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A Short Note on Resolving Singularity Problems in Covariance Matrices
Ezgi Ayyildiz,Vilda Purutcuoglu Gazi,Ernst Wit
International Journal of Statistics and Probability , 2012, DOI: 10.5539/ijsp.v1n2p113
Abstract: In problems where a distribution is concentrated in a lower-dimensional subspace, the covariance matrix faces a singularity problem. In downstream statistical analyzes this can cause a problem as the inverse of the covariance matrix is often required in the likelihood. There are several methods to overcome this challenge. The most well-known ones are the eigenvalue, singular value, and Cholesky decompositions. In this short note, we develop a new method to deal with the singularity problem while preserving the covariance structure of the original matrix. We compare our alternative with other methods. In a simulation study, we generate various covariance matrices that have different dimensions and dependency structures, and compare the CPU times of each approach.
Some Results on the Differential Geometry of Spacelike Curves in De-Sitter Space  [PDF]
Tunahan Turhan, Nihat Ayyildiz
Journal of Applied Mathematics and Physics (JAMP) , 2013, DOI: 10.4236/jamp.2013.13009

The differential geometry of curves on a hypersphere in the Euclidean space reflects instantaneous properties of spherecal motion. In this work, we give some results for differential geometry of spacelike curves in 3-dimensional de-Sitter space. Also, we study the Frenet reference frame, the Frenet equations, and the geodesic curvature and torsion functions to analyze and characterize the shape of the curves in 3-dimensional de-Sitter space.

Turkish Studies , 2009,
Abstract: Masnawis of the classical literature are generally viewed as the works that may be described as precursors of novel in the pre-Tanzimat era literature. Are masnawis novels or to which extent can the be regarded as novels? What characteristics they may have in common with the modern novel? In what respect may they differ modern novel? Can we take the answers to such questions as criteria for delivering a final judgment? This study analyzes Fuzuli’s masnawi, “Layla wu Majnun,” in order to discuss the relations of masnawis to the genre of novel --in terms of similarities and differences. These analyses center on main elements of the narration structure in the novel genre such as narrator, characterization, and expression. Klasik edebiyat n mesnevilerine, genel anlamda, Tanzimat ncesi roman n yerini tutan eserler ola rak bakmak e ilimi yayg nd r. Mesneviler roman m d r ya da ne kadar romand r? Modern roman formuyla aralar nda ne kadar benzerlik g rülür? Nerelerde ayr l r? Bu gibi sorular n yan t , kesin hük me varmada bir l ü olarak al nabilir mi? Bu al mada, mesnevilerin roman türüyle olan ili kisini (benzerlikleri ya da ayr l klar a s ndan) irdelemek amac yla Fuzuli’nin “Leyla vü Mecnun Mesnevisi” oda nda baz zümlemeler yer almaktad r. Bu zümlemeler, roman türünün anlat yap s na ait belli ba l geler etraf nda yap lm t r. Bunlar; “anlat c ”, “karakterler” ve “anlat m” geleri olarak se ilmi olup al mada bu unsurlar ba lam nda yorum yap lm t r.
Determination of Shearing Properties for Tubular Pinewood under Torsion  [PDF]
Ezgi Günay, Emre Uludogan
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.61007
Abstract: In this study, tubular pinewood (Pinus sylvestris L.) specimens are tested and shear strain measurements are performed by applying torsion in z direction in the consideration of light weight aircraft engineering. The objective of this paper is to contribute and generate the nonlinear material model in terms of shear modulus presented with power functions under the consideration of nonlinear behavior of wood under torque. Strain gauge measurements are performed for the maximum shear stresses which develop on the tubular specimen, along the radial r(rin, rout), circumferential Φ(Φin, Φout) and z directions, in a point-wise manner. The data is gathered and examined for the determination of the local variations of empirical shear modulus functions on transversely isotropic surfaces of the specimens. The coordinate dependent shear modulus functions of GzΦ(r), GzΦ(Φ), GzΦ(z) are derived for GzΦ(r, Φ, z)as the function of r, Φ and z, respectively, by analyzing the gathered data. It is proposed to represent the shear modulus functions, GzΦ(Φ) and GzΦ(z) with the parabolic polynomials, and, to represent the shear modulus function GzΦ(r) with a linear equation.
