OpenAIRE Collection / OpenAIRE Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/11147/17

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Citation - WoS: 48
Citation - Scopus: 48
5-Fluorouracil Signaling Through a Calcium-Calmodulin Pathway Is Required for P53 Activation and Apoptosis in Colon Carcinoma Cells
(Nature Publishing Group, 2013-09) Can, G.; Akpınar, B.; Baran, Yusuf; Zhivotovsky, B.; Olsson, M.
5-Fluorouracil (5-FU) is an anti-metabolite that is in clinical use for treatment of several cancers. In cells, it is converted into three distinct fluoro-based nucleotide analogs, which interfere with DNA synthesis and repair, leading to genome impairment and, eventually, apoptotic cell death. Current knowledge states that in certain cell types, 5-FU-induced stress is signaling through a p53-dependent induction of tumor necrosis factor-receptor oligomerization required for death-inducing signaling complex formation and caspase-8 activation. Here we establish a role of calcium (Ca 2+) as a messenger for p53 activation in response to 5-FU. Using a combination of pharmacological and genetic approaches, we show that treatment of colon carcinoma cells stimulates entry of extracellular Ca 2+ through long lasting-type plasma membrane channels, which further directs posttranslational phosphorylation of at least three p53 serine residues (S15, S33 and S37) by means of calmodulin (CaM) activity. Obstructing this pathway by the Ca 2+ -chelator BAPTA (1,2-bis(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic acid) or by inhibitors of CaM efficiently reduces 5-FU-induced caspase activities and subsequent cell death. Moreover, ectopic expression of p53 S15A in HCT116 p53 -/- cells confirmed the importance of a Ca 2+ -CaM-p53 axis in 5-FU-induced extrinsic apoptosis. The fact that a widely used therapeutic drug, such as 5-FU, is operating via this pathway could provide new therapeutic intervention points, or specify new combinatorial treatment regimes. © 2013 Macmillan Publishers Limited.
Citation - WoS: 4
Citation - Scopus: 7
Adaptive Reduced Feedback Links for Distributed Power Allocation in Multicell Miso-Ofdma Networks
(IEEE Computer Society, 2014-04) Özbek, Berna; Le Ruyet, Didier; Pischella, Mylene
For multi-antenna Orthogonal Frequency-Division Multiple Access (OFDMA) based multicell networks, the channel state information (CSI) of all users is required to share among base stations in order to perform distributed power allocation. However, the amount of feedback increases with the number of users, base stations, subcarriers and antennas. Therefore, it is important to perform a selection at the user side to reduce the feedback load and the complexity of resource allocation. In this letter, we propose adaptive reduced feedback links by choosing the users based on their approximate signal to interference noise ratio (SINR) and their locations in the cell to satisfy users' rate constraints. We illustrate the performance results of reduced feedback links by employing distributed resource allocation with link adaptation.
Citation - WoS: 11
Citation - Scopus: 12
The Extended Graetz Problem for Micro-Slit Geometries; Analytical Coupling of Rarefaction, Axial Conduction and Viscous Dissipation
(Elsevier Ltd., 2016-12) Kalyoncu, Gülce; Barışık, Murat
In order to support the recent MEMS and Lab-on-a-chip technologies, we studied heat transport in micro-scale slit channel gas flows. Since the micro convection transport phenomena diverges from conventional macro-scale transport due to rarefaction, axial conduction and viscous heating, an accurate understanding requires a complete coupling of these effects. For such cases, we studied heat transfer in hydrodynamically developed, thermally developing gas flows in micro-slits at various flow conditions. The analytical solution of the energy equation considered both the heat conduction in the axial direction and heat dissipation of viscous forces. Furthermore, updated boundary conditions of velocity slip and temperature jump were applied based on Knudsen number of flow in order to account for the non-equilibrium gas dynamics. Local Nusselt number (Nu) values were calculated as a function of Peclet (Pe), Knudsen (Kn) and Brinkman (Br) numbers which were selected carefully according to possible micro-flow cases. Strong variation of Nu in thermal development length was found to dominate heat transfer behavior of micro-slits with short heating lengths for early slip flow regime. For this instance, influence of axial conduction and viscous dissipation was equally important. On the other hand, high Kn slip flow suppressed the axial conduction while viscous heating in a small surface-gas temperature difference case mostly determined the fully developed Nu and average heat transfer behavior as a function of Kn value.
Citation - WoS: 11
Citation - Scopus: 12
Novel Hybrid Process for the Conversion of Microcrystalline Cellulose To Value-Added Chemicals: Part 1: Process Optimization
(Springer Verlag, 2016-12) Akın, Okan; Yüksel, Aslı
In this paper, a novel hybrid process for the treatment of microcrystalline cellulose (MCC) under hot-compressed water was investigated by applying constant direct current on the reaction medium. Constant current range from 1A to 2A was applied through a cylindrical anode made of titanium to the reactor wall. Reactions were conducted using a specially designed batch reactor (450 mL) made of SUS 316 stainless steel for 30–120 min of reaction time at temperature range of 170–230 °C. As a proton donor H2SO4 was used at concentrations of 1–50 mM. Main hydrolysis products of MCC degradation in HCW were detected as glucose, fructose, levulinic acid, 5-HMF, and furfural. For the quantification of these products, High Performance Liquid Chromatography (HPLC) and Gas Chromatography with Mass Spectroscopy (GC–MS) were used. A ½ fractional factorial design with 2-level of four factors; reaction time, temperature, H2SO4 concentration and applied current with 3 center points were built and responses were statistically analyzed. Response surface methodology was used for process optimization and it was found that introduction of 1A current at 200 °C to the reaction medium increased Total Organic Carbon (TOC) and cellulose conversions to 62 and 81 %, respectively. Moreover, application of current diminished the necessary reaction temperature and time to obtain high TOC and cellulose conversion values and hence decreased the energy required for cellulose hydrolysis to value added chemicals. Applied current had diverse effect on levulinic acid concentration (29.9 %) in the liquid product (230 °C, 120 min., 2 A, 50 mM H2SO4). © 2016, Springer Science+Business Media Dordrecht.
