Cooperative base station for downlink multiple-input-multiple-output (MIMO) system is known as a critical radio technology for worldwide interoperability for microwave access (WiMAX) communications. This study proposes to use zero-forcing beamforming for cooperative base stations in a downlink multicell MIMO system. It is well known that beamforming requires perfect knowledge of channel state information (CSI) at the transmitter, and in practice the perfect CSI may not be available because of channel estimation errors. In this study, using approximate capacity loss analysis the authors are able to analyse the effect of channel estimation errors on system capacity in a cooperative base station system with zero-forcing beamforming. A power allocation policy is proposed to reduce the capacity loss under per base station power constraints. Numerical results show that the approximate capacity loss is very close to the real capacity loss, which can be reduced with the help of the power allocation policy.
Chen, Z.
Tang, H.
Qayyum, R.
Schick, U. M.
Nalls, M. A.
Handsaker, R.
Li, J.
Lu, Y.
Yanek, L. R.
Keating, B.
Meng, Y.
van Rooij, F. J. A.
Okada, Y.
Kubo, M.
Rasmussen-Torvik, L.
Keller, M. F.
Lange, L.
Evans, M.
Bottinger, E. P.
Linderman, M. D.
Ruderfer, D. M.
Hakonarson, H.
Papanicolaou, G.
Zonderman, A. B.
Gottesman, O.
Thomson, C.
Ziv, E.
Singleton, A. B.
Loos, R. J. F.
Sleiman, P. M. A.
Ganesh, S.
McCarroll, S.
Becker, D. M.
Wilson, J. G.
Lettre, G.
Reiner, A. P.
Mei, L.
Xue, Y.
de Leeuw, G.
Holzer-Popp, T.
Guang, J.
Li, Y.
Yang, L.
Xu, H.
Xu, X.
Li, C.
Wang, Y.
Wu, C.
Hou, T.
He, X.
Liu, J.
Dong, J.
Chen, Z.
A novel approach for the joint retrieval of aerosol optical depth (AOD) and aerosol type, using Meteosat Second Generation - Spinning Enhanced Visible and Infrared Imagers (MSG/SEVIRI) observations in two solar channels, is presented. The retrieval is based on a Time Series (TS) technique, which makes use of the two visible bands at 0.6 mu m and 0.8 mu m in three orderly scan times (15 min interval between two scans) to retrieve the AOD over land. Using the radiative transfer equation for plane-parallel atmosphere, two coupled differential equations for the upward and downward fluxes are derived. The boundary conditions for the upward and downward fluxes at the top and at the bottom of the atmosphere are used in these equations to provide an analytic solution for the AOD. To derive these fluxes, the aerosol single scattering albedo (SSA) and asymmetry factor are required to provide a solution. These are provided from a set of six pre-defined aerosol types with the SSA and asymmetry factor. We assume one aerosol type for a grid of 1 degrees x 1 degrees and the surface reflectance changes little between two subsequent observations. A k-ratio approach is used in the inversion to find the best solution of atmospheric properties and surface reflectance. The k-ratio approach assumes that the surface reflectance is little influenced by aerosol scattering at 1.6 mu m and therefore the ratio of surface reflectances in the solar band for two subsequent observations can be well-approximated by the ratio of the reflectances at 1.6 mu m. A further assumption is that the surface reflectance varies only slightly over a period of 30 min. The algorithm makes use of numerical minimisation routines to obtain the optimal solution of atmospheric properties and surface reflectance by selection of the most suitable aerosol type from pre-defined sets. A detailed analysis of the retrieval results shows that it is suitable for AOD retrieval over land from SEVIRI data. Six AErosol RObotic NETwork (AERONET) sites with different surface types are used for detailed analysis and 42 other AERONET sites are used for validation. From 445 collocations representing stable and homogeneous aerosol type, we find that > 75% of the MSG-retrieved AOD at 0.6 and 0.8 mu m values compare favourably with AERONET observed AOD values, within an error envelope of +/- 0.05 +/- 0.15 tau and a high correlation coefficient (R>0.86). The AOD datasets derived using the TS method with SEVIRI data is also compared with collocated AOD products derived from NASA TERRA and AQUA MODIS (The Moderate-resolution Imaging Spectroradiometer) data using the Dark Dense Vegetation (DDV) method and the Deep Blue algorithms. Using the TS method, the AOD could be retrieved for more pixels than with the NASA Deep Blue algorithm. This method is potentially also useful for surface reflectance retrieval using SEVIRI observations. The current paper focuses on AOD retrieval and analysis, and the analysis and validation of reflectance will be given in a following paper.
Chen, Z.
Peng, I-C.
Sun, W.
Su, M.-I
Hsu, P.-H.
Fu, Y.
Zhu, Y.
DeFea, K.
Pan, S.
Tsai, M.-D.
Shyy, J. Y-J.
Endothelial nitric oxide synthase (eNOS) plays a central role in maintaining cardiovascular homeostasis by controlling NO bioavailability. The activity of eNOS in vascular endothelial cells (ECs) largely depends on posttranslational modifications, including phosphorylation. Because the activity of AMP-activated protein kinase (AMPK) in ECs can be increased by multiple cardiovascular events, we studied the phosphorylation of eNOS Ser633 by AMPK and examined its functional relevance in the mouse models. Shear stress, atorvastatin, and adiponectin all increased AMPK Thr172 and eNOS Ser633 phosphorylations, which were abolished if AMPK was pharmacologically inhibited or genetically ablated. The constitutively active form of AMPK or an AMPK agonist caused a sustained Ser633 phosphorylation. Expression of gain-/loss-of-function eNOS mutants revealed that Ser633 phosphorylation is important for NO production. The aorta of AMPK alpha 2(-/-) mice showed attenuated atorvastatin-induced eNOS phosphorylation. Nano-liquid chromatography/tandem mass spectrometry (LC/MS/MS) confirmed that eNOS Ser633 was able to compete with Ser1177 or acetyl-coenzyme A carboxylase Ser79 for AMPK alpha phosphorylation. Nano-LC/MS/MS confirmed that eNOS purified from AICAR-treated ECs was phosphorylated at both Ser633 and Ser1177. Our results indicate that AMPK phosphorylation of eNOS Ser633 is a functional signaling event for NO bioavailability in ECs. (Circ Res. 2009;104:496-505.)