表面催化反应模型中关联噪声诱导非平衡相变

建立含有关联噪声的双分子-单分子(DM)表面催化反应延迟反馈模型,该模型能同时显示一级和二级非平衡动力学相变,即在一级和二级非平衡动力学相变之间的反应窗口展现.讨论双分子在DM延迟反馈模型中两种吸附机制,即局域和随机吸附模型.研究结果表明:1)外部噪声及两噪声关联性致使反应窗口的宽度收缩;2)内部噪声对非平衡动力学相变行为的影响依赖两噪声关联性,即当两噪声负关联,内部噪声致使反应窗口的宽度变宽;而当两噪声正关联时,内部噪声致使反应窗口的宽度收缩;3)关联噪声致使反应窗口变化对DM模型中一级和二级非平衡动力学相变研究具有重要的科学意义.     

Influence of chemical and phase composition on the emergence of the electroplastic effect in titanium alloys

The nature of differently directed stress jumps observed in stress-strain diagrams with tension under a pulsed current is analyzed. It is shown that the amplitude and direction of stress jumps are determined by competition between the electroplastic effect (EPE) and phase transformation, while the EPE is a structurally sensitive property. The EPE diminishes when the structure is refined and even disappears in the nanocrystalline state.     

Experimental observations of complex dynamical behavior during a chemical reaction

We show that the Belousov-Zhabotinsky reaction can display a great variety of dynamical behaviors, most of them being accounted for in term of intermittency.     

Dynamic control and information processing in chemical reaction systems by tuning self-organization behavior

Specific external control of chemical reaction systems and both dynamic control and signal processing as central functions in biochemical reaction systems are important issues of modern nonlinear science. For example nonlinear input-output behavior and its regulation are crucial for the maintainance of the life process that requires extensive communication between cells and their environment. An important question is how the dynamical behavior of biochemical systems is controlled and how they process information transmitted by incoming signals. But also from a general point of view external forcing of complex chemical reaction processes is important in many application areas ranging from chemical engineering to biomedicine. In order to study such control issues numerically, here, we choose a well characterized chemical system, the CO oxidation on Pt(110), which is interesting per se as an externally forced chemical oscillator model. We show numerically that tuning of temporal self-organization by input signals in this simple nonlinear chemical reaction exhibiting oscillatory behavior can in principle be exploited for both specific external control of dynamical system behavior and processing of complex information.     

Observation of a chemical reaction reversibly triggered by a structural phase transition

Two distinct radical species, (AsO₄)^4- and (AsO₃)^2-, created by irradiation in crystals of ND₄D₂AsO₄, undergo (taking into account the deuterons) the following chemical reaction: AsO₃D^- + OD^- ? AsO₄D^2-₂The effect occurs at the antiferroelectric-paraelectric phase transition of the compound. Its essential feature is that the reaction is completely reversible i.e. that it can be triggered by the phase transition, the direction of the reaction depending on the direction of passage of the Curie point. An analogy is presented with a biological process, namely the second step of the cooperative binding of oxygen on haemoglobin.     

Influence of chemical and physical surface heterogeneity on chemical reaction equilibria in carbon micropores

Recent simulation results are presented for the equilibrium yield of the ammonia synthesis reaction in various model microporous carbons. It is found that the reaction equilibria within the micropores is affected by many factors, including pore size, pore shape, connectivity, surface roughness, and surface chemical activation. In order to probe these effects, reactive Monte Carlo simulations of the reaction were performed in several microporous carbon models: smooth slit-shaped carbon pores, a realistic carbon model generated from experimental diffraction data, single-walled carbon nanotubes, and smooth slit-shaped pores activated by carboxyl surface groups. The simulations show that the ammonia conversion is most sensitive to the carbon pore width and to the amount of surface chemical activation. Effects of surface corrugation and pore connectivity on the equilibrium reaction yield are minimal.     

Structure and phase composition of BiFeO3 : La films synthesized by chemical deposition from solutions

The transmission electron microscopy, energy-dispersive, and X-ray powder diffraction analyses have been used to study the changes in the structure and phase composition of lanthanum-doped BiFeO₃ and undoped BiFeO₃ thin films synthesized by chemical deposition from solutions and annealed in the temperature range 500?C700°C. It has been found that the temperature of the onset of crystallization with formation of the rhombohedral phase of BiFeO₃ is 500°C. As the annealing temperature increases, the phase composition of the film is changed: the Bi_3.43Fe_0.57O₆ and Bi₂Fe₄O₉ phases are formed. The lanthanum doping increases the crystallization temperature to 550°C; in this case, the film remains single-phase to T = 700°C.     

