Optimization of the Electrochemical Method of Obtaining Graphene Nanoplatelets (GNPs).

Graphene nanoplatelets (GNPs) were prepared using the electrolytic exfoliation method on graphite foil in an ammonium sulfate solution. A series of experiments were conducted in order to optimize the production of the flakes by varying the pH of the solution, applied voltage and current, duration of electrolysis, temperature in the electrolytic system, and type and duration of the ultrasound interaction. The quality of the produced graphene nanoplatelets was analyzed using X-ray diffraction, Raman and IR spectroscopy, and TEM.

High Critical Current Density in the Textured Nanofiber Structure in Multifilament MgB2 Wires Made by the Powder-In-Tube (PIT) Technique.

We show that the structure of multifilament MgB2 wires made by the powder-in-tube (PIT) method can be texturized by annealing the structure under high isostatic pressure. Our results show that we obtained continuous fibers with a uniform diameter of 250 nm in all 36 filaments, a small grain size of approximately 50 nm and a high density of the superconducting material. These results contribute to a significant improvement in the critical current density in high magnetic fields, e.g., 100 A/mm2 at 14 T and 4.2 K.

Magnetocaloric performance of the three-component Ho1-xErxNi2 (x = 0.25, 0.5, 0.75) Laves phases as composite refrigerants.

To date, significant efforts have been put into searching for materials with advanced magnetocaloric properties which show promise as refrigerants and permit realization of efficient cooling. The present study, by an example of Ho1-xErxNi2, develops the concept of magnetocaloric efficiency in the rare-earth Laves-phase compounds. Based on the magneto-thermodynamic properties, their potentiality as components of magnetocaloric composites is illustrated. The determined regularities in the behaviour of the heat capacity, magnetic entropy change, and adiabatic temperature change of the system substantiate reaching high magnetocaloric potentials in a desired temperature range. For the Ho1-xErxNi2 solid solutions, we simulate optimal molar ratios and construct the composites used in magnetic refrigerators performing an Ericsson cycle at low temperatures. The tailored magnetocaloric characteristics are designed and efficient procedures for their manufacturing are developed. Our calculations based on the real empirical data are very promising and open avenue to further experimental studies. Systems showing large magnetocaloric effect (MCE) at low temperatures are of importance due to their potential utilization in refrigeration for gas liquefaction.

A Study of the Impact of Graphene Oxide on Viral Infection Related to A549 and TC28a2 Human Cell Lines.

Graphene has been one of the most tested materials since its discovery in 2004. It is known for its special properties, such as electrical conductivity, elasticity and flexibility, antimicrobial effect, and high biocompatibility with many mammal cells. In medicine, the antibacterial, antiviral, and antitumor properties of graphene have been tested as intensively as its drug carrying ability. In this study, the protective effect of graphene oxide against Rubella virus infection of human lung epithelial carcinoma cells and human chondrocyte cells was examined. Cells were incubated with graphene oxide alone and in combination with the Rubella virus. The cytopathic effect in two incubation time periods was measured using DAPI dye as a percentage value of the changed cells. It was shown that the graphene oxide alone has no cytopathic effect on any of tested cell lines, while the Rubella virus alone is highly cytopathic to the cells. However, in combination with the graphene oxide percentage of the changed cells, its cytotopathicity is significantly lower. Moreover, it can be concluded that graphene oxide has protective properties against the Rubella virus infection to cells, lowering its cytopathic changes to the human cells.

Effect of Heat Treatments under High Isostatic Pressure on the Transport Critical Current Density at 4.2 K and 20 K in Doped and Undoped MgB2 Wires.

Annealing undoped MgB2 wires under high isostatic pressure (HIP) increases transport critical current density (Jtc) by 10% at 4.2 K in range magnetic fields from 4 T to 12 T and significantly increases Jtc by 25% in range magnetic fields from 2 T to 4 T and does not increase Jtc above 4 T at 20 K. Further research shows that a large amount of 10% SiC admixture and thermal treatment under a high isostatic pressure of 1 GPa significantly increases the Jtc by 40% at 4.2 K in magnetic fields above 6 T and reduces Jtc by one order at 20 K in MgB2 wires. Additionally, our research showed that heat treatment under high isostatic pressure is more evident in wires with smaller diameters, as it greatly increases the density of MgB2 material and the number of connections between grains compared to MgB2 wires with larger diameters, but only during the Mg solid-state reaction. In addition, our study indicates that smaller wire diameters and high isostatic pressure do not lead to a higher density of MgB2 material and more connections between grains during the liquid-state Mg reaction.

