Experimental studies of parameters affecting the heat generation in friction stir welding process

Heat generation is a complex process of transformation of a specific type of energy into heat. During friction stir welding, one part of mechanical energy delivered to the welding tool is consumed in the welding process, another is used for deformational processes etc., and the rest of the energy is transformed into heat. The analytical procedure for the estimation of heat generated during friction stir welding is very complex because it includes a significant number of variables and parameters, and many of them cannot be fully mathematically explained. Because of that, the analytical model for the estimation of heat generated during friction stir welding defines variables and parameters that dominantly affect heat generation. These parameters are numerous and some of them, e. g. loads, friction coefficient, torque, temperature, are estimated experimentally. Due to the complex geometry of the friction stir welding process and requirements of the measuring equipment, adequate measuring configurations and specific constructional solutions that provide adequate measuring positions are necessary. This paper gives an overview of the process of heat generation during friction stir welding, the most influencing parameters on heat generation, constructional solutions for the measuring equipment needed for these experimental researches and examples of measured values

Characterization of aliphatic hyperbranched polyesters by MALDI-TOF mass spectrometry

U okviru ovog rada prikazani su rezultati ispitivanja opsega sporednih proizvoda (ciklika) kod hidroksi-funkcionalnih alifatskih hiperrazgranatih poliestara primenom MALDI-TOF masene spektrometrije. Istovremeno su opisani i osnovni principi MALDI-TOF masene spektrometrije i dat je kratak literaturni pregled.In this work, MALDI-TOF mass spectrometry was used for the characterization of aliphatic hyperbranched polyesters (AHBP), synthesized from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and di-trimethylolpropane. From the obtained results it was concluded that it was not possible to take complete advantages of MALDI-TOF MS in this particular case, since the AHBP used in this work were polydisperse. The intensity of the signals from the high mass tail of these samples (pseudo generation higher than four) was underestimated and insufficient to distinguish it from the baseline and to use it for the analysis of the spectra. As a consequence of that, lower values of the Mn were obtained. At the same time, Mw were also underestimated, which led to very low values of the polydispersity index. On the other hand, it was possible to obtain molar masses of individual molecules from the MALDI-TOF mass spectra of AHBP and to qualitatively determine the extent of cyclization (side reactions) at each degree of polymerization. Using the adequate set of equations and results obtained from MALDI-TOF mass spectra of AHBP, every signal from the spectra was identified. The obtained results show that formation of poly(bis-MPA), intramolecular esterification and intramolecular etherification occurred as side reactions during the synthesis of these polyesters. The relative amount of the cycles increases with the number of pseudo generation (from the second up to the fifth pseudo generation). It was also observed that the relative proportion of the signals which represent cyclic structures increases with the increasing degree of polymerization. In this work the basic principles of MALDI-TOF MS are also presented, as well as, a review of adequate published articles.Ovo je rad Jasne Džunuzović

Some parameters of dried pork produced with lower salt content

Production of meat products with lower salt/sodium content is the goal of today's meat industry because of bad influence of exceed sodium intake by food. In this paper are presented some physico-chemical parameters during processing of dried pork produced with lower salt content. Pork (m. longissimus dorsi) was cured with nitrite curing salt in amount of 3 kg/100 kg of meat. In meat were measured the weight loss during curing and drying; moisture content by standard method SRPS ISO 1442:1998, water activity using awmeter (Wert-Messer, Durotherm) at temperature of 25°C; and pH value by pH-meter (MA-5730; PAT N° 35398, Iskra) according to SRPS ISO 29 17:2004. Average moisture content in dried meat at the end of production was 40.10%. Average weight loss was 2.39% after 7 days of production (after curing) and it is increased up to the end of production, average 34.57%. Acidity of meat during curing, smoking and drying was similar; pH value was around 6.00. Water activity was gradually decreased from average 0.985 after curing (7th day) up to 0.899 at the end of production. During the storage of dried meat under vacuum conditions, pH value decreased from 5.43 in the final product up to 5.11 at the end of storage (120th day). These values are characteristic for curing, drying and fermentation of meat. Dried meat was shelf stable for 120 day under vacuum conditions, without signs of rancidity and without changes in other sensory attributes

