Vladimir A. Blagojević

Thermal properties of

In this work we used the photoacoustic transmission method to characterize CdTe and Hg1−xCdxTe bulk and epitaxially grown single crystals. The thermal properties of our samples were determined by PA amplitude and phase spectra analyses. The effective thermal diffusivity for two layer system (HgCdTe epitaxial layer on CdTe substrata) was obtained.

ADVICE—Educational System for Teaching Database Courses

This paper presents a Web-based educational system, ADVICE, that helps students to bridge the gap between database management system (DBMS) theory and practice. The usage of ADVICE is presented through a set of laboratory exercises developed to teach students conceptual and logical modeling, SQL, formal query languages, and normalization. While working on the exercises, students use the system to access real databases, and the system provides them with feedback about their solutions. From the perspective of an instructor, the system allows easy exercise management and continual progress monitoring. The paper also describes a practical experience with the use of ADVICE on a database course over a three-year period.

Investigation of Zinc-Stannate Synthesis Using Photoacoustic Spectroscopy

Mixtures of ZnO and SnO2 powders, with molar ratio of 2:1, were mechanically activated for 40, 80 and 160 minutes in a planetary ball mill. The resulting powders were compacted into pellets and non-isothermally sintered up to 1200˚C with a heating rate of 5˚C/min. X-ray diffraction analysis of obtained powders and sintered samples was performed in order to investigate changes of the phase composition. The microstructure of sintered samples was examined by scanning electron microscopy. The photoacoustic phase and amplitude spectra of sintered samples were measured as a function of the laser beam modulating frequency using a transmission detection configuration. Fitting of experimental data enabled determination of photoacoustic properties including thermal diffusivity. Based on the results obtained a correlation between thermal diffusivity and experimental conditions as well the samples microstructure characteristics was discussed.

Hydrogen Economy: Modern Concepts, Challenges and Perspectives

Identifying and building a sustainable energy system are two of the most critical issues for any modern society. Ideally, current energy system, based mostly on fossil fuels, which have limited supply and considerable negative environmental impact, would be replaced with a system based on a renewable fuel. Hydrogen, as an energy carrier primarily derived from water, can address the issues of sustainability, environmental emissions and energy security. If one assumes a full hydrogen economy the size of United States, the amount of hydrogen for just purposes of transportation would be about 150 million tons per year, which would amount to consuming, with current production efficiency, between 2 and 5 billion tons of water. As a comparison, current water consumption in United States for purpose of thermoelectric power generation in power plants is around 300 billion tons, with another 1.2 billion tons consumed for gasoline production. Therefore, rather than consume, a hydrogen economy would most likely significantly reduce water consumption for purposes of energy generation (Turner, 2004).

Ni(II) complex with bishydrazone ligand: synthesis, characterization, DNA binding studies and pro-apoptotic and pro-differentiation induction in human cancerous cell lines

A new Ni(II) complex, [Ni(L)(H2O)] (1), with diethyl 3,3′-(2,2′-(1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))bis(hydrazin-1-yl-2-ylidene))bis(3-oxopropanoate) ligand (H2L) was synthesized as a potential chemotherapeutic agent. Polidentate ligand was coordinated to Ni(II) NNN-tridentately, in dianionic form, while monodentate water coordination completed square-planar geometry around metal. Structure in the solution was determined by NMR spectroscopy and the same coordination mode was observed in the solid state using IR spectroscopy and further verified by DFT calculations and electrochemical studies. Thermal stability of 1 was determined in both air and nitrogen atmosphere. Anticancer activity of 1 was investigated on acute monocytic leukemia (THP-1) and pancreatic adenocarcinoma (AsPC-1) cell lines. On THP-1 cells 1 induced powerful apoptotic response (ED50 = 10 ± 3 μM), which was revealed to be only partially caspase-dependent, with activation of caspase-8 as the dominant course. This suggested that experimentally validated covalent binding of 1 to DNA is not the only mechanism responsible for programmed cell death. This was supported with experiments on AsPC-1 cells. Although treatment of those cells with 1 resulted in poor apoptotic response, cell cycle changes showed concentration-dependent shifts indicating a dual mechanism of activity. This study also reviews the results of preliminary biological screening, which demonstrates that 1 displays a unique pattern of anticancer activity with at least two mechanisms involved.

