Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers

In antiferromagnetically coupled superlattices grown on (001) faces of cubic substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or Fe/Cr, the magnetic states evolve under competing influence of bilinear and biquadratic exchange interactions, surface-enhanced four-fold in-plane anisotropy, and specific finite-size effects. Using phenomenological (micromagnetic) theory, a comprehensive survey of the magnetic states and reorientation transitions has been carried out for multilayer systems with even number of ferromagnetic sub-layers and magnetizations in the plane. In two-layer systems (N=2) the phase diagrams in dependence on components of the applied field in the plane include ``swallow-tail'' type regions of (metastable) multistate co-existence and a number of continuous and discontinuous reorientation transitions induced by radial and transversal components of the applied field. In multilayers (N \ge 4) noncollinear states are spatially inhomogeneous with magnetization varying across the multilayer stack. For weak four-fold anisotropy the magnetic states under influence of an applied field evolve by a complex continuous reorientation into the saturated state. At higher anisotropy they transform into various inhomogeneous and asymmetric structures. The discontinuous transitions between the magnetic states in these two-layers and multilayers are characterized by broad ranges of multi-phase coexistence of the (metastable) states and give rise to specific transitional domain structures.Comment: Manuscript 34 pages, 14 figures; submitted for publicatio

One sixth of Amazonian tree diversity is dependent on river floodplains

Amazonia's floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region's floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon's tree diversity and its function.Naturali

Evaluation Methodologies For Cooperative Spectrum Sensing: Towards A Real Time Performance

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The constant search for new spectrum sensing methodologies creates a demand for tools that enable a stronger focus on solution prototyping development. Such tools, generally based on a Software Defined Radio (SDR) platform, need to be flexible in terms of programming as well as presenting compatibility with the various SDR available on the market. In this contribution we present a comparison between real time and non-real time simulation methodologies for implementing some cooperative spectrum sensing algorithms. Tools and their results are compared aiming at demonstrating pros and cons of the evaluation methodologies. There is a clear tradeoff among development cost, simulation flexibility and execution time, specially considering the choice of prototyping methodology and the target application. © 2013 IEEE.Microwave Theory and Techniques Society (IEEE MTT-S),Sociedade Brasileira de Micro-Ondas e Optoeletrenica (SBMO),CNPq,CAPES,FAPERJConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Akyildiz, I.F., Lo, B.F., Balakrishnan, R., Cooperative spectrum sensing in cognitive radio networks: A survey (2011) Phys.Commun., 4 (1), pp. 40-62. , MarArslan, H., (2007) Cognitive Radio, Software Defined Radio, and Adaptative Wireless Systems, , SpringerZeng, Y., Liang, Y.C., Maximum-minimum eingenvalue detection for cognitive radio (2007) International Symposium on Personal, , Indoor and Mobile Radio CommunicationsZeng, Y., Koh, C.L., Liang, Y.C., Maximum eigenvalue detection: Theory and application (2008) International Conference on CommunicationsNadler, B., Penna, F., Garello, R., Performance of eigenvalue-based signal detectors with known and unknown noise level (2011) IEEE International Conference on Communications, pp. 1-5Lim, T.J., Zhang, R., Liang, Y.C., Zeng, Y., GLRT-based spectrum sensing for cognitive radio (2008) IEEE GLOBECOMGuimaraes, D.A., Silva, C.R.N., Souza, R.A.A., Cooperative spectrum sensing using eigenvalue fusion for OFDMA and other wideband signals (2013) Journal of Sensor and Actuator Networks, 2, pp. 1-24Lin, F., Hu, Z., Qiu, R., Wicks, M.C., A combination of quickest detection with oracle approximating shrinkage estimation (2012) Militwy Communications ConferenceHou, S., Qiu, R.C., Spectrum sensing for cognitive radio using kernel-based learning (2011) Proceedings of CoRRKortun, A., Ratnarajah, T., Sellathurai, M., Zhong, C., Papadias, C.B.A., On the performance of eigenvalue-based cooperative spectrum sensing for cognitive radio (2010) IEEE Journal of Selected Topics in Signal Processing, 5, pp. 49-55Chen, D., Li, J., Ma, J., Spectrum sensing for cognitive radio under noise uncertainty (2008) International Conference on Wireless Communications, Networking and Mobile ComputingZayen, B., Hayar, A., Cooperative spectrum sensing technique based on sub space analysis for cognitive radio networks (2009) Cognitive Systems with Interactive Sensors ConferenceBuccardo, A., (2010) A Signal Detector for Cognitive Radio System, , Master's thesis, University of Gavlehttp://gnuradio.org/redmine/projects/gnuradio/wiki, GNU radio websiteAlvarez, P.I.P.A., (2011) Experimental Study on Spectrum Sensing for Cognitive Radio Networks, , Master's thesis, Universidade Tecnica de LisboaZhang, P., Qiu, R., Guo, N., Demonstration of spectrum sensing with blindly learned feature (2011) IEEE Communications Letters, 15, pp. 548-550Teshome, A.T., (2010) FPGA Based Eigenvalue Detection Algorithm for Cognitive Radio, , Master's thesis, University of GavleZayen, B., Hayar, A., Dimension estimation-based spectrum sensing for cognitive radio (2012) Journal on Wireless Communications and NetworkingWei, L., Tirkkonen, O., Analysis of scaled largest eigenvalue based detection for spectrum sensing (2011) IEEE International Conference on Communicationshttp://www.mathworks.comhttp://www.python.org, Python programming language-official websiteJoshi, R., (2006) Introduction to Computers, , G.P.House, Ed.Isha Bookshttp://www.nsnam.org, Network simulator 3http://jist.ece.comell.eduhttp://www.opnet.com, Optimized network engineering tool (OPNET)http://www.scipy.orgBudihal, R., Jamadagni, H.S., Hybrid approach to cognitive radio test bed (2009) International Conference on Ultra Modern Telecommunications & WorkshopsHaykin, S., (2009) Communication Systems, , WileyMitola, J., Software radios Survey, critical evaluation and future directions (1993) Aerospace and Electronic Systems Magazine, 8, pp. 25-36http://www.ettus.coml, Universal software radio peripheral (USRP)Tan, K., Zhang, J., Fang, J., Liu, Y., Ye, H., Wang, S., Zhang, Y., Voelker, G., SORA: High performance software radio using general purpose multi-core processors (2011) Communications of the Association for Computing Machinery, 54, pp. 99-107http://warp.rice.edu/, W.O.-A.R.Platform.Wireless open-access research platformDabcevic, K., (2011) Evaluation of Software Defined Radio Platform with Respect to Implementation of 802.15.4 ZigBee, , Master's thesis, Malardalen UniversityGiordano, L.G., Reggiani, L., (2013) Vehicular Technologies-Deployment and Applicationshttp://www.gppcom.ct.ufrn.br, Grupo de pesquisa em prototipagem rapida de solU(;6es para comunicaao-GppComhttp://www.py2exe.orgStevenson, C.R., Cordeiro, C., Sofer, E., Chouinard, G., (2005) Functional Requirements for the 802.22 WRAM Standard, , IEEE, Tech.Re

