Split-screen single-camera stereoscopic PIV application to a turbulent confined swirling layer with free surface

An annular liquid wall jet, or vortex tube, generated by helical injection inside a tube is studied experimentally as a possible means of fusion reactor shielding. The hollow confined vortex/swirling layer exhibits simultaneously all the complexities of swirling turbulence, free surface, droplet formation, bubble entrapment; all posing challenging diagnostic issues. The construction of flow apparatus and the choice of working liquid and seeding particles facilitate unimpeded optical access to the flow field. A split-screen, single-camera stereoscopic particle image velocimetry (SPIV) scheme is employed for flow field characterization. Image calibration and free surface identification issues are discussed. The interference in measurements of laser beam reflection at the interface are identified and discussed. Selected velocity measurements and turbulence statistics are presented at Re_λ = 70 (Re = 3500 based on mean layer thickness)

Coherence measurements in synthetic turbulent boundary layers

Synthetic turbulent boundary layers were constructed on a flat plate by generating systematic moving patterns of turbulent spots in a laminar flow. The experiments were carried out in a wind tunnel at a Reynolds number based on plate length of 1.7 × 10^6. Spots were generated periodically in space and time near the leading edge to form a regular hexagonal pattern. The disturbance mechanism was a camshaft that displaced small pins momentarily into the laminar flow at frequencies up to 80 Hz. The main instrumentation was a rake of 24 single hot wires placed across the flow in a line parallel to the surface. The main measured variable was local intermittency; i.e. the probability of observing turbulent flow at a particular point in space and time. The results are reported in numerous (x, z, t)-diagrams showing the evolution of various synthetic flows along the plate. The dimensionless celerity or phase velocity of the large eddies was found to be very nearly 0.88, independent of eddy scale. All patterns with sufficiently small scales eventually showed loss of coherence as they moved downstream. A novel phenomenon called eddy transposition was observed in several flows that contained appreciable laminar regions. The original large eddies were replaced by new eddies at new positions, intermediate to the original ones, while preserving the hexagonal pattern. The present results, together with some empirical properties of a turbulent spot, were used to estimate the best choice of scales for constructing a synthetic boundary layer suitable for detailed study as a model for a natural flow. The values recommended are: spanwise period/thickness ≈ 2.5, streamwise period/thickness ≈ 8.0

Alüminyum esaslı in-situ borür takviyeli kompozitlerin üretimi ve özelliklerinin incelenmesi

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Alüminyum?Bor (Al?B) alaşımlarının sıvı fazdan soğutulması sırasında iki farklı borür fazı oluşmaktadır. Bunlar sırası ile AlB12 ve AlB2 fazlarıdır. AlB12 fazı yaklaşık 1000 °C de peritektik reaksiyon sonucu AlB2 fazına dönüşmektedir. AlB2 fazı oda sıcaklığında ve düşük sıcaklıklarda kararlı bir fazdır. AlB2 fazının sıvı alaşım içersinde in?situ oluşması, oda sıcaklığında kararlı olması, sert ve aşınmaya dayanıklı olması geçmişte alüminyum içersinde KBF4 florür tuzlarından bor indirgeme yöntemi ile AlB2/Al tipi kompozitlerin yeni bir metal matris kompozit malzeme olarak üretilebilmelerine yönelik bazı çalışmaların yapılmasını sağlamıştır.Bu çalışmada pahalı KBF4 (florür) tuzları ile üretilmiş Al?B alaşımları yerine Türkiye'de ucuz ve bol bulunan bor minerallerini kullanarak Al/AlB2 kompozitlerinin farklı döküm yöntemleri ile üretimi gerçekleştirilmiştir. AlB2 yapılarının farklı alüminyum alaşımlarına bor mineralinin doğrudan ilavesi ile in?situ yöntemi ile sentezlenmesi sağlanarak üretilen kompozitlerin takviye içeriğini oluşturan AlB2 fazının yapısal özelliklerinin, aspekt oranının ve dağılımının incelenmesi hedeflenmiştir. Çalışmada son olarak, gravite döküm, savurma döküm ve ezme döküm teknikleri kullanılması ile AlB2 oranlarının artırılması ve farklı hacimsel oranlarda AlB2/Al kompozitlerin mekanik özelliklerindeki etkilerinin incelenmesi gerçekleştirilmiştir.Gravite döküm, savurma döküm, ezme döküm, ısıl işlem, optik mikroskop, görüntü analizi, SEM, XRD ve yaş kimyasal analiz tekniklerinin kullanıldığı çalışmada, üretilen kompozitler sertlik, çekme ve basma testlerine tabi tutulmuştur. Sonuçlar üretilen kompozitlerin takviye oranlarının artmasına bağlı olarak sertlik, çekme ve basma dayanımlarında %300 oranına kadar artış olduğunu göstermiştir.During cooling of aluminium?boron (Al?B) alloys two different boride phases come out. These are AlB12 and AlB2 phases. AlB12 transforms into AlB2 at about 1000 °C by a peritectic reaction. AlB2 is a stable phase at room temperature and lower temperatures. Due to formation of AlB2 in?situ within liquid alloy and being stable at room temperature have promoted a few past studies to use of this hard and wear resistant phase in production of new AlB2/Al type metal matrix composites.Throughout this study, instead of using expensive KBF4 (fluoride) salts, using boron containing minerals, which are cheap and ample in Turkey, Al/AlB2 composites have been produced via different casting methods. It is aimed investigating the structural properties such as aspect ratio and distribution of the in?situ formed AlB2 reinforcing phase by directly introducing boron containing minerals into different aluminium alloys. Finally, in this study, the effects of increasing the AlB2 reinforcing ratio, via gravity casting, centrifugal casting and squeeze casting methods, on the mechanical properties of the composites have been investigated.Gravity casting, centrifugial casting, squeeze casting, optical microscope, image analysis, SEM, XRD and wet chemical analysis techniques, hardness, tensile and compression tests were used. Results showed that, depending on the increase in the reinforcement phase, up to 300 % increase in the strength and hardness of the composite has been achieved

