Preparation and voltammetric characterization of electrodes coated with Langmuir-Schaefer ultrathin films of Nafion®

Ultrathin films of Nafion® perfluorinated polymer were deposited on indium-tin oxide electrodes (ITO) by using Langmuir-Schaefer (LS) technique, after optimization of the subphase composition conditions. Morphological characteristics of these coatings were obtained by Atomic Force Microscopy (AFM). Nafion® LS films showed a good uniformity and complete coverage of the electrode surface, however a different organization degree of the polymer layer was evidenced with respect to thin films deposited by spin-coating. ITO electrodes modified with Nafion® LS coatings preconcentrate by ion-exchange electroactive cations, such as Ru[(NH3)6]3+, dissolved in diluted solutions. The electroactive species is retained by the Nafion® LS coated ITO also after transfer of the modified electrode into pure supporting electrolyte. This allowed the use of the ruthenium complex as voltammetric probe to test diffusion phenomena within the Nafion® LS films. Apparent diffusion coefficients (Dapp) of Ru[(NH3)6]3+ incorporated in Nafion® LS films were obtained by voltammetric measurements. Dapp values decrease slightly by increasing the amount of ruthenium complex incorporated in the ultrathin film. They are significantly lower than values typical for recasted Nafion® films, in agreement with the highly condensed nature of the Nafion® LS fims. Filmes ultrafinos do polímero perfluorado Nafion® foram depositados em eletrodos de óxido índio-titânio (ITO) usando a técnica de Langmuir-Scaefer (LS), depois da otimização das condições de composição da subfase. As características morfológicas das camadas foram obtidas por Microscopia de Força Atômica (AFM). Filmes de Nafion® LS mostraram boa uniformidade e cobertura completa da superfície do eletrodo. No entanto, diferentes graus de organização das camadas poliméricas ficaram evidentes com respeito a filmes finos depositados por revestimento rotacional. Eletrodos ITO modificados com camadas de Nafion® LS, pré-concentrados por cátions eletroativos de troca iônica, como o Ru[(NH3)6]3+, dissolveram-se em soluções diluídas. A espécie eletroativa foi retida pelo ITO com camada de Nafion® LS, mesmo depois da mudança do eletrodo modificado para eletrodo de suporte purificado. Isto possibilitou o uso do complexo de rutênio como padrão voltamétrico para o teste do fenômeno de difusão nos filmes de Nafion® LS. Os coeficientes de difusão aparentes (Dapp) do Ru[(NH3)6]3+ incorporado no filme de Nafion® LS foram obtidos por medidas voltamétricas. Os valores de Dapp diminuíram levemente com o aumento da quantidade de complexo de rutênio incorporado no filme ultrafino e foram significativamente mais baixos do que os valores para filmes de Nafion® recapados, em acordo com a natureza altamente condensada dos filmes de Nafion® LS

Investigation of single particle devolatilization in fluidized bed reactors by X-ray imaging techniques

A non-intrusive X-ray imaging technique has been used to investigate the behaviour of solid feedstock particles in a lab-scale fluidized bed reactor operated at temperatures up to 650 °C. Beech wood and polypropylene particles of different sizes have been chosen to represent the main constituents of typical thermochemical processes feedstock. The experiments were conducted under either oxidizing or inert conditions. The presence of oxygen showed a strong effect on the overall devolatilization time, which was found to be in the range of 30-112 seconds and 40-174 seconds for beech wood and polypropylene, respectively. Surprisingly, the oxidizing nature of the fluidizing medium appears to have no influence on the volatiles release within the bed in form of the so-called endogenous bubbles. These volatiles bubbles are responsible for a lift force acting on the feedstock particle itself, which ultimately encourages the segregation towards the bed surface. A one-dimensional physical model has been developed to predict particle axial location over time, taking into account both dynamic and thermal conversion behaviour of a single feedstock particle. A revised version of the model has been proposed due to new knowledge of endogenous bubbles size provided by a novel X-ray imaging approach. Results showed very accurate predictions of the 1D model for biomass particles, which segregate towards the bed surface according to the multiple bubble segregation pattern. However, the model fails in describing plastics behaviour, possibly due to different mechanisms of reactions. The observations reported in this work show the importance of investigation at single particle level and may serve to promote new methods to gain a better understanding of plastics thermal decomposition in fluidized beds, whose mechanism is still uncertain

