Statistical properties of aggregation with injection

We study a generalized aggregation process in which charged particles diffuse and coalesce randomly on a lattice. For one-dimensional and mean-field models, we show that there exists a statistically-invariant steady state when randomly charged particles are continuously injected. The steady-state charge distribution obeys a power law with the exponent depending both on the type of the injection and on the spatial dimension. The response of the system to a perturbation (i.e., relaxation) is characterized by either a power law decay (t ^– ,1) or a compressed exponential decay [exp(–t ),>1].     

On the validity of the counterpoise correction for the basis set superposition error including the fragment relaxation terms

It is demonstrated that relatively large geometrical changes make Emsley et al.'s assumption (J Am Chem Soc (1978) 100:3303) on the counterpoise correction for the basis set superposition error including the fragment relaxation terms unacceptable. Received: 23 September 1997 / Accepted: 31 October 1997     

Effect of high-voltage pulses on electrochemical properties of a molten magnesium electrolyte

Effects of high-voltage pulses on electrochemical properties of a molten magnesium electrolyte is studied experimentally. It is established that the electroconductivity of the melt subjected to the pulses and the electrolysis current at a constant voltage increase by up to 25%. The relaxation time of nonequilibrium melt reaches a few tens of minutes and under certain conditions its dynamics is oscillatory.     

Structure relaxation after temperature jumps in homogeneous polystyrene/poly(styrene-co-bromostyrene) blends

Concentration fluctuations in polymer blends and their change after a temperature jump were studied by time-dependent small angle X-ray scattering experiments. Measurements were conducted on homogeneous mixtures of polystyrene and a partially brominated derivative. Structure factors in thermal equilibrium show the form given by the random phase approximation, thus enabling a direct determination of the-parameter and the mean radius of gyration. TheT-dependence of can be understood as the result of superposed enthalpic contributions and a free volume term. In theT-jump experiments, samples were quenched to temperatures near T_g. Relaxation occurs on the time scale of minutes and is nonexponential, becoming slower with time. Initial relaxation rates increase with increasing scattering vectorsq in accordance with theoretical predictions.     

The asymmetrical orientational behavior of compatible blends of PMMA and PVC

The orientation and relaxation behavior of compatible blends of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) was investigated. The deformation was performed at 9 K above the glass transition temperature. Based on birefringence and IR-dichroic measurements, it was found that the orientation of PMMA is strongly increased in the blends as compared to pure PMMA at identical draw ratios.The orientation of PVC, on the other hand, is not changed by blending. The results are discussed in terms of friction coefficients and their enhancement by molecular interactions.Dedicated to Prof. E. W. Fischer on the occasion of his 665th birthday     

Oxygen transport in La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>3−δ</Subscript>

The surface exchange coefficient and chemical diffusion coefficient of oxygen for the perovskites La_0.6Sr_0.4Co_1–yFe_yO_3– (y=0.2, 0.5 and 0.8) were measured using the conductivity relaxation technique. Measurements were performed between 600 and 800 °C in an oxygen partial pressure range between 10^–4 and 1 bar. Both transport coefficients decrease markedly with decreasing oxygen partial pressure below about 10^–2 bar at all temperatures. This is attributed to ordering of oxygen vacancies. Implications for using La_0.6Sr_0.4Co_1–yFe_yO_3– as an oxygen separation membrane are discussed.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10-12 April 2003     

Molecular motion and interactions in aqueous carbohydrate solutions. I. Dielectric-relaxation studies

Dielectric-relaxation studies in the frequency range 200 kHz to 35 GHz are reported for a range of sugars (from mono- to trisaccharides) in aqueous solution. The complex dielectric spectra were analyzed using a weighted least-squares minimization method to resolve the various component relaxations, and the implications of the analyses in terms of the molecular dynamics of solute and solvent and the interactions between solute and solvent are discussed. For the highest concentration studied (ca. 2M), it was found that the most significant analysis required three discrete relaxation processes, whereas lower concentration samples could usually be satisfactorily fitted with two. Irrespective of any uncertainty in model selection, a number of conclusions regarding the solute-solvent interactions can be made, and it is shown how final quantification of the extents of hydration can be made using the input of information from other techniques.     

High-temperature dielectric properties of Gd2CuO4 ceramics

A sample of Gd₂CuO₄ (GCO) has been prepared through the solid state reaction technique. Dielectric properties of this material have been measured in detail as functions of temperature (between 285 and 450 K) and frequency (20 Hz-10 MHz). A step-like increase below 330 K and a broad peak around 360 K were observed in the real part of the permittivity (ε′) which were found to be originated from the oxygen vacancy hopping motions that cause a dipolar relaxation, followed by a Maxwell-Wagner relaxation as the hopping carriers are blocked by the interfaces and surfaces of the sample.     

Time evolution of the solvated and conformationally relaxed emissive excited state of the anionic form of salophen,a Schiff base

Salophen is a weakly fluorescent Schiff base which forms emissive co-ordination complexes with Zn²⁺ and Al³⁺. The complex with Al³⁺ is significantly more fluorescent than that with Zn²⁺, presumably because the dimeric complex with Zn²⁺ is associated with additional nonradiative channels. This contention has been put to test, through a careful investigation of excited state dynamics of the anionic form of salophen (Sal²⁻), which is the form in which the ligand exists in the complexes. The emissive excited state of the anion (Sal²⁻) has been found to be solvated and conformationally relaxed, over tens of picosecond. It is significantly more fluorescent than the neutral compound, with fluorescence lifetime that is longer by almost two orders of magnitude. Fluorescence lifetime of the anion is in fact longer than that of the complex with Zn²⁺ and slightly less than that of the complex with Al³⁺. So, the earlier hypothesis about additional nonradiative deactivation pathways in the Zn²⁺ complex gains credence from the present study.