Current Contents / Physical, Chemical & Earth Sciences

The weights of criteria in multi-criteria decision-making (MCDM) problems are essential elements that can significantly affect the results. Accordingly, researchers developed and presented several methods to determine criteria weights. Weighting methods could be objective, subjective, and integrated. This study introduces a new method, called MEREC (MEthod based on the Removal Effects of Criteria), to determine criteria’ objective weights. This method uses a novel idea for weighting criteria. After systematically introducing the method, we present some computational analyses to confirm the efficiency of the MEREC. Firstly, an illustrative example demonstrates the procedure of the MEREC for calculation of the weights of criteria. Secondly, a comparative analysis is presented through an example for validation of the introduced method’s results. Additionally, we perform a simulation-based analysis to verify the reliability of MEREC and the stability of its results. The data of the MCDM problems generated for making this analysis follow a prevalent symmetric distribution (normal distribution). We compare the results of the MEREC with some other objective weighting methods in this analysis, and the analysis of means (ANOM) for variances shows the stability of its results. The conducted analyses demonstrate that the MEREC is efficient to determine objective weights of criteria.

A control method for desynchronizing an array of mean-field coupled FitzHugh– Nagumo-type oscillators is described. The technique is based on applying an adjustable DC voltage source to the coupling node. Both, numerical solution of corresponding nonlinear differential equations and hardware experiments with a nonlinear electrical circuit have been performed.

The magnetoresistance of nanostructured La1−xSrx(Mn1−yCoy)zO3±_ (La–Sr–Mn–Co–O) films with substitution of Co for Mn with amount of Co/(La + Sr) = 0.12 and different Mn excess Mn/(La + Sr) = 1.05, 1.07, and 1.11 was investigated at temperatures of 4–230 K in pulsed magnetic fields up to 60 T. It was found that the manganite–cobaltite films exhibit larger magnetoresistance in comparison with manganite films without Co doping. The largest magnetoresistance values and sensitivity to the magnetic field are obtained for La–Sr–Mn–Co–O films having Mn content close to the stoichiometric ratio for manganites: Mn/(La + Sr) = 1.05. It was found that magnetoresistance at high fields (20–60 T) has a minimum at (50–80 K) and increases with the decrease of temperature. The possibility to use these films for magnetic field measurements at cryogenic temperatures is demonstrated.

Scanning electrochemical microscopy (SECM) is an emerging electroanalytical sensing technique, used to investigate the electrochemical properties of the sample by ultra-micro-electrode(UME) scanning probe. UME signal usually is the current, which depends not only on the properties of the evaluated system but also on UME characteristics such as geometry. Variations of UME geometry can decrease accuracy of the measurement, and then correct analysis of the SECM data becomes almost impossible. In the present work, we studied the precision of measurements with three different the most frequent types of defected UME’s ((i) recessed-UME, (ii) out- warded-UME, (iii) cone-UME). Measurement results were compared with that obtained with not defected standard-plane-UME. Computational experiment was performed with SECM model using diffusion equations with non-rectangular border conditions to calculate esti- mated currents for these three types of defected UMEs and to compare them with that for standard-plane-UME. In order to test the correctness of the model, computa- tions for recessed-UME model were compared with data of real-recessed-UME experiment.

Composites designed by employing metal/dielectric composites coupled to the components of the incident electromagnetic (EM) fields are named metamaterials (MMs), and they display features not observed in nature. This type of artificial media has attracted great interest, resulting in groundbreaking theory that bridges the gap between EM and photonic phenomena. Practical applications of MMs have been delayed due to the high losses related to the use of metallic composites, on top of the challenges in manufacturing nanoscale, three-dimensional structures. Novel materials—for instance, graphene or transparent-conducting oxides (TCOs), employed for the production of multilayered MMs—can significantly suppress undesirable losses. It is worthwhile noting that three-layered nanocomposites enable an increase in the frequency range of the surface wave. This work analyzes recent progress in the physics of multilayered MMs. We deliver an outline of key notions, such as effective medium approximation, and present multilayered MMs based on the three-layered structure. An overview of graphene multilayered MMs reveals their ability to support Ferrell–Berreman (FB) modes. We also describe the tunable properties of the multilayered MMs.

