We consider the optimal approximation of certain quantum states of a harmonic oscillator with the superposition of a finite number of coherent states in phase space placed either on an ellipse or on a certain lattice. These scenarios are currently experimentally feasible. The parameters of the ellipse and the lattice and the coefficients of the constituent coherent states are optimized numerically, via a genetic algorithm, in order to obtain the best approximation. It is found that for certain quantum states the obtained approximation is better than the ones known from the literature thus far.
We investigate dynamics of semi-quantal spin systems in which quantum bits are attached to classically and possibly stochastically moving classical particles. The interaction between the quantum bits takes place when the respective classical particles get close to each other in space. We find that with Heisenberg XX couplings quantum homogenization takes place after a time long enough, regardless of the details of the underlying classical dynamics. This is accompanied by the development of a stationary bipartite entanglement. If the information on the details of the motion of a stochastic classical system is disregarded, the stationary state of the whole quantum subsystem is found to be a complete mixture in the studied cases, though the transients depend on the properties of the classical motion.
The low voltage (LV) distribution cable networks were installed some decades ago but the new paradigm in electric power engineering generates new requirements from these old assets. The distributed generation, storage and new appliances can cause high variation of load and reverse power flow, nevertheless the LV cable grid was not designed to these new stresses. The aggregate load and generation can surpass the rated capacity of the cable lines causing short term temperature increasing. This temperature stress can decrease the expected lifetime of the cable lines. In this study the short term thermal overload of LV distribution cables was investigated. The experiments were executed on PVC insulated LV cable samples and electrical and mechanical properties of the cable jacket were investigated. The effect of these short-term overloads on the expected lifetime of cables is introduced and non-destructive measurement for tracking the effect of the short term thermal overloads on the cable is suggested.
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