Scopus

Permanent URI for this collectionhttp://65.108.157.135:4000/handle/123456789/10

Browse

Now showing 1 - 13 of 13

Citation Count: 48
Amidoxime functionalized Polymers of Intrinsic Microporosity (PIM-1) electrospun ultrafine fibers for rapid removal of uranyl ions from water
(Elsevier Science Bv, 2019) Satilmis, Bekir; Isik, Tugba; Demir, Mustafa M.; Uyar, Tamer; Demir, Mustafa
The Polymers of Intrinsic Microporosity (PIM-1) is considered as one of the most promising polymer candidates for adsorption applications owing to its high surface area and the ability to tailor the functionality for the targeted species. This study reports a facile method for the preparation of amidoxime functionalized PIM-1 fibrous membrane (AF-PIM-FM) by electrospinning technique and its practical use for the extraction of U(VI) ions from aqueous systems via column sorption under continuous flow. Fibrous membrane form of amidoxime functionalized PIM-1 (AF-PIM-FM) was prepared by electrospinning method owing to its excellent processability in dimethylformamide. Bead-free and uniform fibers were obtained as confirmed by SEM imaging and average fiber diameter was 1.69 +/- 0.34 mu m for AF-PIM-FM. In addition, electrospun PIM-1 fibrous membrane (PIM-FM) was prepared as a control group. Structural and thermal characterization of powder and membrane forms of the materials were performed using FT-IR, H-1 NMR, XPS, Elemental analyses, TGA, and DSC. The porosity of the samples was measured by N-2 sorption isotherms confirming amidoxime PIM-1 still maintain their porosity after functionalization. Amidoxime functionality along with membrane structure makes AF-PIM-FM a promising material for uranyl adsorption. First, a comparison between powder and membrane form of amidoxime functionalized PIM-1 was investigated using batch adsorption process. Although membrane form has shown slightly lower adsorption performance in the batch adsorption process, the advantage of using the membrane in column adsorption processes makes membrane form more feasible for real applications. In addition, amidoxime modification enhanced the uranium adsorption ability of PIM-FM up to 20 times. The effect of initial concentration and pH were investigated along with regeneration of the adsorbents. AF-PIM-FM was successfully used for five adsorption-desorption cycles without having any damage on the fibrous structure.
Citation Count: 12
Anomalous transmittance of polystyrene-ceria nanocomposites at high particle loadings
(Royal Soc Chemistry, 2013) Parlak, Onur; Demir, Mustafa M.; Demir, Mustafa
Optical nanocomposites based on transparent polymers and nanosized pigment particles have usually been produced at low particle concentrations due to the undesirable optical scattering of the pigment particles. However, the contribution of the particles to many physical properties is realized at high concentrations. In this study, nanocomposites were prepared with transparent polystyrene (PS) and organophilic CeO2 nanoparticles using various compositions in which the particle content was up to 95 wt%. The particles, capped by 3-methacryloxypropyltrimethoxysilane (MPS), were dispersed into PS and the transmittance of the spin-coated composite films was examined over the UV-visible region. When the particle concentration was <20 wt%, the transmittance of the films showed a first-order exponential decay as the Rayleigh scattering theory proposes. However, a positive deviation was observed from the decay function for higher particle contents. The improvement in transmittance may be a consequence of interference in the multiple scattering of light by the quasi-ordered internal microstructure that gradually develops as the particle concentration increases.
Citation Count: 8
BODIPY-based organic color conversion layers for WLEDs
(Elsevier Sci Ltd, 2020) Yuce, Hurriyet; Guner, Tugrul; Dartar, Suay; Kaya, Beraat U.; Emrullahoglu, Mustafa; Demir, Mustafa M.; Demir, Mustafa
The usage of organic dyes in phosphor conversion layer of WLED is an attractive approach since they have high molar extinction coefficient and photostability. Various types of organic pigments have been employed for this purpose such as BODIPY, perylene diimide, Rhodamine B, pyrene, Nile red, etc. Among those, BODIPY-based organic dyes appear to be promising candidate for white light generation. In this work, for the first time, red and green emitting BODIPY-based organic molecules have been used as colour conversion layer. These molecules were associated with PMMA in DMF solution and the resulting solution was subjected to electrospinning. Colorful electrospun mats were embedded into PDMS matrix and their free-standing PDMS composite films were used as color conversion layers over blue LED to produce white light such that CRI of 95 and CCT of 4200 K was achieved. These values show that BODIPY-based organic molecules containing fiber composites are promising candidates to be used as color conversion layers for white light applications.
