Codimension-two border collision bifurcation in a two-class growth model with optimal saving and switch in behavior

Nonlinear Dynamics - We consider a two-class growth model with optimal saving and switch in behavior. The dynamics of this model is described by a two-dimensional (2D) discontinuous map. We obtain...     

Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Catalytically active MnO_x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO_x catalysts form without supports in situ under photocatalytic conditions. Our most active ⁴MnO_x catalyst (～0.84 mmol O₂ mol Mn^?1 s^?1) forms from a Mn₄O₄ bearing a metal–organic framework. ⁴MnO_x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m²g^?1) and small regions of crystallinity and layer flexibility. In contrast, the ^SMnO_x formed from Mn²⁺ salt gives an amorphous species of lower surface area (80 m²g^?1) and lower activity (～0.15 mmol O₂ mol Mn^?1 s^?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p_3/2 core levels detects enriched Mn³⁺ and Mn²⁺ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.     

Color Stabilization of Apulian Red Wines through the Sequential Inoculation of Starmerella bacillaris and Saccharomyces cerevisiae

Mixed fermentation using Starmerella bacillaris and Saccharomyces cerevisiae has gained attention in recent years due to their ability to modulate the qualitative parameters of enological interest, such as the color intensity and stability of wine. In this study, three of the most important red Apulian varieties were fermented through two pure inoculations of Saccharomyces cerevisiae strains or the sequential inoculation of Saccharomyces cerevisiae after 48 h from Starmerella bacillaris. The evolution of anthocyanin profiles and chromatic characteristics were determined in the produced wines at draining off and after 18 months of bottle aging in order to assess the impact of the different fermentation protocols on the potential color stabilization and shelf-life. The chemical composition analysis showed titratable acidity and ethanol content exhibiting marked differences among wines after fermentation and aging. The 48 h inoculation delay produced wines with higher values of color intensity and color stability. This was ascribed to the increased presence of compounds, such as stable A-type vitisins and reddish/violet ethylidene-bridge flavonol-anthocyanin adducts, in the mixed fermentation. Our results proved that the sequential fermentation of Starmerella bacillaris and Saccharomyces cerevisiae could enhance the chromatic profile as well as the stability of the red wines, thus improving their organoleptic quality.     

New trends in the analysis of masonry structures

The modern theory of masonry structures has been set up on the hypothesis of no-tension behaviour, with the aim of offering a reference model, independent of materials and building techniques employed. This hypothesis gives rise to inequalities which have to be satisfied by the stress tensor components and, as a dual aspect, to the kinematic behaviour characteristics of media which can be classified as lying between solids and fluids: the structure of the masonry material consists of particles reacting elastically only when in contact. An examination of the plane-stress problem leads us to define, within the prescribed domain under admissible loads, three different subdomains with null, regular, or non-regular principal stress tensors, respectively. As the boundaries of such subdomains are not known a priori, the problem can be classified as a free boundary value problem. The analysis concerns mainly the subdomains where the stress tensor is non-regular; and a non-regularity condition det =0 is added to the equilibrium equations. This condition makes the stress problem isostatic and leads to a violation of Saint-Venant's compliance conditions on strains. Hence there is a need to introduce a strain tensor, not related to the stress tensor, which can be decomposed into an extensional component and a shearing component; we prove that such strains, of the class ^c, are similar to those of the theory of plastic flow. From the point of view of computational analysis the anelastic strains are considered as given distortions; they are computed by means of the Haar-Kármán principle, modified for computational purposes by an idea of Prager and Hodge.

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Sommario La moderna teoria delle strutture murarie, fondata sulla rigorosa non reagenza a trazione del materiale, ha lo scopo di fornire un modello di riferimento indipendente sia dalle caratteristiche del materiale sia dalle techniche costruttive impiegate. L'ipotesi di non reagenza a trazione si traduce in disuguaglianze che le componenti del tensore di stress devono verificare; dualmente il comportamento caratteristico cinematico può esser classificato di confine, come del resto la stessa statica, tra solidi e fluidi: la struttura ipotizzata del materiale muratura consiste di particelle che reagiscono solo se sono in contatto. L'esame del problema piano porta a definire all'interno del dominio di definizione tre differenti tipi di sub-regioni in cui lo stress è nullo, canonico, o singolare. Poiché le frontiere di queste sub-regioni non sono note a priori il problema può anche essere classificato di frontiera libera. L'analisi concerne fondamentalmente la sub-regione in cui il tensore è non regolare, perché deve verificare anche la condizione det =0. Ciò rende isostatico il problema e conduce anche alla violazione della condizione di integrabilità delle deformazioni. Questo passaggio può essere superato introducendo un tensore di deformazioni a tensioni nulle che si può decomporre in una componente estensionale ed in una componente di scorrimento; si dimostra che queste deformazioni sono equivalenti a quelle che intervengono nella Teoria del flusso plastico. Dal punto di vista computazionale le deformazioni anelastiche sono considerate come distorsioni impresse determinate attraverso il principio di Haar-Kármán modificato, per le techniche computazionali, su idee di Prager e Hodge.

     

Ionic electroactive polymer metal composites: Fabricating,modeling, and applications of postsilicon smart devices

Smart systems adapt to the surrounding environments in a number of ways. They are capable to scavenge energy from available sources, sense and elaborate external stimuli and adequately react. Electro Active Polymers are playing a main role in the realization of smart systems for applications if fields such as bio inspired and autonomous robotics, medicine, and aerospace. This paper focus on the possibility to use Ionic Polymer Metal Composites as a class of materials relevant to the realization of post silicon smart systems. The three main aspects of this new technology, i.e., fabrication methods, modeling, and applications are described with emphasis to most recent results. Attention is given to main challenges and shortcomings to be solved for technology, modelling, and control of IPMC based devices that need to be solved before this new technology can be fully exploited in real world applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013     

Temperature dependence of the time-resolved emissions of CsI:Tl

Abstract

Time-resolved emissions of Csl:T1 are investigated. The system is laser-excited in the A-band at 308 nm and the emissions are observed in the range 370–650 nm, from 30 K to 300 K. Their analysis by means of a deconvolution permits the valuation of decay-times down to 1 ns. At every temperature many bands are observed and some of them show slow and fast components. The decay-times of the fast components are in the range 1–10 ns while the slow ones are even longer than 1 μs. In many cases intermediate decay-times of the order of 100 ns exist. The competition among the bands interests the application of this system as active material for tunable solid-state laser.