Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Yüksek Derecede Kurum Üreten 2b Gazyağı/hava Difüzyon Alevleri Üzerinde Diferansiyel Yayılımın ve Basıncın Etkileri(Gazi Üniversitesi, 2024) Korucu, Ayşe; Miller, RichardBu çalısmada, dört farklı ortam basıncında kurum, oluşum ve yıkım süreçlerini incelemek amacıyla, yoğun kurum üreten Gazyağı/Hava alevleri, gerçek gaz (GG) ve ideal gaz (İG) hal denklemleri ve Lewis (Le) sayısının bir olarak kabul edildiği modeller ele alınmıştır. Yarı-genel kurum oluşum ve yıkım modelini içeren indirgenmiş Gazyağı/Hava mekanizması (29-adım, 10 çeşit gaz) 2 boyutlu (2B) Direk Sayısal Simülasyon (DNS) verilerini oluşturmak için MPI FORTRAN ile kodu yazılmış bir program kullanılmıştır. Le sayısının bire eşit kabul edildiği alev tahminlerinin, Le sayısının bire eşit olmadığı (genelleştirilmiş difüzyon) durumların sayısal sonuçlarından elde edilen alev yapısı ve kurum özelliklerinin istatiksel olarak benzerlik sağlayıp sağlamadığı araştırılmıştır. Bu bağlamda yapılan çalışmanın sonucunda, ortam basınçları 1, 5, 10 ve 35 atm olan Le sayısının bir olarak kabul edildiği GGLE ve İGLE modelleri ile üretilmiş 2B DNS alev tahminlerinin kurum özelliklerinin ve alev yapılarının yanlış hesaplanmasına yol açtığı belirlenmiştir.Article Citation - WoS: 1Citation - Scopus: 2Oluklu alüminyum sandviç panellerde kor yüksekliğinin enerji sönümleme kapasitesine olan etkisi(Gazi Üniversitesi, 2020) Kılıçaslan, Cenk; Güden, MustafaIn this study, energy absorbing capacity of brazed and polyurethane adhesively bonded corrugated aluminum sandwich panels were investigated. In sandwich panels, Al 1050 H14 trapezoidal zig-zag corrugated cores and face and interlayer sheets were used. Each sandwich panel has core orientation of 0 degrees/0 degrees or 0 degrees/90 degrees. The cores used in these panels were smaller, core height is about 3 mm, in contrast to conventional sandwich cores. Impact tests were conducted at 3 and 6 m/s with spherical projectors. Adhesively bonded sandwich panels were also tested at 6 m/s with flat and conical projectors. Numerical models were prepared in LSDYNA to investigated the deformation behavior of cores. Panels tested with flat and conical projectors experienced complete perforation and absorbed more energy at configuration of 0 degrees/0 degrees core orientation. However, panels tested with spherical projectors were not perforated and they absorbed more energy at configuration of 0 degrees/90 degrees core orientation. Energy absorbing capacity of the panels were also compared to the panels having 9 mm height corrugated cores. The results showed that effective collapsing length was seen to increase due to increase in core height and impact energy distributed the whole panel surface more homogenous manner.Article Citation - WoS: 11Citation - Scopus: 13Effect of Cnt Incorporation on Pan/Ppy Nanofibers Synthesized by Electrospinning Method(TÜBİTAK, 2020) İnce Yardımcı, Atike; Tanoğlu, Metin; Yılmaz, Selahattin; Selamet, YusufIn this study, carbon nanotubes (CNTs) added polyacrylonitrile/polypyrrole (PAN/PPy) electrospun nanofibers were produced. Average diameters of the nanofibers were measured as 268 and 153 nm for 10 and 25 wt% of PPy contents, respectively. A relatively higher strain to failure values (23.3%) were observed for the low PPy content. When as-grown CNTs (1 and 4 wt%) were added into the PAN/PPy blends, disordered nanofibers were observed to form within the microstructure. To improve the interfacial properties of CNTs/PAN/PPy composites, CNTs were functionalized with H2SO4/HNO3/HCl solution. The functionalized CNTs were well dispersed within the nanofibers and aligned along the direction of nanofibers. Therefore, beads formation on nanofibers decreased. The impedance of the nanofibers was found to decrease with the PPy content and CNT addition. These nanofibers had a great potential to be used as an electrochemical actuator or a tissue engineering scaffold.Article Citation - WoS: 28Citation - Scopus: 30Bone Marrow Stem Cells Adapt To Low-Magnitude Vibrations by Altering Their Cytoskeleton During Quiescence and Osteogenesis(TUBITAK, 2015) Demiray, Levent; Özçivici, EnginApplication of mechanical vibrations is anabolic to bone tissue, not only by guiding mature bone cells to increased formation, but also by increasing the osteogenic commitment of progenitor cells. However, the sensitivity and adaptive response of bone marrow stem cells to this loading regimen has not yet been identified. In this study, we subjected mouse bone marrow stem cell line D1-ORL-UVA to daily mechanical vibrations (0.15 g, 90 Hz, 15 min/day) for 7 days, both during quiescence and osteogenic commitment, to identify corresponding ultrastructural adaptations on cellular and molecular levels. During quiescence, mechanical vibrations significantly increased total actin content and actin fiber thickness, as measured by phalloidin staining and fluorescent microscopy. Cellular height also increased, as measured by atomic force microscopy, along with the expression of focal adhesion kinase (PTK2) mRNA levels. During osteogenesis, mechanical vibrations increased the total actin content, actin fiber thickness, and cytoplasmic membrane roughness, with significant increase in Runx2 mRNA levels. These results show that bone marrow stem cells demonstrate similar cytoskeletal adaptations to low-magnitude high-frequency mechanical loads both during quiescence and osteogenesis, potentially becoming more sensitive to additional loads by increased structural stiffness.Article Silika Yüzeylerin Islanma Hareketlerinin Moleküler Dinamik ile Modellenmesi(Gazi Üniversitesi, 2018) Barışık, MuratYeni üretim tekniklerine paralel olarak nano-boyutlu teknolojiler çok geniş bir uygulama alanında kullanılmaya başlanmakta ve yeni uygulamalar geliştirmek için keşfedilmesi ve anlaşılması gereken konular süratle artmaktadır. Bu doğrultuda, yeni uygulamalarda sıkça yer bulan silikon ve silikon-dioksitin mikro/nano boyutlardaki malzeme özelliklerinin anlaşılmasına büyük ihtiyaç oluşmaktadır. Özellikle bu yüzeylerin ıslanma hareketlerinin anlaşılabilmesi ve hatta kullanılacak uygulamaya göre ayarlanabilmesi sayısız uygulama için önem arz etmektedir. Bu nedenlerle, nano-teknolojide sıkça kullanılan silikon-dioksit malzemesinin ve su moleküllerinin nano-ölçeklerde moleküler olarak modellenmesi bu çalışmada gerçekleştirildi. Modelleme molekuler dinamik hesaplamaları ile yapıldı. Silikon-dioksit yüzey üzerinde nano su damlacıkları oluşturup, denge halinde oluşan ıslatma açısı ölçümleri yapıldı. Literatürde işlem yükünü azaltmak için sıklıkla uygulanan, katı yüzey termal titreşimlerinin ıslatmaya olan etkisinin ihmal edilmesi ve modellenmemesinin ıslatma açısına olan etkisi incelendi. Katı moleküllerin termal titreşimlerinin ıslatma modellenen ıslatma fiziğine baskın bir etkisi olduğu görüldü. Geçtiğimiz yıllarda doğa taklidi olarak bilinen çalışma çevreleri tarafından hayata geçirilmeye çalışılan Lotus yaprağı etkisi temelli yüzey ıslatma kontrolu moleküler seviyede uygulandı. Yüzey üzerinde oluşturulan nano boyutlardaki yüzey yapılarının ıslanma açısını değiştirebildiği gösterildi. Temiz (0 0 1) silika yüzeyinde nano ölçek çizgi gerilimi etkisi altında ölçülen ıslanma açısının deneysel silika ıslanma açısı aralığında olduğu bulundu.Article Citation - WoS: 21Citation - Scopus: 22Effects of Spaceflight on Cells of Bone Marrow Origin(Aves, 2013) Özçivici, EnginOnce only a subject for science fiction novels, plans for establishing habitation on space stations, the Moon, and distant planets now appear among the short-term goals of space agencies. This article reviews studies that present biomedical issues that appear to challenge humankind for long-term spaceflights. With particularly focus on cells of bone marrow origin, studies involving changes in bone, immune, and red blood cell populations and their functions due to extended weightlessness were reviewed. Furthermore, effects of mechanical disuse on primitive stem cells that reside in the bone marrow were also included in this review. Novel biomedical solutions using space biotechnology will be required in order to achieve the goal of space exploration without compromising the functions of bone marrow, as spaceflight appears to disrupt homeostasis for all given cell types.Article Citation - WoS: 20Citation - Scopus: 22Photocatalytic Antimicrobial Effect of Tio2 Anatase Thin-Film–coated Orthodontic Arch Wires on 3 Oral Pathogens(TUBITAK, 2014) Özyıldız, Figen; Uzel, Ataç; Hazar, Ayşe Serpil; Güden, Mustafa; Ölmez, Sultan; Aras, Işıl; Karaboz, İsmailThe aim of this study was to introduce antimicrobial activity to stainless steel orthodontic arch wires by coating them with TiO2 in anatase form. Stainless steel (0.016 × 0.022 inch), D-rect (0.016 × 0.022 inch), and multistranded hammered retainer wires (0.014 × 0.018 inch) were coated with TiO2 anatase by the sol-gel dip coating method. The wires were assessed for their photocatalytic antimicrobial activity against Streptococcus mutans, Candida albicans, and Enterococcus faecalis. After illumination under UVA (315– 400 nm) at 1.0 mW/cm2 for 1 h, the reduction efficiencies of the anatase-coated arch wires were calculated by using colony-forming unit counts. All anatase-coated arch wires showed remarkable inhibitor effects against the test microorganisms under UVA. The most efficient wire on S. mutans was the stainless steel wire, with a 99.99% reduction in growth, but multistranded hammered retainer wire was the most active against both C. albicans and E. faecalis, with 98.0% and 91.68% reduction rates, respectively. TiO2-coated arch wires exposed to UVA illumination showed significant antimicrobial activity when compared with uncoated samples and coated, but not UVA-exposed, samples. Our results suggest that the antimicrobial effect of TiO2-coated arch wires in long-lasting orthodontic treatments would be beneficial for the prophylaxis of caries.Article Citation - WoS: 12Citation - Scopus: 15Morphological and Molecular Identification of Pennate Diatoms Isolated From Urla, Izmir, Coast of the Aegean Sea(TUBITAK, 2013) Kesici, Kutsal; Tüney, İnci; Sukatar, Atakan; Zeren, Doğuş; Güden, MustafaDiatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as ITS (Internal Transcribed Spacer) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated four diatom samples from Coast of Urla and characterized them using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then, we amplified ITS regions using conventional polymerase chain reaction (PCR), sequenced the PCR products and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia sp., Achnanthes sp., Amphora sp. and Cylindrotheca sp. We believe that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms.