Street-Level Ventilation in Hypothetical Urban Areas

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Wind tunnel study on flows over various two-dimensional idealized urban-like surfaces

Extensive human activities (e.g. increased traffic emissions) emit a wide range of pollutants resulting in poor urban area air quality. Unlike open, flat and homogenous rural terrain, urban surface is complicated by the presence of buildings, obstacles and narrow streets. The irregular urban surfaces thus form a random roughness that further modifies the near-surface flows and pollutant dispersion. In this study, a physical modelling approach is employed to commence a series of wind tunnel experiments to study the urban-area air pollution problems. The flow characteristics over different hypothetical urban roughness surfaces were studied in a wind tunnel in isothermal conditions. Preliminary experiments were conducted based on six types of idealized two-published_or_final_versio

Experimental study on near-ground boundary layer response to the change in different patterns of urban-type surface

The flow behaviour over various two-dimensional (2D) urban-type surfaces was investigated in a laboratory wind tunnel. Square aluminium bars of size 2.5 cm were used to represent flat-roof buildings and the building separation was adjusted to fabricate various types of urban surface of building-height-to-street-width (aspect) ratios of 1, 1/2, 1/8, 1/10 and 1/12. Mean velocities and velocity fluctuations were measured with a 90o X–hotwire anemometry. The current results compare well with our previous large-eddy simulation (LES). Analysis of the turbulence characteristics for different urban surfaces was performed in attempt to examine the near-ground boundary layer response to various street-canyon configurations.postprin

Influence of atmospheric boundary layer depth on the ventilation performance over idealized urban surfaces

The mechanism of flows and scalar transfer over urban areas is complicated by the random city surfaces in which a detailed investigation is required in its parameterization. Despite the collective effort made by the researchers on urban air pollution problems, our knowledge on the interaction between flows and aerodynamic resistance over cities is limited. Apart from the roughness effect induced by the bottom of the urban boundary layer (UBL), the local atmospheric environment conditions and the city-level air quality are closely correlated but their importance is apparently overlooked. Therefore, as a pilot attempt, this study is conceived to examine the effect of UBL depth on the ...published_or_final_versio

Gene discovery and transcript analyses in the corn smut pathogen Ustilago maydis: expressed sequence tag and genome sequence comparison.

BACKGROUND: Ustilago maydis is the basidiomycete fungus responsible for common smut of corn and is a model organism for the study of fungal phytopathogenesis. To aid in the annotation of the genome sequence of this organism, several expressed sequence tag (EST) libraries were generated from a variety of U. maydis cell types. In addition to utility in the context of gene identification and structure annotation, the ESTs were analyzed to identify differentially abundant transcripts and to detect evidence of alternative splicing and anti-sense transcription. RESULTS: Four cDNA libraries were constructed using RNA isolated from U. maydis diploid teliospores (U. maydis strains 518 x 521) and haploid cells of strain 521 grown under nutrient rich, carbon starved, and nitrogen starved conditions. Using the genome sequence as a scaffold, the 15,901 ESTs were assembled into 6,101 contiguous expressed sequences (contigs); among these, 5,482 corresponded to predicted genes in the MUMDB (MIPS Ustilago maydis database), while 619 aligned to regions of the genome not yet designated as genes in MUMDB. A comparison of EST abundance identified numerous genes that may be regulated in a cell type or starvation-specific manner. The transcriptional response to nitrogen starvation was assessed using RT-qPCR. The results of this suggest that there may be cross-talk between the nitrogen and carbon signalling pathways in U. maydis. Bioinformatic analysis identified numerous examples of alternative splicing and anti-sense transcription. While intron retention was the predominant form of alternative splicing in U. maydis, other varieties were also evident (e.g. exon skipping). Selected instances of both alternative splicing and anti-sense transcription were independently confirmed using RT-PCR. CONCLUSION: Through this work: 1) substantial sequence information has been provided for U. maydis genome annotation; 2) new genes were identified through the discovery of 619 contigs that had previously escaped annotation; 3) evidence is provided that suggests the regulation of nitrogen metabolism in U. maydis differs from that of other model fungi, and 4) Alternative splicing and anti-sense transcription were identified in U. maydis and, amid similar observations in other basidiomycetes, this suggests these phenomena may be widespread in this group of fungi. These advances emphasize the importance of EST analysis in genome annotation

Parameterisation of flows and pollutant transport over idealised urban roughness

No. J7.2Atmospheric flow over urban areas basically is a type of turbulent flow over roughness. The flows and pollutant transport process, especially at the lower part of the boundary layer (BL), is strongly modified due to the presence of building geometry. The aerodynamic resistance exerted by the surface roughness reduces the mean velocity in the lower BL but enhances the turbulence intensity. Moreover, the near-wall impingement structures over rough surfaces are attributed to the flow dynamics aloft, leading to increasing aerodynamic resistance and BL depth. However, the dependence on surface morphology and BL depth is not yet well understood. There is ...postprin

Roughness-sublayer correction for the profiles of mean velocity and turbulence over urban areas

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Isolated penile urethral injury: a rare case following male coital trauma

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Oral health status and behaviours of preschool children in Hong Kong.

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Potential use of Niti implant for intra-articular fracture of phalax

Session - New Developments in Orthopaedic Implant Materialspublished_or_final_versio