Natural Calcium‐Based Residues for Carbon Dioxide Capture in a Bubbling Fluidized‐Bed Reactor

Used clamshells (Paphia undulata), as a precursor of calcium oxide (CaO) sorbents, were employed for carbon dioxide (CO₂) adsorption in a bubbling fluidized‐bed reactor. To find the optimal calcination conditions, a 2^k experimental design was used to vary the ground clamshell particle size, heating rate, and calcination time at 950 °C under a nitrogen atmosphere. The heating rate was the most significant factor affecting the CO₂ adsorption capacity of the obtained CaO sorbent. The maximum CO₂ adsorption capacity of the CaO obtained under these study conditions was higher than that of commercial CaO.     

Water quality and uses of the Bangpakong River (eastern Thailand)

The Bangpakong River is the most important watershed in the Eastern part of Thailand. Water quality parameters were sampled from June 1998 through May 1999 at 11 sites along a 227 km gradient, covering the wet season (June-November) and the dry season (December-May). Surface water was collected at three different stations per site (close to the banks and in the middle of the river), and analyzed for temperature, dissolved oxygen, turbidity, suspended solids, pH. ammonia, fecal coliforms, biochemical oxygen demand and chemical oxygen demand as well as conductivity, phosphate, and heavy metals. The Scottish water quality index (WQI) was adaptated to the tropical environment. The averaged WQI was low (41%) and quality declined significantly during the dry season (ANOVA, p<0.001). Although the quality rose somewhat at middle sites, only 27% of the WQI values during wet season and 2.5% during dry season were higher than 50%, denoting poor environmental quality. Within each season, the main sources of variability were the differences between sites along the gradient (48% during the wet season, 63% during the dry season), whereas monthly variability represented less than 20% of the variability. The seasonal results show that the river is suitable only for tolerant fish and wildlife species and is of doubtful use for potable water supply during the dry season. As quality improves during the wet period, water can be used for the production of potable water, but only with advanced treatment, and for indirect and noncontact recreational activities. In the middle stretches of the river, higher water quality permits multiple uses at moderate cost.     

Electrical isolation of dislocations in Ge layers on Si(001) substrates through CMOS-compatible suspended structures

Suspended crystalline Ge semiconductor structures are created on a Si(001) substrate by a combination of epitaxial growth and simple patterning from the front surface using anisotropic underetching. Geometric definition of the surface Ge layer gives access to a range of crystalline planes that have different etch resistance. The structures are aligned to avoid etch-resistive planes in making the suspended regions and to take advantage of these planes to retain the underlying Si to support the structures. The technique is demonstrated by forming suspended microwires, spiderwebs and van der Pauw cross structures. We finally report on the low-temperature electrical isolation of the undoped Ge layers. This novel isolation method increases the Ge resistivity to 280 Ω cm at 10 K, over two orders of magnitude above that of a bulk Ge on Si(001) layer, by removing material containing the underlying misfit dislocation network that otherwise provides the main source of electrical conduction.