Random alloy-like local structure of Fe(Se, S)(1-x)Te(x) superconductors revealed by extended x-ray absorption fine structure

The local structure of Fe(Se, S)(1-x)Te(x) ternary (11-type) chalcogenides has been studied by temperature dependent Fe K-edge extended x-ray absorption fine structure measurements. We find that the Fe-Se and Fe-Te distances in ternary FeSe(1-x)Te(x) are closer to the respective distances in the binary systems, revealing significant divergence of the local structure from the average one. The mean square relative displacements show a systematic change with Te content, consistent with bond relaxation in the inhomogeneous ternary phases. Also, the Fe-Te and Fe-S distances in the FeS(0.2)Te(0.8) ternary system are found to be different in the crystallographically homogeneous structure. The observed features are characteristic of ternary random alloys, suggesting that a proper consideration should be given to the atomic distribution for describing the complex electronic structure of these multi-band Fe-based chalcogenides.     

Li(i=1–3) sub-shell x-ray relative intensities for some compounds of 66Dy at 22.6 and 59.54 keV incident photon energies

The intensity ratios, I_Lk/I_Lα (k=l,β_1,4,β_3,6,β_2,7,9,10,15,γ_1,5,γ_2,3,γ₄,β,γ), have been measured for some compounds of ₆₆Dy, namely, Dy₂O₃, Dy₂(CO₃)₃, Dy₂(SO₄)₃, DyI₂ and Dy metal by creating the L_i(i=1–3) sub-shell vacancies in widely different proportions at two incident photon energies of 22.6 keV and 59.54 keV, in order to check the predicted dependence of these ratios on the incident photon energy and also investigate the influence of chemical effects on these ratios for an f-block element. The measurements were performed using the EDXRF spectrometer involving disk type radioactive sources of Cd¹⁰⁹ and Am²⁴¹ and a Peltier cooled Si PIN x-ray detector arranged in the 90° reflection geometry. The measured intensity ratios have been compared with the theoretical I_Lk/I_Lα values and those calculated using the two sets of fluorescence and Coster–Kronig yields available in literature in order to check the reliability of the theoretical/calculated values. Further, the measured ratio, I_Lγ4/I_Lα, was found to depend on the oxidation state of ₆₆Dy as well as nature of ligand attached to it in a given compound.     

Thermoanalytical behaviour of carbaryl and its copper(II) and zinc(II) complexes

Non-isothermal techniques, i.e. thermogravimetry (TG) and differential scanning calorimetry (DSC), have been applied to investigate the thermal behaviour of carbaryl (1-naphthyl-N-methylcarbamate = 1-Naph-N-Mecbm) and its complexes, M(1-Naph-N-Mecbm)₄X₂, where M = Cu, X = Cl, NO₃ and CH₃COO and M = Zn, X = Cl. Carbaryl and Zn(1-Naph-N-Mecbm)₄Cl₂ complex exhibit two-stage thermal decomposition while the copper(II) complexes exhibit three and four-stage decomposition in their TG curves. The nature of the metal ion has been found to play highly influential role on the nature of thermal decomposition products as well as energy of activation ‘E*’. The presence of different anions does not seem to alter the thermal decomposition patterns. The complexes display weak to medium intensity exothermic and endothermic DSC curves, while the free ligand exhibits two endothermic peaks. The kinetic and thermodynamic parameters namely, the energy of activation ‘E*’, the frequency factor ‘A’ and the entropy of activation ‘S*’ etc. have been rationalized in relation to the bonding aspect of the carbaryl ligand. The nature and chemical composition of the residues of the decomposition steps have been studied by elemental analysis and FTIR data.     

Ordering dynamics in Disordered systems

We review analytical and numerical studies of phase ordering dynamics or domain growth in systems with quenched disorder. These studies are usually based on kinetic versions of the random-exchange Ising model (REIM) or random-field Ising model (RFIM). We also present detailed numerical results which clarify the nature of domain growth in random magnets. These results demonstrate that domain walls are trapped by disorder barriers with a logarithmic dependence on the domain size.     

Some recent advances in the understanding of phase-ordering dynamics

We review some of our recent studies of phase ordering dynamics. Specifically, we describe results from numerical simulations of domain growth in systems with quenched disorder. We also present representative results from numerical studies of phase ordering dynamics in anisotropic systems.     

Reliability of fluctuation-induced transport in a Maxwell-demon-type engine

We study the transport properties of an overdamped Brownian particle which is simultaneously in contact with two thermal baths. The first bath is modeled by an additive thermal noise at temperature T _A . The second bath is associated with a multiplicative thermal noise at temperature T _B . The analytical expressions for the particle velocity and diffusion constant are derived for this system, and the reliability or coherence of transport is analyzed by means of their ratio in terms of a dimensionless Péclet number. We find that the transport is not very coherent, though one can get significantly higher currents.     

Effect of voids and pressure on melting of nano-particulate and bulk aluminum

Molecular dynamics simulations are performed using isobaric–isoenthalpic (NPH) ensembles to study the effect of internal defects in the form of voids on the melting of bulk and nano-particulate aluminum in the size range of 2–9 nm. The main objectives are to determine the critical interfacial area required to overcome the free energy barrier for the thermodynamic phase transition, and to explore the underlying mechanisms for defect-nucleated melting. The inter-atomic interactions are captured using the Glue potential, which has been validated against the melting temperature and elastic constants for bulk aluminum. A combination of structural and thermodynamic parameters, such as the potential energy, Lindemann index, translational-order parameter, and radial-distribution functions, are employed to characterize the melting process. The study considers a variety of void shapes and sizes, and results are compared with perfect crystals. For nano aluminum particles smaller than 9 nm, the melting temperature is size dependent. The presence of voids does not impact the melting properties due to the dominancy of nucleation at the surface, unless the void size exceeds a critical value beyond which lattice collapse occurs. The critical void size depends on the particle dimension. The effect of pressure on the particulate melting is found to be insignificant in the range of 1–300 atm. The melting behavior of bulk aluminum is also examined as a benchmark. The critical interfacial area required for the solid–liquid phase transition is obtained as a function of the number of atoms considered in the simulation. Imperfections such as voids reduce the melting point. The ratio between the structural and thermodynamic melting points is 1.32. This value is comparable to the ratio of 1.23 for metals like copper.     

Ranking in integer linear fractional programming problems

An algorithm is developed which ranks the feasible solutions of an integer fractional programming problem in decreasing order of the objective function values.

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Zusammenfassung Es wird ein Algorithmus angegeben, der die zulässigen Lösungen eines ganzzahligen Quotientenprogrammes nach fallenden Zielfunktionswerten liefert.