Akademik Çıktılar

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Citation Count: 9
Achieving query performance in the cloud via a cost-effective data replication strategy
(Springer, 2021) Tos, Uras; Mokadem, Riad; Hameurlain, Abdelkader; Ayav, Tolga; Ayav, Tolga; Bilgisayar Mühendisliği Bölümü
Meeting performance expectations of tenants without sacrificing economic benefit is a tough challenge for cloud providers. We propose a data replication strategy to simultaneously satisfy both the performance and provider profit. Response time of database queries is estimated with the consideration of parallel execution. If the estimated response time is not acceptable, bottlenecks are identified in the query plan. Data replication is realized to resolve the bottlenecks. Data placement is heuristically performed in a way to satisfy query response times at a minimal cost for the provider. We demonstrate the validity of our strategy in a performance evaluation study.
Citation Count: 24
Advances in Electrospun Fiber-Based Flexible Nanogenerators for Wearable Applications
(Wiley-v C H verlag Gmbh, 2021) Arica, Tugce A.; Isik, Tugba; Guner, Tugrul; Horzum, Nesrin; Demir, Mustafa M.; Demir, Mustafa
In today's digital age, the need and interest in personal and portable electronics shows a dramatic growth trend in daily life parallel to the developments in sensors technologies and the internet. Wearable electronics that can be attached to clothing, accessories, and the human body are one of the most promising subfields. The energy requirement for the devices considering the reduction in device sizes and the necessity of being flexible and light, the existing batteries are insufficient and nanogenerators have been recognized a suitable energy source in the last decade. The mechanical energy created by the daily activities of the human body is an accessible and natural energy source for nanogenerators. Fiber-structured functional materials contribute to the increase in energy efficiency due to their effective surface to volume ratio while providing the necessary compatibility and comfort for the movements in daily life with its flexibility and lightness. Among the potential solutions, electrospinning stands out as a promising technique that can meet these requirements, allowing for simple, versatile, and continuous fabrication. Herein, wearable electronics and their future potential, electrospinning, and its place in energy applications are overviewed. Moreover, piezoelectric, triboelectric, and hybrid nanogenerators fabricated or associated with electrospun fibrous materials are presented.
Citation Count: 0
Analysis of adhesively bonded joints of laser surface treated composite primary components of aircraft structures
(Elsevier Sci Ltd, 2023) Nuhoglu, Kaan; Aktas, Engin; Tanoglu, Metin; Martin, Seckin; Iplikci, Hande; Barisik, Murat; Iris, Mehmet Erdem; Tanoğlu, Metin
The performance of the adhesively bonded aerospace structures highly depends on the adhesion strength between the adhesive and adherents, which is affected by, in particular, the condition of the bonding surface. Among the various surface treatment methods, as state of the art, laser surface treatment is a suitable option for the CFRP composite structures to enhance the adhesion performance, adjusting the roughness and surface free energy with relatively minimizing the damage to the fibers. The aim of this study is the validation and evaluation of the adhesive bonding behavior of the laser surface-treated CFRP composite structures, using the finite element technique to perform a conservative prediction of the failure load and damage growth. Such objectives were achieved by executing both experimental and numerical analyses of the secondary bonded CFRP parts using a structural adhesive. In this regard, to complement physical experiments by means of numerical simulation, macro-scale 3D FEA of adhesively bonded Single Lap Joint and Skin-Spar Joint specimens has been developed employing the Cohesive Zone Model (CZM) technique in order to simulate bonding behavior in composite structures especially skin-spar relation in the aircraft wing-box.
