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Guney E.,Istanbul Arel University
Operational Research | Year: 2017

The budgeted influence maximization problem is a challenging stochastic optimization problem defined on social networks. In this problem, the objective is identifying influential individuals who can influence the maximum number of members within a limited budget. In this work an integer program that approximates the original problem is developed and solved by a sample average approximation (SAA) scheme. Experimental analyses indicate that SAA method provides better results than the greedy method without worsening the solution time performance. © 2017 Springer-Verlag Berlin Heidelberg


Cakir V.,Istanbul Arel University | Gheorghe A.,Old Dominion University
International Journal of Engineering Education | Year: 2017

The present study aims to examine the academic profiles of industrial engineering undergraduate students among a sample group of military college engineering students (N=276) in order to determine the factors impacting academic performance; to compare student groups that were identified by course scores, and to analyse performance changes over four academic years. The study started with data collection, database creation and preparation for clustering study. A two-step clustering methodology was used for grouping courses based on academic performance and context similarities. The clustering methodology results are validated by discriminant analysis. Student movements among clusters over the four years are identified in the longitudinal cluster analysis part of the study. Results showed that there is saturated cluster structure among students which has been preserved over years. It was concluded that the importance of background knowledge and prior motivation are effective in the academic performance rather than the change in environment. Although this study is the final stage of an ongoing project in which more than twenty officers are involved, specific data collection process and the analyses are conducted by the authors. © 2017 Tempus Publications.


The main aim of the present study was to provide additional knowledge about the mediatory processes through which language relates to depression. Although previous research gave clear evidence that language is closely related to depression, the research on intervening variables in the relationship has been limited. The present investigation tested a structural equation model in which self-concept clarity and self-consciousness mediated the relationship between personal perceptions of language and depression. Since "the need for absolute truth" construct has been shown to be important in providing greater consistency in estimates of the relationships among the variables, it has been added to the model as a control variable. The results supported the model and showed that personal perceptions of language predicted self-concept clarity, which in turn predicted the participants' self-reflection and self-rumination. Self-reflection and self-rumination, in turn, predicted depression. © 2013 Copyright Taylor and Francis Group, LLC.


Guney E.,Istanbul Arel University | Aras N.,Istanbul University | Altnel I.K.,Istanbul University | Ersoy C.,Istanbul University
Computers and Operations Research | Year: 2012

Sensors are tiny electronic devices having limited battery energy and capability for sensing, data processing and communicating. They can collectively behave to provide an effective wireless network that monitors a region and transmits the collected information to gateway nodes called sinks. Most of the applications require the operation of the network for long periods of times, which makes the efficient management of the available energy resources an important concern. There are three major issues in the design of sensor networks: sensor deployment or the coverage of the sensing area, sink location, and data routing. In this work, we consider these three design problems within a unified framework and develop two mixed-integer linear programming formulations. They are difficult to solve exactly. However, it is possible to compute good feasible solutions of the sink location and routing problems easily, when the sensors are deployed and their locations in the sensor field become known. Therefore, we propose a tabu search heuristic that tries to identify the best sensor locations satisfying the coverage requirements. The objective value corresponding to each set of sensor locations is calculated by solving the sink location and routing problem. Computational tests carried out on randomly generated test instances indicate that the proposed hybrid approach is both accurate and efficient. © 2011 Elsevier Ltd. All rights reserved.


Quantitative and/or qualitative deficiency of von Willebrand factor (vWF) is associated with the most common inherited bleeding disease von Willebrand disease (vWD). vWD is a complex disease with clinical and genetic heterogeneity. Incomplete penetrance and variable expression due to genetic and environmental factors contribute to its complexity. vWD also has a complex molecular pathogenesis. Some vWF gene mutations are associated with the affected vWF biosynthesis and multimerization, whereas others are associated with increased clearance and functional impairment. Moreover, in addition to a particular mutation, type O blood may result in the more severe phenotype. The present review aimed to provide a summary of the current literature on the molecular genetics of vWD.


Idiopathic absence epilepsies (IAE), that have high prevalence particularly among children and adolescents, are complex disorders mainly caused by genetic factors. Childhood absence epilepsy and juvenile absence epilepsy are among the most common subtypes of IAEs. While the role of ion channels has been the primary focus of epilepsy research, the analysis of mutation and association in both patients with absence epilepsies and animal models revealed the involvement of GABA receptors and calcium channels, but also of novel non-ion channel proteins in inducing spike wave discharges (SWD). Functional studies on a mutated variant of these proteins also support their role in the epileptogenesis of absence seizures. Studies in animal models point to both the thalamus and cortex as the origin of SWDs: the abnormalities in the components of these circuits leading to seizure activity. This review examines the current research on mutations and susceptibility alleles determined in the genes that code for the subunits of GABA receptors (GABRG2, GABRA1, GABRB3, GABRA5, GABA (B1) and GABA (B2)), calcium channels (CACNA1A, CACNA1G, CACNA1H, CACNA1I, CACNAB4, CACNAG2 and CACNG3), and novel non-ion channel proteins, taking into account the results of functional studies on these variants. © 2011 British Epilepsy Association.


