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Article Citation - WoS: 11Citation - Scopus: 12A New Mixed Δ-Shock Model With a Change in Shock Distribution(Springer, 2023) Chadjiconstantinidis, Stathis; Tuncel, Altan; Eryilmaz, SerkanIn this paper, reliability properties of a system that is subject to a sequence of shocks are investigated under a particular new change point model. According to the model, a change in the distribution of the shock magnitudes occurs upon the occurrence of a shock that is above a certain critical level. The system fails when the time between successive shocks is less than a given threshold, or the magnitude of a single shock is above a critical threshold. The survival function of the system is studied under both cases when the times between shocks follow discrete distribution and when the times between shocks follow continuous distribution. Matrix-based expressions are obtained for matrix-geometric discrete intershock times and for matrix-exponential continuous intershock times, as well.Article Citation - WoS: 13Citation - Scopus: 13Reliability Assessment of a Discrete Time Cold Standby Repairable System(Springer, 2021) Kan, Cihangir; Eryilmaz, SerkanThis paper is concerned with the study of a discrete time repairable system consisting of one active and one standby component. The lifetime and repair time are assumed to have discrete phase-type distributions. The system's lifetime is represented as a compound random variable. A matrix-based expression for the probability generating function of the system's lifetime is obtained based on the phase characteristics of lifetime and repair time distributions. The probability generating function is then used to obtain the distribution of the system's lifetime. Reliability and hazard rate functions are computed and evaluated for some particular choices of lifetime and repair time distributions. The limiting behavior of the hazard rates is also investigated.Article Citation - WoS: 33Citation - Scopus: 38Discussion on Barkhausen and Nyquist Stability Criteria(Springer, 2010) Singh, VimalMost textbooks on analog circuits and signal processing describe the Barkhausen criterion pertaining to the determination of sinusoidal oscillations in a closed-loop system. On the other hand, the Nyquist stability criterion is well known, as discussed in most textbooks on control systems. Recently, some examples in which the Barkhausen criterion fails to produce the correct condition for startup of oscillations have been reported. In the present paper, an explanation of oscillation startup based on the Nyquist stability criterion is given and the close relationship between the Barkhausen and the Nyquist criteria highlighted. It is shown that the Nyquist criterion (which is a rigorous technique) is a more robust approach than the Barkhausen criterion concerning the determination of sinusoidal oscillations in a closed-loop system and that the Barkhausen criterion (whenever it yields the correct result) is subsumed by the Nyquist criterion as a special case. The textbooks usually describe the Barkhausen criterion as a separate topic, i.e., do not discuss the relationship of this criterion with the Nyquist criterion. It is, therefore, felt that the present discussion will go a long way to put the subject in a broader perspective.Letter Citation - WoS: 22Citation - Scopus: 24A Note on Determination of Oscillation Startup Condition(Springer, 2006) Singh, VimalThere prevails a widespread notion that, given a closed-loop system, oscillation will commence and build up therein if the magnitude of loop gain is greater than unity at the frequency at which the angle of loop gain is zero degree. Three novel examples in which this notion fails are presented.Article Citation - WoS: 3Citation - Scopus: 3Fibre Products of Kummer Covers and Curves With Many Points(Springer, 2007) Oebudak, Ferruh; Temur, Burcu GuelmezWe study the general fibre product of any two Kummer covers of the projective line over finite fields. Under some assumptions, we obtain an involved condition for the existence of rational points in the fibre product over a rational point of the projective line so that we determine the exact number of the rational points. Using this, we construct explicit examples of such fibre products with many rational points. In particular we obtain a record and a new entry for the table (http://www.science.uva.nl/(similar to)geer/tables-mathcomp15.ps).Article Time Complexity Comparison of Stopping at First Failure and Completely Running the Test(Springer, 2020) Yucesan, Ongun; Ozkil, AltanFor a given test set, we compare two test application techniques, "stopping at first failure" and "complete run", respectively. The former stops the test whenever a failure is encountered. The latter however, carries on till