Vapor phase oxidation of p-xylene

The kinetics of the vapor phase oxidation of p-xylene over ferric molybdate catalyst were studied in an isothermal, differential, tubular flow reactor in the temperature range of 360 to 420° C. The major product obtained was p-tolualdehyde with small amounts of maleic anhydride and p-toluic acid. No terephthalic acid or CO₂ were observed. The reaction rate data collected fit the redox model given by Equation 1. The values of activation energies E_x, E_o and frequency factors A_x, A_o obtained are 72, 63 kJ/mol and 0.64, 2.89 m³/kg catalyst s respectively. The reaction mechanism was established by studying the oxidation of p-tolualdehyde, toluic and terephthalic acids. It is concluded that the reaction follows a parallel-consecutive scheme.     

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     

TVRO Antenna Size, Ku Band Versus C Band

At this point in time, with the advent of high powered Ku band direct broadcast satellites (DBSs) and the ever increasing requirement for TV via satellite, it is safe to say that satellite rooftop receiving antennas will soon shrink in size. This will be true for DBS systems operating in the Ku DBS band, since Ku band EIRP has been increased considerably over C band EIRP. It will not necessarily be true for Ku band satellite systems operating in the broadcast satellite service band, where maximum power flux density, and therefore EIRP, is limited.     

Distribution system compensation using a new binary multilevelvoltage source inverter

A new binary multilevel voltage source inverter with separate DC sources is proposed. This n-level voltage source inverter produces a (2 ⁿ⁺¹-1)-steps AC voltage output with n full bridge inverters connected in series. The use of selective harmonic elimination modulation technique to either completely eliminate or minimize harmonics is studied. A closed-loop controller to control the capacitor voltages and adjust the inverter reactive power output is developed. Application of such a compensator for dynamic compensation of 13.8 kV distribution system is examined through transient studies using a PSCAD/EMTDC program. The proposed inverter configuration not only reduces the system complexity and its size, but also improves the harmonic profile significantly