光子晶体中缺陷的色散导致的群速度降低

利用传输矩阵方法计算了包含色散媒质缺陷的一维光子晶体的复透射系数，其中色散媒质用洛仑兹振子模型描述。计算了由复透射系数定义的等效复折射率并由此研究了频谱位于缺陷模频率附近的光脉冲的群速度。结果发现，由于缺陷模附近的透射谱敏感地依赖于缺陷层的光学厚度，而缺陷层的色散使缺陷层光学厚度随频率变化而改变，从而使包含缺陷的光子晶体的等效色散性质明显地依赖于缺陷的色散行为。由于光脉冲是由多种频率成分的单色场迭加构成的，透射脉冲由各单色场透射后重新迭加构成，因此波包的传播由介质的等效色散性质决定。与包含无色散缺陷的光子晶体相比，缺陷的色散可导致极慢的群速度。通过改变振子强度，群速度可从极慢光速转变为超光速(superluminal)。     

Optical bistability of a composite system induced by a broadband squeezed vacuum

A composite system consisting of a degenerate optical parametric oscillator （DOPO） and N two-level atoms interacting with a broadband squeezed vacuum （SV） centred at frequency cas and an input monochromatic pumping field with a frequency ωp is analysed. The corresponding explicit analytical steady-state solutions in the central mode ωp = ωs are derived, and the result displays optical bistability （OB）. In addition, the influence of the broadband SV on the bistable behaviour is analysed in detail.     

Parametric Oscillations of the Kochin Oscillator with Dissipation

The fundamental properties of parametrically excited oscillatory systems of the Kochin oscillator type with double degeneracy of frequencies are investigated. The qualitative phenomenon of their absence is established for arbitrarily small actions of a dissipative nature. As a result, the resonance motions of the first mode prove to be relatively more substantial; the excitation of subsequent odd modes is difficult in the applied aspect and requires a significant increase in the eigenvalue of the corresponding parameter.     

On the development of plasma relativistic microwave oscillator without strong magnetic field

A method for generating microwave pulses with a power of ～1 GW and a frequency controlled in a band from 2 to 15 GHz during the interaction of relativistic electrons with plasma without strong magnetic field is proposed in the numerical model. The combination of a broadband plasma relativistic microwave oscillator and a monochromatic magnetically insulated transmission line oscillator (MILO) allows the development of a device combining advantages of both prototypes.     

A double quantum well in a driving laser field

The dynamic effect of electrons in a double quantum well under the influence of a monochromatic driving laser field is investigated. Closed-form solutions for the quasienergy and Floquet states are obtained with the help ofSU (2) symmetry. For the case of weak interlevel coupling, explicit expressions of the quasienergy are presented by the use of perturbation theory, from which it is found that as long as the photon energy is not close to the tunnel splitting, the electron will be confined in an initially occupied eigenstate of the undriven system during the whole evolution process. Otherwise, it will transit between the lowest two levels in an oscillatory behavior.     

A switching mechanism of the default-mode network in the brain at criticality

Many works confirm the anti-correlations between the default mode network (DMN) and the central-executive network (CEN) in the brain. However, the switching mechanism of the DMN itself is still lack of understanding from the viewpoint of neural network dynamics. Here we simulate the DMN with the Hindmarsh-Rose (HR) neuron model on the small-world network. We model the state of oscillator death and oscillatory firing as the inhibitory state and the activated state, respectively. We find that the DMN can regenerate from the inhibitory state when the input current of only one synapse is cut off at criticality.     

一种新型的高功率高频率同轴渡越时间振荡器

 提出了一种高频率和高功率的渡越时间振荡器,并且对其进行了理论和数值研究。这种振荡器采用同轴结构，功率容量大，不需要外加引导磁场聚焦电子束，波束相互作用区短，保持了传统渡越时间振荡器在结构上的简单性和输出信号的稳定性；运用电压为225kV和电流为11kA的电子束进行模拟，在X波段获得了峰值功率为1.4GW，频率为8.335GHz的微波输出。     

Wave Instability and Spatiotemporal Chaos in Reaction-Diffusion System with Oscillatory Dynamics

We investigate the Turing-like wave instability of the uniform oscillator in oscillatory mediums using theoretical and numerical methods. A propagating wave pattern originated at the corner of the system emerges when the uniform oscillator becomes unstable via Turing-like wave instability. Bifurcations from periodically propagated wave patterns to quasi-periodically propagated wave patterns, then to spatiotemporal chaos occur, as the system size increases from the instability threshold of the uniform oscillator.     

