Defect and Diffusion Forum Vols. 334-335

Abstract: Although the exact causes for presbyopia are not known with certainty, there is the general understanding that it is associated with aging. This is one of the major paradigms of science because the analysis of the symptoms observed during the treatment of presbyopia in the first author of this paper indicates that presbyopia is associated with metabolic dehydrated secretions that have accumulated in various parts of the eyes. As a process of accumulation it is not difficult to associate it statistically to aging. The metabolic secretions produced by the cells inside the human eye are accumulated simultaneously in the cornea, trabecular meshwork, in the lens and retina, subject only to its origin, however, the symptomatology is well characterized by the location of accumulation. Genetic factors are directly related to how the clumps of metabolic secretions occur and the accumulation form is very specific according to the movement of the eyes based on the activities performed by the patient, so any outcome is unpredictable. In this paper introduces the hypothesis that senile cataract may be caused by transport mechanism failure by forced convection of aqueous humour and metabolic mass produced by the lens cells. The evidence confirms the comparative interpretation of physiology and biochemical constituents of studies between old and young lenses published in scientific literature. Besides that the accumulation produces a loss of elasticity of the lens, due to excess volume and causes its opacity because the metabolic secretion is translucent. It shows evidence of the formation of floaters.

Abstract: Although the exact causes for presbyopia are not known with certainty, there is the general understanding that it is associated with aging. This is one of the major paradigms of science because the analysis of the symptoms observed during the treatment of presbyopia in the first author of this paper indicates that presbyopia is associated with metabolic dehydrated secretions that have accumulated in various parts of the eyes. As a process of accumulation it is not difficult to associate it statistically to aging. The metabolic secretions produced by the cells inside the human eye are accumulated simultaneously in the cornea, trabecular meshwork, in the lens and retina, subject only to its origin, however, the symptomatology is well characterized by the location of accumulation. Genetic factors are directly related to how the clumps of metabolic secretions occur and the accumulation form is very specific according to the movement of the eyes based on the activities performed by the patient, so any outcome is unpredictable. This paper introduces the hypothesis that macular degeneration may be caused by transport mechanism failure by forced convection of nutrients and metabolic mass produced by the retina. The hypothesis examined in this paper considers the symptoms observed during treatment of presbyopia the first author, the analysis of some clinical procedures to diagnose the degeneration, the symptoms described in the publications on this subject as well as showing how some genetic factor may anticipate the disease. It is not hard to make a statistical association of macular degeneration with aging in the hypothesis that it is caused by of metabolic accumulation of secretions produced in the retina.

Abstract: The mechanism of the intercalation/de-intercalation processes during the formation of α-Co (OH)₂ and its conversion to β-Co (OH)₂ is carefuly examined using a new non-invasive technique in a gel matrix. The incorporation of rhodamine molecules inside the interlayer gallery of α samples allows us to monitor the variation of its fluorescence intensity throughout different stages of the reactions. We show after calculating the corresponding activation energies that the formation/transformation reactions exhibit different dynamics depending on the nature of intercalated anions. Moreover, the morphological changes that are revealed from scanning electron micrographs suggest the occurence of an Ostawald ripening mechanism in which perfect and stable crystals are produced at the expense of smaller ones.

Abstract: The structure of high-purity copper and stabilizing copper of Cr-plated Nb₃Sn-strands with different RRR (residual resistance ratio) values has been studied. Cr diffusion into peripheral layers of stabilizing Cu has been revealed. The variations of RRR and Cr content in Cu at annealing have been estimated. It is demonstrated that an additional drop of RRR may be caused by oxygen diffusion from Cr coating obtained by electroplating. Optimal regimes of the diffusion annealing of Cr-plated Nb₃Sn-strands for ITER (International Thermonuclear Experimental Reactor) have been determined.

Abstract: In the arc joining of dissimilar metals, such as steel and Al alloys, a brittle intermetallic phase is formed at the interface. The thickness of this phase should be minimized because it causes solidification cracking. Cold metal transfer (CMT) arc welding technology is widely used throughout the automotive industry because of low spatter formation and heat input. A CMT arc was used to investigate arc joining between the Al 6K32 alloy and mild steel sheets. The behaviors of the interface layers were analyzed on the basis of filler wires and the coating type of the steel sheets. The thickness of the intermetallic phase was maintained under 10 μm and increased joint strength was achieved by selecting the appropriate filler wire and coating type.

