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Citation Count: 0
Determination of activation energy for carbon/epoxy prepregs containing carbon nanotubes by differential scanning calorimetry
(Sage Publications Ltd, 2023) Uz, Yusuf Can; Tanoglu, Metin; Tanoğlu, Metin
The aim of the present study is the thermal characterization of laboratory-scale carbon fiber/epoxy-based prepregs by incorporating single-wall carbon nanotubes (SWCNTs). Investigation of the cure behavior of a prepreg system is crucial for the characterization and optimization of the fiber reinforced polymeric (FRP) composite. To affect dispersion characteristics, SWCNTs were functionalized by oxidizing their surface with carboxyl (-COOH) group using an acid treatment. The modified resin system contained 0.05, 0.1, and 0.2 wt. % functionalized SWCNTs (F-SWCNTs). Carbon fiber (CF) reinforced prepregs containing various amount of F-SWCNTs were prepared using drum-type winding technique. FTIR was performed to identify new bonding groups formed after the functionalization of SWCNTs. Cure kinetics of prepregs prepared with/without F-SWCNTs were investigated using isoconversional methods.
Citation Count: 8
Development and analysis of composite overwrapped pressure vessels for hydrogen storage
(Sage Publications Ltd, 2021) Kartav, Osman; Kangal, Serkan; Yuceturk, Kutay; Tanoglu, Metin; Aktas, Engin; Artem, H. Secil; Tanoğlu, Metin
In this study, composite overwrapped pressure vessels (COPVs) for high-pressure hydrogen storage were designed, modeled by finite element (FE) method, manufactured by filament winding technique and tested for burst pressure. Aluminum 6061-T6 was selected as a metallic liner material. Epoxy impregnated carbon filaments were overwrapped over the liner with a winding angle of +/- 14 degrees to obtain fully overwrapped composite reinforced vessels with non-identical front and back dome layers. The COPVs were loaded with increasing internal pressure up to the burst pressure level. During loading, deformation of the vessels was measured locally with strain gauges. The mechanical performances of COPVs designed with various number of helical, hoop and doily layers were investigated by both experimental and numerical methods. In numerical method, FE analysis containing a simple progressive damage model available in ANSYS software package for the composite section was performed. The results revealed that the FE model provides a good correlation as compared to experimental strain results for the developed COPVs. The burst pressure test results showed that integration of doily layers to the filament winding process resulted with an improvement of the COPVs performance.
Citation Count: 5
Effects of hybrid yarn preparation technique and fiber sizing on the mechanical properties of continuous glass fiber-reinforced polypropylene composites
(Sage Publications Ltd, 2016) Merter, N. Emrah; Baser, Gulnur; Tanoglu, Metin; Tanoğlu, Metin
In this study, hybrid yarns were developed by commingling the continuous polypropylene and glass fibers using air jet and direct twist preparation techniques. The non-crimp fabrics were obtained with +/- 45 degrees fiber orientation from these hybrid yarns. The fabrics were prepared with fiber sizings that are compatible and incompatible with polypropylene matrix to investigate the effect of interfacial adhesion on the properties of the thermoplastic composites. Composite panels were produced from the developed fabrics by hot press compression method and microstructural and mechanical properties of the composites were investigated. It was found that type of the hybrid yarn preparation technique and glass fiber sizing applied on the glass fibers have some important role on the properties of the composites. Composites made of fabrics produced by air jet hybrid yarn preparation technique exhibited better results than those produced by direct twist covering (single or double) hybrid yarn preparation techniques. The highest flexural properties (99.1MPa flexural strength and 9.55 GPa flexural modulus) were obtained from the composites manufactured from fabric containing compatible sizing, due to better adhesion at the interface of glass fibers and polypropylene matrix. The composite fabricated from fabric with polypropylene compatible sizing also exhibited the highest peel resistance (interlaminar peel strength value of 5.87N/mm). On the other hand, it was found that hybrid yarn preparation technique and type of the glass fiber sizing have insignificant effect on the impact properties of the glass fiber/polypropylene composites.
