Fitting curves and impact toughness transition temperature of quenched and tempered steel welds

Welded products of quenched and tempered (QT) structural steels are used from ambient to moderately low design/service temperatures. Therefore, besides base metal, a weld also must possess required minimal design impact toughness (KV) at temperatures lower than transition temperature (TT), where the transition from ductile to brittle fracture occurs. A common way to determine transition temperature is by use of appropriate fitting curves, in accordance with specified standardised criterion. From the point of welding procedure evaluation, it is important to analyse welds for its impact toughness and transition temperature, particularly for three main zones: weld metal, heat-affected zone (HAZ) and base metal. This paper covers welds of two QT steel grades, 690 and 890, which are interesting regarding their yield strength and characteristic weld zones. Basic details of gas metal arc welding (GMAW, process used in this experiment) are provided, while temperatures for impact toughness tests of weld zones were varied from +20 °C down to -60 °C. Based on acquired experimental results of impact toughness, fitting curves were developed by use of Oldfield model, e.g. hyperbolic tangent function. Acquired transition temperatures (TT) from fitting curves show mostly allowable values for all three weld zones. As expected, lower strength grade 690 possess higher impact toughness, in comparison to higher strength grade 890. The standardized criteria of minimal absorbed energy of 30 J (KV) and 50 % of shear fracture (SF) show different transition temperatures (TT-30J and TT-50%SF), while general dependence of impact toughness to shear fracture (KV vs. SF) shows a reasonable trend. Finally, used GMAW procedures may be considered as acceptable, since for both steel grades (690 and 890) all three weld zones show better TT-30J values than minimal required by standard (TT-30J=-40 °C) for QT structural steels

Optimizacija proizvodnje biodizela kukuruznog ulja metanolizom katalizovanom pepelom kurdeljke

The use of low-cost or priceless feedstocks such as byproducts in biodiesel production results in a reduced overall process costs. The present paper reports the use of corn germs and corn cobs as byproducts from corn-based starch production in the biodiesel production by the methanolysis of the oil extracted from corn germs, catalyzed by the ash produced by combustion of corn cobs. The major aim was to optimize the methanol-to-oil molar ratio, catalyst loading, and reaction time in a batch stirred reactor with respect to the content of methyl ester fatty acids (FAME). The statistical modeling and optimization were carried out using a second-order polynomial (quadratic) model developed by the response surface methodology combined with a 33 factorial design with 3 central points. The FAME content was determined by a high-pressure liquid chromatography method. The analysis of variance showed that only the catalyst amount, the reaction time, the catalyst amount interaction with reaction time and all three quadratic terms were the significant model terms with the confidence level of 95 %. The optimum reaction conditions (the catalyst amounts of 19.8 %, the methanol-to-oil molar ratio of 9.4 mol/mol and the reaction time of 31 min) provided the FAME content of 98.1 %, which was in an excellent agreement with the predicted FAME content (98.4 %). Thus, both corn germs and corn cobs may be suitable feedstocks for biodiesel production.Upotreba jeftinih ili bezvrednih sirovina, kao što su sporedni proizvodi, u proizvodnji biodizela ima za rezultat smanjene ukupne troškove procesa. U ovom radu su prikazani rezultati upotrebe kukuruznih klica i okrunjenog kukuruznog klipa (kurdeljke, krudeljke) kao sporednih proizvoda iz proizvodnje kukuruznog skroba u proizvodnji biodizela metanolizom ulja izdvojenog iz kukuruznih klica, katalizovane pepelom dobijenim sagorevanjem kurdeljke. Glavni cilj je bila optimizacija molskog odnosa metanol-ulje, količine katalizatora i reakcionog vremena u šaržnom reaktoru sa mešanjem u odnosu na sadržaj metilestra masnih kiselina (MEMK). Statističko modelovanje i optimizacija izvršeni su korišćenjem kvadratnog modela, razvijenog metodologijom odzivne površine, u kombinaciji sa 33 faktorijelnim planom sa 3 centralne tačke. Sadržaj MEMK-a je određen metodom tečne hromatografije pod visokim pritiskom. Analiza varijanse je pokazala da su samo uticaji količine katalizatora, reakcionog vremena, interakcije količine katalizatora sa reakcionim vremenom i sva tri kvadratna člana statistički značajni sa nivoom pouzdanosti od 95 %. Pod optimalnim reakcionim uslovima (količina katalizatora 19,8 %, molski odnos metanol/ulje 9,4 mol/mol i reakciono vreme 31 min) dobijen je sadržaj MEMK-a od 98,1 %, koji se slaže sa predviđenim sadržajem MEMK-a (98,4 %). Prema tome, i kukuruzne klice i kurdeljka mogu biti pogodne sirovine za proizvodnju biodizela

