Effect of pH on the detailed chemical nature and metal-carbonate species in as synthesized zirconia alumina composites

Zirconia was deposition precipitated on γ-alumina in pH range 7-10 from zirconium oxy-nitrate and soda ash. Zirconium formed its hydroxycarbonate as deduced from ICP-EOS, CHN, and TGA-MS. Higher pH favored formation of carbonate species of zirconium over its hydroxide. TGA-MS indicated formation of three different types of carbonate species. FTIR results corroborated this. Monodentate metal carbonate was observed irrespective of pH of preparation. In addition, bridged bidentate species formed at pH ≤ 8 which changed to chelating bidentate at pH > 8. XRD indicated that all the samples formed tetragonal-zirconia upon calcination irrespective of pH of preparation. Higher pH resulted in smaller crystallites of t-ZrO₂. Changes in chemical moiety with pH reflected on acidity and the deactivation rate for 2-methyl-3-butyn-2-ol which decreased by two orders of magnitude in samples prepared at higher pH. Surface area and pore volume benefited from deposition precipitation. SEM-EDAX showed reasonable distribution of zirconia over γ-Al₂O₃.     

Strontium Zirconate and Strontium Titanate Ceramics for High-Voltage Applications: Synthesis, Processing, and Dielectric Properties

The synthesis, processing, and electrical properties of SrZrO₃ and SrTiO₃ materials have been examined. Phase-pure powders of SrZrO₃ and SrTiO₃ materials were synthesized using the Pechini method. Powder processing routes that used water and 2-propanol as carrier fluids were developed to achieve high green densities, which resulted in sintered densities of >99% of the theoretical density. The relative permittivity and average breakdown strength for carefully processed SrZrO₃ were 60 and 40 V/μm; the corresponding values for SrTiO₃ were 400 and 35 V/μm. The higher breakdown strengths suggest that these materials can be used in high-voltage capacitor applications.     

60MW空内冷汽轮发电机的试制

重点介绍了工厂现有设备条件和技术力量比较薄弱的情况下。通过消化吸收从瑞士ＡＢＢ公司引进的技术、进行认真的技术准备和开展技术攻关，完成首台６０ＭＷ空内冷汽轮发电机考核样机试制的主要经验。     

Dynamic Spectrum Access with QoS and Interference Temperature Constraints

Spectrum is one of the most precious radio resources. With the increasing demand for wireless communication, efficiently using the spectrum resource has become an essential issue. With the Federal Communications Commission's (FCC) spectrum policy reform, secondary spectrum sharing has gained increasing interest. One of the policy reforms introduces the concept of an interference temperature - the total allowable interference in a spectral band. This means that secondary users can use different transmit powers as long as the sum of these power is less than the interference threshold. In this paper, we study two problems in secondary spectrum access with minimum signal to interference noise ratio (quality of service (QoS)) guarantee under an interference temperature constraint. First, when all the secondary links can be supported, a nonlinear optimization problem with the objective to maximize the total transmitting rate of the secondary users is formulated. The nonlinear optimization is solved efficiently using geometric programming techniques. The second problem we address is, when not all the secondary links can be supported with their QoS requirement, it is desirable to have the spectrum access opportunity proportional to the user priority if they belong to different priority classes. In this context, we formulate an operator problem which takes the priority issues into consideration. To solve this problem, first, we propose a centralized reduced complexity search algorithm to find the optimal solution. Then, in order to solve this problem distributively, we define a secondary spectrum sharing potential game. The Nash equilibria of this potential game are investigated. The efficiency of the Nash equilibria solutions are characterized. It is shown that distributed sequential play and an algorithm based on stochastic learning attain the equilibrium solutions. Finally, the performances are examined through simulations     

Corrigendum Static Frequency Assignment in Cellular Networks

Abstract. No abstract.     

