Information on the parameters of polymeric networks obtained by crosslinking in solution can be p... more Information on the parameters of polymeric networks obtained by crosslinking in solution can be provided by deswelling measurements in polymer solutions of different concentration. However, under these conditions, the existing theories describing the swelling behavior are conflicting and no definite conclusion on the network properties seems as yet justifiable. Moreover, excluded volume and chain connectivity effects are not accounted for in either of the theories. Thirdly, the effect of the presence of crosslinkis and the number of connected polymer segments in the network on the value of the Huggins' interaction parameter to be used in the expressions for the free energy of mixing is not clear. Nevertheless, the available experimental data have shown some preference for Hermans' theory over Flory's theory, whereas James and Guth's expression must be rejected altogether. A dependence of the degree of swelling q0, at which the partial molar free energy of elasticity equals zero, on solvent power of the swelling agent has been previously observed and has been further investigated in this study. To this end, methyl methacrylate was copolymerized with small amounts of divinylbenzene in dilute benzene solutions yielding six samples with different crosslink densities and q0 values. A large dependence of q0 on the osmotic second virial coefficient in four solvents was observed. The applicability of current theories for polymer–solvent interaction upon intramolecular chain dimensions to the chains in the networks has been investigated. Flory's expression for volume expansion of polymer chains falls short, but two other relations for the same initial effect show that the second virial coefficient dependence of q0 may be attributed to volume exclusion, similarly as in free chains. The validity of these relations, however, is expected to hold only for a rather limited range of the network parameters.
Fifty-five patients with clinical suspicion of injury to their anterior cruciate ligament (ACL) w... more Fifty-five patients with clinical suspicion of injury to their anterior cruciate ligament (ACL) were examined by graded stress radiography before arthroscopic verification in an effort to determine the loss of ACL function as a result of ligament tearing. Using a commercially available stress device capable of applying varying pressures to the mid-calf, anterior drawers were measured from lateral radiographs at 0-, 7-, 14-, and 21-kiloPascal pressures and used to calculate the equivalent elastic modulus of the remaining ACL fibers. According to viscoelastic theory, this modulus is proportional to the number of elastically active fibers in the ligament. To verify the validity of this concept, the stress-strain relationship of a freshly excised ACL ligament was examined in a tensile testing machine, and the procedure was repeated after the ligament had been partially transsected with a scalpel. Comparison with the elastic modulus of the (intact) ACL of the opposite knee permits an estimate of the percentage of rupture in cases of partial tears. Overstretched ligaments show essentially normal viscoelastic properties once the slack in the ligament has been taken up. Complete tears, on the other hand, show a complete breakdown in the viscoelastic properties of the ACL. The results show that partial tears can be diagnosed by graded stress radiography with a sensitivity of 20% and specificity of 90%. Diagnosis of overstretched ligaments had sensitivity of 50% and specificity of 94%. Complete tears were detected with sensitivity of 88% and specificity of 75% as diagnosed against all other ACL lesions and including normals.(ABSTRACT TRUNCATED AT 250 WORDS)
The measurement of surface tensions of liquids is in general a time‐consuming procedure requiring... more The measurement of surface tensions of liquids is in general a time‐consuming procedure requiring relatively large amounts, i.e. severals mls of liquid. The method to be introduced here is very rapid, using only about two drops of liquid, thereby combining some of the specific advantages of the respective standard methods.The principle is very simple. The pressure required to expel the liquid, of which the surface tension is to be determined, from a narrow pore in a thin glass plate is read on a manometer. According to Laplace's equation this pressure is proportional to the surface tension of the liquidP = γ (1/R1 + 1/R2) (1)where P is the pressure in dynes/cm2, γ the surface tension (dynes/cm) and R1 and R2 the two principal radii of curvature of the liquid surface in the pore (cm.Most organic liquids have contact angles with clean glass which are zero or very nearly so, and if the pore is cylindrical, R1 and R2 will both be equal to r, the radius of the pore, so that equation ...
