Ballast is broken pieces of hard rocks such as sandstones, schist, etc. approximately 25- 60 mm size, over which the railway tracks are laid. The function of the ballast is to transfer the applied load over a large surface, provide adequate elasticity, prevent creep and hold the sleepers in position. Also under wet conditions, it would permit free drainage and allow free grade to be obtained. It is reported that a large proportion of serious accidents occur through derailments of carriages. Many such accidents may be due to the poor quality of ballast stones. The paper discusses the essential properties of ballast stones and methodologies for testing these properties. African Journal of Science and Technology Vol.4(2) 2003: 42-50
{"title":"SELECTION AND TESTING OF BALLAST STONES FOR UNDERGROUND RAILWAY TRACKS","authors":"M. Chanda, R. Krishna","doi":"10.4314/AJST.V4I2.15300","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15300","url":null,"abstract":"Ballast is broken pieces of hard rocks such as sandstones, schist, etc. approximately 25- 60 mm size, over which the railway tracks are laid. The function of the ballast is to transfer the applied load over a large surface, provide adequate elasticity, prevent creep and hold the sleepers in position. Also under wet conditions, it would permit free drainage and allow free grade to be obtained. It is reported that a large proportion of serious accidents occur through derailments of carriages. Many such accidents may be due to the poor quality of ballast stones. The paper discusses the essential properties of ballast stones and methodologies for testing these properties. African Journal of Science and Technology Vol.4(2) 2003: 42-50","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"41 1","pages":"42-50"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87700444","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}
C. Nyamai, E. Mathu, N. Opiyo-Akech, E. Wallbrecher
The largest segment of the Neoproterozoic Mozambique belt in Kenya occurs east of the north-south oriented Rift system. Geological works carried out in the country during the last few decades have progressively revealed the complexity of the geology, structures and tectonics of the Mozambique belt in the region. Important high grade tectono-thermal events in the belt took place between about 845 and 715 Ma. The tectonothermal events attained P/T conditions of 5.5 - 7.1 kbars and 500 - 750o C. The subsequent cooling and uplift of the basement has been traced by K-Ar dates on biotites, which range between 528 and 438 Ma. New lithological units established in the last two decades include widespread granitoid, anorthositic, gabbroic to ultramafic intrusions and limited andesitic volcanics in the central region of this eastern segment of the Mozambique belt (EMBS). Previously the geology of this central region had been considered to consist predominantly of pelitic and semi-pelitic schists and gneisses, migmatites and amphibolites. Further north in the Chanler's Falls and Archer's Post areas, this segment is dominated by paragneisses and schists, marbles and calc-silicate rocks, granulites, as well as metamorphosed mafic and ultramafic rocks. A similar lithological metamorphic assemblage as the one in the north is repeatedly noted in the southern part of the belt. Here in the Taita Hills region, close to the Tanzanian border, paragneisses, marbles, amphibolites and metamorphosed ultramafic rocks, with ophiolitic signatures are widespread. West of the Taita Hills in Kajiado district, quartzites are an additional rock unit while meta-ultramafic rocks are notably absent. Complex folding, exhibiting at least three fold generations, and which occasionally have formed elliptical dome and basin structures, are widespread. These are particularly common in the central region of the EMBS. The entire segment however, has several Neoproterozoic faults, thrust and shear zones, some of which are of regional dimensions. For example, the Yatta shear zone, extending for over 300 km in a NW-SE direction, obliquely subdivides this segment into two. Cenozoic reactivation of some of the fault and shear zones is quite evident. Petrography coupled with limited geochemical analyses indicate the probable existence of Neoproterozoic island arcs in the central region of this segment. In particular, while the sequences in the northern section of the EMBS indicate an ophiolitic- midocean ridge- to island arc setting, the central section show an affinity ranging from volcanic arc- calc-alkaline volcanic arc- to within-plate volcanics setting. The southern section of the EMBS indicate a setting sequence ranging from continental shelfophiolitic sature - midocean ridge – within plate to subduction related volcanics and island arc setting. The sequences in the nothern and southern sections of the belt are interpreted to be parts of the previously deep marine “proto Mozambique ocean” p