the end. Our comparison concludes that although the first technique is generally faster, there is no strong evidence to support a complete rejection of the second technique for it provides statistics useful in test planning. Results support an interchangeable application of both techniques with more frequent use of stopping at first failure. Even though there are numerous studies to decide how to prioritize and select test cases (TC), or to examine dependencies of TCs and codes, the presented comparison of the two test application techniques for a given "test set" has the potential to reduce the total run time of the test.Article Variations in Chemical Composition of Some Steels During Continuous Casting(Springer, 2012) Keskinkilic, E.In this study, chemical composition variations of some steels during continuous casting were investigated in Eregli Iron and Steel Works Co. (ERDEMIR), Turkey. Final chemical analysis of a heat is determined in the continuous casting stage. Three steel specimens are regularly taken from the mould at certain meters of slab strand for each heat. The aim of this work was to evaluate the extent of changes in chemical analysis along the slab strand. Consequently, the leading aim of this study was to determine whether the number of specimens taken for each heat could be decreased without compromising quality control of the continuous casting. This was accomplished for some low-carbon, ultra-low carbon, and structural steels, which constitute the majority part of the ERDEMIR product range. The results revealed that the number of specimens could only be decreased for a limited number of steels and under certain circumstances.Article Citation - WoS: 17Citation - Scopus: 20Positive linear operators generated by analytic functions(Springer, 2007) Ostrovska, SofiyaLet phi be a power series with positive Taylor coefficients {a(k)}(k=0)(infinity) and non-zero radius of convergence r <= infinity. Let xi x, 0 <= x <= r be a random variable whose values alpha(k), k = 0, 1,..., are independent of x and taken with probabilities a(k)x(k)/phi(x), k = 0, 1,.... The positive linear operator (A(phi)f)(x) := E[f(xi x)] is studied. It is proved that if E(xi(x)) = x, E(xi(2)(x)) = qx(2) + bx + c, q, b, c is an element of R, q > 0, then A(phi) reduces to the Szasz-Mirakyan operator in the case q = 1, to the limit q-Bernstein operator in the case 0 < q < 1, and to a modification of the Lupas, operator in the case q > 1.Article Citation - WoS: 3The relationship between dental caries, dietary intake and body composition in school-age children(Springer, 2024) Ozel, Irem Cagla; Unverdi, Gizem Erbas; Eymirli, Pinar Serdar; Ayhan, Nurcan YabanciObjective The aim of this study is to evaluate the relationship between dental caries, food intake, and body composition in school-age children. Methods The study was conducted on 210 children, 105 boys and 105 girls, aged 6-12 years, without mental and/or physical disorders. Oral examinations of the children were performed by paediatric dentists and DMFT-DMFS and dmft-dmfs values were recorded. A detailed food frequency questionnaire was applied to determine the consumption frequency of dairy products and sugar-added foods. Children's height, waist and hip circumference measurements were taken by the researcher; body weight and body composition were evaluated with a Tanita body analyzer. Results The DMFS value of children who consumed white cheese daily is lower than children who did not (p < 0.05). The DMFT and DMFS values were found to be higher in children who consumed sweets, biscuits, and spreadable chocolate daily compared to children who did not (p < 0.05). Body weight and waist circumference are positively correlated with DMFT and negatively correlated with dmft. BMI is positively correlated with DMFT and negatively correlated with dmft (p < 0.05). In binary logistic regression, it was found that maternal education level, frequency of added sugar intake and body fat ratio were predictors of the presence of caries. Conclusion In this study, dental caries was associated with food consumption and body mass index. In children, consumption of sugary foods should be reduced and consumption of dairy products should be increased.Letter Citation - WoS: 23Citation - Scopus: 26Failure of Barkhausen Oscillation Building Up Criterion: Further Evidence(Springer, 2007) Singh, VimalIt has been suggested in many textbooks that, given a closed-loop system, oscillation will commence and build up therein if the magnitude of loop gain is greater than unity at the frequency at which the angle of loop gain is zero degree. A novel ideal op-amp based counterexample to this suggestion is presented. The Letter serves to substantiate the findings in a recent Letter. A discussion relating to the finite gain of op-amp is included.