Comparative Analysis of the Quality Perception in Public Spaces of Duzce City  [PDF]
Elif Kutay Karacor, Ezgi Akcam
Current Urban Studies (CUS) , 2016, DOI: 10.4236/cus.2016.43017
Abstract: Public spaces in urban areas were affected from neoliberal policies in terms of their management and ownership. Accordingly, several researchers handled public spaces from different perspectives considering on advantages or disadvantages of neoliberal policies. Four key attributes of successful places: accessibility, comfort, socialization, and activity are accepted as quality indicators of today’s urban spaces and they became an outline for this study. The aim of this study is to evaluate the quality of different type public spaces and to determine the reason why these differences. Therefore, quality differences resulting from management and ownership were evaluated in scope of public space literature. Our findings put forward that ownership of spaces is not a significant factor perceiving the quality of spaces. Besides, publicly owned urban spaces were found as not always preferable and the ownership was not a basis factor for quality perception.
Metastatic Penile Carcinomas: A Study of Nine Cases and Review of the Literature
F Berkmen, A Ayyildiz
African Journal of Urology , 2005,
Abstract: Objective: Primary penile carcinoma is one of the rarest male genital tract tumors in Turkey, because circumcision is performed routinely. In general, metastatic carcinoma of the penis is the second most common penile tumor. Despite the fact that the penis is rarely affected by metastases, there have been 319 cases reported in the literature. This study was carried out to throw light on the main characteristics of the metastatic disease. Patients and Methods: Nine patients aged between 32 and 68 years (median 62.9 years) with metastatic tumors of the penis were the subject of this study. The clinical history of the cases was reviewed, and the patients\' data were recorded including location, histology of the primary tumor, presence and location of other metastases, clinical findings, treatment and outcome. The microscopic preparations from both the primary tumor and the penile metastases were reviewed in our pathology department to confirm that the penile lesions showed the same histomorphological characteristics as the primary tumor. Results: The primary tumors were located in the genitourinary system in 7 / 9 patients(transitional cell carcinoma of the bladder), while in the remaining two patients the primary site was the lung (squamous cell carcinoma) and the bone marrow (lymphoblastic leukemia), respectively. Percutaneous needle aspiration cytology was performed in all cases and incisional biopsy in one case for diagnosis. Total penectomy was the treatment of choice in 7 cases and bilateral cavernotomy in the leukemia case. No treatment was given to one patient because of multiple metastases in other organs. Survival after treatment lasted from 4 months to 62 months; the longest survival (5 years) was found in the leukemia case. Conclusion: Metastatic penile carcinomas are relatively rare and present a challenging problem. Total penectomy and local excision of solitary nodules or distal penile involvement still represent the treatment of choice. However, because of the association of a penile metastatic lesion with advanced disease, survival rates are limited, and the majority of the patients die within one year. Carcinomes péniens métastatiques: Une étude de neuf cas et revue de la littérature Objectifs : Le carcinome pénien primitif est l\'une des tumeurs génitales masculines les plus rares en Turquie, parce que la circoncision est habituelle. En général, le carcinome métastatique du pénis est la deuxième tumeur pénienne commune. Malgré le fait que le pénis est rarement affecté par des métastases, il y a eu 319 cas rapportés dans la littérature. Cette étude a été réalisée pour déterminer les caractéristiques principales de la maladie métastatique. Patients et méthodes : Neuf patients de 32 à 68 ans (médiane 62,9 ans) présentant des tumeurs métastatiques du pénis étaient le sujet de cette étude. L\'histoire clinique de tous les patients a été revue, et les données des patients ont été enregistrées comprenant le siège, l\'histologie de la tum
Measuring the marketing performances of state forest enterprises in Turkey
D Toksoy, H Ayyildiz
African Journal of Biotechnology , 2010,
Abstract: Today, any enterprise has to consider marketing as important as production. Production and marketing are two complementary activities in enterprises. The increase in marketing effectiveness is achieved through measuring the activity outcomes that can be described as marketing performance. Because marketing is a social science and, therefore, determining the marketing performance system concretely, examining it and determining its principles may not be possible, a need for a new model was felt to represent the real system, and, consequently, a multi dimensional purpose-system model was developed. This model was applied in the eighty-nine state forest enterprises in Turkey which are branches of the General Directorate of Forestry and which are run on the principles of business enterprise. This study covers a limited period of time (1999 - 2003), and 41 variables were developed in order to measure the marketing performances of these enterprises. As a result of the statistical analyses, the total production area (TPA), total production costs (TPC), total number of the personnel working in the management unit (TNPWM), total growing stock (TGS), total investment amount (TIA), number of the assistant personnel separated from the management unit (NAPSM), distance to city center (DCC), total marketing/sale expenditure (TME), total management unit area (TMUA), total sales (TS), total forest area (TFA), total personnel expenditures (TPE), total production amount (TPAM) and total market priced product income (TMPPI) were found to be the most important marketing variables in the state forest enterprises. It was also found that the marketing performance could be explained 77.328% with the 14 variables that were used in this model.