{"title":"A reappraaisal of the geology, geochemistry, structures and tectonics of the Mozambique belt in Kenya, east of the rift system","authors":"C. Nyamai, E. Mathu, N. Opiyo-Akech, E. Wallbrecher","doi":"10.4314/AJST.V4I2.15306","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15306","url":null,"abstract":"The largest segment of the Neoproterozoic Mozambique belt in Kenya occurs east of the north-south oriented Rift system. Geological works carried out in the country during the last few decades have progressively revealed the complexity of the geology, structures and tectonics of the Mozambique belt in the region. Important high grade tectono-thermal events in the belt took place between about 845 and 715 Ma. The tectonothermal events attained P/T conditions of 5.5 - 7.1 kbars and 500 - 750o C. The subsequent cooling and uplift of the basement has been traced by K-Ar dates on biotites, which range between 528 and 438 Ma. New lithological units established in the last two decades include widespread granitoid, anorthositic, gabbroic to ultramafic intrusions and limited andesitic volcanics in the central region of this eastern segment of the Mozambique belt (EMBS). Previously the geology of this central region had been considered to consist predominantly of pelitic and semi-pelitic schists and gneisses, migmatites and amphibolites. Further north in the Chanler's Falls and Archer's Post areas, this segment is dominated by paragneisses and schists, marbles and calc-silicate rocks, granulites, as well as metamorphosed mafic and ultramafic rocks. A similar lithological metamorphic assemblage as the one in the north is repeatedly noted in the southern part of the belt. Here in the Taita Hills region, close to the Tanzanian border, paragneisses, marbles, amphibolites and metamorphosed ultramafic rocks, with ophiolitic signatures are widespread. West of the Taita Hills in Kajiado district, quartzites are an additional rock unit while meta-ultramafic rocks are notably absent. Complex folding, exhibiting at least three fold generations, and which occasionally have formed elliptical dome and basin structures, are widespread. These are particularly common in the central region of the EMBS. The entire segment however, has several Neoproterozoic faults, thrust and shear zones, some of which are of regional dimensions. For example, the Yatta shear zone, extending for over 300 km in a NW-SE direction, obliquely subdivides this segment into two. Cenozoic reactivation of some of the fault and shear zones is quite evident. Petrography coupled with limited geochemical analyses indicate the probable existence of Neoproterozoic island arcs in the central region of this segment. In particular, while the sequences in the northern section of the EMBS indicate an ophiolitic- midocean ridge- to island arc setting, the central section show an affinity ranging from volcanic arc- calc-alkaline volcanic arc- to within-plate volcanics setting. The southern section of the EMBS indicate a setting sequence ranging from continental shelfophiolitic sature - midocean ridge – within plate to subduction related volcanics and island arc setting. The sequences in the nothern and southern sections of the belt are interpreted to be parts of the previously deep marine “proto Mozambique ocean” p","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"19 1","pages":"51-71"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87299475","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}
Np Njandjock, H. Kande, E. Manguelle-Dicourn, Charles T. Tabod, Mt Ndougssa, J. Marcel
An anomaly separation program for gravity (or magnetic) data in prospecting domain is presented. It can be applied to the gravity or magnetic anomaly separation of degree up to three and allows the management of up to 1200 data. Its implementation requires a Turbo Pascal surrounding through a TP7 list on the main root of the computer. The results obtained after execution of the program can be displayed, printed or stocked in a data file. In order to test the program, we have compared our results with those obtained from a Fortran program written by Radhakrisha and Krishnamacharyulu (1990) using the least squares method. The advantage of using our program is that a great number of data can be handled even for a local study, the execution is rapid and the accuracy is greatly improved upon. African Journal of Science and Technology Vol.4(2) 2003: 1-4
