Reductions between types of numberings

This paper considers reductions between types of numberings; these reductions preserve the Rogers Semilattice of the numberings reduced and also preserve the number of minimal and positive degrees in their semilattice. It is shown how to use these reductions to simplify some constructions of specific semilattices. Furthermore, it is shown that for the basic types of numberings, one can reduce the left-r.e. numberings to the r.e. numberings and the k-r.e. numberings to the $(k+1)$-r.e. numberings; all further reductions are obtained by concatenating these reductions.     

Electric Black Holes in a Model of Nonlinear Electrodynamics

The electric counterpart of the magnetic black hole solution found in nonlinear electrodynamics (NED) is presented. The electric field emerges regular and confined whereas the spacetime which satisfies all the energy conditions is singular. Our result is in conformation with a theorem proved before about the existence of regular electric black holes. The thermal properties of the black hole including the first law, Smarr's formula, and the thermal stability are investigated. This provides a chance to compare the electric and magnetic types of black holes in a particular model of NED.     

Initial Carbon−Carbon Bond Formation during the Early Stages of Methane Dehydroaromatization

Methane dehydroaromatization (MDA) is among the most challenging processes in catalysis science owing to the inherent harsh reaction conditions and fast catalyst deactivation. To improve this process, understanding the mechanism of the initial C−C bond formation is essential. However, consensus about the actual reaction mechanism is still to be achieved. In this work, using advanced magic-angle spinning (MAS) solid-state NMR spectroscopy, we study in detail the early stages of the reaction over a well-dispersed Mo/H-ZSM-5 catalyst. Simultaneous detection of acetylene (i.e., presumably the direct C−C bond-forming product from methane), methylidene, allenes, acetal, and surface-formate species, along with the typical olefinic/aromatic species, allow us to conclude the existence of at least two independent C−H activation pathways. Moreover, this study emphasizes the significance of mobility-dependent host–guest chemistry between an inorganic zeolite and its trapped organic species during heterogeneous catalysis.     

A novel formulation and analysis for heat transfer in von Kármán flow involving viscoelastic fluid: OHAM solutions

Journal of Thermal Analysis and Calorimetry - This research concentrates on the von Kármán flow of viscoelastic fluid obeying second grade model over a heated permeable disk. Our interest...     

On Universal Pairs in the Ershov Hierarchy

Siberian Mathematical Journal - We develop the Ershov theory of C-classes for some finite families of sets in the Ershov hierarchy. We generalize the result by Muchnik on multiple $ m $...     

One-Step Hydrothermal Deposition of ZnO–TiO2 Heterojunction Nanostructures as Photoelectrochemical Performance for Sb2S3 Quantum-Dot-Sensitized Solar Cells by High-Efficiency Enhancement

Crystallography Reports - ZnO–TiO2 heterojunction photoanodes consisting of nanoparticles, nanorods, nanopropellers, and nanohedgehogs for dye-sensitized solar cell were first synthesized by...     

Decomposition behavior and properties for tin–antimony alloy with bismuth content

The peritectic alloy Sn–10Sb, was chosen as one of the lead-free solder alloys to be subjected to many studies. Bi atoms were added to this alloy in the range of 1–3 wt%. The experimental results obtained from this study show a complete solubility of Bi atoms when added by 2 wt%. More additions of Bi tend to increase the formation of the intermetallic compound SnSb by reducing the precipitations of Sb as a single phase. This intermetallic compound with the precipitation of Bi as a third phase tends to improve the mechanical properties of this alloy.     

Monte Carlo hyper-heuristics for examination timetabling

Automating the neighbourhood selection process in an iterative approach that uses multiple heuristics is not a trivial task. Hyper-heuristics are search methodologies that not only aim to provide a general framework for solving problem instances at different difficulty levels in a given domain, but a key goal is also to extend the level of generality so that different problems from different domains can also be solved. Indeed, a major challenge is to explore how the heuristic design process might be automated. Almost all existing iterative selection hyper-heuristics performing single point search contain two successive stages; heuristic selection and move acceptance. Different operators can be used in either of the stages. Recent studies explore ways of introducing learning mechanisms into the search process for improving the performance of hyper-heuristics. In this study, a broad empirical analysis is performed comparing Monte Carlo based hyper-heuristics for solving capacitated examination timetabling problems. One of these hyper-heuristics is an approach that overlaps two stages and presents them in a single algorithmic body. A learning heuristic selection method (L) operates in harmony with a simulated annealing move acceptance method using reheating (SA) based on some shared variables. Yet, the heuristic selection and move acceptance methods can be separated as the proposed approach respects the common selection hyper-heuristic framework. The experimental results show that simulated annealing with reheating as a hyper-heuristic move acceptance method has significant potential. On the other hand, the learning hyper-heuristic using simulated annealing with reheating move acceptance (L?CSA) performs poorly due to certain weaknesses, such as the choice of rewarding mechanism and the evaluation of utility values for heuristic selection as compared to some other hyper-heuristics in examination timetabling. Trials with other heuristic selection methods confirm that the best alternative for the simulated annealing with reheating move acceptance for examination timetabling is a previously proposed strategy known as the choice function.