Browsing by Faculty "Faculty of Science"

Now showing 1 - 20 of 8267
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    1+1+2 covariant approach to gravitational lensing in f(R) gravity
    (2009) Nzioki, Anne Marie; Dunsby, Peter
    In this thesis, we develop the 1 + 1 + 2 formalism, a technique originally devised for General Relativity, to treat spherically symmetric spacetimes in for fourth order theories of gravity. Using this formalism, we derive equations for a static and spherically symmetric spacetime for general f(R) gravity. We apply these master eqautions to derive some exact solutions, which are used to gain insight on Birkhoff's theorem in this framework. Additionally, we derive a covariant form of the lensing angle for a specific spherically symmetric solution in f(R) = Rn gravity.
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    [1,2-Bis(diphenylphosphino)ethane]-diiodidoplatinum(II) dichloromethane disolvate
    (2007) Sivaramakrishna, Akella; Su, Hong; Moss, John R
    In the title compound, [PtI2(C26H24P2)]·2CH2Cl2, the PtI2(dppe) [dppe = 1,2-bis­(diphenyl­phosphino)ethane] mol­ecules possess twofold rotation symmetry. The Pt coordination displays a square-planar arrangement, with the sum of the angles around the Pt atom being 360.01 (2)°. The Pt-I distance is 2.6484 (5) Å. In the crystal structure, inter­molecular C-H...I contacts link the PtI2(dppe) mol­ecules into rows along the c axis, with a C...I distance of 3.873 (5) Å.
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    1,7-Dimethylpentacyclo[5.4.0.02,6.-03,10.05,9]undecane-8,11-dione
    (International Union of Crystallography, 2010) Chakka, Sai Kumar; Onajole, Oluseye K; Govender, Thavendran; Maguire, Glenn E M; Su, Hong; Kruger, Hendrik G
    The structure of the title compound, C13H14O2, a pentacycloundecane cage derivative, exhibits unusual Csp3 —Csp3 singlebond lengths ranging from 1.505 (3) to 1.607 (2) A˚ and strained bond angles as small as 88.7 (1) and as large as 121.0 (2). In this meso compound, an internal non-crystallographic mirror plane exists, bisecting the molecule. In the crystal, weak C—HO hydrogen bonds link the molecules into an infinite spiral about a twofold screw axis along the [100] direction.
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    A 1000-year carbon isotope rainfall proxy record from South African baobab trees (Adansonia digitata L.)
    (Public Library of Science, 2015) Woodborne, Stephan; Hall, Grant; Robertson, Iain; Patrut, Adrian; Rouault, Mathieu; Loader, Neil J; Hofmeyr, Michele
    A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab ( Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.
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    A 14C and 15N study of the effects of ammonium or nitrate nutrition on carbon allocation in Triticum aestivum L. and Zea mays L
    (1991) Van der Leij, Martina
    The poor response of some plant species, e.g. wheat, to ammonium nutrition has been attributed to a diversion of carbon allocation from structural material for root extension to functions associated with the assimilation and translocation of ammonium in the root. The aim of this research was to investigate carbon allocation in response to ammonium or nitrate nutrition in wheat, an ammonium intolerant species, and maize, which exhibits ammonium tolerance. Experiments were carried out at 4mM and 12mM nitrogen feeding levels in sand and hydroponic culture respectively. pH of growth media was maintained at 6.0 to 6.5. Measurements made included shoot : root ratios, photosynthetic and root respiratory rates, plant water content, xylem sap analysis, and ¹⁴C and ¹⁵N allocation to soluble and bound nitrogen compounds, and soluble, storage and structural carbohydrates. Stunted root growth occurred in ammonium-fed wheat, which was exacerbated by increasing the NH4 concentration. No difference in growth response was evident between ammonium- and nitrate-fed maize. Photosynthetic rates of ammonium- and nitrate-fed plants within both species were similar but maize showed a 3-fold higher photosynthetic rate than wheat. Root respiration of ammonium- and nitrate-fed wheat was similar, while nitrate-fed maize appeared to have a higher root respiratory rate than ammonium-fed maize. Xylem sap analysis showed that for both species, ammonium-fed plants translocated more amino compounds and more carbon to the shoots than nitrate-fed plants, although maize appeared to have a more rapid translocation-rate than wheat. ¹⁴C allocation to nitrogenous compounds in roots of ammonium-fed plants was greater than that in nitrate-fed counterparts for both species. In wheat this increase appeared to be accommodated by a larger initial diversion of ¹⁴C to the root. In maize, reserve carbon in the root appeared to accommodate this increase. A reduction in ¹⁴C allocation to structural material in ammonium-fed plants compared to nitrate-fed counterparts was not evident in either species. ¹⁵N tracing in maize showed that significantly more nitrogen was taken up by ammonium-fed plants in comparison to nitrate-fed plants. The difference in total N between plants fed ammonium or nitrate was, however, not nearly as pronounced, suggesting that ammonium may be cycled out of the plant again. The response of wheat and maize to ammonium or nitrate nutrition is discussed independently, and suggestions for further research are made.
