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This study proposes a power conversion interface for a DC grid and a single-phase utility. The proposed power conversion interface is configured using an interleaved AC–DC power converter and a DC hybrid power filter. The interleaved AC–DC power converter controls the real power between the DC grid and the single-phase utility in both directions. The interleaved AC–DC power converter can effectively reduce the high-frequency harmonic currents at both the AC side and DC side. A new current-sharing control method is used to equalise the currents in the interleaved power-electronic arms using only one current sensor in the interleaved AC–DC power converter. The DC hybrid power filter is connected between the DC bus of the interleaved AC–DC power converter and the DC grid. The DC hybrid power filter is controlled to be operated as a virtual low-frequency AC resistor connected to the DC grid in series and the low-frequency harmonic for the DC input current of the interleaved AC–DC power converter is suppressed. Accordingly, the problems of harmonic currents for a power conversion interface used between the DC grid and the single-phase utility are attenuated. A hardware prototype is developed to verify the performance of the proposed power conversion interface.

In this review article, we first briefly introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies. The developments of improved quantum molecular dynamics model (ImQMD) and ultra-relativistic quantum molecular dynamics model (UrQMD), are reviewed. The reaction mechanism and phenomena related to the fusion, multinucleon transfer, fragmentation, collective flow and particle production are reviewed and discussed within the framework of the two models. The constraints on the isospin asymmetric nuclear equation of state and in-medium nucleon-nucleon cross sections by comparing the heavy ion collision data with transport models calculations in last decades are also discussed, and the uncertainties of these constraints are analyzed as well. Finally, we discuss the future direction of the development of the transport models for improving the understanding of the reaction mechanism, the descriptions of various observables, the constraint on the nuclear equation of state, as well as for the constraint on in-medium nucleon-nucleon cross sections., 64 pages, 55 figures. Review article for Frontiers of Physics

The three-dimensional Langevin model plus a constraint on the heavy fragment deformation is used to study the fission dynamics for uranium and plutonium isotopes at low excitation energies. The potential energy surface is calculated with the macroscopic-microscopic model based on the two-center shell model. The Werner-Wheeler approximation is used to calculate the inertia tensor and the wall-and-window model is applied to calculate the friction tensor. In this work, the influence of the model parameters on the fission fragment mass distribution is investigated. The fission fragment mass distributions for $^{234,236,239}\mathrm{U}$ and $^{240}\mathrm{Pu}$ at low excitation energies are calculated and compared with the results of gef code as well as the evaluated data of ENDF/B-VIII.0. A nice agreement is found in the comparison, in which the incorporation of the constraint on the heavy fragment deformation plays an important role. In addition, the dependence of the mass distribution on the excitation energies for $n+^{235}\mathrm{U}$ fission is also studied within the model. Furthermore, the correlation between the elongation and mass asymmetry at the scission point and the correlations of the fission time with both the elongation and mass asymmetry are studied. This study may shed light on understanding the dynamics of the superlong channel for symmetric fission and the standard channels for asymmetric fission in the gef model and other phenomenological fission models.

The excitation functions of quasielastic and elastic scattering at backward angles have been measured for the systems of 16 O+ 152 Sm, 6,7 Li+ 208 Pb and 32 S+ 90,96 Zr. The barrier distributions are extracted from these measured excitation functions and compared with the corresponding fusion barrier distributions. Except some details, the barrier distributions derived from the data of fusion and quasielastic/elastic scattering are almost the same for the tightly bound reaction systems. For the reaction systems with weakly bound projectile, the barrier distributions extracted from quasielastic scattering are obviously different from the fusion barrier distributions. However, the barrier distributions extracted from the excitation functions of the quasielastic scattering plus breakup are almost the same as the one extracted from the complete fusion data. This result means that barrier distribution not only bears the information of nuclear structures but also contains the knowledge of reaction mechanisms. Our results show that the complete fusion of the weakly bound projectile with heavy target is suppressed at the above barrier energies as compared with the model predictions. In addition, the measured barrier distribution of 32 S+ 96 Zr is broaden and extends to lower energy than in the case of 32 S+ 90 Zr due to the coupling of neutron transfer with positive Q-values, which result in a significant enhancement of fusion cross sections at the subbarrier energies.