Neoplastic tissue transfiguration in vivo by recombinant human transforming growth factor-β3

Human oral squamous cell carcinomas (hSCCs) are the most common head and neck cancers now presenting with more aggressive biological and clinical features due to smoking and alcohol together with widespread viremia. Transforming growth factor-β (TGF-β) proteins are powerful morphogens that induce rapid and substantial induction of endochondral bone formation but in primates only

Controllability of spin-boson systems

In this paper we study the so-called spin-boson system, namely {a two-level system} in interaction with a distinguished mode of a quantized bosonic field. We give a brief description of the controlled Rabi and Jaynes--Cummings models and we discuss their appearance in the mathematics and physics literature. We then study the controllability of the Rabi model when the control is an external field acting on the bosonic part. Applying geometric control techniques to the Galerkin approximation and using perturbation theory to guarantee non-resonance of the spectrum of the drift operator, we prove approximate controllability of the system, for almost every value of the interaction parameter

Reconstruction of protein structures from a vectorial representation

We show that the contact map of the native structure of globular proteins can be reconstructed starting from the sole knowledge of the contact map's principal eigenvector, and present an exact algorithm for this purpose. Our algorithm yields a unique contact map for all 221 globular structures of PDBselect25 of length $N \le 120$. We also show that the reconstructed contact maps allow in turn for the accurate reconstruction of the three-dimensional structure. These results indicate that the reduced vectorial representation provided by the principal eigenvector of the contact map is equivalent to the protein structure itself. This representation is expected to provide a useful tool in bioinformatics algorithms for protein structure comparison and alignment, as well as a promising intermediate step towards protein structure prediction.Comment: 4 pages, 1 figur

Picard group of hypersurfaces in toric 3-folds

We show that the usual sufficient criterion for a generic hypersurface in a smooth projective manifold to have the same Picard number as the ambient variety can be generalized to hypersurfaces in complete simplicial toric varieties. This sufficient condition is always satisfied by generic K3 surfaces embedded in Fano toric 3-folds.Comment: 14 pages. v2: some typos corrected. v3: Slightly changed title. Final version to appear in Int. J. Math., incorporates many (mainly expository) changes suggested by the refere

Experimental model in vivo for quantitative assessment of bone resorption inhibition.

Quantitative assessment of bone resorption inhibition in vivo is not easily accomplished; methods relying on a count of osteoclasts are questionable, and histomorphometric evaluation of the bone mass presents several technical problems as well. The authors developed a simple method to measure the inhibition of bone resorption by study of the proximal tibial metaphysis of growing rats: the height of the perichondrial bone ring was taken as an index of the balance between osteoblastic and osteoclastic activity because any agent that inhibits osteoclasts (without interference with osteoblasts) produces an increase in the height of this anatomical structure. Since the ring is well demarcated by surrounding tissues, its height can be measured with accuracy and used for quantitative assessment of bone resorption inhibition. This model was tested with salmon calcitonin, and it provides evidence in vivo that this hormone inhibits osteoclastic bone resorption

Phase Transitions of Single Semi-stiff Polymer Chains

We study numerically a lattice model of semiflexible homopolymers with nearest neighbor attraction and energetic preference for straight joints between bonded monomers. For this we use a new algorithm, the "Pruned-Enriched Rosenbluth Method" (PERM). It is very efficient both for relatively open configurations at high temperatures and for compact and frozen-in low-T states. This allows us to study in detail the phase diagram as a function of nn-attraction epsilon and stiffness x. It shows a theta-collapse line with a transition from open coils to molten compact globules (large epsilon) and a freezing transition toward a state with orientational global order (large stiffness x). Qualitatively this is similar to a recently studied mean field theory (Doniach et al. (1996), J. Chem. Phys. 105, 1601), but there are important differences. In contrast to the mean field theory, the theta-temperature increases with stiffness x. The freezing temperature increases even faster, and reaches the theta-line at a finite value of x. For even stiffer chains, the freezing transition takes place directly without the formation of an intermediate globule state. Although being in contrast with mean filed theory, the latter has been conjectured already by Doniach et al. on the basis of low statistics Monte Carlo simulations. Finally, we discuss the relevance of the present model as a very crude model for protein folding.Comment: 11 pages, Latex, 8 figure