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
Analyzing changes of urban pattern through fractal geometry
Get PDFKentsel doku zaman içinde değişen koşullara göre değişen dinamik bir yapıya sahiptir. Her yerleşmenin bu değişim süreciyle oluşan kendine özgü morfolojisi ve doku karakteri olması, dokunun biçimsel özelliklerinden bağımsız olan birtakım ilkelerin sistemin işleyiş ve düzeninde etkili olduğunu göstermektedir. Değişim sürecinde doku karakterine yabancı müdahaleler dokunun kendine özgü karakterini bozar. Bu tür, geleneksel yöntemlerle ölçülmesi zor olan doku karakterinin ve dokuya müdahale etkilerinin incelenmesi, mekânsal organizasyonun işleyişini anlamaya katkıda bulunurken, biçim yerine dokunun mekânsal organizasyonunu değerlendirme yaklaşımı ile farklı dokulara sahip yerleşmelerin karşılaştırılmasına da olanak tanımaktadır. Dokunun zaman içindeki dinamik yapısını ve mekânsal ilişki özelliklerini analiz etmek için kaos teorisi ve fraktal geometriden yararlanmak mümkündür. Kaos teorisi dokunun zaman içindeki sürekliliği ve başlangıç koşullarının dokunun evrimi üzerindeki etkisini değerlendirmeye yardımcı olurken fraktal geometri ise dokunun mekânsal organizasyon açısından değerlendirilmesine yardımcı olmaktadır. Beyazıt Meydanı ve çevresini kapsayan 1km2’lik alan üzerinde yapılan fraktal analiz sonuçları bunu desteklemektedir. Dokunun gelişimi incelendiğinde zaman içindeki değişim sürecinde devamlılık gösteren özelliklerin olduğu görülmektedir. Dokuda belirgin değişim olan dönemlerde fraktal boyutun da önemli ölçüde farklılaşması, doku özellikleri ile fraktal boyut arasındaki ilişkiyi yansıtmaktadır. Diğer yandan, İstanbul’da seçilmiş olan örneklem alanının fraktal boyut değerlerinin dünyadaki diğer örneklerden daha yüksek olduğu görülmüştür. Bu durum birçok farklı kültürün etkisi ve zengin doğal çevrenin etkisi ile evrimleşen dokunun daha yüksek bir karmaşıklık düzeyine sahip olduğunu göstermektedir. Anahtar Kelimeler: Fraktal geometri, mekânsal dönüşüm, kentsel doku, Beyazıt meydanı.There are mainly two concepts that appear with the development process of urban settlements. One of them is change and the other is sustainability or continuity. Unchanged and changed properties are strictly related to the development process itself and they differ in planned and self-generated systems. The present paper is intended to contribute to understanding the principles, which lead to the spatial evolution of cities through time. Beyazıt square covering a 1km x 1km area, with its surroundings was selected for this study as it is one of the historical cores of Istanbul and has a unique character with its built environment and rich urban activities. Analyzing the changes in spatial structure in time shows the effects of the natural environment and the formerly built up environment as an initial condition. Although the general structure, which is shaped mainly by the dominance of historical environment, is unchanged, in the adaptation process for the changing social, economic and several other factors, many changes have occurred. This complicated process is examined by using the methods defined by chaos theory such as analyzing the changes in fractal dimensions in different time periods to explain the changing complexity level of spatial structure. The two key features of fractal dimension concept are generator and initiator. These features can be translated into urban pattern concept as the generation process or transformation rules and existing environment as an initial condition. Planning and self-organization represent two different processes leading to the transformation of the urban pattern. First of them is a top-down process, which has an ability to make changes on the whole urban pattern in a short time period, while second one reflects a bottom-up process, where changes are made by individual decisions and they take longer to change the spatial pattern. Moreover, these two processes generally occur in different scales: Self-organization is closely related to buildings and plots while planning is generally more comprehensive and affects building blocks, transportation routes and the whole urban pattern. Because of these, the urban pattern can be classified into three main components: buildings, building blocks and roads. Fractal dimension in different time periods for each element is calculated separately. Although urban pattern is a fractal object, there is a big difference between computer generated theoretical fractals and urban pattern: Generally theoretical fractals are purely self-similar which is not applicable for real urban patterns. Added to this, urban pattern is a highly complex structure, the fractal dimension changes in different scales and different sub regions. Fractal generation in computer environment starts with the simple initiator object and generation rule, however, in urban realm, generally, the existing patterns are very heterogeneous and there are many interacted factors that affect the evolution process as a generation rule which result in various fractal dimensions. This feature is called as “multifractality”. There are several methods to calculate fractal dimension such as: Hausdorff dimension, Self similarity dimension, Box counting dimension, Divider or ruler dimension, Lyapunov dimension, Information dimension, Dilation dimension. Box counting method is the most preferred to other methods in physical science. Box counting method is relatively easy to calculate and suitable to measure spatial elements of urban pattern. Because of these advantages, box counting method was selected to calculate the fractal dimension of uban pattern. The preliminary measurement results show that the fractal dimension of the Beyazıt sample is over 1.7 that is higher than the values of 1.4-1.6 measured in modern settlement patterns. These results are considered to be a reflection of the complexity of the spatial structure of the study