Stability analysis,dynamical behavior and analytical solutions of nonlinear fractional differential system arising in chemical reaction

In chemical reaction process, mathematical modeling of certain experiments lead to Brusselator system of equations. In this article, the dynamical behaviors of reaction Brusselator system with fractional Caputo derivative is studied. Also, Its stability and chaotic attractors of the commensurate fractional dynamical Brussleator system are discussed. The fractional derivative operators are nonlocal and having weak singularity as compare to the classical derivative operators. To find the analytical solutions of fractional dynamical systems is a big challenge, therefore, new techniques are worth demanding to solve such problems. To overcome this difficulty, the optimal homotopy asymptotic method is extended in this study to the system of fractional partial differential equations. A numerical example is presented as well to investigate the convergence, performance, and effectiveness of this method.     

Collective behavior of active Brownian particles: From microscopic clustering to macroscopic phase separation

A pedagogical introduction to the analytical treatment of the collective behavior of active (self-propelled) Brownian particles with short-ranged interactions is presented. The treatment is based on established concepts from the theories of simple liquids and pattern formation. It is shown how microscopic clustering due to self-blocking of directed particle motion leads to macroscopic phase separation described by effective equilibrium concepts holding on length scales larger than the persistence length of the direction motion.     

Role of sticking coefficients on kinetic phase transitions in catalytic reactions

The kinetic model for irreversible COO₂ surface reaction proposed by Ziff et al. is extended to include the variable sticking coefficients of carbon-monoxide (S_CO) and oxygen (S_O). For all values of S_O and S_CO a steady reactive state (SRS) is ob unless one of them is zero. The same is true for the NOCO reaction. These results are easily understood in terms of the adsorption rates of the reacting agents.     

TiO2 chemical vapor deposition on Si(111) in ultrahigh vacuum: Transition from interfacial phase to crystalline phase in the reaction limited regime

The interaction between the metal organic precursor molecule titanium(IV) isopropoxide (TTIP) and three different surfaces has been studied: Si(111)-(7 × 7), SiO_x/Si(111) and TiO₂. These surfaces represent the different surface compositions encountered during TTIP mediated TiO₂ chemical vapor deposition on Si(111). The surface chemistry of the titanium(IV) isopropoxide precursor and the film growth have been explored by core level photoelectron spectroscopy and x-ray absorption spectroscopy using synchrotron radiation. The resulting film morphology has been imaged with scanning tunneling microscopy. The growth rate depends on both surface temperature and surface composition. The behavior can be rationalized in terms of the surface stability of isopropoxy and isopropyl groups, confirming that growth at 573 K is a reaction limited process.     

Effect of reaction temperature on morphology and electrochemical behavior

LiCoO₂ and LiMn₂O₄ compounds were synthesized using two different methods, viz., low-temperature-aided hydrothermal and high-temperature-assisted co-precipitation method. Keeping the reaction parameters such as type of precursors chosen and the medium of reaction as same for both the hydrothermal and co-precipitation methods, the effect of temperature in producing LiCoO₂ and LiMn₂O₄ with varying physical as well as electrochemical properties has been studied. As expected, the effect of low-temperature-involved hydrothermal method rendered finer particles of nanocrystalline nature with minimum strain, and the high-temperature synthesis of co-precipitation method produced slightly enhanced particle size with an increased strain value. The effect of size-grown particles resulting from co-precipitation method exhibited inferior electrochemical properties such as increasing resistance of the cell upon cycling and a significant decline in capacity behavior, irrespective of LiCoO₂ or LiMn₂O₄ cathodes. On the other hand, hydrothermal synthesis of LiCoO₂ and LiMn₂O₄ has exhibited acceptable specific capacity with an admissible capacity fade behavior and negligible internal resistance of the cell, thus qualifying the same as better-performing cathodes. Hence, the effect of low temperature in producing LiCoO₂ and LiMn₂O₄ cathodes with facile intercalation and de-intercalation of lithium is demonstrated.     

