Causes of reproducibility problem in thin film deposition using magnetron sputtering have been identified. To remedy this problem, one must calibrate deposition rate after installation of a new target or magnetron and should repeat such calibrations as frequently as possible in order to obtain films with reproducible properties. For magnetrons used in our laboratory to be in working condition, the transverse magnetic field strength on the surface of the magnetron should be about 50 mT or more.
{"title":"Causes of film property reproducibility problem in magnetron sputtering","authors":"J. Mwabora, R. Kivaisi","doi":"10.4314/AJST.V1I4.44625","DOIUrl":"https://doi.org/10.4314/AJST.V1I4.44625","url":null,"abstract":"Causes of reproducibility problem in thin film deposition using magnetron sputtering have been identified. To remedy this problem, one must calibrate deposition rate after installation of a new target or magnetron and should repeat such calibrations as frequently as possible in order to obtain films with reproducible properties. For magnetrons used in our laboratory to be in working condition, the transverse magnetic field strength on the surface of the magnetron should be about 50 mT or more.","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"44 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2009-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75677706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Human onchocerciasis is a debilitating disease, which causes lymphatic obstruction and gives rise to genital elephantiasis. The microfilariae also cause severe itching, while invasion of the eyes by large numbers, and the reaction to their presence, lead to river blindness. This results in severe medical, social and economic problems (Stevenson 1987).The implications of the disease bring about the need to control onchocerciasis by understanding the mechanism of the host’s resistance. The aim of this study was to investigate the possibility of using laboratory rodents as models for immunological studies of onchocerciasis. Living adult Onchocerca (O.) armillata and O. volvulus were surgically transplanted into the peritoneal cavities of rats, after initial immunizations or transplantations, in order to investigate the survival rates of the transplanted parasites. Steroid administration significantly improved the survival rate of implanted O. armillata in rats at 60 days (X2 = 3, df =1, P<0.05). A similar effect was produced in O. volvulus with the survival rate being significantly higher than in rats not treated with cortisone (x2 = 6.3, df = 1, P <0.01). Immunization with extracts of O. volvulus and O. armillata or implantation of rats with live adult worms hindered the survival of homologous implants significantly, while no such effect was produced in heterologous implants. Immunization with microfilariae of either species of worms had no effect on the survival rate of subsequent implants of adult worms of the same species. Immunization with the peritoneal exudates, obtained from rats previously implanted with adult O. volvulus had a significant inhibitory effect on the survival of subsequently implanted adult O. volvulus (X2 =27, df = 1, P<. 001). The model is valuable for immunological and chemotherapeutic studies of the two species of Onchocerca.
{"title":"Immunological studies on the mechanism of resistance in experimental onchocerciasis","authors":"D. Akinboye","doi":"10.4314/AJST.V1I4.44620","DOIUrl":"https://doi.org/10.4314/AJST.V1I4.44620","url":null,"abstract":"Human onchocerciasis is a debilitating disease, which causes lymphatic obstruction and gives rise to genital elephantiasis. The microfilariae also cause severe itching, while invasion of the eyes by large numbers, and the reaction to their presence, lead to river blindness. This results in severe medical, social and economic problems (Stevenson 1987).The implications of the disease bring about the need to control onchocerciasis by understanding the mechanism of the host’s resistance. The aim of this study was to investigate the possibility of using laboratory rodents as models for immunological studies of onchocerciasis. Living adult Onchocerca (O.) armillata and O. volvulus were surgically transplanted into the peritoneal cavities of rats, after initial immunizations or transplantations, in order to investigate the survival rates of the transplanted parasites. Steroid administration significantly improved the survival rate of implanted O. armillata in rats at 60 days (X2 = 3, df =1, P<0.05). A similar effect was produced in O. volvulus with the survival rate being significantly higher than in rats not treated with cortisone (x2 = 6.3, df = 1, P <0.01). Immunization with extracts of O. volvulus and O. armillata or implantation of rats with live adult worms hindered the survival of homologous implants significantly, while no such effect was produced in heterologous implants. Immunization with microfilariae of either species of worms had no effect on the survival rate of subsequent implants of adult worms of the same species. Immunization with the peritoneal exudates, obtained from rats previously implanted with adult O. volvulus had a significant inhibitory effect on the survival of subsequently implanted adult O. volvulus (X2 =27, df = 1, P<. 