Birds - Conservation, Research and Ecology [Working Title]
The contour feathers of water birds are well-known to show a variety of structural details that s... more The contour feathers of water birds are well-known to show a variety of structural details that serves to optimally confer a wide range of functions such as signaling, thermoregulation, buoyancy, water repellency, resistance to water penetration and resistance to the impact forces of diving, plunging and alighting. In this article we review these structural details and the manner in which they contribute to the specific functions. Some functions are in conflict with one another from which optimal balances have evolved. By assigning water bird families to a number of foraging niches we are able to quantitatively compare their functional differences. A number of new perspectives have followed from these comparisons.
Journal of the Science of Food and Agriculture, 1967
Extracted protein from Marula nuts were separated into their components by fractional precipitati... more Extracted protein from Marula nuts were separated into their components by fractional precipitation with ammonium sulphate and dilution with water. Two major components, constituting about 90% of the total protein, and the defatted meal were analysed for amino acid composition. The pattern of the constituents of the essential amino acids in Marula nuts differed only slightly from that for human milk and for whole hen's egg.
The purpose of this study was to determine if individuals with unilateral functional ankle instab... more The purpose of this study was to determine if individuals with unilateral functional ankle instability had decreased ability to maintain postural sway, as well as decreased isokinetic eccentric strength of ankle evertors and invertors. SUBJECTS WITH NO PREVIOUS HISTORY OF ANKLE INJURY WERE COMPARED WITH SUBJECTS WITH FUNCTIONAL ANKLE INSTABILITY ON THE FOLLOWING TESTS: isokinetic eccentric inversion and eversion strength and measures of single-limb postural sway. EIGHTEEN SUBJECTS PARTICIPATED IN THIS STUDY: 9 subjects in the functional instability (FI) group (age = 22.89 +/- 3.18 yr, ht = 181 +/- 6.0 cm, wt = 80.25 +/- 12.2 kg) and 9 noninjured (NI) controls (age = 26.22 +/- 2.34 yr, ht = 170 +/- 10.0 cm, wt = 65.08 +/- 12.03 kg). Subjects performed postural sway assessment on a balance system under static and dynamic conditions. Ankle inversion and eversion eccentric strength were evaluated at 90 degrees /sec using an isokinetic dynamometer. Additionally, we assessed the degree of...
To detect by magnetic resonance imaging (MRI) the presence and type of knee injuries in non-profe... more To detect by magnetic resonance imaging (MRI) the presence and type of knee injuries in non-professional runners after running an ultra-marathon, and to determine whether ultra-marathon running exacerbates pre-existing knee injuries or results in new permanent injuries. A prospective MRI study of one knee of 10 randomly selected participants who completed the Comrades Marathon between 1997 and 2002. Their knees were scanned 48 hours before the race, and 48 hours and 1 month after the race. All scans were performed at the Radiology Department, Wentworth Hospital, Durban, and the University of KwaZulu-Natal. Scores of all knee injuries detected on MRI scans immediately before the race, compared with the scores after the race. All scanned knees demonstrated an abnormal amount of joint fluid before the race; this increased immediately after the race in 5 runners and remained unchanged in another 5. At 1 month, 5 knees showed decreased joint fluid and 5 remained unchanged, but these were...
The structural details of the flight and contour feathers of seabirds closely match the requireme... more The structural details of the flight and contour feathers of seabirds closely match the requirements of their habitats and feeding habits. They serve a variety of functions ranging from intraspecific signaling to such physical qualities as thermal insulation, water repellency and resistance to impact. It comes as no surprise, therefore, that they are composed of an array of elements that confer these qualities to the optimal benefit of their avian bearer. In this chapter, the physical bases for these functions are provided in both mathematical and evolutionary terms. Some functions excel at the expense of others, and many species have evolved an optimal balance between functions in terms of both feather microstructure and behavioral patterns that suit their specific habitat and feeding habits. The effects of mechanical forces on feathers are presented in terms of the impact of diving, plunging and alighting, and the structural properties in seabird feathers identifiable as adaptatio...
