional (planet radius, orbital period, stellar mass, and stellar age) linear fit of the valley in log-log space produces slopes in orbital period and stellar mass that are consistent with the results from the two-dimensional analyses, and a weaker slope of 0.07−0.04+0.03 in stellar age. Conclusions. The valley’s shift and shallowing over gigayear timescales point to prolonged atmospheric loss, which is consistent with a core-powered mass-loss scenario. Our findings also highlight the importance of stellar age in the interpretation of exoplanet demographics and motivate improved age determinations, as is expected from future missions such as PLATO.
Advanced graphene–MXene–black phosphorus multilayered metasurface sensor for high-sensitivity terahertz brain tumor detection
(AIP Advances, 2026-03-11) Wekalao, Jacob; Elsayed, Hussein A.; Alqhtani, Haifa A.; Almawgani, Abdulkarem H. M; Gumaih, Hussein S.; Adam, Yousif S.; Mehaney, Ahmed; Ochen, William
In this research, we present a multilayer metasurface sensor design integrating graphene, MXene, black phosphorus, and gold for the ultrasensitive detection of brain tumor biomarkers in liquid biopsy samples. The hierarchical structure consists of a MXene-coated rectangular resonator, a black phosphorus-coated square resonator, a gold-coated circular ring, and a graphene-based circular substrate. This architecture was systematically optimized through comprehensive numerical simulations using COMSOL Multiphysics 6.3, integrated with machine learning frameworks. The proposed sensor demonstrates an outstanding sensitivity of 2308 GHz/RIU across a physiologically relevant refractive index range (1.3333–1.4833), significantly outperforming current state-of-the-art devices. Performance analysis identifies an optimal sensing regime at RI = 1.3425, achieving a figure of merit of 20.79 RIU−1 and a detection limit as low as 0.079 RIU. Detailed investigations of the transmission spectra under varying graphene chemical potentials (0.1–0.9 eV), incident angles (0○ –80○ ), and geometric modifications of the resonators reveal highly tunable sensing behavior. Furthermore, Random Forest Regression models achieve predictive accuracies of 85%–100%, enabling reliable estimation of sensor performance across diverse operating conditions. Collectively, these results establish a solid foundation for employing advanced 2D material–based metasurfaces in minimally invasive and early-stage brain tumor diagnostics, thereby advancing the capabilities of next-generation liquid biopsy technologies.
Terahertz plasmonic metasurface sensor with graphene–CNT–copper integration for enhanced glucose sensing performance
(Indian J Phys, 2026-02-16) Wekalao, J; Elsayed, H A; Bin-Jumah, M; Almawgani, A H M; Gumaih, H S; Adam, Y S; Mehaney, A; Rajakannu, A; Muheki, J
This study presents a simplified terahertz biosensor that synergistically integrates graphene, carbon nanotubes, and copper to achieve an enhanced glucose sensing performance. Meanwhile, our sensing platform consists of a centrally positioned square resonator functionalized with carbon nanotubes, coupled to two copper-modified rectangular resonators lithographically patterned on a silicon dioxide substrate. The numerical findings based on the well-known Finite element method simulations performed in COMSOL Multiphysics identify an optimal operating frequency of 0.58 THz, delivering a maximum sensitivity of 1000 GHzRIU-1 over a refractive index range of 1.335–1.347 RIU. Additionally, our biosensor demonstrates strong performance metrics, including a quality factor (Q-factor) of 8.391, a figure of merit (FOM) of 14.493 RIU-1 , and a detection limit of 0.133. moreover, the machine learning analysis based on Polynomial regression technique is considered to validate the analytical consistency and operational robustness of the device, achieving predictive accuracies exceeding 90% under the variations of both graphene chemical potential and incident angle of the propagating electromagnetic waves. In this regard, we believe that, the combination of high sensitivity, predictive stability, and resilience to multi-parameter perturbations establishes the X-configuration architecture as a competitive platform for glucose biosensing. Moreover, the multi-material engineering strategy constitutes a meaningful advancement in terahertz biosensor design by exploiting complementary physicochemical properties within an optimized X-shaped geometry to enhance functional performance.