{"title":"A Turbo Pascal 7.0 program to fit a polynomial of any order to potential field anomalies based on the analytic least squares method","authors":"Np Njandjock, H. Kande, E. Manguelle-Dicourn, Charles T. Tabod, Mt Ndougssa, J. Marcel","doi":"10.4314/AJST.V4I2.15304","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15304","url":null,"abstract":"An anomaly separation program for gravity (or magnetic) data in prospecting domain is presented. It can be applied to the gravity or magnetic anomaly separation of degree up to three and allows the management of up to 1200 data. Its implementation requires a Turbo Pascal surrounding through a TP7 list on the main root of the computer. The results obtained after execution of the program can be displayed, printed or stocked in a data file. In order to test the program, we have compared our results with those obtained from a Fortran program written by Radhakrisha and Krishnamacharyulu (1990) using the least squares method. The advantage of using our program is that a great number of data can be handled even for a local study, the execution is rapid and the accuracy is greatly improved upon. African Journal of Science and Technology Vol.4(2) 2003: 1-4","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"102 1","pages":"1-4"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82129063","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}
RESUME:- En general, les mecaniciens mettent en œuvre, pour assurer la fiabilite et la perennite, des machines qu'ils concoivent. Et pourtant, des defauts (deformation, fissures et irregularite des profondeurs trempees) surviennent, tantot de facon aleatoire, tantot de facon repetee. Apres avoir traite la trempe superficielle par induction des pieces de geometries simples (cylindriques) [1], nous proposons donc de traiter la trempe de contour des pieces dentees de type engrenages, roues dentees, …, et plus precisement le profil des dents d'une roue dentees. Dans cet article nous presenterons une approche interessante basee sur la recherche d'une frequence optimale du generateur. Nous faisons appel a trois techniques variees : Trempe de contour mono frequence, Trempe bi-frequences et Trempe bi-frequences bi-couches pour en choisir la meilleure description du contour trempe. le choix definitif de la technique sera confirme, a la fin de ce travail, par une simulation et traitement d'un pignon. Mots cles : Chauffage inductif, Trempe de contour, frequence optimale, engrenage. ABSTRACT:- In general, mechanics put in work to assure reliability and the everlastingness of machines that they conceive. And yet, of defaults (distortion, cracks and irregularity of quenched depths) occur, soon of uncertain way, soon of repeated way. After have treated the superficial quench by induction of the simple geometry pieces (cylindrical) [1], we propose to treat the quenching contour of toothed pieces type gearings, toothed wheels, therefore…, more precisely the profile of teeth of a wheel. In this paper we will present an approach interesting based on the research of an optimal frequency of the generator. We make call to three varied techniques: Quenching of contour mono frequency, Quenching bi-frequency and Quenching bi-frequency bilies to choose the best description of the contour quenched. Key Words: Inductive heating, Quenching of contour, optimal frequency, gearing African Journal of Science and Technology Vol.4(2) 2003:95-104
-一般来说，机械师使用他们设计的机器，以确保可靠性和耐久性。然而，偏差(变形、裂缝和不规则深度)是随机和重复发生的。在处理了简单几何形状(圆柱形)零件[1]的感应表面淬火后，我们建议处理齿轮、齿轮等齿轮零件的轮廓淬火，并更精确地处理齿轮的齿形。在本文中，我们将提出一种有趣的方法，基于寻找最优发电机频率。我们使用三种不同的技术:单频淬火、双频淬火和双层双频淬火，以选择淬火轮廓的最佳描述。最终的技术选择将在工作结束时通过模拟和处理小齿轮来确定。关键词:感应加热，轮廓淬火，最佳频率，齿轮。文摘:- In general, mechanics put In work to保证可靠性and the everlastingness of that they机械阻力。And, of defaults(扭曲吗And irregularity of quenched预期寿命)的、重复的美梦of way,吸食大麻的美梦of way。在处理了简单几何件(圆柱形)[1]的表面淬火后，我们建议对齿形件(如齿轮、齿轮)的淬火轮廓进行更精确的处理。在本文中，我们将提出一种有趣的方法，基于对发电机最佳频率的研究。我们使用三种不同的技术:轮廓单频淬火、双频淬火和双频淬火，以选择轮廓淬火的最佳描述。关键词:电感加热，轮廓淬火，最佳频率，齿轮非洲科学技术杂志第4卷(2)2003:95-104
