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Temporal stability of steady-state quasi-one-dimensional bubbly cavitating nozzle flow solutions
Get PDFBu çalışmada, yakınsak-ıraksak bir lülede sanki-bir-boyutlu kavitasyonlu daimi kabarcıklı akış çözümlerinin, kabarcık/kabarcık etkileşmeleri de göz önünde bulundurularak zamana göre kararlılığı incelenmiştir. Bunun için homojen kabarcıklı sıvı akışı modeli kullanılarak sanki-bir-boyutlu daimi olmayan kavitasyonlu lüle akış denklemleri kabarcık dinamiği yasasıyla birlikte (iyileştirilmiş Rayleigh-Plesset denklemi) gözönünde bulundurulmuştur. Çekirdekleşme, kabarcık bölünme ve birleşmeleri ihmal edilmiştir. Tüm sönüm mekanizmaları, viskoz yutulma biçiminde tek bir sönüm katsayısıyla ele alınmış, kabarcıkların büyüme ve büzülmelerinde kabarcık içindeki gaz için politropik yasa kullanılmıştır. Başlangıç dağılımları, giriş koşulları ve lüle geometrisi, lülede kavitasyon oluşacak şekilde alınmıştır. Bu varsayımlar altında, model denklem sistemi, akış hızı ve kabarcık yarıçapı için iki evrim denklemine indirgenmiştir. Evrim denklemleri, daimi olmayan akışa göre pertürbe edilerek kabarcık yarıçapı ve akış hızı pertürbasyonları için kuple lineer kismi diferansiyel denklem sistemi elde edilmiştir. Bu kuple lineer denklem sistemi genelleştirilmiş özdeğer problemine dönüştürülmüş ve lülenin belli bölgeleri için özdeğerler hesaplanmıştır. Özdeğer problemindeki denklem sisteminin tüm katsayılarının hemen hemen sabit olduğu lüle giriş bölgesinde, normal mod analizi yöntemiyle problem kesin olarak çözülmüştür. Çeşitli akış parametrelerinin (kavitasyon sayısı, vs.) k pertürbasyon dalga sayısıyla değişimi için kararlılık diyagramları elde edilmiştir. Elde edilen sonuçlar, kavitasyonlu daimi lüle akışı çözümlerinin sadece çok küçük dalga sayıları için zamana göre kararlı olduğunu göstermiştir. Lüle giriş bölgesi için kararlılık diyagramlarındaki kararlı bölgelerin, türbülanslı cidar kayma gerilmesi etkisi gözönünde bulundurulduğunda genişlediği görülmüştür. Anahtar Kelimeler: Kavitasyonlu akışlar, daimi akış çözümleri, zamana bağlı kararlılık.Cavitating flows through converging-diverging nozzles seem to be the simplest configurations for analysis in hydrodynamic cavitation. They have direct applications in cavitation in ducts and venturi tubes as well as in Diesel injection nozzles. The first model of bubbly liquid flow through a converging-diverging nozzle was proposed by Tangren etal. (1949) using a barotropic relation. The problem was reconsidered by Ishii et al. (1993) by taking into account unsteady effects, but still neglecting bubble dynamics. A summary of barotropic models can be found in the book by Brennen (1995). For cavitating flows it is essential to consider bubble dynamics together with the equations of nozzle flow. A continuum bubbly mixture flow model that couples spherical bubble dynamics, as described by the classical Rayleigh-Plesset equation, to the flow equations was proposed by van Wijngaarden (1968). Steady-state solutions of bubbly cavitating flows through converging-diverging nozzles have been investigated by Wang and Brennen (1998) and by Delale etal. (2001) using the continuum bubbly liquid flow model. Assuming that the gas pressure inside the bubble obeys the polytropic law and lumping all damping mechanisms, in a crude manner, by a single damping coefficient in the form of viscous dissipation, both investigations have demonstrated bifurcation of steady-state solutions to flashing flow instabilities by varying the inlet void fraction (or inlet bubble radius or inlet cavitation number). A numerical investigation of unsteady bubbly cavitating flows in converging-diverging nozzles on the same model has been carried out by Preston etal. (2002). They show that the instabilities encountered in the steady-state solutions of quasi-one-dimensional bubbly nozzle flows may correspond to unsteady bubbly shock waves formed in the diverging section of the nozzle and propagated downstream. The aim of this investigation is to present a detailed analysis of quasi-one-dimensional unsteady bubbly cavitating flows in converging-diverging nozzles with the inclusion of bubble/bubble interactions as discussed in Delale etal. (2001). The description is, therefore, restricted solely to the investigation of the interplay between the overall compressibility of the continuum bubbly mixture and flow unsteadiness. Although the stability of both inviscid and viscous bubbly parallel flows have been investigated by d'Agostino etal. (1997) and d'Agostino and Burzagli (2000), it is important to investigate the temporal stability of cavitating nozzle flows in the quasi-one-dimensional approximation to find out whether such steady-state solutions are stable with respect to temporal perturbations. In this study the stability of steady-state bubbly cavitating nozzle flows is considered. For this reason, quasi-one-dimensional unsteady bubbly cavitating nozzle flows are considered by employing a homogeneous bubbly liquid flow model together with the nonlinear dynamics of cavitating bubbles, described by a modified Rayleigh-Plesset equation. Nucleation, coagulation of bubbles and bubble fission are neglected. The various damping mechanisms are lumped together by a single damping coefficient in the form of viscous dissipation. A polytropic law for the expansion and