A longitudinal study of DNS traffic: understanding current DNS practice and abuse
- Authors: Van Zyl, Ignus
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3707 , vital:20537
- Description: This thesis examines a dataset spanning 21 months, containing 3,5 billion DNS packets. Traffic on TCP and UDP port 53, was captured on a production /24 IP block. The purpose of this thesis is twofold. The first is to create an understanding of current practice and behavior within the DNS infrastructure, the second to explore current threats faced by the DNS and the various systems that implement it. This is achieved by drawing on analysis and observations from the captured data. Aspects of the operation of DNS on the greater Internet are considered in this research with reference to the observed trends in the dataset, A thorough analysis of current DNS TTL implementation is made with respect to all response traffic, as well as sections looking at observed DNS TTL values for ,za domain replies and NX DOMAIN flagged replies. This thesis found that TTL values implemented are much lower than has been recommended in previous years, and that the TTL decrease is prevalent in most, but not all EE TTL implementation. With respect to the nature of DNS operations, this thesis also concerns itself with an analysis of the geoloeation of authoritative servers for local (,za) domains, and offers further observations towards the latency generated by the choice of authoritative server location for a given ,za domain. It was found that the majority of ,za domain authoritative servers are international, which results in latency generation that is multiple times greater than observed latencies for local authoritative servers. Further analysis is done with respect to NX DOM AIN behavior captured across the dataset. These findings outlined the cost of DNS miseonfiguration as well as highlighting instances of NXDOMAIN generation through malicious practice. With respect to DNS abuses, original research with respect to long-term scanning generated as a result of amplification attack activity on the greater Internet is presented. Many instances of amplification domain scans were captured during the packet capture, and an attempt is made to correlate that activity temporally with known amplification attack reports. The final area that this thesis deals with is the relatively new field of Bitflipping and Bitsquatting, delivering results on bitflip detection and evaluation over the course of the entire dataset. The detection methodology is outlined, and the final results are compared to findings given in recent bitflip literature.
- Full Text:
- Date Issued: 2016
- Authors: Van Zyl, Ignus
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3707 , vital:20537
- Description: This thesis examines a dataset spanning 21 months, containing 3,5 billion DNS packets. Traffic on TCP and UDP port 53, was captured on a production /24 IP block. The purpose of this thesis is twofold. The first is to create an understanding of current practice and behavior within the DNS infrastructure, the second to explore current threats faced by the DNS and the various systems that implement it. This is achieved by drawing on analysis and observations from the captured data. Aspects of the operation of DNS on the greater Internet are considered in this research with reference to the observed trends in the dataset, A thorough analysis of current DNS TTL implementation is made with respect to all response traffic, as well as sections looking at observed DNS TTL values for ,za domain replies and NX DOMAIN flagged replies. This thesis found that TTL values implemented are much lower than has been recommended in previous years, and that the TTL decrease is prevalent in most, but not all EE TTL implementation. With respect to the nature of DNS operations, this thesis also concerns itself with an analysis of the geoloeation of authoritative servers for local (,za) domains, and offers further observations towards the latency generated by the choice of authoritative server location for a given ,za domain. It was found that the majority of ,za domain authoritative servers are international, which results in latency generation that is multiple times greater than observed latencies for local authoritative servers. Further analysis is done with respect to NX DOM AIN behavior captured across the dataset. These findings outlined the cost of DNS miseonfiguration as well as highlighting instances of NXDOMAIN generation through malicious practice. With respect to DNS abuses, original research with respect to long-term scanning generated as a result of amplification attack activity on the greater Internet is presented. Many instances of amplification domain scans were captured during the packet capture, and an attempt is made to correlate that activity temporally with known amplification attack reports. The final area that this thesis deals with is the relatively new field of Bitflipping and Bitsquatting, delivering results on bitflip detection and evaluation over the course of the entire dataset. The detection methodology is outlined, and the final results are compared to findings given in recent bitflip literature.
