Search results for: Onur Doğan

Authors: Hans Frenk, Sonya Javadi, Semih Onur Sezer

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We consider the so-called end of life inventory problem for the supplier of a product in its final phase of the service life cycle. This phase starts when the production of the items stops and continues until the warranty of the last sold item expires. At the beginning of this phase, the supplier places a final order for spare parts to serve customers coming with defective items. At any time during the final phase, the supplier may also decide to switch to an alternative and more cost-effective policy. This alternative policy may be in the form of replacing a defective item with a substitutable product or offering discounts / rebates on new generation products. In this setup, the objective is to find a final order quantity and also a switching time which will minimize the total expected discounted cost. We study this problem under a general cost structure in a continuous-time framework where arrivals of defective items are given by a non-homogeneous Poisson process. We consider four formulations which differ by the nature of the switching time. These formulations are studied in detail and properties of the objective function are derived in each case. Using these properties, we provide exact algorithms for efficient numerical implementations. Numerical examples are provided illustrating the application of these algorithms. In these examples, we also compare the costs associated with these different formulations.

Keywords: End-of-life inventory control, martingales, optimization, service parts

Procedia PDF Downloads 305

Authors: Onur Karaman, Ceren Karaman

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In this study, the adsorption of Methylene Blue (MB), a cationic dye, onto Orange Peel Derived Activated Carbon (OPAC) and chitosan(OPAC/Chitosan composite) composite (a low-cost absorbent) was carried out using a batch system. The composite was characterised using IR spectra, XRD, FESEM and Pore size studies. The effects of initial pH, adsorbent dose rate and initial dye concentration on the initial adsorption rate, capacity and dye removal efficiency were investigated. The Langmuir and Freundlich adsorption models were used to define the adsorption equilibrium of dye-adsorbent system mathematically and it was decided that the Langmuir model was more suitable to describe the adsorption equilibrium for the system. In addition, first order, second order and saturation type kinetic models were applied to kinetic data of adsorption and kinetic constants were calculated. It was concluded that the second order and the saturation type kinetic models defined the adsorption data more accurately. Finally, the evaluated thermodynamic parameters of adsorption show a spontaneous and exothermic behavior. Overall, this study indicates OPAC/Chitosan composite as an effective and low-cost adsorbent for the removal of MB dye from aqueous solutions.

Keywords: activated carbon, adsorption, chitosan, methylene blue, orange peel

Procedia PDF Downloads 258

Authors: Serap Kaymakci, Dogan Gundogdu, M. Bugra Yagcioglu

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Erosion (soil erosion) is a phenomenon in which the soil on the slope surface is exposed to natural influences such as wind, rainfall, etc. in open areas. The most natural solution to prevent erosion is to plant surfaces exposed to erosion. However, proper ground and natural conditions must be provided in order for planting to occur. Erosion is prevented in a fast and natural way and the loss of soil is reduced mostly. Lead to allowing plants to hold onto the soil with its three-dimensional and hollow structure are as follows: The types of geomat called MacMat that is used in a case study in Turkey in order to prevent water carry over due to rainfall. The geosynthetic combined with double twisted steel wire mesh. That consists of 95% Zn–5% Al alloy coated double twisted steel wire based that is a reinforced MacMat (geosynthetic three-dimensional erosion control mat) obtained by a polypropylene consisted (mesh type 8x10-Wire diam. 2.70 mm–95% Zn–5% Al alloy coated). That is developed by the progress of the technology. When using reinforced MacMat on top clay liners, fixing pins should not be used as they will rupture the mats. Mats are simply anchored (J Type) in the top trench and, if necessary, in intermediate berm trenches. If the slope angle greater than 20°, it is necessary to use additional rebar depending soil properties also. These applications may have specific technical and installation requirements. In that project, the main purpose is erosion control after that is greening. There is a slope area around the factory which is located in Gebze, İstanbul.

Keywords: erosion, GeoMat, geosynthetic, slope

Procedia PDF Downloads 153

Authors: Sahar S. Tabrizi, Dogan Ibrahim

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Cloud Computing is a convenient model for on-demand networks that uses shared pools of virtual configurable computing resources, such as servers, networks, storage devices, applications, etc. The cloud serves as an environment for companies and organizations to use infrastructure resources without making any purchases and they can access such resources wherever and whenever they need. Cloud computing is useful to overcome a number of problems in various Information Technology (IT) domains such as Geographical Information Systems (GIS), Scientific Research, e-Governance Systems, Decision Support Systems, ERP, Web Application Development, Mobile Technology, etc. Companies can use Cloud Computing services to store large amounts of data that can be accessed from anywhere on Earth and also at any time. Such services are rented by the client companies where the actual rent depends upon the amount of data stored on the cloud and also the amount of processing power used in a given time period. The resources offered by the cloud service companies are flexible in the sense that the user companies can increase or decrease their storage requirements or the processing power requirements at any time, thus minimizing the overall rental cost of the service they receive. In addition, the Cloud Computing service providers offer fast processors and applications software that can be shared by their clients. This is especially important for small companies with limited budgets which cannot afford to purchase their own expensive hardware and software. This paper is an overview of the Cloud Computing, giving its types, principles, advantages, and disadvantages. In addition, the paper gives some example engineering applications of Cloud Computing and makes suggestions for possible future applications in the field of engineering.

Keywords: cloud computing, cloud systems, cloud services, IaaS, PaaS, SaaS

Procedia PDF Downloads 210

Authors: Pinar Dogan, Merve Tarhan, Ahu Kurklu

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Syrian refugees who sheltering due to war has protected by the Government of Turkey since 2011. Since Syria was a medium-low income country prior to the war, it is known that chronic health problems weren’t common among citizens. However, it is also known that they frequently use health services in our country because of the spread of infectious and acute diseases due to insufficient sanitation and crowding after the war. This study was planned to compare the social distances of the community against the Syrian refugees and the perceptions of accessing health care services. The descriptive-cross sectional study was carried out on 1262 individuals living in Istanbul. A questionnaire form consisted of Personal Information Form, The Bogardus Social Distance Scale (BSDS) and The Survey of Access to Healthcare Services (AHS) was used as data collection tool. Descriptive tests and chi-square test were used for statistical analysis. It was found that the majorities of participants was satisfied with the health services and were waiting for more than 40 minutes to be examined. It was determined that participants have high scores from BSDS. At the same time, the majority of participants stated that their level of access to health care is diminishing due to refugees. Participants who experienced disruption in access to health services due to refugees were found to have higher scores from BSDS. The data collection process in the study will continue until 2400 individuals are reached. With these conclusions, it is considered necessary that the effect of the presence of the refugees in reaching the health services and nursing care of the society should be revealed through extensive researches to be conducted in Turkey.

