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71.
Kenan Bulcar Mustafa Akyol Gönül Akça Ali Osman Ayaş Mustafa Topaksu Ahmet Ekicibil 《Journal of Superconductivity and Novel Magnetism》2014,27(11):2631-2637
We have worked on the structural and magnetic properties of Zn0.99?xMn0.01Gd x O δ (for x = 0.02, 0.03, and 0.04) compounds prepared by using a sol–gel method. The x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy were used to understand the structural properties of the samples. We observed that co-substitution of Mn (1 %) and Gd (2–4 %) into the ZnO does not change the hexagonal structure. Scanning electron microscope (SEM) images show us that the grain size decreases with the increasing amount of the Gd into the ZnO matrix. The magnetic properties of the samples have been investigated by using magnetic hysteresis and DC susceptibility measurements. The ZMG1 sample shows a weak ferromagnetic behavior at room temperature, whereas the ZMG2 and ZMG3 samples exhibit a paramagnetic nature. Furthermore, it is also found that the magnetizations of the samples decrease with increasing Gd content in the ZnMnO system due to the enhancing interaction between Gd 3+ ions. We summarize that the co-substitution of Mn and Gd into the ZnO generates a room-temperature ferromagnetism, but it still needs more work to obtain strong and high coercivity magnetic loops for applications. 相似文献
72.
Exhaust gas reforming of propane to a hydrogen-rich mixture in a single, heat-exchange integrated, adiabatic, catalytic microchannel is modeled and simulated at different exhaust gas compositions from conventional gasoline and diesel fueled engines. Propane is considered as the model hydrocarbon for the complex fuels such as gasoline and diesel. The single microchannel is considered to be the characteristic unit of the catalytic exhaust gas reformer involving identical channels located parallel to each other. Steady-state simulations, carried out by the finite volume method, involve parametric variations of the total feed flow rate, and the amounts of propane and steam injected externally into the exhaust gas (reformer feed) stream. The results show that effective heat transfer and uniform temperature distribution, which are critical for the successful operation of the exhaust gas reformer, can be obtained in the microchannel configuration even at low gas hourly space velocities (GHSVs) at which the conventional packed-bed reformers usually lead to remarkable hot-spot formation. Production of H2 and CO is favored by the addition of higher amounts of propane and steam into the reformer feed. Increasing the total feed flow rate, hence the GHSV is found to improve heat distribution along the microchannel at the expense of reduced product yields due to insufficient contact time. 相似文献
73.
The details of the chemical and physical mechanisms of the soot formation process in combustion remain uncertain due to the highly complex nature of hydrocarbon flames, and only a few principles are firmly established mostly for atmospheric conditions. In spite of the fact that most combustion devices used for transportation operate at very high pressures (e.g., aircraft gas turbines up to 40 atm, diesel engines exceeding 100 atm), our understanding of soot formation at these pressures is not at a desirable level, and there is a fundamental lack of experimental data and complementary predictive models. The focus of this review is to assess the experimental results available from laminar co-flow diffusion flames burning at elevated pressures. First, a brief review of soot formation mechanisms in diffusion flames is presented. This is followed by an assessment of soot diagnostics techniques, both intrusive and non-intrusive, most commonly used in soot experiments including the laser induced incandescence. Then the experimental results of soot measurements done at elevated pressures in diffusion flames are reviewed and critically assessed. Soot studies in shock tubes and in premixed flames are not covered. Smoke point fuel mass flow rate is revisited, and shortcomings in recent measurements are pointed. The basic requirements for tractable and comparable measurements as a function of pressure are summarized. Most recent studies at high pressures with aliphatic gaseous fuels show that the soot yield displays a unified behaviour with reduced pressure. The maximum soot yield seems to reach a plateau asymptotically as the pressure exceeds the critical pressure of the fuel. Lack of experimental data on the sensitivity of soot morphology to pressure is emphasized. A short summary of efforts in the literature on the numerical simulation of soot formation in diffusion flames at high pressures is the last section of the paper. 相似文献
74.
