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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: 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
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: 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: 3
Hybrid photonic-plasmonic mode-coupling induced enhancement of the spontaneous emission rate of CdS/CdSe quantum emitters
(Elsevier, 2022) Gokbulut, Belkis; Inanc, Arda; Topcu, Gokhan; Ozcelik, Serdar; Demir, Mustafa M.; Inci, M. Naci; Demir, Mustafa
In this paper, a hybrid photonic-plasmonic resonator, which comprises an electrospun polymer fiber with a micrometer diameter and a core/shell nanostructure with a gold nanoparticle core, is constructed to investigate the dynamics of the coupled spontaneous emission of CdS/CdSe quantum dots (QDs). The gold nanoparticle core; covered with a silica shell, anchored with individual CdS/CdSe QDs, is placed inside a hollow cylindrical nanocavity formed on the surface of the microfiber to enable integration of the optical mode with the plasmonic effect, which is induced by the localized surface plasmons of the metal nanoparticle being present in the vicinity of the dipoles. The spontaneous emission rate of the QDs, coupled into the hybrid photonic-plasmonic mode, is measured to enhance by a factor of 23 via a time-resolved experimental technique. This result suggests that the regeneration of the optical mode-field inside the photonic-plasmonic resonator through the interaction of the dipoles with the localized surface plasmons of a metal nanoparticle strongly enhances the density of the elec-tromagnetic states of the quantum emitters to facilitate an enhanced spontaneous emission within the host medium of the proposed polymer based-photonic structure.
Citation Count: 20
Hydrogeological properties of hyper-saline geothermal brine and application of inhibiting siliceous scale via pH modification
(Pergamon-elsevier Science Ltd, 2015) Baba, Alper; Demir, Mustafa M.; Koc, Gonca A.; Tugcu, Celal; Demir, Mustafa
Scaling is a major obstacle in harnessing of geothermal energy from the geothermal resources. This paper presents a case study for inhibition of metal silicate scaling using formic acid, harvesting more energy in particular case of Tuzla Geothermal Field (TGF), located on Biga Peninsula, in the northwestern of Turkey. TGF is 5 km far from Aegean Sea and 80 km south of Canakkale. Geothermal fluid of TGF has high salinity (EC > 91 mS/cm) and medium temperature (reservoir temperature is 173 degrees C). The acidification of high-salinity brine to mitigate silicate scaling is examined. Results of the study showed that a compromise between scaling and corrosion is achieved by reducing pH of brine to <6 using 55 ppm formic acid. (C) 2014 Elsevier Ltd. All rights reserved.
Citation Count: 15
Increasing solubility of metal silicates by mixed polymeric antiscalants
(Pergamon-elsevier Science Ltd, 2019) Topcu, Gokhan; Celik, Asli; Kandemir, Ali; Baba, Alper; Sahin, Hasan; Demir, Mustafa M.; Demir, Mustafa
The increase of silicate solubility is a big challenge for both hot and cold water because it reduces the deposition of metal silicates frequently observed in such systems and causes operational obstacles. The deposition of silicate coats the inner surface of the pipelines in an uncontrolled manner and reduces the harvesting of energy from brines. In this work, the solubility performance of two commercial water-soluble polymeric agents (poly(ethylene glycol) (PEG) and poly(vinyl alcohol) (PVA)) of various molecular weights employing dosage from 25 to 100 mg/L was examined. Along with dispersant-type antiscalant, poly(acrylamide) (PAM), poly(vinylsulfonic acid, sodium salt) (PVSA), and poly(vinylphosphonic acid) (PVPA) having chelating acidic groups were employed. Metal silicate deposits were obtained artificially in the lab-scale pressurized reactor. The experimental conditions employed were quite similar to a model power plant located in canaldcale, Turkey. The concentration of dissolved silica was increased from 130 to 420 mg/L when 100 mg/L PEG 1500 and 25 mg/L PVSA were employed as a mixture. For the atomic-level understanding of the interaction of chelating groups with metal cations, DFT calculations were performed too.