compression of the gas inside the bubble is assumed. The initial distributions, inlet conditions and nozzle geometry are choosen such that cavitation can occur in the nozzle. Under these assumptions the complete system of equations, by appropriate uncoupling, are reduced to two evolution equations, one for the flow speed and the other for the bubble radius. The evolution equations for the bubble radius and flow speed are then perturbed with respect to flow unsteadiness resulting in a coupled system of linear partial differential equations for the radius and flow speed perturbations. This system of coupled linear PDE's is then cast into an eigenvalue problem. The eigenvalues for the resulting system are found by normal mode analysis in the inlet region of the nozzle where the coefficients of the system of the PDE's are almost constant. Stability diagrams are obtained by varying the various flow parameters (cavitation number, etc.) against the perturbation wave number k. Results found show that the steady-state bubbly cavitating nozzle flow solutions are temporally stable only for perturbations with very small wave numbers. The effect of damping mechanisms on the stability of the steady-state solutions seems to be negligible in the inlet region because of the very small growth rate of the bubbles. The stable regions of the stability diagram for the inlet region of the nozzle are seen to be broadened by the effect of turbulent wall shear stress. Keywords: Bubbly cavitating flows, steady-state solutions, temporal stability
Symbolic meaning of the façade surfacing materials -an evaluative study
Get PDFYapılaşmış çevrenin anlamı üzerine odaklanan pek çok çalışma yapının kendisine ait unsurlarla anlam ilettiğini göstermektedir. Sözü edilen çalışmalar yapının biçimi, büyüklüğü, rengi, mimari tarzı gibi unsurlarına dayanarak yapının anlamını sorgulamaya çalışmıştır. Bu çalışma ise; mimari yapısal çevrenin biçimlendirilmesinde kullanılan ve anlam ilettiği düşünülen malzemenin simgesel anlamı üzerine odaklanmaktadır. Cephe kaplaması olarak kullanılan malzemelerin işlevden bağımsız, kendi başına ilettiği anlam ile bir işleve bağlı olarak biçimlenmiş bir yapıda kullanılması durumunda ilettiği anlamların belirlenmesi ve karşılaştırılması bu çalışmanın konusudur. Bu kapsamda; malzemenin her iki durumda ilettiği anlamlar saptanmış, böylece malzemenin işlevsel bir yapıda kullanılması durumunda anlamının değişip değişmeyeceği sorgulanmıştır. Anlamın değişmesi konusunda yapılacak karşılaştırma için yaygın bir işlev olması ve kullanıcısının kimliğini yansıttığı görüşünden yola çıkarak konut tercih edilmiştir. Malzemelerin uygulandığı konut görüntüleri inşa edilmiş örnekler yerine simulasyonla elde edilmiştir. Böylelikle deneklerin görüntülerde konutun biçim ve büyüklüğü, mimari tarzı gibi konulardan etkilenerek yorum yapması engellenmeye çalışılmıştır. Uygulama için taş, ahşap, sıva, tuğla ve kompozit malzeme seçilmiştir. Konutta kullanılan malzemelerin anlamı, deneklerin konutun varsayılan kullanıcısı hakkında ilettiğini düşündükleri anlamlara dayanarak bulunmuş ve malzemenin işlevden bağımsız ilettiği anlamlarla karşılaştırılmıştır. Uygulama çalışmasından elde edilen sonuçlar seçilen malzemelere göre anlamın hangi yönde değiştiğini gösterirken; malzemelerin ilettikleri anlama dayanarak kullanılabileceği işlev tiplerinin de neler olabileceği konusunda da bilgiler vermektedir. Anahtar Kelimeler: Simgesel anlam, cephe kaplama malzemesi, konut.A great number of studies which focused on the meaning of the built environment pointed out that buildings convey meaning with their components. In the examination of the meaning of a building these studies generally used components such as, form, size, color and style. However this study looks at the symbolic meaning of building materials which were used in the shaping of the built environment and which were thought to be conveying meaning. The subject matter of the study is both the determination and comparison of the meanings that façade finishing materials themselves convey free from their function and the meanings that they convey when used on a building which is shaped in relation to its function. Within this framework the study composed of three stages. The meanings of the materials themselves were determined in the first stage, the meanings of the materials which are used on a functional building were determined in the second stage and the meanings which are obtained in the first and second stages were compared in the last stage of the study. In this way; through the comparison of the meanings that materials convey, it was questioned if the conveyed meanings of the materials differ in relation to function or not. A survey study was conducted to evaluate the conveyed meanings of the materials through the use of semantic differentiation scales. 