Generalized neural network model of alternative refrigerant (R600a) inside a smooth tube

The correct prediction of refrigerant condensation heat transfer performance is important for design of condensers. A generalized neural network correlation for condensation heat transfer coefficient of alternative refrigerant R600a inside horizontal tube has been developed in this paper. Mass flow rate, vapor qualities, saturation temperature, difference value temperature are selected as the input parameters, while the Nusselt number and heat transfer coefficient as the output. Three-layer network is used for predicting the Nusselt number and the heat transfer coefficient. The number of the neurons in the hidden layer was determined by a trial and error process together with cross-validation of the experimental data evaluating the performance of the network and standard sensitivity analysis. The trained network gives the best values over the correlations with less than 4% mean relative error. The experimental data of the heat transfer coefficients of R600a, a hydrocarbon refrigerant, in a horizontal smooth copper tube with an inner diameter of 4 mm and outer diameter of 6 mm are from Agra et al. [O. Agra, “Condensation of refrigerants in a horizontal tube in annular flow regime”, PhD thesis Yildiz Technical University, 2007]. The condensing heat transfer coefficients obtained from the experimental study were seen to be consistent by ± 20% with the correlations developed by Shah [M.M. Shah, A general correlation for heat transfer during film condensation inside pipes, Int. J. Heat Mass Transfer 22 (1979) 547–556], Travis [D.P. Traviss, W.M. Rohsenow, A.B. Baron, Forced convection condensation inside tubes: a heat transfer equation for condenser design, ASHRAE Trans. 79 (1972) 157–165] and Cavallini-Zecchin [A. Cavallini, R. Zecchin, A dimensionless correlation for heat transfer in forced convection condensation, Proceedings of the Fifth International Heat Transfer Conference, vol. 3, 1974, pp. 309–313]. And it is seen that results from the trained network shows good agreement with the experimental data and better results than the correlations given by Shah, Cavallini and Travis.     

Preparation and characterization of aluminum-incorporated cadmium oxide films

Opto-electronic and photovoltaic solar cell technologies which are developing day by day need novel and alternative materials. Also, economic cost is the other important parameter when producing and using these materials. With this purpose, we have prepared aluminum-incorporated CdO films by ultrasonic spray pyrolysis (USP) technique. Firstly, elemental analyses were performed to observe the distribution rate of Al in the structure. We have attempted to explain the structural and electrical properties of these films in detail. The crystalline structure was studied by X-ray diffraction (XRD). Besides, some structural parameters such as texture coefficient, grain size and dislocation density were calculated. Van der Pauw and Hall measurements were used to investigate the electrical properties. Electrical conductivity, carrier concentration and mobility values were determined for all films. Finally, we conclude that Al-incorporated CdO films with low Al concentrations will be promising materials for future works because of their high conductivity and mobility values as compared to others.     

Characterization of ZnO films obtained by ultrasonic spray pyrolysis technique

In this work, ZnO film was deposited onto microscope glass substrates at 300 ± 5 °C by ultrasonic spray pyrolysis technique to investigate its application potential in photovoltaic solar cells. Optical, surface, structural and electrical properties of the film were investigated. Transmittance and absorbance spectra were taken to examine the optical properties, and band gap was calculated by optical method. Scanning electron microscopy micrographs and X-ray diffraction pattern were used to investigate the surface and structural properties of the film, respectively. Temperature dependent current measurements were performed by two-probe method to analyze electrical properties, and electrical conductivity at room temperature and activation energy values were calculated. After all investigations, application potential of ZnO film in photovoltaic cells as transparent conducting oxide contact was searched.     

PhD theses in Turkish sports sciences: A study covering the years 1988–2002

Aims  Undergraduate education in physical education is widely common in Turkey. Postgraduate training is provided mostly by institutes of health sciences, educational science and social sciences. The aim of this study was to evaluate the characteristics of PhD theses in sports sciences. Methods  The database of the Turkish Council of Higher Education has been searched the years 1988–2002 for PhD theses with different combinations of keywords like “Sport(s)”, “All Dissertations” and “Physical Education”. Theses were classified according to the institute, year, university, the title of the mentors and the field of sports sciences. The inter-and intra-validity of ratings were high (Kendall Tau_b=0.84 and 1.00, p <0.01). Results  Most of theses were prepared in Institutes for Health Sciences (n=196, 86.3%), second mostly in Institutes of Social Sciences (n=25, 11.0%). Theses originated mostly from Marmara (n=90, 39.6%), Gazi (n=59, 25.9%) and Dokuz Eylül Universities (n=25, 11.0%). Ninety two theses (46.9%) were prepared in Training and Movement Sciences, 40 (20.4%) in Sports Management, 29 (14.7%) Psycho-Social Fields of Sports Sciences, 23 (11.7%) Sports Health Sciences and 13 (6.6%) in Sports Pedagogy. Conclusion  Most theses were prepared in Institutes of Health Sciences, but the subjects covered the field of training and movement sciences. The unique and multi-disciplinary nature of sports sciences seems to warrant the foundation of an Institute of Sports.     

