Phase transitions and gaps in quantum random energy models

By using a previously established exact characterization of the ground state of random potential systems in the thermodynamic limit, we determine the ground and first excited energy levels of quantum random energy models, discrete and continuous. We rigorously establish the existence of a universal first order quantum phase transition, obeyed by both the ground and the first excited states. The presence of an exponentially vanishing minimal gap at the transition is general but, quite interestingly, the gap averaged over the realizations of the random potential is finite. This fact leaves still open the chance for some effective quantum annealing algorithm, not necessarily based on a quantum adiabatic scheme.Comment: 8 pages, 4 figure

Impurity center in a semiconductor quantum ring in the presence of a radial electric field

The problem of an impurity electron in a quantum ring (QR) in the presence of a radially directed strong external electric field is investigated in detail. Both an analytical and a numerical approach to the problem are developed. The analytical investigation focuses on the regime of a strong wire-electric field compared to the electric field due to the impurity. An adiabatic and quasiclassical approximation is employed. The explicit dependencies of the binding energy of the impurity electron on the electric field strength, parameters of the QR and position of the impurity within the QR are obtained. Numerical calculations of the binding energy based on a finite-difference method in two and three dimensions are performed for arbitrary strengths of the electric field. It is shown that the binding energy of the impurity electron exhibits a maximum as a function of the radial position of the impurity that can be shifted arbitrarily by applying a corresponding wire-electric field. The maximal binding energy monotonically increases with increasing electric field strength. The inversion effect of the electric field is found to occur. An increase of the longitudinal displacement of the impurity typically leads to a decrease of the binding energy. Results for both low- and high-quantum rings are derived and discussed. Suggestions for an experimentally accessible set-up associated with the GaAs/GaAlAs QR are provided.Comment: 16 pages, 8 figure

The effect of fluorine-containing inhibitors of corrosion of copper in atmospheric conditions

The effect of fluorine-containing inhibitors of corrosion of copper in atmospheric conditions was studied by method of removing anodic polarization curves and corrosion of full-scale tests. The introduction of the inhibiting compositions as corrosion inhibitor of copper polyfluorinated amines leads to a decrease of the peak current of active dissolution of copper, which increases the corrosion resistance of copper wire rod during transportation in various climate conditions

A comparison of two magnetic ultra-cold neutron trapping concepts using a Halbach-octupole array

This paper describes a new magnetic trap for ultra-cold neutrons (UCNs) made from a 1.2 m long Halbach-octupole array of permanent magnets with an inner bore radius of 47 mm combined with an assembly of superconducting end coils and bias field solenoid. The use of the trap in a vertical, magneto-gravitational and a horizontal setup are compared in terms of the effective volume and ability to control key systematic effects that need to be addressed in high precision neutron lifetime measurements

ABC of N=8, d=1 supermultiplets

We construct a variety of off-shell $N{=}8, d{=}1$ supermultiplets with finite numbers of component fields as direct sums of properly constrained $N{=}4, d{=}1$ superfields. We also show how these multiplets can be described in $N{=}8, d{=}1$ superspace where the whole amount of supersymmetry is manifest. Some of these multiplets can be obtained by dimensional reduction {}from $N{=}2$ multiplets in $d{=}4$, whereas others cannot. We give examples of invariant superfield actions for the multiplets constructed, including $N{=}8$ superconformally invariant ones.Comment: 28 page

N=8 superconformal mechanics

We construct new models of N=8 superconformal mechanics associated with the off-shell N=8, d=1 supermultiplets (3,8,5) and (5,8,3). These two multiplets are derived as N=8 Goldstone superfields and correspond to nonlinear realizations of the N=8, d=1 superconformal group OSp(4^*|4) in its supercosets OSp(4^*|4)/U(1)_R x SO(5) and OSp(4^*|4)/SU(2)_R x SO(4), respectively. The irreducibility constraints for these superfields automatically follow from appropriate superconformal covariant conditions on the Cartan superforms. The N=8 superconformal transformations of the superspace coordinates and the Goldstone superfields are explicitly given. Interestingly, each N=8 supermultiplet admits two different off-shell N=4 decompositions, with different N=4 superconformal subgroups SU(1,1|2) and OSp(4^*|2) of OSp(4^*|4) being manifest as superconformal symmetries of the corresponding N=4, d=1 superspaces. We present the actions for all such N=4 splittings of the N=8 multiplets considered.Comment: 31 pages, LaTeX, typos corrected, reference adde