Društvene mreže i nauka: trenutno stanje i perspektive

Društvene mreže su sredstva komunikacije i interakcije među korisnicima gde se stvaraju, dele i razmenjuju informacije i ideje. Društvene mreže se posmatraju kao veb lokacije koje povezuju pojedince i/ili različite grupe ljudi i koje uključuju različite sadržaje koje kreiraju korisnici. Posebna grupa korisnika društvenih mreža koju autori u ovom radu posmatraju jesu članovi istraživačkog sektora. Prvi deo rada prikazuje opšte trendove i statistiku korišćenja interneta i društvenih mreža u širem kontekstu, dok se u drugom delu rada daje prikaz najznačajnijij društvenih mreža kreiranih za potrebe istraživačkog sektora

mLab: handheld assisted laboratory

This paper explores the potential of an m-learning environment by introducing the concept of mLab, a remote laboratory environment accessible through the use of handheld devices. We are aiming to enhance the existing e-learning platform and internet-assisted laboratory settings, where students are offered in-depth tutoring, by providing compact tuition and tools for controlling simulations that are made available to learners via handheld devices. In this way, students are empowered by having access totheir simulations from any place and at any time

Efekti lasero-terapije na intrakanalni dentin i cementno tkivo apeksa korena zuba

Laser irradiation during root canal treatment is efficient but in order to prevent irreversible thermal damage to dentine, cementum and other periapical structures continuous water cooling is required. The aim of this study was to ultrastructurally analyze the surface of intracanal dentine and cementum at the root apex after Er:YAG laser irradiation with and without sterile saline solution irrigation. The study involved 70 intact maxillary and mandibular single-rooted and tworooted human teeth, divided into two experimental groups and one control group. In all teeth access cavity was created. For root canal irradiation, Er:YAG laser with the wavelength of 2940 nm, energy output of 140 mJ per pulse, pulse duration of 125-160 ms, pulse repetition rate of 10 Hz and power of 15 W was used. Total irradiation time for each root canal was 10 seconds. The ultrastructural analysis of intracanal dentine and the cementum of the root apex was done by using scanning electron microscope (JEOL JSM-5300 Tokyo Japan). Intracanal Er:YAG laser irradiation without water cooling showed melted circumpulpal dentine with large cracks in it, whereas cementum at the root apex was thermally modified in the form of plates and cracks. Intracanal Er:YAG laser irradiation with continuous water cooling resulted in clean intracanal dentine surface without morphological changes of the cementum. The canal system irradiation is acceptable and possible only when using constant water cooling; otherwise, irreversible thermal damage to intracanal dentine and cementum at the root apex occur.Obrada kanala korena zuba laserom je efikasna, ali zahteva obavezno hlađenje vodom kako bi se sprečila ireverzibilna termička oštećenja dentina, cementa i ostalih periapeksnih struktura. Cilj ovog rada bio je da se ultrastrukturno analizira površina intrakanalnog dentina i cementnog tkiva na apeksu korena zuba posle obrade kanala Er:YAG laserom bez irigacije i sa irigacijom sterilnim fiziološkim rastvorom. Korišćeno je 70 intaktnih maksilarnih i mandibularnih jednokorenih i dvokorenih humanih zuba, podeljenih u dve eksperimentalne i jednu kontrolnu grupu. Kod svih zuba je formiran pristupni kavitet. Za obradu kanala korišćen je Er:YAG laser talasne dužine 2940 nm, izlazne energije za impuls 140 mJ; u pulsnom režimu 125-160ms, stopom pulsne repeticije od 10 Hz i energijom od 15 W. Vreme obrade svakog kanala laserom iznosilo je 10 sekundi. Ultrastrukturna analiza intrakanalnog dentina i cementnog tkiva na apeksnom delu korena zuba urađena je na skening elektronskom mikroskopu (JEOL JSM -5300 Tokyo Japan). Intrakanalna obrada Er:YAG laserom bez vodenog hlađenja pokazuje stopljen cirkumpulparni dentin sa velikim pukotinama u dentinu, a cementno tkivo na apeksu je termički modifikovano u vidu ploča i pukotina. Intrakanalna obrada Er:YAG laserom uz kontinuirano vodeno hlađenje daje čistu intrakanalnu dentinsku površinu bez morfoloških promena cementnog tkiva. Obrada kanalnog sistema zuba je opravdana i moguća samo u uslovima stalnog hlađenja vodom, u protivnom nastaju ireverzibilna termička oštećenja intrakanalnog dentina i cementa na apeksu korena zuba

Friction at Nanoscale

In many technical fields a contact between two surfaces is very important and often the subject of research. The numerous physical phenomena that occur at the contact between two materials indicate the complexity of the processes that take place at the macro, micro or nanoscale. Therefore, friction, lubrication and wear are the subjects that have been attracting attention for many years, especially as part of tribological investigations. The research has shown that these three components are of fundamental importance for surfaces in contact. The aim of this research is to describe friction, and lubrication as a process to control friction, especially at the atomic level. At the atomic and molecular scale there is a possibility to form very thin film with the property to spontaneously assemble themselves into ordered structures. One of the procedures to make these ultrathin organic films of controlled thickness is to prepare self-assembled monolayers. These monolayers are described as a model system to study boundary lubrication

