itüdergisi (E-Journals - İstanbul Teknik Üniversitesi, Istanbul Teknik Uniersity., İTÜ)
itüdergisi (E-Journals - İstanbul Teknik Üniversitesi, Istanbul Teknik Uniersity., İTÜ)Not a member yet
1059 research outputs found
Sort by
Seismic performance of RC systems with friction damper
Get PDFBu çalışmada tek serbest dereceli betonarme sistemlerde hemen kullanım performans seviyesi için sürtünmeli sönüm elemanının rijitliği ve kayma yer değiştirme değerlerinin seçilmesine yönelik yapılan doğrusal olmayan dinamik analizlerin sonuçları sunulmuştur. Farklı betonarme sistem ve sönümleyici elemanların oluşturduğu 360 sistem için maksimum yer değiştirme ve taban kesme kuvveti performans kıstası olarak seçilmiştir. Mevcut betonarme sistemlerde iki farklı akma dayanım ve 0.1 sn-0.9 sn aralığında 9 farklı periyot değeri kullanılmıştır. Sönüm elemanlarında kullanılan dört farklı rijitlik ve beş farklı kayma yer değiştirme değerleri mevcut sistemin rijitlik ve akma yer değiştirme değerlerinin oranları olarak belirlenmiştir. Gevşek ve sıkı zemin profili için faya en fazla 15 km mesafedeki deprem kayıtları kullanılarak oluşan 14400 adet doğrusal olmayan dinamik analizin yapılması için algoritma geliştirilmiştir. Elde edilen sonuçlardan zemin koşuluna bağlı olarak betonarme sistemin özelliğine göre uygun sürtünmeli sönüm elemanının rijitliği ve kayma yer değiştirme değerleri performans kıstası temel alınarak belirlenmiştir. Optimum sürtünmeli sönüm elemanlarının özellikleri karşılaştırıldığında, aynı kayma yük seviyesinde sönüm elemanının rijitliğinin büyük olmasının yer değiştirme talebinde daha büyük azalmaya sebep olduğu gözlemlenmiştir. Akma dayanımı düşük mevcut betonarme sistemler, daha yüksek seviyede kayma yer değiştirme değerine sahip sürtünme sönümlü elemanla birlikte performans kıstaslarını karşılayabilmiştir. Periyodu 0.5 sn’den büyük olan mevcut betonarme sistemler için, kayma yük seviyesi, sıkı zemin profili için azalırken gevşek zemin profili için aynı kalmaktadır. Anahtar Kelimeler: Enerji sönümleyici, doğrusal olmayan dinamik analiz, performans seviyesi.In recent years, researchers have modified masses, stiffness or damping in structures to control their vibration instead of using traditional method which provides dissipation of earthquake-induced energy by the inelastic response of the structural members. Damage due to this yielding action is usually repaired expensively or may be so serious that demolishing of building must be required. Here damping due to friction is considered as an energy dissipation method due to some advantages. Friction devices are generally capable of repeated cycles of displacement without loss of strength, stability or energy dissipation. In addition, since they are fabricated from traditional materials. They require little maintenance; their use in seismic design and retrofit applications appears to be very promising. The new significant feature in performance-based earthquake engineering is the selection of seismic performance level for a given earthquake ground motion. In this article, the effectiveness of friction dampers on reinforced concrete systems for immediate occupancy (IO) performance level is investigated considering the properties of the system and friction damper. A number of studies toward deriving a reasonable criterion for optimal design of frames with supplemental dampers have been reported. Some of them have defined performance indexes which evaluate the performance of the system as the ratio of suitable parameters calculated for the damped brace frame to that for the unbraced frame. The others have used the acceptability limits for the structural response as performance criteria to select appropriate damper properties. In this study, the selection of brace stiffness and slip displacement level of friction damper for SDOF RC systems having different period and strength ratio is made considering the peak response values for IO level obtained from the comprehensive nonlinear time history analyses. The reason of selecting IO performance level is that the structure is only slightly damaged and the capacities of force resisting systems have almost the same pre-earthquake ones in this level. Since both dynamic and inelastic response is modeled in nonlinear dynamic analysis permitted to be used for structures without any restrictions, this procedure is used for the evaluation. Nonlinear time history analyses are performed using the force displacement relationships of bare RC system and friction damped brace. Q-hyst model is considered for nonlinear dynamic response of RC system while elasto-plastic model is used to represent that of the damped brace here. Algorithm is developed to perform 14400 nonlinear dynamic analyses formed by 9 different periods (0.1s-0.9s), 2 strength ratios for bare RC system and 4 brace stiffness, 5 slip displacement values for friction damper using 40 earthquake records. The earthquake records are taken at stations whose closest distances are less than 15 km to the fault. The average peak ground acceleration of 20 unscaled earthquakes for each soil profile is 0.35 g. Peak values of displacements and shear forces are stored. The limit value for average peak displacement is considered as the yielding displacement of bare RC system. The damper properties are selected from the cases providing this limitation with low base shear. As a conclusion, ductility and base shear demand are strongly dependent on the brace to the frame stiffness ratio, the device slip to the frame yield displacement ratio and the soil profile. Generally base shear increases with the ratio of the brace stiffness to the frame stiffness and the device slip to the frame yield displacement. On the other hand, these conditions are opposite for the displacement demands. Although high brace stiffness ratio and slip displacement ratio warrant the displacement limitation, dissipated energy by friction damper decreases and the behavior of the system shows similarity with braced one without any dissipation feature. Higher brace stiffness causes greater decrement in displacement demand under the same slip load which can be obtained by using different brace stiffness and slip displacement ratio. For the period of bare RC system higher than 0.5s, required slip load level decreases for stiff soil profile while almost same load level is required for soft soil profile. In addition, lower slip load level is required to obtain performance objective for lower strength ratio of bare RC system. The results obtained are limited since only IO level is aimed for sites whose closest distances are less than 15 km. Keywords: Energy dissipators, nonlinear dynamic analysis, performance criteria