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    An 15N study of the effects of nitrate, ammonium, and nitrate + ammonium nutrition on nitrogen assimilation in Zea Mays L.
    (1984) Murphy, Andrew Telfer; Lewis, O A M
    A brief review of the literature on the effects of nitrate and ammonium nitrogen sources on plant growth, and the assimilation of those nitrogen sources, has been presented. A water culture technique for the growth of maize was developed. The use of a gravel rooting medium with nutrients recycling through the rooting medium, and an iron supplement in the form of ferric citrate, resulted in superior growth of nitrate-fed plants in comparison to that observed with a hydroponic growth technique and a standard Long Ashton nutrient solution. The effects of nitrogen source on plant growth, organic nitrogen and inorganic nitrogen contents, and the rates of incorporation into nitrogenous compounds were studied. The observed differences were explained with reference to the effects of the various nitrogen sources on the physiology of the plants. The experimental techniques included assays of the enzymes nitrate reductase and glutamine synthetase, whole plant growth studies, and the analysis of nitrogenous compounds of xylem exudate and those extracted from the leaf blade, leaf base, and root regions of maize plants after feeding with a nutrient solution containing nitrogen as 15N.
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    19th century glass trade beads : from two Zulu royal residences
    (1990) Saitowitz, Sharma Jeanette
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    2-Aminophenazine carboxylic acids
    (1962) Brock, David John Henry; Holliman, F G
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    The 2000 year old computer: the antikythera mechanism
    (2014-09-29) Wolfe, David
    In 1900 the first ancient marine wreck was discovered in the Mediterranean. It took a century to understand that the most interesting and unique find was a series of small bronze barnacle encrusted fragments. When investigated with sophisticated technology, they turned out to be from an analogue mechanical computer, built about 70 BCE and capable of predicting planetary positions and eclipses of the Sun and the Moon both in the past and the future. Its sophistication is centuries earlier than any mechanism that even began to emulate such a device. How did it work and who could have designed and built it? This double lecture will offer answers to these absorbing questions.
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    2003 updated assessment for the Merluccius paradoxus hake resource off the south and west coasts
    (2003) Rademeyer, Rebecca A; Butterworth, Doug S
    This document presents an updated assessment of the M. paradoxus hake resource off the south and west coasts of South Africa. The previous assessment of this resource is described in Rademeyer and Butterworth (2002).
