On using AMOS, EQS, LISREL, Mx, RAMONA and SEPATH for structural equation modeling
- Authors: Peprah, Syvester
- Date: 2000
- Subjects: Latent variables , Multivariate analysis , Mathematical statistics -- computer programs
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11082 , http://hdl.handle.net/10948/279 , Latent variables , Multivariate analysis , Mathematical statistics -- computer programs
- Description: Structural Equation Modeling is a common name for the statistical analysis of Structural Equation Models. Structural Equation Models are models that specify relationships between a set of variables and can be specified by means of path diagrams. A number of Structural Equation Modeling programs have been developed. These include, amongst others, AMOS, EQS, LISREL, Mx, RAMONA and SEPATH. A number of studies have been published on the use of some of the applications mentioned above. They include, amongst others, Brown (1986), Waller (1993) and Kano (1997). Structural Equation Models are increasingly being used in the social, economic and behavioral sciences. More and more people are therefore making use of one or more of the Structural Equation Modeling applications on the market. This study is performed with the aim of using each of the Structural Equation Modeling applications AMOS, EQS, LISREL, Mx, RAMONA and SEPATH for the first time and document the experience, joy and the difficulties encountered while using them. This treatise is different from the comparisons already published in that it is based on the use of AMOS, EQS, LISREL, Mx, RAMONA and SEPATH to fit a Structural Equation Model for peer influences on ambition, which is specified for data obtained by Duncan, Haller and Portes (1971), by myself as a first time user of each of the programs mentioned. The impressive features as well as the difficulties encountered are listed for each application. Recommendations for possible improvements to the various applications are also proposed. Finally, recommendations for future studies on the use of Structural Equation Modeling programs are made.
- Full Text:
- Date Issued: 2000
- Authors: Peprah, Syvester
- Date: 2000
- Subjects: Latent variables , Multivariate analysis , Mathematical statistics -- computer programs
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11082 , http://hdl.handle.net/10948/279 , Latent variables , Multivariate analysis , Mathematical statistics -- computer programs
- Description: Structural Equation Modeling is a common name for the statistical analysis of Structural Equation Models. Structural Equation Models are models that specify relationships between a set of variables and can be specified by means of path diagrams. A number of Structural Equation Modeling programs have been developed. These include, amongst others, AMOS, EQS, LISREL, Mx, RAMONA and SEPATH. A number of studies have been published on the use of some of the applications mentioned above. They include, amongst others, Brown (1986), Waller (1993) and Kano (1997). Structural Equation Models are increasingly being used in the social, economic and behavioral sciences. More and more people are therefore making use of one or more of the Structural Equation Modeling applications on the market. This study is performed with the aim of using each of the Structural Equation Modeling applications AMOS, EQS, LISREL, Mx, RAMONA and SEPATH for the first time and document the experience, joy and the difficulties encountered while using them. This treatise is different from the comparisons already published in that it is based on the use of AMOS, EQS, LISREL, Mx, RAMONA and SEPATH to fit a Structural Equation Model for peer influences on ambition, which is specified for data obtained by Duncan, Haller and Portes (1971), by myself as a first time user of each of the programs mentioned. The impressive features as well as the difficulties encountered are listed for each application. Recommendations for possible improvements to the various applications are also proposed. Finally, recommendations for future studies on the use of Structural Equation Modeling programs are made.