Alloying of high purity copper surfaces with cathodic arc aluminum plasma
Get PDFAl-Cu sistemi uzunca bir süredir bilimsel ve teknolojik alanda ilgi odağı olmuştur. Özellikle bakırca zengin aluminyum alaşımları yüksek elektrik ve termal iletkenlikleri ve kolay şekil verilebilir olmalarından dolayı yaygın bir şekilde mühendislik malzemesi olarak kullanılmaktadırlar. Buna ek olarak, Al-Cu faz diagramının bakırca zengin kısmında yer alan aluminyum bronzları mekanik ve fiziksel özelliklerinden dolayı ilgi çekicidirler. Kompozisyonları ağırlıkça %5-%11 arasında aluminyum içeren aluminyum bronzları yüksek mukavemet, sertlik, aşınma dayanımı ve korozyon direncine sahip olmalarından dolayı endüstride yaygın olarak kullanılmaktadırlar. Çeşitli taban malzemelerin yüzeylerinde aluminyum bronz tabakası oluşturmak amacıyla bir takım fiziksel buhar biriktirme teknikleri kullanılmıştır. Bu tekniklerin hemen hemen tamamında, kaplama işleminden sonra, istenilen yapının elde edilmesi için değişik sıcaklık ve sürelerde ısıl işlemlerin yapılması gerekmektedir. Bu çalışmada, katodik ark fiziksel buhar biriktirme (KA-FBB) yöntemi ile yüksek saflıktaki bakır taban malzemesinin yüzeyinin herhangi bir ısıl işleme gerek duyulmadan alaşımlandırılması hedeflenmiştir. KA-FBB deneyleri sırasında aluminyum katod kullanılmış ve taban malzemeye sırasıyla -150 V (kaplama) ve -1000 V (yayındırma) bias voltajı uygulanmıştır. KA-FBB işlemi sırasında uygulanan kaplama ve yayındırma basamaklarının yüzey mikroyapısı üzerindeki etkileri, x ışınları kırınım (XRD) ve taramalı elektron mikroskobu (SEM) çalışmaları ile incelenmiştir. Yapılan deneyler sonucunda yüksek saflıktaki bakır taban malzemenin yüzeyinde ağırlıklı olarak martensitik yapıda β1-AlCu3 yapısı ve (Cu) katı çözeltisi oluşmuştur. Bu fazlara ek olarak, modifiye edilmiş yüzeyde az miktarda γ1-Al4Cu9 intermetalik yapısının da varlığı tespit edilmiştir. Anahtar Kelimeler: Katodik ark fiziksel buhar biriktirme, yüzey modifikasyonu, Al-Cu sistemi, aluminyum bronzları, intermetalik.The Al-Cu system has been a focus of scientific and technological interest over decades. The system is theoretically interesting because of its unresolved phases (Dong et al., 2000; Gulay and Harbrecht, 2004; Liu et al., 1998; Hannech et al., 2003) microstructural characteristics depending on cooling rates (Eskin et al., 2005) and applied magnetic and electrical fields during solidification (Liu et al., 2004; Li et al., 2006), martensitic and massive transformations (Murray, 1985) and metastable Guinier Preston zones (Lochte et al., 1980; Lokker et al., 2001). Al-Cu alloys are used as interconnects in integrated circuits because of their high conductivity and their acceptable processing properties (Lokker et al., 2001) and they could be employed in semi-conductor devices (Ene et al., 2007). Cu-based aluminum alloys are used as engineering materials because of their high electrical and thermal conductivity and easy formability. Considering the copper rich side of Al-Cu phase diagram, aluminum bronze and γ1-Al4Cu9 structures are interesting due to their mechanical and physical properties. A variety of aluminium bronzes of differing compositions ranging from 5% to 11% aluminium by weight have been used in industry for their high strength, high hardness, wear resistance, corrosion resistance and biostatic effects (Alam et al., 2001). The intermetallic compound γ1-Al4Cu9 is reported as one of the hardest and strongest intermetallic compounds in Al-Cu binary system (Rabkin et al., 1970). In addition, low electrical resistivity of γ1-Al4Cu9 intermetallic phase could make them suitable for metallization material application for large scale integration (LSI) technology (Atsushi and Sasaki, 1991). Al-Cu is a complex system which contains many phases and invariant transformations, most of which exists in the Cu-rich side of the binary phase diagram (Murray, 1985). The phase relations of the system are not yet completely clarified and the structures of some high temperature phases are still unresolved (Hannech et al., 2003; Gulay and Harbrecht, 2004). Cu-rich side of the Al-Cu phase diagram involves a eutectoid reaction through which β-AlCu3 phase transforms into α-Cu solid solution and γ-Al4Cu9 at ~567°C. β-AlCu3 phase can also be retained metastably due to the sluggishness of the eutectoid reaction and several metastable reactions such as β→ β1+(Cu) are also present in that region of the phase diagram (Murray, 1985). Aluminum bronze structures have been obtained on the surfaces of various substrates by PVD (Liang et al., 2000) arc spraying (Zhang et al., 2006), thermal spraying (Barik et al., 2005), low pressure plasma spraying (Alam et al., 2001) and laser surface alloying (Tang et al., 2006). In addition, numerous studies about PVD processes that used layered growth and annealing for alloying of the surfaces, have been published (Kanjilal et al., 2002; Cekada et al., 2004). Recently, a cathodic arc physical vapour deposition (CAPVD) technique has been introduced, based on sequential deposition (at low bias voltages) and bombardment (at high bias voltages) of the selected target material on the surface of the substrate (Şireli, 2005; Çorlu and Ürgen, 2009). It was proposed that, surface heating and momentum transfer effects created during energetic metal ion bombardment and the defective structure of the deposits resulted in alloying of the surfaces and formation of intermetallics at the surface. In this study, we aimed to modify the surfaces of copper substrates in order to obtain aluminum bronze (>70 at.% Cu) structures at the surfaces of the substrates by using the CAPVD technique. Surface alloying and intermetallic formation was realized by sequential deposition and bombardment of aluminum on surfaces of copper substrates. The effects of the duration of the deposition- bombardment stages of the process on the structure and chemistry of the treated surfaces were investigated with XRD and SEM. XRD patterns showed that the modified zone mainly consisted of a mixture of martensitic β1-AlCu3 and (Cu) solid solution, which was accompanied by γ1-Al4Cu9 intermetallic phase. For a detailed microstructural analysis, the cross-sectional samples were etched with FeCl3 solution in order to dissolve the (Cu) phase and reveal the β-AlCu3 phase. According to SEM investigations after etching with FeCl3 solution, modified zone, with a thickness of ~15µm, consisted of three phases, which corresponded to (Cu) solid solution, β1-AlCu3 phase and γ1-Al4Cu9 intermetallic phase. Keywords: Cathodic arc physical vapor deposition, surface modification, Al-Cu binary system, aluminum bronzes, intermetallics