area. Detailed measurements of urban pattern revealed the multifractality of Beyazıt sample. Beyazıt has different fractal dimensions in different scales. The more diversity of spatial elements and heterogeneous structure of urban pattern bring together the increase in the range of fractal dimension values. On the other hand, fractal dimension values are generally over 1,7 and very close to each other with the exception of the year of 1819, which demonstrates very different pattern. Similar fractal dimensions of different time periods reflect the continuity of spatial character especially after 1900s. On the other hand, the changes in fractal dimension values are the result of spatial changes such as widened roads or changing building blocks and buildings demonstrating the relationship between fractal dimension and spatial configuration. Keywords:Fractal geometry, spatial transformation, Urban pattern, Beyazıt Square
Bir kamu hastanesinde ISO-9002:1994 Kalite Güvence Yönetimi uygulamasının hasta memnuniyeti ve bazı performans göstergelerine etkisi
Get PDFThe hospitals consuming the 45-75% of the sources set aside for the health services, have come across with the demands for the patient satisfaction, lower costs and higher satisfaction at the beginning of 1990's in Turkey. At the Social Insurance Institution (SSK) hospitals in which there is the most patient unsatisfaction "To Improve the Health Services Quality of SSK ISO-9000 and Continuous Quality Improvement Model" project have been implemented at the beginning of 2000. One of the 32 hospitals at which those studies have been implemented is SSK Kartal Hospital. The subject of our research was the effect of ISO-9000 that started to be implemented on 18.12.2000 according to the Total Quality Management (TQM) principles, on patient satisfaction and some of the performance indicators. The patient staisfaction and the number of the operations increased and laboratory examinations and the medicine consumption amount decreased at SSK Kartal Hospital after the studies of ISO-9000. In these changes the implementation of ISO-9002:1994 Quality Assurance Management was effective, but 3-6 months after documentation of the results, the positive change in some of the indicators decreased and the situation showed a tendency to return back to the previous conditions. Keywords: ISO-9000, quality, quality in hospitals. Ülkemizde kamu hastaneleri arasında en fazla şikayetin ve memnuniyetsizliğin olduğu SSK hastanelerinde 2000 yılında, “SSK Sağlık Hizmetleri Kalitesinin Yükseltilmesi için ISO-9000 ve Sürekli Kalite İyileştirme Modeli” projesi uygulamaya sokulmuştur. Bu çalışmaların uygulandığı 32 hastaneden birisi de SSK Kartal Hastanesi’dir. Bu hastanede 18.12.2000 tarihinde başlayan ve TKY ilkelerine göre yürütülen ISO-9000 uygulamasının hasta memnuniyeti ve bazı kritik performans göstergelerine etkisi araştırmanın konusunu oluşturmaktadır. Yapılan analizde, SSK Kartal Hastanesi’nde yürütülen ISO-9000 çalışması sonucunda ayaktan tedavi hasta memnuniyetinin ve ameliyat sayısının arttığı, ilaç sarfiyat adedi ile laboratuar tetkik sayılarının da azaldığı, bu değişimlerde de ISO-9002:1994 Kalite Güvence Yönetimi standardının uygulanmasının etkisi olduğu, fakat belgelendirmeden 3-6 ay sonra bazı göstergelerde olumlu değişimin azaldığı ve eski duruma dönüş eğiliminin ortaya çıktığı görülmüştür. Anahtar Kelimeler: ISO-9000, kalite, hastanelerde kalite
Development of museums in Turkey
Get PDFBatı’da, koleksiyonların, 18. yüzyılda topluma açılması; bir sistem çerçevesinde kurumsallaşmayı da gerektirmiş, bugün ziyaretçi ve iletişim temelli bir yaklaşımla toplumla bütünleşmeyi hedefleyen müzeler, 19 ve 20. yüzyıl boyunca hızla değişen bir gelişim süreci içerisinde olmuşlardır. Ülkemizde ise müzeler; öncelikle zengin tarihî ve kültürel mirasımızı korumayı hedefleyen, 19. yüzyılın Batılılaşma çabalarının göstergesi olan “çağdaş bir kurum” olarak ortaya çıkmışlardır. Müzenin kurumsallaşma sürecine ilişkin bu tespit, aynı zamanda Türkiye’de müzecilik uygulamalarının biçimlenmesini de etkileyen iki önemli kavramı, “koruma” ve “Batılılaşmanın göstergesi çağdaş bir kurum olma” kavramlarını da vurgulamaktadır. Sunulan bu çalışmanın amacı; Türkiye’de müzeciliğin gelişimini aktarırken, Batılılaşma sürecinin müzecilik uygulamaları ve bunları biçimlendirmedeki etkisini de vurgulamaktır. Anahtar Kelimeler: Türkiye’de müzecilik, koleksiyonların çeşitlenmesi, müze mimarisi.Since the first ages, the motive of collecting flourishing in religios and other sacred traditions were also the basis for art that has also been the core of collections. Collection was the main reason to establish the museums which led foundation of current museums. Upon opening collections to the public in the eighteenth century, brought about the need for systematic corporate approaches, in addition to the exhibitive and informative functions, and with the social, economic and political developments encountered in the nineteenth and twentieth centuries, the museums entered a fast-changing development process. Today, within this process, museums aim at social totality with a visitor and communication based approach. In our country, museums' target is primarily the protection of our rich historical and cultural heritage and the museums emerged as a "contemporary organization" as an indicator of westernization efforts in 19th century. This assumption about organizational process of museums also emphasizes two important factors, which effected the formation of museum applications in Turkey. One of these is: "protection" of historical and cultural heritage and the other concept is: "a contemporary institution as an indicator of westernization". The objective of this study is to emphasize influences of Westernization process in museum applications and formation while discussing development of museums in Turkey. Keywords: Museums in Turkey, ramification of collections, museum architecture.