- Full Text:
- Date Issued: 2000
Ostrich calpastatin purification and partial characterization of the liver inhibitor
- Authors: Roman, Henry James
- Date: 2000
- Subjects: Calpastatin , Protease inhibitors , Ion exchange chromatography , Ostriches
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11090 , http://hdl.handle.net/10948/d1015522
- Description: The isolation and purification of calpastatin from ostrich liver is presented, along with its physicochemical and kinetic properties. By using extraction from liver, ion-exchange chromatography on DEAE-Toyopearl, heating to 90 °C for 10 min and rechromatography on Toyopearl Super-Q 650 S, ostrich calpastatin was isolated and purified from ostrich liver. The purified intact calpastatin showed homogeneity on SDS-PAGE (Mr of 105.6 K). Amino acid analysis showed that ostrich calpastatin resembled that of rabbit liver and human erythrocyte calpastatin. An N-terminal sequence could not be obtained because the N-terminus was found to be blocked by an as yet unknown amino acid residue. The Mr values of degradative forms of ostrich liver calpastatin were determined to be 56 K and 90 K. By using PAG-IEF the pI of the intact form was determined to be 5.1. Ostrich liver calpastatin behaved characteristically like other calpastatins during kinetic analysis. Calpastatin inhibited calpain from pH 6 to 9 and was found to be unaffected by temperatures as high as 100 °C. Calpastatin also inhibited calpain activity at Ca2+ concentrations ranging from 1 to 10 mM. The inhibitor was shown to be phosphorylated because after incubation with alkaline phosphatase there was a decrease in inhibitory activity. No inhibitory effects were detected against other proteases such as chymotrypsin and trypsin, with both proteases inactivating calpastatin completely. Ostrich liver calpain was shown to have a pH optimum of 7.5 and a temperature optimum of 30 °C. In terms of its thermodynamic properties it resembled that of other ostrich proteases; DH, DS and DG being 47.07 kJ/mol, -91.1 J/mol/K and 74.237 kJ/mol, respectively. Ostrich liver calpain showed a Km of 0.14 % (w/v). The enzyme was active at both milli- and micro-molar concentrations of Ca2+. Ostrich liver calpastatin showed many physical, chemical and kinetic properties similar to those of other known calpastatins.
- Full Text: false
- Date Issued: 2000
- Authors: Roman, Henry James
- Date: 2000
- Subjects: Calpastatin , Protease inhibitors , Ion exchange chromatography , Ostriches
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11090 , http://hdl.handle.net/10948/d1015522
- Description: The isolation and purification of calpastatin from ostrich liver is presented, along with its physicochemical and kinetic properties. By using extraction from liver, ion-exchange chromatography on DEAE-Toyopearl, heating to 90 °C for 10 min and rechromatography on Toyopearl Super-Q 650 S, ostrich calpastatin was isolated and purified from ostrich liver. The purified intact calpastatin showed homogeneity on SDS-PAGE (Mr of 105.6 K). Amino acid analysis showed that ostrich calpastatin resembled that of rabbit liver and human erythrocyte calpastatin. An N-terminal sequence could not be obtained because the N-terminus was found to be blocked by an as yet unknown amino acid residue. The Mr values of degradative forms of ostrich liver calpastatin were determined to be 56 K and 90 K. By using PAG-IEF the pI of the intact form was determined to be 5.1. Ostrich liver calpastatin behaved characteristically like other calpastatins during kinetic analysis. Calpastatin inhibited calpain from pH 6 to 9 and was found to be unaffected by temperatures as high as 100 °C. Calpastatin also inhibited calpain activity at Ca2+ concentrations ranging from 1 to 10 mM. The inhibitor was shown to be phosphorylated because after incubation with alkaline phosphatase there was a decrease in inhibitory activity. No inhibitory effects were detected against other proteases such as chymotrypsin and trypsin, with both proteases inactivating calpastatin completely. Ostrich liver calpain was shown to have a pH optimum of 7.5 and a temperature optimum of 30 °C. In terms of its thermodynamic properties it resembled that of other ostrich proteases; DH, DS and DG being 47.07 kJ/mol, -91.1 J/mol/K and 74.237 kJ/mol, respectively. Ostrich liver calpain showed a Km of 0.14 % (w/v). The enzyme was active at both milli- and micro-molar concentrations of Ca2+. Ostrich liver calpastatin showed many physical, chemical and kinetic properties similar to those of other known calpastatins.
