Long-Term Changes in a Heat Exchanger Steel

The steel ASTM A213 P22 is used for superheater outlet header in power plants. During duty cycles lasting over tens of years the temperature is of the order of 545°C and the pressure 125 atm. The microscopic changes in these steels are hard to analyze under working conditions, but they are believed to be responsible for the appearance of creeps in such devices. Investigation of the microscopic modifications will help to predict future failures due to creeps, increasing the reliability and saving a lot of money.We report the investigation of such changes in ASTM A213 P22 steel in use for 30 years as a Superheater header at Haifa power station. The analysis has been carried out using Mössbauer Spectroscopy, X-ray diffraction and optical microscopy. As a result it seems that the morphology and phase change of the carbide phases M₃C/M₇C₃ and M₂₃C₆ are the most prominent changes leading to the material failures.     

The Role of Flavonoids as a Cardioprotective Strategy against Doxorubicin-Induced Cardiotoxicity: A Review

Doxorubicin is a widely used and promising anticancer drug; however, a severe dose-dependent cardiotoxicity hampers its therapeutic value. Doxorubicin may cause acute and chronic issues, depending on the duration of toxicity. In clinical practice, the accumulative toxic dose is up to 400 mg/m² and increasing the dose will increase the probability of cardiac toxicity. Several molecular mechanisms underlying the pathogenesis of doxorubicin cardiotoxicity have been proposed, including oxidative stress, topoisomerase beta II inhibition, mitochondrial dysfunction, Ca²⁺ homeostasis dysregulation, intracellular iron accumulation, ensuing cell death (apoptosis and necrosis), autophagy, and myofibrillar disarray and loss. Natural products including flavonoids have been widely studied both in cell, animal, and human models which proves that flavonoids alleviate cardiac toxicity caused by doxorubicin. This review comprehensively summarizes cardioprotective activity flavonoids including quercetin, luteolin, rutin, apigenin, naringenin, and hesperidin against doxorubicin, both in in vitro and in vivo models.     

Global analysis of the dynamics of a mathematical model to intermittent HIV treatment

The aim of this paper is to study the qualitative dynamics of a piecewise smooth system modeling the intermittent treatment of the human immunodeficiency virus. Typical singularities and closed orbits are observable, and we quantitatively explore the dynamics around those singularities and closed orbits. Moreover, we conclude that this protocol always will be successful since the trajectory passing through any initial condition converges to one of these distinguished orbits. Our formal mathematical results corroborate the real-world observation, where the virus is not eliminated, but the number of infected cells is controlled around a specific value.

     

Sucrose preculture to simplify cryopreservation of banana meristem cultures

A simple cryopreservation method is described for proliferating meristem cultures of banana (Musa spp.). It relies on a 2-week preculture on media containing 0.4 M sucrose followed by rapid cooling in liquid nitrogen. Different preculture media were screened for efficient protection of banana meristems against cryopreservation. Sucrose can be replaced by both fructose and glucose without significantly affecting post-thaw survival rates. A high BA concentration (0.1 mM) in the preculture medium results in less material available for cryopreservation, but does not affect cryoprotection. Culture in liquid media significantly improved post-thaw regeneration. The optimized cryopreservation protocol was applied on 36 banana accessions belonging to 8 different genomic groups. It is shown that post-thaw regeneration frequencies (ranging between 0 and 66 percent) are highly dependent on the genomic constitution of the banana cultivar.     

Multilayered scattering reference mirror for full field optical coherence tomography with application to cell profiling

A multilayered scattering structure is proposed and demonstrated as a reference mirror for use with full field optical coherence tomography (FF-OCT) to increase contrast of tissue imaging and provide compensation. Common-path FF-OCT systems were built demonstrating high resolution cell profiling. The use of this mirror with frequency domain FF-OCT allows 3D images in real time.     

