Abaxial Anthocyanin Layer in Leaves of Tropical Rain Forest Plants: Enhancer of Light Capture in Deep Shade

The permanent pigmentation of the leaves of tropical rain forest herbs with anthocyanin has traditionally been viewed as a mechanism for enhancing transpiration by increased heat absorption. We report measurements to ?+0.1?0C on four Indo-mal- esian forest species polymorphic with respect to color. There were no detectable differences in temperature between cyanic and green leaves. In deeply shaded habitats, any temperature difference would arise from black-body infrared radiation which all leaves absorb and to which anthocyanins are transparent. Reflectance spectra of the lower leaf surfaces of these species re- vealed increased reflectance around 650-750 nm for cyanic leaves compared with green leaves of the same species. In all spe- cies anthocyanin was located in a single layer of cells immediately below the photosynthetic tissue. These observations provide empirical evidence that the cyanic layer can improve photosynthetic energy capture by back-scattering additional light through the photosynthetic tissue.

New fuel cells system for portable application with low temperature cofired ceramic (LTCC) technology

Miniature direct methanol fuel cells (DMFCs) are promising micro power sources for portable appliction. Low temperature cofired ceramic (LTCC), a competitive technology for current MEMS based fabrication, provides cost-effective mass manufacturing route for miniature DMFCs. Porous silver tape is adapted as electrodes to replace the traditional porous carbon electrodes due to its compatibility to LTCC processing and other electrochemical advantages. Electrochemical evaluation of silver under DMFCs operating conditions demonstrated that silver is a good electrode for DMFCs because of its reasonable corrosion resistance, low passivating current, and enhanced catalytic effect. Two catalyst loading methods (cofiring and postfiring) of the platinum and ruthenium catalysts are evaluated for LTCC based processing. The electrochemical analysis exhibits that the cofired path out-performs the postfiring path both at the anode and cathode. The reason is the formation of high surface area precipitated whiskers. Self-constraint sintering is utilized to overcome the difficulties of the large difference of coefficient of thermal expansion (CTE) between silver and LTCC (Dupont 951) tape during cofiring. The graphite sheet employed as a cavity fugitive insert guarantees cavity dimension conservation. Finally, performance of the membrane electrode assembly (MEA) with the porous silver electrode in the regular graphite electrode based cell and the integrated cofired cell is measured under passive fuel feeding condition. The MEA of the regular cell performs better as the electrode porosity and temperature increased. The power density of 10 mWcm-2 was obtained at ambient conditions with 1M methanol and it increased to 16 mWcm -2 at 50°C from an open circuit voltage of 0.58V. For the integrated prototype cell, the best performance, which depends on the balance methanol crossover and mass transfer at different temperatures and methanol concentrations, reaches 1.13 mWcm-2 at 2M methanol solution at ambient pressure. The porous media pore structure increases the methanol crossover resistance. As temperature increased to 60°C, the device increases to 2.14 mWcm-2.