Citation Count: 19
Multilayer design of hybrid phosphor film for application in LEDs
(Elsevier Science Bv, 2016) Guner, Tugrul; Koseoglu, Devrim; Demir, Mustafa M.; Demir, Mustafa
Crosslinked polydimethylsiloxane (PDMS) composite coatings containing luminescent micrometer-sized yellow Y3Al5O12:Ce3+ (YAG:Ce3+) particles were prepared by spraying for potential applications in solid-state lighting. Blue light was down converted by phosphor particles to produce white light, yet poor color properties of YAG:Ce3+ stemmed from a deficiency of red. When nitride-based red phosphor was simply blended into the system, the electrostatic interaction of negatively charged YAG:Ce3+ and positively charged red phosphor particles caused remarkable clustering and heterogeneity in particle dispersion. Consequently, the light is dominantly blue and shifted to cold white. In other case, phosphor particles were sprayed onto the diffused polycarbonate substrate in stacked layers. Coatings with >80% inorganic content by mass with a thickness of 60 mu m were subjected to thermal crosslinking, which the presence of the phosphor particles obstructed, presumably due to the hindrance of large phosphor particles in the diffusion of PDMS precursors. The coating of YAG:Ce3+ first followed by red phosphor in stacked layers produced better light output and color properties than the coating obtained by spraying the mixture at once. Monte Carlo simulation validated the hypothesis. (C) 2016 Elsevier B.V. All rights reserved.
Citation Count: 8
A new method to extend the stress response of triboluminescent crystals by using hydrogels
(Elsevier Science Bv, 2017) Incel, Anil; Reddy, Subrayal M.; Demir, Mustafa M.; Demir, Mustafa
Polyacrylamide hydrogel entrapment of EuD(4)TEA or Cu(NCS)(py)(2)(PPh3) radically extends the emission time of the triboluminescent (TL) crystalline particles by a factor of 10(3), optimized when matching the hydrophilic/hydrophobic characteristics of the TL/gel components. Triboluminescence intensity improves with hydration of the TL/hydrogel composite. The composites may be used in impact-related sensor applications.
Citation Count: 23
Optical enhancement of phosphor-converted wLEDs using glass beads
(Elsevier Science Bv, 2017) Guner, Tugrul; Senturk, Ufuk; Demir, Mustafa M.; Demir, Mustafa
YAG:Ce3+ is a yellow-source compound commonly used in phosphor conversion layers for direct coating or remote phosphor configurations in LED illumination. This material, however, suffers from a high correlated color temperature, and low color-rendering index due to its deficiency in the red spectrum. In this study, glass beads (GB) with an average particle diameter of 10 gm were introduced to the conversion layer of a YAG:Ce3+ particulate-filled polydimethylsiloxane matrix composite structure and found to improve the optical features of the resulting composite. (C) 2017 Elsevier B.V. All rights reserved.
Citation Count: 0
Plasmon-induced spectral tunability of Perovskite nanowires
(Elsevier, 2021) Gokbulut, Belkis; Topcu, Gokhan; Demir, Mustafa M.; Inci, M. Naci; Demir, Mustafa
In this paper, plasmon-assisted spectral tunability in random media, composed of Perovskite (CsPbBr3) nanowires surrounded by Au nanoparticle clusters in polystyrene matrix, is achieved. The interaction between the surface plasmons and the quantum sources is observed to generate photoluminescence from the higher excited state energy levels of the excited semiconductor nanowires, which results in a blueshifted fluorescence emission of 50 nm. The localized surface plasmon properties are also determined to be tuned by plasmonic pumping of the quantum sources at different resonant frequencies. Thus, the first observation of the tunable blueshifted fluorescence emission of the semiconductor nanocrystals surrounded by plasmonic nanoparticle aggregates is achieved. The dramatic changes in the spectral profiles of the fluorescent nanowires are attributed to be due to the fast dynamics surface enhanced fluorescence mechanism.
Citation Count: 2
Testing the Performance of Various Polymeric Antiscalants for Mitigation of Sb-Rich Precipitates Mimicking Stibnite-Based Geothermal Deposits
(Wiley-hindawi, 2020) Ciftci, Celal; Karaburun, Emre; Tonkul, Serhat; Baba, Alper; Demir, Mustafa M.; Yesilnacar, Mehmet Irfan; Demir, Mustafa
Scaling is frequently observed in geothermal fields and reduces the energy harvesting of power plants. Recently, Sb-rich deposits have developed in many fields around the world. Various polymeric macromolecules have been used as antiscalants to mitigate the formation of scale. Testing potential commercial antiscalants in field conditions is a tedious and costly process. The artificial synthesis of geothermal deposits in the lab is a more practical and economical way to test the performance of antiscalants. This study obtained a Sb-rich deposit by refluxing SbCl3 and Na2S center dot 3H(2)O in 18 h. The product was found to be a mixture of Sb2O3 and Sb2S3. We examined the performance of antiscalants such as poly(ethylene glycol), poly(vinyl pyrrolidone), Gelatin, and poly(vinyl alcohol) of various molecular weights at 5 to 100 ppm. The formation of Sb2S3 is suppressed in the presence of the polymeric antiscalants. The dosage was found to be critical for the solubilization of Sb-rich deposits. Gelatin of 5 ppm showed the highest performance under the conditions employed in this study. While low dosages improve the concentration of [Sb3+], high dosages are required to increase the solubility of [S2-]. Moreover, the amount of deposit is reduced by 12.4% compared to the reference (in the absence of any polymeric molecules). Thus, comparatively, Gelatin shows the most promising performance among the molecules employed.