Valuing information technologies investments with real options
Get PDFKarar vericiler, bilişim teknolojileri (BT) yatırımlarını değerlerken risk ve belirsizlikle başa çıkmak zorundadırlar. Net Bugünkü Değer ve İç Verim Oranı gibi klasik değerleme tekniklerinin risk ve belirsizliği değerleme sürecine katmadaki yetersizlikleri yöneticileri karar aşamasında sıklıkla içgüdülerini kullanma zorunluluğunda bırakmaktadır. Reel opsiyonlar yaklaşımı bir yatırımın bünyesinde barındırdığı risk ve belirsizliği değerleme sürecine katan alternatif bir tekniktir. Bu makalede erteleme esnekliğine sahip gerçek bir BT yatırımı reel opsiyonlar yaklaşımıyla incelenmiştir. Bu amaçla standart Black-Scholes modeli üzerinde bazı düzenlemelere gidilerek, riskten kaçınan yatırımcıların beklentilerini dikkate alabilecek ve aynı zamanda, Black yaklaşımıyla, erken uygulanma özelliğine sahip Amerikan tipi opsiyonlar için kullanılabilecek, Microsoft® Excel tabanlı bir matematiksel model oluşturulmuştur. Sunulan model, bir e-ticaret şirketinin önündeki modernizasyon projesinin değerlemesinde kullanılmıştır. Önerilen otomasyon, gerek nakit akışlarını gerekse de ana ekonomik faktörleri dikkate alarak, karar vericiye etkin ve esnek bir çözüm sunmaktadır. Ortaya konan kapsamlı yol haritası model parametreleri cinsinden hassasiyet analizi sunmakta ve parametreler arası bağlantıları ortaya koymaktadır. Çalışmanın neticesinde, negatif NBD’e sahip bir BT projesinin bile bünyesinde barındırdığı potansiyel değerlerle bağlı olarak karlı bir yatırıma dönüşebileceği görülmüştür. Anahtar Kelimeler: BT yatırımları, BT yatırımlarının değerlemesi, BT yatırım riskleri, opsiyon değerleme modelleri, reel opsiyonlar, risk yönetimi.Decision makers, while evaluating information technology (IT) investments, have to cope with risk and uncertainty. The insufficiency of traditional valuation techniques like Net Present Value and Internal Rate of Return, in counting risk and uncertainty to valuation process, forces executives often to rely on their instincts when taking final decisions. There are two widely used methods for the evaluation of capital budgeting decisions, namely Net Present Value (NPV) and Decision Analysis (DA). NPV does not take into account managerial flexibility because it makes implicit assumptions concerning an expected scenario of cash flows and presumes decision makers' passive commitment to a certain operating strategy. NPV is constrained to pre-committing today to a go or no-go decision. It uses information only available today. Therefore, NPV systematically understates projects that include future decisions stages, where management's ability to adapt and revise later decisions introduces asymmetries in the distribution of a project's cash flows. The ability of management to abandon, grow, defer and/or scale up or down a project, introduces an element of flexibility in the system that may act as protection on the downside of uncertainty, while exploiting the benefits from the upside potential. By assuming one cash flow scenario from the beginning, NPV rules out the possibility of these adaptations and therefore, does not take into account the value creation of flexibility. DA is a useful tool for strategic decision-making because it accounts for uncertainty and managerial flexibility. DA allows management to structure the decision problem by mapping hierarchically all the feasible consequences contingent on possible scenario. DA differs from NPV in that it does not only base its decisions on information available today, but assumes that new information will be acquired as the project evolves and this information may even change the optimal choice for the project. Though DA addresses some of the fallbacks observed in traditional valuation methods, its wide spread application in practice is limited because determining the appropriate discount rate is still subject to question and solving the model is analytically cumbersome if all the possible outcomes are embedded inside the model. Nowadays, researchers are convinced that investment models require strategic and financial considerations to be reconciled and integrated. Recognizing the shortcomings of NPV and DA techniques, real options analysis has been suggested as an alternative approach that considers the risks inherent in an investment while recognizing the ability of corporations to defer an investment until a later period with the expectation of better market conditions. With the advancements in options theory and the enhancement in the valuation of a wide range of complex options, the valuation of real-life option cases are getting attainable. This paper introduces a real-life application to the valuation of IT investment projects with deferral flexibility by means of option pricing theory. For this purpose a mathematical model is developed through modifying standard Black and Scholes model that can handle the early exercise feature of American type options via Black approximation and also considers the expectations of the risk-averse investors. The presented model is applied to evaluate an investment opportunity targeting the modernization of the web based sales channel of an e-commerce company. A computer based analysis tool is developed for this purpose. Suggested automation framework provides to the decision maker an efficient and flexible solution, while taking into account all possible cash flows and also major economical factors, to deal with possible different future market scenario. This illustrative road map gives a comprehensive sensitivity analysis in terms of model parameters and exposes their interactions. Further investigations showed that even an IT project with negative NPV, when taking into account strategical formations of market conditions, can turn to a profitable occasion. Keywords: IT investments, IT investment evaluation, IT investment risk, option-pricing models, real options, risk management
The forerunners of abstract art
