Statistical Communication Theory

Contains research objectives and reports on eight research projects

In Situ Real-Time Quantification of Microbial Communities: Applications to Cold and Dry Volcanic Habitats

We report field tests of an instrument using multi-wavelength excitation and detection of fluorescence capable of detection and discrimination of viable cells, non-viable cells (not metabolically active but not decomposed), and spores in extreme arid environments where low microbial abundances are expected. These new results are presented for cold and dry volcanic habitats worldwide, e.g., the arid core of the Atacama Desert, Mt. Kilimanjaro glacier and Kibo area, Pali Aike caldera, and the western US volcanic and desert soils in Utah, Idaho, Nevada, and California. Our results are comparable to previous studies reported in the literature for the same environments. We find these extreme environments there have a base level of ∼103 - 104 cells/g. This is the lower limit of detectable life on terrestrial soils, as we did not observe any quantities less than this, even though the described instrumentation is capable of such measurements. Samples from more conventional environments show much higher microbial cell densities, ca. 108 cells/g or higher, with this same instrument. This base level of microbial life is nearly equal in all the measurements from the extreme environments both hot and cold, and is likely controlled primarily by the sparse nutrients rather than temperature

In Situ Real-Time Quantification of Microbial Communities: Applications to Cold and Dry Volcanic Habitats

We report field tests of an instrument using multi-wavelength excitation and detection of fluorescence capable of detection and discrimination of viable cells, non-viable cells (not metabolically active but not decomposed), and spores in extreme arid environments where low microbial abundances are expected. These new results are presented for cold and dry volcanic habitats worldwide, e.g., the arid core of the Atacama Desert, Mt. Kilimanjaro glacier and Kibo area, Pali Aike caldera, and the western US volcanic and desert soils in Utah, Idaho, Nevada, and California. Our results are comparable to previous studies reported in the literature for the same environments. We find these extreme environments there have a base level of ∼103 - 104 cells/g. This is the lower limit of detectable life on terrestrial soils, as we did not observe any quantities less than this, even though the described instrumentation is capable of such measurements. Samples from more conventional environments show much higher microbial cell densities, ca. 108 cells/g or higher, with this same instrument. This base level of microbial life is nearly equal in all the measurements from the extreme environments both hot and cold, and is likely controlled primarily by the sparse nutrients rather than temperature

Estimating the Spatial Extent of Bottom-Water Hypoxia and Habitat Degradation in a Shallow Estuary

Bottom-water hypoxia (≤ 2 mg 1-1 dissolved oxygen [DO]) greatly modifies the benthic habitat of estuaries, depending upon spatial extent, duration, and frequency. Bottom-water hypoxia often develops under conditions of density stratification, which inhibits vertical mixing, and warm temperatures, which enhance biological oxygen demand. Long-term, mid-channel data from the Neuse River Estuary in North Carolina permitted evaluation of how stratification and temperature combined to affect DO concentrations at the bottom. Salinity stratification (DS) and water temperature (T) explained respectively 30 and 23% of the variance in bottom-water DO concentrations. The amount of salinity stratification required to induce bottom-water hypoxia declined with increasing water temperature. About 80% of observed hydrographic profiles exhibited bottom hypoxia when DS exceeded 5 psu and T exceeded 20°C. Using cross-channel hydrographic surveys as verification, we derived a general set of methods to estimate the lateral extent of low-DO bottom water from midchannel hydrographic profiles. The method involves cross-estuary and along-estuary extrapolation based on assumption of a flat oxycline. Occasional violation of this assumption resulted in modest overestimation in cross-channel extent of low DO. Application of this method produced estimates ranging from 0 to 116 km2 of bottom area (0 to 42% of the estuarine study area) exposed to hypoxia over all sample dates in summer 1997. The maximal bottom area exposed to hypoxia corresponded closely with an independent estimate of the area (100 km2) that experienced almost complete mortality of Macoma spp. clams, the key benthic resource for demersal fishes and crabs. Consequently, mid-channel hydrographic profiles taken along the mid-channel of the estuary can be employed to assess the spatial scale of bottom habitat degradation due to hypoxia

Statistical Communication Theory

Contains reports on six research projects

Statistical Communication Theory

Contains reports on nine research projects

Photophysical and Photochemical Studies of Tricarbonyl Rhenium(I) N-Heterocyclic Carbene Complexes Containing Azide and Triazolate Ligands

Rhenium(I) N-heterocyclic carbene (NHC) complexes of the type fac-[Re(CO)3(NHC)L] with either azide or triazolate ancillary ligands L and pyridyl or pyrimidyl substituted imidazolyl units have been prepared and structurally characterised, and their photophysical and photochemical properties studied. All of the complexes exhibit phosphorescent emission from triplet metal-to-ligand (3MCLT) excited states, typical of tricarbonyl Re(I) complexes, with the triazolate bound complexes having higher quantum yields and longer decay lifetimes compared to the azide bound complexes. The complexes containing pyridyl substituted imidazolyl units are photoreactive when dissolved in acetonitrile and undergo photochemical CO dissociation, the rate of which is significantly greater in the azide cf. triazolate complex. The photochemical mechanism of the azide/pyridyl complex was analysed and appears to give the same products, albeit with different ratios, to previously reported complexes where L is a halide. A reaction mechanism is proposed

Communications and Related Projects

Contains reports on six research projects

Communications Research

Contains reports on seven research projects