Machine learning–enhanced tunable terahertz metasurface sensor with a hybrid multi-resonator architecture for highsensitivity mino acid detection
(Optical and Quantum Electronics, 2026-02-28) Muheki, Jonas; Ahmed, Ashour M.; Ali, M. K. M.; Elsayed, Hussein A.; Kabarokole, Pelluce; Wekalao, Jacob; Mehaney, Ahmed; Rajakannu, Amuthakkannan
Accurate amino acid detection is essential for biomedical diagnostics, clinical monitoring, and biochemical research; however, conventional analytical techniques are often constrained by complex sample preparation, high operational costs, and limited real-time capability. Terahertz (THz) metasurface sensors provide a promising label-free and nonionizing alternative, yet their performance is frequently hindered by weak light–matter interaction and design trade-offs between sensitivity and fabrication feasibility. In this work, a hybrid THz metasurface sensor is proposed, integrating graphene, gold (Au), silver (Ag), copper (Cu), and tungsten disulfide (WS₂) within a hierarchical multiresonator configuration comprising square, circular ring, and L-shaped resonators fabricated on a SiO₂ substrate. The proposed architecture exploits synergistic plasmonic–dielectric coupling and strong near-field confinement to enhance sensitivity to refractive index perturbations induced by amino acid analytes, while maintaining a geometrically simplified structure to ensure manufacturability. Numerical simulations demonstrate excellent sensing performance, achieving a maximum sensitivity of 1000 GHz/RIU, a peak figure of merit (FOM) of 50 RIU⁻1 , and a strong linear relationship (R2=0.96243) between resonance frequency shift and analyte refractive index. Furthermore, machine learning (ML) models are employed to predict and optimize sensor behavior, yielding near-perfect accuracy (R2>0.9995) for variations in graphene chemical potential (0.1–0.9 eV) and circular resonator dimensions (5.5–7.5 µm). The proposed integration of hybrid materials, multi-resonator metasurface design, and ML-driven optimization effectively addresses key challenges in THz biosensing, enabling rapid, sensitive, and scalable amino acid detection for both point-of-care diagnostics and advanced biochemicalresearch.
Feasibility of combined solar cookers and dryers for dual cooking and drying: A systematic review
(Solar Compass, 2026-02-12) Rukaaya, Musa; Abedigamba, Oyirwoth P.; Mawire, Ashmore; Okullo, Willy
Dual-purpose cooking and drying systems offer a promising solution for sustainable food preparation and preservation, particularly in regions with abundant solar radiation. This systematic review assesses the current state of technology and knowledge gaps in solar cooker cum dryers, focusing on design configuration, thermal performance, and sustainability relevance. A comprehensive search of the databases yielded 13 studies that met the inclusion criteria. The review highlights the strengths and weaknesses of the design configurations. The findings revealed that these systems can achieve temperatures up to 150 °C, making them suitable for cooking and drying applications, which reduces fuel costs and lowers carbon emissions. Limited work has been done on combined solar cookers and dryers, and most studies use the same unit for both cooking and drying, and very few have separate units. All reviewed studies on solar cookers combined with dryers have employed flat plate collectors with no work on concentrating systems, and most studies are experimental with limited numerical work. Most studies employed the natural convection mode of air circulation, with only a few focusing on forced convection. Additionally, most solar cookers combined with dryers lack energy storage systems, and there is limited work that has been reported on the economic analysis of the combined systems. These findings inform future research and development for sustainable energy solutions, providing insights for policymakers, researchers, and practitioners. This review aims to contribute to the development of efficient and effective combined solar cookers and dryers, ultimately enhancing food security and reducing reliance on fossil fuels.
Radioactivity and toxic element concentrations in soil and food crops from a copper mining area in Uganda: environmental and public health implications
(Radiation Physics and Chemistry, 2026-02) Turyahabwa, Evarist R.S.; Kyeyune, Farooq; Eric Mucunguzi; Akisophel Kisolo; Manny Mathuthu
Mining activities can lead to the accumulation of radionuclides and metallic elements in surrounding soils, posing risks to food safety and human health. This study assessed radioactivity and contamination with toxic elements in 18 soil and food crop samples from the Kilembe copper mining area in Western Uganda to evaluate potential public health impacts. The samples were analysed for 226Ra, 232Th, and 40K using high-purity germanium (HPGe) gamma spectrometry, while concentrations of Cr, Cu, Co, Ni, Pb, and As were determined using inductively coupled plasma mass spectrometry (ICP-MS). The mean activity concentrations of 226Ra, 232Th, and 40K in soils were 71.16 ± 40.87, 50.85 ± 9.01, and 823.70 ± 231.58 Bq kg−1, respectively, all exceeding world averages. In food crops, 40K levels (1066.51 ± 224.71 Bq kg−1) were also elevated. The estimated annual committed effective dose exceeded the ICRP safety limit of 1 mSv y−1 for infants and children, while the excess lifetime cancer risk surpassed the 2.9 × 10−4 threshold for all age groups. Annual organ-specific dose estimates revealed increased risks to the gastrointestinal tract and bone surfaces. Metallic element analysis showed high concentrations of Cu (541.05 ± 389.83 mg kg−1) and Pb (64.99 ± 32.93 mg kg−1) in soils, with Pb levels in crops exceeding the WHO/FAO limit by 20 %. The health hazard indices for Cu, Pb, and As were above unity in both children and adults, indicating significant non-carcinogenic risks. Total cancer risks from Pb and As were (2.91 ± 1.27) × 10−3 (children) and (1.67 ± 0.73) × 10−3 (adults), which exceeded acceptable thresholds. Statistical analysis indicated shared geochemical behaviour of radionuclides and metals in soils, but distinct uptake pathways in food crops. These findings highlight the need for environmental monitoring, mining waste remediation, and regulating food sources to reduce radiological and chemical health risks in the study area.
Machine-learning-assisted multilayer graphene–silver–ZrN surface plasmon resonance biosensor for high-sensitivity hemoglobin detection
(Materials Technology, 2026-02-09) Ochen, William; Wekalao, Jacob; Muheki, Jonas; Elsayed, Hussein A.; Alqhtani, Haifa A.; Almawgani, Abdulkarem H. M.; Alhawari, Adam R.; Mehaney, Ahmed; Solouma, Emad
This work presents a theoretically optimized multilayer surface plasmon resonance (SPR) biosensor for quantitative hemoglobin detection using the Kretschmann configuration. The sensor integrates a BK-7 prism, silver plasmonic layer, graphene enhancement layer, zirconium nitride (ZrN) protective layer, and aqueous sensing medium. This architecture synergistically combines enhanced electromagnetic confinement with chemical stability, addressing silver's oxidation vulnerability while maintaining superior plasmonic performance. Electromagnetic analysis via transfer matrix method and finite element simulations demonstrates exceptional sensitivity metrics: maximum angular sensitivity of 500°/RIU, figure of merit of 92.25 RIU⁻¹, and detection limit of 0.006 RIU across clinically relevant hemoglobin concentrations (10–40 g/L). Localized electric field enhancement (~10⁶ V/m) at the sensing interface confirms optimal light-matter interaction amplification. Machine learning models predict sensor responses to graphene thickness and refractive index variations with R² > 0.99, enabling rapid optimization. This design advances SPR biosensor technology for sensitive, label-free biochemical detection applications.