Get PDFSanatta soyut eğilimlerin başlangıcını aradığımızda epeyce gerilere gidebiliriz. Romantizm, tüm sanat dallarında olduğu gibi plastik sanatlarda da yepyeni bir bakışın temelini oluşturur. Bu yıllarda sanatta üslup sorunu üzerinde titizlikle durulur ve sanat bir kendini açıklama biçimi olarak görülmeye başlanır. Turner tabiatçı gelecekçilikten uzaklaşma eğilimiyle soyut sanatın ilk habercilerinden biri olarak kabul edilebilir. Fernand Léger’nin de belirttiği gibi, resimsel ifade değiştiyse, bunu modern hayat gerekli kılmıştır. 1840’larda fotoğrafın bulunuşu gibi teknik gelişmelerin soyut sanatın gelişimini hazırlamada önemli katkıları olur. Doğaya farklı bir bakış yöntemi geliştiren izlenimcilik tabiatçı gerçekçiliğin en ileri aşaması ve aynı zamanda çözülüşüdür. İzlenimciliğin ardından, sanatta yansıtma yerine dönüştürmenin konmasını savunan Cézanne, soyut sanatın gelişimine hem sanatsal, hem kuramsal katkılarda bulunur. Sanatçı, Batı sanatı tarihi içerisinde çok önemli bir noktada durur. Bir yanıyla geleneğe bağlıdır, onu sürekli sorgular, öte yandan da yenilikçi ve devrimcidir. Amacı doğayı taklit etmek değil, ona paralel bir görüntü yaratmaktır. Kavram ressamlığı konusunda önemli bir aşama olan kübizm ve özellikle de analitik kübizm, doğadan arınmayı bütünüyle gerçekleştirmemekle birlikte, sanatta bir dönüm noktası oluşturur. Modern sanat kuramcısı Seuphor’un tanımına göre;soyut sanat, gerçeği -bu gerçek sanatçının ister hareket noktası olsun, ister olmasın- hiçbir yönden hatırlatmayan, akla getirmeyen sanattır. Doğadan bütünüyle arınmak ve Seuphor’un tanımladığı ‘soyut sanat’ fikrine ulaşabilmek içinse 1910’ları ve Kandinsky’i beklemek gerekecektir. Anahtar Kelimeler: Soyut sanat, Cézanne, kübizm.According to Michael Seuphor, Abstract Art is "art that in no way resembles or is reminiscent of reality -regardless of whether such reality forms the starting point for the artist." In order for a painting to be designated as abstract, it must not reflect any feature of the reality of the objective world. In fact, abstract work of art is one that reflects nothing other than the elements of pure composition and color. Indeed, Western picture has undergone a variety of phases to attain such absolute level of abstraction. Having witnessed the French Revolution and the Industrial Revolution, and of relevance even in the contemporary world, romanticism has laid the foundation of a brand new perspective in plastic arts as well as in all other kinds of art. During these years, style became a much elaborated issue and art started to be seen as a way of self expression. At a time when there was such a rapid departure from classical principles, Turner's landscapes denoted, so to speak, abstraction of a sensation or euphoria. The predisposition in Turner's art towards a breakaway from naturalistic reality can be viewed as one of the preliminary phases paving the way for abstract art. Numerous technological advances, especially the invention of photography in the 1840s constituted one of the significant stages in the development of abstract art. In other words, modern life can be said to have contributed to the alteration of artistic expression. Following the rapid change brought about by Romanticism, Impressionism became one of the turning points in West European art history as a current signaling the ultimate and hence the dissolving point reached by naturalism. Each impressionistic picture has captured a single moment pertaining to an ever-moving entity and is representative of a delicate balance between conflicting powers that will sooner or later be disturbed. Impressionistic "vision" transforms nature into a process of development and decay. Fauvism was yet another stage in the development of abstraction. The relationship of the artist with nature acquires a more flexible tune in Matisse and Duffy. Nature acquires an abstract character, with its elements changing into motives comprised of colors and lines. Cézanne was a prominent figure in Western art history. On the one hand, he was closely tied to tradition, constantly questioning it; on the other hand, such questioning was of an innovative and revolutionary character. He aimed to create a parallel view of nature rather than an imitation of it. Cézanne believed in the necessity to strip objects down to their pure geometric forms and then to reshape them to the point of their own perfection. This whole notion of "artistic transformation" forms a remarkable starting point in the development of abstract art. The impetus Cézanne provided for abstract art was continued by Picasso and Braque. At an early date as 1910, Picasso displayed a departure from natural forms. Such fragmentation of the form reflected a radical departure from the existing forms of artistic expression. Picasso's methods were inspired by Cézanne's investigations into the fundamental geometric forms. In the first stage of Cubism, artists adhered to the idea of a single point of view, which is an indispensable principle of naturalist painting. However, Analytical Cubism violated this principle, allowing for the opportunity to view objects from four different angles. Although, similar to Impressionists, the starting point of Cubists as well is an attempt at approaching nature, the two currents have a different understanding of nature. While Impressionism seeks elusive impressions, Cubism puts an end to the imitation of nature albeit not abandoning it altogether. Abstract art seeks to rid itself of nature. In this respect, Kandinsky's non-figurative watercolor is considered to signal the beginning of abstraction in Western art history. Following the invention of photography, Impressionism, reflecting the ultimate and dissolving point reached by naturalist realism, has led to the start of a new era witnessing the shift of an emphasis from art as reflection to art as transformation. To conclude, artists such as Cézanne or the currents of Impressionism and Cubism focusing on the picturesque or stylistic rather than the literary or contextual aspects of painting can be said to have characterized the developmental stages of abstract art. Keywords: Abstract art, Cézanne, cubism
Erken Cumhuriyet Dönemi'nde yerli malı kavramı ve İstanbul yerli malı sergileri