Information on the parameters of polymeric networks obtained by crosslinking in solution can be p... more Information on the parameters of polymeric networks obtained by crosslinking in solution can be provided by deswelling measurements in polymer solutions of different concentration. However, under these conditions, the existing theories describing the swelling behavior are conflicting and no definite conclusion on the network properties seems as yet justifiable. Moreover, excluded volume and chain connectivity effects are not accounted for in either of the theories. Thirdly, the effect of the presence of crosslinkis and the number of connected polymer segments in the network on the value of the Huggins' interaction parameter to be used in the expressions for the free energy of mixing is not clear. Nevertheless, the available experimental data have shown some preference for Hermans' theory over Flory's theory, whereas James and Guth's expression must be rejected altogether. A dependence of the degree of swelling q0, at which the partial molar free energy of elasticity equals zero, on solvent power of the swelling agent has been previously observed and has been further investigated in this study. To this end, methyl methacrylate was copolymerized with small amounts of divinylbenzene in dilute benzene solutions yielding six samples with different crosslink densities and q0 values. A large dependence of q0 on the osmotic second virial coefficient in four solvents was observed. The applicability of current theories for polymer–solvent interaction upon intramolecular chain dimensions to the chains in the networks has been investigated. Flory's expression for volume expansion of polymer chains falls short, but two other relations for the same initial effect show that the second virial coefficient dependence of q0 may be attributed to volume exclusion, similarly as in free chains. The validity of these relations, however, is expected to hold only for a rather limited range of the network parameters.
Fifty-five patients with clinical suspicion of injury to their anterior cruciate ligament (ACL) w... more Fifty-five patients with clinical suspicion of injury to their anterior cruciate ligament (ACL) were examined by graded stress radiography before arthroscopic verification in an effort to determine the loss of ACL function as a result of ligament tearing. Using a commercially available stress device capable of applying varying pressures to the mid-calf, anterior drawers were measured from lateral radiographs at 0-, 7-, 14-, and 21-kiloPascal pressures and used to calculate the equivalent elastic modulus of the remaining ACL fibers. According to viscoelastic theory, this modulus is proportional to the number of elastically active fibers in the ligament. To verify the validity of this concept, the stress-strain relationship of a freshly excised ACL ligament was examined in a tensile testing machine, and the procedure was repeated after the ligament had been partially transsected with a scalpel. Comparison with the elastic modulus of the (intact) ACL of the opposite knee permits an estimate of the percentage of rupture in cases of partial tears. Overstretched ligaments show essentially normal viscoelastic properties once the slack in the ligament has been taken up. Complete tears, on the other hand, show a complete breakdown in the viscoelastic properties of the ACL. The results show that partial tears can be diagnosed by graded stress radiography with a sensitivity of 20% and specificity of 90%. Diagnosis of overstretched ligaments had sensitivity of 50% and specificity of 94%. Complete tears were detected with sensitivity of 88% and specificity of 75% as diagnosed against all other ACL lesions and including normals.(ABSTRACT TRUNCATED AT 250 WORDS)
The measurement of surface tensions of liquids is in general a time‐consuming procedure requiring... more The measurement of surface tensions of liquids is in general a time‐consuming procedure requiring relatively large amounts, i.e. severals mls of liquid. The method to be introduced here is very rapid, using only about two drops of liquid, thereby combining some of the specific advantages of the respective standard methods.The principle is very simple. The pressure required to expel the liquid, of which the surface tension is to be determined, from a narrow pore in a thin glass plate is read on a manometer. According to Laplace's equation this pressure is proportional to the surface tension of the liquidP = γ (1/R1 + 1/R2) (1)where P is the pressure in dynes/cm2, γ the surface tension (dynes/cm) and R1 and R2 the two principal radii of curvature of the liquid surface in the pore (cm.Most organic liquids have contact angles with clean glass which are zero or very nearly so, and if the pore is cylindrical, R1 and R2 will both be equal to r, the radius of the pore, so that equation ...
