The microstructure of erbium-ytterbium co-doped oxyfluoride glass-ceramic optical fibers

Oxyfluoride transparent glass-ceramics combine some features of glasses (easier shaping or lower than single crystals cost of fabrication) and some advantages of rare-earth doped single crystals (narrow absorption/emission lines and longer lifetimes of luminescent levels). Since the material seems to be promising candidate for efficient fiber amplifiers, the manufacturing as well as structural and optical examination of the oxyfluoride glass-ceramic fibers doped with rare-earth ions seems to be a serious challenge. In the first stage oxyfluoride glasses of the following compositions 48SiO₂-11Al₂O₃-7Na₂CO₃-10CaO-10PbO-11PbF₂-3ErF₃ and 48SiO₂-11Al₂O₃-7Na₂CO₃-10CaO-10PbO-10PbF₂-3YbF₃-1ErF₃ (in molar%) were fabricated from high purity commercial chemicals (Sigma-Aldrich). The fabricated glass preforms were drawn into glass fibers using the mini-tower. Finally, the transparent Er³⁺ doped and Er³⁺/Yb³⁺ co-doped oxyfluoride glass-ceramic fibers were obtained by controlled heat treatment of glass fibers. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. X-ray diffraction examination (XRD) at each stage of the glass-ceramic fibers fabrication confirmed the undesirable crystallization of preforms and glass fibers has been avoided. The fibers shown their mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. The crystal structure of the grown nano-crystals has been determined by XRD and confirmed by electron diffraction (SAED). Results obtained by both techniques seem to be compatible: Er₃FO₁₀Si₃ (monoclinic; ICSD 92512), Pb₅Al₃F₁₉ (triclinic; ICSD 91325) and Er₄F₂O₁₁Si₃ (triclinic; ICSD 51510) against to initially expected PbF₂ crystals.     

Influence of ultraviolet radiation and aggressive media on epoxy coating degradation

The influence of ultraviolet radiation and of 5% water solutions of sulphuric acid, potassium hydroxide and sodium chloride on an epoxy coating was investigated. It was found that those factors cause generation of characteristic (for a given ageing kind) cracks on the coating surface. UV radiation, for example, gave rise to cracks called silver cracks. It was found as well that ageing changes in the coating influence the mechanical properties such as hardness, statical and dynamical strength.     

Thermo-mechanical and mechanical behavior of hybrid isotactic polypropylene glass fiber reinforced composites (GFRC) modified with calcium carbonate (CaCO3)

The study investigates the thermo-mechanical properties of isotactic polypropylene (iPP) hybrid composites in reference to various amounts of particle- and fiber-shaped inorganic fillers. Three grades of hybrid composites were prepared as a function of filler amount: 5, 10, and 20 wt% and different ratios of glass fiber (GF) and calcium carbonate (CaCO₃). The main objective is to describe the relationship between the hybridization efficiency and mechanical performance of polypropylene-based composites. The analysis of the thermo-mechanical properties of the composites shows that both the total amount of the filler and the ratio of GF and CaCO₃ clearly influence the properties of the composites. Hybrid composites with the highest amount of the GF display improved thermo-mechanical stability. The presence of well-dispersed CaCO₃ in the composites was found to improve elongation at break and Vicat softening temperature values. Even though it is glass fiber, which shows higher filler effectiveness and visibly reinforces the composite samples, causing an increase in tensile strength or reinforcing efficiency, replacing up to 50% of this filler with calcium carbonate does not result in a considerable deterioration of the properties of the material.     

The langmuir-blodgett technique as a tool for homeotropic alignment of fluorinated liquid crystals mixed with arachidic Acid

Some fluoro-substituted liquid crystals mixed with arachidic acid in monolayers formed at air-liquid (Langmuir films) and air-solid substrate (Langmuir-Blodgett films) interfaces were investigated. Molecular organization in Langmuir films was determined on the basis of the analysis of the shape of the surface pressure-mean molecular area isotherm and observations made by means of a Brewster angle microscope. It was found that in the compression process the liquid crystal molecules are pushed out towards the top of the first monolayer being in direct contact with the subphase. Langmuir films were transferred onto the quartz substrates at various surface pressures and mono- and multilayered Langmuir-Blodgett films were obtained. The films were characterized using electronic absorption measurements. The conditions for obtaining the homeotropic orientation of the liquid crystal molecules were determined.     

Observations of Stresses and Strains in a Granular Material

The use of glass ballotini as a granular material provides the opportunity to simultaneously study internal stress fields and internal fields of deformation as a sample is submitted to boundary perturbations. Digital image correlation makes use of the visible fabric of the material to deduce a field of displacements from one digital photographic image to the next. If the glass granules are immersed in a fluid having the same refractive index, then observation with polarized light exploits the photoelastic properties of the glass to reveal information about the stresses. Again, comparison of digital photographs enables changes in stress conditions from one image to the next to be discovered. Tests performed in a simple loading device which forces rotation of principal axes in parts of the granular mass are presented to demonstrate the unique potential of this dual experimental configuration.     

On Maximal Frequent and Minimal Infrequent Sets in Binary Matrices

Given an m×n binary matrix A, a subset C of the columns is called t-frequent if there are at least t rows in A in which all entries belonging to C are non-zero. Let us denote by the number of maximal t-frequent sets of A, and let denote the number of those minimal column subsets of A which are not t-frequent (so called t-infrequent sets). We prove that the inequality (m–t+1) holds for any binary matrix A in which not all column subsets are t-frequent. This inequality is sharp, and allows for an incremental quasi-polynomial algorithm for generating all minimal t-infrequent sets. We also prove that the analogous generation problem for maximal t-frequent sets is NP-hard. Finally, we discuss the complexity of generating closed frequent sets and some other related problems.     

Haemorrhagic pericarditis and cardiac tamponade during chronic haemodialysis

The activities of glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP oxidoreductase, G6PD), 6 phosphate glucono dehydrogenase (6 phospho-D-gluconate: NADP oxidoreductase, 6PGD) lactate dehydrogenase (D-lactate: NAD oxidoreductase, LDH), glutamate oxaloacetate transaminase (L-aspartate: 2-oxo-glutarate aminotransferase, GOT) and hexokinase (ATP: D-hexo-6-phosphotrans-ferase, Hx) were measured over 24 h in isolated lymphocytes of normal subjects and in white cells of patients with chronic lymphatic leukaemia (CLL). The activitty patterns of all enzymes in the normal lymphocytes were similar. A computed pattern of all the results exhibited a circadian rhythm of activity with the highest level at 16.00 hours. The oscillations in the activities of the same enzymes in the CLL cells differed among the patients, although all the enzymes of the same individual showed a similar diurnal rhythmic pattern. All peaks in this group appeared between 20.00 and 08.00 hours. The possible importance of these observations in setting up therapeutic schedules was raised.     

Dynamic response with mass variation of laminated composite twisted plates

In this study, the dynamic response of free vibration of laminated composite twisted (skewed) plate with mass variation via cutout and additional mass is investigated. The mathematical model employs cubic variation of the thickness coordinates in the displacement field. The mathematical formulation also includes the effects of transverse shear and rotatory inertia. A realistic parabolic distribution of transverse shear strains through the plate thickness is assumed and the use of the shear correction factor is avoided. A C⁰ finite element formulation of the mathematical model is developed to analyze the dynamic behavior of laminated composite twisted plate with cutout and additional mass. Given that no results on the present problem of free vibration of laminated composite twisted plate with cutout and additional mass are available in literature, novel results for different twist angles of laminated composite plates along with mode shapes are presented by varying the geometry, boundary conditions, and ply orientations.