Development of a design verification methodology including strength and fatigue life prediction for agricultural tractors

During the operations of an agricultural tractor, front axle and front axle support encounter the worst load conditions of the whole tractor. If the design of these components is not verified by systematic engineering approach, the operators of the tractor may face with sudden failures. This paper aims to develop a verification method, which involves testing an agricultural tractor on a special test track and agricultural field and together with the computer aided engineering analysis, in order to prevent such failures in the lifetime of the agricultural tractor. For this purpose, a strain gage data acquisition system has been designed to measure the strain values on the component in order to determine maximum principle stresses for the calculation of overload safety on the agricultural field and stress data for the prediction of fatigue life on a radial washboard test track. The cycle number of these stress data for the fatigue analysis has been established by rainflow cycle counting method. Total fatigue damage for the front axle support has been calculated considering damage accumulation hypothesis defined by Miner.     

Synchronization of networks with prescribed degree distributions

We show that the degree distributions of graphs do not suffice to characterize the synchronization of systems evolving on them. We prove that, for any given degree sequence satisfying certain conditions, there exists a connected graph having that degree sequence for which the first nontrivial eigenvalue of the graph Laplacian is arbitrarily close to zero. Consequently, complex dynamical systems defined on such graphs have poor synchronization properties. The result holds under quite mild assumptions, and shows that there exists classes of random, scale-free, regular, small-world, and other common network architectures which impede synchronization. The proof is based on a construction that also serves as an algorithm for building nonsynchronizing networks having a prescribed degree distribution.     

Experimental and numerical study of the natural convection from a heated horizontal cylinder

Natural convection heat transfer from a horizontal cylinder is studied experimentally and numerically. Experimental study had taken place in different environmental temperature in a conditioned room which can be maintained at a stable required value and inside a sufficiently designed test cabin. The environmental and cylinder surface temperatures varied between 10 °C–40 °C and 20 °C–60 °C respectively. In the experimental study, two cylinders having different diameters of 4.8 mm–9.45 mm are used and constant heat flux was applied. On the basis of the experimental data, a correlation for the average Nusselt number over the cylinder is proposed in the range of 7.4 10¹ < Ra < 3.4 10³. The proposed correlation is compared with the well known correlations on natural convection heat transfer from a horizontal cylinder in the specified range of Rayleigh number, and it is shown that the results are in satisfactory agreement. The problem is also investigated numerically. The experimental data and the numerical results fall in ± 20% band. The numerical results obtained in this study are also compared with the results of Merkin. The characteristics of trend lines are similar.     

Preparation of polystyrene resin with pendant vicinal dioxime groups

Preparation of macroporous polystyrene beads having pendant vicinal dioxime groups and their metal chelating ability is described. Acetylated polystyrene resin crosslinked with 2 mol-% divinyl benzene was oxidized with SeO₂ to give the polymer bearing glyoxyloyl side groups. Then, treating with hydroxylamine, the polymer possessing dioxime groups was obtained. Metal absorbtivity and decomplexation of the resulting polymeric resin were investigated in a wide pH range.     

Arthroscopic partial resection of the discoid meniscus in children

Thirteen children with 14 lateral discoid menisci were reviewed at an average follow-up of 2.7 years. Their average age at the time of the operation was 12.8 years. Most of the children had vague and intermittent painful symptoms, and the classical "clunk" was demonstrable in nine of the 13 patients in clinical examinations. Thirteen children underwent arthroscopic partial meniscectomy for symptomatic discoid lateral meniscus, by performing partial resection. This procedure, modifying the discoid lateral meniscus to the normal semilunar shape, was indicated only when the capsular attachment was intact. The results were excellent both clinically and radiologically. Furthermore, rehabilitation time was considerably shorter than the time required after open procedures. Arthroscopic discoid meniscus surgery performed by experienced and skilled hands gives better results. According to the literature and our experiences, it is better to perform open techniques in patients with stiff knees. Additionally, it is technically feasible to use small joint instruments in the pediatric age group.