Citation Count: 1
Electrospinning of Fatty Acid-Based and Metal Incorporated Polymers for the Fabrication of Eco-Friendly Fibers
(Wiley-v C H verlag Gmbh, 2022) Erdem, Caglar; Isik, Tugba; Horzum, Nesrin; Hazer, Baki; Demir, Mustafa M.; Demir, Mustafa
Accumulation of plastic wastes occupies large space in gyres of the oceans called the 7(th) continent. This high-level concentration of toxic plastic wastes causes harmful consequences for marine life, therefore petroleum-originated plastics must be replaced (or at least partially) with natural resources. The environmental trends in material preparation promote the utilization of greener methods and materials when the limited primary sources are considered. Starting from the fatty acid macroperoxide initiators, synthesis of bio-based polymers using less commercial chemicals and stepwise green synthesis schemes could be possible in the near future. In this research, autoxidized vegetable oil initiators (castor, limonene, and soybean oil) containing metal nanoparticles (silver, platinum, and gold) are employed for free radical polymerization of vinyl monomers. The metal loaded and vegetable oil-based polymers are processed by electrospinning and end up with the successful fabrication of continuous fibers. Ag-loaded ricinoleic acid based polymers show notable antibacterial activity against Escherichia coli. This approach offers a remarkable minimization of the initiator consumption in the synthesis of such synthetic macromolecules as well as nanoparticle containing polymer composites while still maintaining the ease of processing. Transforming the obtained graft copolymers to electrospun nanofibers facilitates the use as support materials for antibacterial surfaces.
Citation Count: 4
Estimating software robustness in relation to input validation vulnerabilities using Bayesian networks
(Springer, 2018) Ufuktepe, Ekincan; Tuglular, Tugkan; Tuğlular, Tuğkan; Bilgisayar Mühendisliği Bölümü
Estimating the robustness of software in the presence of invalid inputs has long been a challenging task owing to the fact that developers usually fail to take the necessary action to validate inputs during the design and implementation of software. We propose a method for estimating the robustness of software in relation to input validation vulnerabilities using Bayesian networks. The proposed method runs on all program functions and/or methods. It calculates a robustness value using information on the existence of input validation code in the functions and utilizing common weakness scores of known input validation vulnerabilities. In the case study, ten well-known software libraries implemented in the JavaScript language, which are chosen because of their increasing popularity among software developers, are evaluated. Using our method, software development teams can track changes made to software to deal with invalid inputs.
Citation Count: 3
Improving adhesive behavior of fiber reinforced composites by incorporating electrospun Polyamide-6,6 nanofibers in joining region
(Sage Publications Ltd, 2022) Esenoglu, Gozde; Barisik, Murat; Tanoglu, Metin; Yeke, Melisa; Turkdogan, Ceren; Iplikci, Hande; Iris, Mehmet Erdem; Tanoğlu, Metin
Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 +/- 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially.
Citation Count: 16
Investigation of interlayer hybridization effect on burst pressure performance of composite overwrapped pressure vessels with load-sharing metallic liner
(Sage Publications Ltd, 2020) Kangal, Serkan; Kartav, Osman; Tanoglu, Metin; Aktas, Engin; Artem, H. Secil; Tanoğlu, Metin
In this study, multi-layered composite overwrapped pressure vessels for high-pressure gaseous storage were designed, modeled by finite element method and manufactured by filament winding technique. 34CrMo4 steel was selected as a load-sharing metallic liner. Glass and carbon filaments were overwrapped on the liner with a winding angle of [+/- 11 degrees/90 degrees(2)](3) to obtain fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The vessels were loaded with increasing internal pressure up to the burst pressure level. The mechanical performances of pressure vessels, (i) fully overwrapped with glass fibers and (ii) with additional two carbon hoop layers on the cylindrical section, were investigated by both experimental and numerical approaches. In numerical approaches, finite element analysis was performed featuring a simple progressive damage model available in ANSYS software package for the composite section. The metal liner was modeled as elastic-plastic material. The results reveal that the finite element model provides a good correlation between experimental and numerical strain results for the vessels, together with the indication of the positive effect on radial deformation of the COPVs due to the composite interlayer hybridization. The constructed model was also able to predict experimental burst pressures within a range of 8%. However, the experimental and finite element analysis results showed that hybridization of hoop layers did not have any significant impact on the burst pressure performance of the vessels. This finding was attributed to the change of load-sharing capacity of composite layers due to the stiffness difference of carbon and glass fibers.
