Browsing by Author "Bilge, Ayşe Hümeyra"
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(3+3+2) warpedlike product manifolds with Spin(7) holonomy
We consider a generalization of eightdimensional multiply warped product manifolds as a special warped product by allowing the fiber metric to be nonblock diagonal. We define this special warped product as a (3 + 3 + 2) warpedlike manifold of the form M = F x B. where the base B is a twodimensional Riemannian manifold and the fibre F is of the form F = F1 x F2 where the Fi(i = 1 2) are Riemannian 3manifolds. We prove that the connection on M is completely determined by the requirement that ...

An Overview of the 2009 A(H1N1) Pandemic in Europe: Efficiency of the Vaccination and Healthcare Strategies
2009 A(H1N1) data for 13 European countries obtained from the weekly influenza surveillance overview (WISO) reports of European Centre for Disease Prevention and Control (ECDC) in the form of weekly cumulative fatalities are analyzed. The variability of relative fatalities is explained by the health index of analyzed countries. Vaccination and healthcare practices as reported in the literature are used to explain the departures from this model. The timing of the vaccination with respect to the ...

An analysis of price spikes and deviations in the deregulated Turkish power market
The successful operation of a real time market is related to the planning in the day ahead market. We analyze the day ahead and real time market data for the Turkish power market for the period 20122015 to classify price spikes and their causes. We also focus on the levels of deviation between the day ahead market values and the real time market values. We define price deviation and load deviation ratios to measure the level of deviation both in price and demand. The analysis for the load is based ...

Application of epidemic models to phase transitions
Authors:Bilge, Ayşe Hümeyra; Pekcan, Önder; Gürol, M. V.
Publisher and Date:(Taylor & Francis Ltd, 2012)The SusceptibleInfectedRecovered (SIR) and SusceptibleExposedInfectedRecovered (SEIR) models describe the spread of epidemics in a society. In the typical case, the ratio of the susceptible individuals fall from a value S0 close to 1 to a final value Sf, while the ratio of recovered individuals rise from 0 to Rf = 1  Sf. The sharp passage from the level zero to the level Rf allows also the modeling of phase transitions by the number of "recovered" individuals R(t) of the SIR or SEIR ...

Assessment and simulation of water transfer for the megacity Istanbul
Authors:Burak, Selim; Bilge, Ayşe Hümeyra; Ülker, Duygu
Publisher and Date:(Bellwether Publishing, Ltd., 2021)The population of Istanbul increased from three to fifteen million from 1970 to 2018. The city, which has no perennial fresh water resources within its metropolitan boundaries, has long imported water from other basins. In this study, the performance of a reservoir system fed by surface runoff and interbasin water transfer is investigated and applied. Simulations are run for water demand estimates and with Gammadistributed realizations of monthly precipitation, based on 105year temperature and ...

Ayvansaray mahallesinin tarihsel cevre analizi
Portfoy sigortasi yatirimcilari piyasa dususlerinden korumak ve piyasa yukselislerinde portfoyun degerini artirmak icin dunya capinda kullanilan bir stratejidir. Sabit oranli portfoy sigortasi da bu konu basligi altina bulunan yontemlerden bir tanesidir. Sabit oranli portfoy sigortasi portfoyunde riskli ve risksiz varlik bulundurup dinamik bir sekilde denge tutmaktadir. Portfoy sigortasi kullanilan donem basinda kararlastirilan taban degeri koruma sozu vermektedir. Bu dengeyi sabit carpan ve koruma ...

Bankacılık hisse senetleri üzerine endekse dayalı bir alım satım stratejisi önerisi
Batıda uzun zamandır uygulanan, Türkiye'de yeni yeni uygulanmaya başlayan ve her geçen yıl önemini artıran algoritmik alım satım yöntemi yatırımcılara büyük avantajlar sağlamaktadır. Algoritmik alım satım yöntemleri sayesinde küçük yatırımcılar dahi koruma amaçlı fon ( Hedge Fon ) yatırım bankaları ve profesyonel yatırımcılar tarafından uygulanan alım satım tekniklerini uygulayabilmekte ve geriye dönük testlerini yapabilmektedir. Bu tezin amacı algoritmik alım satım teknikleri yardımıyla, eş işlem ...