Hydrodynamic simulation of chaotic dynamics in InGaAs oscillator in terahertz region

Hydrodynamic calculations of the chaotic behaviors in n^+nn^+In0.53Ga0.47As devices biased in terahertz(THz)electric field have been carried out.Their different transport characteristics have been carefully investigated by tuning the n-region parameters and the applied ac radiation.The oscillatory mode is found to transit between synchronization and chaos,as verified by the first return map.The transitions result from the mixture of the dc induced oscillation and the one driven by the ac radiation.Our findings will give further and thorough understanding of electron transport in In0.53Ga0.47As terahertz oscillator,which is a promising solid-state THz source.     

Molecular dynamics study of effects of radius and defect on oscillatory behaviors of C60-nanotube oscillators

Using the micro-canonical ensemble, we investigate the oscillatory behaviors of some selected C60-nanotube oscillators by the classical molecular dynamics (MD) simulations method. The second-generation empirical bond-order potential and the van der Waals potential are used to describe bonding and nonbonding atomic interactions, respectively. In the process of simulation, two factors of the radius and vacancy defect of single-walled carbon nanotubes (SWCNTs) are discussed to investigate their effects on the oscillatory behaviors of C60-nanotube oscillators. The simulation results show that the energy dissipation of the C60-nanotube oscillator is sensitive to the radius and vacancy defect, and that the effect of the vacancy defect on the oscillatory behaviors of oscillator depends obviously on the radius of the outer tube. It is found that a single vacancy defect placed on the outer tube of the C60-(17,0) nanotube oscillator can significantly reduce energy dissipation. For C60-(18,0), C60-(19,0) and C60-(11,11) nanotube oscillators, however, the results show that an oscillator containing a vacancy defect is less stable than the one without defect.     

Synchronization and oscillator death in oscillatory media with stirring

The effect of stirring in an inhomogeneous oscillatory medium is investigated. We show that the stirring rate can control the macroscopic behavior of the system producing collective oscillations (synchronization) or complete quenching of the oscillations (oscillator death). We interpret the homogenization rate due to mixing as a measure of global coupling and compare the phase diagrams of stirred oscillatory media and of populations of globally coupled oscillators.     

Intrinsic noise and division cycle effects on an abstract biological oscillator

Oscillatory dynamics are common in biological pathways, emerging from the coupling of positive and negative feedback loops. Due to the small numbers of molecules typically contained in cellular volumes, stochastic effects may play an important role in system behavior. Thus, for moderate noise strengths, stochasticity has been shown to enhance signal-to-noise ratios or even induce oscillations in a class of phenomena referred to as "stochastic resonance" and "coherence resonance," respectively. Furthermore, the biological oscillators are subject to influences from the division cycle of the cell. In this paper we consider a biologically relevant oscillator and investigate the effect of intrinsic noise as well as division cycle which encompasses the processes of growth, DNA duplication, and cell division. We first construct a minimal reaction network which can oscillate in the presence of large or negligible timescale separation. We then derive corresponding deterministic and stochastic models and compare their dynamical behaviors with respect to (i) the extent of the parameter space where each model can exhibit oscillatory behavior and (ii) the oscillation characteristics, namely, the amplitude and the period. We further incorporate division cycle effects on both models and investigate the effect of growth rate on system behavior. Our results show that in the presence but not in the absence of large timescale separation, coherence resonance effects result in extending the oscillatory region and lowering the period for the stochastic model. When the division cycle is taken into account, the oscillatory region of the deterministic model is shown to extend or shrink for moderate or high growth rates, respectively. Further, under the influence of the division cycle, the stochastic model can oscillate for parameter sets for which the deterministic model does not. The division cycle is also found to be able to resonate with the oscillator, thereby enhancing oscillation robustness. The results of this study can give valuable insight into the complex interplay between oscillatory intracellular dynamics and various noise sources, stemming from gene expression, cell growth, and division.     

