Yazar "Dogan S." seçeneğine göre listele

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    Assessment of turbulence models for flow around a surface-mounted cube
    (International Journal of Mechanical Engineering and Robotics Research, 2017) Dogan S.; Yagmur S.; Goktepeli I.; Ozgoren M.
    Flow over a bluff body constitutes one of the most fundamental phenomena for engineering applications. Even though a cube is considered as a simple bluff body to examine with respect to the flow structure, there is more complicated flow physics around the cube than expected. Thus, a cube just like other bluff bodies is mostly used in the comparison process of numerical and experimental results to determine the more suitable turbulence model in case of undertaken problem. For this reason, in this paper, turbulence models have been employed to investigate the flow characteristics around a surface-mounted cube at Re = 3700 based on the edge length of the cube in terms of Computational Fluid Dynamics (CFD) and then compared with experimental results in the literature. Normalized and time-averaged results of velocity vector fields, streamwise and cross-stream velocity components, vorticity contours and streamline patterns have been numerically obtained by using k-? Re-Normalization Group (RNG), k-? Shear Stress Transport (SST) and Large Eddy Simulation (LES) turbulence models. LES turbulence model has presented the best prediction of hydrodynamic characteristics for the body among the investigated turbulence models in this study. Although k-? SST turbulence model was the second successful one after LES method among the investigated turbulence models for the estimation of flow structure around the cube, k-? RNG turbulence model was failed to capture the flow fluctuations in the wake region of the geometry. © 2017 Int. J. Mech. Eng. Rob. Res.
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    Error checking of input data for web based design calculations of wastewater treatment plant
    (2007) Dogan S.; Dursun S.
    Wastewater treatment plant design calculation is complex and time-consuming task. The person who is in charge of calculations should be sure about the criterias about the unit to be sized and should use appropriate inputs. Vital point of design is generally using the best input within the range to have more sensible results. Web based design calculations of wastewater treatment plant software has been coded. PHP and JavaScript languages have been used to achieve these advantages. With the aid of error checking, the calculations would be performed within a couple of minutes which the same calculations might be resulted in hours manually.
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    Sperm Chromatin Dynamics Associated with Male Fertility in Mammals
    (wiley, 2017) Kutchy N.A.; Dogan S.; Kaya A.; Moura A.; Memili E.
    Instead of two protamines (PRM1 and PRM2) as in human and mouse sperms, presence of only PRM1 in bull sperm raises an interesting question about the mechanism(s) regulating sperm chromatin structure. During spermatogenesis, spermatozoa that are present in syncytium share mRNA and proteins through cytoplasmic bridges and are phenotypically diploid. Chromatin remodeling occurs during spermatogenesis where linker histones are gradually replaced by testis-specific variants, followed by the replacement of histones with transition proteins and then with protamines. Increased percentage of histone retention is expected to cause infertility in males. Although protamines are involved in sperm chromatin condensation and function, there is restrictive positive selection on only a few functional sites. Improper packaging of sperm DNA caused partly by reduced protamination predisposes sperm DNA to damage, which then interferes with fertilization and early embryonic development. Abnormal chromatin condensation in sperm during spermatogenesis and abnormal chromatin decondensation during pronucleus formation (postfertilization) can result in reproductive problems. © 2017 by John Wiley & Sons, Inc. All rights reserved.
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    Sperm protamine-status correlates to the fertility of breeding bulls
    (Society for the Study of Reproduction, 2015) Dogan S.; Vargovic P.; Oliveira R.; Belser L.E.; Kaya A.; Moura A.; Sutovsky P.
    During fertilization, spermatozoa make essential contributions to embryo development by providing oocyte activating factors, centrosomal components, and paternal chromosomes. Protamines are essential for proper packaging of sperm DNA; however, in contrast to the studies of oocyte-related female infertility, the influence of sperm chromatin structure on male infertility has not been evaluated extensively. The objective of this study was to determine the sperm chromatin content of bull spermatozoa by evaluating DNA fragmentation, chromatin maturity/protamination, PRM1 protein status, and nuclear shape in spermatozoa from bulls with different fertility. Relationships between protamine 1 (PRM1) and the chromatin integrity were ascertained in spermatozoa from Holstein bulls with varied (high vs. low) but acceptable fertility. Sperm DNA fragmentation and chromatin maturity (protamination) were tested using Halomax assay and toluidine blue staining, respectively. The PRM1 content was assayed using Western blotting and in-gel densitometry, flow cytometry, and immunocytochemistry. Fragmentation of DNA was increased and chromatin maturity significantly reduced in spermatozoa from low-fertility bulls compared to those from high-fertility bulls. Field fertility scores of the bulls were negatively correlated with the percentage of spermatozoa displaying reduced protamination and fragmented DNA using toluidine blue and Halomax, respectively. Bull fertility was also positively correlated with PRM1 content by Western blotting and flow cytometry. However, detection of PRM1 content by Western blotting alone was not predictive of bull fertility. In immunocytochemistry, abnormal spermatozoa showed either a lack of PRM1 or scattered localization in the apical/acrosomal region of the nuclei. The nuclear shape was distorted in spermatozoa from low-fertility bulls. In conclusion, we showed that inadequate amount and localization of PRM1 were associated with defects in sperm chromatin structure, coinciding with reduced fertility in bulls. These findings are highly significant because they reveal molecular and morphological phenotypes of mammalian spermatozoa that influence fertility. © 2015 by the Society for the Study of Reproduction, Inc.