- Full Text: false
- Date Issued: 2000
Outsourcing for competitive advantage : an evaluation of an owner driver proposition in a South African removals company
- Authors: Coleman, Belinda
- Date: 2000
- Subjects: Contracting out -- South Africa , Storage and removal trade -- Subcontracting -- South Africa , Trucking -- South Africa , Benchmarking (Management) -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:11002 , http://hdl.handle.net/10948/d1015540
- Description: The aim of the research was to assess what competitive advantage a Removals company could expect to gain by outsourcing its driver function to owner drivers. An extensive literature review identified key outsourcing issues. The literature was related to a case study of Stuttaford Van Lines (SVL), a company that is experiencing problems with its current independent contractor driver arrangements and that needs to review its outsourcing decision. In order to learn from best practice in the field of outsourcing to owner drivers, a benchmarking exercise was undertaken at South African Breweries (SAB). The benchmarking exercise identified six key issues that contributed to the success of the SAB owner driver scheme. These points, together with others identified from the literature, were integrated into a recommended outsourcing implementation process for SVL. The research found that it is possible for SVL to outsource the driver function to owner drivers and that such a scheme can be expected to improve customer service levels. The success of the scheme will depend on the selection of the drivers and how effectively it is managed. It was found that it would not be profitable for SVL to outsource to owner drivers using the compensation model proposed. Cost reduction is however only one of the factors to consider in an outsourcing decision.
- Full Text:
- Date Issued: 2000
- Authors: Coleman, Belinda
- Date: 2000
- Subjects: Contracting out -- South Africa , Storage and removal trade -- Subcontracting -- South Africa , Trucking -- South Africa , Benchmarking (Management) -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:11002 , http://hdl.handle.net/10948/d1015540
- Description: The aim of the research was to assess what competitive advantage a Removals company could expect to gain by outsourcing its driver function to owner drivers. An extensive literature review identified key outsourcing issues. The literature was related to a case study of Stuttaford Van Lines (SVL), a company that is experiencing problems with its current independent contractor driver arrangements and that needs to review its outsourcing decision. In order to learn from best practice in the field of outsourcing to owner drivers, a benchmarking exercise was undertaken at South African Breweries (SAB). The benchmarking exercise identified six key issues that contributed to the success of the SAB owner driver scheme. These points, together with others identified from the literature, were integrated into a recommended outsourcing implementation process for SVL. The research found that it is possible for SVL to outsource the driver function to owner drivers and that such a scheme can be expected to improve customer service levels. The success of the scheme will depend on the selection of the drivers and how effectively it is managed. It was found that it would not be profitable for SVL to outsource to owner drivers using the compensation model proposed. Cost reduction is however only one of the factors to consider in an outsourcing decision.
- Full Text:
- Date Issued: 2000
Possible crosstalk between signal transduction pathways in the induction of differentiation in HT-29 cells
- Authors: Jamie, Hajierah
- Date: 2000
- Subjects: Cellular signal transduction , Cell differentiation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11096 , http://hdl.handle.net/10948/d1019684
- Description: The investigation into the mechanisms by which compounds such as butyrate induce differentiation in HT-29 cells, is lacking. The colonic carcinoma cell line, HT-29, undergoes differentiation induction in the presence of butyrate and acetoacetate. The Caco-2 cell line spontaneously differentiates on contact inhibition. In this study, a signal transduction pathway involving ATP, cAMP, Ca2+ and the transcriptional factor CREB was investigated following suggestions that the energy state of the cell and diffferentiation are linked. The activity of the MAP kinase cascade, including possible crosstalk that may exist between these pathways was determined. The HT-29 cells were exposed to 5 mM acetoacetate, butyrate, DMSO and propionate. The results of this differentiation induction were compared to Caco-2 and HeLa cells, which are cervical carcinoma cells. It was found that ATP levels are decreased on differentiation induction in HT-29 cells, which, in turn affected the cAMP concentrations. Theoretically, the inducers do not have any effect on PDE 4 activity, and may facilitate the interaction between cAMP and PKA. Influx of Ca2+ into the cells was inhibited to a degree by the inducers, which was possibly overcome by crosstalk between the cAMP and Ca2+ pathways. CREB activation, lineage-specific gene expression, ERK activity and c-myc expression were all dependent on both the inducers used and the cell-type. PKA played a major role in CREB activation in acetoacetate- and butyrate -induced HT-29, Caco-2 and HeLa cells, while a2+/Calmodulin-dependent kinases I/IV may have a secondary role. Alkaline phosphatase expression in HeLa cells was independent of CREB. Evidence that crosstalk between the MAP kinase cascade and the REBactivation pathways exist, was illustrated by increased CREB activation on ERK inhibition in acetoacetate- and butyrate-induced HT-29 and HeLa cells. Also, the role that ERK played in the cells differed with inducer and cell-type. The dependence of cmyc expression on c-jun and c-fos, appeared to be differentiation induction- and celltype specific. Results from this study indicate the potential use of acetoacetate and butyrate as anti-cancer compounds.
