Impedance measurements at thin polyaniline films – the influence of film morphology

AC impedance measurements of thin 100-nm polyaniline films electrosynthesized in various acidic electrolyte solutions known to support different film morphologies are reported. By carefully defining experimental parameters obtained data could be satisfactorily explained invoking a simple equivalent circuit assuming a double layer capacity assigned to the polymer/solution interface, a pseudocapacity related to the internal _redox capacity of the film, a film and a solution resistance and could be related to film morphologies. The data can be related to structural/morphological features of PANI films in close agreement with generally accepted changes of PANI films as a function of the degree of oxidation and type of anion present during electropolymerization.     

Rapid growth of polymer brushes from immobilized initiators

This report describes the remarkably rapid synthesis of polymer brushes under mild conditions (50 degrees C) using surface-initiated polymerization. The highly active atom transfer radical polymerization catalyst Cu(I)-1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane allows synthesis of 100 nm thick poly(tert-butyl acrylate) brushes from initiator-modified Au surfaces in just 5 min. Using the same catalyst, polymerization of 2-hydroxyethyl methacrylate and methyl methacrylate yielded 100 nm thick films in 10 and 60 min, respectively. Such growth rates are an order of magnitude greater than those for traditional free-radical polymerizations initiated from surfaces. These polymerizations also retain some features of controlled radical polymerizations, such as the ability to form block copolymer brushes.     

The basic theory of infinite time register machines

Infinite time register machines (ITRMs) are register machines which act on natural numbers and which are allowed to run for arbitrarily many ordinal steps. Successor steps are determined by standard register machine commands. At limit times register contents are defined by appropriate limit operations. In this paper, we examine the ITRMs introduced by the third and fourth author (Koepke and Miller in Logic and Theory of Algorithms LNCS, pp. 306–315, 2008), where a register content at a limit time is set to the lim inf of previous register contents if that limit is finite; otherwise the register is reset to 0. The theory of these machines has several similarities to the infinite time Turing machines (ITTMs) of Hamkins and Lewis. The machines can decide all ${\Pi^1_1}Infinite time register machines (ITRMs) are register machines which act on natural numbers and which are allowed to run for arbitrarily many ordinal steps. Successor steps are determined by standard register machine commands. At limit times register contents are defined by appropriate limit operations. In this paper, we examine the ITRMs introduced by the third and fourth author (Koepke and Miller in Logic and Theory of Algorithms LNCS, pp. 306–315, 2008), where a register content at a limit time is set to the lim inf of previous register contents if that limit is finite; otherwise the register is reset to 0. The theory of these machines has several similarities to the infinite time Turing machines (ITTMs) of Hamkins and Lewis. The machines can decide all P¹₁{\Pi^1_1} sets, yet are strictly weaker than ITTMs. As in the ITTM situation, we introduce a notion of ITRM-clockable ordinals corresponding to the running times of computations. These form a transitive initial segment of the ordinals. Furthermore we prove a Lost Melody theorem: there is a real r such that there is a program P that halts on the empty input for all oracle contents and outputs 1 iff the oracle number is r, but no program can decide for every natural number n whether or not n ? r{n \in r} with the empty oracle. In an earlier paper, the third author considered another type of machines where registers were not reset at infinite lim inf’s and he called them infinite time register machines. Because the resetting machines correspond much better to ITTMs we hold that in future the resetting register machines should be called ITRMs.     

Purete radiochimique du complexe technetium-99m-etain-acide diethylene-triamino-pentaacetique

The radiochemical purity of technetium-99m-tin-diethylene-triamino-pentaacetic acid (DTPA) complex is checked by ascending paper chromatography. The percentage of uncomplexed technetium is lower than 5%. The technetium valency state is determined by visible absorption spectrometry.      

Enhancing the ion-transport selectivity of multilayer polyelectrolyte membranes

Alternating adsorption of polycations and polyanions on permeable supports provides a convenient and versatile method for preparing composite membranes with selective, ultrathin polyelectrolyte skins. Control over charge and composition in the polyelectrolyte skin allows highly selective separation of ions according to charge, size, or hydration energy.     

An Invitation to Infinitary Computability

In the last two decades, various machine models of computability have been generalized to work in the transfinite. I will give an overview of these models, some of the main results concerning them and some reasons why studying them is of interest outside of foundational considerations. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phage presentation and affinity selection of a deletion mutant of human lnterleukin-3

A deletion derivative of the cytokine human interleukin-3 (hIL-3^15–125, comprising amino acids 15–125 of the native protein) was produced as a fusion to the filamentous phage surface protein pIII. The cytokine was detected in association with phage particles by protein immunoblotting. Compared to an equivalent quantity of soluble cytokine, phage-presented hIL-3^15–125 exhibited reduced biological activity in a hIL-3-dependent cell proliferation assay. The reduction in activity was attributable to presence of phage particles in the assay, rather than directly owing to physical incorporation of the cytokine into the phage particle. Owing to the position of the amber codon in the phagemid vector, the phagemid-produced free hIL-3^15–125 species (designated hIL-3^15–125 ε) had 20 amino acids appended to its C-terminus; hIL-3^15–125 ε did not exhibit reduced bioactivity. hIL-3^15–125-presenting phage were affinity-selected with either a hIL-3-reactive polyclonal antibody or with cells expressing the heterodimeric hIL-3 receptor. These data are consistent with the use of phage-display technology for the affinity selection of hIL-3 variants with modified biological properties.