Chlorite dismutases (Clds) are heme b-containing oxidoreductases that convert chlorite to chloride and dioxygen. In this work, the thermodynamics of the one-electron reduction of the ferric high-spin forms and of the six-coodinate low-spin cyanide adducts of the enzymes from Nitrobacter winogradskyi (NwCld) and Candidatus "nitrospira defluvii" (NdCld) were determined through spectroelectrochemical experiments These proteins belong to two phylogenetically separated lineages that differ subunit (21.5 and 26 kDa, respectively) and, oligomeric dimeric and pentameric, respectively) structure but exhibit similar chlorite degradation activity. The E-o' values for free and Cyanide-bound proteins :were, determined to be -119. and, -397 mV for NwCld and -113 and -404 mV for NdCld, respectively (pH 7.0, 25 degrees C). Variable-temperature,spectroelectrochemical experiments revealed that the oxidized state of both proteins is enthalpically stabilized. Molecular dynamics simulations suggest that changes in the protein structure are negligible, whereas solvent reorganization is mainly responsible for the increase in entropy during the redox reaction. Obtained data are discussed with respect to the known structures of the two Clds and the proposed, reaction mechanism.

Absent exogenous ROS input, and under conditions that retard hydrogen donor autoxidation, PO reactions can manifest low frequency bursting whereby pulses of ROS are produced at clinically significant intervals.]]>

In this paper, we elucidate the extremely complicated bifurcation structure of a weakly driven relaxation oscillator by focusing on chaos, and notably, on complex mixed-mode oscillations (MMOs) generated in a simple dynamical model. Our model uses the Bonhoeffer-van der Pol (BVP) oscillator subjected to a weak periodic perturbation near a subcritical Andronov-Hopf bifurcation (AHB). The mechanisms underlying the chaotic dynamics can be explained using an approximate one-dimensional map. The MMOs that appear in this forced dynamical model may be more sophisticated than those appearing in three-variable slow-fast autonomous dynamics because the approximate one-dimensional mapping of the dynamics used herein is a circle map, whereas the one-dimensional first-return map that is derived from the three-variable slow-fast autonomous dynamics is usually a unimodal map. In this study, we generate novel bifurcations such as an MMO-incrementing bifurcation (MMOIB) and intermittently chaotic MMOs. MMOIBs trigger an MMO sequence that, upon varying a parameter, is followed by another type of MMO sequence. By constructing a two-parameter bifurcation diagram, we confirmed that MMOIBs occur successively. According to our numerical results, MMOIBs are often observed between two neighboring MMOs. Numerically, MMOIBs may occur as many times as desired. We also derive the universal constant of the associated successive MMOIBs. The existence of the universal constant suggests that MMOIBs could occur infinitely many times. Furthermore, intermittently chaotic MMOs appear in this dynamical circuit. The intermittently chaotic MMOs relate to a type of intermittent chaos that resembles MMOs at first glance, but includes rare bursts over a long time interval. Complex intermittently chaotic MMOs of various types are observed, and we clarify that the intermittently chaotic MMOs are generated by crisis-induced intermittency. (C) 2012 Elsevier B.V.

This article concerns the phenomenon of Mixed-Mode Bursting Oscillations (MMBOs). These are solutions of fast-slow systems of ordinary differential equations that exhibit both small-amplitude oscillations (SAOs) and bursts consisting of one or multiple large-amplitude oscillations (LAOs). The name MMBO is given in analogy to Mixed-Mode Oscillations, which consist of alternating SAOs and LAOs, without the LAOs being organized into burst events. In this article, we show how MMBOs are created naturally in systems that have a spike-adding bifurcation or spike-adding mechanism, and in which the dynamics of one (or more) of the slow variables causes the system to pass slowly through that bifurcation. Canards are central to the dynamics of MMBOs, and their role in shaping the MMBOs is two-fold: saddle-type canards are involved in the spike-adding mechanism of the underlying burster and permit one to understand the number of LAOs in each burst event, and folded-node canards arise due to the slow passage effect and control the number of SAOs. The analysis is carried out for a prototypical fourth-order system of this type, which consists of the third-order Hindmarsh-Rose system, known to have the spike-adding mechanism, and in which one of the key bifurcation parameters also varies slowly. We also include a discussion of the MMBO phenomenon for the Morris-Lecar-Terman system. Finally, we discuss the role of the MMBOs to a biological modeling of secreting neurons.