Çağdaş çalgı tekniklerinin kemençe, ud, kanun ve neye uyarlanması
Get PDFThis study is a research on the application of standardized contemporary instrumental techniques to kemençe, ud, kanun, ney in addition to the proposition of the notation of particular techniques that are unique to those instruments. The main purpose is to contribute to the formation of the common terminology that will enrich the communication between contemporary music composers and traditional Turkish music composers and performers. This communication will strengthen composers’ relation with the tradition in order to create access to unique artistic formations. In order to establish this communication, the possibilities and the characteristics of these four instruments are analyzed; according to the results of this research new notation methods are proposed. Meşk, a system that does not use any written material to transmit the musical works, remained as the only method in the tradition of Turkish Music education. Western notation has been adapted to Turkish Music only at the beginning of the twentieth century but especially by the establishment of the State Conservatory in 1976. Since the tradition focuses on the revelation of the single melodic line, the idiomatic principles of Turkish music instruments are not systemized even by the conservatory. Therefore, the thesis is not a research on the characteristics of the tradition rather is a research based on a practice study. Observations and experiences that are accomplished as a result of this process are enrolled in this dissertation as a proposition of a prototype of the idiomatic studies on Turkish music instruments. Turkish Music tuning system contains microtonal pitches in reference to equal temperament. The notation system which includes these microtonal indications is created by Hüseyin Saadettin Arel and Suphi Ezgi during 1940’s and standardized after the establishment of the Turkish Music State Conservatory in 1976. In Turkish music system the microtonal indications are determined by nine equal divisions of a major second. Each of these equal divisions is called a “koma”. As in equal temperament system the size of a major second (a whole tone) is 200 cents, each of these komas are approximately (200/9= 22.2) 22 cents. In this system, the flat and the sharp signs of the conventional western notation system are being used. However despite the western music system, these signs correspond to different pitch sizes in the Turkish music system. In western music notation flat and sharp are in equal size that divides the major second interval into two equal semitones. In the Turkish music system, flat is larger than the sharp. The flat sign determines five komas where the sharp determines four. The overall Turkish music notation is transposed according to the western system. It is transposed up a perfect fourth. Rast maqam is the fundamental maqam in the Turkish music theory. Rast as a musical note - the finalis (durak) of rast maqam - corresponds to D4 in western music notation. In Turkish music system it is notated as G4 in Turkish music notation system. Nevertheless, this is not a standardized convention. Kemençe, ud, kanun and ney players are not trained and accustomed to interpret musical expression through the indications of notation. They are not familiar with the notations of the musical symbols such as crescendo, marcato, sul ponticello or many others. The techniques that are particular to these instruments – such as hortlatma on ney, fiske on kanun – are generally not indicated in musical scores. Kemençe and Kanun have some constructional problems that cause interferences in the application of contemporary techniques. Kemençe strings are not produced in Turkey. Musicians are rather using cello or violin strings. In kanun, each string group has levers in order to achieve different microtonal pitches that belong to the Turkish music system. The numbers of levers in each string are not standardized. This situation causes intonation problems when they play with different instruments. Turkish music performers are not experienced to perform in ensembles that they play individual lines with the other musicians. They are inexperienced not only to construct a unified ensemble sound, but also to perform the rhythms accurately in a situation that they perform individual lines different from other players’ parts. Keywords: Kemençe, ud, kanun, ney, contemporary instrumental techniques.Bu çalışmanın konusu günümüzde müzikte evrensel olarak kabul görmüş çalgı tekniklerinin Türk müziğinin önde gelen dört çalgısına uyarlanabilirliklerinin araştırılması ve söz konusu çalgılara özgü tekniklerin nota yazımları konusunda öneriler sunulmasıdır. Temel amaç çağdaş müzik alanında eserler veren besteciler ile Türk Sanat Müziği geleneğinden gelen müzisyenlerin iletişimlerini güçlendirecek ortak terminolojinin oluşmasına katkıda bulunmaktır. Böylelikle bu çalgıların özellikleri kullanarak çağdaş müziğe yeni estetik açılımlar kazandırılabilir. Bu amaca ulaşmak için geleneksel Türk Sanat Müziği çalgılarının karakteristik özellikleri ve olanaklarının sınırları, icracıların görüşleri de göz önünde bulundurarak, araştırılmıştır. Türk Müziğinin geleneksel eğitim sisteminde, yirminci yüzyıla değin meşk yöntemi kullanılmıştır. Bu yöntemde eserler nota yazımı kullanılmadan öğrenciye veya icracıya aktarılır. Yirminci yüzyılın ilk yıllarından itibaren çeşitli kurumlarda ve 1976’da kurulan Devlet Konservatuarında batı müziğinin nota sistemi Türk Müziğine uyarlanmıştır. Ancak Türk müziği icrasında temel amaç, çalgıcıların tek bir melodik çizgiyi ortak ve doğru bir entonasyon ve ritmik kavrayışla aktarması olduğundan, her bir çalgıya özgü niteliklerin yazılı literatüre aktarılması kavramı gelişmemiştir. Bu sebepten ötürü, bu çalışma bir gelenek üzerine yapılan bir araştırma değil, belirli icracılarla birlikte yaşanan bir süreç sonucunda elde edilen deneyimlerin ve gözlemlerin aktarılmasıdır. Bu aktarım Türk müziği eğitimine yönelik öneriler olarak görülebilir. Anahtar Kelimeler: Kemençe, ud, kanun, ney, çağdaş çalgı teknikleri
Yeni-primitivizmden Süprematizme Maleviç'in sanatında tersten perspektif dördüncü boyut ilişkisi