001). The model is valuable for immunological and chemotherapeutic studies of the two species of Onchocerca.","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"136 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2009-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86307285","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cet article presente une etude de l’emission infrarouge de lames semi-transparentes non diffusantes, soumises sur une de leurs faces a une excitation periodique de temperature. Un modele non couple de luminance en regime sinusoidal permet de calculer le flux emis par la lame. Au voisinage de la temperature ambiante et pour le materiau considere, les transferts thermiques radiatifs au sein de la lame peuvent - en premiere approximation - etre negliges, ce qui justifie l’emploi du modele non couple. Les ecarts entre les modeles couple et non couple ne depassent pas 4% sur les modules et 3° sur les phases. Une etude experimentale est menee sur des echantillons de PEHD, d’epaisseurs 3 mm et 5 mm, modules autour de la temperature ambiante sous la forme d’une somme de sept sinusoides, de frequences comprises entre 0,78 mHz et 50 mHz. L’analyse spectrale des signaux mesures permet de calculer, pour chaque frequence de modulation, l’amplitude et la phase de la luminance de l’echantillon et de la temperature du support. Par identification des mesures au modele conductif, il est possible de determiner les caracteristiques thermiques du materiau (diffusivite, nombre de Biot) qui sont necessaires dans les modeles thermiques. Les valeurs experimentales de luminance sont en accord, en module et en phase, avec les valeurs calculees. Les incertitudes statistiques calculees sont inferieures a 9% sur les modules et 5° sur les phases, quelle que soit l’epaisseur d’echantillon choisie. Mots cles : Detection synchrone, emissivite, mesure, modelisation, rayonnement, radiometrie
{"title":"Validation expérimentale d’un modèle de luminance non couplé sur des échantillons de polyéthylène haute densité (pehd) soumis à une excitation périodique de température au voisinage de l’ambiance","authors":"Y. N’Guessan, M. Sako, L. N’guessan, P. Gbaha","doi":"10.4314/AJST.V8I1","DOIUrl":"https://doi.org/10.4314/AJST.V8I1","url":null,"abstract":"Cet article presente une etude de l’emission infrarouge de lames semi-transparentes non diffusantes, soumises sur une de leurs faces a une excitation periodique de temperature. Un modele non couple de luminance en regime sinusoidal permet de calculer le flux emis par la lame. Au voisinage de la temperature ambiante et pour le materiau considere, les transferts thermiques radiatifs au sein de la lame peuvent - en premiere approximation - etre negliges, ce qui justifie l’emploi du modele non couple. Les ecarts entre les modeles couple et non couple ne depassent pas 4% sur les modules et 3° sur les phases. Une etude experimentale est menee sur des echantillons de PEHD, d’epaisseurs 3 mm et 5 mm, modules autour de la temperature ambiante sous la forme d’une somme de sept sinusoides, de frequences comprises entre 0,78 mHz et 50 mHz. L’analyse spectrale des signaux mesures permet de calculer, pour chaque frequence de modulation, l’amplitude et la phase de la luminance de l’echantillon et de la temperature du support. Par identification des mesures au modele conductif, il est possible de determiner les caracteristiques thermiques du materiau (diffusivite, nombre de Biot) qui sont necessaires dans les modeles thermiques. Les valeurs experimentales de luminance sont en accord, en module et en phase, avec les valeurs calculees. Les incertitudes statistiques calculees sont inferieures a 9% sur les modules et 5° sur les phases, quelle que soit l’epaisseur d’echantillon choisie. Mots cles : Detection synchrone, emissivite, mesure, modelisation, rayonnement, radiometrie","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"27 1","pages":"87-93"},"PeriodicalIF":0.0,"publicationDate":"2007-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74227988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A three-parametric modification of Berthelot's equation of state with an extra parameter n in the expression for the internal pressure (a generalised Berthelot's equation) was examined. The reduced form of this equation