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Numerical investigation of operating fluid, rotating disk speed effects and number of cavities on drag reduction of micro-textured surfaces for hydrodynamic lubrication

Develi, Ahmet Çağrı | Olcay, Ali Bahadır

Article | 2017 | Sakarya Üniversitesi Fen Bilimleri Enstitüsü Dergisi21 ( 5 ) , pp.1081 - 1087

There have been developments on surface texturing methods providing benefit in a great many engineering applications.Especially, influence on surface texturing in lubrication applications related to frictional properties have been cause of concern.In the present study, it was aimed to work on the computational fluid dynamics (CFD) study of the lubrication system consistingof two parallel plates. While one of the plates was sliding, the other one was stationary and an incompressible two-dimensionalsingle phase flow was assumed between those plates. The scope of the CFD analysis was to determine the relationship betweendrag force and . . .operating fluid properties (i.e., oil types), rotational speed and the amount of the cavities. It was realized that SAE0W-30 was found to be the best fluid among the seven studied oil types providing optimal conditions such as high drag reductionand less drag force. It was noticed that the drag coefficient thus, drag force appeared to be increasing as the rotating disk speedrose. The influence of the number of the cavities along the textured surface was also investigated in the present study and it wasfound that drag reduction was not associated with the number of cavities because 0, 1, 2 and 3 cavities nearly gave the same dragforce values. Yüzey dokusu yöntemlerinde gelişmeler yaşanırken bu gelişmelerden birçok mühendislik uygulamaları fayda sağlayabilir.Özellikle sürtünme özellikleri ile ilgili yağlama uygulamalarında yüzey dokusu etkisi önemli bir etkiye sahiptir. Bu çalışmakapsamında iki paralel plakadan oluşan yağlama sisteminin hesaplamalı akışkanlar dinamiği çalışmasıyla incelenmesihedeflenmiştir. Plakalardan birisi hareket ederken, diğer plaka sabittir ve plakalar arasındaki akış, sıkıştırılamaz, iki boyutlu vetek fazlı olarak kabul edildi. Hesaplamalı akışkanlar dinamiği analizinin amacı direnç kuvvetindeki azalmanın, çalışan akışkanözellikleri (yani yağ çeşidi), açısal hız ve boşluk miktarı ile nasıl ilişkili olduğunu belirlemektir. Bu çalışmada SAE 0W-30 tipiyağın, çalışılan yedi yağ arasında en yüksek direnç düşüşü ve daha az direnç kuvveti sağladığı için en uygun koşulları sağlayanakışkan olduğu belirlenmiştir. Direnç katsayısının ve dolayısıyla direnç kuvvetinin açısal hızın artmasıyla arttığı fark edilmiştir.Boşluk sayısının yüzey dokusuna etkisi de bu çalışma kapsamında araştırılmıştır ve dirençteki azalmanın boşluk sayısı ile ilişkiliolmadığı bulunmuştur. Bunun nedeni 0, 1, 2 ve 3 boşluk yerleştirildiğinde neredeyse aynı direnç kuvvetleri elde edilmiştir Daha fazlası Daha az

A short note on the application of Cholesky matrix factorisation using MATLAB

Keskin, Ali Ümit | Göker, İmran

Article | 2006 | Istanbul University Journal of Electrical and Electronics Engineering6 ( 1 ) , pp.113 - 115

One must first make sure that a given matrix subject to factorization is symmetric, and then use it in Cholesky algorithm, in MATLAB. This may cost machine time to check for symmetry, however, saves much more of it by preventing errors due to inherent structure of the built-in algorithm.

Design of an intraoral artificial larynx

Göker, İmran | Özkan, Mehmet

Article | 2004 | Istanbul University Journal of Electrical and Electronics Engineering4 ( 2 ) , pp.1171 - 1176

In this study,an electronic intra-oral artificial larynx system is designed. The objective of this study is to provide an alternative speech rehabilitation method to the totally-laryngectomized patients that will generate vibrations of fundamental frequency of human vocal cords. A prototype based on that design that is mounted into a dental prosthesis is established. The design of that system is presented in this paper.