Get PDFThe study aims to focus on the relationship between reverse perspective and metageometry as a bridge, which carries Malevich art from neo-primitivism to suprematism. The main sources of the study consist of three different kinds of writings. The first group consists of Malevich's own theoretical writings. Since Malevich based his ideas about fourth dimension and spatial reality on Ouspensky's work, the second main source is Ouspensky's Tertium Organum. The third main source is Florensky's Reverse Perspective. Because his ideas about reverse perspective in painting establish a connection between icon painting and non-Euclidean space concept and creates a conceptual link between Malevich's neo-primitivism and suprematism. Railing's book is also a important source, for it shed a light on metageometrical space concept and its connection with suprematism. At the beginning of second decade of 20th. century Russian painter Kasimir Malevich (1878-1935) was uncomfortable with cultural hegemony of Western artistic and intellectual world on Russian cultural life. Then he shared the idea to turn back elementary values of Russian culture, thus he painted several neo-primitivist canvases between 1910-1912. In these canvases he created a synthesis of Russian folk art, peasant art and icon art with several modern western art movements to achieve this aim. He carried reverse perspective, i.e. a reduction of spatial depth, multi-directional structure and point of view from icon painting, and almond shaped eyes, gigantic hands and feet and stylized figures from peasant art to his neo-primitivist paintings. In these paintings, it is also possible to identify Cezannesque spatial figure ground relationship, fauvist color choice and primitivist attitude which he borrowed from Gauguin as well. Suprematism is geometric abstract painting style which is created by Malevich. This term which Malevich derived from Latin word "supreme", means the highest or most sublime. With this term he aims to imply several meanings. Since suprematism aims to realize and reveal cosmic reality, it can't be related with an earthly perception, so it is connected to the "supreme". Secondly this abstract art style rejects naturalistic, mimetic painting style and wants to give its autonomy back to the painting. In this way it uses most minimalized color and form elements: basic geometrical forms, pure colors and monochromatic canvases. Because of its demand for autonomy it has a "supreme" quality. Malevich created kubo-futurist and "alogical" paintings to declare his anti-naturalist art conception during his pre-suprematist period. This rejection paves the way for a non-objective, non-figurative geometrical abstraction. Malevich intends to express a super-reality conception which base on cosmic relations, on matter as pure energy, on the fourth dimension and on movement as the most inherent quality of matter, instead of geo-centric and traditional conception of reality. In this case he gets his strongest support by Hinton's fourth dimension and metageometry concepts which he got acquaintance through Tertium Organum by Ouspensky. Hinton's metageometry derives from projective geometry, which is developed against Eucleidean geometry that based on three dimension. Principle of metageometry regards the three dimensional world as a cross section of the four dimensional one and it bases on the curvature of the universe. In this curved universe Eucleidean postulats are invalid, since Eucleidean geometry bases on flat space assumption. In fourth dimensional reality, time and movement are'nt sequent but inherent in matter. In his suprematist painting Malevich expresses this "inherent time and movement" concept with the flowing effect which suprematist motives created on the white surface of the canvas, which also symbolizes the space, expresses the movement element as the sign of the fourth dimension, which Malevich regarded as the key of the cosmic-spatial reality. Florensky's argument on reverse perspective accepts the linear perspective as connected to the Eucleidean geometry and the concept of flat space. Then, according to Florensky, linear perspective can?t be an instrument of painting as pure art, which is in the pursuit of the truth. Consequently Florensky's argument provides a conceptual connection between Malevich's neo-primitivist paintings and suprematist works. Keywords: Neoprimitivism, reverse perspective, fourth dimension, Suprematism, Metageometry.Üstün, yüce anlamına gelen Latince supreme sözcüğünden türetilmiş bir kavram ve soyut geometrik bir resim üslubu olan Süprematizmin yaratıcısı Rus ressam Kazimir Maleviç (1878-1935) süprematizmin keşfi öncesi 1910-1912 yıllarında, Rus kültürünün özüne dönme gayreti ile Rus ikona sanatından ödünç aldığı derinliğin azalması, zemin figür birleşmesine eğilim ve tek kaçış noktasının bulunmayışı gibi özellikleri Rus köylü sanatının figürde stilizasyon, aşırı iri beden ve uzuv betimlemesi gibi özellikleriyle, Cézanne’a benzerı bir düzlem anlayışı ve fovist bir renk seçimi ile harmanlayarak. Yeni-primitivist bir resim üslubu oluşturmuştur. Süprematizm kuramsal olarak temelin, üç boyutluluk temeline oturan Eukleides geometrisine karşıt olarak geliştirilmiş bir modern geometrik disiplin olan projektif geometriden türetilen, Hinton’ın dördüncü boyut ve metageometri kavramında bulmaktadır. Süprematizm üç boyutlu dünyayı dört boyutlu olanın bir kesiti olarak gören ve evrenin eğriliğinden yola çıkan metageometrinin ilkelerini ve maddenin saf enerji olduğu, bu nedenle hareketin maddenin en içkin özelliği olduğu düşüncesini, uzaysal gerçekliğin anahtarı olarak ele aldığı ve onun göstergesi olan hareket unsurunu, geometrik Süprematist motiflerin uzayı simgeleyen beyaz zemin üzerinde yaptıkları süzülme etkisi ile ifade etmektedir. Süprematizm Maleviç’in çağdaşı olan Florenski’nin tersten perspektif kuramı, doğrusal perspektifin ancak Eukleides uzayı ile bağlantılı bir uzam anlayışında mümkün olacağı görüşünü ortaya koymaktadır. Florenski’ye göre doğrusal perspektif doğanın-evrenin gerçekliği ile bağlantısı olmayan, resim sanatının ifade etme ihtiyacında olduğu hakikatle bir ilişkisi bulunmayan bir biçim unsurudur. Florenski’nin bu yaklaşımı Maleviç’iYeni-primitivist eserlerinden, Cézanne’nın figür ile yüzeyi birleştirmesine, Süprematizm öncesi denemelerine giriştiği Kübo-fütürist zamansallığa ve çok parçalılığa ve oradan da Süprematizme taşıyan köprü olarak görülebilir. Anahtar Kelimeler: Yeni-primitivizm, tersten perspektif, dördüncü boyut, Süprematizm, metageometri
Dissolution of percolation cluster on UV-cured polymeric films; a fluorescence study
Get PDFUV-cured polimerik filmlerin çözünmesini çalışmak için kararlı durum floresans teknik (SSF)kullanıldı. Bu filmler piren(P) ile etiketli poli(metil metakrilat) (PMMA) zincirlerinden elde edildi. Burada P çözünme işlemini takip etmek için floresans madde olarak tanımlandı. Çeşitli oranlarda etilen-glikol dimetakrilat (EGDM) çapraz bağlayıcı içeren, 3 ve 25 saat UV radyasyonu ile ışınlanmış PMMA filmler %(80-20) klorofrom-heptan karışımında çözdürüldüler. 3 saat ışınlanmış filmler için bulunan perkolasyon eşiği (pc=0.35) nokta perkolasyon modeline uyarken, 25 saat ışınlanmış film için ölçülen perkolasyon eşiği (pc=0.25) bağ perkolasyon modeline uyar. Anahtar Kelimeler: Floresans, çapraz-bağlanma, perkolasyon, çözünme.Steady state fluorescence (SSF) technique was used for studying dissolution of UV-induced polymer films. These films are formed from poly(methyl methacrylate) (PMMA) chains labeled with pyrene (P) which was introduced as a fluorescence probe to monitor the dissolution processes. PMMA films in various ethylene glycol dimethacrylate (EGDM) content, cured by UV radiation for 3 and 25 hours, were dissolved in chloroform-heptane (80%-20%) mixtures. Dissolution of the films were monitored in real-time by the pyrene fluorescence intensity, IP change in the solvent mixture. It was observed that maximum P intensity, IP¥ increased and decreased above a critical EGDM content for 3h and 25h irradiated films, respectively. It was atributed to the formation of a percolation cluster. The percolation treshold (pc=0.35) found for 3h irradiated films obeys site percolation model, however the measured percolation threshold (pc=0.25) for 25h irradiated films obeys the bond percolation model. Desorption rates, Dd were measured for films prepared with various EGDM content was observed that Dd values are much lower above pc than below pc for both films. These UV cured films dissolve much faster below the percolation threshold (pc) where dissolution coefficients were found to be around 10-9 cm2s-1. However above pc highly crosslinked films dissolve at least 4 times slower than low crosslinked films i. e. UV cured films hardly dissolve above critical EGDM content (pc) in the film. Keywords: Fluorescence, cross-linking, percolation, dissolution
