104 research outputs found
Characterisation of airborne particles in London by computer-controlled scanning electron microscopy
No full textThis study assessed the personal exposure of cyclists and Underground train users in London to particulate matter below 5 ?m in diameter (PM5) and provides evidence of the number, shape, size distribution and elemental composition of collected particles. Samples were analysed using computer-controlled scanning electron microscopy (CCSEM) and energy dispersive X-ray detection (EDX), including analysis of samples for low energy elements (carbon) by open window detection. Results were processed and classified using a custom written software package (MIDAS). A total of 33 938 particles were analysed for size and 12 568 particles were classified for size and elemental composition. Samples were also collected for gravimetric analysis. Thirty volunteers cycling commuter routes into central London were selected and monitored according to particulate matter for 1 week during November 1995–February 1996. Samples were also collected by three commuters using London Underground during their daily commuter journeys as a comparison. Cassella personal sampling pumps fitted with cyclone heads incorporating filters were used to collect particles. Carbon particles are clearly the dominant particle type in the road traffic samples with mean particle fractions of 66% carbon. The size distribution of the aerosol sampled by cyclists — high numbers of the smallest sized particles — is typical of vehicle emissions. Samples from the Underground show a distinctly different size distribution and elemental composition. Samples exhibited a higher loading of coarse mode particles with a more even distribution across the particle sizes collected. The most abundant particles in the Underground are Fe/Si-rich particles with 53% (56% in the 20-kV range) of the total number of particles. The average Fe concentration in this particle class was 22.8% and the Si concentration 17.4% together with C, Ca and K. The particle mass concentration in the London Underground trains proved to be almost 10 times higher than those measured by cyclists in traffic generated aerosol.<br/
When is ignorance bliss? The effects of inaccurate self-assessments of knowledge on learning and attrition
No full textStudy of chemical reactions by surface second harmonic generation: p-nitrophenol at the air-water interface
No full textChemical reaction at the interface of a liquid and air has been studied using the technique of surface second harmonic generation. The reaction investigated was the acid-base equilibrium of p-nitrophenol at the air-water interface
ChemInform Abstract: STUDIES OF THE CHEMICAL INTERMEDIATE DIPHENYLCARBENE: INTERSYSTEM CROSSING, SOLVENT EFFECTS ON DYNAMICS, SPIN STATE SELECTIVE CHEMISTRY, PHOTOCHEMISTRY OF THE EXCITED TRIPLET STATE
No full textSemi-arid Grasslands Vegetative Community Response to Prescribed Broadcast Burns and Juniper Thinning and Pile Burning in Central Arizona
No full textabstract: Grassland habitat restoration activities are occurring within the semi-arid grasslands of the Agua Fria National Monument located 65 km north of Phoenix, AZ. The goal of these restoration activities is to reduce woody species encroachment, remove lignified plant materials and recycle nutrients within the ecosystem thus improving range conditions for both wildlife species and livestock. Broadcast burning, juniper thinning and slash pile burns are the principle tools used to accomplish resource objectives. Line cover, belt transect, densities, heights and biomass of vegetation data were collected to determine the response of the vegetative community to habitat restoration activities. Principal Component Analysis (PCA) was used to reduce data analysis to the more influential factors. Regression analysis was conducted for statistically significant response variables. Quadratic regression analysis found low predictive values. In broadcast burn treatment units, all important factors as identified by PCA had low predictive factors but significantly differed (R2 <0.01, p<0.05) between unburned and the years post treatment. Regression analysis found significant, albeit weak, relationships between time since treatment and independent variables. In pile burn treatment units, data reduction by PCA was not possible in a biologically meaningful way due to the high variability within treatment units. This suggests the effect of juniper encroachment on grassland vegetation persists long after junipers have been cut and burned. This study concluded that broadcast burning of the central Arizona grasslands does significantly alter many components of the vegetative community. Fuels treatments generally initially reduced both perennial woody species and grasses in number and height for two year post fire. However, palatable shrubs, in particular shrubby buckwheat, were not significantly different in broadcast burn treatment areas. The vegetative community characteristics of juniper encroached woodlands of central Arizona are unaffected by the removal and burning of junipers aside from the removal of hiding cover for predators for multiple years. It is recommended that habitat restoration activities continue provided the needs of wildlife are considered, especially pronghorn, with the incorporation of state and transition models specific to each of the respective ecological site descriptions and with the consideration of the effects of fire to pronghorn fawning habitat.Dissertation/ThesisM.S. Applied Biological Sciences 201
Rapid and efficient generation of PCR-derived riboprobe templates for in situ hybridization histochemistry.
No full text In situ hybridization histochemistry (ISH) using cRNA probes (riboprobes) has become a powerful technique for the examination of gene expression in tissue sections. The construction of plasmid templates for the synthesis of riboprobes with phage RNA polymerases is often a difficult and time-consuming step. We have therefore developed a rapid, efficient, and flexible method to generate totally artificial riboprobe templates by the polymerase chain reaction (PCR). We have made riboprobe templates using self-priming oligonucleotide primers spanning 146 BP of the 3' end of the human cytokeratin 1 (K1) gene coding region flanked by T7 and T3 promoters. These PCR-derived riboprobe templates were used to synthesize 35S-labeled anti-sense riboprobes as well as sense riboprobes as negative controls. The riboprobes were then applied in ISH to human skin sections made from routinely fixed and paraffin-embedded clinical biopsy material. Consistent with published results, we observed strong expression of K1 mRNA in the suprabasal cell layers of the epidermis but only weak to undetectable signals in the basal and cornified cell layers and in the dermis. With this experimental procedure we see no decrease in probe efficiency or quality compared to conventional methods. The use of PCR-derived riboprobe templates for ISH makes it possible to detect expression of any desired gene of known sequence rapidly and efficiently. </jats:p
- …
