3828 research outputs found
Sort by
Mechanical performance of denture acrylic resin modified with poly(4‐styrenesulfonic acid‐ co ‐maleic anhydride) sodium salt and strontium titanate
No full textSince acrylate-based materials are widely used in dentistry, their drawbacks such as low impact resistance and hardness, require continuous research in the field of materials science in order to avoid sudden fracture caused by chewing or fall. In this study, auto-polymerizing poly(methyl methacrylate) (PMMA), commonly used as denture base material, was reinforced with poly(4-styrenesulfonic acid-co-maleic anhydride) sodium salt (PSSMA) and strontium titanate (STO), with the aim of improving impact behavior and microhardness. Morphological analysis confirmed formation of phase-separated and co-continuous microscopic structures of PSSMA in PMMA, without visible agglomerates of STO nanoparticles, indicating that PSSMA-STO interaction contributed to a better distribution of nanoparticles. Fourier transformed infrared spectroscopy revealed that PSSMA and STO did not interfere in the polymerization of methyl methacrylate. This was further supported by thermal analysis, which also showed that the addition of PSSMA and STO had no significant influence on thermal degradation. On the other side, PSSMA and STO significantly enhanced mechanical performance of PMMA. The modulus of elasticity increased by up to 48.6%, total absorbed impact energy improved by up to 108.4%, and microhardness increased by up to 272.8% when PSSMA was combined with STO for reinforcing denture PMMA. These results demonstrate the significant potential of PSSMA, which could be combined with other ceramic nanoparticles for denture reinforcement in the future. Highlights: This research presents novel dental hybrid composite. Influence of strontium titanate (STO) and poly(4-styrenesulfonic acid-co-maleic anhydride) sodium salt (PSSMA) on poly(methyl methacrylate) (PMMA) was investigated. PSSMA/STO improved modulus of elasticity, microhardness and impact resistance. Sample with 5 wt% PSSMA and 1 wt% STO showed the highest improvement compared to PMMA. Presented hybrid composite could use as denture base material
Properties of La1–xNaxMnO3 thin films deposited on various substrates
No full textLanthanum manganite (LaMnO3) with a perovskite structure has been widely investigated, due to various applications related to its specific electric and magnetic properties. LMO structure is suitable for different ion site substitutions to improve its properties. Particularly, La-site doping with lower valence cations (such as Sr2+ and Ca2+) is interesting since it causes the presence of heterovalent manganese ions, Mn3+ and Mn4+, due to the charge neutrality condition. So-called double exchange, i.e. electric charge transfer between Mn3+ and Mn4+ via oxygen anions, is responsible for the appearance of ferromagnetism, metallic conductivity, and colossal magnetoresistance. These properties allow the utilization of doped lanthan manganites for various applications, such as materials in solid oxide fuel cells (SOFCs), magnetic sensors, and catalysis.