Effects of off line of action contact on static behavior of the high contact ratio spur gear mechanism
Get PDFMekanizmalardan beklenen çalışma hızı ve güç/ağırlık oranı her geçen gün artmaktadır. Özellikle redüktör gibi kimi ekipmanlarda bu istek sadece malzeme ya da tribolojik gelişmelerle değil aynı zamanda güç iletim sistemine ait tasarımının geliştirilmesi ile mümkün olabilmektedir. Bu amaca ulaşmak için kullanılan yöntemlerden biri Yüksek Kavrama Oranına (YKO) sahip dişli çark mekanizmalarından faydalanmaktır. Burada amaç, yükün daha fazla diş tarafından paylaşımı sonucu mekanizmada aşırı bir ağırlık artışı olmaksızın iletilen gücün arttırılmasıdır. Dişli çark mekanizmalarında yüksek kavrama oranı, kavrama oranının 2'den büyük olması anlamına gelir. Bunun anlamı, mekanizmada her an için en az iki diş çiftinin temasta olmasıdır. Dişli çark mekanizmasının kendine özgü davranışını görebilmek için doğru olarak modellenmesine ihtiyaç duyulmaktadır. Bu makalede dişli çarkların analizi için kullanılan model, Yücenur tarafından geliştirilen ve uç girişiminin etkisini de içeren bir modeldir. Uç girişimi olayı; diş çiftinin dişlinin çalışma şartlarından kaynaklanan yük altında elastik şekil değişimi ya da dişlerde bulunan hatalar nedeniyle diş çiftinin temasının kavrama kıtasının öncesinde başlaması ve dışında da sürmesidir. Modelde; dişlerde eğilme ve kayma deformasyonları, dişin gövdeye bağlandığı bölgelerdeki deformasyonlar ve temas bölgesi deformasyonları ayrı ayrı hesaplanmakta ve ilgili konum için dişin yaylanma sayısı bulunmaktadır. Uç temasının olduğu bölgelerde yaylanma sayısı için ayrıca hesap yapılmamakta, bu bölgeler için yaylanma sayısı değerleri iki uçtan lineer olarak ekstropole edilmektedir. Bu makalede uç girişiminin yüksek kavrama oranlı dişli çark mekanizmasında statik zorlanmalara olan etkisi incelenmiştir. Anahtar Kelimeler: Yüksek kavrama oranı, uç teması, dişli çark modeli. Expected performance and power to weight ratio of power transmission systems have been steadily increasing. Especially for the equipments like speed reducers, this requirement can be met only by improvement of power transmission design. Another approach to meet this requirement is to use high contact ratio (HCR) gears. The purpose of using the HCR gears is distribution of the total load to more than one tooth pair; as a result, an increase in the power transmission capacity of the mechanism can be achieved without significant increase in mechanism weight. It is known that, single teeth load on the HCR spur gear is approximately 2/3 of the standard gear teeth for the same working condition. To this end, precise determination of the performance of gears in design phase is crucial. For gear mechanism situation is same. Unfortunately, there is no easy solution algorithm that is valid for the behavior of all gear mechanisms. For that reason, proper gear models are required to observe the specific behavior of each gear mechanism. Although, the studies on gear mechanisms go back to the beginning of the 20th century, there are still some uncertainties even for the standard gears. One of them is premature contact of the teeth; due to heavy tooth load or pitch deviations, tooth pair can meet outside the theoretical first contact point (similarly, contact may continue outside of the last theoretical contact point due to same reasons). This action is known as off line of action contact or corner contact. Many researchers have been trying to adopt this phenomenon to their models, but they could not succeed. In this study, the model utilized for gears also includes the off line of action contact effect, developed by Yücenur and he also represented a paper that included the effect of corner contact to a standard gear mechanism. Author showed that especially for moderately and heavily loaded spur gears, there is a significant effect of corner contact and this effect can not be neglected. In the study, the effect of off line of action contact on the static behavior of a HCR spur gear mechanism has been examined. The load carrying and related stress value for a gear which rotates at low speeds can be assumed as static. HCR can be expressed as; spur gears which have contact ratio larger than two. For the standard spur gears, contact ratio is normally smaller than two. If the change of pressure angle having small effect on contact ratio is neglected, only possibility to achieve HCR is using the extended teeth. It is clear that, of course, these gears can be manufactured only by using special cutting tools; however, this increases the manufacturing cost. In this study, to examine the effect of HCR, mechanisms having extended teeth (namely, mechanisms have HCR) are compared with standard mechanism; both mechanisms have involute teeth. Special efforts have been performed to select mechanisms that have the same characteristic values (such as the same module, the same pressure angle, and the same pitch circle). In this way, objective comparisons can be achieved. In this study, associated gear models are prepared with the aid of a computer program. Analyses are performed for many mechanisms. Then, the results are compared with each other on the same ground. In the analyses, all teeth are assumed to be geometrically perfect. At the end of the study, it is observed that real contact ratio slightly greater than the theoretical contact ratio due to the effect of off line of action. This effect is related with the working condition (transmitted power), and when the tooth load increases, the contact ratio also increases. Hence, it is shown that HCR can be achieved without excessive extension of the addendum circle radius value. In the study, in order to make a reliable comparison, the mechanism with real contact ratio is equal to 2 is also investigated and this mechanism is also compared with the others. In the analyzed examples, it is found that HCR mechanisms have the static tooth load value less than almost 1 / 3 of the standard mechanism value. It is also observed that bending stress at the root of both HCR gear and pinion teeth are reduced as the same degree of the load value. On the other hand, at the point of Hertzian stress, no significant advantages of HCR mechanism have been observed. In some applications, on the other hand, this stress values are slightly greater than those of the standard gears. Keywords: High Contact Ratio (HCR), off line of action, spur gear model.
