Adaptive coupling-enhanced spiking synchronization in Newman-Watts neuronal networks with time delays

In this paper, we study how adaptive coupling with time-periodic growth speed (TPGS) affects the spiking synchronization of weighted adaptive Newman-Watts Hodgkin-Huxley neuron networks with time delays. It is found that the neuronal spiking intermittently exhibits synchronization transitions between desynchronization and in-phase synchronization or anti-phase synchronization as TPGS amplitude or frequency is varied, showing multiple synchronization transitions. These transitions depend on the values of time delay and can occur only when time delay is close to those values that can induce synchronization transitions when the growth speed is fixed. These results show that the adaptive coupling with TPGS has great influence on the spiking synchronization of the neuronal networks and thus plays a crucial role in the information processing and transmission in neural systems.     

BaTiO3/ IPNs的制备及介电性能与阻尼性能的相关性

BaTiO₃/ Interpenetrating Polymer Networks (IPNs) composites were prepared by combination of BaTiO₃nanocrystal in tetragonal system and polyurethane(PU) / unsaturated polyester (UP) interpenetrating polymer networks (IPNs). The tetragonal nanocrystalline BaTiO₃was obtained by hydrothermal process and calcination at 1 200 ℃. The prepared materials were polarized with high voltage and small current, and protected by silicon oil. The morphology of BaTiO₃/ IPNs and the effect of combination of BaTiO₃on the damping behavior of IPNs were studied. The relationship between damping performance and dielectric charater was also discussed in terms of dielectric constant and dielectric loss measured. The results show that the areas under loss modulus (E″) and the values of loss factors (tanδ) were both increased by combination of BaTiO₃into IPNs system. The maximum value of E″ increased above 100 MPa compared with pure IPNs and the extent increased more remarkably after polarizing process. The main and shoulder peak of tanδ curves both moved toward higher temperature ranges, and the temperature ranges of tanδ>0.3 was higher than 100 ℃. Moreover, through polarizing process, the composites exhibited synergistic action caused by elastomeric damping, interfacial abrasive damping and piezoelectric damping mechanisms. The relationship study of damping property and dielectric characters showed that the temperature ranges exhibited excellent consistency of maximum dielectric loss and modulus with damping loss factor.     

Novel Transient Species of DNA Bases From Laser Photolysis

The laser photochemistry and photosensitization of DNA bases were carried out by using a nanosecond kinetic spectroscopy. A novel triplet state of thymine and its OH adduct were observed in N_2 and N_2O saturated aqueous solution respectively. The transient absorption spectra of triplet cytosine, cytidine and deoxycytidine monophosphoric acid were observed for the first time. Triplet guanosine was confirmed and its pK, value, 8.7, was obtained. Kinetic studies of the growth-decay of the above transient species were performed and their reaction mechanisms were elucidated in detail.     

Surface acoustic wave sensor system applied to the kinetic study of urease in plant seeds

A new type of the surface acoustic wave (SAW) sensor system was delivered. Ure-ase from several kinds of plant seeds was extracted with different extracting solvents. The urease activity, Michaelis constant and other kinetic parameters were estimated for the first time by means of the new device-SAW sensor system. Some factors such as pH, temperature, activators and inhibitors are also discussed. The method can be applied to the determination of urea content in human urine and the experimental results consist with those reported.     

REVERSE ATOM TRANSFER RADICAL POLYMERIZATION OF STYRENE WITH COPPER-BASED CATALYST

 "Living"/controlled radical polymerization of styrene was carried out with diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS)/CuCl₂/bipyridine (bipy) initiation system at 120℃. The molecular weights of resultant PSt increased with the monomer conversion and the polydispersities were in the range of 1.37 ～ 1.52. A linear ln([M]o/[M])versus time plot was also obtained indicating the constant concentration of growing radicals during the polymerization with this initiation system. End group analysis by ¹H-NMR spectroscopic studies showed that the end groups of the polymer obtained is cω-functionalized by a chlorine group from the catalyst and a-functionalized by a (carbethoxy-cyano-phenyl)methyl group from the fragments of the initiator. Having C1 atom at the chain end, the PSt obtained can be used as a macroinitiator to promote a chain-extension reaction with fresh St and block copolymerization reaction with a second monomer, such as methyl methacrylate, in the presence of CuC1/bipy catalyst via a conventional ATRP process.     