In this study, we investigated the properties of La1–xNaxMnO3 (x = 0; 0.05; 0.15; 0.30) thin films deposited on various substrates (Si and Si/Pt, and epitaxial films on a SrTiO3 substrate). The precursor solutions of the selected La1–xNaxMnO3 compositions were applied onto the substrates by a polymer-assisted deposition method to form epitaxial thin films. The evolution of epitaxial structure was tracked by annealing the films at various temperatures. Then, they were characterized by a low-angle XRD, scanning electron analysis, and atomic force microscopy. The structure and morphology of La1–xNaxMnO3 thin films were examined with an emphasis on the contributions that originated from the substrates and considering the influence of the thickness of the films
Structural control on the mountainous geothermal reservoirs distributed across the Oligocene andesite-type volcanic complex (Lece massif, southern Serbia)
No full textUpper crustal faults and fractures control a natural thermal and non-thermal fluid circulation in the Lece andesite complex (LAC) (southern Serbia, Vardar Zone). By exhibiting differential conduit-barrier behavior, regional faults, and associated tensional fractures are key elements to this effective natural geothermal system. The combination of field-based hydrogeological prospecting and structural geology (water-bearing structural lineaments) yields several types of geothermal and cold mineral groundwaters that appear to be genetically linked to a cluster of fluid conduit-type extensional faults (hydraulic boundaries). The results further show that geothermal fluid production occurs in the naturally fractured and non-stimulated subsurface reservoirs distributed around the volcanic body (LAC). The geothermal reservoir doublets lie along the external perimeter of the LAC, whereas the abutting geological assemblage is composed of peri-volcanic, much older Neoproterozoic-Paleozoic metamorphic rock. The embedded thermal fluids are formed in the near-surface zones controlled by abundant fractures, particularly those occurring within the propylitized and hydrothermally altered subsegment of the Lece volcanic body. The resulting productivity of these composite aquifers is reaching very high values. The study further yielded several of the most important factors controlling the natural geothermal reservoirs: (i) the important effects of the extensional (neo)tectonic activity and their influence on the reservoirs (fractured lithological assemblage); (ii) the subsurface hydrodynamic conditions within the interval characterized by the highest quantitative mixing of the thermomineral groundwaters, including (iii) the physical and chemical properties of the LAC mineral groundwaters. The study underlines the presence of structural hydraulic boundaries (including the tectonically maintained permeability) having implications for a better assessment of the ongoing fault zone-related geothermal extraction. It further contributes to the overall hydrogeological potential (quantitative and qualitative).Časopis je do kraja 2022. imao naziv "Journal of Petroleum Science and Engineering
Ni-Sn coated Ni foams – suitable cathodes for large-scale alkaline water electrolysis?
No full textDriven by the continuously increasing demand for electricity, diminishing carbon-based energy resources, steadily increasing ecological concerns, the focus has shifted to finding clean and renewable solutions. Electrochemical energy conversion and storage systems have taken the spotlight in shaping a greener future, with hydrogen, obtained through electrolysis, emerging as a leading energy carrier candidate. The scalability and abundance of materials used in alkaline water electrolysis, alongside the maturity of this industrial process, make it a favoured pathway for hydrogen production powered by renewables.
Electrodeposition was firstly investigated through linear sweep voltammetry and controlled potential coulometry1 techniques, in order to obtain high-performance Ni-Sn coated Ni foam. The objective was to achieve coatings of optimal composition to enable outstanding catalytic activity towards hydrogen evolution reaction, characterized by low overpotentials that are below – 100 mV at current density of – 1 A cm-2, normalized per geometric area, in 1 M KOH. Since these electrodes showed promising results, the electrodeposition was further investigated in galvanostatic setting in order to determine the most favourable conditions, as this technique is better suited for industrial-scale plating. Ni-Sn coated Ni foams, deposited at specific constant deposition current density, were additionally tested in zero-gap flow electrolysers where they have shown good stability and low value of overvoltage, which is in alignment with criteria proposed by IRENA2
High floristic diversity despite deforestation: synergism of abiotic and antropogenic factors in the foothills of the Sharr mountain
No full textThe Balkan Peninsula, including Serbia, is one of the most diverse but least studied parts of Europe from a floristic and phytogeographic point of view; in particular, biodiversity status of large areas after recent conflicts is largely unknown. The Sharr National Park in the area of Kosovo is the hotspot of the Balkan floristic diversity and the largest refugium of glacial flora in Europe. We conducted a floristic survey in the southeastern foothills of the Sharr mountain complex, in a valley of about 95 km2 up to an altitude of 1500 m, just beneath this national park. This marginal rural area has been severely modified by decades of uncontrolled deforestation, but also different anthropogenic disturbances such as agriculture, urbanization, eutrofication of waters and soils, introduction of