Up-conversion luminescence of GdVO4:Nd3+/Er3+ and GdVO4:Nd3+/Ho3+ T phosphors under 808 nm excitation

All authors acknowledge to the COST Action CM1403: The European upconversion network - from the design of photon-upconverting nanomaterials to biomedical applications (2014–2018). The authors from the University of Belgrade acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ). K. S. acknowledges the Latvian National Research Program IMIS2 (Grant No. 302/2012 ). T. G. acknowledges the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ).In recent years, there exists a tendency in research of up-conversion materials to shift excitation from 980 nm to shorter wavelengths. Here, in order to produce up-conversion luminescence emission of GdVO4-based materials under 808 nm excitation, polycrystalline powders of GdVO4:Er3+/Nd3+ and GdVO4:Ho3+/Nd3+ were successfully prepared by a high-temperature solid-state reaction technique. The prepared powders were highly crystalline with a single-phase zircon-type GdVO4 structure and consisted of micrometer-sized irregular spherical particles (2–6 μm in diameter). In all studied samples, visible up-conversion luminescence was successfully achieved under 808 nm illumination. Near-infrared pumping produced emission bands in the green, yellow-orange and green regions of the visible spectrum. The bands in the green and red regions of GdVO4: Er3+/Nd3+ as well as GdVO4:Ho3+/Nd3+ were, respectively, characteristic of Er3+ and Ho3+ ions. The dominant band originating from the 4G7/2 → 4I11/2 transition in Nd3+ ions was observed around 597 nm in all samples.COST Action CM1403 (2014–2018); Ministry of Education, Science and Technological Development of the Republic of Serbia (Project Nos. 45020 and 172056 ); Latvian National Research Program IMIS2 (Grant No. 302/2012 ); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 ( 1.1.1.2/16/I/001 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

A comparative study of photocatalytically active nanocrystalline tetragonal T zyrcon- type and monoclinic scheelite-type bismuth vanadate

The authors from Vinča Institute of Nuclear Sciences acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ). The work of K. Smits was supported by Latvian National Research Program IMIS2 (Grant no. 302/2012 ).Monoclinic scheelite-type BiVO4 is currently considered as one of the most promising non-titania photocatalysts, wheras tetragonal zircon-type BiVO4 is still poorly understood. Herein, a new and simple synthetic approach was applied and nanostructured single-phase zircon-type BiVO4 was successfully prepared by a controllable ethylene-glycol colloidal route. In addition, nanostructured monoclinic scheelite-type BiVO4 powders were also fabricated through annealing of the as-prepared samples. A comparative study of the two BiVO4 polymorphs was conducted and it turned out that the novel synthetic approach had a significant impact on porosity and photocatalytic performance of zircon-structured BiVO4. All the prepared materials, as-prepared and annealed, were mesoporous, while measured values of specific surface area of some zircon-structured samples (∼34 m2/g) were ∼7 times higher than those reported thus far for this phase. Interestingly, for the first time, zircon-type BiVO4, previously considered to be a poor photocatalyst, exhibited a better overall performance in degradation of methyl orange compared to monoclinic scheelite-type BiVO4. Hence, it could be expected that the here-presented synthesis and observations will both arouse interest in scarcely studied tetragonal zircon-type BiVO4 and facilitate as well as speed up further research of its properties.Ministry of Education, Science and Technological Development of the Republic of Serbia (Project no: 172056 ); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

Implementation of GIS technologies in assessment and protection of natural values of Tara National Park