The stochastic transport driven by flashing multi-noise sources in a ratchet is studied. The stationary current versus the noise strength and the colored noise correlated time T is obtained. At a fixed flip rate and strength of the colored noises, the novel phenomenon of the current reversal occurs as T reaches a certain value. More than one reversal point exists when a flashing colored noise source and a flashing white noise source are simultaneously taken into account.

For the single-particle potential surface of the two-center shell model, two geometrical quantities which determine the local Liapunov exponents are derived. It is shown that the appearance of a large positive local Liapunov exponent in a large area of the coordinate space leads to the quantum chaotic motion of a single particle in heavy nuclei. For both small and large (or medium) separations of the two centers, the dependence of the quantum chaotic motion on the neck deformation is interpreted from the dynamical point of view.

For the independent-oscillator model (IOM), the explicit expressions of the instantaneously dynamical response functions (chi(t(I) + tau, t(I)), X(t(I) + tau, t(I))) and correlation functions (phi(t(I) + tau, t(I)), Phi(t(I) + tau, t(I))) for both the system and environment are derived. It is shown that for external perturbation the environment of IOM is dynamically stable and the system is oscillatory. Although the external perturbation exists, there is still strongly temporal correlation for the system, for the environment, however, the temporal correlation quickly decays with the second time variable tau and is almost independent of the first time variable t(I), nevertheless is significantly affected by dissipation. It is shown that the environment behaves as a heat bath from the dynamical point of view.

Within the framework of the two-center shell model the classically dynamical behaviour of a nucleon in heavy nuclei is investigated systematically with the change of nuclear shape parameters for the first time. It is found that as long as the nucleonic energy is appreciably higher than the height of the potential barrier there is a good quantum-classical correspondence of nucleonic regular (chaotic) motion. Thus, Bohigas, Giannoni and Schmit conjecture is confirmed once again. We find that the difference between the potential barrier for prolate nuclei and that for oblate ones is reponsible for the energy-dependence difference between the nucleonic chaotic dynamics for prolate nuclei and that for oblate ones. In addition, it is suggested that nuclear dissipation is shape-dependent, and strong nuclear dissipation can be expected for medium or large separations in the presence of a considerable neck deformation built on a pronounced octupole-like deformation, which provides us a dynamical understanding of nuclear shape dependence of nuclear dissipation.

The dependence of the stability of prolate deformed nuclei on the neck parameter is studied from the point of view of the interplay between order and chaos. The statistical properties of level spectra for the deformed space explored by the fission process are presented. It is found that on saddles the single particle motion is unstable against chaos, whereas at minimums it is stable. Based on this investigation a possible understanding of hyperdeformed {sup 144{endash} 146}Ba appearing in the spontaneous fission of {sup 252}Cf is provided. {copyright} {ital 1997} {ital The American Physical Society}

In the framework of the two-center shell model we calculate the nearest neighbor level spacing distribution and spectral rigidity of single-particle energy levels of heavy nuclei when the shape parameters are changed systematically. In the two cases of the single-particle Hamiltonian with and without the spin-orbit coupling l · s and square angular momentum l2 terms, the shape parameter regions are determined respectively, in which both of the spacing distribution and spectral rigidity approach the predictions of the Gaussian orthogonal ensemble of random matrix theory. In both cases it is shown that a considerable octupole-like deformation is necessary to induce the chaotic single-particle motion. Moreover, the occurrence of the chaotic motion not only appears in the heavy nuclei with oblate shapes but also in prolate ones with a proper neck. The neck appreciably influences the occurrence of the chaotic motion when the separation between the two centers is medium or larger. It is exhibited that the level repulsion which is strongly related to the nuclear deformation governs the regularity (chaoticity) of the single-particle motion. We find that the l · s term obviously favors the chaotic motion, however, the l2 term only slightly affects the chaotic motion. In addition, it is implied that when the two terms are taken into account, the chaotic motion occurs even in very elongated nuclei.

