Measurements of CO2 exchange over a woodland savanna (Cerrado Sensu stricto) in southeast Brasil

The technique of eddy correlation was used to measure the net ecosystem exchange over a woodland savanna (Cerrado Sensu stricto) site (Gleba Pé de Gigante) in southeast Brazil. The data set included measurements of climatological variables and soil respiration using static soil chambers. Data were collected during the period from 10 October 2000 to 30 March 2002. Measured soil respiration showed average values of 4.8 molCO2 m-2s-1 year round. Its seasonal differences varied from 2 to 8 molCO2 m-2s-1 (Q10 = 4.9) during the dry (April to August) and wet season, respectively, and was concurrent with soil temperature and moisture variability. The net ecosystem CO2 flux (NEE) variability is controlled by solar radiation, temperature and air humidity on diel course. Seasonally, soil moisture plays a strong role by inducing litterfall, reducing canopy photosynthetic activity and soil respiration. The net sign of NEE is negative (sink) in the wet season and early dry season, with rates around -25 kgC ha-1day-1, and values as low as 40 kgC ha-1day-1. NEE was positive (source) during most of the dry season, and changed into negative at the onset of rainy season. At critical times of soil moisture stress during the late dry season, the ecosystem experienced photosynthesis during daytime, although the net sign is positive (emission). Concurrent with dry season, the values appeared progressively positive from 5 to as much as 50 kgC ha-1day-1. The annual NEE sum appeared to be nearly in balance, or more exactly a small sink, equal to 0.1 0.3 tC ha-1yr-1, which we regard possibly as a realistic one, giving the constraining conditions imposed to the turbulent flux calculation, and favourable hypothesis of succession stages, climatic variability and CO2 fertilization

Demonstration Of 26 Db On-off Gain Of A Two-pump Fiber Optical Parametric Amplifier

Two-pump fiber optical parametric amplifier (FOPA) having ≅26 dB on-off gain with ±1.5 dB ripple over 30 nm bandwidth was demonstrated. An on-off gain >0 dB was obtained over 50 nm. By removing Fabry-Perot filter the noise was also amplified and depleted the pumps when pump power was greater that 120 mW.70636637Hansryd, J., Andrekson, P., Broadband CW pumped fiber optical parametric amplifier with 49 dB gain and wavelength conversion efficiency (2000) PD3, Optical Fiber Communications Conference, , Baltimore, USAMarhic, M.E., Park, Y., Yang, F.S., Kazovsky, L.G., Broadband fiber-optical parametric amplifiers and wavelength converters with low-ripple Chebyshev gain spectra (1996) Opt. Lett., 21, pp. 1354-1356Yang, F.S., Ho, M.C., Marhic, M.E., Kazovsky, L.G., Demonstration of two-pump fibre optical parametric amplification (1997) Electron. Lett., 33, pp. 1812-1813Boggio, J.M.C., Tenenbaum, S., Fragnito, H.L., Four wave mixing induced changes in the noise spectrum in an optical fiber (2001) WDD24, Optical Fiber Communications Conference, , Anaheim, US

