Boundary stabilisation of the wave equation in the presence of singularities

We study the boundary stabilisation of the wave equation by a nonlinear feedback active on a part of the boundary in geometric situations for which the solutions have singularities. These singularities appear at the interfaces at which the mixed Neumann–Dirichlet boundary conditions meet. Under a simple geometrical condition concerning the orientation of the boundary, we obtain sharp energy decay rates under a general growth assumption on the feedback. We show that the singularities do not affect the energy decay rates and give examples.     

A dielectric study of the crystal and amorphous fractions in oriented polyethylenes

Polyethylenes have relaxation processes separately assignable to the crystal and amorphous components. The possibility thus presents itself for studying the interaction between the two phases by investigating the anisotropy of the separate relaxation processes induced by overall orientation of the material. Such a study was carried out here by the dielectric method on samples rendered dielectrically active by the introduction of a few carbonyl groups by oxidation. In addition to the usual advantage of ease of frequency variation, the dielectric method in this case has a very great advantage in interpretation resulting from the similarity of dielectric constants of the two phases. In specimens oriented by solid-state extrusion, it was found that the crystalline relaxation process (α) develops the expected anisotropy resulting from dipoles normal to C-axis alignment in the extrusion direction. In branched polyethylene (BPE) no accompanying anisotropy of the amorphous β and γ processes was observed. Since the extrusion was carried out well above the glass temperature of the amorphous component, this indicates that constraints from the crystal phase are not sufficient to prevent dissipation of amorphous orientation by segmental motion. However in linear polyethylene (LPE) (where there is no well-developed β process) some anisotropy of the γ process was observed. It is proposed that a higher degree of constraint of the amorphous component by the crystals in LPE results in suppression of the glass-rubber (β) relaxation and permits amorphous orientation to accompany crystal orientation.     

Hydroxymethylation and polymerization of plant oil triglycerides

The ene reaction between plant oil triglycerides (such as soybean and sunflower oils) and paraformaldehyde was used to introduce a homoallylic hydroxyl functionality on the triglyceride. Paraformaldehyde and triglyceride were reacted in the presence of a Lewis acid catalyst, ethylaluminum dichloride, and hydroxymethyl derivatives were obtained at yields of 42 and 55% for sunflower oil and soybean oil, respectively. In the next step, hydroxymethyl products were reacted with maleic anhydride at 100°C to produce the maleate half esters. The average number of maleate groups per triglycerides was found to be 1.7 for soybean oil and 1.3 for sunflower oil. In the final step, the free‐radical–initiated copolymerization of the maleinized triglycerides with styrene produced rigid polymers. Characterization of new monomers and polymers was done by ¹H‐NMR, ¹³C‐NMR, and infrared and mass spectrometries. The swelling behavior of the crosslinked network polymers was determined in different solvents. The glass‐transition temperature of the cured resin was also determined by differential scanning calorimetry to be 40°C for soybean‐based polymer and 30°C for sunflower‐based polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4037–4046, 2004     

Die umweltfaktoren, die die verbreitung und entwicklung von Chalcalburnus tarichi (PALL. 1881) (Pisces: Cyprinidae) in Burdur-See begrenzen

Burdur Lake, an entirely closed and brackish water lake, having an area of 190 km² and 76 m depth, is located in the “Lakes Region” of Anatolia, 4 km from the west of Burdur city.There have been made many attempts to breed an economically important fish population but all attempts were unsuccessful. During 1946–1948 some hydrobiological investigations were carried out. According to these investigations, hydrobiological conditions of the lake were found to be suitable for Chalcalburnus tarichi (PALL. 1881) (Pisces: Cyprinidae), a fish which is endemic to the Lake Van in eastern Anatolia. Since 1966 an attempt has been made to breed Chalcalburnus tarichi artificially. This attempt was successful, but the economic productivity was not in the estimated level. These fish live in all the depth of the lake, but during the breeding season, they go into fresh water streams flowing into the lake.To find out the reasons of the productivity losses, new hydrobiological investigations have been going on since 1969. Two research stations have been chosen (Fig. 1), where water, plankton and bottom samplings have been collected for hydrobiological research. Nansen bottles were used to take the water samples, in 10 m intervals, from the surface of water towards the bottom. The chemical analysis of water have been done according to the standard methods given in Welcher (1963). The Winkler method is used to find out the amount of dissolved oxygen (Welcher, 1963).Plankton was collected in 10 m intervals by usual type Closing net (20 cm dia, mesh size of 0.05 mm). The amount of plankton per m³ has been calculated according to the Settling methods of Welch (1948).Bottom samples were collected by Ekman's Dredge at four different regions marked (a), (b), (c), (d), on Fig. 1. Samples were wet sieved through four graded sieves (mesh sizes 0.5–2.0 mm). The number of the collected bottom animals per m² were calculated.Observations showed that, the direct flow of waste waters having organic materials from the Burdur Sugar Mill, Milk-Cheese factories and Attar of Rose industries and Hemp (Cannabis sativa) maceration remnants go to the bottom of the lake, therefore, unoxygenated and thereby a hydrogensulphonized water layer is formed by the above mentioned waste products. The unoxygenated water layer level increases 2–2.5 m per year towards the surface. This pollution has caused this unexpected loss of productivity of fish, for this water layer harms the bottom feeding and planktonic organisms and restricts the spreading and development of the adopted Chalcalburnus tarichi (PALL. 1881). It is also clear that this situation is a threat to the future of the lake and its environment.     