Enhanced Catalytic Activity and Energy Savings with Ni-Zn-Mo Ionic Activators for Hydrogen Evolution in Alkaline Electrolysis

Green hydrogen produced by alkaline electrolysis is a promising solution to address the world’s increasing energy demand while mitigating greenhouse gas emissions. However, the efficient and cost-effective production of green hydrogen via alkaline electrolysis requires improvements. This paper presents an in situ activation process that simplifies the alkaline electrolysis technology while enhancing the catalytic activity of electrodes for the hydrogen evolution reaction. The aim of this research is to enhance the energy efficiency of alkaline electrolysis and decrease the energy consumption for hydrogen production. To achieve this goal, ionic activators comprising Ni, Zn, and Mo were incorporated into the standard electrolyte solution. Our results demonstrate that the anticipated improvement in the catalytic activity of the d-metal combination, surpassing even that of precious metals, has been successfully attained. As a result, a 20% reduction in energy consumption (REC) for the hydrogen produced has been observed. The catalytic activity of the added activators for the hydrogen evolution reaction was discussed by analyzing the mechanism of the reaction via Tafel analysis and EIS techniques. These findings offer a promising approach to improve alkaline electrolysis and enhance the production of green hydrogen

Copper and zinc concentrations in atherosclerotic plaque and serum in relation to lipid metabolism in patients with carotid atherosclerosis

Background/Aim. Some oligoelements are now investigated as possibly having a role in atherosclerosis. The aim of this study was to compare the concentrations of copper and zinc in the serum and carotid plaque and parameters of lipid metabolism in patients with different morphology of carotid atherosclerotic plaque. Methods. Carotid endarterectomy due to the significant atherosclerotic stenosis was performed in 91 patients (mean age 64 ± 7). The control group consisted of 27 patients (mean age 58 ± 9), without carotid atherosclerosis. Atheroscletoric plaques were divided into four morphological groups, according to ultrasonic and intraoperative characteristics. Copper and zinc concentrations in the plaque, carotid artery and serum were measured by atomic absorption spectrophotometry. Results. Serum copper concentrations were statistically significantly higher in the patients with hemorrhagic in comparison to those with calcified plaque (1.2 ± 0.9 μmol/L vs 0.7 ± 0.2 μmol/L, respectively; p = 0.021). Zinc concentrations were statistically significantly lower in plaques of the patients with fibrolipid in comparison to those with calcified plaques (22.1 ± 16.3 μg/g vs 38.4 ± 25.8 μg/g, respectively; p = 0.024). A negative significant correlation was found for zinc and triglycerides in the serum in all the patients (r = -0.52, p = 0.025). In the control group we also demonstrated a positive significant correlation for low-density lipoprotein cholesterol and copper in the serum (r = 0.54, p = 0.04). Conclusion. The data obtained in the current study are consistent with the hypothesis that high copper and lower zinc levels may contribute to atherosclerosis and its sequelae as factors in a multifactorial disease. Further studies are necessary in order to conclude whether high concentration of copper and zinc in the serum could be risk factors for atherosclesrosis

Toksičnost i kinetika otpuštanja insulina iz hormonaktivnih polisaharidnih vlakana