Turbo Trellis Coded Modulation (TTCM) with imperfect phase reference

Uçan, Osman N. | Osman, Onur | Osman, Onur

Article | 2001 | Istanbul University Journal of Electrical and Electronics Engineering1 ( 1 ) , pp.1 - 5

Bu makalede Turbo Kafes Kodlamalı (TKK) sistemlerin AWGN ve Rician ortamlarda faz bozulması durumunda hata başarımı elde edilmiştir. TKK yapısı ikili Turbo modülasyonu gibidir ancak TKK çok boyutludur. Turbo kodlamanın Kafes Kodlama ile birlikte kulanımı kodlayıcı yapısının değişimini gerektirir. Alıcıda ise ikili kodlayıcılarda olduğu gibi iteratif kod çözücü yapısı vardır. Burada 8PSK modülasyonda TKK farklı Rician katsayısı K, faz bozulma katsayısı a için benzetim sonuçları elde edilmiştir. Elde edilen sonuçlar hem genlikte hem de faz daki bozulmayı içermektedir. In this paper, we investigate the performance of Turbo Trellis Code . . .d Modulation (TTCM) over AWGN, and Rician channels and assume that phase disturbance is available. As we know Turbo Trellis Coded Modulation (TTCM) is similer to binary turbo codes, but employs Trellis Coded Modulation (TCM) codes which include multi-dimensional codes. The combination of turbo codes with trellis codes leads to a strigthforward encoder structure, and allows iterative decoding as binary turbo decoder. However, iterative Turbo Decoder needs to be adapted to the decoding of TCM codes. Here, we investigate TTCM for 8PSK for several Rician parameter K and effective signal-to-noise ratio in the cafrier tracking loop a. Thus, our results will reflect the degredations both due to the effects of the fading on the amplitude of the received signal and of a noisy carrier reference Daha fazlası Daha az

A new spreading code for multi-user MC-SS communication systems

Çekiç, Yalçın | Şenay, Seda | Akan, Aydın | Chaparro, Luis F.

Article | 2005 | Istanbul University Journal of Electrical and Electronics Engineering5 ( 2 ) , pp.1411 - 1417

Multi-carrier spread spectrum (MCSS) communication systems are able to mitigate the effects of fading, interferences and Doppler frequency shifts as well as to support multiple access schemes. It is possible to get optimum performance from MCSS systems by carefully choosing the spreading sequences. However, due to inter-user interferences, performance degrades as the number of users increases unless the transmission channels are modeled and estimated. In this paper, we present a new spreading sequence obtained from a complex quadratic sequence multiplied by a pseudo random noise sequence, thus exploiting the properties of constant e . . .nvelope and statistical independence. Our approach is based on the time-frequency characterization of the wireless communication channel by means of discrete evolutionary transform. The properties of the new spreading sequence enables us to estimate the parameters of multi-user channels, both for uplink and downlink transmission cases, and design a receiver that is robust to channel noise, inter-user interference and intentional jammers. The performance of the proposed system is illustrated by simulations Daha fazlası Daha az


Utku, Feride Sermin | Basaran, Kubra | Sunar, Yagmur | Celebıoglu, Hulya | Kapıcı, Ibrahim

Article | 2017 | Istanbul University Journal of Electrical and Electronics Engineering17 ( 2 ) , pp.3439 - 3443

Mineralized natural protein based novel bone replacement materials are investigated for tissue engineering. Mineralized silk fibroin composite foams and films display excellent biocompatibility. In this study, the biomimetic and electrochemical mineralization of orderly oriented silk fibroin scaffolds was studied. Commercially obtained pure silk woven fabric was boiled in 0.02 M Na2CO3 for 20 min. Calcium phosphate was deposited at 37°C for twenty minutes in seven sequential immersion steps, using 250 mM CaCl2 2H2O and 120 mM K2HPO4, containing 0.15 M NaCl and 50mM TRIS-HCl, pH 7.4, followed by electrochemical treatment in modif . . .ied SBF solution at 40°C at a current density of -25mA/cm2 for 60 min. The amount of biomimetically deposited Ca-P increased with the number of immersion steps. SEM images and XRD analysis of the Ca-P deposit indicated the initial formation of brushite with its monoclinic crystal structure and characteristic peak at 11.76 2?, and electrochemical conversion of brushite to hydroxyapatite on silk after electrochemical cathodization as confirmed by XRD and SEM analysis. Thus, a silk-fibroin-hydroxyapatite composite material prepared as a xenograft consisting of biocompatible components, and easily prepared as an economical bone segment replacement material with highly oriented fibers Daha fazlası Daha az

A platform for software engineering course projects

Aygün, Birol

Other | 2004 | Turkish Journal of Electrical Engineering and Computer Sciences12 ( 2 ) , pp.107 - 116