The denaturation and propagation of a nonlinear localized excitation in DNA molecules are studied in a unified way for a new Hamiltonian. The large amplitude motion of DNA is investigated during the propagation of the nonlinear localized excitation. The nonlinear effect on the formation of the localized excitation is disscussed. It is shown that our model not only can reproduce the results of denaturation experiments, but also can describe the process of the localized excitation of fluctuational opening in DNA molecules.

The novel properties of the environment are found in independent oscillator model. 1) If the initial state of the composite system lies in thermal equilibrium, then the environment is equipartition of energy, which, however, is moving with the system. 2) When the environment is in thermal equilibrium, but the system deviates from it at the beginning, the environment is no longer equipartition of energy, but which still moves with the system. These properties are quite different from those of the collection of oscillators discussed by Ford et al. (see Ref. [9])

The single particle-energy levels of U92238 as a function of cranked frequency are given in rotating two-centre shell model. It is found that the curvature distribution approaches the prediction of Gaussian unitary ensemble (GUE) [14] for a certain range of separations between two centers at some cranked frequencies, which is the first support to the prediction in the realistic and complex system like heavy nuclei. Meanwhile, we find that the spacing distributions for various separations have a similar structure when the frequency is high, for which a formulae is suggested to describe this kind of spacing distributions. In addition, we compute the spectral rigidity characterizing the long range correlation of a spectrum.

For the heavy nucleus 92 238 U, the influence of the shape parameters and cranking frequency on single-particle energy levels in a rotating system is examined. It has been found that the level spacing distribution and the two kinds of curvature distributions (with respect to the separation distance and cranking frequency, respectively) of levels individually approach those of the Gaussian unitary ensemble (GUE) in different regions of separation distance and cranking frequency. They, however, share a common parameter region in which they are all close to those of GUE. Furthermore, it is suggested that the chaotic motion in a heavy nucleus is possibly realized under the condition of superdeformation and high spin.

We use a thermodynamic scheme (imaginary free energy method) in terms of the path integral technique to study the quantum decay rates of a metastable state system coupled to a heat bath in the crossover temperature (Tc) region. In this region the transition between thermally activated decay and tunneling occurs. A nonlinear coupling form factor is used to overcome the divergent integral in the partition function nearTc. The decay rate formula based on the steepest descent approximation has been improved. A method is developed to calculate the real and imaginary parts of the partition function which combines a random walk method with fast-Fourier transform Monte-Carlo evaluation. For a nonlinear dissipative system with a damping correlation kernel of exponential form, the accurate numerical calculations are presented. The effects of nonlinear and frequency-dependent damping on the rate are shown.

We study the transport of a Brownian particle moving in a ratchet-like periodic potential driven by multiplicative colored noise, and an analytic expression for the steady current with weak noise-strength is obtained. The results show that the effect of the multiplicative noise is equivalent to additive noise acting on a particle moving in an effective potential with a slope modified from the original one. Then a net steady current may arise even in the cases of white noise and a symmetric periodic potential. Some simple models are studied and discussed.

The steady current for an overdamped ratchetlike system with a multiplicative exponentially correlated colored noise is obtained by solving an appropriate two-variable Fokker-Planck equation in terms of the matrix continued-fraction method. We compare the present results with the established ones in two cases: for weak additive colored noise and a multiplicative white noise source. The dependences of the current on the shape of the potential, the correlation time and the strength of the noise are discussed.

