Publications

This paper demonstrates the possibility of the preparation of Fe3O4/BaTiO3 core-shell composites. BaTiO3-coated Fe3O4 (Fe3O4/BaTiO3) with 5-15 nm Fe3O4 nanoparticles as cores and 2.5-4 nm BaTiO3 shell thickness, was successfully prepared through coprecipitation method and sol-gel deposition technique. High-Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive X-ray Spectrometry (EDXS) and Selected-Area Electron Diffraction (SAED) showed the formation of the core-shell structure with face centered cubic Fe3O4 and tetragonal BaTiO3 phases.

Plates of NiTi chemically etched, electro-polished, and sol gel coated with XO2 (X =Ti, Si, Zr), or coated with oxides and dip-coated polymers of Dextro-Levo-lactide-co-glycolide (DL-PLG, 0.4 mu m thickness), Dextro-Levo-lactic acid (DL-PLA, 1.3 mu m) or poly methyl methacrylate polymer (PMMA, 1.7 mu m) were obtained. Smooth and uniform NiTi surfaces without significant pitting, as revealed by AFM, were prepared for chemical etching of 120 s in HF:HNO3:H2O = 1:5:4, followed by electropolishing 120 s in H2SO4:CH3OH:H2O = 1:4:5 electrolyte and using a potential of 9 V. Dip-coated layer of PMMA has shown cracks and large pores and was eliminated from further experiments. Samples of pristine and coated NiTi were in vivo implanted into rabbits and extracted after 10 and 60 days. Clinically, all implants are biocompatible; all rabbits survived and a recovery process was observed for all cases. NiTi covered with SiO2, DL-PLG and SiO2/DL-PLG have shown the best healing evolution. For 10 and 60 days good recovery was found also for NiTi coated with TiO2. Coatings of ZrO2 and ZrO2/DL-PLG have shown the poorest results. The oxide coating and the roughness R-ZJIS that contains information on the 'deep' large areas in the coatings show the strongest influence on the healing processes. Work indicates the possibility of space- and time- scale controlled variation of the functional properties. (C) 2018 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.

This paper presents the study and analyses on substrate integrated waveguide (SIW) Y-type power dividers. In traditional configurations, a potential stop peak exists and separates the dominant frequency band. To overcome this drawback, a Y-type power divider with an enhanced bandwidth is proposed, where the reflection at the stop peak is reduced. The broadband characteristic relies on the adjustment of the TE10 and TE30 modes in the coupling region. The symmetric topology could ensure balanced phase and amplitude properties at two output ports. For the demonstration, the prototype is fabricated by the printed circuit board (PCB) process. Measurements agree well with simulations, and a fractional bandwidth of 50.26% around the centre frequency of 15 GHz is measured with 10 dB return loss.

In this work, we report the influence of nanocarbon deposited on mesoporous TiO2 by spray method on photoelectrochemical performance of the formed photoanodes. Scanning electron microscopy and transmission electron microscopy images confirmed presence of carbon nanoparticles on the surface of anatase TiO2 films. Nanocarbon decorated TiO2 photoanodes were characterized by electrochemical impedance spectroscopy and Mott-Schottky analysis. Charge recombination process was evaluated by measurement of open-circuit voltage decay after interruption the illumination Only a small enhancement of photoelectrochemical performance of these photoanodes was observed. It was attributed to increasing of charge carrier density as a result of nanocarbon deposition on TiO2 film.

Martel and Lazului are active phreatic/epiphreatic caves with a superimposed vadose morphology. Martel is a branchwork cave developed parallel with the river as a left (north) side meander and is located at about 8 m below the thalweg. The water level in the cave rises and falls along the main gallery, where the lakes/streams at the lightest rain become sumps. The cave is relatively poor in speleothems, except the fossil gallery (CS FV Gallery of Memories) located at the upstream end of the cave, but numerous erosion and corrosion features are present. Lazului is also a branchwork cave, forming a large meander on the right (south) side of the Motru Sec River, where at the lowest points of the cave, five streams are disappearing underground. Erosion and corrosion features are present, and speleothem is found occasionally in the upper level of the cave.

Radiometric methods aimed the use of liquid scintillation counting for tritium evaluation in different environmental compartments, alpha-beta and high resolution gamma spectrometry in determining radionuclides in soils, sediments and building materials. The non radiometric methods were focused on radiocarbon dating by accelerator mass spectrometry of bones, on FTIR and TGA analyzes of raw bone material vs. extracted collagen, and on the PIXE compositional analysis of archaeological materials.

