A deterministic model to quantify pathogen loads in drinking water catchments: pathogen budget for the Wingecarribee.

This paper describes the development and testing of a mathematical model as a tool to quantify pathogen loads in Sydney's drinking water catchments. It has been used to identify, quantify and prioritise sources of Cryptosporidium, Giardia and E. coli in the Wingecarribee catchment. The pathogen model promotes understanding of the relative significance of different sources of pathogen risks as well as their fate and transport as they move through the subcatchments. This pathogen model not only enables water utility managers to identify those catchment segments that may contribute the highest load of pathogens, but also where management options will be most effective.     

FATIGUE CRACK PROPAGATION AND CRACK CLOSURE BEHAVIOR IN POLYCARBONATE AND FIBRE REINFORCED POLYCARBONATE

Abstract— Fatigue crack propagation was investigated in polycarbonate and glass fibre reinforced polycarbonate and the effect of stress ratio and glass fibre content determined. The addition of glass fibre increases the tensile strength, but does not always contribute to an increase in fatigue crack propagation resistance. For polycarbonate the effect of stress ratio can be partly explained by using crack closure concepts as other researchers have suggested, but for glass fibre reinforced polycarbonate this was not possible. Fractography revealed a void growth process, which occurred by decohesion at the interface of the glass fibres and the base material, which was dependent on the maximum stress intensity factor. The process of linking the voids and the main crack growth behavior depended on the stress intensity factor range, Δ K. A proposed crack propagation model can explain the effect of stress ratio on crack propagation in fibre reinforced polycarbonate.     

A proposed method to reconstruct the three‐dimensional dispersion profile of polymeric fibres based on variable wavelength interferometry

In this paper, we suggest a modification to the conventional variable wavelength interferometry. This modification allowed us to calculate the dispersion curve of each point inside polymeric fibres instead of calculating the mean dispersion of these fibres. This modified mathematical treatment was used to calculate the three‐dimensional dispersion profile of isotactic polypropylene fibres suffering from necking deformation. The different steps of calculating the three‐dimensional dispersion profile of the fibre were demonstrated. The application of this modified method revealed the variation of the fibre material dispersion before, inside and after the necking region. In addition, the birefringence profile of the necked isotactic polypropylene was determined using the proposed mathematical treatment. This allowed us to diagnose the interaction of the incident waves with necked polypropylene fibres, which gives extensive information on the orientation of the molecular chains during the formation of the necking phenomenon.     

Lithium polyacrylate as a binder for tin-cobalt-carbon negative electrodes in lithium-ion batteries

A lithium polyacrylate (Li-PAA) binder has been developed by 3M Company that is useful with electrodes comprising alloy anode materials. This binder was used to prepare electrodes made with Sn₃₀Co₃₀C₄₀ material prepared by mechanical attrition. The electrochemical performance of electrodes using Li-PAA binder was characterized and compared to those using sodium carboxymethyl cellulose (CMC) and polyvinylidene fluoride (PVDF) binders. The Sn₃₀Co₃₀C₄₀ electrodes using Li-PAA and CMC binders show much smaller irreversible capacity than the ones using PVDF binder. Poor capacity retention is observed when PVDF binder is used. By contrast, the electrodes using Li-PAA binder show excellent capacity retention for Sn₃₀Co₃₀C₄₀ materials and a specific capacity of 450 mAh/g is achieved for at least 100 cycles. The results suggest that Li-PAA is a promising binder for electrodes made from large-volume change alloy materials.     