STUDY ON CASTOR OIL POLYURETHANE/POLY (METHYL METHACRYLATE) AB CROSSLINKED POLYMERS

Castor oil polyurethane/poly(methyl methacrylate) AB crosslinked polymers (ABCP) were synthesized by free radical copolymerization of MMA and vinyl-terminated castor oil polyurethane which was obtained from isocyanate-terminated castor oil polyurethane and hydroxyethyl methacrylate The mechanical properties, transition and relaxation, as well as compatibility and morphology of the ABCP were investigated by changing the component. The results show that the ABCP is a semicompatible system and the compatibility of the two components decreases with increasing content of the hard segment. The mechanical and damping properties of the ABCP are obviously superior to that of their homopolymers. The damping value is mainly controlled by cross[ink density of the ABCP but the T-g value by component.     

Rebinding kinetics of dissociated amino acid ligand and carbon monoxide to ferrous microperoxidase-11 in aqueous solution

The rebinding kinetics of an amino acid ligand to ferrous microperoxidase-11 (MP11) after photolysis of aggregated ferrous MP11 was measured in aqueous solution with femtosecond transient visible absorption spectroscopy. The kinetics of CO rebinding to ferrous MP11 after photolysis of MP11CO was also measured in aqueous solution with femtosecond transient visible absorption spectroscopy. From these measurements, we found that either Val-11 or Lys-13 rebinds to ferrous MP11 exponentially with an 8 picosecond time constant in aggregated ferrous MP11 solution and that CO rebinds to ferrous MP11 nonexponentially with subnanosecond time scale in MP11CO solution. The kinetics of both the amino acid and CO rebinding to ferrous MP11 in MP11 system mimics that in carbon monoxide oxidation activator protein (CooA) or carboxymethyl cytochrome c (CmCytC) system. We also measured the kinetics of CO rebinding to ferrous MP11 in aqueous solution at different MP11CO concentrations and found that MP11CO concentration has an obvious effect on the kinetics of CO rebinding to ferrous MP11, where both the germinate yield and rate of CO rebinding to ferrous MP11 increase with the increase of MP11CO concentration. These findings suggested that the picosecond amino acid ligand rebinding process could disturb the proximal heme-ligand structure that possibly leads to the subnanosecond CO rebinding kinetics in MP11CO, CooACO and CmCytCCO systems.     

Kinetics of Methanol Carbonylation to Methyl Formate Catalyzed by Sodium Methoxide

Kinetics of synthesis of methyl formate from carbon monoxide and methanol, using sodium methoxide as the catalyst and pyridine as the promoter in a batch reactor, was studied. Kinetic parameters such as the apparent reaction orders, the rate constant and the apparent activation energies were obtained. The experimental results showed that both the reaction orders with respect to CO and methanol equal to 1, the general reaction kinetic equation is (-r)=-dp(CO)/dt=k, p(CO).[MeOH], and the rate constant is k=8.82×10~6exp [-61.19×10~3/(R·T)] in the presence of pyridine. The apparent activation energies had decreased 6.44 kJ/mol and the rate constant had increased more than 1.5 times when pyridine was used as the promoter in the catalyst system.     

Dehydration of glucose into 5-hydroxymethylfurfural in SO_3H-functionalized ionic liquids

The continuous dehydration of D-glucose into 5-hydroxymethylfurfural（HMF） was carried out under mild conditions,using SO3H-functionalized acidic ionic liquids as catalysts and H2O-4-methyl-2-pentanone（MIBK） biphasic system as solvent.High glucose conversion of 97.4% with HMF yield of 75.1%was obtained at 120 8C for 360 min,also,small amounts of levulinic acid（LA） and formic acid were generated.Generally,the dosage of catalyst and the initial content of glucose influenced the reaction significantly; the HMF selectivity decreased with the excessive elevation of temperature and prolonging of time; and water content in the system had a negative effect on the reaction.The ionic liquid catalyst could be recycled and exhibited constant activity for five successful runs.This paper provided a new strategy for HMF production from glucose.     