Biological Activities and Some Physicochemical Properties of Sunflower Honeys Collected from the Thrace Region of Turkey
Elif Sari,Nusret Ayyildiz
Pakistan Journal of Biological Sciences , 2012,
Abstract: Honey is a sweet food made by bees using nectar from flowers. Its quality depends on a number of factors, such as floral type, pH, moisture, free acidity, diastase activity, invert sugar and sucrose. The aim of the study is to examine the qualities of 50 sunflower honey (Helianthus annuus L.) collected from the Thrace region of Turkey, in terms of melissopalynological analysis, important chemical parameters and antioxidant activities . The total phenolic content of the honey samples was determined by the Folin-Ciocalteu method with spectrophotometry. The 1,2-diphenyl-2-picryl hydrazyl (DPPH) method was used to determine anti-radical activity and the phosphomolybdenum method was utilized for antioxidant activity. Correlations between the analysed parameters were found to be statistically significant (p<0.05). The results obtained for physicochemical characteristics of sunflower honey indicate a good quality level, adequate processing, good maturity and freshness and that the sunflower honey samples studied proved to be good source of natural dietary antioxidants. This is the first report of the total phenolic content, antioxidant and antiradical activities of sunflower honeys collected from the Thrace region of Turkey.
Hemostatic abnormalities in liver cirrhosis
Dicle Medical Journal , 2009,
Abstract: In this study, 44 patients with liver cirrhosis were investigated for hemostatic parameters. Patients with spontaneous bacterial peritonitis, hepatocellular carcinoma, hepatorenal syndrome and cholestatic liver diseases were excluded. Patients were classified by Child-Pugh criterion and according to this 4 patients were in Class A, 20 in Class B and 20 in C. Regarding to these results, it was aimed to investigate the haematological disturbances in liver cirrhotic patients.In the result there was a correlation between activated partial thromboplastin time, serum iron, ferritin, transferrin, haptoglobin and Child-Pugh classification. Besides there was no correlation between prothrombin time, factor 8 and 9, protein C and S, anti-thrombin 3, fibrinogen, fibrin degradation products, serum iron binding capacity, hemoglobin, leukocyte, mean corpuscular volume and Child-Pugh classification.There were significant difference, in terms of AST, ferritin, haptoglobulin, sex and presence of ascites between groups (p<0.05). In all groups there were abnormalities and dysfunctions in prothrombin time, fibrinogen, factor 8 and 9, serum iron, ferritin, transferrin, haptoglobin, protein C and S, anti-thrombin 3, hemoglobin and platelets, where there was no in activated partial thromboplastin time, fibrin degradation products, serum iron binding capacity, leucocytes and mean corpuscular volume (p>0.05). In the summary, we have found correlation between hemostatic abnormalities and disease activity and clinical prognosis in patients with liver cirrhosis which is important in the management of these patients. This is also important for identification of liver transplant candidiates earlier.
A Data Envelopment-Based Clustering Approach for Public Sugar Factories in Privatizing Process
Ezgi A. Demirtas
Mathematical Problems in Engineering , 2011, DOI: 10.1155/2011/946549
Abstract: Turkish Sugar Inc., a public enterprise including 25 factories, is the first corporation of Turkish industry. According to the government policy, public sugar factories (PSFs) will be privatized as geography-based 6 portfolio groups in two years. As performance measures of PSF affect government, sugar producers, and several unions in privatizing process, a systematic approach is necessary to measure efficiencies and grouping factories. This paper uses a new DEA- (Data Envelopment Analysis-) based clustering approach for measuring efficiency scores of PSF and grouping them instead of geography- based portfolio groups. This new approach can help decision makers in privatizing process. At the same time, target values obtained by dual model can be used to eliminate inefficiencies of some PSFs.
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