Get PDFPriority was given to consumer products during 1930’s in the Early Republican Period Turkey, as a result of the governmental support on the idea of productivity and on the practice of industrialization, in order to increase the welfare of the nation. Concepts like welfare, hygiene and modernity were emphasized in relation to everyday products. Increase in productivity was aimed by encouraging the use of domestic products. Expanding the idea of consumption and encouraging the use of domestic products were the significant efforts within an economy that was closed to outside and highly state supported. In 1929, National Union of Economy and Savings (MITC) was founded as an offspring of the policy of economy significantly supporting industrialization and mechanization. One of the missions of MITC was “the promotion of increasing the quantity, the quality and the beauty” of Turkish products and to make them known and sold worldwide. MITC organized “the National Models Exhibition” in 1930, “the Agriculture and Technique Exhibition” in 1931, “the Second National Exhibition of Industry” in 1931, “Tenth Year Economy Exhibition” in 1933 and “Ankara Industry Exhibition” in 1934. The most significant events that MITC organized in the context of design history were “the national exhibitions of domestic products”. After the Turkish participation to the first International Great Exhibition in 1851 and to the successor 19th Century and early 20th Century world exhibitions, the idea of exhibiting was carried into a new level of understanding by the agency of MITC during the Early Republican Period. Despite the fact that exhibiting was appropriated for overcoming the hard economic conditions, it was also one of the propaganda tools of the Early Republic serving as an arena of modern socialization. Apart from the ones held in Ankara, MITC encouraged the organization of domestic products exhibitions for ten years of time in Istanbul, between 1929 an 1938. The exhibitions were organized in the large hall of Galatasaray High School. The profile of the exhibitors was heterogeneous including firms from the private sector, state-supported factories, state-owned factories, together with local artisans, and artists. The exhibitions of domestic products provided a platform for the activity of design and practice in different working areas. Products of industry and crafts from a wide range of the Turkish daily life were exhibited. Designing the stands and pavilions of the exhibitors was one of the main design activities for a significant and a limited number of designers. The posters for the announcement and the promotion of the exhibitions and the other activities of MITC were also a telling design activity of the time. MITC, as some of the state organizations, was successful in using graphic design as a strong tool of propaganda and promotion. Among the exhibitors, most of the state institutions and factories, and some of the private firms showed themselves off through high modernist stands, which acted as a face of modern production and positivist thinking. The modernist stands and pavilions of most state firms were designed by the designers/decorators/artsists of the time such as Arif Dino, Vedat Ar and İsmail Hakkı Oygar. These high modernist stands acted as meeting points between modern design and the public. The posters designed by İhap Hulusi, also served the same purpose whilst promoting the use of domestic products. The objective of the İstanbul Domestic Products Exhibitions was to bring the products of Turkey together with large communities under the same roof for setting the idea of money saving and encouraging the consumption and use of domestic products. Another important and significant issue that domestic product exhibitions acted as a key actor was about challenging the negative impressions of the public on the domestic products, and presenting the concept “Türk Malı (Turkish Product)” as reliable. Writers and thinkers of the period supported MITC and the idea of “Türk Malı”, while they also criticized local producers for not reaching the standards that MITC was promoted. Domestic products were not only exhibited but also sold in these exhibitions. It can be argued that these exhibitions acted as the first modern domestic department stores in the Republican Turkey, and triggered a new dimension of the consumer society. Keywords: Early Republican Period, domestic products, domestic product exhibitions, exhibition design.1930’larda fikirde üretkenliğin, uygulamada endüstrileşmenin desteklenmesinin sonucu olarak ulusun refahının arttırılması yolunda tüketim mallarına öncelik verilir. Gündelik yaşam eşyalarıyla refah, hijyen, modernlik gibi konular ilişkilendirilirken, “yerli mal” kullanımı teşvik edilerek üretkenliğin arttırılması hedeflenir. Dışa kapalı ekonomiyle birlikte toplumda tasarruf bilincini uyandırmak ve yerli ürünlerin tüketimini özendirmek amaçlı uygulamalar yapılır. Böylece, 1929’da Milli İktisat ve Tasarruf Cemiyeti (MİTC) kurulur. MİTC’nin Türkiye’de ürün tarihi bağlamındaki en belirgin etkinliği ulusal yerli malları sergilerinin düzenlenmesidir. 1851 uluslararası sergisine katılımın ardından yeni bir kavrayışla düzenlenmeye başlanan sergilerin, MİTC’nin aracılığıyla Erken Cumhuriyet Dönemi’nde sürdürülerek başka bir düzleme taşındığı görülür. “Sergicilik” içine girilen ekonomik koşulların aşılmasına hizmet etme önceliğiyle benimsense de aynı zamanda Erken Cumhuriyet’in propaganda araçlarındandır. Cemiyet Ankara’da düzenlediği sergiler dışında, İstanbul’da 1929-1938 yılları arasında, 10 yıl boyunca “Yerli Malları Sergisi”nin düzenlenmesini sağlar. Sergi salonu olarak Galatasaray Lisesi’nin salonu kullanılır. Yerli malları sergileri sergilenecek ürünler, ürünlerin sergileneceği stantlar ve tanıtımın aracısı afişler gibi farklı alanlarda tasarlama ve uygulama zemini hazırlamıştır. Sergilerin amacı tasarruf bilincini yerleştirmek ve yerli mal kullanımını özendirmek için Türkiye’de üretilen ürünlerin geniş kitlelerle aynı çatı altında buluşmasını sağlamaktı. Bununla birlikte sergilerde halkın yerli ürünler hakkındaki olumsuz fikirlerini değiştirmek, yerli mallarla güven kazanmak da hedeflenmiştir. Satış da yapılan bu sergiler tüketim toplumunun yeni bir boyutu olan departman mağazaları görevini de periyodik olarak üstlenmişlerdir. Bu sergiler Erken Cumhuriyet Türkiye’sinde bazı mimar ve sanatçıların stant tasarımları yapmalarına olanak da sağlamıştır. Anahtar Kelimeler: Erken Cumhuriyet Dönemi, yerli malı, yerli malı sergileri, sergi tasarımı
Solution cross-linked poly(isobutylene) based gels