Keywords: health care services, nursing care, social distances, Syrian refugees

Procedia PDF Downloads 111

Authors: Ahmet Uyar, Zabit Yener, Abdulahad Dogan

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(1). The ameliorative potential and antioxidant capacity of an extract of Urtica dioica seeds (UDS) were investigated using histopathological changes in liver and kidney of broiler, measuring serum marker enzymes, antioxidant defence systems and lipid peroxidation (malondialdehyde (MDA)) content in various tissues of broilers exposed to aflatoxin (AF). (2). A total of 32 broilers were divided randomly into 4 groups: control, UDS extract-treated, AF-treated and AF+UDS extract-treated. Broilers in control and UDS extract-treated groups were fed on a diet without AF. The AF-treated group and AF+UDS extract-treated groups were treated with an estimated 1 mg total AF/kg feed. The AF+UDS extract groups received in addition 30 ml UDS extract/kg diet for 21 days. (3). The AF-treated group had significantly decreased body weight gain when compared to the other groups. (4). Biochemical analysis showed a small increase in the concentrations of serum aspartate aminotransferase, alanine aminotransferase, gamma glutamyl transpeptidase and lactate dehydrogenase in the AF-treated group compared to that of the control group, whereas concentrations of these enzymes were decreased in the AF+UDS group compared to that of the AF-treated group. (5). Administration of supplementary UDS extract helped restore the AF-induced increase in MDA and reduced the antioxidant system towards normality, particularly in the liver, brain, kidney and heart. Hepatorenal protection by UDS extracts was further supported by the almost normal histology in AF +UDS extract-treated group as compared to the degenerative changes in the AF-treated broilers. (6). It was concluded that UDS extract has a protective hepatorenal effect in broilers affected by aflatoxicosis, probably acting by promoting the antioxidative defence systems.

Keywords: aflatoxicosis, biochemistry, broiler, histopathology, Urtica dioica seed extract

Procedia PDF Downloads 308

Authors: Onur Gönülal, Zafer Ceylan, Gülgün F. Unal Sengor

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The differences of Parapenaus longirostris caught from The North Aegean Sea and the Marmara Sea on proximate composition, sensorial analysis (for raw and cooked samples), flesh productivity of the samples were investigated. The moisture, protein, lipid, ash, carbohydrate, energy contents of shrimp caught from The North Aegean Sea were 74.92 ± 0.1, 20.32 ± 0.16, 2.55 ± 0.1, 2.13 ± 0.08, 0.08, 110.1 kcal/100g, respectively. The moisture, protein, lipid, ash, carbohydrate, energy contents of shrimp caught from Marmara Sea were 76.9 ± 0.02, 19.06 ± 0.03, 2.22 ± 0.08, 1.51 ± 0.04, 0.33, 102.77 kcal/100g, respectively. The protein, lipid, ash and energy values of the Northern Aegean Sea shrimp were higher than The Marmara Sea shrimp. On the other hand, The moisture, carbohydrate values of the Northern Aegean Sea shrimp were lower than the other one. Sensorial analysis was done for raw and cooked samples. Among all properties for raw samples, flesh color, shrimp connective tissue, shrimp body parameters were found different each other according to the result of the panel. According to the result of the cooked shrimp samples among all properties, cooked odour, flavours, texture were found to be different from each other, as well. Especially, flavours and textural properties of cooked shrimps of the Northern Aegean Sea were higher than the Marmara Sea shrimp. Flesh productivity of Northern Aegean Sea shrimp was found as 46.42 %, while that of the Marmara Sea shrimp was found as 47.74 %.

Keywords: shrimp, biological differences, proximate value, sensory, Parapenaus longirostris, flesh productivity

Procedia PDF Downloads 252

Authors: Onur Potok, Deniz Deger, Kemal Ulutas, Sahin Yakut, Deniz Bozoglu

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Thalium Selenide (TlSe) is used for optoelectronic devices, pressure sensitive detectors, and gamma-ray detectors. The TlSe samples were grown as large single crystals using the Stockbarger-Bridgman method. The thin films, in the form of Al/TlSe/Al, were deposited on the microscope slide in different thicknesses (300-3000 Å) using thermal evaporation technique at 10-5 Torr. The dielectric properties of (TlSe) thin films, capacitance (C) and dielectric loss factor (tanδ), were measured in a frequency range of 10-105 Hz, and temperatures between 213K and 393K via Broadband Dielectric Spectroscopy analyzer. The dielectric constant (ε’) and the dielectric loss (ε’’) of the thin films were derived from measured parameters (C and tanδ). These results showed that the dielectric properties of TlSe thin films are frequency and temperature dependent. The capacitance and the dielectric constant decrease with increasing frequency and decreasing temperature. The dielectric loss of TlSe thin films decreases with increasing frequency, on the other hand, they increase with increasing temperature and increasing thicknesses. There is two relaxation region in the investigated frequency and temperature interval. These regions can be called as low and high-frequency dispersion regions. Low-frequency dispersion region can be attributed to the polarization of the main part of the chain structure of TlSe while high-frequency dispersion region can be attributed to the polarization of side parts of the structure.

Keywords: thin films, thallium selenide, dielectric spectroscopy, binary compounds

Procedia PDF Downloads 124

Authors: Onur Kaya, Ilknur Tukenmez

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In this study, we consider vehicle routing problems on networks with alternative direct links between nodes, and we analyze a multi-objective problem considering the financial, environmental and social objectives in this context. In real life, there might exist several alternative direct roads between two nodes, and these roads might have differences in terms of their lengths and durations. For example, a road might be shorter than another but might require longer time due to traffic and speed limits. Similarly, some toll roads might be shorter or faster but require additional payment, leading to higher costs. We consider such alternative links in our problem and develop a mixed integer linear programming model that determines which alternative link to use between two nodes, in addition to determining the optimal routes for different vehicles, depending on the model objectives and constraints. We consider the minimum cost routing as the financial objective for the company, minimizing the CO2 emissions and gas usage as the environmental objectives, and optimizing the driver working conditions/working hours, and minimizing the risks of accidents as the social objectives. With these objective functions, we aim to determine which routes, and which alternative links should be used in addition to the speed choices on each link. We discuss the results of the developed vehicle routing models and compare their results depending on the system parameters.

Keywords: vehicle routing, alternative links between nodes, mixed integer linear programming, triple bottom line accounting

Procedia PDF Downloads 374

Authors: Buse A. Ataç, Doğan K. Cenan, Arda Çetinkaya, Naz D. Şahin, Köksal Sanlı, Zeynep Koç, Akın Kısa

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With its spatial data reliability, interpretation and questioning capabilities, Geographical Information Systems make significant contributions to scientists, planners and practitioners. Geographic information systems have received great attention in today's digital world, growing rapidly, and increasing the efficiency of use. Access to and use of current and accurate geographical data, which are the most important components of the Geographical Information System, has become a necessity rather than a need for sustainable and economic development. This project aims to enable sharing of data collected by public institutions and organizations on a web-based platform. Within the scope of the project, INSPIRE (Infrastructure for Spatial Information in the European Community) data specifications are considered as a road-map. In this context, Turkey's National Geographic Information System (TUCBS) Integration Project supports sharing spatial data within 61 pilot public institutions as complied with defined national standards. In this paper, which is prepared by the project team members in the TUCBS Integration Project, the technical process with a detailed methodology is explained. In this context, the main technical processes of the Project consist of Geographic Data Analysis, Geographic Data Harmonization (Standardization), Web Service Creation (WMS, WFS) and Metadata Creation-Publication. In this paper, the integration process carried out to provide the data produced by 61 institutions to be shared from the National Geographic Data Portal (GEOPORTAL), have been trying to be conveyed with a detailed methodology.

Keywords: data specification, geoportal, GIS, INSPIRE, Turkish National Geographic Information System, TUCBS, Turkey's national geographic information system

Procedia PDF Downloads 116

Authors: Recep Keşli, Onur Türkyılmaz, Hayriye Tokay, Kasım Demir

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Objective: Coeliac disease (CD) is a primary small intestine disorder caused by high sensitivity to gluten which is present in the crops, characterized by inflammation in the small intestine mucosa. The goal of this study was to determine and to compare the sensitivity and specificity values of anti-endomysial IgA (EMA IgA) (IFA) and anti-tissue transglutaminase IgA (anti-tTG IgA) (ELISA) antibodies in the diagnosis of patients suspected with the CD. Methods: One thousand two hundred seventy three patients, who have applied to gastroenterology and pediatric disease polyclinics of Afyon Kocatepe University ANS Research and Practice Hospital were included into the study between 23.09.2010 and 30.05.2016. Sera samples were investigated by immunofluorescence method for EMA positiveness (Euroimmun, Luebeck, Germany). In order to determine quantitative value of Anti-tTG IgA (EIA) (Orgentec Mainz, Germany) fully automated ELISA device (Alisei, Seac, Firenze, Italy) were used. Results: Out of 1273 patients, 160 were diagnosed with coeliac disease according to ESPGHAN 2012 diagnosis criteria. Out of 160 CD patients, 120 were female, 40 were male. The EMA specificity and sensitivity were calculated as 98% and 80% respectively. Specificity and sensitivity of Anti-tTG IgA were determined as 99% and 96% respectively. Conclusion: The specificity of EMA for CD was excellent because all EMA-positive patients (n = 144) were diagnosed with CD. The presence of human anti-tTG IgA was found as a reliable marker for diagnosis and follow-up the CD. Diagnosis of CD should be established on both the clinical and serologic profiles together.

Keywords: anti-endomysial antibody, anti-tTG IgA, coeliac disease, immunofluorescence assay (IFA)

Procedia PDF Downloads 232

Authors: Eyup Dogan

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One criticism of the energy-growth-environment literature, to the best of our knowledge, is that only a few studies analyze the influence of tourism on CO₂ emissions even though tourism sector is closely related to the environment. The other criticism is the selection of methodology. Panel estimation techniques that fail to consider both heterogeneity and cross-sectional dependence across countries can cause forecasting errors. To fulfill the mentioned gaps in the literature, this study analyzes the impacts of real GDP, renewable energy and tourism on the levels of carbon dioxide (CO₂) emissions for the top 10 most-visited countries around the world. This study focuses on the top 10 touristic (most-visited) countries because they receive about the half of the worldwide tourist arrivals in late years and are among the top ones in 'Renewables Energy Country Attractiveness Index (RECAI)'. By looking at Pesaran’s CD test and average growth rates of variables for each country, we detect the presence of cross-sectional dependence and heterogeneity. Hence, this study uses second generation econometric techniques (cross-sectionally augmented Dickey-Fuller (CADF), and cross-sectionally augmented IPS (CIPS) unit root test, the LM bootstrap cointegration test, and the DOLS and the FMOLS estimators) which are robust to the mentioned issues. Therefore, the reported results become accurate and reliable. It is found that renewable energy mitigates the pollution whereas real GDP and tourism contribute to carbon emissions. Thus, regulatory policies are necessary to increase the awareness of sustainable tourism. In addition, the use of renewable energy and the adoption of clean technologies in tourism sector as well as in producing goods and services play significant roles in reducing the levels of emissions.

Keywords: air pollution, tourism, renewable energy, income, panel data

Procedia PDF Downloads 158

Authors: Kubra Dogan, Fatih Tornuk

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Due to increasing consumer demand for the high-quality food products and awareness regarding the health benefits of different nutrients in food minimal processing becomes more popular in modern food preservation. To date, heat treatment is often used for inactivation of spoilage microorganisms in foods. However, it may cause significant changes in the quality and nutritional properties of food. In order to overcome the detrimental effects of heat treatment, several alternatives of non-thermal microbial inactivation processes have been investigated. Ultraviolet (UV) inactivation is a promising and feasible method for better quality and longer shelf life as an alternative to heat treatment, which aims to inhibit spoilage and pathogenic microorganisms and to inactivate the enzymes in vegetable juice production. UV-C is a sub-class of UV treatment which shows the highest microcidal effect between 250-270 nm. The wavelength of 254 nm is used for the surface disinfection of certain liquid food products such as vegetable juice. Effects of UV-C treatment on microbiological load and quality parameter of vegetable juice which is a mix of celery, carrot, lemon and orange was investigated. Our results showed that storing of UV-C applied vegetable juice for three months, reduced the count of TMAB by 3.5 log cfu/g and yeast-mold by 2 log cfu/g compared to control sample. Total phenolic content was found to be 514.3 ± 0.6 mg gallic acid equivalent/L, and there wasn’t a significant difference compared to control. The present work suggests that UV-C treatment is an alternative method for disinfection of vegetable juice since it enables adequate microbial inactivation, longer shelf life and has minimal effect on degradation of quality parameters of vegetable juice.

