A novel approach to Lab-In-Syringe Head-Space Single-Drop Microextraction and on-drop sensing of ammonia

A novel approach to the automation technique Lab-In-Syringe, also known as In-Syringe Analysis, is proposed which utilizes a secondary inlet into the syringe void, used as a size-adaptable reaction chamber, via a channel passing through the syringe piston. This innovative approach allows straightforward automation of head-space single-drop microextraction, involving accurately controlled drop formation and handling, and the possibility of on-drop analyte quantification.     

Gas-diffusion flow injection determination of Hg(II) with chemiluminescence detection

A gas-diffusion flow injection method for the chemiluminescence detection of Hg(II) based on the luminol-H₂O₂ reaction was developed. The analytical procedure involved the injection of Hg(II) samples and standards into a 1.50 M H₂SO₄ carrier stream, which was subsequently merged with a reagent stream of 0.60% (w/v) SnCl₂ in 1.50 M H₂SO₄ to reduce Hg(II) to metallic Hg. The gas-diffusion cell was thermostated at 85 °C to enhance the vaporisation of metallic Hg. Mercury vapour, transported across the Teflon membrane of the gas-diffusion cell into the acceptor stream containing 1.00 × 10⁻⁴ M KMnO₄ in 0.30 M H₂SO₄, was oxidised back to Hg(II). The acceptor stream was merged with a reagent stream containing 2.50 M H₂O₂ in deionised water and then the combined stream was merged with another reagent stream containing 7.50 × 10⁻³ M luminol in 3.00 M NaOH at a confluence point opposite to the photomultiplier tube of the detection system. The chemiluminescence intensity of the luminol-H₂O₂ reaction was enhanced by the presence of Hg(II) in the acceptor stream. The corresponding increase was related to the original concentration of Hg(II) in the samples and standards. Under optimal conditions, the chemiluminescence gas-diffusion flow injection method was characterised by a linear calibration range between 1 μg L⁻¹ and 100 μg L⁻¹, a detection limit of 0.8 μg L⁻¹ and a sampling rate of 12 samples per hour. It was successfully applied to the determination of mercury in seawater and river samples.     

Numerical investigation of the plasma processes for propellant heating in electrothermal plasma thruster for nanosatellites

Numerical investigation of the plasma processes in a cylindrical chamber with small dimensions of a novel microwave electrothermal plasma thruster for nanosatellites has been conducted. The absorbed microwave power from the electrons in the plasma column of the surface wave discharge is included in the computational model as a heat source with Gaussian distribution. The computational model takes into account the elastic and inelastic collisions of the electrons with the atoms in the ground state and two excited states (−s, −p) and the processes of recombination and deactivation of the plasma species in the volume and on the walls of the chamber. The computational model includes the flow of neutral gas and the processes in the plasma for effective heating of neutral particles by collisions not only with electrons but also with ions. Selected combinations of input power and propellant mass flow rates are used as initial parameters for the numerical investigation. The results show that at higher mass flow rates the heating of the neutral gas is more effective and at power levels of 4 W and propellant mass flow rate of 3 mg/s the electrothermal plasma thruster demonstrates effective performance and thrust levels in the order of 1 mN.     

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

The molybdenum blue reaction, used predominantly for the determination of orthophosphate in environmental waters, has been perpetually modified and re-optimised over the years, but this important reaction in analytical chemistry is usually treated as something of a 'black box' in the analytical literature. A large number of papers describe a wide variety of reaction conditions and apparently different products (as determined by UV–visible spectroscopy) but a discussion of the chemistry underlying this behaviour is often addressed superficially or not at all. This review aims to rationalise the findings of the many 'optimised' molybdenum blue methods in the literature, mainly for environmental waters, in terms of the underlying polyoxometallate chemistry and offers suggestions for the further enhancement of this time-honoured analytical reaction.     

Log-supermodularity of weight functions, ordering weighted losses, and the loading monotonicity of weighted premiums

The paper is motivated by a problem concerning the monotonicity of insurance premiums with respect to their loading parameter: the larger the parameter, the larger the insurance premium is expected to be. This property, usually called the loading monotonicity, is satisfied by premiums that appear in the literature. The increased interest in constructing new insurance premiums has raised a question as to what weight functions would produce loading-monotonic premiums. In this paper, we demonstrate a decisive role of log-supermodularity or, equivalently, of total positivity of order 2 (TP₂) in answering this question. As a consequence, we establish-at a stroke-the loading monotonicity of a number of well-known insurance premiums, and offer a host of further weight functions, and consequently of premiums, thus illustrating the power of the herein suggested methodology for constructing loading-monotonic insurance premiums.     

Experimental and computational studies of the structure and vibrational spectra of aminomethyl-dimethyl-phosphine oxide and its 15N labeled isomer

Infrared (4000-100 cm(-1)) spectra of aminomethyl-dimethyl-phosphine oxide and 15N-aminomethyl-dimethyl-phosphine oxide have been measured. Geometric parameters (bond distances and angles), net electronic charges and vibrational spectroscopic data of both compounds calculated at various levels of theory (B3LYP/6-31G* and Moeller-Plesset perturbational theory (MP2)/6-31G*) are reported. The theoretical spectral results are discussed mainly in terms of comparison with infrared (4000-100 cm(-1)) spectral data. Better coincidence was achieved with the frequencies calculated at the MP2/6-31G* level: the standard deviation is 16 cm(-1). The calculated isotopic frequency shifts, induced by the 15N labeling, are in good accordance with the measured ones. Complete vibrational assignment is made with the help of MP2 force field calculations. Data obtained here are used to reassign some of the vibrational frequencies.     

A tensor artificial viscosity using a finite element approach

We derive a tensor artificial viscosity suitable for use in a 2D or 3D unstructured arbitrary Lagrangian–Eulerian (ALE) hydrodynamics code. This work is similar in nature to that of Campbell and Shashkov [1]; however, our approach is based on a finite element discretization that is fundamentally different from the mimetic finite difference framework. The finite element point of view leads to novel insights as well as improved numerical results. We begin with a generalized tensor version of the Von Neumann–Richtmyer artificial viscosity, then convert it to a variational formulation and apply a Galerkin discretization process using high order Gaussian quadrature to obtain a generalized nodal force term and corresponding zonal heating (or shock entropy) term. This technique is modular and is therefore suitable for coupling to a traditional staggered grid discretization of the momentum and energy conservation laws; however, we motivate the use of such finite element approaches for discretizing each term in the Euler equations. We review the key properties that any artificial viscosity must possess and use these to formulate specific constraints on the total artificial viscosity force term as well as the artificial viscosity coefficient. We also show, that under certain simplifying assumptions, the two-dimensional scheme from [1] can be viewed as an under-integrated version of our finite element method. This equivalence holds on general distorted quadrilateral grids. Finally, we present computational results on some standard shock hydro test problems, as well as some more challenging problems, indicating the advantages of the new approach with respect to symmetry preservation for shock wave propagation over general grids.     

Harmonic Factorization and Reconstruction of the Elasticity Tensor

In this paper, we study anisotropic Hooke’s tensor: we propose a factorization of its fourth-order harmonic part into second-order tensors. We obtain moreover explicit equivariant reconstruction formulas, using second-order covariants, for transverse isotropic and orthotropic fourth-order harmonic tensors, and for trigonal and tetragonal fourth-order harmonic tensors up to a cubic fourth order covariant remainder.