21 Adjective pairs were selected and used in all phases of the survey. The subject group consisted of 14 academics working at Çukurova University, Department of Architecture, showing a homogenous character in terms of their education, income level and profession. For the comparison of the changes in the meaning, dwelling was selected as the functional building type because of it is considered as a building type which reflects its users' identity naturally. A large number of studies on the meaning of dwelling reveal that qualities of dwelling convey meanings about its user's characteristics. Façade finishing materials which are used at dwellings are also thought to be conveying meanings about their users. Therefore; in order to be able to follow the changes in the meanings that materials convey in relation to function, the conveyed meaning is inquired through the characteristics of the users of the dwellings. At this stage of the study; the subjects are requested to evaluate the personal characteristics of the users by considering the materials used in the dwelling. In this way it is intended to ascertain the meanings that materials convey in relation to their use in the dwelling. The images of the dwellings and materials themselves obtained by using simulation techniques instead of using the images of previously built dwellings. In this way it is aimed to prevent the subjects' evaluations to be influenced from the form, style and size of the dwelling. Five different building materials were selected for the study; stone, wood, plaster, brick and composite materials. Meanings of the materials which are used on the dwellings are mainly obtained depending on the characteristics of the constructed users of the simulated dwellings. These meanings are compared with the meanings that the materials themselves convey. With the comparison of materials themselves and materials in relation to function, clear findings were reached that the conveyed meaning changes. For example; subjects evaluated stone as the material which conveys the meaning of impolite most. On the other hand plaster was evaluated as the material that conveys the meaning of impolite most when used on a dwelling. It is assumed, that, regardless of function, subjects evaluated the meaning of stone as impolite regarding to its nature. However when evaluation was made in relation to function, the subjects evaluated the constructed user of the dwelling and taken impoliteness as a negative personal characteristic. As a result they have described impoliteness with plaster to which they ascribed negative meanings. With these results it is confirmed that the conveyed meaning of a material can change in relation to function and façade finishing materials of a dwelling can affect the evaluation of the characteristics of the users. Furthermore it was determined that; meanings of materials emanate from physical characteristics of materials and whether the material is natural or artificial affect these meanings. In conclusion the findings of the study designate the direction of differentiations in the conveyed meanings of the chosen materials. Also the results give us some clues about the appropriate functions in which different materials could be used. Keywords: Symbolic meaning, façade surfacing materials, dwelling.
On establishment of the relationship between social research and policy formation
Get PDFBu yazı UNESCO’nun MOST programı son yıllarda gündemine aldığı sosyal araştırmalarla politikaların oluşturulması arasında sıkı bir bağ kurulamayışı sorununu irdeliyor. Bu irdeleme yerel niteliği ağır basan toplumsal sorunların çözümünde modernitenin evrenselci yaklaşımlarının yetersiz kalması ve toplumsal sorunların çözümünde yerel araştırmaya dayanılmasının gereğinin anlaşılmasıyla yakından ilişkilidir. Bu yazıda yerel karar çevrelerinin özelliklerine bağlı olarak ne tür araştırma taleplerinin ortaya çıktığı araştırılmaktadır. Ülkelerin araştırma arzını sağlayan kurum komplekslerinin nasıl oluştuğu ve performanslarının niteliği ortaya konmaktadır. Bunun için arzın talebi belirleme özellikleri ele alınmaktadır. Bunun için politikacı araştırmacı ilişkisinin nasıl geliştirileceğine ilişkin kavramlaştırma modelleri üzerinde durmak gerekir. Araştırma ile politika oluşturma ve uygulama işlevleri arasında geri beslemenin varlığını göz önüne alan kavramsal ele alışlar daha başarılı bir araştırma politika ilişkisi kurulması yolunda yapılabilecekler konusundaki olanaklar yelpazesini artırmaktadır.This study discusses the failure of establishment of close interrelation between social research and formation of relevant policies which took place on the recent agenda of the MOST program of UNESCO. It is closely related to the fact that universal approach of modernity remains inefficient in the solution of social problems the local aspects of which are dominant and to the fact that it is now accepted that local research should provide the basis for the solution of social problems. In the related literature the existence of relationship among policies based on social research is interpreted as of instrumentalist nature with a very narrow limited context. The existence of such a relation may be accepted on condition that the subject of the research, its method and the format of presentation of its final results reaches a level of quality which enables actors, who have the authority and responsibility to develop policy, to use this research directly in the process of development of their policies. Emphasis should be given to the conceptual models related to how politician/researcher interrelationship is to be developed. Conceptual approaches considering feed back relations between research and policy structuration and implementation increase the range of opportunities for establishing more successful research/policy relationship
İstanbul'da Tanzimat sonrası Galata-Şişli hattında Rum cemaati ve eğitim yapılarının arka planı
