Sum Rates, Rate Allocation, and User Scheduling for Multi-User MIMO Vector Perturbation Precoding

This paper considers the multiuser multiple-input multiple-output (MIMO) broadcast channel. We consider the case where the multiple transmit antennas are used to deliver independent data streams to multiple users via vector perturbation. We derive expressions for the sum rate in terms of the average energy of the precoded vector, and use this to derive a high signal-to-noise ratio (SNR) closed-form upper bound, which we show to be tight via simulation. We also propose a modification to vector perturbation where different rates can be allocated to different users. We conclude that for vector perturbation precoding most of the sum rate gains can be achieved by reducing the rate allocation problem to the user selection problem. We then propose a low-complexity user selection algorithm that attempts to maximize the high-SNR sum rate upper bound. Simulations show that the algorithm outperforms other user selection algorithms of similar complexity.Comment: 27 pages with 6 figures and 2 tables. Accepted for publication in IEEE Trans. Wireless Comm

The Role of Starburst-AGN composites in Luminous Infrared Galaxy Mergers: Insights from the New Optical Classification Scheme

We investigate the fraction of starbursts, starburst-AGN composites, Seyferts, and LINERs as a function of infrared luminosity (L_IR) and merger progress for ~500 infrared-selected galaxies. Using the new optical classifications afforded by the extremely large data set of the Sloan Digital Sky Survey, we find that the fraction of LINERs in IR-selected samples is rare (< 5%) compared with other spectral types. The lack of strong infrared emission in LINERs is consistent with recent optical studies suggesting that LINERs contain AGN with lower accretion rates than in Seyfert galaxies. Most previously classified infrared-luminous LINERs are classified as starburst-AGN composite galaxies in the new scheme. Starburst-AGN composites appear to "bridge" the spectral evolution from starburst to AGN in ULIRGs. The relative strength of the AGN versus starburst activity shows a significant increase at high infrared luminosity. In ULIRGs (L_IR >10^12 L_odot), starburst-AGN composite galaxies dominate at early--intermediate stages of the merger, and AGN galaxies dominate during the final merger stages. Our results are consistent with models for IR-luminous galaxies where mergers of gas-rich spirals fuel both starburst and AGN, and where the AGN becomes increasingly dominant during the final merger stages of the most luminous infrared objects.Comment: 30 pages, 19 figures, 10 tables, ApJ accepte

On analysis of chemical reactions coupled gas flows in SOFCs

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Solid oxide fuel cell (SOFC) is among others one of the most promising technologies for electricity energy generation. A recent new trends is to reduce its operating temperature from 1000oC to 800oC by employing a thick porous layer as the supporting structure. Various transport processes occurred are strongly affected by catalytic chemical/electrochemical reactions appearing in nano- or/and microstructured and multi-functional porous electrodes. It is particularly true if methane is used as the fuel, and internal reforming reactions within the microstructured porous anodes enable the conversion of the methane into H2 and CO. To deeply understand the chemical reaction coupled gas flow and heat transfer in the microstructured porous anode, a fully three-dimensional numerical calculation procedure (CFD) is developed and applied. The species mass/heat generation and consumption related to the internal reforming reactions and the electrochemical reaction have been identified and employed in the study. The variable thermalphysical properties and transport parameters of the fuel gas mixture have also been taken into account. Furthermore, the heat transfer due to the fuel gas flow is implemented into the energy balance based on multi-component diffusion models. Finally, various issues connecting to the micro models of the surface reactions are discussed and reviewed.Thi study is supported by the Swedish Research Council (VR) and the National Natural Science Foundation of China (NSFC-50706004)