Axisymmetric extrusion and drawing through a die of arbitrary form

Axisymmetric extrusion and drawing through a die of arbitrary shape is analyzed by the Orowan method. The stress state in a representative element is determined by solving a boundary value problem of plasticity theory.     

Adaptive PID controllers: State of the art and development prospects

We give a survey of modern forms of PID controllers and algorithms for their automated tuning and adaptive control. We consider various autotuning and adaptation algorithms. We also consider the frequency adaptive control algorithm in more detail.     

A limit load solution for a highly weld strength undermatched tensile panel with an arbitrary crack

A new plane strain upper bound solution for highly undermatched welded tensile panels with a crack is proposed. A distinguished feature of this solution is that the crack is arbitrarily located within the weld and its shape is also arbitrary, though some restrictions do apply. The latter are explained in detail such that the class of structures for which the solution is applicable is precisely specified. The solution is given in a very simple closed form.     

Key Pairing Interaction in Cuprate Superconductors

It has been now over 20 years since the discovery of the first high temperature superconductor by Georg Bednorz and Alex Müller and yet, despite intensive effort, no universally accepted theory exists about the origin of superconductivity in cuprates. A controversial issue on weather the electron?Cphonon interaction (EPI) is crucial for high-temperature superconductivity or weak and inessential has been one of the most challenging problems of contemporary condensed matter physics. Here, it is suggested that the true origin of high-temperature superconductivity is found in a proper combination of strong electron?Celectron correlations with a significant finite-range (Fröhlich) EPI so that low energy quasi-particles are small mobile polarons and bipolarons in cuprate superconductors. Our recent development of the bipolaron theory of tunnelling accounting for two energy scales, their temperature and doping dependencies, asymmetry and inhomogeneity of tunnelling spectra of cuprate superconductors is briefly discussed.     

On the theory of solidification with a two-phase concentration supercooling zone

The directional solidification of binary systems is theoretically studied in the presence of an extended phase-transition zone. A mathematical model is developed for this process, and its approximate analytical solution is constructed with allowance for a nonlinear liquidus line equation.     

A corrosion study of nickel–copper and nickel–copper–palladium welding filler metals

In an effort to reduce the release of fumes containing carcinogenic Cr⁶⁺ during arc welding of stainless steel, Cr‐free filler metals for welding of SS304 have been developed. Corrosion studies were carried out on 304L stainless steel samples welded with these Cr‐free consumables. The corrosion properties of gas tungsten arc (GTA) and shielded metal arc (SMA) welds fabricated with Ni? Cu and Ni? Cu? Pd consumables were found to be comparable to those of welds fabricated with SS308L, the standard filler metal used with SS304. Although the breakdown potentials of the welds made using both welding processes were lower than that of the SS308L GTA weld, the repassivation potentials of these welds were much higher. Generally, the repassivation potential is a more conservative measure of susceptibility to localized corrosion. Accordingly, the Ni? Cu and Ni? Cu? Pd welds were more resistant to crevice corrosion than SS308L welds. The addition of a small amount of Pd improved the corrosion resistance relative to Ni? Cu welds, which is consistent with previous studies from specially‐prepared button samples and bead‐on‐plate samples. Other corrosion studies such as creviced and uncreviced long time immersion, atmospheric exposure, and slow strain rate testing suggest that Ni? Cu? Pd filler metal can be a potential replacement for the conventional SS308L filler metal for joining SS304.     

Phase Separation of Electrons Strongly Coupled with Phonons in Cuprates and Manganites

Recent advanced Monte Carlo simulations have not found superconductivity and phase separation in the Hubbard model with on-site repulsive electron–electron correlations. We argue that microscopic phase separations in cuprate superconductors and colossal magnetoresistance (CMR) manganites originate from a strong electron–phonon interaction (EPI) combined with unavoidable disorder. Attractive electron correlations, caused by an almost unretarded EPI, are sufficient to overcome the direct inter-site Coulomb repulsion in these charge-transfer Mott–Hubbard insulators, so that low energy physics is that of small polarons and small bipolarons (real-space electron (hole) pairs dressed by phonons). They form clusters localized by disorder below the mobility edge, but propagate as the Bloch states above the mobility edge. I identify the Fröhlich finite-range EPI with optical phonons as the most essential for pairing and phase separation in superconducting layered cuprates. The pairing of oxygen holes into heavy bipolarons in the paramagnetic phase (current-carrier density collapse (CCDC)) explains also CMR of doped manganites due to magnetic break-up of bipolarons in the ferromagnetic phase. Here I briefly present an explanation of high- and low-resistance phase coexistence near the ferromagnetic transition as a mixture of polaronic ferromagnetic and bipolaronic paramagnetic domains due to unavoidable disorder in doped manganites.