Showing papers by "Istanbul Technical University published in 2009"

Review of methods to determine antioxidant capacities.

Abstract: Antioxidant capacity is related with compounds capable of protecting a biological system against the potentially harmful effect of processes or reactions involving reactive oxygen and nitrogen species (ROS and RNS). These protective effects of antioxidants have received increasing attention within biological, medical, nutritional, and agrochemical fields and resulted in the requirement of simple, convenient, and reliable antioxidant capacity determination methods. Many methods which differ from each other in terms of reaction mechanisms, oxidant and target/probe species, reaction conditions, and expression of results have been developed and tested in the literature. In this review, the methods most widely used for the determination of antioxidant capacity are evaluated, presenting the general principals, recent applications, and their strengths and limitations. Analysis conditions, substrate, and antioxidant concentration should simulate real food or biological systems as much as possible when selecting the antioxidant capacity method. The total antioxidant capacity value should include methods applicable to both lipophilic and hydrophilic antioxidants, with regards the similarity and differences of both hydrogen atom transfer and electron transfer mechanism. The methods including various ROS/RNS also have to be designed to comprehensively evaluate the antioxidant capacity of a sample.

Recent advancement on polybenzoxazine—A newly developed high performance thermoset

Abstract: Polybenzoxazine is a newly developed addition polymerized phenolic system, having a wide range of interesting features and the capability to overcome several shortcomings of conventional novolac and resole type phenolic resins. They exhibit (i) near zero volumetric change upon curing, (ii) low water absorption, (iii) for some polybenzoxazines Tg much higher than cure temperature, (iv) high char yield, (v) no strong acid catalysts required for curing, (vi) release of no byproduct during curing and also possess thermal and flame retarding properties of phenolics along with the mechanical performance. Though benzoxazine based materials possess several advantages, they have not yet became very attractive to the industries. To improve the mechanical properties and processibility several strategies have been reported including (i) synthesis of benzoxazine monomers with additional functionality, (ii) incorporation of benzoxazine in polymer chain, and (iii) benzoxazine based composites or alloys. In this article, we have discussed about the recent development of benzoxazine chemistry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5565–5576, 2009

Timing and climatic impact of Greenland interstadials recorded in stalagmites from northern Turkey

Abstract: A 50 kyr-long exceptionally well-dated and highly resolved stalagmite oxygen (δ 18O) and carbon (δ 13C) isotope record from Sofular Cave in northwestern Turkey helps to further improve the dating of Greenland Interstadials (GI) 1, and 3–12. Timing of most GI in the Sofular record is consistent within ±10 to 300 years with the “iconic” Hulu Cave record. Larger divergences (>500 years) between Sofular and Hulu are only observed for GI 4 and 7. The Sofular record differs from the most recent NGRIP chronology by up to several centuries, whereas age offsets do not increase systematically with depth. The Sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern Mediterranean to GI, whereas a phase lag of ∼100 years between climate and full ecosystem response is evident. Finally, results of spectral analyses of the Sofular isotope records do not support a 1,470-year pacing of GI.

Fuzzy AHP-based decision support system for selecting ERP systems in textile industry by using balanced scorecard

Abstract: An enterprise resource planning system (ERP) is the information backbone of a company that integrates and automates all business operations. It is a critical issue to select the suitable ERP system which meets all the business strategies and the goals of the company. This study presents an approach to select a suitable ERP system for textile industry. Textile companies have some difficulties to implement ERP systems such as variant structure of products, production variety and unqualified human resources. At first, the vision and the strategies of the organization are checked by using balanced scorecard. According to the company's vision, strategies and KPIs, we can prepare a request for proposal. Then ERP packages that do not meet the requirements of the company are eliminated. After strategic management phase, the proposed methodology gives advice before ERP selection. The criteria were determined and then compared according to their importance. The rest ERP system solutions were selected to evaluate. An external evaluation team consisting of ERP consultants was assigned to select one of these solutions according to the predetermined criteria. In this study, the fuzzy analytic hierarchy process, a fuzzy extension of the multi-criteria decision-making technique AHP, was used to compare these ERP system solutions. The methodology was applied for a textile manufacturing company.

Fuzzy performance evaluation in Turkish Banking Sector using Analytic Hierarchy Process and TOPSIS

Abstract: The performance evaluation of banks has important results for creditors, investors and stakeholders since it determines banks' capabilities to compete in the sector and has a critical importance for the development of the sector. The aim of this study is to propose a fuzzy multi-criteria decision model to evaluate the performances of banks.The largest five commercial banks of Turkish Banking Sector are examined and these banks are evaluated in terms of several financial and non-financial indicators. Fuzzy Analytic Hierarchy Process (FAHP) and Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) methods are integrated in the proposed model. After the weights for a number of criteria are determined based on the opinions of experts using the FAHP method, these weights are input to the TOPSIS method to rank the banks. The results show that not only financial performance but also non-financial performance should be taken into account in a competitive environment.

