Prediction of hydrogen solubility in heavy hydrocarbons over a range of temperatures and pressures using molecular dynamics simulations

Using the method of molecular dynamics (MD), we have estimated the solubility of hydrogen in heavy hydrocarbons for a range of temperatures and pressures. Heavy hydrocarbon systems are known to be challenging not only for experimental measurements but also for reliable estimations using traditional equations of state (EOS). The simulation system used was designed with semi-permeable membranes to mimic actual experimental studies of gas solubility. Binary interaction parameters between the solute gas and the solvent (heavy hydrocarbons) components were adjusted when necessary to improve agreement with experimental results and then used in subsequent multi-component studies. Temperature and pressure ranges studied included higher temperatures and pressures which are especially difficult to investigate experimentally. Simulation results were finally used to adjust the binary interaction parameters (BIP) in simulation packages (e.g. Aspen) to enable quick and reliable predictions.     

Robust detection of exotic infectious diseases in animal herds: A comparative study of three decision methodologies under severe uncertainty

When animals are transported and pass through customs, some of them may have dangerous infectious diseases. Typically, due to the cost of testing, not all animals are tested: a reasonable selection must be made. How to test effectively whilst avoiding costly disease outbreaks? First, we extend a model proposed in the literature for the detection of invasive species to suit our purpose, and we discuss the main sources of model uncertainty, many of which are hard to quantify. Secondly, we explore and compare three decision methodologies on the problem at hand, namely, Bayesian statistics, info-gap theory and imprecise probability theory, all of which are designed to handle severe uncertainty. We show that, under rather general conditions, every info-gap solution is maximal with respect to a suitably chosen imprecise probability model, and that therefore, perhaps surprisingly, the set of maximal options can be inferred at least partly—and sometimes entirely—from an info-gap analysis.     

Low level determination of p-toluenesulfonate and benzenesulfonate esters in drug substance by high performance liquid chromatography/mass spectrometry

GC/FID and HPLC/MS single ion monitoring methods have been evaluated for the determination of trace levels of methyl, ethyl and isopropyl esters of p-toluenesulfonic acid and methyl, ethyl, isopropyl and n-butyl esters of benzenesulfonic acid in drug substances. These sulfonate esters have been highlighted as potential genotoxins. HPLC/MS was found to be more promising and limits of quantification were between 2.5 and 5 ng/mL, which enabled detection limits in drug substance at 0.01-0.1 ppm for a 50 mg/mL solution. For one drug substance excellent recoveries of 94-95% were obtained at the 1.0 ppm level, however, with a second drug substance, a besylate salt, recoveries ranged from 86% to 100% and were dependant on the sample preparation. Limited stability of the sulfonate esters in various potential sample solutions indicated that samples may need to be prepared immediately before injection.     

Improvements to a surface plasmon resonance-based immunoassay for the steroid hormone progesterone

The effects of modifications to an existing protocol for a surface plasmon resonance biosensor-based inhibition immunoassay for progesterone in cow's milk with a sensitivity of 3.5 ng/mL were examined to establish if the detection limit could be further reduced to broaden the potential applications of the assay. The mean relative standard deviation of duplicate measurements was 0.62% and the high precision resulted in very low values for the lower detection limits. Hence, the standard concentrations giving 95% maximum binding [effective dose (ED 95)] were compared instead. The ED 95 was not affected within a running temperature range of 20-37 degrees C, or at a flow rate and a contact time above 20 microL/min and 90 s, respectively. Increasing both the absolute sample volume and the antibody dilution improved sensitivity. However, there was a simultaneous reduction in the working range when the assay was applied to milk due to nonspecific binding. Less antibody was associated with large decreases in the maximum binding, but because the high precision extended over a broad analytical range, an ED 95 of 0.4-0.6 ng/mL in milk and 35-60 pg/mL in HBS-EP buffer were achieved. Thus, simple procedural modifications with the same sensor chip can alter performance characteristics of the assay as required for different applications.     

Removal of shallow shell restriction from Touratier kinematic model

A mathematical model to quantify the variation of the displacement field through the thickness of a laminated shell has been proposed previously by Beakou and Touratier (1993). Transverse shear deformations were taken into account and thickness correction factors were not required but the analysis was restricted to shallow shells (i.e. the principal radii of shell curvature were both assumed to be large relative to the shell thickness). In this technical note the later restriction is removed by replacing the Cartesian coordinate form of elasticity tensor with the more general curvilinear form. The modified laminate level model coefficients are derived from the expressions for the curvilinear transverse shear stress components by: applying zero transverse shear stress boundary conditions at the top and bottom of the shell and enforcing interlayer layer continuity at each internal lamina interface. The purpose of this model enhancement is to facilitate the development of a degenerate finite element type that can be used to compute the deformation of a non-shallow laminated shell.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Molecular dynamics of a model of one ion in 225 polar molecules

Calculations are reported which explore the effect of an ion on the arrangement and motion of the surrounding solvent molecules in a highly polar medium. It is found that the ion and its nearest neighbours are strongly associated and this also applies - to a lesser extent - to groups of solvent molecules.