and formulae for the calculation of the spinodal were obtained. The spinodal of water was calculated. For a series of substances, the parameters of the spinodal at zero pressure and zero thermodynamic temperature were calculated. It was established that, in the region of positive pressures, the generalised Berthelot's equation describes the position of the spinodal on the phase diagram better than the generalised van der Waals equation, while preference is given to the generalised van der Waals equation in the region of negative pressures at low temperatures, since it gives an idea of the theoretical tensile strength of the liquid phase of a substance. Keywords : binodal, spinodal, Berthelot's equation, critical point, metastable liquid, negative pressure, theoretical tensile strength, van der Waals equation African Journal of Science and Technology Vol. 5(2) 2004: 1-8
{"title":"The boundary curve of thermodynamic stability of the liquid phase on the basis of a generalised Berthelot's equation","authors":"P. Tamanga, D. Lissouck, F. Lontisi, M. Tchoffo","doi":"10.4314/AJST.V5I2.15337","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15337","url":null,"abstract":"A three-parametric modification of Berthelot's equation of state with an extra parameter n in the expression for the internal pressure (a generalised Berthelot's equation) was examined. The reduced form of this equation and formulae for the calculation of the spinodal were obtained. The spinodal of water was calculated. For a series of substances, the parameters of the spinodal at zero pressure and zero thermodynamic temperature were calculated. It was established that, in the region of positive pressures, the generalised Berthelot's equation describes the position of the spinodal on the phase diagram better than the generalised van der Waals equation, while preference is given to the generalised van der Waals equation in the region of negative pressures at low temperatures, since it gives an idea of the theoretical tensile strength of the liquid phase of a substance. Keywords : binodal, spinodal, Berthelot's equation, critical point, metastable liquid, negative pressure, theoretical tensile strength, van der Waals equation African Journal of Science and Technology Vol. 5(2) 2004: 1-8","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"11 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91418068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Dampare, D. Asiedu, S. Osae, J. Manu, B. Banoeng-Yakubo
The Birim Diamondiferous field from which most of the alluvial diamonds are recovered is underlain by Lower Proterozoic Birimian metasedimentary and associated mafic rocks. Bulk rock geochemistry was carried out on the sandstones from the metasedimentary rocks to constrain the tectonic setting during the early Proterozoic. Bulk rock geochemical studies on greywackes show that they are characterized by moderately low but variable SiO2 contents, generally high Al2O3 and ferromagnesian element (e.g., Fe, Mg, Cr, V, Co, Sc) contents, and K2O/Na20 commonly less than 1. The geochemical data indicate that the greywackes were deposited in an active continental margin environment. The detritus were mainly derived from the upper continental crust but with an admixture of mafic component. Recent studies have shown that some of the mafics/ultramafics are diamondiferous metakimberlites. The inferred tectonic (arc) setting makes the emplacement of the so-called Proterozoic diamondiferous metakimberlites unlikely, if we are to go by the Clifford's Rule. However, if these ultramafic rocks are really metakimberlites and the source of the diamonds, then the Clifford's Rule may not be applicable in the Ghanaian situation, and the Birim field may be one of the few exceptions to this general rule. This would, then, present a typical example of subduction zone related diamondiferous kimberlites. Keywords : Birim Diamondiferous field, Birimian, geochemistry, Ghana, tectornc setting African Journal of Science and Technology Vol. 5(2) 2004: 9-18
{"title":"Geochemistry of lower proterozoic greywackes from the Birim diamondiferous field, Ghana","authors":"S. Dampare, D. Asiedu, S. Osae, J. Manu, B. Banoeng-Yakubo","doi":"10.4314/AJST.V5I2.15326","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15326","url":null,"abstract":"The Birim Diamondiferous field from which most of the alluvial diamonds are recovered is underlain by Lower Proterozoic Birimian metasedimentary and associated mafic rocks. Bulk rock geochemistry was carried out on the sandstones from the metasedimentary rocks to constrain the tectonic setting during the early Proterozoic. Bulk rock geochemical studies on greywackes show that they are characterized by moderately low but variable SiO2 contents, generally high Al2O3 and