{"title":"Modelisation et optimisation de la trempe de contour des pièces dentées","authors":"M. Kchaou, D. Durand, D. Coupard","doi":"10.4314/AJST.V4I2.15303","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15303","url":null,"abstract":"RESUME:- En general, les mecaniciens mettent en œuvre, pour assurer la fiabilite et la perennite, des machines qu'ils concoivent. Et pourtant, des defauts (deformation, fissures et irregularite des profondeurs trempees) surviennent, tantot de facon aleatoire, tantot de facon repetee. Apres avoir traite la trempe superficielle par induction des pieces de geometries simples (cylindriques) [1], nous proposons donc de traiter la trempe de contour des pieces dentees de type engrenages, roues dentees, …, et plus precisement le profil des dents d'une roue dentees. Dans cet article nous presenterons une approche interessante basee sur la recherche d'une frequence optimale du generateur. Nous faisons appel a trois techniques variees : Trempe de contour mono frequence, Trempe bi-frequences et Trempe bi-frequences bi-couches pour en choisir la meilleure description du contour trempe. le choix definitif de la technique sera confirme, a la fin de ce travail, par une simulation et traitement d'un pignon. Mots cles : Chauffage inductif, Trempe de contour, frequence optimale, engrenage. ABSTRACT:- In general, mechanics put in work to assure reliability and the everlastingness of machines that they conceive. And yet, of defaults (distortion, cracks and irregularity of quenched depths) occur, soon of uncertain way, soon of repeated way. After have treated the superficial quench by induction of the simple geometry pieces (cylindrical) [1], we propose to treat the quenching contour of toothed pieces type gearings, toothed wheels, therefore…, more precisely the profile of teeth of a wheel. In this paper we will present an approach interesting based on the research of an optimal frequency of the generator. We make call to three varied techniques: Quenching of contour mono frequency, Quenching bi-frequency and Quenching bi-frequency bilies to choose the best description of the contour quenched. Key Words: Inductive heating, Quenching of contour, optimal frequency, gearing African Journal of Science and Technology Vol.4(2) 2003:95-104","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"7 1","pages":"95-104"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81025435","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}
Kiluli Swamp is an extensive valley swamp near the lower limit of the montane forest on the eastern slopes of Mount Kenya, East Africa. The swamp is fed by a small spring on the northeastern margin, and the water table lies a few centimetres below the surface. The swamp's sediments modify water chemistry: the Na-Mg-HCO 3 water-type at the input changes to a Ca- Mg-HCO 3 water-type in the central parts of the swamp. A short sediment core (2.12m) was retrieved from the central part of the swamp using a modified Livingstone piston corer. The sediments were mainly composed of silty organic mud, silty clay and coarse silt. Three radiocarbon dates were obtained. A suite of sedimentological analyses was carried out in order to reconstruct the palaeoenvironmental history of the area, and these included: mineral magnetic characteristics (susceptibility, IRM etc.); total organic carbon (TOC); total nitrogen (TN), and stable carbon isotopes. The sediment record stretches from about 4,000 yr BP (before present) to present. Indications are that the valley was initially dry and the catchment vegetation was characterised by dominant C 4 -type grassland. The initiation of true swamp conditions occurred at ca.470 yr BP immediately following a phase of deep ponding and high diatom productivity within the swamp between 600 and 470 yr BP. A high incidence of charcoal from 470 to 0 yr BP probably marks the period of persistent anthropogenic activities within the catchment. There is a change in vegetation type from a predominantly C 4 -type to predominantly C 3 -type at about 130 yr BP that is attributed to crop cultivation within the swamp rather than due to climate change, since the arid phase which marks this zone would have, under natural conditions, abetted the continued dominance of C 4 plants which are more drought-resistant than C 3 plants. The changes observed are broadly synchronous with other palaeoenvironmental records from Mount Kenya and the surrounding region. African Journal of Science and Technology Vol.4(2) 2003: 12-23
{"title":"LATE HOLOCENE SEDIMENTOLOGY AND PALAEOENVIRONMENT OF KILULI SWAMP, MOUNT KENYA","authors":"Dd Olago, F. Street-Perrott, R. Perrott, E. Odada","doi":"10.4314/AJST.V4I2.15308","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15308","url":null,"abstract":"Kiluli Swamp is an extensive valley swamp near the lower limit of the montane forest on the eastern slopes of Mount Kenya, East Africa. The swamp is fed by a small spring on the northeastern margin, and the water table lies a few centimetres below the surface. The swamp's sediments modify water chemistry: the Na-Mg-HCO 3 water-type at the input changes to a Ca- Mg-HCO 3 water-type in the central parts of the swamp. A short sediment core (2.12m) was retrieved from the central part of the swamp using a modified Livingstone piston corer. The sediments were mainly composed of silty organic mud, silty clay and coarse silt. Three radiocarbon dates were obtained. A suite of sedimentological analyses was carried out in order to reconstruct the palaeoenvironmental history of the area, and these included: mineral magnetic characteristics (susceptibility, IRM etc.); total organic carbon (TOC); total nitrogen (TN), and stable carbon isotopes. The sediment record stretches from about 4,000 yr BP (before present) to present. Indications are that the valley was initially dry and the catchment vegetation was characterised by dominant C 4 -type grassland. The initiation of true swamp conditions occurred at ca.470 yr BP immediately following a phase of deep ponding and high diatom productivity within the swamp between 600 and 470 yr BP. A high incidence of charcoal from 470 to 0 yr BP probably marks the period of persistent anthropogenic activities within the catchment. There is a change in vegetation type from a predominantly C 4 -type to predominantly C 3 -type at about 130 yr BP that is attributed to crop cultivation within the swamp rather than due to climate change, since the arid phase which marks this zone would have, under natural conditions, abetted the continued dominance of C 4 plants which are more drought-resistant than C 3 plants. The changes observed are broadly synchronous with other palaeoenvironmental records from Mount Kenya and the surrounding region. African Journal of Science and Technology Vol.4(2) 2003: 12-23","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"113 1","pages":"12-23"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80730216","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 fate of propoxur in a cocoa ecosystem has been studied using TLC and GC. Residues of propoxur as determined by both TLC and GC were not significantly different. TLC analysis of propoxur residues in soil, cocoa leaves and pods may not need any rigorous clean up since residues measured from cleaned and uncleaned extracts were not significantly different. The residue levels of propoxur in the soil were found to decrease rapidly and, by the 21st day, none was detected in the topsoil (0 – 15cm). Evidence of leaching of propoxur residues in the soil environment has also been demonstrated. The amount left in the top soil after the first seven days were 27%, 23% and 24% as determined by the TLC only, TLC with clean-up and GLC respectively. About 38% of pesticides detected on the cocoa pod on the day of treatment remained as residues on the pod seven days after treatment. The residue detected on the leaves on the day of treatment was higher than that for the soil. This decreased rapidly to 1.7% in 21 days compared to 16% for the soil and 23% for the pod. No propoxur residue was detected 21 days after spraying. African Journal of Science and Technology Vol.4(2) 2003: 24-28
{"title":"Comparison of thin layer chromatography (TLC) and gas chromatograph determination of propoxur residues in a cocoa ecosystem","authors":"P. Yeboah, S. Lowor, C. Akpabli","doi":"10.4314/AJST.V4I2.15311","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15311","url":null,"abstract":"The fate of propoxur in a cocoa ecosystem has been studied using TLC and GC. Residues of propoxur as determined by both TLC and GC were not significantly different. TLC analysis of propoxur residues in soil, cocoa leaves and pods may not need any rigorous clean up since residues measured from cleaned and uncleaned extracts were not significantly different. The residue levels of propoxur in the soil were found to decrease rapidly and, by the 21st day, none was detected in the topsoil (0 – 15cm). Evidence of leaching of propoxur residues in the soil environment has also been demonstrated. The amount left in the top soil after the first seven days were 27%, 23% and 24% as determined by the TLC only, TLC with clean-up and GLC respectively. About 38% of pesticides detected on the cocoa pod on the day of treatment remained as residues on the pod seven days after treatment. The residue detected on the leaves on the day of treatment was higher than that for the soil. This decreased rapidly to 1.7% in 21 days compared to 16% for the soil and 23% for the pod. No propoxur residue was detected 21 days after spraying. African Journal of Science and Technology Vol.4(2) 2003: 24-28","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"1 1","pages":"24-28"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89096267","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}
RESUME :- Une formation herbeuse semi-aquatique a Cyclosorus striatus (Schum.) Ching (Thelipteridaceae) est decrite dans la region de Yaounde, comme une nouvelle association. Un tableau phytosociologique est presente et interprete a l'aide de differents spectres ecologiques (types biologiques, types de distribution phytogeographique, types de dimension foliaire, types de dissemination et groupes ecosociologiques). L'association est pauvre en especes et comprend principalement les geophytes et des especes largement repandues. La moitie des especes sont distribuees par le vent. ABSTRACT :- The herbaceous semi-aquatic Cyclosorus striatus (Schum.) Ching (Thelipteridaceae) vegetation is described as a new association in the Yaounde region. A phytosociological table is presented and interpreted using various ecological spectra (biological, phytogeographical distribution, leaf size and dissemination types, as well as eco-sociological groups). Poor in species, the association comprises mainly geophytes and widely distributed species ; half of the species are wind-disseminated. African Journal of Science and Technology Vol.4(2) 2003: 29-37
{"title":"ASSOCIATION SEMI-AQUATIQUE À CYCLOSORUS STRIATUS (SCHUM.) CHING (THELIPTERIDACEAE) DANS LA RÉGION DE YAOUNDÉ (CAMEROUN)","authors":"E. Noumi, Etienne Kitio","doi":"10.4314/AJST.V4I2.15305","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15305","url":null,"abstract":"RESUME :- Une formation herbeuse semi-aquatique a Cyclosorus striatus (Schum.) Ching (Thelipteridaceae) est decrite dans la region de Yaounde, comme une nouvelle association. Un tableau phytosociologique est presente et interprete a l'aide de differents spectres ecologiques (types biologiques, types de distribution phytogeographique, types de dimension foliaire, types de dissemination et groupes ecosociologiques). L'association est pauvre en especes et comprend principalement les geophytes et des especes largement repandues. La moitie des especes sont distribuees par le vent. ABSTRACT :- The herbaceous semi-aquatic Cyclosorus striatus (Schum.) Ching (Thelipteridaceae) vegetation is described as a new association in the Yaounde region. A phytosociological table is presented and interpreted using various ecological spectra (biological, phytogeographical distribution, leaf size and dissemination types, as well as eco-sociological groups). Poor in species, the association comprises mainly geophytes and widely distributed species ; half of the species are wind-disseminated. African Journal of Science and Technology Vol.4(2) 2003: 29-37","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"135 1","pages":"29-37"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77567761","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 new mineral membranes made of sintered clay are performed and characterized in terms of porosity, hydraulic resistance, pore diameter and mechanical resistance. It is shown that these membranes can be used as microfiltration membrane. The variations of the filtrate flux as a function of time are measured during the crossflow microfiltration operation of dilute suspensions of bentonite and talc, for different transmembrane pressure values and mean flow rates. Four membranes of different porosities are tested. The crossflow microfiltration of a biologic fluid model is realized in a membrane bioreactor. We showed that according to the average pores diameter, this new clay membranes could have used in different applications; treatment of waters or to be integrated into a bioreactor. Key Words: Clay; Membranes; crossflow microfiltration; Membrane bioreacteur African Journal of Science and Technology Vol.4(2) 2003: 38-41
{"title":"New membranes made of sintered clay application to crossflow microfiltration","authors":"J. Bentama, K. Ouazzani, A. Elgarouani","doi":"10.4314/AJST.V4I2.15299","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15299","url":null,"abstract":"The new mineral membranes made of sintered clay are performed and characterized in terms of porosity, hydraulic resistance, pore diameter and mechanical resistance. It is shown that these membranes can be used as microfiltration membrane. The variations of the filtrate flux as a function of time are measured during the crossflow microfiltration operation of dilute suspensions of bentonite and talc, for different transmembrane pressure values and mean flow rates. Four membranes of different porosities are tested. The crossflow microfiltration of a biologic fluid model is realized in a membrane bioreactor. We showed that according to the average pores diameter, this new clay membranes could have used in different applications; treatment of waters or to be integrated into a bioreactor. Key Words: Clay; Membranes; crossflow microfiltration; Membrane bioreacteur African Journal of Science and Technology Vol.4(2) 2003: 38-41","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"31 1","pages":"38-41"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81530572","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 problem of estimating the variance of an estimator of the population total when missing values have been filled using a Nearest Neighbour (NN) imputation method is considered. The estimator is developed assuming a more general model than those considered in earlier studies. In an empirical study involving two artificial populations, the proposed estimator is found to perform better or as well as other two estimators in the current use. African Journal of Science and Technology Vol.4(2) 2003: 5-11
