Thermoelectrics of Interacting Nanosystems -- Exploiting Superselection instead of Time-Reversal Symmetry

Thermoelectric transport is traditionally analyzed using relations imposed by time-reversal symmetry, ranging from Onsager's results to fluctuation relations in counting statistics. In this paper, we show that a recently discovered duality relation for fermionic systems -- deriving from the fundamental fermion-parity superselection principle of quantum many-particle systems -- provides new insights into thermoelectric transport. Using a master equation, we analyze the stationary charge and heat currents through a weakly coupled, but strongly interacting single-level quantum dot subject to electrical and thermal bias. In linear transport, the fermion-parity duality shows that features of thermoelectric response coefficients are actually dominated by the average and fluctuations of the charge in a dual quantum dot system, governed by attractive instead of repulsive electron-electron interaction. In the nonlinear regime, the duality furthermore relates most transport coefficients to much better understood equilibrium quantities. Finally, we naturally identify the fermion-parity as the part of the Coulomb interaction relevant for both the linear and nonlinear Fourier heat. Altogether, our findings hence reveal that next to time-reversal, the duality imposes equally important symmetry restrictions on thermoelectric transport. As such, it is also expected to simplify computations and clarify the physical understanding for more complex systems than the simplest relevant interacting nanostructure model studied here.Comment: 38 pages (23 main paper, 15 appendix), 8 figure

Orbital bleeding in rats while under diethylether anaesthesia does not influence telemetrically determined heart rate, body temperature, locomotor and eating activity when compared with anaesthesia alone

The question addressed was whether orbital bleeding in rats, while under diethylether anaesthesia, affects their locomotor activity, body core temperature, heart rate rhythm and eating pattern. Roman High Avoidance (RHA) and Roman Low Avoidance (RLA) rats were used to enhance generalization of the results. Orbital bleeding when the rats were under diethylether anaesthesia was compared with diethylether anaesthesia alone. To take into account any effects of handling, the rats were also subjected to sham anaesthesia. The RHA rats urinated more during anaesthesia, needed more time to recover from the anaesthesia and showed a greater endocrine stress response to diethylether anaesthesia when compared with the RLA rats. During anaesthesia, the RHA rats showed a greater fall of body temperature and bradycardia than did the RLA rats. Diethylether anaesthesia reduced locomotor activity in the RHA rats, but had no effect in the RLA rats. In neither RHA nor RLA rats did anaesthesia plus orbital puncture, versus anaesthesia alone, influence body temperature, heart rate rhythm, locomotor and eating activity. The lack of effect of orbital puncture occurred both in the short term (within 2 h) and long term (within 48 hours) and thus this study indicates that orbital puncture had, at least with respect to variables measured in the present study, no effect superimposed on that of diethylether anaesthesia

Mobile Robot Localization using Panoramic Vision and Combinations of Feature Region Detectors

IEEE International Conference on Robotics and Automation (ICRA 2008, Pasadena, California, May 19-23, 2008), pp. 538-543.This paper presents a vision-based approach for mobile robot localization. The environmental model is topological. The new approach uses a constellation of different types of affine covariant regions to characterize a place. This type of representation permits a reliable and distinctive environment modeling. The performance of the proposed approach is evaluated using a database of panoramic images from different rooms. Additionally, we compare different combinations of complementary feature region detectors to find the one that achieves the best results. Our experimental results show promising results for this new localization method. Additionally, similarly to what happens with single detectors, different combinations exhibit different strengths and weaknesses depending on the situation, suggesting that a context-aware method to combine the different detectors would improve the localization results.This work was partially supported by USC Women in Science and Engineering (WiSE), the FI grant from the Generalitat de Catalunya, the European Social Fund, and the MID-CBR project grant TIN2006-15140-C03-01 and FEDER funds and the grant 2005-SGR-00093

High-Speed Curtain Recoating for Stereolithography

The University of Leuven uses a liquid curtain recoating system for resin deposition in stereolithography. This system deposits new liquid layers of photo-polymer by means of a liquid curtain travelling over the build vat. Experiments have been carried out to increase the speed of the liquid curtain while depositing a layer. Speeds up to 1.2 m/s, and accelerations up to 1 g have been tested successfully, meaning that it is possible to coat high-quality layers of 75 µm thickness with this recoating technique. However, the curtain restores too slowly after acceleration. This paper discusses possible reasons and tries to formulate adequate solutions. Possible solutions consist in controlling small pressure differences in the curtain’s neighbourhood. A solution to this problem is necessary, as to make the travelling length of the curtain, and so the machine length acceptable with respect to the dimensions of the build vat.Mechanical Engineerin

Anisotropic bulk and planar Heisenberg ferromagnets in uniform, arbitrarily oriented magnetic fields

Today, further downscaling of mobile electronic devices poses serious problems, such as energy consumption and local heat dissipation. In this context, spin wave majority gates made of very thin ferromagnetic films may offer a viable alternative. However, similar downscaling of magnetic thin films eventually enforces the latter to operate as quasi-two dimensional magnets, the magnetic properties of which are not yet fully understood, especially those related to anisotropies and external magnetic fields in arbitrary directions. To this end, we have investigated the behaviour of an easy-plane and easy-axis anisotropic ferromagnet -- both in two and three dimensions -- subjected to a uniform magnetic field, applied along an arbitrary direction. In this paper, a spin-1/2 Heisenberg Hamiltonian with anisotropic exchange interactions is solved using double-time temperature-dependent Green's functions and the Tyablikov decoupling approximation. We determine various magnetic properties such as the Curie temperature and the magnetization as a function of temperature and the applied magnetic field, discussing the impact of the system's dimensionality and the type of anisotropy. The magnetic reorientation transition taking place in anisotropic Heisenberg ferromagnets is studied in detail. Importantly, spontaneous magnetization is found to be absent for easy-plane two-dimensional spin systems with short range interactions

Computing Curie temperature of two-dimensional ferromagnets in the presence of exchange anisotropy

status: publishe