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  • Author or Editor: Gordana Jovanović x
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Abstract  

The present paper discusses the results of assessing thermal properties, vulcanization kinetic and swelling properties of acrylonitrile butadiene rubber (NBR) reinforced by carbon black (N-330) with mass ratio 0 to 100 phr. The kinetic parameters were determined from two high temperature rheokinetic curves (T1=180°C and T2=190°C). The cross-linking density was calculated using swelling measurements. Thermal stability of the samples was measured in the temperature range between 25 and 750°C.

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Abstract  

The influence of two types of carbon black filler N330 and N990 (primary particle size 46 nm and >230 nm) on elastomeric composites based on acrylonitrile-butadiene rubber (NBR) have been investigated. The activation energy (E a) were determined from two high temperature rheokinetic curves (T 1 = 180 °C and T 2 = 190 °C). For tensile testing, the compounds with different content of carbon black were vulcanized in a hydraulic press at 150 °C. The stress-strain experiments were performed before and after ageing the specimens in an air-circulating oven at 100 °C for 168 h. The thermal degradation and thermal stability of carbon black filled NBR rubber was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 10 °C/min.

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Journal of Thermal Analysis and Calorimetry
Authors: Gordana Marković, Suzana Samaržija-Jovanović, Vojislav Jovanović, and Milena Marinović-Cincović

Abstract  

The properties of filled polymers depend on the properties of the matrix and the filler, the concentration of the components and their interactions. In this research we investigated the rheological and mechanical properties and thermal stability of polychloroprene/chlorosulfonated polyethylene (CR/CSM) rubber blends filled with nano- and micro-silica particles. The density of the nano-silica filled CR/CSM rubber blends was lower than that of the micro-silica filled samples but the tensile strength and elongation at break were much higher. The nano-silica filled CR/CSM rubber blend has higher V r0/V rf values than micro-silica composites and show better polymer–filler interaction according to Kraus equation. The nano-silica filled CR/CSM rubber blends were transparent at all filler concentration, and have higher glass transition values than micro-silica filled compounds. The higher values of the glass transition temperatures for the nano- than the micro-filled cross-linked systems are indicated by DMA analysis. The nano-filled cross-linked systems have a larger number of SiO–C links than micro-filled cross-linked systems and hence increased stability.

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Acta Geologica Hungarica
Authors: Nadežda Krstić, Ljubinko Savić, Gordana Jovanović, and Elvira Bodor

The sea existing till the end of Oligocene was dotted with many islands in what is today the Balkan Peninsula area. At the very beginning of the Miocene this region became dry land, the Balkan Land, which was covered through time by lake systems of variable extent. During the Lower Miocene a succession of three lake systems spread not only over the Balkan Peninsula (comprising ex-Yugoslavia, NE Macedonia, SW and SE Bulgaria, and central Greece) but also over the northern parts of the Central and some of the Western Paratethys. Lacustrine environment ended shortly after the beginning of the Middle Miocene, when waters of the epicontinental Paratethys Sea covered the Balkan Land from the north. In this paper we do not consider any of the Upper Miocene and Pliocene lakes.

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Scientometrics
Authors: Milica Jovanovic, Veljko Jeremic, Gordana Savic, Milica Bulajic, and Milan Martic

Abstract

The aim of this paper is to present new ideas in evaluating Shanghai University's Academic Ranking of World Universities (ARWU). In particular, this paper shall try to determine whether the normalization of data affects University ranks. In accordance with this, both the normalized and original (raw) data for each of the six variables has been obtained. Based on a sample containing the 54 US universities which are placed in the ARWU top 100, the statistical I-distance method was performed. The results showed great inconsistencies between university ranks obtained for the original and normalized data. These findings were then analyzed and the universities that had the greatest fluctuation in their ranks were noted.

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The chromatographic behavior of four groups of s -triazine derivatives (15 compounds) has been studied on aminoplast and cellulose thin layers with two mobile phases, methanol-water-acetonitrile, 30 + 20 + X , where X = 1–10 ( v/v ), and methanol-dilute acetic acid, 30 + 20 ( v/v ). The mechanism of retention was investigated by changing of volume fraction of acetonitrile in the first mobile phase. Reversed-phase chromatography occurs on both supports. Retention constants, R M o were determined by extrapolation and good correlation was obtained between retention constants, R M o and log P . These retention constants can be used as the measure of the lipophilicity of compounds. The effect of mobile phase pH on the chromatographic retention of s -triazine derivatives was examined and approximate protonation constants, pK a , were determined on the basis of the dependence of retention on pH. These constants correlated well with Hammett substituent constants σ .

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Journal of Thermal Analysis and Calorimetry
Authors: Suzana Samaržija-Jovanović, Vojislav Jovanović, Sandra Konstantinović, Gordana Marković, and Milena Marinović-Cincović

Abstract

The thermal stability of pure urea–formaldehyde resin (PR) and modified urea–formaldehyde (UF) resins with hexamethylenetetramine-HMTA (Resin 1), melamine-M (Resin 2), and ethylene urea (EU, Resin 3) including nano-SiO2 was investigated by non-isothermal thermo-gravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA) supported by data from IR spectroscopy. Possibility of combining inorganic filler in a form of silicon dioxide with UF resins was found investigated and percentage of free formaldehyde was determined. The shift of DTG peaks to a high temperature indicates the increase of thermal stability of modified UF resin with EU (Resin 3) which is confirmed by data obtained from the FTIR study. The minimum percentage (6%) of free formaldehyde was obtained in Resin 3.

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Acta Microbiologica et Immunologica Hungarica
Authors: Ina Gajic, Lazar Ranin, Dusan Kekic, Natasa Opavski, Aleksandra Smitran, Vera Mijac, Snezana Jovanovic, Mirjana Hadnadjev, Maja Travar, and Gordana Mijovic

Abstract

Tigecycline can be effective to treat infections of carbapenem-resistant Acinetobacter baumannii (CRAB) however, no interpretive criteria have been approved so far. The objectives of this study were to evaluate the proportion of CRAB isolates and to compare gradient test with a broth microdilution (BMD) method for tigecycline susceptibility testing of A. baumannii.

This study included 349 multidrug-resistant (MDR) Acinetobacter spp. collected from Serbia, Montenegro, Bosnia and Herzegovina in 2016 and 2017. Antibiotic susceptibility testing was performed by disk diffusion, VITEK2, gradient, ComASP Colistin. Tigecycline susceptibilities were interpreted according to breakpoints of European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Food and Drug Administration (FDA).

Majority of the tested isolates were CRAB (92.8%). Tigecycline MIC50/MIC90 values were 4/8 μg/mL by BMD and 0.5/4 μg/mL by gradient test. Essential agreement for BMD and gradient test amounted to 65.1%. With EUCAST breakpoints, categorical agreement (CA) was achieved in 38% isolates. Major discordance (MD-false susceptibility/resistance) and minor discordance (mD-false categorization involving intermediate results) were observed in 10% and 57% A. baumannii, respectively. With FDA breakpoints, CA, MD and mD were observed in 44%, 16% and 47% isolates, respectively. Colistin resistance was 2.1%.

The study highlights a high proportion of CRAB and several discordances between BMD and gradient test which may lead to inappropriate therapy.

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