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The impact of technological advances on consumer information search: A model
Get PDFHiç şüphesiz 20. yüzyılın en önemli teknolojik gelişmelerinden biri kabul edilen İnternet, genel olarak tüketici satın alma karar sürecini, özelde ise bilgi arama aşamasını önemli düzeyde etkilemektedir. İnternet ile birlikte, üretici ve perakende firmalarının web sayfaları, e-forumlar gibi çeşitli online bilgi kaynakları ortaya çıkmıştır. Pazarlama yöneticilerinin, tüketicilerin bilgi arama aşamasını yönlendirmek ve tüketicilerin tercihlerini etkileyebilmek için etkin iletişim stratejileri geliştirmeleri gerekmektedir. Dolayısıyla, tüketici bilgi arama davranışını, özellikle bilgi kaynaklarının kullanımını, etkileyen değişkenlerin belirlenmesi ve bu değişkenlerin etkilerinin incelenmesi önemlidir. Bu çalışmada, online bilgi kaynaklarının ortaya çıkmasıyla satış elemanı, arkadaş ve yakın çevre ve reklamlar gibi geleneksel bilgi kaynaklarının kullanımının nasıl etkilendiği araştırılmaktadır. İlk olarak tüketici bilgi arama davranışı ile ilgili literatür gözden geçirilerek bilgi kaynaklarının kullanımını etkileyen bir model önerilmiştir. Daha sonra ise önerilen model, cep telefonu satınalma kararı bağlamında Yapısal Denklik Modelleme (Structural Equation Modeling) ile test edilmiştir. Araştırmanın sonuçlarına göre, cep telefonu satınalma durumunda, geleneksel bilgi kaynaklarının hala önemli ölçüde kullanıldığı görülmektedir. Ayrıca, algılanan risk, eğlence odaklı alışveriş eğilimi, ürüne yönelik ilgi düzeyi ve geleneksel bilgi kaynaklarının kullanımında algılanan faydanın, bilgi kaynakları kullanımı farkını geleneksel kaynakların lehine pozitif yönde etkilediği ortaya konulmuştur. Buna karşılık, çevresinde uyaran arama eğilimi, kalite-odaklı alışveriş yöneliminin, online bilgi kaynakları kullanımında algılanan faydanın ve nesnel ve öznel ürün bilgisinin hem online hem de geleneksel bilgi kaynaklarının aynı düzeyde kullanılmasında etkili olduğu görülmüştür. Anahtar Kelimeler: Bilgi arama davranışı, online bilgi kaynakları, geleneksel bilgi kaynakları.With the help of the technological advances, online information sources offer new alternatives for consumers to get product information. For this reason, consumer information behavior could occur not only in an online environment or offline environment but also within the combination of both environments. This study is a pioneer study investigating consumer information search behavior through online information sources along with traditional information sources. The proposed conceptual model seeks to determine the variables that might influence the extent of usage of online information sources over offline information sources. The central construct of the proposed model is the gap between the use of online information sources and that of offline information sources. The variables included in the study are listed as product involvement, general perceived risk, optimum stimulation level, perceived benefits of online information sources, perceived benefits of offline information sources, objective and subjective product knowledge, attribute importance, time availability, recreational shopping orientation, economic-conscious shopping orientation and quality-conscious shopping orientation. Additionally, the conceptual model suggests link between the difference online and offline information search behavior and search outcomes. Thirteen testable hypotheses were proposed to test the causal paths between the main constructs of the model. The proposed model is tested for purchasing of a cellular phone. The reason behind choosing cellular phone as a focal product for this study is that a variety of online and offline information sources are available for consumers to obtain product information about cellular phones. Moreover, 20% of cellular phone users in Turkey want to purchase a new one within the range of six months or at most one year, while the average usage of cellular phone in Europe is two years. As a data collection method, a questionnaire was designed and face to face surveys were conducted. All measures for the constructs have been adapted from existing literature. The survey instrument is composed of four main sections. In the first section, filter questions were asked to reach the target respondents. The following second and third section included the questions associated with information search behavior for the purchasing of a cellular phone. In the last section, questions dealing with personal characteristics including optimum stimulation level, shopping orientations and demographics were asked. Prior to survey administration, a pilot study was conducted by using a student sample. Feedback was obtained regarding the wording of the questions asked in the questionnaire, and also asked to evaluate layout of the survey. In scope of the sampling and design process of the study, the population is defined as "the people who has bought a new cellular phone in last one year and living in Istanbul". Besides, the population consists of males and females using both online information sources and offline (traditional) information sources to get product information. Thus, the Internet usage is the prerequisite of the consumers should be selected as sample members. The sampling procedure used in this study is the cluster sampling method and 685 face-to-face surveys were carried out with consumers. Structural Equation Modeling was applied to test the proposed model. Confirmatory factor analysis and structural model testing were performed using the Lisrel 8.7. Overall, the model fit indices confirmed that the model was valid for the focal product of cellular phone. Besides, modification indices calculated by LISREL propose structural relations among latent variables to improve the main model. The results of the analysis of structural model suggest adding a path from involvement to search outcomes. This proposed relationship between involvement and search outcomes was found to be statistically significant. The major finding of this thesis is that although online information sources have received more attention in recent years, traditional information sources are still important to consumers for seeking product information. Specifically, perceived risk has a positive impact on the difference the use of online information sources and traditional information sources in the favor of traditional information sources for cellular phones. Furthermore, at the pre-purchase information search stage in the case of purchasing a cellular phone, it was found that as recreational shopping orientation and product involvement increase, the difference between the use of online information sources and traditional information sources increases in the favor of traditional information sources. Keywords: Consumer information search behavior, online information sources, traditional sources.