热声发动机的起振过程是一个产生并维持自激振荡的过程, 研究热声自激振荡机理有助于进一步了解热声效应的实质. 根据热声网络理论, 建立了驻波热声发动机的整机网络. 将热声网络比拟成电网络, 利用厄米特式计算了输入热声网络的视在功流, 功流平衡对应自激, 在角频率虚部为零的情况下计算了热声发动机的阈值温度和运行频率. 结果表明, 计算值与实验值符合得较好, 充气压力与阈值温度和运行频率的耦合关系大致相同. 所得结论有助于进一步探究热声效应机理以及热声发动机系统的优化设计.

The onset process of a thermoacoustic prime mover is a process generating and maintaining self-excited oscillation. It is helpful to have a better understanding of thermoacoustic effect by investigating the mechanism of thermoacoustic self-excited oscillation. The network model of a representative standing-wave thermoacoustic prime mover is established on the basis of thermoacoustic network theory. Comparing thermoacoustic network to electric network, the apparent power flux which inputs the thermoacoustic network is calculated by using the Hermitian form. In the network, the apparent power flux balance means establishing the self-excited oscillation. Based on the above, the threshold temperature and operation frequency of a thermoacoustic prime mover are calculated on condition that the imaginary part of angular frequency is equal to zero. The calculation results are in good agreement with the experimental results. For the coupling relationship of the main pressure with the threshold temperature and operation frequency, the calculation results are roughly close to the experimental results. The obtained results are helpful for the further studying of the thermoacoustic effect and the optimal designing of a thermoacoustic system.

考虑旋转机械中两种频率不同的周期参数激励同时存在对其传动系统的影响，基于拉格朗日方程，建立一类含准周期参激刚度和摩擦阻尼的非线性扭振系统的动力学方程。运用多尺度法对该扭振系统进行求解，得到系统在1/2亚谐波主参数共振下的幅频特性方程和分岔响应方程。在此基础上，研究了当两种周期参激的频率相差较大时非线性扭振系统的周期簇发现象，分析了快变参激和慢变参激对扭振系统的周期簇发的影响。通过数值仿真，给出了产生周期簇发的参数取值区域。在该区域内系统发生静息态与激发态的相互转迁，当快变激励的幅值减小时，激发态区域扩大，簇发的时间延长，通过调节慢变参激幅值会改变系统簇发的类型和轨迹]]>

Considering the effects caused by the coexist of two different periodic parametric excitation in rotary machinery driving system, the dynamical equation of nonlinear torsional vibration system is established based on Lagrange equation. The model contains quasi-periodic parametrically excited stiffness and friction damping. The amplitude-frequency characteristic equation and bifurcation response equation are obtained by solving the torsional vibration system using multi-scale method. On this basis, the periodic bursting of the nonlinear torsional vibration system is studied when the two periodic parametrical excitations have large difference gap. The influence of fast-varying parametrical excitation and slow-varying parametrical excitation on the periodic bursting of the torsional vibration system is analyzed. The parameter regions of periodic bursting are given by numerical simulation. The mutual transition between the quiescent state and the spiking state of the system occurs in this region, when the amplitude of the fastly varying excitation reduces, the area of spiking state extends, the time of bursting prolongs. The bursting type and trajectory of the system can be changed from regulating amplitude of slow-varying parametric excitation.]]>

2 root 3/9, while if gamma