Praistorija „Dunavskog koridora“ u Đerdapu. Istraživanje u 2020. godini

Projekat U pokretu: praistorijska mobilnost i širenje poljoprivrede u Evroaziji ima za cilj da između ostalih proučavanih regija šireg prostora jugoistočne Evrope i istočnog i centralnog Mediterana, vrati istraživački fokus na Đerdapsku klisuru i teritoriju severoistočne Srbije. On jednim delom predstavlja nastavak projekta Praistorija severoistočne Srbije u okviru koga su od 2004. do 2009. godine rađena arheološka istraživanja ranije nepoznatih praistorijskih nalazišta (Pećina iznad Trajanove table, Pešćera Mare, Dubočka pećina, Aria Babi, a po prvi put nakon 1971. godine kada je puštena u rad Hidroelektrana Đerdap I, otkriveni su i sistematski istraženi sačuvani mezolitski i ranoneolitski slojevi na Vlascu, na samoj dunavskoj obali

Istraživanje praistorije „Dunavskog koridora“ u Đerdapu

Letnja i jesenja terenska sezona 2019. godine u okviru projekta U pokretu: praistorijska mobilnost i širenje poljoprivrede u Evroaziji u Đerdapskoj klisuru na teritoriji severoistočne Srbije (sl. 1), fokusirala se na sistematska istraživanja dva lokaliteta (Pećina iznad Trajanove Table i Vlasac) i uzorkovanje sedimenata dva ranije istraživana nalazišta (Dubočka pećina–Kozja i Pećina iznad Trajanove Table), u cilju rekonstrukcije paleo-okruženja i apsolutno-hronološkog datovanja. Ovi radovi su deo šireg projekta istraživanja Đerdapske klisure i njenog zaleđa koja se vrše na osnovu ugovora o međunarodnoj saradnji između Arheološkog instituta u Beogradu i Univerziteta Kolumbija u Njujorku, SAD

Strain field measurements of glass ionomer cement

Extensive evolution of glass ionomer cements (GIC) has marked a significant shift in the practice of luting indirect dental restorations limiting the use of zinc-phosphate and zinc-polycarboxylate cements to a few indications. GIC are now one of the materials of choice for cementation of all ceramics, fiber reinforced composite posts and veneers. GICs are determined by unique properties like chemical adhesion to tooth and base metals, low thermal expansion coefficients similar to dentin and minimal microleakage at the tooth-enamel interface due to low shrinkage. Shrinkage strain is identified as the cause, and the associated stress as the mechanism for the loss of marginal adaption and cohesive fracture within the material. The aim of this study is to measure the strain and displacement field in a conventional GIC (Riva Luting, SDI, Australia) related to different cement diameter, using 3D Digital Image Correlation (DIC) method. The experiment is done for samples with thickness of 1 mm combined with diameters of 4 mm (Group I) and 3 mm (Group II). The strain field is measured using 3D 11optical system Aramis 2M (GOM, Braunschweig, Germany). This study provides valuable data about strain behaviour and displacement as a possible failure factor in GIC, Riva Luting. Visible differences between Group I and Group II were observed

Strain field measurements of glass ionomer cement

Extensive evolution of glass ionomer cements (GIC) has marked a significant shift in the practice of luting indirect dental restorations limiting the use of zinc-phosphate and zinc-polycarboxylate cements to a few indications. GIC are now one of the materials of choice for cementation of all ceramics, fiber reinforced composite posts and veneers. GICs are determined by unique properties like chemical adhesion to tooth and base metals, low thermal expansion coefficients similar to dentin and minimal microleakage at the tooth-enamel interface due to low shrinkage. Shrinkage strain is identified as the cause, and the associated stress as the mechanism for the loss of marginal adaption and cohesive fracture within the material. The aim of this study is to measure the strain and displacement field in a conventional GIC (Riva Luting, SDI, Australia) related to different cement diameter, using 3D Digital Image Correlation (DIC) method. The experiment is done for samples with thickness of 1 mm combined with diameters of 4 mm (Group I) and 3 mm (Group II). The strain field is measured using 3D 11optical system Aramis 2M (GOM, Braunschweig, Germany). This study provides valuable data about strain behaviour and displacement as a possible failure factor in GIC, Riva Luting. Visible differences between Group I and Group II were observed

