Valuation of national park system visitation: the efficient use of count data models, meta-analysis, and secondary visitor survey data.

The National Park Service (NPS) currently manages a large and diverse system of park units nationwide which received an estimated 279 million recreational visits in 2011. This article uses park visitor data collected by the NPS Visitor Services Project to estimate a consistent set of count data travel cost models of park visitor willingness to pay (WTP). Models were estimated using 58 different park unit survey datasets. WTP estimates for these 58 park surveys were used within a meta-regression analysis model to predict average and total WTP for NPS recreational visitation system-wide. Estimated WTP per NPS visit in 2011 averaged $102 system-wide, and ranged across park units from $67 to $288. Total 2011 visitor WTP for the NPS system is estimated at $28.5 billion with a 95% confidence interval of $19.7-$43.1 billion. The estimation of a meta-regression model using consistently collected data and identical specification of visitor WTP models greatly reduces problems common to meta-regression models, including sample selection bias, primary data heterogeneity, and heteroskedasticity, as well as some aspects of panel effects. The article provides the first estimate of total annual NPS visitor WTP within the literature directly based on NPS visitor survey data.

Functionalized paramagnetic nanoparticles for waste water treatment.

An approach to the design, development and implementation of a new separation technology for use in the decontamination of radioactive waste streams is reported here. Calixarene-crown-6 derivatives with terminal carboxyl groups were synthesised and attached to nano-sized magnetoferritin molecules and their ability to sequester radioactive caesium(i) ions from aqueous solution was demonstrated.

Modelling oral malodour from a tongue biofilm.

A new model about the genesis of malodour emanating from the tongue is introduced. A new approach uses mathematical formulae to combine existing empirical knowledge and bring it into context. The resulting description of halitosis includes the three-dimensional structure of the tongue dorsum surface as the substratum, and the transfer of oxygen and metabolites based on a four-dimensional partial differential equation solved by finite element analysis. The transport mechanisms of diffusion, flow, volatilization and chemical reaction are considered. The model predicts the majority of volatiles emanating from the back of the tongue at the end of a swallowing cycle, which correlates with empirical findings. Because the model is conceptual it allows greater freedom and precision than in vivo experimentation.

Actinide speciation in relation to biological processes.

In case of accidental release of radionuclides into the environment, actinides represent a severe health risk to human beings following internal contamination (inhalation, ingestion or wound). For a better understanding of the actinide behaviour in man (in term of metabolism, retention, excretion) and in specific biological systems (organs, cells or biochemical pathways), it is of prime importance to have a good knowledge of the relevant actinide solution chemistry and biochemistry, in particular of the thermodynamic constants needed for computing actinide speciation. To a large extent, speciation governs bioavailability and toxicity of elements and has a significant impact on the mechanisms by which toxics accumulate in cell compartments and organs and by which elements are transferred and transported from cell to cell. From another viewpoint, speciation is the prerequisite for the design and success of potential decorporation therapies. The purpose of this review is to present the state of the art of actinide knowledge within biological media. It is also to discuss how actinide speciation can be determined or predicted and to highlight the areas where information is lacking with the aim to encourage new research efforts.

Experimental and computer modelling speciation studies of the effect of pH and phosphate on the precipitation of calcium and magnesium salts in urine.

BACKGROUND: pH and phosphate concentration are the major determinants of precipitation in urine of the salts of calcium and magnesium. This study aims to model the process of salt precipitation and establish whether the acidification of urine samples is necessary for the accurate measurement of calcium and magnesium in a clinical laboratory setting. METHODS: Urine samples were collected from 21 patients, aliquots were taken from each patient sample and the pH was adjusted to cover the range 2.0-10.0. The analytical and biological variation for each analyte was established and used to calculate percentage changes and critical differences. The critical difference was used to assess whether there was a significant difference between acidified and un-acidified samples. The JESS (Joint Expert Speciation System) thermodynamic computer-modelling program was used to predict the distribution of salt species formed with varying pH values and phosphate levels in simulated urine. RESULTS: The results showed that at a pH greater than 6.5, measured calcium, magnesium and phosphate significantly decreased as a result of precipitation (p<0.0001), although the critical difference was generally not exceeded. Computer modelling showed that both pH and phosphate concentration affected the distribution of salt species formed, as well as the precipitation patterns of calcium and magnesium phosphates. Overall, calcium phosphate precipitation tends to predominate at lower phosphate concentrations and at pH values below about 6.5, while both calcium and magnesium phosphate precipitation occur at higher phosphate concentrations and pH values greater than 6.5. CONCLUSIONS: For accurate analysis of these analytes in urine, the pH should be routinely measured and acidification should be undertaken prior to analysis if the pH is greater than 6.5. Based on the findings of this study, acidification or the lack of it does not result in a clinically significant change in calcium, magnesium and phosphate measured in urine. This study also predicted the likely salt species formed at varying urinary pH values and phosphate concentrations.

Assessing the relationship between concentrations of malodor compounds and odor scores from judges.

BACKGROUND: The purpose of this review was to assess the relationship between mean organoleptic scores (using a 0-to-5 scale) and concentrations of putative odorants representative of those thought to be important in oral malodor, as well as to propose a simple model that explains the dose-response curves obtained from a group of odor judges. METHODS: The model assumes that the scale is rooted at the detection threshold (0), the maximum score (5) is fully saturating and the brain and olfactory nervous system can act as a faithful transducer of the state of binding (occupancy) of the smell receptors in the nose. The authors predicted that the response would be exponential or sigmoidal in nature. They tested this using published empirical data based on seven odor judges and eight odor compounds. RESULTS: Analysis of the data by different plotting methods showed the odorants to be significantly different from each other (P < .01 by regression analysis) with regard to thresholds and slopes. The lower the threshold, the stronger the inherent odor of the compound. The greater the slope, the greater the odor power. Volatile sulfur compounds had low smell thresholds and high odor power and were highly volatile, while indole was less volatile but had a very low threshold. Both compounds may be significant in human oral malodor. CONCLUSIONS: The authors found that the organoleptic scale was exponential in practice. These findings imply that when inhibitory agents are tested against odor-generating bacteria, a given percentage inhibition of the volatile compound production rate by a treatment (such as an antimicrobial mouthwash) will result in an equal incremental reduction on the scale, regardless of the starting position on the scale. Understanding the scale enables dental professionals to develop better ways of training, calibrating and standardizing odor judges, along with better ways of designing clinical trials and interpreting data regarding the efficacy of antiodor treatments.