Dietitians view the horizon

In honor of the American Dietetic Association's landmark 75th anniversary, FM asked ADA members representing six market sectors to share their perspectives on the opportunities & challenges for dietitians in the '90s. An exciting era lies ahead.     

Emulsion polymerization of styrene in a continuous stirred reactor

The emulsion polymerization of styrene has been carried out in a continuous stirred reactor at 50°C. Polymerization rates were initially very high but declined subsequently. These rates did not always attain a steady value, but sometimes oscillated with time. Size analysis of the polymer particles showed that particle nucleation almost stopped soon after start-up. A new generation of particles appeared later in the process. The average number of radicals per particle was usually, but not always, >0.5. The time-average polymerization rate was only weakly dependent on the initiator concentration but varied with the first power of the emulsifier concentration.     

Deciphering the kinetic mechanism of spontaneous self-assembly of icosahedral capsids

Self-assembly of viral proteins into icosahedral capsids is an interesting yet poorly understood phenomenon of which elucidation may aid the exploration of beneficial applications of capsids in materials science and medicine. Using molecular dynamics simulations of coarse-grained models for capsid proteins, we show that the competition between the formation of full capsids and nonidealized structures is strongly dependent upon the protein concentration and temperature, occurring kinetically as a cascade of elementary reactions in which free monomers are added to the growing oligomers on a downhill free-energy landscape. However, the insertion of the final subunits is the rate-limiting, energetically unfavorable step in viral capsid assembly. A phase diagram has been constructed to show the regions where capsids or nonidealized structures are stable at each concentration and temperature. We anticipate that our findings will provide guidance in identifying suitable conditions required for in vitro viral capsid assembly experiments.     

Why a Water Soft Path,Why Now and What Then?

The best way to achieve a sustainable future for fresh water is to develop decision-making processes, institutions, and technologies that emphasize both efficiency and conservation. These two terms are commonly treated as synonyms, but, respectively, they reflect anthropogenic and ecological bases for making decisions. Recognizing that both perspectives are valid, this article outlines a new approach to water planning and management called the water soft path. This approach differs fundamentally from conventional, supply-based approaches. The article reviews the transfer of the original soft path concept from energy to water, and summarizes the first applications of water soft path analytics to specific geographic areas: one urban area, one province, and one watershed in Canada. The article concludes with suggestions for further research, as well as steps to improve recognition of the water soft path as a planning tool that can move management and policies towards economic, ecological, and social sustainability.     

Investigations on the surface structure and properties of silica‐polyamine composites on the nanoscales and microscales

The structure and properties of silica polyamine composites (SPC) made from microparticles of amorphous silica gel (300–600 microns) and silica nanoparticles (10–20 nm) modified with aminopropyltrimethoxysilane (APTMS), poly(allylamine) (PAA) or poly(ethyleneimine) (PEI) have been studied. The APTMS nano‐hybrids showed batch capacities for copper equal to or better than the corresponding polymer‐based micro‐hybrids. Loading of the PEI on the nanoparticles was independent of molecular weight of the polymer. Dynamic light scattering measurements showed that the SiO₂ nanoparticles and the composites made from them aggregate in water and the degree of aggregation is dependent on the surface modification. All of the amine‐modified materials were catalysts for the Knoevenagel reaction but interestingly, the microparticles modified with APTMS were better catalysts than the corresponding nanoparticles or the polyamine modified composites. Solid‐state ¹⁹Si NMR has been used to elucidate the surface structure of the various composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42271.     

Dramatic Effects of Scalable SNN‐Assisted Melt Dispersion on Thermal Conductivity and Coefficient of Thermal Expansion of Nanocomposites

It is demonstrated that SNN‐assisted melt dispersion can lead to a significant improvement of the thermal conductivity of PC/MWCNT composites accompanied by a dramatic reduction in their linear CTE. The thermal conductivity of the SNN‐containing composites after the 2‐step process was about 95% higher than that of neat PC and 25% higher than that from 1‐step processing at same loading. The CTE below the glass‐transition temperature of composites with a 1.0 wt.‐% MWCNT loading is substantially reduced compared to the neat polymer. A reduction in the CTE of up to 60.8% is observed for composites from the 2‐step process. Simultaneous achievement of high thermal conductivity and low CTE is required for electronic packaging in microelectronics for device protection.