SEM Evaluation of Tooth Surface after a Composite Filling Removal Using Er:YAG Laser, Drills with and without Curettes, and Optional EDTA or NaOCl Conditioning.

(1) Background: This study aimed to evaluate the microporosity of the tooth surface structure adjacent to the cemento-enamel junction (CEJ) after the removal of composite fillings with a drill in comparison with removal by an Er:YAG laser and after cleaning with a periodontal curette, chemical EDTA and NaOCl (sodium hypochlorite) conditioning. (2) Methods: The research material consisted of 30 extracted premolars with cervical composite fillings. The teeth were divided into six groups according to the method of tooth preparation: group G1 (n = 5)-a diamond drill; group G2 (n = 5)-a diamond drill + curette; group G3 (n = 5)-a diamond drill + 24% EDTA (PrefGel, Straumann, Switzerland); group G4 (n = 5)-an Er:YAG laser (LightWalker, Fotona, Ljubljana, Slovenia) set with the following parameters: power: 1.65 W (composite removal, CR), 1.2 (tooth conditioning, TC), energy: 110 mJ (CR), 80 mJ (TC), frequency: 15 Hz, pulse duration: 50 µs, tip diameter: 1 mm, air/fluid cooling: 4, distance 1.5 mm, energy density: 14.01 J/cm2 (CR), 10.19 J/cm2 (TC); group G5 (n = 5)-an Er:YAG laser + 2% sodium hypochlorite (NaOCl); group G6 (n = 5)-an Er:YAG laser + 5.25% NaOCl. In each tooth, three cavities were made and subjected to analysis. The dentin surface was evaluated using a scanning electron microscope (SEM). (3) Results: Groups G1 and G2 exhibited mechanical damage to the tooth surface structure caused by the rotary motion of a diamond drill. The SEM image showed a smear layer that could only be removed chemically using 24% EDTA gel (group G3). The tooth surfaces prepared with the Er:YAG laser (groups G4-G6) revealed a homogeneous structure without damage along with open dentinal tubules (without smear layer) and visible denaturation of collagen fibers. The sodium hypochlorite (NaOCl) conditioning did not increase the visibility of dentinal tubules. (4) Conclusions: Dentin surfaces have open dentinal tubules after removal of the composite filling using the Er:YAG laser and therefore do not require additional NaOCl conditioning.

Influence of Amorphous Boron Grain Size, High Isostatic Pressure, Annealing Temperature, and Filling Density of Unreacted Material on Structure, Critical Parameters, N-Value, and Engineering Critical Current Density in Mgb2 Wires.

Our results show that a lower density of unreacted Mg + B material during an Mg solid-state synthesis reaction leads to a significant reduction in the quantity of the superconducting phase and lowers the homogeneity of the superconducting material. It also significantly reduces the irreversible magnetic field (Birr), critical temperature (Tc), upper magnetic field (Bc2), engineered critical current density (Jec), and n-value, despite high isostatic pressure (HIP) treatment and the use of nanoboron in the sample. Our measurements show that samples with large boron grains with an 8% higher density of unreacted Mg + B material allow better critical parameters to be achieved. Studies have shown that the density of unreacted material has little effect on Birr, Tc, Bc2, Jec, and the n-value for an Mg liquid-state synthesis reaction. The results show that the critical parameters during an Mg liquid-state synthesis reaction depend mainly on grain size. Nanoboron grains allow for the highest Birr, Tc, Bc2, Jec, and n-values. Scanning electron microscopy (SEM) images taken from the longitudinal sections of the wires show that the samples annealed under low isostatic pressure have a highly heterogeneous structure. High isostatic pressure heat treatment greatly improves the homogeneity of MgB2.

