Radiation effects on luminescent and structural properties of YPO4: Pr3+ nanophosphors

ABSTRACT

YPO₄ phosphors doped with trivalent ion Pr³⁺ were prepared by sol–gel method and treated with different doses of gamma radiation, from 0.25 MGy to 4 MGy. Effects of radiation on morphology, structure and luminescent properties were analyzed. Also, the influence of radiation on the change in the color of the samples was examined. The color efficiency of powders was evaluated by colorimetric analysis (CIE and L * a * b system). It has been observed that powders change color under the influence of radiation, i.e. they pass from white to pinkish red. Also, it has been determined that the radiation affects morphology change, as the particle size increases with increasing of the radiation dose. With the increase in the radiation dose, the emission intensity of samples decreases. The structure remains almost unchanged after irradiation, and the intensity constantly decreases with increasing of dose.     

Strongly dominating sets of reals

We analyze the structure of strongly dominating sets of reals introduced in Goldstern et al. (Proc Am Math Soc 123(5):1573–1581, 1995). We prove that for every ${\kappa < \mathfrak{b}}$ κ < b a ${\kappa}$ κ -Suslin set ${A\subseteq{}^\omega\omega}$ A ? ω ω is strongly dominating if and only if A has a Laver perfect subset. We also investigate the structure of the class l of Baire sets for the Laver category base and compare the σ-ideal of sets which are not strongly dominating with the Laver ideal l ⁰.     

Study of optical properties and biocompatibility of DLC films characterized by sp3 bonds

Optical and biomedical properties of diamond-like carbon (DLC) films of various sp², sp³ bonds were studied. The layers were prepared by pulsed laser deposition (PLD) for laser energy densities from 4 J?cm^?2 to 14 J?cm^?2. The percentage of sp² and sp³ bonds was calculated using X-ray photoelectron spectroscopy (XPS). In dependence on density the films contained up to 70 % of sp³ bonds. Optical properties were measured using spectroscopic ellipsometry in region from 250 nm to 1000 nm (n=2.6–2.7; k=0.07–0.25) and by transmission measurement (from 200 nm to 1100 nm). The adhesion and growth of human fibroblasts and keratinocytes of DLC films were tested in vitro.     

Analysis of cytokinin nucleotides by capillary zone electrophoresis with diode array and mass spectrometric detection in a recombinant enzyme in vitro reaction

A capillary zone electrophoresis (CZE) method for separation of adenosine and N⁶-isopentenyladenosine (cytokinin) nucleotides was developed, optimized and validated. Aqueous solutions of several amino acids were evaluated as the background electrolyte constituents. Separation of six nucleotides in less than 20 min with high theoretical plate number (up to 400 000 for isopentenyladenosine triphosphate) was achieved using a 100 mM sarcosine/ammonia buffer at pH 10.0. The detection limits of the CZE-UV method are in the low micromolar range (0.69–1.27 μmol L⁻¹). Good repeatability of migration times (within 1.3%), peak areas (within 1.8%) and linearity (R² > 0.999) was achieved over the concentration range 5–1000 μmol L⁻¹. The method was used to assay the activity of the recombinant Arabidopsis thaliana isopentenyltransferase 1 (AtIPT1). Baseline separation of isopentenylated nucleotides by CE–ESI-MS using a volatile buffer (30 mM ammonium formate; pH 10.0) was accomplished. The identities of the reaction products – isopentenyladenosine di- and triphosphate were confirmed by HPLC-QqTOF-MS. Dephosphorylation of ATP was observed as a parallel reaction.     

The influence of a quaternary ammonium salt and MMT on the in situ intercalative polymerization of PMMA

Poly(methylmetacrylate)/montmorillonite (PMMA)/(MMT) nanocomposites were prepared by a one-step in situ intercalative solution polymerization involving the simultaneous modification of the MMT with a quaternary ammonium salt (cetyl-trimethylammonium bromide (CTMAB)), polymerization and polymer intercalation. Using benzoyl peroxide as an initiator, intercalated nanocomposites were formed and characterized by NMR, DSC, TGA, XRD, TEM and SEC. It was observed that it was not the MMT, but rather the CTMAB, that influences the polymerization reaction, especially the reaction yield, the molar mass averages and the molar mass distribution of the PMMA. The thermal stability of the PMMA was improved by the addition of both the MMT and/or the CTMAB.     

The effect of the number of carbohydrate moieties on the azaphthalocyanine properties

A series of azaphthalocyanines (AzaPc) bearing one, two, four or eight isopropylidene-protected galactosyl units was prepared by azide-alkyne click reaction or by classical Pc template cyclotetramerization of the corresponding dicyanopyrazine and AzaPc properties important for photodynamic therapy were compared. All compounds absorbed at long wavelengths (above 650 nm) and belonged to strong singlet oxygen producers (Φ(Δ) = 0.58-0.64) retaining significant fluorescence emission (Φ(F) = 0.026-0.23). The only exception was the compound with four isopropyliden-protected galactosyl units where partial aggregation was observed. Removal of protecting groups increased the polar character of all AzaPc. However, only AzaPc bearing eight galactoses was found to be water-soluble (105 mg mL(-1)) but noticeably aggregated in water as well as in organic solvents (DMF, DMSO). Amphiphilic AzaPc bearing one deprotected galactose was incorporated into the lipidic bilayer of liposomes in a nonaggregated form. Liposomes may therefore be a suitable delivery system for this amphiphilic photosensitizer.     

Glycogen as a Biodegradable Construction Nanomaterial for in vivo Use

It is demonstrated that glycogen as a biodegradable and inexpensive material coming from renewable resources can be used as a carrier for the construction of in vivo imaging nanoagents. The model system considered is composed of glycogen modified with gadolinium and fluorescent labels. Systematic studies of properties of these nanocarriers by a variety of physical methods and results of in vivo tests of biodegradability are reported. This represents, to the authors' best knowledge, the first such use of glycogen.

     

Compact complex surfaces with geometric structures related to split quaternions

We study the problem of existence of geometric structures on compact complex surfaces that are related to split quaternions. These structures, called para-hypercomplex, para-hyperhermitian and para-hyperkähler, are analogs of the hypercomplex, hyperhermitian and hyperkähler structures in the definite case. We show that a compact 4-manifold carries a para-hyperkähler structure iff it has a metric of split signature together with two parallel, null, orthogonal, pointwise linearly independent vector fields. Every compact complex surface admitting a para-hyperhermitian structure has vanishing first Chern class and we show that, unlike the definite case, many of these surfaces carry infinite-dimensional families of such structures. We provide also compact examples of complex surfaces with para-hyperhermitian structures which are not locally conformally para-hyperkähler. Finally, we discuss the problem of non-existence of para-hyperhermitian structures on Inoue surfaces of type S⁰$S^0$ and provide a list of compact complex surfaces which could carry para-hypercomplex structures.     

Dynamic stability of fcc crystals under isotropic loading from first principles

Lattice dynamics and stability of four fcc crystals (Al, Ir, Pt and Au) under isotropic (hydrostatic) tensile loading are studied from first principles using the linear response method and the harmonic approximation. The results reveal that, contrary to former expectations, strengths of all the studied crystals are limited by instabilities related to soft phonons with finite or vanishing wavevectors. The critical strains associated with such instabilities are remarkably lower than those related to the volumetric instability. On the other hand, the corresponding reduction of the tensile strength is by 20% at the most. An analysis of elastic stability conditions is also performed and the results obtained by means of both approaches are compared.