Motility-induced phase separation and coarsening in active matter

Active systems, or active matter, are self-driven systems that live, or function, far from equilibrium – a paradigmatic example that we focus on here is provided by a suspension of self-motile particles. Active systems are far from equilibrium because their microscopic constituents constantly consume energy from the environment in order to do work, for instance to propel themselves. The non-equilibrium nature of active matter leads to a variety of non-trivial intriguing phenomena. An important one, which has recently been the subject of intense interest among biological and soft matter physicists, is that of the so-called “motility-induced phase separation”, whereby self-propelled particles accumulate into clusters in the absence of any explicit attractive interactions between them. Here we review the physics of motility-induced phase separation, and discuss this phenomenon within the framework of the classic physics of phase separation and coarsening. We also discuss theories for bacterial colonies where coarsening may be arrested. Most of this work will focus on the case of run-and-tumble and active Brownian particles in the absence of solvent-mediated hydrodynamic interactions – we will briefly discuss at the end their role, which is not currently fully understood in this context.     

化学激光器燃烧室两步反应法的实验研究

在环柱型增益发生器实验系统燃烧室的设计中,将主稀释剂He从两个不同的区域注入燃烧室,其中一部分与D2预混以后通过D2喷注孔注入,另一部分通过主喷管叶片后端的后向喷注孔注入。讨论了不同区域的主稀释剂流量的变化对激光器特性的影响。实验结果表明：后He流量改变时,激光器的功率变化及点火稳定性等明显优于前He流量改变的情况。若要增加主稀释剂比例,应优先考虑调整后He。     

化学激光器燃烧室两步反应法的实验研究

 在环柱型增益发生器实验系统燃烧室的设计中,将主稀释剂He从两个不同的区域注入燃烧室,其中一部分与D2预混以后通过D2喷注孔注入,另一部分通过主喷管叶片后端的后向喷注孔注入。讨论了不同区域的主稀释剂流量的变化对激光器特性的影响。实验结果表明：后He流量改变时,激光器的功率变化及点火稳定性等明显优于前He流量改变的情况。若要增加主稀释剂比例,应优先考虑调整后He。     

Some comments on nonequilibrium phase transitions in chemical systems

Two new approaches for investigating critical fluctuations near an instability point of unstable chemical models are proposed. The master equation approach is used. For a homogeneous system without the effect of diffusion, three single-component chemical systems exhibiting critical behavior are considered. The cumulant functions are expanded in a small parameter-the inverse size of the system-and singular perturbation solutions of the master equation are developed. Exponents describing the divergence of the second-order variance are found to be classical. For a system including diffusion effects, spatial correlations for a quasi-one-dimensional case are investigated by considering scale transformation behavior within the multivariate master equation formalism.This work was supported in part by NSF grants MPS-7411925 and CHE 76-05583.     

Influence of sintering conditions on chemical composition of NASICON

The influence of various sintering conditions on the chemical composition and on some physical properties of undoped and CaO or MgO doped NASICON ceramics was studied. The synthesized material was characterized by a few experimental techniques, including the wet chemical analysis and the admittance spectroscopy. The dopants were found to be located in the glassy phase formed during sintering of NASICON material. The electrical properties of NASICON were strongly affected by sintering conditions.     

Solvation and chemical reaction of sodium in water clusters

Na_m(H₂O)_n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium atoms are picked up. At low sodium vapour pressure ( < 1×10^-4 mbar) pure Na(H₂O)_n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10^-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)_n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster the reaction occurs in pairs as in the macroscopic reaction. Received 4 December 2000     

Two-parameter coherent resonance behavior in catalytic oxidation of CO on platinum surface

We study the effects of two-parameter noises on rate oscillations during CO oxidation on platinum surface, in a parameter region sub-threshold to deterministic Hopf bifurcation. It is found that the performance of noise-induced oscillations, characterized by an effective signal-to-noise ratio, shows ridge shape in the DCO∼DO₂ plane, where DCO and DO₂ measure the strength of two different parameter noises. It is indicating that the ‘two-parameter coherent resonance’ phenomenon occurs. Stochastic normal form theory is employed to analyze the non-trivial effects of two-parameter noises and the simulation results are well reproduced.