Publications

We investigate by different complementary methods the processes occurring when a polydimethylsiloxane film is used as interlayer for a silver doped hydroxyapatite coating. The X-ray diffraction and Fourier Transform Infrared Spectroscopy measurements show that the hydroxyapatite doped with silver is in a crystalline form and some SiO44- ions formation takes place at the surface and in the bulk of the new hydroxyapatite doped with silver/polydimethylsiloxane composite layer. The possibility of SiO44- ions incorporation in the structure of silver doped hydroxyapatite by the mechanism of SiO44-/PO43- ions substitution is analysed. The new formed silver doped hydroxyapatite/polydimethylsiloxane composite layer is compact, homogeneous, with no cracks as it was shown by Scanning Electron Microscopy and Glow Discharge Optical Emission Spectrometry.

Radar Cross Section (RCS) is a very important parameter of an aircraft. It is given by the overall signal reflected by the target when it is irradiated by electromagnetic waves in order to be detected and localized. The measurement of RCS for some aircrafts in real scenarios is a very complex and costly process because it needs a certain area for experiments, special equipment and a number of flights. Hence, in most cases the evaluation of RCS is made by measuring a scaled model aircraft in an anechoic chamber. This paper proposes a measurement scenario for IAR 99 and analysis the experimental data. This is the first evaluation of the IAR 99 radar cross section using measurements in time and frequency domain.

We study the generation of p-shell excitons in optically active disk-shaped quantum dots subjected to ultrafast optical pulses. The single-particle spectral properties are obtained from the four-band kp theory, whereas the Coulomb interaction is taken into account within the configuration-interaction approach, particular attention being payed to configuration mixing due to electron-hole correlations. The effect of intraband relaxation processes is included in the non-unitary dynamics derived from the von-Neumann Lindblad equation. We find that the fast hole relaxation processes drive the p-shell excitons to intermediate states which eventually evolve to s-shell excitons via slower electron relaxation.

A new class of thermotropic lanthanidomesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 degrees C). Depending on the alkyl length spacer, these complexes exhibit a SmA phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.

Samarium doped hydroxyapatite (Sm:HAp), Ca10-xSmx(PO4)(6)(OH)(2) (HAp), bionanoparticles with different x(Sm) have been successfully synthesized by coprecipitation method. Detailed characterization of samarium doped hydroxyapatite nanoparticles (Sm: HAp-NPs) was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The biocompatibility of samarium doped hydroxyapatite was assessed by cell viability. The antibacterial activity of the Sm: HAp-NPs was tested against Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) andGram-positive bacteria (Enterococcus faecalis and Staphylococcus aureus). A linear increase of antimicrobial activity of P. aeruginosa has been observed when concentrations of Sm: HAp-NPs in the samples with x(Sm) = 0.02 were higher than 0.125 mg/mL. For Sm: HAp-NPs with x(Sm) = 0.05 a significant increase of antibacterial activity on E. coli was observed in the range 0.5-1 mg/mL. For low concentrations of Sm: HAp-NPs (x(Sm) = 0.05) from 0.031 to 0.125 mg/mL a high antibacterial activity on Enterococcus faecalis has been noticed. A growth of the inhibitory effect on S. aureus was observed for all concentrations of Sm: HAp-NPs with x(Sm) = 0.02.

New type of dielectric resonator antennas (DRAs) with axial symmetry are proposed for frequencies around 5.8 GHz. Each element uses a high permittivity cylindrical resonator and a low permittivity resonator of a truncated cone shape. Two types of microstrip-fed DRAs were investigated. By coupling the resonance modes, the first type and the second type DRA exhibit fractional impedance bandwidth of 15.6% and 19.7%, respectively.

The paper presents a CDRA (Cylindrical Dielectric Resonator Antenna) designed for wireless military and commercial applications. The antenna has been designed to radiate at 6.7 GHz, with a 160 MHz bandwidth at -10 dB. The antenna is made from a dielectric material with high quality factor. The dielectric resonator is Ba1-xPbxNd2Ti5O14 (BNT) and its relative permittivity has a value of 55.2. The feed technique used is direct coupling to micro strip-line.

In this paper we report electro-optic (EO) sampling of THz pulses using ferroelectric crystal in the non-collinear Cherenkov phase-matching scheme, where an effective velocity matching is achieved in an EO crystal with a large refractive index in the THz frequency region. We demonstrate efficient THz EO sampling using LiNbO3 and BaTiO3 crystals in the Cherenkov-phase-matching scheme. It is shown that the efficiency of EO sampling with BaTiO3 is smaller than that with LiNbO3, even though the EO coefficient (r(33)) of BaTiO3 is three times higher than that of LiNbO3. The reason of the poor performance of BaTiO3 is attributed to the strong absorption in the THz frequency region.