Thermodynamics of phenylated polyphenylene between 0 and 340 K

In an adiabatic vacuum calorimeter, the temperature dependence of the heat capacity C _p of phenylated polyphenylene and initial comonomer 1,4-bis(2,4,5-triphenylcyclopentadienone-3-yl)benzene was studied between 6 and 340 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield their energies of combustion DUcomb were measured. From the experimental data, the thermodynamic functions C _p ⁰ (T), H ⁰(T)-H ⁰(0), S ⁰(T)-S⁰(0), G ⁰(T)-H ⁰(0) were calculated from 0 to 340 K, and standard enthalpies of combustion ΔH _comb ⁰ and thermodynamic parameters of formation-enthalpies ΔH _f ⁰, entropies ΔH _f ⁰, Gibbs functions ΔG _f ⁰ - of the substances studied were estimated at T=298.15 K at standard pressure. The results were used to calculate the thermodynamic characteristics (ΔH _f ⁰ ,ΔS _f ⁰, ΔG _f ⁰) of phenylated polyphenylene synthesis in the range from 0 to 340 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of total heterogeneity and fractal dimensions of high-temperature superconductors

Using thermo-analytical and sorptometric methods physicochemical properties and especially surface heterogeneity of HgBa₂Ca₂Cu₃O₈₊, (Hg-1223) was investigated. The desorption energy distribution was derived from mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption in quasi-isothermal conditions of pre-adsorbed n-octane and water vapour. It is shown that the superconducting Hg-1223 phase is highly sensitive to water vapours. The mechanism of water adsorption depends largely on the activation time. By water vapour saturation in a period of 90 min, physisorption takes place. Prolonged periods result in a chemical decomposition. From nitrogen ad- and desorption isotherms the fractal dimension of superconductors were calculated. A new approach is proposed to calculate fractal dimension from Q-TG curves.This revised version was published online in November 2005 with corrections to the Cover Date.     

Orthokinetic Aggregation in Two Dimensions of Monodisperse and Bidisperse Colloidal Systems

Orthokinetic aggregation of colloids trapped at the air–liquid interface was studied by direct imaging in a couette cell. This method allowed us to follow the temporal evolution of both the cluster-mass distribution and the cluster structure at a shear rate where Brownian aggregation is suppressed. The interactions between the monodisperse latex particles floating at the air–liquid interface were controlled either by varying the electrolyte concentration or by creating a bidisperse system through the addition of small particles. The results show that the clusters in all of the systems are characterized by a high fractal dimension, indicating that the clusters are rearranged and densified by the shear. Kinetic analysis suggests that aggregation of monodisperse systems mainly proceeds through homogeneous aggregation, i.e., large clusters sticking to other large clusters. The bidisperse system, finally, with a size ratio around 10, favored a more heterogeneous aggregation among small and large clusters throughout the aggregation process; a slightly lower fractal dimension was observed compared to the strongly aggregated monodisperse system.     

On guaranteed stability of uncertain linear systems via linear control

This paper addresses the problem of stabilizing an uncertain linear system. The uncertaintyq(·) which enters the dynamics is nonstistical in nature. That is, noa priori statistics forq(·) are assumed; only boundsQ on the admissible variations ofq(·) are taken as given. The results given here applied to so-called matched systems differ from previous results in two ways. Firstly, the stabilizing control in this paper is linear; for this same class of problems, many of the existing results would require a nonlinear control. Furthermore, those results which do in fact yield linear controls are only valid when a certain matrix (q) (formed using the given data) is negative definite for allq Q. In contrast, the theory given here only requires compactness of the bounding setQ. Secondly, we show that the so-called matching conditions (used in earlier work) can be generalized so as to encompass a larger class of dynamical systems.This research was supported by the US Department of Energy under Contract No. ET-78-S-01-3390.     

