Papers by Keyword: CrN

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Authors: Shou Tao Lv, Ze Yang Dai, Jian Liu
Abstract: In cognitive radio networks (CRNs), the secondary users (SUs) need to continuously detect whether the primary users (PUs) occupy the spectrum. In order to improve the spectrum sensing accuracy, a novel reliable cooperative spectrum sensing strategy based on the detection results relayed twice from the secondary relays (SRs) to the secondary source (SS), referred to as CSS-DRT, is proposed in this paper. In this scheme, the spectrum sensing slot is divided into four equal sub-slots. In the first and third sub-slots, the SS and SRs detect the PU by themselves. Then, in the second sub-slot, if the SRs that detect the PU during the first sub-slot are more than or equal to a prespecified quantity, the corresponding SRs will send their flag signals (FSs) to the SS while the others keep quiet, where the FS is narrowband and indicates that the PU is present. Otherwise, if the SRs that detect the PU during the first sub-slot are less than the prespecified quantity, all the SRs will keep quiet in the second sub-slot. Meanwhile, the SS detects the PU based on the received signals from the PU and SRs. And, the SS uses the same method as employed in the second sub-slot to detect the PU in the last sub-slot wherein the SRs send their FSs based on their detections made during the third sub-slot. Finally, an ultimate decision is made by the OR ruler based on the SS detection results obtained during the spectrum sensing slot. Besides, we derive the closed-form expressions of the false alarm and detection probabilities for the proposed CSS-DRT scheme. In the end, simulation and numerical results show that our proposed scheme can achieve better performance than the non-cooperative method and an existing cooperative spectrum sensing method.
Authors: Adem Demir, Zafer Tatli, F. Caliskan, A.O. Kurt
Abstract: In this study, α-Si3N4 powder was produced by carbothermal reduction and nitridation (CRN) of quartz from Can-Canakkale. Carbon with a specific surface area of 110 m2g−1 and quartz powders were mixed then the powder mix was placed in an alumina tube furnace and reacted in between 1300-1500°C for 4 hours under nitrogen flow. The quartz powder was carbothermally reduced and nitrided to form silicon nitride powders. XRD results showed that the reaction product was mainly α-Si3N4 and contained some β-Si3N4 and residual quartz. In order to reduce amount of unreacted quartz, the raw materials mixture was grinded either with carbon black or with no carbon. After CRN reactions of separate grinded quartz powders with carbon, residual quartz was disappeared, reaction temperature was decreased and α-Si3N4 rate was increased. Hence, a better mixing of carbon and fine silica enhanced the α phase formation. SEM images and XRD pattern showed that sub micron particles (0.6–0.87m), high α-phase content Si3N4 powders can be produced at 1450°C for 4 h in flowing nitrogen gas during the CRN process.
Authors: A.M. Peters, John J. Moore, Ivar Reimanis, Brajendra Mishra, Roland Weiss
Authors: Xiao Mei Yuan, Shi Liang Yang, Teng Li, Guan Gan Zhang
Abstract: The CrN films and CrBN films were successfully deposited by medium frequency magnetron sputtering in a mixture gas of nitrogen and argon. X-ray diffraction analysis shows that the CrN have preferential orientation of (111), (200) and (222). And the patterns of CrBN films is similar to that of CrN. The CrN films have smooth surfaces with dense and continuous microstructure and the CrBN films have glassy packed structure without columnar grains. The hardness of CrBN films were remarkable improved because of B attending.
Authors: Fritz Klocke, Olaf Dambon, Kyriakos Georgiadis
Abstract: The complexity of optical components increases steadily in recent years, while their dimension de-crease. This situation makes the production of state of the art optical components by grinding and polishing very difficult and expensive. However, the technology of precision glass molding can be used to replace these traditional manufacturing methods by a single step replicative process. To achieve economies of scale with precision glass molding, a long molding tool lifetime is necessary. This can only be realized by applying protective PVD coatings on the molding tool surfaces. Well known thin hard coatings like TiAlN or CrN, as well as noble metal coatings are possible candidates. However, practical testing of carious coating-glass combinations in precision glass molding machines is not feasible due to long process times that make such testing very expensive and time consuming. In this work, these coatings are compared with each other and in combination with various glass types by performing oxidation and contact angle tests. The results of these tests are compared to the results of practical tests, in order to determine to which extent such model tests can replace practical testing.