Keywords: heat treatment, phenolic content, shelf life, ultraviolet (UV-C), vegetable juice

Procedia PDF Downloads 180

Authors: Ceren Karaman, Onur Karaman

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The adsorption of Remazol Black B (RBB), an anionic dye, onto dried orange pulp (DOP) adsorbent prepared by only drying and by treating with cetyltrimetylammonium bromide (CTAB), a cationic surfactant, surface-modified orange pulp (SMOP) was studied in a stirred batch experiments system at 25°C. The adsorption of RBB on each adsorbent as a function of surfactant dosage, initial pH of the solution and initial dye concentration was investigated. The optimum amount of CTAB was found to be 25g/l. For RBB adsorption studies, while working pH value for the DOP adsorbent system was determined as 2.0, it was observed that this value shifted to 8.0 when the 25 g/l CTAB treated-orange pulp (SMOP) adsorbent was used. It was obtained that the adsorption rate and capacity increased to a certain value, and the adsorption efficiency decreased with increasing initial RBB concentration for both DOP and SMOP adsorbents at pH 2.0 and pH 8.0. While the highest adsorption capacity for DOP was determined as 62.4 mg/g at pH 2.0, and as 325.0 mg/g for SMOP at pH 8.0. As a result, it can be said that permanent cationic coating of the adsorbent surface by CTAB surfactant shifted the working pH from 2.0 to 8.0 and it increased the dye adsorption rate and capacity of orange pulp much more significantly at pH 8.0. The equilibrium RBB adsorption data on each adsorbent were best described by the Langmuir isotherm model. The adsorption kinetics of RBB on each adsorbent followed a pseudo-second-order model. Moreover, the intraparticle diffusion model was used to describe the kinetic data. It was found that diffusion is not the only rate controlling step. The adsorbent was characterized by the Brunauer–Emmett–Teller (BET) analysis, Fourier-transform-infrared (FTIR) spectroscopy, and scanning-electron-microscopy (SEM). The mechanism for the adsorption of RBB on the SMOP may include hydrophobic interaction, van der Waals interaction, stacking and electrostatic interaction.

Keywords: adsorption, Cetyltrimethylammonium Bromide (CTAB), orange pulp, Remazol Black B (RBB), surface modification

Procedia PDF Downloads 214

Authors: Mehmet Demir Kaya, Engin Gökhan Kulan, Onur İleri, Süleyman Avcı

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Due to variation in seed size, shape and oil content of safflower cultivars, germination and emergence performance have been severely influenced by seed characteristics. This study aimed to determine genotypic variation among safflower genotypes for one thousand seed weight, oil content, germination and seed vigor using electrical conductivity (EC) and cold test. In the study, safflower lines ES37-5, ES38-4, ES43-11, ES55-14 and ES58-11 which were developed by single seed selection method, and Dinçer and Remzibey-05 were used as standard varieties. The genotypes were grown under rainfed conditions in Eskişehir, Turkey with four replications. The seeds of each genotype were subjected to standard germination and emergence test at 25°C for 10 days with four replications and 50 seeds per replicate. Electrical conductivity test was performed at 25°C for 24 h to assess the seed vigor. Also, cold test were applied to each safflower genotype at 10°C for 4 days and 25°C for 6 days. Results showed that oil content of the safflower genotypes were different. The highest oil content was determined in ES43-11 with 36.6% while the lowest was 25.9% in ES38-4. Higher germination and emergence rate were obtained from ES55-14 with 96.5% and 73.0%, respectively. There was no significant difference among the safflower genotypes for EC values. Cold test showed that ES43-11 and ES55-14 gave the maximum germination percentages. It was concluded that genotypic factors except for soil and climatic conditions play an important role for determining seed vigor because safflower genotypes grown at the same condition produced various seed vigor values.

Keywords: Carthamus tinctorius L., germination, emergence, cold test, electrical conductivity

Procedia PDF Downloads 326

Authors: Dogan Cetin, Burak Turk, Mahmut Candan

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Landslides cause remarkable damage and loss of human life every year around the world. They may be made more likely by factors such as earthquakes, heavy precipitation, and incorrect construction activities near or on slopes. The stadium of Karabük University is located at the bottom of a very high slope. After construction of the stadium, severe deformations were observed on the social activity area surrounding the stadium. Some inclinometers were placed behind the stadium to detect the possible landslide activity. According to measurements of the inclinometers, irregular soil movements were detected at depths between 20 m and 45 m. Also, significant heaves and settlements were observed behind the stadium walls located at the toe of the slope. The heaves indicate that the stadium walls were under threat of a significant landslide. After inclinometer readings and field observations, the potential failure geometry was estimated. The protection system was designed based on numerous numerical analysis performed by 2-D Plaxis software. After the design was completed, protective geotechnical work was started. Before the geotechnical work began, new inclinometers were installed to monitor earth movement during the work and afterward. The total horizontal length of the possible failure surface is 220 m. Geotechnical work included two-row-pile construction and three-row-pile construction on the slope. The bored piles were 120 cm in diameter for two-row-pile construction, and 150 cm in diameter for three-row-pile construction. Pile length is 31.30 m for two-row-pile construction and 31.40 m for three-row-pile construction. The distance between two-row-pile and three-row-pile construction is 60 m. With these bored piles, the landslide was divided into three parts. In this way, the earth's pressure was reduced. After a number of inclinometer readings, it was seen that deformation continued during the work, but after the work was done, the movement reversed, and total deformation stayed in mm dimension. It can be said that the protection work eliminated the possible landslide.

Keywords: landslide, landslide protection, inclinometer measurement, bored piles

Procedia PDF Downloads 115

Authors: Onur Kaya, Halit Bayer

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Global grocery and supermarket sales are among the largest markets in the world and perishable products such as fresh produce, dairy and meat constitute the biggest section of these markets. Due to their deterioration over time, the demand for these products depends highly on their freshness. They become totally obsolete after a certain amount of time causing a high amount of wastage and decreases in grocery profits. In addition, customers are asking for higher product variety in perishable product categories, leading to less predictable demand per product and to more out-dating. Effective management of these perishable products is an important issue since it is observed that billions of dollars’ worth of food is expired and wasted every month. We consider coordinated inventory and pricing decisions for perishable products with a time and price dependent random demand function. We use stochastic dynamic programming to model this system for both periodically-reviewed and continuously-reviewed inventory systems and prove certain structural characteristics of the optimal solution. We prove that the optimal ordering decision scenario has a monotone structure and the optimal price value decreases by time. However, the optimal price changes in a non-monotonic structure with respect to inventory size. We also analyze the effect of 1 different parameters on the optimal solution through numerical experiments. In addition, we analyze simple-to-implement heuristics, investigate their effectiveness and extract managerial insights. This study gives valuable insights about the management of perishable products in order to decrease wastage and increase profits.

