Effects of Y- and La-doping on the magnetic ordering, Kondo effect, and spin dynamics in Ce1-xMxRu2Al10

The influence of Y- and La-substitution for Ce on the competing Kondo effect and magnetic ordering, as well as on spin dynamics in the Kondo semiconductor CeRu₂Al₁₀have been investigated by means of thermal, electronic, and magnetic properties. The parent compound CeRu₂Al₁₀is known to be a controversial antiferromagnet with high magnetic ordering temperatureT₀= 27 K. A small negative chemical pressure caused by La-doping results rapid suppression ofT₀and spin gap energy Δ_m, compared to a small positive pressure caused by Y-doping. Upon Y- and La-doping, the electrical resistivityρ(T) illustrates the evolution from dense Kondo semiconductor to incoherent single-ion Kondo behaviour, and hence weakens thec-fhybridization and thus lowers the Kondo temperature. The 5% Y- and La-doped compounds show enormous enhancement in the thermoelectric power and complex behaviour in the Hall resistivity belowT₀due to an abrupt change in charge carrier mobility with temperature. The magnetic contribution to electrical resistivityρ_mag(T) (≳50% La) and specific heatC_P(T)/T(≳70% La) evidence non-Fermi-liquid behaviour at low temperature in the La-doped system, due to interplay of atomic disorder with spin-fluctuation. Application of magnetic field suppresses the spin-fluctuation inC_P(T)/Tand eventually emerges to Fermi-liquid state in the 95% La-doped compound in 9 T. The magnetic phase diagram illustrates that the strength of the Kondo interaction in the doped systems are primarily controlled by the effect of volume change as described by the compressible Kondo lattice model. We ascribe the fascinating observation ofT_K≃ 4T₀to anisotropy in the single-ion crystal electric field in the presence of strong anisotropicc-fhybridization.

Comment on “Atmospheric chemistry of iodine anions: elementary reactions of I−, IO− and IO2− with ozone studied in the gas-phase at 300 K using an ion trap” Teiwes et al., Phys. Chem. Chem. Phys., 2018, , 20608

Analytical solution for the set of differential equations solved numerically in the original article

Ketone Body Acetoacetate Buffers Methylglyoxal via a Non-enzymatic Conversion during Diabetic and Dietary Ketosis

The α-oxoaldehyde methylglyoxal is a ubiquitous and highly reactive metabolite known to be involved in aging- and diabetes-related diseases. If not detoxified by the endogenous glyoxalase system, it exerts its detrimental effects primarily by reacting with biopolymers such as DNA and proteins. We now demonstrate that during ketosis, another metabolic route is operative via direct non-enzymatic aldol reaction between methylglyoxal and the ketone body acetoacetate, leading to 3-hydroxyhexane-2,5-dione. This novel metabolite is present at a concentration of 10%-20% of the methylglyoxal level in the blood of insulin-starved patients. By employing a metabolite-alkyne-tagging strategy it is clarified that 3-hydroxyhexane-2,5-dione is further metabolized to non-glycating species in human blood. The discovery represents a new direction within non-enzymatic metabolism and within the use of alkyne-tagging for metabolism studies and it revitalizes acetoacetate as a competent endogenous carbon nucleophile.

Further Comparisons of Finite Difference Schemes for Computational Modelling of Biosensors

Simulations are presented for a reaction-diffusion system within a thin layer containing an enzyme, fed with a substrate from the surrounding electrolyte. The chemical term is of the nonlinear Michaelis-Menten type and requires a technique such as Newton iteration for solution. It is shown that approximating the nonlinear chemical term in these systems by a linearised form reduces both the accuracy and, in the case of second-order methods such as Crank-Nicolson, reduces the global error order from O(δT2) to O(δT). The first-order methods plain backwards implicit with and without linearisation, and Crank-Nicolson with linearisation are all of O(δT) and very similar in performance, requiring, for a given accuracy target, an order of magnitude more CPU time than the efficient methods backward implicit with extrapolation and Crank-Nicolson, both with Newton iteration to handle the nonlinearity. Steady state computations agree with expectations, tending to the known solutions for limiting cases. The Crank-Nicolson method shows some concentration oscillations close to the outer layer boundary but this does not propagate to the inner boundary at the electrode. The backward implicit methods do not result in such oscillations and if concentration profiles are of interest, may be preferred.

