An Inter-Comparison of Two Black Carbon Aerosol Instruments and a Semi-Continuous Elemental Carbon Instrument in the Urban Environment

Aerosol absorption coefficients were obtained using two versions of the Magee Scientific Aethalometer and a Particle Soot Absorption Photometer (PSAP) in Riverside, California during July and August of 2005. These measurements were subsequently compared to each other and to hourly elemental carbon (EC) mass concentrations as determined by a Sunset Labs semi-continuous OCEC analyzer. Measurements from all four instruments were shown to be highly correlated (R ² = 0.83 to 0.92). Differences between absorption values measured by the PSAP and the Aethalometer were found to be dominated by differences in the filter media used by the respective instruments. Comparison of optical and thermal measurements revealed that the specific attenuation cross section (σ _ATN ) of light absorbing carbon (LAC) varied as a function of the time of the day, most notably during weekdays. Minimum σ _ATN values were observed during morning rush hour when EC concentrations were at their greatest and maxima were seen in the late afternoon. These variations correlated with changes in the OC/EC ratio and the Angstrom exponent for absorption, which is consistent with changes in the mixing state of elemental carbon associated with secondary aerosol condensation on primary EC particles.     

Crystallization of Zircon in Stoneware Glazes

High levels of zircon are required to impart opacity in glazes. Zircon additions of <3 wt% dissolve into the glassy phase; additions of >12% cause all the zircon to crystallize from the glaze. Dynamic high-temperature X-ray diffraction has shown that, during heating, a portion of the zircon dissolves and subsequently recrystallizes, using undissolved zircon crystals as seeds. This recrystallization does not occur at lesser zircon levels, because of a lack of seed crystals. When zirconia is added to the glaze, zircon is formed as elongated crystals at the glaze surface. Lesser zircon levels have been observed in the glazes that have zirconia additions.     

Apportionment of primary and secondary organic aerosols in southern California during the 2005 study of organic aerosols in riverside (SOAR-1)

Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.     

Geomorphic comparison of two Atlantic coastal rivers: Toward an understanding of physical controls on Atlantic salmon habitat

River channel substrate size and mobility are important to Atlantic salmon spawning and rearing success. We compare morphology and bed sediment between two North American Atlantic coastal streams (Narraguagus River, Maine, USA and Jacquet River, New Brunswick, Canada). The watersheds have similar drainage areas and mean annual precipitation, but differing relief structure, channel longitudinal profiles and numbers of returning salmon. The lower‐relief Narraguagus River is segmented into steeper (gradient >0.002) and flatter reaches (gradient <0.0005). Flat reaches, including mainstem lakes, act as sediment sinks, preventing the continuity of downstream sediment transport. Based on field measurements, the Narraguagus River has a larger high‐flow width to depth ratio than the Jacquet River, but this difference is principally the result of outliers from low‐gradient channel reaches. Measurements of substrate grain size reveal finer river‐bed sediments on the Narraguagus River, however, Shields parameter calculations indicate that bed sediment should be mobile during high flows in both streams. We use the Shields equation to predict grain size based on channel slope, width and drainage area measured from digital elevation models (DEM) and aerial photographs. Predictions of median grain size agree with field measurements within a factor of 2 for 62–70% of the survey stations. We suggest ways that model misfits may provide opportunities to prioritize reach‐based restoration efforts. Based on expected grain size, we estimate 62% spawning and 68% rearing habitat along the length of the Narraguagus River, and 28 and 95% respectively on the Jacquet. Overall, glacial history and relief structure appear to be the first‐order controls on substrate grain size and habitat quality in these two rivers. Copyright © 2010 John Wiley & Sons, Ltd.     

The natural history and fisheries ecology of Lake Chilwa,southern Malawi

Lake Chilwa produces between zero and 24,000 metric tons of fish per year, making it one of the most productive but variable lakes in Africa. The size of the lake varies seasonally and among years, sometimes drying completely. Its surrounding wetland and floodplain provide habitat for a diversity of birds and economically valuable grasses and reeds. When the lake has water, there is considerable activity on its shores and temporary fishing villages spring up. People move in and out of the lake basin in concert with these seasonal and longer term changes. This paper examines the environmental dynamics of Lake Chilwa and its surrounding wetlands, presents an overview of the socio-economic context of the area and discusses threats to this resilient system that might occur as a result of climate change. We conclude that management of Lake Chilwa must place the lake in the wider economic and ecological system in which it is situated. Ultimately, land-use practices within the basin present more of a threat to the resilience of the fishery and people's livelihoods than overfishing or a strict focus on the lake's resources. These perspectives present significant challenges to conventional fisheries governance.     