Mount Tara is among the most important centers of Balkan and European ecosystem and species biodiversity. It is characterized by diversified and well-maintained communities of old deciduous and mixed coniferous forests (beech/fir/spruce). They represent a unique example of well preserved forests in SE Europe with numerous endemic and relict species of indigenous flora and fauna. The geographical information system (GIS) that we have created has proved an excellent tool for valorization and protection of all natural values and potentials of Tara National Park.Geografski informacioni sistem je: organizovan skup računarskog hardvera softvera, geografskih podataka i kadra, dizajniran da efikasno prikuplja smešta, nadgrađuje, manipuliše, analizira i prikazuje sve forme geografski referencirane informacije. Za ekologe GIS je otvorio nove mogućnosti za istraživanja i aplikaciju sakupljenih informacija. Zbog same kompleksnosti sistema životne sredine mi najčešće nastojimo da ih proučavamo koristeći redukcionistički pristup, fokusirajući ce na male, diskretne pojednostavljene aspekte. Međutim većina problema u životnoj sredini su više faktorijalni i zahtevaju razmatranje širokog spektra izvora informacija pitanja i interesa. Za većinu ekoloških studija potrebne su nam eksplicitnije i kvalifikovanije terenske informacije vezane za faktore koji bi mogli da objasne posmatranu ekosistemsku, faunističku i florističku raznovrsnost u dimenziji prostorne i vremenske distribucije uključujući i podatke o geologiji, klimi, pedologiji, distribuciji i ponašanju istrživanih vrsta. Ovde svoju ulogu pronalaze geografski informacioni sistemi (GIS). Nacionalni park Tara obuhvata najveći deo planine Tare u zapadnoj Srbiji prosečne nadmorske visine 1000-1200 m na 180 km od Beograda. Ukupna površina zaštićenog područja Nacionalnog parka je 19.175 ha, a 37.584 ha predstavlja zaštitnu zonu oko Nacionalnog parka. Pripada opštini Bajina Bašta. Planina Tara predstavlja jednu od vrućih tačaka specijskog i ekosistemskog diverziteta sa 35 različitih šumskih zajednica lišćarskog, mešovito četinarskog tipa, kao i 19 opisanih livadskih zajednica. Mnoge od njih posebno one sa Pančićevom omorikom, imaju reliktan ili endemoreliktan karakter. U tom smislu sasvim je opravdano što se Tara danas našla na listi područja značajnih za očuvanje ptičijeg sveta (IBA) i dnevnih leptira Evrope (PBA), a u toku je njeno uključivanje u međunarodnu listu područja značajnog za očuvanje svetske flore (IPA). Kako se gazdovanje i upravljanje praktično svim prirodnim potencijalima NP Tara, do sada dominantno zasnivalo na principima šumarske tehnologije i inženjeringa ovaj rad ima svoju punu naučnu opravdanost u pokušaju implementacije savremenih naučnih saznanja iz oblasti zaštite biodiverziteta, konzervacione ekologije geografije i prostornog planiranja u mehanizam upravljanja prirodnim nacionalnim resursima. Ovaj tip vrednovanja i zaštite otvara mogućnost primene održivog/usklađenog korišćenja resursa NP Tara. Tokom 2002. i 2003. godine formirane su teme GIS NP Tara koje obuhvataju prirodne (geomorfologija, geologija, pedologija, hidrologija, vegetacija, flora fauna), korišćene (eksploatacija šuma) i veštačke (antropogene) sadržaje (puteve, brane, naselja, turističke sadržaje i granice). Geografski informacioni sistem koji je formiran za NP Taru sa temama koje ga čine da prati okvire sličnih projekata rađenih u Evropi i svetu i jedan je od tipičnih geografskih informacionih sistema (iz oblasti ekologije, zaštite životne sredine, šumarstva, itd), koji sadrži gotovo sve vrste podataka (izuzev satelitskih snimaka) u GIS (rasterske, vektorske, DEM, baza podataka i aerofotogrametrijske snimke).Projekat ministarstv

