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Aintshop Production Line Optimization Using Response Surface Methodology
(2007) Dengiz, Berna; Belgin, Onder; 0000-0001-6702-2608; K-1080-2019
This paper deals with the problem of determining the optimum number of workstations to be used in parallel and workers at some stations using simulation optimization approach in a paint shop line of an automotive factory in Ankara, Turkey. In the optimization stage of the study Response Surface Methodology (RSM) is used to find the optimum levels of considered factors. Simulation model and optimization stage integration is used both to analyse the performance of the current paint shop line and determine the optimum working conditions, respectively, with reduced cost, time and effort.
A hybrid ant colony optimization approach for the design of reliable networks
(2007) Dengiz, B.; Altiparmak, F.; Belgin, O.; 0000-0003-1730-4214; 0000-0001-6702-2608; AAF-7020-2021; K-1080-2019
This paper presents a new solution approach, which is a hybridization of ant colony optimization (ACO) and simulated annealing (SA), called (h_ACO) to design of communication networks. The design problem is to find the optimal network topology where total cost is minimum and all-terminal reliability is not less-than a given level of reliability. The effectiveness of the h_ACO is investigated comparing its results with those obtained by SA and ACO, which are basic forms of the h_ACO, and also GAs given in the literature for the design problem. Computational results show that the h_ACO is an effective heuristic approach to design of reliable networks.
A Hybrid Simulated Annealing For A Multi-Objective Stochastic Assembly Line Balancing Problem
(2008) Cakir, Burcin; Dengiz, Berna; Altiparmak, Fulya; Xia, GP; Deng, XQ; 0000-0003-1730-4214; AAF-7020-2021
Asssembly line balancing is the problem of assigning tasks to the workstations, while optimizing one or more objectives without violating restrictions imposed on the line. In practice, task times may be random due to the worker fatigue, low skill levels, job dissatisfaction, poorly maintained equipment, defects in raw material, etc. When stochastic task times are taken consideration in assembly lines, balancing procedure is more complex due to the probability of incompleteness of stations times in a given cycle time. In this study, a multi-objective simulated annealing algorithm (m_SAA) is proposed for single-model, stochastic assembly line balancing problem with the aim of minimizing of smoothness index and total design cost. To obtain Pareto-optimal solutions, m_SAA implements tabu list and a multinomial probability mass function approach. The effectiveness of the proposed m_SAA is comparatively investigated using another SA using weight-sum approach on the test problems. Computational results show that m_SAA with multinomial probability mass function approach is more effective than SA with weight-sum approach in terms of quality of Pareto-optimal solutions.
An International Facility Design Project
(2008) Lacksonen, Thomas; Dengiz, Berna
This paper describes an international facilities design project for Manufacturing and Industrial Engineering students. American and Turkish engineering students collaborated to create and implement the re-design of a Turkish wheelchair manufacturing facility. The company needed engineering assistance to improve the efficiency and increase the capacity of their existing factory. Turkish Industrial Engineering students went on-site to collect data and draw the existing facility layout. American Manufacturing Engineering students analyzed the data and developed new layout designs. Four American students traveled to Turkey between semesters to implement the initial phases of their design. In the second semester, the Turkish students simulated the new layout to see the performance improvements, completing their project. Student learning outcomes were positive for both groups of students. The paper explains critical steps in identifying projects and partners. Lessons are shown about successes and shortcomings in planning, operating, and communicating with design teams across cultures.
A General Neural Network Model for Estimating Telecommunications Network Reliability
(2009) Altiparmak, Fulya; Dengiz, Berna; Smith, Alice E.; 0000-0003-1730-4214; 0000-0001-8808-0663; AAF-7020-2021; AAK-2318-2021
This paper puts forth a new encoding method for using neural network models to estimate the reliability of telecommunications networks with identical link reliabilities. Neural estimation is computationally speedy, and can be used during network design optimization by an iterative algorithm such as tabu search, or simulated annealing. Two significant drawbacks of previous approaches to using neural networks to model system reliability are the long vector length of the inputs required to represent the network link architecture, and the specificity of the neural network model to a certain system size. Our encoding method overcomes both of these drawbacks with a compact, general set of inputs that adequately describe the likely network reliability. We computationally demonstrate both the precision of the neural network estimate of reliability, and the ability of the neural network model to generalize to a variety of network sizes, including application to three actual large scale communications networks.
A Local Search Heuristic with Self-tuning Parameter for Permutation Flow-Shop Scheduling Problem
(2009) Dengiz, Berna; Alabas-Uslu, Cigdem; Sabuncuoglu, Ihsan
In this paper, a new local search metaheuristic is proposed for the permutation flow-shop scheduling problem. In general, metaheuristics are widely used to solve this problem due to its NP-completeness. Although these heuristics are quite effective to solve the problem, they suffer from the need to optimize parameters. The proposed heuristic, named STLS, has a single self-tuning parameter which is calculated and updated dynamically based on both the response surface information of the problem field and the performance measure of the method throughout the search process. Especially, application simplicity of the algorithm is attractive for the users. Results of the experimental study show that STLS generates high quality solutions and outperforms the basic tabu search, simulated annealing, and record-to-record travel algorithms which are well-known local search based metaheuristics.
A cross entropy approach to design of reliable networks
(2009) Dengiz, Berna; Altiparmak, Fulya; 0000-0003-1730-4214; AAF-7020-2021
One of the most important parameters determining the performance of communication networks is network reliability. The network reliability strongly depends on not only topological layout of the communication networks but also reliability and availability of the communication facilities. The selection of optimal network topology is an NP-hard problem so that computation time of enumeration-based methods grows exponentially with network size. This paper presents a new solution approach based on cross-entropy method, called NCE, to design of communication networks. The design problem is to find a network topology with minimum cost such that all-terminal reliability is not less than a given level of reliability. To investigate the effectiveness of the proposed NCE, comparisons with other heuristic approaches given in the literature for the design problem are carried out in a three-stage experimental study. Computational results show that NCE is an effective heuristic approach to design of reliable networks. (C) 2008 Elsevier B.V. All rights reserved.
A Tabu Search Algorithm for the Training of Neural Networks
(2009) Dengiz, B.; Alabas-Uslu, C.; Dengiz, O.
The most widely used training algorithm of neural networks (NNs) is back propagation ( BP), a gradient-based technique that requires significant computational effort. Metaheuristic search techniques such as genetic algorithms, tabu search (TS) and simulated annealing have been recently used to cope with major shortcomings of BP such as the tendency to converge to a local optimal and a slow convergence rate. In this paper, an efficient TS algorithm employing different strategies to provide a balance between intensification and diversification is proposed for the training of NNs. The proposed algorithm is compared with other metaheuristic techniques found in literature using published test problems, and found to outperform them in the majority of the test cases.
A Self-adaptive Local Search Algorithm for the Classical Vehicle Routing Problem
(2011) Alabas-Uslu, Cigdem; Dengiz, Berna
The purpose of this study is introduction of a local search heuristic free from parameter tuning to solve classical vehicle routing problem (VRP). The VRP can be described as the problem of designing optimal delivery of routes from one depot to a number of customers under the limitations of side constraints to minimize the total traveling cost. The importance of this problem comes from practical as well as theoretical point of view. The proposed heuristic, self-adaptive local search (SALS), has one generic parameter which is learnt throughout the search process. Computational experiments confirm that SALS gives high qualified solutions to the VRP and ensures at least an average performance, in terms of efficiency and effectiveness, on the problem when compared with the recent and sophisticated approaches from the literature. The most important advantage of the proposed heuristic is the application convenience for the end-users. SALS also is flexible that can be easily applied to variations of VRP. (C) 2011 Elsevier Ltd. All rights reserved.