ferromagnesian element (e.g., Fe, Mg, Cr, V, Co, Sc) contents, and K2O/Na20 commonly less than 1. The geochemical data indicate that the greywackes were deposited in an active continental margin environment. The detritus were mainly derived from the upper continental crust but with an admixture of mafic component. Recent studies have shown that some of the mafics/ultramafics are diamondiferous metakimberlites. The inferred tectonic (arc) setting makes the emplacement of the so-called Proterozoic diamondiferous metakimberlites unlikely, if we are to go by the Clifford's Rule. However, if these ultramafic rocks are really metakimberlites and the source of the diamonds, then the Clifford's Rule may not be applicable in the Ghanaian situation, and the Birim field may be one of the few exceptions to this general rule. This would, then, present a typical example of subduction zone related diamondiferous kimberlites. Keywords : Birim Diamondiferous field, Birimian, geochemistry, Ghana, tectornc setting African Journal of Science and Technology Vol. 5(2) 2004: 9-18","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87713360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The effects of different fillet radii, clamp area dimensions, and pinhole loading through a hole located in the clamp area of a dog bone specimen were investigated using the Finite Element Analysis (FEA) software Abaqus. Changes in the fillet radius were shown to have little effect on the distribution and magnitude of the von Mises stresses. Different dimensions of the clamp section gave different von Mises stress distributions within the clamp section, with the maximum values remaining within the gauge section, thus implying that limitations of available cutters and material could be accommodated by varying the dimensions of test specimens. Introduction of pinhole loading in order to minimise torsion, led to a shift of the maximum von Mises stress from the gauge section to the edge of the pinhole, an indication that the benefits of minimising torsion required to be weighed carefully. The observed shift was only significant however, for failure load levels and for cyclic loading. A set percentage change rather than the absolute convergence of the von Mises stresses was shown to be a more economical way of arriving at an optimal mesh density, a characteristic that was seen to vary from one location to another. African Journal of Science and Technology Vol. 5(2) 2004: 60-72
{"title":"Dimensioning of dog bone specimens and numerical analysis of the effects of different fillet radii, clamp area and pinhole loading on the stresses in such specimens","authors":"M. Maringa","doi":"10.4314/AJST.V5I2.15331","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15331","url":null,"abstract":"The effects of different fillet radii, clamp area dimensions, and pinhole loading through a hole located in the clamp area of a dog bone specimen were investigated using the Finite Element Analysis (FEA) software Abaqus. Changes in the fillet radius were shown to have little effect on the distribution and magnitude of the von Mises stresses. Different dimensions of the clamp section gave different von Mises stress distributions within the clamp section, with the maximum values remaining within the gauge section, thus implying that limitations of available cutters and material could be accommodated by varying the dimensions of test specimens. Introduction of pinhole loading in order to minimise torsion, led to a shift of the maximum von Mises stress from the gauge section to the edge of the pinhole, an indication that the benefits of minimising torsion required to be weighed carefully. The observed shift was only significant however, for failure load levels and for cyclic loading. A set percentage change rather than the absolute convergence of the von Mises stresses was shown to be a more economical way of arriving at an optimal mesh density, a characteristic that was seen to vary from one location to another. African Journal of Science and Technology Vol. 5(2) 2004: 60-72","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"32 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77279538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dissolution of phosphate rock (PR) depends on inherent chemical and physical properties of the rock and on external factors such as soils and plants. The objective of this study was to investigate, with a soil incubation experiment, the relationship between selected soil factors and extractable phosphorus (P) in order to assess the potential of using nonconventional phosphate fertilizers derived from unreactive Dorowa (Zimbabwe) PR on Zimbabwe soils. Three phosphate fertilizer materials: finely ground (0.150-mm screen) Dorowa PR (DPR); DPR partially acidulated with 