Citation Count: 34
Chemically modified optical fibers in advanced technology: An overview
(Elsevier Sci Ltd, 2019) Shukla, S. K.; Kushwaha, Chandra Shekhar; Guner, Tugrul; Demir, Mustafa M.; Demir, Mustafa
In recent years, chemically modified optical fibers have widely used for development of several advanced chemical and biosensors, biomedical technology and environmental monitoring. The chemically modified optical fiber bears several valuable properties like energy loss, catalytic behaviour, refractive index, and mechanical strength to advance the optical fiber technology. In this article, we reviewed the chemically-modified optical fiber and their applications in different optical fiber-based technologies. The basics of optical fiber and their modification are discussed along with the adopted methodologies. The advancements in different optical fiber based technologies viz sensing, imaging, tomography, magnetic resonance imaging, photodynamic therapy, optogenics, surgery and environmental monitoring are discussed in the light of the contribution of chemically modified optical fibers. In conclusion, success and challenges for the use of chemically modified-optical fiber are presented on the basis of existing literature.
Citation Count: 11
Cryopreservation of a cell-based biosensor chip modified with elastic polymer fibers enabling ready-to-use on-site applications
(Elsevier Advanced Technology, 2021) Ozsoylu, Dua; Isik, Tugba; Demir, Mustafa M.; Schoning, Michael J.; Wagner, Torsten; Demir, Mustafa
An efficient preservation of a cell-based biosensor chip to achieve a ready-to-use on-site system is still very challenging as the chip contains a living component such as adherent mammalian cells. Herein, we propose a strategy called on-sensor cryopreservation (OSC), which enables the adherent cells to be preserved by freezing (-80 degrees C) on a biosensor surface, such as the light-addressable potentiometric sensor (LAPS). Adherent cells on rigid surfaces are prone to cryo-injury; thus, the surface was modified to enhance the cell recovery for OSC. It relies on i) the integration of elastic electrospun fibers composed of polyethylene vinyl acetate (PEVA), which has a high thermal expansion coefficient and low glass-transition temperature, and ii) the treatment with O-2 plasma. The modified sensor is integrated into a microfluidic chip system not only to decrease the thermal mass, which is critical for fast thawing, but also to provide a precisely controlled micro-environment. This novel cryo-chip system is effective for keeping cells viable during OSC. As a proof-of-concept for the applicability of a ready-to-use format, the extracellular acidification of cancer cells (CHO-K1) was evaluated by differential LAPS measurements after thawing. Results show, for the first time, that the OSC strategy using the cryo-chip allows label-free and quantitative measurements directly after thawing, which eliminates additional post-thaw culturing steps. The freezing of the chips containing cells at the manufacturing stage and sending them via a cold-chain transport could open up a new possibility for a ready-to-use on-site system.
Citation Count: 63
Development and characterization of tubular composite ceramic membranes using natural alumino-silicates for microfiltration applications
(Elsevier Science inc, 2015) Ghouil, Boudjemaa; Harabi, Abdelhamid; Bouzerara, Ferhat; Boudaira, Boukhemis; Guechi, Abdelkrim; Demir, Mustafa M.; Figoli, Alberto; Demir, Mustafa
The preparation and characterization of porous tubular ceramic composite microfiltration membranes, using kaolins and calcium carbonates, were reported. The porous gehlenite (2CaO center dot Al2O3 center dot SiO2) and anorthite (CaO center dot Al2O3 center dot 2SiO(2)) based ceramics were obtained by a solid state reaction. A ceramic support, sintered at 1250 degrees C, within an average pore size of about 8 mu m, a porosity of about 47% and a compression strength around 40 MPa, was prepared. The microfiltration active top layer was added on the support by a slip casting from clay powder suspensions. The novel microfiltration membrane layer has a thickness of 40 mu m and an APS value of about 0.2 mu m. This average pore size value was improved and considerably lower than those reported in the literature (0.5 mu m). The performance of the novel microfiltration ceramic membrane was determined for evaluating both the water permeability and rejection. This proved the potentiality of the membrane produced in the microfiltration field. Moreover, the good adhesion, between the support and the active microfiltration layer membranes, was also proved. A correlation between microstructures of used powders and physicochemical properties was discussed. Finally, the origin of the unique two powder order membrane depositions was also proposed. (C) 2015 Elsevier Inc. All rights reserved.
