Modern Physics Letters B

The problem of a quantum particle moving in a narrow, bent two-dimensional channel is used to illustrate features of collisions in systems with semi-constrained structures. The collision theory of such systems is developed and, under certain general restrictions on the geometry, the following properties are rigorously established: (1) The (localized) Møller wave operator exist and the S operator is unitary in the scattering channels. (2) The singular spectrum is discrete in intervals away from the continuum thresholds. The discussion is based on a time-dependent approach.

We investigate entanglement for the two-mode field in three-level atomic systems. Entanglement of the system is demonstrated according to the Duan's criterion.¹⁶ It shows that the entanglement has a close relation with the pump intensity. For large pump intensity, particular choice of its phase, zero detuning and cooperativity parameter, perfect entanglement for the two-mode field can be generated outside the cavity.

The transient properties of a tumor cell growth system are investigated when both the multiplicative noise and the coupling between additive and multiplicative noises are colored with different correlation times τ₁ and τ₂. The explicit expression of the mean first-passage time (MFPT) of the tumor cell growth system is obtained. The numerical computations show that the MFPT decreases with increases in D (multiplicative colored intensity) and α (additive white intensity). However, τ₁ (correlation time of the multiplicative colored noise) can only linearly enhance the MFPT. It is interesting that the curves of the MFPT appears a peak structure as λ (correlation intensity) and τ₂ (coupling correlation time) increases; namely, the MFPT can be enhanced for the small value of λ and τ₂ and reduced for the large value of λ and the τ₂.

A series of nitrogen-doped Zn_0.93Co_0.07O thin films grown on glass substrates were prepared by magnetron sputtering, which have shown ferromagnetic property at room temperature. The largest moment of about 4.92 μ_B/Co and Curie temperature (T_c) of about 300 K were observed for Zn_0.93Co_0.07O thin film. P-type Co-doped ZnO thin films with room temperature ferromagnetism were obtained. We demonstrated a clear correlation between nitrogen and transition temperature and an inverse correlation between nitrogen and magnetization per Co ion.

Polarization and capacitance studies as a function of applied electric field were done on the Nd and Nb-doped polycrystalline ceramic samples. The result indicates that the ceramic samples show low values of remnant polarization. The capacitance value indicates that microwave sintered samples shows higher capacitance tunability when compared to conventional sintered samples. The results obtained from electromechanical studies are also discussed.

This work focuses on theoretically-obtained state solutions on molecular crystals with order–disorder phenomena in both the orientation and position of molecules. The stable, metastable and unstable solutions of the modified Pople–Karasz theory of molecular crystals are studied using two different methods. The first displays the free energy surfaces in the form of the contour mapping. The second obtains the flow diagrams and the relaxation curves by solving the dynamical equations. At temperatures lower than the lower limit of the stability temperature (T_l), two solutions, namely unstable and stable, are obtained. At these temperatures the system always relaxes to a stable state. Between the lower limit and the upper limit of the stability temperatures (T_u), there are three solutions: stable, metastable and unstable. In this case, the system relaxes to either a stable or a metastable state. The unstable state is a saddle-point which plays an important role in explaining how to get a system frozen-in in the metastable state. Above T_u, there is a single stable solution. The solutions obtained from these two methods are in exact agreement with each other for a given temperature and coupling constant.