invasive species, and mining. Collected herbarium material of 545 vascular species was classified into 310 genera
from 75 families; this represents about 13.6% of the total floristic richness of Serbia, documented on only about
0.11% of its territory. Such a high floristic diversity at an intermediate level of disturbance can be related to an exceptional heterogeneity of small-scale environmental factors, including small individual farmers plots and a variety of management practices, and also depopulation trends. This phenomenon of high diversity in a successional matrix of secondary fallow vegetation has been known mostly from tropical agroecosystems. Despite the utter negligence for nature protection, about 14% of all the taxa recorded in this study represented characteristic syntaxonomic elements of deciduous forests, what indicates ecological and floristic possibilities for restoring the natural forest vegetation
DIVERSITYAND PROPERTIES OF CULTIVABLE YEASTS ISOLATED FROM GRAPE BERRIES OF PROKUPAC
No full textThe aim of this work was to study the biodiversity of yeasts isolated from grape berries of Prokupac (Vitis vinifera L.; proles pontica, subproles balcanica), the autochthonous Serbian red wine variety. The grapes were harvested from vineyards in two geographically different wine regions in Serbia (Šumadija and Toplica), which differ in both soil and climatic characteristics. Epiphytes and endophytes were isolated from the grape berries and additionally from the must during one-week spontaneous alcoholic fermentations. Different restriction profiles of the ITS-5.8S rDNA region corresponding to Rhodotorula glutinis, Hanseniaspora uvarum, Aureobasidium pullulans, and Saccharomyces cerevisiae were observed. The presence of yeasts varied considerably in the grape berries and in the grape must, where we could only detect S. cerevisiae. The glucose concentration (0.5, 1, 1.5, and 2%) and the influence of the pH (4, 6.4, 8, and 10) of the YPD medium on the non- Saccharomyces yeasts were calculated. The results showed that the sugar concentration influenced
A. pullulans the most, while the pH of the medium of 10 completely interrupted the growth of A. pullulans as well as that of R. glutinis. H. uvarum was the most resistant species to pH changes and glucose availability. No geographical variability in yeast diversity was detected in our study, suggesting the influence of grape variety rather than environment. This is the first report on the population dynamics of “culturable” microbiota diversity of Prokupac (the most important Serbian red wine), which allows us to provide the basis for improved management of wine yeasts (both with non-Saccharomyces and Saccharomyces) for the production of typical wines with pronounced terroir impact
Zgornjekredni turbiditi južnega obrobja Beograda: Podrobna opredelitev začetka santonijske konvergence, dokazi iz Savske šivne cone (Guberevac-Babe, severna Šumadija, Srbija)
No full textTurbiditi, kot sedimentacijski sistemi, vezani na aktivne robove celin, so turbiditi nosilci pomembnih podatkov o orogenem razvoju območja. V tem članku so predstavljeni novi stratigrafski in strukturni podatki o enem od alpskih turbiditnih sistemov iz časa pozne krede (območje Guberevac-Babe-Ropočevo; Srbija). Znotraj Savske šivne cone in Vzhodne Vardarske cone sta bili odloženi dve sinorogeni zaporedji, pri čemer je bilo prvo podvrženo poznokrednim kompresijskim in ekstenzijskim deformacijam. Glede na nove biostratigrafske podatke je do nastanka kompresijskih
struktur prišlo v santoniju. V deformiranem delu santonijskega klastično-karbonatnega turbiditnega zaporedja v bližini Guberevaca so vidne nove pomembne kompresijske strukture. Gube, reverzni prelomi in tektonski stiloliti so vidni nekaj kilometrov stran od primarne deformacije (nariv Bela Reka), v talnini narinjene Vzhodne Vardarske cone.O kompleksnosti geoloških procesov na območju Guberevac-Babe-Ropočevo pričajo tudi plasti zgornjekrednih kamnin, ki so bile predhodno kartirane na širšem območju. V sklopu naše terenske študije smo izvedli statistično analizo strukturnih elementov, kot so prelomi, gube in plasti, kar prispeva k boljšemu razumevanju Savske šivne cone. Opazovane kompresijske strukture, kot so mezoskopske gube, narivi in klivažne ravnine dveh generacij, kot tudi pridobljeni statistični
podatki o strukturah, se večinoma pojavljajo v prednarivnem čelu ali znotraj mešanih klastično-karbonatnih turbiditov
Savske šivne cone (območje Guberevac-Babe). Celotna študija kaže, da je bil preiskovani segment talnine, ki ga predstavljajo
deformirani turbiditi Savske šivne cone, izpostavljen tektonskemu krčenju v santoniju (začetek konvergence). Po koncu glavnega dogodka debeljenja skorje je bil šivni segment Guberevac-Babe-Ropočevo večkrat reaktiviran (postorogena ekstenzija). Preučevani segment neotetidine vardarske paleosuture je med pozno kredo in miocenom skupaj doživel štiri faze deformacij. Te vključujejo pozno-oligocensko reaktivacijo ter umestitev pozno-oligocenskega subvulkanskega telesa Glavčina-Parlozi in nekoliko mlajšega, miocenskega magmatskega sistema Stenička bara
Photosynthetic insights into winter-green leaves in Quercus pubescens Willd. seedlings
No full textQuercus pubescens Willd. is a deciduous species that can retain leaves in the winter either as dead, standing leaves
(marcescence), or as living, winter-green leaves. The retention of green leaves through winter is rare in continental areas.