Synthesis and Triethylamine‐catalyzed Cyclization Reaction of 4‐Pentyne‐1,3‐dione System Having Various Substituents

4-Pentyne-1,3-dione system having various substituents was synthesized in two steps and the cyclization behavior of the obtained 1,3-dicarbonyl compounds was examined. γ-Pyrones and 2-alkylidene-2,3-dihydro-3-furanones were obtained by the triethylamine-catalyzed cyclization of the 4-pentyne-1,3-dione system having a diketone moiety. Furthermore, a phenol derivative was obtained in the case of 4-pentyne-1,3-dione system having an ester moiety. Thus, it was found that the kind of substituents in the 4-pentyne-1,3-dione system remarkably influenced the selectivity in the cyclization.     

Chaos Synchronization in the Belousov-Zhabotinsky Chemical Reaction by Self-Adaptive Parameter Adjustment Scheme

Employing the self-adaptive parameter adjustment scheme, the chaotic dynamical behaviors in the coupled Belousove-Zhabotinsky-CSTR chemical system were investigated numerically. The confirmation of synchronization is using the criteria of maximum transverse Lyapunov exponent. The results show that when all the variables are involved in the parameter adjustment rule, the chaos synchronization between the response and the target systems were obtain. However, as only some of the variables can be detected easily in the real experiment, there are difficulties in employing this scheme experimentally. Therefore, that scheme to investigate the role of single variable separately were modified. The results show that no chaos synchronization can be obtained when Br- and HBrO2 are used separately, except when Ce4+ and BrMA are used. However, there is no easy way to detect BrMA in the experiment, Ce4+ becomes the unique feasible variable involved in the adjustment role. Besides, the synchronization efficiency of different combinations of stiff constant and damping constants has been studied by means of synchronization-arriving time.     

Belousov-Zhabotinsky化学体系中超混沌及其同步的研究

曾有报道在Belousov-Zhabotinsky (BZ)体系的实验研究中未实现超混沌。但 通过不同类型的变量耦合方式,我们在该体系的Montanatar模型中得到了超混沌发 现无论采用何种耦合方式,只要耦合强度足够小,均能得到超混沌。另外,对两个 所产生的超混沌BZ体系,在全变量耦合、双变量耦合及K-B空间标量耦合法的策略 下,均实现了同步调制,并且从横截Lyapunov指数判据理论给予验证。探索了个别 状态变量在耦合中对同步所起的作用。通过双变量耦合发现[Ce~(4+)]不起作用; 通过K-B空间标量耦合法发现只有[Br~-]和[HBrO_2]的线性组合能起作用,可能由 于它们出现在同一个基元反应中。     

Identification of two aromatic isomers between 3- and 4-hydroxy benzoic acid by their perturbation on the potential oscillations of a Belousov-Zhabotinsky system

A novel method for identification of two aromatic isomers of mono hydroxy benzoic acid (HBA) was reported by using their different perturbation effects on the potential oscillations of a Belousov-Zhabotinsky (BZ) system. In such a system, a macrocyclic complex of Cu [CuL](ClO₄)₂ was used as catalyst in which ligand L is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. To the BZ system, 3-hydroxy benzoic acid (3-HBA) could temporarily quench and regenerate potential oscillations with damping characters after inhibition time (t_in) while 4-hydroxy benzoic acid (4-HBA) could only change the oscillation amplitude (ΔA) to give damping oscillations with no inhibition time. Thus, these two isomers of HBA were identified. Reaction mechanisms of BZ have been proposed by FKN model. An explanation of perturbation mechanism is that, although 3-HBA reacted with BrO₂ while 4-HBA reacted with BrO₃⁻, they all produced 1,4-quinone.     

Rebirth of a dead Belousov-Zhabotinsky oscillator

Long time behaviors of the Belousov-Zhabotinsky (BZ) reaction are experimentally analyzed in a closed reactor. The amplitude of the oscillation is suddenly damped after about 10 h. After about 5-20 h, the dead oscillator is suddenly restored with nearly the same amplitude as before it stopped its oscillation for certain values of the concentrations of sodium bromate and malonic acid (MA). With the other domains of the concentrations, the oscillator simply damps and never restores its oscillation. The phase diagram of the different types of damping behaviors as a function of the concentrations is obtained.     

Transient response of a Brownian particle with general damping

We study the transient response of a Brownian particle with general damping in a system of metastable potential well. The escape rate is evaluated as a function of time after an infinite wall is removed from the potential barrier. It takes a relaxation time for the rate to reach its limit value and this rate relaxation time differs from the relaxation time of the majority of the probability around the bottom of the potential well. The rate relaxation time is found to depend on the temperature as well as the damping constant. It involves the diffusion time and the instanton time, in general agreement with recent studies of the overdamped case by Bier et al. [Phys. Rev. E 59, 6422 (1999)].     