Türkmenceden Türkçeye bilgisayarlı metin çevirisi
Get PDFDiller arasında bilgisayar kullanılarak çeviri yapılması konusu, doğal dil işleme alanının en önemli dallarından bir tanesidir. Ancak teknolojideki ve yöntemlerdeki gelişmelere karşın, genel amaçlı, yüksek başarıma sahip çeviri sistemleri henüz genel kullanıma sunulamamıştır. Bunun temel nedeni, diller arasındaki büyük yapısal ve anlatım farklılıklardır. Bu noktadan hareketle, benzer diller arasında Bilgisayarlı Çeviri (BÇ) gerçeklemenin daha kolay olabileceği akla gelmektedir. Nitekim son yıllarda Çekçe-Slovakça, Çekçe-Lehçe, İspanyolca-Katalanca gibi çok yakın diller arasında yüksek başarımlı çıktılar üretebilen sistemler geliştirilebilmiştir. Üstelik bu sistemler, farklılıkların derin olduğu, Japonca-İngilizce gibi dil çiftleri arasında BÇ için gerek duyulan karmaşık yöntemlere göre daha basit ve kolay gerçeklenebilir yöntemler kullanmaktadırlar. Bu çalışma kapsamında, aynı dil ailesi içinde sınıflandırılan ve birçok yönden benzerlikler gösteren Türkmence ile Türkçe dilleri arasında bir BÇ sistemi geliştirilmiştir. Söz konusu bu diller ne kadar benzer özellikler gösterse de, çözülmesi gereken farklılıklar azımsanmayacak boyuttadır. Türk Dilleri arasındaki farklılıklar, yukarıda anılan dil çiftlerinden daha fazladır ve karşılıklı anlaşılabilirlik söz konusu değildir. Sistem, hem kural tabanlı hem de istatistiksel bileşenlerden oluşan karma bir çeviri modeli kullanarak, Türkmence tümcedeki sözcüklerin sırasını değiştirmeden sözcük-sözcük Türkçeye aktarım yapılması ilkesini temel almıştır. Ancak bitişken yapılı Türk Dillerinin karmaşık biçimbilimsel özellikleri nedeniyle, diğer dillerde kullanılabilen basit doğrudan aktarım yöntemleri geliştirilerek kullanılmıştır. BLEU yöntemi ile sistemin başarım ölçümü yapılmış ve modelin başarılı sonuçlar üretebileceği gösterilmiştir. Anahtar Kelimeler: Bilgisayarlı çeviri, Türk Dilleri, Türkmence, Türkçe.Machine translation is a popular but hard field of natural language processing. Despite of the huge development of technology and inventions of new methods, general purpose full automatic Machine Translation (MT) systems do not exist. Today's MT systems either require post-editing or far from generating high quality translations, particularly of unrestricted texts. Primary reasons for that are the morphological, syntactical and lexical differences between different languages. The more distant language pairs are selected as source and target languages, the more complex methods or models must be used to build an MT system between those languages. Intuitively, this fact implies that MT between related languages can be easier than languages that have completely different structures (i.e. Japan and English). Recently, MT between related languages like Czech to Slovak, Czech to Polish and Spanish to Catalan have been implemented and these studies showed that successful translations can be produced with relatively simpler efforts. In this work our aim is building an MT model between Turkic languages. Some of the Turkic languages are Turkish, Azerbaijani, Uzbek, Turkmen, Kyrgyz, Kazakh and Uighur. All of the Turkic languages are agglutinative languages which have productive inflectional and derivational morphology. A high level of similarity can be observed between Turkic languages, especially in word order and syntactic structure. They have similar morphological structure and share some common word roots. However, some divergences preventing the mutual intelligibility are observed between these languages. From the point of view of extending previous studies to Turkic languages, some serious problems emerge due to both agglutinative structure of the languages and resource scarcities. Except Turkish, most of the Turkic languages are computationally resource poor languages and that means the lack of training corpus, morphological analyzers, POS Taggers and machine readable dictionaries. The model we have presented in this work is a hybrid model that has both rule based and statistical components. Since the word order of Turkic languages are almost same, a direct transfer approach is used in translation by means of word-by-word translation. Morphological processing, which can generate ambiguous results, is the first step of almost every NLP task for agglutinative languages. Then, the actual transfer is carried out by transferring the root words and morphological features to the target language. During the transfer of root word, another type of ambiguity, lexical ambiguity, is emerged in the process. As an exception of word-by-word transfer approach, some additional sentence level processing is done in order to translate Multi-Word Units (MWU) correctly. The two types of ambiguities are resolved by the disambiguation component that exploits Statistical Language Models (SLM) trained on the target language. In next component, a target language morphological generator produces the surface forms of the resulting candidate translation. As a last step, some work is done in sentence level because of some long distance dependencies and a number transfer rules for some phrase structures. The statistical disambiguation component is based on SLMs which are normally generated by using surface forms from the training corpus. But for an agglutinative language, such a training will heavily suffer from sparse data problem, so we propose some SLM types in which various parts of the full morphological parses are modeled. The performances of these types are investigated as well as the performance of the whole system. To evaluate the practical performance of our model, we have implemented a generic MT framework based on our model and built a Turkmen to Turkish MT system by using this framework. The rule based modules of the system are implemented as Finite State Transducers (FST) using Xerox Finite State Toolkit. A Turkmen morphological analyzer is implemented in a two-level manner while an existing wide-coverage Turkish morphological analyzer is used in the generating direction as the target language morphological generator. We have used BLEU as the automatic evaluation metric for our MT system. The results showed that general purpose MT between Turkic languages can be achieved, even relatively easier, and can generate high quality translations. Keywords: Machine Translation, Turkic languages, Turkmen Language, Turkish.