Get PDFThe relations with the Western countries which were increased and intensified rapidly after the Tanzimat Period especially through the second part of the 19th century, educating masses of people became a priority and provided non-Muslims with the means of building a national/ideological/social identity for themselves to be an eligible part of the rising kapitalist system in the new era as the new educational ways formed by the Enlightment ideas worked as a mechanism of social transformation. Thus, along with the Tanzimat reforms guaranteeing individuals their rights to private property, they started to build a new model of urbanization of their own in Galata and Pera region in İstanbul. Pera located just North of Galata became both a residancial area and employment centre specifically for the European diplomatic missions starting from the 16th century onwards while Galata was reserved rather for business and finance characterizing the region as westernized by the co-existance of the Ottoman Greeks, Armenians, Jews and Levantines with the European community. Greeks gaining great economical power from state-lending, commercial and banking activities in the 19th century, Pera became increasingly favorable center of social importance in Istanbul accompanied with the social and economical rise of a Greek middle class. The Greeks were more to make use of new opportunities by the civil rights they were entitled according to the continuous reforms and new legislations during the post-Tanzimat period as they had preceding contacts with the West for establishing business relations with the European countries as traders and dragoman in diplomatic missions etc.. Due to various reasons such as new means of transportation, new types of buildings emerging with new functions like, schools, hospitals, train stations, universities, police stations, barracks, factories, bridges, apartment blocks, clock towers etc. changing the pattern of the daily life with increased standards of living as well as the great conflagrations like in Hocapaşa in the Historical Peninsula as well as Galata and Pera, the Greek, Armenian and Jews are moved from Fener, Balat, Hasköy, Kumkapı and Samatya to the more favoured areas and different parts of the northern region like Kurtuluş, Feriköy, Şişli, Nişantaşı and Maçka along the route between Galata and Şişli towards the end of the 19th century. The buildings by the Ottoman non-muslim communities had their contributions in the western type of urbanization process in these regions. Along with the gradual Greek Orthodox population flow to the area, the Greek community character became more significant. Historically, generally, education took place in the nartex or in the courtyards of the churches. The Institutional differentiation was to emerge following the Tanzimat period, with the creation of educational institutions expressing a particular character that is serving for a mass education to produce more consciousness of a national identity. Among of all the building types, the educational buildings indicated the changing paradigms with the rising notions in the era, indicating the impacts of the cultural transformation in the building environment. Parallel to the changing state of economical, political and social affairs at the Ottoman Empire following the Tanzimat, they went through a social transformation period which reflected itself directly to the building environment. The upper classes of the Greek Orthodox communities composed of big merchants, state officials and bankers based in Istanbul took the lead to bring a new aspect, a new context to the educational and cultural environment with the means in their power. Thus, the Greek community built their schools for higher education in order to become a well educated and a modern society using European concepts both in teaching programmes and buildings as a strong architectural language. The educational institutions including primary, secondary and higher schools established all through the 19th century were not isolated formations but parts of a larger social, cultural and educational context following the examples in the European countries both ideologically and architectural wise representing and conveying the Enlightment and modernization ideas gradually forming their own national identity in order to transform the community. These school buildings erected were clearly reflecting the life styles in the era, making a great contribution in the urbanization process in order to state the results of the social and political context created by the Western impact and the new paradigms that the 19th c. brought with. Keywords: Minorities, Ottoman Greeks, non-Muslims’ educational buildings. Tanzimat temelinde çok çeşitli sivil hak ve özgürlüklere kavuşan gayrimüslimler içinde Rumlar, Batılı ülkelerle geçmiş yüzyıllara uzanan bağlarını güçlendirmiş, imparatorluk içinde ağırlıklı oranda ticaret ve parayla uğraşan kesim olarak mesleki avantajlarının ve konjonktürün getirdiği fırsatları değerlendirerek ekonomik ve toplumsal alanda parlak bir yükselme elde etmişlerdir. Ticari ilişkilerinin bir yan getirisi olarak Rönesans ve Fransız devriminin yarattığı Batılı yeni dünya anlayışı ve endüstriyel gelişme ile imparatorluk içinde herkesten önce tanışmışlardır. Yeni dünya sistemi içinde