Asian Journal of Research and Reviews in Physics

Statistical Approaches to Environmental and Atmospheric Influences on Fifth-generation Mobile Signal Propagation in Tropical Regions: A Critical Review

2026-09-02T10:48:05+00:00

Tropical and equatorial territories combine the most intense sustained rainfall on the planet with an accelerating rollout of fifth-generation mobile networks in the centimetre and millimetre wave bands. The statistical apparatus used to translate environmental and atmospheric measurements into propagation predictions, however, was assembled largely from temperate-latitude datasets and from fixed links considerably longer than the urban small cells that dominate contemporary deployment. This review critically evaluates how statistical methods have been applied to environmental and atmospheric parameters governing fifth-generation propagation in the tropics, and asks whether the resulting evidence supports the confidence routinely placed in it. Five method families are examined: the estimation of point rainfall rate distributions and the conversion of long integration-time records to the one-minute reference; the regression of specific attenuation on rainfall rate through power-law coefficients derived from drop size spectra; the spatial statistics embedded in path reduction factors, effective rainfall rate formulations and site diversity models; the correlational and regression treatment of water vapour, temperature, refractivity, wind and vegetation; and supervised learning applied to path loss and attenuation time series. Convergent evidence establishes that rainfall rates exceeded for one hundredth of one per cent of an average year in equatorial sites are roughly an order of magnitude above temperate values, and that standard international recommendations systematically misestimate attenuation on paths shorter than one kilometre. Beyond this, the evidence weakens sharply. Reported model rankings rest on single-year records from a small number of sites, are assessed with inconsistent error statistics and almost never carry uncertainty intervals, so apparent superiority is frequently indistinguishable from sampling variation. Studies of non-precipitation parameters report correlations that reverse sign between seasons and regression models that explain little of the observed variance, yet these are often interpreted causally. Machine learning results are constrained by small, spatially autocorrelated datasets, by evaluation protocols that permit optimistic bias, and in some cases by reliance on simulator output as ground truth. Progress requires coordinated multi-site campaigns, open data, formal uncertainty quantification and validation protocols that test transfer rather than fit.

Application of Artificial Intelligence in Satellite Orbit and Clock Correction: A Review

2026-09-08T13:09:45+00:00

Aims: This review examines AI-assisted methods for satellite orbit determination and prediction, clock-bias forecasting, thermospheric-density calibration, atmospheric-delay modelling, and integrated GNSS correction. It identifies recurrently successful approaches, limitations in the current evidence, and priorities for future research.

Study Design: A structured narrative synthesis of foundational and recent literature published through early 2026 was undertaken. Targeted keyword searches and backward citation checking were used to identify studies of classical machine learning, recurrent and attention-based networks, ensembles, graph neural networks, and physics-informed neural networks. Evidence was organised by task, data regime, baseline, forecast horizon, metric, and reported limitation; no pooled meta-analysis was performed.

Results: Across the reviewed orbit studies, hybrid residual-learning schemes were the most recurrently successful design, although no pooled effect was estimated. In one thermospheric-density evaluation, AI calibration improved mean absolute percentage error by 61% against NRLMSISE-00 and 39% against JB-08. In one one-day GPS clock experiment, QP-assisted BPNN, WNN, LSTM, and GRU models improved on quadratic polynomial prediction by about 39%, 58%, 27%, and 29%, respectively. In a separate four-city dataset, a graph-based model reduced horizontal positioning error by 40-80% relative to the tested deep-learning baselines. These values are study-specific, not general effect estimates. Common barriers were limited cross-satellite generalisation, scarce precise LEO data, computational constraints, weak uncertainty calibration, and separate orbit and clock pipelines.

Conclusion: AI can improve specific parts of the orbit and clock correction chain when models are evaluated against suitable physical or statistical baselines. The evidence favours transferable, physics-informed, uncertainty-aware, and computationally efficient joint models, supported by common benchmarks and independent validation.