Modelling the damage by microstretch theory and Eshelby tensors
Get PDFBu çalışmada hasarlı malzemeler mikrogermeli ortam teorisi ile modellenerek tanımlanmış ve ortaya çıkan bilinmeyen malzeme katsayıları, kompozit malzemeler ve hasarlı malzeme arasında kurulan analoji ile hesaplanmaya çalışılmıştır. Bu amaç için kullanılan homojenleştirme yöntemlerinin çoğunda ilgili Eshelby tansörlerinin bulunması öncelikli problemlerden biridir. Bu nedenle bu çalışmada da Eshelby tansörlerinin küresel katkı maddeleri içeren mikrogermeli ortam için bulunması problemi ele alınmıştır. Bu amaca ulaşmak için öncelikle mikrogerme teorisi ile modellenen bir ortamın yerdeğiştirme, mikrodönme ve hacimsel mikrogenleşme büyüklükleri için temel çözümler verilmiştir. Bu temel çözümler kullanılarak katkı maddelerinin varlığından kaynaklanan elastik alanlar Green fonksiyonları yardımıyla elde edilmiştir. Son olarak bu elastik alanların mikrogermeli ortamın bünye denklemlerinde kullanılması ile klasik teoride verilen Eshelby tansörleri mikrogermeli ortama genelleştirilmiştir. Klasik elastisitede benzer problem için tek bir Eshelby tansörü elde edilirken, mikrogermeli ortam için dördü dört, ikisi iki boyutlu ve biri de skaler olmak üzere toplam yedi Eshelby tansörü elde edilmiştir. Klasik Eshelby tansörü elipsoidal katkı maddeleri içinde homojen olmasına rağmen, mikrogermeli ortam için elde edilen Eshelby tansörleri küresel katkı maddeleri içinde bile homojen değildir. Çalışmada, mikrogermeli ortamın mikrodönme ile ilgili malzeme sabitlerinin sıfır alınması durumunda mikrogenleşen ortam için Eshelby tansörlerinin elde edilebildiği gösterilmiştir. Ayrıca mikrogermeli ortamın mikrogenleşme ile ilgili malzeme sabitlerinin sıfır alınması durumunda mikropolar ortamın Eshelby tansörlerine ve her iki grup mikro ortamın malzeme sabitlerinin sıfır alınması durumunda ise klasik elastisite için elde edilen Eshelby tansörlerine indirgendikleri de görülmektedir. Anahtar Kelimeler: Eshelby tansörleri, hasarlı malzeme, mikrogermeli ortam, homojenleştirme yöntemleri.Eshelby tensors for the materials modelled by micropolar theory including spherical inclusions are given by Cheng and He (1995). Later on similar work is carried on for microelongation theory by Kiris and Inan (2005). It is assumed that the material particles undergo only microrotation in micropolar theory and volumetric microelongation in microelongation theory in addition to the classical components. Although it is more meaningful to model damaged materials with microelongation theory rather than micropolar theory, because growth of the voids reflects the damage phenomena better than their rotation, both theories are not good enough to model the damaged materials. The reason of the improperness of modelling also with the microelongation theory is that the voids volumetric ratio is very low and thus modelling with microelongation theory accounts only volumetric micro elongation of the whole body. Therefore, to model the damaged materials with microstretch theory is a better approach (Kiris and Inan, 2006). In the present work, the damaged materials are modelled by the microstretch theory, developed by Eringen (1990) by assuming that the material particles can make both microrotation and volumetric microelongation, in addition to the classical bulk deformation. Then, the concept of Eshelby tensors which constitutes the basis of most of the homogenization methods, is extended to microstretch theory to use the analogy between damaged materials with composites which is proposed by Inan (1998). Then we present the fundamental solutions for the displacement and the microrotation vectors and the microelongation scalar in static case, and extend the "eigenstrain" and "microeigenstrain" concepts to the microstretch theory. With the help of these solutions and Green's functions technique, the elastic fields of the material defined by microstretch theory due to the existence of the spherical inclusions are calculated. By substituting these elastic fields to the strain expressions of the microstretch theory, Eshelby tensors for microstretch medium having spherical inclusions, are obtained. In this work, seven Eshelby tensors, as four of them in four dimension, two in two dimension and one scalar are obtained for the microstretch theory, as oppose of the four Eshelby tensors all in four dimension for micropolar theory, four Eshelby tensors as one in four dimension, two in two dimension and one scalar for microelongation theory and lastly one Eshelby tensor in four dimension for the classical theory of elasticity. Furthermore, Eshelby tensors obtained for microstretch theory reduce to Eshelby tensors for micropolar theory, while all microelongational material constants are taken as zero, and correspondingly reduce to Eshelby tensors for microelongation theory, while all micropolar material constants are taken as zero, and finally reduce to the classical Eshelby tensors while all micro material constants are taken as zero. These tensors are not homogeneous in even spherical inclusions as of micropolar and microelongation theories, unlike their classical forms. Besides, the results of the microstretch theory show that, the field quantities related with both micropolar and microelongation theories have contribution to Eshelby tensors corresponding to 'eigenstrain' due to macro deformations, but it is observed that the field quantities related with microelongation theory do not have any contribution to Eshelby tensors corresponding to 'microeigenstrain' due to microrotation. And in the same way the field quantities related with micropolar theory also do not have any contribution to Eshelby tensors corresponding to "micro-eigenstrain" due to micro elongation. The main objective of obtaining Eshelby tensors for these micro theories is to determine the effective properties of the materials modelled with micro elastic theories by use of these tensors in the homogenization methods. Although our starting point was to use these tensors in damage mechanics, all the obtained results are quite general. Namely, Eshelby tensors obtained for the micro elastic theories may be used to determinate effective properties of composite materials as well as the damaged materials. Since Eshelby tensors obtained for all the micro theories are not homogeneous, one can not express the homogenization process analytically, unlike the Eshelby tensors obtained for classical case. It is expected that the homogenization methods like Mori-Tanaka's method can be extended to these micro theories by taking average processes and integrating over the inclusions. Keywords: Eshelby tensors, damaged materials, microstretch medium, homogenization methods
Bitmiş Li-iyon ikincil pillerinden lityum ve kobalt geri kazanımı