Get PDFPIB jelleri, butil kauçuğunun toluen çözeltisi içerisinde çözünmesi ve sülfürmonoklorürün (S2Cl2) çözelti içinde çapraz bağlayıcı olarak kullanılması ile hazırlanmıştır. Çözelti polimerizasyonu ile silindirik şekilli, süspansiyon polimerizasyonu ile çapları 0.1-2 mm arasında değişebilen jel küreler sentezlemiştir. Sentezlenen bu jellerin çözücü karışımlarındaki şişme davranışları incelenmiştir. Toluen içersinde şişirilen jellerin şişme kapasiteleri sülfürmonoklorür konsantrasyonun azalmasıyla artmıştır. Çözelti içerisinde çapraz bağlanan PIB jellerinin çözünürlük parametresi 16.8 ± 0.8 Mpa0.5 olarak bulunmuştur. Bu değer çözücüsüz (bulk) çapraz bağlı jeller için belirlenmiş değere karşılık gelmektedir. Anahtar Kelimeler : PIB, Butil kauçuğu, Sülfürmonoklorür, jel, süspansiyon polimerizasyonu.We prepared several series of PIB gels starting from butyl rubber in dulite toluene solutions using sulfur monocloride as a crosslinking agent. By using solution and suspension cross-linking techniques, PIB gels in the form of rods or beads in the size range of 0.1-2mm were prepared and subjected to swelling in solvent-nonsolvent mixtures. The swelling capacity of the gels in toluene increased with decreased concentration of sulfur monocloride or butyl rubber in the organic phase. The swelling ratio of the gels first increased rapidly with increasing swelling time but then decreased rapidly with increasing swelling time but then decreased until an equilibrium was obtained. The solubility parameter of the solution cross-linked PIB gels was found to be 16.8± 0.8 MPa0.5, in accord with the reported value for bulk cross-linked gels. The cross-linking reactions between the PIB chains via sulfur monochloride were believed to proceed in steps as in the reaction between ethylene and sulfur monochloride. We tried to follow the development of the cross-linking process by using IR spectroscopy. However, the concentration of cross-linked units in the network was too low for IR detection. The dried PIB gels after synthesis were also subjected to sulfur analysis. Thus, the cross-linker concentration increased in the feed also increased the sulfur content of the networks. Keywords: PIB, Buthyl rubber, Sulfur monocloride, jel, suspension polymerization
Separation and determination of polyaromatic hydrocarbons by capillary electrokinetic chromatography
Get PDFPoliaromatik hidrokarbonların (PAH çevrede bulunma sıklığı ve insan sağlığı üzerindeki zararlı etkileri nedeniyle bu bileşikler, pek çok alanda ön plana çıkmakta ve bunların bir karışımdan ayrılarak tayinleri de önem kazanmaktadır. Bu çalışmada sodyum dodesilbenzensülfonat (SDBS), hidrofobik poliaromatik hidrokarbonların (PAH) su-organik faz ortamında elektrokinetik kromatografi yöntemi ile ayrılmalarında sahte sabit faz olarak kullanılmıştır. PAH moleküllerinin, SDBS iyonu ile solvofobik etkileşimi sonucu negatif yük kazanan PAH türleri, elektrik alan altında hareket edebilirler. Böylece farklı halka (1-5) sayısına sahip 8 adet PAH ve 3 adet aromatik bileşik içeren örnek karışımının 130.000-230.000 arası teorik plaka etkinliği ile ayırımı başarılmıştır. Geliş zamanına göre bağıl tekrarlanırlık değerleri % 1.15-1.55 RSD, pik alanına göre ise % 2-9 RSD arasındadır. Anahtar Kelimeler: Poliaromatik hidrokarbonlar, sodyum dodesilbenzensülfonat, kapiler elektroforez, elektrokinetik kromatografi.Due to the abundance of polyaromatic hydrocarbons (PAHs) in the environment and the adverse health effects to which they have been linked, these compounds have been the focus of considerable attention in a number of areas including chemical separations. Especially, nowadays due to many advantages of the capillary electrophoresis technique (CE), detection and analyses of these kinds of compounds by using CE have become more important. In order to separate nonionic compounds in CE, an interaction with a charged carrier in the buffer should be provided. Both PAHs can be separated in CE by using additives which cause selectivity change and resolution of PAHs having the same electrophoretic mobility, not only due to electrostatic interaction but also due to a combination of other effects like hydrophobicity, hydrogen bonding, dipole-dipole interaction, etc. Sodium dodecylbenzenesulfonate (SDBS) was evaluated as potential pseudo-stationary phase for the separation of highly hydrophobic polycyclic aromatic hydrocarbons (PAHs) with electrokinetic chromatography in aqueous-organic media. PAH molecules undergo a solvophobic interaction with the SDBS ion, forming negatively charged species that can migrate in an electric field. Thus electrophoretic separations of 8 PAHs and 3 aromatic compounds having different ring numbers (1-5) were achieved with efficiencies between 130.000-230.000 theoretical plates. Reproducibilities of migration times range between 1.15 and 1.55 %RSD and peak areas between 2 and 9 %RSD. Keywords: Polyaromatic hydrocarbons, sodium dodecylbenzenesulfonate, capillary electrophoresis, electrokinetic chromatography
The phase transitions in liquid crystal polymers
Get PDFFoton geçirgenliği yöntemi kullanılarak sıvı kristal akrilat monomer, (6-4-siyanobifenil-4’-oksi)hekzil akrilat (LC6), homopolimeri (PLC6) ve politetrahidrofuranla aşılanmış aşı kopolimerinin (GLC6) faz dönüşümleri incelendi. Faz dönüşümleri polarizasyon mikroskobuyla doğrulandı. LC6 monomerinde izotropik-nematik-smektik A-smectik C faz dönüşüm serisi gözlenirken PLC6 ve GLC6 polimerlerinde, nematik ve smektik A fazları baskın görünmektedir. LC6 monomerinde nematik-smektik A faz dönüşümü ikinci dereceden olup düzen parametresi için efektif kritik üstel olarak hesaplandı. Gözlenen nematik-smektik A faz dönüşümü PLC6’da birinci derece ve GLC6’da ikinci derece olurken dönüşüm sıcaklığı aynı kalmaktadır. GLC6’daki donmuş rastlantısal bağların etkisnini donmuş rastlantısal etkileşmelerin kuramsal sonuçlarıyla tutarlı olduğu görüldü. GLC6 aşı polimerinde nematik-smektik A faz dönüşümünde kritik üsteli olarak hesaplandı. Anahtar Kelimeler: Foton geçirgenliği yöntemi, sıvı kristal homopolimer, aşı kopolimeri, nematik düzen, donmuş rastlantısal bağlar.The photon transmission technique was used to study the phase transitions of a liquid crystalline acrylate monomer, 6-(4-cyanobiphenyl-4-oxy)hexyl acrylate (LC6), its homopolymer (PLC6) and its graft copolymer (GLC6) with polytetrahydrofuran grafts.The structure of the phases was identified by polarizing microscopy. The transition temperatures were also determined by polarizing microscopy, from changes in the characteristic texture of the phases observed under cross polarizers. We observed the phase transition sequence isotropic-nematic-smectic A-smectic C in the LC6 monomer. In LC6 monomer, the nematic-smectic A transition was found to be of second order as observed by Mc Millan ratio. The effective critical exponent of the order parameter was found to be near the nematic-smectic A transition. The value of the exponent was very close to the tricritical value. Nematic-smectic A transition is first order in PLC6 and second order in GLC6, with the transition temperature remaining the same. It has been argued that first-order phase transitions are converted to second-order phase transitions by the introduction of frozen disorder into a system. The effect of quenched random constraints introduced in GLC6 are consistent with the theory of quenched random interactions. Keywords: Photon transmission technique, liquid crystal homopolymer, graft copolymer, nematic order, quenched random constraints