Food Science and Biotechnology - In this study, lactic acid bacteria diversity during the fermentation of homemade and commercially prepared Tarhana, a traditional fermented cereal food from... 相似文献
75.
Ahmet Gokceoglu Yaning Zou Mikko Valkama Paschalis C. Sofotasios 《Mobile Networks and Applications》2014,19(4):473-486
For the development of highly integrated, flexible and low-cost cognitive radio (CR) devices, simple transceiver architectures, like direct-conversion receiver, are expected to be deployed and provide viable radio frequency (RF) spectrum sensing solutions for practical implementation. Yet, this can be very challenging task especially if spectrum sensing and down-conversion are conducted over multiple RF channels simultaneously for improved efficiency in channel scans. Then, the so-called dirty RF problem that degrades link performance of traditional transmission systems starts to be influential from spectrum sensing perspective as well. The unavoidable RF impairments, e.g., oscillator phase noise in direct-conversion receiver, could generate crosstalk between multiple channels that are down-converted simultaneously, and thus considerably limit the spectrum sensing capabilities. Most of the existing spectrum sensing studies in literature assume an ideal RF receiver and have not considered such practical RF hardware problem. In this article, we study the impact of oscillator phase noise on energy detection (ED) based spectrum sensing in multi-channel direct-conversion receiver scenario. With complex Gaussian primary user (PU) signal models, we first derive the detection and false alarm probabilities in closed-form expression. The analytical results, verified through extensive simulations, show that the wideband multi-channel sensing receiver is very sensitive to the neighboring channel crosstalk induced by oscillator phase noise. More specifically, it is shown that the false alarm probability of multi-channel energy detection increases significantly, compared to the ideal RF receiver case. The exact performance degradation depends on the power of neighboring channels as well as statistical characteristics of the phase noise in the deployed receiver. In order to prevent such performance degradation in spectrum identification, an enhanced energy detection technique is proposed. The proposed technique calculates the leakage power from neighboring channels for each channel and improves the sample energy statistics by subtracting this leakage power from the raw values. An analytical expression is derived for the leakage power which is shown to be a function of power spectral levels of neighboring channels and 3-dB bandwidth of phase noise process. Practical schemes for estimating these two quantities are discussed. Extensive computer simulations show that the proposed enhanced detection yields false alarm rates that are very close to those of an ideal RF receiver and hence clearly outperforms classical energy detection. 相似文献
76.
Mehmet Ali Yurdusev Ahmet Ali Kumanlıoğlu Yüksel Abalı M. Sadrettin Zeybek 《Construction and Building Materials》2009,23(5):1871-1877
In this study, usability of wastes produced in phosphoric acid plants in structural brick manufacture has been investigated. There are several parameters involved in using these wastes in brick production namely the rate of added waste, firing speed and firing temperature. The performance of these parameters can be measured by several criteria such as natural drying shortening, water absorption and weight loss. Therefore, so many experiments are needed to investigate the effects of these parameters on the bricks produced with these wastes. The result of a series of experiments were utilized to achieve this end. The results have shown that the industrial wastes considered improve the performance of the bricks in terms of the criteria mentioned above. However, the results have also shown that further investigations are needed to explore the effects of interim values on the performance of the bricks. To achieve that end, a neural experimental study is adopted. For this purpose, the results of the experiments conducted were used to construct an artificial neural network. The trained and tested network was then used to check the effects of 280 different combinations for each type of material mixtures mentioned. The outcome of these artificial tests have provided the optimal values for the waste addition rate, firing speed and firing temperature based on the four criteria mentioned previously. 相似文献
77.