Authors: Chang Wei Zou, Jun Zhang, Wei Xie, Le Xi Shao
Abstract: CrN films with deposition rates of 30-190 nm/min were deposited on Si (111) substrates by middle-frequency magnetron sputtering methods. XRD, SEM, EDS and microhardness tests were used to investigate the effects of bias voltages and total gas pressure on the structure and mechanical properties of the resulting CrN films. With the increasing of bias voltages and total gas pressure, the preferential diffraction orientation changed from (111) to (200). A smooth surface was observed by the SEM experiments and the thickness of the film was about 2 µm. The deposition rates and Cr content of resulting films were highly influenced by the magnitude of the bias voltage and total gas pressure. RMS and Ra properties of the CrN films increased when increased total gas pressure or decreased bias voltage. CrN films produced under optimal conditions have an almost 1:1 Cr:N ratio as determined by EDS. The hardness of the CrN film increased from 2200 to 2700 HV when increased the bias voltages from 0 to 200 V.
Authors: Marek Betiuk
Abstract: The formation of anti-wear coatings on the inner surface of steel cylinders and pipes presents a difficult process-related problem for PA PVD methods. This problem is associated with a strictly limited geometry of the reaction space and dimensions of plasma sputtering-sources. Among the main factors behind physical and chemical phenomena occurring the reaction space, formed within a low-temperature plasma and at its boundaries with a solid object, there are type, concentration, unobstructed path for reacting substances, as well as values and geometry of electrical/magnetic/thermal fields [1-5]. In the research on the plasma-based technology in confined space, the lowest possible distance between the surface being modified and the source of ions of metallic and gaseous elements is taken into account.
Authors: Edgar S. Ashiuchi, Volker F. Steier, Cosme R.M. Silva, Tales D. Barbosa, Tiago F.O. Melo, Jsé A. Araújo
Abstract: The endurance of components made of aluminum and aluminum alloys is often limited by their low yield strength and by their low wear resistance. The aim of this paper is to investigate the effect of different methods that can improve wear resistance of aluminum alloys. As a first approach, a highly wear resistant chromium nitrite layer was deposited by plasma vapor deposition on the surface of the aluminum alloy AA 6101-T4. In the second method, an ultra-deep cryogenic treatment was selected. Both methods have been previously used to improve the wear resistance of other harder substrate materials, like tool steel. To investigate the impact of the two methods on the wear resistance of such alloy, micro abrasive wear tests were carried out and an analysis based on the Archard’s law was considered. The results showed a decrease of the wear rate by 29% and 26% for the coated and for the cryogenically treated specimens, respectively, when compared to the as received material. The work also investigated the performance of three different methods (Allsopp, Double Intercept and Polynomial AT) usually considered to calculate the wear rate of coated samples. The three methods presented similar measures of wear rate for the substrate and for the coating
Authors: Adem Demir, F. Caliskan
Abstract: In this study, the production of β-Si6-zAlzOzN8-z (z =3) powders by the carbothermal reduction and nitridation of kaolin (Al2O3.2SiO2.2H2O) of Turkish origin (Can-Canakkale) was carried out with different processing parameters. It was found that the morphology of the produced SiAlON powder was mixture of irregular and whisker like grains. Therefore this morphology is suitable for liquid metal infiltration since the powders are already high porous. The kaolin powder containing stoichiometric rate carbon black and 30 % charcoal were pressed and reacted under nitrogen flow (2 lt/min) between 1400-1475°C for 4 h. After a carbothermal reduction and nitridation (CRN) process, porous β- SiAlON ceramic was produced from natural kaolin. Residual carbon and charcoal in the produced ß-SiAlON ceramic were fired at 1000°C giving extra porosity. The porous ß-SiAlON ceramics were sintered under N2 atmosphere at 1550°C for 2 h to make preform for infiltration process. SEM image analyses were carried out to determine preform and pore morphology and XRD analysis were performed for phase transformation.
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