{"title":"ROBUST ESTIMATION OF VARIANCE IN THE PRESENCE OF NEAREST NEIGHBOUR IMPUTATION","authors":"C. Wafula, R. Otieno, Mugo Maxwell Mwenda","doi":"10.4314/AJST.V4I2.15310","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15310","url":null,"abstract":"The problem of estimating the variance of an estimator of the population total when missing values have been filled using a Nearest Neighbour (NN) imputation method is considered. The estimator is developed assuming a more general model than those considered in earlier studies. In an empirical study involving two artificial populations, the proposed estimator is found to perform better or as well as other two estimators in the current use. African Journal of Science and Technology Vol.4(2) 2003: 5-11","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"117 1","pages":"5-11"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85474784","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}
In this paper asymmetrical single replicate factorial designs are constructed from symmetrical single replicate factorial designs using the deletion technique. The study is along the lines of Voss(1986), Chauhan(1989) and Gachii and Odhiambo(1997). We give results for the general order deletion designs of the form s n-m 1 (s – L) m 1 . . which are proper, for 1 1 less than or equal to the number of generators of the preliminary single replicate generalized cyclic design. We generalize results by earlier authors. Results identifying the set of estimable factorial effects of the deletion designs based on the information available from the preliminary factorial design are given. Simple formulas for calculating the loss of information due to confounding with blocks are given. Efficiency with respect to the number of treatment combinations needed to estimate a given set of interactions of the preliminary factorial design is compared with that of the resulting deletion designs. Keywords and phrases: Factorial spaces, generalized cyclic designs, loss of information. African Journal of Science and Technology Vol.4(2) 2003: 72-79
本文利用删除技术在对称单重复因子设计的基础上构建了非对称单重复因子设计。这项研究是沿着Voss(1986)， Chauhan(1989)和Gachii和Odhiambo(1997)的思路进行的。给出了形式为s n- m1 (s - L) m1的一般序删除设计的结果。对于1个小于或等于初步单重复广义循环设计的产生器数的条件下，是适当的。我们推广早期作者的结果。根据初步析因设计提供的信息，给出了确定删除设计的可估计析因效应集的结果。给出了计算块混淆导致的信息损失的简单公式。对初步析因设计中估计一组给定的相互作用所需的治疗组合数量的效率与最终的删除设计的效率进行比较。关键词:阶乘空间，广义循环设计，信息损失。非洲科学技术Vol.4(2) 2003: 72-79
{"title":"GENERALISED DELETION DESIGNS","authors":"Michael Kamau Gachii, J. Odhiambo","doi":"10.4314/AJST.V4I2.15302","DOIUrl":"https://doi.org/10.4314/AJST.V4I2.15302","url":null,"abstract":"In this paper asymmetrical single replicate factorial designs are constructed from symmetrical single replicate factorial designs using the deletion technique. The study is along the lines of Voss(1986), Chauhan(1989) and Gachii and Odhiambo(1997). We give results for the general order deletion designs of the form s n-m 1 (s – L) m 1 . . which are proper, for 1 1 less than or equal to the number of generators of the preliminary single replicate generalized cyclic design. We generalize results by earlier authors. Results identifying the set of estimable factorial effects of the deletion designs based on the information available from the preliminary factorial design are given. Simple formulas for calculating the loss of information due to confounding with blocks are given. Efficiency with respect to the number of treatment combinations needed to estimate a given set of interactions of the preliminary factorial design is compared with that of the resulting deletion designs. Keywords and phrases: Factorial spaces, generalized cyclic designs, loss of information. African Journal of Science and Technology Vol.4(2) 2003: 72-79","PeriodicalId":7641,"journal":{"name":"African Journal of Science and Technology","volume":"3 1","pages":"72-79"},"PeriodicalIF":0.0,"publicationDate":"2004-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90694978","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：