Integral representation of solutions to a coupled linear wave system
Get PDFBu çalışmada, homojen olmayan kuple lineer iki dalga denklem sisteminin çözümlerinin integral gösterimi elde edilmiştir. Bu denklemler; sonsuz, homojen, zayıf nonlineer ve zayıf dispersif elastik bir ortamda (2+1) (iki uzay ve bir zaman) boyutlu uzun ve kısa dalga etkileşimi probleminden türetilen eliptik-hiperbolik-hiperbolik (EHH) halindeki genelleştirilmiş Davey-Stewartson (GDS) sisteminin bir parçasını oluşturmaktadır. GDS sisteminin EHH ve diğer durumları, sistemin katsayılarının işaretine göre sınıflandırılmasıyla belirlenmiştir. EHH durumdaki GDS sistemi, bir nonlineer Schrödinger (NLS) tipi denklem ve simetrik olmayan kuple lineer dalga sisteminden oluşmuştur. İkinci mertebe iki bilinmeyen içeren simetrik olmayan kuple lineer dalga sistemi, dört karakteristik değişken yardımıyla birinci mertebe dört bilinmeyen içeren bir lineer sisteme indirgenmiştir. Sistem karakteristik değişkenlere göre integre edilmiş ve sisteminin hiperbolik-hiperbolik (HH) olmasından dolayı karakteristik değişkenler üzerinde tanımlanan sınır koşulları kullanılarak çözüm elde edilmiştir. Böylece kuple lineer dalga sisteminin çözümlerinin integral gösterimi bulunmuştur. Bu gösterim tek dalga denkleminin çözümlerinin integral gösterimi ile karşılaştırılarak, dalga sisteminin dört karakteristik değişkene bağlı olmasının çözümlerde neden olduğu karmaşık yapı tartışılmıştır. Ayrıca çözümlerinin integral gösteriminin en basit uygulaması olarak, karakteristik değişkenlerden yararlanılarak, üç bileşenli GDS sistemi yerel olmayan terimleri içeren tek NLS denklemine indirgenmiştir. Bu integral gösteriminin GDS sisteminin başlangıç değer probleminin incelenmesinde ve bazı lokalize çözümlerinin elde edilmesinde nasıl kullanılabileceği kısaca tartışılmıştır. Anahtar Kelimeler: Kısmi türevli diferansiyel denklemlerin integral gösterimi, kuple dalga sistemi, genelleştirilmiş Davey-Stewartson sistemi.In the present study, we consider a system of two asymmetrically coupled linear wave equations with nonhomogeneous terms. This is a part of a generalized Davey-Stewartson (GDS) system which can be reduced to the Davey-Stewartson (DS) equation through a nonlinear variable transformation for some special parameters values. The GDS system has been derived to model (2+1) dimensional wave propagation in a bulk medium composed of an elastic material with coupled stresses. This system consists of one nonlinear Schrödinger (NLS) type equation for the complex amplitude of a short wave coupled with two linear wave equations for long waves propagating in the medium. The GDS system can be classified with respect to the parameter values. This classification is based on the eigenvalues of the coefficient matrix of a first order linear system with four equations equivalent to the second order linear system. The GDS system in the elliptic-hyperbolic-hyperbolic (EHH) case can be written in a dimensionless form as where and are spatial coordinates and is time; is the complex amplitude of the short transverse wave mode, and are the long longitudinal and long transverse wave modes, respectively. and also are constants. The purpose of the present study is to obtain integral representations of solutions to the coupled linear nonhomogeneous wave equations. Our argument is a modification of the method which is used to find an integral representation of a solution for a single wave equation. This method is that the wave equation is written in characteristic coordinates and integrations are performed along them. In order to obtain the integral representation of the solution and , the coupled wave system is transformed to a system of first order equations and can be solved directly. The coefficient matrix of the new system has four real distinct eigenvalues, which enables us to define the following four characteristic coordinates and Since the system does not decouple in characteristic coordinates, there is no natural pair of characteristics. On the other hand, we can either choose the characteristic pair or to define a coordinate transformation from the plane to a plane formed by a set of the characteristic variables. In this study, we will choose the pair and express in terms of . Because of the hyperbolic nature of the system, the radiation type homogeneous boundary conditions on and will also be assumed and Than we perform integrations along characteristics and make use of the radiation boundary values along the characteristics to determine the unknown functions and . After long calculations, we obtain the representation of the solutions and for . We are able to see the complex interactions among the four characteristics in the limits of the integrals appearing in the representation of solutions. As a special case, when , the system reduced to the decoupled system because of Thus, solutions and are the same as the solution for the single wave equation. In conclusion, the GDS system can be reduced to a non-local NLS equation by using the representation of solution to the coupled wave equations. This equation allows us to present some localized solutions to the GDS system for some special choices of the parameters and find some estimates of the solutions to the system. Moreover; it also helps us to investigate the global existence of the solution to the GDS system for small initial data, blow up of the solutions, asymptotic behavior of the solutions and the local existence in time of solutions without smallness condition on the data. Keywords: Integral representations of partial differential equations, coupled wave system, generalized Davey-Stewartson system
CFD modeling of emissions formation and reduction in heavy duty diesel engines