Evaluation of Butyl Rubber as Sorbent Material for the Removal of Oil and Polycyclic Aromatic Hydrocarbons from Seawater

Abstract: Ecological disasters resulting from oil spills have created a great need to find more efficient materials for oil spill cleanup This research highlights the use of a novel macroporous polymeric material based on butyl rubber (BR) as a sorbent in an oil spill cleanup The sorption capacity of BR for crude oil and petroleum products is 15−23 g g−1 as compared to the value of 10−16 g g−1 obtained using a nonwoven polypropylene (PP), a widely used commercial oil sorbent BR sorbent is reusable after simple squeezing and its continuous sorption capacity for crude oil is 76 g g−1 in each cycle, about 3 times the capacity of the PP sorbent BR sorbents also remove efficiently polycyclic aromatic hydrocarbons (PAHs) such as acenaphthene and pyrene from seawaters The results suggest that the rubber sorbents are a better alternative to the widely used PP sorbents by improving the efficiency of oil sorption and the reusability of the sorbent

Treatment of azo dye production wastewaters using Photo-Fenton-like advanced oxidation processes: Optimization by response surface methodology

Abstract: Treatability of synthetic azo dye production wastewaters from Acid Blue 193 and Reactive Black 39 production and real Reactive Black 39 production effluent via Photo-Fenton-like process was investigated. Response surface methodology was employed to assess individual and interactive effects of critical process parameters (Fe 3+ , H 2 O 2 concentrations; initial chemical oxygen demand (COD) and reaction time) on treatment performance in terms of color, COD and total organic carbon (TOC) removal efficiencies. Optimized reaction conditions for synthetic AB 193 production wastewater were established as Fe 3+ = 1.5 mM; H 2 O 2 = 35 mM for CODs ≤ 200 mg/L and a reaction time of 45 min. Under these conditions, 98% color, 78% COD and 59% TOC removals were experimentally obtained and fitted the model predictions well. The same model also described the treatment of synthetic Reactive Black 39 production wastewater satisfactorily. Experimentally achieved removals were considerably lower than model predictions for real Reactive Black 39 production effluent due to its high chloride content.

A decision support system for demand forecasting with artificial neural networks and neuro-fuzzy models: A comparative analysis

Abstract: An organization has to make the right decisions in time depending on demand information to enhance the commercial competitive advantage in a constantly fluctuating business environment. Therefore, estimating the demand quantity for the next period most likely appears to be crucial. This work presents a comparative forecasting methodology regarding to uncertain customer demands in a multi-level supply chain (SC) structure via neural techniques. The objective of the paper is to propose a new forecasting mechanism which is modeled by artificial intelligence approaches including the comparison of both artificial neural networks and adaptive network-based fuzzy inference system techniques to manage the fuzzy demand with incomplete information. The effectiveness of the proposed approach to the demand forecasting issue is demonstrated using real-world data from a company which is active in durable consumer goods industry in Istanbul, Turkey.

Geochemical and temporal evolution of Cenozoic magmatism in western Turkey: Mantle response to collision, slab break-off, and lithospheric tearing in an orogenic belt

Abstract: Post-collisional magmatism in western Anatolia began in the Eocene, and has occurred in discrete pulses throughout the Cenozoic as it propagated from north to south, producing volcano- plutonic associations with varying chemical compositions. This apparent SW migration of magma- tism and accompanying extension through time was a result of the thermally induced collapse of the western Anatolian orogenic belt, which formed during the collision of the Sakarya and Tauride-Anatolide continental blocks in the late Paleocene. The thermal input and melt sources for this prolonged magmatism were provided first by slab break-off-generated aesthenospheric flow, then by lithospheric delamination-related aesthenospheric flow, followed by tectonic extension-driven upward aesthenospheric flow. The first magmatic episode is represented by Eocene granitoid plutons and their extrusive carapace that are linearly distributed along the Izmir- Ankara suture zone south of the Marmara Sea. These suites show moderately evolved com- positions enriched in incompatible elements similar to subduction zone-influenced subalkaline magmas. Widespread Oligo-Miocene volcanic and plutonic rocks with medium- to high-K calc- alkaline compositions represent the next magmatic episode. Partial melting and assimilation- fractional crystallization of enriched subcontinental lithospheric mantle-derived magmas were important processes in the genesis and evolution of the parental magmas, which experienced decreasing subduction influence and increasing crustal contamination during the evolution of the Eocene and Oligo-Miocene volcano-plutonic rocks. Collision-induced lithospheric slab break-off provided an influx of aesthenospheric heat and melts that resulted in partial melting of the previously subduction-metasomatized mantle lithosphere beneath the suture zone, producing the Eocene and Oligo-Miocene igneous suites. The following magmatic phase during the middle Miocene (16- 14 Ma) developed mildly alkaline bimodal volcanic rocks that show a decreasing amount of crustal contamination and subduction influence in time. Both melting of a subduc- tion-modified lithospheric mantle and aesthenospheric mantle-derived melt contribution played a significant role in the generation of the magmas of these rocks. This magmatic episode was attended by region-wide extension that led to the formation of metamorphic core complexes and graben systems. Aesthenospheric upwelling caused by partial delamination of the lithospheric root beneath the western Anatolian orogenic belt was likely responsible for the melt evolution of these mildly alkaline volcanics. Lithospheric delamination may have been caused by 'peeling off' during slab rollback. The last major phase of magmatism in the region, starting c.12 Ma, is represented by late Miocene to Quaternary alkaline to super-alkaline volcanic rocks that show OIB-like geochemical features with progressively more potassic compositions increasing toward south in time. These rocks are spatially associated with major extensional fault systems that acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface. The melt source for this magmatic phase carried little or no subduction component and was pro- duced by the decompressional melting of aesthenospheric mantle, which flowed in beneath the atte- nuated continental lithosphere in the Aegean extensional province. This time-progressive evolution of Cenozoic magmatism and extension in western Anatolia has been strongly controlled by the interplay between regional plate-tectonic events and the mantle dynamics, and provides a realistic template for post-collisional magmatism and crustal extension in many orogenic belts.