Rheological and thermal properties of boltorn® hyperbranched polyesters

Rheological (in solution and in melt) and thermal properties of aliphatic hydroxyfunctional Boltorn® hyperbranched polyesters of different pseudo generation were investigated in this work. The obtained results show that 40 wt.% solutions of Boltorn® samples in N-methyl-2-pyrrolidinon exhibit Newtonian behaviour at 30 oC and that zero shear viscosity increases with increase of the generation number, i.e. molar mass. On the other side, vales of the Tg show only slight increase with increase of the molar mass. Thermal stability of investigated samples increases with increase of the number of generation

The electrochemical investigation of inclusion complexes of nifedipine and amlodipine with ß-cyclodextrin and (2-hydroxypropyl)-ß-cyclodextrin

The electrochemical behavior of inclusion complexes of nifedipine (Nif) and amlodipine (Aml), a long-acting calcium channel blockers dihydropyridine (DHP) class, with ß-cyclodextrin (ßCD) and (2-hydroxypropyl)-ß-cyclodextrin (HPßCD), is examined using cyclic and square wave voltammetry in 0.05 M NaHCO3 and phosphate buffer (pH=11) on a gold electrode. The voltammograms show a single irreversible anodic wave with the current controlled by adsorption. It was found that phosphate buffer favorites the electrochemical activity of both complexes of Nif with the linear dependency of the oxidative currents on their concentrations. In phosphate buffer, only HPßCD-Aml complex showed linear dependency of the oxidative currents on the concentration. In 0.05 M NaHCO3 as electrolyte only HPßCD-Nif exhibited apparent activity. The initial potential of the anodic reaction as well as the value of the potential for anodic currents maximum of all the examined complexes in both electrolytes were shifted to the positive direction compared to their standards. In addition, the value of anodic currents decreased

Geosite Assessment Using Three Different Methods; a Comparative Study of the Krupaja and the Zagubica Springs - Hydrological Heritage of Serbia

Hydrological heritage is a relatively new concept in the field of geosite assessment. The principal aim of this study is to apply M-GAM (Modified geosite assessment model) for comparative analysis of the Krupaja spring and the Zagubica (Mlava) spring, located in Homolje area, in Eastern Serbia. According to the classification of geosites of Institute for Nature Conservation of Serbia, these sites are on the list of protected sites ("hydro(geo)logical" heritage sites) of extraordinary national importance; however, they still have not gained necessary recognition in Serbia. Thus, their assessment according to different target groups should provide a clearer picture of their current condition. As M-GAM considers that not all indicators for evaluation of geosites are of the same importance, this paper applies two methods for comparing and determining the importance of indicators and subindicators in the model (Analytical-hierarchy process (AHP) and descriptive statistics conducted by SPSS). Also, it is assumed that different target groups will give different importance to some indicators in the model, which would result in various evaluation scores for the same geosites. The paper also provides a comparative analysis of the assessment carried out by two different target groups - potential geotourists and geoexperts. The results obtained by AHP and descriptive statistics are quite similar, which confirms the reliability of respondents' answers and the results gained. The analyzed sites are differently positioned in the evaluation matrix, and implications are further discussed in the paper

The effect of natural and human-induced habitat conditions on number of roe deer: case study of Vojvodina, Serbia

Roe deer (Capreolus capreolus L.) have greatly expanded in both distribution and abundanceduring the last few decades, and are the most abundant cervids in Europe today. The aim of this paper is to determine the factors that have the most considerable impact on roe deer numbers in the Vojvodina region (North Serbia). Environmental (area in ha, total area of forest and total area of meadows and pastures in hunting ground) and anthropogenic (number of registered hunters, number of hunting sections, number of gamekeepers and roads in km on 1,000 ha) factors had been shown to influence the number of roe deer in Vojvodina region. A multiple regression analysis was carried out as the main statistical approach. The mapping of certain parameters was done using ArcGIS 9.2 software in order to establish the relation between the roe deer population and the different environmental and anthropogenic conditions. The results signify that the roe deer number dependency in the Vojvodina region is a very complex and multi-factorial phenomenon, strongly influenced by human induced modifications