Monte—Carlo model of the diffusion-limited reaction kinetics in microheterogeneous media. Comparison with the experimental plots of the forward and backward electron phototransfer kinetics on the pore diameter in silica gel

The kinetics of the diffusion-limited decay reaction A + B B was simulated by the Monte—Carlo method on a two-dimensional square lattice with defects presented by randomly distributed sites. The cases were considered where [B] [A] at the random initial distribution (quenching reaction) and [B] = [A] with the initial distribution of the A and B particles on neighboring sites (geminate recombination). The kinetic curves were approximated by the simplest analytical equation [A]/[A]₀ = (1 – )exp[–(kt)^1–h ] + (where k and are constants). The plots of the heterogeneity parameter (h) and time-averaged first-order rate constant vs. concentration of defects (p) or B particles (in the case of quenching) were obtained and compared with similar correlations obtained earlier by the experimental study of the kinetics of forward (quenching reaction) and backward (geminate recombination) electron phototransfer on the surface of different porous silica gels. The experimental plots of h vs. silica gel porosity are in satisfactory agreement with the plots of h vs. p in the model space, if the fraction of volume inaccessible for reactants, calculated from the free silica gel volume, is chosen as the p parameter for silica gel.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1536–1541, August, 2004.     

On the structure formation of hydrophobed particles in the boundary layer of water and octane phases

Two-dimensional aggregation of the surface modified glass beads was carried out in the boundary layer of water and octane phases. The effect of particles' hydrophobicity was investigated on the structure of forming aggregates and the growth process. The structure of the aggregates and their growth were characterized by a density function which demonstrates the change of mean particle density as a function of aggregate size. The growth yielded fractal or nonfractal structures in the investigated systems. The fractal structure of the aggregates was observed to be dependent on restructuring processes controlled by the surface properties of the beads.The experimental results are compared with earlier findings for aggregation of hydrophobic beads in the boundary layer of water and air phases.On leave from Loránd Eötvös University, Budapest, Hungary     

The Aggregation Kinetics of Colloidal Particles of Basic Yttrium Carbonate

Studyofthegrowthprocessofcolloidalparticlesofnonequilibriumandirreversibilityisanactiveareaofresearch.Therecognitionofcolloidalaggregatesasfractalobjectshasinspiredalargenumberofexperimentalandtheoreticalstudiesonthestructuralandkineticaspectsofaggregationprocesses"'.Morerecently,kineticsofhematiteaggregationbypolyacrylicacidhavebeenstudiedbyzhangandBume3.Theprimaryhematiteparticleswerequiteuniformandfairlyspherical.Inthispaper,wewillreportthesizeevolutionoffractalaggregatesofinitiallypolydis…     

Dynamic Properties of Two-Dimensional Polydisperse Granular Gases

We propose a two-dimensional model of polydisperse granular mixtures with a power-law size distribution in the presence of stochastic driving. A fractal dimension D is introduced as a measurement of the inhomogeneity of the size distribution of particles. We define the global and partial granular temperatures of the multi-component mixture. By direct simulation Monte Carlo, we investigate how the inhomogeneity of the size distribution influences the dynamic properties of the mixture, focusing on the granular temperature, dissipated energy, velocity distribution, spatial clusterization, and collision time. We get the following results: a single granular temperature does not characterize a multi-component mixture and each species attains its own "granular temperature"; The velocity deviation from Gaussian distribution becomes more and more pronounced and the partial density of the assembly is more inhomogeneous with the increasing value of the fractal dimension D; The global granular temperature decreases and average dissipated energy per particle increases as the value of D augments.     

具有数据丢失的网络化控制系统的基于观测器的镇定

研究具有数据丢失的网络化控制系统的基于观测器的镇定问题。受控对象是由T-S模糊模型描述的非线性时滞系统。把数据丢失过程建模成独立同分布过程。利用模糊Lyapunov函数方法得到了闭环系统随机稳定的充分条件,其基于观测器的反馈控制器可通过求解一组线性矩阵不等式来设计。一个仿真例子说明方法的有效性。     

一类带有回馈控制的捕食-食饵模型正周期解的存在性(英文)

研究了一类具有Hassell-Varely功能性反应函数的食饵-捕食模型的回馈控制系统,利用比较连续定理和一致度定理,证明了系统正周期解的存在性,并通过构造Lyapunov函数给出了系统全局稳定性的充分条件和证明.