Get PDFIn recent years, consumer demand for smaller and more powerful electronic devices has led to a large increase in the usage of batteries worldwide. Advances in sophisticated electronic items such as laptop computers and mobile phones require these batteries to be more sustainable, smaller and lightweight. The gravimetric energy density is 110-160 and 30-50 Wh/kg for lithium ion and lead acid batteries respectively. Owing to its merit, such as a high energy density, a high working voltage, a long cyclic life and negligible memory loss effects, the lithium ion batteries are state of the art and also remain the battery system with the highest potential for future development. With increasing use of such batteries in the developed countries for transportable applications, and large untapped markets in the developing countries, the need for lithium ion batteries will increase by orders of magnitude. This has led to growing concerns worldwide about the disposal of batteries and the potentially harmful impact they may have on the environment. However, spent batteries also represent a concentrated source of high value metal. Therefore, it is important that a system for recycling and regenerating waste lithium ion batteries is developed. Owing to the explosive nature of metallic lithium, spent lithium primary batteries cannot be disposed safely unless metallic lithium is properly removed from them. In contrast, lithium ion secondary batteries use a lithium conducting cathode made from a non-explosive 'mixed oxide', allowing a wider selection of recycling techniques. These mixed oxides often contain valuable cobalt, which has a high economic value for recycling owing to the fact that natural sources for cobalt are limited, and its uses are diverse and steadily increasing. The objective of the present work is to outline the dissolution characteristics of the cathodic active materials from spent lithium ion secondary batteries in sulfuric acid media, and to recover cobalt and lithium separately as their sulfates by sulfate precipitation method using ethanol. Despite long leaching time and high leaching temperature, it was observed that cobalt, which is present in the LiCoO2 compound, dissolved into concentric sulfuric acid media with poor dissolution efficiency. The reason for this is that the oxidation level of the cobalt in the LiCoO2 compound is +3, so it should be reduced to +2. Hydrogen peroxide, known as both good oxidizer and reducer, is an ideal option for this reduction. Using 5% H2O2, at 80oC, at 300 rpm, the LiCoO2 compound was found to dissolve into 4M H2SO4 in an hour with 100% dissolution efficiency. Cobalt was recovered in two steps. During the first step, 92% of the cobalt is recovered as CoSO4 by the use of ethanol at a volume ratio of 3:1. Ethanol removes water ligands from the Co2+ cation, and caused the precipitation of cobalt as cobalt sulfate monohydrate. In the second step, the remaining cobalt was precipitated as cobalt hydroxide (Co(OH)2) by increasing the pH value up to 10 with the addition of lithium hydroxide (LiOH). Lithium, which remained in the solution, was then recovered as lithium sulfate (Li2SO4) with up to 98% recovery efficiency by the addition of ethanol at a 3:1 volume ratio. It was shown that metals could be precipitated separately by this technique depending on their concentrations present in the solution. Using this selective precipitating characteristic of ethanol, it was managed to precipitate the cobalt with high efficiency without promoting the precipitation of the lithium. The advantage of this technique over more classical techniques for salt crystallization is that no temperature shift is needed, and the product will be intrinsically low in water, unlike the more classical separation by crystallization, which requires heat (or at least temperature control) and tends to yield a metal sulfate with a high amount of crystalline water. The leach acids may be reused in feedback loops. Also, it is possible to recover ethanol by distillation. By doing so, the recovered ethanol could be reused for precipitating sulfates from sulfuric acid solutions. The proposed process can be used to treat spent Li-ion secondary batteries, and to recover valuable cobalt and lithium without posing environmental problem. Keywords: Li-ion batteries, recycling, precipitation method with ethanol, Li and Co recovery. Bu çalışmada, lityum iyon ikincil pillerinde katodik aktif malzeme görevi gören lityum kobalt oksit (LiCoO2) bileşiğinin sülfürik asit ile liç davranışları optimize edilerek, çözeltiye geçen lityum ve kobaltın etanol sülfat çöktürme tekniği ile sülfatları şeklinde çöktürülme şartları incelenmiştir. Yeniden kullanılabilir malzemeleri maksimum seviyede geri kazanmak ve böylece bitmiş pillerin çevreye yapacağı kirliliği minimuma indirmek amaçlanmıştır. 80oC sıcaklıkta 1 saat boyunca çözümlendirme işlemi için kullanılan %5 hidrojen peroksit içeren 4M sülfürik asit çözeltisi ile lityum ve kobaltın tamamı çözeltiye geçmiştir. Çözeltiye geçen kobalt iki aşamada geri kazanılmıştır. Birinci adımda, çözeltideki kobalt iyonları, 3:1 etanol/çözelti hacimsel oranında etanol ilavesiyle CoSO4 şeklinde %92 verim ile çöktürülmüştür. Etanol, çözeltideki sülfat ligant bağlarının kırılmasını sağlayarak kobaltın, kobalt sülfat tuzu (CoSO4) şeklinde çökmesini sağlamıştır. İkinci adımda, etanol ile çökmeyen kobalt iyonları, lityum hidroksit ile pH 10’a getirilerek kobalt hidroksit (Co(OH)2) şeklinde çöktürülmüştür. Çözeltideki lityum iyonları da sülfürik asit ile asitlendirildikten sonra 3:1 etanol/çözelti hacimsel oranında etanol ilavesiyle %98 verim ile lityum sülfat (Li2SO4) şeklinde çöktürülmüştür. Etanol sülfat çöktürme tekniği ile metallerin başlangıç konsantrasyonlarına bağlı olarak selektif olarak çöktürüldükleri gösterilmiştir. Ayrıca diğer metotların aksine etanol sülfat çöktürme metodu ile yapılan çöktürme işleminde sıcaklık değişimine ihtiyaç yoktur ve elde edilen ürün düşük miktarda kristal su içermektedir. Anahtar Kelimeler: Li-iyon pilleri, geri dönüşüm, etanol sülfat çöktürme, Li ve Co kazanımı. 
Spinodal phases in Cr coated low carbon steel through cathodic arc PVD technique
Get PDFBu çalışmada, katodik ark fiziksel buhar biriktirme yöntemi ile krom kaplanan, krom kaplama sonrası farklı sürelerde yüksek bias voltajı etkisi ile krom iyonu bombardımanı uygulanan ve darbeli bias voltajı uygulaması ile krom kaplanan düşük karbonlu çelik malzemelerde meydana gelen spinodal fazlar karakterize edilerek, gelişimleri incelenmiştir. Elektron mikroskopisi, elementel analizler ve kesitlerden alınan derinlik profili çalışmaları ile gerek kaplama sonrası uygulanan krom bombardımanı, gerekse darbeli bias uygulamasında yüksek bias periyodlarındaki krom bombardımanının, krom kaplama ve düşük karbonlu çelik taban malzeme arasında radyasyon destekli yayınma mekanizması ile gerçekleşen bir iyon demeti karışımı prosesine neden olduğu tespit edilmiştir. Bunun sonucunda, taban malzemeden kaplama yüzeyine büyük oranda demir atomu yayınmış ve yüzeylerde çok kısa süreler içerisinde spinodal ayrışma fazları meydana gelmiştir. Bu fazların morfolojileri, literatürde demir-krom (Fe-Cr) sistemindeki spinodal ayrışma çalışmalarında elde edilen mikroyapılar ve bilgisayar simülasyonu ile oluşturulan spinodal yapılar ile oldukça büyük benzerlikler göstermiştir. Ayrıca bombardıman uygulanan örneklerde, spinodal ayrışma yapılarının bir karakteristiği olan tepe/vadi oluşumları ile fazlar arasındaki bileşimsel dalgalanmalar gibi sonuçların gözlenmesi de spinodal fazların oluşumunu doğrulamaktadır. Elde edilen mikroyapılara bakıldığında, taneli taban malzeme üzerinde epitaksik olarak büyüyen kaplamalardaki bazı tanelerde, spinodal ayrışma fazları oluşmadığı görülmüştür. Bununla birlikte, bombardıman süresinin artması ile bu tanelerde de spinodal ayrışma yapılarına benzer oluşumlar gözlenmiştir. Anahtar Kelimeler: İyon bombardımanı, radyasyon destekli yayınma, spinodal ayrışma.In this study, spinodal decomposition phases formed in low carbon steel samples which were Cr coated, Cr coated and bombarded with Cr ions through applying high bias voltage (1 keV) and Cr coated through applying pulsed bias voltage in a cathodic arc physical vapour deposition (PVD) system were characterized and compared. 