Citation Count: 5
Long Noncoding RNAs in Human Cancer and Apoptosis
(Bentham Science Publ Ltd, 2023) Erdogan, Ipek; Sweef, Osama; Akgul, Bunyamin; Akgül, Bünyamin
Genome annotations have uncovered the production of at least one transcript from nearly all loci in the genome at some given time throughout the development. Surprisingly, many of these transcripts do not code for proteins and are relatively long in size, thus called long noncoding RNAs (lncRNAs). Next- and third-generation sequencing technologies have amassed numerous lncRNAs expressed under different phenotypic conditions, yet many remain to be functionally characterized. LncRNAs regulate gene expression by functioning as scaffold, decoy, signaling, and guide molecules both at the transcriptional and post-transcriptional levels, interacting with different types of macromolecules, such as proteins, DNA, and RNA. Here, we review the potential regulatory role of lncRNAs in apoptosis and cancer as some of these lncRNAs may have the diagnostic and therapeutic potential in cancer.
Citation Count: 3
MicroRNAs and Long Non-coding RNAs as Novel Targets in Anti-cancer Drug Development
(Bentham Science Publ Ltd, 2023) Cetinkaya, Melisa; Baran, Yusuf; Baran, Yusuf
Non-coding RNAs comprise the majority of RNAs that have been transcribed from the human genome, and these non-coding RNAs have essential regulatory roles in the cellular processes. They have been discovered to influence the expression of the genes, including tumor-suppressive and oncogenes, that establish the non-coding RNAs as novel targets for anti-cancer drug development. Among non-coding RNAs, microRNAs have been extensively studied in terms of cancer biology, and some microRNA-based therapeutics have been reached in clinical studies. Even though most of the research regarding targeting non-coding RNAs for anti-cancer drug development focused on microRNAs, long non-coding RNAs have also started to gain importance as potential therapeutic targets for cancer therapy. In this chapter, the strategies and importance of targeting microRNAs and long non-coding RNAs will be described, along with the clinical studies that involve microRNA-based cancer therapeutics and preclinical studies that involve long non-coding RNA-based therapeutics. Finally, the delivery strategies that have great importance in the effective delivery of the non-coding RNA-based cancer therapeutics, hence the therapy's effectiveness, will be described.
Citation Count: 1
Noncoding RNAs: A New Layer of Functional RNAs
(Bentham Science Publ Ltd, 2023) Gurer, Dilek Cansu; Akgul, Bunyamin; Akgül, Bünyamin
The conventional central dogma of molecular biology dictates that the genetic information contained within deoxyribonucleic acid (DNA) is passed onto messenger ribonucleic acids (mRNAs), which are then used as templates to synthesize proteins. Although these types of protein-coding genes have been historically prioritized in typical phenotype-genotype studies with a parallel disregard to the rest of the genome, the completion of genome projects has unveiled a surprising layer of genetic information that can play critical roles in cellular processes without coding for proteins. These types of genes are called noncoding genes as they do not code for proteins. Noncoding genes come in different sizes and shapes, and they are just as versatile in carrying out cellular biochemical processes as proteins. In this review, we cover a comprehensive review of housekeeping and regulatory noncoding genes and their mode of action.