Li Huijun; Lee Donghyuck; Pfeiffer Steven I.; Kamata Akihito; Kumtepe Alper T.; Rosado Javier 《Canadian Metallurgical Quarterly》2009,24(3):186
This study examined measurement invariance of the Gifted Rating Scales—School Form (GRS–S) across the United States, Puerto Rico, China, South Korea, and Turkey, using multigroup confirmatory factor analysis. A total of 1,817 students were rated by 287 teachers using either translated versions of GRS–S or the original English GRS–S. Results indicate a similar factor structure for the GRS–S across the five locations; six factors with each of the 72 items equivalently loaded to the same latent variable across groups. The metric invariance test and the factor variance and covariance invariance tests reveal that the patterns of factor loadings and the factor variances and covariances are invariant across the five groups. Moreover, the scalar invariance test indicates that item means are equivalent across the groups. These results suggest that the GRS–S has intercultural utility and can be similarly interpreted. Implications and limitations of the present research for gifted identification are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
78.
Synthesis and characterization of PMMA composites activated with starch for immobilization of L‐asparaginase
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Poly (methyl methacrylate) (PMMA)–starch composites were prepared by emulsion polymerization technique for L‐asparaginase (L‐ASNase) immobilization as highly activated support. The hydroxide groups on the prepared composites offer a very simple, mild and firm combination for enzyme immobilization. The pure PMMA and PMMA‐starch composites were characterized as structural, thermal and morphological. PMMA‐starch composites were found to have better thermal stability and more hydrophilic character than pure PMMA. L‐ASNase was immobilized onto PMMA‐starch composites contained the different ratio of starch (1, 3, 5, and 10 wt %). Immobilized L‐ASNase showed better performance as compared to the native enzyme in terms of thermal stability and pH. Km value of immobilized enzyme decreased approximately eightfold compared with the native enzyme. In addition to, immobilized L‐ASNase was found to retain 60% of activity after 1‐month storage period at 4 °C. Therefore, PMMA‐starch composites can be provided more advantageous in terms of enzymatic affinity, thermal, pH and storage stability as L‐ASNase immobilization matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43421. 相似文献
79.
Elif Kacar Ahmet Erdem Mesure Mutlu Sanli Asgar Kayan Levent Candan Ufuk Yildiz Arif Demir 《Journal of Inorganic and Organometallic Polymers and Materials》2016,26(4):895-906
It is important to give water-repellent and antibacterial properties to the acrylonitrile butadiene styrene (ABS) surfaces of the hearing aids. In this study, the sol–gel Si and sol–gel Ti solutions were prepared from the reactions of silicon ethoxide, titanium butoxide and methacrylic acid. The catalyst and Dynasylan F8815 were added to the sol–gel solutions to give hydrophobic properties onto the ABS surfaces. Additionally, silver nanoparticles were synthesized by nanosecond laser and added to the coating solutions to give extra antibacterial properties. The surfaces of the ABS targets were coated using the sol–gel dip coating and pulsed laser deposition techniques. The coatings with good adhesion between film and substrate and good water-repellent properties were achieved. The average contact angles for the coated ABS surfaces were measured in the range between 120 and 125 degrees. The obtained sol–gel materials and produced thin films onto the ABS surfaces were also analyzed in terms of the antibacterial properties. The highly antibacterial properties were observed in the sol–gel solutions and the thin films. 相似文献
80.
Doğuş Özkan Yaman Erarslan Egemen Sulukan Levent Kara M. Alper Yılmaz M. Barış Yağcı 《Tribology Letters》2018,66(4):152
In this study, ~?3.5 µm thick multilayer titanium alumina nitride (TiAlN), alumina titanium nitride (AlTiN), and alumina chromium nitride (AlCrN) coatings were deposited on the H13 steel surface by cathodic arc physical vapor deposition (CAPVD) method. The tribological performance of the coatings was evaluated by a tribometer at boundary lubrication condition. Then, coating surfaces were observed by optical microscope, optical profilometer, and atomic force microscope to evaluate the morphological changes, wear volumes, and tribofilm thickness. Also, scanning electron microscopy (energy dispersive X-ray) and X-ray photoelectron spectrometry analyses were applied to coating surfaces for the tribochemical evolution of the tribofilm. Results showed that AlCrN coating performed the best tribological behavior at boundary lubricated condition, when compared to TiAlN and AlTiN coatings and it can be used as a wear resistant cam tappet coating in internal combustion engines. 相似文献