Antiperovskite materials are of high research interest because of their unusual physical properties and technological applications. Here, we report the structural stability and transport properties of Sr3AsN from first-principles study. The calculated equilibrium lattice parameters are in good agreement with the available data. We find that Sr3AsN is mechanically, energetically and dynamically stable at ambient conditions. Our calculated electronic structure indicates that it is a direct band gap semiconductor, with a band gap value ∼1.2 eV. Sr-4d and N-2p orbitals predominantly contribute to the formation of the direct band gap. The calculated Seebeck coefficient of Sr3AsN is high (298 μV/K at 300 K), while the lattice thermal conductivity is comparatively low (1.73 W/m K). The considerable mass difference between Sr, As, and N gives rise to an intense phonon scattering that results in such low lattice thermal conductivity. Our calculated maximum thermoelectric figure of merit (ZT) is 0.75 at 700 K, indicating that it is a potential material for thermoelectric device applications.

In this paper we show that entropy can be used within a functional for the stress relaxation time of solid materials to parametrise finite viscoplastic strain-hardening deformations. Through doing so the classical empirical recovery of a suitable irreversible scalar measure of work-hardening from the three-dimensional state parameters is avoided. The success of the proposed approach centres on determination of a rate-independent relation between plastic strain and entropy, which is found to be suitably simplistic such to not add any significant complexity to the final model. The result is sufficiently general to be used in combination with existing constitutive models for inelastic deformations parametrised by one-dimensional plastic strain provided the constitutive models are thermodynamically consistent. Here a model for the tangential stress relaxation time based upon established dislocation mechanics theory is calibrated for OFHC copper and subsequently integrated within a two-dimensional moving-mesh scheme. We address some of the numerical challenges that are faced in order to ensure successful implementation of the proposedmodel within a hydrocode. The approach is demonstrated through simulations of flyer-plate and cylinder impacts.

The time-dependent virtual waiting time in a M/G/1 queue converges to a proper limit when the traffic intensity is less than one. In this paper we give precise rates on the speed of this convergence when the service time distribution has a heavy regularly varying tail.

The result also applies to the classical ruin problem. We obtain the exact rate of convergence for the ruin probability after time t for the case where claims arrive according to a Poisson process and claim sizes are heavy tailed.

Our result supplements similar theorems on exponential convergence rates for relaxation times in queueing theory and ruin probabilities in risk theory.

A technique is developed for the analysis of the asymptotic behaviour in the long run of queueing systems with two waiting lines. The generating function of the time-dependent joint queue-length distribution is obtained with the aid of the theory of boundary value problems of the Riemann–Hilbert type and by introducing a conformal mapping of the unit disk onto a given domain. In the asymptotic analysis an extensive use is made of theorems on the boundary behaviour of such conformal mappings.