Cracks,repair and reconstruction of bucket wheel excavator slewing platform

This paper discusses the results of the investigation of occurrence of cracks in the structure of bucket wheel excavator (BWE) slewing platform, the repair procedure and the reconstruction of the slewing platform. The results of the finite elements analysis (FEA) point out the pronounced stress concentration in the zones of crack occurrence. The values of calculated stresses in the said zones exceed the yield stress of the material. The design solution for the slewing platform reconstruction is chosen based on the comparative analysis of stress–strain states of alternative solutions. The adopted solution enabled the repair and reconstruction in field conditions, without previously dismantling components of the BWE superstructure. Moreover, the regular maintenance procedure has not been impeded. Experimental analysis of the stress state of the reconstructed slewing platform in regular working conditions has confirmed the validity of the reconstruction design. After the reconstruction the BWE has dug up more than 2.9 × 10⁶ m³ of overburden. Visual inspection of slewing platform proved that there are no defects in the structure.     

Correlation Between Surface Chemistry and Electrocatalytic Properties of Monodisperse PtxNi1‐x Nanoparticles

Monodisperse and homogeneous Pt_xNi_1‐x alloy nanoparticles of various compositions are synthesized via an organic solution approach in order to reveal the correlation between surface chemistry and their electrocatalytic properties. Atomic‐level microscopic analysis of the compositional profile and modeling of nanoparticle structure are combined to follow the dependence of Ni dissolution on the initial alloy composition and formation of the Pt‐skeleton nanostructures. The developed approach and acquired knowledge about surface structure‐property correlation can be further generalized and applied towards the design of advanced functional nanomaterials.     

Platinum-alloy nanostructured thin film catalysts for the oxygen reduction reaction

In an effort to study advanced catalytic materials for the oxygen reduction reaction (ORR), a number of metallic alloy nanostructured thin film (NSTF) catalysts have been characterized by rotating disk electrode (RDE). Optimal loadings for the ORR and activity enhancement compared to conventional carbon supported nanoparticles (Pt/C) were established. The most efficient catalyst was found to be PtNi alloy with 55 wt% of Pt. The enhancement in specific activity is more than one order of magnitude, while the improvement factor in mass activity is 2.5 compared to Pt/C. Further lowering of the platinum to nickel ratio in NSTF catalysts did not lead to increased mass activity values.     

Changes of properties of cured and uncured disiloxane bisbenzocyclobutene thin films under irradiation

The effects induced by α-particles and laser beam irradiation in air atmosphere in uncured and cured bisbenzocyclobutene (BCB) 2 μm thick films, spin-coated on glass/ITO surface have been investigated. α-Particle irradiation was done by means of a thin film ²⁴¹Am source (E_α = 5.486 MeV), up to the total fluence of about 5 × 10¹⁰ particles/cm². Laser irradiation was performed by a Nd³⁺:YAG (λ = 1.06 μm) laser in the free generation and the Q-switch regime, using both focused and unfocused beams. Irradiation induced changes were investigated using Light and Atomic Force Microscopy (AFM), infrared (IR), Ultraviolet/visible (UV/vis) and Raman spectroscopy by inspecting several uncured and cured BCB films before and after irradiation. It has been found that both types of irradiation under investigated conditions have produced a novel phase in the material, which is not present either in the uncured or the cured BCB films. Possible implications of the observed effects on curing and degradation of BCB films have been discussed.     

Investigation of crystal growth of borax in single and dual impeller batch cooling crystallizer

Abstract

The purpose of this work was to investigate and compare the influence of fluid flow in a single and dual impeller batch cooling crystallizer on crystal growth kinetics of borax decahydrate. Examinations were conducted in a crystallizer of 15?dm³ stirred by a single pitched blade turbine and straight blade turbine as well as their dual configurations. Kinetics parameters of crystal growth determined at applied mixing conditions were correlated with hydrodynamic conditions. In this paper, hydrodynamics was characterized by mixing time, which was experimentally determined, and by fluid flow patterns, which were simulated by the means of computational fluid dynamic (CFD). It was found that although the crystal growth in all systems investigated was controlled by the integration mechanism, the crystal growth rate constant changed significantly with impeller configuration. Regarding the characteristics of the final product, a dependence of the crystal size distribution on the fluid flow pattern was noticed while the number of impellers did not affect the product properties. On the other hand, mixing efficiency differed significantly with the type and number of impellers.     

Magnetic Hysteresis Loops Revisited: Step Closer to Understand the Role of Exterior Angles

The characterization of nanocomposite samples which contain Cu, Fe-species, prepared by the sol-gel method, was established by Nikoli? et al., in a previous article (Nikoli? et al. in Journal of Solid State Physics 513:1, 2021). In this study, the magnetic behavior of nanocomposite samples was examined. The basic parameters of the room- and low-temperature magnetic hysteresis loops are discussed. To better describe the shape of magnetic hysteresis loop, the authors proposed to consider additional parameters - measures of the exterior angles of the hysteresis curve. Behavior of hysteresis parameters and exterior angles, caused by annealing treatment, was investigated by measuring hysteresis loops at two measured temperatures: 298K, and 5K. Correlation between changes in the behavior of hysteresis parameters and exterior angles was discussed. An attempt has been made to attribute physical meaning to chosen measured angles, which would allow a better understanding of the magnetic hysteresis curve.

     

Modeling and optimization of hybrid solar thermoelectric systems with thermosyphons

We present the modeling and optimization of a new hybrid solar thermoelectric (HSTE) system which uses a thermosyphon to passively transfer heat to a bottoming cycle for various applications. A parabolic trough mirror concentrates solar energy onto a selective surface coated thermoelectric to produce electrical power. Meanwhile, a thermosyphon adjacent to the back side of the thermoelectric maintains the temperature of the cold junction and carries the remaining thermal energy to a bottoming cycle. Bismuth telluride, lead telluride, and silicon germanium thermoelectrics were studied with copper–water, stainless steel–mercury, and nickel–liquid potassium thermosyphon-working fluid combinations. An energy-based model of the HSTE system with a thermal resistance network was developed to determine overall performance. In addition, the HSTE system efficiency was investigated for temperatures of 300–1200 K, solar concentrations of 1–100 suns, and different thermosyphon and thermoelectric materials with a geometry resembling an evacuated tube solar collector. Optimizations of the HSTE show ideal system efficiencies as high as 52.6% can be achieved at solar concentrations of 100 suns and bottoming cycle temperatures of 776 K. For solar concentrations less than 4 suns, systems with thermosyphon wall thermal conductivities as low as 1.2 W/mK have comparable efficiencies to that of high conductivity material thermosyphons, i.e. copper, which suggests that lower cost materials including glass can be used. This work provides guidelines for the design, as well as the optimization and selection of thermoelectric and thermosyphon components for future high performance HSTE systems.     

Failure analysis and redesign of the bucket wheel excavator two-wheel bogie

This paper discusses the cause of the failure in the vital part of the crawler travel gear of the bucket wheel excavator (BWE) – two-wheel bogie (TWB). The results of the finite element analysis (FEA) point out that the main reason of the TWB failure is its insufficient strength under lateral forces acting during curve travel. The weak points in the TWB structure are removed by suitable redesign while keeping in mind all restrictions ensuing from installation conditions and functionality of the existing crawler travel gear. In addition to the numerical analysis (FEA), a parallel experimental analysis of the original as well as the redesigned TWB is conducted on a test board especially designed for this purpose. The experimental results have confirmed the considerably improved response on lateral loads of the redesigned TWB. The exploitation of the redesigned TWB with no failures has confirmed the validity of the reconstruction design.     

Fuzzy J-Means: a new heuristic for fuzzy clustering

A fuzzy clustering problem consists of assigning a set of patterns to a given number of clusters with respect to some criteria such that each of them may belong to more than one cluster with different degrees of membership. In order to solve it, we first propose a new local search heuristic, called Fuzzy J-Means, where the neighbourhood is defined by all possible centroid-to-pattern relocations. The “integer” solution is then moved to a continuous one by an alternate step, i.e., by finding centroids and membership degrees for all patterns and clusters. To alleviate the difficulty of being stuck in local minima of poor value, this local search is then embedded into the Variable Neighbourhood Search metaheuristic. Results on five standard test problems from the literature are reported and compared with those obtained with the well-known Fuzzy C-Means heuristic. It appears that solutions of substantially better quality are obtained with the proposed methods than with this former one.     

Efficient domination in circulant graphs with two chord lengths

Domination is an important property in the design of efficient computer interconnection networks. We provide a complete characterization of circulant graphs with two chord lengths that admit an efficient dominating set. In particular, for 3-regular and 4-regular circulant graphs, we give necessary and sufficient conditions for the existence of efficient dominating sets and we describe their exact structure according to the relationship between chords.