A wind tunnel study of effects of twisted wind flows on the pedestrian-level wind field in an urban environment.

The influence of twisted wind flows on the pedestrian-level wind (PLW) field of an urban area was evaluated by testing a typical urban site (Tsuen Wan, Hong Kong) in a boundary layer wind tunnel. Four twisted wind profiles with different magnitudes and directions of yaw angles were employed to investigate variations in wind speed with the properties of the twisted wind flows at the pedestrian level. An additional conventional wind profile with similar wind speeds and turbulence intensities to the twisted winds but with zero yaw angles was simulated for comparisons. The mean wind speeds at 77 locations including the perimeter, roadsides, and groups of high-rise buildings were analysed for the conventional and the four twisted wind flows. The comparisons show a tendency of twisted winds to generate higher wind speeds at the pedestrian level than the conventional wind profile. The wind speeds of the twisted winds have a strong dependence on the magnitude and direction of the yaw angles, particularly at locations where the densities of buildings in the neighbourhood are low and hence local wind circulations are significantly modified by the twisted winds.

New inflow boundary conditions for modeling twisted wind profiles in CFD simulation for evaluating the pedestrian-level wind field near an isolated building.

The hilly topography of Hong Kong influences oncoming winds and gradually changes their wind directions along the profiles' height. The vertical variation in wind directions, or the twist effect, significantly influences the Pedestrian Level Wind (PLW) field in urban areas of Hong Kong, thus it is a topic demanding systematic investigations. In this study, a new set of inflow boundary conditions are proposed to model twisted wind flows in Computational Fluid Dynamic (CFD) simulations. The new inflow boundary condition derived based on the horizontal homogeneous assumption, specifies a vertical profile of lateral wind speeds at the inlet boundary to sustain the twist effect in the empty computational domain. The proposed boundary conditions are used to simulate the PLW fields near three isolated buildings with different Height-to-Width ratio using two CFD codes; OpenFOAM, and FLUENT. The results reveal that OpenFOAM is more reliable in simulating PLW fields in twisted wind flows using the new set of boundary conditions. The three-dimensional flow field provided by the OpenFOAM simulation shows sparse streamlines downstream the buildings, indicating lack of organized eddies in the building far wake, which negatively affects the dispersion of air pollutants in twisted winds.

Integrating twisted wind profiles to Air Ventilation Assessment (AVA): The current status.

Twisted wind flows generated by the complex terrain of Hong Kong induce two types of complication to Air Ventilation Assessment (AVA), first, imposing a false boundary condition on the wind tunnel tests done for AVA and, second, creating an ambiguity in determining the approaching wind direction in calculating the probability of occurrence of winds. The latter issue is partially solved using correction methods in post-analysis of AVA but the accuracy of these methods is not yet accessed. This study employs two twisted wind profiles to test an urban area in a boundary layer wind tunnel to investigate the influence of twisted wind flows on the outcomes of AVA and to estimate the accuracy of three common correction methods: No-Shift, Threshold, and Proportional methods. The results reveal significant differences in wind speeds at the pedestrian level for twisted and conventional wind flows at locations with low building densities. The discrepancies in wind speeds are minimum at the locations where the density of buildings is high. The indicators calculated by the No-Shift method frequently deviate from those of the twisted wind flows, while the Threshold and Proportional methods routinely over-predict the indicators of AVA.

Evaluation of pedestrian wind comfort near 'lift-up' buildings with different aspect ratios and central core modifications.

Owing to the void space at lower heights, lift-up buildings have high building permeability at ground level and subsequently improve the air circulation in congested urban areas. Despite this advantage, the lift-up design has been sparsely adopted for buildings in urban areas partly because of the lack of understanding of the combined effects of building dimensions and lift-up design on the surrounding pedestrian level wind (PLW) field. Therefore, this study aims to investigate the influence of lift-up buildings with different aspect ratios (height/width) on the surrounding PLW field and pedestrian wind comfort level. Five lift-up buildings with aspect ratios 4:1 to 0.5:1 were tested in a boundary layer wind tunnel and results were compared with those of five buildings with similar dimensions but without lift-up design. The results reveal a strong dependence of the maximum wind speed in lift-up areas with building height, which results subsequently a small area of acceptable wind conditions near tall and slender lift-up buildings. Lift-up designs adopted for short and wide buildings produce larger areas of pedestrian wind comfort. The central cores modified with corner modifications are effective in increasing the pedestrian wind comfort in the lift-up area of tall and slender buildings.

Adopting 'lift-up' building design to improve the surrounding pedestrian-level wind environment.

Modern megacities are teeming with closely-spaced tall buildings, which limit air circulation at the pedestrian level. The resultant lack of air circulation creates poorly ventilated areas with accumulated air pollutants and thermal discomfort in the summer. To improve air circulation at the pedestrian level, buildings may be designed to have a 'lift-up' shape, in which the main structure is supported by a central core, columns or shear walls. However, a lack of knowledge on the influence of the 'lift-up' design on the surrounding wind environment limits the use of 'lift-up' buildings. This study aims to investigate the influence of 'lift-up' buildings and their dimensions on the pedestrian-level wind environments using wind tunnel tests. A parametric study was undertaken by using 9 'lift-up' building models with different core heights and widths. The results were compared with the surrounding wind environment of a control building with similar dimensions. The results reveal that the 'lift-up' core height is the most influential parameter and governs the area and magnitude of high and low wind speed zones around such buildings. Based on wind tunnel test results and a selected comfort criterion, appropriate core dimensions could be selected to have acceptable wind conditions near lift-up buildings.

