University of Al-Qadisiyah

Co-contamination of paddy soils with antimony (Sb) and nickel (Ni) poses significant risks to soil quality, crop productivity, and food safety. This study evaluated the effectiveness of iron-titanium oxide-engineered biochar (Fe-Ti-BC) in mitigating Sb and Ni mobility in contaminated paddy soil and examined associated changes in soil carbon dynamics and microbial communities. Compared with the control, Fe-Ti-BC application reduced CaCl2-extractable Sb and DTPA-extractable Ni by 20.31-34.31% and 39.87-79.67%, respectively. Amendment with Fe-Ti-BC and unmodified biochar enhanced the carbon pool management index (CPMI) and labile organic carbon fractions, indicating improved carbon sequestration potential and nutrient cycling capacity. Rice biomass significantly increased following biochar treatments. Iron and titanium concentrations in root Fe plaque were approximately 20-fold and twofold higher, respectively, in Fe-Ti-BC-amended soils than in the control, suggesting enhanced plaque-mediated immobilization of trace elements. Consequently, Sb and Ni concentrations in rice grains decreased by 20.02-78.18% and 60.17-69.79%, respectively. High-throughput sequencing revealed that Fe-Ti-BC reshaped soil bacterial community composition and metabolic activity, promoting keystone taxa including Actinobacteria, Proteobacteria, and Firmicutes. Partial least squares path modeling (PLS-PM) identified CaCl2-extractable Sb, DTPA-extractable Ni, and Fe-Ti plaque formation as key determinants governing trace element accumulation in rice grains. Overall, Fe-Ti-BC effectively stabilized Sb and Ni through coupled geochemical and biological mechanisms, thereby reducing metal transfer to edible tissues while enhancing soil carbon functionality and productivity. These findings highlight the potential of engineered biochar as a sustainable remediation strategy for multi-metal contaminated paddy systems with direct implications for environmental health and food security.

Solar air heaters (SAHs) are economical solar energy converters for low- and medium-temperature applications. Even though they are efficient, their use is restricted due to inherently low heat transfer rates. To avoid this limitation, the present work utilizes a numerical analysis to study a new design of the absorber plate with modified wedge-shaped ribs of convex surface. Two-dimensional CFD simulations were conducted in ANSYS Fluent with the RNG K-ε turbulence model to capture the phenomenon of turbulent transport. The major performance parameters—i.e., average Nusselt number ( Nu ), friction factor ( f ), and thermal performance factor ( TPF )—were analyzed to study the system’s thermo-hydraulic behavior. The simulations were performed for a relative roughness pitch range of 7.14 ≤ P/e ≤ 17.86 and Reynolds numbers between 4000 and 20,000 under a uniform heat flux of 1000 W m−2. The relative roughness height was maintained at a constant value of e/Dh = 0.042. The findings demonstrate that incorporating modified wedge-shaped ribs substantially boosts the thermal performance of the SAH with Nu improves by as much as 3.73 times that of the smooth duct. The gain is, however, also accompanied by fluid friction penalty of approximately 3.13 times. The overall performance is good, even with the existence of this penalty, and the TPF is between 1.26 and 2.28, which proves the effectiveness of the suggested rib construction. Finally, nonlinear regression analysis was utilized to establish correlations between Nu and f as functions of Re and P/e.