- Full Text:
- Date Issued: 2016
An investigation into the dietary requirements of Oreochromis Mossambicus fry and the formulation and preparation of a dry food for use in aquaculture
- Authors: Thorpe, Peter Stuart
- Date: 1989
- Subjects: Cichlids , Tilapia -- Nutrition , Aquaculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5184 , http://hdl.handle.net/10962/d1001960 , Cichlids , Tilapia -- Nutrition , Aquaculture
- Description: The need for developing a dry feed which satisfied the nutrient requirements of Oreochromis mossambicus fry was identified. The spawning and grading techniques which resulted in a higher fecundity and ensured uniformity within and between samples of fry are discussed. Preparation techniques were developed which met the physical requirements of fry feeds. An analysis of the flesh and yolk sac fry for amino acid composition was undertaken. The initial test diet was based on these results, as well as on the natural feeding ecology of the species. Feeding trials were undertaken and growth responses monitored to determine the optimum levels of the various dietary components. A feed was developed which gave superior growth to that obtained with natural food organisms. This feed consisted of Torula yeast (47%), Weider Super Protein (44.39%), Vitamin supplement (0.45% - multivitamin), additional vitamin C supplement (0.16%), Spirulina (5%), and methionine supplement (3%). An optimum particle size range for O. mossambicus fry (between 5 & 25mm) was established at 125-200um. The fry should be fed the following feed ratios depending on age: 30.4% body weight/day up to day 5, 30.6% body weight/day up to day 10 and 25.1% body weight/day up to day 15. An optimum feeding frequency of 8/10hr day was recommended. A feed conversion ratio of 1.24:1 and a protein efficiency ratio of 0.682:1 was obtained. Digestable energy of the feed was determined at 16.1 kj/g feed. The established dry feed is suitable for use in commercial hatcheries, and as a formulation for further research on the intensive rearing of O. mossambicus fry.
- Full Text:
- Date Issued: 1989
- Authors: Thorpe, Peter Stuart
- Date: 1989
- Subjects: Cichlids , Tilapia -- Nutrition , Aquaculture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5184 , http://hdl.handle.net/10962/d1001960 , Cichlids , Tilapia -- Nutrition , Aquaculture
- Description: The need for developing a dry feed which satisfied the nutrient requirements of Oreochromis mossambicus fry was identified. The spawning and grading techniques which resulted in a higher fecundity and ensured uniformity within and between samples of fry are discussed. Preparation techniques were developed which met the physical requirements of fry feeds. An analysis of the flesh and yolk sac fry for amino acid composition was undertaken. The initial test diet was based on these results, as well as on the natural feeding ecology of the species. Feeding trials were undertaken and growth responses monitored to determine the optimum levels of the various dietary components. A feed was developed which gave superior growth to that obtained with natural food organisms. This feed consisted of Torula yeast (47%), Weider Super Protein (44.39%), Vitamin supplement (0.45% - multivitamin), additional vitamin C supplement (0.16%), Spirulina (5%), and methionine supplement (3%). An optimum particle size range for O. mossambicus fry (between 5 & 25mm) was established at 125-200um. The fry should be fed the following feed ratios depending on age: 30.4% body weight/day up to day 5, 30.6% body weight/day up to day 10 and 25.1% body weight/day up to day 15. An optimum feeding frequency of 8/10hr day was recommended. A feed conversion ratio of 1.24:1 and a protein efficiency ratio of 0.682:1 was obtained. Digestable energy of the feed was determined at 16.1 kj/g feed. The established dry feed is suitable for use in commercial hatcheries, and as a formulation for further research on the intensive rearing of O. mossambicus fry.
- Full Text:
- Date Issued: 1989
Changes in the aerobic saprophytic microbial flora during biltong production with special reference to the micrococcaceae
- Authors: Taylor, M B
- Date: 1976
- Subjects: Micrococcaceae , Saprophytism
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4120 , http://hdl.handle.net/10962/d1013308
- Description: Ninety-four presumptive Micrococcus and Staphylococcus strains isolated from both commercial beef biltong and game biltong, were identified using a scheme based on the system used by Baird-Parker. The changes occurring in both the aerobic, saprophytic microbial flora and the environmental factors, during conversion of beef to biltong, were examined. The predominantly Gram-negative, halo-sensitive flora initially present on the meat, was replaced by Gram-positive, halo-tolerant staphylococci and micrococci, which form the dominant component of the microflora of the final product. This replacement was attributed to changing environmental factors, principally to the increasing sodium chloride concentration and associated decline in water activity. The presence of the antifungal antibiotic, pimaricin, during processing did not influence the bacterial flora of the product. However, the addition of potassium sorbate altered the microbial profile of the product significantly. The presence of these two preservatives, at the concentrations used, could not be detected organoleptically. The importance of the saprophytic microflora of the product ln relation to the environmental factors during processing, is also discussed.