Evaluation and Calibration of Downward Longwave Radiation Models under Clear Sky Condition across the Sahelian Region of Nigeria

2026-09-01T10:36:02+00:00

Downward longwave radiation (DLR) is a major component of the surface energy budget, yet the transferability of empirical clear-sky DLR models across Nigeria’s Sahelian climatic zone remains uncertain. This study evaluated eleven existing empirical DLR models and five locally calibrated modifications for Kano and Sokoto. Monthly mean relative humidity, air temperature, and DLR data covering 1984–2023 were used, with 1984–2015 allocated to model development and 2016–2023 reserved for validation. Model performance was assessed using Mean Bias Error, Root Mean Square Error, Mean Percentage Error, t-test, Index of Agreement, correlation coefficient for the modified models, and an overall ranking procedure. Among the existing models, the Idso formulation ranked first at both locations. For Kano, the modified Guest model was the best-performing calibrated model and also ranked ahead of the existing Idso model in the direct comparison. For Sokoto, the modified Idso model ranked first among the calibrated models; however, the existing Idso model retained the better overall rank in the direct comparison. Seasonal analysis showed higher DLR during the rainy season and lower values during the dry Harmattan season, with relative humidity and atmospheric moisture varying concurrently with DLR. The results indicate that local calibration can improve empirical DLR estimation, although the benefit depends on location and model formulation.

Empirical Measurement of 5G Mobile Signal Path Loss in Southern and Northern Urban Metropolis of Nigeria

2026-09-03T13:38:15+00:00

Accurate characterisation of large-scale radio attenuation is important for fifth-generation (5G) network planning, particularly in heterogeneous urban environments. This study reports a drive-test assessment conducted in Lagos and Ibadan in southern Nigeria and Abuja and Kano in northern Nigeria at 3.5-3.6 GHz. The reported measurement configuration used a receiver height of 1.5 m, a transmitting-antenna height of approximately 40-45 m, and transmitter-receiver separations of about 50-500 m. Reference Signal Received Power, Reference Signal Received Quality, signal-to-noise ratio, throughput, and Global Positioning System coordinates were logged using TEMS Investigation, a 5G signal analyser, and a vehicle-mounted measurement setup. A locally calibrated log-distance relation with city-specific intercept terms was graphically juxtaposed with Okumura-Hata, COST-231 Hata, Egli, and the ITU-R P.833-9 vegetation-attenuation formulation. The plots show substantial divergence among model families and among city/operator panels, demonstrating that model choice and local calibration assumptions materially affect predicted attenuation trends. The ITU-R P.833-9 series is interpreted only as a vegetation-attenuation benchmark rather than a complete urban path-loss model. The results do not support a universal north-south ranking of propagation loss; instead, they indicate site-, route-, and configuration-dependent behaviour. Because complete route-level residuals, uncertainty estimates, and all fitted model parameters are not available for every panel, the comparison is intentionally descriptive and does not claim statistical superiority of one model. The findings support cautious, measurement-informed calibration of 5G propagation models for Nigerian urban deployments.

Influence of Electron Beam Irradiation on the Structural, Optical, and Electrical Properties of Ag₂Se Thin Films

2026-09-04T05:54:02+00:00

The present work aims to investigate the effect of electron irradiation on the properties of silver selenide thin films. In this work, dendritic Ag₂Se thin films were synthesised via a facile, low-cost potentiostatic electrodeposition technique on fluorine-doped tin oxide (FTO) glass substrates. Silver nitrate (AgNO₃) and selenium dioxide (SeO₂) were employed as precursor sources, while ethylenediaminetetraacetic acid (EDTA) served as a complexing agent to regulate ion release and crystal growth (5 mM AgNO₃ + 2.5 mM SeO₂ + 0.05 M EDTA). The phase composition, crystallographic structure, surface morphology, and optical properties of the deposited films were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical absorption spectroscopy. XRD analysis confirmed the formation of crystalline Ag₂Se without detectable secondary phases, whereas SEM revealed the evolution of highly branched dendritic architectures with well-defined fractal characteristics. Optical studies demonstrated the characteristic absorption behaviour of Ag₂Se, indicating its suitability for semiconductor-based applications. Furthermore, the growth mechanism of the dendritic structures was explained through a comparative investigation of the as-deposited films and those subjected to electron-beam irradiation, providing insights into the role of diffusion-limited growth and post-deposition structural evolution. The present electrodeposition strategy offers a scalable and energy-efficient route for fabricating Ag₂Se dendritic thin films with controlled morphology, opening new opportunities for their integration into advanced optoelectronic, thermoelectric, and energy-conversion devices.

