Solving a robust airline crew pairing problem with column generation

In this study, we solve a robust version of the airline crew pairing problem. Our concept of robustness was partially shaped during our discussions with small local airlines in Turkey which may have to add a set of extra flights into their schedule at short notice during operation. Thus, robustness in this case is related to the ability of accommodating these extra flights at the time of operation by disrupting the original plans as minimally as possible. We focus on the crew pairing aspect of robustness and prescribe that the planned crew pairings incorporate a number of predefined recovery solutions for each potential extra flight. These solutions are implemented only if necessary for recovery purposes and involve either inserting an extra flight into an existing pairing or partially swapping the flights in two existing pairings in order to cover an extra flight. The resulting mathematical programming model follows the conventional set covering formulation of the airline crew pairing problem typically solved by column generation with an additional complication. The model includes constraints that depend on the columns due to the robustness consideration and grows not only column-wise but also row-wise as new columns are generated. To solve this dicult model, we propose a row and column generation approach. This approach requires a set of modifications to the multi-label shortest path problem for pricing out new columns (pairings) and various mechanisms to handle the simultaneous increase in the number of rows and columns in the restricted master problem during column generation. We conduct computational experiments on a set of real instances compiled from a local airline in Turkey

Seed yield and quality of pepper plants grown under salt stress

The effect of salinity on seed yield and quality of pepper plants were evaluated. Plants were grown in five salt levels (electrical conductivity, EC): 1.0, 1.5, 2.0, 4.0 to 6.0 dSm-1 in glasshouse. Seed yield was assessed by seed weight/fruit, seed weight/plant and individual seed weight. Seed quality was measured by germination, mean germination time, seedling growth and germination percentages after cold (10°C, 7 days, 25°C 10 days) accelerated ageing (45°C, 48 h) and high temperature germination (35°C, 14 days) tests. Results indicate that seed yield per fruit greatly reduced from 1990 mg at control to 460 mg at 4 dSm-1 but individual seed weight did not change until 1.5 dSm-1 EC. Seed quality concerning all criteria maintained high up to 2.0 dSm-1 EC while seed germination and vigour were significantly reduced at 4.0 dSm-1 EC. Pepper plants did not yield seeds at 6 dS-1 EC. It can be concluded that pepper seed yield reduced significantly at even very low salinity (1 dSm-1), however, quality began to decline after 2.0 dSm-1 EC.Key words: Pepper, fruit yield, seed quality, salinity

The Analysis of the Levels of 4th Grade Students Conscious Usage of School Canteen

This research was conducted to determine the levels of conscious use of school canteens by the 4th grade primary school students.  For the validity and reliability, scale was applied for 231 primary school 4th grade students. Exploratory Factor Analysis (EFA) was used for construct validity according to the data obtained from this application. The Cronbach Alpha reliability coefficient of .70, which is 16 items, explains 42.14% of the variance. Using School Canteen Consciously Scale (USCCS), which consists of subdimensions such as “quality”, “responsibility” and “need”. After the pre-implementation, the scale was applied to 1071 elementary school students in 4 primary schools, 513 (48%) girls and 558 (52%) boys. As a result of the research, it was found that 4th grade primary school students did not consciously use the school canteen at the desired level and it differentiated significantly in favor of women at the level of using school canteen consciously in terms of gender of students, those studying at private schools in terms of the quality of type of school, and those who always go to school after having breakfast at home in terms of whether they go to school by having breakfast before school or not. It differs to a great extent against the students with low levels of family income in terms of quality, liability and scale according to their family income levels; according to the situation of getting money from their families, quality, responsibility, level of the needs and in terms of the total scale it differs in favor of the students who take weekly allowances

Havacılık Sektöründe Ekip Planlama Yönetimi: Bir Türk Havayolu Örneği Crew Planning Management in Aviation Industry: A Turkish Airline Case