Citation Count: 57
Effect of polyamide-6,6 (PA 66) nonwoven veils on the mechanical performance of carbon fiber/epoxy composites
(Elsevier Sci Ltd, 2018) Beylergil, Bertan; Tanoglu, Metin; Aktas, Engin; Tanoğlu, Metin
In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness.
Citation Count: 0
Enhanced electrocaloric effect of P(VDF-TrFE)-based nanocomposites with Ca and Sn co-doped BaTiO3 particles
(Elsevier Sci Ltd, 2023) Tokkan, Melike; Demir, Mustafa M.; Adem, Umut; Demir, Mustafa
We report on the enhancemenent of electrocaloric effect in solution cast polymer nanocomposites based on Poly (vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE) 55-45] with Ca and Sn co-substituted BaTiO3 ceramic fillers (Ba0.94Ca0.06Ti0.925Sn0.075O3, BCST). Saturated hysteresis loops and normal ferroelectric behaviour of the copolymer-based nanocomposites-as opposed to the relaxor ferroelectric nature of the terpolymer-based ones-allow the utilization of the indirect method to estimate the electrocaloric properties. Both the dielectric constant and electrocaloric temperature change (AT) increases as the particle content increases. Maximum adiabatic temperature change was obtained as 6.96 K under 900 kV/cm for the 10 vol % BCST containing polymer composite around the Curie temperature of the copolymer (70 degrees C). This relatively large electrocaloric strength is slightly lower than those obtained for terpolymer-based nanocomposites.
Citation Count: 3
Experimental apparatus for simultaneous measurement of triboelectricity and triboluminescence
(Elsevier Sci Ltd, 2020) Arica, Tugce A.; Topcu, Gokhan; Pala, Atamert; Demir, Mustafa M.; Demir, Mustafa
Triboelectricity is a phenomenon caused by the accumulation of opposite electric charges on the surfaces of two different materials as a result of contact with each other. The phenomenon of emitting cold light when the material is subjected to physical deformation is called triboluminescence. This paper presents an experimental apparatus that allows simultaneous measurement of both triboelectricity and triboluminescence of a model composite system based on poly (vinylidene fluoride) (PVDF) and europium tetrakis (dibenzoylmethide) triethylammonium (EuD(4)TEA). While the former component was studied in contact-separation mode giving triboelectricity, the latter emits triboluminescence upon application of mechanical impact. The device was operated at varying range of frequencies from 0.5 to 4.8 Hz and the force in the range of 5.4-9.5 N. (C) 2019 Elsevier Ltd. All rights reserved.
Citation Count: 23
Perylene-embedded electrospun PS fibers for white light generation
(Elsevier Sci Ltd, 2019) Guner, Tugrul; Aksoy, Erkan; Demir, Mustafa M.; Varlikli, Canan; Demir, Mustafa
Perylene dyes have been employed in the fabrication of white light due to their superior photophysical properties and relatively easy synthetic methods. However, their molecular aggregation in solid state is one of the main handicaps since it causes deviation in their optical properties and quenches photoluminescence quantum yields (Phi(f)). Investigation of the photophysical properties of a green (PTE), a yellow (PDI) and a new red (DiPhAPDI) emitting perylene derivative in solution, drop-casted films, polystyrene (PS) fibers and PS fibers embedded in poly (dimethyl siloxane) (PDMS) showed that PS:dye fibers prevent aggregation to some extend and allows high Of of dyes. The Of values of PTE, PDI and DiPhAPDI were all higher than 93.0% in solution and 84.8%, 94.3% and 73.6%, respectively in PS:dye fibers. Embedding the fibers in PDMS improved the photostabilities of the dyes two folds compared to their solution phases. The prepared dye containing fibers were combined together into a single PDMS film and utilized as a frequency conversion layer on a blue LED. Fabricated samples were found to show high color rendering index (>= 90), adjustable CCT (7500 K-5000 K), and power efficiency values exceeding 2001m/W depending on the used fiber amount in mass.
