Convective heat transfer during hot pressing in wood-based composite panel manufacturing is widely accepted as the most important means of heat transport for resin curing. The rate of convective heat transfer to the panel core is controlled by its permeability. Permeability in the plane of the panel also controls the flow of vapor to the panel edges, thereby influencing the potential for panel "blowing". This research considers how flake thickness, flake alignment and changing mat density during hot-pressing influences OSB mat permeability, through its thickness and in the plane of the panel. Some previous research exists but it fails to address the affects of horizontal and vertical density gradients as well as flake alignment. An apparatus was designed to allow cold pressing of aligned flakes to desired densities while enabling permeability measurements through the mat thickness. An additional apparatus was designed to allow the measuring of permeability in the plane of the mat. These designs permitted permeability measurements in mats that had no vertical density gradient, allowing for the direct study of permeability versus density (compaction ratio). Superficial permeability was determined using Darcy's law and for each sample, multiple readings were made at five different pressure differentials. Permeability through the mat thickness was highly dependent on compaction ratio and to a lesser extent flake thickness. As the compaction ratio is increased, the initial reduction in permeability is severe, once higher compaction ratios are achieved the reduction in permeability is less pronounced. Permeability decreased with decreasing flake thickness. Permeability in the plane of the mat decreases with increasing compaction ratio but in a less severe manner than through the mat thickness. In this case, the permeability-compaction ratio relationship appears linear in nature. Again, permeability decreases with decreasing flake thickness. / Master of Science

M.Sc. (Med. (Paediatric Cardiology)), Faculty of Health Sciences, University of the Witwatersrand, 2008 / Left ventricular (LV) noncompaction is characterized by the presence of an extensive trabecular myocardial layer within the luminal aspect of the compact myocardium of the ventricular wall. The trabeculae are both excessive in number and more prominent than normal. Noncompaction may occur in isolation usually with clinical features of dilated cardiomyopathy, or it may be associated with congenital or acquired heart diseases. Echocardiography is the reference standard for diagnosis, where a ratio of thickness of trabecular-to-compact myocardium (compaction ratio) of >2 is a major diagnostic criterion. Noncompaction is usually considered to result from persistence of the highly trabeculated myocardium found in early cardiogenesis of the human embryo. If persistence of excess trabeculae is the only determinant of the compaction ratio it would be expected that it would remain a consistent measurement in postnatal life. However, temporal changes in the degree of noncompaction in individual case reports have raised the question as to whether the compaction ratio might be sensitive to haemodynamic or other factors. In the present dissertation, I assessed echocardiographically whether the compaction ratio is associated with increases in indices of LV volume preload in 100 children or adolescents with ventricular septal defects (VSD), and 36 with chronic rheumatic heart disease (RHD). Compared to 79 normal controls (compaction ratio=1.4±0.07), patients with VSDs (compaction ratio=2.0±0.2, p<0.0001) and RHD (compaction ratio = 2.0±0.3, p< 0.0001) had a marked increase in the compaction ratio. A compaction ratio>2 was found in 42% of patients with VSDs and 47% with RHD. In VSDs, independent of age and gender, the compaction ratio was positively associated with LV mass index (LVMI) (partial r=0.44, p<0.0001), VSD size (partial r=0.4, p<0.0001), LV end diastolic diameter indexed (LVEDD) (partial r=0.24, p= 0.01), and the presence of additional shunts (partial r=0.21, p=0.02). In RHD, independent of age and gender, the compaction ratio was positively associated with LVEDD (partial r=0.62, p=0.0001), and LVMI (partial r=0.48, p=0.005), and negatively with LV ejection fraction (partial r=0.31, p=0.03). The strong association of indices of LV volume load and the compaction ratio would suggest that haemodynamic influences are contributing to the compaction ratio both in congenital and acquired cardiac disease in childhood. Thus an increased compaction ratio may be the consequence of an increased volume preload, and therefore may not necessarily occur only as a result of persistence of embryonic patterns.