Citation Count: 3
Prioritizing MCDC test cases by spectral analysis of Boolean functions
(Wiley, 2017) Ayav, Tolga; Ayav, Tolga; Bilgisayar Mühendisliği Bölümü
Test case prioritization aims at scheduling test cases in an order that improves some performance goal. One performance goal is a measure of how quickly faults are detected. Such prioritization can be performed by exploiting the fault exposing potential (FEP) parameters associated to the test cases. The FEP is usually approximated by mutation analysis under certain fault assumptions. Although this technique is effective, it could be relatively expensive compared to the other prioritization techniques. This study proposes a cost-effective FEP approximation for prioritizing modified condition decision coverage (MCDC) test cases. A strict negative correlation between the FEP of an MCDC test case and the influence value of the associated input condition allows to order the test cases easily without the need of an extensive mutation analysis. The method is entirely based on mathematics and it provides useful insight into how spectral analysis of Boolean functions can benefit software testing.
Citation Count: 27
Protoporphyrin IX-loaded magnetoliposomes as a potential drug delivery system for photodynamic therapy: Fabrication, characterization and in vitro study
(Elsevier, 2016) Basoglu, Harun; Bilgin, Mehmet Dincer; Demir, Mustafa Muammer; Demir, Mustafa
Background: Protoporphyrin IX (PpIX) is a well-known photosensitizer that has great potential for use in photodynamic therapy (PDT). However, aggregation behavior of PpIX in neutral water makes it inappropriate for physiological studies. PpIX-loaded magnetoliposomes (MLs) were fabricated to increase PpIX biocompatibility. PpIX-loaded ML physical properties were characterized, and PpIX-loaded ML drug release behavior was investigated under the influence of an external magnetic field and heat. Toxicity and photodynamic effects of the complex were also examined using in vitro experiments with MCF-7 human breast cancer cells. Methods: The magnetoliposomes were prepared with DPPC, DSPE-PEG2000 lipids and Fe3O4 nanoparticles. The toxicity and in vitro photodynamic effects of the PpIX-loaded MLs at various concentrations were studied using the MCF-7 cell line. Results: The produced PpIX-loaded MLs exhibited an average hydrodynamic diameter of 221 nm; however, TEM measurements indicated that the diameter of the PpIX-loaded MLs varied between 166 and 720 nm. The iron content of the MLs affected cell viability less than the content of the iron free liposomes. Cell viability was reduced to 66% when the concentration of the PpIX-loaded MLs was 350 nM, but when white light was applied for 5 min, all of the cells that were exposed to concentrations of 250 nM and higher PpIX died within 24 h. Conclusion: The results of this study demonstrated the effective application of PpIX-loaded MLs for in vitro photodynamic therapy at nanomolar concentrations. The results also indicated that an LED light source provided sufficient energy to stimulate the PpIX molecules. (C) 2015 Elsevier B.V. All rights reserved.
Citation Count: 73
A Review on Halide Perovskites as Color Conversion Layers in White Light Emitting Diode Applications
(Wiley-v C H verlag Gmbh, 2018) Guner, Tugrul; Demir, Mustafa M.; Demir, Mustafa
In the last decade, halide perovskites have attracted great interest due to many reasons, including their low cost, solution-processability, superior PL properties, broad range of color tunability, color purity, and defect tolerance, among others. They are in increasing demand for a wide range of applications, such as solar cells, light emitting diodes (LEDs), white LEDs (WLED), and lasers. Yellow phosphors have been heavily employed in solid-state lighting, since its illumination by blue yields white light with various optical features, such as high/low CRI, CCT, and luminous efficiency. However, phosphors as pigments are seldom found and are costly material. In this sense, halide perovskites may offer a promising alternative to phosphors for future solid-state lighting. In this study, the synthesis and optical properties of halide perovskites, as well as their application in WLED as a conversion layer are investigated.

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