Essays on nonlinear dynamics in optimal growth models

Ankara : Department of Economics İhsan Doğramacı Bilkent University, 2014.Thesis (Ph. D.) -- Bilkent University, 2014.Includes bibliographical references leaves 79-84.Economic models with time delay have long been considered in economic theory. It is considered that delay forces the economic system into persistent cycles which can be interpreted as intrinsic crises of the capitalist economy. The e§ect of delay on economic dynamics is analyzed by Hopf bifurcation according to the recent developments in economics and mathematics. Hopf bifurcation depends on the existence of a pair of pure imaginary eigenvalues of the Jacobian matrix evaluated at the steady state. However, recent studies are inconsistent in a determinate way to decide whether the optimal growth model with investment lags admits persistent cycles or not. In the second chapter of this thesis, the author tries to sharpen the analysis of one sector optimal growth model with one control and one state variables and time delay. We Örstly give a brief outline of the mathematical history and ëknow-howíof delays in economic models, as well as its interpretation, and then, we further the analysis set of the model of Asea and Zak (1999) and try to introduce of a new technique for the exposition of the eigenvalues of the characteristic equation of these type of models in a generalized framework. In the third chapter we introduce a new technique (see Louisell, 2001) to the study of economic models with delays and incorporate this technique to evaluate the cycleinducing e§ects of capital dependent population growth in economic models with time delay. We employ the Solow-Kalecki framework and show that the presence of capital dependent population growth induces cycles. Other than the introduction of a new technique into the area of economics, one particular contribution of this chapter is that the results clearly shows that delay is not su¢ cient in inducing cycles even in the most simple economic models. In the forth chapter, we show that Hopf bifurcation may emerge in an overlapping generations resource economy through a feedback mechanism between population and resource availability. In overlapping generations resource economy models, the cycle inducing factor is mainly the nonlinearity of the regeneration of the resources. On the contrary, we assume linear regeneration and yet, endogenize the population growth rate. We show that the interaction between instantenous population growth and regeneration rate triggers persistent cycles in the economy. In the Öfth chapter, we employ a continuous delay structure in the process of recruitment in the population growth in an optimal growth model and hence obtain cyclic solutions. We exploit Erlangian process in the population growth mechanism. As far as we know, the incorporation of Erlangian process in optimal growth models is handled in this chapter for the Örst time in economic literature. Through this mechanism, not only the population is considered as a function of per capita capital, or in other words, population growth is endogenized, but also the current level of population growth is linked with those of older generations. We Önd out that the interaction between the e§ect of older generationsífertility choices and the accumulation of capital induces cyclic behaviour in the economy. The sixth and the last chapter concludes with future research agenda. Overall, the thesis considers the e§ects of delay and endogenized population on the economies of interest (Solow, overlapping generations, optimal growth model) economically and tries to introduce the existing methods and develop new ones to investigate the e§ects of delay and endogenized population on the eigenvalues of the Jacobians that the drive the economies of interest at their steady states.Yüksel, Mustafa KeremPh.D

On the existence of Hopf cycles in optimal growth models with time delay

Ankara : The Department of Economics and the Institute of Economics and Social Sciences of Bilkent University, 2008.Thesis (Master's) -- Bilkent University, 2008.Includes bibliographical refences.In this thesis, we analyzed the existence of cycles `a la Poincar´e-AndronovHopf in optimal growth models with time delay. The analysis builds upon a new method developed, which investigates the number of pure imaginary roots of the characteristic equation. The method was applied to the time-tobuild models of Asea and Zak (1999) and Winkler (2004).Yüksel, Mustafa KeremM.S

Türkiye’de bütçe harcamaları: Farklı dağılımların ekonomik büyümeye etkisi

Bu çalışma, Türkiye'nin 2001 krizi sonrasında uyguladığı maliye politikasına bütçe harcamaları perspektifinden baktıktan sonra, kamu harcamalarının büyümeye katkısını, dinamik bir model çerçevesinde incelenmektedir. Sonuçlar, 2001 sonrasında izlenen maliye politikasının bütçe disiplini üzerindeki olumlu etkilerini göstermekle beraber, son dönemde bütçenin harcama katılığında ve yapısal bütçe dengesinde bazı olumsuzlukları da tartışmaya açmaktadır. Bununla beraber, kamunun üretimi arttıracak altyapı yatırımlarına daha fazla ağırlık vermesi gerektiği bulunmaktadır. Eğitim ve sağlığa ayrılan kamu sermaye stokunun büyüme üzerindeki etkileri ise fiziksel altyapı yatırımlarına ayrılan kamu sermaye stoku kadar yüksek değildir. Son olarak, kamunun idari harcamalarında verimlilik yoluyla sağlanacak bir azalmanın toplumsal fayda üzerinde önemli ve pozitif etkileri görülmektedir. Bu sonuç da, önümüzdeki dönemde kamu verimliliğini arttırıp idari harcamaları kısacak önlemlerin bir politika önceliği olması gerektiğini söylemektedir

