Search results

The purpose of this paper is to investigate the stability of a small scale six-degree-of-freedom nonlinear helicopter model at translator velocities and angular displacements while it is transiting to hover with different initial conditions.

In this study, model predictive controller and linear quadratic regulator are designed and compared within each other for the stabilization of the open loop unstable nonlinear helicopter model.

This study shows that the helicopter is able to reach to the desired target with good robustness, low control effort and small steady-state error under disturbances such as parameter uncertainties, mistuned controller.

The purpose of using model predictive control for three axes of the autopilot is to decrease the control effort and to make the close-loop system insensitive against modeling uncertainties.

This chapter reviews recent research regarding behavior interventions for young children. We first consider the implications of allowing maladaptive behavior to remain untreated in young children. The reasons that people may select for inaction are illustrated through a case example of an individual who manifested behavior problems that were allowed to continue through accommodations rather than being addressed through interventions. We then consider several examples of promising behavior interventions for very young children that can be carried out in home and preschool environments. Next, we review promising interventions that are appropriate for school-based settings. We conclude with the observation that while it is absolutely necessary to deal with urgent situations evoked by maladaptive behavior, it is critical to keep sight of the goal that we should always work to promote more mature, self-regulated, and acceptable behaviors across settings.

This paper aims to propose output feedback-based control algorithms for the flight control system of a scaled, un-crewed helicopter in its hover flight mode.

The proposed control schemes are based on H_∞ control and composite nonlinear control. The gains of the output feedback controllers are obtained as the solution of a set of linear matrix inequalities (LMIs).

In the proposed schemes, the finite-time convergence of system states to trim condition is achieved with minimum deviation from the steady-state. As the proposed composite nonlinear output feedback design improves the transient response, it is well suited for a scaled helicopter flight. The use of measured output vector instead of the state vector or its estimate for feedback provides a simple control structure and eliminates the need for an observer in real-time application. The proposed control strategies are relevant to situations in which a simple controller is essential due to economic factors, reliability and hardware implementation constraints.

The proposed control strategies are relevant to situations in which a simple controller is essential due to economic factors, reliability and hardware implementation constraints. They also have significance in applications where the number of measurement quantities needs to be minimized such as in a fully functional rotor-craft unmanned aerial vehicle.

The developed output feedback control algorithms can be used in small-scale helicopters for numerous civilian and military applications.

This work addresses the LMI-based formulation and solution of an output feedback controller for a hovering un-crewed helicopter. The stability and robustness of the closed-loop system are proved mathematically and the performance of the proposed schemes is compared with an existing strategy via simulation studies.

The introduction of consumer products can be traced back to the invention of the wheel, and after the first invention, humankind discovered that what can be consumable is marketable. Therefore, it is safe to suggest that the development of marketing, in thought and practice, has always been hand-in-hand with the evolution of humankind. Modern Turkey or Anatolia, one of the cradles of civilisation located in the Fertile Crescent or, in other words, Old Mesopotamia, has always been the centre of trade and marketing. As an emerging economy, Turkey has a lot to combine the ways of western practices with market dynamics unique to her, whereas authors find the development of marketing practices in Turkey exceptionally interesting. Therefore, this chapter aims to provide an insight and a brief history regarding the development of the Turkish marketing context throughout the years. We believe that this contribution will be helpful to those who are interested in the development of marketing in an emerging economy in an academic fashion, as well as for those who are attracted to follow the footprints of the modern era’s business environment.

In recent years, additive manufacturing (AM) has started to be used for manufacturing real functional parts and assemblies for critical applications in aerospace, automotive, and machinery industries. Most complex or assembled parts require internal features (IF) such as holes, channels, slots, or guides for locational and mating requirements. Therefore, it is critical to understand and compare the structural and mechanical properties of additively manufactured and conventionally machined IFs.

In this study, mechanical and microstructural properties of Inconel 718 (Inc718) alloy internal features, manufactured either as-built with AM or machining of additively manufactured (AMed) part thereafter were investigated.

The results showed that the average ultimate tensile strength (UTS) of additively manufactured center internal feature (AM-IF) is almost analogous to the machined internal feature (M-IF). However, the yield strength of M-IF is greater than that of AM-IF due the greater surface roughness of the internal feature in AM-IF, which is deemed to surpass the effect of microstructure on the mechanical performance. The results of digital image correlation (DIC) analysis suggest that AM-IF and M-IF conditions have similar strain values under the same stress levels but the specimens with as built IF have a more locally ductile region around their IF, which is confirmed by hardness test results. But this does not change global elongation behavior. The microstructural evolution starting from as-built (AB) and heat-treated (HT) samples to specimens with IF are examined. The microstructure of HT specimens has bimodal grain structure with d phase while the AB specimens display a very fine dendritic microstructure with the presence of carbides. Although they both have close values, machined specimens have a higher frequency of finer grains based on SEM images.

