Experimental investigation on the thermal stability of some new zero ODP refrigerants

Five zero ODP (ozone depletion potential) hydro-fluorocarbon refrigerants (HFC-23, HFC-143a, HFC-227ea, HFC-236fa, HFC-245fa) were tested to define their maximum usable temperature and their thermal degradation threshold. Pyrolysis is detected (a) as a pressure change at constant temperature and volume; (b) as a departure of the vapour pressure curve of the heated fluid from that of the original substance. Visual inspection of the vessel walls and fluid chemical analysis complement the method. The minimum detectable degradation rate is believed to be less than 1% in 50 h. All the fluids exhibit a variable, but excellent thermal stability up to the following temperatures at which no decomposition was observable in 50–100 h: 425 °C for HFC-227ea, 400 °C for HFC-23 and HFC-236fa, 350 °C for HFC-143a and 300 °C for HFC-245fa. Clear degradation signs were observed at temperatures 25–50 °C higher. Most of the fluids heated up to their thermal stability threshold exhibited an induction period of 5–50 h in which no decomposition was detectable but after which an observable degradation started. For a given fluid such period decreases at increasing temperatures. The use of fluids in a cyclic process in which the working medium permanence at the top temperature is very brief could take advantage of this behaviour with a reduction in degradation rates or with an increase in the limiting temperature. The influence of the decomposition products on the functionality of a thermodynamic power cycle was investigated by means of an appropriate computer code. The working fluid was assumed to be a binary mixture with 1 to 3% concentration of a light decomposition product of the methane series. Chemical species such as CH₄ and CF4 with a critical temperature much lower than that of the base fluid strongly affect the cycle configuration. On the contrary species with critical temperatures closer to that of the base fluid such as CH₃F, CH₂F₂ or CHF₃ influence only marginally the cycle performance. In general a small concentration of decomposition products in the working medium is likely to be acceptable without noticeable drawbacks.

Résumé

Five zero ODP (ozone depletion potential) hydro-fluorocarbon refrigerants (HFC-23, HFC-143a, HFC-227ea, HFC-236fa, HFC-245fa) were tested to define their maximum usable temperature and their thermal degradation threshold. Pyrolysis is detected (a) as a pressure change at constant temperature and volume; (b) as a departure of the vapour pressure curve of the heated fluid from that of the original substance. Visual inspection of the vessel walls and fluid chemical analysis complement the method. The minimum detectable degradation rate is believed to be less than 1% in 50 h. All the fluids exhibit a variable, but excellent thermal stability up to the following temperatures at which no decomposition was observable in 50–100 h: 425 °C for HFC-227ea, 400 °C for HFC-23 and HFC-236fa, 350 °C for HFC-143a and 300 °C for HFC-245fa. Clear degradation signs were observed at temperatures 25–50 °C higher. Most of the fluids heated up to their thermal stability threshold exhibited an induction period of 5–50 h in which no decomposition was detectable but after which an observable degradation started. For a given fluid such period decreases at increasing temperatures. The use of fluids in a cyclic process in which the working medium permanence at the top temperature is very brief could take advantage of this behaviour with a reduction in degradation rates or with an increase in the limiting temperature. The influence of the decomposition products on the functionality of a thermodynamic power cycle was investigated by means of an appropriate computer code. The working fluid was assumed to be a binary mixture with 1 to 3% concentration of a light decomposition product of the methane series. Chemical species such as CH₄ and CF4 with a critical temperature much lower than that of the base fluid strongly affect the cycle configuration. On the contrary species with critical temperatures closer to that of the base fluid such as CH₃F, CH₂F₂ or CHF₃ influence only marginally the cycle performance. In general a small concentration of decomposition products in the working medium is likely to be acceptable without noticeable drawbacks.     

Inferring the left ventricle dynamical behavior using a free-form deformations model

A computational 4D (3D + time) model for simulating the dynamical shape of the left ventricle (LV) based on free-form deformations (FFD) techniques is described. The simulation model is useful as a teaching tool for understanding the normal left ventricle motion. The model is also useful for initializing 3D segmentation algorithms and for understanding the relation between pathologies and variation of parameters defining the ventricular function. Validation of this computational model is performed by synthesizing 4D sequences of the left ventricle, comprising the interval going from end-systole to end-diastole. From the resulting 4D shapes, several mechanical parameters such as the left ventricle volume, the radial contraction and torsion are calculated and compared with results of works previously reported based in MR-tagging images. A comparison is also performed with respect to mechanical parameters extracted from the additional time instants in the same multislice computerized tomography (MSCT) database used for extracting the LV wall surfaces required for initialization. First results show a good match between parameters compared.     

Measurements of projected areas of seated and standing people of southern Italy based on a statistical analysis

One of the most important components affecting the human thermal balance is represented by its radiative exchange with the surrounding surfaces. The projected area of the human body is an important parameter of these thermal exchanges. Unfortunately, although the anthropometric measures of people are characterized by significant differences among various populations, the experimental data currently available in the literature refers to a small group of people. Moreover, measurements are generally performed regardless of the statistical significance of the involved subjects with respect to the population to which they belong.In this study, a statistical study is introduced that is based on a large analysis of the anthropometric characteristics of the analysed population. Moreover, a new experimental procedure is applied to evaluate the projected area factor and the effective radiating area of a sample of people belonging to the population of southern Italy.The calculated projected area factors are fairly in accordance with those originally proposed by Fanger for standing people. For seated people, however, the experimental values of the present study show some differences from those of the literature. This study provided a tentative explanation for these discrepancies.     