The importance of projects in software engineering courses is well known. Both synthetic and real-life projects have various advantages and disadvantages. Our aim was to create a framework where students can develop projects which reflect some of the complexities of real-life, involving many concurrent, interacting, asynchronous processes, each in a different stage of development, with wide temporal differences among them - some occurring- within millisconds of each other and others executing sporadically over much longer periods. In this project, which was carried out in different arrangements in several software engineering course . . .s in three universities, the students developed both the sub- and super-structures required, with varying degrees of success. The projects were performed in parallel with and subsequent to one-semester courses in software engineering. The development was performed in accordance with the principles established in the lectures. The sub-structure consists of a discrete-time event simulator and a message passing mechanism. It can support many different super-structures. The super-structure we created was an e-business community simulator where a manufacturer, its trading partners and the transactions among them were simulated. In this paper we summarize the project and our experiences during the development. A literature search for similar projects for software engineering education did not yield any hits. However several reported industrial projects for virtual supply chain management were examined. Our project on the other hand was tailored for implementation by student groups in one semester with the primary purpose of getting experience in complex, multi-group software development rather than immediate industrial use of the software Daha fazlası Daha az

Turkish entity discovery with word embeddings

Kalender, Murat | Korkmaz, Emin Erkan

Other | 2017 | Turkish Journal of Electrical Engineering and Computer Sciences25 ( 3 ) , pp.2388 - 2398

Entity-linking systems link noun phrase mentions in a text to their corresponding knowledge base entities in order to enrich a text with metadata. Wikipedia is a popular and comprehensive knowledge base that is widely used in entity-linking systems. However, long-tail entities are not popular enough to have their own Wikipedia articles. Therefore, a knowledge base created by using Wikipedia entities would be limited to only popular entities. In order to overcome the knowledge base coverage limitation of Wikipedia-based entity-linking systems, this paper presents an entity-discovery system that can detect semantic types of entities t . . .hat are not defined in Wikipedia. The effectiveness of the proposed system was validated empirically through the use of generated data sets for the Turkish language. The experimental results show that, in terms of accuracy, our system performs competitively in comparison to the previous methods in the literature. Its high performance is achieved through a method that learns word embeddings for candidate entitie Daha fazlası Daha az

Energy savings in simultaneous multi-threaded processors through dynamic resizing of datapath resources

Küçük, Gürhan | Mesta, Mine

Article | 2012 | Turkish Journal of Electrical Engineering and Computer Sciences20 ( 1 ) , pp.125 - 139

Nowadays, all the designers of systems from high-performance servers to battery-operated handheld devices aim for reliability, high-performance and longevity. Central within these aims the issue of processor power consumption is becoming increasingly important. In this study, we aim to adapt our already-provenmethod for single-threaded superscalar processors to simultaneous multi-threaded (SMT) processors for energy savings. The original method focused on resizing datapath resources according to the demands of running applications. To achieve this, the targeted resources are physically divided into multiple partitions, and turned on . . . and off according to the needs of the applications. Since, the energy consumption of the turned-off datapath resources is quite low, as a result, it becomes possible to have great amount of energy savings within a processor. However, special care must be taken when there are multiple threads racing against each other to gain access to shared datapath resources. As a result, our proposed microarchitectural technique achieves 0.5% Instructions Per Cycle (IPC) and 3.2% Total number of instructions Per Cycle (TPC) improvement, while it turns off 45% of the Reorder Buffer (ROB), 59% of the Load-Store Queue (LSQ), 43% of the Issue Queue (IQ), 30% of the integer Physical Register Files (PRF) and, finally, 48% of the floating PRF, on the average across all simulated benchmarks. According to our estimates, the total processor power is reduced by 12%, on the average Daha fazlası Daha az

