Some specijal types of curves, frames and surfaces in Minkowski spaces

Teorija Rimanovih i semi-Rimanovih podmnogostrukosti je jedna od najinteresantnijih oblasti u klasičnoj i savremenoj diferencijalnoj geometriji. Pored toga, diferencijalna geometrija podmnogostrukosti u prostorima Minkovskog je oblast istraživanja koja je poslednjem periodu dala mnoge nove rezultate, naročito u teoriji svetlosnih podmnogostrukosti. U ovoj doktorskoj disertaciji predstavljene su neke specijalne vrste krivih, repera i površi u prostorima Minkovskog. Dobijene su eksplicitne parametarske jednačine prostornih rektifikacionih krivih u prostoru Minkovskog E31 čija je projekcija na prostornu, vremensku ili svetlosnu ravan normalna kriva. Takođe su date eksplicitne parametarske jednačine prostornih normalnih krivih u istom prostoru čija je projekcija na svetlosnu ravan u odnosu na izabranu skrin distribuciju rektifikaciona W-kriva.The theory of Riemannian and semi-Riemannian submanifolds is one of the most interesting areas in classical and modern differential geometry. Besides, differential geometry of submanifolds in Minkowski spaces is the reasearch area that recently has given many new results in investigations, in particular in the theory of lightlike submanifolds. In this thesis, we present some special types of curves, frames and surfaces in Minkowski spaces. We obtain explicit parameter equations of the spacelike rectifying curves in Minkowski space R 3 1 whose projection onto spacelike, timelike and lightlike plane is a normal curve. We also obtain explicit parameter equations of the spacelike normal curves in the same space whose projection onto lightlike plane with respect to a chosen screen distribution, is a rectifying W-curve. In this thesis it is proved that there are no null Mannheim curves in Minkowski space. It is also proved that the only pseudo null Mannheim curves in Minkowski space are pseudo null straight lines and pseudo null circles. The notion of Mannheim curves is further generalized by introducing the generalized null Mannheim curves in Minkowski space-time. Such curves and their generalized Mannheim mate curves are characterized in terms of their curvature functions. In particular, the relations between their frames are obtained. In this thesis we also define the generalized partially null Mannheim curves and the generalized pseudo null Mannheim curves in Minkowski space-time. We prove that there are no non-geodesic generalized partially null Mannheim curves, by considering the cases when the corresponding mate curve is spacelike, timelike, null Cartan, partially null, or pseudo null Frenet curve

Some relations between rectifying and normal curves in Minkowski 3-space

In this paper, we obtain explicit parameter equations of spacelike rectifying curves in $E^3_1$ whose projection onto spacelike, timelike and lightlike plane of $E^3_1$ is a normal curve. We also obtain explicit parameter equations of spacelike normal curves in $E^3_1$ whose projection onto lightlike plane of $E^3_1$, with respect to a chosen screen distribution, is a rectifying W-curve

Odnos između totalnog kapaciteta za vezivanje gvožđa i koncentracije transferina kod novorođene prasadi tretirane gvožđe-dekstranom

