International Journal of Modern Physics B

We apply the functional field-theoretical renormalization group methodology up to two-loop order to the 2D attractive Hubbard model for weak bare interaction. Since the momentum-resolved quasiparticle weight Z_Λ(p) is always close to unity in the RG flow, higher-order quantum fluctuations do not affect crucially the low-energy dynamics in this case. As a result, we observe a s-wave singlet superconducting quasi-long-range order phase as a function of doping in good agreement with other numerical methods. To assess the role played by the fluctuations we compare the critical temperature T_c in which the quasi-long-range superconducting order phase takes place within our approach with mean-field theory and quantum Monte Carlo results.

We show that rotational excited aggregates with an electric dipole moment may be created in polar liquids. Under proper storage conditions, the life times of the aggregates are very long, e.g., days and even years. In solutions, the aggregates are composed of solvent molecules only or a combination of these and solute particles. The process steps leading to the formation of the aggregates are: (1) vigorous succussing the liquid or its solution; (2) adding nonsuccussed liquid; (3) repetition of step (1) and (2). In solutions, formation of the aggregates requires that these steps are repeated until the concentration is reduced below a solvent and solute specific molarity, which under room temperature and pressure conditions, typically, is of the order of 10^-4 M or below. The characteristics of liquids containing aggregates with an electric dipole, theoretically derived in this paper, conform to the experimentally observed ones, reported in the literature.

The polycrystalline sample of KPb₂V₅ O₁₅ was prepared by a mixed-oxide method relatively at low temperature (i.e., 550°C). X-ray diffraction studies of the compound showed the formation of single phase orthorhombic crystal structure at room temperature. SEM micrograph showed the homogeneous distribution of grains throughout the sample. Electric properties were analyzed using the complex impedance spectroscopy. The modulus plot showed the presence of both the grain and grain boundary effect. The bulk impedance evaluated from the Nyquist plots was observed to decrease with the rise in temperature, showing a negative temperature coefficient of resistance. The variation of AC electrical conductivity (σ_AC) was measured in a wide temperature (30–500°C) and frequency (10²–10⁶ Hz) range. The activation energy of the compound calculated from both the impedance and modulus spectrum was found to be the same.

Unidirectional coupled synchronization of two identical or different chaotic systems has been carefully studied based on the master–slave synchronization scheme, where the synchronous state is that of the master system and cannot be changed after they realized synchronization. In this paper, a general bidirectional synchronization scheme is presented which made the master–slave scheme a special case. It is straightforward to tune the synchronous state by just changing the value of a parameter. Based on the general bidirectional synchronization scheme, active control method is used to tune the synchronous state of two pairs of different chaotic systems: the Lorenz and Chen systems; and then the Lü and Rössler systems.

Based on techniques from the state observer design and the pole placement technique, we present a systematic design procedure to synchronize a class of chaotic systems by a scaling factor (projective synchronization). Compared with the method proposed by Wen and Xu, this method eliminates the nonlinear item from the output of the drive system. Furthermore, the scaling factor can be adjusted arbitrarily in due course of control without degrading the controllability. Finally, feasibility of the technique is illustrated for the unified chaotic system.

The temperature-dependent resistivity measurements of our Ag–Ni–Si silicide films with 51–343 nm thicknesses are studied as a function of temperature and film thickness over the temperature range of 100–900 K. The most striking behavior is that the variation of the resistivity of the Ag–Ni–Si silicide films with temperature exhibits an unusual temperature-dependent behavior with respect to those of the transition and untransition metals. Our measurements show that the total resistivity of the Ag–Ni– Si silicide films increases linearly with temperature up to a T_m temperature at which resistivity reaches a maximum thereafter T_m decreases rapidly and finally to zero at ~850 K. T_m temperature is found to decrease with decreasing film thickness. We have shown that in the temperature range of 100-T_m K, electron–phonon resistivity and grain boundary resistivity components responsible for the total resistivity increase. But the grain boundary scattering is dominant mechanism for the resistivity increase in our Ag–Ni–Si silicide films.

In this paper, a shell model for the energy cascade in three-dimensional turbulence at varying the viscosity is studied. When the viscosity parameter ν is large enough, the phase orbit of each shell in the system is a stable fixed point. As ν diminishes down to a critical value, the point becomes unstable and a stable periodic orbit appears via a supercritical Hopf bifurcation. For the quasiperiodic solution of the system, each shell has a own dynamic behavior. At ν = 6.88×10^-5, the system initiates a complex scenario of bifurcations, where the phase orbits of u_n and u_n+3 begin to form a intersected section. Farther decreasing ν, we observe a transition from quasiperiodic solution to chaos through a sequence of Neimark–Sacker bifurcations. The behaviors can be vividly shown in the change of the average energy function E with ν. At last, the transition to chaos in the ν–δ parameter space is also obtained.

The stochastic resonance (SR) for a stochastic bistable system driven by a static force and a periodic square-wave signal as well as by additive white noise is considered from the view of signal-to-noise ratio (SNR). It is found that the SNR appears SR behavior when it is plotted as a function of the additive noise strength or as a function of the system parameters. Moreover, the influence of the static force is opposite to that of the amplitude of the stochastic potential.

The two-dimensional, soft-sphere molecular dynamics simulations have been performed to study the granular segregation behaviors in a binary granular mixture in tilted compartmentalized container under vertical vibration. It is found that there exist mixed state, left segregated state and right segregated state, which depend on the grain properties such as size ratio and density ratio as well as shaking properties. The particles with large density favor moving to right and the particles with large diameter prefer moving to left, so binary granular mixtures with large density ratio prefer forming right segregation state and the binary mixtures with large diameter favor forming left segregation state. The tilted compartmentalized container can be regarded as a container with a sawtooth base, which leads to stratified flows and thus forming horizontal segregation state under vertical vibration. The tilted bed plays a key role in forming segregation states, whereas the central wall enhances the segregation behaviors.

This paper presents tracking control and synchronization strategies for Chen system. Two universal controllers, a tracking controller and a synchronization controller based on Backstepping design method were designed. It is proved theoretically that the tracking controller enables the error signal exponentially to converge to zero. The validity of Backstepping synchronization controller is also proved. Numerical simulations further validated the two controllers.

The effects of sintering temperature on the electrical and magneto-transport properties of La_0.8Sr_0.2 MnO₃ compounds prepared by employing a chemical co-precipitation route sintered at 1120°C, 1220°C and 1320°C are reported. The X-ray powder diffraction patterns for all samples can be indexed to the rhombohedra structure with R3C space group. The insulator–metal transition temperature remained nearly constant (~291 K) for all samples. The magneto resistance (MR) values were found to decrease noticeably as the sintering temperature was increased from 1120°C to 1320°C. Above 0.3 T, the magneto resistance was influenced by T_o values, which indicates the bending of Mn–O–Mn bond. The resistivity data were fitted with several equations in the metallic (ferromagnetic) region. In the insulating (paramagnetic) region, the variable range hopping and small polaron hopping models were used to compute the density of states at the Fermi level, N(E_F), and activation energy (E_a) of the electrons. The resistivities can be fitted well with ρ–T² and ρ–T^2.5 curves. The variable range hopping model and small polaron hopping model fitted very well at high temperature regions, indicating that small polaron hopping might be responsible for the conduction. La_0.8 Sr_0.2MnO₃ sintered at 1220°C demonstrated the highest MR of 6.5% in 1 T magnetic field.