Citation Count: 30
Apoptotic Effects of Quercitrin on DLD-1 Colon Cancer Cell Line
(Frontiers Media Sa, 2015) Cincin, Zeynep Birsu; Unlu, Miray; Kiran, Bayram; Bireller, Elif Sinem; Baran, Yusuf; Cakmakoglu, Bedia; Baran, Yusuf
Quercetin, which is the most abundant bioflavonoid compound, is mainly present in the glycoside form of quercitrin. Although different studies indicated that quercitrin is a potent antioxidant, the action of this compound is not well understood. In this study, we investigated whether quercitrin has apoptotic and antiproliferative effects in DLD-1 colon cancer cell lines. Time and dose dependent antiproliferative and apoptotic effects of quercitrin were subsequently determined by WST-1 cell proliferation assay, lactate dehydrogenase (LDH) cytotoxicity assay, detection of nucleosome enrichment factor, changes in caspase-3 activity, loss of mitochondrial membrane potential (MMP) and also the localization of phosphatidylserine (PS) in the plasma membrane. There were significant increases in caspase-3 activity, loss of MMP, and increases in the apoptotic cell population in response to quercitrin in DLD-1 colon cancer cells in a time- and dose-dependent manner. These results revealed that quercitrin has antiproliferative and apoptotic effects on colon cancer cells. Quercitrin activity supported with in vivo analyses could be a biomarker candicate for early colorectal carcinoma.
Citation Count: 46
Challenges in the Preparation of Optical Polymer Composites With Nanosized Pigment Particles: A Review on Recent Efforts
(Wiley-v C H verlag Gmbh, 2012) Demir, Mustafa M.; Wegner, Gerhard; Demir, Mustafa
Blends of nanosized pigment particles and polymers are widely believed to offer the potential for the design of novel or at least improved materials. This review critically evaluates the recent literature with regard to the following issues: (a) why and how does the size of the particles matter, (b) what are the requirements to create compatibility between amorphous polymers and nanoparticles, (c) carbon allotropes as nanosized pigments, (d) bulk polymerization of monomer/pigment mixtures, (e) interaction of growing chains with the particles in the polymerization, (f) depletion flocculation as a mechanism to counteract homogeneous distribution of the particles in the polymer matrix and ways to suppress the undesirable flocculation, and (g) optical properties of the blends as well as methods of optical characterization.
Citation Count: 1
Characterization of Sb scaling and fluids in saline geothermal power plants: A case study for Germencik Region (Buyuk Menderes Graben, Turkey)
(Pergamon-elsevier Science Ltd, 2021) Tonkul, Serhat; Baba, Alper; Demir, Mustafa M.; Regenspurg, Simona; Demir, Mustafa
Turkey is located on the seismically active Alpine-Himalayan belt. Although tectonic activity causes seismicity in the Anatolian plate, it also constitutes an important geothermal energy resource. Today, geothermal energy production is heavily concentrated in Turkey's Western Anatolia region. Graben systems in this region are very suitable for geothermal resources. The Buyuk Menderes Graben (BMG) is an area of complex geology with active tectonics and high geothermal potential power. Germencik (Aydin) is located in the BMG, where the geothermal waters include mainly Na-Cl-HCO3 water types. This study examined the stibnite scaling formed in the preheater system of the Germencik Geothermal Field (GGF). The formation of the stibnite scaling on the preheater system dramatically reduces the energy harvesting of the GGF. Considering the stibnite scaling in the surface equipment, the optimum reinjection temperature was determined as 95 degrees C to prevent stibnite scaling in the GGF.
