Correction to: Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

Meccanica - In the original publication of the article, Eqs. (26)–(28) are incorrect due to a missing ρ symbol, inadvertently omitted when reporting the equations in the article.     

p-Sulfonic acid calix[n]arenes as homogeneous and recyclable organocatalysts for esterification reactions

Esterification yields were significantly improved using calix[n]arenes catalysts under simple conditions. p-Sulfonic acid calix[4]arene and p-sulfonic acid calix[6]arene were powerful organocatalysts in several esterification reactions, which showed activity comparable or even superior to other well-established acids catalysts, such as, sulfuric acid, p-toluenesulfonic acid, and p-hydroxybezenesulfonic acid described in the literature.     

Analysis of mercury traces by means of solid sample atomic absorption spectrometry

Analyses of Hg traces on 32 different samples, mostly food, e.g. cereals, milk and fish, have been carried out. To this purpose the AMA-254 Hg analyzer has been employed. This unit does not require any sample digestion: the instrumental reading takes place on the sample as it is (either solid or liquid) by means of atomic absorption Spectrometry at the wavelength of 253.65 nm. Usual global working range is estimated in 0-2 mg/kg, with particular suitability in the interval 0-0.2 mg/kg. Accuracy is evaluated by resorting to reference materials. Precision is assessed on both homogeneous and heterogeneous samples. The limit of detection is calculated to be 0.5 gmg/kg.     

Numerical evaluation of entropy generation in isolated airfoils and Wells turbines

In recent years, a number of authors have studied entropy generation in Wells turbines. This is potentially a very interesting topic, as it can provide important insights into the irreversibilities of the system, as well as a methodology for identifying, and possibly minimizing, the main sources of loss. Unfortunately, the approach used in these studies contains some crude simplifications that lead to a severe underestimation of entropy generation and, more importantly, to misleading conclusions. This paper contains a re-examination of the mechanisms for entropy generation in fluid flow, with a particular emphasis on RANS equations. An appropriate methodology for estimating entropy generation in isolated airfoils and Wells turbines is presented. Results are verified for different flow conditions, and a comparison with theoretical values is presented.     

Microwave-assisted multicomponent synthesis of julolidines using silica-supported calix[4]arene as heterogeneous catalyst

The application of immobilizing calixarene onto the surface of silica using a sol-gel method, as an efficient heterogeneous catalyst (CX4SO₃HSi(n)) for multicomponent Povarov reaction has been described. Catalytic activity of the CX4SO₃HSi(n) for the synthesis of julolidines under greener and environmentally benign conditions in simple and efficient method was explored. Notably, only 0.5 mol% of the catalyst is sufficient to catalyze the Povarov solvent-free reaction under microwave-assistance. Besides, this protocol allows the construction of four new C–C bonds and two C–N bonds in a single step. To the best of our knowledge, this consists the first silica support calix[4]arene as a heterogeneous catalyst for multicomponent synthesis of julolidines.