Numerically flat Higgs vector bundles

After providing a suitable definition of numerical effectiveness for Higgs bundles, and a related notion of numerical flatness, in this paper we prove, together with some side results, that all Chern classes of a Higgs-numerically flat Higgs bundle vanish, and that a Higgs bundle is Higgs-numerically flat if and only if it is has a filtration whose quotients are flat stable Higgs bundles. We also study the relation between these numerical properties of Higgs bundles and (semi)stability.Comment: 11 page

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

Optimisation of through-thickness embedding location of Fibre Bragg grating sensor in CFRP for impact damage detection

Aerospace composites are susceptible to barely visible impact damage (BVID) produced by low-velocity-impact (LVI) events. Fibre Bragg grating (FBG) sensors can detect BVID, but often FBG sensors are embedded in the mid-plan, where residual strains produced by impact damage are lower, leading to an undervaluation of the damage severity. This study compares the residual strains produced by LVI events measured by FBG embedded at the mid-plan and other through-thickness locations of carbon fibre reinforced polymer (CFRP) composites. The instrumented laminates were subjected to multiple low-velocity impacts while the FBG signals were acquired. The FBG sensor measurements allowed not only for the residual strain after damage to be measured, but also for a strain peak at the time of impact to be detected, which is an important feature to identify the nature and presence of BVID in real-life applications. The results allowed an adequate optical fibre (OF) embedding location to be selected for BVID detection. The effect of small- and large-diameter OF on the impact resistance of the CFRP was compared.This research was funded by the European Regional Development Fund, grant number NORTE-01-0145-FEDER-000015, and the APC was funded by the European Space Agency’s Network/Partnering Initiative Program, with contract number 4000123315

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