Michigan Technological University

About: Michigan Technological University is a education organization based out in Houghton, Michigan, United States. It is known for research contribution in the topics: Population & Volcano. The organization has 8023 authors who have published 17422 publications receiving 481780 citations. The organization is also known as: MTU & Michigan Tech.

Benthic diatoms as indicators of eutrophication in tropical streams

Abstract: Diatoms are frequently used as indicators of eutrophication in temperate systems, but little is known about their application to impacted African tropical systems. Five streams located within Gombe Stream National Park and five streams supporting human settlements draining into Lake Tanganyika, East Africa, were investigated for species composition, richness and diversity of epilithic algae. In addition, a trophic diatom index (TDI) developed for monitoring European rivers was applied to these tropical systems. 54 specific and infraspecific diatom taxa representing 20 genera were identified for all sites with Achnanthes s.l., Gomphonema and Navicula s.l. being the most common genera. Species richness varied between 10 and 21 in disturbed streams and 13 and 19 in undisturbed streams. Nutrients were significantly enriched in streams draining the deforested watersheds but indices of diversity and evenness (Shannon H, J and Simpson–Yule D, E) did not show any significant differences between streams in forested and deforested watersheds. Significant differences were observed between pooled data for the TDI between forested and deforested watersheds. Analysis of percent pollution tolerant diatom taxa indicates that organic pollution of streams in deforested watersheds may be contributing to eutrophication. This study shows that African diatoms, cosmopolitan or resembling well-known North American and European taxa, allows for trophic indices tailored to the autecological preferences of species to be applied to new regions, although intensive studies on these African taxa will lead to more accurate results. Measures of species-richness and diversity, historically used to describe the state of an ecosystem, may not be suitable to evaluate streams which are not grossly polluted.

Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry

Abstract: . Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gas- and particulate-phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at the Storm Peak Laboratory near Steamboat Springs, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh-resolution mass spectra of the samples after using a reversed-phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen-containing compounds (CHNO compounds), sulfur-containing compounds (CHOS and CHNOS compounds) and other oxygen-containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ∼0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of α-pinene, β-pinene, d-limonene, and β-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOx oxidation. Multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite were observed, indicating the significance of nitrate radical reactions on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur-containing compounds) were also observed; however further investigation is needed to determine the origin of the reduced sulfur-containing compounds. Overall, the molecular composition determined using ultrahigh-resolution Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry provides an unambiguous identification of the cloud water organic anion composition in the Rocky Mountain area that could help to improve the understanding of aqueous-phase processes.

Flat-top response in one-dimensional magnetic photonic bandgap structures with Faraday rotation enhancement

Abstract: The transmission and Faraday rotation characteristics of one-dimensional photonic crystals in cerium-substituted yttrium iron garnet (Ce:YIG) with multiple defects in the optical bandgap are studied theoretically at /spl lambda/ = 1.55 /spl mu/m. It is found that the interdefect spacing can be adjusted to yield a flat top response, with close to 100% transmission and 45/spl deg/ Faraday rotation, for film structures as thin as 30 to 35 /spl mu/m. This is better than a three-fold reduction in thickness compared to the best Ce:YIG films for comparable rotations, and may allow a considerable reduction in size in manufactured optical isolators. Transmission bands as wide as 7 nm are predicted, which constitutes a considerable improvement over previously reported bandwidths for magnetic photonic crystals. Diffraction across the structure corresponds to a longer optical path length than the thickness of the film, calling for the use of guided optics to minimize insertion losses in integrated devices. The basis for the flat-top transmission in ferrite photonic crystals is presented and discussed.

Effect of Oxygen Content on Structures of Graphite Oxides

Abstract: Graphite oxide was synthesized by the oxidation of graphite via a modified Hummers approach. The oxygen content of graphite oxide was tuned by changing the oxidation time. The saturated ratio of oxygen to carbon is 0.47. Furthermore, the effect of oxygen content on the structures of graphite oxide was evaluated by using SEM, TEM, XRD, Raman, FTIR, TG, TPD-MS, and nitrogen adsorption. It was found that the types of functional groups in graphite oxides, which are epoxy, hydroxyl, and carboxyl groups, were independent of oxygen content. However, the interplanar space and BET surface area of graphite oxide linearly increased with increasing O/C ratio. Furthermore, the structure of graphite can be easily and remarkably disordered even by partial oxidation.