Nutritional Evaluation of Typical and Reformulated Italian Cheese

The aim of this work was the nutritional evaluation of reformulated dairy products (caciotta-type cheese) and manufactured either with a low-sodium chloride content (different salting time and/or composition of the brine) or low-fat content (different partially skimmed milks). These cheeses were intended for people on low-energy or low-sodium diets. A comparison was made between these new products and three typical Italian cheeses (Provolone, Taleggio and Pecorino Romano). The nutrient content of the products was determined. Amino acids by chromatographic methods, protein digestibility by an enzymatic method and lysine availability determined spectrophotometrically were shown not to be influenced by the salt reduction. The salt reduction also did not affect vitamin contents (riboflavin, retinols, carotenes and tocopherols) measured by HPLC methods, while the reduced fat contents (310 g kg^-1, 160 g kg^-1 and 87 g kg^-1) led to significant decreases in concentrations of fat-soluble vitamins (38% for tocopherols and 7% for total retinols) and a decrease in riboflavin (13%) due to the loss of riboflavin enzymes located on the fat globules (ie xanthine oxidase). Both the typical cheeses and the new formulations represent good sources of calcium and protein. Protein digestibility was affected by the ripening time; in fact, in Pecorino Romano, ripened for 6–9 months it reached 62% in 6 h, whereas in Taleggio and in all caciotta–cheeses it reached only 32–37%. The nutritional profiles of the reformulated caciotta cheese showed that these products could represent a good choice in low-energy and low-sodium diets, but an enrichment of fat-soluble vitamins is advisable in the low-fat products. © 1997 SCI.     

Polycaprolactone blends for fracture fixation in low load-bearing applications

There is a need to replace surgical plates and screws in orthopedic surgery. Absorbable polymers are an alternative to metal where load bearing is of a less concern. Polycaprolactone (PCL) is biocompatible, yet it has low mechanical strength and its surface chemistry does not promote cell adhesion. The objective of this work was to create PCL adhesive blends with poly(glycolic) acid (PGA), thermoplastic starch (TPS), chitosan, and tricalcium phosphate (TCP) to be used as potential fracture fixation devices. The differential scanning calorimetry (DSC) data showed that the primary melting points (T _m1 °C) of blends were often lower than PCL, with the exception of chitosan blends, which may indicate an improvement for surgical use. PCL/PGA blends showed secondary and tertiary melting points (T _m) and enthalpies (ΔH _m) indicating poor miscibility of PGA in the blends. The binary PCL/TCP mixture has a higher enthalpy compared to the binary PCL/PGA blend, but the secondary melting temperature is lower in ternary mixtures. Ternary blends of PCL/PGA/TCP, however, retained the adhesive strength of the parent PCL adhesive while having an improvement in hydrophilicity. These blends are recommended for fracture fixation devices especially in low load-bearing applications such as maxillofacial surgery, orthopedics, and neurosurgery. © 2020 Wiley Periodicals Inc. J. Appl. Polym. Sci. 2020 , 137, 48940.     

Natural antioxidants in the unsaponifiable fraction of virgin olive oils from different cultivars

An investigation on carotene, α-tocopherol and squalene contents of olives from six different cultivars and 15 virgin olive oils produced in Molise region in 1995 was carried out. Olives were harvested at different stages of ripeness and oil was extracted in industrial plants by pressure or centrifugation systems. The concentration of carotenes, α-tocopherol and squalene have been correlated, both in fruit and oil samples, with the olive ripeness index. In particular a significant linear correlation (R²=0·95) has been found between olive ripeness index and olive carotene content. In order to evaluate the stability of the extracted oil, a 6 month storage test at room temperature in the dark has been carried out. In addition to the nutritional relevance of β-carotene and α-tocopherol, the compounds studied are also characterised by antioxidant activities. Within the same cultivar, tocopherol and squalene stability was inversely related to the degree of ripeness. In general, storage losses ranged, probably due to different antioxidant mechanisms, from 0 to 10% for carotene, from 14 to 32% for tocopherol and from 26 to 47% for squalene. © 1998 SCI.     

Molecular Lego of Human Cytochrome P450: The Key Role of Heme Domain Flexibility for the Activity of the Chimeric Proteins

The cytochrome P450 superfamily are heme-thiolate enzymes able to carry out monooxygenase reactions. Several studies have demonstrated the feasibility of using a soluble bacterial reductase from Bacillus megaterium, BMR, as an artificial electron transfer partner fused to the human P450 domain in a single polypeptide chain in an approach known as ‘molecular Lego’. The 3A4-BMR chimera has been deeply characterized biochemically for its activity, coupling efficiency, and flexibility by many different biophysical techniques leading to the conclusion that an extension of five glycines in the loop that connects the two domains improves all the catalytic parameters due to improved flexibility of the system. In this work, we extend the characterization of 3A4-BMR chimeras using differential scanning calorimetry to evaluate stabilizing role of BMR. We apply the ‘molecular Lego’ approach also to CYP19A1 (aromatase) and the data show that the activity of the chimeras is very low (<0.003 min⁻¹) for all the constructs tested with a different linker loop length: ARO-BMR, ARO-BMR-3GLY, and ARO-BMR-5GLY. Nevertheless, the fusion to BMR shows a remarkable effect on thermal stability studied by differential scanning calorimetry as indicated by the increase in T_onset by 10 °C and the presence of a cooperative unfolding process driven by the BMR protein domain. Previously characterized 3A4-BMR constructs show the same behavior of ARO-BMR constructs in terms of thermal stabilization but a higher activity as a function of the loop length. A comparison of the ARO-BMR system to 3A4-BMR indicates that the design of each P450-BMR chimera should be carefully evaluated not only in terms of electron transfer, but also for the biophysical constraints that cannot always be overcome by chimerization.