1.5 mm thick IF (interstitial free) steel sheets were used as substrate. The bombardment periods after the coating were 1 minute, 2 minutes and 3 minutes. In pulsed bias mode, bias voltage was alternately increased to 1 keV for 5 seconds (bombardment section) and decreased to 150 eV for 10 seconds (coating section) along 10 minutes. Total bombardment time was 3.3 minutes in 10 minutes of pulsed bias. In order to determine the spinodal decomposition phases, Field Emission Microscopy (FEM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectral Analysis (EDS) and Glow Discharge Optic Emission Spectroscopy (GDOES) studies were performed. Not only the bombardment applied after the coating process, but also the one applied during the high bias voltage period in the pulsed bias mode caused radiation enhanced diffusion between Cr coating and low carbon steel substrate. This was proven by EDS analysis, GDOES analysis and elemental maps taken from cross sections of the samples. Fe content of coatings increased gradually by increasing bombardment time. As a result of ion beam mixing, severe iron diffusion from the substrate to the Cr coating?s surface took place and this resulted in formation of spinodal decomposition phases in a very short time. These phases? morphologies were quite similar to microstructures obtained from spinodal decomposition studies in Fe-Cr system and computer simulated spinodal structures in literature. Besides, it was observed through the EDS analysis and FEM studies of the bombarded samples that hill/valley formations and compositional fluctuations which were the characteristics of spinodal decomposition process were also present. Hills were Cr rich and valleys were Fe rich parts of the spinodal structures. It was observed in FEM micrographs that hills and valleys were getting wider with increasing bombardment period and it was another characteristic of spinodal decomposition structures. When the average cohesive energy of the Fe-Cr system (4.19 eV) and the relationship between the cohesive energy and the critical temperature (Tc»100Ekoh) at which radiation enhanced diffusion (RED) would be efficient were taken into consideration, ion beam mixing in our system woud take place through RED regime. Altough both metals have similar cohesive energies, dominant Fe movement to the Cr coating was observed in pulsed bias mode instead of an isotropic mixing. While Fe-Cr alloys must be heat treated for very long times (up to 500 hours) in conventional spinodal decomposition processes, it is very interesting that the spinodal decomposition phases formed in 1-3 minutes in this study. It is believed that the diffusion enhanced by the radiation effected the spinodal decomposition kinetics. As a result of thermally activated migration of defects caused by Cr ion bombardment and short range diffusions in very hot thermal spikes formed by the collisions between bombarding ions and target atoms accelerated the diffusion processes which make the spinodal decomposition occur. In some grains of the coatings which grew on grained microstructure of the substrate material epitaxially, spinodal decomposition was not observed. These smooth grains with no hill/valley structure were supposed to be s phase which was not decomposed during the bombardment and cooling periods. The coherency strain between the grains may have displaced the spinodal line (coherent spinodal) in some grains resulting in not occuring spinodal decomposition in chemical spinodal line. However, spinodal structures started to form in those smooth grains by increasing the bombardment time and temperature. It was observed via EDS analysis taken from the samples which were not only bombarded after coating but also coated through applying pulsed bias that Fe content increased by increasing the bombardment time. Formation of spinodal structures in smooth grains and increasing of the Fe content concurrently by increasing the bombardment time points that spinodal decomposition occurs in Fe rich part of the spinodal line in those smooth grains. As a potential development of this study, more efficient temperature control should be applied to determine chemical and coherent spinodal lines in Fe-Cr alloys produced by ion bombardment of Cr coated low carbon steels.Keywords: Ion bombardment, radiation enhanced diffusion, spinodal decomposition
A secure mobile agent system
Get PDFHareketli etmen mimarisi istemci-sunucu çalışma modeline karşın dağıtık işlemeye farklı bir yaklaşım sunmaktadır. Kodun hareketliliğine dayanan hareketli etmen sistemlerinde, güvenlik düşünülmesi gereken önemli bir unsurdur; çünkü artık durağan bir yazılım parçası değil, kodunu ve verisini uzak düğümlere taşıyabilen yazılımlar, yani etmenler söz konusudur. Bu türden hareketli yazılımların hem kodunun hem de verisinin izlenme veya değiştirilmesi gibi yeni güvenlik risklerinin ortaya çıkması kaçınılmazdır. Birbirleri ile haberleşebilen etmenlerin mesajlaşmaları sırasında da aynı tehlikeler söz konusudur. Daha da önemlisi, güvenlik riskleri ile karşı karşıya olan sadece etmenler değildir, etmenleri üzerlerinde çalıştıran düğümler de aynı ölçüde risk altındadırlar. Bu yazıda, hareketli etmen sistemlerindeki mevcut güvenlik tehlikelerini ortadan kaldıracak yeni bir mimarinin tasarım ve gerçeklenme ayrıntıları incelenmiştir. Geliştirilen güvenli etmen sistemi, hem etmenlerin güvenlik gereksinimlerine yanıt vermek, hem de kolay kullanımlı ve esnek bir çalışma ortamı sunmak üzere tasarlanmış ve gerçeklenmiştir. Gelişmiş güvenlik özellikleri yanında sistem, değişen güvenlik ihtiyaçlarına kolay ve anında uyum sağlayabilmek için güvenlik politikalarını kullanmaktadır. Güvenlik politikaları, değişen güvenlik ihtiyaçlarına, hızlı ve etmenin yeniden programlanmasını gerektirmeden cevap verebilmeyi sağlar. Sistem ayrıca sadece etmenlerin değil, etmenlere çalışma ortamı sunan düğümlerin güvenliği için de gerekli mekanizmaları sunmaktadır. Geliştirilmiş olan hareketli etmen sistemi, güçlü bir mesajlaşma altyapısı sunmasının yanında, izlenilebilirlik, yönetilebilirlik ve süreklilik için de esnek arayüzler barındırmaktadır. Sistem katmanlı bir mimariye sahiptir ve geliştirilmeye açıktır. Anahtar Kelimeler: Etmen, hareketli etmen sistemleri, hareketli etmen sistemlerinde güvenlik.According to the accepted definition, an agent is a small application with some special features. Being autonomous, capable of adapting itself to its environment, communicating with other agents for coordination or cooperation, intelligence, ability to clone itself and ability to make decisions are the features that can distinguish an agent from ordinary