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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6

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Now showing 1 - 6 of 6
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    PublicationOpen Access
    A class of Banach algebras whose duals have the Schur property
    (TÜBİTAK, 1999) Mustafayev, H.; Department of Mathematics; Ülger, Ali; Faculty Member; Department of Mathematics; College of Sciences
    Call a commutative Banach algebra A a γ-algebra if it contains a bounded group Λ such that aco(Λ) contains a multiple of the unit ball of A. In this paper, first by exhibiting several concrete examples, we show that the class of γ-algebras is quite rich. Then, for a γ-algebra A, we prove that A* has the Schur property iff the Gelfand spectrum Σ of A is scattered iff A* = ap(A) iff A* = Span(Σ).
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    PublicationOpen Access
    Cost of disease of heart failure in Turkey: a Delphi panel-based analysis of direct and indirect costs
    (Galenos Yayınevi, 2022) Çavuşoğlu, Yüksel; Altay, Hakan; Aras, Dursun; Çelik, Ahmet; Ertaş, Fatih Sinan; Kılıçaslan, Barış; Nalbantgil, Sanem; Temizhan, Ahmet; Yıldırımtürk, Özlem; Yılmaz, Mehmet Birhan; Ural, Dilek; Faculty Member; School of Medicine; Koç University Hospital; 1057
    Background: heart failure (HF) is considered a significant public health issue with a substantial and growing epidemiologic and economic burden in relation to longer life expectancy and aging global population Aims: to determine cost-of-disease of heart failure (HF) in Turkey from the payer perspective. Study Design: cross-sectional cost of disease study. Methods: in this cost-of-disease study, annual direct and indirect costs of management of HF were determined based on epidemiological, clinical and lost productivity inputs provided by a Delphi panel consisted of 11 experts in HF with respect to ejection fraction (EF) status (HF patients with reduced EF (HFrEF), mid-range EF (HFmrEF) and preserved EF (HFpEF)) and New York Heart Association (NYHA) classification. Direct medical costs included cost items on outpatient management, inpatient management, medications, and non -pharmaceutical treatments. Indirect cost was calculated based on the lost productivity due to absenteeism and presenteeism. Results: 51.4%, 19.5%, and 29.1% of the patients were estimated to be HFrEF, HFmrEF, and HFpEF patients, respectively. The total annual direct medical cost per patient was $887 and non-pharmaceutical treatments ($373, 42.1%) were the major direct cost driver. Since an estimated nationwide number of HF patients is 1,128,000 in 2021, the total annual national economic burden of HF is estimated to be $1 billion in 2021. The direct medical cost was higher in patients with HFrEF than in those with HFmrEF or HFpEF ($1,147 vs. $555 and $649, respectively). Average indirect cost per patient was calculated to be $3,386 and was similar across HFrEF, HFmrEF and HFpEF groups, but increased with advanced NYHA stage. Conclusion: Our findings confirm the substantial economic burden of HF in terms of both direct and indirect costs and indicate that the non-pharmaceutical cost is the major direct medical cost driver in HF management, regardless of the EF status of HF patients.
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    PublicationOpen Access
    Effect of echocardiographic epicardial adipose tissue thickness on success rates of premature ventricular contraction ablation
    (Galenos Yayınevi, 2019) Kanat, Selçuk; Karaduman, Bilge Duran; Tütüncü, Ahmet; Tenekecioğlu, Erhan; Bayram, Nihal Akar; Mutluer, Ferit Onur; Doctor; Koç University Hospital
    Background: idiopathic premature ventricular contractions are frequently detected ventricular arrhythmias, and radiofrequency ablation is an effectively treatment for improving symptoms and eliminating premature ventricular contractions. Studies have reported a relationship between an elevated epicardial adipose tissue thickness and myocardial structural pathologies. However, the association between epicardial adipose tissue thickness and success rates of premature ventricular contraction ablation has not yet been investigated. Aims: to assess the relationship between epicardial adipose tissue thickness and success rates of premature ventricular contraction ablation. Study Design: retrospective case-control study. Methods: this study enrolled a total of 106 consecutive patients who have had a high premature ventricular contraction burden of >10,000/24-h assessed using ambulatory Holter monitorization and underwent catheter ablation. A frequency of premature ventricular contractions of more than 10,000/day was defined as frequent premature ventricular contraction. Epicardial adipose tissue thickness was measured using 2D transthoracic echocardiography. A successful ablation was defined as >80% decrease in pre-procedural premature ventricular contraction attacks with the same morphology during 24-h Holter monitorization after a 1-month follow-up visit from an ablation procedure. Results: successful premature ventricular contraction ablation was achieved in 87 (82.1%) patients. Epicardial adipose tissue thickness was significantly higher in patients with unsuccessful ablation (p<0.001). Procedure time, total fluoroscopy time, and radiofrequency ablation time were statistically higher in the unsuccessful group (p<0.001). Stepwise multivariate logistic regression analysis showed that epicardial adipose tissue thickness and pseudo-delta wave time were independently associated with procedural success (both p values <0.001). In the receiver-operating curve analysis, epicardial adipose tissue thickness was found to be an important predictor for procedural success (area under the receiver-operating characteristic curve= 0.85, p=0.001), with a cutoff value of 7.7 mm, a sensitivity of 92%, and a specificity of 68%. Conclusion: epicardial adipose tissue thickness is higher in patients with premature ventricular contraction ablation failure, which may be indicative of procedural success.
