International Journal of Modern Physics B

We consider the relationship between the tight-binding Hamiltonian of the two-dimensional honeycomb lattice of carbon atoms with nearest neighbor hopping only and the 2 + 1 dimensional Hamiltonian of quantum electrodynamics, which follows in the continuum limit. We pay particular attention to the symmetries of the free Dirac fermions including spatial inversion, time reversal, charge conjugation and chirality. We illustrate the power of such a mapping by considering the effect of the possible symmetry breaking, which corresponds to the creation of a finite Dirac mass, on various optical properties. In particular, we consider the diagonal AC conductivity with emphasis on how the finite Dirac mass might manifest itself in experiment. The optical sum rules for the diagonal and Hall conductivities are discussed.

Decoherence is the main process behind the quantum to classical transition. It is a purely quantum mechanical effect by which the system loses its ability to exhibit coherent behavior. The recent experimental observation of diffraction and interference patterns for large molecules raises some interesting questions. In this context, we identify possible agents of decoherence to take into account when modeling these experiments, and study their visible (or not) effects on the interference pattern. We thereby present an analysis of matter wave interferometry in the presence of a dynamic quantum environment, and study how much the visibility fringe is reduced and in which timescale the decoherence effects destroy the interference of massive objects. Finally, we apply our results to the experimental data reported on fullerenes and cold neutrons.

By using Green's functional method, we investigated the influence of different strength constants at defected bonds and the junction's size on the transmission properties of the lattice wave in a one-dimensional chain. The heat currents of several defected chains are also calculated. The results show that correlation transmission between two defected bonds in a chain different from electron behaviors. Furthermore, for a large-size junction embedded in a chain, the transmission of high frequency phonons will disappear while having smaller strength constant in the junction than in two semi-infinity chains. On the other hand, for larger strength constant than in two semi-infinite chains, all phonons can transport through the junction with a certain transmission value, although the number of transmission peaks decreases. Finally, the lower frequency lattice waves have better transmission through a junction with a series of strength constants according to the Fibonacci sequence.

We studied the theoretical Curie temperature of a dual-phase nanomagnetic system by Monte Carlo simulation of a modified Heisenberg model on a 3D complex lattice consisting of single- and cluster-spins. We also systematically investigated the experimental Curie temperature of a dual-phase nanomagnetic alloy and performed a direct comparison between theory and experiment. The exchange coupling between two component magnetic phases substantially affects the Curie temperature of the intergranular amorphous region of a dual-phase nanomagnetic system. The depends upon the nanocrystallite size d, the volume fraction V_c and the interspace among crystallites ξ. Large crystallized volume fraction V_c, small grain size d, and thin interphase thickness ξ lead to an obvious enhancement of Curie temperature (ECT) of intergranular amorphous region, whereas the Curie temperature of nanocrystallites decreases slightly. By simulation, we worked out a relationship between the reduced ECT and ξ, as , and it conforms to the experimental result. In addition, we also simulated the demagnetization of a hard–soft nanocomposite system. The exchange coupling between two component phases affects the cooperativity of two-phase magnetizations, the coherent reversal of magnetizations, and coercivity.

Acoustic Emission (AE) and hysteresis parameters were studied from PZT-5A (soft) and PZT-8 (hard) ceramics during the application of ac fields in the frequency range of 0.2 Hz to 5 Hz. AE was found to occur mainly due to domain switching in these ceramics during the application of ac fields. In PZT-5A, a threshold field was observed for the AE activity to begin in both the direction of the applied field and in general, it was found to decrease with increasing frequency. Apart from this, AE activity was found to decrease with increasing number of applied ac cycles, and is attributed to domain pinning. In the case of PZT-8, AE was found to occur even at zero field at higher frequencies and AE activity was found to increase with increasing number of field cycles. These are explained on the basis of the defect dipole — domain interaction in these ceramics.

The energy levels and far-infrared spectra of two electrons confined in quantum dots and quantum rings under a magnetic field have been investigated. The size and shape effects of quantum rings on the levels and the spectra are clearly revealed. It is found that the spin oscillation of two electrons in a quantum ring with a magnetic field is caused by the Coulomb interaction. The transitions of two-electron far-infrared spectra are clearly shown from quantum dots to quantum rings. The influence of electron–electron interaction on the energy levels and far-infrared spectra has been discussed. The quantum size effects predict a possibility to observe phenomena related to electron-electron interaction in quantum rings.

Mesoscopic damped mutual inductance coupled double resonance RLC circuit is quantized by the method of damped harmonic oscillator quantization and linear transformation. The energy levels of this circuit are given. By thermo-field dynamics (TFD), the quantum fluctuations of the current and voltage of each loop are researched in the thermal vacuum state, thermal coherent state and thermal squeezed state. It is shown that the quantum fluctuations of the current and voltage are related not only to the circuit inherent parameter and coupled magnitude of mutual inductance, but also squeezed coefficients, squeezed angle, environmental temperature and damped resistance. Furthermore, because of environmental temperature and damped resistance, the quantum fluctuations increase with the increase of temperature and decay along with time.

The paper analyses the limitation of Baptista cryptography in partitioning an attractor, and proposes two new attractor-partition methods: uniform-partition algorithm and dynamic-partition algorithm. They are different from the equal-interval-partition algorithm in Baptista cryptography, but dividing the attractor according to the attractor's natural invariant density and plaintext density, respectively. The comparative experiment indicates: the two new methods improve the unbalanced cryptograph distribution and cryptograph length in Baptista cryptography, they are also able to reduce the iteration time in chaotic systems effectively, which has improved decryption time and cryptographies' security.