- Full Text:
- Date Issued: 1976
- Authors: Taylor, M B
- Date: 1976
- Subjects: Micrococcaceae , Saprophytism
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4120 , http://hdl.handle.net/10962/d1013308
- Description: Ninety-four presumptive Micrococcus and Staphylococcus strains isolated from both commercial beef biltong and game biltong, were identified using a scheme based on the system used by Baird-Parker. The changes occurring in both the aerobic, saprophytic microbial flora and the environmental factors, during conversion of beef to biltong, were examined. The predominantly Gram-negative, halo-sensitive flora initially present on the meat, was replaced by Gram-positive, halo-tolerant staphylococci and micrococci, which form the dominant component of the microflora of the final product. This replacement was attributed to changing environmental factors, principally to the increasing sodium chloride concentration and associated decline in water activity. The presence of the antifungal antibiotic, pimaricin, during processing did not influence the bacterial flora of the product. However, the addition of potassium sorbate altered the microbial profile of the product significantly. The presence of these two preservatives, at the concentrations used, could not be detected organoleptically. The importance of the saprophytic microflora of the product ln relation to the environmental factors during processing, is also discussed.
- Full Text:
- Date Issued: 1976
Comparison of different notions of compactness in the fuzzy topological space
- Authors: Morapeli, E Z
- Date: 1989
- Subjects: Fuzzy mathematics Fuzzy topology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5393 , http://hdl.handle.net/10962/d1001982
- Description: Various notions of compactness in a fuzzy topological space have been introduced by different authors. The aim of this thesis is to compare them. We find that in a T₂ space (in the sense that no fuzzy net converges to two fuzzy points with different supports) all these notions are equivalent for the whole space. Furthermore, for N-compactness and f-compactness (being the only notions that are defined for an arbitrary fuzzy subset) we have equivalence under a stronger condition, namely, a T₂ space in the sense that every prime prefilter has an adherence that is non-zero in at most one point
- Full Text:
- Date Issued: 1989
- Authors: Morapeli, E Z
- Date: 1989
- Subjects: Fuzzy mathematics Fuzzy topology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5393 , http://hdl.handle.net/10962/d1001982
- Description: Various notions of compactness in a fuzzy topological space have been introduced by different authors. The aim of this thesis is to compare them. We find that in a T₂ space (in the sense that no fuzzy net converges to two fuzzy points with different supports) all these notions are equivalent for the whole space. Furthermore, for N-compactness and f-compactness (being the only notions that are defined for an arbitrary fuzzy subset) we have equivalence under a stronger condition, namely, a T₂ space in the sense that every prime prefilter has an adherence that is non-zero in at most one point
- Full Text:
- Date Issued: 1989
Geomorphic and ambient environmental impacts on lichen distribution on two inland Nunataks in western Dronning Maud Land, Antarctica
- Authors: Dwight, Rosemary Anne
- Date: 2015
- Subjects: Lichens -- Antarctica -- Queen Maud Land , Lichen communities -- Antarctica -- Queen Maud Land , Lichens -- Climatic factors -- Antarctica -- Queen Maud Land , Lichens -- Effect of environment on -- Antarctica -- Queen Maud Land , Biotic communities -- Antarctica -- Queen Maud Land , Biotic communities -- Climatic factors -- Antarctica -- Queen Maud Land , Biodiversity -- Climatic factors -- Antarctica -- Queen Maud Land
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4889 , http://hdl.handle.net/10962/d1018189
- Description: Feedbacks between abiotic variables and community structure in Antarctica are poorly understood. Research is, therefore, required to elucidate the patterns of biodiversity that exist and the factors that influence them, particularly under changing climates. Landscape processes affect environmental heterogeneity, which in turn affect patterns of biodiversity. Two inland Antarctic nunataks, Robertskollen and the Northern Buttress of Vesleskarvet, were selected for investigation to determine the potential impact of selected environmental factors on lichen distribution and abundance, at the intra- and inter-nunatak scales. Lichens were found to prefer rock faces with dips between 1° and 45°, and northern/southern aspects. Lichen colonisation was mostly in microtopographical features that result from rock weathering. The distribution of lichens was found to be regular at the intra- and inter-nunatak scale, whereas lichen abundance was found to be mostly influenced by temperature. On the Northern Buttress, rock hardness displays a similar pattern to lichen abundance, both of which are suggested to be a function of exposure time, which is dependent on deglaciation. The two nunataks serve as excellent laboratories that can potentially be used as proxies for investigating the possible impacts of climate change