software. Even though mobility, ability to migrate from one host to another host, is not a required feature, agents with this ability have advantages especially in terms of distributed data processing. A mobile agent is not restricted to the node where it is running and can migrate to anywhere on the network of its own accord. While moving from one host to another, not only the agent's executable code is transferred, but also data that the agent has collected or constructed are transferred as well. Thus, the agent can preserve its state even when it is mobile. The execution framework necessary for a mobile agent is provided by a mobile agent system. This framework simply provides the basic agent related tasks and functions such as agent creation, activation, migration, communication, cloning and destruction. The competence and power of a mobile agent system depends on the flexibility of these functions. Even though using mobile agent technologies provides potential benefits to applications, an agent's ability to move introduces significant security risks. Mobile agents are under security threats during their life times. Since the code is mobile, it can be stolen or altered by a third party. The same danger is present for the messages agents send to each other and for the data that determines the agent's state. Furthermore, not only the agents but also hosts are also under many security risks in mobile agent systems. Several mobile agent systems have been proposed and developed up to now. They all have their software agent specific features. Although most of them have enough features for mobile agents to communicate with each other and migrate to remote hosts, agent security related tasks are not available in most of them. Some provide limited security for agents, but do not provide any features to protect hosts. Most of these mobile agent systems leave the security to agent programmer or to the traditional net work security solutions which may be very difficult and inefficient to implement or integrate. The mobile agent system is expected to include all necessary security mechanisms for both agents and computers hosting mobile agents. The scope of this paper is the design and implementation of a new, secure, flexible, highly available and fast mobile agent system (SECMAP). The architecture of the system is especially designed for security purposes, and requirements not only for agent security but also for host security are also provided. Besides ensuring security of both agents and hosts, SECMAP also presents a very flexible agent programming interface. Naturally, these features play an important role on the usability and popularity of the system. SECMAP also presents a policy based management framework to protect system-level resources and agents against unauthorized access, as well. The policy architecture allows for dynamic manipulation of policy content, which results in an adaptive and flexible framework that eliminates the reprogramming of the agents on changing conditions. Logging and monitoring of the basic agent activities are also possible. Availability is very important for the collaborating agents. For this reason, a mobile agent system should be up and running even only one host in the system is active. When necessary the system should be able to transfer the duties of a dead host to another one in the system. SECMAP includes very powerful algorithms to ensure the availability of the overall system. It accomplishes this by assigning special working modes to different agent servers in the system. Another important feature is that the system and agents can be managed and monitored from a browser in the network. All agents present in the system can be monitored from a single window. Any module of the system can also be managed by a browser from remote hosts. SECMAP is worth being used not only for the security features it presents for agents and hosts, but also for its flexibility and powerful agent programming interface. The system has a layered architecture and is open to be improved with more powerful features. Keywords: Agents, Mobile agent systems, Security in mobile agent systems
Two-dimensional ARMA parameter identification with two-channel AR lattice approach
No full textİki-boyutlu zamanla değişmeyen bir ARMA(M,N) sistemin parametrelerini tanılamak için yeni bir yöntem önerilmiştir. Burada M, AR kısmının derecesini, N ise MA kısmının derecesini temsil etmektedir. Bu yeni yöntem, önceden önerilen iki-kanallı AR kafes modelleme yaklaşımının, AR ve MA derecelerinin farklı olduğu durumları da içerecek şekilde genişletilmiş bir şeklidir. Yeni önerilen yöntem, hem iki-kanallı, hem de tek-kanallı kafes yapılarını barındırması nedeni ile bir “karma kafes yapısı” olarak da adlandırılabilir. Bu karma kafes yapısı, hem çeyrek düzlem, hem de simetrik olmayan yarı düzlem modellerine uygulanabilmektedir. AR derecesinin MA derecesine eşit olduğu durumlarda, karma kafes yapısı ortadan kalkmakta, yalnızca iki-kanallı iki-boyutlu AR kafes yapıları ile çözüme gidilmektedir. Bu çalışma kapsamında ayrıca, ARMA parametreleri hesaplamak için, b0 parametresini ve her iki kanala ilişkin ileri yönde öngörü süzgeçlerinin katsayı ağırlıklarını da içine alan ve M ³ N, M < N durumları için kullanılabilecek yeni bir formülasyon yaklaşımı önerilmiştir. Önerilen yöntemin doğrulanması amacıyla, bilgisayar benzetimleri kullanılmıştır. Bu benzetimlerin her birinde, karşılaştırmaya esas olarak LS kestirimleri alınmıştır. Ayrıca L1, L2 ve L¥ vektör normları ile Itakura-Saito uzaklığı, başarım ölçütleri olarak kabul edilmiş ve her bir bilgisayar benzetimi için hesaplanmıştır. Elde edilen parametre tanılama sonuçları, karma kafes yönteminin, oldukça küçük veri alanı boyutları için bile kabul edilebilir nitelikte olduğunu göstermektedir.Anahtar Kelimeler: ARMA sistem tanılama, iki-kanallı AR modelleme, iki-boyutlu kafes yapıları.The field of multi-dimensional digital signal processing has become increasingly important in recent years due to a number of trends in digital signal processing. Parametric representations of two-dimensional (2-D) random fields in the form of autoregressive (AR), moving average (MA) and autoregressive moving average (ARMA) models are useful in many applications such as image synthesis, classification, spectral estimation, radar imaging, etc. There are a number of advantages and disadvantages related with AR and MA modelings. The major advantage of both models is that the solution for the model parameters involves only linear equations. In the MA models the solution is unbiased in the presence of additive noise on the system output as long as the noise and system input are uncorrelated. MA models are always stable since they are non-recursive. One of the most serious disadvantages of either AR or MA modeling is the fact that to adequately represent even simple linear systems, both methods may require a large number of parameters (a high order model). This problem arises since, from a transfer function standpoint, AR and MA models attempt to model the system using only poles or only zeros, in spite of the fact that physical systems may have both zeroes and poles. The ARMA (M, N) model is a generalization of the Mth order AR and