Search Results

You are looking at 21 - 28 of 28 items for

  • Author or Editor: D. Živković x
  • Refine by Access: All Content x
Clear All Modify Search

Non-isothermal thermogravimetric analysis was used for determination of the kinetics of aluminium hydroxide dehydration in an air atmosphere and for processing of the experimental results by the method due to Chatterjee.

Restricted access

In this paper, the results of copper-lead matte investigations are presented. Investigated copper-lead matte is intermediate product of the lead production in TREPCA-Zvečan. In the first part of the paper characterization of starting material is presented, consisting of: chemical composition analysis (XRQ), scanning electron microscopy (SEM) and diffractometry (XRD). Thermal properties of investigated matte were determined using differential thermal analysis (DTA) at characteristic temperatures. Using results of induced analysis, mechanism of matte oxidation process was determined. In the second part of the paper kinetic parameters describing oxidative roasting of copper-lead matte are presented. For activation energy calculations, non-isothermal methods defined by Kissinger and Ozawa were used [1, 2]. Kinetic equation describing oxidation process was determined using Sharps method of reduced half time of reaction [3].

Restricted access

Abstract  

The non-oxidative thermal degradation of poly (di-2-chloroethyl itaconate) (PD2CEI) was studied by TG and by analysing the thermal products. The major processes occurring during thermal analysis are crosslinking, depolymerisation and carbonisation. The thermal degradation activation energy increased with increasing sample mass loss. The thermal degradation of PD2CEI was compared to that of the structurally similar poly(2-chloroethyl methacrylate) (P2CMA).

Restricted access

The influence of seasonal variations on the chemical composition and composition of fatty acids in five commercially important freshwater fish species from the Danube: white bream, bream, vimba, zope, and Prussian carp, during May, July and September was determined. Changes in the chemical composition of meat of all examined species had the same tendencies. Water and protein content in the meat decreased, while fat content increased. The most frequent fatty acids in the meat of all the examined fish were the following: 18:1 n-9 (oleic), 16:0 (palmitic), 16:1 (palmitoleic), 18:2 n-6 (linoleic), 20:1 (eicosenoic), 20:5 n-3 eicosapentaenoic acid (EPA), 20:4 n-6 arachidonic acid and 22:6 n-3 docosahexaeonic acid (DHA). The content of saturated fatty acids (SFA) ranged from 25.03% to 32.43% and displayed a tendency to increase during the observed period. The total content of the n-6 group in the meat of Prussian carp was higher than in other species, which was probably a consequence of specific diet. The total content of n-3 fatty acids in the meat of white bream, bream, vimba and zope was the highest in May, and it declined during July-September. We can conclude that the meat of white bream and vimba contains high nutritional values in terms of EPA and DHA content. The n-3/n-6 ratio was also very favourable: 0.9 to 2.0 in the meat of white bream, bream, vimba and zope, with a clear downward tendency in the observed period.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
D. Zivkovic
,
N. Štrbac
,
V. Trujić
,
Ž. Živković
,
M. Vuksan
,
Z. Živković
,
B. Milosavljević
,
M. Cocić
, and
V. Andricć

Abstract  

Results of physico-chemical investigations of slag occurrences from site Rgotski Kamen (Timok region, Serbia), obtained by using chemical analysis, XRD analysis, EDXRF spectroscopy, thermal analysis, mass spectrometry and optical microscopy, are presented in this paper.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
Z. D. Zivkovic
,
N. Milosavljevic
,
M. Grotowska
, and
W. Wojciechowski

In this paper the results of comparative thermal analysis TG-DTG-DTA-DSC for the thermal decomposition process of [Cr(NH3)6]Cl3 in air atmosphere are given. The kinetics and mechanism of this complex thermal decomposition, process enthalpy as the changes of specific thermal capacity of solid products reaction with temperature were determined.

Restricted access

This study aimed to assess the role of H2S in homocysteine-induced cardiodynamic effects in the isolated rat heart. The hearts were retrogradely perfused according to the Langendorff technique. The maximum and minimum rates of pressure in the left ventricle (dp/dt max, dp/dt min), systolic and diastolic left ventricular pressures (SLVP, DLVP), heart rate (HR), and coronary flow (CF) were measured. A spectrophotometrical method was used to measure the following oxidative stress markers: index of lipid peroxidation (thiobarbituric acid reactive substances, TBARS), nitrite level (NO2 ), superoxide anion radicals (O2 •−), and hydrogen peroxide (H2O2) concentrations. The administration of 10 µmol/l DL-homocysteine (DL-Hcy) alone decreased dp/dt max, SLVP, and CF but did not change any oxidative stress parameters. The administration of 10 µmol/l DL-propargylglycine (DL-PAG) decreased all cardiodynamic parameters and increased the concentration of O2 •−. The co-administration of DL-Hcy and DL-PAG induced a significant decrease in all estimated cardiodynamic parameters and decreased the concentration of NO2 and O2 •− but increased the levels of TBARS and H2O2. Homocysteine shows a lower pro-oxidative effect in the presence of hydrogen sulfide (H2S), which indicates a potential anti-oxidative capacity of H2S.

Restricted access
Acta Physiologica Hungarica
Authors:
V. Zivkovic
,
P. Lazarevic
,
D. Djuric
,
D. Cubrilo
,
M. Macura
,
M. Vuletic
,
N. Barudzic
,
M. Nesic
, and
Vladimir Jakovljevic

Despite worldwide popularity of soccer, there are still insufficient data about the effects of training process on oxidative stress-induced damage, which may occur during chronic exercise. The present study aimed to determine the effects of a six-month training programme on basal redox status of young male soccer players. The study included 26 male soccer players, aged 12–13, who participated in a six-month training programme, and 26 age-matched non-athletes who were not implemented in the training process. Blood samples were collected (before and after six-month training programme) in order to measure the following oxidative stress markers: index of lipid peroxidation (measured as TBARS), nitrites (NO2 ), superoxide anion radical (O2 ), hydrogen peroxide (H2O2), superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH) level. After six months, the levels of TBARS and NO2 were significantly increased, while the O2 and H2O2 remained unchanged. On the other hand, SOD and CAT activity increased, while GSH decreased. A carefully prepared training programme could strengthen most components of antioxidant defence systems and, except lipid peroxidation, does not promote oxidative stress in response to regular physical activity. These findings could help in the improvement of training programmes for young athletes.

Restricted access