- Full Text:
- Date Issued: 2015
- Authors: Dwight, Rosemary Anne
- Date: 2015
- Subjects: Lichens -- Antarctica -- Queen Maud Land , Lichen communities -- Antarctica -- Queen Maud Land , Lichens -- Climatic factors -- Antarctica -- Queen Maud Land , Lichens -- Effect of environment on -- Antarctica -- Queen Maud Land , Biotic communities -- Antarctica -- Queen Maud Land , Biotic communities -- Climatic factors -- Antarctica -- Queen Maud Land , Biodiversity -- Climatic factors -- Antarctica -- Queen Maud Land
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4889 , http://hdl.handle.net/10962/d1018189
- Description: Feedbacks between abiotic variables and community structure in Antarctica are poorly understood. Research is, therefore, required to elucidate the patterns of biodiversity that exist and the factors that influence them, particularly under changing climates. Landscape processes affect environmental heterogeneity, which in turn affect patterns of biodiversity. Two inland Antarctic nunataks, Robertskollen and the Northern Buttress of Vesleskarvet, were selected for investigation to determine the potential impact of selected environmental factors on lichen distribution and abundance, at the intra- and inter-nunatak scales. Lichens were found to prefer rock faces with dips between 1° and 45°, and northern/southern aspects. Lichen colonisation was mostly in microtopographical features that result from rock weathering. The distribution of lichens was found to be regular at the intra- and inter-nunatak scale, whereas lichen abundance was found to be mostly influenced by temperature. On the Northern Buttress, rock hardness displays a similar pattern to lichen abundance, both of which are suggested to be a function of exposure time, which is dependent on deglaciation. The two nunataks serve as excellent laboratories that can potentially be used as proxies for investigating the possible impacts of climate change
- Full Text:
- Date Issued: 2015
Impact of smallholder irrigation schemes on rural livelihoods of farmers in the Eastern Cape Province of South Africa: the case of Melani Irrigation Scheme
- Authors: Magqibelo, Sinovuyo
- Date: 2016
- Subjects: Irrigation farming -- Economic aspects Irrigation -- South Africa -- Eastern Cape Farms, Small -- South Africa -- Eastern Cape , Rural development -- South Africa -- Eastern Cape Agriculture -- Economic aspects -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/1774 , vital:27557
- Description: Irrigation farming is one of the most important rural development investments that can have both direct and indirect impacts on poverty and food security. The irregular and unreliable rainfall in the Eastern Cape Province has caused the smallholder farmers to deepen the irrigation farming systems as a strategy to cope with food shortage, income and poverty. South Africa has invested substantially in smallholder irrigation to benefit smallholder farmers in the less developed areas. Although the investment on small scale irrigation was to improve the welfare of the people, the performance and welfare impact of smallholder irrigation schemes has been poor and fall far short of the expectations of many stakeholders. The broad objective of the study was to examine the contribution of smallholder irrigation scheme on rural livelihoods of smallholder farmers at the project area. The null hypothesis was that smallholder irrigation schemes have no impact on farmer’s livelihoods. The alternative hypothesis for this study was that Melani irrigation scheme is contributing in improving rural livelihoods of smallholder farmers in the area. Cross study research design was used in the methodology. The purposive sampling was applied in order to choose a sample of 107 respondents that were interviewed using questionnaires, including both irrigating and non-irrigating farmers. A multiple linear regression analysis was used to find out whether the performance of the two groups of farmers is different and to what extent. To determine the specific role of irrigation an Independent T-Test was ran. Out of the selected sample 68 percent of households were farmers, 7.5 percent informal employed and 27 percent unemployed. It was found that the majority of participants were males and were uneducated. They depended on social grants for a living. The findings from the study showed that 84 percent of the respondents agreed that there is no market available in the village and farmers had limited access to credits. The crop income was the most contributing factor to household income. The results showed that whether the farmer is a non-irrigator or an irrigator the performance is not significant. Irrigation scheme improvement attained by smallholder farmers need to be maintained.
