Polymer-Enhanced DNAPL Flushing from Low-Permeability Media: An Experimental Study

Remediation of dense nonaqueous phase liquids (DNAPLs) is recognized as one of the most difficult problems associated with ground water pollution. The pump-and-treat technique, usually consisting of a continuous operation of extraction-injection wells, is widely used for ground water remediation. In a stratified or otherwise heterogeneous aquifer, however, this technique suffers from tailing and rebound problems, which limit its cleanup efficiency and result in higher operation costs. The tailing and rebound is usually due to slow diffusion of contaminants out of lower- permeability heterogeneities into the flow regime of the higher-permeability zone. In this study, we conduct bench-scale experiments to investigate a novel polymer system and injection method to improve the pump-and-treat technique for DNAPL trapped in a layer of porous media that has a relatively low permeability compared to the surrounding media. This technique might be useful, for example, to remove DNAPL from these low-permeability zones after removal of DNAPL from the higher-permeability zones by a more traditional remediation method. The polymer system consists of a mixture of anionic and cationic polyacrylamides in solution and the injection method is based on flow-induced polymer adsorption, called bridging adsorption. The study includes single and parallel-column experiments. The measured polymer penetration depths were compared with values predicted from a numerical simulation, which was developed previously by the authors of this paper. The experiments and simulations show that the polymer injection leads to a modification of the permeability contrast that favors a more efficient pump-and-treat process. These results suggest that additional research to upscale the technology to pilot scales is warranted.     

Observations of the 18.6-year cycle of air pressure and a theoretical model to explain certain aspects of this signal

Evidence from barometric data in Japan, USSR, southern Europe, southern Africa, and South America shows that air pressure variations with period near 18.6-years can attain amplitudes as high as 0.9 mb, and are identified as induced by the luni-solar constituent tide M _n (M for moon and n for nodal). Luni-solar waveforms commonly exhibit modulation effects due to the superposition of a longer period component with 180° changes in phase. Thus, the waveform amplitudes can be highly nonstationary. Pressure gradients at this period over subcontinental distances show that the amplitudes imply nonequilibrium conditions. A theoretical coupling mechanism between E-W and N-S wind systems and the Coriolis force is envoked to explain the sub-continental extent and the, sometimes abrupt, amplitude changes of the pressure systems over small distances.     

Describing gonad development and gametogenesis in southern Africa’s endemic box jellyfish Carybdea branchi (Cubozoa,Carybdeidae)

Information on the reproductive development of species of box jellyfish (class Cubozoa) is poor globally, despite their significance as potent stingers and worrying projections about range expansions. While most species are confined to tropical and subtropical waters, the South African box jellyfish Carybdea branchi is commonly found in the cold-water (especially southern) Benguela ecosystem. Its biology is unknown. Here, we examine reproductive development and describe gametogenesis in this dioecious species. Four and five maturity classes were determined for males and females, respectively, as well as five oocyte developmental stages. Oocyte sizes differed significantly between developmental stages. Mature and immature medusae differed significantly in size, but males and females did not. Individuals matured at approximately 30 mm average bell dimensions. Carybdea branchi displayed gonadal development characteristic of a semelparous organism.     

First record of dinosaur trackway from Tibet,China

Three sauropod trackways comprise eight tracks that resemble Brontopodus tracks have been found at the Morong track site in Changdu Prefecture, Tibet, China. These wide- (or sub-wide)-gauge tracks suggest that there was a large sauropod, possibly a member of Titanosauriformes, in Changdu Prefecture during the Early-Middle Jurassic. The sauropod fauna from Changdu Prefecture, Tibet not only has elements in common with the sauropod fauna from the Sichuan Basin, but may include more diverse faunal components.     