Removal of Composite Restoration from the Root Surface in the Cervical Region Using Er: YAG Laser and Drill-In Vitro Study.

BACKGROUND: Recently, the defects of the tooth surface in the cervical region are often restored using composite filling materials. It should meet the needs of the patients regarding esthetics and material stability. The aim of the study was to analyze the tooth root surface at the cervical region after the removal of the composite filling material by means of the Erbium-doped Yttrium Aluminium Garnet (Er: YAG) laser or drill using the scanning electron microscopy (SEM) and fluorescence microscopy. MATERIALS AND METHODS: For the purposes of this study, 14 premolar teeth (n = 14) were removed due to orthodontic reasons. The rectangular shape cavities with 3 mm in width and 1.5 mm in height were prepared with a 0.8 mm bur on high-speed contra-angle in the tooth surface just below cemento-enamel junction (CEJ) and filled with the composite material. The composite material was removed with the Er: YAG laser at a power of 3.4 W, energy 170 mJ, frequency 20 Hz, pulse duration 300 µs, tip diameter 0.8 mm, air/fluid cooling 3 mL/s, and time of irradiation: 6 sec, at a distance from teeth of 2 mm (G1 group, n = 7) or a high-speed contra-angle bur (G2 group, n = 7). After the removal of composite material, the surfaces of teeth were examined using the scanning electron microscopy (SEM) and fluorescence microscopy. RESULTS: The Er: YAG irradiation allowed to remove completely the composite material from the tooth cavity. The study confirmed, that the ends of collagen fibers were only partially denatured after the Er: YAG laser application. CONCLUSION: It has been proved that using the Er: YAG laser is an effective and safe method of composite removal for the dentin surface.

Lanthanum molybdate nanoparticles from the Bradley reaction: factors influencing their composition, structure, and functional characteristics as potential matrixes for luminescent phosphors.

Interaction of lanthanum isopropoxide with molybdenum(VI) alkoxides in La/Mo ratios varying from 3:1 to 1:1 in acetophenon or allyl alcohol as solvents offers nanosized poorly crystalline products of complex composition, where the precipitation of Mo-rich ones is followed by the formation of La-rich ones with conservation of the reaction stoichiometry in total. Thermal treatment of the precipitates at temperatures over 700 °C leads to the formation of stoichiometric phases of the α- and ß-La2Mo2O9 compositions. Introduction of smaller Re(3+) cations such as Sm(3+) by doping favors stabilization of the La2-xRExMo2O9 phase with improved crystallinity even after lower-temperature thermal treatment. The doping is successful only when the Re(3+) (Sm(3+), Eu(3+), and Tb(3+)) is introduced as an alkoxide: application of Re(3+)(acac)3 as Re(3+) sources leads to materials free from Re(3+). The produced samples were characterized by XPD, TGA, SEM, and TEM studies as well as the luminescent properties for the Sm(3+)-doped phases.

Structure and phase stability of nanocrystalline Ce(1-x)Ln(x)O(2-x/2-delta) (Ln = Yb, Lu) in oxidizing and reducing atmosphere.

The structure and phase evolution of nanocrystalline Ce(1-x)Ln(x)O(2-x/2-delta) (Ln = Yb, Lu, x = 0 - 1) oxides upon heating in H(2) was studied for the first time. Up to 950 degrees C the samples were single-phase, with structure changing smoothly with x from fluorite type (F) to bixbyite type (C). For the Lu-doped samples heated at 1100 degrees C in the air and H(2), phase separation into coexisting F- and C-type structures was observed for ~0.40 < x < ~0.70 and ~0.25 < x < ~0.70, respectively. It was found also that addition of Lu(3+) and Yb(3+) strongly hinders the crystallite growth of ceria during heat treatment at 800 and 950 degrees C in both atmospheres. Valency of Ce and Yb in Ce(0.1)Lu(0.9)O(1.55-delta) and Ce(0.95)Yb(0.05)O(1.975-delta) samples heated at 1100 degrees C was studied by XANES and magnetic measurements. In the former Ce was dominated by Ce(4+), with small contribution of Ce(3+) after heating in H(2). In the latter, Yb existed exclusively as 3+ in both O(2) and H(2).