kurdukları ilişkilerle Rumlar imparatorluğun başşehrinde önce ekonomik güç elde etmiş, arkasından kendilerine sunulan tarihsel geçmişle geleceği Aydınlanma fikirleri rehberliğinde yorumlayan entelektüel sınıflarını yaratmışlardır. Zenginleşme ve zenginliğin sağladığı olanaklarla ortaya çıkan gayrimüslim burjuvazi, Batıda gördüğü yaşam biçimini yüzyıllardır yaşadığı imparatorluk sınırları içinde, İstanbul’da yaratabilmek için en başta eğitime ağırlık vermiştir. Çağdaş kitlesel eğitimle biçimlendirilecek olan Rum milleti, modern yaşam biçimlerini şehirde yeniden üretecektir. Kentsel bağlamdaki yansımaları ise, Galata-Şişli hattında modern yapı biçimlerinin örneklendiği ilk kentsel prototipin oluşmasına katkılarıdır. Yer aldıkları kentsel doku içerisinde benimsedikleri yeni dünya görüşünü etkili biçimde yansıtmışlar, Avrupai yaşam şeklini mekansal bağlamda ifade ederken devrin batılı fikirlerinden etkilenen yeni dünya ideallerini kendi bakış açıları doğrultusunda mimarlık alanında da yansıtmışlardır. Bu bağlamda işlevine yönelik tasarlanıp inşa edilen eğitim yapıları, mimari dil bağlamında dönemin sözcülüğünü yapan anıtsal binalardandır. Şehrin modernleşmesi ve yeni oluşan kentsel yapılanma içinde dönemin referanslarına temel katkıda bulunan önemli yenilikçi binalar olarak yerlerini almışlardır. Anahtar Kelimeler: Azınlıklar, Osmanlı Rumları, gayrimüslim cemaat okulları
Senaryo analizi için dinamik bir yaklaşım önerisi
Get PDFThis paper proposes a dynamic scenario analysis approach in order to understand the uncertainties about the future. The development of alternative futures/scenarios is an important part of strategy making. This paper's objective is to propose an improved scenario analysis model based on Powell's scenario analysis approach, namely, EFAR (Extended Field Anomaly Relaxation) (Powell, 1997). This improved model is referred as REFAR (Revised EFAR) hereinafter and is expected to provide a useful guide both in public and private organizations, during their scenario planning activities. REFAR aims to eliminate the basic drawbacks of EFAR and improve its efficiency by the help of cognitive maps and artificial neural networks. In the application part of the research, REFAR is applied to Turkey's inflation analysis. Initially the probable scenarios are built, and the transitions between them are analysed. The basic scenarios finally reached through REFAR, the transition among each key scenarios as well as among the scenarios grouped under each key scenario are explained in detail. The scenarios within each key scenario clusters provide a detailed picture of all the possible futures that may be encountered. Using them, it is also possible to see the possible transition and the resulting changes that will occur within the other scenarios in the same key cluster and in the scenarios of other clusters that the scenario of interest is in direct relation with. Keywords: Cognitive mapping, neural networks, scenarios.Bu çalışmada, gelecekteki belirsizlikleri anlamaya yönelik olarak kullanılan senaryo analizi için dinamik bir yaklaşım önerilmektedir. Powell (1997) tarafından ortaya konan EFAR (Durum Bozukluklarının Giderilmesine Yönelik Bir Yaklaşım / Extended Field Anomaly Relaxation) modeli; senaryo analizine dinamik bir yapı kazandırmıştır. Ancak bazı zayıf yönleri mevcuttur ve geliştirilmeye açıktır. Bu amaçla, bu çalışmada EFAR yaklaşımındaki zayıf yönleri gidermeyi ve böylece onu, daha etkinleştirmeyi hedefleyen yeni bir model: REFAR (Düzeltilmiş / Revised EFAR) modeli önerilmektedir. Bu doğrultuda bilişsel haritalar ve yapay sinir ağlarından yararlanılmıştır. Uygulamada REFAR modeli aracılığıyla, Türkiye’de enflasyon konusunda karar vericilere destek olabilecek nitelikte dinamik bir senaryo analiz yapısı oluşturulmuştur. Anahtar Kelimeler: Bilişsel haritalar, senaryolar, yapay sinir ağları
Türkiye'de "en hakiki mürşit" ne kadar "ilimdir"? Bir sosyal bilimcinin hatırladıkları
Get PDFThis article considers the interactive relationship between Social Sciences and the structure of thought of individuals. The author relates some of his experiences from his years at different schools and colleges as well as from those years during which he served as a staff member or research associate at various institutions of higher learning, and attempts to figure out to what extent those experiences could have contributed to the flourishing of an analytical mind in individuals and, conversely, to what degree they could hamper the training of minds in the same direction. Keywords: Memorizing by heart vs. thinking, description vs. analysis, analytical method.Bu çalışmada, Türkiye’de Sosyal Bilimler ile kişilerin düşünce yapısı arasındaki karşılıklı etkileşim konusu ele alınmaktadır. Yazar, kendi öğrenim ve öğretim hayatından bazı özgün deneyimlerini nakletmekte ve zikrettiği deneyimlerinin kişinin analitik bir düşünce yapısına sahip olmasına ne kadar katkıda bulunabileceğini ve ne kadar böyle bir düşünce yapısının ortaya çıkmasını engelliyebileceğini irdelemektedir. Anahtar Kelimeler:Ezberleme-düşünme, betimleme-irdeleme, analitik yöntem
Credit scoring of companies: Application to the ISEM companies
