International Journal of Modern Physics B

We review the quantum fidelity approach to quantum phase transitions in a pedagogical manner. We try to relate all established but scattered results on the leading term of the fidelity into a systematic theoretical framework, which might provide an alternative paradigm for understanding quantum critical phenomena. The definition of the fidelity and the scaling behavior of its leading term, as well as their explicit applications to the one-dimensional transverse-field Ising model and the Lipkin–Meshkov–Glick model, are introduced at the graduate-student level. Besides, we survey also other types of fidelity approach, such as the fidelity per site, reduced fidelity, thermal-state fidelity, operator fidelity, etc; as well as relevant works on the fidelity approach to quantum phase transitions occurring in various many-body systems.

The effect of two types of oil palm fibres (bunch and fruit) on mechanical properties of polyester composites is examined in the current work considering different volume fractions. Tensile, compression, and flexural properties of the composites were investigated. In addition to that, tensile strengths were calculated theoretically using Hirsch model. Scanning electron microscope (SEM) was used to observe the fracture mechanism of the specimens. Single fibre pull-out tests were performed to determine the interfacial shear strength between polyester resin and both types of oil palm fibres. Results revealed that both types of oil palm fibres enhanced the mechanical performance of polyester composites. At a higher volume fraction (40–50%), tensile strength of the polyester composite was improved, i.e., 2.5 times improvement in the tensile strength value. Experimental tensile strength values of oil palm bunch/polyester composites have a good correlation with the theoretical results, especially at low volume fractions of fibre. Flexural strength of polyester worsened with oil palm fibres at all volume fractions of fibre.

By using chaos synchronization between nonidentical multiple time delay semiconductor lasers with optoelectronic feedbacks, we demonstrate numerically how fast dynamic logic gates can be constructed. The results may be helpful in obtaining computational hardware with reconfigurable properties.

Parameter fluctuation, which is often induced by the noise, temperature, deformation of the media etc., plays an important role in changing the dynamics of the system. In this paper, the problem of parameter fluctuation-induced pattern transition in the Complex Ginzburg–Landau equation (CGLE) is investigated. At first, the perpendicular-gradient initial values are used to generate spiral wave and spiral turbulence under appropriate parameters. At second, the parameter is perturbed with the periodical and/or random signal to simulate the parameter fluctuation, respectively. Then a class of linear error feedback is used to induce transition of the spiral wave and spiral turbulence. It is found that target waves can be induced by the complete feedback forcing, while the local feedback forcing seldom induce a target wave. In the case of spiral turbulence, spiral wave is generated and the spiral turbulence is removed by the new appeared spiral wave as the linear error feedback began to work on the whole media. Finally, the common negative feedback is also used to control the parameter-fluctuated CGLE, and the results are compared with the linear error feedback control, it is found that the whole system become homogeneous when the negative feedback is imposed on the whole media, and the local negative feedback can induce new target wave to remove the spiral wave while it is in vain to generate new target or spiral wave to overcome and eliminate the spiral turbulence.

Taking account the presence of external magnetic field, we study the conductance properties in spin field-effect transistors (SFET). It is shown that the conductance of the SFET exhibits an excellent magnetic switching characteristic for high potential barriers, and it is more and more pronounced with the potential barrier strength increasing. According to the effect, we can switch the SFET on or off by tuning the strength of the magnetic field. We also study how the conductance of the SFET is manipulated by spin–orbit coupling strength and spin polarization in source and drain.

It is shown that certain nonlinear wave evolution equations in (1+1)-dimensional space-time in the soliton theory: sine-Gordon (SG), sinh-Gordon (ShG), the nonlinear Schrödinger equation (NLS), the φ⁴ equation in quantum field theory, the Burgers diffusion equation (Brg) and the Huxley equation (Hsl) in biophysics, the Boussinesq equation (Bsq), can be solved in terms of hypergeometric functions of _pF_q-type. Such approach allows to establish the connection between "model" equations and simple functional relations (in the form of diagrams) of these functions; the latter gives the possibility to consider a number of "inverse problems" in the soliton theory in a new way and to get new "models" of solitary waves.

The effect of post-deposition annealing in forming gas on the structural and electrical properties of sol–gel derived SiO₂ thick film on n-type 4H–SiC has been systematically investigated. Tetraethylorthosilicate-based precursor with H₂SO₄ as catalyst was prepared and prior to film deposition, substrate surface was treated by hexamethyldisilizane. The spin-coated film was annealed at 750–950°C for 30 min with an approximately 185-nm thick film. It was found that oxide annealed at the highest temperature revealed the densest film, lowest oxide defects, and lowest total interface trap density. As a result, this oxide had demonstrated the lowest leakage current density if compared with other oxides.

The steady velocities and volume flow rates (up to the second order) of an Eyring-fluids along the cross-section of an (approximated) wavy-rough nanotube are obtained analytically by using the verified fluid model and boundary perturbation method. Our results show that the wavy-roughness could tune the flow rate especially for larger forcing due to the larger surface-to-volume ratio and slip-velocity effect. The effects of wave number and slip length are also addressed.

The effect of slip boundary on the particle motions in a micro-planar channel is studied by lattice Boltzmann method. The property of the particle in different surface slip conditions is investigated extensively by simulating the particle trajectories and analyzing the trajectory differences between slip and nonslip conditions. The simulation results show that the particle behavior is affected by the surface slip conditions, especially in the region, which is between the critical position and the channel center, for nonsymmetrical boundary slip. The factors affecting the critical position, including boundary slip velocity and flow Reynolds number, are also studied numerically. The results are expected to find extensive applications and may be helpful to understand recent observations on micro-slip flows with suspensions.

PbTiO₃ (PT) nanoparticles have been prepared by chemical route using polyvinyl alcohol (PVA) as an efficient surfactant. The effect of PVA to reduce the particle's sizes of PT has been observed. X-ray diffraction (XRD) pattern shows that the PT nanoparticles are tetragonal with distortion ratio, c/a ~1.061. The average particle's size calculated from XRD and transmission/scanning electron microscopy is ~24 nm for PT powder sintered at 700°C. The nanostructured grains were also observed in PT pellet sintered at 1000°C. The dielectric properties of PT pellet have been measured from room temperature to 200°C and in the frequency range of 0.075 to 10 MHz. The values of room temperature dielectric constant and tanδ are 117 and 0.05 respectively, measured at 0.5 MHz. It is found that the dielectric constant of PT nanoparticles can be controlled up to higher frequency region of 5 MHz.

In this paper, the dynamics of the coupled Hodgkin–Huxley neurons (HHn) is investigated. At first, appropriate initial values and reasonable parameters are used to induce spiral wave in the coupled HHn. The temperature and channel noise are also considered to induce the birth and transition of spiral wave, respectively. It is found that the spiral wave can be generated in the absence of channel noise, and the seed of spiral wave cannot grow up when the intensity of channel noise exceeds the threshold (the noise is distributed on all the channels and s describes the membrane patch, the threshold is suggested with s = 3.2). The spiral wave disappears and all the coupled HHn become homogeneous when the temperature exceeds the threshold about T = 22°C.

In this paper, the separation transformation approach is extended to some high dimensional non-linear wave equations, such as the (N+1)-dimensional Zhiber–Shabat equation, the generalized (N+1)-dimensional complex non-linear Klein–Gordon equation and the generalized (N+1)-dimensional Toda lattice equation. As a result, a class of special exact solutions of these equations are obtained. The solutions obtained contain one or two arbitrary functions which may lead to abundant structures of the high dimensional non-linear wave equations.

In this paper recursive and adaptive backstepping nonlinear controllers are designed to, respectively, control and synchronize the triple-well or Φ⁶ Van der Pol oscillators (VDPOs) with both parametric and external excitations. The designed recursive backstepping nonlinear controller is capable of stabilizing the Φ⁶-VDPO at any position as well as controlling it to track any trajectory that is a smooth function of time. The designed adaptive backstepping nonlinear controller globally synchronizes two Φ⁶-VDPOs evolving from different initial conditions and its application to secure communications is computationally demonstrated. The results are all validated by numerical simulations.

The cycle model established here, for which the heat leakage and internal irreversibility are considered, consists of two irreversible non-isentropic adiabatic and two isomagnetic field processes. The working substance is composed of many non-interacting spin systems. Based on quantum master equation of an open system in the Heisenberg picture and semi-group approach, the general performance analysis of quantum refrigeration cycle is performed. Expressions for several important performance parameters, such as the cooling rate, coefficient of performance, rate of entropy production and power input, are derived. By using numerical calculations, the cooling rate as a natural optimization goal for a refrigerator is optimized with respect to external magnetic field. The characteristic curves of the cooling rate, rate of entropy production and power input subject to coefficient of performance are plotted. The optimal regions of the cooling rate, coefficient of the performance (COP) and temperatures of the working substance, are determined.

A quantum key distribution (QKD) protocol based on constructed nonorthogonal states is proposed. By transmitting the photons from Bell states in random order the sender constructs nonorthogonal states, which can prevent an eavesdropper from extracting the key information. At the destination, the receiver performs Bell measurements and then obtains secure key. Different from previous nonorthogonal-states-based QKD protocols, our protocol exhibits a new feature, that is, the users can also obtain some key bits even when they choose different "bases"! Thus it can reach a higher efficiency in theory. Besides, we present a trade-off between the information that an eavesdropper can elicit and the corresponding error rate he/she would introduce, which shows that our protocol is secure.

In this paper, a new hyperchaotic system is formulated by introducing an additional state into the third-order unified system. Some of its basic dynamical properties, such as Lyapunov exponent, bifurcation diagram and the Poincáre section are investigated. It was found that the system is hyperchaotic in several different regions of the parameters. The analysis of equilibrium points and stability are also given. Two different methods, i.e., nonlinear hyperbolic function feedback control and tracking control methods, are used to control hyperchaos in the new hyperchaotic system. Based on the Routh–Hurwitz criteria, the conditions suppressing hyperchaos to unstable equilibrium point are discussed. A tracking control method is proposed. It is also proved that the strategy can make the system approach any desired smooth orbit at an exponential rate. Numerical results have shown the effectiveness of the control methods.