An automated method for analyzing the shape and size of dimples of ductile tearing formed during static and impact fracture of titanium alloys VT23 and VT23M is proposed. The method is based on the analysis of the image topology. The method contains the operations of smoothing the initial fractographic image; its convolution with a filter to identify the topological ridges; thresholding with subsequent skeletonization to identify boundaries between dimples; clustering to isolate the connected areas that represent the sought objects—dimples. For each dimple, the following quantitative characteristics were calculated: area, coefficient of roundness and visual depth in units of image intensity. The surface of ductile tearing was studied by analyzing the peculiarities of parameter distribution of the found dimples. The proposed method is applied to fractograms of fracture surfaces of titanium alloys VT23 and VT23M.

The stability bounds and error estimates for a compact higher order Numerov-Crank-Nicolson scheme on non-uniform spatial meshes for the 1D time-dependent Schrödinger equation have been recently derived. This analysis has been done in L2 and H1 mesh norms and used the non-standard "converse'' condition hw ≤ c0Ƭ, where hw is the mean spatial step, Ƭ is the time step and c0>0. Now we prove that such condition is necessary for some families of non-uniform meshes and any spatial norm. Also computational results for zero and non-zero potentials show unacceptably wrong behavior of numerical solutions when Ƭ decreases and this condition is violated.

The results of fabrication of nanostructured La1-x Sr (x) MnO3 films grown by pulsed injection metalorganic chemical vapour deposition technique onto special disordered glass-ceramics substrate are presented. Two groups of films were produced in order to determine what would be their main physical properties when certain fabrication changes were introduced: (1) films with thicknesses in the range of 25-900 nm, which were grown at a temperature of 750 A degrees C; and (2) films having thicknesses of 400 nm, which were grown at different deposition temperatures ranging from 600 A degrees C up to 775 A degrees C in steps of 25 A degrees C. It was determined that the morphology and microstructure of the films depends on the thicknesses of these films and their deposition temperatures. The thinnest films (25 nm) grew mainly in amorphous phase, while the thicker films had well-pronounced structure made of column-shaped crystallites. These had average column widths of 40-65 nm, were spread throughout the whole thickness of the films, and were separated by 5-10-nm-thick grain boundaries. The influence of growth conditions on the colossal magnetoresistance effect in these films was studied in pulsed magnetic fields of up to 20 T. The dependences of the magnetoresistance on the magnetic flux density were analysed using modified Mott's hopping model. It was demonstrated that these nanostructured films behave as superparamagnetic materials with reduced magnetic properties due to disordered grain boundaries. The obtained results allow the tuning of the resistivity, magnetoresistance and the anisotropy of La1-x Sr (x) MnO3 manganite films, which were deposited onto glass-ceramic substrates, and thus to use them for the fabrication of high pulsed magnetic field sensors.

A phenomenological model of CO oxidation with NO reaction proceeding over composite (supported) catalysts is proposed and solved numerically using the finite difference method. The model is based on the coupled system of PDEs subject to nonclassical conjugate conditions at the catalyst-support interface and includes: the bulk diffusion of reactants from a bounded vessel towards the catalyst surface and the bulk one of the reaction products from the surface into the same vessel, adsorption and desorption of particles of reactants, and surface diffusion of adsorbed molecules. The readsorption of the reaction product N2O is also taken into account. The influence of the rate constants of the adsorbed particle jumping via the catalyst-support interface and reaction rate constants on the surface reactivity is investigated. It is shown that the turnover rates of the CO and NO into products N2O, CO2, and N2 are nonmonotonic time functions and depending on values of the kinetic parameters may possess one or two maxima. The N2O readsorption in case of the existence of two maxima essentially increases the turnover rates and extends the duration of their high values. The mechanism and conditions for arising of the second maximum is discussed. It is also shown that the variation of the particle jumping rate constants influences differently the size of the jump discontinuity of concentrations of different adsorbates at the catalyst-support interface.

The paper presents the study of the influence of mechanical damage on the safe operation of gas transmission pipelines. The main types of pipeline damage with the actual parameters and their influence on the operational parameters are analysed. The damaged fractures of the section of the pipeline Kaunas (Lithuania)–Kaliningrad (Russia) were investigated in the laboratory. The main operational characteristics and the structure of the pipeline’s metal after the period of long-term operation were determined using various research and experimental methods. The influence of the pipeline’s damage was modelled by using the Finite Element Method and the ANSYS code. The predictions of the failure pressure were made, taking into consideration the actual properties of the pipeline’s metal. Techniques including the hardness and microhardness measurement, chemical analysis, the impact strength test, and metallography analysis with an optical microscope, were used in the experimental study.