Citation Count: 7
Comparative development of knowledge-based bioeconomy in the European Union and Turkey
(informa Healthcare, 2014) Ozan, Didem Celikkanat; Baran, Yusuf; Baran, Yusuf
Biotechnology, defined as the technological application that uses biological systems and living organisms, or their derivatives, to create or modify diverse products or processes, is widely used for healthcare, agricultural and environmental applications. The continuity in industrial applications of biotechnology enables the rise and development of the bioeconomy concept. Bioeconomy, including all applications of biotechnology, is defined as translation of knowledge received from life sciences into new, sustainable, environment friendly and competitive products. With the advanced research and eco-efficient processes in the scope of bioeconomy, more healthy and sustainable life is promised. Knowledge-based bioeconomy with its economic, social and environmental potential has already been brought to the research agendas of European Union (EU) countries. The aim of this study is to summarize the development of knowledge-based bioeconomy in EU countries and to evaluate Turkey's current situation compared to them. EU-funded biotechnology research projects under FP6 and FP7 and nationally-funded biotechnology projects under The Scientific and Technological Research Council of Turkey (TUBITAK) Academic Research Funding Program Directorate (ARDEB) and Technology and Innovation Funding Programs Directorate (TEYDEB) were examined. In the context of this study, the main research areas and subfields which have been funded, the budget spent and the number of projects funded since 2003 both nationally and EU-wide and the gaps and overlapping topics were analyzed. In consideration of the results, detailed suggestions for Turkey have been proposed. The research results are expected to be used as a roadmap for coordinating the stakeholders of bioeconomy and integrating Turkish Research Areas into European Research Areas.
Citation Count: 11
Design of Polymeric Antiscalants Based on Functional Vinyl Monomers for (Fe, Mg) Silicates
(Amer Chemical Soc, 2017) Topcu, Gokhan; Celik, Asli; Baba, Alper; Demir, Mustafa M.; Demir, Mustafa
Silica/silicate scaling is one of a few detrimental problems that cause high economical loss in the geothermal and petroleum fields. The prevention of silica/silicate has been attempted using antiscalants with functional groups, particularly -NH2; however, metal silicates are commonly found in the fields, and the antiscalants developed thus far are not effective against these compounds. In this work, polymeric antiscalants have been developed by merging two or-snore functional-comonomers consisting of various chelating groups for metal cations. Homo- and copolymers of acrylamide (AM), the sodium salt of vinyl sulfonic acid (VSA), and vinyl phosphonic acid (VPA) were synthesized to examine their antiscaling performance against metal silicate scaling. Lab-scale metal silicates were obtained in a pressured autoclave reactor. The, antiscalants were tested at various dosages (25, 50, and 100 ppm), and their effects were investigated from the leftover decaritates after isolation of the solid precipitates. The polymeric antiscalants were found to be particularly effective against metal silicates and ineffective against simple silica precipitates. Acidic groups may be coordinating the metal cations, which prevents the-formation of precipitates. Among these acidic comonomers; VSA-containing polymers, in particular, increased the solubility-of metal silicates.
Citation Count: 9
Dispersion of organophilic Ag nanoparticles in PS-PMMA blends
(Elsevier Science Sa, 2015) Tuzuner, Seyda; Demir, Mustafa M.; Demir, Mustafa
The preparation of stable composites with well-controlled particle location is one of the challenges in formulating new polymer/nanoparticle mixtures. In this study, cetyltriammonium bromide (CTAB)capped monodisperse Ag nanoparticles were prepared and mixed with an equimass blend of polystyrene (PS) and poly(methyl methaaylate) (PMMA) in solution. The surface of the blend film without nanoparticles showed spherical pits with a size of 4.5 mu m in diameter. The integration of CTAB-capped nanoparticles into the blend film developed surface bumps with a size of 0.4 mu m in diameter. The organophilic Ag nanoparticles were distributed heterogeneously in the immiscible PS-PMMA blend. When the diameter of particle domains reached approximately 20 nm, particles were preferentially located at the interface of the PS and PMMA domains. Larger particle domains with a diameter of 90 nm were found to be in the PMMA-rich phase. Isothermal post-treatment of the PS-PMMA/Ag composite films directs the particle domains into PS domains. Thermodynamic factors that contribute to the observed morphologies are discussed. (C) 2015 Elsevier B.V. All rights reserved.