- Full Text:
- Date Issued: 2016
- Authors: Magqibelo, Sinovuyo
- Date: 2016
- Subjects: Irrigation farming -- Economic aspects Irrigation -- South Africa -- Eastern Cape Farms, Small -- South Africa -- Eastern Cape , Rural development -- South Africa -- Eastern Cape Agriculture -- Economic aspects -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/1774 , vital:27557
- Description: Irrigation farming is one of the most important rural development investments that can have both direct and indirect impacts on poverty and food security. The irregular and unreliable rainfall in the Eastern Cape Province has caused the smallholder farmers to deepen the irrigation farming systems as a strategy to cope with food shortage, income and poverty. South Africa has invested substantially in smallholder irrigation to benefit smallholder farmers in the less developed areas. Although the investment on small scale irrigation was to improve the welfare of the people, the performance and welfare impact of smallholder irrigation schemes has been poor and fall far short of the expectations of many stakeholders. The broad objective of the study was to examine the contribution of smallholder irrigation scheme on rural livelihoods of smallholder farmers at the project area. The null hypothesis was that smallholder irrigation schemes have no impact on farmer’s livelihoods. The alternative hypothesis for this study was that Melani irrigation scheme is contributing in improving rural livelihoods of smallholder farmers in the area. Cross study research design was used in the methodology. The purposive sampling was applied in order to choose a sample of 107 respondents that were interviewed using questionnaires, including both irrigating and non-irrigating farmers. A multiple linear regression analysis was used to find out whether the performance of the two groups of farmers is different and to what extent. To determine the specific role of irrigation an Independent T-Test was ran. Out of the selected sample 68 percent of households were farmers, 7.5 percent informal employed and 27 percent unemployed. It was found that the majority of participants were males and were uneducated. They depended on social grants for a living. The findings from the study showed that 84 percent of the respondents agreed that there is no market available in the village and farmers had limited access to credits. The crop income was the most contributing factor to household income. The results showed that whether the farmer is a non-irrigator or an irrigator the performance is not significant. Irrigation scheme improvement attained by smallholder farmers need to be maintained.
- Full Text:
- Date Issued: 2016
Microstructural and analytical characterization of plasma dissociated zircon
- Authors: Minnaar, Ettiénne Gerald
- Date: 2012
- Subjects: Zircon , Zirconium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10547 , http://hdl.handle.net/10948/d1015972
- Description: This dissertation focuses on the microstructural and analytical characterization of plasma dissociated zircon (PDZ) which was produced by the South African Nuclear Energy Corporation (NECSA). The techniques used in the analysis of the material include scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy and wavelength dispersive X-ray spectrometry (EDS and WDS), infrared spectroscopy, Raman spectroscopy and X-ray diffraction (XRD). The differences in morphology of the zirconia (ZrO2) crystals observed in the PDZ are related to the thermal history of the material. Large zirconia crystals grow in a spherulitic manner and have the monoclinic crystal structure. Some smaller crystals formed via a rapid cooling process appear to retain the tetragonal or cubic crystal structures rather than relaxing to the monoclinic structure, and this may be because such nanocrystals are stabilised by small surface area or constraints from surrounding materials. Impurity distribution analysis of the PDZ showed that majority of the impurities present in zircon segregates to the silica phase during the dissociation process. The infrared and Raman spectroscopy analysis of the PDZ material indicated that the zirconia is present in the monoclinic and tetragonal polymorphs. X-ray diffraction revealed the presence of monoclinic, tetragonal and cubic zirconia phases. Rietveld refinement of the XRD patterns revealed zirconia to be predominantly found in the monoclinic polymorph followed by the tetragonal and cubic polymorphs. A Fourier transform infrared (FTIR) spectrometer equipped with an attenuated total reflectance (ATR) cell proved to be a viable method for determining the percentage dissociated zircon in PDZ.