Keywords: age-dependent demand, dynamic programming, perishable inventory, pricing

Procedia PDF Downloads 224

Authors: Recep Kesli, Gulsah Asik, Cengiz Demir, Onur Turkyilmaz

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Objective: Pseudomonas aeruginosa (P. aeruginosa) is an important nosocomial pathogen which causes serious hospital infections and is resistant to many commonly used antibiotics. P. aeruginosa can develop resistance during therapy and also it is very resistant to disinfectant chemicals. It may be found in respiratory support devices in hospitals. In this study, the antibiotic resistance of P. aeruginosa strains isolated from bronchial aspiration samples was evaluated retrospectively. Methods: Between October 2013 and September 2015, a total of 318 P. aeruginosa were isolated from clinical samples obtained from various intensive care units and inpatient patients hospitalized at Afyon Kocatepe University, ANS Practice and Research Hospital. Isolated bacteria identified by using both the conventional methods and automated identification system-VITEK 2 (bioMerieux, Marcy l’etoile France). Antibacterial resistance tests were performed by using Kirby-Bauer disc (Oxoid, Hampshire, England) diffusion method following the recommendations of CLSI. Results: Antibiotic resistance rates of identified 318 P. aeruginosa strains were found as follows for tested antibiotics; 32 % amikacin, 42% gentamicin, 43% imipenem, 43% meropenem, 50% ciprofloxacin, 57% levofloxacin, 38% cefepime, 63% ceftazidime, and 85% piperacillin/tazobactam. Conclusion: Resistance profiles change according to years and provinces for P. aeruginosa, so these findings should be considered empirical treatment choices. In this study, the highest and lowest resistance rates found against piperacillin/tazobactam % 85, and amikacin %32.

Keywords: Pseudomonas aeruginosa, antibiotic resistance rates, intensive care unit, Pseudomonas spp.

Procedia PDF Downloads 261

Authors: Recep Keşli, Cengiz Demir, Onur Türkyılmaz

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Objective: The aim of this study was to determine the prevalence of Mycoplasma hominis and Ureaplasma urealyticum as the causative agents in men with non-gonococcal urethtritis, and anti-bacterial resistance rates. Methods: The Study was carried out in the two Medical Microbiology Laboratories belonging to: Konya Education and Research Hospital and ANS Practice and Research Hospital, Afyon Kocatepe University, between January 2012 and December 2015. Urethral samples were obtained from patients by using a swab. Mycoplasma hominis and Ureaplasma urealyticum were detected by using Mycoplasma IST-2 kit (bio-Mérieux, Marcy l'Étoile, France). Neisseria gonorrhoea was excluded by Gram staining and culture methods. Results: Of all the one hundred and eighty-eight male patients with urethritis, forty M. hominis and forty two U. urealyticum were detected. Resistance rates of M. hominis strains against to doxycycline, ofloxacin, erythromycin, tetracycline, ciprofloxacin, azithromycin, clarithromycin, and pristinamycin were found as 5 %, 65 %, 25 %, 5 %, 80 %, 20 %, 20 %, 20 %, 5 %, respectively. Resistance rates of U. urealyticum strains against to doxycycline, ofloxacin, erythromycin, tetracycline, ciprofloxacin, azithromycin, clarithromycin, and pristinamycin were found as 4.7 %, 66.6 %, 23.8 %, 4.75 %, 81 %, 19 %, 19 %, 4.7 % respectively. No resistance was detected against to josamycin, for both the strains. Conclusions: It was concluded that; ciprofloxacin and ofloxacin had the weakest; josamycin, doxycycline, and tetracycline had the strongest in vitro anti-bacterial activity, for treatment of the NGU. So josamycin, doxycycline, and tetracycline should be preferred as the first choice of anti-bacterial agents, for treatment of the patients with non-gonococcal male urethritis.

Keywords: antimicrobial resistance, Mycoplasma hominis, non-gonococcal urethritis, Ureaplasma urealyticum

Procedia PDF Downloads 212

Authors: Onur Yel

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This study represents the removal of harmful dye substances from wastewaters by using waste and cheap adsorbents. Rapid population growth and industrialization occasion anthropogenic pollution which gives irreversible damage to the environment. One of the ways in which water pollution occurs is caused by the release of the dyestuffs in the textile industry. The release of dyestuffs to the environment directly damages the living creatures that have acquired water habitat. Especially, wastewater cannot be used for nutritional purposes. In addition, some adsorbents have mutagenic and/or carcinogenic effects. By blocking photosynthesis, it hinders the inhibition of photosynthetic bacteria in the water, which damages the ecological balance and also causes the formation of malodorous compounds. Moreover, the lack of oxygen can pose a serious danger to the lives of other living organisms that need oxygen. In recent years, some physical and chemical methods are preferred for the removal of dyestuffs. However, the utilization of these methods is expensive. For this reason, the availability of new and cheap adsorbents becomes the more significant issue. In this study, an investigation of various variables on the removal of Methylene Blue and Acid Red-88 dyestuffs from wastewaters by the usage of pulverized cypress cones has been carried out. Thus, various masses of absorbent (0.1-0.25-0.5-1-2-4-5 grams) are used in 50, 100, 150, 200, 300 ppm concentrations of Methylene Blue and Acid Red-88 dyestuffs’ solutions, and with a variety of the interaction time (0.25-0.5-1-2-4-5 hours). The mixtures were centrifuged and the absorbance of the filtrates was measured on a UV spectrophotometer to determine their remaining concentrations. In the study, the highest removal ratio of Acid Red-88 dyestuff was found to be 81% at 200 ppm of dyestuff with 2 grams of adsorbent at 300 minutes. For Methylene Blue experiments, the removal percentage was found as 98% where 2 grams of adsorbent is used in 200 ppm dyestuff solution at 120 minutes of interaction.

