Development of a coupled reactor model for prediction of organic contaminant fate in landfills

Models describing the behavior of organic chemicals in landfills can be useful to predict their fate and transport and also to generate input data for estimates of exposure and risk. The landfill coupled-reactor (LFCR) model developed in this work simulates a landfill as a series of fully mixed reactors, each representing a daily volume of waste. The LFCR model is a numerical model allowing time-variable input parameters such as gas generation, and cover type and thickness. The model was applied to three volatile organic chemicals (acetone, toluene, benzene) as well as naphthalene and the chemical warfare agent sarin under three landfill conditions (conventional, arid, bioreactor). Sarin was rapidly hydrolyzed, whereas naphthalene was largely associated with the landfill solid phase in all scenarios. Although similar biodegradation rates were used for acetone and toluene, toluene was more persistent in the landfill due to its hydrophobicity. The cover soil moisture content had a significant impact on gaseous diffusive losses.     

Detection of the human specific Bacteroides genetic marker provides evidence of widespread sewage contamination of stormwater in the urban environment

Human sewage contamination of surface waters is a major human health concern. We found urban stormwater systems that collect and convey runoff from impervious surfaces act as a conduit for sewage originating from breeches in sanitary sewer infrastructure. A total of 828 samples at 45 stormwater outfalls were collected over a four-year period and assessed by culture based methods, PCR, and quantitative PCR (qPCR) to test for traditional and alternative indicators of fecal pollution. All outfalls had the HF183 (human) Bacteroides genetic marker detected in at least one sample, suggesting sewage contamination is nearly ubiquitous in the urban environment. However, most outfalls were intermittently positive, ranging from detection in 11%-100% of the samples. Positive results did not correlate with seasonality, rainfall amounts, or days since previous rainfall. Approximately two-thirds of the outfalls had high (>5000 copy number, i.e. CN, per 100 ml) or moderate levels (1000-5000 CN per 100 ml) of the human Bacteroides genetic marker. Escherichia coli (E. coli) and enterococci levels did not correlate to human Bacteroides. A total of 66% of all outfall samples had standard fecal indicator levels above 10,000 CFU per 100 ml. A tiered assessment using this benchmark to identify high priority sites would have failed to flag 35% of the samples that had evidence of sewage contamination. In addition, high fecal indicators would have flagged 33% of samples as priority that had low or no evidence of sewage. Enteric virus levels in one outfall with high levels of the human Bacteroides genetic marker were similar to untreated wastewater, which illustrates stormwater can serve as a pathway for pathogen contamination. The major source of fecal pollution at four of five river sites that receive stormwater discharge appeared to be from sewage sources rather than non-human sources based on the ratios of human Bacteroides to total Bacteroides spp. This study shows the feasibility and benefits of employing molecular methods to test for alternative indicators of fecal pollution to identify sewage sources and potential health risks and for prioritization of remediation efforts.     

Effects of rice straw ash amendment on Cu solubility and distribution in flooded rice paddy soils

Rice straw burning is a common post-harvest practice on rice paddy land, and it leads to the accumulation of rice straw ash (RSA) in paddy soil. To understand the role of RSA in determining the mobility and bioavailability of metal contaminants, this study investigated the effects of RSA amendment on the solubility and distribution of Cu in contaminated rice paddy soils with flooding incubation. The addition of RSA to the soils suppressed the release of Cu into the soil solutions, which was primarily attributed to the metal-binding capacity of the RSA. Additionally, after the soils were flooded, the increase in soil pH and decrease in redox potential resulted in the transformation of Cu into less soluble forms. The RSA amendment appeared to enhance the changes in pH and redox potential of the flooded soils and, consequently, the immobilization of Cu in the soils. The results suggest that the RSA can retard the bioavailability and movement of the metal in contaminated soils and, thus, lower the potential environmental risk of Cu toxicity.     