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    The 2004 age-structured production model assessments and projections for the South Coast rock lobster resource
    (2004) Johnston, Susan J; Butterworth, Doug S
    The assessment conducted in 2003 has been routinely extended, taking account of a further year’s catch, CPUE and catch-at-age data. CPUE shows a continuation of the increase that commenced in 1998. Results are generally more optimistic than those for the 2003 assessment; this is shown to be a result of both the new abundance data now available as well as the revision of the historic catch series, with the former having slightly the larger effect. The Reference Case (RC) scenario suggests that a TAC of 360 MT or less would be appropriate to prevent biomass decline in the future. Other scenarios suggest either higher or lower values than this. If the catch-at-age data are down-weighted, then this appropriate level for the TAC is increased to 390 MT. On the other hand, the scenario which assumes the 1995+ recruitment to be equal to the average of the previous 10 years is more pessimistic and suggests an appropriate TAC level of only some 300 MT
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    The 2004 re-assessment of the South African sardine and anchovy populations to take account of revisions to earlier data and recent record abundances
    (National Inquiry Services Centre (NISC), 2009) de Moor, Carryn L; Butterworth, Doug S
    Hydroacoustic surveys off the coast of South Africa over the early years of the 21st century indicated that both the sardine Sardinops sagax and anchovy Engraulis encrasicolus populations had simultaneously reached record abundances. The South African pelagic fishery is regulated using an Operational Management Procedure (OMP). The OMP in use at that time had been developed using data from the two populations prior to this rapid and substantial increase in abundances. This paper documents the revised assessments that were urgently required to provide a basis to update the OMP. These assessments resulted in a changed perception of the status and productivity of these populations. In particular, estimates of the stock-recruitment relationships and the extent of variation about them, which play a key role in evaluating risk when developing OMPs, altered substantially from estimates derived from earlier assessments.
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    The 2005 Age-Structured Production Model assessments and constant catch projections for the south coast rock lobster resource
    (2005) Johnston, Susan J; Butterworth, Doug S
    The 2005 assessment was routinely extended, taking account of a further year’s catch, CPUE and catch-at-age data. CPUE shows a continuation of the increase that commenced in 1998. However, sustainable yield estimates are generally less than those for the 2004 assessment, although estimates of current biomass levels relative to K increase. The Reference Case (RC) scenario suggests that a TAC of about 360 MT or less would be appropriate to prevent biomass decline in the future. Other scenarios suggest either higher or lower values than this. If the catch-at-age data are down-weighted, then this 360 MT level for the TAC is increased to 390 MT. On the other hand, the scenario which assumes the 1996+ recruitment to be equal to the average of the previous 10 years is more pessimistic and suggests an appropriate TAC level of only some 300 MT or less to prevent biomass decline. A model (Model 2) which allows for time-varying selectivity is presented and shows promising results. Model 2 is better able to reproduce the recent CPUE trend. Preliminary results for a model that fits to catch-at-length rather than catch-at-age data, using a selectivity-at-length rather than selectivity-at-age function, are presented, but these do not as yet reflect satisfactory fits to the data so that they should not be considered reliable in the context of stock status estimates. These different scenarios reflect very different interpretations of the recent increase in CPUE for the resource. If the catch-at-age data are down-weighted, the model fit essentially ignores them and suggests a recent increase in abundance. However, under either the effort saturation or the time-varying selectivity approaches, spawning biomass is estimated to have decreased further over recent years.
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    The 2006 age-structured production model assessments and projections for the South Coast rock lobster resource-routine update
    (2006) Johnston, Susan J; Butterworth, Doug S
    The assessment conducted in 2006 has been routinely extended, taking account of a further year’s catch, CPUE and catch-at-age data. CPUE shows a continuation of the increase that commenced in 1998. The sustainable yield estimates are generally very similar to those for the 2005 assessment, although estimates of current biomass levels relative to K increase. The Reference Case (RC) scenario suggests that a TAC of about 360 MT or less would be appropriate to prevent biomass decline in the future. Other scenarios suggest either higher or lower values than this. If the catch-at-age data are down-weighted, then this 360 MT level for the TAC is increased to 390 MT. On the other hand, the scenario which assumes the 1996+ recruitment to be equal to the average of the previous 10 years is more pessimistic and suggests an appropriate TAC level of only some 300 MT or less to prevent biomass decline.
