排序方式: 共有74条查询结果,搜索用时 46 毫秒
21.
Seyfettin Bayraktar Meral Bayraktar Nurten Vardar 《International Journal of Computational Fluid Dynamics》2013,27(5):331-339
In this paper, water flow in a rib-roughened channel is investigated numerically by using Reynolds stress turbulence models (RSM) on a three-dimensional (3-D) domain. Computational results for mean streamwise velocity component and turbulent kinetic energy show good agreements with available experimental data. Five rib pitch-to-height ratios (p/h) of 1, 5, 10, 15 and 20 are analysed for six different Reynolds numbers (Re) of 3000, 7000, 12,000, 20,000, 40,000 and 65,000. Velocity vectors, streamlines and Reynolds stresses are showed for these ratios and Re numbers. Streamlines revealed that Reynolds numbers do not affect flowfield but play an important role in the Reynolds stresses. 相似文献
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23.
Sema Akyil Sule Aytas D.A. Turkozu Mahmoud A.A. Aslani Sabriye Yusan Meral Eral 《Radiation measurements》2009,44(4):390-395
The aim of this study is to determine the radioactivity levels as a baseline for further studies and to obtain the distribution patterns of radioactivity in lake surface water around Izmir/Turkey. In this study, surface water samples were collected from three lakes around Izmir–Turkey. Surface water samples were analyzed for pH, mV conductivity and alkalinity content. The gross alpha/beta and uranium concentrations were investigated in the collected lake water samples. Mean gross alpha and gross beta activity concentrations in the surface water were found to be between (0.03 and 2.62) Bq l−1 for Karagol Lake, (0.75 and 2.35) Bq l−1 for Golcuk Lake, (0.03 and 1.77) Bq l−1 for Cakalbogaz Lake, respectively. Uranium concentration varied between (0.05 and 900) μg l−1 for Karagol Lake, (0.05 and 0.95) μg l−1 for Golcuk Lake and (3.33 and 10) μg l−1 for Cakalbogaz Lake. Radioactivity contour maps were produced and their data were evaluated statistically. 相似文献
24.
From Dark to Light to Fluorescence Resonance Energy Transfer (FRET): Polarity‐Sensitive Aggregation‐Induced Emission (AIE)‐Active Tetraphenylethene‐Fused BODIPY Dyes with a Very Large Pseudo‐Stokes Shift
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Esra Şen Dr. Kadem Meral Dr. Serdar Atılgan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):736-745
The work presented herein is devoted to the fabrication of large Stokes shift dyes in both organic and aqueous media by combining dark resonance energy transfer (DRET) and fluorescence resonance energy transfer (FRET) in one donor–acceptor system. In this respect, a series of donor–acceptor architectures of 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) dyes substituted by one, two, or three tetraphenylethene (TPE) luminogens were designed and synthesised. The photophysical properties of these three chromophore systems were studied to provide insight into the nature of donor–acceptor interactions in both THF and aqueous media. Because the generation of emissive TPE donor(s) is strongly polarity dependent, due to its aggregation‐induced emission (AIE) feature, one might expect the formation of appreciable fluorescence emission intensity with a very large pseudo‐Stokes shift in aqueous media when considering FRET process. Interestingly, similar results were also recorded in THF for the chromophore systems, although the TPE fragment(s) of the dyes are non‐emissive. The explanation for this photophysical behaviour lies in the DRET. This is the first report on combining two energy‐transfer processes, namely, FRET and DRET, in one polarity‐sensitive donor–acceptor pair system. The accuracy of the dark‐emissive donor property of the TPE luminogen is also presented for the first time as a new feature for AIE phenomena. 相似文献
25.
The uranium concentrations of the natural water samples collected from Northern Aegean Region, were measured by laser-excited fluorescence technique for hydrogeochemical prospecting. The reconnaissance survey measurements were made using external standards and detailed analysis realised with internal standard method to correct the quenching. Uranium concentrations for waters of all types range from below the detection limit of 0.05 ppb to 309.09 ppb and have a mean of 16.07 ppb. The precision of the method as shown by standard deviation is satisfactory. The laser-induced fluorescence method was applied easily and successfully in the uranium prospecting program and the data might indicate a uranium deposite in Saricaoglu Region. 相似文献
26.