Experimental analysis of R134a condensation in vertical narrow channels
Get PDFHerhangi bir ısıl sistemde faz değişimi olması halinde, olmaması haline göre daha fazla ısı geçişinin gerçekleşmesi, araştırmacıları bu alanda çalışma yapmaya sevk etmiştir. Bu husus göz önünde tutularak bu çalışmada; bir faz değişimi olan yoğuşma, deneysel olarak incelenmiştir. Deneysel çalışma kapsamında kurulan deney tesisatında; R134a soğutucu akışkanının, aralarında silindirik tüpün de bulunduğu 5 farklı düşey mini kanaldaki laminer yoğuşması incelenmiştir. Deneylerde kullanılan test üniteleri; silindirik tüp ile 4 adet çok-girişli kanallardır. Pratikte bundy boru olarak adlandırılan silindirik kanalın iç çapı 3.3 mm olup, üzeri bakır kaplı çelikten imal edilmiştir. Çok-girişli kanallar ise; farklı hidrolik çaplarda olmak üzere, 3-girişli, 5-girişli, 6-girişli ve 14-girişli olup alüminyumdan imal edilmiş kanallardır. Söz konusu bu çok-girişli kanalların hidrolik çapları sırasıyla, 4.74 mm, 3.6 mm, 1.53 mm ve 1.02 mm’dir. Böylece; kanal geometrisinin ve hidrolik çapının, R134a yoğuşmasında ısı geçişi ve basınç düşümü üzerindeki etkisi deneysel olarak tespit edilmiştir. Deneyler; farklı doyma sıcaklıkları ve farklı kütlesel akılar için tekrarlanmıştır. Böylece; düşey kanallardaki R134a soğutucu akışkanının yoğuşması, farklı doyma sıcaklıkları ve farklı kütlesel akılar için karşılaştırılabilmiştir. Ayrıca; bütün kanallardaki deneysel sonuçlardan hareketle, soğutucu akışkanların yoğuşması ile ilgili olarak literatürde yaygın bir şekilde yer alan korelasyonlara benzer bir korelasyon geliştirilmiştir. Yoğuşmada Nu sayısı için geliştirilen bu boyutsuz korelasyonun, literatürdeki korelasyonlar ile oldukça uyumlu olduğu görülmüştür. Anahtar Kelimeler: R134a yoğuşması, ısı taşınım katsayısı, sürtünme faktörü, düşey silindirik tüp, çok-girişli kanallar. In any thermal system, the fact that more heat is transferred in the occurrence of phase change is a motivation for the researchers to work on. Furthermore, it has become inevitable to build smaller (more compact) heating and cooling systems, while the technology is improving more and more. This resulted in the necessity of the occurrence of phase changes in smaller spaces. Therefore it is required to know the mechanisms of phase change in narrow spaces and to improve heat transfer. Taking these facts into consideration, this study is performed to investigate condensation, which is a frequently encountered phase change in thermal systems, in experimental aspect. In the experimental study, laminar condensation of coolant R134a is investigated for five different vertical mini channels including the vertical cylindrical tube and the other four multi-port channels. The cylindrical channel with an inner diameter of 3.3 mm is made of steel coated with copper. The other four multi-port mini channels, which have 3 ports, 5 ports, 6 ports and 14 ports, are made of aluminum. The hydraulic diameters of these multi-port channels are 4.74 mm, 3.6 mm, 1.53 mm and 1.02 mm, respectively. In this way, the effects of channel configuration and hydraulic diameter on heat transfer and pressure drop for R134a condensation are determined experimentally. In the experimental investigation, the average values of thermal parameters and pressure drop are obtained along the test unit. The experiments are repeated for different saturation temperatures (therefore different saturation pressures) and for different mass fluxes. Condensation data are taken for refrigerant R134a at 32 °C and 42 °C saturation temperatures for all mini channels. Therefore, it has been possible to compare the condensation of coolant R134a in cylindrical and multi-port channels for different saturation temperatures and different mass fluxes. The experimental setup established for this study consists of the following twelve main items: coolant pump, flowmeter to measure the flow rate of the coolant R134a, pre-heating section, heating section (superheater), condensation unit, a transparent Plexiglass heat exchanger covering the condensation unit, a rotameter to measure the flow rate of the cooling water, pre-cooling section, cooling section, a receiver, a thermostatic reservoir for cooling water supply and a data acquisition system. As shown in Figure 1, refrigerant R134a enters the test section at a known vapor quality. It is condensed in the test section against the cooling water flowing in the annulus. The two-phase mixture leaving the test section enters a post- condenser. The subcooled liquid is then passed through a receiver which is in a cooler and the coolant pump. The pump moves the liquid to the pre-heater and the electric post-heater (superheater) which fixes the test section inlet vapor quality. The flowmeter is placed between the pump and the pre-heater to measure refrigerant flow rate in liquid phase. The refrigerant flow rate can be independently controlled by the pump. The inlet vapor quality is determined by the heat input to the electric post heater which can be independently controlled. The test section saturation temperature is controlled by adjusting the cooling water flow rate. The experimental results are investigated in two parts, thermal and hydrodynamic analysis. In the thermal analysis, graphs are obtained for the variation of average heat transfer coefficient with respect to average steam quality. As a result, it is shown that the average heat transfer coefficient increases when the average steam quality is increased. Also, graphs are obtained for the variation of average Nu number with respect to equivalent Re number. Similarly as a result, it is shown that the average Nu number increases when the equivalent Re number is increased. In the hydrodynamic analysis part, graphs are obtained for the variation of the pressure loss due to friction during condensation with respect to average steam quality. Also, other graphs are obtained for the two-phase friction coefficient during condensation with respect to equivalent Re number. As a result, mathematical relations are developed between ftp and Reeq for all mini channels. It is found that the two-phase friction coefficient decreases when the Reeq number is increased similar to Moody chart. As a result, a simple dimensionless correlation is developed for Nu number in refrigerant condensation which is in good agreement with the correlations in literature. Keywords: R134a condensation, heat convective coefficient, friction factor, vertical cylindrical tube, multi-port channels.
