Ab initio study of magnetism at the TiO2/LaAlO3 interface

In this paper we study the possible relation between the electronic and magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism found in undoped TiO2 films grown on LaAlO$_3$. We concentrate on the role played by structural relaxation and interfacial oxygen vacancies. LaAlO3 has a layered structure along the (001) direction with alternating LaO and AlO2 planes, with nominal charges of +1 and -1, respectively. As a consequence of that, an oxygen deficient TiO2 film with anatase structure will grow preferently on the AlO2 surface layer. We have therefore performed ab-initio calculations for superlattices with TiO2/AlO2 interfaces with interfacial oxygen vacancies. Our main results are that vacancies lead to a change in the valence state of neighbour Ti atoms but not necessarily to a magnetic solution and that the appearance of magnetism depends also on structural details, such as second neighbor positions. These results are obtained using both the LSDA and LSDA+U approximations.Comment: Accepted for publication in Journal of Materials Scienc

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and x-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T, showing a minor but significant dependence of the dielectric constant on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.Comment: 10 pages, 11 figure

THEORETICAL AND EXPERIMENTAL COMPARISONS FOR ROTORDYNAMIC COEFFICIENTS OF A MULTI-SCRATCHED TILTING PAD JOURNAL BEARING

This paper presents a Thermos-Elasto-Hydrodynamics model (TEHD) based on a mass conservative generalized Reynolds equation, coupled with 3D energy equations for the oil film, and a full 3D thermo-mechanical model for the pads. The model uses a regularization technique to consider film thickness discontinuities created by scratches. The numerical results are compared to the experimental results obtained from a rocker-backed, five tilting pads journal bearing TPJB with single and multiple scratches. The numerical model achieved good agreement especially with respect to pad temperatures and dynamic coefficients. Discrepancies were observed at low speed but only on the stiffness in the load direction. The numerical model shows significant drop in the pressure field at the location of the scratches, and a significant pressure rise between two consecutive scratches accompanied by a decrease of film thickness

A Multi Agent Scheduling Integrating Planning and Maintenance for Generalized Floor Shops

International audienceMulti-agent scheduling offers reactivity and distributed decision-making for floor shop control. Agents, which may represent any entities that act in production, negotiate to find best schedules. In this paper, we present a new multi-agent scheduling method that integrates both planning and maintenance activities. Actually, more than one plan can be generated for a job production. We suppose that plan selection must depend on information about machines maintenance and states to offer realistic schedules. Tests demonstrate that despite increasing time resolution with the agents’ number, our system is scalable with reduced Cmax and machines failure risk

A Multi Agent Scheduling Integrating Planning and Maintenance for Generalized Floor Shops

International audienceMulti-agent scheduling offers reactivity and distributed decision-making for floor shop control. Agents, which may represent any entities that act in production, negotiate to find best schedules. In this paper, we present a new multi-agent scheduling method that integrates both planning and maintenance activities. Actually, more than one plan can be generated for a job production. We suppose that plan selection must depend on information about machines maintenance and states to offer realistic schedules. Tests demonstrate that despite increasing time resolution with the agents’ number, our system is scalable with reduced Cmax and machines failure risk