Browsing by Subject "Gases"
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Item Open Access Binary coded identification of industrial chemical vapors with an optofluidic nose(OSA - The Optical Society, 2016) Adamu, A. I.; Ozturk, F. E.; Bayındır, MehmetAn artificial nose system for the recognition and classification of gas-phase analytes and its application in identifying common industrial gases is reported. The sensing mechanism of the device comprises the measurement of infrared absorption of volatile analytes inside the hollow cores of optofluidic Bragg fibers. An array of six fibers is used, where each fiber targets a different region of the mid-infrared in the range of 2-14 ìm with transmission bandwidths of about 1-3 μm. The quenching in the transmission of each fiber due to the presence of analyte molecules in the hollow core is measured separately and the cross response of the array allows the identification of virtually any volatile organic compound (VOC). The device was used for the identification of seven industrial VOC vapors with high selectivity using a standard blackbody source and an infrared detector. The array response is registered as a unique six digit binary code for each analyte by assigning a threshold value to the fiber transmissions. The developed prototype is a comprehensive and versatile artificial nose that is applicable to a wide range of analytes.Item Open Access Many-body properties of a disordered charged Bose gas superlattice(Academic Press, 2000) Tanatar, Bilal; Das, A. K.We study some many-body properties of a disordered charged Bose gas (CBG) superlattice-an infinite array of CBG layers each of which containing disorder. The latter is assumed to cause collisions with the charged bosons, the effect of collisions being taken into account through a number-conserving relaxation time approximation incorporated within the random phase approximation (RPA) at T = 0. We go beyond the RPA and include a local-field correction G(q, q z) which is assumed to be collision independent, as an approximation. The resulting density-density correlation function is then used to calculate a number of many-body quantities of physical interest, e.g. (a) collective modes, (b) static structure factor, (c) energy-loss function, (d) plasmon density of states, and (e) groundstate energy. The effects of collisions on these quantities are discussed, and the results are compared with the corresponding results for an electron gas superlattice.Item Open Access P-doping-free InGaN/GaN light-emitting diode driven by three-dimensional hole gas(2013) Zhang, Z.-H.; Tiam Tan, S.; Kyaw, Z.; Liu W.; Ji, Y.; Ju, Z.; Zhang X.; Wei Sun X.; Volkan Demir H.Here, GaN/AlxGa1-xN heterostructures with a graded AlN composition, completely lacking external p-doping, are designed and grown using metal-organic-chemical-vapour deposition (MOCVD) system to realize three-dimensional hole gas (3DHG). The existence of the 3DHG is confirmed by capacitance-voltage measurements. Based on this design, a p-doping-free InGaN/GaN light-emitting diode (LED) driven by the 3DHG is proposed and grown using MOCVD. The electroluminescence, which is attributed to the radiative recombination of injected electrons and holes in InGaN/GaN quantum wells, is observed from the fabricated p-doping-free devices. These results suggest that the 3DHG can be an alternative hole source for InGaN/GaN LEDs besides common Mg dopants. © 2013 AIP Publishing LLC.Item Open Access Real-space condensation in a dilute Bose gas at low temperature(Natsional'na Akademiya Nauk Ukrainy, 2001) Kulik, I. O.We show with a direct numerical analysis that a dilute Bose gas in an external potential - which is choosen for simplicity as a radial parabolic well - undergoes at certain temperature Tc a phase transition to a state supporting macroscopic fraction of particles at the origin of the phase space (r = 0, p = 0). Quantization of particle motion in a well wipes out sharp transition but supports a distribution of radial particle density p(r) peacked at r = 0 (a real-space condensate) as well as the phase-space Wigner distribution density W(r, p) peaked at r = 0 and p = 0 below the crossover temperature Tc* of order of Tc. Fixed-particle-number canonical ensemble which is a combination of the fixed-N condensate part and the fixed-μ excitation part is suggested to resolve the difficulty of large fluctuation of the particle number (δN ∼ N) in the Bose-Einstein condensation problem treated within the orthodox grand canonical ensemble formalism.Item Open Access Visible photoluminescence from SiOx films grown by low temperature plasma enhanced chemical vapor deposition(Pergamon Press, 1995) Timofeev, F. N.; Aydınlı, Atilla; Ellialtioglu, R.; Turkoglu, K.; Gure, M.; Mikhailov, V. N.; Lavrova, O. A.a-SiOx films of varying stoichiometry have been prepared by low temperature plasma enhanced chemical vapor deposition. The majority of films showed photoluminescence (PL) and films prepared in a narrow range of gas flows exhibited much stronger PL after annealing. Peak PL energies ranging from the ultraviolet to the near infrared have been observed. PL, infrared and X-ray diffraction on selected samples indicate formation of Si clusters in the films. The effects of annealing on the PL properties of the films have been found to depend on initial stoichiometry of the films. © 1995.Item Open Access VOC gas leak detection using pyro-electric infrared sensors(IEEE, 2010) Erden, Fatih; Soyer, E. B.; Toreyin, B. U.; Çetin, A. EnisIn this paper, we propose a novel method for detecting and monitoring Volatile Organic Compounds (VOC) gas leaks by using a Pyro-electric (or Passive) Infrared (PIR) sensor whose spectral range intersects with the absorption bands of VOC gases. A continuous time analog signal is obtained from the PIR sensor. This signal is discretized and analyzed in real time. Feature parameters are extracted in wavelet domain and classified using a Markov Model (MM) based classifier. Experimental results are presented. ©2010 IEEE.