Citation Count: 23
Dynamic replication strategies in data grid systems: a survey
(Springer, 2015) Tos, Uras; Mokadem, Riad; Hameurlain, Abdelkader; Ayav, Tolga; Bora, Sebnem; Ayav, Tolga; Bilgisayar Mühendisliği Bölümü
In data grid systems, data replication aims to increase availability, fault tolerance, load balancing and scalability while reducing bandwidth consumption, and job execution time. Several classification schemes for data replication were proposed in the literature, (i) static vs. dynamic, (ii) centralized vs. decentralized, (iii) push vs. pull, and (iv) objective function based. Dynamic data replication is a form of data replication that is performed with respect to the changing conditions of the grid environment. In this paper, we present a survey of recent dynamic data replication strategies. We study and classify these strategies by taking the target data grid architecture as the sole classifier. We discuss the key points of the studied strategies and provide feature comparison of them according to important metrics. Furthermore, the impact of data grid architecture on dynamic replication performance is investigated in a simulation study. Finally, some important issues and open research problems in the area are pointed out.
Citation Count: 1
Effect of high salinity and temperature on water-volcanic rock interaction
(Springer, 2021) Goren, A. Yagmur; Topcu, Gokhan; Demir, Mustafa M.; Baba, Alper; Demir, Mustafa
In order to understand the processes occurring in natural hydrothermal systems, it was carried out a series of water-volcanic rock interaction studies in the laboratory and an intermediate volcanic rock samples from geothermal production wells in Tuzla geothermal field (TGF) in western Turkey. A high-pressure autoclave was used to conduct water-rock interaction experiments under similar conditions of the field. Rainwater and seawater were treated with volcanic rocks at 140 degrees C (reservoir temperature) and 4.5 bar pressure. The change in the ionic content of the resulting fluids was examined in terms of the type of volcanic rocks and mineral saturation index. The results indicate that talc and diopside minerals in geothermal systems may cause scaling at high temperatures depending on the geothermal fluid and pH.
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: 6
Enhanced Spontaneous Emission Rate in a Low-Q Hybrid Photonic-Plasmonic Nanoresonator
(Amer Chemical Soc, 2019) Gokbulut, Belkis; Inanc, Arda; Topcu, Gokhan; Unluturk, Secil S.; Ozcelik, Serdar; Demir, Mustafa M.; Inci, M. Naci; Demir, Mustafa
In this paper, CdTe quantum dots (QDs)-doped single electrospun polymer nanofibers are partially coated with gold nanoparticles to form distinct hybrid photonic-plasmonic nanoresonators to investigate the critical role of the cavity-confined hybrid mode on the modification of the spontaneous emission dynamics of the fluorescent emitters in low-Q photonic cavities. A total enhancement factor of 11.2 is measured via a time-resolved experimental technique, which shows that there is an increase of about three times in the spontaneous emission rate for the QDs-doped gold nanoparticle-decorated nanofibers as they are compared with those uncoated ones. The physical mechanism affecting the spontaneous emission rate of the encapsulated QDs in such a hybrid photonic-plasmonic nanoresonator is explained to be due to regeneration of the mode field in the nanofiber cavity upon the interaction of the dipoles with the surface plasmons of distinctive gold nanoparticles that surround the outer surface of the nanofiber.
Citation Count: 77
Enhancement of interlaminar fracture toughness of carbon fiber-epoxy composites using polyamide-6,6 electrospun nanofibers
(Wiley, 2017) Beylergil, Bertan; Tanoglu, Metin; Aktas, Engin; Tanoğlu, Metin
In this study, carbon fiber-epoxy composites are interleaved with electrospun polyamide-6,6 (PA 66) nanofibers to improve their Mode-I fracture toughness. These nanofibers are directly deposited onto carbon fabrics before composite manufacturing via vacuum infusion. Three-point bending, tensile, compression, interlaminar shear strength, Charpy impact, and double cantilever beam tests are performed on the reference and PA 66 interleaved specimens to evaluate the effects of PA 66 nanofibers on the mechanical properties of composites. To investigate the effect of nanofiber areal weight density (AWD), nanointerlayers with various AWD are prepared by changing the electrospinning duration. It is found that the electrospun PA 66 nanofibers are very effective in improving Mode-I toughness and impact resistance, compressive strength, flexural modulus, and strength of the composites. However, these nanofibers cause a decrease in the tensile strength of the composites. The glass-transition temperature of the composites is not affected by the addition of PA 66 nanofibers. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45244.