The relationship between coronary collateral artery development and inflammatory markers
(2014) Oguz, Didem; Atmaca, Yusuf; Ozdol, Cagdas; Ozdemir, Ayhan Ongun; Kaya, Cansin Tulunay; Erol, Cetin
Objective: This study aims to show the effect of myeloperoxidase (MPO), hsCRP, TNF-alpha values and leukocyte count on the development of coronary collateral arteries in patients with severely diseased coronary arteries. Methods: Current study is an observational cross-sectional study. In the study, 295 patients who had functional obstruction or total coronary occlusion at least 1 month on their angiograms were included. We divided the study population into two groups according to their collateral grade as good collateral (Group 1) (169 patients) and poor collateral (Group 2) (126 patients). Multiple logistic regression analysis was used for independent variables associated with the coronary collateral grade. Results: History of stable angina pectoris was statistically more prevalent in good collateral group (61.5% and 48.4%, p=0.025). Furthermore, MPO activation was higher in good collateral group and the difference was statistically significant (3.7 U/mL and 3.0 U/mL p=0.001). In multiple logistic regression analysis, stable angina pectoris [OR 1.7, 95% CI (1.05-2.8), p=0.03] and high MPO levels [OR 2.7, 95% CI (1.7-4.3), p<0.001] were found to be independent predictors of good collateral development. Conclusion: We think that proinflammatory enzymes and cytokines released from these cells rather than inflammatory cells themselves may play an important role on the collateral development.
THE COST-EFFECTIVENESS ANA LYSIS FOR HIV TREATMENT ALTERNATIVES IN TURKEY
(2014) Kockaya, G.; Yenilmez, F.B.; Zengin, Elbir T.; Dalgic, C.; Malhan, S.; Cerci, P.; Oksuz, E.; Tayfun, K.; Unal, S.; 27202504
Effect of Topical Tetracycline on Seroma Formation in the Lichtenstein Technique: A Prospective Randomized Study
(2014) Turk, Emin; Karagulle, Erdal; Coban, Gokcen; Yildirim, Erkan; Moray, Gokhan
We sought to investigate whether application of topical tetracycline has a limiting effect on seroma formation in patients undergoing hernia repair using a polypropylene mesh. This study was conducted in 96 patients undergoing an elective groin hernia repair. Patients were randomized and divided into 2 groups. After the graft was placed, and before external oblique muscle aponeurosis was closed, 5 mL tetracycline was administered on the graft in the tetracycline group (tetra group, n = 50), and 5 mL isotonic saline was administered in the control group (n = 46) without putting in a drain. Seroma checks via surface ultrasonography were done. Seroma amounts measured on the first day were significantly higher in the tetra group (P = 0.04). There were no significant differences regarding seroma measurements on the seventh day or in the first and second months. Topical tetracycline application has no limiting effect on seroma formation after a groin hernia operation.
Interrelation of RDW and coronary flow reserve in patient with idiopathic dilated cardiomyopathy
(2014) Ozulku, Mehmet; Caliskan, Mustafa; Gullu, Hakan; Erdogan, Dogan; Caliskan, Zuhal; Muderrisoglu, Haldun
Objective: Idiopathic dilated cardiomyopathy (IDC) impairs and reduces coronary flow reserve (CFR). High level of red cell distribution width (RDW) is an independent risk factor for cardiovascular diseases. Therefore, in this observational case-control study we have aimed to determine whether RDW level is associated with CFR impairment in patients with IDC. Methods: We examined 36 patients with IDC and 35 healthy subjects formed as a control group. In addition to this, patients with IDC were divided into two subgroups according to their CFR levels [normal CFR group (CFR value >= 2) and lower CFR group (CFR value<2)]. Control and patients groups were compared using the student t-test for multiple comparisons. The subgroups were compared using the Mann-Whitney U test for continuous variables and chi-square for categorical variables. The Pearson's and Spearman correlation analysis was used to test the possible associations between CFR and the study variables as appropriate. The receiver-operating characteristic (ROC) curve was determined to evaluate the predictive performance of RDW to detect low CFR. Results: There were no significantly differences between the lower and higher CFR groups' clinical data, baseline hemodynamic, medication and biochemical data except RDW and high-sensitivity C-reactive protein (hsCRP) levels. We found that RDW level was a good predictor of low CFR at the receiver-operating characteristic curve. The area under the curve (AUC) was 73% (95% confidence interval between 0.56-0.90 is 95%, p:0.018) After adjusting potential confounders include age, body-mass index, blood pressure, lipid and glucose, RDW independently associated with CFR level (Beta:-0.374; p=0.015) and hsCRP value (Beta:-0.520; p=0.001) were the independent predictors of lower CFR. Conclusion: Results showed that there was an independent correlation between RDW level and CFR level in patients with IDC.
