Million atom molecular dynamics simulations of materials on parallel computers

Recent advances in computing tecnology — parallel computer architectures, portable software and development of robust O(N) algorithms — have revolutionized the field of computer simulation. Using the space-time multiresolution molecular dynamics algorithms it is possible to carry out multimillion atom simulations of materials in different ranges of density, temperature and uniaxial strain.     

Modeling of ferrite growth in nodular cast iron

In nodular cast iron, ferrite forms around the graphite nodules and growth proceeds until pearlite nucleates and consumes the remaining austenite. In order to simulate the structure, it is therefore necessary to have accurate models for the ferrite growth. Some investigators have proposed that the growth is completely governed by carbon diffusion through the ferrite shell. In the present work, it is shown that the ferrite growth in nodular cast iron can be divided into three different stages where the growth initially is governed by carbon diffusion in the austenite until the graphite nodule is entirely enveloped by a ferrite shell. During the second stage, it is proposed that the growth is controlled by the incorporation rate of carbon atoms on the graphite nodule. During the later stages of the transformation, the diffusion distance has increased considerably, and therefore, the diffusion of carbon through the ferrite shell will determine the growth rate.     

Deposition of Au colloids on plasmachemically modified carbon nanofibers

The surface properties of fishbone (FB) carbon nanofibers (CNFs) were altered. This was achieved by H₂O-plasma treatment (FB-plasma) and oxidation in HNO₃ (FB-HNO₃). By zeta-potential measurements, the surfaces of as-grown and acid treated CNFs were found to be negatively charged at all pHs. Meanwhile, basic entities were introduced by H₂O-plasma treatment, indicated by an isoelectric point of pH 4.6. Ultraviolet-visible measurements indicated the successful deposition of negatively charged Au colloids on FB-plasma, and incomplete deposition on FB-HNO₃. The nature of the basic sites accommodating colloid deposition is discussed based on X-ray photoelectron spectroscopy (XPS) results. The XPS study indicated significant differences in the type and amount of surface groups. Also, a variation in the fraction of defect and/or edge sites was found. The possible sites responsible for colloid immobilization are discussed based on the XPS results. Plasma treatment is demonstrated as a simple and effective procedure for altering the surface characteristics of CNFs.     

Au–TiO2 catalysts on carbon nanofibres prepared by deposition-precipitation and from colloid solutions

Au catalysts have been prepared (i) on TiO₂, (ii) on carbon nanofibres (CNF) and (iii) on TiO₂ deposited onto CNF. Catalysts prepared from deposition-precipitation (DP) and from colloid solutions have been characterised using XRD, TEM, TGA and XAS and tested in the water–gas shift (WGS) reaction. DP yields large Au particles (>50 nm) on CNF-containing supports. High Au dispersion on carbon nanofibres requires preparation via other methods such as colloid formation. Au particle growth is more pronounced during the synthesis steps than during thermal treatments. This increase is not observed for the Au particles on TiO₂ but only when CNF is present, indicating that the surface properties of TiO₂ are altered by the CNF. TiO₂ XANES analyses show that distortions in the lattice symmetry of TiO₂ are introduced when the oxide is deposited on CNF. The distortion of the TiO₂ structure by the CNF may also introduce changes that promote the turnover frequencies. The WGS activity significantly improves when titania is present. This shows that coexistence of Au and TiO₂ is needed to obtain high catalytic activity in the WGS reaction, indicating that the active sites are either on the Au–TiO₂ interface or that the reaction follows a bifunctional mechanism.     

Thermal responses at three low ambient temperatures: Validation of the duration limited exposure index

The objective of the study was to validate the DLE (duration limited exposure) index, which provides a method to determine acceptable time limits when, in a cold environment, clothing insulation is not sufficient to protect the wearer from body cooling. The thermal responses of ten male subjects dressed in winter clothing to −6, −14 and −22°C during very light exercise were studied. The individual variation of peripheral temperature responses was large. The majority of the subjects stated that they would accept the exposure once a day, but not continuously. DLE was on the ‘safe side' according to the body net heat debt and rectal temperature, but at the same time it allowed for low skin temperatures, especially of the extremities at low ambient temperatures. At predicted time limits, the mean skin temperature criteria of DLE suggested in the ISO document ISO/TR 11079 were not met at −14 and −22°C. Introduction of limit criteria for extremity cooling in prediction models would render a more complete assessment of cold stress.Relevance to industrySince the protective clothing worn by the worker is not always sufficient for the actual low ambient temperature there is a need for accurate predictions of exposure time.     

Advancing the industrial aluminum process: 20th century breakthrough inventions and developments

In connection with the 125th anniversary of the Hall-Héroult process this year, we will review the most important progress that has been made in the twentieth century. What were the most significant improvements in this period, and which scientists and engineers came up with the ideas for these improvements? In this paper we will try to answer these questions. We will highlight the major technological breakthroughs and mention those people who played important roles in the development of these improvements.