Relationship between solidification microstructure and hot cracking susceptibility for continuous casting of low-carbon and high-strength low-alloyed steels: A phase-field study

© The Minerals, Metals & Materials Society and ASM International 2013Hot cracking is one of the major defects in continuous casting of steels, frequently limiting the productivity. To understand the factors leading to this defect, microstructure formation is simulated for a low-carbon and two high-strength low-alloyed steels. 2D simulation of the initial stage of solidification is performed in a moving slice of the slab using proprietary multiphase-field software and taking into account all elements which are expected to have a relevant effect on the mechanical properties and structure formation during solidification. To account for the correct thermodynamic and kinetic properties of the multicomponent alloy grades, the simulation software is online coupled to commercial thermodynamic and mobility databases. A moving-frame boundary condition allows traveling through the entire solidification history starting from the slab surface, and tracking the morphology changes during growth of the shell. From the simulation results, significant microstructure differences between the steel grades are quantitatively evaluated and correlated with their hot cracking behavior according to the Rappaz-Drezet-Gremaud (RDG) hot cracking criterion. The possible role of the microalloying elements in hot cracking, in particular of traces of Ti, is analyzed. With the assumption that TiN precipitates trigger coalescence of the primary dendrites, quantitative evaluation of the critical strain rates leads to a full agreement with the observed hot cracking behavior. © 2013 The Minerals, Metals & Materials Society and ASM International

Amplitude differences of evoked alpha and gamma oscillations in two different age groups

The aim of this study was to investigate whether the amplitude of gamma-band activity is influenced by the factor age. We examined alpha- and gamma-band EEG activity and event-related potentials (ERPs) of 12 subjects. Six subjects constituted the younger (mean age=36.6 years) and another six the older age group (mean age=47.6 years). Subjects performed a visual discrimination task which required a response to Kanizsa squares (targets) among Kanizsa-triangles and non-Kanizsa figures. The ERPs of the younger group revealed a significantly larger N170 amplitude. The amplitudes of evoked alpha- and gamma-band activity were also found to be significantly higher in the younger group. We discuss the implications of these findings and possible reasons for a change of the oscillatory activity in the older age group

On the structure of the energy distribution function in the hopping regime

The impact of the dispersion of the transport coefficients on the structure of the energy distribution function for charge carriers far from equilibrium has been investigated in effective-medium approximation for model densities of states. The investigations show that two regimes can be observed in energy relaxation processes. Below a characteristic temperature the structure of the energy distribution function is determined by the dispersion of the transport coefficients. Thermal energy diffusion is irrelevant in this regime. Above the characteristic temperature the structure of the energy distribution function is determined by energy diffusion. The characteristic temperature depends on the degree of disorder and increases with increasing disorder. Explicit expressions for the energy distribution function in both regimes are derived for a constant and an exponential density of states.Comment: 16 page

On dispersive energy transport and relaxation in the hopping regime

A new method for investigating relaxation phenomena for charge carriers hopping between localized tail states has been developed. It allows us to consider both charge and energy {\it dispersive} transport. The method is based on the idea of quasi-elasticity: the typical energy loss during a hop is much less than all other characteristic energies. We have investigated two models with different density of states energy dependencies with our method. In general, we have found that the motion of a packet in energy space is affected by two competing tendencies. First, there is a packet broadening, i.e. the dispersive energy transport. Second, there is a narrowing of the packet, if the density of states is depleting with decreasing energy. It is the interplay of these two tendencies that determines the overall evolution. If the density of states is constant, only broadening exists. In this case a packet in energy space evolves into Gaussian one, moving with constant drift velocity and mean square deviation increasing linearly in time. If the density of states depletes exponentially with decreasing energy, the motion of the packet tremendously slows down with time. For large times the mean square deviation of the packet becomes constant, so that the motion of the packet is ``soliton-like''.Comment: 26 pages, RevTeX, 10 EPS figures, submitted to Phys. Rev.

Taxonomic diversity and identification problems of oncaeid microcopepods in the Mediterranean Sea

The species diversity of the pelagic microcopepod family Oncaeidae collected with nets of 0.1-mm mesh size was studied at 6 stations along a west-to-east transect in the Mediterranean Sea down to a maximum depth of 1,000 m. A total of 27 species and two form variants have been identified, including three new records for the Mediterranean. In addition, about 20, as yet undescribed, new morphospecies were found (mainly from the genera Epicalymma and Triconia) which need to be examined further. The total number of identified oncaeid species was similar in the Western and Eastern Basins, but for some cooccurring sibling species, the estimated numerical dominance changed. The deep-sea fauna of Oncaeidae, studied at selected depth layers between 400 m and the near-bottom layer at >4,200 m depth in the eastern Mediterranean (Levantine Sea), showed rather constant species numbers down to ∼3,000 m depth. In the near-bottom layers, the diversity of oncaeids declined and species of Epicalymma strongly increased in numerical importance. The taxonomic status of all oncaeid species recorded earlier in the Mediterranean Sea is evaluated: 19 out of the 46 known valid oncaeid species are insufficiently described, and most of the taxonomically unresolved species (13 species) have originally been described from this area (type locality). The deficiencies in the species identification of oncaeids cast into doubt the allegedly cosmopolitan distribution of some species, in particular those of Mediterranean origin. The existing identification problems even of well-described oncaeid species are exemplified for the Oncaea mediacomplex, including O. media Giesbrecht, O. scottodicarloi Heron & Bradford-Grieve, and O. waldemari Bersano & Boxshall, which are often erroneously identified as a single species (O. media). The inadequacy in the species identification of Oncaeidae, in particular those from the Atlantic and Mediterranean, is mainly due to the lack of reliable identification keys for Oncaeidae in warm-temperate and/or tropical seas. Future efforts should be directed to the construction of identification keys that can be updated according to the latest taxonomic findings, which can be used by the non-expert as well as by the specialist. The adequate consideration of the numerous, as yet undescribed, microcopepod species in the world oceans, in particular the Oncaeidae, is a challenge for the study of the structure and function of plankton communities as well as for global biodiversity estimates

Implementation of an Integrated Thermal Building Model for Investigations of Heat Flows

A model of the building heating system, consisting of energy source, a distributed automatic control system, elements of individual heating unit and heating system is designed. Application Simulink of mathematical package Matlab is selected as a platform for the model. There are the specialized application Simscape libraries in aggregate with a wide range of Matlab mathematical tools allow to apply the "acausal" modeling concept. Implementation the "physical" representation of the object model gave improving the accuracy of the models

Modification of aluminum alloy surface properties by wave-long laser texturing

Change of the static contact angle (SCA) of 10 [mu]L distilled water droplet on laser textured aluminium alloy (AMG-6) substrates was studied. The texture was deposited by a laser system based on a fiber laser. An increase in the power of laser radiation is found to lead to a decrease in the SCA measured on the first day after texturing. Change of dispersion and polar surface energy components of textured substrates is determined. Under the influence of the environment, the surface properties of AMG-6 change with time. SCA increased and reached stable state on the twentieth day after texturing

Raman spectra of olivine measured in different planetary environments

Missions to bodies of our solar system are coming up and imply new instrumentation to be applied remotely and in situ. In ESA’s ExoMars mission the Raman Laser Spectrometer (RLS) will identify minerals and organic compounds in Martian surface rocks and soils. Here we present the results of a Raman study of different olivines with variable Fo and Fa contents. We chose olivine because it is a rock forming mineral and is found as an abundant mineral in Martian meteorites. We determined the Raman spectra in different environmental conditions that include vacuum, 8 mbar CO2 atmosphere and temperatures between room temperature and 10 K. These environmental conditions resemble those on asteroids as well as on Mars and Moon. Thus our study investigates the influence of these varying conditions on the position and band width of the Raman lines, which is to be known when such investigations are performed in future space missions

Ac hopping conduction at extreme disorder takes place on the percolating cluster

Simulations of the random barrier model show that ac currents at extreme disorder are carried almost entirely by the percolating cluster slightly above threshold; thus contradicting traditional theories contributions from isolated low-activation-energy clusters are negligible. The effective medium approximation in conjunction with the Alexander-Orbach conjecture leads to an excellent analytical fit to the universal ac conductivity with no nontrivial fitting parameters