Linear assembly and 3D networks of peptide modified gold nanoparticles

Kalay, Saban | Blanchet, Clement | Culha, Mustafa

Article | 2014 | Turkish Journal of Chemistry38 ( 5 ) , pp.686 - 700

The charge and size of molecules chemically attached to nanoparticles (NPs) play an important role in their interaction behavior in suspensions. Gold nanoparticles (AuNPs) were modified systematically with peptides and the modification was verified with surface-enhanced Raman scattering (SERS). The behavior of the modified AuNPs in suspension and at the liquidsolid interface was monitored using small angle X-ray scattering (SAXS), UV/Vis spectroscopy and dynamic light scattering (DLS) in suspension, and atomic force microscopy (AFM) at the solid liquid interface. It was found that while negatively charged peptide modified AuNPs beha . . .ve very similar to citrate reduced AuNPs due to their negatively charged surface, positively charged peptide modified AuNPs showed significantly different assembly/aggregation properties in suspension. The formation of linear assemblies of positively charged peptide (CKRHSKRHRSKRHSKRHSKRHSKR) modified AuNPs was clearly observed from the AFM analysis of the droplet areas of its colloidal suspension. The combined analyses of data obtained from the employed techniques suggest that the positively charged large peptide modified AuNPs can form linear and 3D-like networks in the suspension. This study reveals important information regarding the surface property dependent behavior of NPs that may help in efforts to build higher structures using NPs as building blocks Daha fazlası Daha az

Square wave voltammetric determination of valproic acid in pharmaceuticalPreparations

Acar, Ebru Türköz | Onar, Atiye Nur

Article | 2016 | Turkish Journal of Chemistry40 ( 1 ) , pp.106 - 116

The electrochemical behavior of valproic acid (VAL) was investigated using square wave voltammetry, cyclicvoltammetry, and sampled direct current polarography and a new square wave voltammetric method was developed fordetermination of VAL in pharmaceutical preparations. VAL showed two reduction peaks at about {0.2 V and {0.8 V vs.Ag/AgCl 3 M KCl with a hanging mercury drop electrode in 0.05 M pH 3.3 Britton{Robinson (BR) buffer. These peakswere named peak I and peak II, respectively. The types of limiting current of both peaks were determined as diffusioncontrolled based on cyclic voltammetry studies. A linear calibration graph was . . .obtained in the range 1.46104{1.0103M. The limit of detection (LOD) and limit of quanti cation (LOQ) were 1.09104M (21.05g/mL) and1.10104M (144.20g/mL), respectively. Recovery studies for the accuracy of the method were performed byadding known amounts of VAL and it was found to be 109.674.85%. The proposed method was successfully appliedto pharmaceutical products on the market Daha fazlası Daha az

Birikimli hasar teorileri ve yorulma çatlağına göre ömür değerlendirmeleri

Saatçı, Gökhan Erkin | Tahralı, Necati

Other | 2003 | Havacılık ve Uzay Teknolojileri Dergisi1 ( 2 ) , pp.33 - 39

Daha önceden bilindiği üzere, malzemelerin Wohler eğrisini elde etmek oldukça güçtür. Ancak işletmelerde dinamik yüklemelere maruz makina parçalarının servis ömürlerini tayin edebilmek için birikimli hasar teorilerine ihtiyaç duyulmakta ve teorileri kullanabilmek içinse malzemelerin zorlandığı gerilmelerdeki maksimum ömür değerlerinin bilinmesi gerekmektedir. Bu ömür değerleri ise Wohler eğrilerinden okunmaktadır. Bu çalışmada Wohler eğrilerinden bağımsız olarak eşdeğer yorulma ömrünün hesaplanması amaçlanmıştır. Dolayısıyla birikimli hasar teorilerinin ihtiyaç duyduğu ömür değerleri, yorulma çatlağının artışını toplama prensibine d . . .ayanan ampirik bir ifadeden elde edilmiştir. Çalışmada öncelikle bu ampirik ifade tanıtılmış ve 1013. Ord. Ana. Tam. Fabrikasında üretilen GTD model 4X4 askeri aracın çeşitli değişken gerilmeler altında çalışan aktarma elemanının yorulma ömrü hesaplarında kullanılarak eşdeğer ömür hesabı yapılmıştır. As known before, obtaining Woehler diagrams of the materials are very difficult. But to predict the service life of machine elements that are subject to cyclic loads, the cumulative damage theories are needed, and to use the teories maximum life values at the stresses that the specimen is loaded must known. These values are being read from Woehler diagrams: In this study, it is aimed to calculate the equivalent fatigue life, independent from Woehler diagrams. Therefore life values that are needed for cumulative failure theories, are obtained from an emprical expression that is related to fatigue crack growth rate. First of all, this emprical expression is described and then it is used to calculate the equivalent life of the transmission component of "GTD model 4X4 military vehicle" that is being produced in "1013. Ord. Ana. Tarn. Fabrikası" which is working under several variable stresses Daha fazlası Daha az

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