Biosynthesized nickel oxide honeycomb nanostructures for DSSC counter electrode: a joint experimental and density functional theory study
(Materials Research Express, 2026-01-05) Nasejje, Stella; Mushebo, Emmanuel; Birabwa, Denise Joanitah; Diale, Mmantsae; Mukhokos, Emma Panzi
The urgent need to address fossil fuel challenges has led to a surge in green energy technologies, including solar cells. Nanodimensional particles, particularly 2D nanostructures, have shown great potential in these technologies due to their high surface area-to-volume ratio. Nickel oxide (NiO) is a promising p-type semiconductor for solar cell photo-cathodes, offering remarkable physical and chemical properties at a relatively low cost. However, its surface morphology, area, and pores have a significant impact on performance.Traditional chemical synthesis methods for NiO nanostructures have several drawbacks, including the use of hazardous precursors.To address this, we present for the first time a novel bioengineering method using bamboo shoot extract to produce 2D NiO nanostructures. The results have been supported by Density Functional Theory (DFT) calculations. The DFTcalculations revealed that NiO is a p-type semiconductor with direct band gap for spin-down at Г.The results show that the bioengineered NiO nanostructures exhibit high crystallinity and a honeycomb-like morphology.We successfully integrated these nanoparticles into a dye-sensitized solar cell (DSSC), demonstrating their viability as a counter electrode.The cell exhibits promising performance,with a short-circuit current density of 0.113 mA cm−2 and an efficiency of 0.0057%.This study presents a straight forward, cost-effective, and environmentally friendly method for bioengineering NiO honeycomb-like nanostructures,thereby paving the way for sustainable energy solutions.
High-sensitivity terahertz metasurface biosensor for multi-cancer detection: a machine learningenhanced approach using graphene–MXene– silver–copper hybrid architecture
(Materials Technology Advanced Performance Materials, 2025-12-19) Wekalao, Jacob; Elsayed, Hussein A.; Mehaney, Ahmed; Ochen, William; Othman, Sarah I.; Bellucc, Stefano; Amuthakkannan, Rajakannu; Ahmed, Ashour M.; Muheki, Jonas
Early cancer detection requires highly sensitive diagnostic tools beyond the capabilities of conventional imaging and biopsy methods. We present a terahertz (THz) metasurface biosensor that integrates a copper-coated H-shaped resonator with three silver rectangular resonators enclosed within an MXene circular ring. The design incorporates complex electromagnetic interactions, nonlocal effects, and coupled-mode modelling to optimise performance. The biosensor achieves a sensitivity of 1000 GHz/RIU, a quality factor of 3.6–3.747, and a figure of merit up to 13.333 RIU⁻¹. It maintains stable absorption (52.789–53.804%) across 0.27–0.281 THz, with a linear resonance–refractive-index response (R² = 0.95276). Machine-learning optimisation of graphene chemical potential further enhances predictive accuracy (R² = 0.93). By enabling simultaneous detection of multiple cancer biomarkers through frequency-shift analysis, this noninvasive platform offers strong potential for real-time, early-stage cancer screening.
AI-Augmented terahertz metamaterial biosensor for rapid and accurate isoquercitrin detection in herbal medicines
(Taylor and Francis, 2025-12-01) Wekalao, Jacob; Jonas Muheki; Hussein A. Elsayed; Haifa A. Alqhtani; Mayi Bin-Jumah; Amuthakkannan Rajakannu; Ahmed Mehaney; Stefano Belluci
We present a novel metamaterial-based terahertz biosensor integrated with AI for rapid isoquercitrin detection in herbal medicines. The sensor, optimized through COMSOL simulations, delivers exceptional sensitivity (300GHzRIU-1) and detects refractive index changes as small as 0.05 RIU. Its precision is validated by a near-perfect linear correlation (R2 ¼ 99.73%) and stable performance metrics, including a 0.015 THz FWHM and Quality Factor of 47. Uniquely, a one-dimensional convolutional neural network augments predictive capability, achieving R2 values up to 1.00 across diverse conditions. This synergistic approach—combining terahertz spectroscopy, metamaterial-enhanced signal amplification, and AI-driven modeling—offers a transformative solution for standardizing and quality-controlling botanical therapeutics. By enabling fast, accurate, and scalable quantification of bioactive compounds, the system sets a new benchmark for analytical methodologies in natural product research.