Canonical forms for families of anticommuting diagonalizable linear operators
It is well known that a commuting family of diagonalizable linear operators on a finite dimensional vector space is simultaneously diagonalizable. In this paper we consider a family A = {A(a)} A(a) : V > V a = 1... N of anticommuting (complex) linear operators on a finite dimensional vector space. We prove that if the family is diagonalizable over the complex numbers then V has an Ainvariant direct sum decomposition into subspaces V(alpha) such that the restriction of the family A to V(alpha) ...

COMPUTATION OF MONTHLY RUNOFF COEFFICIENTS FOR ISTANBUL
Authors:Bilge, Ayşe Hümeyra; Ülker, Duygu; Burak, Selman
Publisher and Date:(VINCA INST NUCLEAR SCI, 2021)Water demand for Istanbul is supplied both by impounded reservoirs located within its provincial boundaries and by water transfer from Western and Eastern regions in peripheral areas, located in SouthWest Black Sea region. The runoff coefficient defined as the ratio of the streamflow to the precipitation, plays a key role in the calculation of the surface water yield of water catchment areas. In this paper, we present the computation of monthly runoff coefficients for an accurate estimation of ...

The critical point of a sigmoidal curve
Let y(t) be a monotone increasing curve with lim(t >+/infinity) y((n))(t) = 0 for all n and let t(n) be the location of the global extremum of the nth derivative y((n))(t). Under certain assumptions on the Fourier and Hilbert transforms of y(t), we prove that the sequence {t(n)} is convergent. This implies in particular a preferred choice of the origin of the time axis and an intrinsic definition of the even and odd components of a sigmoidal function. In the context of phase transitions, the ...

Determination of epidemic parameters from early phase fatality data: A case study of the 2009 A(H1N1) pandemic in Europe
Authors:Bilge, Ayşe Hümeyra; Samanlıoğlu, Funda
Publisher and Date:(World Scientific Publ Co Pte Ltd, 2018)This paper demonstrates that the susceptibleinfectedremoved (SIR) model applied to the early phase of an epidemic can be used to determine epidemic parameters reliably. As a case study the SIR model is applied to the fatality data of the 2009 fall wave cycle of the A(H1N1) pandemic in 12 European countries. It is observed that the best estimates of the basic reproduction number R0 and the mean duration of the infection period 1/eta lie on a curve in the scatterplots indicating the existence of ...

Determining the critical point of a sigmoidal curve via its fourier transform
Authors:Bilge, Ayşe Hümeyra; Özdemir, Yunus
Publisher and Date:(Institute of Physics Publishing, 2016)A sigmoidal curve y(t) is a monotone increasing curve such that all derivatives vanish at infinity. Let tn be the point where the nth derivative of y(t) reaches its global extremum. In the previous work on solgel transition modelled by the SusceptibleInfected Recovered (SIR) system, we observed that the sequence {tn } seemed to converge to a point that agrees qualitatively with the location of the gel point [2]. In the present work we outline a proof that for sigmoidal curves satisfying fairly ...

Epidemic models for phase transitions: application to a physical gel
Authors:Bilge, Ayşe Hümeyra; Pekcan, Önder; Kara, Selim; Öǧrenci, Arif Selçuk
Publisher and Date:(Taylor & Francis Ltd, 2017)Carrageenan gels are characterized by reversible solgel and gelsol transitions under cooling and heating processes and these transitions are approximated by generalized logistic growth curves. We express the transitions of carrageenanwater system as a representative of reversible physical gels in terms of a modified SusceptibleInfectedSusceptible epidemic model as opposed to the SusceptibleInfectedRemoved model used to represent the (irreversible) chemical gel formation in the previous work. ...

An equivalence class decomposition of finite metric spaces via Gromov products
Authors:Bilge, Ayşe Hümeyra; Çelik, Derya; Koçak, Şahin
Publisher and Date:(Elsevier Science Bv, 2017)Let (X, d) be a finite metric space with elements Pi, i = 1,..., n and with the distance functions d(ij) The Gromov Product of the "triangle" (Pi, Pj, Pk) with vertices Pt, Pj and Pk at the vertex Pi is defined by Delta(ijk) = 1/2(d(ij) + d(ik)  d(jk)). We show that the collection of Gromov products determines the metric. We call a metric space Deltageneric, if the set of all Gromov products at a fixed vertex Pi has a unique smallest element (for i = 1,., n). We consider the function ...

