In situ determination of adsorption kinetics of proteins in a finite bath

A method for fast in situ measurement of adsorption kinetics based on a finite bath was developed. We modified the conventional finite bath by replacing the external loop by a dip probe which enables in situ measurement of the concentration change in the contactor. Deposition of adsorbent particles on the reflection surface of the dip probe compromised measurements. Different membranes, a polyamide, a polypropylene and a nylon membrane were tested to protect the internal reflection surface of the dip probe from fouling with adsorbent particles. The nylon membrane provided efficient protection and high mass transfer evaluated by response time experiments. Unspecific adsorption of the model protein on the membrane could also be excluded. To corroborate the measurements of the dip probe the results were compared to a conventional finite bath and to a shallow-bed. The uptake curves for human polyclonal IgG at different concentrationes (0.1-3 g/l) on rProtein A Sepharose FF and MabSelect were used as model system. The effective diffusion coefficients were determined using a pore diffusion model. These values were in good agreement for all methods.     

Crystallization Temperature Limit of (Ba,Sr)TiO<Subscript>3</Subscript> Thin Films Prepared by a Non Oxocarbonate Phase Forming CSD Route

A new chemical solution deposition (CSD) route for the fabrication of Ba_0.7Sr_0.3TiO₃ (BST) thin films has been developed which completely prevents the formation of an intermediate oxo-carbonate phase. The latter has been reported previously by several authors to be responsible for increased crystallization temperatures. Barium and strontium diaminoethoxides were synthesized starting from pure barium and strontium metal and aminoethanol. These alkoxides were found to be readily soluble in a wide range of solvents and thus were excellent candidates for the CSD process. To prepare a stable precursor solution the aminoalkoxides were dissolved in 2-butoxyethanol and then used for the deposition of BST thin films. We conclude that the minimum crystallization temperature of 600C to be independent of the formation of the oxo-carbonate phase. DTA-TGA were performed on the precursors and their solutions to study their decomposition behaviour. All films annealed at different temperatures were physically characterized by XRD, IR, and SEM. The films prepared by this route at 650C were found to have high dielectric constant and the leakage currents were comparable to BST films prepared by normal carboxylate based routes at 750C.     

Electrostatic lattice coefficients and binding energy of orthorhombic La2-x Sr x CuO4

Three valency models for orthorhombic La_2-x Sr _x CuO₄ were investigated for increasing Sr concentrationsx (0x0.21): 1. Cu²⁺Cu³⁺, 2. apex O^2–O^– and 3. in-plane O^2–O^–. All calculations were done by using structural parameters valid for the temperature range from 10 to 22 K. We thereby calculated the electrostatic interaction energy which, next to ionization potentials and electron affinities, comprises a major of the binding energyE _B of crystals. Second-order effects were accounted for by calculating the strength of ionic dipole moments induced by crystal electric fields at relevant lattice sites. Their largest strengths are comparable to the dipole moment of the water molecule. Three out of five dipoles in La_2-x Sr _x CuO₄ vanish during the transition from the orthorhombic to the tetragonal phase. The binding energy differences between the different models suggest that the system is in a state of model 1. However, the differences are very small, being in the order of 0.3 to 0.76 eV atx=0.13.     

The distribution of the likelihood ratio for mixtures of densities from the one-parameter exponential family

We here consider testing the hypothesis ofhomogeneity against the alternative of a two-component mixture of densities. The paper focuses on the asymptotic null distribution of 2 log _n , where _n is the likelihood ratio statistic. The main result, obtained by simulation, is that its limiting distribution appears pivotal (in the sense of constant percentiles over the unknown parameter), but model specific (differs if the model is changed from Poisson to normal, say), and is not at all well approximated by the conventional ₍₂₎ ² -distribution obtained by counting parameters. In Section 3, the binomial with sample size parameter 2 is considered. Via a simple geometric characterization the case for which the likelihood ratio is 1 can easily be identified and the corresponding probability is found. Closed form expressions for the likelihood ratio _n are possible and the asymptotic distribution of 2 log _n is shown to be the mixture giving equal weights to the one point distribution with all its mass equal to zero and the ²-distribution with 1 degree of freedom. A similar result is reached in Section 4 for the Poisson with a small parameter value (0.1), although the geometric characterization is different. In Section 5 we consider the Poisson case in full generality. There is still a positive asymptotic probability that the likelihood ratio is 1. The upper precentiles of the null distribution of 2 log _n are found by simulation for various populations and shown to be nearly independent of the population parameter, and approximately equal to the (1–2)100 percentiles of ₍₁₎ ² . In Sections 6 and 7, we close with a study of two continuous densities, theexponential and thenormal with known variance. In these models the asymptotic distribution of 2 log _n is pivotal. Selected (1–) 100 percentiles are presented and shown to differ between the two models.     

On the integrated density of states for crystals with randomly distributed impurities

In the present paper, we discuss spectral properties of a periodic Schrödinger operator which is perturbed by randomly distributed impurities; such operators occur as simple models for crystals (or semi-conductors) with impurities. While the spectrum itself is independent of the concentrationp of impurities, for 0<p<1, we focus our attention on the limiting behavior of the integrated density of states _p of the random Schrödinger operator, inside a spectral gap of the periodic operator, asp0. Denoting byU ₀ the set of eigenvalues (in the gap) of the reference problem having precisely one impurity (located at the origin, say), we show that the integrated density of states concentrates around the points ofU ₀, in the sense that _p (U ) is of orderp, for any fixed -neighborhoodU ofU ₀, while _p (K)C·p ², for any compact subsetK of the gap which does not intersectU .Research partially supported by Deutsche Forschungsgemeinschaft