Keywords: acid red-88, biosorption, methylene blue, cypress cones, water pollution

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Authors: Recep Kesli, Merih Simsek, Cengiz Demir, Onur Turkyilmaz

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Objective: Goal of this study was to determine the antibiotic resistance of Staphylococcus aureus (S. aureus) and Methicillin resistant staphylococcus aureus (MRSA) strains isolated at Medical Microbiology Laboratory of ANS Application and Research Hospital, Afyon Kocatepe University, Turkey. Methods: S. aureus strains isolated between October 2012 and September 2016, from various clinical specimens were evaluated retrospectively. S. aureus strains were identified by both the conventional methods and automated identification system -VITEK 2 (bio-Mérieux, Marcy l’etoile, France), and Meticillin resistance was verified using oxacillin disk with disk-diffusion method. Antibiotic resistance testing was performed by Kirby-Bauer disc diffusion method according to CLSI criteria, and intermediate susceptible strains were considered as resistant. Results: Seven hundred S.aureus strains which were isolated from various clinical specimens were included in this study. These strains were mostly isolated from blood culture, tissue, wounds and bronchial aspiration. All of 306 (43,7%) were oxacillin resistant. While all the S.aureus strains were found to be susceptible to vancomycin, teicoplanin, daptomycin and linezolid, 38 (9.6 %), 77 (19.5 %), 116 (29.4 %), 152 (38.6 %) and 28 (7.1 %) were found to be resistant aganist to clindamycin, erythromycin, gentamicin, tetracycline and sulfamethoxazole/trimethoprim, retrospectively. Conclusions: Comparing to the Methicillin sensitive staphylococcus aureus (MSSA) strains, increased resistance rates of, trimethoprim-sulfamethoxazole, clindamycin, erythromycin, gentamicin, and tetracycline were observed among the MRSA strains. In this study, the most effective antibiotic on the total of strains was found to be trimethoprim-sulfamethoxazole, the least effective antibiotic on the total of strains was found to be tetracycline.

Keywords: antibiotic resistance, MRSA, Staphylococcus aureus, VITEK 2

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Authors: Ekin Ece Gürer, Tarık Onur Tiryaki, Sevgi Kalayoğlu Beşışık, Fatma Savran Oğuz, Uğur Sezerman, Fatma Erdem, Gülşen Günel, Dürdane Serap Kuruca, Zerrin Aktaş, Oral Öncül

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Aim: Chemotherapytreatment in HodgkinLymphomaandNon-HodgkinLymphoma (NHL) diseasescausesgastrointestinalepithelialdamage, disruptstheintestinalmicrobiotabalanceandcausesdysbiosis. Inourstudy, it wasaimedtoshowtheeffect of thedamagecausedbychemotherapy on themicrobiotaandtheeffect of thechangingmicrobiota flora on thecourse of thedisease. Materials And Methods: Seven adult HL and seven adult HL patients to be treatedwithchemotherapywereincluded in the study. Stoolsamplesweretakentwice, beforechemotherapytreatmentandafterthe 3th course of treatment. SamplesweresequencedusingNextGenerationSequencing (NGS) methodafternucleicacidisolation. OTU tableswerepreparedusing NCBI blastnversion 2.0.12 accordingtothe NCBI general 16S bacterialtaxonomyreferencedated 10.08.2021. Thegenerated OTU tableswerecalculatedwith R Statistical Computer Language version 4.04 (readr, phyloseq, microbiome, vegan, descrand ggplot2 packages) to calculate Alpha diversityandtheirgraphicswerecreated. Statistical analyzeswerealsoperformedusing R Statistical Computer Language version 4.0.4 and studio IDE 1.4 (tidyverse, readr, xlsxand ggplot2 packages). Expression of IL-12 and IL-17 cytokineswasperformedbyrtPCRtwice, beforeandaftertreatment. Results: InHL patients, a significantdecreasewasobserved in themicrobiota flora of Ruminococcaceae_UCG-014 genus (p:0.036) andUndefined Ruminococcaceae_UCG-014 species (p:0.036) comparedtopre-treatment. When the post-treatment of HL patientswerecomparedwithhealthycontrols, a significantdecreasewasfound in themicrobiota of Prevotella_7 genus (p:0.049) andButyricimonas (p:0.006) in the post-treatmentmicrobiota of HL patients. InNHL patients, a significantdecreasewasobserved in themicrobiota flora of Coprococccus_3 genus (p:0.015) andUndefined Ruminoclostridium_5 (p:0.046) speciescomparedtopre-treatment. When post-treatment of NHL patientswerecomparedwithhealthycontrols, a significantabundance in theBacilliclass (p:0.029) and a significantdecrease in theUndefinedAlistipesspecies (p:0.047) wereobserved in the post-treatmentmicrobiota of NHL patients. While a decreasewasobserved in IL-12 cytokineexpressionuntilbeforetreatment, an increase in IL-17 cytokineexpressionwasdetected. Discussion: Intestinal flora monitoringafterchemotherapytreatmentshowsthat it can be a guide in thetreatment of thedisease. It is thoughtthatincreasingthediversity of commensalbacteria can alsopositivelyaffecttheprognosis of thedisease.

Keywords: hodgkin lymphoma, non-hodgkin, microbiota, cytokines

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Authors: Göksel Doğan, Murat Öztürk, Didar Tuğçe Karakulak, Mehmet Nurullah Orman, Nicolas Sylvius, Matthew Blades, Mustafa Sandıkçı, Cengiz Ünsal, Mehtap Kılıç Eren, Funda Kıral, Levent Karagenç

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Assisted reproduction is associated with impaired glucose metabolism in adulthood. miRNAs are key regulators of glucose metabolism. Whether embryo culture and/or transfer alters the expression of miRNAs and to what extent this process affects glucose metabolism remain largely unknown. The purpose of the present study was to examine the expression of miRNAs in the liver in mice obtained by the transfer of blastocysts. The study was comprised of an experimental (EG) and a control group (CG). EG was generated by embryo transfer to pseudo-pregnant females. Mice born from naturally ovulating females were used as the CG. Differential expression of miRNAs, blood glucose, plasma insulin, liver glycogen, and activities of some of the rate-limiting enzymes involved in glucose metabolism were determined at ten weeks of age. Blood glucose, plasma insulin, and glycogen concentrations were similar between the groups in both sexes. Activities of enzymes were similar among females. EG males had significantly less glucokinase and phosphofructokinase activity compared to CG males. None of the miRNAs were differentially expressed in males. On the other hand, miR-143-3p expression was upregulated in EG females. Expression of none of the genes targeted by miR143-3p differed between the groups. These results demonstrate that miR143-3p, a novel regulator of type 2 diabetes, is upregulated in mice generated by assisted reproduction in a sexually-dimorphic manner with no apparent effect on glucose and insulin levels at ten weeks of age. It remains to be determined if this process is associated with impaired glucose homeostasis in the long term.