Serum iron concentration and iron saturation of transferrin (Trf) are measures of body iron stores after administration of iron supplements. In clinical and experimental research, the complex determination of Trf was replaced by the simple determination of total iron binding capacity (TIBC). The objective of this work was to define if TIBC could be an adequate measure for Trf in neonatal piglets after i.m. iron administration. Treated piglets received 150 mg of iron-dextran i.m. the first day of life, and were compared to the untreated control group. Prior to iron administration, as well as on days 2, 8 and 12 after iron administration, serum iron and TIBC concentration were analyzed by an automatized chemical analyzer and Trf was determined by densitometry of electrophoretic strips. Our results show that regardless of iron treatment, TIBC is not a measure of Trf concentration in neonatal piglets two days after birth. At day 8 of their life a high correlation coefficient of these two parameters was established in non-treated animals, while in iron-treated piglets the same correlation was established 12 days after iron treatment. Thus, we suggest that in neonatal piglets, TIBC could be used as a measure of Trf concentration only 12 days after i.m. iron treatment.Određivanje statusa gvožđa u organizmu jedinke posle primene određenog preparata ovog mikroelementa moguće je utvrditi određivanjem njegove koncentracije u serumu i zasićenja transferina (Trf) gvožđem. U kliničkoj i eksperimentalnoj praksi složeno određivanje koncentracije Trf zamenjeno je jednostavnim određ ivanjem ukupnog serumskog kapaciteta za vezivanje gvožđa (TIBC). Cilj ovog rada je bio da se na modelu porasta serumskog Fe po i.m. aplikaciji Fe-dextrana novorođenoj prasadi, utvrdi odnos TIBC i Trf po aplikaciji ovog mikroelementa, kako bi se utvrdilo da li visoke doze gvožđa u serumu utiču na vrednost TIBC kao mere za određivanje koncentracije Trf. Vrednosti za serumsko Fe, TIBC i Trf poređene su između grupe životinja koja je odmah po rođenju dobila 150 mg Fe-dextrana i kontrolne grupe u kojoj životoinje nisu tretirane Fe-dextranom. Krv je uzorkovana pre aplikacije Fe-dextrana, drugog, osmog i dvanaestog dana po aplikaciji preparata gvožđa. Koncentracija gvožđa u serumu i TIBC su određivani standarnim kliničkim biohemijskim analizama, dok je koncenracija Trf određena denzitometrijom elektroforetskih traka. Dobijeni rezultati ukazuju da bez obzira na primenu preparata Fe, TIBC nije adekvatna mera za Trf kod novorođene prasadi u prva tri dana po rođenju. Osmog dana života prasadi, utvrđen je visoki stepen korelacije ova dva parametra kod životinja koje nisu bile tretirane, dok je kod tretiranih jedinki taj stepen korelacije postignut dvanaestog dana. Na osnovu izloženih rezultata se može zaključiti da se kod novorođene prasadi TIBC može koristiti kao mera za Trf tek 12 dana nakon i.m. tretmana Fe-dextranom

Catalitic effect of Co on hydrogen desorption form nanostucturated magnesium hydride

To study the influence of 3d transition metal addition on desorption kinetics of MgH2 ball milling of MgH2-Co blends was performed under Ar. Microstructural and morphological characterization, performed by XRD and SEM, show a huge correlation with thermal stability and hydrogen desorption properties investigated by DSC. A complex desorption behavior is correlated with the dispersion of the metal additive particles on hydride matrix. The activation energy for H-2 desorption from MgH2-Co composite was calculated from both non-isothermal and isothermal methods to be 130 kJ/mol which means that mutually diffusion and nucleation and growth of new phase control the dehydration process.6th Conference of Young Researchers, Dec 24-26, 2007, Belgrade, Serbi

The Catalytic Effect of Vanadium on Sorption Properties of MgH2-Based Nanocomposites Obtained Using Low Milling Time

The effects of catalysis using vanadium as an additive (2 and 5 wt.%) in a high-energy ball mill on composite desorption properties were examined. The influence of microstructure on the dehydration temperature and hydrogen desorption kinetics was monitored. Morphological and microstructural studies of the synthesized sample were performed by X-ray diffraction (XRD), laser particle size distribution (PSD), and scanning electron microscopy (SEM) methods, while differential scanning calorimetry (DSC) determined thermal properties. To further access amorph species in the milling blend, the absorption spectra were obtained by FTIR-ATR analysis (Fourier transform infrared spectroscopy attenuated total reflection). The results show lower apparent activation energy (Eapp) and H2 desorption temperature are obtained for milling bland with 5 wt.% added vanadium. The best explanation of hydrogen desorption reaction shows the Avrami-Erofeev model for parameter n = 4. Since the obtained value of apparent activation energy is close to the Mg-H bond-breaking energy, one can conclude that breaking this bond would be the rate-limiting step of the process

