Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Effects of the herbicide roundup on freshwater microbial communities: a mesocosm study

Abstract: The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays, and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup) and two treatments of 6 and 12 mg/L of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters showing statistically significant differences between treatments and controls were the downward vertical spectral attenuation coefficient kd(lambda), where lambda is wavelength, and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio kd(490 nm)/k(d)(550 nm) and an eightfold increase in TP. Roundup affected the structure of phytoplankton and periphyton assemblages. Total micro- and nano-phytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of picocyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of two). Similar patterns were observed in the periphytic assemblages, which showed an increased proportion of dead: live individuals and increased abundances of cyanobacteria (about 4.5-fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, the phytoplankton absorption spectra, and the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than an indirect effect mediated by phosphorus enrichment.

Direct Imaging of Anisotropic Exciton Diffusion and Triplet Diffusion Length in Rubrene Single Crystals

Abstract: We visualize exciton diffusion in rubrene single crystals using localized photoexcitation and spatially resolved detection of excitonic luminescence. We show that the exciton mobility in this material is strongly anisotropic with long-range diffusion by several micrometers associated only with the direction of molecular stacking in the crystal, along the b axis. We determine a triplet exciton diffusion length of 4.0 ± 0.4 μm from the spatial exponential decay of the photoluminescence that originates from singlet excitons formed by triplet-triplet fusion.

Encapsulation of inorganic particles via miniemulsion polymerization. II. Preparation and characterization of styrene miniemulsion droplets containing TiO2 particles

Abstract: The encapsulation of titanium dioxide (TiO2) particles via styrene miniemulsion polymerization requires two successive dispersion steps. First, the TiO2 particles must be successfully dispersed in the monomer phase. Second, this phase must be dispersed in an aqueous surfactant solution to form stable submicron droplets. The oil/water interface between the droplets and the aqueous phase can be affected not only by the surfactant used but also the components present in the oil phase. Interfacial tensions between the phases were measured. The presence of insufficient or excess stabilizer both reduced the interfacial tensions. This was attributed to migration of the partially covered hydrophilic TiO2 particles or the excess OLOA 370 stabilizer (polybutene–succinimide pentamine) to the oil/water interface. The free surfactant in the aqueous phase and the average droplet size of the miniemulsions were characterized as a function of the process variables. The presence of TiO2 particles within the droplets limited the ability of the process to reduce the droplet size although miniemulsion droplets in the size range of 150–200 nm were still obtained for subsequent polymerizations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4431–4440, 2000