Multi-resonator plasmonic metasurface biosensor with graphene enhancement for ultra-sensitive terahertz pregnancy detection using machine learning optimization
(Journal of Electromagnetic Waves and Applications, 2025-11-27) Wekalao, Jacob; Muhek,Jonas; Elsayed, Hussein A.; Mehaney,Ahmed; Othmane, Sarah I.; Abukhadra, Mostafa R.; Bellucci, Stefano; Rajakannu,Amuthakkannan; Ochen, William
This study presents a multi-resonator plasmonic metasurface biosensor operating in the terahertz range for detecting human chorionic gonadotropin (hCG), a primary pregnancy biomarker. The sensor consists of four resonators with different geometries and dimensions made from graphene, copper, aluminum, and gold. Its operation is based on surface plasmon resonance. Finite element simulations showed that transmittance varied from 98.428% to 30.736% as the graphene chemical potential changed from 0.1 to 0.45 eV. The optimized sensor achieved a sensitivity of 1000 GHz per refractive index unit (RIU) and a figure of merit of 13.333 RIU−1 . A Gradient Boosting Regressor model was used to predict sensor behavior. The model produced R 2 values between 0.90 and 1.00 for variations in incident angle, square ring geometry, and graphene chemical potential. Resonance frequency shifted from 0.32 to 0.30 THz with refractive index changes, following a linear relationship (R2 = 0.88947) that allows calibration for hCG detection.
Design and optimization of a hybrid graphene–gold–silver terahertz metasurface biosensor for high-sensitivity sperm detection with machine learning for behavior prediction
(Journal of Electronic Materials, 2025-11-25) Muheki, Jonas; Elsayed, Hussein A.; Alfassam, Haifa E.; Ochen, William; Rajakannu, Amuthakkannan; Mehaney, Ahmed; Wekalao, Jacob
This study introduces a plasmonic-based sensor for sperm detection, integrating gold, graphene, and black phosphorus within a tailored multilayer structure. The sensor design consists of a silver-coated circular ring resonator (radius: 2–2.5 µm), a black phosphorus-coated square ring (7–8 µm), and four gold-coated circular resonators (each with a 2 µm radius) placed on a graphene-coated square platform. Electromagnetic simulations performed using COMSOL Multiphysics indicate optimal sensing performance within the 0.1–0.6 THz frequency range. The sensor demonstrates remarkable sensitivity of 5000 GHz per refractive index unit (RIU−1), a figure of merit of 90.909 RIU−1, and a detection limit of 0.02 RIU. It is capable of detecting sperm concentrations in a range of 17–197 million/mL, corresponding to refractive index variations from 1.33 to 1.3461. Furthermore, performance optimization through XGBoost machine learning achieved perfect prediction accuracy (R2 = 1.00) across all test cases. This high-efficiency sensor marks a significant step forward in sperm detection technologies, with promising applications in male fertility assessment and reproductive medicine
Atomic force microscopy in structural and functional studies of biomolecules
(Biophysical Reviews and Letters, 2025-10) Uzorka, Afam; Mukhokosi, Emma Panzi
Atomic force microscopy (AFM) has emerged as a cornerstone technology in molecular and cellular biophysics, offering nanometer-scale resolution under near-physiological conditions. Unlike electron microscopy (EM), AFM preserves native biomolecular states and enables simultaneous acquisition of topographical and mechanical data. This review synthesizes the principles, applications, methodological advances, and future directions of AFM in both structural and functional studies of biomolecules. Structural applications include high-resolution imaging of proteins, nucleic acids, and membrane systems, while functional investigations leverage single-molecule force spectroscopy (SMFS), binding interaction analysis, and mechanobiology assays. Methodological innovations such as high-speed AFM (HS-AFM), functionalized probes, and correlative multi-modal techniques have expanded AFM’s capacity to probe dynamic processes in real time. Despite challenges such as tip-induced artefacts, throughput limitations, and data interpretation complexities, emerging trends point toward AI-assisted image analysis, in-cell AFM, and integration with molecular simulations. Functionalized nanosensors and automated platforms promise to transform AFM from a specialized research instrument into a high-throughput, intelligent biophysical tool. By bridging the gap between structural detail and functional insight, AFM is poised to play a pivotal role in advancing our understanding of biomolecular mechanisms, disease pathology, and therapeutic development.
