Mathematical Modeling of the Coupled Transport Phenomena and Color Development: Finish Drying of Trellis-Dried Sultanas

A mathematical model for simulation of simultaneous heat and mass transport was developed to describe the drying kinetics during finish drying of trellis-dried sultanas. In this model, the governing partial differential equations for heat and mass transfer for a solid spherical body were numerically solved using a finite difference technique. In addition, a kinetic model was coupled to the heat and mass transfer calculations to simultaneously predict the evolution of product color during the drying process. This allows predictions of moisture content, temperature, and color profiles of the product in a space–time domain during the drying process as a function of various operating conditions.

Predictions compared well with the experimental values, implying that the proposed numerical model can be used with confidence for the simulation of the important transport phenomena in optimizing the design and operation of a drying system for sultanas that maximizes the retention of the desired product color. The work has demonstrated the importance of establishing optimal and closely controlled drying conditions because significant effects of the key operational parameters on drying kinetics and the associated changes of product color were found. The modeling approach proposed here can be extended to other products and for incorporation of other product quality indices.     

Phytoplankton community composition of Saginaw Bay,Lake Huron,during the zebra mussel (Dreissena polymorpha) invasion: A multivariate analysis

The colonization of the zebra mussel (Dreissena polymorpha) in Saginaw Bay dramatically altered the phytoplankton community composition resulting in exclusion of light sensitive species and dominance of species with oligotrophic preferences and light resistance. In 1990, the NOAA Great Lakes Environmental Research Laboratory initiated a 7-year survey program to monitor changes in the lower food web of Saginaw Bay, where zebra mussels became established in the fall of 1991. To investigate shifts in the phytoplankton community composition over the 7-year period from 1990 to 1996 we searched for clusters of similar composition using multivariate principal component analysis (PCA) on proportions of 22 taxonomic groupings of the total phytoplankton density (cells per milliliter). We then used an agglomerative hierarchical clustering analysis of the PCA scores. We identified five characteristic phytoplankton communities in configurations that allowed recognizing four distinct periods in Saginaw Bay linked to the zebra mussel invasion. Significant changes were indicative of increased water clarity and eutrophic conditions being replaced by more oligotrophic conditions as clusters dominated by light sensitive species, such as the cyanobacteria Oscillatoria redekii, became immediately rare and clusters dominated by diatoms such as Cyclotella spp. became common. Microcystis spp., a light tolerant cyanobacteria not grazed by zebra mussel, dominated assemblages after 1994. The shifts in phytoplankton composition confirm that zebra mussels effects on phytoplankton communities are mediated by both direct (filtration) and indirect (nutrient cycling) mechanisms and also suggests that increased light penetration is an important mechanism behind some changes.     

Kelvin probe force microscopy on surfaces of UHV cleaved ionic crystals

Force spectroscopy and Kelvin probe force microscopy (KPFM) measurements taken on (001) surfaces of UHV cleaved NaCl, KCl and MgO are presented for the first time. With the help of force spectroscopy we show first that the charging of (001) surfaces of alkali halide crystals, which generally occurs after UHV cleavage, vanishes after a couple of days due to their sufficiently high ionic conductivity at room temperature. KPFM images of these (001) surfaces show that the surface potential is not uniform but exhibits variations of up to 1?V at a nanometre length scale. Variations on terraces as well as a strong contrast at step edges can be observed, of which the latter is probably due to trapped charges. On MgO(001), we observe strong changes in the surface potential, especially at previously reported adstructures. These changes explain why imaging MgO(001) is difficult.     

Dye-sensitized solar cells incorporating a "liquid" hole-transporting material

We present the first application of an amorphous "liquid" organic semiconductor in an optoelectronic device, demonstrating that it is highly suited for use as a hole-transporting material in nanostructured dye-sensitized solar cells. For such devices, we obtain power conversion efficiencies of up to 2.4% under simulated air mass 1.5 solar spectrum at 100 mWcm(-2), and incident photon-to-electron quantum efficiencies in excess of 50%.     

Comparative GC-EAD Responses of A Specialist (<Emphasis Type="Italic">Microplitis croceipes</Emphasis>) and A Generalist (<Emphasis Type="Italic">Cotesia marginiventris</Emphasis>) Parasitoid to Cotton Volatiles Induced by Two Caterpillar Species

Plants emit volatile blends that may be quantitatively and/or qualitatively different in response to attack by different herbivores. These differences may convey herbivore-specific information to parasitoids, and are predicted to play a role in mediating host specificity in specialist parasitoids. Here, we tested the above prediction by using as models two parasitoids (Hymenoptera: Braconidae) of cotton caterpillars with different degree of host specificity: Microplitis croceipes, a specialist parasitoid of Heliothis spp., and Cotesia marginiventris, a generalist parasitoid of caterpillars of several genera including Heliothis spp. and Spodoptera spp. We compared GC-EAD (coupled gas chromatography electroantennogram detection) responses of both parasitoid species to headspace volatiles of cotton plants damaged by H. virescens (a host species for both parasitoids) vs. S. exigua (a host species for C. marginiventris). Based on a recent study in which we reported differences in the EAG responses of both parasitoids to different types of host related volatiles, we hypothesized that M. croceipes (specialist) would show relatively greater GC-EAD responses to the herbivore-induced plant volatile (HIPV) components of cotton headspace, whereas C. marginiventris (generalist) would show greater response to the green leaf volatile (GLV) components. Thirty volatile components were emitted by cotton plants in response to feeding by either of the two caterpillars, however, 18 components were significantly elevated in the headspace of H. virescens damaged plants. Sixteen consistently elicited GC-EAD responses in both parasitoids. As predicted, C. marginiventris showed significantly greater GC-EAD responses than M. croceipes to most GLV components, whereas several HIPV components elicited comparatively greater responses in M. croceipes. These results suggest that differences in the ratios of identical volatile compounds between similar volatile blends may be used by specialist parasitoids to discriminate between host-plant and non-host-plant complexes.     

Naturally ventilated and mixed-mode buildings—Part II: Optimal control

Natural ventilation and a combination of natural ventilation and fan-assisted cooling, in lieu of or as a supplement to air conditioning, offer significant reductions in building energy use in appropriate climates. In current practice, such buildings are operated with heuristic control strategies, involving the opening of windows under suitable indoor and outdoor conditions. Such methods are sub-optimal because they do not account for building thermal dynamics and predicted weather and therefore do not make decisions on the basis of estimated future conditions. This paper uses building thermal predictions from a data-driven thermal model to assess the impact of window and internal openings and fan operation. It then develops a means of ranking and choosing among a set of cooling strategies, with the objective of maintaining occupied-period temperatures within a specified range and minimizing fan energy use. The control algorithms were assessed with data from a test building.