Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time, and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space. While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes, vast areas of the tropics remain understudied. In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity, but it remains among the least known forests in America and is often underrepresented in biodiversity databases. To worsen this situation, human-induced modifications may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge, it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

The problem of achieving high second-order nonlinearities in glasses: The role of electric conductivity in poling of high index glasses

Efficient thermal poling of electronically conducting glass is prevented by the inherent difficulty to record a large electrostatic field within such glasses. To overcome this limitation, a waveguide/substrate configuration has been proposed, in which the glass for poling was deposited as a film of appropriate thickness on a substrate chosen for its higher ionic conductivity. Owing to this configuration, the poling voltage drops entirely across the glass film, allowing high electrostatic field to be recorded in spite of the high electronic conductivity of the glass. The proposed method was demonstrated here in the case of bismuth-zinc-borate glasses, which possess high potential for poling because of their high intrinsic χ(3). A four-fold enhancement of χ(2) compared to bulk glass, from ~ 0.5 to ~ 2 pm/V, is demonstrated. It is also shown that the χ(2) values obtained are the highest sustainable by the glass limited by the onset of nonlinear conductivity. The waveguide/substrate configuration intrinsically allows obtaining perfect overlap of the poling induced second-order nonlinearity with the guiding region of the waveguide. An equivalent RC-circuit model describing the poled glass reveals that the value of the poling-induced second-order nonlinearity is strongly dependent on the ratio β between ionic and electronic conductivity. The most promising glass systems for poling are found to be the ones displaying the highest product χ(3)β. This work is performed on bismuth-zinc-borate heavy metal oxide glasses but the waveguide/substrate configuration proposed here is likely to be equally successful in enhancing the second-order nonlinearity in high χ(3) electronic conducting glasses such as for example telluride and chalcogenide glasses

Depletion Region In Thermally Poled Fused Silica

The depletion-layer width and the recorded electric field in thermally poled fused silica are investigated experimentally as a function of the applied voltage. The depletion-layer width is observed to vary linearly with the poling voltage. The average electric field recorded in the depletion region was found to be (5.3±0.3) x 10 8 V/m for all samples, independently of the poling voltage. © 2000 American Institute of Physics.761824962498Myers, R.A., Mukherjee, N., Brueck, S.R.J., (1991) Opt. Lett., 16, p. 1732Mukherjee, N., Myers, R.A., Brueck, S.R.J., (1994) J. Opt. Soc. Am. B, 11, p. 665Takebe, H., Kazansy, P.G., Russel, P.St.J., Morinaga, K., (1996) Opt. Lett., 21, p. 468Kazansky, P.G., Smith, A.R., Russell, P.St.J., Yang, G.M., Sessler, G.M., (1996) Appl. Phys. Lett., 68, p. 269Pruneri, V., Samoggia, F., Bonfrate, G., Kazansky, P.G., Yang, G.M., (1999) Appl. Phys. Lett., 74, p. 2423Kazansky, P.G., Russel, P.St.J., (1994) Opt. Commun., 110, p. 611Alley, T.G., Brueck, S.R.J., Myers, R.A., (1998) J. Non-Cryst. Solids, 242, p. 165Alley, T.G., Brueck, S.R.J., (1998) Opt. Lett., 23, p. 1170Carlson, D.E., Hang, K.W., Sockdale, G.F., (1972) J. Am. Ceram. Soc., 55, p. 337Krieger, U.K., Lanford, W.A., (1988) J. Non-Cryst. Solids, 102, p. 50Alley, T.G., Brueck, S.R.J., Wiedenbeck, M., (1999) J. Appl. Phys., 86, p. 6634Margulis, W., Laurell, F., (1996) Opt. Lett., 21, p. 1789Lesche, B., Garcia, F.C., Hering, E.N., Margulis, W., Carvalho, I.C.S., Laurell, F., (1997) Phys. Rev. Lett., 78, p. 2172Carlson, D.E., Hang, K.W., Sockdale, G.F., (1974) J. Am. Ceram. Soc., 57, p. 295Cordeiro, C.M.B., Borges, C., Valente, L.C.G., Carvalho, I.C.S., Lesche, B., Margulis, W., (1999) J. Non-Cryst. Solids, 247, p. 183Agarwal, A., Tomozawa, M., (1997) J. Non-Cryst. Solids, 209, p. 166Carlson, D.E., (1974) J. Am. Ceram. Soc., 57, p. 291Lynch, W.T., (1972) J. Appl. Phys., 43, p. 3274Imai, H., Horinouchi, S., Asakuma, N., Fukao, K., Matsuki, D., Hiroshima, H., Sasaki, K., (1998) J. Appl. Phys., 84, p. 5415Xu, W., Wong, D., Fleming, S., (1999) Electron. Lett., 35, p. 922Wong, D., Xu, W., Fleming, S., (1999) WDM Components, , Optical Society of America Trends in Optics and Photonics Series Optical Society of America, Washington, D

Dissolution of embedded gold nanoparticles in sol-gel glass film

Materials with metallic nanoparticles are widely investigated in order to fabricate plasmonic devices, for which the control of the material properties is required. A simple way to control the metal surface plasmon resonance in selected regions of the material is to dissolve the embedded metallic nanoparticles by means of d.c. electric field. Dissolution of embedded silver and copper nanoparticles has been demonstrated recently through poling-assisted bleaching of Ag-doped and Cu-doped nanocomposite glasses, respectively. The next challenge is the dissolution of other metallic nanoparticles, such as gold, which are more difficult to ionize. Here, we demonstrate the dissolution of gold nanoparticles (15 nm in diameter) by d.c. electric field thanks to a novel material design in which the nanoparticles were embedded in a high resistivity sol-gel film on top of a soda-lime-silicate glass substrate with a higher conductivity compared to the film. The role of the film resistivity is made obvious by studying two different film compositions. This result brings about the possibility to use other metallic nanoparticles for tailoring the region of transparency of glasses and opens perspectives for the fabrication of new plasmonic devices