Assessment of the Performance of International Reference Ionosphere Models 2016 and 2020 in Predicting TEC in the Low-Latitude Ionosphere over Africa and South America
(Elsevier, 2025-10-15) Geoffrey, Cele; Geoffrey Andima; Valence Habyarimana; Edward Jurua; Oyirwoth Patrick Abedigamba
The sparse distribution of Global Navigation Satellite System (GNSS) receivers in low-latitude region has hindered continuous monitoring of the ionosphere. To address this challenge, ionospheric models such as the International Reference Ionosphere (IRI) are often used. This study compares the performance of IRI-2020 and its predecessor (IRI-2016) with the Global Positioning System (GPS) observations over African and South American low-latitude regions during quiet conditions. The GPS Vertical Total Electron Content (VTEC) measurements from Addis Ababa (Geog. 38.77°E, 9.04°N), Sao Luis (Geog. −44.21°E, −2.59°N), Malindi (Geog. 40.19°E, −3.00°N), Libreville (Geog. 9.67°E, 0.35°N), Brasilia (Geog. −47.88°E, −15.95°N) and Cacoheira Paulista (Geog. −45.00°E, −22.68°N) stations for the high, moderate and low solar activity years 2014, 2016 and 2018 were compared with IRI-derived VTEC values. To objectively assess the model accuracy, the Mean Absolute Percentage Error (MAPE) and Normalized Root Mean Squared Error (NRMSE) metrics were employed, offering intuitive and reliable benchmarks for quantifying the model discrepancies. The monthly performance indicates that IRI-2020 and its predecessor significantly underestimate VTEC over Addis Ababa, yet slightly overestimate it over Libreville and Cacoheira Paulista across all studied years. Seasonal analysis reveals the largest discrepancies at the Equatorial Ionisation Anomaly (EIA) trough and Southern crest during solstice seasons. An evaluation of the latitudinal performance of IRI-2016 and IRI-2020 highlights better accuracy over the EIA trough. Furthermore, longitudinal assessment shows superior performance of both models at Libreville station, with IRI-2020 and IRI-2016 achieving notably low annual MAPE (aMAPE) values of and , respectively. Comparative analysis based on NRMSE shows IRI-2020’s improvement of at the dip equator, while its performance declines by at the EIA Southern crest. This study reveals significant discrepancies in the performance of IRI-2020 model over Africa and South America low-latitude, emphasizing the need for continuous model improvement.
Green synthesis of ZnO nanoparticles for DSSC photoanode : a joint experimental and density functional theory study
(Materials Research Express, 2025-09-29) Balabye, Stephen Emma; Mushebo, Emmanuel; Nasejje, Stella; Egor, Moses; Mukhokosi, Emma Panzi
Green synthesis, a biological method for nanoparticle preparation, has been suggested as a possible eco-friendly alternative to chemical and physical methods. In this study, we report on first principles calculations and the green synthesis of zinc oxide (ZnO) nanoparticles (NPs) from Erythrina abyssinica stem bark extract calcined under different temperatures (300-700 ℃) for application as a photoanode in dye sensitized solar cells (DSSCs). Synthesized ZnO NPs were subjected to characterization using X-Ray diffraction, Scanning Electron Microscopy, Energy Dispersive X-Ray spectroscopy, Ultraviolet–Visible spectroscopy and photoluminescence analysis. The analysis revealed that highly crystalline hexagonal ZnO NPs were formed at 700 ℃, with the nanospheres agglomeration into non-uniform distinct NPs with a band gap energy of 3.12 eV. The DSSC exhibited a short circuit current density (Jsc) of 56 µA cm-2, open circuit voltage (Voc) of 161 mV, a fill factor of 0.265, and a power conversion efficiency of 0.0024% using 100 mWcm-2 illumination. Density Functional Theory (DFT) calculations were performed on the structural, electronic, and dielectric properties of ZnO at the atomic level. The Projected Density of States (PDOS) analysis revealed that Zn-4s and O-2p orbitals contributed significantly to the conduction band minimum (CBM) and valence band maximum (VBM), respectively, and a direct band gap at Gamma in the electronic band structure. Dielectric function analysis revealed anisotropy in the refractive index and dielectric function, with noticeable transparency in the visible spectrum and strong absorption in the ultraviolet, making them potential candidates in a set of photoelectrochemical applications.
