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The spin-1 quantum Ising systems with three-spin interactions on two-dimensional triangular lattices are studied by mean-field method. The thermal variations of order parameters and phase diagrams are investigated in detail. The stable, metastable and unstable branches of the order parameters are obtained. According to the stable conditions at critical point, we find that the systems exhibit tricritical points. With crystal field and biquadratic interactions, the system has rich phase diagrams with single reentrant or double reentrant phase transitions for appropriate ranges of the both parameters. [ABSTRACT FROM AUTHOR]

Using semi-classical approximation method, the Bose-Einstein condensation (BEC) of a relativistic ideal boson gas (RIBG) in random box is studied. The exact BEC transition temperature Tc and Helmholtz free energy at Tc are derived. The phase diagrams in the (Δ, T) plane are obtained, where Δ is the fluctuation of the box length and T is the temperature of the system. We find that Tc is lowered by the presence of the quenched disorder caused by the random boundary conditions. The effects of antibosons on the RIBG are also studied and it is found that the Helmholtz free energy of the system with antibosons at Tc is lower than that of the system without antibosons. This implies that the omission of antibosons always leads to a metastable state. [ABSTRACT FROM AUTHOR]

The state function entropy and its quantum thermodynamical implication for two typical dissipative systems with anomalous spectral densities are studied by investigating on their low-temperature quantum behavior. In all cases, it is found that the entropy decays quickly and vanishes as the temperature approaches zero. This reveals a good conformity with the third law of thermodynamics and provides another evidence for the validity of fundamental thermodynamical laws in the quantum dissipative region. [ABSTRACT FROM AUTHOR]

The ferromagnetic properties of the spin-1 BEG model on finite-size Cayley tree are investigated using the exact recursion method. The spontaneous magnetization of the system is studied in detail for different values of the reduced crystal-field interaction D/J, and it is found that there is an unusual behavior (anti-Curie temperature) when D/J > 2.0. We also obtain the Curie temperature of this finite-size system. When the system size is large enough, our results will fit well with that in the thermodynamic limit. [ABSTRACT FROM AUTHOR]

Distinguishing the long-range bonds with the regular ones, the critical temperature of the spin-lattice Gaussian model built on two typical small-world networks is studied. The results show much difference from the classical case, and thus may induce some more accurate discussion on the critical properties of the spin-lattice systems combined with the small-world networks. [ABSTRACT FROM AUTHOR]

The q-deformed Bose–Einstein distribution is used to study the Bose–Einstein condensation (BEC) of a q-deformed Bose gas in random box. It is shown that the BEC transition temperature is lowered due to random boundary conditions. The effects of q-deformation on the properties of the system are also discussed. We find some properties of a q-deformed Bose gas, which are different from those of an ordinary Bose gas. Similar results are also shown for q-bosons confined in a harmonic oscillator potential well. [ABSTRACT FROM AUTHOR]