3D Digital Image Correlation Analysis of the Shrinkage Strain in Four Dual Cure Composite Cements

The introduction of resin-based cements and an adhesive-bonding system in daily dental practice has given the opportunity to increase the retention of previously conventional cemented restorations and the optimal results in esthetic. This experimental study employed the 3D Digital Image Correlation Method (3D-DIC) for detecting shrinkage strain in four dual cured composite cements. The aim was to visualize measure, analyze, and compare strain fields in four resin-based cements using the 3D-DIC method. A total of 72 samples were divided into 4 groups considering variations in sample types, diameter, and thickness. Four types of composite cements: RelyX U200 (3 M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Multilink Automix (Ivoclar Vivadent, Schaan, Liechtenstein), and SeT PP (SDI, Australia) were used. Each type had diameters of 3 mm, 4 mm, and 5 mm, respectively, combined with two different values of thickness: 1 mm and 2 mm. Thickness had an important role on strain detected in all tested materials showing higher strain in samples with 2 mm thickness compared to 1 mm samples. Shrinkage strain values were the highest in Set PP samples indicated the possibility of undesirable de-bonding

Ground stone artefacts from Aria Babi

The Early Neolithic settlement at the site of Aria Babi (the Danube Gorges or Iron Gates area, northeastern Serbia) is chronologically contemporaneous with the Starčevo horizon at Lepenski Vir, and it is located in its immediate vicinity. Our analysis of the stone tools ncompassed the material from trench 1–2/2005, investigated in 2005 and 2006. Judging on the basis of the ground stone assemblage from this site, and with the same conclusion reached based on the ceramic analysis, a rural household was identified in this place, in a small settlement with ispersed dug-in features, typical of the Starčevo culture. In this household, the every-day life of the community was probably focused on farming. There were items found which were used for food preparation – aside from pottery, such as stone querns – but there were also tools and household items produced from materials softer than stone, such as wood and bone, which were not preserved. Various fragments of raw material, not so numerous in this assemblage, indirectly point to a small-scale ground stone tool production at this place. The secondary use of fragmented abrasive tools bears witness to, in most cases, expedient tools used by the inhabitants of this household. It is probable that in the mountainous hinterland of the Early Neolithic sites discovered along the Danube’s banks in this region existed smaller villages which provided both agricultural and perhaps also some artisanal products

3D Digital Image Correlation Analysis of the Shrinkage Strain in Four Dual Cure Composite Cements

The introduction of resin-based cements and an adhesive-bonding system in daily dental practice has given the opportunity to increase the retention of previously conventional cemented restorations and the optimal results in esthetic. This experimental study employed the 3D Digital Image Correlation Method (3D-DIC) for detecting shrinkage strain in four dual cured composite cements. The aim was to visualize measure, analyze, and compare strain fields in four resin-based cements using the 3D-DIC method. A total of 72 samples were divided into 4 groups considering variations in sample types, diameter, and thickness. Four types of composite cements: RelyX U200 (3 M ESPE, St. Paul, MN, USA), MaxCem Elite (Kerr, Orange, CA, USA), Multilink Automix (Ivoclar Vivadent, Schaan, Liechtenstein), and SeT PP (SDI, Australia) were used. Each type had diameters of 3 mm, 4 mm, and 5 mm, respectively, combined with two different values of thickness: 1 mm and 2 mm. Thickness had an important role on strain detected in all tested materials showing higher strain in samples with 2 mm thickness compared to 1 mm samples. Shrinkage strain values were the highest in Set PP samples indicated the possibility of undesirable de-bonding

