Incipient Motion of Gravel Bedload Considering the Secondary Flow in Bend

The transport of gravel bedload in river bend is one of the basic problems of river dynamics. However, both the complicated bend flow structure and the stochastic bedload transport make explaining the problem theoretically difficult. Flow is the power of the bedload transport, so obtaining the precise theoretical flow structure is fundamental. Through considering the velocity-dip phenomenon and giving the matched boundary conditions, we have obtained the completed three-dimensional bend flow structure in the previous study. Combining the flow structure and the influences of the two-way exposure, we did further research on the incipient motion of the gravel bedload in bend in this paper. It turns out that, because of the existence of the secondary flow, the particle in bend forced by both the longitude and the transverse velocities in the plane. The two-way velocities form an intersection angle which influences the incipient velocity and direction of the particle movement. Moreover, the non-uniform distribution of the bend flow structure along the cross-section decides the differences of the intersection angle, incipient velocity, transport speed of the bedload in the bed surface. Then, the above differences result in the change of the sediment gradation and partition behaviour of the bedload transport.

Partition behaviour of iron and zinc in the catchment alluvial sediments of River Gbako flood plains around Baddegi, central Bida basin, Nigeria

Partition behaviors of iron (Fe) and zinc (Zn) were studied in the alluvial sediments of River Gbako floodplains around Baddegi using empirical formulas. The samples were cored from three pits locations (TR-1, TR-2, and TR-3). Particle size distribution and geochemical analysis were performed. Particle size distribution results indicated that the sediments are sand dominated. They have more than 50% sand with smaller percentages of clay and silt. Average partition coefficient values of Fe in the sediments are 1.02, 0.83, and 0.88 for TR-1, TR-2, and TR-3, respectively, and for Zn are 1.02, 0.95, and 0.83, for TR-1, TR-2 and TR-3, respectively. The average velocities of Fe mobilization in the sediments are 0.08 m/day, 0.07 m/day and 0.09 m/day for TR-1, TR-2 and TR-3, respectively, and for Zn mobilization are 0.07 m/day, 0.07 m/day and 0.09 m/day, for TR-1, TR-2, and TR-3, respectively. The metals were preferentially partitioned in the sediments than the water percolating through them, with average hydraulic conductivity (K) of 4.2 m/day. The partition behavior of the metals is used to explain contaminant transportation in the alluvial sediments of the River Gbako floodplains around Baddegi and the principle behind groundwater purification in the shallow alluvial aquifers of these floodplains. Index Terms: Partition coefficient, hydraulic conductivity, alluvial sediments, floodplain, Nigeria

PARTITION OF POLYCYCLIC AROMATIC HYDROCARBONS IN WATER-SEDIMENT SYSTEM CONTAINING HUMIC ACID

Natural dissolved organic matter (DOM) in the water environment has the potential to enhance the solubility of PAHs into the water phase, resulting in strong influence on their environmental fate. In this study, Nordic aquatic humic acid (HA) was used as a DOM. The effect of HA on the partition behaviour of PAHs in the sediment water system was examined by comparing the partition of three PAHs: Phenanthrene (Phe), Pyrene (Pyr), and Benzo[a]pyrene (BaP) in the water sediment system. An isotherm partition of PAHs between water and sediment was studied. The presence of HA in the sediment water system shifted the sediment water partition of PAHs to the water phase. The more hydrophobic the PAH was, the stronger the effect of HA on Kd was. Observed KDOM fitted well the linear free energy relationship. A three-phase partitioning model was established and successfully described the partition behavior of PAHs in water-sediment system.

Hg (II) extraction in a PEG-based aqueous two-phase system in the presence of halide ions. I. Liquid phase analysis

The partition behaviour of Hg (II) was studied in an aqueous polyethylene glycol (PEG) — (NH4)2SO4 two-phase system as a function of halide, halide concentration, and pH. For a system prepared by mixing equal volumes of 40 % (w/w) PEG (1550) with 40 % (w/w) (NH4)2SO4, Hg(II) remains almost exclusively in the salt-rich phase. The addition of NaX (X = Cl−, Br−, I−) enhances Hg (II) partition into the PEG-rich phase due to the formation of halide complexes. The efficiency of halide extractants increases in the order: Cl− < Br− < I−. Mercury extraction is improved at lower halide ion concentration by higher stock salt solution acidity. From the distribution coefficients determined as a function of halide ion concentration, the extracted species were identified. The Hg (II) extractability is determined by the type and stability of the Hg (II) halide species, and depends on the stock salt solution acidity. The observed behaviour is discussed and a possible extraction mechanism is proposed.

Canonical Vertex Partitions

Let σ be a finite relational signature, let be a set of finite complete relational structures of signature σ, and let be the countable homogeneous relational structure of signature σ which does not embed any of the structures in .When σ consists of at most binary relations and is finite, the vertex partition behaviour of is completely analysed, in the sense that it is shown that a canonical partition exists and the size of this partition in terms of the structures in is determined. If is infinite some results are obtained, but a complete analysis is still missing.Some general results are presented which are intended to be used in further investigations when σ contains relational symbols of arity larger than two or when the set of bounds is infinite.