Experimental Investigation On Data And Control Planes Of The Omega Test Bed

We describe the OMEGA test bed, an all-optical five-node IP over WDM re-configurable two-layer network. Its data plane is evaluated in physical impairments experiments, based on measurements of BER, eye-diagram and OSNR, with emphasis on the influence of number of hops, number of channels, amplifier location (before or after the node), and channel power fluctuation after routing over different length paths. The OMEGA control plane provides protection and restoration functionalities with wavelength routing. Its operation is demonstrated in two transmission experiments: Gb-Ethernet and IP over WDM with protection at the optical layer.5358Wei, J.Y., IP over WDM network traffic engineering approaches (2002) Proc. OFC 2002, pp. 102-104. , MarGrammel, X.S., Coltro, C., The Introduction of a Control Plane in Deployed Networks ECOC 2001, , paper 501Ali, M., (2001) Transmission-efficient Design and Management of Wavelength-routed Optical Networks, 1st Ed., , Kluwer Adademic Publishers, MassachusettsMoral, A.R., Bonefant, P., Baroni, S., Wu, R., Optical Data Networking: Protocols, Technologies, and Architectures for Next Generation Optical Transport Networks and Optical Internetworks (2000) IEEE J. of Lightwave Techno., 18 (12), pp. 1855-1870Kazovsky, L.G., Shrikhande, K., White, I.M., Rogge, M., Wonglumson, D., Optical Metropolitan Area Networks (2001) Proc. OFC'2001, , paper WU1Rocha, M.L., Rossi, S.M., Barros, M.R.X., Pezzolo, L., Rosolem, J.B., Oliveira, M.F., Paradisi, A., Experimental performance evaluation of five-node IP over WDM laboratory test-bed (2002) IEE Electronics Letters, 38 (23), pp. 1460-1462Rocha, M.L., Rossi, S.M., Barros, M.R.X., Pezzolo, L., Rosolem, J.B., Oliveira, M.F., Paradisi, A., Gavler, A., Amplifier placement in a metro-scaled wavelength-routed network (2003) IEE Electronics Letters, 39 (3), pp. 302-304. , FebDesurvire, E., (1994) Erbium-doped Fibre Amplifiers - Principles and Applications, pp. 140-153. , John Wiley & SonsAbbade, M.L.F., Paradisi, A., Rossi, S.M., De Barros, M.R.X., Rocha, M.L., Impact of linear transmission impairments on a metropolitan optical network scale (2001) 19 Simpósio Brasileiro de Telecomunicações, SBrT, , Brazil, SepRossi, S.M., Rocha, M.L., Barros, M.R.X., Rosolem, J.B., Paradisi, A., Optical WDM networks with distributed IP-centric control plane Proceedings of X Brazilian Microwave and Optoelectronics Symposium, , SBMO'2002, paper 170, Recife. BrazilRocha, M.L., Rossi, S.M., Barros, M.R.X., Pezzolo, L., Rosolem, J.B., Oliveira, M.F., Paradisi, A., Experimental performance evaluation of five-node IP over WDM laboratory test-bed (2002) IEE Electronics Letters, 38 (23), pp. 1460-1462. , NovRossi, S.M., Padua, F.J.L., Barros, M.R.X., Rocha, M.L., Rosolem, J.B., Moschim, E., Paradisi, A., Impact of physicallayer impairments on optical network performance Proceedings of International Telecommunications Symnposium, , IEEE ITS'2002, paper 148, Natal, Brazi

Nitrate role in basic cation leaching under no-till

Especially under no-tillage, subsuface soil acidity has been a problem, because it depends on base leaching, which has been associated with the presence of low molecular weigth organic acids and companion anions. The objective of this study was to evaluate exchangeable base cation leaching as affected by surface liming along with annual urea side-dressing of maize and upland rice. Treatments consisted of four lime rates (0, 1500, 3000, and 6000 kg ha-1) combined with four nitrogen rates (0, 50, 100, and 150 kg ha-1) applied to maize (Zea mays) and upland rice (Oryza sativa), in two consecutive years. Maize was planted in December, three months after liming. In September of the following year, pearl millet (Pennisetum glaucum) was planted without fertilization and desiccated 86 days after plant emergence. Afterwards, upland rice was grown. Immediately after upland rice harvest, 18 months after surface liming, pH and N-NO3-, N-NH4+, K, Ca, and Mg levels were evaluated in soil samples taken from the layers 0-5, 5-10, 10-20 and 20-40 cm. Higher maize yields were obtained at higher N rates and 3000 kg ha-1 lime. Better results for upland rice and pearl millet yields were also obtained with this lime rate, irrespective of N levels. The vertical mobility of K, Ca and Mg was higher in the soil profiles with N fertilization. Surface liming increased pH in the upper soil layers causing intense nitrate production, which was leached along with the base cations