Citation Count: 25
Types of the scaling in hyper saline geothermal system in northwest Turkey
(Pergamon-elsevier Science Ltd, 2014) Demir, Mustafa M.; Baba, Alper; Atilla, Vedat; Inanli, Mustafa; Demir, Mustafa
Tuzla is an active geothermal area located in northwestern Turkey, 80 km south of the city of Canakkale and 5 km from the Aegean Coast. The geothermal brine from this area, which is dominated by NaCl, has a typical temperature of 173 degrees C. Rapid withdrawal of fluid to ambient surface conditions during sampling causes precipitation of various compounds known as scaling. Scaling is one of the important problems in Tuzla geothermal system that reduces the efficiency of the geothermal power plant and causes economical loss. The aim of this study was to determine the type of scaling as a first step towards preventing its formation. The scales formed in the geothermal system were divided into two groups according to location: the ones that formed in downhole and the ones that accumulated along the surface pipeline. Both scales were examined in terms of their elemental composition, structure and morphology using XRF, XRD, and SEM, respectively. The former was found to be mainly composed of PbS (Galena) and CaCO3 (aragonite or calcite). In contrast, the latter was heterogeneous in nature and consisted of mainly saponite like amorphous structure along with submicrometer-sized amorphous silica particles, layered double magnesium and iron hydroxide, and NaCl. (C) 2013 Elsevier Ltd. All rights reserved.
Citation Count: 12
An update on molecular biology and drug resistance mechanisms of multiple myeloma
(Elsevier Science inc, 2015) Mutlu, Pelin; Kiraz, Yagmur; Gunduz, Ufuk; Baran, Yusuf; Baran, Yusuf
Multiple myeloma (MM), a neoplasm of plasma cells, is the second most common hematological malignancy. Incidance rates increase after age 40. MM is most commonly seen in men and African-American population. There are several factors to this, such as obesity, environmental factors, family history, genetic factors and monoclonal gammopathies of undetermined significance (MGUS) that have been implicated as potentially etiologic. Development of MM involves a series of complex molecular events, including chromosomal abnormalities, oncogene activation and growth factor dysregulation. Chemotherapy is the most commonly used treatment strategy in MM. However, MM is a difficult disease to treat because of its marked resistance to chemotherapy. MM has been shown to be commonly multidrug resistance (MDR)-negative at diagnosis and associated with a high incidence of MDR expression at relapse. This review deals with the molecular aspects of MM, drug resistance mechanisms during treatment and also possible new applications for overcoming drug resistance. (C) 2015 Elsevier Ireland Ltd. All rights reserved.
Citation Count: 6
Utilization of Electrospun Polystyrene Membranes as a Preliminary Step for Rapid Diagnosis
(Wiley-v C H verlag Gmbh, 2016) Isik, Tugba; Horzum, Nesrin; Yildiz, U. Hakan; Liedberg, Bo; Demir, Mustafa M.; Demir, Mustafa
Recent advances in clinical practice drive deoxyribonucleic acid (DNA) as an important class of biomarker. Monitoring the change in their concentration suggests the initiation and/or progression of various disorders. However, low quantity of DNA biomarkers in body fluids requires a delicate isolation methodology that provides efficient separation and easy handling. This study describes a newer-generation separation technology relying on electrospun fibers of sub-micrometer diameter of a commodity polymer for DNA biomarkers in simulative serum. Fibrous polystyrene membranes are prepared by electrospinning and they are subjected to post-modification with Au. The composite membranes may provide a convenient environment for the removal of bovine serum albumin (BSA) from BSA and DNA mixtures. The eluent can be used as an efficient tool for detection of DNA biomarkers associated with diagnosis of numerous life-threatening diseases.

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