Browsing by Subject "Experimental data"

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Open Access
A comparative study on the processing of ultrasonic arc maps
(IEEE, 2008-08) Barshan, Billur
The directional maximum (DM) technique for processing ultrasonic arc maps is proposed and compared to previously existing techniques. The method processes ultrasonic arc maps directionally to extract the map of the environment and overcome the intrinsic angular uncertainty of ultrasonic sensors. It also eliminates noise and cross-talk related misreadings successfully. The comparison is based on experimental data and three complementary error criteria. The DM technique offers a very good compromise between mean absolute error and correct detection rate, with a processing time less than tenth of a second. It is superior to existing techniques in range accuracy and in eliminating artifacts, resulting in the best overall performance. The results indicate several trade-offs in the choice of ultrasonic arc-map processing techniques.
Open Access
Comparison of low complexity UWB range estimators based on experimental data
(IEEE, 2012) Soğancı, Hamza; Gezici, Sinan; Tan, A.S.
In this paper, performances of low complexity time based range estimators that are employed for ultra wide-band (UWB) systems are compared using experimental data. These estimators are widely used in practical applications due to their low complexity. However, performances of these estimators vary depending on the choice of certain parameters such as the threshold value and window size. The optimal values for these parameters are investigated for several situations using the data acquired in the experiments. © 2012 IEEE.
Open Access
Determination of the in-plane effective mass and quantum lifetime of 2D electrons in AlGaN/GaN based HEMTs
(2011) Celik O.; Tiras, E.; Ardali, S.; Lisesivdin, S.B.; Özbay, Ekmel
Magnetoresistance and Hall resistance measurements have been used to investigate the electronic transport properties of AlGaN/GaN based HEMTs. The Shubnikov-de Haas (SdH) oscillations from magnetoresistance, is obtained by fitting the nonoscillatory component to a polynomial of second degree, and then subtracting it from the raw experimental data. It is shown that only first subband is occupied with electrons. The two-dimensional (2D) carrier density and the Fermi energy with respect to subband energy (EF-E1) have been determined from the periods of the SdH oscillations. The in-plane effective mass (m*) and the quantum lifetime (τq) of electrons have been obtained from the temperature and magnetic field dependencies of the SdH amplitude, respectively. The in-plane effective mass of 2D electrons is in the range between 0.19 m0 and 0.22 m0. Our results for in-plane effective mass are in good agreement with those reported in the literature © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
LOS/NLOS detection for UWB signals: A comparative study using experimental data
(IEEE, 2010) Decarli, N.; Dardari, D.; Gezici, Sinan; D'Amico, A.A.
In this paper the problem of detecting the channel state between LOS and NLOS conditions is addressed using UWB signals. A new distribution-based identification approach is proposed and its performance is compared with that of other classic schemes. To this purpose experimental data collected in realistic environments have been used. © 2010 IEEE.
Open Access
Magnetic resonance electrical impedance tomography (MREIT) based on the solution of the convection equation using FEM with stabilization
(Institute of Physics Publishing, 2012-07-27) Oran, O. F.; Ider, Y. Z.
Most algorithms for magnetic resonance electrical impedance tomography (MREIT) concentrate on reconstructing the internal conductivity distribution of a conductive object from the Laplacian of only one component of the magnetic flux density (∇ 2B z) generated by the internal current distribution. In this study, a new algorithm is proposed to solve this ∇ 2B z-based MREIT problem which is mathematically formulated as the steady-state scalar pure convection equation. Numerical methods developed for the solution of the more general convectiondiffusion equation are utilized. It is known that the solution of the pure convection equation is numerically unstable if sharp variations of the field variable (in this case conductivity) exist or if there are inconsistent boundary conditions. Various stabilization techniques, based on introducing artificial diffusion, are developed to handle such cases and in this study the streamline upwind Petrov-Galerkin (SUPG) stabilization method is incorporated into the Galerkin weighted residual finite element method (FEM) to numerically solve the MREIT problem. The proposed algorithm is tested with simulated and also experimental data from phantoms. Successful conductivity reconstructions are obtained by solving the related convection equation using the Galerkin weighted residual FEM when there are no sharp variations in the actual conductivity distribution. However, when there is noise in the magnetic flux density data or when there are sharp variations in conductivity, it is found that SUPG stabilization is beneficial.
