Heavy doping and band engineering by potassium to improve the thermoelectric figure of merit in p-type PbTe, PbSe, and PbTe(1-y)Se(y)

We present detailed studies of potassium doping in PbTe(1-y)Se(y) (y = 0, 0.15, 0.25, 0.75, 0.85, 0.95, and 1). It was found that Se increases the doping concentration of K in PbTe as a result of the balance of electronegativity and also lowers the lattice thermal conductivity because of the increased number of point defects. Tuning the composition and carrier concentration to increase the density of states around the Fermi level results in higher Seebeck coefficients for the two valence bands of PbTe(1-y)Se(y). Peak thermoelectric figure of merit (ZT) values of ~1.6 and ~1.7 were obtained for Te-rich K(0.02)Pb(0.98)Te(0.75)Se(0.25) at 773 K and Se-rich K(0.02)Pb(0.98)Te(0.15)Se(0.85) at 873 K, respectively. However, the average ZT was higher in Te-rich compositions than in Se-rich compositions, with the best found in K(0.02)Pb(0.98)Te(0.75)Se(0.25). Such a result is due to the improved electron transport afforded by heavy K doping with the assistance of Se.     

Important aspects in the formulation of solid–fluid debris-flow models. Part I. Thermodynamic implications

This article points at some critical issues which are connected with the theoretical formulation of the thermodynamics of solid–fluid mixtures of frictional materials. It is our view that a complete thermodynamic exploitation of the second law of thermodynamics is necessary to obtain the proper parameterizations of the constitutive quantities in such theories. These issues are explained in detail in a recently published book by Schneider and Hutter (Solid–Fluid Mixtures of Frictional Materials in Geophysical and Geotechnical Context, 2009), which we wish to advertize with these notes. The model is a saturated mixture of an arbitrary number of solid and fluid constituents which may be compressible or density preserving, which exhibit visco-frictional (visco-hypoplastic) behavior, but are all subject to the same temperature. Mass exchange between the constituents may account for particle size separation and phase changes due to fragmentation and abrasion. Destabilization of a saturated soil mass from the pre- and the post-critical phases of a catastrophic motion from initiation to deposition is modeled by symmetric tensorial variables which are related to the rate independent parts of the constituent stress tensors.     

Asymmetric Domain Walls of Small Angle in Soft Ferromagnetic Films

We focus on a special type of domain wall appearing in the Landau–Lifshitz theory for soft ferromagnetic films. These domain walls are divergence-free \({\mathbb{S}^2}\)-valued transition layers that connect two directions \({m_\theta^\pm \in \mathbb{S}^2}\) (differing by an angle \({2\theta}\)) and minimize the Dirichlet energy. Our main result is the rigorous derivation of the asymptotic structure and energy of such “asymmetric” domain walls in the limit \({\theta \downarrow 0}\). As an application, we deduce that a supercritical bifurcation causes the transition from symmetric to asymmetric walls in the full micromagnetic model.     

Polytopal Affine Semigroups with Holes Deep Inside

Given a positive integer $k$ k , we construct a lattice $3$ 3 -simplex $P$ P with the following property: The affine semigroup $Q_P$ Q P associated to $P$ P is not normal, and every element $q \in \overline{Q}_P \setminus Q_P$ q ∈ Q ¯ P ? Q P has lattice distance at least $k$ k above every facet of $Q_P$ Q P .     

On the refined modeling of the force distribution in a bistable magnetoelastic energy harvesting system due to a magnetic field

Abstract: The problem of a bistable magnetoelastic beam under base excitation was discussed in [1] under the aspect of chaotic behaviour in mechanical systems. Three decades later the system was used in [2] to design an energy harvesting system which performs well under harmonic excitation for a broad range of excitation frequencies due to its bistability. The initial modeling was tailored to obtain a model with one degree of freedom based on the assumption that the magnetic force acts on the beam tip only. A more appropriate model can be found when considering a distributed force along the beam. The authors present the force distribution on a ferromagnetic beam due to the magnetic field of two permanent magnets. A semi-analytic method is used to compute the magnetic field. The force distribution can in future be used to derive a refined nonlinear dynamical model for the ferromagnetic elastic beam. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of Inviscid and Viscous Two‐Phase Calculations of Cavitating Pump Flow

In cavitating flows there is a strong interaction between the fine dispersed vapor bubbles and turbulence. Therefore in two‐phase flow calculations the prediction of turbulence is a matter of great difficulties and uncertainties. To get an idea of the influence of turbulence modelling on the calculated result, viscous and inviscid two‐phase calculations of cavitating pump flow were performed. In the inviscid calculations the influence of cavitation is isolated from turbulence effects. In the viscous calculations the effect of turbulence is modelled with a k – ϵ turbulence model. The results show that the influence of viscous effects on the flow field is weak in comparison to cavitation. However, in contrast to the steady cavitation behaviour predicted by the viscous calculations, the inviscid calculations show unsteady behaviour of the cavitation (as can be seen in the experiment).