Determination of lowest carbon concentrations in steel ‐ a challenge to the steelworks laboratory

A working group of the chemists’ committee of Verein Deutscher Eisenhüttenleute, VDEh (The German Iron and Steel Institute), was engaged in the elaboration of suitable procedures for the reliable determination of carbon concentrations <50 μg/g in steel, which can be routinely applied in the steelworks laboratory. Besides the shape of the sample and the kind of its preparation, the influences of quantity and purity of the combustion additives, and of quality and pretreatment of the crucibles on the analytical result were studied. Furthermore, the execution of the combustion analysis with commercially available instruments was optimized. Round‐robin tests on nine steel samples with carbon concentrations between 1 and 40 μg/g showed that with the optimized procedure concentrations >5 μg/g C can be successfully determined; for accurate results at lower concentrations most careful execution and a most recent type of carbon analyzer are required. The calibration of the instruments with micro‐samples of carbonaceous compounds of exactly known stoichiometry (primary standards) was also subject of investigation, in order to meet the requirements of traceability to SI units for the certification of standard reference materials.     

Parametrizing Del Pezzo surfaces of degree 8 using Lie algebras

For a Del Pezzo surface of degree 8 given over the rationals we decide whether there is a rational parametrization of the surface and construct one in the affirmative case. We define and use the Lie algebra of the surface to reach the aim.     

Alignment of Semiconductor Nanowires Using Ion Beams

Gallium arsenide nanowires are grown on 〈100〉 GaAs substrates, adopting the epitaxial relation and thus growing with an angle around 35° off the substrate surface. These straight nanowires are irradiated with different kinds of energetic ions. Depending on the ion species and energy, downwards or upwards bending of the nanowires is observed to increase with ion fluence. In the case of upwards bending, the nanowires can be aligned towards the ion beam direction at high fluences. Defect formation (vacancies and interstitials) within the implantation cascade is identified as the key mechanism for bending. Monte Carlo simulations of the implantation are presented to substantiate the results.     

Electric and Kinetic Properties of Screen-Printed Strontium Titanate Films at High Temperatures

By eliminating the admixture of glass components to the original powder when making the paste, screen-printed structures can be produced from strontium titanate with reproducible properties. The ways that the film structure and the temperature profile affect the dependence of the electric conductivity on the oxygen partial pressure during the burn-in process are examined. The consequences of the surface/volume ratio of the grain structures on the response behavior of SrTiO₃ layers during rapid changes in oxygen partial pressure are investigated. Possible influences of the composition of grain boundaries on conductivity characteristics and the time-governing steps of the interaction between oxygen vacancies in the lattice and the oxygen molecules of the gaseous environment are also discussed.     

Cellular neural networks: Theory and circuit design

Cellular neural networks or CNNs are a novel neural network architecture introduced by Chua and Yang which is very general and flexible, has some important properties desirable for design applications and can be efficiently implemented on custom hardware based on analogue VLSI technology. In this paper an abstract normalized definition of cellular neural networks with arbitrary interconnection topology is given. Instead of stability, the property of convergence is found to be of central importance: large classes of convergent CNNs in practice always asymptotically approach some stable equilibrium where each component of the corresponding output is binary-valued. A highly efficient CMOS-compatible CNN circuit architecture is then presented where a basic cell consists of only two fully differential op amps, two capacitors and several MOSFETs, while a variable interconnection weight is realized with only four MOSFETs. Since all these elements are standard components in the current analogue IC technology and since all network functions are implemented directly on the device level, this architecture promises high cell and interconnection densities and extremely high operating speeds.     

The effect of conditions of mixing of polypropylene/ethylene-propylene elastomer blends on their morphological structure and impact strength

The dependence of morphological structure and notch impact strength of polypropylene/ethylene-propylene elastomer blends on conditions of mixing was investigated. Two types of polypropylene and two types of ethylene-propylene elastomer having different viscosities were used. At low rates and short times of mixing the samples contain both regions showing fine dispersion and regions showing large elastomeric inclusions surrounded with pure polypropylene. With increasing rate and time of mixing the large inclusions gradually disappear. The conditions of mixing which are necessary for reaching a homogeneous structure of the blends depend on viscosities of the components. The independence of particle size of the rate of mixing in homogeneous samples is discussed on the basis of a dynamic equilibrium between the break up and coalescence of droplets. The notch impact strength of the individual samples of the same blend is determined by the size and number of inhomogeneities (large inclusions) in the given sample.     

Polarization-insensitive high-contrast GaAs/AlGaAs waveguidemodulator based on the Franz-Keldysh effect

A GaAs/AlGaAs p-i-n double heterostructure waveguide modulator based on the Franz-Keldysh effect is reported. On/off ratios up to 40 dB are obtained over a broad range of wavelengths (⩾32 dB between 905 nm and 960 nm), while absorption loss in the on-state is very low (<1 cm^-1). The polarization dependence of the Franz-Keldysh effect is relatively weak and only causes a shift of the transmission-voltage characteristics of TE-polarized light towards higher reverse bias compared to the corresponding TM curves. Therefore, very high contrast ratios are achievable over the whole range of wavelengths even for arbitrary polarization of the light     

Fast nearest-neighbor search in dissimilarity spaces

A fast nearest-neighbor algorithm is presented. It works in general spaces in which the known cell techniques cannot be implemented for various reasons, such as the absence of coordinate structure or high dimensionality. The central idea has already appeared several times in the literature with extensive computer simulation results. An exact probabilistic analysis of this family of algorithms that proves its O(1) asymptotic average complexity measured in the number of dissimilarity calculations is presented