Citation Count: 19
Recent developments of colorimetric mechanical sensors based on polymer composites
(Royal Soc Chemistry, 2020) Inci, Ezgi; Topcu, Gokhan; Guner, Tugrul; Demirkurt, Merve; Demir, Mustafa M.; Demir, Mustafa
Colorimetric mechanical (force, pressure, strain, and impact) sensors allow naked-eye visualization of existing structural deformations of a system occurring upon application of a mechanical action. The combination of mechanochromic materials with polymers offers a practical approach to designing and fabricating these sensors. Polymers as matrices can tolerate a wide range of forces and permits reusability of the sensors. On the other hand, mechanochromic materials provide unique colour properties depending on the type of mechanical action. They have also been frequently employed for the quantification of mechanical forces. As an example, non-centrosymmetric crystals are combined with polymers for sensing impact forces. Structures with photoluminescence and scattering and plasmonic resonances can be used to fabricate strain and pressure responsive composite materials, respectively. This study reviews recent advances in colorimetric mechanical sensor systems prepared using polymers and inorganic and organic mechanochromic materials working under a wide range of forces.
Citation Count: 95
Synthesis of amidoximated polyacrylonitrile fibers and its application for sorption of aqueous uranyl ions under continuous flow
(Elsevier Science Sa, 2012) Horzum, Nesrin; Shahwan, Talal; Parlak, Onur; Demir, Mustafa M.; Demir, Mustafa
This study reports a feasible method for the removal of radioactive U(VI) ions from aqueous systems via column sorption under continuous flow. Electrospun polyacrylonitrile (PAN) fibers were used as sorbent materials in a homemade minicolumn. The nitrite groups on the fibers' surface were modified to amidoxime groups using hydroxylamine hydrochloride. Surface modification was observed to enhance the sorption capacity of PAN fibers toward uranium ions by more than 4-fold by virtue of the chelating ability of the amidoxime groups. The experiments investigated the effect of pH, initial concentration, and repetitive loading on the sorption properties of amidoximated PAN fibers. Based on the overall results, the surface-modified fibers seem to be a suitable potential sorbent material for applications in environmental cleanup, particularly for nuclear plants. (C) 2012 Elsevier B.V. All rights reserved.
Citation Count: 3
Tracking Code Bug Fix Ripple Effects Based on Change Patterns Using Markov Chain Models
(Ieee-inst Electrical Electronics Engineers inc, 2022) Ufuktepe, Ekincan; Tuglular, Tugkan; Palaniappan, Kannappan; Tuğlular, Tuğkan; Bilgisayar Mühendisliği Bölümü
Change impact analysis evaluates the changes that are made in the software and finds the ripple effects, in other words, finds the affected software components. Code changes and bug fixes can have a high impact on code quality by introducing new vulnerabilities or increasing their severity. A recent high-visibility example of this is the code changes in the log4j web software CVE-2021-45105 to fix known vulnerabilities by removing and adding method called change types. This bug fix process exposed further code security concerns. In this article, we analyze the most common set of bug fix change patterns to have a better understanding of the distribution of software changes and their impact on code quality. To achieve this, we implemented a tool that compares two versions of the code and extracts the changes that have been made. Then, we investigated how these changes are related to change impact analysis. In our case study, we identified the change types for bug-inducing and bug fix changes using the Quixbugs dataset. Furthermore, we used 13 of the projects and 621 bugs from Defects4J to identify the common change types in bug fixes. Then, to find the change types that cause an impact on the software, we performed an impact analysis on a subset of projects and bugs of Defects4J. The results have shown that, on average, 90% of the bug fix change types are adding a new method declaration and changing the method body. Then, we investigated if these changes cause an impact or a ripple effect in the software by performing a Markov chain-based change impact analysis. The results show that the bug fix changes had only impact rates within a range of 0.4-5%. Furthermore, we performed a statistical correlation analysis to find if any of the bug fixes have a significant correlation with the impact of change. The results have shown that there is a negative correlation between caused impact with the change types adding new method declaration and changing method body. On the other hand, we found that there is a positive correlation between caused impact and changing the field type.

Browse

Browsing Scopus by Scopus Q "Q1"