Density functional theory (DFT) remains a central tool in thermochemical modeling, yet its predictive reliability is strongly system-dependent and often obscured by global statistical metrics. In this work, a diagnostic analysis of the B3LYP functional is presented to identify the dominant physical origins of systematic thermochemical errors. Rather than introducing new calculations, previously published benchmark datasets are reorganized within a unified, semi-quantitative diagnostic framework that links molecular descriptors to characteristic error mechanisms. The analysis reveals distinct failure modes associated with molecular size, structural compactness, dispersion-dominated interactions, and electron density localization. Linear hydrocarbons exhibit cumulative size-dependent errors consistent with missing medium-range correlation effects, while branching-sensitive isomerizations show pronounced overstabilization of linear structures that is significantly—but not fully—reduced by dispersion corrections. In contrast, heteroatom-containing systems display strong sensitivity to diffuse basis functions, indicating that density localization and polarization effects dominate over dispersion. Comparative analysis further shows that polarization and dispersion corrections provide only moderate improvements in these systems relative to diffuse functions. These results demonstrate that B3LYP accuracy cannot be uniformly improved by a single correction strategy and must instead be interpreted within a system-specific, physically informed framework. The analysis is based on previously published thermochemical benchmark datasets comprising neutral closed-shell organic molecules and representative isomerization reactions. Electronic structure methods considered include Hartree–Fock (HF), B3LYP with the 6—31G(d), 6—31G(d,p), and 6—31 + G(d,p) basis sets, dispersion-corrected B3LYP variants, and the semiempirical PDDG/PM3 Hamiltonian. No new quantum chemical calculations were performed; instead, published heats of formation and isomerization energies were systematically reorganized and evaluated using mean absolute errors (MAEs) and structure-dependent diagnostic classifications to identify reproducible performance trends.

Diesel (straight-run gasoil, SRGO) is pivotal to global energy systems, and any increase in throughput must preserve specification compliance. This plant–model case study at the Diwaniyah Refinery evaluates a no-CAPEX lever: reducing the atmospheric kerosene side-draw while holding other product draws at plant averages. In controlled plant trials, the side-draw was reduced from 5 to 1 m3/h; SRGO increased by approximately 44 percent, from 9 to 13 m3/h. Quality outcomes were as follows: sulfur decreased from 15,100 to 10,000 ppm, with the ≤ 10,000 ppm limit met only at 1 m3/h; flash point decreased from 85 to 70 °C yet remained at or above 60 °C across all tests; cetane number remained at or above 50 (minimum 50.2); diesel index improved from 48.23 to 56.16–56.98, meeting the ≥ 55 threshold at 2–1 m3/h; and kinematic viscosity decreased from 1.8 to 1.4 cSt, always within the ≤ 5.6 cSt limit. Aspen Hysys simulation program was used to evaluate scenarios for increasing SRGO and maintaining its specifications. Following laboratory validation, the simulation model showed good agreement with plant data, reproducing the observed operational trends. In addition, Minitab program was used to develop simple empirical models over the 1–5 m3/h range to quantify the effect of kerosene side-draw on SRGO yield and other specifications, and to select an operating point (1 m3/h) that maximizes SRGO while maintaining specification compliance. The results provide actionable guidance for refineries seeking higher diesel output while respecting quality specifications.

This paper provides a comprehensive investigation of the factors affecting the shear strength of steel fiber-reinforced concrete beams without shear reinforcement through an integrated experimental and numerical approach. The geometric and material properties of the numerical model were based on the experimentally tested model. The experimental model was numerically simulated using the ABAQUS program for finite element analysis. After achieving agreement between the numerical and experimental results in terms of ultimate load, deflection, and failure mode, using the finite element software ABAQUS/Standard thirty-two models of reinforced concrete beams with different configurations were proposed to study the combined effect of multiple variables on shear strength, including compressive strength, cross-sectional beam area, beam depth, compression zone reinforcement, flexural reinforcement diameter, and shear span ratio. The results of the numerical analysis of concrete specimens revealed a direct relationship between compressive strength and ultimate strength. Higher strength grades generally diminish this effect. The results indicated that the beam with a T-section shape had a higher strength compared to the rectangular cross-section, and this strength increased with increasing flange depth. Furthermore, increasing the beam depth and the compression reinforcement ratio also improved the shear strength. A slight increase in shear strength was achieved by increasing the number of bars and decreasing the diameter of the flexural reinforcement while maintaining a constant ratio of ( A_sf_y) . However, the results were opposite for the shear span ratio, as the ultimate bearing strength of the specimens decreased with increasing shear span ratio (a/d). The numerical study also proved the efficiency of steel fibers in improving the behavior of concrete beams and their ability to withstand loads. These results provide useful insights for the design of beams without shear reinforcement, especially when considering sustainable alternatives such as the use of steel fibers and some parameters that increase the strength of concrete beams.