A GUM-compliant uncertainty budget for the analysis of total carbon dioxide (TCO<Subscript>2</Subscript>) in equine plasma

Samples of plasma from chosen horses are collected prior to racing for the analysis of total carbon dioxide (TCO₂). Five or six (dependent on jurisdiction) tubes of blood are taken as required for a screen, followed (if positive) by confirmation (two tubes in quadruplicate) and, further confirmation (two tubes in quadruplicate) at a second referee laboratory. The threshold limit prescribed by the rules of racing is an amount concentration of 36.0 mM, with further action ensuing if the reported concentration is greater than 37.2 mM. Using QC data and an analysis of the measurement procedure, the combined standard measurement uncertainty of a measurement result was estimated to be 0.22 mM. This leads to a conclusion that the odds of incorrectly deciding that a sample at the threshold limit exceeded the action concentration, are 13 000 000:1 against. The combined standard measurement uncertainty could be reduced to 0.20 mM by combining results from the first and referee laboratories. An allowance for uncertainty of measurement of 1.0 mM is proposed, which leads to odds of 185 000:1 against concluding a sample is over the threshold limit when, in fact, it is not.     

Multifunctional mixed SAMs that promote both cell adhesion and noncovalent DNA immobilization

The ability of DNA strands to influence cellular gene expression directly and to bind with high affinity and specificity to other biological molecules (e.g., proteins and target DNA strands) makes them a potentially attractive component of cell culture substrates. On the basis of the potential importance of immobilized DNA in cell culture and the well-defined characteristics of alkanethiol self-assembled monolayers (SAMs), the current study was designed to create multifunctional SAMs upon which cell adhesion and DNA immobilization can be independently modulated. The approach immobilizes the fibronectin-derived cell adhesion ligand Arg-Gly-Asp-Ser-Pro (RGDSP) using carbodiimide activation chemistry and immobilizes DNA strands on the same surface via cDNA-DNA interactions. The surface density of hexanethiol-terminated DNA strands on alkanethiol monolayers (30.2-69.2 pmol/cm2) was controlled using a backfill method, and specific target DNA binding on cDNA-containing SAMs was regulated by varying the soluble target DNA concentration and buffer characteristics. The fibronectin-derived cell adhesion ligand GGRGDSP was covalently linked to carboxylate groups on DNA-containing SAM substrates, and peptide density was proportional to the amount of carboxylate present during SAM preparation. C166-GFP endothelial cells attached and spread on mixed SAM substrates and cell adhesion and spreading were specifically mediated by the immobilized GGRGDSP peptide. The ability to control the characteristics of noncovalent DNA immobilization and cell adhesion on a cell culture substrate suggests that these mixed SAMs could be a useful platform for studying the interaction between cells and DNA.     

Numerical Simulation of Nonequilibrium Species Diffusion in a Low-Power Nitrogen–Hydrogen Arcjet Thruster

Species distributions in a low-power arcjet thruster are investigated using a two-dimensional thermal and chemical nonequilibrium numerical model that incorporates the self-consistent effective binary diffusion coefficient approximation treatment of diffusion. Plasma flows in arcjet thruster with different input mole ratios of nitrogen to hydrogen are modelled. It is found that species separation due to nonequilibrium chemical kinetic processes occurs mainly in the regions where the dissociation and ionization of nitrogen and hydrogen species take place. The enrichment of nitrogen molecules at the fringes of the arc and hydrogen molecules near the anode wall of the thruster occurs mainly because the recombination processes of these two gases occur in different temperature ranges. In the expansion portion of the thruster nozzle, the gas residence times are of the same order as some chemical kinetic processes. Comparison between the nitrogen and hydrogen species profiles at the constrictor and thruster exit shows that the recombination of hydrogen ions and atoms are dominant kinetic processes near the thruster centreline, while the chemical reactions of nitrogen species are almost frozen in the high speed flow. The effects of temperature and pressure gradients on the species diffusion inside the arcjet thruster are also presented, with thermal diffusion found to have a much larger influence than pressure diffusion.     

Diisobutylaluminum borohydride: An efficient reagent for the reduction of tertiary amides to the corresponding amines under ambient conditions

A synthetically simple mixed metal hydride, diisobutylaluminum borohydride [(iBu)₂AlBH₄], is easily generated from a 1:1 mixture of borane-dimethylsulfide (BMS) and diisobutylaluminum hydride (DIBAL). The reduction of tertiary amides using (iBu)₂AlBH₄ is complete within five minutes under ambient conditions and the product tertiary amines were isolated in 70–99% yields by a simple acid-base extraction. This new methodology, reported herein, works well for reduction of tertiary aliphatic and aromatic amides as well as lactams to the corresponding amines and product isolation and purification does not require column chromatography.     