- Full Text:
- Date Issued: 2000
- Authors: Jamie, Hajierah
- Date: 2000
- Subjects: Cellular signal transduction , Cell differentiation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11096 , http://hdl.handle.net/10948/d1019684
- Description: The investigation into the mechanisms by which compounds such as butyrate induce differentiation in HT-29 cells, is lacking. The colonic carcinoma cell line, HT-29, undergoes differentiation induction in the presence of butyrate and acetoacetate. The Caco-2 cell line spontaneously differentiates on contact inhibition. In this study, a signal transduction pathway involving ATP, cAMP, Ca2+ and the transcriptional factor CREB was investigated following suggestions that the energy state of the cell and diffferentiation are linked. The activity of the MAP kinase cascade, including possible crosstalk that may exist between these pathways was determined. The HT-29 cells were exposed to 5 mM acetoacetate, butyrate, DMSO and propionate. The results of this differentiation induction were compared to Caco-2 and HeLa cells, which are cervical carcinoma cells. It was found that ATP levels are decreased on differentiation induction in HT-29 cells, which, in turn affected the cAMP concentrations. Theoretically, the inducers do not have any effect on PDE 4 activity, and may facilitate the interaction between cAMP and PKA. Influx of Ca2+ into the cells was inhibited to a degree by the inducers, which was possibly overcome by crosstalk between the cAMP and Ca2+ pathways. CREB activation, lineage-specific gene expression, ERK activity and c-myc expression were all dependent on both the inducers used and the cell-type. PKA played a major role in CREB activation in acetoacetate- and butyrate -induced HT-29, Caco-2 and HeLa cells, while a2+/Calmodulin-dependent kinases I/IV may have a secondary role. Alkaline phosphatase expression in HeLa cells was independent of CREB. Evidence that crosstalk between the MAP kinase cascade and the REBactivation pathways exist, was illustrated by increased CREB activation on ERK inhibition in acetoacetate- and butyrate-induced HT-29 and HeLa cells. Also, the role that ERK played in the cells differed with inducer and cell-type. The dependence of cmyc expression on c-jun and c-fos, appeared to be differentiation induction- and celltype specific. Results from this study indicate the potential use of acetoacetate and butyrate as anti-cancer compounds.
- Full Text:
- Date Issued: 2000
The isolation and partial characterization of a2-antiplasmin and plasminogen from ostrich plasma
- Authors: Thomas, Adele René
- Date: 2000
- Subjects: Serpins , Ostriches , Antifibrinolytic agents , Plasminogen , Plasmin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11080 , http://hdl.handle.net/10948/274 , http://hdl.handle.net/10948/d1005751 , Serpins , Ostriches , Antifibrinolytic agents , Plasminogen , Plasmin
- Description: This study reports the isolation, purification and partial characterisation of the ostrich serpin, a2AP, as well as its target enzyme, ostrich plasmin, in its active and inactive proenzyme, viz. plasminogen, forms. Three different procedures were undertaken to isolate and purify ostrich a2AP. The first one involved L-lysine-Sepharose chromatography, ammonium sulfate fractionation, ion-exchange chromatography on Toyopearl Super-Q 650S, and ostrich plasminogen-Sepharose affinity chromatography. The second procedure replaced the latter chromatographic step with gel filtration on Sephadex G-200 and hydroxylapatite chromatography, while the third one employed instead the theoretically more efficient LBSI-Sepharose chromatographic step. The third procedure yielded purified ostrich a2AP, but the degree of purity and yield were relatively low. Ostrich plasminogen was highly purified after L-lysine-Sepharose chromatography and ostrich plasmin was obtained by the urokinase-activation of the purified ostrich plasminogen Ostrich a2AP revealed an Mr of 77-84 K and two isoelectric forms of pI 3.85 and 6.18. Nterminal sequence analysis showed ostrich a2AP to have only 2 out of 11 residues in common with both those of human and bovine a2AP. Ostrich