Improved survivability analysis for SONET SHRs

Recently, a special type of Markov model called parametric state reward Markov model (SRMM/p) [H.C. Cankaya, V.S.S. Nair, in: IEEE Proceedings of GLOBECOM 97, vol. 1, IEEE Computer Soc. Press, Silver Spring, MD, 1997, pp. 252–256] and a set of survivability metrics comprising reliability, availability, and restorability have been proposed for the evaluation of self-healing SONET mesh networks [H.C. Cankaya, V.S.S, Nair, in: Proceedings of ISCIS 'XII, vol. 1, Bogazici University, Bogazici University Press, 1997, pp. 269–276]. The SRMM/p accommodates multiple consecutive link failures and uses topology-free approximation in order to calculate the average performance loss due to a failure. The SRMM/p is equally applicable to the analysis of self-healing SONET rings by considering a ring as a special case of a mesh topology [H.C. Cankaya, V.S.S. Nair, in: IEEE Proceedings of GLOBECOM '98, vol. 4, IEEE Computer Soc. Press, Silver Spring, MD, 1998, pp. 2276–2281]. Further, the topological uniformity and simplicity of rings allow one to include more detailed features of the network in the model so that the analysis will be more accurate. For this purpose, we propose an improved approach to the survivability analysis of self-healing SONET rings which employs a probability-tree based evaluation of the probability of various system states resulting from all possible combinations of node and link failures. The corresponding tree-construction and traversal algorithms are presented. Survivability of rings with distinctive demand patterns are studied with the improved analysis and compared experimentally. One limitation to the model is the high run-time complexity caused mainly by the disparity between transition rates amongst various states in the SRMM/p [H.C. Cankaya, V.S.S. Nair, ACM Comput. Commun. Rev. 28 (4) (1998) 268–277]. In this paper, we also present an approach to circumvent this problem by state aggregation method and compare the results in terms of run-time complexity and accuracy by conducting an experimental study.     

The effects of heat treatment temperatures on photocatalytic activity of cobalt ferrite nanoparticles synthesised by microwave-assisted combustion method

In this study, the effects on the photocatalytic activities of particles after heat treatment has been applied to cobalt ferrite nanoparticles produced by microwave-assisted combustion method were observed. The heat treatment applied to the samples was produced with only the microwave effect, at temperatures ranging from 300 to 1000°C. Thermogravimetric analysis was performed on the precursor sample in air atmosphere. During this analysis, the gases released up to 1200°C were identified with a Fourier-transform infrared (FTIR) spectrometer integrated into a thermogravimetric analysis system. Then, the cobalt ferrite nanoparticles produced with heat treatments applied at various temperatures were used as a photocatalyst to remove the dyestuff content in synthetic wastewaters prepared by using Astrazon Red GTL textile dye by photocatalytic oxidation, and their photocatalytic activities were compared. In these experiments, the operational parameters for photocatalysis processes were applied as 400 rpm for stirring speed, 50 mg/L for initial contaminant concentration, 0.5 g/L for catalyst dosage, 25°C for temperature, and 4400 μW/cm² for light intensity. As a result of the experiments, it was observed that the crystal structure of the cobalt ferrite nanoparticles produced with the increase of the applied heat treatment temperature improved significantly. The obtained data show a strong relationship between the structural properties of materials and their photocatalytic activities. In addition, it was determined that the dyestuff in the solution was completely degraded in the experiments, and it was determined that all processes were compatible with the pseudo-first-order kinetic model.     

Enhancing magnetic levitation and guidance force and weight efficiency of high-temperature superconducting maglev systems by using sliced bulk YBCO

We aimed to enhance the magnetic force efficiency of Maglev systems without increasing total weight. For this aim, we divided YBCO bulks into three slices horizontally to utilize the YBCO-permanent magnetic guideway (PMG) interaction surface as much as possible. We used whole YBCO above PMGs with different magnetic pole directions (PMG-A and PMG-B) in two lying positions of transversal and longitudinal and investigated levitation and guidance force performances. It is determined that levitation and guidance forces by using YBCO in transversal lying mode are bigger compared to the longitudinal mode. For sliced YBCO, the maximum levitation force increased by 69% and 78%, while the guidance force enhancements are determined as 212% and 91%, compared to the whole YBCO above PMG-A and PMG-B, respectively. The levitation and guidance force density with respect to the total mass of unit a set of slices YBCO increased by 92% and 106%, respectively, compared to the whole YBCO above PMG-B in transversal mode. Since the higher levitation force and the lower total weight of the onboard unit are important parameters in point of the energy efficiency in Maglev and other levitation applications, the result of this study supplies useful data for the engineers and industrial partners.