Effect of Dopants and Sintering Method on the Properties of Ceria-Based Electrolytes for IT-SOFCs Applications

Doped and co-doped ceria ceramics are used as electrolyte materials in solid oxide fuel cells. In this work, ceria-based oxides, Ce_0.90Gd_0.06Y_0.02M_0.02O_2?δ (M?=?Ca, Fe, La, and Sr) were prepared by conventional as well as microwave processing from the precursors prepared by the mixed oxide method. The consolidated calcined powders in pellet form were sintered in microwave energy at 1400°C for 20 min and in an electric furnace of IR radiation at 1400°C for 6 h. The x-ray diffraction analysis confirmed that all the compositions were crystallized into a cubic fluorite structure. Surface morphology of the sintered products was studied using scanning electron microscopy and the microhardness was investigated using the Vickers hardness test. The comparative results analysis shows that the microwave-sintered samples have uniform grain growth, higher density and higher microhardness than the corresponding conventionally sintered products. The microwave-sintered sample of composition Ce_0.90Gd_0.06Y_0.02Sr_0.02O_2?δ was found to have the highest microhardness among the four compositions due to its high density and smallest grain size.     

The state of the art in intelligent real-time FMS control: a comprehensive survey

Flexible manufacturing systems (FMS) have been developed with the hope that they would provide a means to tackle a threefold challenge — better quality, lower cost and shorter lead times — by integrating machine tools, robots, material handling and storage systems, and computers. Control of the integrated system presented a new set of problems as well as challenges, which have been receiving considerable attention from the academic community as well as from industrial system users. Intelligent control, which involves using computers to assist in decision making at various stages of the control process, has been advocated by many researchers as a possible avenue to reach a solution to these problems. This paper provides a review of the state of the art in intelligent control of FMS, in an attempt to supplement earlier general reviews via a more focused perspective. The principles of several techniques, namely simulation, knowledge based, example based, petri nets, and hybrid approaches are briefly introduced, and publications are reviewed, followed by discussions ontheir potential. Suggestions for further research and development are also enumerated.     

Modeling the effective properties and thermomechanical behavior of SMA‐SMP multifunctional composite laminates

The research work presents the modeling of effective properties and thermo‐mechanical behavior of shape memory fiber (SMF) and shape memory polymer (SMP) composite laminates using micromechanical approaches based on the method of mixtures (MOM) and method of cells (MOC). The fiber is made of a nickel‐titanium (Ni‐Ti) shape memory alloy (SMA), while the matrix consists of a shape memory thermoset epoxy polymer (SMP). The use of an SMP matrix provides large strain compatibility with the SMA fiber, while being active at high temperatures without losing its elastic properties. Additionally, the SMP matrix is also able to produce similar pseudoelastic and shape memory effects, which are noticed in SMAs. In the analysis, a two step homogenization scheme is followed. In the first step the effective properties of each layer are determined via a micromechanics approach with iso‐strain conditions. In the second step the effective properties of the SMF‐SMP composite are computed making a thin plate theory assumption, which takes into account the transverse shear deformations. The possible elastic couplings for SMF‐SMP laminates are discussed, and the laminate force and moment resultants are computed for various laminate configurations. The analysis takes into account the effects of phase transformations and the resulting change in the fiber–matrix modulus. The results have been compared by considering different fiber volume fractions, temperatures, fiber orientations, and lamina stacking sequences. The results show that adaptive SMA‐SMP composites laminates can be developed that provide shape controllability via tunable laminate stiffnesses leading to optimal response. Furthermore, the work presents the necessary framework for a reliable and efficient analysis of SMA‐SMP laminates for practical applications. The theory can be directly used in established plate and shell formulations of finite element analysis. Finally, the variations in force and moment resultants with respect to fiber orientations and stacking sequences are presented, which are useful to study the bending and buckling characteristics of active composites for shape control of adaptive structures. The work concludes that efficient adaptive laminate development for high performance composite applications, exhibiting large shape adaptivity, high stresses, and increased stiffness, are feasible as compared to SMA composites without active matrix. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers