Determination of a Solid Phase Mass Transfer Coefficient for Modeling an Adsorption Bed System Using Ammonium Molybdophosphate-Polyacrylonitrile (AMP-PAN) as a Sorbent for the Removal of 137Cs from Acidic Nuclear Waste Solutions

Ammonium molybdophosphate (AMP) immobilized on a polyacrylonitrile (PAN) support is an engineered form of cesium selective sorbent material developed at the Czech Technical University in Prague. This material is being investigated as a sorbent for removing ¹³⁷Cs from Idaho National Engineering and Environmental Laboratory (INEEL) acidic sodium bearing waste (SBW) solution. As part of this study, a computer program to solve the partial differential equations (PDE's) for continuity and rate of exchange in a fixed bed system has been developed using numerical finite difference algorithms. These equations are solved iteratively in order to derive a mass transfer coefficient that agrees with the results of bench scale column experiments. This mass transfer coefficient is then applied in the PDE solutions to predict breakthrough behavior in a semi-scale column experiment. The model provided excellent agreement with the semi-scale data with a mass transfer coefficient of 0.0126 min^–1.     

The synthesis of 1-(2-dialkylaminoethyl)-5 (and 6)-methoxy-2-methyl (and H)-benzimidazoles

The syntheses of twenty 1-(2-dialkylaminoethyl)-5 (and 6)-methoxy-2-methyl (and H)-benzimidazoles in which the dialkylamino groups are dimethylamino, diethylamino, pyrrolidino, piperidino and morpholino, are presented. These compounds failed to show any significant biological activity.     

Highly specific and sensitive liquid chromatography-tandem mass spectrometry method for the determination of 3-desmethylthiocolchicine in human plasma as analyte for the assessment of bioequivalence after oral administration of thiocolchicoside

A sensitive method for the determination of 3-desmethylthiocolchicine in plasma was developed, using high-performance liquid chromatographic separation with tandem mass spectrometric detection. The plasma samples were extracted with ethyl acetate and separated on a Phenomenex Luna C18(2) 5 microm, 150x2 mm column with a mobile phase consisting of acetonitrile-0.005% formic acid (350:650, v/v) at a flow rate of 0.35 ml/min. Detection was achieved by an Applied Biosystems API 2000 mass spectrometer (LC-MS-MS) set at unit resolution in the multiple reaction monitoring mode. TurbolonSpray ionisation was used for ion production. The mean recovery for 3-desmethylthiocolchicine was 70%, with a lower limit of quantification set at 0.39 ng/ml. The increased selectivity of mass spectrometric (MS-MS) detection allowed us to distinguish between thiocolchicoside and its primary metabolite 3-desmethylthiocolchicine in human plasma, thereby giving more insight about the pharmacokinetics of the drug in humans.     

Calculations on the rate of the ion-molecule reaction between NH3+ and H2

The rate coefficient for the ion-molecule reaction NH3(+) + H2 --> NH4(+) + H has been calculated as a function of temperature with the use of the statistical phase space approach. The potential surface and reaction complex and transition state parameters used in the calculation have been taken from ab initio quantum chemical calculations. The calculated rate coefficient has been found to mimic the unusual temperature dependence measured in the laboratory, in which the rate coefficient decreases with decreasing temperature until 50-100 K and then increases at still lower temperatures. Quantitative agreement between experimental and theoretical rate coefficients is satisfactory given the uncertainties in the ab initio results and in the dynamics calculations. The rate coefficient for the unusual three-body process NH3(+) + H2 + He --> NH4(+) + H + He has also been calculated as a function of temperature and the result found to agree well with a previous laboratory determination.     

Modeling of gas adsorption equilibrium over a wide range of pressure: a thermodynamic approach based on equation of state

A thermodynamic approach based on the Bender equation of state is suggested for the analysis of supercritical gas adsorption on activated carbons at high pressure. The approach accounts for the equality of the chemical potential in the adsorbed phase and that in the corresponding bulk phase and the distribution of elements of the adsorption volume (EAV) over the potential energy for gas-solid interaction. This scheme is extended to subcritical fluid adsorption and takes into account the phase transition in EAV. The method is adapted to gravimetric measurements of mass excess adsorption and has been applied to the adsorption of argon, nitrogen, methane, ethane, carbon dioxide, and helium on activated carbon Norit R1 in the temperature range from 25 to 70 degrees C. The distribution function of adsorption volume elements over potentials exhibits overlapping peaks and is consistently reproduced for different gases. It was found that the distribution function changes weakly with temperature, which was confirmed by its comparison with the distribution function obtained by the same method using nitrogen adsorption isotherm at 77 K. It was shown that parameters such as pore volume and skeleton density can be determined directly from adsorption measurements, while the conventional approach of helium expansion at room temperature can lead to erroneous results due to the adsorption of helium in small pores of activated carbon. The approach is a convenient tool for analysis and correlation of excess adsorption isotherms over a wide range of pressure and temperature. This approach can be readily extended to the analysis of multicomponent adsorption systems.     

When, how, and why prove theorems? A methodology for studying the perspective of geometry teachers

While every theorem has a proof in mathematics, in US geometry classrooms not every theorem is proved. How can one explain the practitioner’s perspective on which theorems deserve proof? Toward providing an account of the practical rationality with which practitioners handle the norm that every theorem has a proof we have designed a methodology that relies on representing classroom instruction using animations. We use those animations to trigger commentary from experienced practitioners. In this article we illustrate how we model instructional situations as systems of norms and how we create animated stories that represent a situation. We show how the study of those stories as prototypes of a basic model can help anticipate the response from practitioners as well as suggest issues to be considered in improving a model.