650 GHz正弦波导返波管的模拟计算

提出了一种利用正弦波导慢波结构设计的太赫兹频段大功率返波管的新方案。3维粒子模拟研究结果显示:在20 kV的工作电压和5 mA的驱动电流下,该返波管在645.9 GHz频率处将具有1.55 W的峰值功率输出,互作用效率为1.55%,频谱纯净,输出模式为TE10模。通过在15～25 kV之间进行电压调谐,可获得80 GHz的调谐带宽,且峰值输出功率都在1 W以上。     

The parametric Doppler effect in a medium with Lorentz dispersion

The frequency conversion under the parametric Doppler effect, which occurs when weak probe radiation reflects off from a refractive index inhomogeneity induced in a nonlinear medium by intense pumping, has been analyzed. Under these conditions, the frequency dispersion of the medium is assumed to correspond to the single Lorentz oscillator model. It is shown that the presence of resonance and a spectral range forbidden for propagation may lead to a complex Doppler effect, where the incident radiation is single-frequency but the reflected radiation consists of two or three monochromatic waves, one of which has a phaseconjugated wavefront.     

Model of a proposed superconducting phase slip oscillator: a method for obtaining few-photon nonlinearities

We theoretically investigate a driven oscillator with the superconducting inductance subject to quantum phase slips (QPS). We find uncommon nonlinearities in the proposed device: they oscillate as a function of the number of photons N with a local period of the order of √N. We prove that such nonlinearities result in multiple metastable states encompassing few photons and study oscillatory dependence of various responses of the oscillator. Such nonlinearities enable new possibilities for quantum manipulation of photon states and very sensitive measurements to confirm the coherence of phase slips.     

Oscillatory nonequilibrium Nambu systems: the canonical-dissipative Yamaleev oscillator

We study the emergence of oscillatory self-sustained behavior in a nonequilibrium Nambu system that features an exchange between different kinetical and potential energy forms. To this end, we study the Yamaleev oscillator in a canonical-dissipative framework. The bifurcation diagram of the nonequilibrium Yamaleev oscillator is derived and different bifurcation routes that are leading to limit cycle dynamics and involve pitchfork and Hopf bifurcations are discussed. Finally, an analytical expression for the probability density of the stochastic nonequilibrium oscillator is derived and it is shown that the shape of the density function is consistent with the oscillator properties in the deterministic case.     

Structure of the control parameter space for a nonautonomous piecewise linear oscillator

The variation of the structure of the control parameter space for a nonautonomous nonlinear oscillator is demonstrated with a harmonically excited nonautonomous oscillatory circuit with a piecewise linear capacitance.     

Modeling and visualization of quantum bifurcations in phase space

We investigate quantum-mechanical counterpart of a classical instability in a phase space by the numerical method of quantum trajectories with moving basis. As an application the model of coupled two oscillators driven by a monochromatic force in the presence of dissipation (intracavity second harmonic generation) is analyzed. The system of interest is characterized by two bifurcations leading to ranges of instability: the Hopf bifurcation which connects a steady state dynamics of the oscillatory modes to a self-pulsing temporal dynamics and the bifurcation of the period-doubling. The both two regimes are analyzed on the framework of the semiclassical phase trajectories and the Wigner functions of the oscillatory modes in phase space.     

Resurgence of oscillation in coupled oscillators under delayed cyclic interaction

This paper investigates the emergence of amplitude death and revival of oscillations from the suppression states in a system of coupled dynamical units interacting through delayed cyclic mode. In order to resurrect the oscillation from amplitude death state, we introduce asymmetry and feedback parameter in the cyclic coupling forms as a result of which the death region shrinks due to higher asymmetry and lower feedback parameter values for coupled oscillatory systems. Some analytical conditions are derived for amplitude death and revival of oscillations in two coupled limit cycle oscillators and corresponding numerical simulations confirm the obtained theoretical results. We also report that the death state and revival of oscillations from quenched state are possible in the network of identical coupled oscillators. The proposed mechanism has also been examined using chaotic Lorenz oscillator.