Get PDFBu çalışmada firmaların kredi yeterlilik kararında kullanılan finansal analizin objektif bir ölçüt olarak kullanılmasını sağlamak amacıyla, bir skorlama modeli geliştirilmiş ve geliştirilen model İMKB’de yer alan 117 firmaya 1993 - 2002 yılları arasında uygulanmıştır. Çıkan sonuçlar, firmaların gerçek mali yapıları ile karşılaştırılmış, bu sayede hem önerilen derecelendirme modelinin tutarlılığı belirlenmiş, hem de bir firmanın mali yapısındaki olumlu ve olumsuz gelişmelerin nedenleri ortaya konmuştur. Geliştirilen skorlama modelinde büyüme, likidite, borçluluk, faaliyet döngüsü ve kârlılık kriterleri, sektör analizi ve trend analizi olmak üzere iki farklı açıdan analiz edilmiş ve toplam on kriterin hesaplanan puanları toplanarak firma puanı ve kredi notu saptanmıştır. Anahtar Kelimeler: Finansal analiz, kredi derecelendirme, derecelendirme, skorlama.In this study, a scoring model is developed to make financial analysis of the companies with objective criteria. Then the model is applied to 117 companies at the ISEM (IMKB), between the years 1993 and 2002. The financial scorings of the companies derived from the model are compared with the actual financial strength and credibility using the ISEM news. This helps to verify both the consistency of the model and the positive and negative factors that affect the financial strength of the companies. The model is composed of five different financial criteria: Growth, liquidity, leverage, working capital management and profitability. These five financial criteria are analyzed from two different points: Trend analysis and industrial analysis. At trend analysis the five financial criteria are compared with the previous year where at industrial analysis, the criteria are compared with the industry averages. The scores of each criterion for both trend analysis and industrial analysis are added and the company credit score and note is calculated. There are both external and internal factors that cause the credit score to decrease. Economic crisis, industrial crisis are external factors where, insufficient equity, investment at different industries, problem at group companies are the main internal factors for decrease at credit score. Key words: Financial analysis, credit rating, rating, scoring
Thermal, microstructural and spectroscopic properties of the fluorotelluride optical glasses
Get PDFTelürit esaslı cam malzemeler, katıhal lazer malzemelerinden lazer malzemesi olarak, fiber optik yükselticilerinde ve doğrusal olmayan optik camlarda kullanılan önemli fotonik malzemelerdir. Bu nedenle, telürit camlarının spektroskopik özellikleri deneysel araştırmacıların başlıca araştırma konusu haline gelmiştir. Telürit camlarının en önemli özellikleri olarak, geniş iletim bölgesine (0.35- 5 µm), en yaygın oksitli camlar arasında en düşük fonon enerjisine, yüksek kırılma indisine, düşük erime sıcaklığına, yüksek dielektrik sabitine sahip olmasıdır. Ayrıca, yakın morötesinden orta kızılaltı bölgeye kadar, geniş bir geçirgenlik bölgesine sahiptir. Bu çalışmada fotonik malzeme olarak kullanılma potansiyeli olan (1-x)TeO2-xPbF2 (x=0.10, 0.15 ve 0.25 mol) optik cam malzemelerin sentezi gerçekleştirilmiştir. Bu malzemelerin termal, mikroyapı ve spektroskopik özellikleri incelenmiştir. Cam geçiş, kristallenme ve erime sıcaklıkları her bir kompozisyon için 10 °C/dak ısıtma hızı ile ölçülen DTA eğrileri kullanılarak belirlenmiştir. Kompozisyonun ve kristallenmenin bu camların yapısına etkisi X-ışını kırınımı, (XRD), Taramalı elektron mikroskopu, (SEM), Optik mikroskop (OM) ve Raman spektroskopisi (FT-IR Raman) kullanılarak incelenmiştir. Bu cam malzemeler, fiber optik iletişim ağlarında optik yükseltici olarak kullanılabilme potansiyelini araştırmak amacıyla, bir nadir toprak iyonu olan tulyum iyonu ile katkılanmıştır. Katkılanan malzemelerin (yakın kızılaltı) bölgesindeki ışıma özelliklerine tulyum iyonu konsantrasyonu etkisi lazer spektroskopisi kullanılarak incelenmiştir. 0.2 mol Tm3+ katkılı cam malzemenin (0.9TeO2-0.1PbF2) en yüksek ışınım kuvantum verimine sahip olması nedeniyle 1470 nm dalga boyunda fiber optik yükseltici olarak kullanılma potansiyeline sahip olduğu görülmektedir. Anahtar kelimeler: Fotonik malzeme, lazer yükseltici, telürit, raman spektroskopi.Tellurite based glasses with doped rare-earth ions have attracted for the structural study and from the technological and academic point of view. Recently, considerable effort has been devoted to dielectric materials and design for optical fibers, waveguide devices and optical fiber amplifiers to improve the telecommunication sysytems. In that case, many researches have been focused on to the producing new photonic devices which have low-loss optical waveguides. Er3+ and Tm3+-doped tellurite photonic materials are potential candidate material for the applications in fiber-optic amplifier and fiber laser devices. Therefore, developing more stable tellurite based materials are important for applications as a technological devices. In this research, transparent tellurite glasses were prepared by using reagent TeO2, and PbF2. The batch materials (7 g) were well mixed in a platinum crucible and melted at 800oC for 60 min in the electrically heated furnace in air atmosphere. The glass melts were than removed from the furnace at 800oC and air-quenched by pressing between two rectangular graphite slabs at room temperature. The density of each glass sample was measured by using Archimede?s principle with distilled water as the immersion liquid (Kabalci vd. 2004). The measured density was about 6.3 g/cm3 