Havayolu taşımacılığının günümüzde ortadan kalkmış olan sınırlar ve müşteri ihtiyaçlarının anında karşılanma isteği gibi nedenler dolayısıyla gün geçtikçe artması havayolu işletmelerinin ihtiyaç duyduğu uçuş personeli sayısını da arttırmaktadır. Bu sebeple bu çalışmada havacılık sektöründe ekip planlama fonksiyonunun faaliyetleri incelenmiş, ekip planlama yönetiminde dikkate alınan matematiksel kısıtlar kadar insani kısıtların da önemine vurgu yapılmak istenmiştir. Bu doğrultuda Türkiye’de faaliyet gösteren bir havayolu şirketinde üst düzey yöneticiler ve ekip planlama çalışanlarıyla odak grup görüşmeleri yapılmıştır. Ekip planlamanın iki temel fonksiyonu olan ekip eşleme (pairing) ve ekip atama (rostering) faaliyetleri yerine getirilirken dikkate alınan ve uygulanan unsurlar çalışmanın sonucunda elde edilen bulgulardır. Ekip planlama uygulamalarının bilimsel literature uygunluğu da dikkate alınmıştır. Ayrıca bu bulgulardan yola çıkarak ekip planlama faaliyetleri için 5 temel unsur ortaya konmuş olup bu unsurlar; kurallara ve zindelik seviyesine uyum, insan kaynağını hoyratça kullanmama, çalışan memnuniyetini sağlama, birim ekip maliyetlerinin düşürülmesi ve hizmet düzeyinin yüksek tutulması olarak sıralanmaktadır. Use of air transport is increasing steadily, due to the fact that today’s boundaries have been lifted and customer needs are being met instantaneously, which allows growth in the aviation industry. In this study, the activities of crew planning were examined and it was aimed to emphasize the importance of human constraints as well as the mathematical constraints considered in crew planning management. In line with this, focus group interviews were conducted with senior managers and crew planning personnel who are working in an airline company operating in Turkey. When crew pairing and rostering activites are carried out, the factors taken into account and applied are the findings obtained as a result of the study. Academic literature conformity of crew planning applications is also taken into consideration. Finally, five basic dimensions for crew planning activities have been set out from these findings; compliance with rules and personnel wellness level, not using human resourses harshly, ensuring employee satisfaction, reducing unit crew costs and keeping service level high

The effects of rivaroxaban, an oral anticoagulant, on human IVD primary cultures

Introduction: The present study aimed to investigate the potential effects of rivaroxaban, an oral anticoagulant that inhibits the effects of factor Xa, on intact intervertebral disc tissue cells and the extracellular matrix (ECM). Material and methods: Rivaroxaban was applied to primary human cell cultures prepared from tissues of the intervertebral disc. Comparative molecular analyses were performed on non-drug-treated control group samples. Descriptive statistics were presented as the mean +/- standard deviation. An analysis of variance test was performed to determine whether there were significant differences in the mean across the groups. When differences across groups were observed, Tukey's honestly significant difference post-hoc test was used for multiple pairwise comparisons. The significance of the obtained data was determined statistically. The alpha significance value was < 0.05. Results: The cells in the control group and in the rivaroxaban-treated group were viable, healthy, and proliferated (p < 0.05). However, the expression levels of the chondroadherin gene (CHAD), cartilage oligo matrix protein (COMP), matrix metalloproteinase (MMP)-13, and MMP-19 genes were changed (p < 0.05). Conclusions: Although rivaroxaban does not suppress cell proliferation due to morphological, biological, and biochemical changes in the intervertebral disc tissue, it may change the expression of genes that are related to ECM maintenance

The association between different molecular weights of hyaluronic acid and CHAD, HIF-1 alpha, COL2A1 expression in chondrocyte cultures

The aim of the present study was to investigate the effects of three different formulations of hyaluronic acid (HA): Low molecular weight (MW) Sinovial One((R)), medium MW Viscoplus((R)) and high MW Durolane((R)), on chondrocyte proliferation and collagen type II (COL2A1), hypoxia-inducible factor 1 alpha (HIF-1 alpha) and chondroadherin (CHAD) expression in primary chondrocyte cultures. Standard primary chondrocyte cultures were established from osteochondral tissues surgically obtained from 6 patients with gonarthrosis. Cell morphology was evaluated using an inverted light microscope; cell proliferation was determined with a MTT assay and confirmed with acridine orange/propidium iodide staining. Levels of CHAD, COL2A1 and HIF-1 alpha expression were assessed using specific TaqMan gene expression assays. The results demonstrated the positive effect of HA treatment on cell proliferation, which was independent from the MW. COL2A1 expression increased in the medium and high MW HA treated groups. It was observed that HIF-1 alpha expression increased in the high MW treated group alone. CHAD expression increased only in the medium MW HA treated group. Evaluation of gene expression revealed that levels of expression increased as the duration of HA application increased, in the medium and high MW HA treated groups. In terms of increased viability and proliferation, a longer duration of HA application was more effective. Taken together, it may be concluded that the administration of medium and high MW HA may be a successful way of treating diseases affecting chondrocytes in a clinical setting