In this paper an account of biocompatibility of a hormonactive fiber in the form of biologically active complex chitosan-insulin is presented. The behavior of artificial depots of insulin containing 180-330mg of insulin per gram of fiber has been studied. The artificial depot of insulin has been characterized from the standpoint of its behavior in physiological solution (in the culture of L929 cells and in organism of an experimental animal). In vitro conditions, the intensity of desorption depends on the nature of solution and on pH of medium. It has been shown that insulin is controllably delivered in physiological solutions in quantities of 1.3-1.6mg of insulin during 24 hours, at pH about 7. The quantity of insulin delivered has been assessed by UV Sprectrophotometry. Biocompatibility of hormone-active fibers in the form of artificial depot of insulin has been determined in pre-clinical conditions through determination of the degree of harmfulness (toxicity) to the organism of the experimental animal. Tests have been performed according to the matrix for testing of biocompatibility and according to recommendations and guides published in Guidelines ISO 10993. Noxiousness has been assessed by testing: citotoxicity, sensitivization and irritation. Qualitative and quantitative citotoxicity tests in direct contact on L929 cells culture have shown that a hormone-active fiber does not provoke the citotoxic effect. The results obtained have shown that quantities of controllably released insulin could satisfy basal needs of an organism and that the artificial depot does not show effects of toxicity. On the bases of the obtained results from tests and calculated index of sensitivitization it follows that the artificial depot of insulin does not cause sensitivization. Also, the results obtained by subcutaneous irritation testing showed that the fibrous artificial depot of insulin could be eveluated as a non-irritating bioactive material.U ovom radu kao deo pretkliničkog ispitivanja biokompatibilnosti, ispitivana je toksičnost i efikasnost veštačkih depoa insulina. Veštački depoi insulina sadržali su 180-330 mg insulina po gramu vlakna hitozana. Cilj rada je bio: 1. odrediti kinetiku otpuštanja insulina iz hormonaktivnog vlakna u in vitro uslovima, 2. ispitati senzibilizaciju in vivo; 3. ispitati primarnu kutanu iritaciju in vivo i 4. ispitati citotoksični efekat in vitro. Metode: Količina otpuštenog insulina praćena je UV spektrofotometrijom. Pretklinička ispitivanja biokompatibilnosti hormonaktivnih vlakana izvršena su prema preporukama i vodičima publikovanih u Guidelines ISO 10993 kao i prema matriksu za ispitivanje biokompatibilnosti. Toksičnost je ispitana kroz testiranje: senzibilizacije i primarne kutane iritacije in vivo i testiranje citotoksičnosti (kvalitativno i kvantitativno) u kulturi L929 ćelija. Pokazano je da se insulin kontrolisano otpušta u fiziološkom rastvoru u količinama od 1.3-1.6 mg insulina u toku 24 sata, pri pH oko 7. Prema dobijenim rezultatima ispitivanja i izračunatog indeksa senzibilizcije sledi da veštački depo ne izaziva senzibilizaciju. Takođe, dobijeni rezultati ispitivanja primarne kutane iritacije su pokazali da se vlaknasti veštački depo insulina može oceniti kao neiritirajući bioaktivni materijal. Kvalitativni i kvantitativni testovi citotoksičnosti u direktnom kontaktu na kulturi ćelija L929 su pokazali da hormonaktivno vlakno ne izaziva citotoksični efekat. U cilju dalje karakterizacije biokompatibilnosti (toksičnosti i efikasnosti) hormonaktivnih polisahaidnih vlakana, dalja istraživanja su neophodna pre njihove kliničke primene

Mathematical Model of Gentamicin Sulfate Release from a Bioactive Textile Material as a Transdermal System Under In Vitro Conditions