50 % of the sulfuric acid required for complete acidulation (PADPR); and a compacted mixture of DPR + triple superphosphate (TSP) + urea + potassium chloride (DTUK) with half of the P from DPR and half from TSP, were made from Dorowa rock. Their relative effectiveness in supplying P was compared with that of single superphosphate on soils that varied in properties thought to influence PR dissolution and P availability. The effectiveness of the P sources in supplying Bray-I P after a 40-day and Pi P after a 90-day soil incubation period followed the order of SSP>DTUK>PADPR>DPR=Check. Soils high in clay, soil organic matter, and iron oxides content yielded significantly less extractable P than soils with low content. African Journal of Science and Technology Vol. 5(2) 2004: 73-82
{"title":"Evaluation of dissolution of nonconventional phosphate fertilizers in Zimbabwe soils: effects of soil properties","authors":"E. Govere, Shiuan-Yuh Chien, R. Fox","doi":"10.4314/AJST.V5I2.15327","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15327","url":null,"abstract":"Dissolution of phosphate rock (PR) depends on inherent chemical and physical properties of the rock and on external factors such as soils and plants. The objective of this study was to investigate, with a soil incubation experiment, the relationship between selected soil factors and extractable phosphorus (P) in order to assess the potential of using nonconventional phosphate fertilizers derived from unreactive Dorowa (Zimbabwe) PR on Zimbabwe soils. Three phosphate fertilizer materials: finely ground (0.150-mm screen) Dorowa PR (DPR); DPR partially acidulated with 50 % of the sulfuric acid required for complete acidulation (PADPR); and a compacted mixture of DPR + triple superphosphate (TSP) + urea + potassium chloride (DTUK) with half of the P from DPR and half from TSP, were made from Dorowa rock. Their relative effectiveness in supplying P was compared with that of single superphosphate on soils that varied in properties thought to influence PR dissolution and P availability. The effectiveness of the P sources in supplying Bray-I P after a 40-day and Pi P after a 90-day soil incubation period followed the order of SSP>DTUK>PADPR>DPR=Check. Soils high in clay, soil organic matter, and iron oxides content yielded significantly less extractable P than soils with low content. African Journal of Science and Technology Vol. 5(2) 2004: 73-82","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"87 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80595874","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cashew nut shell liquid (CNSL) a natural product that consists of a mixture of phenolic compounds was separated into cardanol, cardol, and 2 - methylcardol using column chromatography. The separation was aimed at recovering cardanol that can be used in the synthesis of cation-exchange resin. The separation was effected using a mixture of equal portions of benzene and chloroform as the mobile phase in a column packed with silica gel adsorbent of particle size 60–120 mesh as the stationary phase. The mean RF-values determined from the study were cardanol (0.516), cardol (0.173) and 2-methylcardol (0.148). The corresponding RM-values calculated were cardanol (-0.040), cardol (0.673), 2-methylcardol (0.753). The RF-value is a measure of the affinity of the component for the mobile phase. The results show that the component that eluted first from the column which was cardanol had the highest affinity for the mobile phase, followed by cardol while the 2-methylcardol had the least affinity. The RM-value is a measure of the polarity of the component and its affinity for the stationary phase. The results of this study show that the component that eluted last from the column which was 2-methylcardol was the most polar. The molecular structures of these three components also show that 2-methylcardol is the most polar followed by cardol and the least polar was cardanol. The RF-value of cardanol obtained in this study could be used in the design of an industrial chromatographic column for its separation from CNSL. African Journal of Science and Technology Vol. 5(2) 2004: 92-95