Integrated Human Health and Radiological Risk Assessment of Heavy Metals and Naturally Occurring Radionuclides in Soil and Water from Oil

2026-09-08T10:56:45+00:00

Oil and gas exploration can both introduce and redistribute potentially toxic metals and naturally occurring radioactive material across the soils and water bodies of surrounding communities, opening exposure pathways that reach well beyond the immediate production site. This study evaluated the human-health risk from heavy metals and the radiological risk from naturally occurring radionuclides in soil and water sampled from the Apkai and Umusedege oil-field communities in Ndokwa East and Ndokwa West Local Government Areas of Delta State, Nigeria. Sixty-three soil samples and eleven water samples were analysed using atomic absorption spectrophotometry, X-ray fluorescence spectroscopy, gross alpha/beta counting and gamma-ray spectrometry, covering Ni, Cr, Cu, Co, Pb, Cd, Fe, Mn, As and Zn. Human-health risk was modelled for children and adults using USEPA exposure equations across ingestion, inhalation and dermal-contact pathways; the pathway-level components were audited directly against their own reported totals by direct summation of their reported pathway contributions. Once audited, the combined soil-and-water hazard index came to 2.53 for children and 13.60 for adults, with ingestion the dominant soil pathway for both groups and an unusually large adult water-dermal contribution driving the adult total; both hazard indices exceed the HI = 1 screening threshold. Total excess lifetime cancer risk from heavy-metal exposure was 7.18×10⁻⁶ for children and 2.40×10⁻⁶ for adults, both remaining within the USEPA-adopted acceptable range. In water, gross alpha and beta activities averaged 1184 and 2164 mBq L⁻¹ respectively, peaking at 3160 and 6145 mBq L⁻¹, with corresponding mean annual effective doses of 2.154, 1.133 and 0.566 mSv y⁻¹ (alpha) and 4.087, 2.106 and 1.053 mSv y⁻¹ (beta) for adults, children and infants respectively. Gamma spectrometry of soil gave mean activity concentrations of 36.102 Bq kg⁻¹ for ²²⁶Ra, 50.237 Bq kg⁻¹ for ²³²Th and 251.903 Bq kg⁻¹ for ⁴⁰K, with a mean absorbed dose rate of 42.22 nGy h⁻¹, annual effective dose of 0.076 mSv y⁻¹ and radium equivalent activity of 91.627 Bq kg⁻¹. Mean external hazard, internal hazard, gamma representative-level and alpha indices were 0.247, 0.335, 0.376 and 0.162 respectively, and the calculated radiological cancer risks were 3.18×10⁻⁶ for adults and 4.32×10⁻⁶ for the whole population. Taken together, the audited results point to heavy-metal exposure with elevated hazard indices for both children and adults as the primary human-health concern, while soil NORM levels imply comparatively low external radiological hazard. Water, in contrast, showed elevated gross alpha/beta activity and associated doses alongside the dominant adult dermal hazard quotient, and therefore warrants continued radiological and chemical monitoring, more targeted radionuclide-specific follow-up, and independent verification of the adult water-dermal exposure calculation.

Radiological Characterization of Dredged Sediments from the Nun River, Nigeria, and their Implications for Building Material Use

2026-09-11T13:15:32+00:00

This study assesses the radiological safety of sediments obtained from dredging activities along the Nun River, Bayelsa State, Nigeria, where such materials are commonly used in residential construction. Given the potential contribution of naturally occurring radionuclides in building materials to indoor radiation exposure, the study is guided by radiation protection principles aimed at minimising exposure to ionising radiation. Sediment samples from ten locations in two Local Government Areas were analysed using a NaI(Tl) gamma spectrometry system. This study is the first extensive radiological characterisation of dredged sediments from the Nun River, Nigeria, and provides a critical baseline for the Niger Delta region. The mean activity concentrations of ⁴⁰K (402.22 Bq/kg) and ²³⁸U (28.10 Bq/kg) were within the limits set by UNSCEAR, whereas ²³²Th (6.04 Bq/kg) was significantly below the corresponding limit, a pattern characteristic of the mineralogy of the Niger Delta. The radiological hazard indices, including Raeq (mean 67.71 Bq/kg), Hₑₓ (mean 0.18), Hᵢₙ (mean 0.24), and Iγ (mean 0.50), were all below the internationally recommended safety limits. The gamma index (Iγ) ranged from 0.24 to 0.91, indicating that most Nun River sediments meet the initial screening criterion for use in construction applications. Multiple linear regression revealed that ⁴⁰K contributed the most to the variability of Iγ (β=0.486), followed by ²³⁸U (β=0.386) and ²³²Th (β=0.262); the model fit was excellent. Shared mineralogical controls were further suggested by strong correlations among the radionuclides. The results, particularly the hazard indices and Iγ, were well below unity, indicating that the sediments pose negligible indoor exposure risks.