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Department: search.filters.department.Department of PhysicsSubject: search.filters.subject.Electrical electronics engineering

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Now showing 1 - 10 of 25
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    Automated system for weak periodic signal detection based on duffing oscillator
    (Wiley, 2020) Akilli, Mahmut; Akdeniz, Kamil Gediz; Department of Physics; Yılmaz, Nazmi; Teaching Faculty; Department of Physics; College of Sciences; 178427
    The periodic signals that have predictable and deterministic characteristics are used in the analysis and modelling of dynamical systems in diverse fields. These signals can be detected as the weak signals within the time series obtained from the measurable processes of dynamical systems. The Duffing oscillator is effective in detecting weak periodic signals with a very low signal-to-noise ratio. In this study, the authors present a method to automate the weak periodic signal detection of the Duffing oscillator using a quantitative index for the classification of the periodic and non-periodic signals. In this method, the authors use the wavelet scale index as the quantitative index in the classification of signals. Thus, they are able to plot the wavelet scale index spectrum of the Duffing oscillator where the frequency values of the weak periodic signals correspond to near-zero wavelet scale index parameters. First, the authors perform simulations using the method and detect weak periodic signals embedded in noise. Then, they employ two electroencephalogram signals to demonstrate the feasibility of the proposed method in the empirical data. Lastly, they compare the method to the periodogram power spectral density estimate based on fast Fourier transform.
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    Direct experimental determination of the optimum chromium concentration in continuous-wave Cr2(+): ZnSe lasers
    (Institute of Electrical and Electronics Engineers (IEEE), 2007) Demirbaş, Ümit; Department of Physics; Department of Chemistry; Department of Chemistry; Sennaroğlu, Alphan; Somer, Mehmet Suat; Kurt, Adnan; Faculty Member; Faculty Member; Teaching Faculty; Department of Physics; Department of Chemistry; College of Sciences; College of Sciences; College of Sciences; 23851; 178882; 194455
    We employed several experimental techniques to measure the concentration dependence of the important laser parameters, and directly determine the optimum ion concentration for continuous-wave (CW) operation in room temperature Cr2+:ZnSe lasers. By using diffusion doping, 40 polycrystalline Cr2+ :ZnSe samples with ion concentrations in the range of 0.8 x 10(18) to 66 x 10(18) ions/cm(3) were prepared and used in this paper. Based on the spectroscopic measurements, empirical formulae showing the concentration dependence of the passive laser losses, fluorescence lifetime, and the fluorescence efficiency were obtained. By using the fluorescence efficiency data, the optimum chromium concentration, which maximizes the 2400-nm fluorescence intensity at a fixed excitation power, was determined to be 6 x 10(18) ions/cm(3). The dependence of the optimum concentration on sample length was further discussed. The CW power performance of the samples was also evaluated. At an incident pump power of 2.1 W, the optimum concentration for lasing was determined to be 8.5 X 10(18) ions/cm' that was in good agreement with the fluorescence measurements. The predictions of the fluorescence analysis and laser power measurements were in good agreement at low chromium concentrations. The observed discrepancy at higher doping levels was attributed to thermal loading.
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    Dual-wavelength temporal dynamics of a gain-switched 2-mu m Tm3+:Lu2O3 ceramic laser
    (IEEE-Inst Electrical Electronics Engineers Inc, 2018) N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Canbaz, Ferda; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 23851
    We provide a detailed experimental investigation of the energy efficiency and rich temporal dynamics of a gain-switched 2-mu m Tm3+:Lu2O3 ceramic laser pumped near 800 nm. A tunable Ti3+:sapphire laser was used to determine the full excitation spectrum and the optimum pumping bands for the 1.5% Tm3+:Lu2O3 ceramic gain medium. These bands were centered at 774, 796, and 811 nm. The highest output pulse energy was obtained when the pump wavelength was set to 796 nm. In the experiments, a free-running x-cavity was used to investigate the energy efficiency of the Tm3+:Lu2O3 ceramic laser. Extracavity grating-dispersed output and prism-tuned resonator were used to further assess the role of cross-relaxation for the 1.5% Tm3+:Lu2O3 ceramic. Finally, we demonstrate that as the pump energy was increased, a transition occurred from-single-wavelength output (2068 nm) to dual-wavelength multipulse output (2068 and 1968 nm). We performed systematic temporal and spectral characterization measurements by using the free-running resonator, extracavity-grating-dispersed laser output, and prism-tuned resonator to investigate how the laser pulses at 1968 and 2068 nm evolved in time. A plane-wave rate equation model was further used to investigate the temporal dynamics of the Tm3+:Lu2O3 ceramic laser and provided predictions in qualitative agreement with experimental data.
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    Electrooptical tuning of a ruby microsphere morphology dependent resonance in a liquid crystal medium
    (IEEE, 2009) Beccherelli, Romeo; N/A; N/A; Department of Physics; Webb, Kurt David; Murib, Mohammed Sharif; Serpengüzel, Ali; Master Student; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; 27855
    A simulation describing the shifts in resonant peaks of scattered light from a waveguide coupled microsphere resonator immersed in nematic liquid crystal is discussed.