It was shown that the concurrent creation of the IF during AM can provide a final part with a preserved ultimate tensile strength and elongation but a decreased yield strength. The variation in UTS of AM-IF increases due to the surface roughness near the internal feature as compared to smooth internal surfaces in M-IF. Hence, the outcomes of this study are believed to be valuable for the industry in terms of determining the appropriate production strategy of parts with IF using AM and postprocessing processes.

This study aims to test the emerald model on the regional basis for the identification of the most important sources of competitiveness in the states of the US.

Using the emerald model and its assertions, data are collected over the period 1998-2013 from 47 states in the US. Multiple regression analysis is performed with a lag structure of four, six and eight years as alternative time intervals to explain the dependent variable.

The empirical results support the emerald model except for its R&D attractiveness dimension in its ability to explain competitiveness in the states of the US. In the longer term (eight-year lag), cluster attractiveness has the highest impact, followed by environmental attractiveness, ownership attractiveness, educational attractiveness and talent attractiveness. Comparison of regression models with different time lags indicates that once the very early phase is over, the impacts of most attractiveness dimensions become rather consistent across time and do not disappear.

The study contributes to the literature on the measurement of regional competitiveness by performing an overall assessment of the emerald model and by analyzing the impacts of the model’s dimensions on competitiveness over time. On the other hand, the identification of the sources of regional competitiveness paves the way for a more efficient allocation of resources regarding policies and improvement programs.

The purpose of this paper is to introduce an empirical model for house price spillovers between real estate markets. The model is presented by using data from the US-UK and London-New York housing markets over a period of 1975Q1-2016Q1 by employing both static and dynamic methodologies.

The research analyzes long-run static and dynamic spillover elasticity coefficients by employing three methods, namely, autoregressive distributed lag, the fully modified ordinary least square and dynamic ordinary least squares estimator under a Kalman filter approach. The empirical method also investigates dynamic correlation between the house prices by employing the dynamic control correlation method.

The paper shows how a dynamic spillover pricing analysis can be applied between real estate markets. On the empirical side, the results show that country-level causality in housing prices is running from the USA to UK, whereas city-level causality is running from London to New York. The model outcomes suggest that real estate portfolios involving US and UK assets require a dynamic risk management approach.

One of the findings is that the dynamic conditional correlation between the US and the UK housing prices is broken during the crisis period. The paper does not discuss the reasons for that break, which requires further empirical tests by applying Markov switching regime shifts. The timing of the causality between the house prices is not empirically tested. It can be examined empirically by applying methods such as wavelets.

The authors observed a unidirectional causality from London to New York house prices, which is opposite to the aggregate country-level causality direction. This supports London’s specific power in the real estate markets. London has a leading role in the global urban economies residential housing markets and the behavior of its housing prices has a statistically significant causality impact on the house prices of New York City.

The house price co-integration observed in this research at both country and city levels should be interpreted as a continuity of real estate and financial integration in practice.

The paper is the first research which applies a dynamic spillover analysis to examine the causality between housing prices in real estate markets. It also provides a long-term empirical evidence for a dynamic causal relationship for the global housing markets.

This study investigates the effect of business cycles on school enrollment in Turkey. During recessions, school enrollment might increase as opportunity cost of schooling declines, yet it might also decrease because of reduced income households have for education. Which effect dominates depends on the context. We empirically explore this in a context displaying canonical features of developing countries.

Using the Turkish Household Labor Force Survey data for a period covering the Great Recession, we estimate the effect of unemployment rate separately for enrollments in general and vocational high schools and in undergraduate programs. To understand the cyclicality, we use a probit model with the regional and time variations in unemployment rates. We also build a simple theoretical model of work-schooling choice to interpret the findings.

We find that the likelihood of enrolling in general high schools and undergraduate programs declines with higher adult unemployment rates, but the likelihood of enrollment in vocational high schools increases. Confronting these empirical findings with the theoretical model suggests that the major factor in enrollment cyclicality in Turkey is how parental resources allocated to education change during recessions by schooling type.

Our finding of pro-cyclical enrollment in academically oriented programs is in contrast with counter-cyclicality documented for similar programs in developed countries, which highlights the importance of income related factors in developing-country contexts. Our heterogeneous findings for general and vocational high schools are also novel.