Microstructure characterization of porous microalloyed aluminium-silicate ceramics

Kaolinite and bentonite clay powders mixed with active additives, based on Mg(NO3)2 and Al(NO3)2, sintered at high temperatures produce very porous ceramics with microcrystalline and amorphous regions and highly developed metalized surfaces (mainly with magnesium surplus). Microstructure investigations have revealed non-uniform and highly porous structure with broad distribution of grain size, specifically shaped grains and high degree of agglomeration. The ceramics samples were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction analysis (XRD) and IR spectroscopy analysis, prior and after treatment in “synthetic water”, i.e. in aqueous solution of arsenic-salt. Grain size distribution for untreated and treated samples was done with software SemAfore 4. It has shown great variety in size distribution of grains from clay powders to sintered samples

Haemoglobin level in relation to vitamin D status in infants and toddlers

Introduction: Vitamin D Deficiency (VDD) is defined as the level of 25(OH)D in the serum < 30 ng/ml. According to the contemporary research, even the slight vitamin D deficiency can adversely affect our body in many ways. Numerous studies indicate that vitamin D deficiency is very common in children. The study aimed to research the frequency of vitamin D deficiency in infants and toddlers, the connection between VDD and iron deficiency anemia (IDA), as well as the correlation between 25-hydroxycholecalciferol (25(OH)D) and haemoglobin (Hb) in the examinees. Method: The study includes 150 children, 73 (49%) newborns and 77 (51%) infants. Vitamin D status was determined through the amount of 25(OH)D in blood, using the electrochemiluminescence. Results: Vitamin D Deficiency was found in 58% of infants and toddlers (severe vitamin D deficiency was found in 16% of examinees, vitamin D deficiency was found in 23% of examinees, while vitamin D insufficiency was found in 19% of examinees). Vitamin D deficiency (VDD) and anaemia were found in 80% of examined infants and toddlers. VDD was found in 49% of newborns that were not anaemic. We have observed the substantial difference between the examinees suffering from both anaemia and VDD and the examinees suffering from VDD only. Conclusion: The highest level on anaemia was found in the children with severe vitamin D deficiency, while in the examined infants and toddlers, there was a connection between the level of 25(OH)D and Hb in the serum

Prevalence of Human Cytomegalovirus and Epstein-Barr Virus in Chronic Periapical Lesions

Objective: The aim of this study was to investigate the presence of human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV) in the tissue of chronic periapical lesions, and to compare the results in relation to the symptoms of patients and the size of the lesion. Methods: Periapical lesions analyzed in the study were collected from the roots of the teeth indicated for extraction. Samples were divided according to the symptoms into groups of symptomatic and asymptomatic, and according the size into groups of small and large lesions. Polymerase chain reaction was used to detect HCMV and EBV. The amplification was performed in a DNA Thermal Cycler (Hybaid). Results: Symptomatic lesions were 7.68 times more likely to be infected with HCMV than asymptomatic lesions (p lt 0.001). Large symptomatic lesions were 73.50 times more likely to harbor HCMV than small symptomatic lesions (p lt 0.001). Large symptomatic lesions were 7.64 times more likely to be infected with EBV than small symptomatic lesions (p = 0.05). Large symptomatic lesions were 5.38 times more likely to harbor dual HCMV/EBV infection than small symptomatic lesions (p = 0.115). Conclusion: Detection of HCMV and EBV in the samples of periapical lesions suggests an important role of herpesviruses in periapical tissue destruction

Electrophysical properties of microalloyed alumo-silicate ceramics as active dielectric

In this paper, electrophysical properties of porous alumo-silicate ceramics, modified by alloying with magnesium and microalloying with aluminum, were investigated. Complex multiphase system, as active microalloyed ceramics, has specific behavior under influence of external electrical field, which involves changes of dielectric losses and impedance, depending on frequency and temperature. Dielectric properties were measured in the frequency range 20 Hz - 1 MHz. Values for permittivity (εr) ranged between 140 - 430. Order of magnitude for electrical resistivity was about 106 Ωm, for impedance 104 - 108 Ω, and loss tangent had values about and greater than 0.05. Current flow through active dielectric takes place through dielectric barrier and throughout conduction bands of thin aluminum and magnesium metal films. Permittivity has nonlinear distribution and complex functional dependences because of significant nonhomogeneity of active microalloyed ceramics. Lower values of electrical resistivity are the result of complex electron and ion transfer of charge through solid phase and pores, with decreased potential barriers height, due to the influence of additives, ingredients and defects. [Projekat Ministarstva nauke Republike Srbije, br. III 45012 i br. ON 172057