Steady seepage near an impermeable obstacle

The problem of an obstacle with maximum cross-sectional area has been analytically solved in terms of a model for 2-D seepage flow with a capillary fringe. The boundary of the obstacle appears to show a 'blunt configuration', that is, the pressure reaches its maximum value at the vertex and decreases monotonically downstream. With a sufficiently large size of obstacle, a positive pressure domain in the form of a 'bubble' is formed in the vicinity of its vertex. This result has been verified by computations for saturated-unsaturated flows in terms of the finite element method for the Richards equation. It has also been shown that an obstacle can transform the initial fully saturated flow into unsaturated flow inside the 'dry shadow' domain. The shape of an obstacle in a confined aquifer that provides a minimum water head drop has been determined within the scope of the Dupuit model. A 'critical cavity shape' has been found, i.e. a cavity for which the boundary is simultaneously an isobar and a stream line. © 1992

Nanostructured Al2O3/Graphene Additive in Bio-Based Lubricant: A Novel Approach to Improve Engine Performance

Personal and industrial use of internal combustion engines (ICEs) is projected to continue until 2050 and beyond. Yet demands to reduce global dependence on petrochemicals and fossil fuel-derived lubricants are increasing and environmentally necessary. New strategies for maintaining and enhancing ICE performance by reducing friction, wear, fuel consumption, and exhaust emissions will reduce the depletion of mineral and fossil fuel reserves and environmental pollution. This paper reports the tribological enhancement of nano-bio lubricants formulated using 2D nanocomposites of Al2O3/graphene as novel additives in coconut oil, whose performance as a lubricant compares favourably with the mineral-based engine oil 15W40. Structural, compositional, and morphological characterization of an Al2O3/graphene nanocomposite synthesized via thermal annealing revealed an ultra-fine particle size (<10 nm) with spherical/laminar morphology and a rich sp2 domain, exhibiting a consistent colloidal stability when formulated as nanofluid. Through the use of various characterisation techniques, including friction and wear analysis we gained valuable insight into the tribological mechanism. Our optimisation of 2D tribological system using coconut oil formulation resulted significant reductions in the coefficient of friction (28%), specific fuel consumption (8%), and exhaust pollutants (CO, SO2, and NOx) emissions. This work demonstrates the benefits of using nano-bio lubricant formulated using coconut oil and 2D based hybrids as base stock and additives, delivering solutions to global challenges such as improving fuel consumption while reducing environmental pollution; solutions that can be transferred to other areas where lubricants are a necessity

Engineering Nitrogen-Doped Carbon Quantum Dots: Tailoring Optical and Chemical Properties through Selection of Nitrogen Precursors

The process of N-doping is frequently employed to enhance the properties of carbon quantum dots. However, the precise requirements for nitrogen precursors in producing high-quality N-doped carbon quantum dots (NCQDs) remain undefined. This research systematically examines the influence of various nitrogen dopants on the morphology, optical features, and band structure of NCQDs. The dots are synthesized using an efficient, eco- friendly, and rapid continuous hydrothermal flow technique. This method offers unparalleled control over synthesis and doping, while also eliminating convention-related issues. Citric acid is used as the carbon source, and urea, trizma base, beta-alanine, L-arginine, and EDTA are used as nitrogen sources. Notably, urea and trizma produced NCQDs with excitation-independent fluorescence, high quantum yields (up to 40%), and uniform dots with narrow particle size distributions. Density functional theory (DFT) and time-dependent DFT modelling established that defects and substituents within the graphitic structure have a more significant impact on the NCQDs’ electronic structure than nitrogen-containing functional groups. Importantly, for the first time, this work demonstrates that the conventional approach of modelling single-layer structures is insufficient, but two layers suffice for replicating experimental data. This study, therefore, provides essential guidance on the selection of nitrogen precursors for NCQD customization for diverse applications

Nuclear Shadowing in a Parton Recombination Model

Deep inelastic structure functions $F_2^A(x)$ are investigated in a $Q^2$ rescaling model with parton recombination effects. We find that the model can explain experimentally measured $F_2^A(x)$ structure functions reasonably well in the wide Bjorken$-x$ range ($0.005<x<0.8$). In the very small $x$ region ($x<0.02$), recombination results are very sensitive to input sea-quark and gluon distributions.Comment: preprint MKPH-T-93-04, IU/NTC 92-20, 25 pages, TEX file (without Figs. 1-14)., (address after April 1: Saga U., Japan

Steady seepage near an impermeable obstacle

The problem of an obstacle with maximum cross-sectional area has been analytically solved in terms of a model for 2-D seepage flow with a capillary fringe. The boundary of the obstacle appears to show a 'blunt configuration', that is, the pressure reaches its maximum value at the vertex and decreases monotonically downstream. With a sufficiently large size of obstacle, a positive pressure domain in the form of a 'bubble' is formed in the vicinity of its vertex. This result has been verified by computations for saturated-unsaturated flows in terms of the finite element method for the Richards equation. It has also been shown that an obstacle can transform the initial fully saturated flow into unsaturated flow inside the 'dry shadow' domain. The shape of an obstacle in a confined aquifer that provides a minimum water head drop has been determined within the scope of the Dupuit model. A 'critical cavity shape' has been found, i.e. a cavity for which the boundary is simultaneously an isobar and a stream line. © 1992

Steady seepage near an impermeable obstacle

The problem of an obstacle with maximum cross-sectional area has been analytically solved in terms of a model for 2-D seepage flow with a capillary fringe. The boundary of the obstacle appears to show a 'blunt configuration', that is, the pressure reaches its maximum value at the vertex and decreases monotonically downstream. With a sufficiently large size of obstacle, a positive pressure domain in the form of a 'bubble' is formed in the vicinity of its vertex. This result has been verified by computations for saturated-unsaturated flows in terms of the finite element method for the Richards equation. It has also been shown that an obstacle can transform the initial fully saturated flow into unsaturated flow inside the 'dry shadow' domain. The shape of an obstacle in a confined aquifer that provides a minimum water head drop has been determined within the scope of the Dupuit model. A 'critical cavity shape' has been found, i.e. a cavity for which the boundary is simultaneously an isobar and a stream line. © 1992

Investigating the effect of N‐doping on carbon quantum dots structure, optical properties and metal ion screening

Carbon quantum dots (CQDs) derived from biomass, a suggested green approach for nanomaterial synthesis, often possess poor optical properties and have low photoluminescence quantum yield (PLQY). This study employed an environmentally friendly, cost-effective, continuous hydrothermal flow synthesis (CHFS) process to synthesise efficient nitrogen-doped carbon quantum dots (N-CQDs) from biomass precursors (glucose in the presence of ammonia). The concentrations of ammonia, as nitrogen dopant precursor, were varied to optimise the optical properties of CQDs. Optimised N-CQDs showed significant enhancement in fluorescence emission properties with a PLQY of 9.6% compared to pure glucose derived-CQDs (g-CQDs) without nitrogen doping which have PLQY of less than 1%. With stability over a pH range of pH 2 to pH 11, the N-CQDs showed excellent sensitivity as a nano-sensor for the highly toxic highly-pollutant chromium (VI), where efficient photoluminescence (PL) quenching was observed. The optimised nitrogen-doping process demonstrated effective and efficient tuning of the overall electronic structure of the N-CQDs resulting in enhanced optical properties and performance as a nano-sensor