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    2006 assessment of the toothfish (Dissostichus eleginoides) resource in the Prince Edward Islands vicinity
    (2006) Brandão, Anabela; Butterworth, Doug S
    The ASPM assessment of the Prince Edward Islands toothfish resource by Brandão and Butterworth (2005) that permitted annual fluctuations about a deterministic stockrecruitment relationship is updated to take account of further catch, GLM standardised CPUE and catch-at-length information that has become available for the years 2005 and 2006. The assessment allows for a second fleet to accommodate data from a pot fishery that operated in 2004 and 2005. Updated biological parameter values for Subarea 48.3 are incorporated and lead to less optimistic results. The resource is estimated to be at about 40% of its average pre-exploitation level in terms of spawning biomass. It is suggested that it would be prudent to restrict annual legal catches to 500 tonnes or less, unless a large proportion of the catch is to be taken by pots (which avoid the cetacean predation associated with longlining). Specific issues raised at WGFSA-SAM 2006 about this assessment are addressed.
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    The 2006 operational management procedure for the South African Merluccius paradoxus and M. capensis resources
    (2006) Rademeyer, Rebecca A; Glazer, Jean Patricia
    The algorithm for the 2006 Operational Management Procedure (OMP) to provide TAC recommendations for the South African Merluccius paradoxus and M. capensis resources is empirical, increasing or decreasing the TAC in relation to the magnitude of recent trends in CPUE and survey abundance estimates for both species. The basis for the associated computations is set out below.
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    The 2007 Age-Structured Production Model assessments and projections for the South Coast rock lobster resource-routine update using model fitting to catch-at-age data
    (2007) Johnston, Susan J; Butterworth, Doug S
    The assessment conducted in 2006 (WG/06/06/WCRL3) has been routinely extended, taking account of a further year’s catch, CPUE and catch-at-age data. The observed CPUE shows a slight decrease for 2005 (2005/06 season). The sustainable yield estimates are generally very similar to those for the 2006 assessment, although estimates of current biomass levels relative to K increase. The Reference Case (RC) scenario suggests that a TAC of about 330 MT or less would be appropriate to prevent biomass decline in the future. The other two scenarios reported suggest higher values than this. If the catch-at-age data are down-weighted, then this 360 MT level for the TAC is increased to 390 MT.
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    The 2007 age-structured production model assessments and projections for the South Coast rock lobster resource-routine update using Pope's approximation model fitting to catch-at-age data including scenarios for time-varying selectivity
    (2007) Johnston, Susan J; Butterworth, Doug S
    The assessment conducted in 2006 (WG/06/06/WCRL3) has been routinely extended (except that the Baranov equation has been replaced by Pope’s approximation), taking account of a further year’s catch, CPUE and catch-at-age data. The observed CPUE shows a slight decrease for 2005 (2005/06 season). The sustainable yield estimates are generally very similar to those for the 2006 assessment, although estimates of current biomass levels relative to K increase. The Reference Case (RC) scenario suggests that a TAC of a little less than 330 MT or less would be appropriate to prevent biomass decline in the future. The other four scenarios reported suggest higher values than this, ranging from 350 MT to 405 MT. Spawning biomass trends over the last 10 years are downward for all the models considered.
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    2007 assessment of the toothfish (Dissostichus eleginoides) resource in the Prince Edward Islands vicinity
    (2006) Brandão, Anabela; Butterworth, Doug S
    The ASPM assessment of the Prince Edward Islands toothfish resource by Brandão and Butterworth (2006) that permitted annual fluctuations about a deterministic stock-recruitment relationship is updated to take account of further catch, GLM standardised CPUE and catch-at-length information that has become available for the years 2006 and 2007. The assessment allows for a second fleet to accommodate data from a pot fishery that operated in 2004 and 2005. Biological parameter values adopted for Subarea 48.3 are used. The resource is estimated to be at about 37% of its average pre-exploitation level in terms of spawning biomass. It is suggested that it would be prudent to restrict annual legal catches to 500 tonnes or less, unless a large proportion of the catch is to be taken by pots (which avoid the cetacean predation associated with longlining).
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    2007 Routine update of the South African hake baseline assessment
    (2007) Rademeyer, Rebecca A; Butterworth, Doug S
    This paper presents a routine update of the South African hake assessment, including new commercial (catches and CPUE) and survey (abundance estimates and catch-at-age) data. Only one scenario (M1-H1-C1-SR2) of the Reference Set, which is that with the highest likelihood, has been run – it is termed the ‘baseline’ assessment.