Research at the Institute of electrotechnology in the field of induction heating

The paper informs generally about the activities at the Institute of Electrotechnology in Hannover, Germany in the fields of education and research in Electrotechnology. Several actual research projects are described in detail in the field of induction heating. A second paper written by Baake and Spitans gives an overview about the activities at the institute in induction melting

Fishtail effect and vortex dynamics in LiFeAs single crystals

We investigate the fishtail effect, critical current density ($J_c$) and vortex dynamics in LiFeAs single crystals. The sample exhibits a second peak (SP) in the magnetization loop only with the field $||$ c-axis. We calculate a reasonably high $J_c$, however, values are lower than in 'Ba-122' and '1111'-type FeAs-compounds. Magnetic relaxation data imply a strong pinning which appears not to be due to conventional defects. Instead, its behavior is similar to that of the triplet superconductor Sr$_2$RuO$_4$. Our data suggest that the origin of the SP may be related to a vortex lattice phase transition. We have constructed the vortex phase diagram for LiFeAs on the field-temperature plane.Comment: 5 pages, 5 figure

Design improvements for increasing lifetime of single-shot coils applied at rotating workpieces

In the industry, induction hardening of rotationally symmetrical workpieces by a single-shot process is a widespread method. Due to only partial superimposition of the workpiece areas to be heated by the coil, high power densities are often needed there. These lead to local hot spots, amounting to an intensive material stress and often result in a short lifetime of the inductor. In this paper, some numerically investigated models will be presented, revealing approaches, how to reduce mechanical stress in the single-shot coil and thus, enabling an increase of service life

Telepresence and the Role of the Senses

The telepresence experience can be evoked in a number of ways. A well-known example is a player of videogames who reports about a telepresence experience, a subjective experience of being in one place or environment, even when physically situated in another place. In this paper we set the phenomenon of telepresence into a theoretical framework. As people react subjectively to stimuli from telepresence, empirical studies can give more evidence about the phenomenon. Thus, our contribution is to bridge the theoretical with the empirical. We discuss theories of perception with an emphasis on Heidegger, Merleau-Ponty and Gibson, the role of the senses and the Spinozian belief procedure. The aim is to contribute to our understanding of this phenomenon. A telepresence-study that included the affordance concept is used to empirically study how players report sense-reactions to virtual sightseeing in two cities. We investigate and explore the interplay of the philosophical and the empirical. The findings indicate that it is not only the visual sense that plays a role in this experience, but all senses

Phase diagram for K(1-x)(NH4)(x)H2PO4 (x = 0 – 0.15) solid solutions embedded into magnetic glasses

Effect of magnetic field application on phase transition in nanostructured solid solutions (1-x)KH2PO4 – (x)(NH4)H2PO4 at x = 0, 0.05 and 0.15 has been studied by dielectric spectroscopy at B = 0 – 10T. The samples have been prepared by impregnation of magnetic porous glasses by KDP-ADP solid solutions. The average pore diameter in glasses was 50(5) nm. The temperatures of the ferroelectric phase transition have been determined, and the phase diagrams for these nanocomposite materials (NCM) on cooling and heating (including at magnetic field application) were constructed. The interface “matrix-nanoparticles” was shown to play the principal role in phase diagram formation

Low-temperature magnetostriction and distortions in the rare-earth Laves phases

The effects of partial substitution of dysprosium in Tb0.2Dy0.8Co2 by terbium and gadolinium on the structure and magnetic properties have been studied. Two compositions, Tb0.3Dy0.7Co2 and Tb0.2Dy0.7Gd0.1Co2 have been synthesized. Their crystal structure, in contrast to the structure of the original compound, has both tetragonal distortions and rhombohedral distortions at lower temperatures. Anomalies of magnetostriction and magnetocaloric effect near the observed magnetic phase transitions have been studied. The sign-alternating temperature dependences of the longitudinal and transverse magnetostrictions associated with various types of crystal structure distortions of the alloys are revealed

Numerical studies of the melting process in the induction furnace with cold crucible

Purpose - Aims to present recent activities in numerical modeling of cold crucible melting process. Design/methodology/approach - 3D numerical analysis was used for electromagnetic problem and 3D large eddy simulation (LES) method was applied for fluid flow modeling. Findings - The comparative modeling shows, that higher H/D ratio of the melt is more efficient when total power consumption is considered, but this advantage is held back by higher heat losses through the crucible walls. Also, calculations reveal that lower frequencies, which are energetically less effective, provide better mixing of the melt. Originality/value - 3D electromagnetic model, which allows to take into account non-symmetrical distribution of Joule heat sources, together with transient LES fluid flow simulation gives the opportunity of accurate prediction of temperature distribution in the melt. © Emerald Group Publishing Limited

Particle transport in recirculated liquid metal flows

Purpose - Aims to present recent activities in numerical modeling of turbulent transport processes in induction crucible furnace. Design/methodology/approach - 3D large eddy simulation (LES) method was applied for fluid flow modeling in a cylindrical container and transport of 30,000 particles was investigated with Lagrangian approach. Findings - Particle accumulation near the side crucible boundary is determined mainly by the ρp/ρ ratio and according to the presented results. Particle settling velocity is of the same order as characteristic melt flow velocity. Particle concentration homogenization time depends on the internal flow regime. Separate particle tracks introduce very intensive mass exchange between the different parts of the melt in the whole volume of the crucible. Originality/value - Transient simulation of particle transport together with LES fluid flow simulation gives the opportunity of accurate prediction of admixture concentartion distribution in the melt. © Emerald Group Publishing Limited

Çifte intikam

Ahmet Mithat'ın Tercüman-ı Hakikat'te tefrika edilen Çifte İntikam adlı roman