Higher-order spatial discretisations in electrochemical digital simulations. Part 4. Discretisation on an arbitrarily spaced grid

A systematic approach to the construction of finite difference formulae for the approximation to first and second derivatives with respect to space on an arbitrarily spaced grid is presented. The finite difference formulae, combined with backward implicit (BI) and extrapolation methods, are used for electrochemical simulations and tested for efficiency. Excellent results are obtained with second and third order discretisations even for very small space intervals in the vicinity of the electrode and strongly expanding grid spacings. This ensures efficient simulation of kinetic-diffusion systems where, due to a fast homogeneous reaction, a thin reaction layer is formed adjacent to the electrode.

Damping of Crank-Nicolson error oscillations

The Crank-Nicolson (CN) simulation method has an oscillatory response to sharp initial transients. The technique is convenient but the oscillations make it less popular. Several ways of damping the oscillations in two types of electrochemical computations are investigated. For a simple one-dimensional system with an initial singularity, subdivision of the first time interval into a number of equal subintervals (the Pearson method) works rather well, and so does division with exponentially increasing subintervals, where however an optimum expansion parameter must be found. This method can be computationally more expensive with some systems. The simple device of starting with one backward implicit (BI, or Laasonen) step does damp the oscillations, but not always sufficiently. For electrochemical microdisk simulations which are two-dimensional in space and using CN, the use of a first BI step is much more effective and is recommended. Division into subintervals is also effective, and again, both the Pearson method and exponentially increasing subintervals methods are effective here. Exponentially increasing subintervals are often considerably more expensive computationally. Expanding intervals over the whole simulation period, although capable of satisfactory results, for most systems will require more cpu time compared with subdivision of the first interval only.

High-order spatial discretisations in electrochemical digital simulation. Part 3. Combination with the explicit Runge-Kutta algorithm

The application of fourth-order finite difference discretisations of the second derivative of concentration with respect to distance from the electrode, in electrochemical digital simulations, is examined further. In the bulk of the diffusion space, a central 5-point scheme is used, and 6-point asymmetric schemes are used at the edges. In this paper, four Runge-Kutta schemes have been used for the time integration. The observed efficiencies, for the Cottrell experiment and chronopotentiometry, are satisfactory, going beyond those for the 3-point scheme. However, it is third-order Runge-Kutta, rather than the fourth-order scheme, which is the most efficient, the two resulting in practically the same errors. This is probably due to the computational procedure where a constant ratio of delta(t)/h2 was used.

High order spatial discretisations in electrochemical digital simulation. 2. Combination with the extrapolation algorithm

The application of fourth order discretisations of the second derivative of concentration with respect to distance from the electrode, in electrochemical digital simulations, is examined. In the bulk of the diffusion space, a central five-point scheme is used, and six-point asymmetric schemes are used at the edges. In this paper, the scheme is applied to the extrapolation technique, based on the backward implicit (BI) algorithm for temporal integration, which (with extrapolation) allows higher orders in time as well. The method is found to be stable, using both the von Neumann and matrix methods. Exceptional efficiency is obtained both for Cottrell and chronopotentiometry simulations, requiring as few as 3-5 steps in time, starting at the dimensionless time t = 0 to gain four-decimal accuracy at t = 1.

High order spatial discretisations in electrochemical digital simulation. 2. Combination with the extrapolation algorithm

The application of fourth order discretisations of the second derivative of concentration with respect to distance from the electrode, in electrochemical digital simulations, is examined. In the bulk of the diffusion space, a central five-point scheme is used, and six-point asymmetric schemes are used at the edges. In this paper, the scheme is applied to the extrapolation technique, based on the backward implicit (BI) algorithm for temporal integration, which (with extrapolation) allows higher orders in time as well. The method is found to be stable, using both the von Neumann and matrix methods. Exceptional efficiency is obtained both for Cottrell and chronopotentiometry simulations, requiring as few as 3-5 steps in time, starting at the dimensionless time t = 0 to gain four-decimal accuracy at t = 1.