Birds - Conservation, Research and Ecology [Working Title]
The contour feathers of water birds are well-known to show a variety of structural details that s... more The contour feathers of water birds are well-known to show a variety of structural details that serves to optimally confer a wide range of functions such as signaling, thermoregulation, buoyancy, water repellency, resistance to water penetration and resistance to the impact forces of diving, plunging and alighting. In this article we review these structural details and the manner in which they contribute to the specific functions. Some functions are in conflict with one another from which optimal balances have evolved. By assigning water bird families to a number of foraging niches we are able to quantitatively compare their functional differences. A number of new perspectives have followed from these comparisons.
Journal of the Science of Food and Agriculture, 1967
Extracted protein from Marula nuts were separated into their components by fractional precipitati... more Extracted protein from Marula nuts were separated into their components by fractional precipitation with ammonium sulphate and dilution with water. Two major components, constituting about 90% of the total protein, and the defatted meal were analysed for amino acid composition. The pattern of the constituents of the essential amino acids in Marula nuts differed only slightly from that for human milk and for whole hen's egg.
The purpose of this study was to determine if individuals with unilateral functional ankle instab... more The purpose of this study was to determine if individuals with unilateral functional ankle instability had decreased ability to maintain postural sway, as well as decreased isokinetic eccentric strength of ankle evertors and invertors. SUBJECTS WITH NO PREVIOUS HISTORY OF ANKLE INJURY WERE COMPARED WITH SUBJECTS WITH FUNCTIONAL ANKLE INSTABILITY ON THE FOLLOWING TESTS: isokinetic eccentric inversion and eversion strength and measures of single-limb postural sway. EIGHTEEN SUBJECTS PARTICIPATED IN THIS STUDY: 9 subjects in the functional instability (FI) group (age = 22.89 +/- 3.18 yr, ht = 181 +/- 6.0 cm, wt = 80.25 +/- 12.2 kg) and 9 noninjured (NI) controls (age = 26.22 +/- 2.34 yr, ht = 170 +/- 10.0 cm, wt = 65.08 +/- 12.03 kg). Subjects performed postural sway assessment on a balance system under static and dynamic conditions. Ankle inversion and eversion eccentric strength were evaluated at 90 degrees /sec using an isokinetic dynamometer. Additionally, we assessed the degree of...
To detect by magnetic resonance imaging (MRI) the presence and type of knee injuries in non-profe... more To detect by magnetic resonance imaging (MRI) the presence and type of knee injuries in non-professional runners after running an ultra-marathon, and to determine whether ultra-marathon running exacerbates pre-existing knee injuries or results in new permanent injuries. A prospective MRI study of one knee of 10 randomly selected participants who completed the Comrades Marathon between 1997 and 2002. Their knees were scanned 48 hours before the race, and 48 hours and 1 month after the race. All scans were performed at the Radiology Department, Wentworth Hospital, Durban, and the University of KwaZulu-Natal. Scores of all knee injuries detected on MRI scans immediately before the race, compared with the scores after the race. All scanned knees demonstrated an abnormal amount of joint fluid before the race; this increased immediately after the race in 5 runners and remained unchanged in another 5. At 1 month, 5 knees showed decreased joint fluid and 5 remained unchanged, but these were...
The structural details of the flight and contour feathers of seabirds closely match the requireme... more The structural details of the flight and contour feathers of seabirds closely match the requirements of their habitats and feeding habits. They serve a variety of functions ranging from intraspecific signaling to such physical qualities as thermal insulation, water repellency and resistance to impact. It comes as no surprise, therefore, that they are composed of an array of elements that confer these qualities to the optimal benefit of their avian bearer. In this chapter, the physical bases for these functions are provided in both mathematical and evolutionary terms. Some functions excel at the expense of others, and many species have evolved an optimal balance between functions in terms of both feather microstructure and behavioral patterns that suit their specific habitat and feeding habits. The effects of mechanical forces on feathers are presented in terms of the impact of diving, plunging and alighting, and the structural properties in seabird feathers identifiable as adaptatio...
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