(R1958) On Deferred Statistical Convergence of Fuzzy Variables

In this paper, within framework credibility theory, we examine several notions of convergence and statistical convergence of fuzzy variable sequences. The convergence of fuzzy variable sequences such as the notion of convergence in credibility, convergence in distribution, convergence in mean, and convergence uniformly virtually certainly via postponed Cesàro mean and a regular matrix are researched using fuzzy variables. We investigate the connections between these concepts. Significant results on deferred statistical convergence for fuzzy variable sequences are thoroughly investigated

ON SOME GENERALIZED DEFERRED STATISTICAL CONVERGENCE OF ORDER αβ FOR FUZZY VARIABLE SEQUENCES IN CREDIBILITY SPACE

In this paper, we investigate the concepts of deferred statistical convergence of order αβ and strongly s-deferred Cesaro summability of order αβ for fuzzy variable sequences in credibility space. Furthermore, the conditions of deferred statistical convergence almost surely of order αβ, deferred statistical convergence in credibility of order αβ, deferred statistical convergence in mean of order αβ, deferred statistical convergence in distribution of order αβ, and deferred statistical convergence uniformly almost surely of order αβ of fuzzy variable sequences have been examined. We have proved relations between these notions

ON LACUNARY CONVERGENCE IN CREDIBILITY SPACE

In this paper, we present the notions of lacunary statistically convergent sequence for fuzzy variables, lacunary statistically Cauchy sequence in credibility space, and present a kind of lacunary statistical completeness for credibility space. Also, we present lacunary strong convergence concepts of sequences of fuzzy variables of different types

Fonksiyonel Derecelendirilmiş TiB2/Al Kompozitlerin Üretimi Üzerine Bir Çalışma

Bu çalışmada, Fonksiyonel derecelendirilmiş TiB2/Al kompozitlerin savurma döküm tekniği ile üretimi ve özelliklerinin araştırılması amaçlanmıştır. TiB2 takviye fazı, sıvı alüminyum içerisinde in-situ tekniği ile kendiliğinden oluşturulmuştur. Savurma döküm tekniğinden faydalanılarak kompozitler fonksiyonel olarak derecelendirilmiş ve son şekilleri verilmiştir. Üretilen kompozitlerin özellikleri, optik mikroskobu, SEM, XRD, yoğunluk ve sertlik analizleri kullanılarak detaylandırılmıştır. Çalışmada Al-Ti-B sistemi kullanılarak alüminyum matris içerinde in-situ tekniği ile TiB2 borür yapılarının sentezlene bildiğini görülmüştür. Aynı zamanda kompozit malzemelerin savurma kuvveti yönünden mikro yapı özelliklerinin değiştiği ve bu değişime bağılı olarak kompozitlerin yoğunluk ve sertlik değerlerinde önemli bir değişim tespit edilmiştir. Sonuçlar aynı zamanda alüminyum matrise %19 TiB2 ilavesi ile %83’lük, %12 TiB2 ilavesi ile de %50’lik sertlik artışı sağladığını göstermiştir

Multiphase deployment models for fast self healing in wireless sensor networks

The majority of studies on security in resource limited wireless sensor networks (WSN) focus on finding an efficient balance among energy consumption, computational speed and memory usage. Besides these resources, time is a relatively immature aspect that can be considered in system design and performance evaluations. In a recent study(Castelluccia and Spognardi, 2007), the time dimension is used to lower the ratio of compromised links, thus, improving resiliency in key distribution in WSNs. This is achieved by making the old and possibly compromised keys useful only for a limited amount of time. In this way, the effect of compromised keys diminish in time, so the WSN selfheals. In this study we further manipulate the time dimension and propose a deployment model that speeds up the resilience improvement process with a tradeoff between connectivity and resiliency. In our method, self healing speeds up by introducing nodes that belong to future generations in the time scale. In this way, the duration that the adversary can make use of compromised keys become smaller

Population Growth of Bosmina longirostris Fed Chlorella vulgaris and Scenedesmus subspicatus in Different Densities

In this study, the effects of the different densities of Chlorella vulgaris (0.05 x 106, 0.1 x 106, 0.2 x 106, 0.4 x 106, or 0.8 x 106 cells/ml) and Scenedesmus subspicatus (0.05 x 106, 0.1 x 106, 0.2 x 106, or 0.4 x 106 cells/ml) on culture of the water flea, Bosmina longirostris, were investigated. The experiment was carried out in a photoperiod of 16 h light:8 h dark at 25±1°C. At the beginning of the experiment, one B. longirostris individual (<24 h old) was put into each vessel, and the number of individuals and rate of population increase were determined for 30 days. Increasing the food density increased the number of individuals and the rate of population. The maximum number of B. longirostris individuals (7.1±2.08 ind/ml) and maximum rate of population increase (0.2±0.004/day) was in the group fed 0.2 x 106 cells/ml S. subspicatus. The effect on the number of the individuals was statistically significant (p<0.05)