Calcium-dependent secretory vesicle-binding and lipid-binding proteins of Saccharomyces cerevisiae

Yeast (Saccharomyces cerevisiae) cytosol was examined for the presence of calcium-dependent membrane- or lipid-binding proteins that might play fundamental roles in membrane-associated phenomena in stimulated cells. A complex group of proteins was isolated from late log phase cultures of yeast strain YP3 on the basis of calcium-dependent association with yeast secretory vesicles isolated from the temperature-sensitive sec6-4 secretory mutant. The masses of the major proteins in this group were 32, 35, 47, 51, 55, 60 and 120 kDa. A similar group of proteins was isolated by calcium-dependent association with bovine brain lipids enriched in the predominant acidic phospholipids of the yeast secretory vesicles. The 47 kDa protein was highly purified when commercial yeast cake was used as the source of yeast cytosol. The 32 kDa and 60 kDa proteins were demonstrated to reassociate with lipids at calcium concentrations of 100 microM or higher, while no association was promoted by 2 mM-magnesium. The 47 kDa protein could be removed from lipids by reducing the calcium concentration to between 1 and 32 microM. The sequences of peptides isolated from digests of several of these proteins indicate that they are novel proteins but are insufficient to judge the possible homology of these proteins with mammalian membrane-binding proteins. The sequence data may be adequate to permit isolation and modification of the corresponding genes in order to assess the possible function of this class of proteins in stimulated cells.     

Nanowire Structural Evolution from Fe3O4 to ϵ‐Fe2O3

The ?‐Fe₂O₃ phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe₂O₃) to hematite (α‐Fe₂O₃). The routine method of synthesis for ?‐Fe₂O₃ crystals uses γ‐Fe₂O₃ as the source material and requires dispersion of γ‐Fe₂O₃ into silica, and the obtained ?‐Fe₂O₃ particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe₃O₄ powder as a source material, the synthesis of not only one‐dimensional Fe₃O₄ nanowires but also high‐yield ?‐Fe₂O₃ nanowires is reported for the first time. A detailed transmission electron microscopy (TEM) study shows that the nanowires of pure magnetite grow along [111] and <211> directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the <110> direction are found in every instance to accompany a new phase, ?‐Fe₂O₃, with some micrometer‐sized wires even fully transferring to ?‐Fe₂O₃ along the fixed structural orientation relationship, (001) ∥ (111), [010] ∥ <110>. Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe₂O₃ formation during the synthesis process; the phase transition may be described as being from Fe₃O₄ to ?‐Fe₂O₃, then to α‐Fe₂O₃. The detailed structural evolution process has been revealed by using TEM. 120° rotation domain boundaries and antiphase boundaries are also frequently observed in the ?‐Fe₂O₃ nanowires. The observed ?‐Fe₂O₃ is fundamentally important for understanding the magnetic properties of the nanowires.     

The expectation-maximization algorithm for symbol unsynchronizedsequence detection

The expectation-maximization (EM) algorithm for maximizing likelihood functions, combined with the Viterbi algorithm, is applied to the problem of sequence detection when symbol timing information is not present. Although the EM algorithm is noncausal, results obtained using the algorithm on the problem of nonsynchronized sequence detection indicate that it converges most of the time in three iterations, making it both of theoretical and of practical interest. A practical algorithm based on the EM algorithm is introduced. It reduces the computational burden and improves performance by making use of timing estimates in previous observation windows     

Comment on the letter ''imaging in transient regional osteoporosis''

Canada's hospitals are slowly coming to grips with the millennium bug, but Anita Elash reports that no one really knows what impact the move into the year 2000 will have on computers and medical devices, either in the hospital or doctor's office.