The impacts of Radio Frequency Identification (RFID) technology on supply chain costs

Abstract: Radio Frequency Identification (RFID) is regarded as a promising technology for the optimization of supply chain processes since it improves manufacturing and retail operations from forecasting demand to planning, managing inventory, and distribution. This study uses a simulation model to calculate the expected benefits of an integrated RFID system on a three-echelon supply chain obtained through performance increases in efficiency, accuracy, visibility, and security level. The study investigates how the product value, lead time, and demand uncertainty affect the performance of the integrated RFID supply chain in terms of cost factors at the echelon level.

Solution of fractional integro-differential equations by using fractional differential transform method

Abstract: In this study, fractional differential transform method (FDTM), which is a semi analytical numerical technique, is extended to solve fractional integro-differential equations of Volterra type. New theorems for the transformation of integral terms having degenerate kernels that never existed before are introduced with their proofs. This implemented new technique is validated by solving and comparing four different examples that exist in the literature. It is observed that, FDTM can be utilized as a powerful and reliable tool for the solution of fractional integro-differential equations.

General Properties of Hydrogels

Abstract: In the application areas of polymer hydrogels, precise information on their molecular constitution as well as their elastic properties is required. Several interesting molecular features control the elastic properties of the hydrogels. In this chapter, we describe general properties of hydrogels formed by free-radical cross-linking copolymerization of vinyl/divinyl monomers in aqueous solutions. Special attention is paid to the relationships between the formation conditions of hydrogels and their properties such as swelling behaviour, elastic modulus, and spatial inhomogeneity. New developments achieved in the design of hydrogels with a good mechanical performance and a fast response rate is also presented.

Charactiristies of migrant entrepreneurship in Europe

Abstract: The present paper aims to investigate and compare various modalities of migrant entrepreneurship in European countries in order to design a systematic classification of migrant entrepreneurship and to highlight key factors of migrant entrepreneurship in Europe. The paper is based on a comparative assessment of available quantitative data and qualitative information derived from a broad review of findings from previous studies in the literature. Our quantitative evaluation includes the European OECD countries, while our qualitative investigation addresses migrant entrepreneurship experiences in eight European countries: Denmark, Germany, Greece, Italy, the Netherlands, Portugal, Sweden, and the UK. The results of our comparative analysis show that the general picture of European migrant entrepreneurship is determined by some distinct push factors such as high unemployment rates and low participation rates or low status in the labour market as well as by an accompanying factor, namely mixed embeddedness. Th...

Application of fuzzy extended AHP methodology on shipping registry selection: The case of Turkish maritime industry

Abstract: Selection of the suitable shipping registry alternative for the existing fleet or new building ships is one of the critical decision milestones of the shipping business. The main aim of this paper is to structure a practical decision support mechanism on ensuring multiple criteria analysis of shipping registry selection. Fuzzy AHP methodology, based on Chang's extent analysis, is determined to be utilized in order to model the shipping registry selection. After structuring the fundamental hierarchy, the model is performed with a case application on Turkish maritime industry to be able to obtain illustrative results. The shipping registries of Turkiye, Panama, and Malta are determined to evaluate as the potential alternatives for Turkish ship owners. When the literature was examined for the applications of analytical methodologies on maritime business, it was seemed that they were so rare. Therefore, the originality of this study appears on modeling of the critical process under multidisciplinary philosophy in ship management.

A new multi-attribute decision making method: Hierarchical fuzzy axiomatic design

Abstract: Axiomatic design (AD) provides a framework to describe design objects and a set of axioms to evaluate relations between intended functions and means by which they are achieved. Fuzziness in axiomatic design (FAD) has been handled by some researchers to evaluate alternatives under fuzzy environment. In this paper, three important tolls are added FAD method so as to supply its deficiency. The first one is the hierarchy which has the ability of taking the hierarchical structures into account. The second is the crisp toll which has the ability of taking the positive information into consideration under fuzzy environment. The last one is the ranking ability. As a matter of fact, FAD method is developed to be used for the solution of all manners of multi-attribute decision making problems. Moreover, an application to a teaching assistant selection problem is made to show the usability of the developed method.