Winter-green leaves were observed on one-year-old seedlings of Q. pubescens in the winter of 2020 in the nursery of the
Faculty of Forestry that lasted until the end of April 2021. The photosynthetic activity of photosystem II was measured using
the rapid light curve method based on modulated pulse chlorophyll fluorescence. We assessed the potential photosynthetic
activity of the leaves across the range of physiological stages: winter-green leaves retained from the previous growing season
and on the leaves from the first, second, and third growth flush during the growing season. Photosystem II of winter-green
leaves attained ~50-60% of the maximal photosynthetic activity obtained in spring and summer leaves, respectively. Climate
data indicated that winter-green leaves exhibited frost resistance in the winter of 2020/2021, as their photosynthetic activity
was preserved despite 33 days with sub-zero temperatures. The rapid light curve method also revealed the gradual acclimation
of seedlings on a flush level, with leaves from the third flush best able to use available light under high temperatures
and insolation efficiently. The results of rapid light use as an indicator of seedling acclimation are discussed. Some remarks
on the possible practical significance of the winter-green leaves phenomenon (as in genetic selection) are highlighted
Content of eight heavy metals in poplar and willow clonescultivated in pots using soil from a landfill sites
No full textThe research on poplar and willow clones for this study is particularly relevant due to the historicalcultivation of these species for environmental benets. Both poplars and willows are known for theirfast growth, extensive root systems, and high tolerance to various environmental conditions, includingheavy metal contamination. This study is focused on evaluation of the potential of certain poplar andwillow clones in pot trial for phytoextraction of heavy metals from substrate based on soil from landllsites near Novi Sad and Belgrade. By examining the content of nine heavy metals (Cd, Cr, Cu, Fe, Mn,Ni, Pb, and Zn) in different clones grown in soil from the landll, it has been aimed to identify themost suitable candidates based on their ability to thrive and accumulate heavy metals in thischallenging substrate. Among the clones, the willow clone (107/65-9) in Belgrade and Easterncottonwood clone S1-8 in Novi Sad, showed differences in zinc tolerance. The I-214 clone is notablefor its copper accumulation, while the Pannonia and PE19/66 clones accumulated the highest amountsof manganese from Belgrade landll soil. It can be recorded that the willow clone is better suited forincreased watering on the heavier soil from Belgrade landll soil, whereas the S1-8 clone performs wellon the soil with higher sand content such as landll soil from Novi Sad
GENOFOND DRVENASTIH VRSTA NA PODRUČJU STROGOG REZERVATA PRIRODE „FELJEŠANA“
No full textForests of primeval character in Europe usually receive the highest
protection status. The importance of these ecosystems is highlighted in the BIO2023 Strategy,
which outlines specific guidelines for the identification and protection of primeval forests
within the European Union. Endemic ecosystems characteristic of Europe, such as pure
beech forests, are facing numerous threatening factors in the context of climate change and
are considered one of the most endangered habitats. Efforts to preserve and enhance forest
ecosystems, as an initial step, involve conservation and long-term monitoring to gain insight
into the adaptation and evolutionary strategies of the present species and ecosystems as a
whole. The extremely strict protection conditions prescribed in strict reserves impose very
limited human intervention, while non-invasive scientific research is considered a desirable