Predicting company merger and acquisition with the help of artificial neural networks
Get PDFDeğişen pazar yapısı ve rekabet koşulları şirketleri, yeni çözümler geliştirme zorunluluğu ile karşı karşıya bırakmıştır. Birleşmeler, şirketlerin yeni çözüm arayışları sonucu gündeme gelmiş buluşlardan bir tanesidir. Faaliyetlerin daha etkin yürütülmesi, faaliyet sinerjisi ve finansal sinerji elde edilmesi, yönetim etkinliğinde artış, piyasa payı, ürün geliştirme ve dağıtım sistemindeki ilerlemeler, marka, patent birleşmelerin başlıca nedenlerini oluşturur. Birleşmelerin doğru bir strateji olabilmesi için, birleşilecek veya satın alınacak şirket seçiminin, çok iyi analiz edilmesi gerektiği, bu makalede önemle vurgulanmıştır. Birleşmeler sağlıklı yapılması durumunda anlamlı olacaktır. Bu da birleşme sürecinde doğru tekniklerin kullanılması anlamını taşır. Makale kapsamında, şirketleri birleşmeye iten nedenler ve birleşen firmalarda performans artışının gerçekleştiği, stratejik planlamanın şirket birleşmeleri ile olan ilintisi anlatılmış, birleşme süreci yapay sinir ağları ile analiz edilmiş, karar vericiye sunulmak üzere, birleşme için bir yapay sinir ağı modeli oluşturulmuş, modelin oluşturulmasında MATLAB yazılımı kullanılmıştır. Neden sinir ağları sorusunun cevabı ise, onun teori gereksinimi esnektir, araştırma yaklaşımı kuralcı değildir ve bilinmeyeni sunuş şekli bulanık küme tabanlıdır ve en önemli özelliği gerçek dünya problemlerine uygulanabilir olmasıdır. Türkiye’de şirket birleşmeleri henüz gelişme aşamasındadır ve tam anlaşılamamıştır. Yöntemleri konusunda yatırımcılar yeterli bilgiye sahip değildir. Makalenin amacı birleşmenin şirketlerin büyümesi için bir yöntem olduğu, bu sürecin çok iyi analiz edilmesi gerektigi ve en doğru şirketi bulmak için sinir ağları modeli kullanılmasi önerilmiş, Türkiye’nin bir eksikliğine katkı sağlanması amaçlanmıştır.Anahtar Kelimeler: Şirket birleşme ve satınalmaları, yapay sinir ağları, karar verme.Today companies have been engaged in a new pursuit for adapting themselves to the changing market and competition conditions. Mergers are among the trends which have gained wider interest, especially in recent years. In order for the mergers to be a true strategy, the choice of company which will be merged or acquired has to be perfectly analyzed. This process was analyzed via artificial neural networks. Predictor variables selection is important factor about quality of the prediction model to get success. Predictor variables that used as inputs on the neural network model are specified on the basis of six hypotheses being frequently suggested in academic and popular financial literature. These are inefficient management hypothesis, growth resource mismatch hypothesis, industry disturbance hypothesis, size hypothesis, market-to-book hypothesis, price-earning hypothesis. 12 predictor variables that support these hypothesis are average excess return (AER), return on equity (ROE), average turnover (AVTURNOV), average growth (AVGROWTH), average liquidity (AVLIQUID), average leverage (AVLEV), GRDUMMY to see AVGROWTH, AVLIQUID, AVLEV combination, IDUMMY to see sector impact on merger and acquisition, total net book value of asset (SIZE), market-to-book (MTB), price and earnings (PE), average payout (AVPAYOUT). Based on inefficient management hypothesis, inefficiently managed firms are often acquired. AER, ROE, AVTURNOVER are chosen predictor variables to measure firm's management's performance. Growth-research mismatch hypothesis, firms with high growth and low resources or with low growth and high resources are likely to be acquired. The combination of AVGROWTH, AVLIQUID and AVLEV is to form GRDUMMY variable that shows growth-research mismatch impact. IDUMMY variable will be selected based on industry hypothesis to cluster industry impact on merger and acquisition. Based on size hypothesis, smaller firms are more likely to be acquired than larger firms. Size will be selected as a variable as well. Market-to-book hypothesis, the companies have got low market-to-book ratios are likely to be targets and same logic deals with price-earnings hypothesis. For these 12 variables, the data were obtained from COMPUSTAT. Most of the data items for variables were averaged over three to four years prior to observation year. Merger and acquisition process has been analyzed by the artificial neural network. To train the multilayer network to predict the company merger and acquisition, back propagation algorithm has been used. The advantages of back propagation algorithm is provided with a set of examples of proper network behavior where an input to the network and corresponding target output. Working approach of algorithm is to adjust the network parameters in order to minimize the mean square error. The first part of the article deals with the stimulators of the merger, the performance increase in merged companies, and the connection of strategic planning with company mergers. In the second part, artificial neural networks, the method used in the merger and acquisition process, is investigated in scope and structure. The reason for handling the artificial neural networks is that their requirement for a theory is flexible, their research approach is not prescriptive, their presentation of the unknown is fuzzy based, and most importantly, its adaptability to the real world problems. It is a considerably difficult process to determine the layer number and number of nodes on these layers that are optimum for acquiring the best neural network model. Several combinations of hidden layers and nodes are tried before reaching the satisfactory model. This process takes a long time and the optimal network is produced after many trials. The activation acquiring process cannot be realized without the computer support. In this process MATLAB 6.5 is utilized which is explained in the third part. In Turkey company mergers have not reached their maturity and they can not be completely understood. Investors do not have sufficient information on its methods. This article aims to support the view that a merger is a way for a company to grow, and to contribute to a better understanding in Turkey by making use of neural network models for identifying the best company to acquire. Keywords: Merger and acquisiton, artificial neural network, decision making
Real options approach for valuation of enterprise resource planning systems
