On controlling stresses in a complexly loaded steel construction by magnetoelastic demagnetization

Dependences of magnetic leakage field strength during magnetoelastic demagnetization of local magnetization in a steel disk (St3 steel) on the value of its biaxial deformation in the elastic domain have been studied. Deformation-induced mechanical stresses that act in radial and tangential directions have been calculated. Dependences of changes in the normal component of the magnetic leakage field of steel on the effective stress value are given. It is shown that mechanical stresses in a complexly loaded construction can be tested by the value of its magnetoelastic demagnetization.     

PCB assembly scheduling for collect-and-place machines using genetic algorithms

In printed circuit board (PCB) assembly, collect-and-place machines, which use a revolver-type placement head to mount electronic components onto the board, represent one of the most popular types of assembly machinery. The assignment of feeders to slots in the component magazine and the sequencing of the placement operations are the main optimisation problems for scheduling the operations of an automated placement machine. In this paper, we present different genetic algorithms (GAs) for simultaneously solving these highly interrelated problems for collect-and-place machines in PCB assembly. First we consider single-gantry machines as the basic type of machinery. In the conventional GA approach all placement operations and the feeder-slot assignment are represented by a single chromosome. In order to increase the efficiency of the genetic operators, we present a novel GA approach, which integrates a clustering algorithm for generating sub-sections of the PCB and grouping the corresponding placement operations. It is shown that the proposed GAs can be extended to schedule dual-gantry placement machines, which are equipped with two independent placement heads and two dedicated component magazines. Hence, component feeders have to be allocated between the two magazines. To solve this allocation problem, two different heuristic strategies are proposed. Finally, detailed numerical experiments are carried out to evaluate the performances of the proposed GAs.     

Application of probabilistic methods to validate NPP pipewhip impact simulations

Piping in nuclear power plants is vital to the proper operation and safety of these facilities. To assure safety in the unlikely event of a pipe break, it is necessary to evaluate the consequences from the resulting whipping pipe on neighboring components and structures. Numerical simulations allow for rapid evaluation of these consequences. Before simulations can be accepted, however, the methodology and computer codes must be validated against experimental results. This paper uses a probabilistic approach to validate pipe whip simulations against limited experimental results. Probabilistic analysis software was developed and coupled to existing deterministic finite element software. An example of a whipping pipe impacting against a reinforced concrete slab was simulated. The described probabilistic approach was used to validate the numerical simulations. The conclusions obtained were that the numerical simulations of whipping pipe impact were validated, even though the numerical results did not exactly agree with experimental results. The chosen points of comparison – namely, time-to-impact and total reaction force – were within the 95% confidence interval.     

Acoustooptic interaction in uniaxial gyrotropic paratellurite crystals

An analysis is made of an intermediate mode of light diffraction by ultrasound in a uniaxial gyrotropic paratellurite crystal. A system of coupled wave equations is presented to calculate the polarization and energy characteristics of the diffracted light for the Raman-Nath, intermediate, and Bragg modes of acoustooptic interaction. The diffraction of light propagating at small angles to the crystal optic axis by a slow ultrasonic shear wave propagating along the [110] crystallographic axis is studied. The amplitude-frequency characteristics of a modulator-deflector for optical radiation are investigated. Curves of the diffraction efficiency as a function of the ultrasonic wave intensity are plotted for various acoustooptic interaction lengths. Pis’ma Zh. Tekh. Fiz. 23, 84–89 (January 12, 1997)     

Porous Single Crystals of Calcite from Colloidal Crystal Templates: ACC Is Not Required for Nanoscale Templating

This article investigates the formation of nanostructured single crystals of calcite using direct, ion‐by‐ion precipitation methods and shows that single crystals with complex morphologies and curved surfaces can readily be formed using this technique. Calcite crystals with inverse opal and direct opal structures are prepared using templates of colloidal crystals and polystyrene reverse opals, respectively, and excellent replication of the template structures are achieved, including the formation of 200‐nm spheres of calcite in the direct opal structure. These highly porous crystals also display extremely regular, crystalline gross morphologies. The methodology is extremely versatile and challenges the preconception that nanostructured crystals cannot be prepared by simple diffusion of reagents into the template due to blocking of the channels. The results are also discussed in light of alternative templating methods using amorphous calcium carbonate (ACC) as a precursor phase and provide insight into the role of ACC in biological calcification processes.     

Giant Incident Photon‐to‐Current Conversion with Photoconductivity Gain on Nanostructured Bismuth Oxysulfide Photoelectrodes under Visible‐Light Illumination

Nanostructured layered bismuth oxysulfide films synthesized by chemical bath deposition reveal a giant incident photon‐to‐current conversion efficiency (IPCE). This study shows that surprisingly for the cathodic photocurrent in the photoreduction process, the IPCE reaches ≈2500% in aqueous solutions containing [Fe(CN)₆]^3?. The giant IPCE is observed starting from a certain minimal oxidizer concentration (c > 10^?3m for [Fe(CN)₆]^3?) and decreases nonlinearly with an increase of illumination intensity. Giant IPCE is determined by the decrease in resistivity of the bismuth oxysulfide film under illumination with photoconductivity gain, which provides the possibility of charge carriers from an external circuit to participate in the photoreduction process. Giant IPCE is observed not only in [Fe(CN)₆]^3? solutions, but also in electrolytes containing other photoelectron acceptors: Fe³⁺, I₃^?, quinone, H₂O₂. In all, solution‐processed layered bismuth oxysulfide films offer large‐area coverage, nontoxicity, low cost, and compatibility with a wide range of substrates. Abnormally high photoelectrochemical activity, as well as a band gap energy value favorable for efficient conversion of solar light (1.38 eV, direct optical transitions), proves the potential of bismuth oxysulfide photoelectrodes for a new generation of high‐performance photoconverters.     

Droplet Microfluidics XRD Identifies Effective Nucleating Agents for Calcium Carbonate

The ability to control crystallization reactions is required in a vast range of processes including the production of functional inorganic materials and pharmaceuticals and the prevention of scale. However, it is currently limited by a lack of understanding of the mechanisms underlying crystal nucleation and growth. To address this challenge, it is necessary to carry out crystallization reactions in well‐defined environments, and ideally to perform in situ measurements. Here, a versatile microfluidic synchrotron‐based technique is presented to meet these demands. Droplet microfluidic‐coupled X‐ray diffraction (DMC‐XRD) enables the collection of time‐resolved, serial diffraction patterns from a stream of flowing droplets containing growing crystals. The droplets offer reproducible reaction environments, and radiation damage is effectively eliminated by the short residence time of each droplet in the beam. DMC‐XRD is then used to identify effective particulate nucleating agents for calcium carbonate and to study their influence on the crystallization pathway. Bioactive glasses and a model material for mineral dust are shown to significantly lower the induction time, highlighting the importance of both surface chemistry and topography on the nucleating efficiency of a surface. This technology is also extremely versatile, and could be used to study dynamic reactions with a wide range of synchrotron‐based techniques.     

Thermal decomposition of natural dolomite

We have studied thermal modification of natural dolomite chips, which has allowed us to optimize conditions for the preparation of supports for manganese oxide catalysts with appropriate physicochemical properties (elevated carbon dioxide partial pressure and calcination temperature no higher than 800°C).