Nth order MA models and accomplishes exactly modeling the unknown system with poles and zeroes, representing the system in rational transfer function form. Therefore this has motivated a considerable interest in the more general pole-zero (ARMA) model. The primary concern of this research is the determination of discrete time models for 2-D LSI systems from sampled observations of the system input x(k1, k2) and system output y(k1, k2), using 2-D orthogonal lattice structures, assuming that the order of the ARMA(M, N) model is known. The ARMA model order is represented by the (M, N) pair, where M represents the order of the AR polynomial and N represents the order of the MA polynomial. Here we present a "hybrid lattice" structure in order to identify the ARMA(M, N) system parameters, provided that x(k1, k2) and y(k1, k2) are given. This structure can be applied to both quarter-plane (QP) and asymmetric half plane (ASHP) models and it is based on the two-channel AR lattice approach proposed by Kayran for equal AR and MA orders. The novelties brought about by this proposed structure can be listed as follows. We extend Kayran's approach to the case where M and N can take arbitrary values different from each other. We accomplish this with the help of our proposed hybrid lattice structure where both 2-D two-channel AR and 2-D single-channel AR lattice stages are incorporated. We also propose a modification in terms of the channel inputs of the two-channel lattices. We drive the first channel input by a difference signal of u(k1, k2) = y(k1, k2)-x(k1, k2) instead of y(k1, k2), which was formerly proposed. The second channel input, which was formerly proposed as x(k1, k2), is driven by a newly defined signal t(k1, k2), which is related with the orders of the AR and MA polynomials. If M > N, t(k1, k2) is equal to x(k1, k2), if (M < N, t(k1, k2) is equal to y(k1, k2). We propose modifications in the b0 parameter estimates for the cases where (M ³ N and M < N, in accordance with our newly proposed channel inputs. We derive a new formulation for the ARMA (M,N) parameter estimates, taking into account the estimated parameter b0 and the forward prediction error filters tap weights related with both channels. In order to make a verification of the proposed method, we give computer simulation examples where we compare the hybrid lattice estimates with the LS (Least Squares) estimates. As performance measures, we use the L1, L2 and L¥ vector norms and the Itakura-Saito distance measure, which indicates the similarity between the original and identified power spectrums.Keywords: ARMA system identification, two-channel AR modeling,two-dimensional lattice structures
Multivariate interpolation applications of different high dimensional model representations
Get PDFBu çalışmada adet bağımsız değişkene bağlı olan birçok değişkenli fonksiyonun değerlerinin bağımsız değişkenlerin sonlu sayıda değer takımı için verildiği ve fonksiyonun analitik yapısının istendiği çok değişkenli interpolasyon problemlerinin daha az değişkenli interpolasyon problemlerine indirgenmesi amaçlanmıştır. Böylelikle, hesaplama karmaşıklığı düşürülecek ve problemin bilgisayar ortamında programlanması da kolaylaşacaktır. Bu amaçla, değişkenli bir interpolasyon problemi adet tek bağımsız değişkenli interpolasyon problemi haline getirilmektedir. Belirtilen indirgeme için ilk olarak I.M. Sobol tarafından tasarlanan Yüksek Boyutlu Model Gösterilim (YBMG) yöntemi geliştirilmiştir. Bu yöntem çok değişkenli verinin hiperprizmatik örgünün tüm düğümlerinde verildiği problemlerde veri bölümlemesinde kullanılmaktadır. Bölümleme sonucunda elde edilen tek değişkenli veri kümesinden çok değişkenli fonksiyon için aranılan analitik yapı yaklaşık olarak elde edilebilmektedir. Yöntemin temel felsefesini oluşturan sonlu terimden oluşan açılımın yapısı baskın olarak toplamsal özellikler taşıyan çokdeğişkenli veri kümelerine ait interpolasyon problemlerinde gerçek sonuca yakın gösterilimler elde etmeyi sağlamaktadır. Aranılan analitik yapı, yani verilen çok değişkenli veri kümesinin yapısı, toplamsal özelliklerden uzaklaşıp çarpımsal veya melez özelliklere sahip olmaya başladığında YBMG yönteminin verimi düşmektedir. Bu bağlamda alternatif yöntemlere ihtiyaç duyulmaktadır. Bu amaçla, problemde verilen veri takımının yapısına göre Çarpımsallaştırılmış Yüksek Boyutlu Model Gösterilim (ÇYBMG) ve Melez Yüksek Boyutlu Model Gösterilim (MYBMG) yöntemleri de oluşturulmuştur. Belirtilen bu yöntemler YBMG yöntemi aracılığıyla bölümlenmiş veriyi kullanarak çarpımsal veya melez yapıya sahip fonksiyonlar için daha iyi yaklaşıklık elde eden gösterilimler oluşturmayı hedeflemektedir. Anahtar Kelimeler: Yüksek boyutlu model gösterilim, çokdeğişkenli fonksiyonlar, interpolasyon, yaklaştırım.In this work, the main purpose is to reduce the multivariate interpolation problems to the less-variate interpolation problems in which the values of a multivariate function having number of independent variables are given for a finite number of data and it is asked to determine an analytical structure for this function. As a result, the computational complexity of the problem will decrease and it will become easier to write programs for the computer-based applications. For this purpose, a package of number of univariate interpolation problems is constructed from a dimensional interpolation problem. High Dimensional Model Representation (HDMR) method is developed for the mentioned reduction process of the interpolation problem to determine approximate representation for the analytical structure of the sought function. HDMR is a divide conquer method and was first proposed by I.M. Sobol, then generalized by H. Rabitz. HDMR has an expansion for a given multivariate function such that its components are ordered starting from a constant component (zeroth order multivariance) and continuing in ascending multivariance, that is, univariate, bivariate, trivariate components and so on. Components of this representation are determined by using an imposition of vanishing integrals. Since the main purpose of this work is to partition the given multivariate data into lower variate data, HDMR algorithm is reconstructed for data partitioning. This new method can be used for partitioning the data of multivariate interpolation problems in which the values of the sought function are given at all nodes of the hyperprismatic grid. Using these partitioned data the analytical structure for the sought function is obtained through Lagrange interpolation formula. When the nature of the HDMR expansion given below and the numerical implementations are examined it is seen that new methods are needed to obtain better approximate representations when the sought function does not have purely or dominantly additive nature. Hence, it can be said that the nature of the sought multivariate function and the features of the given data set have characteristic roles on the development of these methods. The sought function may have a multiplicative or an intermediate nature. Certain other methods are developed for interpolation problems having these types of structures. Factorized form of the HDMR method is called Factorized High Dimensional Model Representation (FHDMR). This method has a multiplicative expansion and the components of FHDMR expansion are evaluated by making comparisons between the HDMR and the FHDMR expansions of the multivariate function. To construct a unique comparison procedure certain idempotent operators are inserted into the HDMR expansion. After inserting these mentioned operators and expanding the FHDMR expansion into an additive expression, relations for FHDMR components of the multivariate function can be obtained in terms of the components of the data partitioning technique. In most cases the nature of the given multivariate data and the sought multivariate function have neither a purely additive nor a purely multiplicative nature. They have a hybrid nature. So, a new method is developed to obtain better results and it is called Hybrid High Dimensional Model Representation (HHDMR). This new method has an expansion including both the HDMR and the FHDMR expansions of the multivariate function through a hybridity parameter. The main problem in this method is to determine the best value for this parameter to obtain the best representation in the given interpolation problem. A cost functional is defined to obtain this mentioned value for the hybridity parameter. Another cost functional is defined to find the best representation obtained through three methods that were mentioned; HDMR, FHDMR and HHDMR for the sought multivariate function. Several numerical implementations are also given in this paper to test the efficiency of all these three methods. Various test functions are selected to examine the performance of the given methods. When the norm values, defined for finding the best representation, obtained for each representation method in the implementations are examined the best representation for the purely or dominantly additive functions are obtained through HDMR method. If the sought function has a purely or dominantly multiplicative nature, FHDMR method gives the best representation. On the other hand when the sought function has an intermediate nature then HHDMR method is needed to determine a better representation. Keywords: High dimensional model representation, multivariate functions, interpolation, approximation
100 kV DC high voltage divider having lower than 100 ppm measurement uncertainty
Get PDFBu makalede, 100 ppm ölçüm belirsizliğine sahip, kalibrasyon standardı olarak kullanılmak üzere tasarımı ve yapımı gerçekleştirilen 100 kV’luk bir yüksek doğru gerilim bölücüsüyle ilgili yapılan çalışmalar sunulmuştur. Yüksek doğru gerilimlerin ölçülmesinde yaygın olarak dirençsel gerilim bölücüler kullanılır. Bunların çevirme oranları, kesin olarak bilinmeli ve gerilime bağlı olmamalıdır. Uygulanan gerilimin yüksekliğiyle çevirme oranı, temelde üç faktöre bağlı olarak değişir. Bunlar, dirençlerin ısınmasına bağlı olarak direnç değerlerindeki değişim, kaçak akımlar ve korona boşalmalarıdır. Gerilim bölücünün yapımı, bu faktörler hesaplanarak gerçekleştirilmiştir. Yapım sonrasında performans deneyleri yapılmıştır. Deney sonuçları ile teorik sonuçların uyumlu oldukları görülmüştür. Son olarak gerilim bölücünün belirsizlik bütçesi oluşturulmuştur.Anahtar Kelimeler: Yüksek doğru gerilim bölücüsü, ölçüm belirsizliği, yüksek gerilim izlenebilirliği.The aim of this paper is to show that the designing and constructing of the direct current (DC) high voltage divider having lower than 100 ppm (part per million) measurement uncertainty (k = 2) for using as a standard divider at 100 kV. The ratio of a resistive standard divider used for precisely measuring DC high voltages should have been known accurately and independent of voltage. A change in effective resistance of a divider with voltage may be due to combination of three factors. These are heating of entire resistance wire related to temperature coefficient, current leakage which increases with voltages through the insulation material and corona discharges may occur at location of high electrical field along to the entire resistor. The aim of this study is to construct an accurate DC high voltage reference divider considering these factors. This divider is constructed by considering these factors, theoretically. After construction of the divider, performance tests are carried out experimentally. These are stability, linearity, temperature distribution, corona, leakage current, partial discharge and scale factor tests. The results obtainedfrom the tests have been compared with theoretical calculations and it has been shown that the results are compatible. Finally the uncertainty budget of the high voltage divider has been formed and uncertainty of the divider has been obtained to be 66 ppm. Keywords: DC high voltage divider, measurement uncertainty, high voltage traceability
Anaerobic treatment of low strength wastewaters at temperate regions
Get PDFEtkili hacimleri 6.45 litre olan iki adet Yukarı Akışlı Çamur Yataklı (YAÇY) reaktör, evsel atıksu karakterindeki sentetik su beslenerek, sürekli sistemler olarak çalıştırılmıştır. Mezofilik YAÇY reaktör 35±2.0°C’de çalıştırılırken psikrofilik (soğuk seven) reaktör başlangıçta oda sıcaklığında çalıştırılmış, daha sonra sıcaklık adım adım 10±2.0°C’e düşürülmüştür. 10±1.0°C ve 35±2.0°C’de, 12 saat hidrolik bekleme süresinde sırasıyla %82 ve %92 civarında KOİ giderimleri gözlenmiştir. Biyogaz üretimleri, ³ 16°C’de her iki reaktörde hemen aynı gözlenmiş, sıcaklık 10±1.0°C’e düşürüldükten sonra belirgin bir azalma göstermiştir. Psikrofilik reaktör verimi daha düşük ölçülse bile, düşük kirlilik yükündeki atıksuların havasız arıtımı başarılı şekilde gerçekleştirilmiş, ilave ısıtma ihtiyacı göstermeyerek daha ekonomik arıtım sağlanmıştır. Anahtar Kelimeler: Düşük maliyetli arıtım, düşük kirlilikte atıksular, psikrofilik, YAÇY reaktör.In this study, two identical lab-scale Upflow Anaerobic Sludge Bed (UASB) reactors with an effective volume of 6.45 l were used and operated as continuous systems for about 12 months. The mesophilic UASB reactor was operated at 35±2.0°C whereas the psychrophilic UASB reactor was operated at room temperature at the start-up and reduced to around 10±2.0°C step by step. In the study, synthetic wastewater characterizing domestic sewage was fed to both reactors. Results indicated around 82% COD removal at 10±1.0°C at a hydraulic retention time of around 12 h while at the same hydraulic retention time total COD removal could be observed around 92% at 35±2.0°C. The total biogas productions were observed about the same amount at temperatures above 16°C in both reactors. However, when the temperature in the psychrophilicUASB reactor was reduced to 10±1.0°C, total biogas production decreased significantly. pH values in the effluent of the mesophilic UASB reactor were measured slightly higher than the pH values in the effleunt of the psychrophilic UASB reactor. Although average COD removals at the psychrophilic UASB reactor was observed lower than the mesophilic UASB reactor, anaerobic treatment of low strength wastewaters could be well established and more feasible system due to no heating requirement could be achieved successfully. Keywords: Low-cost treatment, low strength wastewater, psychrophilic, UASB reactor
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