Citation - WoS: 9
Citation - Scopus: 10
Novel Hybrid Process for the Conversion of Microcrystalline Cellulose To Value-Added Chemicals: Part 2: Effect of Constant Voltage on Product Selectivity
(Springer Verlag, 2017-11) Akın, Okan; Yüksel, Aslı
In this study, electrochemical degradation of microcrystalline cellulose (MCC) under hot-compressed water was investigated via application of constant voltage on reaction medium. Constant voltage ranges from 2.5 to 8.0 V was applied between anode (Titanium) and cathode (reactor wall). As an electrolyte and proton source 5–25 mM of H2SO4 was used. Reactions were carried out in a specially designed batch reactor (450 mL) made of T316 for 240 min at temperature of 200 °C.MCC decomposition products such as glucose, fructose, furfural, 5-HMF and levulinic acid were detected and quantified by High Performance Liquid Chromatography (HPLC). In the absence of electrolyte, applied voltage (2.5 and 4.0 V) decreased the total organic carbon (TOC) yield, in contrast at 8.0 V, TOC yield increased to 13%. Application of 8.0 V in hydrothermal conditions alter MCC decomposition pathway selectively to furfural (15%). Addition of electrolyte (5 mM, H2SO4) and application of 2.5 V potential increased TOC (54%) and changed the decomposition pathway in favor of 5-HMF (30%) and levulinic acid (21%). The structural changes in solid residues of electrochemically reacted MCC was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) and found that MCC particles functionalized by carboxylic acid and sulfonated groups by the application of constant voltage to reaction medium. In the presence of electrolyte, under certain voltage (2.5 V), functionalization of solid particles became more obvious in FTIR spectrum results. Therefore, change in the selectivity values of degradation products were conducted with the functionalization of MCC particles due to applied voltage under sub-critical conditions.
Citation - WoS: 33
Citation - Scopus: 37
Steam Gasification of Safflower Seed Cake and Catalytic Tar Decomposition Over Ceria Modified Iron Oxide Catalysts
(Elsevier Ltd., 2014-10) Duman, Gözde; Watanabe, Taichi; Uddin, Md Azhar; Yanık, Jale
Catalytic steam gasification of safflower seed cake was carried out using a double-bed microreactor in a two-stage process in the presence of ceria oxide (CeO2) modified iron oxide (Fe2O3) catalysts with different CeO2-Fe2O3 ratios. The effects of both catalyst and the temperature of catalytic bed on the tar decomposition and the overall gaseous product yield were investigated comparatively. It was found that ceria modified iron oxide catalysts had higher reactivity than that of the individual Fe2O3 and CeO2 for the catalytic tar decomposition in safflower seed cake steam gasification. The CeO2-Fe2O3 catalyst with 50 wt.% of Fe 2O3 exhibited the excellent performance for tar conversion at 700 °C. A comparison of tar decomposition from thermal run and catalytic run showed that in thermal run tar decomposition was progressed via steam reforming only. However, in the presence of catalyst, tar decomposition occurred via both steam reforming and water gas shift reaction. As a conclusion, ceria promoted iron catalysts were found to be active for both hydrogen production and tar decomposition in steam gasification of lignocellulosic biomass.
Citation - WoS: 19
Citation - Scopus: 22
Valorization of Hazelnut Shell Waste in Hot Compressed Water
(Elsevier Ltd., 2017) Gözaydın, Gökalp; Yüksel, Aslı
Hydrothermal conversion of waste hazelnut shell in hot compressed water, green and environmentally friendly medium, was investigated under different operating conditions to clarify the effects of reaction temperature, reaction time, acid concentration and acid kind (H2SO4 and H3PO4) on the production of value-added chemicals with high temperature/high pressure autoclave. In literature, to our best knowledge, there is no study about the production of levulinic acid, as a high value chemical, from waste hazelnut shell in hot-compressed water without using any mineral and heterogeneous catalyst. Hydrothermal reactions were conducted at 150–280 °C for reaction times of 15 to 120 min with various H2SO4 and H3PO4 concentrations varying from 0 to 125 mM. The detailed liquid product species were identified with High Performance Liquid Chromatography (HPLC) and gaseous products were analyzed by Gas Chromatography with a Thermal Conductivity Detector (GC-TCD). The main identified liquid compounds were levulinic acid, acetic acid and furfural while carbon dioxide and carbon monoxide were the major gaseous products. Increasing the reaction temperature (280 °C) and reaction time (120 min) resulted in a significant increment on the conversion (65.40%) as well as levulinic acid yield (13.05%). The production of levulinic acid was enhanced with H2SO4 addition; whereas treatments with H3PO4 improved the furfural production.

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