Finansal piyasalarda karanlık havuzlar ve optimal stratejiler
Karanlık havuzlar, 1980'li yılların son dönemlerinde ortaya çıkmış, öncelikle gelişmiş ülkelerde kullanılmış, finansal piyasalarda yaşanan küreselleşme ile hız kazanarak gelişmekte olan ülkelerde de yeni bir finansal yapı olarak yerleşmeye başlamıştır. Finansal piyasalarda karanlık havuzlar, daha çok büyük hacimde işlem yapan yatırımcı profilinin piyasa dalgalanmalarından etkilenmemek amacıyla tercih ettikleri alternatif bir alım ve satım sistemidir. Dünyadaki karanlık havuz piyasaları ve bu ...

Forecasting electricity demand for Turkey: Modeling periodic variations and demand segregation
In deregulated electricity markets the independent system operator (ISO) oversees the power system and manages the supply and demand balancing process. In a typical day the ISO announces the electricity demand forecast for the next day and gives participants an option to prepare offers to meet the demand. In order to have a reliable power system and successful market operation it is crucial to estimate the electricity demand accurately. In this paper we develop an hourly demand forecasting method ...

Forecasting Models For Daily Natural Gas Consumption Considering Periodic Variations And Demand Segregation
Authors:Yükseltan, Ergün; Yücekaya, Ahmet; Bilge, Ayşe Hümeyra; Ağca Aktunç, Esra
Publisher and Date:(Elsevier Ltd, 2020)Due to expensive infrastructure and the difficulties in storage, supply conditions of natural gas are different from those of other traditional energy sources like petroleum or coal. To overcome these challenges, supplier countries require takeorpay agreements for requested natural gas quantities. These contracts have many preclauses; even if they are not met due to low/high consumption or other external factors, buyers must completely fulfill them. A similar contract is then imposed on ...

The Fourier Transform of the First Derivative of the Generalized Logistic Growth Curve
Authors:Bilge, Ayşe Hümeyra; Özdemir, Yunus
Publisher and Date:(International journal of advances in engineering and pure sciences (Online), 2020)The “generalized logistic growth curve” or the “5point sigmoid” is a typical example for sigmoidal curves without symmetry and it is commonly used for nonlinear regression. The “critical point” of a sigmoidal curve is defined as the limit, if it exists, of the points where its derivatives reach their absolute extreme values. The existence and the location of the critical point of a sigmoidal curve is expressed in terms of its Fourier transform. In this work, we obtain the Fourier transform of ...

Futbol kulüpleri hisse senetleri üzerinden portföy oluşturulması ve finansal bir ürün olarak modellenmesi
Bu çalışmada Borsa İstanbul'da işlem gören Beşiktaş, Fenerbahçe, Galatasaray ve Trabzonspor takımlarının hisse senetlerini de içeren modern portföy teorisine uygun bir portföy oluşturulması amaçlanmıştır. Bu çalışma yapılırken takımların oynadıkları maç sonuçlarının kulüplerin hisse senetlerinin normal üzeri (abnormal) getirilerine etkisi incelenmiş ve futbol kulüpleri hisseleri ile BİST100 endeksi arasındaki korelasyona ve farklı sektörlerde faaliyet gösteren şirketlerin hisseleri ile olan ...

Gromov product structures, quadrangle structures and split metric spaces
Authors:Bilge, Ayşe Hümeyra; Çelik, Derya; Koçak, Şahin; Rezaeinazhad, Arash Mohammadian
Publisher and Date:(Elsevier B.V., 202106)Let (X,d) be a finite metric space with elements Pi, i=1,…,n and with distances dij≔d(Pi,Pj) for i,j=1,…,n. The “Gromov product” Δijk, is defined as [Formula presented]. (X,d) is called Δgeneric, if, for each fixed i, the set of Gromov products Δijk has a unique smallest element, Δijiki. The Gromov product structure on a Δgeneric finite metric space (X,d) is the map that assigns the edge Ejiki to Pi. A finite metric space is called “quadrangle generic”, if for all 4point subsets {Pi,Pj,Pk,Pl}, ...