Kinetic behavior of MgH2-transition metal composites: towards hydrogen storage

Hydrogen as an energy vector represents great potential, due to its high gravimetric density and low mass, as well as the fact that combustion does not emit harmful chemical byproducts. Hydrogen has the highest energy density per unit mass compared to any other fuel but a rather low energy density per unit volume. Further, hydrogen storage is a key technology for developing a hydrogen and fuel cell-based economy [1]. Metal hydrides as alternative hydrogen carriers have a wide range of performance parameters such as operating temperature, sorption kinetics, activation conditions, cyclic options, and equilibrium hydrogen pressure. These parameters can be improved or adjusted to meet the technical requirements of different applications. The most commonly used method for hydride destabilization is nanostructuring by mechanical milling which leads to a reduction in the particle and crystallite size of the MgH2 powder. Nanostructuring is often combined with catalyst addition and composite formation [2,3]. The most of research is focused on the morphological, structural, and thermodynamic effects typical for long milling times, while in this work we have followed the changes taking place under short milling times. The thermal stability of magnesium hydride is related to - changes in the crystallites and powder particle size. The analysis also considered the changes in activation energy. MgH2-M composites were prepared by mechanical milling of the as-received MgH2 powder (Alfa Aesar, 98% purity) with the addition of 2 and 5 wt.% of M (M= V, W, Mo). Mechanical milling was performed in s SPEX 5100 Mixer Mill using 8mm diameter milling ball. Samples were milled for 15-45 minutes under the inert atmosphere of argon and a ball-to-powder ratio 10:1 Figure 1. shows the kinetic curves obtained for composites with 5wt% of vanadium. To investigate the desorption process in detail, different models of solid-state kinetics were used as implemented in the code developed in our group. The ratelimiting step of the desorption reaction was determined using the iso-conversional kinetic method due to better accuracy of obtained apparent activation energies. As shown in Table 1 a decrease in apparent activation energies has been observed. It is obvious that the sorption kinetics is affected by material preparation because the reactivity of magnesium with hydrogen is strongly modified by changes in several surface parameters that govern the chemisorption, the dissociation of molecular hydrogen, and hydride nucleation7th MESC-IS 2023 : International Symposium on Materials for Energy Storage and Conversion : 11th INESS : International Conference on Nanomaterials & Adv. Energy Storage Systems : October 7-10, Baku, 2023

Hydrogen Storage in Metal Hydrides: Experimental Approach

The paper deals with the destabilization methods for improving the storage properties of metal hydrides. The experimental approach was used to point out the influence of various types of defects on the structure and stability of hydrides. As a case study, Mg-based hydrides have been investigated. As shown by our research, ion irradiation is the way to introduce a well-defined concentration of defects (Frankel pairs) at the surface and sub-surface layers of a material. Defects at the surface play the main role in sorption reactions since they enhance the dissociation of hydrogen. Further, our research shows that ball-milling introduces defects through the entire sample volume, refines the structure and thus decreases the path for hydrogen diffusion. Surface-modified material demonstrates better thermodynamic and kinetics properties than bulk modified hydride materials.Published in Bulletin of the Chemists and Technologistsof Bosnia and Herzegovina as Special Issue (2024)

On generalized partially null Mannheim curves in minkowski space-time

© 2016, Institute of Mathematics. All rights reserved. In this paper we define generalized partially null and pseudo null Mannheim curves in Minkowski space-time E 41. We prove that there are no non-geodesic generalized partially null Mannheim curves in E 41, by considering the cases when the corresponding mate curve is a spacelike, timelike, null Cartan, partially null or pseudo null Frenet curve. We also answer the question: ”Can a partially null Frenet curve be a generalized mate curve of the generalized pseudo null Mannheim curve in Minkowski space-time?”

Katalitički uticaj Co na kinetiku dehidriranja MgH2

MgH2 se može koristiti za skladištenje vodonika, ali je kinetika procesa hidriranje/dehidriranje na sobnoj temperaturi spora. Mehaničko legiranje sa 3d prelaznim metalima predstavlja najčešće korišćen metod ubrzanja reakcije dehidriranja. Mehaničkim mlevenjem su sintetisani kompoziti MgH2-Co. Određeni su parametri reakcije dehidriranja (n i k) i energija aktivacije EA izotermalnom JMA metodom. Dobijene vrednosti energije aktivacije za dehidriranje su oko 130kJ/mol, vrednosti konstanti brzina reakcije dehidriranja reda veličine 10-4, dok se vrednosti Avramijevog parametra nalaze u graničnoj oblasti (n ≈ 1). Dobijeni rezultati ukazuju da proces difuzije i proces nukleacije i rasta nove faze istovremeno kontrolišu proces dehidriranja kompozita MgH2-Co

Microwave synthesis of novel chenodeoxycholic acid esters and comparative study of chromatographic behavior and lipophilicity

In this study, eco-friendly microwave-assisted esterification reactions of chenodeoxycholic acid with medium-chain diols (1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol) or tetraethylene glycol were accomplished. The synthesized bile acid esters were obtained with high yields (up to 81 %) and purity in a short reaction time (15 min). It is shown that the microwave technique is a suitable method for the preparation of chenodeoxycholic acid esters. In order to obtain detailed insight into the lipophilic behavior of the studied chenodeoxycholic acid esters, a comparative study of chromatographic behavior and lipophilicity was performed. Also, the present study deals with the estimation of pH – logD profiles in order to get an overview of the changes in lipophilicity related to the pH value changes. The obtained results indicate that studied compounds have logD values in the range acceptable for potential drug candidates. Chromatographic lipophilicity of synthesized chenodeoxycholic acid esters successfully correlate with in silico lipophilicity descriptors