Get PDFBu çalışmada, özellikle ağır vasıta dizel motorunda azot oksit (NOx) ve is (C(s)) emisyonlarının oluşumu ve azaltılması, Sayısal Akışkanlar Dinamiği (CFD) modellemesi yardımıyla incelenmektedir. KIVA-3VR2 ve CHEMKIN-II paketi modelleme için kullanılmıştır. Chalmers University of Technology’de geliştirilen n-heptan ve toluen karışımından oluşan dizel yakıt modeli (Disesel Oil Surrogate, DOS), türbülans/yanma etkileşimin içini kısmi karışımlı reaktör modeli (Partially Stirred Reactor, PaSR), detaylı reaksiyon mekanizması ve geliştirilmiş demet modeli KIVA-3VR2'ye uyarlanmış ve modellemeler gerçekleştirilmiştir. Dizel yakıt modeli ve reaksiyon mekanizması sabit hacimli bomba deneylerinde, değişik basınç ve hava fazlalık katsayısı (HFK, l), değerleri için, sıcaklığa bağlı tutuşma gecikmesi (TG) esas alınarak doğrulanmıştır. Sonraki aşamada Volvo D12C ağır vasıta dizel motorunda 18.5 ve 14.0 sıkıştırma oranları, farklı yük, püskürtme zamanı değerleri ve egzoz gazı geri dönüşü (EGR) oranları için modelleme çalışmaları yapılarak deney verileri ile karşılaştırılmıştır. Elde edilen sonuçlara göre, silindir içi basınç ve sıcaklık değerleri, ısı açığa çıkış hızı ve yanma verimi deney sonuçlarıyla uyumludur. NOx ve is emisyonları eğilim olarak deney sonuçlarıyla uyumludur ancak nicel olarak geliştirmeye ihtiyaç vardır. Emisyonlardaki farklılığın nedeni olarak, modelleme için kullanılan detaylı reaksiyon mekanizmasındaki is yanması, NOx ve CO oluşum reaksiyonları arasındaki çok hassas ve birbirini etkileyen dengenin henüz tam olarak sağlanamamış olması gösterilebilir. Bu konuda geliştirmeye ihtiyaç duyulmaktadır. Anahtar Kelimeler: Dizel motoru, modelleme, NOx-is emisyonları. The main emission problem for conventional diesel combustion is NOx-soot tradeoff (diesel dilemma) which could not be completely eliminated with the in-cylinder combustion techniques till now and still after-treatment process is necessary to meet the present emission legislations. Also with the development of the new engines which have different combustion regimes such as Homogeneous Charge Compression Ignition (HCCI), Modulated Kinetics (MK), Low Temperature Combustion (LTC), Premixed Charge Compression Ignition (PCCI), new emissions such as HC and CO became significant for compression ignition engines. This study mainly investigates formation and reduction of NOx and soot emissions in diesel engine combustion, especially in Heavy Duty Diesel (HDD) engines with the help of CFD engine modeling. KIVA-3VR2 and CHEMKIN-II package were used for the modeling purposes. CHALMERS' Diesel Oil Surrogate (DOS) model based on a blend of aliphatic (n-heptane, 70%) and aromatic (toluene, 30%) components, turbulence/chemistry interaction approach with Partially Stirred Reactor (PaSR) model, detailed chemical mechanism and modified spray model were implemented into the KIVA-3VR2 code for the modeling tasks. DOS and detailed chemical mechanism were validated comparing the ignition delay (ID) times with the present available shock tube data for different temperatures at different pressure and excess air ratios, l. Validation of the DOS and its constituents shows that developed reaction mechanism represents well enough ID and Negative Temperature Dependence behavior. Also it is calculated that for different l values (1 / Equivalence Ratios, ER) ignition delay time reduces with the increasing of ER (e.g., for rich mixtures) which is consistent with the experiments. Then modeling results for Volvo D12C engine at MK combustion (Compression Ratio, CR, 18.0) and LTC (CR = 14.0) regimes were compared with the experimental data. Present reaction mechanism is modified in order to improve its NOx-soot emissions behavior which has a good emission calculation tendency, but still quantitatively weak. Different fuel injection times, loads and both EGR-free and EGR cases were studied to extend the modeling capability. The MK combustion regimes in the Volvo D12C DI diesel engine realized under selected retarded fuel injections (e.g. Start of Injection, SOI, varied from -5 till to 10 Crank Angle Degree (CAD) After Top Dead Centre (ATDC) causing the ID to be longer than the injection duration. For injection timings, -5, 0, 5 and 10 ATDC, predicted trends clearly indicate that the combustion mode shifts from conventional diesel-like to HCCI-like mode following from early to late injection cases. This behavior is not clear in the pressure vs. crank angle curves because these retarded injections corresponds to the expansion part of the cycle, and expansion avoids sudden pressure rise sourced from HCCI-like combustion. However it is clearly visible from the Rate of Heat Release (RoHR) curves that, in retarded injection conditions, RoHR maxima increase as expected because of the increased premixed combustion phase, which increases ID times in such a way that ignition occurs after the completion of fuel injection process similar to the HCCI combustion mode. For all cases, calculation results for in-cylinder pressure, temperature, RoHR and combustion efficiency are in a good agreement with experimental results. NOx and soot emissions are reasonably well also. Although tendency of the calculated emissions is good, a quantitative improvement for emission predictions, especially for soot emissions, is required. In diesel combustion, most of the combustion process takes place over soot-formation and soot-oxidation path and soot emission is the difference between these formed and oxidized soot amount, which corresponds to only a small fraction of formed soot ( =1%). Hence modeling of soot emissions is very hard, e.g., even 1% calculation error for soot oxidation will drastically affect the resulted soot emissions. NOx formation is also strictly coupled with the soot-oxidation process because the remained oxygen radical which is necessary for NO formation depends on the soot-oxidation process. If soot-oxidation part is dominant in the mechanism, then excessive soot oxidation process can result lower soot emissions than the real amount by consuming most of the available oxygen radical which will be used later for the NO formation reactions. In conclusion excessive soot oxidation gives less soot emissions and indirectly prevents proper amount of NO formation. For this reason more accurate modeling of NOx-soot emissions in the presented detailed chemistry approach requires a proper balance between soot-oxidation and NO, CO formation reactions. Keywords: Diesel combustion, NOx-soot emissions, CFD modeling.
Data sources:
Access Repository Dashboard
Do you manage itüdergisi (E-Journals - İstanbul Teknik Üniversitesi, Istanbul Teknik Uniersity., İTÜ)? Access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard!