13 sonuçlar
Arama Sonuçları
Listeleniyor 1 - 10 / 13
Yayın A DBN based reactive maintenance model for a complex system in thermal power plants(Elsevier Sci Ltd, 2019-10) Özgür Ünlüakın, Demet; Türkali, Busenur; Karacaörenli, Ayşe; Aksezer, Sezgin ÇağlarThermal power plants consist of several complex systems having many interacting hidden components. Any unexpected failure may lead to prolonged downtime and serious lost profits. Therefore, implementing an effective maintenance policy is crucial for this sector. Although preventive maintenance has become a more popular strategy, it does not completely prevent the need for corrective maintenance. Our aim in this study is to tackle the corrective maintenance implementation problem of a multi-component partially observable dynamic system based on a regenerative air heater in a thermal power plant. We propose eight methods having different efficiency measures with respect to time, effect and probability criteria to minimize the total number of maintenance activities in a given planning horizon. Performances of these methods are evaluated under corrective maintenance strategy using dynamic Bayesian networks. The results show that fault effect methods with best working state probability measure perform better than the others considering both the total amount of maintenance activities and also the solution time. We also point out how the methods can be implemented in real-life and how the results can be used for requirements planning. Furthermore, the proposed methods can be used for the corrective maintenance of all systems having hidden interacting components.Yayın Neuropsychiatric outcomes and caregiver distress in primary progressive aphasia(Wiley, 2023-01) Seçkin, Mustafa; Yıldırım, Elif; Demir, İlayda; Orhun, Ömer; Bülbül, Ezgi; Velioğlu, H. Aziz; Öget, Öktem; Yeşilot, Nilüfer; Çoban, Oğuzhan; Gürvit, HakanBackground: In this study, we aimed to outline the neuropsychiatric consequences of primary progressive aphasia (PPA) and to understand how neuropsychiatric symptomatology affects distress in caregivers. Methods: The Neuropsychiatric Inventory (NPI) including the distress index (NPI-Distress) was used. Additional information about the caregiver burden was obtained using Zarit Burden Interview (ZBI). NPI, NPI-Distress, and ZBI data from 17 patients with a clinical diagnosis of PPA were compared with 10 stroke aphasia patients. Neuropsychiatric symptomatology was investigated based on three clusters; Mood, Frontal/Comportmental, and Psychotic/Disruptive. Additionally, the Activities of Daily Living Questionnaire (ADLQ) was used to outline the functional impairment. Twelve healthy controls were included to compare the neurocognitive test scores with PPA and stroke aphasia groups. Results: A greater number of neuropsychiatric symptoms were observed in the PPA group compared to the stroke aphasia group. The number of symptoms in Mood, and Frontal/Comportmental clusters were greater than the number of symptoms in Psychotic/Disruptive clusters in the PPA group, whereas no significant relationship between the number of symptoms and symptom clusters was found in the stroke aphasia group. In the PPA group, a strong correlation was found between the NPI-Frequency × Severity scores and the NPI-Distress scores. Moreover, the NPI-Distress scores in the PPA group strongly correlated with the ZBI scores. Scores for anxiety, irritability/lability, and apathy had a stronger correlation with the NPI-Distress scores compared to the other NPI symptoms. The Communication subscale was the most impaired domain in the PPA group. Travel, and Employment and Recreation subscales showed greater functional impairment in the stroke aphasia group compared to the PPA group. Conclusions: Neuropsychiatric symptoms in PPA in our study were more frequent than previously reported. Furthermore, the distress index of the NPI was not only correlated with the severity of the neuropsychiatric symptoms but also reflected the overall burden on the caregivers in the PPA group.Yayın Dating fossil root cast (Black Sea coast, Turkey) using thermoluminescence: Implications for windblown drift of shelf carbonates during MIS 2(Elsevier Ltd., 2016-05-16) Polymeris, George S.; Kitis, George; Güneç Kıyak, Nafiye; Theodosoglou, Eleni; Tsirliganis, Nestor C.; Ertek, Topçu Ahmet; Erginal, Ahmet EvrenRhizoliths are mostly sub-aerially exposed root prints which appear through removal of the rock units that cap them. A horizontal-lying residual of a rhizolith, consisting purely of soft inner core material of white color was recovered 10 km west of Şile, Istanbul, in northwest Turkey within laminated oolithic massive aeolianite. The inner part, consisting purely of calcium carbonate, was dated by applying thermoluminescence, while for the outer shelves optically stimulated luminescence of quartz was used for age assessment. The age of the CaCO3 infill occupying the original place of the decayed plant roots was found to be 26.8 (±5.0) ka, corresponding to MIS 2. When compared with the ages of the middle (105.2 ± 15.6 ka) and outer (127 ± 9 ka) layers, corresponding to the later stage of MIS 5e or early stage of MIS 5d, the inner core coincides with the last glacial period when the sea-level was lower than the present, promoting transportation of ooids by offshore winds in conjunction with the exposed shelf carbonates. Based on the results yielded, rhizolith is much younger than the host rock aeolianite and witnesses to last glacial sea level lowstand when removal of shelf carbonates by offshore winds was promoted from the exposed shallow shelf plain. The results provide strong evidence that rhizoliths may not be coeval with the aeolianites within which they are embedded.Yayın Failure analysis and warranty modeling of used cars(Pergamon-Elsevier Science Ltd, 2011-09) Aksezer, Sezgin ÇağlarReliability is an important aspect of product perception and manufacturers are compelled to take corrective actions on the items failing within the warranty period. Automotive manufacturers are being exposed to significant operating costs as a result of warranty claims affecting an individual unit or mandatory (sometimes voluntary) recalls affecting a batch. Underlying principles of warranty modeling are built by considering both subjective issues and objective constraints such as competition, quality, and performance under the goal of achieving desired levels of reliability and cost in a balanced manner. This paper reviews the warranty cost models with an emphasis on the failure analysis of used vehicles. Expected warranty costs are calculated by taking into account the age, usage, and maintenance data of the product in question. Failure intensities and characteristics are identified in order to propose a policy that highlights the trade-off between the cost and the warranty length. A case study on a popular brand's initiation of factory certified pre-owned program for the local automobile market of Turkey is presented in detail. (C) 2011 Elsevier Ltd. All rights reserved.Yayın Reliability, validity, and factorial structure of the Turkish version of the Empathy Quotient (Turkish EQ)(Taylor & Francis Ltd, 2018-07-03) Köse, Samet; Çam Çelikel, Feryal; Kulacaoğlu, Filiz; Akın, Ercan; Yalçın, Mehmet; Ceylan, VedatOBJECTIVES: Empathy is an essential ability that allows us to tune into how others are feeling or thinking. Empathy makes it possible to resonate with others' positive and negative feelings alike so that we can thus feel happy when we vicariously share the joy of others and we can share the experience of suffering when we empathize with someone in pain. Empathy training not only promotes prosocial behaviour, but also augments positive affect and resilience, which in turn fosters better coping with stressful situations. The Empathy Quotient (EQ) is a self-report questionnaire that was developed to measure the cognitive, affective, and behavioural aspects of empathy. Here, we aimed to examine the validity, reliability, and factor structure of the EQ in a Turkish sample. METHODS: Participants were 436 mostly college students and civil servants (195 female, 241 male). Sociodemographic information, the Turkish version of the EQ, Marlowe-Crowne Social Desirability Scale (MC-SDS) 33-item full version and MC-SDS 13-item shorter versions were administered. All statistical analyses were performed by using SPSS version 23 for Windows. RESULT: EQ scores were significantly higher in female participants ((X) over bar (Female)=46.45, SDFemale=0.62) compared to the male participants ((X) over bar (Male)=43.68, SD (Male)=0.56). The Cronbach's alpha coefficient