Surgical Interventions for Late Complications of Arteriovenous Fistulas
(2014) Belli, Sedat; Yabanoglu, Hakan; Aydogan, Cem; Parlakgumus, Alper; Yildirim, Sedat; Haberal, Mehmet; 25058786
Our aim was to determine the most effective surgical treatment for arteriovenous fistula (AVF) complications after all other methods of salvage have failed. We evaluated 110 patients for 139 complications that occurred after the initial AVF placement and for whom surgical intervention was the last hope for retaining fistula access. Vascular steal syndrome and venous hypertension were the most common complications seen in our patients. The anastomoses of 17 of the vascular steal syndrome cases were narrowed either by stitches or by a polytetrafluoroethylene graft. The second most performed revision surgery was excision of the aneurysm and repair with primary suturing, followed by excision of the aneurysm and interposition grafting. Successful surgical outcomes were achieved in 111 of 139 procedures after revision surgery without constructing a new AVF. AVF salvage surgery is of paramount importance in order to increase the patency rate, which prolongs survival and increases the patient's quality of life.
Timing studies of X Persei and the discovery of its transient quasi-periodic oscillation feature
(2014) Acuner, Z.; Inam, S.C.; Sahiner, S.; Serim, M.M.; Baykal, A.; Swank, J.
We present a timing analysis of X Persei (X Per) using observations made between 1998 and 2010 with the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE) and with the INTEGRAL Soft Gamma-Ray Imager (ISGRI). All pulse arrival times obtained from the RXTE-PCA observations are phase-connected and a timing solution is obtained using these arrival times. We update the long-term pulse frequency history of the source by measuring its pulse frequencies using RXTE-PCA and ISGRI data. From the RXTE-PCA data, the relation between the frequency derivative and X-ray flux suggests accretion via the companion's stellar wind. However, the detection of a transient quasi-periodic oscillation feature, peaking at similar to 0.2 Hz, suggests the existence of an accretion disc. We find that double-break models fit the average power spectra well, which suggests that the source has at least two different accretion flow components dominating the overall flow. From the power spectrum of frequency derivatives, we measure a power-law index of similar to-1, which implies that, on short time-scales, disc accretion dominates over noise, while on time-scales longer than the viscous time-scales, the noise dominates. From pulse profiles, we find a correlation between the pulse fraction and the count rate of the source.
