Belousov-zhabotinskii Oscillations In A Batch Reactor

The oscillations of the Belousov-Zhabotinskii reaction in a batch reactor vanish due to the consumption of the main reactants, i.e. bromate and malonic acid. This behavior has been analyzed first using the classical Oregonator model, where reactant concentrations are kept constant, and then introducing a modified model, in which the reactant concentration is allowed to vary according to the stoichiometry of the considered set of chemical reactions. Two different routes to the extinction of oscillations have been found, depending on whether the Oregonator exhibits a subcritical or a supercritical Hopf bifurcation. These theoretical findings are consistent with the experimental observations, that indicate that the disappearance of the oscillations takes place in two rather different ways: either suddenly after a series of practically undamped oscillations or through very slowly damped oscillations

Bifurcation-analysis of the Oregonator Model In the 3-d Space Bromate Malonic-acid Stoichiometric Coefficient

By considering the classical Oregonator model, the effect of the main reactants, i.e., bromate and malonic acid, on the behavior of the Belousov-Zhabotinskii system is studied. This analysis is a prerequisite for the understanding of the occurrence and disappearance of oscillations in batch reactors. A parametric analysis of the Oregonator in the three-dimensional space spanned by the bromate concentration, the malonic acid concentration, and the stoichiometric coefficient f is performed. Through asymptotic stability analysis the Hopf bifurcation set in the parameter space is determined analytically, whereas its character is defined through normal form analysis. In this study the most plausible values of the kinetic parameters, namely the ''Lo'' values proposed by Tyson (Tyson, J. J. In Oscillations and Traveling Waves in Chemical Systems; Field, R. J., Burger, M., Eds.; Wiley-Interscience: New York, 1985), are used. The system may exhibit both sub- and supercritical Hopf bifurcations, and near the latter the phenomenon of canard explosion has been observed. The results obtained with the ''Hi'' values are also reported for a comparison with previous studies in the literature

Has COVID-19 pushed digitalisation in SMEs? The role of entrepreneurial orientation

Purpose: The authors\u2019 aim is to investigate if entrepreneurial orientation (EO) has a role in interpreting an external crisis, such as COVID-19, as an opportunity for investing in digital transformation. Design/methodology/approach: The authors undertook multiple case study research on the digital transformation of seven \u201cMade in Italy\u201d SMEs and proposed a conceptual framework that sees an external stimulus (e.g. the pandemic) as a driver of the digitalisation, filtered by the entrepreneurial orientation of SMEs. Findings: The authors\u2019 results show how EO deals with the changing environment and helps address the market opportunities related to digitalisation. Research limitations/implications: This study contributes to the existing literature on EO and digital transformation of SMEs, creating a new model for forthcoming studies on this topic. In addition, interesting insights are offered on the role of EO to promote the introduction of digital transformation in SMEs operating in the \u201cMade in Italy\u201d sectors. Practical implications: This study shows the role of EO as a reactive characteristic during a crisis. Thus, the authors\u2019 suggestion to SMEs is to develop their EO as a part of the strategic orientation. In addition, this work encourages policymakers to invest in the promotion of specific interventions aimed at supporting entrepreneurs in enhancing their capacity to effectively manage digital transformation. Originality/value: Identifying the most important triggers of digitalisation in times of crisis remains an underexplored area of research. Thus, this study adds value to both digital transformation and entrepreneurial orientation topics

La gestione degli acquisti. Strategia, implementazione, controllo

Il manuale ha l'obiettivo di fornire al manager degli acquisti una guida completa su tutti gli aspetti che caratterizzano la sua funzione, ai differenti livelli di responsabilit\ue0, dalla base al vertice e in contesti aziendali articolati. Un'attenzione particolare \ue8 rivolta al processo di acquisto, nonch\ue9 alle procedure che sottendono alle diverse attivit\ue0, con esempi applicabili all'interno dei diversi tipi di azienda, a seconda che venga esercitato un controllo pi\uf9 o meno centralizzato. Si spazia dal vendor rating all'analisi del valore; dal redesign to cost agli strumenti informatici; da come affrontare in maniera idonea una negoziazione a come misurare la performance in termini di KPI: tutti temi che devono far parte del bagaglio culturale di ogni buyer, insieme alla valutazione della qualit\ue0 dei fornitori e agli aspetti legali del rapporto di fornitura. Il taglio fortemente pratico del testo permette di trattare con il dovuto approfondimento anche gli aspetti giuridici legati a questa attivit\ue0, che se da una parte costituiscono un vincolo dall'altra sono spesso uno strumento fondamentale nella relazione con il fornitore. Inoltre anche i temi pi\uf9 teorici legati alla sfera economica finanziaria e al TCO o quelli inerenti la strategia e la stesura del piano degli acquisti, sono sempre affrontati in un'ottica molto pragmatica e finalizzata all'applicazione. La preparazione degli autori e la completezza della trattazione fanno di quest'opera un manuale essenziale per tutte le esigenze di una professione sempre pi\uf9 complessa e in cui l'orizzonte delle competenze necessarie si amplia continuamente in ragione di un mercato dinamico, globale e imprevedibile

The alpine lake Gistova (mount Gramoz, Albania-Greece border). Biodiversity of an isolated microcosm

The zooplankton composition of the lake Gistova has been studied for the first time. The lake is a small, permanent water body, of glacial origin, at 2365 m above the sea level. A total of 6 zooplankton samples were collected (with nets of different mesh size), and 2 samples of the muddy sediments, too. Crustacea were represented by 7 species. Five rotifer species completed the zooplankton composition. Sediments contained at least 12 different types of resting stages, whose correspondence with active stages has been ascertained only in 4 cases

The zooplankton of the glacial lake Gijstova (Southern Albania, Mounth Gramoz)

The alpine lake Gijstova (2365 m asl) has been repeatedly visited in 4 years. samples of zooplankton and of bottom muds have been used to establish the community composition

Sympathetic activation and baroflex dysfunction in the metabolic syndrome

Sympathetic activation and baroflex dysfunction in the metabolic syndrom