A mathematical model was developed to estimate the release of gentamicin sulfate from a bioactive textile material as a transdermal system for wound dressing. The gentamicin sulfate released from the antibiotic/chitosan hydrogel complexes was measured in vitro by the Franz diffusion cell technique. The diffusive transport of gentamicin sulfate through three connected compartments, that is, chitosan hydrogel, membrane, and solution, was considered by the formulation of a model based on Fick's second law. Initially, the total amount of gentamicin sulfate was placed within an already swollen chitosan hydrogel. The value of the diffusivity coefficient of the drug through the chitosan hydrogel was calculated for every initial amount of the active substance. For the initial concentration of gentamicin sulfate, which was lower than 2.81 x 10(4) mu g/mL, the diffusion coefficient was approximately constant. A higher amount of gentamicin sulfate in the hydrogel reduced its own transport as a consequence of an increase in the intensity of the interaction field between the molecules of gentamicin sulfate. The model provides the possibility of optimizing the process of drug release by ensuring a compromise between a higher value of the diffusivity coefficient and a desirable amount of gentamicin sulfate and a constant concentration within the solution over 48 h

A contribution to the elucidation of oil migration mechanisms through water-wet sediments: Crushed rock environment as example

In order to gain insight into oil transformations which occur during migration, and to contribute to the elucidation of migration mechanisms in water-wet environments, the content and composition of heavy fuel oil from an accidental oil spill near the railway station of Ušće (Kraljevo) was determined in crushed rock samples from various depths and distances from the oil spill. The group composition (saturated hydrocarbons, aromates, NSO-compounds and residue) of heavy fuel oil extracts was determined. n-Alkanes and isoprenoid alkanes, pristane (Pr) and phytane (Phyt), in the saturated hydrocarbon fraction were identified by gas chromatography (GC). X-ray diffraction analysis (XRD) was applied on the inorganic residue in order to determine its mineralogical composition. The observed differences in the group composition (increase in NSO-compounds content with depth and distance), and in the distribution of n-alkanes and isoprenoid alkanes (the shift of the n-alkane-maximum and the shift of Pr/n-C17-and Phyt/n-C18-ratios towards higher values with depth and distance) lead to the conclusion that heavy fuel oil migration through the crushed rock environment occurred in the presence of water by the colloidal micelle mechanism

Efficiency and Biocompatibility of Antimicrobial Textile Material of Broad Spectrum Activity

the antimicrobial textile material. The material is in the form of plaster wound dressing which is consisting of a nonwoven textile base containing polypropylene (PP)/viscose, a polymer carrier, and an antimicrobial active substance. The polymer carrier is the polysaccharide D-glucosamine (chitosan), and the active antimicrobial substance is antibiotic gentamicin sulfate. The amount of gentamicin sulfate immobilized into the polymer matrix of the polymer carrier was 0.15-0.20 mg/cm(2) or 2.0-2.5% of the mass of the nonwoven textile material. The antimicrobial textile material has been studied in vitro and in vivo conditions through the efficiency of the antimicrobial effects on different kinds of pathogenic microorganisms, as well as the biocompatibility in preclinical research. The results of these experiments indicate that all bioactive textile materials were biocidal in vitro for all pathogenic test organisms. Good biocompatibility, the existence of the correlation between the in vitro and in vivo results, concerning efficiency, qualifies these antimicrobial biornaterials for clinical use

Internal carotid artery occlusion or subocclusion: Contemporary diagnostic challenges: Case report

Introduction. Measurement of vessel stenosis using ultrasonography or magnetic resonance is still the principal method for determining the severity of carotid atherosclerosis and need for endarterectomy. Case Outline. A 56-year-old male was admitted to the Cardiovascular Institute 'Dedinje' due to a clinically asymptomatic restenosis of the operated left internal carotid artery (ICA). Angiography and magnetic resonance angiography (MRA) in previous hospitalization had revealed occluded right ICA. However, routine duplex ultrasonography revealed a highgrade restenosis (85%) of the left ICA and subocclusion of the right ICA by an ulcerated plaque (confirmed on repeated MRA). Conclusion. Selective arteriography examination could misrepresent the degree of stenosis especially in patents with the ICA that seems to be occluded. MRA is considered the method of choice for identifying pseudo-occlusions of ICA