for the glass sample. A Rigaku Thermoflex Differantial Thermal analyzer equipped with a PTC-10A temperature control unit was used in order to determine the thermal parameters. The samples of about 20 mg were heated it heating at heating rate of 10oC/min in a platinum crucible and using the same amount of Al2O3 as the reference material in the temperature range between 20 and 600oC. The Tg temperature is selected as mid-point between the onset and the minimum temperature. The Tc and Tg temperatures were measured at the onset crystallization, and the Tp temperature was measured at the peak of crystallization. The microstructural characterization of the as-cast and annealed glass samples were carried out using X-ray diffraction (XRD), and scanning electron microscopy (SEM), optical microscope and Raman spectrophotometer techniques. The x-ray diffraction investigations were carried out in a PhilipsTM Model PW3710 using CuKa radiation at 40 kV and 40 mV settings in the 2q range from 10 to 90o. The crystallized phases were identified by comparing the peak positions and intensities with those in the JCPDS (Joint Committee on Power Diffraction Standards) data files. Scanning electron microscope (SEM) investigations were conducted in a JEOLTM Model JSM-T330 operated at 25 kV, and JEOL JSM 5410 scanning microscope, linked with a Zmax 30 Boron-up light element energy dispersive spectrometer (EDS) detector. For the SEM investigations, optical mount specimens were prepared using standard metallographic techniques followed by chemical etching in a HF solution (5%) for a minute. The etched optical samples were coated with golden. The Nikon Eclipse L150 Optical Microscope (OM) were used for microscopic observations and to obtain optical micrographs of the surfaces. The magnification levels (combined with eye-piece magnification) are, 50X, 100X, and 200X. Its magnification can be further enhanced by taking a digital image and zooming it with any image software. The Raman spectra were measured with a digilab FTS 7000 spectrophotometer in the spectral range 0-1000 cm-1. The glass samples were excited with a Nd:YAG laser at 1064 nm with power of about 500 mW. The digital intensity data were recorded at intervals 1 cm-1, with 64 scans, and at resolution 8 cm-1 with a Ge detector cooled to liquid nitrogen temperature. In fluorescence measurements, samples were excited with a 25-mW continuous-wave diode laser at 785 nm. After passing through a 0.5-m Czerny-Turner type monochromator, the fluorescence signal was detected with a PbS detector and amplified in two stages by using a preamplifier and a lock-in amplifier. We also have investigated the variation of the luminescence strengths as a function of Tm3+ ion concentration in a new type of Tm3+ doped tellurite glass. Tm3+ doped glasses have two emission bands that peak around 1470 nm and 1800 nm in the near infrared. Keywords: Photonic material, laser amplifier, raman spectroscopy
Wave propagation in an elastic medium: Generalized Davey-Stewartson equations
Get PDFBu çalışmada, iki uzay ve bir zaman boyutlu nonlineer dalga yayılımı problemi ele alınmıştır. Sonsuz, homojen, zayıf nonlineer ve zayıf dispersif elastik bir ortamda (2+1) (iki uzay ve bir zaman) boyutlu dalgaların modülasyonu incelenmiştir. Modülasyon problemi için dalgaların asimptotik davranışını tanımlayan (2+1) boyutlu nonlineer evolüsyon denklemleri türetilmiştir. Denklemler türetilirken indirgeyici pertürbasyon yöntemi olarak adlandırılan bir asimptotik yöntem kullanılmış ve dalgaların modülasyonu probleminin üçlü bir nonlineer kısmi diferansiyel denklem sistemi ile karakterize edildiği gösterilmiştir. Bu denklemler, bir kısa enine dalga, bir uzun enine dalga ve bir uzun boyuna dalga olmak üzere üç dalganın etkileşimlerini içermiş ve “genelleştirilmiş Davey-Stewartson denklemleri” olarak adlandırılmıştır. Türetilen denklemlerde beliren parametre değerleri üzerinde alınan bazı kısıtlar altında, genelleştirilmiş Davey-Stewartson denklemlerinin literatürde sıkça karşılaşılan nonlineer Schrödinger denklemine veya Davey-Stewartson denklemlerine indirgendiği gösterilmiştir. Ayrıca, türetilen genelleştirilmiş Davey-Stewartson denklemlerinin bazı özel çözümleri elde edilmiştir. Özel çözümler hesaplanırken, gezen dalga dönüşümlerini esas alan bir yöntem yardımı ile kısmi diferansiyel denklemler adi diferansiyel denklemlere indirgenmiş ve çözümler Jacobi eliptik fonksiyonları cinsinden verilmiştir. Son olarak, elde edilen özel çözümlerin bazı durumlarda hiperbolik fonksiyonlara indirgendiği gösterilmiş ve parametre değerlerinde alınan kimi kısıtlar altında sech-tanh-tanh ve tanh-tanh-tanh yapılarındaki yalnız dalga (solitary wave) çözümlerini içerdiği ifade edilmiştir. Anahtar kelimeler: Nonlineer elastik dalga yayılımı, genelleştirilmiş Davey-Stewartson denklemleri, gezen dalga çözümleri.It is well-known that the envelope of a (1+1) (one spatial and one temporal) dimensional quasi-monochromatic wave train is governed by the single nonlinear Schrödinger equation where t is time, x is the spatial coordinate and A denotes the complex amplitude. The nonlinear Schrödinger equation appears to be a generic equation describing unidirectional wave modulation. If modulations transverse to the wave propagation direction are also allowed, second spatial coordinate effect should be taken into account and new (2+1) evolution equations should be derived. A natural way to obtain two-dimensional modulations of nonlinear waves is simply to replace the one dimensional dispersive term with a two dimensional dispersive term. However, in many two dimensional systems both short waves and long waves may co-exist and the modulation of such a system can be characterized by Davey-Stewartson equations. Where A is the complex amplitude of the short wave and is the long wave amplitude. The Davey-Stewartson system is a model for the evolution of weakly nonlinear packets of water waves that travel in one direction but in which the amplitudes of waves are modulated in two spatial directions. The main purpose of the present study is to extent the analysis of Davey and Stewartson to describe (2+1) dimensional wave motion in a bulk medium composed of an elastic material with couple stresses. To this aim, a multi-scale expansion of quasi-monochromatic wave solutions is used to derive (2+1) non-linear model equations for the description of elastic waves in the far field. By using the reductive perturbation method, the contribution of the second spatial coordinate effect on the propagation of a quasi-monochromatic wave and zero harmonic modes is determined. It is shown that the modulation of waves in the above mentioned medium is governed by the following system of three non-linear evolution equations which may be called the ?generalized Davey-Stewartson equations?: where A is the complex amplitude of the free short transverse wave mode whereas and are the free long longitudinal and free long transverse wave modes, respectively. These coupled equations govern (2+1) dimensional weakly nonlinear waves in a generalized elastic solid, that travel mostly in the x direction and whose amplitudes are slowly modulating in both x and y directions. Since the nonlinear interaction of the quasi-monochromatic transverse wave and the zero harmonic transverse and longitudinal waves is considered, i.e., a free short transverse, a free long longitudinal and a free long transverse wave modes are included, these evolution equations present a generalized form of the Davey-Stewartson equations. It is also shown that under some restrictions on the parameter values, the generalized Davey-Stewartson equations is reduced to the nonlinear Schrödinger equation and to the Davey-Stewartson equations. Finally, some special solutions of the generalized Davey-Stewartson equations are obtained. By using the traveling wave transformations, the partial differential equations are reduced to ordinary differential equations and the special solutions are given in terms of Jacobian elliptic functions. It is also shown that, these solutions involve secant hyperbolic and tangent hyperbolic type solitary wave solutions for some values of the parameters. These solutions can be given briefly as follows: Keywords: Non-linear elastic wave propagation, generalized Davey-Stewartson equations, travelling wave solutions
A Study on the venom gland and the venom of the spider Alopecosa fabrilis (Clerck, 1757) (Araneae, Lycosidae)
Get PDFAlopecosa fabrilis (Clerck, 1757) örümceğinin zehir bezinin morfolojik yapısı taramalı elektron mikroskobun (SEM)’da incelenmiştir. Prosomada yer alan zehir bezi bir çift olup silindir şeklindedir. Bezin tüp şeklinde bir gövde kısmı ve bununla bağlantılı bir kanaldan meydana geldiği görülmüştür. Bezin etrafı ise çizgili kas lifleri ile kuşatılmıştır. Zehir bezinde üretilen zehir gerek insanlar gerekse de diğer canlılar için toksiktir. Na+ ve Ca++ elementlerince zengin olduğu bulunmuştur. Bu analiz sonuçları zehir içeriğinin sinir ve kas sistemi üzerine etkili olduğunu göstermiştir. Anahtar Kelimeler: Alopecosa fabrilis, elementer analiz, taramalı elektron mikroskop (SEM), zehir bezi.The venom glands vary in shape and position. The size of the venom gland is not necessarily related to the size of the spider. In this study the morphological structure of the venom gland of the spider Alopecosa fabrilis (Clerck, 1757) was studied using scanning electron microscope (SEM). Alopecosa fabrilis has a small body, the size of its venom gland is rather large. The venom gland situated at the prosoma has a pair and has cylindrical in shape. The glands were determined to be one lobed. and observed to be composed of a stem part being similar to tube in shape and a channel connected with it. The dorsal surfaces of the glands are surrounded by numerous spirally arranged straite musculer fiber.When the spider bites,the venom fang moves out of the groove and penetrates the prey. At the same time, the venom is injected into the prey from a tiny opening at the tip of the venom fang. Venom is produced in a pair of venom glands situated in the interior portion of the prosoma. The venom produced in the venom gland is toxic for humans and other living things. However the spider venom is obtained for use in medical treatment of diseases such as cardiac disturbance and for production of new antibacterial reagent. At elementary analysis of the venom content, it was found to be rich for Na+ and Ca++ elements. These analysis results were demostrated that content of the venom has effective on nervous and muscular system. Keywords: Alopecosa fabrilis, elementarical analysis, scanning electron microscope (SEM), venom glands
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