Vertically integrated flows, discharge potential, and the Dupuit-Forchheimer approximation

We summarize observations made by various researchers regarding the discharge potential, vertically integrated flows, and the Dupuit-Forchheimer approximation. If a regional flow model is formulated in terms of the discharge potential and the boundary conditions can be written in terms of the discharge potential and the boundary discharges, then the discharges are correct throughout the model domain, without embracing any additional simplifying assumptions.     

Matrix-bound phosphine in sediments from Lake Illawarra, New South Wales, Australia

Matrix-bound phosphine (MBP) has been measured in sediment from two cores in Lake Illawarra on the south east coast of Australia. The sediments were also dated in the upper layers. MBP concentrations found range from 142 to 1813 ng kg⁻¹, dw (dry weight of sediment) with some values being amongst the highest ever measured. Values of MBP in deeper sediments were higher than for near surface samples, but the patterns with depth were not consistent. Strong correlations were noted between MBP and organic phosphorus (OP, r > 0.8) and with total phosphorus (TP, r > 0.7), but only moderate correlations were found with organic carbon (OC, r > 0.5). No correlations were found between MBP concentrations and the age of the sediments. It was confirmed that high MBP concentrations are indicative of a phosphorus rich environment. The results tend to support the premise that MBP is generated by microbial attack on OP under anaerobic conditions.     

A tracer dilution method for fracture characterization in bedrock wells

This investigation was undertaken to develop an integrated method of downhole fracture characterization using a tracer. The method presented can be used to locate water-bearing fractures that intersect the well, to determine the ambient fracture flow rate and hydraulic head, and to calculate fracture transmissivity. The method was tested in two fractured crystalline bedrock wells located at the University of Connecticut in Storrs. The method entails injecting a tracer (uranine dye) into the well, while at the same time water is pumped out of the well. After steady-state conditions are reached, a borehole tracer concentration profile is developed. The dilution of the tracer is used to locate the inflowing fractures and to determine their flow rate. The fracture flow rate, plus the drawdown in the well, is then used to determine the fracture hydraulic head, transmissivity, and ambient flow rate.     

A practical model for mobile, residual, and entrapped NAPL in water-wet porous media

Flow of nonvolatile nonaqueous phase liquid (NAPL) and aqueous phases that account for mobile, entrapped, and residual NAPL in variably saturated water-wet porous media is modeled and compared against results from detailed laboratory experiments. Residual saturation formation in the vadose zone is a process that is often ignored in multifluid flow simulators, which might cause an overestimation of the volume of NAPL that reaches the ground water. Mobile NAPL is defined as being continuous in the pore space and flows under a pressure gradient or gravitational body force. Entrapped NAPL is defined as being occluded by the aqueous phase, occurring as immobile ganglia surrounded by aqueous phase in the pore space and formed when NAPL is replaced by the aqueous phase. Residual NAPL is defined as immobile, nonwater entrapped NAPL that does not drain from the pore spaces and is conceptualized as being either continuous or discontinuous. Free NAPL comprises mobile and residual NAPL. The numerical model is formulated on mass conservation equations for oil and water, transported via NAPL and aqueous phases through variably saturated porous media. To account for phase transitions, a primary variable switching scheme is implemented for the oil-mass conservation equation over three phase conditions: (1) aqueous or aqueous-gas with dissolved oil, (2) aqueous or aqueous-gas with entrapped NAPL, and (3) aqueous or aqueous gas with free NAPL. Two laboratory-scale column experiments are modeled to verify the numerical model. Comparisons between the numerical simulations and experiments demonstrate the necessity to include the residual NAPL formation process in multifluid flow simulators.     

Young Red Spheroidal Galaxies in the Hubble Deep Fields: Evidence for a Truncated Initial Mass Function at approximately 2 M middle dot in circle and a Constant Space Density to z approximately 2

The optical-IR images of the northern and southern Hubble Deep Fields are used to measure the spectral and density evolution of early-type galaxies. The mean spectral energy distribution is found to evolve passively toward a mid-F star-dominated spectrum by z approximately 2, becoming more sharply peaked around the 4000 ? break. We demonstrate with realistic simulations that hotter elliptical galaxies would be readily visible if evolution progressed blueward and brightward at z>2, following a standard initial mass function (IMF). The color distributions are best fitted by a "red" IMF, deficient above approximately 2 M middle dot in circle and with a spread of formation in the range 1.51 results from a selection bias against distant red galaxies in the optical, where the flux is too weak for morphological classification, but is remedied with relatively modest IR exposures that reveal a roughly constant space density to z approximately 2, with 32 and 16 elliptical galaxies detected above and below z=1, respectively. We point out that the lack of high-mass star formation inferred here and the requirement of metals implicates cooling flows of preenriched gas in the creation of the stellar content of spheroidal galaxies. Deep-field X-ray images will be very helpful in examining this possibility.