activity. One of the first protected pure beech forests in Serbia is the Strict Nature Reserve
"Felješana" which, despite being protected since 1950, has not been thoroughly and
systematically studied from the aspect of woody species diversity. The aim of this paper is to
provide, for the first time,data on the available gene pool of woody species in the primeval
beech forest "Felješana". The field research methodology included recording woody species
in the tree, shrub, and ground layers at pre-determined monitoring points and identifying
and georeferencing target species. For the georeferenced individuals of the target species,
height, diameter at breast height, breast circumference, and horizontal crown projection
were determined. A total of 27 native woody species were recorded, with 14 species in the
tree layer, 25 in the shrub layer, and 19 in the ground layer. Although beech is the dominant
species across all three vegetation layers throughout the area, the recorded number of
species in the shrub and ground layers indicates the potential for changes in species
distribution and composition in this reserve in the future. All recorded species are of native
origin, among which six species belong to one of the categories of rare, endangered, and
vulnerable species in the forest fund of Serbia. Georeferencing and determining the basic
characteristics of the target species individuals have provided a solid foundation for long term monitoring of the gene pool and the conservation of woody species in SNR "Felješana".Šume prašumskog karaktera u Evropi obično imaju najviši oblik zaštite.
Značaj ovih ekosistema ističe i Strategija BIO2023, koja predviđa posebne smernice za
izdvajanje i zaštitu šuma prašumskog karaktera u okvirima Evropske Unije. Endemični
ekosistemi karakteristični za Evropu su i čiste bukove šume, koje se u kontekstu klimatskih
promena susreću sa nizom ugrožavajućih faktora i predstavljaju jedno od najugroženijih
staništa. Napori da se sačuvaju i unaprede šumski ekosistemi kao inicijalni korak
podrazumevaju sprovođenje konzervacije i dugoročnog monitoringa kako bi se stvorio uvid
u adaptaciju I evolucione strategije prisutnih vrsta i ekosistema u celini. Izuzetno strogi
uslovi zaštite propisani u strogim rezervatima imaju veoma ograničavajuće devovanje
čoveka, neinvazivna naučna istraživanja se smatraju poželjnim aktivnostima. Jedna od prvih
zaštićenih čistih bukovih šuma u Srbiji je i Strogi rezervat prirode „Felješana”, koji iako je
zaštićen još od 1950. godine, nije detaljno i sistematičo izučavan sa aspekta diverziteta
drvenastih vrsta. Cilj ovog rada je da, po prvi put, pruži podatke o dostupnom genofondu
drvenastih vrsta u bukovoj prašumi „Felješana”. Metodologija za terenska istraživanja
obuhvatila je evidentiranje drvenastih vrsta u spratovima drveća, žbunja i prizemne
vegetacijei na unapred određenim monitoring tačkama, kao i izdvajanje i georeferenciranje
ciljnih vrsta. Georefernciranim individuama ciljnih vrsta su određeni visina, prsni prečnik,
prsni obim i horizontalna projekcija krošnje. Ukupno je evidentirano 27 autohtonih
drvenastih vrsta, od toga, 14 vrsta se javlja u spratu drveća, 25 u spratu žbunja, a 19 u spratu
prizemne flore. Iako je bukva dominantna vrsta u sva tri sprata vegetacije na celom području,
evidentirani broj vrsta u spratu žbunja i prizemne vegetacije ukazuje na mogućnost promene
distribucije i sastava vrsta u rezervatu u budućnosti. Sve evidentirane vrste su autohtonog
porekla, među kojima čak šest vrsta pripada jednoj od kategorija retkih, ugroženih i ranjivih
vrsta šumskog fonda Srbije. Georeferenciranje i određivanje osnovnih karakteristika jedinki
ciljnih vrsta pružilo je čvrstu osnovu za dugoročno praćenje genofonda i konzervaciju
drvenastih vrsta u SRP „Felješana”