Surface functionalization of PLGA nanoparticles by non-covalent insertion of a homo-bifunctional spacer for active targeting in cancer therapy

This work reports the surface functionalization of polymeric PLGA nanoparticles by non-covalent insertion of a homo-bifunctional chemical crosslinker, bis(sulfosuccinimidyl) suberate (BS3) for targeted cancer therapy. We dissolved BS3 in aqueous solution of PVA during formulation of nanoparticles by a modified solid/oil/water emulsion solvent evaporation method. The non-covalent insertion of BS3 was confirmed by Fourier transform infrared (FTIR) spectroscopy. Curcumin and annexin A2 were used as a model drug and a cell specific target, respectively. Nanoparticles were characterized for particle size, zeta potential and surface morphology. The qualitative assessment of antibody attachment was performed by transmission electron microscopy (TEM) as well as confocal microscopy. The optimized formulation showed antibody attachment of 86%. However, antibody attachment was abolished upon blocking the functional groups of BS3. The availability of functional antibodies was evaluated by the presence of a light chain fraction after gel electrophoresis. We further evaluated the in vitro release kinetics of curcumin from antibody coated and uncoated nanoparticles. The release of curcumin is enhanced upon antibody attachment and followed an anomalous release pattern. We also observed that the cellular uptake of nanoparticles was significantly higher in annexin A2 positive cells than in negative cells. Therefore, these results demonstrate the potential use of this method for functionalization as well as to deliver chemotherapeutic agents for treating cancer.     

A comparison between gravimetric and volumetric techniques of wear measurement of UHMWPE acetabular cups against zirconia and cobalt-chromium-molybdenum femoral heads in a hip simulator

Five cobalt-chromium-molybdenum (CoCrMo) and five zirconia femoral head components have been wear tested against 28 mm diameter ultra high molecular weight polyethylene (UHMWPE) acetabular cups for 5 million cycles in the Durham hip joint wear simulator using bovine serum as a lubricant. Wear measurements used gravimetric and volumetric techniques and no statistically significant difference was found between the measurement methods. The wear rates of the acetabular cups against both femoral heads are presented for both measurement methods. The UHMWPE acetabular cups showed a statistically significant higher linear wear rate for the first 2 million cycles than the lower linear wear rate from 2 million cycles to the end of the test, against both femoral head materials. Over the full duration of the wear test, the wear rates of acetabular cups articulating against zirconia femoral heads were lower than against CoCrMo femoral heads. The wear rates up to 2 million cycles and from 2 to 5 million cycles for both femoral head materials were consistent with other studies.     

Relationships between psychophysically acceptable and maximum voluntary hand force capacity in the context of underlying biomechanical limitations

This research investigated if proportional relationships between psychophysically acceptable and maximum voluntary hand forces are dependent on the underlying biomechanical factor (i.e. whole body balance or joint strength) that limited the maximum voluntary hand force. Eighteen healthy males completed two unilateral maximal exertions followed by a 30 min psychophysical load-adjust protocol in each of nine pre-defined standing scenarios. Center of pressure (whole body balance) and joint moments (joint strength) were calculated to evaluate whether balance or joint strength was most likely limiting maximum voluntary hand force. The ratio of the psychophysically acceptable force to the maximal force was significantly different depending on the underlying biomechanical factor. Psychophysically acceptable hand forces were selected at 86.3 ± 19.7% of the maximum voluntary hand force when limited by balance (pulling exertions), 67.5 ± 15.2% when limited by joint strength (downward pressing) and 78 ± 23% when the limitation was undefined in medial exertions.     

多层绝热层间压强的估计与测量

分析了用玻璃布作间隔物的多层绝热。预测了不同层数的层间压强。在相同的层密度和层数下,将这一预测值同实验结果作了比较,观察到层间压强随多层层数的增多而增大,从而气体传导的程度也随层数增大。     

Use of laser-induced ionization to detect soot inception in premixed flames

Experimental measurements of laser-induced ionization were performed for ethene-air premixed flames operated near the soot inception point. Soot was ionized with a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the postflame region. Ionization signals were collected by use of both single-electrode and dual-electrode configurations. Earlier laser-induced-ionization studies focused on the use of a single biased electrode to generate the electric field, with the burner head serving as the path to ground. In many practical combustion systems, a path to ground is not readily available. To apply the laser-induced-ionization diagnostic to these geometries, a dual-electrode geometry must be employed. The influence of electrode configuration, flame equivalence ratio, and flame height on ionization signal detection was determined. The efficacy of the laser-induced-ionization diagnostic in detecting soot inception in the postflame region of a premixed flame by use of a dual-electrode configuration was investigated. Of the dual-electrode configurations tested, the dual-electrode geometry oriented parallel to the laser beam was observed to be most sensitive for detecting the soot inception point in a premixed flame.