Abstract: Zn-Al-Cu type alloys are characterized by a number of advantageous properties which include: good castability, good tribological properties, low energy value needed for forming of the product. As compared to bronze, Al-Zn-Cu alloys are characterized by a lower density. Improved properties of Zn-Al alloys can be obtained by addition of copper and silicon. Advantageous results can also be obtained by heat treatment. There is an extensive literature on the effect of heat treatment upon the structure of Al-Zn-Cu alloys. However, few articles discuss the effect of heat treatment on the corrosion resistance of alloys. The purpose of this examination was to determine the effect of heat treatment on corrosion resistance of ZnAl22Cu3 alloy. The unmodified alloy containing 22% Al mass. and 3%. Cu (Zn - remain) was subjected to the examinations. Tested alloys underwent the following operations: soaking at the temperature of 185°C for 10 hours with cooling in water, soaking at the temperature of 380°C for 10 hours with cooling in water and soaking at the temperature of 380°C for 10 hours with subsequent soaking at the temperature of 170°C with cooling in water. Potentiodynamic and potentiostatic examinations in a solution of acid rain with pH = 3.5 were carried out. Then the tests were followed by examination of the corroded sample surface.The carried out examinations showed a decrease in corrosion resistance after heat treatment at the temperature of 380°C and a slight increase after heat treatment at the temperature of 185°C.

Abstract: Different concentrations of CaF₂ were incorporated in mica glass-ceramics to evaluate their effects on the crystallization and microstructure. The kinetics of phase transformations, and the microstructures of the final crystalline phase were found to be dependent on the concentration of nucleation agents. The results showed that CaF₂ in high concentration had a synergistic effect and enhanced the formation of interlocked mica crystals. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses were changed in the range of 235-405 kJ/mol, while the crystallization activation energies of samples with addition of CaF₂ were changed in the range of 419-747 kJ/mol.

Abstract: The study aimed at developing a methodology for the design and appropriate use of materials in the pipes for the collection and distribution of biogas. The increasing use of biogas for distributed generation in agro-industries, sewage treatment effluent and anaerobic landfills, and the absence of a specific standard for biogas pipes led to the development of the work. Because there is no standard for design and delivery of pipes for the collection and distribution of biogas, the main eco-efficient energy projects implemented in the country, units digester / bike generator 50 kVA to 200 kVA, were used duct poly vinyl chloride (PVC) that permeable to gases, suffers from contamination of biogas network to air, leaks, reduce the efficiency of filter retention of H2S and reduced life of the motor generator. The methane in biogas reacts with PVC and decomposition occurs, dissolution, swelling and loss of ductility of the tube. Since polyethylene is the material world-known and most suitable for transportation of gas fuels, and the fact that its raw material, ethylene in the chain of thermoplastics derived from petroleum, polyethylene comes before the PVC, which makes it more economical and safe.

Abstract: In this study, it is aimed to observe diffusion of sodium in soil samples by using radiotracing technique. To produce the radiotracer ²⁴Na, sodium-carbonate compound was irradiated at ITU TRIGA Mark II Research reactor at Energy Institute of Istanbul Technical University. The irradiated sodium-carbonate samples were sprinkled to the surface of soil columns. Then soil was watered with representative amounts of water according to selected rain regimes in Istanbul. Radioactivity measurements were carried out by using high efficiency gamma-ray measurement system at the outside of the column for different soil depths in different times.

Abstract: In this study, criteria for internal mass transfer given in the literature were investigated by considering tortuosity (τ) in the porous catalysts. Uncertainties in τ, which may have values between 2 to 7, have a big impact on the effective diffusivity (D_eff) which also affects the Thiele Modulus (Φ). Since effectiveness factor (η) is function of Φ, then the criteria given for limitations are questionable. The value of D_eff, and in turn the value of Φ calculated for the τ=2 to 7. At low Φ the effects are very small, but when the Φ increases the effect becomes more pronounced. As a result, when using internal mass transfer limitations, one has to be very careful not to get trapped by the disguised kinetics, results of which may end up with disaster.