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    PublicationOpen Access
    On elastic graph spines associated to quadratic Thurston maps
    (TÜBİTAK, 2022) Department of Mathematics; Yetişer, Ali Berkay; Faculty Member; Department of Mathematics; College of Sciences
    For a quadratic Thurston map having two distinct critical points and n postcritical points, we count the number of possible dynamical portraits. We associate elastic graph spines to several hyperbolic quadratic Thurston rational functions. These functions have four postcritical points, real coefficients, and invariant real intervals. The elastic graph spines are constructed such that each has embedding energy less than one. These are supporting examples to Dylan Thurston's recent positive characterization of rational maps. Using the same characterization, we prove that with a combinatorial restriction on the branched covering and a cycle condition on the dynamical portrait, a quadratic Thurston map with finite postcritical set of order n is combinatorially equivalent to a rational map. This is a special case of the Bernstein-Levy theorem.
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    PublicationOpen Access
    Linear connections on light-like manifolds
    (Scientific and Technological Research Council of Turkey (TUBITAK), 2008) Koçak, Ş.; Limoncu, M.; Department of Physics; Dereli, Tekin; Faculty Member; Department of Physics; College of Sciences; 201358
    It is well-known that a torsion-free linear connection on a light-like manifold (M, g) compatible with the degenerate metric g exists if and only if Rad(TM) is a Killing distribution. In case of existence, there is an infinitude of connections with none distinguished. We propose a method to single out connections with the help of a special set of 1-forms by the condition that the 1-forms become parallel with respect to this connection. Such sets of 1-forms could be regarded as an additional structure imposed upon the light-like manifold. We consider also connections with torsion and with non-metricity on light-like manifolds.
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    PublicationOpen Access
    Intensity-modulated radiotherapy versus 3-dimensional conformal radiotherapy strategies for locally advanced non-small-cell lung cancer
    (Galenos Yayınevi, 2014) Bölükbaşı, Yasemin; Welsh, James William; Topkan, Erkan; N/A; Selek, Uğur; Faculty Member; School of Medicine; 27211
    Chemoradiotherapy is the current standard of care in patients with advanced inoperable stage IIIA or IIIB non-small cell lung cancer (NSCLC). Three-dimensional radiotherapy (3DCRT) has been a trusted method for a long time and has well-known drawbacks, most of which could be improved by Intensity Modulated Radiotherapy (IMRT). IMRT is not currently the standard treatment of locally advanced NSCLC, but almost all patients could benefit to a degree in organ at risk sparing, dose coverage conformality, or dose escalation. The most critical step for a radiation oncology department is to strictly evaluate its own technical and physical capabilities to determine the ability of IMRT to deliver an optimal treatment plan. This includes calculating the internal tumor motion (ideally 4DCT or equivalent techniques), treatment planning software with an up-todate heterogeneity correction algorithm, and daily image guidance. It is crucial to optimise and individualise the therapeutic ratio for each patient during the decision of 3DCRT versus IMRT. The current literature rationalises the increasing use of IMRT, including 4D imaging plus PET/CT, and encourages the applicable knowledge-based and individualised dose escalation using advanced daily image-guided radiotherapy.