Uncertainty evaluation by gamma transmission measurements and CFD model comparison in a FCC cold pilot unit

The solid flow in air-catalyst in circulating fluidized bed was simulated with CFD model to obtain axial and radial distribution. Therefore, project parameters were confirmed and steady state operation condition was improved. Solid holds up axial end radial profiles simulation and comparison with gamma transmission measurements are in a good agreement. The transmission signal from an 241Am radioactive source was evaluated in NaI(Tl) detector coupled to multichannel analyzer. This non intrusive measuring set up is installed at riser of a cold pilot unit to determine parameters of FCC catalyst flow at several concentrations. Mass flow rate calculated by combining solid hold up and solid phase velocity measurements was compared with catalyst inlet measured at down-comer. Evaluation in each measured parameter shows that a relative combined uncertainty of 6% in a 95% interval was estimated. Uncertainty analysis took into account a significant correlation in scan riser transmission measurements. An Eulerian approach of CFD model incorporating the kinetic theory of granular flow was adopted to describe the gas–solid two-phase flows in a multizone circulating reactor. Instantaneous and local gas-particle velocity, void fraction and turbulent parameters were obtained and results are shown in 2 D and 3D graphics

Uncertainty evaluation by gamma transmission measurements and CFD model comparison in a FCC cold pilot unit

The solid flow in air-catalyst in circulating fluidized bed was simulated with CFD model to obtain axial and radial distribution. Therefore, project parameters were confirmed and steady state operation condition was improved. Solid holds up axial end radial profiles simulation and comparison with gamma transmission measurements are in a good agreement. The transmission signal from an 241Am radioactive source was evaluated in NaI(Tl) detector coupled to multichannel analyzer. This non intrusive measuring set up is installed at riser of a cold pilot unit to determine parameters of FCC catalyst flow at several concentrations. Mass flow rate calculated by combining solid hold up and solid phase velocity measurements was compared with catalyst inlet measured at down-comer. Evaluation in each measured parameter shows that a relative combined uncertainty of 6% in a 95% interval was estimated. Uncertainty analysis took into account a significant correlation in scan riser transmission measurements. An Eulerian approach of CFD model incorporating the kinetic theory of granular flow was adopted to describe the gas–solid two-phase flows in a multizone circulating reactor. Instantaneous and local gas-particle velocity, void fraction and turbulent parameters were obtained and results are shown in 2 D and 3D graphics