Magnetostriction of a Superconductor: -Results from the Critical-State Model

In many cases, the critical-state theory can be treated as a suffi ciently accurate approximation for the modelling of the magnetic properties of superconductors. In the present work, the magnetostrictive hysteresis is computed for a quite general case of the modified Kim-Anderson model. The results obtained reproduce many features of the giant magnetostriction (butterfly-shaped curves) reported in the literature for measurements made on single-crystal samples of the high-temperature superconductor $Bi_2Sr_2CaCu_2O_8$. It is shown that addition of a contribution to the magnetostriction in the superconducting state which is of similar origin as in the normal state, offers a broader phenomenological interpretation of the complex magnetostriction hysteresis found in such heavy-fermion compounds as $UPt_3$, $URu_2Si_2$ or $UBe_{13}$.Comment: 9 LaTeX pages, 4 Postscript figures, WWW version available at http://is.dal.ca/~zkoziol/super.htm

Ecology and power in the periphery of Maasina : the case of the Hayre in the nineteenth century

This article explores political tensions between successive nineteenth-century rulers of the inland delta of the Niger in central Mali (the Fulbe Diina of Hamdullahi and the Futanke successors of al-Hajj Umar) and the pastoral interests of the Fulbe chiefdoms on their eastern periphery, in a region known as the Hayre. A close study of changing forms of local governance and natural resource management demonstrates that although different strategies were employed by the Fulbe and Futanke states to control the Hayre, the internal dynamics of the region can only partly be explained by the influence of these central powers

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part I: Experimental methods and current-overvoltage experiments

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd2Zr2O7 (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m2). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process

Rigorous Bounds on the Free Energy of Electron-Phonon Models

We present a collection of rigorous upper and lower bounds to the free energy of electron-phonon models with linear electron-phonon interaction. These bounds are used to compare different variational approaches. It is shown rigorously that the ground states corresponding to the sharpest bounds do not exhibit Off-Diagonal Long-Range Order in the two-particle density matrix.

Predicting the term structure of interest rates incorporating parameter uncertainty, model uncertainty and macroeconomic information

We forecast the term structure of U.S. Treasury zero-coupon bond yields by analyzing a range of models that have been used in the literature. We assess the relevance of parameter uncertainty by examining the added value of using Bayesian inference compared to frequentist estimation techniques, and model uncertainty by combining forecasts from individual models. Following current literature we also investigate the benefits of incorporating macroeconomic information in yield curve models. Our results show that adding macroeconomic factors is very beneficial for improving the out-of-sample forecasting performance of individual models. Despite this, the predictive accuracy of models varies over time considerably, irrespective of using the Bayesian or frequentist approach. We show that mitigating model uncertainty by combining forecasts leads to substantial gains in forecasting performance, especially when applying Bayesian model averaging

Oxygen ion and mixed conductivity in compounds with the fluorite and pyrochlore structure

The effect of pyrochlore order in solid solutions with the defect fluorite structure was studied. The amount of order was changed by various heat treatments or by varying the cation composition. Examples of short range order and microdomain-formation have been observed in Tb2Zr2O7+x and Gd2Zr2O7. Pyrochlore order results in a decrease of the activation enthalpy and pre-exponential factor for oxygen ion conduction. The results are explained by a model based on the occurrence of a preferential diffusion path with a low strain energy component in ΔH. Optimal conductivity is achieved in materials which are not completely ordered. Mixed conductivity in Ln2Zr2O7 with P structure can be realized by partial replacement of Ln by Tb. This results in good ionic as well as electronic conductivities

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part II: Small signal analysis

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd2Zr2O7 (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m2). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process

How do neural networks see depth in single images?

Deep neural networks have lead to a breakthrough in depth estimation from single images. Recent work often focuses on the accuracy of the depth map, where an evaluation on a publicly available test set such as the KITTI vision benchmark is often the main result of the article. While such an evaluation shows how well neural networks can estimate depth, it does not show how they do this. To the best of our knowledge, no work currently exists that analyzes what these networks have learned. In this work we take the MonoDepth network by Godard et al. and investigate what visual cues it exploits for depth estimation. We find that the network ignores the apparent size of known obstacles in favor of their vertical position in the image. Using the vertical position requires the camera pose to be known; however we find that MonoDepth only partially corrects for changes in camera pitch and roll and that these influence the estimated depth towards obstacles. We further show that MonoDepth's use of the vertical image position allows it to estimate the distance towards arbitrary obstacles, even those not appearing in the training set, but that it requires a strong edge at the ground contact point of the object to do so. In future work we will investigate whether these observations also apply to other neural networks for monocular depth estimation.Comment: Submitte

Parental care in Hemisus (Anura: Hemisotidae)

Accounts of parental care in Anura frequently include mention of the South African frog genus Hemisus and derive their infonnation from what was written by the late Vincent Wager, An analysis is given of what exactly is known and what has been written, either from original observations or derived from other publications. S, Afr. J, Zool. 1997,32(2