Get PDFGünümüzde tüm dünya genelindeki sağlık kurumları, hizmet kalitelerini iyileştirmeyi ve maliyetleri düşürmeyi amaçlayan bilişim teknolojileri yatırımlarının önemini kavramışlardır. Sağlık sektörünün sürekli yükselen standartları ve sigorta sistemlerinin artan gereksinimleri karar vericileri, hastanelerde Kurumsal Kaynak Planlama (KKP) sistemlerinin sağlık sektörünün gerek ve ihtiyaçlarına göre uyarlanmış ve geliştirilmiş hali olan Hastane Bilgi Sistemi (HBS) yatırım uygulamalarını dikkate almalarını zorunlu kılmaktadır. Bu tür yatırımların ekonomik değerlemesi karmaşık yapıları nedeniyle her zaman zor olmuştur. Bununla beraber bu yatırımların, bünyelerinde barındırdığı ve firmalara rekabet ortamında avantajlar sağlayan birçok faydası da mevcuttur. Geleneksel iskontolanmış nakit akışı yöntemleri, bu sistemlerin içinde varolan ve yatırım kararını haklı çıkartacak, yönetsel ve stratejik esnekliklerin değerini dikkate almamaktadır. Reel opsiyon yaklaşımı karar vericilere, geleneksel değerleme yöntemlerindeki bu yetersizliklerin üstesinden gelme olanağını sunmaktadır. Bu çalışmada, reel opsiyonları temel alan bir yaklaşımla, birden fazla opsiyonun birarada yer aldığı bir KKP sistemi yatırımının değerlemesine imkan tanıyan bir model önerilmektedir. Binom ağacı modelini temel alarak geliştirilen değerleme modelinin yapısı KKP yatırım fırsatının bünyesindeki birleşik opsiyonları değerlemeye imkan tanıyacak şekilde genişletilmiş ve dolayısıyla karar vericilere yeni bir katma değer sunulmuştur. Geliştirilen modelin potansiyel uygulaması gerçek bir HBS yatırımı değerlemesiyle gösterilmektedir. Yapılan uygulama geleneksel değerleme yöntemlerince kabul edilir görülmeyen yatırımların bile, bünyelerinde barındırdıkları stratejik ve yönetsel unsurlar sayesinde ve gelecekte oluşması muhtemel koşullar dahilinde kabul edilebilir bir hal alabileceğini ortaya koymaktadır. Anahtar Kelimeler: KKP yatırımlarının değerlemesi, reel opsiyonlar, birleşik opsiyonlar, opsiyon değerleme modelleri.Nowadays in order to improve the quality of care delivery and reduce costs, healthcare organizations globally recognize the importance of investing in information technologies (IT). The key drivers of healthcare sector like continuous improvement of healthcare standards and insurance systems have introduced new requirements for hospitals, which in return provided a solid ground for decision-makers to consider implementing hospital information system investment. Hospital information systems (HIS) are the customized and improved versions of enterprise resource planning (ERP) systems, designed according to the needs and the requirements of healthcare sector. It has been always difficult to value such investments in monetary terms due to their complex nature. This type of investments also has many inherent benefits that can provide significant competitive advantages. These inherent benefits can only be viable for decision support if strategic and managerial flexibilities can be utilized. However, traditional capital budgeting techniques, such as net present value (NPV), do not enable decision-makers to consider these flexibilities. Due to its idle valuation approach, NPV only considers a static scenario that ignores the possible dynamic changes in the market affecting future cash flows and interest rates. NPV's passive commitment strategy also forces the decision-makers pre-committing today to a "go" or "no-go" decision considering information only available today. Thus, it is clear that the traditional NPV methods ignore the value of managerial and strategic flexibility inherent in the investments which undermines a company's strategic opportunities. Investment science experts agreed that it is a must to integrate financial and strategic issues and study them together for making an investment decision. Recognizing the shortcomings of traditional NPV methods, real options (RO) technique has been suggested as an alternative approach. RO whose methodology is based upon financial options theory enable the decisions makers to analyze the true value of a real life investment opportunity through better modeling of the uncertainty within the investment. RO method does not only value the managerial flexibility through the investment horizon, it also supports and expands the firm's strategic frame. It gives a road map to the managers to optimize the medium and long-term strategies according to the expectations. RO can be categorized to six main managerial options according to the flexibility they have: option to defer, option to stage, option to expand/contract, option to abandon, option to switch and growth option. In a real-life investment scenario it is usually viable to have more than one real option concurrently. The first applications of real options are about mining and operating natural resource investments. Besides, the new application areas for RO are growing rapidly. Regardless of an industry, it can be used in many cases like entering a new market, deciding the initial scale of an investment, scaling up or down in the future according to the needs, managing multi-staged complex projects, and freezing up or completely ending an investment. Developing with dynamic market conditions due to the continuous improvements, IT investments are also an appropriate application area for RO. This study introduces a RO based methodology that enables decision-makers to value an ERP system investment incorporating multiple options. The option valuation model developed in this study extends the binomial lattice framework to model an ERP investment opportunity with compound options. The potential application of the proposed model is presented to evaluate an HIS implementation project of a Turkish health care organization. For this purpose, considering the ever changing dynamics of the market affecting possible cash flows, a computer-based decision support framework is developed to provide a flexible and efficient solution to decision-makers. In this manner, for simulating various possible future market conditions, different scenarios are generated via triggering conditional changes in model variables and parameters. Results are interpreted with tables and graphs for submitting a thorough road map to decision-makers that can be utilized as a managerial asset for understanding the interactions between model parameters. Further investigations have shown that even an investment that is not approved to be undertaken with traditional valuation methods, can be valuable for a firm considering the strategic and managerial flexibilities inherent in the investment, with the effect of the possible market conditions in the future. Thus, it is also emphasized that real options approach generally presents a new point of view for valuing IT investment projects. Keywords: Evaluation of ERP investments, real options, compound options, option valuation models
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!