Unveiling the variability and chemical composition of AL Col
(MDPI Galaxies, 2025-08-14) Surath, C. Ghosh; Santosh Joshi; Samrat Ghosh; Athul Dileep; Otto Trust; Mrinmoy Sarkar; Jaime Andrés Rosales Guzmán; Nicolás Esteban Castro-Toledo; Oleg Malkov; Harinder P. Singh; Kefeng Tan; Sarabjeet S. Bedi
In this study, we present analysis of TESS photometry, spectral energy distribution (SED),high-resolution spectroscopy, and spot modeling of the α 2 CVn-type star AL Col (HD 46462). The primary objective is to determine its fundamental physical parameters and investigate its surface activity characteristics. Using TESS short-cadence (120 s) SAP flux, we identified a rotational frequency of 0.09655 d −1(Prot = 10.35733 d). Wavelet analysis reveals that while the amplitudes of the harmonic components vary over time, the strength of the primary rotational frequency remains stable. A SED analysis of multi-band photometric data yields an effective temperature (Teff) of 11,750 K. High-resolution spectroscopic observations covering wavelengthrange 4500–7000 Å provide refined estimates of Teff = 13,814 ± 400 K, log g = 4.09 ± 0.08 dex, and υ sin i = 16 ± 1 km s−1. Abundance analysis shows solar-like composition of O II, Mg II, S II, and Ca II, while helium is under-abundant by 0.62 dex. Rare earth elements (REEs) exhibit over-abundances of up to 5.2 dex, classifying the star as an Ap/Bp-type star. AL Col has a radius of R = 3.74 ± 0.48R⊙, with its H–R diagram position estimating a mass of M = 4.2 ± 0.2M⊙ and an age of 0.12 ± 0.01 Gyr, indicating that the star has slightly evolved from the main sequence. The TESS light curves were modeled using a three-evolving-spot configuration, suggesting the presence of differential rotation. This star is a promising candidate for future investigations of magnetic field diagnostics and the vertical stratification of chemical elements in its atmosphere.
Assessment of indoor radon (222Rn) levels and associated radiological risks in occupational buildings and dwellings in Kampala, Uganda
(The European Physical Journal Plus, 2025-08-09) Farooq, Kyeyune; Ivan Ssikubwabo; Thomas Baluku; Evarist R. S. Turyahabwa
Radon-222 (222Rn) is a naturally occurring radioactive gas and the second leading cause of lung cancer after smoking, posing a public health concern. Assessing indoor 222Rn levels in occupational and residential environments is essential for radiological risk evaluation. In this study, indoor 222Rn concentrations were measured using a continuous radon monitor (CRM) in 20 buildings across Kampala City, Uganda. In occupational buildings, 222Rn concentrations ranged from 8.7 ± 1.5 to 95.8 ± 8.0 Bq m−3, with a mean of 30.8 ± 4.5 Bq m−3. Poorly ventilated storage rooms showed elevated levels, with a maximum of 194.8 ± 21.2 Bq m−3, exceeding the WHO reference level of 100 Bq m−3. In dwellings, concentrations ranged from 15.3 ± 2.3 to 188.2 ± 8.2 Bq m−3, averaging 71.7 ± 17.5 Bq m−3. Some dwellings recorded values above the WHO threshold. The average annual effective doses were 0.32 ± 0.05 mSv y−1 in occupational buildings and 0.75 ± 0.18 mSv y−1 in dwellings, both below the recommended public limit of 1.0 mSv y−1. Additional radiological parameters, including annual equivalent dose, excess lifetime cancer risk and potential lung cancer cases, were also evaluated. Statistical analysis revealed a strong positive correlation between 222Rn concentrations and radiological hazard indices, as well as a positive correlation with indoor humidity and a weak negative correlation with temperature. These findings highlight the importance of controlling humidity and enhancing ventilation to mitigate indoor radon risks. Although indoor 222Rn levels in the surveyed buildings were generally low and unlikely to pose significant health risks, continued monitoring is recommended to capture seasonal variability and ensure long-term radiological protection for occupants.