In this study 1-benzyl-2-(4-benzyloxyphenyl)-5,6-dichloro-1H-benzimidazole, II, was synthesised. Elemental analyses, 1H-NMR, and single-crystal structure determination have been carried out. The benzimidazole
ring system is planar as expected. The molecules of II are arranged in rows running parallel to the b-axis with the molecules in adjacent rows inverted. 相似文献
27.
Hasan Efeog
lu Tevhit Karacali Kadem Meral brahim Y. Erdog
an Yavuz Onganer 《Journal of luminescence》2010,130(1):157-162
Photoluminescence (PL) of Al2O3 films obtained by anodization of thermally evaporated and annealed thin Al films on p++Si in 0.3 M oxalic acid has been investigated. Thermal annealing at 200–950 °C under the dry nitrogen atmosphere was used for deactivation of luminescence centres. Luminescence from as grown films was broad and located at 425 nm. This luminescence reached to highest level after annealing at 600 °C. Maximum 10 min was required for full optical activation and prolonged annealing up to 4 h did not change the luminescence intensity. Because of deep levels, absorption band edge of as grown films was shifted to the lower energy which is 3.25 eV. Annealing above 800 °C reduced the PL intensity and this observation was correlated with the blue shift of band edge as the defects annealed out. Disappearing PL intensity and blue shift of band edge absorption after annealing at 950 °C was mainly attributed to the oxygen-related defects and partly to impurities that may be originated from oxalic acid. AFM results did not show any hexagonally ordered holes but uniformly distributed nanosized Al2O3 clusters that were clearly seen. XRD measurements on as grown Al2O3 showed only [1 1 0] direction of α phase. Debye–Scherer calculation for this line indicates that cluster size is 35.7 nm. XRD and AFM pictures suggest that nanocrystalline Al2O3 are embedded in amorphous Al2O3. 相似文献
28.
There is a correspondence between functions in the maximal ideal of the local ring of a rational singularity and certain positive
divisors supported on the exceptional fiber of a resolution of the singularity. Here we give an algorithm to obtain a generating
set over ℤ of these divisors. 相似文献
29.
Meral Arnavut 《Journal of Pure and Applied Algebra》2007,208(2):739-760
In this article we consider finitely generated torsion-free modules over certain one-dimensional commutative Noetherian rings R. We assume there exists a positive integer NR such that, for every indecomposable R-module M and for every minimal prime ideal P of R, the dimension of MP, as a vector space over the field RP, is less than or equal to NR. If a nonzero indecomposable R-module M is such that all the localizations MP as vector spaces over the fields RP have the same dimension r, for every minimal prime P of R, then r=1,2,3,4 or 6. Let n be an integer ≥8. We show that if M is an R-module such that the vector space dimensions of the MP are between n and 2n−8, then M decomposes non-trivially. For each n≥8, we exhibit a semilocal ring and an indecomposable module for which the relevant dimensions range from n to 2n−7. These results require a mild equicharacteristic assumption; we also discuss bounds in the non-equicharacteristic case. 相似文献
30.
Meral FC Royston TJ Magin RL 《The Journal of the Acoustical Society of America》2011,129(2):1036-1045
A previous study of the authors published in this journal focused on mechanical wave motion in a viscoelastic material representative of biological tissue [Meral et al., J. Acoust. Soc. Am. 126, 3278-3285 (2009)]. Compression, shear and surface wave motion in and on a viscoelastic halfspace excited by surface and sub-surface sources were considered. It was shown that a fractional order Voigt model, where the rate-dependent damping component that is dependent on the first derivative of time is replaced with a component that is dependent on a fractional derivative of time, resulted in closer agreement with experiment as compared with conventional (integer order) models, such as those of Voigt and Zener. In the present study, this analysis is extended to another configuration and wave type: out-of-plane response of a viscoelastic plate to harmonic anti-symmetric Lamb wave excitation. Theoretical solutions are compared with experimental measurements for a polymeric tissue mimicking phantom material. As in the previous configurations the fractional order modeling assumption improves the match between theory and experiment over a wider frequency range. Experimental complexities in the present study and the reliability of the different approaches for quantifying the shear viscoelastic properties of the material are discussed. 相似文献