In the recent years, there is an extensive effort concentrated towards the development of nanoparticles with near-infrared emission within the so called second or third biological windows induced by excitation outside 800-1000 nm range corresponding to the traditional Nd (800 nm) and Yb (980 nm) sensitizers. Here, we present a first report on the near-infrared (900-1700 nm) emission of significant member of cubic sesquioxides, Er-Lu2O3 nanoparticles, measured under both near-infrared up-conversion and low energy X-ray excitations. The nanoparticle compositions are optimized by varying Er concentration and Li addition. It is found that, under ca. 1500 nm up-conversion excitation, the emission is almost monochromatic (>93%) and centered at 980 nm while over 80% of the X-ray induced emission is concentrated around 1500 nm. The mechanisms responsible for the up-conversion emission of Er - Lu2O3 are identified by help of the up-conversion emission and excitation spectra as well as emission decays considering multiple excitation/emission transitions across visible to near-infrared ranges. Comparison between the emission properties of Er-Lu2O3 and Er-Y2O3 induced by optical and X-ray excitation is also presented. Our results suggest that the further optimized Er-doped cubic sesquioxides represent promising candidates for bioimaging and photovoltaic applications.

The strong modulation of the AC magnetic response in the magnetic field-temperature region of the DC magnetization peak effect (PE) occurring just below the DC irreversibility line (IL) of weakly pinned superconducting single crystals is well known. However, it is not yet clear if the AC magnetic signal registered at usual frequencies and amplitudes is significantly affected by the presence of the second magnetization peak (SMP) in the DC magnetic hysteresis curves, since the SMP appears in specimens with stronger pinning and is located well below the IL. We investigated the AC magnetic response of several La2 - xSrxCuO4 and 122-type pnictide superconducting single crystals exhibiting a pronounced DC SMP. It was found that in the case of small demagnetization effects, the AC magnetic signal across the SMP remains in the linear regime, with no detectable distortions in the SMP range (within the high sensitivity of a Physical Property Measurement System). This indicates reduced values of the Campbell penetration depth compared with the London magnetic penetration depth. A clearly nonmonotonic, SMP-related variation has only been obtained for the DC field dependence of the out of phase component of the AC magnetic moment in the nonlinear regime. The nonlinear AC Bean regime far below the IL has been attained in the conditions of enhanced demagnetization effects (plate-like specimens in perpendicular magnetic fields).

We investigated in this paper a novel bilayer composite obtained by sol-gel and spin coating of the ferroelectric 0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) (abbreviated as BNT-BT0.08) and ferromagnetic CoFe2O4 phases, for miniature low-frequency magnetic sensors and piezoelectric sensors. This heterostructure, deposited on Si-Pt substrate (Si-Pt/CoFe2O4/BNT-BT0.08), was characterized using selected method such as: X-ray diffraction, dielectric spectroscopy, piezoelectric force microscopy, SQUID magnetometry, atomic force microscopy/magnetic force microscopy, and advanced methods of transmission electron microscopy. CoFe2O4/BNT-BT0.08 ferromagnetic-piezoelectric thin films show good magnetization, dielectric constant and piezoelectric response. The results of analyses and measurements reveal that this heterostructure can have applications in high-performance magnetoelectric devices at room temperature.

This paper proposes a novel, flexible, low cost administration patch which could be used as a non-invasive, controlled transdermal drug delivery system. The fabricated device consists in a flexible microfiber architecture heater covered with a thermoresponsive hydrogel, namely poly(N-isopropylacrylamide), as a matrix for the incorporation of active molecules. The manufacturing process consists of two main steps. First, the electrospun poly(methyl methacrylate) fiber networks are sputter coated with a thin gold layer and attached to flexible poly(ethylene terephthalate) substrates to obtain the heating platforms. Second, the heaters are encapsulated in poly(ethylene terephthalate) foils and covered with poly(N-isopropylacrylamide) hydrogel sheets. In order to illustrate the functionality of the fabricated patch, the hydrogel layer is loaded with methylene blue aqueous solution and is afterwards heated via Joule effect, by applying a voltage on the metalized fibers. The methylene blue releasing profiles of the heated patch are compared with those of the unheated one and the influence of parameters such as hydrogel composition and morphology, as well as the applied voltage values for microheating are investigated. The results indicate that the fabricated patch can be used as a drug administration instrument, while its performance can be tuned depending on the targeted application.