Autoionization in liquid water

The dissociation of a water molecule in liquid water is the fundamental event in acid-base chemistry, determining the pH of water. Because of the short time scales and microscopic length scales involved, the dynamics of this autoionization have not been directly probed by experiment. Here, the autoionization mechanism is revealed by sampling and analyzing ab initio molecular dynamics trajectories. We identify the rare fluctuations in solvation energies that destabilize an oxygen-hydrogen bond. Through the transfer of protons along a hydrogen bond "wire," the nascent ions separate by three or more neighbors. If the hydrogen bond wire connecting the two ions is subsequently broken, a metastable charge-separated state is visited. The ions may then diffuse to large separations. If, however, the hydrogen bond wire remains unbroken, the ions recombine rapidly. Because of their concomitant large electric fields, the transient ionic species produced in this case may provide an experimentally detectable signal of the dynamics we report.     

Standardized evaluation and rating of biofilters: II. Manufacturer''s and user''s perspective

As manufacturers of biofilters we feel that it is important that our customers have a standardized set of criteria that can be used to compare the many different commercially available biofilters on the market today. The purpose of this paper is to show how a variety of manufacturers size their own filters, establish commonalities between the methods and suggest, to the engineering community, the needs of the industry that are required to develop a uniform sizing criteria. Similarities in sizing methodologies include standard information supplied by the consumer (system volume, feed rate, etc.) as well as those estimated by the manufacturer (TAN production, and hydraulic requirements). Differences in sizing methodology include the use of in situ nitrification and system flushing. From the various examples of biofilter sizing, it is clear that manufacturers use a sizing methodology based on either an areal or volumetric TAN conversion rate (ATR or VTR). As manufacturers, we should be able to publish ATR or VTR for each of three trophic levels (oligotrophic, mesotrophic and eutrophic) with appropriate correction factors for water temperature and salinity. A standardized labeling system that would allow system designers to accurately and rapidly determine which biofilter(s) meet their needs is proposed. We leave it to the engineering community to devise a standardized scheme by which VTR values could be determined to facilitate this comparison.     

Uptake of metal toxicants by fungal hyphae colonising CCA-impregnated wood

Summary Electronmicroscope microanalyser (EMMA-4) analysis of Poria monticola colonising pine wood treated with a copper-chrome-arsenate preservative has shown that the fungus removes copper chromium and arsenic from the wood and stores these elements within the hyphae to the extent of 3–4% on a mycelial dry weight basis. The total uptake of each element varies from spot to spot examined (each 0.2 m dia.) but is on an average correlated with the concentration of the element in the impregnated wood. It appears that the rate of copper uptake is higher than of arsenic uptake.     

FACTORS CONTRIBUTING TO POSTWEANING DIARRHOEA IN A LARGE INTENSIVE PIGGERY

Some aspects of postweaning diarrhoea (PWD) in a piggery during the first week after early weaning were investigated. A haemolytic enterotoxigenic strain of E. coli (0149: K88: H10) was regularly recovered from piglets with PWD while rotavirus was demonstrated on a number of occasions. Prior to weaning piglets were either free of, or shed very few, haemolytic E. coli in their faeces. However, all piglets were excreting haemolytic E. coli between 5 and 7 days after weaning. The role of rotavirus in PWD was unclear. There appeared to be a direct relationship between serum antibodies to rotavirus in the sow at farrowing and those of the piglets soon after birth. The decline of maternal neutralising antibody to rotavirus coincided with the immediate postweaning period (3 to 5 weeks after birth). This was followed by an increase in antibody levels, 5 to 8 weeks after birth. There was no significant difference in the growth rate between affected and unaffected piglets over a period of 120 days. Medication of water during the first week after weaning had no significant effect on the incidence of PWD in the herd. A change in both the weaner diet and the weaning procedure reduced piglet mortality associated with PWD by more than half.     

CONTROL AND EVALUATION OF BLOOD SERUM ASSAYS FOR PENICILLIN

A method for adequate control and evaluation of blood serum assays for penicillin is given and the effectiveness of the method for controlling the several types of penicillin is shown.     

Chloride in the pore water and water column of Onondaga Lake,N.Y., U.S.A.

The vertical distributions of Cl in the pore waters of the sediments and in the water column of Onondaga Lake, New York, are documented and used to estimate the diffusion flux of Cl across the sediment-water interface, and establish the reduction in lake concentrations that has occurred as a result of the closure of an industrial source of Cl. Despite the industrial enrichment of the water column with Cl over the last 100 yr, gradients within the upper sediments toward the overlying water of 6.9 to 8.5 × 10^?2 mg cm^?3 cm^?1 exist in the deep basins of the lake. These upwards gradients are apparently a manifestation of the salt deposits that underlie the region. The estimated diffusion flux from the sediments to the water column, 3.2 × 106 kg yr^?1, represents a small percentage of the external load during the operation of the industry (0.4%) and after its closure (1.6%). The Cl concentration has decreased approximately 70% in response to an approximately equal percent reduction in external loading, as a result of closure of the industry. This supports the position that the lake's concentrations largely reflect external loading and lake flushing associated with surface inputs.     

Estimating landscape resistance to dispersal

Dispersal is an inherently spatial process that can be affected by habitat conditions in sites encountered by dispersers. Understanding landscape resistance to dispersal is important in connectivity studies and reserve design, but most existing methods use resistance functions with cost parameters that are subjectively chosen by the investigator. We develop an analytic approach allowing for direct estimation of resistance parameters that folds least cost path methods typically used in simulation approaches into a formal statistical model of dispersal distributions. The core of our model is a frequency distribution of dispersal distances expressed as least cost distance rather than Euclidean distance, and which includes terms for feature-specific costs to dispersal and sex (or other traits) of the disperser. The model requires only origin and settlement locations for multiple individuals, such as might be obtained from mark–recapture studies or parentage analyses, and maps of the relevant habitat features. To evaluate whether the model can estimate parameters correctly, we fit our model to data from simulated dispersers in three kinds of landscapes (in which resistance of environmental variables was categorical, continuous with a patchy configuration, or continuous in a trend pattern). We found maximum likelihood estimators of resistance and individual trait parameters to be approximately unbiased with moderate sample sizes. We applied the model to a small grizzly bear dataset to demonstrate how this approach could be used when the primary interest is in the prediction of costs and found that estimates were consistent with expectations based on bear ecology. Our method has important practical applications for testing hypotheses about dispersal ecology and can be used to inform connectivity planning efforts, via the resistance estimates and confidence intervals, which can be used to create a data-driven resistance surface.