Keywords: assisted reproduction, blastocyst, embryo culture, glucose metabolism, miR143-3p, oxygen

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Authors: Ndeye Tiguida Sarr, Onur Akpinar

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The tourism industry, being the sector that includes all the activities related to the organization and satisfaction of tourists during their trip, also has a very important role in the national economy of the host country. In order to measure the stakes of tourism on the economy, microeconomic and macroeconomic factors are elements of analysis. While microeconomics is limited to an individual perspective, macroeconomics extends to a global perspective and treats the economy as a whole by focusing on social and economic actors in general. It is in this context that this study focuses on macroeconomic variables in order to determine the factors that influence the financial performance of tourism firms in Turkey, which is one of the world's major destinations. The aim of the study is to demonstrate the relationship between macroeconomic variables and the financial performance of tourism firms. Data from 2011 to 2020 are collected, from a sample of 16 companies that represent the tourism sector in Borsa Istanbul. Tobin’s Q ratio, Market to Book ratio, Return on Invested Capital, and Return on Assets as the financial performance indicators were dependent variables of the study. Gross Domestic Products, Inflation, Interest Rates, and Unemployment as macroeconomic indicators were independent variables. Again, Size, Liquidity, Leverage, and Age were control variables of the study. According to the results, value indicators, which are Tobin’s Q ratio and Market to Book ratio, have a statistically significant relationship with Inflation, Interest Rates, and Unemployment. A negative relationship is found between value indicators and Interest rates and a positive relationship between value indicators and Unemployment and Inflation. On the other hand, there is no significant relationship between profit indicators (Return on Invested Capital and Return on Assets) and macroeconomic variables. Accordingly, Interest rates negatively affect the financial performance of tourism firms and stand out as a factor that decreases the value.

Keywords: financial performance, macroeconomic variables, panel data, Tobin Q

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Authors: Dogan Can Hatunoglu, Cengiz Hakan Gurkanlı, Hatice Merve Demirci

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Today, the maker movement is regarded as a socio-cultural movement that represents designing and building objects for innovations. In these creativity-based activities of the movement, individuals from different backgrounds such as; inventors, programmers, craftspeople, DIY’ers, tinkerers, engineers, designers, and hackers, form a community and work collaboratively for mutual, open-source innovations. Today, with the accessibility of recently emerged technologies and digital fabrication tools, the Maker Movement is continuously expanding its scope and has evolved into a new experience, and for many, it is now considered as new kind of industrial revolution. In this new experience, makers create new things within their community by using new digital tools and technologies in spots called makerspaces. In these makerspaces, activities of learning, experience sharing, and mentoring are evolved into maker events. Makers who share common interests in making benefit from makerspaces as meeting and working spots. In literature, there are many sources on Maker Movement, maker communities, and their activities, especially in the field of business administration. However, there is a gap in the literature about the maker communities in Turkey. This research aims to be an information source on the dynamics and process design of “making” activities in Turkish maker communities and also aims to provide insights to sustain and enhance local maker communities in the future. Within this aim, semi-structured interviews were conducted with founders and facilitators from selected Turkish maker communities. (1) The perception towards Maker Movement, makers, activity of making, and current situation of maker communities, (2) motivations of individuals who participate the maker communities, and (3) key drivers (collaboration and decision-making in design processes) of maker activities from the perspectives of main actors (founders, facilitators) are all examined deeply with question on personal experiences and perspectives. After a qualitative approached data analysis concerning the maker communities in Turkey, this research reveals that there are two main conclusions regarding (1) the foundation of the Turkish maker mindset and (2) emergence of self-sustaining communities.

Keywords: Maker Movement, maker community, makerspaces, open-source design, sustainability

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Authors: Recep Kesli, Onur Turkyilmaz, Cengiz Demir

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Objective: Autoimmune collagen diseases occur with the immune reactions against the body’s own cell or tissues which cause inflammation and damage the tissues and organs. In this study, it was aimed to compare seropositivity rates and patterns of the anti-nuclear antibodies (ANA) in the diagnosis of four different autoimmune collagen tissue diseases (Rheumatoid Arthritis-RA, Systemic Lupus Erythematous-SLE, Scleroderma-SSc and Sjogren Syndrome-SS) with each other. Methods: One hundred eighty-eight patients applied to different clinics in Afyon Kocatepe University ANS Practice and Research Hospital between 11.07.2014 and 14.07.2015 that thought the different collagen disease such as RA, SLE, SSc and SS have participated in the study retrospectively. All the data obtained from the patients participated in the study were evaluated according to the included criteria. The historical archives belonging to the patients have been screened, assessed in terms of ANA positivity. The obtained data was analysed by using the descriptive statistics; chi-squared, Fischer's exact test. The evaluations were performed by SPSS 20.0 version and p < 0.05 level was considered as significant. Results: Distribution rates of the totally one hundred eighty-eight patients according to the diagnosis were found as follows: 82 (43.6%) were RA, 38 (20.2%) were SLE, 22 (11.7%) were SSc, and 46 (24.5%) were SS. Distribution of ANA positivity rates according to the collagen tissue diseases were found as follows; for RA were 54 (65,9 %), for SLE were 36 (94,7 %), for SSc were 18 (81,8 %), and for SS were 43 (93,5 %). Rheumatoid arthritis should be evaluated and classified as a different class among all the other investigated three autoimmune illnesses. ANA positivity rates were found as differently higher (91.5 %) in the SLE, SSc, and SS, from the RA (65.9 %). Differences at ANA positivity rates for RA and the other three diseases were found as statistically significant (p=0.015). Conclusions: Systemic autoimmune illnesses show broad spectrum. ANA positivity was found as an important predictor marker in the diagnosis of the rheumatologic illnesses. ANA positivity should be evaluated as more valuable and sensitive a predictor diagnostic marker in the laboratory findings of the SLE, SSc, and SS according to RA.

Keywords: antinuclear antibody (ANA), rheumatoid arthritis, scleroderma, Sjogren syndrome, systemic lupus Erythemotosus

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Authors: Yusuf Ersoy Yildirim, Ismail Tas, Ceren Gorgusen, Tugba Yeter, Aysegul Boyacioglu, K. Mehmet Tugrul, Murat Tugrul, Ayten Namli, H. Sabri Ozturk, M. Onur Akca

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In recent years, a lot of research has been done for the sustainable use of scarce resources in the world. Especially, effective and sustainable use of water resources has been researched for many years. Sub-surface drip irrigation (SDI) is one of the most effective irrigation methods in which efficient and sustainable use of irrigation water can be achieved. When the literature is taken into consideration, it is often emphasized that, besides its numerous advantages, it also allows the application of irrigation water to the plant root zone along with air. It is stated in different studies that the air applied to the plant root zone with irrigation water has a positive effect on the root zone. Plants need sufficient oxygen for root respiration as well as for the metabolic functions of the roots. Decreased root respiration due to low oxygen content reduces transpiration, disrupts the flow of ions, and increases the ingress of salt reaching toxic levels, seriously affecting plant growth. Lack of oxygen (Hypoxia) can affect the survival of plants. The lack of oxygen in the soil is related to the exchange of gases in the soil with the gases in the atmosphere. Soil aeration is an important physical parameter of a soil. It is highly dynamic and is closely related to the amount of water in the soil and its bulk weight. Subsurface drip irrigation; It has higher water use efficiency compared to irrigation methods such as furrow irrigation and sprinkler irrigation. However, in heavy clay soils, subsurface drip irrigation creates continuous wetting fronts that predispose the rhizosphere region to hypoxia or anoxia. With subsurface drip irrigation, the oxygen is limited for root microbial respiration and root development, with the continuous spreading of water to a certain region of the root zone. In this study, the change in sugar beet yield caused by air application in the SDI system will be explained.

Keywords: sugar beet, subsurface drip irrigation, air application, irrigation efficiency

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Authors: Recep Keşli, Gülşah Aşık, Cengiz Demir, Onur Türkyılmaz

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Objective: Proteus mirabilis (P. mirabilis) is one of Gram-negative pathogens in human and it causes urinary tract and nosocomial infections. P. mirabilis is susceptible to β-lactams, aminoglycosides, fluoroquinolones, and trimethoprim/sulfamethoxazole. It was aimed to investigate the resistance status to antimicrobial agents of Proteus mirabilis strains produced from samples sent to Afyon Kocatepe University, ANS Research and Practice Hospital, Microbiology Laboratory from different clinics and polyclinics during the period of 24 months. Methods: Between October 2013 and September 2015, a total of 30 Proteus were isolated from clinical samples of patients were hospitalized in intensive care units and in various departments of Afyon Kocatepe University, ANS Research and Practice Hospital. Identification of the bacteria was determined by conventional methods and VITEK 2 system (bioMérieux, France) was used additionally. Antibacterial susceptibility tests were performed by Kirby Bauer disc (Oxoid, Hempshire, England) diffusion method following the recommendations of CLSI. Results: Of the total 30 Proteus strains isolated from clinical samples, 19 from urine, 7 from wound, 4 from tracheal aspiration materials were isolated. Antimicrobial resistant for these strains were determined to 24,3% for meropenem, 26.2% for imipenem, 20.2% for amikacin 10.5% for cefepim, 33.3% for ciprofloxacin and levofloxacine, 31.6% for ceftazidime, 20% for ceftriaxone, 15.2% for gentamicin and 26.6% for amoxicillin-clavulanate, 26.2% trimethoprim-sulfamethoxale. Conclusion: In the present study, the highest number of clinical isolates of P. mirabilis were isolated from urine (63,3%), followed by the others (36,6%). The distribution of samples P. mirabilis strains to the clinics were as fallows; 16,8% intensive care unit (ICU), 29,9% polyclinics, 53,3% hospital service units The most effective antibiotic on the total of strains were found to be cefepim, the least effective antibiotics on the total of strains were found to be trimethoprim-sulfamethoxale.

Keywords: proteus mirabilis, antibiotic resistance, intensive care unit, Proteus spp.

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Authors: Eyup Dogan

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The number of research articles analyzing the integration properties of energy variables has rapidly increased in the energy literature for about a decade. The stochastic behaviors of energy variables are worth knowing due to several reasons. For instance, national policies to conserve or promote energy consumption, which should be taken as shocks to energy consumption, will have transitory effects in energy consumption if energy consumption is found to be stationary in one country. Furthermore, it is also important to know the order of integration to employ an appropriate econometric model. Despite being an important subject for applied energy (economics) and having a huge volume of studies, several known limitations still exist with the existing literature. For example, many of the studies use aggregate energy consumption and national level data. In addition, a huge part of the literature is either multi-country studies or solely focusing on the U.S. This is the first study in the literature that considers a form of energy consumption by sectors at sub-national level. This research study aims at investigating unit root properties of electricity consumption for 12 regions of Turkey by four sectors in addition to total electricity consumption for the purpose of filling the mentioned limits in the literature. In this regard, we analyze stationarity properties of 60 cases . Because the use of multiple unit root tests make the results robust and consistent, we apply Dickey-Fuller unit root test based on Generalized Least Squares regression (DFGLS), Phillips-Perron unit root test (PP) and Zivot-Andrews unit root test with one endogenous structural break (ZA). The main finding of this study is that electricity consumption is trend stationary in 7 cases according to DFGLS and PP, whereas it is stationary process in 12 cases when we take into account the structural change by applying ZA. Thus, shocks to electricity consumption have transitory effects in those cases; namely, agriculture in region 1, region 4 and region 7, industrial in region 5, region 8, region 9, region 10 and region 11, business in region 4, region 7 and region 9, total electricity consumption in region 11. Regarding policy implications, policies to decrease or stimulate the use of electricity have a long-run impact on electricity consumption in 80% of cases in Turkey given that 48 cases are non-stationary process. On the other hand, the past behavior of electricity consumption can be used to predict the future behavior of that in 12 cases only.

Keywords: unit root, electricity consumption, sectoral data, subnational data

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Authors: Yunus Onur Yildiz, Mesut Kirca

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In this study, mechanical properties of a nanoporous metal coated with a different metallic material are studied through a new atomistic modelling technique and molecular dynamics (MD) simulations. This new atomistic modelling technique is based on the Voronoi tessellation method for the purpose of geometric representation of the ligaments. With the proposed technique, atomistic models of nanoporous metals which have randomly oriented ligaments with non-uniform mass distribution along the ligament axis can be generated by enabling researchers to control both ligament length and diameter. Furthermore, by the utilization of this technique, atomistic models of coated nanoporous materials can be numerically obtained for further mechanical or thermal characterization. In general, this study consists of two stages. At the first stage, we use algorithms developed for generating atomic coordinates of the coated nanoporous material. In this regard, coordinates of randomly distributed points are determined in a controlled way to be employed in the establishment of the Voronoi tessellation, which results in randomly oriented and intersected line segments. Then, line segment representation of the Voronoi tessellation is transformed to atomic structure by a special process. This special process includes generation of non-uniform volumetric core region in which atoms can be generated based on a specific crystal structure. As an extension, this technique can be used for coating of nanoporous structures by creating another volumetric region encapsulating the core region in which atoms for the coating material are generated. The ultimate goal of the study at this stage is to generate atomic coordinates that can be employed in the MD simulations of randomly organized coated nanoporous structures. At the second stage of the study, mechanical behavior of the coated nanoporous models is investigated by examining deformation mechanisms through MD simulations. In this way, the effect of coating on the mechanical behavior of the selected material couple is investigated.

Keywords: atomistic modelling, molecular dynamic, nanoporous metals, voronoi tessellation

Procedia PDF Downloads 259