Prognostic factors in patients with metastatic urothelial carcinoma who have treated with atezolizumab

Background Atezolizumab (ATZ) has demonstrated antitumor activity and manageable safety in previous studies of patients with metastatic platinum-resistant urothelial carcinoma. However, the response rate of Atezolizumab was modest. In the current study, we evaluated the pretreatment prognostic factors for overall survival in patients with metastatic urothelial carcinoma who have progressed after first-line chemotherapy in the Expanded-Access Program of Atezolizumab. Patients and methods In this study, we present a retrospective analysis of 113 patients with urothelial cancer treated with ATZ after progression on first-line chemotherapy. Data of the patients was obtained from patient files and hospital records. Eligible patients included metastatic urothelial carcinoma patients treated with at least one course of ATZ. Univariate analysis was used to identify clinical and laboratory factors that significantly impact OS. Variables were retained for multivariate analysis if they had a statistical relationship with OS (p 3, liver metastases, baseline creatinine clearance less (GFR) than 60 ml/min, Eastern Cooperative Oncology Group (ECOG) performance status (1 >=), and hemoglobin levels below 10 mg/dl were all the significantly associated with OS. Three of the five adverse prognostic factors according to the Bellmunt criteria were independent of short survival: liver metastases HR 3.105; 95% CI 1.673-5.761; p =) HR 2.184; 95% CI 1.120-4.256; p = 0.022, and Hemoglobin level below 10 mg/dl HR 2.680; 95% CI 1.558-4.608; p 3 hazard ratio [HR] 2.092; 95% CI 1.031-4.243; p = 0.041 and GFR less than 60 ml/min HR 1.829; 95% CI 1.1-3.041; p = 0.02, maintained a significant association with OS in multivariate analysis. Conclusions This model confirms the Bellmunt model with the addition of NLR > 3 and GFR less than 60 ml/min and can be associated with clinical trials that use immunotherapy in patients with bladder cancer

Atezolizumab in patients with metastatic urothelial carcinoma who have progressed after first-line chemotherapy: Results of real-life experiences

Background: Atezolizumab (ATZ) has demonstrated antitumor activity and manageable safety in previous studies in patients with locally advanced or metastatic platinum resistant urothelial carcinoma. Objective: To compare the real-life experience and data of clinical trials on ATZ treatment in metastatic urothelial carcinoma. Design, setting, and participants: Patients with urothelial cancer treated with ATZ after progression on first-line chemotherapy from an expanded access program were retrospectively studied. Data of patients were obtained from their files and hospital records. Safety was evaluated for patients treated with at least one cycle of ATZ. Outcome measurements and statistical analysis: The primary endpoint was objective response rate (ORR). The secondary endpoints are overall survival (OS), progression-free survival (PFS), duration of response, and safety profile of patients. Kaplan-Meier methods were used to calculate median follow-up and estimate PFS and OS. Results and limitations: Data of 115 enrolled patients were analyzed. Most of the patients (92.3%, n = 106) had received chemotherapy regimen only once prior to ATZ. The median follow-up duration was 23.5 mo. The complete response rate, partial response rate, and ORR were 8.7% (n = 10), 20.0% (n = 23), and 28.7% (n = 33), respectively. The median duration of response was 20.4 mo (95% confidence interval [CI], 6.47-28.8). Of the 33 patients who responded to treatment, 60% (n = 20) had an ongoing response at the time of the analysis. PFS and OS with ATZ were 3.8 mo (95% CI, 2.25-5.49) and 9.8 mo (95% CI, 6.7-12.9), respectively. All-cause and any-grade adverse events were observed in 113 (98%) patients. Of the patients, 64% experienced a treatment-related adverse event of any grade and 24 (21.2%) had a grade 3-4 treatment-related adverse event. Limitations of the study included its retrospective design, and determination of treat-ment response based on clinical notes and local radiographic studies. Conclusions: In these real-life data, ATZ was effective and well tolerated in patients with metastatic urothelial carcinoma who have progressed with platinum-based first-line chemotherapy. ATZ is an effective and tolerable treatment for patients with locally advanced or metastatic platinum-resistant urothelial carcinoma in our study, similar to previously reported trials. Patient summary: Atezolizumab is effective and well-tolerated in patients with meta-static urothelial cancer who progressed with first-line chemotherapy, consistent with the outcomes of the previous clinical trials in this setting