     

Microbial source tracking in a rural watershed dominated by cattle

Antibiotic resistance analysis (ARA), frequency of sampling, and seasonality were evaluated in a rural Virginia watershed dominated by cattle. The selected watershed (Mill Creek) was 3767 ha in size, included two small communities (one sewered and one unsewered), and several farms that when combined contained over 3800 beef and dairy cattle. Monthly monitoring of fecal coliforms at two sampling sites in Mill Creek from January to December, 2001, revealed that the recreational standard (1000 colony forming units, CFUs/100 ml) was exceeded a total of eight times for a 33% violation rate at each site. In addition, stream samples were collected weekly for 4 consecutive weeks during seasonal high flows (March) and seasonal low flows (September-October), plus daily for 7 consecutive days within the weekly schedules for a combined total of 60 stream samples (30 at each of two sites). The recreational standard was exceeded once during seasonal high flow and nine times during seasonal low flow. Microbial source tracking (MST) was performed by ARA to assess the impact of cattle on water quality within the different sampling routines. The resistance patterns of 2880 water isolates and 1158 known source (host-origin) isolates were determined with seven antibiotics at 28 different concentrations. The 1158 isolate database was reduced to 562 unique isolates when clonal ARA patterns were removed. This database of 562 unique isolates had an average rate of correct classification (ARCC) of 95.4%, and several statistical procedures confirmed the library as accurate and representative. Sixty-five percent of 50 challenge-set isolates from sources, but not samples, used in the library were correctly identified. The 562 unique pattern database was used to classify Escherichia coli isolates from water samples into six host source categories. The ARA results showed that cattle were the major source of pollution in the stream and cattle were the dominant source in over 60% of the water samples. Sampling frequency and seasonality had no effect on the MST results, as cattle dominated both seasons and samplings. Deer were a minor contributor in the summer (high water demand), and geese were a minor contributor in the winter when migratory flocks were observed moving through the watershed. An unexpected human allocation was found, especially under seasonal high flow conditions. The exact origin of this human allocation is not known. This project demonstrated that a host-origin library, based on a phenotypic method, could be developed for a well-defined watershed and was both representative of the sources in the watershed and performed reasonably well against a challenge set.     

Bacterial growth phase influences methylmercury production by the sulfate-reducing bacterium Desulfovibrio desulfuricans ND132

The effect of bacterial growth phase is an aspect of mercury (Hg) methylation that previous studies have not investigated in detail. Here we consider the effect of growth phase (mid-log, late-log and late stationary phase) on Hg methylation by the known methylator Desulfovibrio desulfuricans ND132. We tested the addition of Hg alone (chloride-complex), Hg with Suwannee River natural organic matter (SRNOM) (unequilibrated), and Hg equilibrated with SRNOM on monomethylmercury (MMHg) production by ND132 over a growth curve in pyruvate-fumarate media. This NOM did not affect MMHg production even under very low Hg:SRNOM ratios, where Hg binding is predicted to be dominated by high energy sites. Adding Hg or Hg-NOM to growing cultures 24 h before sampling (late addition) resulted in ~ 2× greater net fraction of Hg methylated than for comparably aged cultures exposed to Hg from the initial culture inoculation (early addition). Mid- and late-log phase cultures produced similar amounts of MMHg, but late stationary phase cultures (both under early and late Hg addition conditions) produced up to ~ 3× more MMHg, indicating the potential importance of growth phase in studies of MMHg production.     

Survey of raw milk cheeses for microbiological quality and prevalence of foodborne pathogens

Cheese may be manufactured in the United States using raw milk, provided the cheese is aged for at least 60 days at temperatures not less than 35 °F (1.7 °C). There is now increased concern among regulators regarding the safety of raw milk cheese due to the potential ability of foodborne pathogens to survive the manufacturing and aging processes. In this study, 41 raw milk cheeses were obtained from retail specialty shops, farmers’ markets, and on-line sources. The cheeses were then analyzed for the presence of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, Staphylococcus aureus, and Campylobacter. Aerobic plate counts (APC), coliform and yeast/mold counts were also performed. The results revealed that none of the enteric pathogens were detected in any of the samples tested. Five samples contained coliforms; two of those contained E. coli at less than 10² cfu/g. Three other cheese samples contained S. aureus. The APC and yeast-mold counts were within expected ranges. Based on the results obtained from these 41 raw milk cheeses, the 60-day aging rule for unpasteurized milk cheeses appears adequate for producing microbiologically safe products.