Skin Care in Organ Transplant Patients Europe Meeting Report from Annual Meeting, Leiden, The Netherlands, 15-18 May 2014
(2014) Hofbauer, Guenther F.L.; Seckin, Deniz; Gjersvik, Petter; Bavinck, Jan Nico Bouwes; 25381765
A rare cause of circulatory shock
(2014) Altin, Cihan; İzmir, Arzu; Osmanoglu, Sevda; Gezmis, Esin; Sagduyu, Afsin; 25233504
The investigation of the frequency of menstrual irregularity and hypertrichosis due to isotretinoine usage in female patients
(2014) Demirci, Gulsen Tukenmez; Mertsoylu, Eda; Altunay, Ilknur Kivanc; Atis, Guldehan; Kucukunal, Asli
Background and Design: To investigate the rate of hypertrichosis and menstrual irregularity in female patients receiving isotretinoin treatment. Materials and Methods: In our study, we included female acne patients who were started isotretinoin treatment and who had no history of menstrual irregularities and hypertrichosis within 6 months prior to isotretinoin use and had no any systemic disease and did not take any medicine except isotretinoin. They were started 0.5-0.8 mg/kg isotretinoin treatment and followed by routine laboratory tests until the total cumulative dose of isotretinoin therapy was completed. They were controlled if they had menstrual irregularity or hypertrichosis after starting isotretinoin. Results: Fifty-six patients were included in the study. The mean age of the patients was 24.91 +/- 5.72 years. The mean treatment period was 6.28 +/- 0.56 months. We found that 16 of 56 (28.8%) patients had menstrual irregularity. Six patients had prolonged interval (delay), -4, hypomenorrhea, -2, hypomenorrhea and prolonged interval, -2, metrorrhagia, - 1, shortened interval, and 1 patient had missed period. Of the 56 patients, 11 patients (23.8%) had hypertrichosis. 5 (45.45%) patients with hypertricchosis were found to have also menstrual irregularity while 5(31.25%) of 16 menstrual irregularity patients were found to have hypertrichosis. Nine patients reported having a stressful life event. One of them were both had menstrual irregularity and hypertrichosis, 2 of them had only hypertrichosis, 2 of them had only menstrual irregularity and 4 of them had no more finding. Conclusion: Our study showed that the complaints of menstrual irregularity and hypertrichosis may develop during isotretinoin therapy. Based on this result, we assume that further laboratory tests and controlled studies investigating the effects of isotretinoin on hormones are needed.
Delayed failure of rectovaginal fistula embolization with Amplatzer vascular plug 2
(2014) Kilickesmez, Ozgur; Andic, Cagatay; Oguzkurt, Levent; 25323835
Thyroid volume in patients with glucose metabolism disorders
(2014) Duran, Ayse Ocak; Anil, Cuneyd; Gursoy, Alptekin; Nar, Asli; Inanc, Mevlude; Bozkurt, Oktay; Tutuncu, Neslihan Bascil; 25465604
Objective: Thyroid volume and the prevalence of thyroid nodules are higher in patients with insulin resistance. A relationship between thyroid volume and glucose metabolism disorders (GMD) has not as yet been clarified. The present retrospective study aimed to investigate the association between GMD and thyroid volume. Subjects and methods: We investigated the data of 2,630 patients who were evaluated for thyroid biopsy in our hospital. The study population included 602 patients with GMD, 554 patients with diabetes mellitus (DM) and 1,474 patients with normal glucose metabolism as a control group. We obtained the levels of serum thyroid stimulating hormone (TSH) and the thyroid volumes of those patients retrospectively. Results: The median ages for the control group, GMD group and DM group were 55 (15-91) years, 60 (27-97) years, and 65 (27-91) years respectively and there was a statistically significant difference between the groups with regard to age and gender (p < 0.001). Levels of TSH were similar in all groups. The median total thyroid volumes for patients with DM and GMD were significantly higher than that of the control group [22.5 (3-202) mL, 20.2 (4-190) mL, and 19.2 (3-168) mL respectively, p <= 0.001 for all parameters]. Also the median total thyroid volume for patients with DM was significantly higher than that of the GMD group (p < 0.001). According to the correlation analysis, thyroid volume was significantly correlated with age (r = 0.92, p < 0.001) and TSH (r = 0.435, p < 0.001). Age, gender, TSH levels, GMD and DM diagnosis were independently correlated with thyroid volume. Conclusion: The thyroid gland is one of the target tissues of metabolic disorders. We reported a positive correlation between GMD/type 2 DM and thyroid volume. Further controlled, prospective, randomized studies on this subject are required to gain more information.