The Effect of Nanoparticle Shape on the Photocarrier Dynamics and Photovoltaic Device Performance of Poly(3‐hexylthiophene):CdSe Nanoparticle Bulk Heterojunction Solar Cells

The charge separation and transport dynamics in CdSe nanoparticle:poly(3‐hexylthiophene) (P3HT) blends are reported as a function of the shape of the CdSe‐nanoparticle electron acceptor (dot, rod, and tetrapod). For optimization of organic photovoltaic device performance it is crucial to understand the role of various nanostructures in the generation and transport of charge carriers. The sample processing conditions are carefully controlled to eliminate any processing‐related effects on the carrier generation and on device performance with the aim of keeping the conjugated polymer phase constant and only varying the shape of the inorganic nanoparticle acceptor phase. The electrodeless, flash photolysis time‐resolved microwave conductivity (FP‐TRMC) technique is used and the results are compared to the efficiency of photovoltaic devices that incorporate the same active layer. It is observed that in nanorods and tetrapods blended with P3HT, the high aspect ratios provide a pathway for the electrons to move away from the dissociation site even in the absence of an applied electric field, resulting in enhanced carrier lifetimes that correlate to increased efficiencies in devices. The processing conditions that yield optimum performance in high aspect ratio CdSe nanoparticles blended with P3HT result in poorly performing quantum dot CdSe:P3HT devices, indicating that the latter devices are inherently limited by the absence of the dimensionality that allows for efficient, prolonged charge separation at the polymer:CdSe interface.     

Population structure of Cladophora-borne Escherichia coli in nearshore water of Lake Michigan

We previously reported that the macrophytic green alga Cladophora harbors high densities (up to 10(6) colony-forming units/g dry weight) of the fecal indicator bacteria, Escherichia coli and enterococci, in shoreline waters of Lake Michigan. However, the population structure and genetic relatedness of Cladophora-borne indicator bacteria remain poorly understood. In this study, 835 E. coli isolates were collected from Cladophora tufts (mats) growing on rocks from a breakwater located within the Indiana Dunes National Lakeshore in northwest Indiana. The horizontal fluorophore enhanced rep-PCR (HFERP) DNA fingerprinting technique was used to determine the genetic relatedness of the isolates to each other and to those in a library of E. coli DNA fingerprints. While the E. coli isolates from Cladophora showed a high degree of genetic relatedness (92% similarity), in most cases, however, the isolates were genetically distinct. The Shannon diversity index for the population was very high (5.39). Both spatial and temporal influences contributed to the genetic diversity. There was a strong association of isolate genotypes by location (79% and 80% for lake- and ditch-side samplings, respectively), and isolates collected from 2002 were distinctly different from those obtained in 2003. Cladophora-borne E. coli isolates represented a unique group, which was distinct from other E. coli isolates in the DNA fingerprint library tested. Taken together, these results indicate that E. coli strains associated with Cladophora may be a recurring source of indicator bacteria to the nearshore beach.     

Phosphorus feeding levels and critical control points on dairy farms

A viable and cost-effective approach to managing P on dairy farms is to minimize excess P in diets, which in turn leads to less excretion of P in manure without impairing animal performance. A questionnaire survey was conducted, coupled with on-site feed and fecal sample collection and analysis on dairy farms in New York, Pennsylvania, Delaware, Maryland, and Virginia. The purpose was to assess dietary P levels and to identify critical control points pertaining to P feeding management. Survey responses, 612 out of 2500 randomly selected farms, revealed a wide range of dietary P concentrations for lactating cows, from 3.6 to 7.0 g/kg of feed DM. The mean was 4.4 g/kg, which was 34% above the level recommended by the NRC for 27.9 kg milk/d, the mean milk yield in the survey. Higher P concentrations in diets were not associated with higher milk yields (n = 98, R2 = 0.057 for the survey farms; n = 92, R2 = 0.043 for farms selected for on-site sampling). However, higher dietary P led to higher P excretion in feces (n = 75, R2 = 0.429), with much of the increased fecal P being water soluble. Phosphorus concentrations in diet samples matched closely with P concentrations in formulated rations, with 67% of the feed samples deviating <10% from the formulations. On 84% of the survey farms, ration formulation was provided by professionals rather than producers themselves. Most producers were feeding more P than cows needed because it was recommended in the rations by these consultants. In conclusion, P fed to lactating cows averaged 34% above NRC recommendations; to reduce excess dietary P, ration formulation is the critical control point.