Ex vivo amplification of human hematopoietic stem and progenitor cells in an alginate three-dimensional culture system.

INTRODUCTION: One of the key factors critical for a successful human cord blood transplantation in treating patients with hematopoietic disorders is the number of hematopoietic stem/progenitor cells derived from human cord blood. Here, we report an alginate three-dimensional (3D) culture system for the expansion of CD34+ cells in cord blood mononuclear cells (CBMCs). METHODS: Cord blood mononuclear cells were isolated from human cord blood and encapsulated in 3D alginate beads. The cells were grown with different concentrations of cytokines. At day 0, 3, 6, 9, and 12, respectively, the percentage of CD34+ cells was quantified by flow cytometry. Colony-forming cell assay was performed to determine the potential of hematopoietic reconstruction of the amplified cells under the 3D culture system. RESULTS: After culturing for 12 days, the CBMCs encapsulated in the 3D alginate beads were amplified 5.89 ± 0.72 fold, CD34+ cells increased from 2.60 ± 0.52% to 13.27 ± 2.65%, and the colony-forming assay showed that the colony-forming unit-granulocyte/granulocyte-macrophage (CFU-G/GM) increased from 363.34 ± 34.47/105 cells to 3423.33 ± 645.14/105 cells (P < 0.001). In comparison, the conventional two-dimensional (2D) culture system showed that the CBMCs, CD34+ cells and the CFU-G/GM were 0.68 ± 0.16 fold, 0.45 ± 0.17%, and 532.92 ± 82.97/105 cells, respectively. CONCLUSION: This study demonstrates a new and efficient method to amplify the CD34+ human cord blood hematopoietic stem/progenitor cells in a 3D alginate culture system ex vivo for extended periods while retaining the hematopoietic reconstruction capacity.

Prenatal sonographic diagnosis of familial Holt-Oram syndrome associated with type B interrupted aortic arch.

We present a rare case of familial Holt-Oram syndrome diagnosed sonographically at 18 weeks of gestation. The foetus had serious bilateral upper limb malformations, a ventricular septal defect and a type B interrupted aortic arch, while the mother had bilateral upper limb malformations only. The pregnancy was terminated. A pathological and radiological examination of the foetus confirmed the prenatal sonographic findings. Although genetic investigation of TBX5 mutations was not available in our locality at the time of diagnosis, the geneticists made a clinical diagnosis of familial Holt-Oram syndrome. The clinical features of our case completely fulfilled the strict diagnostic criteria for the syndrome. The cardiac malformations most commonly associated with Holt-Oram syndrome are atrial or ventricular septal defects. To the best of our knowledge, a prenatal diagnosis of Holt-Oram syndrome in association with a type B interrupted aortic arch has not been reported in the English literature before.

Rapid aneuploidy testing (knowing less) versus traditional karyotyping (knowing more) for advanced maternal age: what would be missed, who should decide?

OBJECTIVES: The application of rapid aneuploidy testing as a stand-alone approach in prenatal diagnosis is much debated. The major criticism of this targeted approach is that it will not detect other chromosomal abnormalities that will be picked up by traditional karyotyping. This study aimed to study the nature of such chromosomal abnormalities and whether parents would choose to terminate affected pregnancies. DESIGN: Retrospective study on a cytogenetic database. SETTING: Eight public hospitals in Hong Kong. PARTICIPANTS: The karyotype results of 19 517 amniotic fluid cultures performed for advanced maternal age (>or=35 years) from 1997 to 2002 were classified according to whether they were detectable by rapid aneuploidy testing. The outcomes of pregnancies with abnormal karyotypes were reviewed from patient records. RESULTS: In all, 333 (1.7%) amniotic fluid cultures yielded abnormal karyotypes; 175 (52.6%) of these were detected by rapid aneuploidy testing, and included trisomy 21 (n=94, 28.2%), trisomy 18 or 13 (n=21, 6.3%), and sex chromosome abnormalities (n=60, 18.0%). The other 158 (47.4%) chromosomal abnormalities were not detectable by rapid aneuploidy testing, of which 63 (18.9%) were regarded to be of potential clinical significance and 95 (28.5%) of no clinical significance. Pregnancy outcomes in 327/333 (98.2%) of these patients were retrieved. In total, 143 (42.9%) of these pregnancies were terminated: 93/94 (98.9%) for trisomy 21, 20/21 (95.2%) for trisomy 18 or 13, 19/60 (31.7%) for sex chromosome abnormalities, and 11/63 (17.5%) for other chromosomal abnormalities with potential clinical significance. There were no terminations in the 95 pregnancies in which karyotyping results were regarded to be of no clinical significance. CONCLUSIONS: 'Knowing less' by the rapid aneuploidy stand-alone testing could miss about half of all chromosomal abnormalities detectable by amniocentesis performed for advanced maternal age. Findings from two fifths of the latter were of potential clinical significance, and the parents chose to terminate one out of six of the corresponding pregnancies. If both techniques are available, parents could have enhanced autonomy to choose.

Is antenatal antibody screening worthwhile in Chinese?

A total of 1997 pregnant women were screened during their first antenatal visit for irregular antibodies for the prevention of haemolytic disease of the newborn. Patient sera were tested against a panel of group O screen cells including one with the expression of Miltenberger determinants GP.Mur. 17 women (0.85%) had irregular antibodies of which four were of potential clinical significance, including one with anti-D, two with anti-E and one with anti-D, anti-E and anti-G. Although antenatal antibody screening is mandatory in Western populations, our results suggest that this may not be necessary in the Chinese population except for those who are Rh D-negative or who have a history of haemolytic disease of the newborn.