The effects of phosphorus additions on the sedimentation of contaminants in a uranium mine pit-lake

We investigated the usefulness of phytoplankton for the removal of surface water contaminants. Nine large mesocosms (92.2m(3)) were suspended in the flooded DJX uranium pit at Cluff Lake (Saskatchewan, Canada), and filled with highly contaminated mine water. Each mesocosm was fertilized with a different amount of phosphorus throughout the 35 day experiment to stimulate phytoplankton growth, and to create a range in phosphorus load (g) to examine how contaminants may be affected by different nutrient regimes. Algal growth was rapid in fertilized mesocosms (as demonstrated by chlorophyll a profiles). As phosphorus loads increased there were significant declines (p<0.05) in the surface water concentrations of As, Co, Cu, Mn, Ni, and Zn. This decline was near significant for uranium (p=0.065). The surface water concentrations of Ra-226, Mo, and Se showed no relationship to phosphorus load. Contaminant concentrations in sediment traps suspended at the bottom of each mesocosm generally showed the opposite trend to that observed in the surface water, with most contaminants (As, Co, Cu, Mn, Ni, Ra-226, U, and Zn) exhibiting a significant positive relationship (p<0.05) with phosphorus load. Selenium and Mo did not respond to nutrient treatments. Our results suggest that phytoremediation has the potential to lower many surface water contaminants through the sedimentation of phytoplankton. Based on our results, we estimate that the Saskatchewan Surface Water Quality Objectives (SSWQO) for DJX pit would be met in approximately 45 weeks for Co, 65 weeks for Ni, 15 weeks for U, and 5 weeks for Zn.     

Severe jaw enlargement associated with uremic hyperparathyroidism

Marked enlargement of the jaws is a rare complication of renal osteodystrophy. This report describes a localized enlargement of the mandible due to a brown tumor in a patient undergoing chronic hemodialysis. Literature on jaw involvement in secondary hyperparathyroidism is reviewed.     

Control of methane flame properties by hydrogen fuel addition: Application to power plant combustion chamber

This study presents a numerical investigation of the effects of mixing methane/hydrogen on turbulent combustion processes taking place in a burner similar to that integrated in gas turbine power plants. Thereby, in comparison to the reference case where the burner is fuelled by 100% of methane, the variations of the axial velocity field, temperature field and mass fraction of carbon monoxide field are examined for different percentages of hydrogen fuel injection. The computed results, obtained by using the software Fluent-CFD, are compared and validated against experimental reference data. Results show that the hydrogen addition to the methane has an impact on all physical and chemical parameters of the reactive system.     

Development of Ultra-high Purity (UHP) Fe-Based Alloys with High Creep and Oxidation Resistance for A-USC Technology

Metallurgical and Materials Transactions A - The design of ultra-high purity (UHP) Fe-based model alloys for advanced ultra-supercritical (A-USC) technology is attempted in this work. Creep testing...     

Fabrication of transparent polymer-matrix nanocomposites with enhanced mechanical properties from chemically modified ZrO<Subscript>2</Subscript> nanoparticles

Optically transparent nanocomposites with enhanced mechanical properties were fabricated using stable dispersions of sub 10 nm ZrO₂ nanoparticles. The ZrO₂ dispersions were mixed with a commercially available bisphenol-A-based epoxy resin (RIMR 135i) and cured with a mixture of two amine-based curing agents (RIMH 134 and RIMH 137) after complete solvent removal. The colloidal dispersions of ZrO₂ nanoparticles, synthesized through a non-aqueous approach, were obtained through a chemical modification of the ZrO₂ nanoparticle surface, employing different organic ligands through simple mixing at room temperature. Successful binding of the ligands to the surface was studied utilizing ATR–FT-IR and thermogravimetric analysis. The homogeneous distribution of the nanoparticles within the matrix was proven by SAXS and the observed high optical transmittance for ZrO₂ contents of up to 8 wt%. Nanocomposites with a ZrO₂ content of only 2 wt% showed a significant enhancement of the mechanical properties, e.g., an increase of the tensile strength and Young’s modulus by up to 11.9 and 12.5%, respectively. Also the effect of different surface bound ligands on the mechanical properties is discussed.     

Calculation of Excitation Function of Some Structural Fusion Material for (n, p) Reactions up to 25 MeV

Fusion serves an inexhaustible energy for humankind. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, Furthermore, there are not radioactive nuclear waste problems in the fusion reactors. In this study, (n, p) reactions for some structural fusion materials such as ²⁷Al, ⁵¹V, ⁵²Cr, ⁵⁵Mn and ⁵⁶Fe have been investigated. The new calculations on the excitation functions of ²⁷ Al(n, p) ²⁷ Mg, ⁵¹ V(n, p) ⁵¹ Ti, ⁵² Cr(n, p) ⁵² V, ⁵⁵ Mn(n, p) ⁵⁵ Cr and ⁵⁶ Fe(n, p) ⁵⁶ Mn reactions have been carried out up to 30 MeV incident neutron energy. Statistical model calculations, based on the Hauser–Feshbach formalism, have been carried out using the TALYS-1.0 and were compared with available experimental data in the literature and with ENDF/B-VII, T = 300 K; JENDL-3.3, T = 300 K and JEFF-3.1, T = 300 K evaluated libraries.