Objective: Severe neurologic deficit due to chronic ligamentum flavum hematoma (cLFH) of the lumbar spine has received only very little attention. This article presents the first case series reporting severe neurologic deficits due to cLFH. Material: Tha authors report a case series of 5 patients with cLFH in the lumbar spine seen within a period of 8 years. Five patients (68–81yrs) presented with severe neurological deficits due to cLFH and were all operated by unilateral microsurgical decompression at the according level. Results: All hematomas were localized in the lumbar region; two were at the L4-L5 level, two were at the L3-L4 level, and one was at the L2-L3 level. While two of them had partial cauda equina syndrome, three of them had unilateral radiculopathy. Preoperative symptoms regressed within weeks. Follow-up examinations up to 2 years postoperatively were unremarkable. Conclusion: cLFH is a very rare cause of severe neurologic deficit. The patients are usually in seventh to ninth decades. Microsurgical unilateral spinal canal decompression should be the treatment of choice to resolve symptoms in cLFH. The clinical, radiological and surgical features are described. This report is first case series about cLFH. © 2015, Ege University Press. All rights reserved.


Berk C.,Istanbul Arel University
International Journal of Energy Economics and Policy | Year: 2016

Brent crude and West Texas intermediate (WTI) are major indices for purchases of oil worldwide among with some others such as OPEC basket. Brent is traditionally a European index whereas WTI representing slightly sweeter and lighter crude is more applicable in USA. Until 2010, the spread between WTI and Brent hasn’t been more than few dollars. However in recent years, the spread is widening in favor of Brent and then returning to the mean. WTI which historically taken over Brent, has fallen below Brent which is now claimed to be the global oil index for the World. This is sometimes argued with the Shale production and over-supply in the U.S. and several macroeconomic events such as Libyan crisis. The aim of this paper is to analyze which of these indices is a better indicator for the energy industry. The variables from NYSE exchange traded funds namely energy select sector SPDR ETF (XLE), Teucrium WTI crude oil ETF (CRUD), and United States Brent oil ETF (BNO) for the period December 1994 and September 2014. The variables are analyzed for long-run and short-run relationships with unit root tests, vector autoregression models, and vector error correction models as well as cointegration and Granger causality tests. © 2016, Econjournals. All rights reserved.


With the increasing importance given to smart grid solutions in end-user premises, demand response (DR) strategies applied to smart households are important topics from both real time application and academic theoretic analysis perspectives, recently. In this study, a mixed-integer linear programming (MILP) framework based evaluation of such a smart household is provided. Electric vehicles (EVs) with bi-directional power flow capability via charging and V2H operating modes, energy storage systems (ESSs) with peak clipping and valley filling opportunity and a small scale distributed generation (DG) unit enabling energy sell back to grid are all considered in the evaluated smart household structure. Different case studies including also different DR strategies based on dynamic pricing and peak power limiting are conducted to evaluate the technical and economic impacts of ESS and DG units. Besides, shiftable loads such as washing machine and dishwasher are also considered in Home Energy Management (HEM) system structure for the effective operation of the household. Moreover, a further sensitivity analysis is realized in order to discuss the impact of ESS and DG sizing on daily cost of smart household operation considering further pros and cons. © 2014 Elsevier Ltd.


Kotil K.,Istanbul Arel University
Journal of Craniovertebral Junction and Spine | Year: 2012

Background: Rheumatoid arthritis (RA) can have very destructive effects, especially in the cervical spine. Bone quality is poor in these patients. The purpose of this study is to evaluate the feasibility of fusion and accuracy of fluoroscopy in cervical transpedicular fixation (CPF) in a standardized clinical protocol for RA patients. Materials and Methods: 96 pedicles of 15 patients operated between January 2000 and ay 2010 due to atlanto-axial and subaxial cervical subluxation were investigated for post-operative malposition of the transpedicular screws. Three-dimensional computed tomography was used as a useful tool in preoperative planning and in transarticular or transpedicular screw placement with the free hand technique in the cervical spine of RA patients. Fixation and reduction with fusion was performed in all of the patients, and autogrefts from iliac wing were used for fusion. Ranawat′s and Nurick scales were used to assess the results. All screws were evaluated by Kast′s criteria. Fusion or stability was evaluated on plain radiographs taken 3 weeks and 6, 12 and 60 months after the surgery. Results: Female to male ratio was 6/9. The mean age at the time of surgery was 57.4 years (range 44-72 years). Five of the patients were operated for both C1-2 and subaxial subluxation. Two of the 15 patients had only C1-2 subluxation and the remaining eight patients had only subaxial cervical subluxation. The screws were at their correct places in 84 pedicles (87.5.%) while minor breach was detected in 9 (10.9%). According to Ranawat′s criteria, seven patients remained the same, and eight patients showed improvement. Instrumentation failure, loss of reduction or non-union was not observed at the final follow-up (average 31.5 months; range 24-60 months). Conclusion: CPF provides a very strong three column stabilization and solid fusion in the osteoporotic vertebrae, but also carries a risk of vascular injury without nerve damage or in the RA patients, but the risk is low in experienced hands.

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