Radiocarbon measurements of black carbon in aerosols and ocean sediments

Black carbon (BC) is the combustion-altered, solid residue remaining after biomass burning and fossil fuel combustion. Radiocarbon measurements of BC provide information on the residence time of BC in organic carbon pools like soils and sediments, and also provide information on the source of BC by distinguishing between fossil fuel and biomass combustion byproducts. We have optimized dichromate-sulfuric acid oxidation for the measurement of radiocarbon in BC. We also present comparisons of BC ¹⁴C measurements on NIST aerosol SRM 1649a with previously published bulk aromatic ¹⁴C measurements and individual polycyclic aromatic hydrocarbon (PAH) ¹⁴C measurements on the same NIST standard.Dichromate-sulfuric acid oxidation belongs to the chemical class of BC measurement methods, which rely on the resistance of some forms of BC to strong chemical oxidants. Dilute solutions of dichromate-sulfuric acid degrade BC and marine-derived carbon at characteristic rates from which a simple kinetic formula can be used to calculate concentrations of individual components (Wolbach and Anders, 1989). We show that: (1) dichromate-sulfuric acid oxidation allows precise, reproducible ¹⁴C BC measurements; (2) kinetics calculations give more precise BC yield information when performed on a % OC basis (vs. a % mass basis); (3) kinetically calculated BC concentrations are similar regardless of whether the oxidation is performed at 23°C or 50°C; and (4) this method yields ¹⁴C BC results consistent with previously published aromatic ¹⁴C data for an NIST standard.For the purposes of intercomparison, we report % mass and carbon results for two commercially available BC standards. We also report comparative data from a new thermal method applied to SRM 1649a, showing that thermal oxidation of this material also follows the simple kinetic sum of exponentials model, although with different time constants.     

L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system

We present L ' and M ' photometry, obtained at the United Kingdom Infrared Telescope (UKIRT) using the Mauna Kea Observatories Near-Infrared (MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L ' standards include 25 from the in-house 'UKIRT Bright Standards' with magnitudes deriving from Elias et al. and observations at the Infrared Telescope Facility in the early 1980s, and 21 fainter stars. The M ' magnitudes derive from the results of Sinton and Tittemore. We estimate the average external error to be 0.015 mag for the bright L ' standards and 0.025 mag for the fainter L ' standards, and 0.026 mag for the M ' standards. The new results provide a network of homogeneously observed standards, and establish reference stars for the MKO system, in these bands. They also extend the available standards to magnitudes which should be faint enough to be accessible for observations with modern detectors on large and very large telescopes.     

Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation,Ischigualasto Provincial Park,San Juan,Argentina

The Ischigualasto Formation in northwestern Argentina contains abundant fluvial channel sandstones, overbank mudstones, and paleosols that were deposited in a northwest-trending continental-rift basin during Late Triassic time. In the study area the formation progressively thins from ～700 m in the west to ～400 m in the east, over a distance of 7 km. This thinning is accompanied by a relative decrease in the abundance of fluvial channel sandstones and an increase in mud-rich overbank deposits and paleosols. While preserved channel deposits in the formation are highly variable in terms of their size and stratigraphic distribution, four general channel forms can be recognized based on their overall cross sectional geometry and internal sedimentary structures. Of these, the dominant channel-body types are interpreted as the deposits of sandy multi-channel fluvial systems. The internal stratigraphic architecture of the Ischigualasto Formation indicates that during deposition, the central part of the basin was the location of a long-lived, north flowing, fluvial channel belt that received relatively continuous channel and proximal overbank deposition. To the east, however, channel-related deposition was more infrequent, resulting in enhanced pedogenic modification of alluvial deposits. The overall thickness and facies trends observed in the Ischigualasto Formation most likely correspond to variations in fault-related accommodation development within the basin during the time of deposition.     

Geomagnetic line spectra-2 to 70 years

Application of a new data adaptive approach to power spectrum estimation has yielded greatly improved knowledge of the geomagnetic spectrum in the range 2 to 70 yr. The first successful line spectrum detection of the solar and double solar cycle variations in absolute geomagnetic element data are presented; also detected are the first four harmonics of the solar cycle and, excepting one, the first nine harmonics of the double solar cycle. Finally, evidence is found for a 60 yr line. The implications of these results for a variety of problems in planetary and space physics are discussed.