Recovery and characterisation of hybrid firs (Abies alba x A. cephalonica, Abies albax A. numidica) embryogenic tissues after cryopreservation

Embryogenic tissues of hybrid firs were cryopreserved using a slow freezing protocol. The procedure involved preculture of tissues for 24, 48 or 72 h in media with different sorbitol concentrations (0.4 or 0.8 M) and addition of 5% (v/v) DMSO as cryoprotectant. The cell lines tested withstood cryopreservation, even though tissue regrowth after thawing was dependent on treatment and cell line. For cell line AN72, regrowth was 100% for all experimental conditions tested. With cell line AC78, regrowth was 100% except after shorter pretreatment durations, which produced 83% and 86% regrowth for 0.4 M and 0.8 M sorbitol pretreatment, respectively. Cell lines AC1 and AC4 were more sensitive to cryopreservation with 37.5 to 100% regrowth, respectively. Growth parameters evaluated 3 months after cryopreservation showed cell line and treatments effects. In most cases, cryopreservation had no negative effect on growth of tissues. Statistically significant differences in fresh mass accumulation were found for four samples out of 24 investigated, although growth increase of these tissues still reached 79.4-84.6%, compared with non-cryopreserved ones (100% increase). Maturation capacity and genetic fidelity were studied in tissues whose growth was not negatively influenced by cryopreservation. Maturation capacity of embryogenic tissues cryopreserved using the optimal protocol was comparable to that of non-frozen controls. RAPD analysis of 88 genomic regions per cell line did not reveal any changes in genetic fidelity of cryopreserved tissues compared to non-cryopreserved controls.     

Methods for the efficient quantification of fruit provitamin A contents

As part of a screening program to identify micronutrient-rich banana and plantain (Musa) varieties, a simple, robust, and comparatively rapid protocol for the quantification of the provitamin A carotenoids contents of fruit pulp and peel tissues by HPLC and by spectrophotometry has been developed. Major points to note include the use lyophilisation and extensive tissue disruption procedures to ensure quantitative recoveries, and the avoidance of saponification and/or concentration steps which lead to significant losses of provitamin A carotenoids. The protocol showed excellent reproducibility between replicate extractions, without the need for an internal standard. Application of the methodology demonstrated that Musa fruit pulp has a relatively simple provitamin A carotenoids content, quite different from the overlying peel, and that the proportions of alpha- and beta-carotene are characteristic for each genotype. The protocol was also used to profile the provitamin A carotenoids of several other fruits.     

On the Teixeira singularity bifurcation in a DC–DC power electronic converter

Nonlinear Dynamics - The electronic circuit of a DC–DC boost power converter under a specific sliding mode control strategy is analyzed. This circuit is modeled as a discontinuous piecewise...     

Mechanism of adhesion between protein-based hydrogels and plasma treated polypropylene backing

We studied the mechanism of adhesion between N₂ plasma treated polypropylene (PP/N₂) backing and a hybrid hydrogel (HG) produced by chemical crosslinking between poly(ethylene glycol) and soy albumin. The work of adhesion, measured by peel testing, was found to be 25 times higher for PP/N₂ compared to untreated PP (≈5.0 J/m² versus ≈0.2 J/m²). In order to understand the adhesion mechanism, we performed a detailed analysis of the surface chemical composition of PP and PP/N₂ using X-ray photoelectron spectroscopy (XPS), chemical derivatization and attenuated total reflectance infra-red (ATR-IR) measurements. The results confirm incorporation of different nitrogen- (amine, amide,…) and oxygen- (hydroxyl, carboxyl,…) containing chemical groups on the PP/N₂ surface. The derivatized functions were primary amine, hydroxyl, carboxyl and carbonyl groups. Chemical derivatization reactions validated the XPS results (except for carbonyl groups), and they clearly underlined the essential role of primary amine groups in the adhesion process. In fact, after derivatization of the amine functions, the work of adhesion was found to be 0.41 ± 0.12 J/m². Participation of amine groups in the formation of covalent bonds at the interface between PP/N₂ and HG was directly confirmed by ATR-IR measurements.