Istanbul Technical University

About: Istanbul Technical University is a education organization based out in Istanbul, Turkey. It is known for research contribution in the topics: Fuzzy logic & Large Hadron Collider. The organization has 12889 authors who have published 25081 publications receiving 518242 citations. The organization is also known as: İstanbul Teknik Üniversitesi & Technical University of Istanbul.

Effect of ion nitriding on fatigue behaviour of AISI 4140 steel

Abstract: Ion nitriding has become a popular thermo-chemical surface treatment, which is being used to develop fatigue and wear characteristics of steels. Besides the increased strength, the formation of high compressive residual stresses in the case region causes remarkable improvement in fatigue properties of steels. In this study, the effect of case depth on fatigue performance of AISI 4140 low alloy steel has been investigated by conducting a series of rotary bending fatigue tests at the frequency of 95 Hz, on hour glass shaped, 4 mm diameter specimens, which had been ion nitrided at 748 K for 1, 3, 8 and 16 h. Up to 50% improvement in fatigue strength of the steel has been attained by ion nitriding, depending on the case depth formed during the process. The comparison of test results between ion and liquid nitrided specimens having the same case and core properties, has shown that a 12% increase in fatigue strength could be reached by ion nitriding with respect to conventional, salt bath nitriding process. An attempt was made to establish some empirical relationships between the parameters defining relative case depth, which consider case depth and specimen size together, and fatigue strength of ion nitrided steel. It was obtained that the subsurface ‘fish eye’ type crack formation is the dominant fatigue crack initiation mechanism in ion nitrided AISI 4140 steel, and a map has been constructed to illustrate the locations of crack origins depending upon the case depth and the cyclic stress acting on specimens. It was also tried to explain the conditions promoting the ‘fish eye’ crack formation by analysing the combined effects of residual and applied stress patterns as well as inclusion size.

A fuzzy logic multi-phased signal control model for isolated junctions

Abstract: Dynamic signal control is a complex phenomenon that includes both increasing intersection capacity and decreasing delays at the same time. New methods such as fuzzy logic and artificial intelligence are recommended for use in dynamic signal control. In this study, a Fuzzy Logic Multi-phased Signal Control (FLMuSiC) model for isolated signalised intersections has been developed. This model comprises two systems, which are based on fuzzy logic. One of these systems arranges phase green times (duration) and the other phase sequences using traffic volumes. The developed FLMuSiC model has been compared with the traffic-actuated simulation and the aaSIDRA vehicle actuated models with respect to the average delays of vehicles. Comparison of models was performed using simulation methods. An isolated four-armed intersection is selected to compare the performances of the models. Three and four phased controlling situations with equal and different traffic volumes on approaches of intersections are considered in comparisons. Results of comparisons show that the performance of the FLMuSiC is better than both the traffic actuated simulation and the aaSIDRA models one, especially in the case of the higher variability of volumes. In addition, the FLMuSiC model is compared with earlier studies. Encouraged results are obtained.

Search for long-lived neutral particles decaying to quark-antiquark pairs in proton-proton collisions at √s =8TeV

Abstract: A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of 18.5 inverse femtobarns. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, H, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral X particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For X with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically 0.5-200 fb. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of 2-40 cm, the upper limits on the cross section are typically 0.5-3 fb. The above limits are the most stringent on these channels to date.