Temperature dependent microstructural defects and surface charge effects on antioxidant activity of green synthesized nanoceria
(Scientific Reports, 2025-08-08) Musa Kabagambe; IsaAhuura; Sam Kinyera Obwoya; Emma Panzi Mukhokosi
This study reports a novel eco-friendly route for synthesizing cerium dioxide nanoparticles (nanoceria) that converts waste coffee husks into both reagent and process medium. Polyphenol rich phytochemicals chelate Ce3+, guide hydrolysis, and locally modulate redox conditions, imprinting abundant surface Ce3+ and oxygen vacancies that underpin activity. Reuse of the clarified supernatant in successive cycles boosts yield exponentially without added metal oxide precursor, highlighting intrinsic process efficiency. Subsequent calcination turns the bio templated precipitate into phase pure fluorite CeO₂ whose crystallite size, strain, and defect concentration can be tuned by temperature alone. Higher temperatures enlarge particles and improve crystallinity while removing vacancies and strain. Radical scavenging assays show the highest activity in uncalcined material and a steady decline with increasing temperature that parallels the loss of surface Ce3+ and vacancies. Statistical analysis confirms that antioxidant performance depends on defect density, quantum confinement, and surface charge, whereas external morphology and residual organics are negligible. The unique mechanism is phytochemical-directed defect engineering, which couples the use of agricultural waste with precise control of redox-active sites to deliver tuneable nanoceria for biomedical, agricultural, and environmental remediation applications.
A dye-sensitized solar cell based on an in-situ hydrothermally grown hematite photo-anode
(Springer Nature Link, 2025-07-22) Nasejje, Stella; Mukhokosi, Emma Panzi; Mmantsae, Diale
Transition metal-oxides have gained research attention for applications in optoelectronics devices like dye-sensitized solar cells (DSSCs). This contribution presents an α-Fe2O3-Pt DSSC configuration. An in-situ hydrothermal technique was used to grow spherically shaped α-Fe2O3 thin films on an FTO substrate, forming the photo-anode. The surface morphology, structural, and optical properties were characterized by standard techniques, confirming the samples’ purity. Pt was drop-cast on the FTO substrate, forming the counter electrode. The photo-anode was soaked in N719 ruthenium dye for 24 h. The electrodes were assembled using crocodile clips, and the iodide electrolyte was injected into the space between them. At an intensity of 100 mW/cm2, the α-Fe2O3-Pt DSSC yielded a short-circuit photocurrent density, open-circuit voltage, fill factor, and efficiency of 0.098 mAcm−2, 0.410 V, 0.247, and 0.01%, respectively. These results provide a simple, cost-effective strategy for synthesizing spherical nanoporous α-Fe2O3 thin films for potential application as photo-anodes in n-DSSCs.
Green synthesis of hematite nano flakes and their application as a counter electrode in dye-sensitized solar cells
(Scientific Reports, 2025-06-05) Mukhokosi, Emma Panzi; Mushebo, Emmanuel; Nassejje, Stella; Botha, Nandipha L.; Velauthapillai, Dhayalan; Maaza, Malik
This study pioneers using hematite nanoflakes as a viable alternative to traditional platinum counter-electrodes in dye-sensitized solar cells (DSSCs), demonstrating its effectiveness for the first time. Besides such a novelty, the used hematite nanoflakes were bio-engineered using ginger extract as an effective chelating reducing agent. From the X-ray diffraction studies, it was observed that the sample annealed at 700 °C formed a highly crystalline α-Fe2O3, with a crystallite nano-scaled size of the order of 46.3 nm. The scanning electron microscopy investigations indicated a preferred layered nanoflakes morphology while the optical properties revealed a direct band gap of 2.30 eV. Using N-719 dye as a sensitizer on TiO2 photoanode and I−/I3− as electrolyte, the DSSC was fabricated. Such a cell exhibited significant DSSC responses, namely; a short circuit current density (JSC) of 7.0 mAcm−2, an open circuit voltage (VOC) of 389 mV, and a fill factor (FF) of 75.3% in addition to an efficiency (η) of 2.05%. Based on such a significant photo-conversion response using bio-engineered active counter electrodes, this study provides a cost-effective approach for synthesizing hematite NFs that have potential applications not only in DSSC but also in sensors, water splitting, and electrochemical devices.

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