Yazar "Koysal, Oguz" seçeneğine göre listele

Listeleniyor 1 - 4 / 4
  • [ X ]
    Öğe
    Conductivity and dielectric properties of cholesteric liquid crystal doped with single wall carbon nanotube
    (Elsevier Science Sa, 2010) Koysal, Oguz
    In this work, we have studied the conductivity (sigma) and dielectric anisotropy (Delta epsilon) change in cholesteric liquid crystal (CLC) system doped with single wall carbon nanotube (SWCNT). Samples were investigated in frequency range 100 kHz to 10 MHz at various bias voltages by using dielectric spectroscopy technique. Pure CLC and SWCNT doped samples exhibit positive dielectric anisotropy as a function of the driving frequency in working range. Also critical frequency and relaxation times were determined for investigated samples. The results lead to the conclusion that the enhancement of the electrical conductivity and the change of the dielectric anisotropy in the SWCNT doped cell is mainly caused by the aligning effect of cholesteric liquid crystal system. (C) 2010 Elsevier B.V. All rights reserved.
  • [ X ]
    Öğe
    Determination of birefringence dispersion in nematic liquid crystals by using an S-transform
    (Optical Soc Amer, 2007) Ozder, Serhat; Coskun, Emre; Koysal, Oguz; Kocahan, Ozlem
    An analysis of the transmittance signal of the 5CB-coded nematic liquid crystal by using an S-transform is presented. The transmittance spectrum of this liquid crystal is acquired in the 1.26-2.22 mu m(-1) region at room temperature. The dispersion curve of birefringence is obtained for 5CB by this analysis, and data are fitted to the Cauchy formula, whereby the dispersion parameters are extracted. The result is found to be in favorable accordance with the Merck catalog value. (c) 2007 Optical Society of America.
  • [ X ]
    Öğe
    Molecular reorientation based diffraction in a hybrid liquid crystal system applicable for two different laser sources simultaneously
    (Elsevier Sci Ltd, 2007) Koysal, Oguz; San, S. Eren; Okutan, Mustafa; Ozder, Serhat
    The change of refractive index, originated by photo induced molecular reorientation, brings about a concordant diffraction capability in a hybrid liquid crystal system consisting two different dyes, effective in different regions of the spectrum, at the same time. Results of grating diffraction experiments are reported for a sample set including two different doping agents with two variable lasers. Accessible diffraction efficiency is similar to 10% and similar to 7% for He-Cd and He-Ne lasers, respectively, under optimum circumstances in the hybrid system. Analyzed results propose this novel system to be compatible for two lasers at the same time. (c) 2005 Elsevier Ltd. All rights reserved.
  • [ X ]
    Öğe
    Nonlinear experimental dye-doped nematic liquid crystal optical transmission spectra estimated by neural network empirical physical formulas
    (Elsevier, 2010) Yildiz, Nihat; San, Sait Eren; Koysal, Oguz
    In this paper, two complementary objectives related to optical transmission spectra of nematic liquid crystals (NLCs) were achieved. First, at room temperature, for both pure and dye (DR9) doped E7 NLCs, the 10-250W halogen lamp transmission spectra (wavelength 400-1200 nm) were measured at various bias voltages. Second, because the measured spectra were inherently highly nonlinear, it was difficult to construct explicit empirical physical formulas (EPFs) to employ as transmittance functions. To avoid this difficulty, layered feedforward neural networks (LFNNs) were used to construct explicit EPFs for these theoretically unknown nonlinear NLC transmittance functions. As we theoretically showed in a previous work, a LFNN, as an excellent nonlinear function approximator, is highly relevant to EPF construction. The LFNN-EPFs efficiently and consistently estimated both the measured and yet-to-be-measured nonlinear transmittance response values. The experimentally obtained doping ratio dependencies and applied bias voltage responses of transmittance were also confirmed by LFFN-EPFs. This clearly indicates that physical laws embedded in the physical data can be faithfully extracted by the suitable LFNNs. The extraordinary success achieved with LFNN here suggests two potential applications. First, although not attempted here, these LFNN-EPFs, by such mathematical operations as derivation, integration, minimization etc., can be used to obtain further transmittance related functions of NLCs. Second, for a given NLC response function, whose theoretical nonlinear functional form is yet unknown, a suitable experimental data based LFNN-EPF can be constructed to predict the yet-to-be-measured values. (C) 2010 Elsevier B.V. All rights reserved.