- Full Text:
- Date Issued: 2012
- Authors: Minnaar, Ettiénne Gerald
- Date: 2012
- Subjects: Zircon , Zirconium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10547 , http://hdl.handle.net/10948/d1015972
- Description: This dissertation focuses on the microstructural and analytical characterization of plasma dissociated zircon (PDZ) which was produced by the South African Nuclear Energy Corporation (NECSA). The techniques used in the analysis of the material include scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy and wavelength dispersive X-ray spectrometry (EDS and WDS), infrared spectroscopy, Raman spectroscopy and X-ray diffraction (XRD). The differences in morphology of the zirconia (ZrO2) crystals observed in the PDZ are related to the thermal history of the material. Large zirconia crystals grow in a spherulitic manner and have the monoclinic crystal structure. Some smaller crystals formed via a rapid cooling process appear to retain the tetragonal or cubic crystal structures rather than relaxing to the monoclinic structure, and this may be because such nanocrystals are stabilised by small surface area or constraints from surrounding materials. Impurity distribution analysis of the PDZ showed that majority of the impurities present in zircon segregates to the silica phase during the dissociation process. The infrared and Raman spectroscopy analysis of the PDZ material indicated that the zirconia is present in the monoclinic and tetragonal polymorphs. X-ray diffraction revealed the presence of monoclinic, tetragonal and cubic zirconia phases. Rietveld refinement of the XRD patterns revealed zirconia to be predominantly found in the monoclinic polymorph followed by the tetragonal and cubic polymorphs. A Fourier transform infrared (FTIR) spectrometer equipped with an attenuated total reflectance (ATR) cell proved to be a viable method for determining the percentage dissociated zircon in PDZ.
- Full Text:
- Date Issued: 2012
Molybdeunum mineralization with emphasis on porphyry systems genesis and exploration
- Authors: Puig-Pichuante, R M
- Date: 1986
- Subjects: Molybdenum , Porphyry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5023 , http://hdl.handle.net/10962/d1006840
- Description: Mo became very important in the last century, because of its sophisticated properties and its use in the new technology of alloys . Porphyry systems (porphyry Cu-Mo and Mo) contribute a significant proportion (90 - 95 per cent) to the Mo world's production. This type of deposit is associated mainly with Phanerozoic orogenic belts. Above 87per cent of the world resources are in the American Circumpacific belts , both Andean and Cordilleran . Ore grade in porphyry Cu-Mo range from 0,005 to 0,04per cent Mo, whereas in porphyry Mo grades range from 0,08 to 0,75per cent Mo . These deposits are associated with a magmatism which shows an evolution from calcic in island arcs, to calc-alkaline in magmatic back arcs, with an increase of the Mo content in the same direction. Porphyry Mo deposits display several features in common with porphyry Cu deposits. hydrothermal Similarities include nature of host alteration patterns and distribution of rock intrusives, ore minerals. An interesting difference is found in the Re contents of the molybdenite mineral. This element is higher in the molybdenites of porphyry Cu, than in those of the porphyry Mo. The ore genesis process begins involves partial melting, within enriched zones of the upper mantle and magma differentation, liquid state thermogravitational diffusion, magma convection and boiling. These processes progressively concentrate Mo in the fluids, which are released at some stage, into sulphidic hydrothermal systems, under complex geologictectonic conditions involving fracturing, brecciation and hydrothermal alteration. Major concentrations of the ore mineral are always associated with potassic alteration, and with late magmatic-early hydrothermal stages (Chilean and Western North American porphyries). Geological mapping and a close understanding of alteration and mineralization patterns, and lithogeochemistry are important tools for the exploration of porphyry Mo deposits. Geochemical prospecting, using soils, vegetation and water as sampling media, and regional aeromagnetic, gravity surveys, aerial photography and remote sensing, are us.