Hydrothermal synthesis and controlled growth of vanadium oxide nanocrystals

0-, 1- and 2-dimensional nanocrystals of different vanadium oxides were synthesized using hydrothermal reaction of commercial bulk monoclinic VO2 and V2O3 precursor, which, depending on reaction conditions, produced nanoparticles, nanoribbons and nanosheets of different vanadium oxides. Addition of acetone was used to direct growth and produce two-dimensional nanosheets, whose aspect ratio depends on acetone-to-precursor concentration, while addition of different alcohols as ligands successfully controlled the nanoribbon size. Variation of pH also changes the product dimensionality, allowing production of nanosheets at pH < 3, nanoribbons at 3 < pH < 7 and, through inhibition of reaction, nanoparticles at high pH. Products of different morphology exhibit systematic increase in unit cell volume with decrease in thickness of nanocrystals. The reaction occurs with VO2+ ion as the primary reactant, requiring only a source of VO2+ ions, and not necessarily crystalline VO2(M), allowing use of other precursors, like VOSO4. Calculations indicate that nanoribbon formation is primarily caused by differences in relative stability of individual crystal planes of VO2. Addition of different amounts of hydrogen peroxide changes the oxidation state of vanadium to produce V3O7 and V2O5, without affecting the product morphology, while use of bulk V2O3 as a precursor leads to the formation of V2O3 nanoribbons, nanoleaves and nanoparticles with similar mechanisms of size and shape control.

Kinetics, mechanism, and DFT calculations of thermal degradation of a Zn(II) complex with N-benzyloxycarbonylglycinato ligands

A Zn(II) complex with N-benzyloxycarbonylglycinato ligands was studied by non-isothermal methods, in particular Kissinger–Akahira–Sunose’s method, and further analysis of these results was performed by Vyazovkin’s algorithm and an artificial compensation effect. Density functional theory calculations of thermodynamic quantities were performed, and results obtained by both methods are consistent, thus clarifying the mechanism of this very interesting multi-step degradation.Graphical abstract

Thermal stability and degradation of binuclear hexaaqua-bis(ethylenediamine)-( μ 2 -pyromellitato)dinickel(II) tetrahydrate

Thermal degradation of ternary transition metal complex containing tetraanion of pyromellitic acid, pyr, and ethylenediamine, en, [Ni2(en)2(H2O)6(pyr)]·4H2O, 1, was investigated under non-isothermal conditions. The mechanism of thermal degradation, which occurs in three steps, was clarified by TG/DSC measurements in conjunction with FT-IR spectroscopy and XRPD analysis. The complexity of all degradation steps has been revealed using isoconversional methods. Dehydration comprises the loss of ten water molecules in a relatively narrow temperature interval, resulting in a very complicated reaction mechanism. In addition, density functional theory calculations have been applied for better understanding of dehydration. The second degradation step, related to loss of en, was separated into two single-step processes with Fraser–Suzuki function. The obtained individual steps were described by Johnson–Mehl–Avrami A2 model and Šesták–Berggren model, respectively. Validation of the proposed kinetic triplets for individual steps was performed using master plot and Pérez-Maqueda criteria. The third degradation step is related to the fragmentation of pyr ion most likely followed with the release of a number of gaseous products.

Nanocrystal Growth in Thermally Treated Fe75Ni2Si8B13C2 Amorphous Alloy

Thermal treatment of amorphous Fe75Ni2Si8B13C2 alloy leads to crystallization of the stable α-Fe(Si) and Fe2B as well as to the metastable Fe3B phase. The study of the mechanism of crystal growth of the α-Fe(Si) phase revealed that the mechanism of α-Fe(Si) growth changes from two dimensional in the early stage to one dimensional in the later stage of crystallization. The Fe2B phase was found to crystallize through two independent routes: from the amorphous phase and from the metastable Fe3B phase, which leads to a different mechanism of crystal growth for each route. Both routes exhibit a change in the mechanism of crystal growth: from two dimensional to one dimensional and from three dimensional to two dimensional, respectively. The respective mechanisms of crystal growth correlate well with the observed changes in preferential orientation of the crystallites of the Fe2B phase.

Synthesis and thermal stability of cis -dichloro[ (E) -ethyl-2-(2-((8-hydroxyquinolin-2-il)methylene)hidrazinyl)acetate-κ 2 N ]-palladium(II) complex

The structure of new cis-dichloro[(E)-ethyl-2-(2-((8-hydroxyquinolin-2-il)methylene)hidrazinyl)acetate-κ2N]-palladium(II) complex was determined using a combination of XRD and IR measurements and DFT calculations. Inherent flexibility of its structure is evident from the complexity of its IR spectrum, which could only be theoretically reproduced as a combination of several closely related structures, involving rotation around C–O bond and changes in hydrogen interactions of its –OH group. Its thermal stability and decomposition were studied non-isothermally, and the thermal decomposition mechanism was proposed using correlation with DFT calculations at the molecular level. It was determined that the initial degradation step consists of the release of Cl free radical, which then reacts with both the initial compound and the degradation products. Besides the endothermic steps, there are exothermic ones, contributing to the complex shape of the DSC curve, consisted of overlapping endothermic and exothermic peaks. Deconvolution of DTG curve allowed identification of primary fragments of the initial degradation process and, in conjunction with DFT calculations, construction of the most likely reaction mechanism.