Fission fluctuation-dissipation dynamics of heavy nuclei has been studied using Langevin Monte Carlo simulations. The covariant form of the fission transport equation and the coefficients related to it are investigated. To learn about the influence of the dynamics from the ground state to the saddle point on the kinetic energy distributions we have studied various systems and compared the calculations both starting from the ground state and from the saddle point. Both the mean total kinetic energy of the fission fragments and its variances can fit with the experimental values in terms of a finite neck radius as scission condition.

The stationary nuclear fission rate including both thermodynamic and quantal fluctuations are studied by using the partition function method, which is related to the imaginary part of the free energy by ( is the partition function). We calculate the classical fission rate with a coordinate-dependent mass within a one-dimensional model. The contributions of additional degrees of freedom, angular momentum and viscosity to the quantal fission rate at finite temperature are also discussed. Differences between the two- or three-dimensional and the one-dimensional cases are analyzed by using the parametrization.

We study in this paper the classical stationary fission rate including a coordinate-dependent mass and a realistic potential. The results show that our numerical rate formula is a good approximation to the realistic Langevin simulation even if the nuclear temperature is not smaller than the fission barrier.

We develop a path-integral Monte Carlo method to calculate the stationary quantum decay rate of a metastable system with coordinate-dependent inertia and friction at finite temperature. The mass and the coupling form factor between the collective coordinate and the heat-bath environmental oscillators are assumed to be functions of the coordinate, respectively. Applying the results to a spectrum of heat-bath oscillators, large influences of the coordinate-dependent mass on the decay rate are found at high temperatures, while large nonlinear effects of dissipation are found at low temperatures.

A Monte Carlo random walk algorithm for evaluating the path integral expression for coordinate matrix elements of the Boltzmann operator with the coupling term is suggested and discussed.

The average kinetic energy and its variance of fission fragments for the compound nucleus are calculated by four-dimensional Langevin equation. Two collective coordinates are taken into account: the distance between the centers of the nascent fragments and the neck parameter using the parametrization. The model allows for a realistic coordinate dependence of all coefficients appearing in the Langevin equation as computed by the Werner-Wheeler method. The diffusion process for thc fissioning nuclear system from the ground state to the scission line on the realistic energy surface is investigated. The results are in good agreement with the experiments.

The harmonic noise is used as an external stochastic source in non-Markovian equilibrium system. A bi-peak resonance phenomenon is carried out due to the external noise frequency close to the frequencies of damped linear-oscillator and internal noise, respectively.

An accurate and fast Monte Carlo algorithm is proposed for solving the Ginzburg-Landau equation with multiplicative colored noise. The stable cases of solution for choosing time steps and trajectory numbers are discussed.

A flashing correlation ratchet model is proposed, in which the transport of Brownian particles driven by additive colored noise of Ornstein-Uhlenbeck type in a flashing ratchet is studied by Monte Carlo simulation. The stationary current vs the noise strength and the correlation time is obtained and analyzed. For a fixed rate of potential flashing, the novel phenomena of current reversal and reentry occur. The conditions for the occurrence of these phenomena are found. The influence of the flipping rate is also discussed. This finding might be relevant to the fact that the protein motors with similar structure can move in opposite directions on the same kind of microtubule.

Within the framework of the two-center shell model, the classically dynamical behaviour of a nucleon in heavy nuclei is investigated when nuclear shape parameters are changed systematically. It is found that there is a good quantum-classical correspondence of nucleonic regular (chaotic) motion so that Bohigas, Giannoni and Schmit conjecture is confirmed once again.

The partition of the total excitation energy between the fission fragments for the n th +235 U and n(En = 5.55 MeV)+235 U fission reactions are analyzed with the experimental data available. Our results show that the total excitation energy is not shared by the fragments in proportion of their masses but support the so-called energy sorting-mechanism. The temperature of the heavy fragment is generally lower than that of the light one when the shell effect does not play a strong role. As soon as the mass of heavy fragment closes to 132, its temperature becomes higher than the complementary light one because of strong shell effect. Our results also show that the heavy fragments gain more energy than the complementary light ones when the incident neutron energy increases.