Evaluation of coupling terms between intra- and intermolecular vibrations in coarse-grained normal-mode analysis: does a stronger acid make a stiffer hydrogen bond?

Using theory of harmonic normal-mode vibration analysis, we developed a procedure for evaluating the anisotropic stiffness of intermolecular forces. Our scheme for coarse-graining of molecular motions is modified so as to account for intramolecular vibrations in addition to relative translational/rotational displacement. We applied this new analytical scheme to four carboxylic acid dimers, for which coupling between intra- and intermolecular vibrations is crucial for determining the apparent stiffness of the intermolecular double hydrogen bond. The apparent stiffness constant was analyzed on the basis of a conjunct spring model, which defines contributions from true intermolecular stiffness and molecular internal stiffness. Consequently, the true intermolecular stiffness was in the range of 43-48 N m(-1) for all carboxylic acids studied, regardless of the molecules' acidity. We concluded that the difference in the apparent stiffness can be attributed to differences in the internal stiffness of the respective molecules.     

Transient complex oscillations in a closed chemical system with coupled autocatalysis

In this study, hydroquinone was introduced to the classic Belousov-Zhabotinsky (BZ) reaction to build up coupled autocatalytic feedbacks. Various complex dynamical behaviors including successive period-adding bifurcations, irregular oscillations, and frequency modulations were observed in the coupled reaction system. Not only the complexity of oscillations but also the time period during which complex oscillations persist were found to depend greatly on the initial concentration of hydroquinone, which was expected to manifest the coupling strength in the studied system. Dependence of the observed transient complex oscillations on concentrations of ferroin, sulfuric acid, bromate, and malonic acid was also characterized systematically. Numerical simulations with a modified BZ model via incorporating reactions involving hydroquinone and products of hydroquinone qualitatively reproduced the influence of hydroquinone seen in experiments.     

Loss of coherence in a population of diffusively coupled oscillators

The authors investigate the relationship between the natural frequency distribution of diffusively coupled chemical oscillators and their entrainment by pacemakers. The system consists of micrometer-sized catalyst beads which are coupled to their neighbors by diffusion of the activator/inhibitor species through the catalyst-free Belousov-Zhabotinsky (BZ) reaction solution. The frequency distribution is measured as a function of the beads' number of neighbors. With the maximum number of neighbors, either target waves or disordered patterns are observed in the reaction domain and there is a shift to higher frequencies than those observed in the natural frequency distribution. The loss of coherence between neighbor oscillators is quantified by a decrease in the phase synchronization index. The experimental results are reproduced in simulations which demonstrate that the decrease in the degree of synchronization is correlated with the appearance of a small fraction of permanently excited beads in BZ populations of high mean frequency and/or large width.     

Periodic, Mixed-Mode, and Chaotic Regimes in the Belousov–Zhabotinskii Reaction Catalyzed by Ferroin

The periodic, mixed-mode, and chaotic regimes in the ferroin-catalyzed Belousov–Zhabotinskii (BZ) reaction observed in a continuous stirred tank reactor (CSTR) reactor at various flow rates were experimentally studied. It was found that an increase in the flow rate resulted in the appearance of various complex oscillations. The possibility of the numerical simulation of experimentally observed asymptotic mixed-mode oscillations and chaotic regimes with the use of a kinetic scheme that includes experimental rate constants of each step of the ferroin-catalyzed BZ reaction was first demonstrated. The reaction scheme adequately describes the bifurcation sequence of experimentally observed oscillating regimes.     

Coexistence of wave propagation and oscillation in the photosensitive Belousov-Zhabotinsky reaction on a circular route

The photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated on a circular ring, which was drawn using computer software and then projected on a film soaked with BZ solution using a liquid-crystal projector. Under the initial conditions, a chemical wave propagated with a constant velocity on the black ring under a bright background. When the background was rapidly changed to dark, coexistence of the oscillation on part of the ring and propagation of the chemical wave on the other part was observed. These experimental results are discussed in relation to the nature of the photosensitive BZ reaction and theoretically reproduced based on a reaction-diffusion system using the modified Oregonator model.