for the scale was 0.76, Guttman's split-half reliability coefficient was 0.61, and test-retest reliability coefficient was 0.95. A positive and statistically significant correlation was found between the Turkish EQ and MC-SDS Full version (r=0.299, p<.01) and short form of MC-SDS (r=0.273, p<.01). A three-factor solution that accounted for 25.28% of the variance observed. CONCLUSIONS: The Turkish version of the EQ has satisfactory validity, good internal and test-retest reliability with a robust factorial structure to use in a clinical population in Turkey. Moreover, as predicted, women scores were statistically significantly higher on the EQ than men. This result was consistent with a series of earlier studies reporting gender differences (female superiority) on questionnaires that measure empathy. A better knowledge of empathy will have important implications for the examination and understanding of certain neurological and psychiatric disorders, including autism, narcissistic and antisocial personality disorders, and may also provide important clues about the relevant brain circuitry underlying empathy.Yayın Performance analysis of an aggregation and disaggregation solution procedure to obtain a maintenance plan for a partially observable multi-component system(Elsevier Sci Ltd, 2017-11) Özgür Ünlüakın, Demet; Bilgiç, TanerWe analyze the performance of an aggregation and disaggregation procedure in giving the optimal maintenance decisions for a multi-component system under partial observations in a finite horizon. The components deteriorate in time and their states are hidden to the decision maker. Nevertheless, it is possible to observe signals about the system status and to replace components in each period. The aim is to find a cost effective replacement plan for the components in a given time horizon. The problem is formulated as a partially observable Markov decision process (POMDP). We aggregate states and actions in order to reduce the problem space and obtain an optimal aggregate policy which we disaggregate by simulating it using dynamic Bayesian networks (DBN). The procedure is statistically compared to an approximate POMDP solver that uses the full state space information. Cases where aggregation performs relatively better are isolated and it is shown that k-out-of-n systems belong to this class.Yayın Software defect prediction using Bayesian networks(Springer, 2014-02) Okutan, Ahmet; Yıldız, Olcay TanerThere are lots of different software metrics discovered and used for defect prediction in the literature. Instead of dealing with so many metrics, it would be practical and easy if we could determine the set of metrics that are most important and focus on them more to predict defectiveness. We use Bayesian networks to determine the probabilistic influential relationships among software metrics and defect proneness. In addition to the metrics used in Promise data repository, we define two more metrics, i.e. NOD for the number of developers and LOCQ for the source code quality. We extract these metrics by inspecting the source code repositories of the selected Promise data repository data sets. At the end of our modeling, we learn the marginal defect proneness probability of the whole software system, the set of most effective metrics, and the influential relationships among metrics and defectiveness. Our experiments on nine open source Promise data repository data sets show that response for class (RFC), lines of code (LOC), and lack of coding quality (LOCQ) are the most effective metrics whereas coupling between objects (CBO), weighted method per class (WMC), and lack of cohesion of methods (LCOM) are less effective metrics on defect proneness. Furthermore, number of children (NOC) and depth of inheritance tree (DIT) have very limited effect and are untrustworthy. On the other hand, based on the experiments on Poi, Tomcat, and Xalan data sets, we observe that there is a positive correlation between the number of developers (NOD) and the level of defectiveness. However, further investigation involving a greater number of projects is needed to confirm our findings.Yayın A novel kernel to predict software defectiveness(Elsevier Science Inc, 2016-09) Okutan, Ahmet; Yıldız, Olcay TanerAlthough the software defect prediction problem has been researched for a long time, the results achieved are not so bright. In this paper, we propose to use novel kernels for defect prediction that are based on the plagiarized source code, software clones and textual similarity. We generate precomputed kernel matrices and compare their performance on different data sets to model the relationship between source code similarity and defectiveness. Each value in a kernel matrix shows how much parallelism exists between the corresponding files of a software system chosen. Our experiments on 10 real world datasets indicate that support vector machines (SVM) with a precomputed kernel matrix performs better than the SVM with the usual linear kernel in terms of F-measure. Similarly, when used with a precomputed kernel, the k-nearest neighbor classifier (KNN) achieves comparable performance with respect to KNN classifier. The results from this preliminary study indicate that source code similarity can be used to predict defect proneness.Yayın Treatment of preschool children with obsessive compulsive disorder(SAGE Publications Ltd, 2023-04) İnci İzmir, Sevim Berrin; Ercan, Eyüp SabriThe aim was to examine the clinical features of Obsessive-Compulsive Disorder (OCD) in preschool and the effectiveness of aripiprazole with a standardized Cognitive-Behavioral Family Therapy (CBFT) in the treatment of preschoolers with OCD. Twelve preschool children, 36–72 months of age were diagnosed with OCD according to the Diagnostic and Statistical Manual of Mental Disorders, the Fifth Edition criteria by a fellowship-trained child and adolescent psychiatrist. They were evaluated with Kiddie Schedule for Affective Disorders and Schizophrenia for School-Age Children Present and Lifetime version and Childhood Yale-Brown Obsessive Compulsive Scale (CY-BOCS) at baseline, at the end of the 12th and 24th weeks of treatment. The baseline mean of total CY-BOCS score decreased from 33.67 to 13.83 at the 12th week and 5.58 at the end of the 24th week of treatment. Also, 66.7% of them had at least one psychiatric comorbidity. Overall, this study revealed the effect of aripiprazole with CBFT in preschool-aged children with OCD. Also, the presence of comorbidity that is seen frequently in preschoolers with OCD may complicate the treatment. Therefore, there is a need to increase awareness of OCD and its comorbidities in preschoolers to supply treatment at an early age.Yayın Elevated sTREM2 and NFL levels in patients with sepsis associated encephalopathy(Taylor & Francis, 2023-03-04) Orhun, Günseli; Esen, Figen; Yılmaz, Vuslat; Ulusoy, Canan; Şanlı, Elif; Yıldırım, Elif; Gürvit, İbrahim Hakan; Ergin Özcan, Perihan; Sencer, Serra; Bebek, Nerses; Tüzün, ErdemPurpose: Sepsis-associated encephalopathy (SAE) is a common manifestation of sepsis that may lead to cognitive decline. Our aim was to investigate whether the neurofilament light chain (NFL) and soluble triggering receptor expressed on myeloid cells 2 (sTREM2) could be utilized as prognostic biomarkers in SAE. Materials and methods: In this prospective observational study, baseline serum levels of sTREM2 and cerebrospinal fluid (CSF) levels of sTREM2 and NFL were measured by ELISA in 11 SAE patients and controls. Patients underwent daily neurological examination. Brain magnetic resonance imaging (MRI) and standard electroencephalography (EEG) were performed. Cognitive dysfunction was longitudinally assessed after discharge in 4 SAE patients using the Mini-Mental State Examination (MMSE) and Addenbrooke’s Cognitive Examination-Revised (ACE-R) tests. Results: SAE patients showed higher CSF sTREM2 and NFL levels than controls. sTREM2 and NFL levels were not correlated with the severity measures of sepsis. Three months after discharge, 2 SAE patients displayed ACE-R scores congruent with mild cognitive impairment (MCI), persisting in one patient 12 months after discharge. SAE patients with MCI showed higher CSF NFL levels, bacteremia, and abnormal brain MRI. Patients with increased serum/CSF sTREM2 levels showed trends towards displaying poorer attention/orientation and visuo-spatial skills. Conclusions: sTREM2 and NFL levels may serve as a prognostic biomarker for cognitive decline in SAE. These results lend further support for the involvement of glial activation and neuroaxonal degeneration in the physiopathology of SAE.