- Full Text:
- Date Issued: 1986
- Authors: Puig-Pichuante, R M
- Date: 1986
- Subjects: Molybdenum , Porphyry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5023 , http://hdl.handle.net/10962/d1006840
- Description: Mo became very important in the last century, because of its sophisticated properties and its use in the new technology of alloys . Porphyry systems (porphyry Cu-Mo and Mo) contribute a significant proportion (90 - 95 per cent) to the Mo world's production. This type of deposit is associated mainly with Phanerozoic orogenic belts. Above 87per cent of the world resources are in the American Circumpacific belts , both Andean and Cordilleran . Ore grade in porphyry Cu-Mo range from 0,005 to 0,04per cent Mo, whereas in porphyry Mo grades range from 0,08 to 0,75per cent Mo . These deposits are associated with a magmatism which shows an evolution from calcic in island arcs, to calc-alkaline in magmatic back arcs, with an increase of the Mo content in the same direction. Porphyry Mo deposits display several features in common with porphyry Cu deposits. hydrothermal Similarities include nature of host alteration patterns and distribution of rock intrusives, ore minerals. An interesting difference is found in the Re contents of the molybdenite mineral. This element is higher in the molybdenites of porphyry Cu, than in those of the porphyry Mo. The ore genesis process begins involves partial melting, within enriched zones of the upper mantle and magma differentation, liquid state thermogravitational diffusion, magma convection and boiling. These processes progressively concentrate Mo in the fluids, which are released at some stage, into sulphidic hydrothermal systems, under complex geologictectonic conditions involving fracturing, brecciation and hydrothermal alteration. Major concentrations of the ore mineral are always associated with potassic alteration, and with late magmatic-early hydrothermal stages (Chilean and Western North American porphyries). Geological mapping and a close understanding of alteration and mineralization patterns, and lithogeochemistry are important tools for the exploration of porphyry Mo deposits. Geochemical prospecting, using soils, vegetation and water as sampling media, and regional aeromagnetic, gravity surveys, aerial photography and remote sensing, are us.
- Full Text:
- Date Issued: 1986
Studies on the ecology and molecular biology of transferable drug resistance factors in coliform bacteria
- Authors: Marcos, David
- Date: 1973
- Subjects: Enterobacteriaceae , Molecular biology , Microbial ecology , Bacteria -- Ecology , Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4249 , http://hdl.handle.net/10962/d1007494 , Enterobacteriaceae , Molecular biology , Microbial ecology , Bacteria -- Ecology , Ecology
- Description: From Introduction: It was as early as 1904 that Paul Ehrlich propounded the idea of a “magic bullet”. This “magic bullet”, or chemotherapeutic agent, as he also called it, had to meet certain requirements: (a) a high activity against pathogenic micro-organisms; (b) easy absorption by the body; (c) activity in the presence of body fluids and tissue; (d) a low degree of toxicity; (e) must not allow the development of resistant micro-organisms. The discovery of the sulphonamide, Prentosil, by Domagk in 1935 was one of the initial steps in the search for this “magic bullet”. This, together with the production and purification of the antibiotics penicillin, by Fleming, Florey and Chain in 1942 and streptomycin, by Waksman in 1943, heralded a new era in the fight against bacterial infections. The majority of modern antibacterial agents have to a large extent met the requirements of Ehrlich’s ‘magic bullet”. They have however failed to prevent the development of resistant bacterial strains. This has been particularly noticeable in the past twenty years since the sudden emergence of multiple-resistant bacteria, many of which can transfer to several drugs in one step by a process of conjugation. This phenomenon which has serious medical implications has prompted numerous studies on the origin, epidemiology, biochemistry and genetics of transferable drug resistance.
- Full Text:
- Date Issued: 1973
- Authors: Marcos, David
- Date: 1973
- Subjects: Enterobacteriaceae , Molecular biology , Microbial ecology , Bacteria -- Ecology , Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4249 , http://hdl.handle.net/10962/d1007494 , Enterobacteriaceae , Molecular biology , Microbial ecology , Bacteria -- Ecology , Ecology
- Description: From Introduction: It was as early as 1904 that Paul Ehrlich propounded the idea of a “magic bullet”. This “magic bullet”, or chemotherapeutic agent, as he also called it, had to meet certain requirements: (a) a high activity against pathogenic micro-organisms; (b) easy absorption by the body; (c) activity in the presence of body fluids and tissue; (d) a low degree of toxicity; (e) must not allow the development of resistant micro-organisms. The discovery of the sulphonamide, Prentosil, by Domagk in 1935 was one of the initial steps in the search for this “magic bullet”. This, together with the production and purification of the antibiotics penicillin, by Fleming, Florey and Chain in 1942 and streptomycin, by Waksman in 1943, heralded a new era in the fight against bacterial infections. The majority of modern antibacterial agents have to a large extent met the requirements of Ehrlich’s ‘magic bullet”. They have however failed to prevent the development of resistant bacterial strains. This has been particularly noticeable in the past twenty years since the sudden emergence of multiple-resistant bacteria, many of which can transfer to several drugs in one step by a process of conjugation. This phenomenon which has serious medical implications has prompted numerous studies on the origin, epidemiology, biochemistry and genetics of transferable drug resistance.
