Accessible Capacity of Secondary Users

A new problem formulation is presented for the Gaussian interference channels (GIFC) with two pairs of users, which are distinguished as primary users and secondary users, respectively. The primary users employ a pair of encoder and decoder that were originally designed to satisfy a given error performance requirement under the assumption that no interference exists from other users. In the scenario when the secondary users attempt to access the same medium, we are interested in the maximum transmission rate (defined as {\em accessible capacity}) at which secondary users can communicate reliably without affecting the error performance requirement by the primary users under the constraint that the primary encoder (not the decoder) is kept unchanged. By modeling the primary encoder as a generalized trellis code (GTC), we are then able to treat the secondary link and the cross link from the secondary transmitter to the primary receiver as finite state channels (FSCs). Based on this, upper and lower bounds on the accessible capacity are derived. The impact of the error performance requirement by the primary users on the accessible capacity is analyzed by using the concept of interference margin. In the case of non-trivial interference margin, the secondary message is split into common and private parts and then encoded by superposition coding, which delivers a lower bound on the accessible capacity. For some special cases, these bounds can be computed numerically by using the BCJR algorithm. Numerical results are also provided to gain insight into the impacts of the GTC and the error performance requirement on the accessible capacity.Comment: 42 pages, 12 figures, 2 tables; Submitted to IEEE Transactions on Information Theory on December, 2010, Revised on November, 201

Mechanism Study of Shale Gas Conversion via Chemical Looping and Heterocatalytic Processes

The shale gas revolution has significantly changed the energy landscape in US. The technical-feasible, energy-effective schemes for shale gas combustion and utilization, especially from remote resources, have attracted increasing interest due to expensive transportation/distribution cost. In this research, for the first time, chemical looping combustion (CLC) of methane with inherent CO2 capture, oxidative coupling of methane (OCM) and dehydro-aromatization (DHA) of ethane are systematically studied as promising alternatives at O2-rich, O2-lean and non-oxidative conditions, respectively. Chemical looping combustion is bridging clean fuel combustion in energy production with inherent CO2 capture. CLC utilized an oxygen carrier (OC) to transfer oxygen to the fuel source in O2-rich conditions. However, the fundamental kinetics of surface structure with oxygen transfer on OC, as well as the reduction activity and coupled selectivity have yet been established. OCM directly converts methane to produce C2 hydrocarbons (C2H6 and C2H4) in O2-lean condition. Perovskite catalysts have shown promising activity and selectivity to C2, but the role of surface acidity of perovskite-type catalyst on OCM kinetics has not been revealed. Non-oxidative ethane DHA provides an economical and environmentally friendly alternative for aromatics and H2 production. Pillared ZSM-5 with hierarchical pores could amplify the mass/heat transfer, which is a promising catalyst for DHA reaction. However, very few studies have been reported to directly associate the thickness of lamellar layers with reactant diffusion, Si/Al ratios, surface acidities as well as catalytic reactivity of ethane-DHA reaction. The research objective is to provide fundamental insights of surface structure-performance relationship of model catalysts for catalytic C2/C3 conversion in three aspects: 1) the oxygen transfer mechanisms in CLC by using surface calcium-doped (1, 2 and 4 wt%) copper oxides based OC; 2) the effect of surface compositions of perovskites on the OCM by using SrTiO3 as a model catalyst is investigated; and 3) a regenerable MoOx/lamellar ZSM-5 based on the strategy of optimizing micro/mesopores structure of zeolite framework, targeting high ethane conversion and aromatic selectivity by optimizing Si/Al ratio, surface acidity and diffusion path. The work offers several economic-viable and technical-feasible solutions for shale gas utilization to value-added products

Mechanism of linear and nonlinear optical effects of chalcopyrite AgGaX2 (X=S, Se, and Te) crystals

[[abstract]]The electronic band structures for AgGaX(2) (X=S, Se, Te) chalcopyrites have been calculated using a pseudopotential total energy method. First-principles calculations of the linear and nonlinear optical properties are presented for these crystals, with the electronic band structures obtained from pseudopotential method as input. The theoretical refractive indices and nonlinear optical coefficients are in good agreement with available experimental values. The origin of the nonlinear optical effects is explained through real-space atom-cutting analysis. The contribution of the GaX(2) group (X=S, Se, Te) for second harmonic generation (SHG) effect is dominant while that of the cation Ag is negligible. In addition, the percentage contribution to the SHG coefficients from the different bonds increase with increase of the bond order.[[notice]]補正完畢[[booktype]]紙本[[booktype]]電子