Citation Count: 24
Ensuring performance and provider profit through data replication in cloud systems
(Springer, 2018) Tos, Uras; Mokadem, Riad; Hameurlain, Abdelkader; Ayav, Tolga; Bora, Sebnem; Ayav, Tolga; Bilgisayar Mühendisliği Bölümü
Cloud computing is a relatively recent computing paradigm that is often the answer for dealing with large amounts of data. Tenants expect the cloud providers to keep supplying an agreed upon quality of service, while cloud providers aim to increase profits as it is a key ingredient of any economic enterprise. In this paper, we propose a data replication strategy for cloud systems that satisfies the response time objective for executing queries while simultaneously enables the provider to return a profit from each execution. The proposed strategy estimates the response time of the queries and performs data replication in a way that the execution of any particular query is still estimated to be profitable for the provider. We show with simulations that how the proposed strategy fulfills these two criteria.
Citation Count: 1
Experimental modeling of antimony sulfides-rich geothermal deposits and their solubility in the presence of polymeric antiscalants
(Pergamon-elsevier Science Ltd, 2022) Karaburun, Emre; Sozen, Yigit; Ciftci, Celal; Sahin, Hasan; Baba, Alper; Akbey, Umit; Demir, Mustafa M.; Demir, Mustafa
Antimony (Sb)-rich geothermal deposits have been observed in many geothermal power plants worldwide. They occur as red-colored, sulfidic precipitates disturbing energy-harvesting by clogging the geothermal installations. In order to prevent the formation of this scale, information on its physicochemical features is needed. For this purpose, Sb-rich sulfide-based deposits were synthesized at controlled conditions in a pressurized glass reactor at geothermal conditions (135 degrees C and 3.5 bar). Various polymeric antiscalants with different functional groups, such as acrylic acid, sulphonic acid, and phosphonic acid groups were tested for their effect on Sb sulfide solubility. An additional computational study was performed to determine the binding energy of Sb and S atoms to these groups. The results suggest that sulfonic acid groups are the most affective. Therefore, it was concluded that these macromolecule containing sulfonic acid groups and poly (vinyl sulfonic acid) derivatives could potentially act as antiscalants for the formation of antimony sulfide.
Citation Count: 10
Experimental modeling of silicate-based geothermal deposits
(Pergamon-elsevier Science Ltd, 2017) Celik, Ash; Topcu, Gokhan; Baba, Alper; Akdogan, Yasar; Senturk, Ufuk; Demir, Mustafa M.; Demir, Mustafa
Scaling by metal silicates represents a major obstacle for geothermal systems. A composition that enables the fabrication of artificial deposits is necessary for the rapid testing of potential inhibitors. In this work, artificial deposits were synthesized by employing experimental conditions similar to those in the Tuzla Geothermal Field in Turkey. Although refluxing enabled the formation of a precipitate that was similar to naturally formed deposits in color and texture, their elemental composition and morphology showed a mismatch. An autoclave enabled the production of a precipitate that more closely resembled naturally formed deposits in color, texture, elemental composition, and structure.
Citation Count: 445
Flow cytometry: basic principles and applications
(Taylor & Francis Ltd, 2017) Adan, Aysun; Alizada, Gunel; Kiraz, Yagmur; Baran, Yusuf; Nalbant, Ayten; Baran, Yusuf
Flow cytometry is a sophisticated instrument measuring multiple physical characteristics of a single cell such as size and granularity simultaneously as the cell flows in suspension through a measuring device. Its working depends on the light scattering features of the cells under investigation, which may be derived from dyes or monoclonal antibodies targeting either extracellular molecules located on the surface or intracellular molecules inside the cell. This approach makes flow cytometry a powerful tool for detailed analysis of complex populations in a short period of time. This review covers the general principles and selected applications of flow cytometry such as immunophenotyping of peripheral blood cells, analysis of apoptosis and detection of cytokines. Additionally, this report provides a basic understanding of flow cytometry technology essential for all users as well as the methods used to analyze and interpret the data. Moreover, recent progresses in flow cytometry have been discussed in order to give an opinion about the future importance of this technology.
Citation Count: 46
Gd³⁺-Doped α-CsPbI₃ Nanocrystals with Better Phase Stability and Optical Properties
(Amer Chemical Soc, 2019) Guvenc, C. Meric; Yalcinkaya, Yenal; Ozen, Sercan; Sahin, Hasan; Demir, Mustafa M.; Demir, Mustafa
Black alpha-CsPbI3 perovskites are unable to maintain their phase stability under room conditions; hence, the alpha-CsPbI3 phase transforms into a thermodynamically stable yellow delta-CsPbI3 phase within a few days, which has a nonperovskite structure and high band gap for optoelectronic applications. This phase transformation should be prevented or at least retarded to make use of superior properties of alpha-CsPbI3 in optoelectronic applications. In this study, Gd3+ doping was employed with the aim of increasing the stability of alpha-CsPbI3. All doped alpha-CsPbI3 nanocrystals with various levels of Gd3+, between 5 and 15 mol %, have shown greater phase stability than that of the pure alpha-CsPbI3 phase from 5 days up to 11 days under ambient conditions. This prolonged phase stability can be attributed to three potential reasons: increased tolerance factor of the perovskite structure, distorted cubic symmetry, and decreased defect density in nanocrystals. Urbach energy values suggest the reduction of defect density in the doped nanocrystals. Also, use of 10 mol % Gd3+ as a dopant material increases the photoluminescence quantum yield from 70 to 80% and fluorescence lifetime of alpha-CsPbI3 from 47.4 to 64.4 ns. Further, density functional theory calculations are in a good agreement with the experimental results.
Citation Count: 7
HER2-Targeted, Degradable Core Cross-Linked Micelles for Specific and Dual pH-Sensitive DOX Release
(Wiley-v C H verlag Gmbh, 2022) Bayram, Nazende Nur; Ulu, Gizem Tugce; Topuzogullari, Murat; Baran, Yusuf; Isoglu, Sevil Dincer; Baran, Yusuf
Here, a targeted, dual-pH responsive, and stable micelle nanocarrier is designed, which specifically selects an HER2 receptor on breast cancer cells. Intracellularly degradable and stabilized micelles are prepared by core cross-linking via reversible addition-fragmentation chain-transfer (RAFT) polymerization with an acid-sensitive cross-linker followed by the conjugation of maleimide-doxorubicin to the pyridyl disulfide-modified micelles. Multifunctional nanocarriers are obtained by coupling HER2-specific peptide. Formation of micelles, addition of peptide and doxorubicin (DOX) are confirmed structurally by spectroscopical techniques. Size and morphological characterization are performed by Zetasizer and transmission electron microscope (TEM). For the physicochemical verification of the synergistic acid-triggered degradation induced by acetal and hydrazone bond degradation, Infrared spectroscopy and particle size measurements are used. Drug release studies show that DOX release is accelerated at acidic pH. DOX-conjugated HER2-specific peptide-carrying nanocarriers significantly enhance cytotoxicity toward SKBR-3 cells. More importantly, no selectivity toward MCF-10A cells is observed compared to HER2(+) SKBR-3 cells. Formulations cause apoptosis depending on Bax and Caspase-3 and cell cycle arrest in G2 phase. This study shows a novel system for HER2-targeted therapy of breast cancer with a multifunctional nanocarrier, which has higher stability, dual pH-sensitivity, selectivity, and it can be an efficient way of targeted anticancer drug delivery.

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