a2AP showed the largest inhibitory effects on ostrich plasmin, followed by comm. bovine chymotrypsin, trypsin and plasmin, in that order, and it appeared to be a much less potent plasmin inhibitor than bovine aprotinin, but a much more potent one than the synthetic inhibitors, DFP and EACA. Ostrich plasminogen showed an Mr of 92 K and multiple isoelectric forms (~7) in the pI range 6.01-9.18, with a major one of pI 6.01. It showed a total of 775 amino acid residues and its N-terminal sequence showed ~53 percent identity with those of human, rabbit, cat, and ox plasminogens. Ostrich plasmin revealed an Mr of 78 K, two isoelectric forms of pI 4.07 and 6.01, and a total of 638 amino acid residues. N-terminal sequence analysis showed that 2-4 residues are identical to the 5 of human, cat, dog, rabbit, and ox plasmins. The pH and temperature optima of ostrich plasmin were determined as 8.0 and 40 oC, respectively. The thermodynamic and kinetic parameters of ostrich plasmin were computed, and plasmin was shown to prefer Lys to Arg residues in the S1 position. In conclusion, ostrich a2AP, plasminogen and plasmin showed definite similarities to their mammalian counterparts, but there were also significant differences.
- Full Text:
- Date Issued: 2000
- Authors: Thomas, Adele René
- Date: 2000
- Subjects: Serpins , Ostriches , Antifibrinolytic agents , Plasminogen , Plasmin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11080 , http://hdl.handle.net/10948/274 , http://hdl.handle.net/10948/d1005751 , Serpins , Ostriches , Antifibrinolytic agents , Plasminogen , Plasmin
- Description: This study reports the isolation, purification and partial characterisation of the ostrich serpin, a2AP, as well as its target enzyme, ostrich plasmin, in its active and inactive proenzyme, viz. plasminogen, forms. Three different procedures were undertaken to isolate and purify ostrich a2AP. The first one involved L-lysine-Sepharose chromatography, ammonium sulfate fractionation, ion-exchange chromatography on Toyopearl Super-Q 650S, and ostrich plasminogen-Sepharose affinity chromatography. The second procedure replaced the latter chromatographic step with gel filtration on Sephadex G-200 and hydroxylapatite chromatography, while the third one employed instead the theoretically more efficient LBSI-Sepharose chromatographic step. The third procedure yielded purified ostrich a2AP, but the degree of purity and yield were relatively low. Ostrich plasminogen was highly purified after L-lysine-Sepharose chromatography and ostrich plasmin was obtained by the urokinase-activation of the purified ostrich plasminogen Ostrich a2AP revealed an Mr of 77-84 K and two isoelectric forms of pI 3.85 and 6.18. Nterminal sequence analysis showed ostrich a2AP to have only 2 out of 11 residues in common with both those of human and bovine a2AP. Ostrich a2AP showed the largest inhibitory effects on ostrich plasmin, followed by comm. bovine chymotrypsin, trypsin and plasmin, in that order, and it appeared to be a much less potent plasmin inhibitor than bovine aprotinin, but a much more potent one than the synthetic inhibitors, DFP and EACA. Ostrich plasminogen showed an Mr of 92 K and multiple isoelectric forms (~7) in the pI range 6.01-9.18, with a major one of pI 6.01. It showed a total of 775 amino acid residues and its N-terminal sequence showed ~53 percent identity with those of human, rabbit, cat, and ox plasminogens. Ostrich plasmin revealed an Mr of 78 K, two isoelectric forms of pI 4.07 and 6.01, and a total of 638 amino acid residues. N-terminal sequence analysis showed that 2-4 residues are identical to the 5 of human, cat, dog, rabbit, and ox plasmins. The pH and temperature optima of ostrich plasmin were determined as 8.0 and 40 oC, respectively. The thermodynamic and kinetic parameters of ostrich plasmin were computed, and plasmin was shown to prefer Lys to Arg residues in the S1 position. In conclusion, ostrich a2AP, plasminogen and plasmin showed definite similarities to their mammalian counterparts, but there were also significant differences.
- Full Text:
- Date Issued: 2000
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