Open Access
Methods for probing charging properties of polymeric materials using XPS
(2010) Sezen, H.; Ertas, G.; Süzer, Şefik
Various thin polystyrene, PS, and poly(methyl methacrylate), PMMA and PS + PMMA blend films have been examined using the technique of recording X-ray photoelectron spectrum while the sample is subjected to ±10 V d.c. bias, and three different forms of (square-wave (SQW), sinusoidal (SIN) and triangular (TRG)), a.c. pulses. All films exhibit charging shifts as observed in the position of the corresponding C1s peak under d.c. bias. The a.c. pulses convert the single C1s peak to twinned peaks in the case of the square-wave form, and distort severely in the cases of the SIN, and TRG forms, and all three of them exhibit strong frequency dependence. In order to mimic and better understand the behavior of these polymeric materials, an artificial dielectric system consisting of a clean Si-wafer coupled to an external 1 MΩ resistor and 56 nF capacitor is created, and its response to different forms of voltage stimuli, is examined in detail. A simple electrical circuit model is also developed treating the system as consisting of a parallel resistor and a series capacitor. With the help of the model, the response of the artificial system is successfully calculated as judged by comparison with the experimental data. Using one high frequency SQW measurements, the off-set in the charging shift due to the extra low-energy neutralizing electrons is estimated. After correcting the corresponding off-set shifts, the XPS spectra of the three different PS films, one PMMA, and one PS + PMMA blend film are re-examined. As a result of these detailed analysis, there emerges a clear relationship between the thicknesses of the PS films with their charging abilities. In the blend film, PS and PMMA domains are electrically separated, and exhibit different charging shifts, however, the presence of one is felt by the other. Hence, the PS component shifts are larger in the blend, due to the presence of PMMA domains, which has intrinsically a larger Reff, and conversely the PMMA component shifts are smaller due to the presence of PS domains.
Open Access
Prefetch throttling and data pinning for improving performance of shared caches
(IEEE, 2008-11) Öztürk, Özcan.; Son, S. W.; Kandemir, M.; Karaköy, M.
In this paper, we (i) quantify the impact of compilerdirected I/O prefetching on shared caches at I/O nodes. The experimental data collected shows that while I/O prefetching brings some benefits, its effectiveness reduces significantly as the number of clients (compute nodes) is increased; (ii) identify interclient misses due to harmful I/O prefetches as one of the main sources for this reduction in performance with increased number of clients; and (iii) propose and experimentally evaluate prefetch throttling and data pinning schemes to improve performance of I/O prefetching. Prefetch throttling prevents one or more clients from issuing further prefetches if such prefetches are predicted to be harmful, i.e., replace from the memory cache the useful data accessed by other clients. Data pinning on the other hand makes selected data blocks immune to harmful prefetches by pinning them in the memory cache. We show that these two schemes can be applied in isolation or combined together, and they can be applied at a coarse or fine granularity. Our experiments with these two optimizations using four disk-intensive applications reveal that they can improve performance by 9.7% and 15.1% on average, over standard compiler-directed I/O prefetching and no-prefetch case, respectively, when 8 clients are used. © 2008 IEEE.
Open Access
Slowing surface plasmon polaritons on plasmonic coupled cavities by tuning grating grooves
(American Institute of Physics, 2010-09) Balcı, Sinan; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, Atilla
We investigate slow surface plasmon polaritons (SPPs) in plasmonic waveguiding bands formed by coupled plasmonic cavities on Moiŕ surfaces. We demonstrate controlling the group velocity and dispersion of the SPPs by varying the depth of the plasmonic Bragg grating groove. Changing the grating depth results in modification of coupling coefficients between the cavities and hence the SPPs group velocity is altered. Variation in the group velocity and dispersion of SPPs can be measured with polarization dependent spectroscopic reflection measurements. Dispersion of SPPs has been calculated by finite-difference time-domain method in agreement with the experimental data.
Open Access
Study of junction and bias parameters in readout of phase qubits
(2012) Zandi H.; Safaei, S.; Khorasani, S.; Fardmanesh, M.
The exact numerical solution of the nonlinear Ginzburg-Landau equation for Josephson junctions is obtained, from which the precise nontrivial current density and effective potential of the Josephson junctions are found. Based on the resulting potential well, the tunneling probabilities of the associated bound states are computed which are in complete agreement with the reported experimental data. The effects of junction and bias parameters such as thickness of the insulating barrier, cross sectional area, bias current, and magnetic field are fully investigated using a successive perturbation approach. We define and compute figures of merit for achieving optimal operation of phase qubits and measurements of the corresponding states. Particularly, it is found that Josephson junctions with thicker barriers yield better performance in measurements of phase qubits. The variations of characteristic parameters such as life time of the states due to the above considered parameters are also studied and discussed to obtain the appropriate configuration setup.
Open Access
Warm-White light-Emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering: Reply to comment
(2011) Nizamoglu, S.; Erdem, T.; Sun X.W.; Demir, Hilmi Volkan
The correlated color temperatures and the corresponding color rendering indices calculated using actual experimental data (and not any prediction) in the original Letter [Opt. Lett. 35, 3372 (2010)] are correct. In addition, here the color rendering of our white LEDs integrated with nanocrystal quantum dots (NQDs) is provided for all test samples. Also, a new NQD-LED design with both high luminous efficacy of optical radiation and CRI is presented to have a chromaticity point in the quadrangle stated in the comment Letter [Opt. Lett. 36, 2851 (2011)]. The points made in the original Letter and all the calculation results provided therein are valid. © 2011 Optical Society of America.