{"title":"Separation of cashew nut shell liquid by column chromatography","authors":"P. Oghome, A. Kehinde","doi":"10.4314/AJST.V5I2.15328","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15328","url":null,"abstract":"Cashew nut shell liquid (CNSL) a natural product that consists of a mixture of phenolic\u0000compounds was separated into cardanol, cardol, and 2 - methylcardol using column chromatography. The separation was aimed at recovering cardanol that can be used in the synthesis of cation-exchange resin. The separation was effected using a mixture of equal portions of benzene and chloroform as the mobile phase in a column packed with silica gel adsorbent of particle size 60–120 mesh as the stationary phase. The mean RF-values determined from the study were cardanol (0.516), cardol (0.173) and 2-methylcardol (0.148). The corresponding RM-values calculated were cardanol (-0.040), cardol (0.673), 2-methylcardol (0.753). The RF-value is a measure of the affinity of the component for the mobile phase. The results show that the component that eluted first from the column which was cardanol had the highest affinity for the mobile phase, followed by cardol while the 2-methylcardol had the least affinity. The RM-value is a measure of the polarity of the component and its affinity for the stationary phase. The results of this study show that the component that eluted last from the column which was 2-methylcardol was the most polar. The molecular structures of these three components also show that 2-methylcardol is the most polar followed by cardol and the least polar was cardanol. The RF-value of cardanol obtained in this study could be used in the design of an industrial chromatographic column for its separation from CNSL. African Journal of Science and Technology Vol. 5(2) 2004: 92-95","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"445 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78185434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper addresses the concerns of Faraway and Chatfield (1998) who questioned the forecasting ability of Artificial Neural Networks (ANN). In particular the paper compares the performance of Artificial Neural Networks (ANN) and ARIMA models in forecasting of seasonal (monthly) Time series. Using the Airline data which Faraway and Chatfield (1998) used and two other data sets and taking into consideration their suggestions, we show that ANN are not as bad as Faraway and Chatfield put it. A rule of selecting input lags into the input set based on their relevance/ contribution to the model is also proposed.
{"title":"SEASONAL TIME SERIES FORECASTING: A COMPARATIVE STUDY OF ARIMA AND ANN MODELS","authors":"J. Kihoro, R. Otieno, C. Wafula","doi":"10.4314/AJST.V5I2.15330","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15330","url":null,"abstract":"This paper addresses the concerns of Faraway and Chatfield (1998) who questioned the forecasting ability of Artificial Neural Networks (ANN). In particular the paper compares the performance of Artificial Neural Networks (ANN) and ARIMA models in forecasting of seasonal (monthly) Time series. Using the Airline data which Faraway and Chatfield (1998) used and two other data sets and taking into consideration their suggestions, we show that ANN are not as bad as Faraway and Chatfield put it. A rule of selecting input lags into the input set based on their relevance/ contribution to the model is also proposed.","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"83 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86949259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fuzzy random variable (frv) is one of the most successful mathematical tool for taking an intellectual step towards situations where randomness and fuzziness co-occur. This hybrid concept is discussed in this paper along with an outline of its key features. We also list some applications of fuzzy random variables in solving concrete problems and we provide a numerical example showing how randomness and fuzziness can be combined in an optimization setting. The paper ends with some concluding remarks emphasizing perspectives on potential research directions. Keywords : random variable, fuzzy number, fuzzy random variable, optimization African Journal of Science and Technology Vol. 5(2) 2004: 51-59
{"title":"Combining randomness and fuzziness","authors":"M. Luhandjula","doi":"10.4314/AJST.V5I2.15329","DOIUrl":"https://doi.org/10.4314/AJST.V5I2.15329","url":null,"abstract":"Fuzzy random variable (frv) is one of the most successful mathematical tool for taking an intellectual step towards situations where randomness and fuzziness co-occur. This hybrid concept is discussed in this paper along with an outline of its key features. We also list some applications of fuzzy random variables in solving concrete problems and we provide a numerical example showing how randomness and fuzziness can be combined in an optimization setting. The paper ends with some concluding remarks emphasizing perspectives on potential research directions. Keywords : random variable, fuzzy number, fuzzy random variable, optimization African Journal of Science and Technology Vol. 5(2) 2004: 51-59","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2006-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89664430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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