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    Experimental and numerical investigation of thermal effects in end-pumped Cr/sup 4+/: forsterite lasers near room temperature
    (IEEE-Inst Electrical Electronics Engineers Inc, 1998) Department of Physics; Department of Physics; Sennaroğlu, Alphan; Pekerten, Barış; Faculty Member; Undergraduated Student; Department of Physics; College of Sciences; College of Sciences; 23851; N/A
    The results of a study which employs both experimental and theoretical methods to investigate the role of thermal effects in room-temperature Cr4+:forsterile lasers are presented. A novel model was developed to calculate the incident threshold pump power required to attain oscillation by taking into account absorption saturation and pump-induced thermal loading in the gain medium, Experimentally, the incident threshold pump power was measured as a function of the crystal boundary temperature for three Cr4+:forsterite laser crystals with different small-signal differential absorption coefficients alpha(p0) and/or cross-sectional areas. Excellent agreement was obtained between theory and experiment for values of the stimulated emission cross section comparable to those from previously reported data. The model was then used to numerically determine the optimum value of alpha(p0) which minimizes the incident threshold pump power in room-temperature Cr4+:forsterite lasers, At a crystal boundary temperature of 15 degrees C, the optimum value of alpha(p0) was determined to be 0.64 cm(-1) for a 2-cm-long Cr4+:forsterite crystal, corresponding to an unsaturated absorption of 72%. The use of crystals with an optimum absorption coefficient should lead to the realization of highly efficient CW Cr4+:forsterite lasers at room temperature.
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    Femtosecond pulse generation from an extended cavity Cr4+: forsterite laser using graphene on YAG
    (Optical Society of America (OSA), 2013) Ozharar, Sarper; Balci, Osman; Pince, Ercag; Kocabas, Coskun; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A, N/A; 23851
    A room temperature, multipass-cavity, femtosecond Cr4+:forsterite laser was modelocked with a single-layer graphene saturable absorber on a YAG substrate. The resonator produced nearly transform-limited 92 fs pulses near 1250 nm with 53 kW of peak power.
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    Few-shot learning for segmentation of yeast cell microscopy images
    (IEEE, 2021) Alkan, Muhammet; Kiraz, Berna; Eren, Furkan; N/A; Department of Physics; Uysallı, Yiğit; Kiraz, Alper; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 22542
    Cell segmentation from microscopic images can be performed using deep neural networks or image processing techniques. In addition to their inherent difficulties, these techniques come together with the requirement of feeding the neural network with a large number of image samples in order to obtain a good result. However, this is not sustainable in terms of collecting and labeling microscopic images and represents a costly and time-consuming solution for every new microscopic image and cell type. Instead, fine-tuning can be employed by taking advantage of the adaptation ability of a model trained using meta-learning algorithms. In this way, while more general and better results can be obtained with fewer samples, the training process does not start from scratch for each new cell type or data set. In this article, microscopic images of yeast cells were recorded and analyzed using Reptile algorithm. After fine-tuning with a small number of samples, an average success rate of 81 % IoU (Intersection over Union) was obtained on the test pictures in addition to the model accuracy reaching up to 87%.
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    GaInNAs microspheres for wavelength division multiplexing
    (Institute of Electrical and Electronics Engineers (IEEE), 2003) Bilici, T; Işçi, S; Kurt, A.; Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855
    The GaInNAs range of compounds is suitable for optoelectronic device applications in 1.3 and 1.55 mum lasers, because of the large conduction band discontinuity resulting in good electron confinement and improved temperature characteristics. GaInNAs is suited to wavelength division multiplexing (WDM) applications in high-speed optical Communication networks. Since WDM techniques are available for steady-state traffic, there is a need for an all-optical packet-switching layer at the end of the optical to electronic conversion domain, which consists of all-optical gates, such as semiconductor optical amplifiers, channel dropping filters, interferometers, resonant cavity enhanced photodetectors, and optical random access memory elements. In these planar lightwave circuits, GaInNAs microspheres with their morphology-dependent resonances, can be used as compact optical filtering elements. The spectral filtering characteristics of GaInNAs microspheres are analysed by calculating the elastic scattering spectra optimised for both transverse electric and transverse magnetic resonance modes at the optical communication wavelengths of 1.3 and 1.55 mum.
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    Generation of 23-fs pulses at 850 nm from a carbon nanotube mode-locked solid-state laser
    (Optical Society of America (OSA), 2019) Bae, Ji Eun; Rotermund, Fabian; Demirbaş, Ümit; N/A; N/A; N/A; Department of Physics; Tanısalı, Gökhan; Toker, Işınsu Baylam; Canbaz, Ferda; Sennaroğlu, Alphan; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 23851
    We report, to the best of our knowledge, direct generation of the shortest pulses from a single-walled carbon nanotube mode-locked solid-state laser with a Cr:LiSAF gain medium, yielding 23-fs, nearly transform-limited pulses at 850 nm.
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    Graphene supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation
    (Optical Society of America (OSA), 2014) Ozharar, Sarper; Ozan Polat E.; Kocabas, Coskun; N/A; N/A; Department of Physics; Toker, Işınsu Baylam; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; PhD Student; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; N/A, N/A; 23851
    For the first time to our knowledge, we employed a graphene supercapacitor as a voltage controlled saturable absorber at bias voltages of 0.5-1V to generate 84-fs pulses from a solid-state laser near 1255 nm.