- Full Text:
- Date Issued: 1973
Turbidite-hosted gold deposits
- Authors: Leeming, Prudence Mary
- Date: 1985
- Subjects: Gold ores , Turbidites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5010 , http://hdl.handle.net/10962/d1005939 , Gold ores , Turbidites
- Description: Turbidite-hosted gold deposits contribute a significant proportion to world lode gold production and have also provided substantial gold to alluvial resources. Turbidity current deposits occur throughout geological time within Archaean greenstone belts, Proterozoic orogenic belts and rifted passive continental margins, and Palaeozoic geosynclines. Representing the end member of the sedimentary cycle, turbidites have the attribute of preservation not only on an individual bed basis but also due to below wave base accumulation in submarine deeps. Cyclic deposition according to the Bouma sequence punctuates turbidite deposition by a series of diastems. Accumulation of organic, pelagic and chemical sediments may concentrate gold to protore enrichment levels i n a primary sedimentary environment. Dewatering during diagenesis and low-grade metamorphism under reducing conditions may redistribute gold with transport as low energy organo- and thio-complexes. Gold may precipitate with diagenetic pyrite and silica near black shale and/or partially replace fine carbonate detritus. Gold solubility increases with high grade amphibolite facies metamorphism (T 400ºC) when efficient leaching of gold and transport by simple chloro- and hydroxychloro - complexes to lower greenschist regions takes place. Reduced permeability of turbidite strata induces hydrofracturing which focuses dewatering solutions. Gold is deposited due to pressure and temperature decrease or local changes in physico - chemico conditions caused by the reaction of fluids with wall rocks (reactive beds in turbidites are predominantly carbonaceous strata). The largest of turbidite - hosted goldfields are confined to back -arc or marginal sea basins with restricted oceanic circulation. The richest concentrations of gold occur proximal to the original source within the greenschist facies formations lowermost in a thick turbidite sequence and exhibit strong combined structural and lithological association. Turbidites represent important strata for the concentration and preservation of gold not only during sedimentation and diagenesis but also during later deformation and metamorphism.
- Full Text:
- Date Issued: 1985
- Authors: Leeming, Prudence Mary
- Date: 1985
- Subjects: Gold ores , Turbidites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5010 , http://hdl.handle.net/10962/d1005939 , Gold ores , Turbidites
- Description: Turbidite-hosted gold deposits contribute a significant proportion to world lode gold production and have also provided substantial gold to alluvial resources. Turbidity current deposits occur throughout geological time within Archaean greenstone belts, Proterozoic orogenic belts and rifted passive continental margins, and Palaeozoic geosynclines. Representing the end member of the sedimentary cycle, turbidites have the attribute of preservation not only on an individual bed basis but also due to below wave base accumulation in submarine deeps. Cyclic deposition according to the Bouma sequence punctuates turbidite deposition by a series of diastems. Accumulation of organic, pelagic and chemical sediments may concentrate gold to protore enrichment levels i n a primary sedimentary environment. Dewatering during diagenesis and low-grade metamorphism under reducing conditions may redistribute gold with transport as low energy organo- and thio-complexes. Gold may precipitate with diagenetic pyrite and silica near black shale and/or partially replace fine carbonate detritus. Gold solubility increases with high grade amphibolite facies metamorphism (T 400ºC) when efficient leaching of gold and transport by simple chloro- and hydroxychloro - complexes to lower greenschist regions takes place. Reduced permeability of turbidite strata induces hydrofracturing which focuses dewatering solutions. Gold is deposited due to pressure and temperature decrease or local changes in physico - chemico conditions caused by the reaction of fluids with wall rocks (reactive beds in turbidites are predominantly carbonaceous strata). The largest of turbidite - hosted goldfields are confined to back -arc or marginal sea basins with restricted oceanic circulation. The richest concentrations of gold occur proximal to the original source within the greenschist facies formations lowermost in a thick turbidite sequence and exhibit strong combined structural and lithological association. Turbidites represent important strata for the concentration and preservation of gold not only during sedimentation and diagenesis but also during later deformation and metamorphism.
- Full Text:
- Date Issued: 1985
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