The sTOF,a Favorable Geometry for a Time-of-Flight Analyzer

A new geometry for the flight region in a time-of-flight mass spectrometer is presented. It consists of two opposing electrostatic sectors of about 255° each and straight sections with a length appropriate to the turns. The resulting geometry folds into a compact space. The first-order aberrations for position, angle, and energy are all zero. The transverse focusing properties are also excellent. For an energetic, high-divergence ion source such as laser ablation, the sTOF has higher resolution and ion transmission than a reflectron of similar physical size.

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Graphical Abstract ?

     

Simplified predictive criteria for the onset of chaos

Two alternative criteria for predicting the onset of chaos are presented. Both are based on the notion that it is the interaction between a stable and nearby unstable limit cycle pair in the phase space that disrupts the stable motion, thereby producing chaotic behavior. The first criterion is based upon an intersection of the unstable and stable limit cycle orbits in the phase plane. The second criterion proposes that an energy equivalence between the stable and unstable limitcycles may be responsible for the loss of periodicity of the stable motion. Both criteria are tested numerically using three distinct softening spring oscillators and their predictive capabilities are discussed. The results of this study, particularly for the energy criterion, are encouraging.     

Mechanistic insights into hydroacylation with non-chelating aldehydes

The combination of a small-bite-angle diphosphine bis(dicyclohexylphosphino)methane (dcpm) and [Rh(cod)OMe]₂ catalyses the hydroacylation of 2-vinylphenols with a wide range of non-chelating aldehydes. Here we present a detailed experimental study that elucidates the factors contributing to the broad aldehyde scope and high reactivity. A variety of catalytically relevant intermediates were isolated and a [Rh(dcpm)(vinylphenolate)] complex was identified as the major catalytically relevant species. A variety of off-cycle intermediates were also identified that can re-enter the catalytic cycle by substrate- or 1,5-cyclooctadiene-mediated pathways. Saturation kinetics with respect to the 2-vinylphenol were observed, and this may contribute to the high selectivity for hydroacylation over aldehyde decarbonylation. A series of deuterium labelling experiments and Hammett studies support the oxidative addition of Rh to the aldehyde C–H bond as an irreversible and turnover-limiting step. The small bite angle of dcpm is crucial for lowering the barrier of this step and providing excellent reactivity with a variety of aldehydes.     

Tensionless contact of a finite circular plate

A general formulation is developed for the contact behavior of a finite circular plate with a tensionless elastic foundation. The gap distance between the plate and elastic foundation is incorporated as an important parameter. Unlike the previous models with zero gap distance and large/infinite plate radius, which assumes the lift-off/separation of a flexural plate from its supporting elastic foundation, this study shows that lift-off may not occur. The results show how the contact area varies with the plate radius, boundary conditions and gap distance. When the plate radius becomes large enough and the gap distance is reduced to zero, the converged contact radius close to the previous ones is obtained.     

Generalisations of the strain-energy function of linear elasticity to model biological soft tissue

Strain measures consistent with the linear, infinitesimal form of the strain-energy function are obtained within the context of isotropic, homogeneous, compressible, and non-linear elasticity. It will be shown that there are two distinct families of such measures. One family has already been much studied in the literature, the most important member being the strains whose principal values are a function only of the corresponding principal stretches. The second family of strains appears new. The motivation for studying such strains is the intuitive expectation that, for at least moderate deformations, a good fit with experimental data from material characterisation tests will be obtained with the corresponding strain-energy functions. In particular, there is the expectation that such models could prove useful for the modelling of biological soft tissue, whose physiological response is characterised by moderate strains. It will be shown that this is indeed the case for simple tension tests on porcine brain tissue.     

Simple Shearing of Incompressible and Slightly Compressible Isotropic Nonlinearly Elastic Materials

The classical problem of simple shear in nonlinear elasticity has played an important role as a basic pilot problem involving a homogeneous deformation that is rich enough to illustrate several key features of the nonlinear theory, most notably the presence of normal stress effects. Here our focus is on certain ambiguities in the formulation of simple shear arising from the determination of the arbitrary hydrostatic pressure term in the normal stresses for the case of an incompressible isotropic hyperelastic material. A new formulation in terms of the principal stretches is given. An alternative approach to the determination of the hydrostatic pressure is proposed here: it will be required that the stress distribution for a perfectly incompressible material be the same as that for a slightly compressible counterpart. The form of slight compressibility adopted here is that usually assumed in the finite element simulation of rubbers. For the particular case of a neo-Hookean material, the different stress distributions are compared and contrasted.