Functionalized porous nanocomposite as phenol derivatives sorbent

Nanocomposite of poly (glycidyl methacrylate-co-ethylene glycol dimethacrylate) and acid modified bentonite was prepared by radical suspension copolymerization. The porosity of the obtained nanocomposite was confirmed by mercury porosimetry. In order to be tested as sorbent for phenol derivatives the composite was functionalized with diethylene triamine and denoted CP-SA-deta. Sorption at constant temperature (25 °C) was performed on water solutions of three phenol derivatives: 4-nitrophenol (4NP), 2-nitrophenol (2NP) and 2-chloro-4-nitrophenol (2Cl4NP). The influence of pH, sorption time and initial concentration of sorbates on sorption efficiency of CP-SA-deta was studied. The isotherm data were best fitted with Langmuir model, while the sorption dynamics obeyed the pseudo-second-order kinetic model for all derivates. Under the same experimental conditions the sorption capacity of CP-SA-deta toward phenol derivatives increased in the following order qmax(2NP)=0.34 mmol g-1 < qmax(4NP)=0.58 mmol g-1 < qmax(2Cl4NP)=0.70 mmol g-1. On the other hand the sorption rate was similar for 2NP and 4NP, but somewhat slower for 2Cl4NP. The synthesized functionalized nanocomposite can be regarded as promising sorbent for phenol derivatives

BIOMECHANICAL ANALYSIS OF DIFFERENT MODES OF THE SAME COMPOSITE CEMENT USING THE DIGITAL IMAGE CORRELATION METHOD

Recently, resin based cements have become very popular in dental practice for cementation of dental restorations, especially considering all-ceramics, due to improved adhesion features. The aim of this study was to visualize and compare strain in the self-cured and dual-cured MaxCem Elite and to investigate hardness of these two curing modes of the same cement. Strain field was measured using 3D optical system Aramis 2M (GOM, Braunschweig, Germany) based on digital image correlation method. Ten, 5 × 2 mm sized samples of the self-cured and dual-cured Maxcem Elite (Kerr, Orange, CA, USA) were prepared by filling plastic ring-type molds. Analysis of the strain fields was done using sections and stage points created by software. The distribution of the overall strain was found to be more expressive and uniform in the self-cured samples. Overall shrinkage strain ranged from 0 to 12%. Samples with dual-curing mode showed higher strain peripherally, compared to self-cured samples where the overall strain was distributed all over the sample surface. The Vickers measurements could not be carried out on self-cured samples due to incomplete chemical polymerization. The values of hardness were relatively equal in dual-cured Maxcem Elite due to hardness is interpreted as a statistical magnitude practically depends on the composition of the tested structure. Additionally, closeness between cements layers and led lamp was a factor for increasing hardness values in dual–cured Maxcem Elite. The study provided valuable data about strain behavior of Maxcem Elite during polymerization and highlighted dual-cured over self-cured mode

BIOMECHANICAL BEHAVIOR OF RESIN BASED CEMENTMAXCEM ELITE

Resin based cements (RBCs) have become very popular in dental practice for cementation of dental restorations, especially considering all-ceramics, due to improved adhesion features. However, one of the major concerns for the clinical performance of resin based cements is the polymerization shrinkage i.e. strainthat accompanies the chain-growth polymerization of dimethacrylate monomers. Also, RBCs can produce a considerable amount of heat, due to the light energy from the curing lights and exothermic reaction of polymerization. The purpose of this study was to determine the temperature changes during the photo-polymerization using thermocouples and to measure strain field of the self-etching, self-adhesive RBC, Maxcem Elite (Kerr, Orange, CA, USA) using 3D optical system Aramis 2M (GOM, Braunschweig, Germany) based on Digital Image Correlation method. Three 05×2 mm sized and three 05×1 mm samples of Maxcem Elite were prepared by filling teflon ring-type moulds. Digital images were recorded immediately after photo-polymerization of the samples with a LED-curing unit for 20 s, according to manufacturer's recommendation. All measurements were performed at room temperature. Temperature curves indicated similar patterns. DIC showed that peripheral zone of the samples had the highest strain values in both groups. All the results were material-dependent and probably correlated to the composition of each material, which is not fully disclosed by the manufacturers